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October 2020

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How herpes infection may impair human fetal brain development — ScienceDaily

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Three cell-based models shed light on how herpes simplex virus type 1 (HSV-1) infection, which can spread to the fetal brain during pregnancy, may contribute to various neurodevelopmental disabilities and long-term neurological problems into adulthood, according to a study published October 22, 2020 in the open-access journal PLOS Pathogens by Pu Chen and Ying Wu of Wuhan University, and colleagues.

HSV-1 is a highly prevalent pathogen that can cause lifelong neurological problems such as cognitive dysfunction, learning disabilities, and dementia. But progress in understanding the role of HSV-1 in human fetal brain development has been hampered by restricted access to fetal human brain tissue as well as limitations of existing animal models. To address this gap in knowledge, the researchers generated three different cell-based neurodevelopmental disorder models, including a 2D layer of cells and a 3D brain-like structure. These models are based on human induced pluripotent stem cells (hiPSCs) — immature, embryonic stem cell-like cells that are generated by genetically reprogramming specialized adult cells.

HSV-1 infection in neural stem cells derived from hiPSCs resulted in activation of the caspase-3 apoptotic pathway, which initiates programmed cell death. HSV-1 infection also impaired the production of new neurons, and hindered the ability of hiPSC-derived neural stem cells to convert into mature neurons through a process called neuronal differentiation. Moreover, the HSV-1-infected brain organoids mimicked the pathological features of neurodevelopmental disorders in the human fetal brain, including impaired neuronal differentiation and abnormalities in brain structure. In addition, the 3D model showed that HSV-1 infection promotes the abnormal proliferation and activation of non-neuronal cells called microglia, accompanied by the activation of inflammatory molecules, such as TNF-α, IL-6, IL-10, and IL-4. According to the authors, the findings open new therapeutic avenues for targeting viral reservoirs relevant to neurodevelopmental disorders.

The authors add, “This study provides novel evidence that HSV-1 infection impaired human brain development and contributed to the neurodevelopmental disorder pathogen hypothesis.”

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Langerhans cells are up to the job, they just need a chance — ScienceDaily

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Blood stem cell transplants are an important part of treatment for a variety of serious conditions. However, adverse reactions of the host to donor cells present a significant risk. Now, researchers from the University of Tsukuba have pinpointed cell level behavior that could be used to help the host fight back, their findings are published in Journal of Investigative Dermatology.

A significant proportion of patients who receive blood stem cells develop acute graft-versus-host disease (aGVHD), which is a fatal immune disorder in which the white blood cells of the stem cell donor attack the organs of the recipient. This attack leads to damage to the skin, liver, and gastrointestinal tract.

One of the types of skin cell that is attacked is Langerhans cells (LCs). LCs are known to negatively or positively regulate various types of immune responses — that is, to induce, or prevent them. However, these antigen-presenting cells are known to be killed by T cells in the early phase of aGVHD. Therefore, working out their roles in the disease is difficult.

The researchers carried out two experiments using mice with mucocutaneous aGVHD lesions to assess different aspects of the roles played by LCs.

“We investigated mice with normal and depleted amounts of LCs and found that when LCs were depleted at the outset, the lesions became more severe,” study corresponding author Professor Naoko Okiyama explains. “In another experiment we found that the exacerbated disease resulted from a lack of death of OT-I cells that infiltrate the skin.”

It was also found that the ability of LCs to cause the programmed death of OT-I cells and stop them from multiplying is partly the result of their expression of proteins in the B7 family.

“Having determined the proteins that contribute to LCs inducing the death of OT-I cells, we can explore the possibility that enhancing the expression of B7 proteins on LCs could provide an opportunity to prevent aGVHD development,” says Professor Okiyama. “This could significantly improve treatments and have a positive effect on patient quality of life.”

It is hoped that future work to enhance the expression of specific proteins on LCs will lead to more successful blood stem cell transplants.

