It’s all in the ink: Gelatin and a bioengineered ovary

You can 3D print just about anything these days. I can order a mad-scientist action figure in my own likeness or print a specialized electric guitar. Novelties aside, this technology has practical and life saving applications with proven effectiveness in customized prosthetic limbs and medical implants (such as pacemakers). With this technology branching into the field of medicine, it seems just a matter of time until we are printing entire biological structures, but can we ever print fully functional organs?

Growing in vitro organs is the holy grail of medicine; the ability to generate a human organ outside of the body would revolutionize modern medicine. Progress is being made on this front, researchers were recently able to use stem cells to grow a human ear on the back of a rat1; remarkable as this research is, it still relies on an animal to grow the organ. With advancing technology, many are wondering if it will one day be possible to construct an organ outside of an animal’s body entirely.

Scientists tackled one aspect of this in a recent study. Laronda et al explored the possibility of 3-D printing a structural support for a synthetic ovary2.   Using a special gelatin ink, these researchers were able to print scaffolds that could then be strategically populated with cells. The preciseness of this technique allowed not only for a proof-of-concept method for organ generation, but also created the opportunity to explore scaffold geometry required to make a functional ovary.

Constructing an organ scaffold is not just constrained by current technology; it is limited by our knowledge. Organs are not simply a mass of cells, they are complex structures and any old gelatin platform isn’t going to work. Organs need to protect the cells, and create structural support for them without interfering with their function. In the case of an ovary, cells need support to maintain their shape, but they also need to secrete hormones and release an egg during ovulation.

The authors experimented with the size and angle of the gelatin matrix to find a combination that balanced these needs. Their work resulted in a structure capable of hormone synthesis and the ability to ovulate in culture.

A biologically engineered ovary working outside of an animal is an amazing step forward, but taking it further, Laronda et al implanted the ovaries into surgically sterilized female mice. Remarkably, the implanted ovary became vascularized following the surgery, meaning the blood vessels connected to the bioengineered ovary and created circulation without further intervention from the scientists. The ovary integrated into the mouse’s body through natural regenerative processes, and eventually led to confirmed offspring. It seems that the human constructed ovary both integrated into the mouse body, and restored the ability to reproduce. It is hard to over state how amazing this research is, and how much excitement it has brought to the medical and scientific community.

We are a far distance away from printing a customized organ ready for transplant, but we are now quite a lot closer that we were just a few years ago.

 

  1. Bernstein, Jaime L., et al. “Fabrication of the First Full-Scale Human Auricular Chondrocyte Derived Ear Scaffold for Clinical Application.” Plastic and Reconstructive Surgery–Global Open 5.4S (2017): 94-95.
  2. Laronda, Monica M., et al. “A bioprosthetic ovary created using 3D printed microporous scaffolds restores ovarian function in sterilized mice.” Nature Communications 8 (2017).

Wound healing and cancer; two sides of the same coin?

We are imperfect beings. We do silly, reckless things, or sometimes-just fall up the stairs; but either way, we get injured and those injuries must heal. Wound healing is just one of the many outputs of our body’s ability to regenerate, which is pretty remarkable in itself. Regeneration is achieved through functional stem cells resident in our tissues. These stem cells haven’t differentiated, they haven’t committed to any one path, so they are able to duplicate and produce new tissue. For instance, there are two types of stem cells in your skin, epidermal stem cells and hair follicle stem cells. Each is responsible for generating a certain kind of tissue. Hair follicle stem cells keep your hair growing, and epidermal stem cells rejuvenate your skin with new cells. This is their normal day-to-day function; my skin is slowly replaced and I’m not stuck with a bad haircut for the rest of my life.

When things get a little too imperfect, they are also there to save the day. If the epidermis is damaged and an open cut needs to be healed, both types of stem cells can kick into action to regenerate and repair the skin. Based on signals from near by tissue, these cells know when to turn off this rapid regeneration, they can sense when enough cells have been made to heal the wound. Suppose these amazing, regenerating cells didn’t stop; what would happen if they lost the ability to pick up on these cues?

