Apobec2 deficiency causes mitochondrial defects and mitophagy in skeletal muscle

Abstract

Apobec2 is a member of the activation-induced deaminase/apolipoprotein B mRNA editing enzyme catalytic polypeptide cytidine deaminase family expressed in differentiated skeletal and cardiac muscle. We previously reported that Apobec2 deficiency in mice leads to a shift in muscle fiber type, myopathy, and diminished muscle mass. However, the mechanisms of myopathy caused by Apobec2 deficiency and its physiologic functions are unclear. Here we show that, although Apobec2 localizes to the sarcomeric Z-lines in mouse tissue and cultured myotubes, the sarcomeric structure is not affected in Apobec2-deficient muscle. In contrast, electron microscopy reveals enlarged mitochondria and mitochondria engulfed by autophagic vacuoles, suggesting that Apobec2 deficiency causes mitochondrial defects leading to increased mitophagy in skeletal muscle. Indeed, Apobec2 deficiency results in increased reactive oxygen species generation and depolarized mitochondria, leading to mitophagy as a defensive response. Furthermore, the exercise capacity of Apobec2−/− mice is impaired, implying Apobec2 deficiency results in ongoing muscle dysfunction. The presence of rimmed vacuoles in myofibers from 10-mo-old mice suggests that the chronic muscle damage impairs normal autophagy. We conclude that Apobec2 deficiency causes mitochondrial defects that increase muscle mitophagy, leading to myopathy and atrophy. Our findings demonstrate that Apobec2 is required for mitochondrial homeostasis to maintain normal skeletal muscle function.—Sato, Y., Ohtsubo, H., Nihei, N., Kaneko, T., Sato, Y., Adachi, S.-I., Kondo, S., Nakamura, M., Mizunoya, W., Iida, H., Tatsumi, R., Rada, C., Yoshizawa, F. Apobec2 deficiency causes mitochondrial defects and mitophagy in skeletal muscle.

Physiological and Pathological Mitochondrial Clearance Is Related to Pectoralis Major Muscle Pathogenesis in Broilers With Wooden Breast Syndrome

“…These vacuoles are thus termed autophagic vacuoles (AVs) in skeletal muscle (Malicdan and Nishino, 2012), and their appearance therein constitutes the pathognomonic morphological hallmark of autophagic vacuolar myopathy, which is a group of human hereditary myopathies including Pompe and Danon disease (Nishino, 2006;Cho and Noguchi, 2013;Castets et al, 2016). It has been reported that rimmed vacuoles are outcomes of impaired normal autophagy and represent frequent pathological characteristics in the chronic muscle damage of atrophy and myopathies (Suzuki et al, 2002;Sato et al, 2018). During autophagy, the accumulation of protein aggregates disturbs the maturation and fusion steps of autophagosome formation and enlarges the autophagic vesicles, where the rimmed vacuoles originate (Castets et al, 2016).…”

“…In mouse studies, deficiency of apolipoprotein B messenger RNA (mRNA) editing enzyme catalytic polypeptide 2 (APOBEC2), a member of the zincdependent cytidine deaminase protein family, has been reported to lead to a loss of skeletal muscle mass and atrophy (Sato et al, 2009). Notably, APOBEC2 deficiency does not affect the sarcomeric structure but rather causes mitochondrial morphological abnormalities in the murine skeletal myofibers, with the abnormal mitochondria being surrounded by AVs and removed by mitophagy (Sato et al, 2018). In comparison, in the myofibers of broilers analyzed in the present study, the myofibrils surrounding the AVs were ultrastructurally healthy and intact, indicating that the engulfment and digestion of these vacuoles is limited to the mitochondria likely through the mitophagy process.…”

“…Based on the ultrastructural observations of the active metabolism of mitochondria as revealed by autophagylike vacuoles, the correlations between the expression of mitochondrial dynamics-related genes and that of autophagy-/mitophagy-related genes were also analyzed (Table 4). Specifically, the microtubule-associated protein 1 light chain 3 alpha, beta (MAP1LC3A, B) genes, also termed LC3A and LC3B, constitute the primary genes related to autophagosome development and maturation (Schaaf et al, 2016), whereas parkin RBR E3 ubiquitin protein ligase (PARK2) acts as a specific regulator of mitophagy (Sato et al, 2018). We found that the expression of MFN1, MFN2, OPA1, and DRP1 was significantly positively correlated with that of all three autophagy-/mitophagy-related genes.…”

Rrm2b deletion causes mitochondrial metabolic defects in renal tubules

“…Mitochondrial genomic DNA was co-purified with nuclear genomic DNA, and quantitative real-time PCR was performed for detection of mt-Co2 (Cytochrome c oxidase subunit 2; mitochondrial DNA-encoded) and 18S rRNA (18S ribosomal RNA; nuclear DNA-encoded). The relative mtDNA copy number was calculated via normalization to 18S rRNA gene expression (mtDNA/nDNA) 19,20 .…”

Contribution of cytosine desaminases of AID/APOBEC family to carcinogenesis

“…It is necessary for the normal development of muscles and weight gain in mice (Sato et al, 2009). In the absence of APOBEC2, animals develop age-dependent myopathy (Sato et al, 2009), which was related to mitochondrial function defects (Sato et al, 2017). Heterologous expression of APOBEC2 in yeast and bacteria did not lead to a mutator phenotype (Lada et al, 2011a), and APOBEC2 does not deaminate DNA in vitro (Harris et al, 2002;Lada et al, 2011a).…”