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New therapeutic approach against leukemia — ScienceDaily

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Leukemia frequently originates from the so-called leukemic stem cell, which resides in a tumor promoting and protecting niche within the bone marrow. Scientists from the Max Planck Institute of Biochemistry in Martinsried, Germany, have found a new way to make these cells vulnerable by specifically dislodging these cells from their niches.

Since blood cells have a limited lifespan, are lost during bleeding or are used up during infections, they must be replaced continuously. This supply is ensured by the so-called hematopoietic stem cells in the bone marrow. These cells can develop into any type of blood cell.

In chronic myeloid leukemia, the hematopoietic stem cell undergoes a genetic mutation by recombining chromosome 9 and 22. As a result, gene building blocks fuse that would otherwise not be in contact with each other. The incorrectly assembled chromosome is called Philadelphia chromosome and harbors the construction manual for the so-called BCR-ABL oncogene. This causes the leukemic stem cell to behave selfishly and divide at the expense of healthy blood stem cells.

Without Kindlin-3 no leukemia

A leukemic stem cell creates an environment termed the malignant niche that ensure its survival and proliferation. To remain in this tumor-promoting niche, the leukemic stem cell uses so-called integrins to attach itself to a scaffold of extracellular proteins, the so-called extracellular matrix, and to neighboring cells. In the leukemic stem cell, the activity and function of the integrins is facilitated by an intracellular protein called Kindlin.

Peter Krenn, first author of the study, explains: “The isoform Kindlin-3 is only used by blood cells. If mice harbor leukemic stem cells that lack Kindlin-3, they do not develop leukemia. Without Kindlin-3 and active integrins, the leukemic stem cells cannot attach themselves to their niche environment and are released from the bone marrow into the blood. Since they cannot home elsewhere either, they remain in the blood. There the leukemic stem cells lack the urgently needed support, which they usually receive from the niche, and die.”

New therapeutic approach: Kindlin-3 and CTLA-4

The new finding that the leukemic stem cells express a protein called CTLA-4 on their surface, which is absent from healthy blood stem cells, allowed the researchers to distinguish a leukemic blood stem cell from a healthy blood stem cell. The scientists used the CTLA-4 receptor as a shuttle to deliver a Kindlin-3 destroying compound, into leukemic stem cells. Peter Krenn explains: “CTLA-4 is only briefly present on the cell surface and is then rapidly recycled back into the cell and then back to the cell surface again. This enabled us to introduce a Kindlin-3 degrading siRNA into the cell by coupling it to a CTLA-4-binding RNA sequence, which is called aptamer. The leukemic stem cell without Kindlin-3 is flushed from the bone marrow and the leukemia loses its origin and runs out of fuel.”

Peter Krenn summarizes: “In our current study we have developed a new therapeutic approach to treat chronic myeloid leukemia in mice. However, the principle of the therapy is universally valid. The inhibited Kindlin-3 production and consequent loss of integrin function prevents the cancer cells from being able to adhere and settle in tumor-promoting niches. I assume that this method will also prevent the cancer cells of other types of leukemia from settling and that these diseases could thus become much more treatable.”

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Delivering proteins to testes could someday treat male infertility — ScienceDaily

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According to the Mayo Clinic, about 15% of couples are infertile, and male infertility plays a role in over one-third of these cases. Often, problems with sperm development are to blame. Now, researchers reporting in ACS Nano have found a way to deliver a protein important for sperm cell production directly to mouse testicles, where it restored normal sperm development and allowed previously infertile mice to father pups.

Male infertility often happens because of a lack of sperm in the semen, which can result from damage to the blood-testis barrier (BTB). This barrier protects reproductive cells from harmful toxicants and drugs, and a protein called PIN1 is important for its function. Mice genetically engineered to lack PIN1 are infertile, with small testes, depleted sperm stem cells and a low sperm count. Although scientists have considered gene therapies to treat male infertility, these procedures are risky because they could cause unwanted genetic changes in reproductive cells that might be passed onto offspring. Hyun-Mo Ryoo and colleagues wanted to develop a system to deliver proteins (such as PIN1) instead of genes to the testes, but first they had to find a way to get proteins through the complex tubes of the testicles and into cells.

