MicroRNA-31 targets FIH-1 to positively regulate corneal epithelial glycogen metabolism

Corneal epithelium relies on abundant glycogen stores as its primary energy source. MicroRNA-31 (miR-31), a corneal epithelial-preferred miRNA, negatively regulates factor inhibiting hypoxia-inducible factor-1 (FIH-1). Since HIF-1 alpha is involved in anaerobic energy production, we investigated the role that miR-31 and FIH-1 play in regulating corneal epithelial glycogen. We used antagomirs (antago) to reduce the level of miR-31 in primary human corneal epithelial keratinocytes (HCEKs), and a miR-31-resistant FIH-1 to increase FIH-1 levels. Antago-31 raised FIH-1 levels and significantly reduced glycogen stores in HCEKs compared to irrelevant-antago treatment. Similarly, HCEKs retrovirally transduced with a miR-31-resistant FIH-1 had markedly reduced glycogen levels compared with empty vector controls. In addition, we observed no change in a HIF-1 alpha reporter or known genes downstream of HIF-1 alpha indicating that the action of FIH-1 and miR-31 on glycogen is HIF-1 alpha-independent. An enzyme-dead FIH-1 mutation failed to restore glycogen stores, indicating that FIH-1 negatively regulates glycogen in a hydroxylase-independent manner. FIH-1 overexpression in HCEKs decreased AKT signaling, activated GSK-3 beta, and inactivated glycogen synthase. Treatment of FIH-1-transduced HCEKs with either a myristolated Akt or a GSK-3 beta inhibitor restored glycogen stores, confirming the direct involvement of Akt/GSK-3 beta signaling. Silencing FIH-1 in HCEKs reversed the observed changes in Akt-signaling. Glycogen regulation in a HIF-1 alpha-independent manner is a novel function for FIH-1 and provides new insight into how the corneal epithelium regulates its energy requirements.-Peng, H., Hamanaka, R. B., Katsnelson, J., Hao, L., Yang, W., Chandel, N. S., Lavker, R. M. MicroRNA-31 targets FIH-1 to positively regulate corneal epithelial glycogen metabolism. FASEB J. 26, 3140-3147 (2012). www.fasebj.org