Influences of high fat diet and ischemia on skeletal muscle pericytes

Abstract

Pericytes are mural cells on the abluminal surface of capillaries that play an essential role in capillary stabilization. They also regulate angiogenesis by guiding vessel sprouting and the maturation of newly formed sprouts. Furthermore, pericytes may have adipogenic differentiation potential. Muscle ischemia, as seen in peripheral artery disease, causes oxidative and nutrient‐deprivation stress and ultimately death of skeletal myocytes. Ischemia is a stimulus for angiogenesis, a crucial process for muscle regeneration. However, newly formed capillaries are structurally and functionally aberrant, which might be explained by dysfunction of pericytes. Recently, we showed that high‐fat (HF) diet in mice provokes a shift in skeletal muscle pericytes towards a pre‐adipocyte phenotype. This alteration may disrupt capillary remodeling processes and contribute to the worsened prognosis of PAD patients with diabetes. Thus, the purpose of this study was to assess the effects of HF diet and ischemia on skeletal muscle pericytes. We hypothesized that the number of capillary‐associated pericytes will be altered by each HF diet and ischemia and together, they may exert an additive effect. Two groups of 8 weeks old NG2/DsRed mice (that express DsRed protein under the control of the pericyte NG2 promoter) were fed normal (NC) or high fat (HF) diets (10% or 60% kcal from fat, respectively) for two weeks. The second group also underwent unilateral femoral artery ligation surgery to induce ischemia and were euthanized 14 days post‐ischemia. Analysis of EDL muscle longitudinal sections showed that HF diet decreased pericyte number/100 μm2 vascular area (30.1 ± 0.6 (n=5) vs. 23.1 ± 2.4 (n=6) in NC and HF, respectively p<0.05). PDGFRβ+ pericytes isolated from the muscles of these mice exhibited a HF diet‐induced increase in the relative mRNA levels of leptin (0.51 ± 0.11 (n=7) vs. 0.83 ± 0.16 (n=6) in NC and HF, respectively p<0.05) and the pre‐adipocyte commitment marker Zfp423 (0.92 ± 0.11 (n=7) vs. 1.10 ± 0.14 (n=7) in NC and HF, respectively p<0.05), suggesting a shift in pericyte phenotype. Ischemic muscles of both NC and HF‐fed mice had increased numbers of capillary‐associated pericytes compared to non‐ischemic muscle (1.6 ± 0.4 and 1.4 ± 0.1fold increases in NC and HF, respectively. n=3, p<0.05). Capillary area relative to muscle area did not differ with diet or ischemia. These samples will be used to quantify pericyte proliferation and markers of pericyte phenotype in the ischemic muscles. These data provide a valuable first step in defining the behavior and functions of pericytes during muscle adaptations to the pathophysiological conditions of HF diet and ischemia.