The researchers developed a delivery system called Fibroplex, which consisted of spherical nanoparticles made of silk fibroin and a coating of lipids. They loaded PIN1 into Fibroplex, and showed that the particles appeared safe and didn’t show signs of toxicity or testicular damage in mice. When the team injected the PIN1-loaded Fibroplex into the testes of young mice with PIN1 deletions, the treatment restored nearly normal PIN1 levels and sperm stem cell numbers and repaired the BTB. Treated mice had normal testicular weight and size and about 50% of the sperm count of wild-type mice. Until about 5 months after treatment, when the protein degraded, the PIN1-Fibroplex-treated mice fathered a similar number of pups as wild-type mice, whereas untreated mice with PIN1 deletions remained infertile. This is the first demonstration of direct delivery of proteins into the testis to treat male infertility, the researchers say.

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Damaged muscles don’t just die, they regenerate themselves — ScienceDaily

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While building a muscle damage model in a cultured system, a research collaboration between Kumamoto University and Nagasaki University in Japan has found that components leaking from broken muscle fibers activate “satellite” muscle stem cells. While attempting to identify the proteins that activate satellite cells, they found that metabolic enzymes, such as GAPDH, rapidly activated dormant satellite cells and accelerated muscle injury regeneration. This is a highly rational and efficient regeneration mechanism in which the damaged muscle itself activates the satellite cells that begin the regeneration process.

Skeletal muscle is made up of bundles of contracting muscle fibers and each muscle fiber is surrounded by satellite cells — muscle stem cells that can produce new muscle fibers. Thanks to the work of these satellite cells, muscle fibers can be regenerated even after being bruised or torn during intense exercise. Satellite cells also play essential roles in muscle growth during developmental stages and muscle hypertrophy during strength training. However, in refractory muscle diseases like muscular dystrophy and age-related muscular fragility (sarcopenia), the number and function of satellite cells decreases. It is therefore important to understand the regulatory mechanism of satellite cells in muscle regeneration therapy.

In mature skeletal muscle, satellite cells are usually present in a dormant state. Upon stimulation after muscle injury, satellite cells are rapidly activated and proliferate repeatedly. During the subsequent myogenesis, they differentiate and regenerate muscle fibers by fusing with existing muscle fibers or with together. Of these three steps (satellite cell activation, proliferation, and muscle differentiation), little is known about how the first step, activation, is induced.

Since satellite cells are activated when muscle fibers are damaged, researchers hypothesized that muscle damage itself could trigger activation. However, this is difficult to prove in animal models of muscle injury so they constructed a cell culture model in which single muscle fibers, isolated from mouse muscle tissue, were physically damaged and destroyed. Using this injury model, they found that components leaking from the injured muscle fibers activated satellite cells, and the activated cells entered the G1 preparatory phase of cell division. Further, the activated cells returned to a dormant state when the damaged components were removed, thereby suggesting that the damaged components act as the activation switch.

The research team named the leaking components “Damaged myofiber-derived factors” (DMDFs), after the broken muscle fibers, and identified them using mass spectrometry. Most of the identified proteins were metabolic enzymes, including glycolytic enzymes such as GAPDH, and muscle deviation enzymes that are used as biomarkers for muscle disorders and diseases. GAPDH is known as a “moonlighting protein” that has other roles in addition to its original function in glycolysis, such as cell death control and immune response mediation. The researchers therefore analyzed the effects of DMDFs, including GAPDH, on satellite cell activation and confirmed that exposure resulted in their entry into the G1 phase. Furthermore, the researchers injected GAPDH into mouse skeletal muscle and observed accelerated satellite cell proliferation after subsequent drug-induced muscle damage. These results suggest that DMDFs have the ability to activate dormant satellite cells and induce rapid muscle regeneration after injury. The mechanism by which broken muscle activates satellite cells is a highly effective and efficient tissue regeneration mechanism.

