Endoplasmic reticulum stress and autophagy in homocystinuria patients with remethylation defects

Abstract

Proper function of endoplasmic reticulum (ER) and mitochondria is crucial for cellular homeostasis, and dysfunction at either site as well as perturbation of mitochondria-associated ER membranes (MAMs) have been linked to neurodegenerative and metabolic diseases. Previously, we have observed an increase in ROS and apoptosis levels in patientderived fibroblasts with remethylation disorders causing homocystinuria. Here we show increased mRNA and protein levels of Herp, Grp78, IPR1, pPERK, ATF4, CHOP, asparagine synthase and GADD45 in patient-derived fibroblasts suggesting ER stress and calcium perturbations in homocystinuria. In addition, overexpressed MAM-associated proteins (Grp75, σ-1R and Mfn2) were found in these cells that could result in mitochondrial calcium overload and oxidative stress increase. Our results also show an activation of autophagy process and a substantial degradation of altered mitochondria by mitophagy in patientderived fibroblasts. Moreover, we have observed that autophagy was partially abolished by antioxidants suggesting that ROS participate in this process that may have a protective role. Our findings argue that alterations in Ca homeostasis and autophagy may contribute to the development of this metabolic disorder and suggest a therapeutic potential in homocystinuria for agents that stabilize calcium homeostasis and/or restore the proper function of ER-mitochondria communications.Ministerio de Ciencia e Innovación (SAF2010-15284 to ER), Ministerio de Economía y Competividad: Instituto de Salud Carlos III (PI13/01239 to BP), MITOLAB (S2010/BMD-2402 to BP), Ministerio de Economía y Competividad (SAF2013-43005-R to ER and LRD), and an Institutional grant from Fundación Ramón Areces to the Centro de Biología Molecular “Severo Ochoa”Peer Reviewe