Disruption of endoplasmic reticulum structure and integrity in lipotoxic cell death

TLDR

Lipid accumulation in non‑adipose tissues causes lipotoxic cell death, contributing to obesity and type‑2 diabetes, yet the underlying mechanisms remain poorly understood. This study investigates whether palmitate directly impairs endoplasmic reticulum function through a mechanism independent of reactive oxygen species. Palmitate is rapidly incorporated into microsomal phospholipids and triglycerides, remodeling the ER membrane, while AMPK‑mediated beta‑oxidation reduces incorporation, chaperone release, caspase activation, and cell death. The results show that palmitate increases saturated lipid content in the ER, causing dilatation, chaperone redistribution, and compromised membrane integrity, thereby linking ER structural disruption to fatty‑acid‑induced cell death.

Abstract

Cell dysfunction and death induced by lipid accumulation in nonadipose tissues, or lipotoxicity, may contribute to the pathogenesis of obesity and type 2 diabetes. However, the mechanisms leading to lipotoxic cell death are poorly understood. We recently reported that, in Chinese hamster ovary (CHO) cells and in H9c2 cardiomyoblasts, lipid overload induced by incubation with 500 muM palmitate leads to intracellular accumulation of reactive oxygen species, which subsequently induce endoplasmic reticulum (ER) stress and cell death. Here, we show that palmitate also impairs ER function through a more direct mechanism. Palmitate was rapidly incorporated into saturated phospholipid and triglyceride species in microsomal membranes of CHO cells. The resulting membrane remodeling was associated with dramatic dilatation of the ER and redistribution of protein-folding chaperones to the cytosol within 5 h, indicating compromised ER membrane integrity. Increasing beta-oxidation, through the activation of AMP-activated protein kinase, decreased palmitate incorporation into microsomes, decreased the escape of chaperones to the cytosol, and decreased subsequent caspase activation and cell death. Thus, palmitate rapidly increases the saturated lipid content of the ER, leading to compromised ER morphology and integrity, suggesting that impairment of the structure and function of this organelle is involved in the cellular response to fatty acid overload.