Tag Archives: tissue

The extracellular matrix, and how it keeps you in tip top shape

Would you live in a city without streets? Or in a flat with no walls? Probably not — and the cells in our bodies expect the same level of comfort. Today, we’re taking a look at the tissues that create and maintain an ideal working environment for our tissues: the extracellular matrix.

A mammalian trachea cross-section, magnified 200 times.
Image credits Berkshire Community College Bioscience Image Library / Flickr.

We’ve had a look at the differences between animal and plant cells before (here’s a refresher). One of the key differences between them is that plants reinforce their cells with thick, sturdy walls. These walls are why plant tissues such as wood can get so resilient. However, the reverse of the coin is that it also limits plant cells somewhat: a muscle made out of wood wouldn’t be very effective.

Animals need cells that can perform a wide variety of activities, but these cells also need biological and mechanical support to perform their tasks. That’s where the extracellular matrix, or “ECM”, comes in.

So what is it?

The ECM is a complex mix of proteins and carbohydrates that fills the spaces between cells; it is comprised of the basement membrane and interstitial matrix. Going forward, I’ll use the term ECM quite loosely to mean both ‘the extracellular matrix’ and ‘the interstitial matrix’. If I don’t mention the basement membrane specifically, I’m probably talking about the interstitial matrix (as it’s the more dynamic and frankly more interesting half of the topic).

Think of the basement membrane as a sheet of plastic wrap the body stretches over every individual tissue or organ to keep everything tidy and in place. This membrane is made up of two layers of cells and it’s quite fibrous and hard to rip.

X-ray of an elbow. The ECM in our joints (the empty volume between the bones) uses more collagen to become tough and resistant to wear.
Image via Wikimedia.

The interstitial matrix is, for lack of a better term, the goo that our cells live in. Most of the time, it looks and feels a bit like a clear gel. It’s produced by the cells themselves, which secrete and release certain compounds around them.

The simplest definition of the extracellular matrix is that it represents the sum of non-cellular components present within all tissues and organs. As we go forward, keep in mind that the ECM isn’t the same everywhere.

What’s it made of?

“Although, fundamentally, the ECM is composed of water, proteins, and polysaccharides, each tissue has an ECM with a unique composition and topology that is generated during tissue development,” Christian Frantz, Kathleen M. Stewart, Valerie M. Weaver, 2010.

Collagen, the most abundant protein in mammals, is the main component of the ECM. Outside the cell, collagen binds with carbohydrate molecules and assembles into long molecules called collagen fibrils. These fibrils extend through the ECM and lend flexibility and strength to the material, acting similarly to the role of rebar in reinforcing concrete (which is tough but inflexible). Collagen fibrils are flexible and tough to break, so they’re used to ‘bind together’ the rest of the ECM. In humans, genetic disorders that affect collagen (such as Ehlers-Danlos syndrome) cause tissues to become fragile and tear easily.

While the ECM contains a wide range of proteins and carbohydrates, another important set of compounds alongside collagen are proteoglycans (groups of proteins tied to simple sugars). Proteoglycans come with many shapes and functions, depending on which proteins and sugars they’re made of, and perform a wide range of tasks in the ECM. They can also bind to each other, to collagen (forming cartilage), or to hyaluronic acid, making them even more versatile. As a rule of thumb, proteoglycans act as fillers and regulate the movement of molecules through the ECM among other functions.

Collagen fibers in rabbit skin.
Image via Wikimedia.

Their overall structure looks like a tree: the ‘sugar’ part of the polyglycans are twigs set on a branch (the protein), which ties to a trunk made out of polysaccharide (‘many-sugar’) molecules. A class of proteins in the membranes of cells, called integrins, serve as connection ports between the membrane and material in the ECM (such as collagen fibers and proteoglycan-polysaccharide bundles). Beneath the membrane, integrins tie into the cell’s support ‘girders’ (the cytoskeleton).

The type of ECM I’ve described so far is your run of the mill variety that you’ll find in skin, around muscle fibers, in adipose tissue (fat), and so on. But each tissue has an ECM that fully supports its function — blood plasma is the interstitial matrix of blood. Unlike the ECM of muscles, for example, which is meant to reduce friction and wear in the tissue, blood plasma primarily works as a medium to carry blood cells around. Blood vessels are coated with a basement membrane, and together, they form the ECM of blood. Each type of animal connective tissue has its own type of ECM, even bone.

What does it do?

Cross-section of compact human bone, magnified 100 times.
Image credits Berkshire Community College Bioscience Image Library / Flickr.

Seeing as there are many types of ECM out there, it stands to reason that there are many functions they perform. However, by and large, there are a few functions that all ECMs fulfill.

The first and perhaps most important function is that they provide support to tissues, segregate (separate) them, and that they mediate intercellular communication. The ECM is also what regulates a cell’s ‘dynamic behavior’ — i.e. whether a cell moves around, and how. The ECM keeps cells in place so we don’t simply unravel. The connections formed between the ECM and integrins on a cell’s membrane also function as signaling pathways.

It is also essential for the good functioning of tissues at large. The ECM creates and maintains the proper environmental conditions for cells to develop, multiply, and form functioning tissues. While the exact details are still unknown, the ECM has been found to cause tissue regrowth and healing after injury. In human fetuses, for example, the extracellular matrix works with stem cells to grow and regrow all parts of the human body. Fetuses can regrow anything that gets damaged in the womb, but since babies can’t, we suspect that the matrix loses this function after full development. Researchers are looking into applying it for tissue regeneration in adults.

The ECM can also act as a storage space for various compounds. In joints, it contains more hyaluronic acid which in turn absorbs water and acts as a mechanical cushion. ECMs can also store a wide range of cellular growth factors and release them as needed. This allows our bodies to activate cell growth on a dime when needed without having to produce and ship these factors to a certain area.