“In this study, we proposed a new muscle injury-regeneration model. However, the detailed molecular mechanism of how DMDFs activate satellite cells remains an unclear issue for future research. In addition to satellite cell activation, DMDF moonlighting functions are expected to be diverse,” said Associate Professor Yusuke Ono, leader of the study. “Recent studies have shown that skeletal muscle secretes various factors that affect other organs and tissues, such as the brain and fat, into the bloodstream, so it may be possible that DMDFs are involved in the linkage between injured muscle and other organs via blood circulation. We believe that further elucidation of the functions of DMDFs could clarify the pathologies of some muscle diseases and help in the development of new drugs.”

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The functional importance of estrogen receptor beta — ScienceDaily

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Researchers at Kumamoto University, Japan generated mice lacking the estrogen receptor beta (ERβ) gene, both fiber-specific and muscle stem cell-specific, which resulted in abnormalities in the growth and regeneration of skeletal muscle in female mice. This was not observed in male mice that lacked the ERβ gene, suggesting that estrogen and its downstream signals may be a female-specific mechanism for muscle growth and regeneration.

In humans, skeletal muscle mass generally peaks in the 20s with a gradual decline beginning in the 30s, but it is possible to maintain muscle mass through strength training and a healthy lifestyle. Skeletal muscle can be damaged through excessive exercise or bruising, but it has the ability to regenerate. The muscle stem cells that surround muscle fibers are essential for this regeneration; they also play a part in increasing muscle size (hypertrophy). Muscle stem cell dysfunction is thought to be associated with various muscle weakness, such as age-related sarcopenia and muscular dystrophy. Although basic research on skeletal muscle has progressed rapidly in recent years, most studies were conducted on male animals and gender differences were given much consideration.

Estrogen is a female hormone that maintains the homeostasis of various tissues and organs. A decrease in estrogen levels due to amenorrhea, menopause, or other factors can lead to a disturbance in biological homeostasis. When estrogen binds to estrogen receptors (ERs) in cells, it is transferred into the nucleus and binds to genomic DNA to induce the expression of specific genes as transcription factors. There are two types of ERs, ERα and ERβ. While both ERα and ERβ have high binding capacity to estrogen, their tissue distribution is different, they do not have a common DNA-binding domain, and they may act as antagonists to each other, suggesting that they have different roles. Furthermore, estrogen’s effects on cells can be both ER-mediated and non-ER-mediated.

An epidemiological study of pre and postmenopausal women in their 50s indicated an association between decreased blood estrogen levels and muscle weakness. A research group at Kumamoto University previously showed that estrogen is important for skeletal muscle development and regeneration using an ovariectomized estrogen deficiency mouse model (Kitajima and Ono, J Endocrinol 2016). They also examined the effectiveness of nutritional interventions in estrogen-deficient conditions (Kitajima et al., Nutrients 2017). However, whether estrogen acts directly on the ER of muscle fibers and muscle stem cells to regulate skeletal muscle growth and regeneration, or whether it acts indirectly through other tissues and organs was unclear. In this study, the researchers generated mice with either myofiber-specific or muscle stem cell-specific ERβ gene deletion and analyzed the function of ERβ in skeletal muscle.

To clarify the role of ERβ in the growth of skeletal muscle, researchers generated mice (mKO) in which the action of the ERβ gene could be turned off in myofibers with the administration of the drug doxycycline. ERβ deficiency was induced at 6 weeks of age, and muscle fiber area and strength of the tibialis anterior muscle was measured at 10-12 weeks. Compared to control mice, both indices were reduced in female mKO mice but not in male mice. Since there was no change in the expression of muscle atrophy-related genes, this reduced growth of female mice was not thought to be due to an increase in muscle atrophy. Ovariectomy-induced estrogen deficiency is known to be associated with muscle quality changes, such as a relative increase in the proportion of fast-type fibers (Kitajima and Ono, J Endocrinol 2016), but no such qualitative changes were observed in mKO mice. It was therefore suggested that, while it may have a direct effect on myofiber growth via ERβ (as expressed in myofibers), estrogen may also regulate the quality of myofibers in a non-ERβ-mediated manner.