Cancer is a complicated and case-specific disease, but one common thread is that these are aggressive cells that grow without ‘listening’ to near by tissues telling them to stop. It has been described as “a wound that never heals”, and with good reason; there are some strange links between wound healing and cancer. Observationally it has been noted that individuals with chronic wounds have increased risk of cancer. Conversely, genetically inhibiting wound healing in mice reduces the likelihood of that animal developing cancer1. Given what we now know about stem cells and their regenerative abilities, there may be a clear biological link.

Ge and colleagues published an article directly addressing the behaviors of epidermal and hair follicle stem cells in wound healing and cancer2. Theses authors have some astonishing findings. First, during wound healing hair follicle stem cells can lose their identity, they can temporarily become epithelial stem cells to generate skin instead of hair. Once the wound is healed, these cells reassume their molecular identity and resume their existence as a hair follicle cell. This means that the three dimensional organization of their DNA actually changes during this time and key epithelial gene programs are turned on. When the wound heals, a molecular switch is flipped and this all returns back to the original hair follicle stem cell state.

The authors also examined a specific form of cancer known as small cell carcinoma. It was observed that this cancer type shares the molecular signatures of both hair follicle stem cells and epidermal stem cells. The argument made is that when wounded, cell fate barriers are transiently removed to rapidly fix a tissue, resulting in a highly proliferative and adaptive stem cell. However, in wound healing, the epithelial and hair follicle programs regulate each other. In malignancies, this regulation is lost. The up shot is that genetically interfering with these wound healing molecular signatures in cancer cells limits the tumor growth, and this is an area where new therapeutics are greatly needed.

Getting a severe wound is not going to give you cancer, but as Ge et al. illustrated, there is a mechanistic link between the two. As scientists better understand these pathways and the molecular switches, they can move towards enhanced wound healing technologies and cancer treatments.

  1. Schober, Markus, and Elaine Fuchs. “Tumor-initiating stem cells of squamous cell carcinomas and their control by TGF-β and integrin/focal adhesion kinase (FAK) signaling.” Proceedings of the National Academy of Sciences 108.26 (2011): 10544-10549.
  2. Ge, Yejing, et al. “Stem Cell Lineage Infidelity Drives Wound Repair and Cancer.” Cell (2017).

Not another Rouge One Stardust reference; this is interstellar space dust

Happy May 4th to all of my fellow Star Wars geeks! We might not be able to jump into hyperspace just yet, but we do have a pretty great space program. The Cassini spacecraft has been orbiting Saturn since 2004 and is now maneuvering its months-long grand finale of high-risk dives around Saturn’s rings, before plummeting into the gas giant’s atmosphere1. With Cassini’s long voyage coming to an end I thought that it would be worth a look back at one of its many discoveries.

Space is not empty: The ‘void’ between solar systems has much more going on than a massive expanse of nothingness. Dark matter aside, this part of space is still quite complicated; the interstellar medium contains cosmic rays, gases (mostly hydrogen and helium), and dust particles, to name a few of its components. This area of space is particularly interesting because we have such a limited picture of it. What exactly is out there? Are those dust particles the same presolar dust that created our solar system? Ignoring our human compulsion to just want to know, these are practical questions. Having just some of this information will give insight to the active conditions and physical realities in this region of space. We can understand what makes up of our solar neighborhood, and vastly improve interstellar modeling.

Cassini did not venture into the local interstellar space. Instead, it identified and tested particles that were blown into our solar system through an interstellar dust stream. First identified by the Ulysses spacecraft, this flow of interstellar particles is carried into the region around Saturn during certain parts of its orbit. Based on the speed and direction of the dust particle, Cassini was able to separate the interstellar dust from the local dust around Saturn. Over ten years, 36 interstellar dust particles were collected. Vaporized upon collision, Cassini’s Cosmic Dust Analyzer could detect the chemical composition of each particle.