It also seems to impact cell differentiation and gene expression. Cells can switch genes on or off depending on the elasticity of the ECM around them. Cells also seem to want to migrate towards stiffer areas of the ECM generally (durotaxis) from less-firm ones.

The ECM isn’t very well known today, and it definitely goes unsung. But no matter how you cut it, it is a key part of biology as we know it today. Without it, both animals and plants would be formless, messy blobs — quite literally. And I don’t know about you but I love it when my tissues stay where they’re supposed to, the way they’re supposed to.


Hyaluronic acid.

What is hyaluronic acid

Your average 70 kg (154-pound) person has around 15 grams of this substance in their body. Roughly one-third of it breaks down and replenishes daily. This high turnover rate suggests that hyaluronic acid — also called hyaluronan or hyaluronate — is quite important for our well being.

But what is this hyaluronic acid? Let’s find out.

Hyaluronic acid.

 

The basics

Hyaluronic acid, when you boil away all the bells and whistles, is a really long polymer molecule. It’s basically a long chain made up of thousands of sugar molecules. It is found throughout the cells in your body but only occurs in high concentrations in certain areas. It also serves a different role in various tissues and cells.

For example, hyaluronan acts as a building block for cellular membranes (their ‘walls’). It’s also found in cartilage, especially in those joints at the end of long bones, where it reduces wear and tear on the tissue and serves to absorb shock (in the form of an oil-like ‘synovial liquid’). The acid also lubricates active tissues such as muscle and cartilage. As a rule of thumb, the compound is either used to keep tissues running or to give them resilience and flexibility. It has an important part to play in skin health, wound healing, cell mobility, building tissues that insulate other tissues, and keeping the fluids in your eyes gooey. The vitreous humor inside your eyeballs is almost completely made up of hyaluronic acid.

Hyaluronic acid is extremely hydrophilic (it absorbs water), and it’s this property that allows it to function as a lubricant in our bodies. It can absorb up to 1000 times its weight in water. All that water it holds also makes it an excellent moisturizer.

Calf eye vitreous humor.

Anterior view of a dissected calf eye. The transparent goo is the vitreous humor.
Image credits: Mark Fickett / University of Pennsylvania.

It looks like a transparent gel and has the consistency to fit its look. To give you a rough idea of how hyaluronic acid looks, feels, and behaves, Endre Balazs — a doctor and professor of medicine who spent seven decades of his life studying the compound — tried to patent hyaluronic acid as a bakery substitute for egg white in 1942. He was granted the patent and went on to become a leading research figure on the matter of hyaluronic acid and its uses.

In the skin

One of the main jobs hyaluronic acid has to do is to act as the mortar between our cells. It keeps us together in the correct shape.

In biology, that mortar is called the extracellular matrix (ECM) and it is a gelatinous fluid which surrounds almost every one of our living cells. The ECM is made up of fibrous elements (generally elastin and collagen) affixed in a gelatinous substance — hyaluronic acid. It’s this acid’s job of keeping the ECM stretchy and hydrated, and it also ferries nutrients and waste between these structures and the rest of the body.

The skin, bones, tendons, ligaments, and cartilage are among the tissues richest in ECM. The skin takes the hyaluronic cake, as it contains roughly 50% of our body’s total of the compound. Skin needs a lot of it because it has to stretch without breaking, as well as bend and then bounce back. The acid doesn’t do that itself — that’s collagen’s job — but it does keep those collagen fibers hydrated and in tip-top shape. If you want to see how hyaluronic affects the skin, just wait 20, maybe 30 years: our skin loses some of its ability to produce the acid as we age.

Bereft of its hyaluronic acid, our skin loses the ability to hold water and, thus, to properly hydrate itself and its collagen. On the one hand (and every other bit covered by skin), this makes it drier and less flexible. The acid, which basically works to store water in a gooey state, also acts as a filler agent, keeping the skin free of wrinkles. So, on the other hand, aging also makes our skin wrinkly.

In medicine and beauty products

Hand cream.

Image via Pixabay.

Hyaluronic acid saw its first recorded medical use in 1943, during the height of the Second World War. Nickolay Gamaleya used it to create complex bandages for the treatment of frostbitten soldiers at the Soviet field hospital nr. 1321, according to Hyaluronic Acid: Production, Properties, Application in Biology and Medicine. Gamaleya christened the hyaluronic acid in those bandages, the book notes, as the “factor of regeneration”. The compound was so effective that it was later approved by the USSR’s Ministry of Health under the name ‘Regenerator’ — only in Russian, one would assume.

A number of somewhat exotic uses for hyaluronan followed: as a prosthesis for the treatment of retinal detachment, to prevent post-operatory tissue soldering, to heal the aching joints of racehorses suffering from arthritis, and even to help with implanted ocular lenses.

Today, people take hyaluronic acid for various joint disorders, such as osteoarthritis. The FDA has also approved its use during certain eye surgeries such as cataract removal, corneal transplantation, and repair of a detached retina. It is injected into the eye during such procedures to help replace fluids such as the vitreous humor. It’s also mixed into some skin-applicable products intended to promote healing of wounds, burns, or skin ulcers. Note, however, that there is only limited clinical evidence for its effectiveness in this role.

Plastic surgeons and their patients are also big fans of hyaluronic acid. It’s often used as a filler — just like its natural role — in plastic surgery, in procedures to make lips fuller or to reduce wrinkles, for example. It also sees a lot of use as a moisturizer in various creams.

