Biology subjects

Olwin, B. B.

Publications and source records attributed to Olwin, B. B..

8 recordsLinked to original sources

bioRxiv2026

Redundant YAP and TAZ functions are essential for skeletal muscle regeneration

Muscle stem cells orchestrate skeletal muscle regeneration through complex fate decisions. The transcriptional co-activators Yes-associated protein 1 (YAP) and WW domain-containing transcription regulator 1 (TAZ) contribute to multiple stages of myogenesis, yet their individual contributions to regeneration remain unclear due to substantial functional overlap. We genetically titrated YAP and TAZ expression in MuSCs with double knockout and single allele mutants by crossing Pax7CreERT mice with TAZflox/flox;YAPflox/flox mice. Conditional deletion of both YAP and TAZ in muscle stem cells severely disrupted muscle regeneration with dramatically increased fibrosis and impaired myofiber formation following injury. In contrast, a single allele of either YAP or TAZ was sufficient to rescue injured muscle weight and myofiber cross-sectional area. Similarly, the reduced proliferation of double knockout muscle stem cells on isolated myofibers was restored by a single allele of either YAP or TAZ. In addition, disrupted actin cytoskeleton organization and reduced focal adhesion formation drove double knockout muscle stem cell migration defects, negatively impacting muscle stem cell congregation prior to fusion. Thus, YAP and TAZ function redundantly as critical transcriptional co-activators to regulate progenitor proliferation and migration during muscle regeneration. By challenging myogenesis with double knockout of both YAP and TAZ, we unmasked regenerative requirements previously undetected in single-gene loss models, highlighting genetic redundancy as a key principle buffering regenerative robustness.

cell biology↗

bioRxiv2026

Fibroblasts impair muscle stem cell self-renewal via excessive fibronectin deposition in viscoelastic hydrogel co-cultures

Muscle satellite cells (SCs) regenerate skeletal muscle, but their regenerative capacity declines with age, in part due to extracellular matrix (ECM) remodeling and aberrant fibroblast activation within the SC niche. In regenerating young mouse muscle, fibronectin remodeling is transient, whereas in aged mouse muscle, fibronectin remodeling is prolonged and disorganized. Fibroblasts in aged mice are activated, increasing fibronectin deposition and expressing elevated -smooth muscle actin (SMA), which negatively influence SC fate. We develop a viscoelastic hydrogel co-encapsulation system, enabling three-dimensional co-culture of intact myofibers with primary fibroblasts. Using this 3D co-culture system, we show that fibroblasts from young mice support SC quiescence and self-renewal, whereas fibroblasts from aged mice aberrantly activate SCs and promote their differentiation on myofibers isolated from either young or aged mice. Knocking down fibronectin (Fn1) in fibroblasts from aged mice partially restores SC function, promoting quiescence and limiting differentiation. Using a novel 3D hydrogel co-culture system, we demonstrate that fibroblast-deposited fibronectin is a key age-associated regulator negatively affecting SC fate within the SC niche of aged mice.

bioengineering↗

bioRxiv2026

The Muscle Tissue Environment Limits Muscle Stem Cells in Aged Mice

Frailty arising from loss of muscle function and mass is a significant health concern impacting quality of life and dramatically increasing health care costs as our population ages. Ameliorating frailty derived from reduced muscle function is thus a critical research priority to improve health span. Cell intrinsic defects in muscle stem cells (MuSC), or satellite cells, occur as skeletal muscle ages, reducing the capacity of MuSCs to maintain and repair skeletal muscle and are accompanied by cell nonautonomous changes. Although rejuvenating stem cells in aged tissues or organs has potential to improve muscle aging phenotypes, we found that the extracellular environment in aged mice abrogates rejuvenated muscle stem cell potential. MuSCs from young mice were unable to grow on extracellular matrix derived from aged mice that contains elevated collagen protein levels, establishing a critical role for the environment in contributing to muscle phenotypes in aging. Combining an inducible FGF receptor 1 (FGFR1) to rescue MuSC intrinsic aging defects with a drug to reduce fibrosis partially rescued muscle mass loss in aged mice. We conclude that aging affects tissues, and particularly skeletal muscle tissue, via complex multifactorial processes requiring multifaceted interventions to improve aging phenotypes.

cell biology↗

bioRxiv2026

Activating FGFR1 restores Integrin-β1--mediated fibronectin sensing in satellite cells of aged mice

Muscle satellite cells (SCs), essential for skeletal muscle regeneration, decline in number and function with age, contributing to sarcopenia. A fully defined viscoelastic hydrogel that preserves SC-myofiber interactions and supports tunable densities of fibronectin-derived RGD ligands was used to investigate age-related defects in extracellular matrix sensing by SCs. Elevating RGD density increased the number of activating and proliferating SCs on myofibers from young mice, whereas SCs from aged mice were unresponsive. Loss of FGF receptor 1 signaling in SCs from aged mice abrogated the coordinated Syndecan-4 and Integrin-{beta}1 matrix response observed in SCs from young mice. Activating Integrin-{beta}1 promoted asymmetric division and self-renewal in SCs from young mice whereas combined FGFR1 and Integrin-{beta}1 signaling drove symmetric expansion. In SCs from aged mice, FGFR1 dysfunction disrupted this balance, impairing asymmetric division, but constitutive FGFR1 activation restored receptor co-localization, self-renewal, and fibronectin responsiveness. Therefore, FGFR1 integrates matrix and growth factor signals, suggesting that targeting the FGFR1-Integrin-{beta}1 axis may enhance SC regenerative potential in aging organisms.

