Biology subjects

Tiwari, R. L.

Publications and source records attributed to Tiwari, R. L..

3 recordsLinked to original sources

bioRxiv2020

A Wnt5a-Cdc42 axis controls aging and rejuvenation of hair-follicle stem cells

Normal hair growth occurs in cycles, comprising growth (anagen), cessation (catagen) and rest (telogen). Upon aging, the initiation of anagen is significantly delayed, which results in impaired hair regeneration. Hair regeneration is driven by hair follicle stem cells (HFSCs). We show here that aged HFSCs present with a decrease in canonical Wnt signaling and a shift towards non-canonical Wnt5a driven signaling which antagonizes canonical Wnt signaling. Elevated expression of Wnt5a in HFSCs upon aging results in elevated activity of the small RhoGTPase Cdc42 as well as a change in the spatial distribution of Cdc42 within HFSCs. Treatment of aged HFSC with a specific pharmacological inhibitor of Cdc42 activity termed CASIN to suppress the aging-associated elevated activity of Cdc42 restored canonical Wnt signaling in aged HFSCs. Treatment of aged mice in vivo with CASIN induced anagen onset and increased the percentage of anagen skin areas. Aging-associated functional deficits of HFSCs are at least in part intrinsic to HFSCs and can be restored by rational pharmacological approaches.

cell biology↗

bioRxiv2020

Metabolism of glucose and glutamine is critical for skeletal muscle stem cell activation.

Injury to muscle tissue induces the resident, quiescent, skeletal muscle stem cells (MuSCs) to activate - to exit quiescence and enter the cell cycle. Previous work has shown that MuSC activation is associated with significant metabolic changes, however the substrates that MuSCs consume to support activation are poorly understood. Here, we show that MuSCs generate the majority of their energy through mitochondrial respiration, and that oxidative phosphorylation is required for MuSC activation. Furthermore, we have found that while glucose, glutamine, and fatty acids all significantly, and roughly equally, contribute to ATP production in MuSCs during activation, they do not have equal functional role in the dynamics of MuSC activation. Pharmacologic suppression of glycolysis, using 2-deoxy-D-glucose, or glutaminolysis, using BPTES, significantly impairs MuSC cell cycle entry. However, etomoxir-mediated inhibition of mitochondrial fatty acid transport has minimal effect on MuSC cell cycle progression. Our findings suggest that apart from their roles in fueling ATP production by the mitochondria, glucose and glutamine may generate metabolic intermediates needed for MuSC activation.

cell biology↗

bioRxiv2020

PDH Mediated Mitochondrial Respiration Controls the Speed of Muscle Stem Cell Activation in Muscle Repair and Aging

Decline in the skeletal muscle stem cell (MuSC) function is a major contributor to age-associated impairments in muscle regeneration and function. The ability of MuSCs to activate (i.e. exit quiescence, enter the cell cycle, and divide) following injury is a critical step that initiates muscle regeneration. However, the mechanisms that regulate MuSC activation function are poorly understood. Here, we show that the activation function, specifically the speed by which cells progress through G0-G1, declines tremendously with age in mouse MuSCs. Using a number of in vivo models and ex vivo assays of MuSC activation and muscle regenerative functions, live cell metabolic flux analyses, and metabolomics we present data indicating that changes in MuSC mitochondrial flux underlie age-associated changes in MuSC activation. We show that, in the course of MuSC activation, there is a profound,16-fold, increase in ATP production rates, which is fueled largely by increases in pyruvate flux into mitochondria. We found that MuSCs from aged mice display progressive defects in the ability to increase mitochondrial flux during activation and that this correlates with higher levels of phosphorylated, inactivated, pyruvate dehydrogenase (PDH). Importantly, we demonstrate that pharmacologic and physiologic methods to induce dephosphorylation and activation of PDH in MuSCs are sufficient to rescue the activation and muscle regenerative functions of MuSCs in aged mice. Collectively the data presented show that MuSC mitochondrial function is a central regulator of MuSC activation and muscle regenerative functions. Moreover, our results suggest that approaches to increase MuSC pyruvate oxidation may have therapeutic potential to promote muscle repair and regeneration.

cell biology↗