Defective endoplasmic reticulum-mitochondria contacts and bioenergetics in SEPN1-related myopathy.

SEPN1-related myopathy (SEPN1-RM) is a muscle disorder due to mutations of the SEPN1 gene, which is characterized by muscle weakness and fatigue leading to scoliosis and life-threatening respiratory failure. Core lesions, focal areas of mitochondria depletion in skeletal muscle fibers, are the most common histopathological lesion. SEPN1-RM underlying mechanisms and the precise role of SEPN1 in muscle remained incompletely understood, hindering the development of biomarkers and therapies for this untreatable disease. To investigate the pathophysiological pathways in SEPN1-RM, we performed metabolic studies, calcium and ATP measurements, super-resolution and electron microscopy on in vivo and in vitro models of SEPN1 deficiency as well as muscle biopsies from SEPN1-RM patients. Mouse models of SEPN1 deficiency showed marked alterations in mitochondrial physiology and energy metabolism, suggesting that SEPN1 controls mitochondrial bioenergetics. Moreover, we found that SEPN1 was enriched at the mitochondria-associated membranes (MAM), and was needed for calcium transients between ER and mitochondria, as well as for the integrity of ER-mitochondria contacts. Consistently, loss of SEPN1 in patients was associated with alterations in body composition which correlated with the severity of muscle weakness, and with impaired ER-mitochondria contacts and low ATP levels. Our results indicate a role of SEPN1 as a novel MAM protein involved in mitochondrial bioenergetics. They also identify a systemic bioenergetic component in SEPN1-RM and establish mitochondria as a novel therapeutic target. This role of SEPN1 contributes to explain the fatigue and core lesions in skeletal muscle as well as the body composition abnormalities identified as part of the SEPN1-RM phenotype. Finally, these results point out to an unrecognized interplay between mitochondrial bioenergetics and ER homeostasis in skeletal muscle. They could therefore pave the way to the identification of biomarkers and therapeutic drugs for SEPN1-RM and for other disorders in which muscle ER-mitochondria cross-talk are impaired.

High hepatic glutathione stores alleviate Fas-induced apoptosis in mice.

BACKGROUND/AIMS: The agonistic Jo2 anti-Fas antibody reproduces human fulminant hepatitis in mice. We tested the hypothesis that enhancing hepatic glutathione (GSH) stores may prevent Jo2-induced apoptosis. METHODS: We fed mice with a normal diet or a sulfur amino acid-enriched (SAA(+)) diet increasing hepatic GSH by 63%, and challenged these mice with Jo2. RESULTS: The SAA(+) diet markedly attenuated the Jo2-mediated decrease in hepatic GSH and the increase in the oxidized glutathione (GSSG)/GSH ratio in cytosol and mitochondria. The SAA(+) diet prevented protein kinase Czeta (PKCzeta) and p47(phox) phosphorylations, Yes activation, Fas-tyrosine phosphorylation, Bid truncation, Bax, and cytochrome c translocations, the mitochondrial membrane potential collapse, caspase activation, DNA fragmentation, hepatocyte apoptosis, and mouse lethality after Jo2 administration. The protective effect of the SAA(+) diet was abolished by a small dose of phorone decreasing hepatic GSH back to the levels observed in mice fed the normal diet. Conversely, administration of GSH monoethyl ester after Jo2 administration prevented hepatic GSH depletion and attenuated toxicity in mice fed with the normal diet. CONCLUSIONS: The SAA(+) diet preserves GSSG/GSH ratios, and prevents PKCzeta and p47(phox) phosphorylations, Yes activation, Fas-tyrosine phosphorylation, mitochondrial permeabilization, and hepatic apoptosis after Fas stimulation. GSH monoethyl ester is also protective, suggesting possible clinical applications.