Revascularization and muscle adaptation to limb demand ischemia in diet-induced obese mice

Abstract

Background Obesity and type 2 diabetes are major risk factors for peripheral arterial disease (PAD) in humans which can result in lower limb demand ischemia and exercise intolerance. Exercise triggers skeletal muscle adaptation including increased vasculogenesis. The goal of this study was to determine whether demand ischemia modulates revascularization, fiber size, and signaling pathways in the ischemic hind limb muscles of mice with diet-induced obesity (DIO). Materials and Methods DIO mice (n=7) underwent unilateral femoral artery ligation (FAL) and recovered for 2-weeks followed by 4-weeks with daily treadmill exercise to induce demand ischemia. A parallel sedentary ischemia group (n=7) had FAL without exercise. The contralateral limb muscles of sedentary ischemia served as control. Muscles were examined for capillary density, myofiber cross-sectional area (CSA), cytokine levels, and phosphorylation of STAT3 and ERK1/2. Results Exercise significantly enhanced capillary density (p<0.01) and markedly lowered CSA (p<0.001) in demand ischemia compared to sedentary ischemia. These findings coincided with a significant increase in G-CSF (p<0.001) and IL-7 (p<0.01) levels. In addition, phosphorylation of STAT3 and ERK1/2 (p<0.01) were increased while UCP-1 and MCP-1 protein levels were lower (p<0.05) without altering VEGF and TNFα protein levels. Demand ischemia increased the PGC1α mRNA (p<0.001) without augmenting PGC1α protein levels. Conclusions Exercise induced limb demands ischemia in the setting of DIO causes myofiber atrophy despite an increase in muscle capillary density. The combination of persistent increase in TNFα, lower VEGF and failure to increase PGC1α protein may reflect a deficient adaption to demand ischemia in DIO.

Impact of aerobic exercise type on blood flow, muscle energy metabolism, and mitochondrial biogenesis in experimental lower extremity artery disease

“…the advanced stage of LEAD), Lejay et al 37 reported that moderate forced treadmill running for 3 weeks induced increased transcript levels of PGC-1α, PGC-1β and NRF-1 in both non-ischemic and non-ischemic tibialis muscle 37 . In LEAD mice, results are inconsistent with the study from Albadawi et al 24 showing upregulation of ischemic tibialis muscle PGC-1α mRNA level 24 , and the study of Nagase et al 21 , which like ours observed no increase in ischemic soleus muscle PGC-1α mRNA expression 21 after treadmill exercise. Again, none of these animal studies have examined whether mitochondrial content and expression of genes involved in mitochondrial-related biogenesis can be influenced by exercise type, as well as whether such possible adaptations translate into a functional gain in hindlimb use.…”

“…Moreover, Willmann et al 23 reported increased ischemic muscle microvessel density and VEGF receptor 2 protein expression after 4 weeks of forced treadmill exercise in C57BL/6 mice with unilateral hindlimb ischemia 23 . Lastly, in mice with diet-induced obesity and unilateral femoral artery ligation, daily forced treadmill running for 4 weeks enhanced capillary density, but mRNA and protein levels of VEGF in the tibialis anterior muscle remained unchanged 24 . While these differences might be attributed, in part, to inter-laboratory differences in methodology and protocol, we have strived in our LEAD mouse study to identify which exercise regimen is effective at improving voluntary exercise capacity, and whether or not underlying mechanisms implicate hemodynamic and/or metabolic adaptations.…”

Physical Performance and Skeletal Muscle Transcriptional Adaptations Are Not Impacted by Exercise Training Frequency in Mice with Lower Extremity Peripheral Artery Disease

“…In agreement with our data, Kivela et al reported no difference in muscle VEGFA mRNA expression between trained and sedentary mice, but also between three and five times per week exercised mice [38]. In ischemic hindlimb muscle tissues, previous studies from our lab and from Albadawil et al also showed no effect of treadmill running five times/week [13] and seven times/week [17] on VEGFA and/or HIF-1α mRNA expression. Altogether, one could hypothesize that exercise frequency does not modulate VEGFA and/or HIF-1α expression in ischemic and non-ischemic muscles, at least at the transcriptional level.…”

“…In line with our study, Nagase et al demonstrated no increase in ischemic muscle PGC-1α gene expression after three weeks of treadmill exercise performed twice a week despite increased endurance performance [15]. In contrast, Albadawil et al showed enhanced PGC-1α mRNA expression in ischemic muscle of mice that underwent 60 min of daily treadmill exercise over 4 weeks [17]. Additional research is to be considered to clarify the role of exercise frequency on mitochondrial biogenesis in skeletal muscle ischemic disorders.…”

“…The frequency of training sessions is also an important parameter when considering the magnitude of ET-induced physiological adaptations, especially at the muscular level. Previous studies conducted by our group and others have examined the effects of different types/modes of ET (forced running, voluntary running, and forced swimming) on muscle energy metabolism and/or mitochondrial function in mouse models of PAD/hindlimb ischemia [13,[15][16][17]. However, to our knowledge, no study has specifically investigated whether the frequency of ET could influence lower extremity muscle transcriptional response in PAD.…”