ER stress aggravates diaphragm weakness through activating PERK/JNK signaling in obesity hypoventilation syndrome.

Abstract

Obesity hypoventilation syndrome is associated with diaphragmatic dysfunction. This study aimed to explore the role of endoplasmic reticulum (ER) stress in mediating obesity-induced diaphragmatic dysfunction. A pulmonary function test and ultrasound were applied to evaluate diaphragmatic function and magnetic resonance imaging was applied to measure diaphragmatic lipid deposition in human patients. For the mechanistic study, obese mice were introduced to a high-fat diet for 24 weeks, followed by diaphragmatic ultrasound measurement, transcriptomic sequencing, and respective biochemical analysis. Automatic force mapping was applied to measure the mechanical properties of C2C12 myotubes. People with obesity showed significant diaphragm weakness and lipid accumulation, which was further confirmed in obese mice. Consistently, diaphragms from obese mice showed altered gene expression profile in lipid metabolism and activation of ER stress response, indicated by elevated protein kinase R-like ER kinase (PERK) and c-Jun NH2 -terminal kinase (JNK) activation. In C2C12 myotubes, inhibition of PERK or JNK signaling abrogated lipotoxicity-induced intracellular lipid deposition and insulin resistance. Inhibition of JNK signaling reversed lipotoxicity-induced impairment of elasticity in C2C12 myotubes. These data suggest that ectopic lipid deposition impairs the diaphragmatic function of people with obesity. Activation of PERK/JNK signaling is involved in the pathogenesis of lipotoxicity-induced diaphragm weakness in obesity hypoventilation syndrome.