The endoplasmic reticulum-mitochondria interface is perturbed in PARK2 knockout mice and patients with PARK2 mutations

Abstract

Mutations in PARK2, encoding the E3 ubiquitin protein ligase Parkin, are a common cause of autosomal recessive Parkinson's disease (PD). Loss of PARK2 function compromisesmitochondrial quality by affectingmitochondrial biogenesis, bioenergetics, dynamics, transport and turnover. We investigated the impact of PARK2 dysfunction on the endoplasmic reticulum (ER)- mitochondria interface, whichmediates calcium(Ca2+)exchange between the two compartments and is essential for Parkindependentmitophagy. Confocal and electron microscopy analyses showed the ER and mitochondria to be in closer proximity in primary fibroblasts fromPARK2 knockout (KO) mice and PD patients with PARK2 mutations than in controls. Ca2+flux to the cytosol was alsomodified, due to enhanced ER-to-mitochondria Ca2+transfers, a change that was also observed in neurons derived from induced pluripotent stem cells of a patient with PARK2mutations. Subcellular fractionation showed the abundance of the Parkin substratemitofusin 2 (Mfn2), which is known to modulate the ER-mitochondria interface, to be specifically higher in the mitochondrion-associated ER membrane compartment in PARK2 KO tissue. Mfn2 downregulation or the exogenous expression of normal Parkin restored cytosolic Ca2+transients in fibroblasts from patients with PARK2 mutations. In contrast, a catalytically inactive PD-related Parkin variant had no effect. Overall, our data suggest that Parkin is directly involved in regulating ER-mitochondria contacts and provide new insight into the role of the loss of Parkin function in PD development.