Mitochondrial Theory of Aging in Human Age-Related Sarcopenia

Understanding age-related sarcopenia and, more importantly, devising counterstrategies require an intimate knowledge of the underlying mechanism(s) of sarcopenia. The mitochondrial theory of aging (MTA) has been a leading theory on aging for the last decade; however, there is relatively little information from human tissue to support or rebut the involvement of the MTA in aging skeletal muscle. It is believed that mitochondria may contribute to sarcopenia in a stochastic fashion where regions of fibers containing dysfunctional mitochondria are forced to atrophy. Resistance exercise, a known hypertrophic stimulus, has been shown to improve the mitochondrial phenotype of aged skeletal muscle. Furthermore, activation of skeletal muscle stem cells by resistance exercise may attenuate sarcopenia in two ways. First by inducing nuclear addition to postmitotic fibers, and, second, by increasing the proportion of functional mitochondria donated by muscle stem cells in a process termed 'gene shifting'. In this chapter we review the evidence supporting the MTA, the potential to attenuate the MTA with a known hypertrophic stimuli and explore the role of muscle stem cells in gene shifting to determine the connection between mitochondrial dysfunction and age-related sarcopenia.