MicroRNA-33b-5p is overexpressed and inhibits GLUT4 by targeting HMGA2 in polycystic ovarian syndrome: An in vivo and in vitro study

Polycystic ovary syndrome (PCOS) is a common endocrine and metabolic disease, but its pathogenesis remains largely unknown. The present study explored the role of microRNA-33b-5p (miR-33b-5p) in PCOS pathogenesis, with a particular focus on its role in regulating glucose transporter 4 (GLUT4). A rat model of PCOS was developed by injecting female SD rats with insulin and HCG. miR-33b-5p, GLUT4, sterol regulatory element-binding protein 1 (SREBF1), and high mobility group A2 (HMGA2) expression in rat ovarian tissues was examined by qRT-PCR and immunohistochemistry. The effect of a high dose of either glucose or insulin on miR-33b-5p, GLUT4, SREBF1 and HMGA2 expression was also examined in cultured adipocytes by qRT-PCR and western blotting. Additionally, the luciferase reporter assay and chromatin immunoprecipitation (ChIP) were used to explore the role of miR-33b-5p in regulating HMGA2, SREBF-1 and/or GLUT4. Elevated levels of miR-33b-5p expression were detected in the ovarian tissues of insulin resistant PCOS rats, and those levels were negatively correlated with those of GLUT4, HMGA2 and SREBF1 expression (P<0.05). Immunohistochemistry studies revealed that GLUT4, SREBF1, and HMGA2 expression levels in the ovarian tissues of insulin resistant PCOS rats were significantly lower than those in other groups of rats. In cultured adipocytes, excess extracellular glucose or insulin increased miR-33b-5p expression but reduced GLUT4, SREBF1 and HMGA2 expression, whereas the levels of GLUT4, SREBF1 and HMGA2 were elevated by inhibition of miR-33b-5. HMGA2 could directly bind to the 5-promoter region of GLUT4 and promote its expression, and could also promote SREBF1 expression. Moreover, SREBF1 could also directly bind to the 5-promoter region of GLUT4 and promote its expression. Our findings revealed that miR-33b-5p was over-expressed in the ovarian tissues of insulin resistant PCOS rats, and thus may play an important role in the development of insulin resistance in PCOS patients. miR-33b-5p can inhibit GLUT4 production by targeting HMGA2, and in addition, HMGA2 and SREBF1 are important molecules involved in modulating GLUT4 expression.