Loss of HtrA2/Omi protease activity induces mitonuclear imbalance and sarcopenia via differential regulation of mitochondrial biogenesis

Abstract Background Cellular homeostasis requires tight coordination between nucleus and mitochondria, organelles that each possess their own genomes. Disrupted mitonuclear communication has been found to be implicated in many aging processes. However little is known about mitonuclear signaling regulator in sarcopenia which is a major contributor to the risk of poor health-related quality of life, disability and premature death in older people. HtrA2/Omi is a mitochondrial protease and play an important role in mitochondrial proteostasis. HtrA2 mnd2(-/-) mice harboring protease-deficient HtrA2/Omi Ser276Cys missense mutants exhibit premature aging phenotype. Additionally, HtrA2/Omi has been established as a signaling regulator in nervous system and tumors. We therefore asked whether HtrA2/Omi participates in mitonuclear signaling regulation in aging muscle.Methods Using motor functional, histological and molecular biological methods, we characterized the muscle phenotype of HtrA2 mnd2(-/-) mice. We employed bioinformatics analysis and identified HtrA2/Omi as a gene differentially associated with nDNA/mtDNA gene expression in sarcopenia. Further, we isolated the gastrocnemius muscle of HtrA2 mnd2(-/-) mice and determined expression of genes in UPR mt , mitohormesis, electron transport chain (ETC), and mitochondrial biogenesis.Results Here, we showed that HtrA2/Omi protease deficiency induced denervation-independent skeletal muscle degeneration. Despite of mitochondrial hypofunction, upregulation of UPR mt and mitohormesis related genes and elevated reactive oxygen species (ROS) production were not observed in HtrA2 mnd2(-/-) mice, contrary to previous assumptions that loss of protease activity of HtrA2/Omi would lead to mitochondrial dysfunction as a result of proteostasis disturbance and ROS burst. Instead, we showed that HtrA2/Omi protease deficiency results in different changes between the expression of nDNA and mtDNA encoded ETC subunits, which is in consistent with their transcription factors NRF-1/2 and coactivator PGC-1α, suggesting that HtrA2/Omi protease activity may differentially regulate mitonuclear signaling via mitochondrial biogenesis in sarcopenia. Besides, Akt1 but not GSK3β showed increased expression level in HtrA2 mnd2(-/-) muscles, indicating an involvement of Akt1 in PGC-1α regulation response to HtrA2/Omi protease deficiency.Conclusions HtrA2/Omi protease deficiency induces mitonuclear imbalance and sarcopenia via differential regulation of mitochondrial biogenesis. The novel mechanistic insights may be of importance in developing new therapeutic strategies for sarcopenia.