Glaucoma is a neurodegenerative disease that causes vision loss and blindness due to a damaged optic nerve. More than 200,000 people are affected by glaucoma in the United States each year. Unfortunately, there is currently no treatment. In a newly published paper in Communications Biology, researchers found neurons use mitochondria for a steady source of energy, and restoring mitochondrial homeostasis in the diseased neurons can protect the optic nerve cells from being damaged.

“Age-related neurodegenerative disease, which includes glaucoma, Parkinson’s disease, and amyotrophic lateral sclerosis (ALS), is the biggest global health problem,” said Arupratan Das, PhD, assistant professor of ophthalmology and principal investigator of the study. “The fundamental mechanisms that we discovered can be used to protect neurons in glaucoma and be tested for the other diseases. We have identified a critical step of complex mitochondrial homeostasis process, which rejuvenates the dying neuron, similar to giving a lifeline to a dying person.”

The research team, led by Michelle Surma and Kavitha Anbarasu from the Department of Ophthalmology, used induced pluripotent stem cells (iPSCs) from patients with and without glaucoma as well as clustered regularly interspaced short palindromic repeats (CRISPR) engineered human embryonic stem cells with glaucoma mutation. Using stem cell differentiated retinal ganglion cells (hRGCs) of the optic nerve, electron microscopy and metabolic analysis, researchers identified glaucomatous retinal ganglion cells suffer mitochondrial deficiency with more metabolic burden on each mitochondrion. This leads to mitochondrial damage and degeneration. Mitochondria are the tube like structures in cells which produce adenosine triphosphate, cell’s energy source.

However, the process could be reversed by enhancing mitochondrial biogenesis by a pharmacological agent. The team showed retinal ganglion cells are highly efficient in degrading bad mitochondria, but at the same time producing more to maintain homeostasis.

“Finding that retinal ganglion cells with glaucoma produce more adenosine triphosphate even with less mitochondria was astonishing,” Das said. “However, when triggered to produce more mitochondria, the adenosine triphosphate production load was distributed among more mitochondrion which restored the organelle physiology. It is similar to a situation where a heavy stone is carried by fewer people versus a greater number of people — each person will have less pain and injury, just like each mitochondrion will have less difficulty and damage.”

In the future, Das would like to test if these mechanisms protect the optic nerve in animal models under injury before testing in humans to hopefully lead to new clinical interventions.

Just as teams of elite athletes train alongside staffs of coaches, ensembles of neurons in the brain’s motor cortex depend on nearby astrocytes to help them learn to encode when and how to move, and the optimal timing and trajectory of a motion, the study shows. Describing a series of experiments in mice, the new paper in the Journal of Neuroscience reveals two specific ways that astrocytes directly impact motor learning, maintaining an optimal molecular balance in which the neuronal ensembles can properly refine movement performance.

“This finding is part of a body of work from our lab and other labs that elevate the importance of astrocytes to neuronal encoding and hence to behavior,” said senior author Mriganka Sur, Newton Professor of Neuroscience in The Picower Institute and MIT’s Department of Brain and Cognitive Sciences. “This shows that while the population coding of behaviors is a neuronal function, we need to include astrocytes as partners with them.”

Picower Institute Postdoc Jennifer Shih and former Sur Lab postdocs Chloe Delepine and Keji Li are the paper’s co-lead authors.

“This research highlights the complexity of astrocytes and the importance of astrocyte-neuron interactions in fine-tuning brain function by providing concrete evidence of these mechanisms in the motor cortex,” Delepine said.

Messing with motor mastery

The team gave their mice a simple motor task to master. When cued with a tone, the mice had to reach for and push down a lever within five seconds. The rodents showed they could learn the task over a few days and master it within a couple of weeks. They not only performed the task more accurately, but also their reactions quickened and the trajectory of their reaching and pushing became smoother and more uniform.

