Abstract
BACKGROUND: Emerging evidence suggests that skeletal muscle cells (SKMC) play critical roles in the defective angiogenic response in diabetic critical limb ischemia. However, the molecular mechanisms linking skeletal muscle to impaired angiogenic properties of endothelial cells (EC) remain unidentified. The current study investigates how muscle-specific miR-499-5p may impair EC function in diabetic ischemic limbs. METHODS: Eight-week-old, male C57BL/6 J, db/ + and db/db mice were employed. Hind limb ischemia was established by unilateral ligation of the left femoral artery, and blood flow recovery was monitored using Laser Doppler perfusion imaging (LDPI). ECs and SKMCs were isolated from sham or ischemic hind limbs (IHL). SKMC-derived small extracellular vesicles (SKMC-sEVs) were isolated from the culture medium of SKMCs by ultra-centrifugation. RESULTS: miR-499-5p level was markedly increased in SKMCs and unexpectedly in ECs from hindlimb of db/db mice. Ischemic injury further enhanced miR-499-5p levels in ECs from IHL of db/db mice. Angiogenic activity was reduced in ECs from IHL of db/db mice and in miR-499-5p-overexpressing ECs. Intramuscular injection of lentiviral-anti-miR-499-5p improved blood perfusion and angiogenesis in IHL of db/db mice. Mechanistically, we found that diabetic SKMC sEVs carried high levels of miR-499-5p and transferred miR-499-5p to ECs. Intramuscular injection of diabetic SKMC-sEVs repressed IHL recovery in wildtype mice. Blocking sEV biosynthesis/release by GW4869 markedly improved neovascularization and blood perfusion in IHL of db/db mice. We identified that SRY (Sex-Determining Region Y)-Box 6 (SOX6) is a direct downstream target of miR-499-5p. Silencing of SOX6 suppressed release of proangiogenic factors from ECs. Targeted reduction of miR-499-5p significantly enhanced SOX6 levels in ECs from IHL of db/db mice. Finally, overexpression of SOX6 improved the angiogenic property of ECs from IHL of db/db mice. CONCLUSIONS: SKMC-sEV-mediated transfer of myo-miR-499-5p and subsequent suppression of SOX6 plays a critical role in diabetes-impaired neovascularization in IHL of db/db mice. Targeting miR-499-5p-mediated pathogenic communication between SKMCs and ECs may be a novel therapeutic avenue for critical limb ischemia in diabetic patients.