Some people may be eager to sell hyaluronic acid to you as the be all end all ‘fountain of youth’. While it does seem to have a moisturizing effect — which definitely helps your skin shine — there is no evidence to support the view that this compound actually prevents or undoes changes associated with aging.

Whether you take it by mouth or apply it on your skin, its effects on wrinkles seem to be only skin deep.

Elephant skin.

Collagen networks and hyaluronic acid literally keep you in shape, new study reports

Our tissues have to handle stress and deformation every day. New research is looking into how it copes so well.

Elephant skin.

Image via Pixabay.

We tend to take our bodies for granted but even the most mundane of actions — walking around, breathing — exerts mechanical stress and subsequent deformation of it. And yet, day after day, our tissues take the brunt of it with grace and even heal themselves without any conscious effort on our part.

Curious to see how it pulls off such a feat, researchers from the Wageningen University & Research (WUR) and the AMOLF Institute found that two components in soft tissue, collagen and hyaluronic acid, work together to underpin how tissues respond to mechanical stress.

Feeling stressed

Pull on your earlobe and it will be soft and flexible. Keep pulling, increase the force you apply, and it will become progressively stiffer. It’s not just your earlobes — skin, muscles, the cartilage in your joints and ribs behave the same way.

They’re designed to work like that. While soft, such tissues are easily traversed by cells — but they also need to provide mechanical protection to underlying structures, meaning it has to be tough too, and hard to break. Finally, it’s vital that such tissue is able to transition between the two states.

Needless to say, that’s quite a list of demands. But, our soft tissues rise to the challenge through the use of collagen, hyaluronic acid, and the interactions between the two, a new study reports. The findings not only help us better understand how our bodies function, but may also point the way towards new, synthetic polymers that mimic these impressive properties.

It’s the particular way in which collagen proteins order themselves in soft tissues that give them their resilience. They arrange in a structure known as a sparse network (meaning the proteins don’t form the maximum possible number of bonds between each other). Previous research has gauged the physical resilience of this sparse network in in-vitro conditions: collagen networks were extracted from samples of animal skin and reformed inside a rheometer, an instrument which measures the response of a material during deformation. Such efforts, the team explains, only capture part of the image, however.

“Real tissues are far more complex: they are composed of different molecules that have different sizes and interact with each other in still unknown ways,” says Simone Dussi, postdoc in the WUR Physical Chemistry and one of the study’s corresponding authors. “Because of this complexity, real tissues are way more adaptive than the networks studied so far, made of only collagen.”

“[The presence of hyaluronic acid] significantly changed the mechanical response of the composite networks and we were eager to understand why.”

The team reports that, unlike collagen, hyaluronic acid — a polymer made of much smaller and more flexible molecules — is electromagnetically charged. Because of this, electrostatic interactions generate stress between its individual blocks which accumulates as the tissue is subjected to deformation. According to the team, this buildup of stress basically opposes the deformation.

Networks with a larger amount of hyaluronic acid are “already stiffer at small deformation[s]”, explains co-author Justin Tauber. They also become stiffer in response to larger deformation than networks poor in the acid, the adds.

“We managed to construct a theoretical model and performed computer simulations that matched the experimental results. The key ingredients were identified: In addition to the network structure and the bending rigidity of the collagen fibres, the elasticity and the internal stress generated by the hyaluronic acid are crucial,” Tauber explains.

“The model allows us to make a step further in understanding how real tissues exploit the balance of all these effects. In addition, our findings can be translated into material science to create novel synthetic polymeric materials with more tunable properties.”

The paper “Stress management in composite biopolymer networks” has been published in the journal Nature.

Frog pre-amputation.

Experimental bioreactor helps frogs regenerate lost limbs

We’re one leg closer to developing functional limb regeneration.

Frog pre-amputation.

Xenopus laevis pre-amputation
Image credits Celia Herrera-Rincon / Tufts University.

A team of researchers from the Tufts University wishes that everyone could lose a foot and have it, too. The group successfully “kick-started” partial tissue regrowth in adult African clawed frogs (Xenopus laevis) through the use of a bioreactor and electroceutical (electrical cell-stimulating) techniques.

The cradle of life

“At best, adult frogs normally grow back only a featureless, thin, cartilaginous spike,” says senior author Michael Levin, developmental biologist at the Tufts University’s Allen Discovery Center.

“Our procedure induced a regenerative response they normally never have, which resulted in bigger, more structured appendages. The bioreactor device triggered very complex downstream outcomes that bioengineers cannot yet micromanage directly.”

The scientists split up the frog models into three groups — one experimental, one control, and one ‘sham’ group. Each animal had one of its hindlimbs amputated for the trial. Next, they 3D printed a “wearable bioreactor” out of silicon and filled it with hydrogel (a tissue-like mix of water and polymers). This hydrogel was mixed with certain silk proteins that provided a “pro-regenerative environment” and “enhanc[ed] bone remodeling”, according to the authors.

Next came the trial proper: frogs in the experimental and sham groups received the bioreactor (which was sutured on) immediately after the amputation procedure. The difference between the two is that the hydrogel for the experimental group was further laced with progesterone. Progesterone is a hormone that works to prepare the body for pregnancy but has also been shown to promote tissue repair, from nerves to bone. The control group received no treatment. Twenty-four hours later, the devices were removed.

Observations carried out at various times over the following nine-and-a-half months show that the bioreactor induced a degree of regeneration in the experimental group that had no counterpart in the other two groups. Instead of the typical spike-like structure, frogs treated with the bioreactor-progesterone combo re-grew a paddle-like structure — closer to a fully formed limb than what unaided regeneration processes created.

Results comparison.

Image credits Celia Herrera-Rincon et al., 2018, Cell Reports.

