Fight Aging! Newsletter, March 8th 2021

A trio of recent studies highlight the need to incorporate behavioral and social science alongside the study of biological mechanisms in order to slow aging. Exciting biological discoveries about rate of aging in non-human species are sometimes not applicable or lost when we apply them to humans. Including behavioral and social research can support translation of geroscience findings from animal models to benefit human. "The move from slowing fundamental processes of aging in laboratory animals to slowing aging in humans will not be as simple as prescribing a pill and watching it work. Compared to aging in laboratory animals, human aging has many behavioral/social in addition to cellular origins and influences. These influences include potential intervention targets that are uniquely human, and therefore are not easily investigated in animal research."

Several of these human factors have big impacts on health and mortality: stress and early life adversity, psychiatric history, personality traits, intelligence, loneliness and social connection, and purpose in life are connected to a variety of late-life health outcomes. These important factors need to be taken into account to get a meaningful prediction of human biological aging. "Geroscience can be augmented through collaboration with behavioral and social science to accomplish translation from animal models to humans, and improve the design of clinical trials of anti-aging therapies. It's vital that geroscience advances be delivered to everyone, not just the well-to-do, because individuals who experience low education, low incomes, adverse early-life experiences, and prejudice are the people who age fastest and die youngest."

"Social hallmarks of aging" can be strongly predictive of age-related health outcomes - in many cases, even more so than biological factors. While the aging field commonly discusses the biological hallmarks of aging, we don't tend to include the social and behavioral factors that lead to premature aging. Researchers have called the main five factors "the Social Hallmarks of aging" and poses that these should not be ignored in any sample of humans and the concepts should be incorporated where possible into non-human studies.

Researchers examined data that was collected in 2016 from the Health and Retirement Study, a large, nationally representative study of Americans over the age of 56 that incorporates both surveys regarding social factors and biological measurements, including a blood sample for genetic analysis. For the study, she focused the five social hallmarks for poor health outcomes: 1) low lifetime socioeconomic status, including lower levels of education, 2) adversity in childhood and adulthood, including trauma and other hardships, 3) being a member of a minority group, 4) adverse health behaviors, including smoking, obesity, and problem drinking, 5) adverse psychological states, such as depression, negative psychological outlook and chronic stress. The presence of these five factors were strongly associated with older adults having difficulty with activities of daily living, experiencing problems with cognition, and multimorbidity (having five or more diseases).

A new study shows how the formation of new neurons is impaired with advancing age. Protein structures in the nuclei of neural stem cells make sure that harmful proteins accumulating over time are unevenly distributed onto the two daughter cells during cell division. This seems to be an important part of the cells' ability to proliferate over a long time in order to maintain the supply of neurons. With advancing age, however, the amounts of nucleic proteins change, resulting in defective distribution of harmful proteins between the two daughter cells. This results in a decrease in the numbers of newly generated neurons in the brains of older mice.

The central element in this process is a nuclear protein called lamin B1, the levels of which decrease as people age. When the researchers increased lamin B1 levels in experiments in aging mice, stem cell division improved and the number of new neurons grew. The research is part of several ongoing projects aiming to reactivate aging stem cells. The ability to regenerate damaged tissue generally declines with age, thus affecting almost all types of stem cells in the body. These latest findings are an important step towards exploring age-dependent changes in the behavior of stem cells. "We now know that we can reactivate aging stem cells in the brain. Our hope is that these findings will one day help increase levels of neurogenesis, for example in older people or those suffering from degenerative diseases such as Alzheimer's. Even if this may still be many years in the future."

Neural stem cells (NSCs) generate neurons throughout life in the hippocampal dentate gyrus. With advancing age, levels of neurogenesis sharply drop, which has been associated with a decline in hippocampal memory function. However, cell-intrinsic mechanisms mediating age-related changes in NSC activity remain largely unknown. Here, we show that the nuclear lamina protein lamin B1 (LB1) is downregulated with age in mouse hippocampal NSCs, whereas protein levels of SUN-domain containing protein 1 (SUN1), previously implicated in Hutchinson-Gilford progeria syndrome (HGPS), increase. Balancing the levels of LB1 and SUN1 in aged NSCs restores the strength of the endoplasmic reticulum diffusion barrier that is associated with segregation of aging factors in proliferating NSCs. Virus-based restoration of LB1 expression in aged NSCs enhances stem cell activity in vitro and increases progenitor cell proliferation and neurogenesis in vivo. Thus, we here identify a mechanism that mediates age-related decline of neurogenesis in the mammalian hippocampus.