cell biology↗

bioRxiv2021

Myonuclear maturation dynamics in aged and adult regenerating mouse skeletal muscle

Skeletal muscle cells are multinucleated syncytial cells arising from cell fusion, yet despite sharing a common cytoplasm individual myonuclei express distinct transcriptional programs. Whether individual myonuclei acquire heterogenous transcriptional states via differences in their progenitors, during differentiation, or once their anatomical position is acquired, is not known. We performed transcriptome and pseudotime analysis of single myogenic nuclei from uninjured and post-injury murine skeletal muscle to assess when myonuclear heterogeneity is acquired. Two distinct progenitors contribute to myonuclei, one a non-myogenic fibroblast subtype, and skeletal muscle stem cells the other. Both progenitors enter a single pseudotime trajectory that bifurcates as myonuclei mature into two branches segregated by myosin isoform expression and metabolic profiles, suggesting transcriptional heterogeneity is acquired as myonuclei mature. In aged skeletal muscle myogenic progenitor expansion is perturbed and nuclei from aged muscle display distinct pseudotemporal kinetics compared to nuclei from young mice. In aged mice, the inferred myogenic differentiation trajectory is delayed, altering the distribution of myogenic nuclei in pseudotime, suggesting that altered transcriptional dynamics in nuclei in aged mice may drive age-associated muscle deficits and bias myonuclei towards acquiring oxidative metabolic profiles.

molecular biology↗

bioRxiv2021

RNA-BINDING PROTEINS DIRECT MYOGENIC CELL FATE DECISIONS

RNA-binding proteins (RBPs) are essential for skeletal muscle regeneration and RBP dysfunction causes muscle degeneration and neuromuscular disease. How ubiquitously expressed RBPs orchestrate complex tissue regeneration and direct cell fate decisions in skeletal muscle remains poorly understood. Single cell RNA-sequencing of regenerating skeletal muscle reveals that RBP expression, including numerous neuromuscular disease-associated RBPs, is temporally regulated in skeletal muscle stem cells and correlates to stages of myogenic differentiation. By combining machine learning with RBP engagement scoring, we discover that the neuromuscular disease associated RBP Hnrnpa2b1 is a differentiation-specifying regulator of myogenesis controlling myogenic cell fate transitions during terminal differentiation. The timing of RBP expression specifies cell fate transitions by providing a layer of post-transcriptional regulation needed to coordinate stem cell fate decisions during complex tissue regeneration.

molecular biology↗

bioRxiv2019

Skeletal muscle stem cell self-renewal and differentiation kinetics revealed by EdU lineage tracing during regeneration

Skeletal muscle maintenance and repair is dependent on the resident adult muscle stem cell (MuSC). During injury, and in diseased muscle, stem cells are engaged to replace or repair damaged muscle, which requires the stem cells to exit quiescence and expand, followed by differentiation to regenerate myofibers and self-renewal to replenish the stem cell population. Following an injury, little is known regarding the timing of MuSC (skeletal muscle stem cell) self-renewal, myoblast expansion or myoblast differentiation. To determine the timing and kinetics of these cell fate decisions, we employed DNA-based lineage tracing to label newly replicated cells and followed cell fates during skeletal muscle regeneration. MuSCs activate and expand as myoblasts rapidly following injury, where the majority differentiate into myonuclei, establishing the centrally located myonuclear pool. Re-establishing the majority MuSC pool by self-renewal occurs after 5 days post-muscle injury, accompanied by low levels of myonuclear accretion that generate only peripheral myonuclei. In aged mice, possessing [~]1/2 the number of MuSCs present in young adult mice, the timing of post injury MuSC self-renewal is delayed, and although MuSCs expansion as myoblasts in aged muscle is impaired, the number of MuSC unexpectedly recovers to young adult levels during regeneration. Following an induced muscle injury, we found that myonuclei are generated within the first four days post injury derived from myoblasts expanding from activated MuSCs. Only later during regeneration, from 5 d to 14 d post injury, is the MuSC pool replenished by self-renewal, accompanied by generation of peripheral myonuclei.

cell biology↗

bioRxiv2019

A cellular atlas of skeletal muscle regeneration and aging

Skeletal muscle stem cells (MuSCs) are essential for muscle regeneration and maintenance. While MuSCs typically are quiescent and reside in an asymmetric niche between the basal lamina and myofiber membrane: to repair or maintain muscle, MuSCs activate, proliferate and differentiate to repair injured tissue, and self-renew to replenish MuSCs. Little is known about the timing of MuSC self-renewal during muscle regeneration and the cellular processes that direct MuSC self-renewal fate decisions. Using DNA-based lineage tracing, we find that during muscle regeneration most MuSCs self-renew from 5-7 days post-injury, following fusion of myogenic cells to regenerate myofibers. Single cell sequencing of the myogenic cells in regenerating muscle reveals that non-cell autonomous signaling networks regulate MuSC self-renewal allowing identification of asymmetrically distributed proteins in self-renewing MuSCs. Cell transplantation experiments verified that the regenerating environment signals MuSC self-renewal. Our results define the critical window for MuSC self-renewal emphasizing the temporal contribution of the regenerative muscle environment on MuSC fate, establishing a new paradigm for restoring the MuSC pool during muscle regeneration.

cell biology↗