In some of the mice, however, the team employed precision molecular interventions to disrupt two specific functions of astrocytes in the motor cortex. In some mice, they disrupted the astrocytes’ ability to soak up the neurotransmitter glutamate, a chemical that excites neural activity when it is received at connections called synapses. In other mice they hyperactivated the astrocytes’ calcium signals, which affected how they function. In both ways, the interventions disrupted the normal process by which neurons would form or change their connections with each other, a process called “plasticity” that enables learning.

The interventions each affected the performance of the mice. The first one (a knockdown of the glutamate transporter GLT1) didn’t affect whether the mice pushed the lever or how quickly they did so. Instead it disrupted the smoothness of the motion. Mice with GLT1 disrupted remained erratic and shaky, as if unable to refine their technique. Mice subjected to the second intervention (activation of Gq signaling) showed deficits not only in the smoothness of their motion trajectory but also in their understanding of when to push the lever and their quickness in doing so.

The team dug deeper into how these deficits emerged. Using a two-photon microscope they tracked neural activity in the motor cortex in unaltered mice and mice treated with each intervention. Compared to what they saw in normal mice, the mice with GLT1 disrupted showed less correlated activity among neurons. Mice with Gq activation showed excessive correlated activity compared to the normal mice.

“The data suggest that an optimal level of neuronal correlation is required for the emergence of functional neuronal ensembles that drive task performance,” the authors wrote. “Meaningful correlations that carry information are what drive motor learning rather than the absolute magnitude of potentially non-specific correlations.”

The team dug even deeper still. They carefully isolated astrocytes from the motor cortex of mice, including some who were untrained in the motor task as well as ones who were trained, including mice who were unaltered and mice who underwent each intervention. In all these samples of purified astrocytes, they then sequenced RNA to assess how they differed in their expression of genes. They found that in trained vs. untrained mice, astrocytes exhibited greater expression of genes related to GLT1. In mice where they intervened they saw lowered expression. That evidence further suggested that the glutamate transporter process is indeed fundamental to training in motor tasks.

“Here we show that astrocytes have an important role in enabling neurons to encode information properly, both the learning and the execution of a movement for example,” Sur said.

Pierre Gaudeaux is a co-author of the paper. The research was funded by The National Institutes of Health, the Simons Foundation, and The JPB Foundation.

Leukaemia (blood cancer) is a group of malignant and aggressive diseases of the blood-forming cells in the bone marrow. Very intensive chemotherapy and in some cases a bone marrow transplant are the only cure. Like all cancers, leukaemia is caused by changes in the DNA, the heredity material present in human cells in the form of 46 chromosomes. In many forms of leukaemia, large parts of these chromosomes are altered. People with Down syndrome, who have three copies of chromosome 21 (trisomy 21) are highly vulnerable: the risk of developing aggressive Acute Myeloid Leukaemia (AML) in the first four years of their life is more than 100 times greater for children with Down syndrome. Down syndrome is the most common congenital genetic disorder, affecting about one in 700 newborn babies.

RUNX1 transcription factor is responsible

The research group led by Professor Jan-Henning Klusmann, Director of the Department of Paediatric and Adolescent Medicine at University Hospital Frankfurt, has now discovered how the additional chromosome 21 can promote AML. With the help of genetic scissors (CRISPR-Cas9), they examined each of the 218 genes on chromosome 21 for its carcinogenic effect. It emerged that the RUNX1 gene is responsible for the chromosome’s specific carcinogenic properties. In further analyses, the researchers were able to corroborate that only one particular variant — or isoform — of the gene promotes the development of leukaemia. Klusmann explains: “Other RUNX1 isoforms were even able to prevent the cells from degenerating. This explains why RUNX1 has so far not stood out — in several decades of extensive cancer research.”