Aging is the greatest risk factor for a multitude of diseases including cardiovascular disease, neurodegeneration, and cancer. Despite decades of research dedicated to understanding aging, the mechanisms underlying the aging process remain incompletely understood. The widely-accepted free radical theory of aging (FRTA) proposes that the accumulation of oxidative damage caused by reactive oxygen species (ROS) is one of the primary causes of aging.

To define the relationship between ROS and aging, there have been two main approaches: comparative studies that measure outcomes related to ROS across species with different lifespans, and experimental studies that modulate ROS levels within a single species using either a genetic or pharmacologic approach. Comparative studies have shown that levels of ROS and oxidative damage are inversely correlated with lifespan. While these studies in general support the FRTA, this type of experiment can only demonstrate correlation, not causation.

Experimental studies involving the manipulation of ROS levels in model organisms have generally shown that interventions that increase ROS tend to decrease lifespan, while interventions that decrease ROS tend to increase lifespan. However, there are also multiple examples in which the opposite is observed: increasing ROS levels results in extended longevity, and decreasing ROS levels results in shortened lifespan. While these studies contradict the predictions of the FRTA, these experiments have been performed in a very limited number of species, all of which have a relatively short lifespan.

Overall, the data suggest that the relationship between ROS and lifespan is complex, and that ROS can have both beneficial or detrimental effects on longevity depending on the species and conditions. Accordingly, the relationship between ROS and aging is difficult to generalize across the tree of life.

Gerontology is perhaps the biological discipline that has given rise to the largest number and variety of theories even before the development of modern science. Most theories aimed not only at elucidating the mechanism of aging but also at providing effective interventions to slow aging down. In the late 1950s the focus of research attention moved to DNA as the likely driver of aging either by expressing a program of aging or by being the target of endogenous and external insults that accumulated damage on the molecule during the lifetime of an organism. Up to this stage, aging was considered as an essentially irreversible process. However, with the discovery of cell reprogramming, early in this century, a view began to emerge that considers aging as a reversible epigenetic process.

The hypothesis proposing the epigenome as the driver of aging was significantly strengthened by the converging discovery that DNA methylation at specific CpG sites could be used as a highly accurate biomarker of age defined by the Horvath clock. The strong correlation between the dynamics of DNA methylation profiles and the rate of biological aging leads to the idea that the epigenetic clock may in fact be the pacemaker of aging or at least a component of it. And it is at this point where epigenetic rejuvenation comes into play as a strategy to reveal to what extent biological age can be set back by making the clock tick backwards.

The few initial results already documented seem to suggest that when the clock is forced to tick backwards in vivo, it is only able to drag the phenotype to a partially rejuvenated condition. Nevertheless, it would be premature to draw firm conclusions from the scanty experimental results so far documented. What seems to be clear is that epigenetic rejuvenation by cyclic partial reprogramming or alternative non-reprogramming strategies holds the key to both understanding the mechanism by which the epigenome drives the aging process and arresting or even reversing organismal aging.

Nowadays, we are constantly bombarded by media, physicians, and other health professionals to engage in physical/sports activities to reduce physical/psychological stress, improve our health, and reduce the risk of chronic disease. The literature has clearly demonstrated aerobic fitness as one of the best indicators of resilience. This is supported by evidence from a number of studies showing that physical fitness confers physiological and psychological benefits and protects against the development of stress-related disorders, as well as improves cognition and motor function that are a consequence of aging and of neurological disorders.

Although we have learned about neurobiological mechanisms of physical fitness from the neuroplasticity and neuroprotection that confer resilience, these effects and mechanisms are diverse and complex and need to be further explored. However, we can summarize that exercise modulates several mechanisms that may increase brain health and counteract brain disorders. Exercise positively influences neuronal reserve by increasing BDNF expression which promotes neurogenesis and synaptic plasticity, reduces oxidative stress and inflammation, and enhances cerebral and peripheral blood flow, which stimulates angiogenic factors that lead to positive changes in the structure and morphology of brain vasculature. All these changes shape brain activity and serve as a buffer against stress-related disorders.

