miR-199a Knockdown Alleviates Insulin Resistance and Inflammation by Targeting DDIT4 via the PI3K/AKT Pathway in vitro and in vivo.

BACKGROUND: Insulin resistance (IR) is a pivotal pathological feature in the development of type 2 diabetes mellitus (T2DM). MicroRNA-199a (miR-199a) has been implicated in various metabolic disorders, but its precise role and mechanism in hepatic IR remain largely unexplored. This study aimed to investigate the role of miR-199a in IR and inflammation and to determine whether its effects are mediated through DDIT4 and the PI3K/AKT pathway. METHODS: An in vitro IR model was established in HepG2 cells using palmitic acid, and an in vivo T2DM model was induced in mice using a high-fat diet combined with streptozotocin injection. Functional assays, including glucose uptake and ELISA, were employed to assess metabolic and inflammatory responses. The interaction between miR-199a and its putative target, DDIT4, was validated by luciferase reporter and RNA immunoprecipitation assays. Key proteins in the PI3K/AKT signaling pathway were analyzed by Western blotting. RESULTS: We found that miR-199a was significantly upregulated, while DDIT4 was downregulated in both IR HepG2 cells and diabetic mice. Mechanistically, we identified DDIT4 as a direct target of miR-199a. Knockdown of miR-199a ameliorated insulin resistance and suppressed inflammation, whereas concomitant depletion of DDIT4 abolished these protective effects. Furthermore, miR-199a inhibition activated the PI3K/AKT pathway, as evidenced by increased phosphorylation of PI3K, AKT, and AS160, and decreased phosphorylation of FOXO1. These signaling changes were also dependent on DDIT4. In vivo, inhibition of miR-199a improved glucose homeostasis, attenuated systemic inflammation, and activated pancreatic PI3K/AKT signaling in T2DM mice. CONCLUSION: Our findings reveal a novel miR-199a/DDIT4 axis that regulates insulin sensitivity and inflammation via the PI3K/AKT pathway, suggesting miR-199a as a potential therapeutic target for T2DM.