Lipid mediated ER stress contributes to the pathogenesis of mitochondrial myopathies.

Abstract

Mitochondrial diseases are a heterogeneous group of genetic disorders caused by impaired oxidative phosphorylation (OxPhos). When skeletal muscle is predominantly affected, they are defined as primary mitochondrial myopathies. Although the genetic causes of mitochondrial myopathies and the resulting bioenergetic impairments are well established, the metabolic drivers behind progressive muscle dysfunction remain poorly defined. This gap in knowledge may contribute to the lack of effective treatments for these disorders. OxPhos defective muscle initiates a metabolic response coordinated by systemic signals which results in muscle and adipose tissue wasting. Here, we show ectopic muscle lipid accumulation in a COX10 KO mouse model of mitochondrial myopathy due to inability to oxidize fatty acids in muscle. In both the mouse model and in mitochondrial patients, we find an increase in ceramides, which is mechanistically linked to chronic ER stress, phosphorylation of eIF2α, and activation of ATF4 signaling. We propose that Ph-eIF2α-mediated attenuation of global protein synthesis and ATF4-initiated atrophy pathways contribute to muscle wasting and weakness. Importantly, inhibition of de novo synthesis of ceramides with myriocin reduces ER stress and ATF4 signaling and improves muscle proteostasis, body weight, and motor functions in the COX10 KO mouse. Together, these findings highlight the role of lipid metabolism as a contributor to mitochondrial myopathy and identify lipid-mediated stress pathways that can be targeted therapeutically.

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