While several models of physical activity or exercise may impact positively on brain resilience such yoga, dance, martial arts, etc., in this review we aimed to focus mainly on the effects of aerobic exercise of low and moderate intensity or resistance exercise. Thus, physiological markers including heart rate variability, blood pressure, and cortisol might be regularly used as indicator of stress to determine the impact of exercise on brain resilience. Some examples of stress systems are the immune-inflammatory system, the hypothalamic-pituitary-adrenal (HPA) axis and the autonomic nervous system. Disturbance of these systems could lead to hyperactivity of the HPA-axis, sympathetic activation, and systemic inflammation.

However, there are still unanswered questions concerning (1) whether physical exercise in early life can prevent or delay cognitive decline in later life, (2) the effectiveness of exercise programs for individuals across the life span and for those with neurological diseases, and (3) how much exercise is necessary to gain beneficial effects on cognitive health. This is a field of research that deserves more attention.

The number of compounds that have been shown to increase longevity in preclinical models is growing exponentially: it was approximately 300 in 2005, 1300 in 2015, and most recently to 2000 in 2020. Meanwhile, the discovery of longevity-associated genes has plateaued, following an exponential growth until approximately 2010 before transitioning to a slower growth over the last decade. There are probably many more longevity genes left, but the incentives for their discovery are reduced since most newly discovered genes now tend to eventually lead towards already known pathways.

The number of longevity companies has also doubtlessly increased dramatically, although this is harder to subjectively measure, as it is difficult to define what makes a company longevity-focused. Most of these companies deal with the hallmarks of aging, most notably oxidative stress and mitochondrial dysfunction, cellular senescence, and pathways implicated in caloric restriction, such as mTOR. The acquisition of longevity companies by big pharma, for example the purchase of Alkahest by Grifols, is also just beginning to occur. One concern is the lack of strategic diversity. It is possible that too much weight is being put on these areas despite the much broader range of potential strategies.

Recently, the field has also seen its first clinical failures, a notable rite of passage for all new fields of medicine. In 2019, ResTORbio's mTOR inhibitor RTB101 failed its Phase 3 trial for a lung disease, and Unity Biotechnology's senolytic UBX0101 failed to meet its endpoints in osteoarthritis just last year. A myriad of challenges can complicate translation, such as a lack of genetic diversity in preclinical models, pathways that are not conserved between species, and the selection of proper primary endpoints. However, the list of ongoing clinical trials is constantly growing, with active studies including COVID-19, macular degeneration, frailty, and neurodegenerative diseases. The TAME trial of metformin represents a pivotal proof-of-concept study, which may pave the way for future therapies aiming to broadly target longevity in their applications to the FDA rather than any specific disease. Interest has also been growing in off-label prescriptions and nutritional supplements.

There has also been a ramping up of computer-based methods being applied to the field of longevity. Bioinformatics, machine learning, and artificial intelligence, -omics approaches, and large public databases are just beginning to be fully utilized. These techniques may someday improve our abilities to predict the outcomes of clinical trials. They also aim to identify candidate drugs and biomarker and may eventually play a role in the application of personalized, precision medicine. When taken as a whole, these trends characterize a vibrant, growing longevity industry in its early maturation stage. There are many parallels to the early days of some fields of pharmacology that are now well established, such as cancer and heart disease.

In a previous study, the whole transcriptome of the vastus lateralis muscle from sedentary elderly and from age-matched athletes with an exceptional record of high-intensity, life-long exercise training was compared - the two groups representing the two extremes on a physical activity scale. Exercise training enabled the skeletal muscle to counteract age-related sarcopenia by inducing a wide range of adaptations, sustained by the expression of protein-coding genes involved in energy handling, proteostasis, cytoskeletal organization, inflammation control, and cellular senescence. Building on the previous study, we examined here the network of non-coding RNAs participating in the orchestration of gene expression and identified differentially expressed microRNAs and long-non-coding RNAs and some of their possible targets and roles.

Unsupervised hierarchical clustering analyses of all non-coding RNAs were able to discriminate between sedentary and trained individuals, regardless of the exercise typology. Validated targets of differentially expressed microRNA were grouped by KEGG analysis, which pointed to functional areas involved in cell cycle, cytoskeletal control, longevity, and many signaling pathways, including AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR), which had been shown to be pivotal in the modulation of the effects of high-intensity, life-long exercise training. The analysis of differentially expressed long-non-coding RNAs identified transcriptional networks, involving long-non-coding RNAs, microRNAs and messenger RNAs, affecting processes in line with the beneficial role of exercise training.

