McClung, J. M. | bioRxiv Science

bioRxiv2020

Muscle progenitor cells are required for the regenerative response and prevention of adipogenesis after limb ischemia

Peripheral artery disease (PAD) is nearly as common as coronary artery disease, but few effective treatments exist, and it is associated with significant morbidity and mortality. Although PAD studies have focused on the vascular response to ischemia, skeletal muscle cells play a critically important role in determining the phenotypic manifestation of PAD. Here, we demonstrate that genetic ablation of Pax7+ muscle progenitor cells (MPCs, or satellite cells) in a murine model of hind limb ischemia (HLI) resulted in a complete absence of normal muscle regeneration following ischemic injury, despite a lack of morphological or physiological changes in resting muscle. Compared to ischemic muscle of control mice (Pax7WT), the ischemic limb of Pax7-deficient mice (Pax7{Delta}) was unable to generate significant force 7- or 28-days after HLI in ex vivo force measurement studies. A dramatic increase in adipose infiltration was observed 28 days after HLI in Pax7{Delta} mice, which replaced functional muscle. To investigate the mechanism of this adipogenic change, mice with inhibition of fibro/adipogenic precursors (FAPs), another pool of MPCs, were subjected to HLI. Inhibition of FAPs decreased muscle adipose fat but increased fibrosis. MPCs cultured from mouse muscle tissue failed to form myotubes in vitro following depletion of satellite cells in vivo, and they displayed an increased propensity to differentiate into fat in adipogenic medium. Importantly, this phenotype was recapitulated in patients with critical limb ischemia (CLI), the most severe form of PAD. Skeletal muscle samples from CLI patients demonstrated an increase in adipose deposition in more ischemic regions of muscle, which corresponded with a decrease in the number of satellite cells in those regions. Collectively, these data demonstrate that Pax7+ MPCs are required for normal muscle regeneration after ischemic injury, and they suggest that targeting muscle regeneration may be an important therapeutic approach to prevent muscle degeneration in PAD.

pathology↗

bioRxiv2019

Effects of fasting induced carbohydrate depletion on murine ischemic skeletal muscle function.

Stored muscle carbohydrate supply and energetic efficiency constrain muscle functional capacity during exercise and are influenced by common physiological variables (e.g. age, diet, and physical activity level). Whether these constraints affect overall functional capacity or the timing of muscle energetic failure during acute ischemia is not known. We interrogated skeletal muscle contractile properties in two anatomically distinct hindlimb muscles that have well characterized differences in energetic efficiency (locomotory-extensor digitorum longus (EDL) and postural-soleus muscles) under conditions of reduced carbohydrate supply. 180 mins of acute ischemia resulted in complete energetic failure in all muscles tested, indicated by: loss of force production, substantial reductions in total adenosine nucleotide pool intermediates, and increased adenosine nucleotide degradation product - inosine monophosphate (IMP). These changes occurred in the absence of apparent myofiber structural damage assessed histologically by both transverse section and whole mount. Restriction of the available intracellular carbohydrate pool by fasting (~50% decrease in skeletal muscle) did not significantly alter the timing to muscle functional impairment or affect the overall force/work capacities of either muscle type. Fasting did cause rapid development of passive tension in both muscle types, which may have implications for optimal timing of reperfusion or administration of precision therapeutics.

physiology↗