To determine the function of ERβ in muscle stem cells, the researchers generated scKO mice in which the ERβ gene could be deleted in muscle stem cells with the administration of the drug tamoxifen. They then evaluated muscle regenerative capacity by locally inducing muscle damage. While muscle regeneration was efficient in control mice, the regenerated muscle tissue of female scKO mice showed thin regenerated muscle fibers, fibrosis caused by collagen deposition, and significantly reduced muscle regenerative capacity. Muscle regeneration in male scKO mice, however, was not impaired. Because impaired muscle regeneration in females was not exacerbated by ovariectomies that made them estrogen deficient, the researchers thus thought that estrogen regulates muscle regeneration via ERβ expressed by muscle stem cells.

To further investigate the cause of reduced muscle regenerative capacity, researchers isolated and cultured muscle stem cells for evaluation. ERβ in cells from scKO mice was evaluated in several experiments using siRNAs and inhibitors. ERβ was found to contribute to the promotion of muscle stem cell proliferation and the inhibition of cell death. Gene expression analysis (RNA-seq) of scKO muscle stem cells showed that the expression of “niche”-related genes, which are required for the maintenance of stem cell properties, was reduced in scKO muscle stem cells. Therefore, the researchers hypothesize that the inactivation of ERβ may have affected the proliferation and survival of muscle stem cells by inhibiting the formation of stem cell niches.

This study is thought to be the first to show that ERβ in genetic mouse models plays an important role in the growth and regeneration of skeletal muscle through its function in both muscle fibers and muscle stem cells. However, the role of ERβ in male mice has not yet been elucidated and remains to be addressed even though its expression in both male and female mice is comparable.

“Amenorrhea is induced in female athletes through rigorous training or excessive dieting and has become one of three major problems, together with low energy availability and osteoporosis, faced by female athletes worldwide,” said study leader Associate Professor Yusuke Ono. “Although the animal findings of this study cannot be directly applied to humans, they do suggest that decreased estrogen during amenorrhea may suppress ERβ activity in muscle fibers and muscle stem cells. For female athletes, this may lead to poor athletic performance and delayed recovery from injuries, and puts them at risk for adverse competitive conditions. Our plan is to continue investigating the pathogenesis of age-related sarcopenia and muscular dystrophy by targeting ERβ and its downstream signals with the goal of developing treatments.”

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Researchers make counterintuitive discoveries about immune-like characteristics of cells — ScienceDaily

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Vanderbilt University researchers have reported the counterintuitive discovery that certain chemotherapeutic agents used to treat tumors can have the opposite effect of tissue overgrowth in normal, intact mammary glands, epidermis and hair follicles. The researchers also are the first to report the discovery of an innate immune signaling pathway in fibroblasts — the spindle-shaped cells responsible for wound healing and collagen production — that causes cells to proliferate. Such signaling pathways previously were attributed only to immune cells.

The article describing the research, “DNA Damage Promotes Epithelial Hyperplasia and Fate Mis-specification via Fibroblast Inflammasome Activation,” was published in the journal Developmental Cell on Oct. 13.

The findings of this work, led by postdoctoral fellow Lindsey Seldin and Professor and Chair of the Department of Cell and Developmental Biology Ian Macara, have broad implications for diseases associated with the immune system like psoriasis, as well as cancer and stem cell research.

Understanding the functionality of stem cells and the way that their behavior is regulated has been a longstanding research interest for Seldin. “Normal stem cells have an amazing ability to continuously divide to maintain tissue function without forming tumors,” she explained. “We wanted to understand what happens to these cells in their native environment when subjected to damage, and if the response was connected to a specific tissue.”

By testing perturbations to the epidermis, mammary gland and hair follicles vis-à-vis mechanical damage or DNA damage through chemotherapeutic agents, the researchers saw a paradoxical response: Stem cells, which otherwise would divide slowly, instead divided rapidly, promoting tissue overgrowth.

When the tissues were subjected to DNA damage, their stem cells overly proliferated, giving rise to different cells than they normally would. “This was a very perplexing result,” said Seldin, the paper’s lead author. “We were determined to figure out if this was a direct response by the stem cells themselves or by inductive signals within their environment.” The key clue was that stem cells isolated from the body did not behave the same way as in intact tissue — an indication that the response must be provoked from signals being sent to the stem cells from other surrounding cell types.

