Descending Expression of miR320 in Insulin-Resistant Adipocytes Treated with Ascending Concentrations of Metformin

Non-coding RNA genes modulate PI3K/AKT signaling pathway in polycystic ovary syndrome

BACKGROUND

The PI3K protein kinase B (PI3K/AKT) signaling pathway has crucial roles in insulin signaling and other endocrine disorders. The purpose of this study is to validate the association of PCOS with PI3K/AKT pathway target genes, miRNA486-5p, and miRNA483-5p as well as to evaluate the outcome of metformin on the pathogenesis of PCOS.  METHODS: This case-controlled study included 3 subject groups: twenty healthy females (control group), twenty PCOS females before treatment, and twenty PCOS females treated with metformin at a dose (500 mg 3 times per day for 3 months). The following gene expressions were assessed by real-time PCR: PI3K, AKT, ERK, GLUT4, miRNA486-5p, and miRNA483-5p in the whole blood.

RESULTS

There was a significant decrease in miRNA486-5p and miRNA483-5p in the PCOS group with a significant negative correlation between miRNA486-5p and PI3K and a significant negative correlation between miRNA483-5p and ERK. Metformin treatment resulted in significant elevation of the studied miRNA, significant downregulation of PI3K/AKT target genes, and significant amelioration of the gonadotrophic hormonal imbalance and insulin resistance markers: fasting blood glucose, HBA1C, fasting insulin, and GLUT4 gene expression.

CONCLUSIONS

miRNA486 and miRNA483 downregulation may contribute to the etiology of PCOS, influence glucose metabolism, and result in IR in PCOS. Metformin's upregulation of those miRNAs affects glucose metabolism by controlling the expression of GLUT4, ameliorates PCOS-related insulin resistance, and improves PCOS-related hormonal imbalance by controlling the PI3K/AKT signaling pathway.

Metformin and insulin-resistant related diseases: Emphasis on the role of microRNAs

Metformin is one of the most prescribed drugs in type II diabetes (T2DM) which has recently found new applications in the prevention and treatment of various illnesses, from metabolic disorders to cardiovascular and age-related diseases. Metformin improves insulin resistance (IR) by modulating metabolic mechanisms and mitochondrial biogenesis. Alternation of microRNAs (miRs) in the treatment of IR-related illnesses has been observed by metformin therapy. MiRs are small non-coding RNAs that play important roles in RNA silencing, targeting the 3'untranslated region (3'UTR) of most mRNAs and inhibiting the translation of related proteins. As a result, their dysregulation is associated with many diseases. Metformin may alter miRs levels in the treatment of various diseases by AMPK-dependent or AMPK-independent mechanisms. Here, we summarized the therapeutic role of metformin by modifying the aberrant expression of miRs as potential biomarkers or therapeutic targets in diseases in which IR plays a key role.

Metformin downregulates miR223 expression in insulin-resistant 3T3L1 cells and human diabetic adipose tissue

AIMS AND DESIGNS

Metformin, an anti-diabetic drug, is the first line medication for the treatment of type 2 diabetes mellitus and some studies show its relationship with micro-RNAs. This study set up to determine the effect of metformin on miR223 expression and content of AKT/GLUT4 proteins in insulin resistant signaling in 3T3L1 cells and adipocyte of human diabetic patients.

MATERIALS AND METHODS

Subcutaneous adipose tissues were taken from newly diagnosed diabetic patients (HOMA-IR > 1.8), before and after three months treatment with 500 mg of metformin twice a day. Cellular homogenate was prepared and miR223 expression and AKT/GLUT4 protein expression were determined by quantitative real-time PCR and western blotting. The results were compared to insulin resistant 3T3L1 adipocytes that were treated with 10 mM Metformin.

RESULTS

MiR223 expression was significantly overexpressed both in insulin-resistant 3T3L1 adipocytes compared to non-insulin resistant adipocytes and in human diabetic adipose tissue, compared to non-diabetics (P value < 0.01). Metformin treatment downregulated miR223 expression in both adipocytes and human diabetic adipose tissue. In contrast the IRS/PI3-K/AKT pathway signaling components, Akt and GLUT4 increased in insulin-resistant 3T3L1 adipocytes and human diabetic adipose tissue after three months of metformin treatment.

CONCLUSIONS

Metformin reduced insulin resistance in adipocytes by reduction of miR223 expression and improving of IRS/Akt/GLUT4 signaling pathways. Plasma miR223 expression of human diabetic patients was reduced by metformin treatment. These results point to a novel mechanism of miR223 in insulin resistance.