The RUNX1 gene encodes a “transcription factor” — a protein responsible for regulating the activity of other genes. RUNX1 regulates many processes, including embryonic development and early and late haematopoiesis, or blood formation. Disruption of this important regulator is therefore a key event in the development of AML. “Thanks to our research results, we now have a better understanding of what happens in leukemogenesis,” explains Klusmann, an expert in paediatric cancer. “The study underlines how important it is to examine all gene variants in carcinogenesis. In many cases, certain mutations in cancer cells alter how these variants form,” he says.

Development of more sophisticated therapeutic approaches

These insights are important for a better understanding of the complex mechanisms of carcinogenesis, as Klusmann explains: “In this way, we have laid the groundwork for developing more sophisticated therapeutic approaches. Through our biochemical analyses, we now know exactly how the gene variant alters the blood cells. From there, we were able to use specific substances that block the disease mechanism.” The intention now is to further explore the effect of these substances for use in medical care. Klusmann: “On the basis of our expertise, we now want to develop therapies to correct this malfunction. Applying them in clinical practice will certainly take a few more years, but hopefully they will lead in the future to sparing our young patients from intensive chemotherapy.”

The knots make the material far tougher than identically structured but unknotted materials: they absorb more energy and are able to deform more while still being able to return to their original shape undamaged. These new knotted materials may find applications in biomedicine as well as in aerospace applications due to their durability, possible biocompatibility, and extreme deformability.

“The capability to overcome the general trade-off between material deformability and tensile toughness [the ability to be stretched without breaking] offers new ways to design devices that are extremely flexible, durable, and can operate in extreme conditions,” says former Caltech graduate student Widianto P. Moestopo (MS ‘ 19, PhD ’22), now at Lawrence Livermore National Laboratory. Moestopo is the lead author of a paper on the nanoscale knots that was published on March 8 in Science Advances.

Moestopo helped develop the material in the lab of Julia R. Greer, the Ruben F. and Donna Mettler Professor of Materials Science, Mechanics and Medical Engineering; Fletcher Jones Foundation director of the Kavli Nanoscience Institute; and senior author of the Science Advances paper. Greer is at the forefront of the creation of such nano-architected materials, or materials whose structure is designed and organized at a nanometer scale and that consequently exhibit unusual, often surprising properties.

“Embarking on understanding how the knots would affect the mechanical response of micro-architected materials was a new out-of-the-box idea,” Greer says. “We had done extensive research on studying the mechanical deformation of many other types of micro-textiles, for example, lattices and woven materials. Venturing into the world of knots allowed us to gain deeper insights into the role of friction and energy dissipation, and proved to be meaningful.”

Each knot is around 70 micrometers in height and width, and each fiber has a radius of around 1.7 micrometers (around one-hundredth the radius of a human hair). While these are not the smallest knots ever made — in 2017 chemists tied a knot made from an individual strand of atoms — this does represent the first time that a material composed of numerous knots at this scale has ever been created. Further, it demonstrates the potential value of including these nanoscale knots in a material — for example, for suturing or tethering in biomedicine.

The knotted materials, which were created out of polymers, exhibit a tensile toughness that far surpasses materials that are unknotted but otherwise structurally identical, including ones where individual strands are interwoven instead of knotted. When compared to their unknotted counterparts, the knotted materials absorb 92 percent more energy and require more than twice the amount of strain to snap when pulled.

The knots were not tied but rather manufactured in a knotted state by using advanced high-resolution 3D lithography capable of producing structures in the nanoscale. The samples detailed in the Science Advancespaper contain simple knots — an overhand knot with an extra twist that provides additional friction to absorb additional energy while the material is stretched. In the future, the team plans to explore materials constructed from more complex knots.

Moestopo’s interest in knots grew out of research he was conducting in 2020 during the COVID-19 lockdowns. “I came across some works from researchers who are studying the mechanics of physical knots as opposed to knots in a purely mathematical sense. I do not consider myself a climber, a sailor, or a mathematician, but I have tied knots throughout my life, so I thought it was worth trying to insert knots into my designs,” he says.