“The bioreactor device created a supportive environment for the wound where the tissue could grow as it did during embryogenesis,” says Levin. “A very brief application of bioreactor and its payload triggered months of tissue growth and patterning.”

The regenerated structures of the experimental groups were thicker, had better-developed bones, nerve bundles, and blood vessels. Video footage of the frogs in their tanks also showed that these frogs could swim more like un-amputated ones, the team adds. Scarring and immune responses were also dampened in the bioreactor-treated frogs, suggesting that the progesterone limited the body’s natural reaction to injury in a way that benefited the regeneration process.

So, why exactly did the device work? Genetic tests performed by the team showed that the bioreactor-progesterone combo altered gene expression in cells at the amputation site. Genes involved in oxidative stress, serotonergic signaling, and white blood cell activity were upregulated, while some other signaling-related genes were downregulated.

Regeneration results 2.

Anatomical outcome (bottom) and X-ray images (top) of regenerates formed in adult Xenopus hindlimb amputation after no treatment (Ctrl, A) and after 24-hr combined treatment of drug-loaded device (Prog-device, B–D).
Image credits Celia Herrera-Rincon et al., 2018, Cell Reports.

“In both reproduction and its newly discovered role in brain functioning, progesterone’s actions are local or tissue-specific,” says first author Celia Herrera-Rincon, neuroscientist in Levin’s lab at Tufts University.

“What we are demonstrating with this approach is that maybe reproduction, brain processing, and regeneration are closer than we think. Maybe they share pathways and elements of a common — and so far, not completely understood — bioelectrical code.”

The team plans to expand their research in mammal subjects. Previous research hinted that mice can partially regenerate tissue (such as amputated fingertips) under the right conditions. Life on land, however, hinders this process. “Almost all good regenerators are aquatic,” Levin explains, adding that “a mouse that loses a finger or hand, and then grinds the delicate regenerative cells into the flooring material as it walks around, is unlikely to experience significant limb regeneration.” Still, let’s keep our fingers crossed that the team finds an elegant and efficient solution to this problem — it may, after all, be our limbs that we regrow one day!

But there’s much work to be done until then. Levin says the next step is to add sensors to the device for remote monitoring and optogenetic stimulation, which should give the team a degree of control over how tissues regenerate in the bioreactor. They also plan to expand on their work with bioelectric processes in the hopes of successfully inducing regeneration in the spinal cord, and to the merits of this approach for tumor reprogramming

The paper “Brief Local Application of Progesterone via a Wearable Bioreactor Induces Long-Term Regenerative Response in Adult Xenopus Hindlimb” has been published in the journal Cell Reports.

Reticular adhesions.

New structure that keeps cells bound together discovered in human cells

Researchers at the Karolinska Institutet, Sweden, report discovering a new structure in human cells. The role of this cellular structure protein seems to be fixing cells to surrounding tissues and aiding in division, the team reports.

Reticular adhesions.

Three-dimensional projection of a cancer cell that has been rounded to undergo cell division and adheres to the substrate with reticular adhesions. Blue – Chromatin (DNA); Red – Cell’s outer shell (membrane); Green/Yellow – Reticular adhesions. The image was created using a confocal microscope.
Image credits John Lock.

Cells are round-ish, soft-ish things. So then how do they tie together to form robust tissues? Well, the secret lies in a structure that surrounds them — a net-like formation known as the extracellular matrix. Much like the mortar in between bricks, this matrix brings cells together into a coherent whole.

Still, the matrix is an exclusive place — only those with special receptor molecules (adhesion complexes) on their surface are admitted. The structure discovered by the team is one such adhesion complex.

Yet more to discover

“It’s incredibly surprising that there’s a new cell structure left to discover in 2018,” says principal investigator Staffan Strömblad, professor at the Department of Biosciences and Nutrition at the Karolinska Institutet.

“The existence of this type of adhesion complex has completely passed us by.”

The team discovered a new type of protein complex that cells use to attach to their surroundings and plays a key part in cell division. Much like other adhesion complexes, it connects the outside to the cell interior and informs the cell about its immediate environment, affecting its properties and behavior. What’s special about this one is its unique molecular composition and shape — the team christened the structure ‘reticular adhesions’ to reflect their net-like shape.

While other known adhesion complexes break down during division, reticular adhesions remain intact and attached to the cell wall during the process. This discovery could help solve the long-standing question of how cells remain attached to the matrix as they divide. The team further reports that the new structure controls where daughter cells go after division, ensuring that they occupy the right place in the overall tissue.

“Our findings raise many new and important questions about the presence and function of these structures,” says Professor Strömblad. “We believe that they’re also involved in other processes than cell division, but this remains to be discovered.”

For the study, the team looked at human cell lines using confocal microscopy and mass spectrometry. To better understand the function of reticular adhesions, they add, further research efforts will need to examine them in living organisms.

Apart from the direct scientific merits of the discovery, the biggest takeaway (for me) from this research is that nature is way more complex and complicated than we give it credit for. We shouldn’t rest on our laurels because we’ve ‘discovered everything’ — we’re nowhere near done yet.

The paper “Reticular adhesions are a distinct class of cell-matrix adhesions that mediate attachment during mitosis” has been published in the journal Nature Cell Biology.

Fluorescent 3d-printed tissue.

New 3D-printing process creates ligaments, tendons for transplant — paves the way for replacement organs

New research is merging 3D printing with human stem cells to provide on-demand tissues such as ligaments and tendons for transplant.

Fluorescent 3d-printed tissue.

Fluorescent cells the team printed to showcase their new process.
Image credits Robby Bowles / University of Utah College of Engineering.

