Long-chain saturated free fatty acids induce pancreatic β−cell lipotoxic stress via H2O2−mediated mitochondria-associated membrane remodeling

Introduction Type 2 diabetes (T2D) is characterized by progressive pancreatic β-cell dysfunction and loss, driven by chronic exposure to elevated circulating free fatty acids (FFAs). Mitochondria-associated endoplasmic reticulum membranes (MAMs), the specialized contact sites between the endoplasmic reticulum (ER) and mitochondria, regulate cellular metabolism and survival, yet their role in β−cell lipotoxicity remains unclear. Methods We examined the impact of physiologically relevant long−chain saturated (palmitic and stearic acid) and unsaturated (palmitoleic and oleic acid) FFAs, applied alone or in combination, on MAM formation in insulin−secreting INS−1E cells. ER-mitochondria contacts were quantified by proximity−ligand assay (PLA), transmission electron microscopy and genetically encoded MAM sensors. The role of reactive oxygen species was investigated using the H 2 O 2 −scavenging enzyme glutathione peroxidase 8 (GPX8). To test causality, ER−mitochondria coupling was artificially enhanced with a synthetic ER−mitochondrial linker. Results Saturated FFAs significantly increased ER-mitochondria contacts, whereas unsaturated FFAs had no negative effect and counteracted the saturated FFA-induced MAM formation. Expression of GPx8 suppressed palmitate−induced MAM formation, indicating that H 2 O 2 −mediated oxidative stress is required for the saturated FFA-induced MAM remodeling. Cells expressing the synthetic linker displayed heightened susceptibility to lipotoxic stress, confirming that sustained ER−mitochondria coupling promotes β−cell death. Conclusions Our data demonstrate that dysregulated MAMs constitute a mechanistic link between saturated−FFA-induced lipotoxic stress and β−cell failure in T2D. Targeting MAM remodeling or the upstream H 2 O 2 signal may represent a novel therapeutic avenue to preserve β−cell function under lipotoxic conditions.