# MAPK Phosphatase-3 Mediates Chronic Endoplasmic Reticulum Stress Promoting Hepatic Gluconeogenesis

## TL;DR

This study shows that chronic ER stress increases MKP-3, which promotes glucose production in the liver, contributing to high blood sugar in obesity.

## Contribution

The study identifies MKP-3 as a novel mediator of chronic ER stress-induced hepatic gluconeogenesis.

## Key findings

- Chronic ER stress increases Mkp-3 and gluconeogenic gene expression in mouse hepatocytes.
- Liver-specific Mkp-3 knockout reverses high-fat diet-induced hyperglycemia and gluconeogenesis.
- PERK activation promotes Mkp-3 expression, linking ER stress to glucose production.

## Abstract

Long-term nutritional excess causes hepatic steatosis, endoplasmic reticulum (ER) stress, hyperglycemia, and hyperlipidemia. Mitogen-activated protein kinase phosphatase-3 (MKP-3) is a well-established stress-regulated protein and a regulator of gluconeogenesis. Our previous study revealed that acute ER stress reduced gluconeogenesis and MKP-3 protein stability. However, the expression of MKP-3 and its regulatory mechanisms in chronic ER stress remain unclear. The aim of this study was to investigate the effects of chronic ER stress on hepatic MKP-3 expression and its role in the regulation of gluconeogenesis. The results show that long-term administration of thapsigargin (Tg) or palmitic acid promoted gene expression of Mkp-3 and gluconeogenic genes Pepck, G6pc, and Pgc1α in primary mouse hepatocytes. In addition, a long-term high-fat diet (HFD) or Tg administration significantly increased hepatic ER stress and blood glucose level in mice, while inducing the expression of Mkp-3 and hepatic gluconeogenic genes Pepck, G6pc and Pgc1α. Further study revealed that liver-specific Mkp-3 knockout (Mkp-3 LKO) reversed the blood glucose level and expression levels of gluconeogenic genes those were induced by long-term HFD in mice. Moreover, activation of the PKR-like ER kinase (PERK) by its agonist increased hepatic Mkp-3 expression, whereas inhibitor of PERK suppressed the expression of Mkp-3 under Tg administration. These results suggest that chronic high-fat diet might promote hepatic gluconeogenesis via the PERK/MKP-3 pathway. Consequently, this study identified a potential therapeutic target for treating obesity-related hyperglycemia.