It’s a tough life, and sometimes, our bodies pay the price. Such tolls, however, needn’t be permanent — and, new research from the University of Utah is making it easier than ever before to repair the damage. The team’s efforts pave the way to 3D-printed human tissues such as ligaments and tendons that can be used from transplant.

Break a leg! We can fix it later

“This is a technique in a very controlled manner to create a pattern and organizations of cells that you couldn’t create with previous technologies,” says University of Utah biomedical engineering assistant professor and paper co-author Robby Bowles.

“It allows us to very specifically put cells where we want them.”

Patients that require replacement tissues currently also need to supply it themselves from another part of the body or receive it from a cadaver. Such procedures carry their own risks, involve quite a lot of discomfort on the part of the patient, and (especially in the case of cadaver-sourced tissues) may be very off-putting for certain people. There’s also the risk that replacement tissue is of poor quality, either due to wear and tear or complications in the material’s retrieval from the body.

In an effort to work around these issues and reduce the total number of surgeries a potential patient would have to go through to receive a replacement, Bowles’ team worked on developing a 3D-printing method which can produce viable biological tissues.

Development of the process took two years to complete, the team reports. It relies on stem cells harvested from a patient’s body fat, which are printed on a hydrogel layer to form a tendon or ligament. These cells are grown in vitro (in the lab) in a culture and then implanted. According to the team, the technique can be used to create replacements for connective tissue such as ligaments, tendons, or cartilage — even complex structures such as spinal disks. Such disks are very complex structures that include bony interfaces (transitional areas), and must be reconstructed completely for a successful transplant, they add.

“[The 3D-printing process] will allow patients to receive replacement tissues without additional surgeries and without having to harvest tissue from other sites, which has its own source of problems,” says Bowles.

Much of the research went exactly into tackling complex structures such as spinal disks. Connective tissue is never ‘pure’ — it always includes multiple and complex patterns of interweaving cells. The tendons that flank your muscles, for example, must have transition zones to gradually shift into and attach to adjacent tissues, be them bone or muscle.

Bowles and his co-author David Ede, a former biomedical engineering master’s student at Utah, teamed up with Salt Lake City-based company, Carterra, Inc., which develops microfluidic devices for medicine. They developed their printer starting from a piece of hardware that Carterra typically uses to print antibodies for cancer screening applications. Bowles’ team developed a new printhead for the device that can lay down human cells with a high degree of control. The printhead, Bowles adds, could be adapted for any kind of 3-D printer.

As a proof of concept, the duo printed genetically-modified, fluorescent cells, so they could analyze the structure of the final tissue.

Bowles, with a background in musculoskeletal research, said the technology currently is designed for creating ligaments, tendons and spinal discs. However, he excitedly adds that “it literally could be used for any type of tissue engineering application”. Eventually, the team hopes their technique can be used to print out whole organs, which would be a major breakthrough for patients on transplant waiting lists the world over.

The paper “Microfluidic Flow Cell Array for Controlled Cell Deposition in Engineered Musculoskeletal Tissues” has been published in the journal Tissue Engineering Part C: Methods.

The earliest vertebrates with a mineralised skeleton were armoured jawless fishes such as Anglaspis heintzi, a heterostracan that lived approximately 419 million years ago. Credit: Wikimedia Commons.

Earliest evidence of bone solves mysterious origin of our skeletons

The earliest vertebrates with a mineralised skeleton were armoured jawless fishes such as Anglaspis heintzi, a heterostracan that lived approximately 419 million years ago. Credit: Wikimedia Commons.

“The earliest vertebrates with a mineralized skeleton were armored, jawless fish like Anglaspis heintzi, a heterostracan that lived approximately 419 million years ago. Credit: Wikimedia Commons.

For 160 years, scientists have been debating what tissue types made up the earliest vertebrate skeletons. Now, a new study that used powerful X-rays to peer inside a 400-million-year-old fossilized skeleton has finally cracked this mystery. Researchers concluded that a “spongy” tissue called aspidin was used in the earliest evidence of bone in the fossil record.

The very first bones were dramatically different from our own

Today, the skeletons of vertebrates are built out of four different tissue types. These are bone, cartilage, (a rubber-like padding that covers and protects the ends of long bones at the joints and is a structural component of many body parts), dentine, and enamel. Dentine is the hardest material in the body because of its high inorganic content and low water composition, while enamel is the outermost layer that covers dentine.

These tissues become mineralized as they grow, offering the skeleton strength and rigidity. Millions of years ago, however, there were likely other types of tissue that constructed bones.

To get to the bottom of things, a team of researchers at the University of Manchester, the University of Bristol and the Paul Scherrer Institute in Switzerland examined in excruciating detail the fossils of a group of fish called heterostracans, which lived 400 million years ago. In order to peer inside the ancient skeletons, the researchers employed a special type of CT scan which uses high energy X-rays produced by a particle accelerator. It was all a laborious process, however, which involved scanning different heterostracan species and requiring numerous trips to the Swiss Light Source, Switzerland and over 100 hours of scanning time.

High-power X-rays allowed researchers to create detailed models of the skeletal tissue. Credit: Keating et al. 2018.

High-power X-rays allowed researchers to create detailed models of the skeletal tissue. Credit: Keating et al. 2018.

This technique allowed the researchers to discover what kind of tissue heterostracan skeletons are made of. Heterostracans are some of the oldest vertebrates with a mineralized skeleton and by studying them, it is possible to deconstruct what the earliest bones looked like and how they transitioned to their current form.

