INS and diabetes mellitus: It is also reported that endothelial progenitor cells from diabetic mice can regenerate islet ECs but fail to promote β cell regeneration, unlike those from normal mice [66], indicating functional impairment despite increased EC numbers in our study, as the crosstalk between ECs and β cells—mediated by cytokines (e.g., VEGF, insulin, CTGF, and HGF) that mutually regulate proliferation, hormone secretion, and structural and functional maintenance—might be disrupted in diabetes [64].