The investigators turned their attention to fibroblasts, the predominant component of the tissue microenvironment. When fibroblasts in the epidermis were removed, the stem cell responsiveness to DNA damage was diminished, indicating that they played an important role. RNA sequencing revealed that fibroblasts can signal by way of inflammasomes — complexes within cells that help tissues respond to stress by clearing damaged cells or pathogens, which also in this case caused stem cells to divide. “This is an astounding discovery,” said Macara. “Inflammasome signaling has previously been attributed only to immune cells, but now it seems that fibroblasts can assume an immune-like nature.”

Seldin intends to replicate this work in the mammary gland to determine whether fibroblasts initiate the same innate immune response as in the epidermis, and more broadly how fibroblasts contribute to the development of cancer and other diseases associated with the immune system.

This work was supported by NCI/NIH grants R35CA132898, F32CA213794 and T32CA119925, as well as American Cancer Society grant PF-18-007-01-CCG.

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Materials provided by Vanderbilt University. Original written by Marissa Shapiro. Note: Content may be edited for style and length.

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Hair loss might be prevented by regulating stem cell metabolism — ScienceDaily

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Hair follicle stem cells, which promote hair growth, can prolong their life by switching their metabolic state. In experiments conducted with mice, a research group active in Helsinki and Cologne, Germany, has demonstrated that a protein called Rictor holds a key role in the process.

The study was published in the Cell Metabolism journal.

Mechanisms that regulate stem cells

Ultraviolet radiation and other environmental factors damage our skin and other tissues every day, with the body continuously removing and renewing the damaged tissue. On average, humans shed daily 500 million cells and a quantity of hairs weighing a total of 1.5 grams.

The dead material is replaced by specialised stem cells that promote tissue growth. Tissue function is dependent on the activity and health of these stem cells, as impaired activity results in the ageing of the tissues.

“Although the critical role of stem cells in ageing is established, little is known about the mechanisms that regulate the long-term maintenance of these important cells. The hair follicle with its well understood functions and clearly identifiable stem cells was a perfect model system to study this important question,” says Sara Wickstrom.

Reduced metabolic flexibility in stem cells underlying hair loss

At the end of hair follicles’ regenerative cycle, the moment a new hair is created, stem cells return to their specific location and resume a quiescent state. The key finding in the new study is that this return to the stem cell state requires a change in the cells’ metabolic state. They switch from glutamine-based metabolism and cellular respiration to glycolysis, a shift triggered by signalling induced by a protein called Rictor, in response to the low oxygen concentration in the tissue. Correspondingly, the present study demonstrated that the absence of the Rictor protein impaired the reversibility of the stem cells, initiating a slow exhaustion of the stem cells and hair loss caused by ageing.

The research group created a genetic mouse model to study the function of the Rictor protein, observing that hair follicle regeneration and cycle were significantly delayed in mice lacking the protein. Ageing mice suffering from Rictor deficiency showed a gradual decrease in their stem cell, resulting in loss of hair.

Precursors for developing hair loss drug therapies

Further research will now be conducted to investigate how these preclinical findings could be utilised in human stem cell biology and potentially also in drug therapies that would protect hair follicles from ageing. In other words, the mechanisms identified in the study could possibly be utilised in preventing hair loss.

“We are particularly excited about the observation that the application of a glutaminase inhibitor was able to restore stem cell function in the Rictor-deficient mice, proving the principle that modifying metabolic pathways could be a powerful way to boost the regenerative capacity of our tissues,” Wickstrom explains.

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Study finds that compressing cells, and crowding their contents, can coax them to grow and divide — ScienceDaily

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The closer people are physically to one another, the higher the chance for exchange, of things like ideas, information, and even infection. Now researchers at MIT and Boston Children’s Hospital have found that, even in the microscopic environment within a single cell, physical crowding increases the chance for interactions, in a way that can significantly alter a cell’s health and development.