“When we had collected the data, I began the painstaking process of creating a 3D digital model of aspidin, in order to determine the shape and orientation of the mysterious tubes. Images from previous studies seem to show the tubes branching; resembling the branching processes of bone cell-spaces. However, I found that these tubes were strictly linear, lacking any kind of branching. The images from previous studies seem to be a result of 2-dimensional sectioning through tangled and overlapping tubes, giving the appearance of branching. This discovery was an important piece in the puzzle, allowing me to rule out the possibility that these tubes were bone or dentine cell-spaces,” Dr. Joseph Keating, from Manchester’s School of Earth of Environmental Scientists, told ZME Science.

According to the results, heterostracan skeletons were made of aspidin — a strange tissue, crisscrossed by tiny tubes, which doesn’t even remotely resemble any other tissue found in vertebrates today.

 

Researchers were able to identify the mysterious tissue ‘aspidin’ and provide new insight into the evolution of our skeleton. Credit: Keating et al.

Researchers were able to identify the mysterious tissue ‘aspidin’ and provide new insight into the evolution of our skeleton. Credit: Keating et al.

Keating and colleagues conclude that these tiny tubes used to house fiber-bundles of collagen inside them. Collagen is a type of protein found in the skin and bones.

However, heterostracan skeletons bear some important differences when compared to modern vertebrate bones.

“Heterostracan aspidin lacks two key features of bone in most living vertebrates. Firstly, aspidin is acellular: it lacks cell spaces, as our research has revealed. The bone of most modern vertebrates, including humans, contains a network of interconnected spaces housing living cells, called osteocytes, that maintain bone tissue,” Keating said.

“Secondly, The bone of modern vertebrates is constantly restructured via a process called resorption, whereby bone cells called osteoclasts break down the mineralised tissue. New mineralised tissue is then deposited by another type of bone cell called osteoblasts. This ability allows our skeletons to grow dynamically through life. Heterostracan skeletons show some evidence of resorption, but it appears to be much less common than in the skeletons of most living vertebrates.”

“These two features of modern bone evolved later in vertebrate evolution.”

Aspidin was once thought to be the precursor of vertebrate mineralized tissues. These findings published in Nature Ecology and Evolution suggest that aspidin is, in fact, the earliest evidence of bone in the fossil record, changing our view of the evolution of the skeleton.

“Our results suggest that all types of mineralised tissues found in living vertebrates appear simultaneously in the fossil record, around 420 million years ago. This raises two important questions: when did these tissues first evolve? And why do they appear in the fossil record at the same time? One possible explanation is that the sudden appearance of mineralised tissues is due to the evolution of mineralisation, rather than the evolution of the tissues themselves. Bone and dentine may have first evolved as distinct layers of the skin long before vertebrates evolved the genetic pathways necessary for tissue mineralisation. As such, the early history of these tissues may not be preserved in the fossil record, as unmineralised tissues are prone to decay. Alternatively, there may be a missing fossil record of older vertebrates showing earlier stages in the evolution of the skeleton. These may be fossils we are yet to discover, or fossils sitting in museum draws which have not yet been recognized for their significance,” Keating told ZME Science.

Cells printer.

Newly-developed 3D printing method uses cells, biomolecules to recreate tissues

UK researchers have developed a new 3D printing technique — but this press prints not in plastic, glass, or metal, but rather in cells and molecules you’d normally find in living tissue.

Cells printer.

Cells spreading on the outside of 3D-printed scaffold.
Image credits Clara Hedegaard.

Ever felt the need for a piece of living matter but without all the messy “organism” part that just complicates everything? Well, you’re in luck, because a team from the Queen Mary University in London has developed a 3D printing technique “capable of encapsulating and spatially distributing multiple cell types within tuneable pericellular environments.”

The process embeds cells and other molecules in an ink that simulates conditions inside living organisms. Because of this, the building blocks used in printing can behave largely as they would in the body, allowing researchers to explore new avenues of study for biological structures.

“The technique opens the possibility to design and create biological scenarios like complex and specific cell environments, which can be used in different fields such as tissue engineering by creating constructs that resemble tissues or in vitro models,” says Professor Alvaro Mata, the paper’s corresponding author. “[These constructs] can be used to test drugs in a more efficient manner.”

The technique actually mixes two ‘printing’ styles together: molecular self-assembly, described in a university press release as “building structures by assembling molecules like Lego pieces”, and additive manufacturing, the layer-upon-layer approach used in more traditional 3D printing.

Using the two processes in tandem allows the researchers to digitally design and then manufacture structures “with molecular precision” while creating cells and other bioconstructs that mimic tissues or whole body parts.

“This method enables the possibility to build 3D structures by printing multiple types of biomolecules capable of assembling into well defined structures at multiple scales,” says lead author Clara Hedegaard.

“Because of this, the self-assembling ink provides an opportunity to control the chemical and physical properties during and after printing, which can be tuned to stimulate cell behaviour.”

The research addresses a major shortcoming of current 3D-printing techniques: a very limited capacity to stimulate the cells that are being printed, the authors note. The structures printed using this new method hold promise as test-bed-tissues for tissue engineering or regenerative medicine.

The paper “Hydrodynamically Guided Hierarchical Self-Assembly of Peptide-Protein Bioinks” has been published in the journal Advanced Functional Materials.

Scaffolding

If stem cells don’t grow as you want them to, just add a dash of parsley-husk scaffolding

University of Wisconsin-Madison researchers are investigating de-cellularized plant husks as potential 3D scaffolds which, when seeded with human stem cells, could lead to a new class of biomedical implants and tailored tissues.

Scaffolding

Image via Pixabay.

We may like to call ourselves the superior being or top of the food chain and all that, but as far as design elegance and functionality is concerned, the things nature comes up with make us look like amateurs. Luckily, we’re not above emulating/copying/appropriating these designs, meaning that structures created by plants and animals have long and liberally been used to advance science and technology.

