APLN and type 1 diabetes mellitus: The intravenous injection of Apelin-13 (400 pmol/kg twice per day for 10 weeks) significantly improves islet mass and INS levels in Akita mice with spontaneous T1DM Akita and inhibits the expression of inositol-requiring protein 1α (IRE1α) and phosphorylation of protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), two endoplasmic reticulum (ER) stress receptors in pancreatic tissues.