Physical exercise in aging human skeletal muscle increases mitochondrial calcium uniporter expression levels and affects mitochondria dynamics

<jats:title>Abstract</jats:title><jats:p>Age‐related sarcopenia is characterized by a progressive loss of muscle mass with decline in specific force, having dramatic consequences on mobility and quality of life in seniors. The etiology of sarcopenia is multifactorial and underlying mechanisms are currently not fully elucidated. Physical exercise is known to have beneficial effects on muscle trophism and force production. Alterations of mitochondrial Ca<jats:sup>2+</jats:sup> homeostasis regulated by mitochondrial calcium uniporter (<jats:styled-content style="fixed-case">MCU</jats:styled-content>) have been recently shown to affect muscle trophism in vivo in mice. To understand the relevance of <jats:styled-content style="fixed-case">MCU</jats:styled-content>‐dependent mitochondrial Ca<jats:sup>2+</jats:sup> uptake in aging and to investigate the effect of physical exercise on <jats:styled-content style="fixed-case">MCU</jats:styled-content> expression and mitochondria dynamics, we analyzed skeletal muscle biopsies from 70‐year‐old subjects 9 weeks trained with either neuromuscular electrical stimulation (<jats:styled-content style="fixed-case">ES</jats:styled-content>) or leg press. Here, we demonstrate that improved muscle function and structure induced by both trainings are linked to increased protein levels of <jats:styled-content style="fixed-case">MCU</jats:styled-content>. Ultrastructural analyses by electron microscopy showed remodeling of mitochondrial apparatus in <jats:styled-content style="fixed-case">ES</jats:styled-content>‐trained muscles that is consistent with an adaptation to physical exercise, a response likely mediated by an increased expression of mitochondrial fusion protein <jats:styled-content style="fixed-case">OPA</jats:styled-content>1. Altogether these results indicate that the <jats:styled-content style="fixed-case">ES</jats:styled-content>‐dependent physiological effects on skeletal muscle size and force are associated with changes in mitochondrial‐related proteins involved in Ca<jats:sup>2+</jats:sup> homeostasis and mitochondrial shape. These original findings in aging human skeletal muscle confirm the data obtained in mice and propose <jats:styled-content style="fixed-case">MCU</jats:styled-content> and mitochondria‐related proteins as potential pharmacological targets to counteract age‐related muscle loss.</jats:p>