Joining this noblest of scientific traditions, UWM scientists have turned to de-celled husks of plants such as parsley, vanilla, or orchids to create 3D scaffolds which can be seeded with human stem cells and optimized for growth in lab cultures. This approach would provide an inexpensive, easily scalable and green technology for creating tiny structures which can be used to repair bits of our bodies using stem cells.

Plantfolding

The technology draws on the natural qualities of plant structures — strength, porosity, low weight, all coupled with large surface-to-volume ratios — to overcome several of the limitations current scaffolding methods, such as 3D printing or injection molding, face in creating efficient feedstock structures for biomedical applications.

“Nature provides us with a tremendous reservoir of structures in plants,” explains Gianluca Fontana, lead author of the new study and a UW-Madison postdoctoral fellow. “You can pick the structure you want.”

“Plants are really special materials as they have a very high surface area to volume ratio, and their pore structure is uniquely well-designed for fluid transport,” says William Murphy, professor of biomedical engineering and co-director of the UW-Madison Stem Cell and Regenerative Medicine Center, who coordinated the team’s efforts.

The team worked together with Madison’s Olbrich Botanical Gardens’ staff and curator John Wirth to identify which species of plants could be used for the tiny scaffolds. In addition to parsley and orchids, the garden’s staff also found that bamboo, elephant ear plants, and wasabi have structures that would be useful in bioengineering for their shape or other properties. Bulrush was also found to hold promise following examinations of plants in the UW Arboretum.

Human fibroblast cells growing on decellularized parsley.
Image credits Gianluca Fontana / UW-Madison.

Plants form such good scaffolds because their cellular walls are rich in cellulose — probably the most abundant polymer on Earth, as plants use it to form a rough equivalent of our skeleton. The UWM team found that if they strip away all the plant’s cells and chemically treat the left-over cellulose, human stem cells such as fibroblasts are very eager to take up residence in the husks.

Even better, the team observed that stem cells seeded into the scaffolds tended to align to the scaffold’s structure. So it should be possible to use these plant husks to control the structure and alignment of developing human tissues, Murphy says, a critical achievement for muscle or nerve tissues — which don’t work unless correctly aligned and patterned. Since there’s a huge variety of plants — with unique cellulose structures — in nature, we can simply find one that suits our need and use that to tailor the tissues we want.

“Stem cells are sensitive to topography. It influences how cells grow and how well they grow,” Fontana added.

“The vast diversity in the plant kingdom provides virtually any size and shape of interest,” notes Murphy. “It really seemed obvious. Plants are extraordinarily good at cultivating new tissues and organs, and there are thousands of different plant species readily available. They represent a tremendous feedstock of new materials for tissue engineering applications.”

Another big plus for the plantfolds is how easy they are to produce and work with, being “quite pliable […] easily cut, fashioned, rolled or stacked to form a range of different sizes and shapes,” according to Murphy. They’re also easy and cheap to mass produce as well as renewable on account of being, you know, plants.

So far, these scaffolds seem to hold a huge potential. They’ve yet to be tested in living organisms, but there are plans to do so in the future.

The scaffolds have yet to be tested in an animal model, but plans are underway to conduct such studies in the near future.

“Toxicity is unlikely, but there is potential for immune responses if these plant scaffolds are implanted into a mammal,” says Murphy.

“Significant immune responses are less likely in our approach because the plant cells are removed from the scaffolds.”

The full paper “Biomanufacturing Seamless Tubular and Hollow Collagen Scaffolds with Unique Design Features and Biomechanical Properties” has been published in the journal Advanced Healthcare Materials.

Cells nudge each other with proteins when moving to keep your body in one piece

A new signaling mechanism that epithelial cells use to communicate during motion has been uncovered, explaining how individual (or groups of) cells can move inside of a tissue without compromising its structure.

Image credits Umberto Salvagnin / Flickr.

One cell left to its own devices can move about pretty easily if needed. Its motion is similar to a ‘flow’ of sorts, with the cell’s leading edge extending a protrusion and its trailing edge drawing itself along. The same process of motion is used by cells included in tissues, with the extra requirement that the overall structure remains intact. So how do these tiny bits of life communicate and co-ordinate their motions in the context of tissues?

Protein nudges

When you need to pass through a tightly-packed group of people, your best bet is to communicate your intention of moving forward (verbally or through nudging) so they’ll make way. Cells in tissues do the same thing, but with proteins. Some of the signal proteins used in this process have been documented for some time now, but research from the University of Chicago has identified a new protein-driven signaling system that epithelial cells use to coordinate individual movements to move whole tissues at once.

Top view of Drosophila’s ventral cells undergoing apical constriction and invagination (cells taking on a wedge-like shape to create a cavity).
Image credits Institute Pasteur via giphy.

Cell biologist Sally Horne-Badovinac, PhD, and colleagues from the UoC found that two membrane proteins work in tandem to coordinate epithelial migration in Drosophila, the common fruit fly. The first one is called Lat, and works on the leading edge of the cell. The other, Fat2, acts at the trailing edge. Lets say we have three cells, A, B, and C, one behind the other, as the whole tissue needs to move.

For B to migrate, its Fat2 molecules first signal to the Lar behind it, which causes that cell (A) to extend its edge and go under B. In turn, B extends its leading edge under C, nudged by C’s Fat2. When A finishes its motion, its Lar signals to B’s Fat2, which retracts its leading edge — and the same happens between B and C.

Through this step-by-step process, neighboring cells can coordinate and move the whole tissue at the same time without leaving any holes in it.

“The protrusion of one cell goes underneath edge of the cell ahead, so you get what looks like overlapping shingles on a roof,” said Horne-Badovinac, an assistant professor of molecular genetics and cell biology and first author of the study.