Cancer stem cells (CSCs) constitute a cancer cell subpopulation similar to the other stem cell types in terms of self-renewal and multilineage differentiation potential but drive tumor development besides heterogeneity and dissemination of cancer cells. Targeting CSCs for therapeutic purposes is a goal of the scientific community. Currently, cancer treatments target the bulk population of the tumor cells without identifying and targeting CSCs. The significant problem in this regard is the lack of identification marker/s specific for CSCs.

Macrophages are large specialized phagocytic cells that exist in tissues or at infection sites. They arise from monocytes in the bone marrow and perform different functions and roles in the microenvironments of normal and tumor tissue. Macrophages differentiate into classically activated subtypes: CD68 expressing M1 mainly involved in pro-inflammatory activities, and CD163 expressing M2, that promote anti-inflammatory processes. In tumors, tumor-associated macrophages (TAM) comprise up to 50% of the tumor mass, with M2 phenotype being most abundant in the TME. The primary signals provided by TAMs include interleukin 4 (IL-4) and transforming growth factor-beta (TGF-β). TAMs play a key role in tumor initiation, development, and cancer cell propagation.

TAMs promote tumor growth by inducing neoangiogenesis, supporting CSCs, and downregulating tumour-targeting immune cells' number and function. Due to the significance of the tasks in which TAMs are involved, TAMs are increasingly becoming principal targets of novel therapeutic approaches, especially in the field of nanomedicine. The roles, connections, and functions of the crosstalk between TAMs and CSCs have been studied in-depth during the recent past. The interactions may be direct or indirect, and the effects on CSCs include chemoresistance, preservation, and the capacity to differentiate. TAMs produce cytokines including milk fat globule epidermal growth factor 8 (MFG-E8); interleukin 6 (IL-6), which can activate STAT3; and the Hedgehog signaling pathway, which seems to be one of the causes of drug resistance. For example, in hepatocarcinoma, IL-6 promotes the expression of CD44, inducing tumor development.

In-depth understanding of interaction between TAMs and CSCs is needed to develop novel treatment strategies in future. In this direction, researchers have already reported the presence of CSCs in many solid tumors as the leading cause of cancer relapse and chemotherapeutic drug resistance. In addition to this subpopulation of cells, macrophages and other immune cells also participate in interactions that may aid or impede the fight against cancer. For this reason, the targeting TAMs offer a novel treatment option against cancer. We believe that targeting TAMs may trigger various stromal reactions in the tumor milieu that are difficult to predict, even if the variability from patient to patient is kept as a consideration. Targeting TAMs could not only inhibit the tumor microenvironment, but also renovate the tumor "soil" to build a tumor-suppressive microenvironment, thereby suppressing tumor development. This strategy may become an effective therapeutic intervention that may be used either alone or in combination with other therapeutic strategies to treat cancer.

Immunologists have discovered that tumors use a unique mechanism to switch on regulatory T cells to protect themselves from attack by the immune system. Surprisingly, the mechanism does not affect regulatory T cell function outside the tumor and may therefore limit the immune-associated toxicities of targeting regulatory T cells. The finding offers the promise of drug treatment to selectively shut down regulatory T cells in a tumor, rendering the tumor vulnerable to cancer immunotherapies that activate the immune system to kill the tumor. The researchers showed that blocking tumor-associated regulatory T cell activity eliminated tumors cells in mice and sensitized the cells to cancer immunotherapy called anti-PD-1 therapy.

Researchers discovered the pathway by challenging mice with melanoma cells and then analyzing which genes were switched on in regulatory T cells. Investigators compared tumor-infiltrating regulatory T cells with regulatory T cells in other tissues to compare gene activation. The experiment revealed a master genetic switch that was activated only in regulatory T cells in the tumor microenvironment. The switch was a transcription factor family called SREBP.

The researchers determined that the tumor-specific regulatory T cell pathway was switched on in a range of cancers - melanoma, breast cancer, and head and neck cancer. The tumor-specific pathway was not switched on in animal models of inflammation or autoimmune disease. Genetically blocking the SREBP pathway selectively in regulatory T cells led to rapid clearance of tumor cells in mice with melanoma and colon adenocarcinoma. Targeting the pathway also reduced tumor growth in mice with established tumors. Blocking the pathway had no effect on the proliferation of regulatory T cells or their overall function in the body.

