Mitofusin 2 expression in muscle decreases during aging and generates a gene signature characteristic of aged muscle

Mitochondrial fusion and fission proteins regulate mitochondrial quality control and mitochondrial metabolism. In turn, mitochondrial dysfunction is associated with aging, although its causes are still under debate. Here, we show that aging is characterized by a progressive reduction of Mitofusin 2 (Mfn2) in mouse skeletal muscle and that skeletal muscle Mfn2 ablation in mice generates a gene signature linked to aging. Furthermore, muscle Mfn2-deficient mice show unhealthy aging characterized by altered metabolic homeostasis and sarcopenia. Mfn2 deficiency impairs mitochondrial quality control, which contributes to an exacerbated age-related mitochondrial dysfunction. Surprisingly, aging-induced Mfn2 deficiency triggers a ROS-dependent retrograde signaling pathway through induction of HIF1 transcription factor and BNIP3. This pathway ameliorates mitochondrial autophagy and minimizes mitochondrial damage. Our findings reveal that repression of Mfn2 in skeletal muscle during aging is determinant for the loss of mitochondrial quality, contributing to age-associated metabolic alterations and loss of muscle fitness.