“This process is understood really well at the single cell level, but when you hook these cells all together in a tight sheet, it becomes something more coordinated.”

The team used fruit flies to study this signaling process. As female embryos develop, the tissues which will later form egg chambers stretch and rotate into their final position. Scientists knew that both Fat2 and Lar were involved in this process, but it wasn’t clear if the cells were migrating because the tissues rotate around the circumference of a circular chamber, not moving in a straight line.

So Horne-Badovinac and her team grew the egg chambers in cell cultures outside of the female flies to get a better look at how they behaved. In groups of normal cells located behind cells edited to lack Fat2, the leading edge protrusions didn’t form. In groups of normal cells placed in front of Lar-missing patches, the trailing edges weren’t retracted.

“It was surprising, because what we knew was that the protein [Fat2] was at the trailing edge of the cell, but we were seeing an effect at the leading edge of the cell. So initially that made absolutely no sense,” said Horne-Badovinac.

“It required careful analysis along those cloned boundaries to really figure it out.”

Horne-Badovinac said there are still a lot of questions regarding the interaction between these proteins, and thinks there are other proteins which handle motion signaling to organelles inside the cell — especially the cytoskeletal machinery, which drives cellular movement.

Uncovering the mechanisms of coordinated cell movement could help us better understand critical stages of embryonic development, wound healing, and even cancer spread.

 

The full paper “Fat2 and Lar Define a Basally Localized Planar Signaling System Controlling Collective Cell Migration” has been published in the journal Developmental Cell.

Photograph comparing muscles made by coiling (from left to right) 150 μm, 280 μm, 860 μm and 2.45 mm nylon 6 monofilament fibers. Photo: Science

Synthetic muscle made from nylon is 100 times stronger than human muscle

Sometimes, I come across stories or various research that make me wonder “why the heck hasn’t anyone else thought of this before?” We should be grateful, nevertheless, that researchers from University of Texas at Dallas have found a way to manufacture artificial muscle that is up to 100 times stronger than the flimsy tissue that makes up the human biceps. The material is made out of nylon fibers – the stuff fishnets are made of – that are tensed almost to the upper limit and thermal processed to retain a high energy density.

Like very thin springs, the synthetic muscle is cheap, easy to make and durable. Of course it has some drawbacks, however the researchers envision its introduction in the industry extremely fast considering the facts. Applications include artificial muscles for robots, exoskeleton suits, or automatically heat-regulated window shutters and ventilation systems.

Photograph comparing muscles made by coiling (from left to right) 150 μm, 280 μm, 860 μm and 2.45 mm nylon 6 monofilament fibers. Photo: Science

Photograph comparing muscles made by coiling (from left to right) 150 μm, 280 μm, 860 μm and 2.45 mm nylon 6 monofilament fibers. Photo: Science

The process through which the synthetic sinew is coiled is quite trivially simple. Basically, it boils down to making sure you apply the right tension and weight to the thread when twisting it. Actually, according to the scientists involved in the work, similar nylon coils like the ones they produced can be made by regular people at home.

Nylon or polyethylene gets twisted under high tension over and over again until it reaches a certain strain threshold. Once the plastic can’t twist any more, it starts to coil up on itself like a curled telephone cord. The coil is then thermally treated so it gets locked in place; along with energy stored in the coil. When the resulting coil is heated, it begins to untwist, but in the process the whole whole material begins to compress.

“At first it seems confusing, but you can think of it kind of like a Chinese finger-trap,” says Ray Baughman, a materials scientist with the team. “Expanding the volume of the finger-trap, or heating the coil, actually makes the device shorten.”

By braiding and twisting different threads together and coiling them in different ways, you can end up with different kinds of variations in muscle strength, depending on the kind of application you’re looking for. Also, by blending in conductive wire or wrapping the muscle with a light-absorbing coating, the researchers can control the muscles’ movements with electricity and light instead of direct heat.

Photo: University of Texas at Dallas.

Photo: University of Texas at Dallas.

At the moment, the nylon artificial muscle isn’t all that efficient. While work is presently underway to solve inefficiency issues, by itself, even in its current form, this research is extremely impressive and will most likely get used in real-world applications real soon. It also is a great example of what you can achieve with readily available materials and technology just by applying novel tricks and strategies.

You can find out more in the paper published just today in the journal Science.

System To Build Transplant Tissue Created

 

cartilage

Organ transplants are no longer a novelty,  but transplants could help save a lot of lives of people who need certain tissues to live. There is probably going to be a day when laboratories could be able to grow synthetically engineered tissues such as muscle or cartilage needed for transplants [later edit: Scientists create 3D tissue printer that prints cartilage]. A big step forward has been made by Cornell engineers who describe in the journal Nature Materials a microvascular system they have created – it can nourish growing tissues, and this is probably bigger than most people think, meaning that the system could accommodate many kinds of tissue. They have created tiny channels within a water-based gel that mimic a vascular system at the cellular scale and can supply oxygen, essential nutrients and growth factors to feed individual cells.

“A significant impediment to building engineered tissues is that you can’t feed the core,” said Abraham Stroock, Cornell assistant professor of chemical and biomolecular engineering and one of the paper’s senior authors. “Simply embedding this mimic of a microvascular system allows you to maintain the core of the tissue during culture.” Gel scaffolds, he said, “are the culture flasks of the future.”.

Researchers are able to provide just the right nutrients and proteins to certain parts of the growing tissue to make it grow different on one side than the other. Like a bone on one side and cartilage on the other.

This gives solutions to the physical engineering aspects of growing tissues synthetically. But the biological problems remain and they are very hard to solve; scientists have not found a a source of cells which could be grown without changing the cell’s characteristics.