Analysis of all 36 particles revealed some interesting things. First this dust is mainly silica based, containing high levels of magnesium, calcium, and iron inclusions. This composition means that the dust particles are tiny building blocks of rock. Secondly, these interstellar dust particles are unexpectedly similar to one another: Presolar dust grains, particles around at the formation of our solar system, are made up of highly diverse heavy elements, so interstellar dust is very clearly different.  It would seem that this interstellar dust is highly processed, cycling through destruction and reconstitution. The similarity of these particles indicates that they have been mixing and homogenizing, breaking apart and joining back together. The authors suggest that this process occurs when the particles shift between various temperature and density zones within the interstellar medium, colliding and devolatilizing in warm zones while condensing in cold regions. Until we can venture into the far reaches of interstellar space, these types of experiments are giving us some of the most meaningful insight into the nature and cosmic processes of our galaxy.

  1. NASA: Jet Propulsion Laboratory. “Cassini: The grand finale: Timeline”. NASA. Accessed: 05/03/2017. https://saturn.jpl.nasa.gov/the-journey/timeline/#launch-from-cape-canaveral
  2. Altobelli, N., et al. “Flux and composition of interstellar dust at Saturn from Cassini’s Cosmic Dust Analyzer.” Science 352.6283 (2016): 312-318.

Plant defense compounds: “The enemy of my enemy …”

Plants really have it rough; they struggle for sunlight, fight for resources with neighbors, and just have to make the best of things being at the bottom of the food chain. They are victims of circumstance, if they root in a sunny fertile meadow life might be smooth sailing, but if the neighborhood gets rough and predators are abundant, packing up and leaving town isn’t exactly an option. Just thinking about it makes me claustrophobic, but most plants are far from defenseless. Evolution has lead to some creative defensive adaptations that make herbivores think twice before munching away. The most noticeable herbivore deterrents include spines, thorns, toxins, and foul tasting compounds, but there is so much more going on in the world of plant protection than just these direct defenses.

For years it has been known that some plants emit volatile compounds when mechanically damaged. A chemical signal is released when a leaf or stem is broken, and traditionally it was understood that this chemical is relaying a message to other branches of the same tree, or nearby plant neighbors; acting as a SOS or call to man the molecular defenses1. A recent paper investigated this topic and found that, at least in one case, these volatile compounds are actually signaling to insects2.

In a two-year field study Schuman and colleagues tested the role of herbivory-induced plant volatiles (HIPV) in the wild tobacco plant (Nicotiana attenuata).   This research explored the HIPVs as part of a defense strategy against the tobacco hornworm, a natural and aggressive predator of the tobacco plant. The authors found that following the HIPV signal, higher order predators would flock to the besieged tobacco plant. In this case, the chemical signal isn’t really a SOS but perhaps it is a dinner bell. These higher order predators would make a meal of the tobacco hornworm and inadvertently defend the tobacco plant. Genetically engineered plants, unable to produce HIPVs, experienced much higher herbivore damage, highlighting the importance of this process.

It seems like cut-and-dry symbiosis, where everyone except the hornworm benefits from this arrangement of HIPV signaling. However, the tobacco plant leaves nothing to chance, and taking the role of dinner host seriously, it produces a secondary defense compound. An anti-digestive (trypsin protease inhibitor) is generated that makes the hornworms sluggish and easier prey, ensuring that more hornworms are removed from the plant. It is astonishing to realize how much time and energy plants have invested into defenses that are entirely external, relying on communication with other organisms for protection. Although not the first to suggest this, Schuman et al. provide a compelling argument for HIPV signaling as interspecies communication, and they remind us that nothing is ever as simple as it would seem, not even a plant.

