Is miRNA-30d a good pharmological target for treatment of diabetes?

Summary of: Zhao, X., Mohan, R., Ozcan, S., and Tang, X. (2012). MicroRNA-30d Induces Insulin Transcription Factor MafA and Insulin Production by Targeting Mitogen-activated Protein 4 Kinase 4 (MAP4K4) in Pancreatic β-Cells. The Journal of Biological Chemistry. Vol. 287, No. 37, pp. 31155 – 31164.

(written by Emma Frair and Yeana Jang)

What is diabetes? Diabetes is a metabolic condition in which a person’s body is either unable to produce or properly use insulin. A small organ near the stomach called the pancreas is responsible for producing and secreting all the insulin in one’s body.

Why is insulin so important? So… what’s the big deal if we don’t have insulin or if it doesn’t function properly? Well, we all know that the cells in our body that need a source of energy to funciton properly. That energy comes from food, which a majority of is turned into glucose or sugar serving as the source of our cell’s energy. Insulin is responsible for conducting and getting the glucose into the cells. Without proper insulin function one’s cells are not able to maintain energy in the necessary places.

What are these different types of diabetes?

Type 1- Only 5-10% of those diagnosed with diabetes have Type 1 diabetes. The type 1 diabetic patient’s pancrease produce little to no insulin. TREATMENT- These patients will have to have a daily injection or permanent pump to deliver his or her insulin. The blood glucose levels will have to be checked at least 4 to 5 times a day.

Type 2- Type 2 can also be a result from the depletion of insulin secretion; however, the difference from type 1 is that even if the patient’s pancreas is producing insulin his or her body has become resistant to its effects. TREATMENT- Type 2 diabetes can be treated with healthier eating and daily exercise. While the body remains resistant to insulin patients must treat it the same way as type 1 diabetics.

What do high glucose levels in the blood actually do?  Diabetes can still lead to serious health problems including: heart disease, blindness, kidney failure, and loweer-extremity amputations. Diabetes is also the seventh leading cause of death in the United Sates.

How is this related to the study of the inflammatory system? The β-cells in the pancreas are responsible for exclusively expressing and secreting the insulin transcription factors, PDX-1 and MafA. The inflammatory cytokine, TNF-⍺, is also secreted from the β-cells in the pancreas.

How do microRNAs work? microRNAs are a class of small non-coding RNAs that regulate function of a gene by binding the untranslated (UTR) end of the target gene and inhibiting the translation or secretion of that gene. It has been found that the relative high levels of mRNA-375 is responsible for inhibiting the glucose-induced insulin secretion. High levels of miRNA-375 (and any levels of miRNA-21, 34A, and 146) lead to negative regulation of insulin transcription factors made in the β-cells of the pancreas, resulting in a decrease of insulin production.

This is where the story begins…

It was hypothesized that the upregulation of miRNA-30d results in insulin production, which protects any β-cell functions that are impaired by the TNF-α cytokines. Intentional overexpression of miR-30d is beneficial in the prevention of diabetes.

In order to test this hypothesis, an insulin-secreting cell line MIN6 was transfected with siRNA against MAP4K4 compared with the negative control. This was analyzed by real-time PCR after incubation of TNF-α. The protein and mRNA levels of insulin increased when the levels of miR-30d and MafA were also increased, but there was a reduction of both TNF-α and MAP4K4. The expression of MafA and IRS2 could effectively inhibit TNF-α by silencing MAP4K4 (Figure 6).

Furthermore, pancreas of 10-week-old diabetic mice and heterozygous (normal) mice were isolated to analyze by MAP4K4 antisense LNA probe. Western blog and real-time PCR were used to further analyze. The normal mice had increased expression of miR-30d whereas the diabetic mice had decreased expression, and it was vice versa with M4P4K4 (Figure 7).

Overall, it is important to understand the signaling pathway of insulin production in β-cells by observing the roles of miRNA and MafA. Studying this mechanism could potentially provide new therapeutic agents for diabetes.