Researchers have discovered that forces created from walking or running are transmitted from bone surfaces along arteriolar blood vessels into the marrow inside bones. Bone-forming cells that line the outside of the arterioles sense these forces and are induced to proliferate. This not only allows the formation of new bone cells, which helps to thicken bones, but the bone-forming cells also secrete a growth factor that increases the frequency of cells that form lymphocytes around the arterioles. Lymphocytes are the B cells and T cells that allow the immune system to fight infections. When the ability of the bone-forming cells to sense pressure caused by movement was blocked, it reduced the formation of new bone cells and lymphocytes, causing bones to become thinner and reducing the ability of mice to clear a bacterial infection.

The skeletal stem cells that give rise to most of the new bone cells that form during adulthood in the bone marrow. They are Leptin Receptor+ (LepR+) cells. They line the outside of blood vessels in the bone marrow and form critical growth factors for the maintenance of blood-forming cells. Researchers also found that a subset of LepR+ cells synthesize a previously undiscovered bone-forming growth factor called Osteolectin. Osteolectin promotes the maintenance of the adult skeleton by causing LepR+ to form new bone cells.

In the current study, researchers looked more carefully at the subset of LepR+ cells that make Osteolectin. They discovered that these cells reside exclusively around arteriolar blood vessels in the bone marrow and that they maintain nearby lymphoid progenitors by synthesizing stem cell factor (SCF) - a growth factor on which those cells depend. Deleting SCF from Osteolectin-positive cells depleted lymphoid progenitors and undermined the ability of mice to mount an immune response to bacterial infection. "The findings in this study show Osteolectin-positive cells create a specialized niche for bone-forming and lymphoid progenitors around the arterioles. Therapeutic interventions that expand the number of Osteolectin-positive cells could increase bone formation and immune responses, particularly in the elderly."

Neurofilament light chain (NfL) is a structural protein found in nerve cells. The nervous system has been implicated in aging and longevity, so the fact that NfL can be detected in human bodily fluids makes it potentially useful as a biomarker for aging. NfL levels are known to increase with age and in response to neurodegenerative diseases, strengthening the case for its use as a biomarker.

To test the idea, an international team of scientists measured NfL levels in blood plasma from a cohort of people aged 21 to 107. They found a non-linear increase and greater variability with age. Plasma proteome data had already been generated from the same cohort, and NfL levels correlated with 53 of the proteins (out of roughly 1300). The proteins correlated with NfL levels are involved in apoptosis as well as synapse formation and plasticity, supporting the notion that plasma NfL levels reflect the activity of pathways associated with neuronal function.

The researchers then evaluated NfL as a predictor of mortality. They collected blood from separate cohorts of centenarians and nonagenarians, measured NfL levels, and tracked the cohorts over the next few years (or until death). They used activities of daily living (ADL) and Mini-Mental State Examination (MMSE) measures to assess the health of the participants. Overall, individuals with lower NfL levels lived longer than those with higher levels and did better on MMSE and ADL measures, though the difference was smaller for ADL. Finally, the team also showed that NfL levels increase with age in mice and that dietary restriction, which is known to extend the lifespan of mice, brings down NfL levels.

A better understanding of the cellular and molecular mechanisms underlying aging is central to the successful development and clinical translation of novel therapies and prevention strategies. Recent work has demonstrated that changes in mitochondrial permeability transition pore (mPTP) function may contribute directly to cellular dysfunction with aging. These changes include increases in reactive oxygen species (ROS) production, induction of cellular senescence (particularly in aging stem cells), and activation of the inflammasome, the latter contributing directly to the chronic state of inflammation often referred to as "inflammaging". mPTP dysfunction has been cited as a key factor in neurodegenerative pathologies through its role in collapsing mitochondrial membrane potential, repressing mitochondrial respiratory function, releasing mitochondrial Ca2+ and cytochrome c, and enhancing ROS generation. Thus, the mPTP has received increased attention as a potential therapeutic target.

The relationship between the mPTP and the generation of mitochondrial reactive oxygen species (mROS) has attracted significant interest within the context of aging and age-related tissue degeneration. Recently, it was found that mROS can stimulate the opening of the mPTP, which can lead to further mROS production and release. This positive feedback mechanism ultimately leads to an excessive amount of ROS accumulation. ROS accumulation in turn damages nuclear DNA, activates pro-apoptotic signaling pathways, and drives cellular aging. On the other hand, ROS can in some cases activate protective pathways, decrease stress on the mitochondria, and increase lifespan. It is currently thought that the mPTP plays an important role in integrating the effects of mROS and hence may play a vital role in the aging process. In this review, we discuss the various mechanisms inducing activation of the mPTP and the age-associated cell damage seen as a byproduct of mPTP activation. Furthermore, we discuss potential therapies that target the mPTP and may therefore inhibit the effects of aging and injury.