  1. Heil, Martin, and Juan Carlos Silva Bueno. “Within-plant signaling by volatiles leads to induction and priming of an indirect plant defense in nature.” Proceedings of the National Academy of Sciences 104.13 (2007): 5467-5472.
  2. Schuman, Meredith C., Kathleen Barthel, and Ian T. Baldwin. “Herbivory-induced volatiles function as defenses increasing fitness of the native plant Nicotiana attenuata in nature.” Elife 1 (2012): e00007

Neurotoxic stress; Garbage disposal V.S. landfill?

Neurons are pretty amazing cells. They are complicated and beautiful units of a massively complex network; and without them running at high efficiency I would struggle to remember critical facts such as ‘coffee is delicious’. Like any finely tuned machine, neurons need things to be in strict order. Proteins are where they need to be, and in the right amount. Neurons, like many other cells, have mechanisms that allow precise control of proteins and organelles under healthy conditions. The proteasome and lysosome are the not-so-glamorous stars of the waste management process1. I like to think of them as the garbage disposals of the cell: Breaking down excess or defective proteins and organelles for reuse, and generally keeping the cell as clutter-free as possible.

This is more than good housekeeping, when misfolded protein aggregates accumulate we tend to find neurological pathologies. Irregular proteins and dysfunctional mitochondria are both associated with age-related cognitive decline and neurological disorders such as Parkinson’s disease. What’s more, that old colloquialism “one bad apple can spoil the barrel” seems not to be too off target in this case; misfolded proteins appear to spread between neurons, although exactly how remains a bit of a mystery2. There are proposed models that explain parts of this damaged protein sharing and disease progression, but scientists still don’t have a complete picture.

A recent study by Melentijevic et al. may be shedding some light on this long-standing black box of protein (and organelle) transfer3. Using C elegans as a model system, the authors described an alternative waste disposal method in neurons. Rather than being degraded within the cell, harmful or excess proteins are selectively removed. Neurons were observed concentrating these aberrant proteins and then pinching off this portion of the cell. These exiled regions of the cell, termed exophers, remain connected to the cell body by thread-like tube that allows for shuttling of additional proteins and damaged components into the exopher. Eventually the exopher is released entirely from the cell, relegated to being a floating sack of biological junk and hazardous waste. It’s not a pretty picture, but there is an upshot, the neuron that uses the ‘land fill’ option has improved function. It makes a degree of sense, when neurons were genetically manipulated to express Hunntington’s protein aggregates or Alzheimer’s disease amyloid-beta fragment protein (both notoriously difficult to degrade through the proteasome), the cell had an alternative way of removing these disease associated aggregates.

Maybe this is a selfish act, that one neuron improves function, but what ever happens to the jettisoned membrane-bound garbage bag? Does it end up in a designated land fill, or does it find its way into someone else’s back yard? The authors found that coelomocytes, a specialized type of phagocytic leukocyte, would scavenge for, and degrade, the exophers; but if these disease proteins can find their way into distant coelmocytes, who is to say that they cant also find their way into neighboring neurons? It is speculative, but Melentijevic and colleagues argue that this may be a mechanism behind neurodegenerative disease progression. It is a fascinating possibility, but even if disproven these authors described a new method of protein homeostasis control, adding to our understanding of the biological complexity of neurons, and that is a pretty impressive achievement in itself.

  1. Tai, Hwan-Ching, and Erin M. Schuman. “Ubiquitin, the proteasome and protein degradation in neuronal function and dysfunction.” Nature Reviews Neuroscience 9.11 (2008): 826-838.
  2. Guo, Jing L., and Virginia MY Lee. “Cell-to-cell transmission of pathogenic proteins in neurodegenerative diseases.” Nature medicine 20.2 (2014): 130-138.
  3. Melentijevic, Ilija, et al. “C. elegans neurons jettison protein aggregates and mitochondria under neurotoxic stress.” Nature 542.7641 (2017): 367-371.

