Adipose-derived stem cell-secreted exosomes enhance angiogenesis by promoting macrophage M2 polarization in type 2 diabetic mice with limb ischemia via the JAK/STAT6 pathway

Diabetic lower limb ischemia is an intractable disease that leads to amputation and even death. Recently, adipose-derived stem cell-secreted exosomes (ADSC-Exo) have been reported as a potential therapeutic approach, but its specific mechanism of action is unknown. Studies have found that exosomes derived from stem cells can reduce inflammation and promote tissue repair. Macrophages play an important role in the development and repair of inflammation in lower limb ischemic tissue, but the specific regulation of ADSC-Exo in macrophages has rarely been reported. The present study aimed to verify whether ADSC-Exo could promote angiogenesis by regulating macrophages to reduce the level of inflammation in diabetic ischemic lower limbs. In this study, adipose-derived stem cells (ADSCs) were obtained and identified, and ADSC-Exos were isolated using ultracentrifugation and characterized using transmission electron microscopy, nanoparticle tracking analysis, and western blotting analysis. The uptake of ADSC-Exos by macrophages was observed using immunofluorescence, and macrophage polarization induced by ADSC-Exos was identified by flow cytometry, immunofluorescence and ELISA. The effects of ADSC-Exos on the proliferation, apoptosis, migration and adhesion of macrophages were evaluated using CCK-8 assay, flow cytometry, Transwell assay, scratch and adhesion experiments, and ELISA assay. The polarization-related JAK/STAT6 signaling pathway was explored by using western blotting. A lower limb ischemic model of type 2 diabetic mice was established and ADSC-Exos was intramuscularly injected into the mice. The blood flow in the lower limbs was assessed using a laser Doppler flowmeter, while the level of angiogenesis was determined using immunohistochemistry and immunofluorescence. The results of this study prove that ADSC-Exos induced M2-phenotype polarization of macrophages via the JAK/STAT6 signaling pathway can promote the proliferation, migration and adhesion of M2 macrophages, inhibit the apoptosis of macrophages, and promote the angiogenesis and revascularization of ischemic lower limbs in type 2 diabetic mice. Thus, this study provides a theoretical and experimental basis for the clinical treatment of diabetic lower limb ischemic disease.