Elastrin, a biotechnology start-up leveraging a platform technology to develop therapeutics that render calcified tissue and organs supple again, will receive seed funding from Kizoo Technology Capital. It is the latest addition to the growing portfolio of Kizoo, a rejuvenation biotech investor focused on reversing age-related damage on a cellular and molecular level. Elastrin's lead asset is a nanoparticle conjugated with a novel monoclonal antibody to treat heart valve and vascular calcification. The platform targets and restores degraded elastin by removing the harmful calcification that stiffens arteries, improving the efficacy of drugs and eliminating side-effects by combining particle design with elastin targeting.

"Elastin fibers are critical for the homeostasis of tissues around the body, including the skin, vasculature, and pulmonary tissues. As elastin fibers become damaged over time, arterial walls weaken, and the body's physiological response results in aortic wall stiffening, aneurysms, and hypertension." The Elastrin team has developed a platform that can restore vascular health by removing pathological calcification, specifically from sites where elastin has been degraded. This is achieved via targeting albumin nanoparticles loaded with therapeutic agents directly to the tissue site of interest with the company's anti-elastin monoclonal antibody.

"Cardiovascular diseases are the number one cause of death globally, taking an estimated 18 million lives each year. On top of that, everyone above 30 years old is suffering from damage to the cardiovascular system, resulting in severe symptoms one day. Our technology can reverse damage to the arteries and heart and bring the body back to a state before the damage even occurred. This is a true game-changer in the industry and one of the puzzle pieces towards healthy aging. Nobody wants to live forever in an old and sick body, but we do want to live long in a healthy one."

In serious injuries such as those sustained in car accidents or tumor resection which results in a volumetric muscle loss (VML), the muscle's ability to recover is greatly diminished. A promising strategy to improve the functional capacity of the damaged muscle is to induce de novo regeneration of skeletal muscle via the integration of transplanted cells. Diverse types of cells, including satellite cells (muscle stem cells), myoblasts, and mesenchymal stem cells, have been used to treat muscle loss.

An important issue is controlling the three-dimensional microenvironment at the injury site to ensure that the transplanted cells properly differentiate into muscle tissues with desirable structures. A variety of natural and synthetic biomaterials have been used to enhance the survival and maturation of transplanted cells while recruiting host cells for muscle regeneration. However, there are unsolved, long-lasting dilemmas in tissue scaffold development. Natural scaffolds exhibit high cell recognition and cell binding affinity, but often fail to provide mechanical robustness in large lesions or load-bearing tissues that require long-term mechanical support. In contrast, synthetic scaffolds provide a precisely engineered alternative with tunable mechanical and physical properties, as well as tailored structures and biochemical compositions, but are often hampered by lack of cell recruitment and poor integration with host tissue.

To overcome these challenges, a research team has devised a novel protocol for artificial muscle regeneration. The team achieved effective treatment of VML in a mouse model by employing direct cell reprogramming technology in combination with a natural-synthetic hybrid scaffold. Direct cell reprogramming, also called direct conversion, is an efficient strategy that provides effective cell therapy because it allows the rapid generation of patient-specific target cells using autologous cells from the tissue biopsy. Fibroblasts are the cells that are commonly found within the connective tissues, and they are extensively involved in wound healing. As the fibroblasts are not terminally differentiated cells, it is possible to turn them into induced myogenic progenitor cells (iMPCs) using several different transcription factors. Herein, this strategy was applied to provide iMPC for muscle tissue engineering.

In order to provide structural support for the proliferating muscle cells, polycaprolactone (PCL), was chosen as a material for the fabrication of a porous scaffold due to its high biocompatibility. However, the synthetic PCL fiber scaffolds alone do not provide optimal biochemical and local mechanical cues that mimic muscle-specific microenvironment. Hence the construction of a hybrid scaffold was completed through the incorporation of decellularized muscle extracellular matrix (MEM) hydrogel into the PCL structure.

The resultant bioengineered muscle fiber constructs showed mechanical stiffness similar to that of muscle tissues and exhibited enhanced muscle differentiation and elongated muscle alignment in vitro. Furthermore, implantation of bioengineered muscle constructs in the VML mouse model not only promoted muscle regeneration with increased innervation and angiogenesis but also facilitated the functional recovery of damaged muscles.