Lamarck, Darwin, and a bunch of scared mice

For better or worse, I look a lot like my mother. I have her eyes and we share the same smile. Putting aside our collective fears of one day turning into our parents, the question of how it is that I physically resemble my mother is pretty well settled. In fact, the mechanism behind inheritance of traits from our parents had already become dogmatic by the mid twentieth century. DNA had been discovered, our genetic alphabet revealed.   We learned that these letters code for proteins, or words in this metaphor; and by the time that I was conceived, it was clear that I would be born with a genetic book of instruction, half of the words from each of my parents.

More than a century before the structure of DNA was uncovered, a battle raged about the fundamental questions and nature of evolution. Two competing theories divided the scientific community. At the center were Lamarck and Darwin, both agreed that physical characteristics were not random, but rather heritable through generations. The pressing question was how traits were conferred. Could an animal adapt over the course of its life and give these adaptations to its offspring? For example, if someone living in southern California developed a deep tan in response to prolonged sun exposure, is it possible that his/her offspring would be born with darker skin as a result? Lamarck thought that it was precisely these kinds of pressures from the environment that could lead to physical traits passing from one generation to the next. On the other side of things was Darwin; his proposition was that physical traits of the next generation were predetermined. If adaptations arose over the life of an animal, they will not be passed along. Darwin and his like-minded colleagues didn’t know about DNA, but they argued that there was something intrinsic in the animal responsible for the physical characteristics of one’s offspring. They suggested that there was something deeper than just the physical condition of the parent at the time of conception responsible for heritability.

In the end, Darwin’s theory won out: but maybe that’s not the end of the story. What if we get more from our parents? To stick with my book metaphor; what if we get the letters, but also the notes they wrote in the margins, things that might change the meaning of the ‘book’ itself? Although features such as eye color follow classic genetic patterns, some of our traits and predispositions might be influenced by our parents’ choices and experiences. With mounting data to this effect, most of us have now shifted over to an “its complicated” relationship status with genetic inheritance.

A paper published in 2013 does a beautiful job illustrating exactly how complicated it really is1. In this study, male mice were exposed to acetophenone, a sweet-smelling aromatic ketone, which was paired with a mild shock. Over time the mice became fearful around this smell, freezing in place and startling more readily. The truly remarkable finding was the impact that this experience had on the sons of these mice: When the authors tested the next generation of mice, they seemed to have an implicit negative reaction to the smell. This suggests that adults can pass along information acquired though direct experiences, in this case the information that this new smell is something to be avoided.

It seems that changes in development are responsible for this inherited fear. Sensory neurons, able to detect a particular odor were more abundant in these mice, being borne with an enhanced ability to detect acetophenone. The authors of this paper found that the fearful mice were genetically identical to their non-fearful counterparts. Letter for letter, the DNA was the same between the sons of scared and not-scared mice, but chemical augmentation accessorizing the DNA was different; effectively changing the genetic instructions without directly modifying the words.

Not surprisingly, the more scientist probe this topic, the less cut-and-dry things become. In some cases parents can pass along acquired adaptations or information about environmental conditions to their children. It remains unclear how wide spread this is, but metabolic disorders and odor predispositions are on the running list of confirmed cases1,2,3. Whether it was serendipitous or inspired insight, Lamarck is having another say on the nature of inheritance.

 

  1. Dias, Brian G., and Kerry J. Ressler. “Parental olfactory experience influences behavior and neural structure in subsequent generations.” Nature neuroscience 17.1 (2014): 89-96.
  2. Kaati, Gunnar, Lars O. Bygren, and Soren Edvinsson. “Cardiovascular and diabetes mortality determined by nutrition during parents’ and grandparents’ slow growth period.” European journal of human genetics: EJHG 10.11 (2002): 682.
  3. Rechavi, Oded, Gregory Minevich, and Oliver Hobert. “Transgenerational inheritance of an acquired small RNA-based antiviral response in C. elegans.” Cell 147.6 (2011): 1248-1256.