In a paper published today in the journal Cell Stem Cell, the researchers have shown that physically squeezing cells, and crowding their contents, can trigger cells to grow and divide faster than they normally would.

While squeezing something to make it grow may sound counterintuitive, the team has an explanation: Squeezing acts to wring water out of a cell. With less water to swim in, proteins and other cell constituents are packed closer together. And when certain proteins are brought in close proximity, they can trigger cell signaling and activate genes within the cell.

In their new study, the scientists found that squeezing intestinal cells triggered proteins to cluster along a specific signaling pathway, which can help cells maintain their stem-cell state, an undifferentiated state in which can quickly grow and divide into more specialized cells. Ming Guo, associate professor of mechanical engineering at MIT, says that if cells can simply be squeezed to promote their “stemness,” they can then be directed to quickly build up miniature organs, such as artificial intestines or colons, which could then be used as platforms to understand organ function and test drug candidates for various diseases, and even as transplants for regenerative medicine.

Guo’s co-authors are lead author Yiwei Li, Jiliang Hu, and Qirong Lin from MIT, and Maorong Chen, Ren Sheng, and Xi He of Boston Children’s Hospital.

Packed in

To study squeezing’s effect on cells, the researchers mixed various cell types in solutions that solidified as rubbery slabs of hydrogel. To squeeze the cells, they placed weights on the hydrogel’s surface, in the form of either a quarter or a dime.

“We wanted to achieve a significant amount of cell size change, and those two weights can compress the cell by something like 10 to 30 percent of their total volume,” Guo explains.

The team used a confocal microscope to measure in 3D how individual cells’ shapes changed as each sample was compressed. As they expected, the cells shrank with pressure. But did squeezing also affect the cell’s contents? To answer this, the researchers first looked to see whether a cell’s water content changed. If squeezing acts to wring water out of a cell, the researchers reasoned that the cells should be less hydrated, and stiffer as a result.

They measured the stiffness of cells before and after weights were applied, using optical tweezers, a laser-based technique that Guo’s lab has employed for years to study interactions within cells, and found that indeed, cells stiffened with pressure. They also saw that there was less movement within cells that were squeezed, suggesting that their contents were more packed than usual.

Next, they looked at whether there were changes in the interactions between certain proteins in the cells, in response to cells being squeezed. They focused on several proteins that are known to trigger Wnt/?-catenin signaling, which is involved in cell growth and maintenance of “stemness.”

“In general, this pathway is known to make a cell more like a stem cell,” Guo says. “If you change this pathway’s activity, how cancer progresses and how embryos develop have been shown to be very different. So we thought we could use this pathway to demonstrate how cell crowding is important.”

A “refreshing” path

To see whether cell squeezing affects the Wnt pathway, and how fast a cell grows, the researchers grew small organoids — miniature organs, and in this case, clusters of cells that were collected from the intestines of mice.

“The Wnt pathway is particularly important in the colon,” Guo says, pointing out that the cells that line the human intestine are constantly being replenished. The Wnt pathway, he says, is essential for maintaining intestinal stem cells, generating new cells, and “refreshing” the intestinal lining.

He and his colleagues grew intestinal organoids, each measuring about half a millimeter, in several Petri dishes, then “squeezed” the organoids by infusing the dishes with polymers. This influx of polymers increased the osmotic pressure surrounding each organoid and forced water out of their cells. The team observed that as a result, specific proteins involved in activating the Wnt pathway were packed closer together, and were more likely to cluster to turn on the pathway and its growth-regulating genes.

The upshot: Those organoids that were squeezed actually grew larger and more quickly, with more stem cells on their surface than those that were not squeezed.

“The difference was very obvious,” Guo says. “Whenever you apply pressure, the organoids grow even bigger, with a lot more stem cells.”

He says the results demonstrate how squeezing can affect a organoid’s growth. The findings also show that a cell’s behavior can change depending on the amount of water that it contains.

“This is very general and broad, and the potential impact is profound, that cells can simply tune how much water they have to tune their biological consequences,” Guo says.

