Muscle progenitor cells are required for skeletal muscle regeneration and prevention of adipogenesis after limb ischemia.

Skeletal muscle injury in peripheral artery disease (PAD) has been attributed to vascular insufficiency, however evidence has demonstrated that muscle cell responses play a role in determining outcomes in limb ischemia. Here, we demonstrate that genetic ablation of Pax7+ muscle progenitor cells (MPCs) in a model of hindlimb ischemia (HLI) inhibited muscle regeneration following ischemic injury, despite a lack of morphological or physiological changes in resting muscle. Compared to control mice (Pax7WT), the ischemic limb of Pax7-deficient mice (Pax7Δ) was unable to generate significant force 7 or 28 days after HLI. A significant increase in adipose was observed in the ischemic limb 28 days after HLI in Pax7Δ mice, which replaced functional muscle. Adipogenesis in Pax7Δ mice corresponded with a significant increase in PDGFRα+ fibro/adipogenic progenitors (FAPs). Inhibition of FAPs with batimastat decreased muscle adipose but increased fibrosis. In vitro, Pax7Δ MPCs failed to form myotubes but displayed increased adipogenesis. Skeletal muscle from patients with critical limb threatening ischemia displayed increased adipose in more ischemic regions of muscle, which corresponded with fewer satellite cells. Collectively, these data demonstrate that Pax7+ MPCs are required for muscle regeneration after ischemia and suggest that muscle regeneration may be an important therapeutic target in PAD.

Patterns-of-care disparities among uninsured versus insured patients with anorectal carcinoma referred for radiotherapy at an Urban Safety-Net Hospital.

Background: To compare patterns-of-care and clinical outcomes among uninsured versus insured patients (IPs) with anorectal malignancies referred for radiotherapy at an urban safety-net hospital. This topic is important because uninsured patients (UPs) in the US often have limited access to health care, which can result in worse health outcomes. Methods: We reviewed the medical records of 59 patients with biopsy-proven, non-metastatic anal and rectal cancers who received curative-intent primary or neoadjuvant/adjuvant radiotherapy between May 2002 and August 2012. Data regarding patient and disease characteristics, weight loss, insurance status at symptom onset, date of first therapeutic intervention, and survival status at last follow-up, were collected and analyzed. Results: The percentage of IPs presenting with T4 tumors was 7% versus 40% among the uninsured (P=0.005). The median interval between first symptom onset and diagnosis date was 89 (range, 0-1,428) days for IPs and 221 (range, 0-1,576) days for UPs (P=0.01). The median interval between first symptom onset and treatment initiation was 172 (range, 9-1,498) days for IPs and 302 (range, 35-1,624 days) days for UPs (P=0.01). The 5-year overall survival rate was 59% for the entire cohort, 62% for the insured patients, and 55% for the uninsured patients (P=0.76). Conclusions: Differences in health insurance status demonstrated various disparities in patterns-of-care, including significant delay in diagnosis, more advanced-stage disease at presentation, and treatment initiation delays among UPs. Nevertheless, overall survival at 5 years was not statistically significant between the insured and the uninsured.

Methods for Acute and Subacute Murine Hindlimb Ischemia.

Peripheral artery disease (PAD) is a leading cause of cardiovascular morbidity and mortality in developed countries, and animal models that reliably reproduce the human disease are necessary to develop new therapies for this disease. The mouse hindlimb ischemia model has been widely used for this purpose, but the standard practice of inducing acute limb ischemia by ligation of the femoral artery can result in substantial tissue necrosis, compromising investigators' ability to study the vascular and skeletal muscle tissue responses to ischemia. An alternative approach to femoral artery ligation is the induction of gradual femoral artery occlusion through the use of ameroid constrictors. When placed around the femoral artery in the same or different locations as the sites of femoral artery ligation, these devices occlude the artery over 1 - 3 days, resulting in more gradual, subacute ischemia. This results in less substantial skeletal muscle tissue necrosis, which may more closely mimic the responses seen in human PAD. Because genetic background influences outcomes in both the acute and subacute ischemia models, consideration of the mouse strain being studied is important in choosing the best model. This paper describes the proper procedure and anatomical placement of ligatures or ameroid constrictors on the mouse femoral artery to induce subacute or acute hindlimb ischemia in the mouse.

Subacute limb ischemia induces skeletal muscle injury in genetically susceptible mice independent of vascular density.

OBJECTIVE: The primary preclinical model of peripheral artery disease, which involves acute limb ischemia (ALI), can result in appreciable muscle injury that is attributed to the acuity of the ischemic injury. A less acute model of murine limb ischemia using ameroid constrictors (ACs) has been developed in an attempt to mimic the chronic nature of human disease. However, there is currently little understanding of how genetics influence muscle injury following subacute arterial occlusion in the mouse. METHODS: We investigated the influence of mouse genetics on skeletal muscle tissue survival, blood flow, and vascular density by subjecting two different mouse strains, C57BL/6 (BL6) and BALB/c, to ALI or subacute limb ischemia using single (1AC) or double (2AC) AC placement on the femoral artery. RESULTS: Similar to ALI, the 2AC model resulted in significant tissue necrosis and limb perfusion deficits in genetically susceptible BALB/c but not BL6 mice. In the 1AC model, no outward evidence of tissue necrosis was observed, and there were no differences in limb blood flow between BL6 and BALB/c. However, BALB/c mice displayed significantly greater muscle injury, as evidenced by increased inflammation and myofiber atrophy, despite having no differences in CD31(+) and SMA(+) vascular density and area. BALB/c mice also displayed significantly greater centralized myonuclei, indicating increased muscle regeneration. CONCLUSIONS: The susceptibility of skeletal muscle to ischemia-induced injury is at least partly independent of muscle blood flow and vascular density, consistent with a muscle cell autonomous response that is genetically determined. Further development of preclinical models of peripheral artery disease that more accurately reflect the nature of the human disease may allow more accurate identification of genetic targets for therapeutic intervention.