Going forward, he and his colleagues plan to explore cell squeezing as a way to speed up the growth of artificial organs that scientists may use to test new, personalized drugs.

“I could take my own cells and transfect them to make stem cells that can then be developed into a lung or intestinal organoid that would mimic my own organs,” Guo says. “I could then apply different pressures to make organoids of different size, then try different drugs. I imagine there would be a lot of possibilities.”

This research is supported, in part, by the National Cancer Institute and the Alfred P. Sloan Foundation.

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Human intestinal organoids grown from stem cells used to model congenital disorder in babies — ScienceDaily

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Scientists at Cincinnati Children’s used human intestinal organoids grown from stem cells to discover how our bodies control the absorption of nutrients from the food we eat. They further found that one hormone might be able to reverse a congenital disorder in babies who cannot adequately absorb nutrients and need intravenous feeding to survive.

Heather A. McCauley, PhD, a research associate at Cincinnati Children’s Hospital Medical Center, found that the hormone peptide YY, also called PYY, can reverse congenital malabsorption in mice. With a single PYY injection per day, 80% of the mice survived. Normally, only 20% to 30% survive.

This indicates PYY might be a possible therapeutic for people with severe malabsorption.

Poor absorption of macronutrients is a global health concern, underlying ailments such as malnutrition, intestinal infections and short-gut syndrome. So, identification of factors regulating nutrient absorption has significant therapeutic potential, the researchers noted.

McCauley was lead author of a manuscript published Sept. 22 in Nature Communications, which reported that the absorption of nutrients — in particular, carbohydrates and proteins — is controlled by enteroendocrine cells in the gastrointestinal tract.

Babies born without enteroendocrine cells — or whose enteroendocrine cells don’t function properly — have severe malabsorption and require IV nutrition.

“This study allowed us to understand how important this one rare cell type is in controlling how the intestine absorbs nutrients and functions on a daily basis,” McCauley said.

The Cincinnati Children’s study, “Enteroendocrine cells couple nutrient sensing to nutrient absorption by regulating ion transport,” was the first to describe a mechanism linking enteroendocrine cells to the absorption of macronutrients like carbohydrates and amino acids.

One key finding of the study is how these cells, upon sensing ingested nutrients, prepare the intestine to absorb nutrients by controlling the influx and outflux of electrolytes and water, the researchers stated. Absorption of carbohydrates and protein is then linked to the movement of ions in the intestine.

For this study, the scientists relied on human intestinal organoid models created in a lab, said James Wells, PhD, senior author of the study and chief scientific officer of the Center for Stem Cell and Organoid Medicine (CuSTOM) at Cincinnati Children’s.

Grown from stem cells, organoids are small formations of human organ that have an architecture and functions that are similar to their full-size counterparts.

Cincinnati Children’s launched efforts to make organoids from human pluripotent stem cells in 2006, said Wells, who is also director for basic research in the Division of Endocrinology at the medical center and an Allen Foundation Distinguished Investigator.

“What this study highlights is how decades of basic research into how organs are made and how they function is now leading to breakthroughs in identifying new therapeutics,” said Wells, who has led a team of investigators at Cincinnati Children’s who developed some of the first human organoid technologies that are now used globally.

The study on malabsorption used three different human small intestinal tissue models — all derived from pluripotent stem cells, which can form any kind of tissue in the body.

“The human organoids are essentially a much more realistic avatar to these patients with these rare mutations,” Wells said. “They allow us to model much more faithfully the human disease.”

McCauley and Wells conceived and initiated the recent study on malabsorption, designed the experiments and wrote the manuscript. Contributors to the study included intestinal physiology experts Marshall “Chip” Montrose, PhD, and Eitaro Aihara, PhD, of the University of Cincinnati.

The study was supported by grants from the National Institutes of Health (U19 AI116491, P01 HD093363, UG3 DK119982, U01 DK103117); S&R Foundation and American Physiological Society; the American Diabetes Association (1-17-PDF-102); the Shipley Foundation and the Allen Foundation. Support was also received from the Digestive Disease Research Center (P30 DK078392).

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