During ageing, muscle stem-cell regenerative function declines. At advanced geriatric age, this decline is maximal owing to transition from a normal quiescence into an irreversible senescence state. How satellite cells maintain quiescence and avoid senescence until advanced age remains unknown. Here we report that basal autophagy is essential to maintain the stem-cell quiescent state in mice. Failure of autophagy in physiologically aged satellite cells or genetic impairment of autophagy in young cells causes entry into senescence by loss of proteostasis, increased mitochondrial dysfunction and oxidative stress, resulting in a decline in the function and number of satellite cells. Re-establishment of autophagy reverses senescence and restores regenerative functions in geriatric satellite cells. As autophagy also declines in human geriatric satellite cells, our findings reveal autophagy to be a decisive stem-cell-fate regulator, with implications for fostering muscle regeneration in sarcopenia.

Autophagy maintains stemness by preventing senescence

Nrf2-Keap1 signaling in oxidative and reductive stress.

Adult stem cells (SCs) are essential for tissue maintenance and regeneration yet are susceptible to senescence during aging. We demonstrate the importance of the amount of the oxidized form of cellular nicotinamide adenine dinucleotide (NAD(+)) and its effect on mitochondrial activity as a pivotal switch to modulate muscle SC (MuSC) senescence. Treatment with the NAD(+) precursor nicotinamide riboside (NR) induced the mitochondrial unfolded protein response and synthesis of prohibitin proteins, and this rejuvenated MuSCs in aged mice. NR also prevented MuSC senescence in the mdx (C57BL/10ScSn-Dmd(mdx)/J) mouse model of muscular dystrophy. We furthermore demonstrate that NR delays senescence of neural SCs and melanocyte SCs and increases mouse life span. Strategies that conserve cellular NAD(+) may reprogram dysfunctional SCs and improve life span in mammals.

https://science.sciencemag.org/content/sci/early/2016/04/27/science.aaf2693.full.pdf

NAD+ repletion improves mitochondrial and stem cell function and enhances life span in mice

Regeneration of skeletal muscle depends on a population of adult stem cells (satellite cells) that remain quiescent throughout life. Satellite cell regenerative functions decline with ageing. Here we report that geriatric satellite cells are incapable of maintaining their normal quiescent state in muscle homeostatic conditions, and that this irreversibly affects their intrinsic regenerative and self-renewal capacities. In geriatric mice, resting satellite cells lose reversible quiescence by switching to an irreversible pre-senescence state, caused by derepression of p16INK4a (also called Cdkn2a). On injury, these cells fail to activate and expand, undergoing accelerated entry into a full senescence state (geroconversion), even in a youthful environment. p16INK4a silencing in geriatric satellite cells restores quiescence and muscle regenerative functions. Our results demonstrate that maintenance of quiescence in adult life depends on the active repression of senescence pathways. As p16INK4a is dysregulated in human geriatric satellite cells, these findings provide the basis for stem-cell rejuvenation in sarcopenic muscles. This study shows that ageing satellite cells undergo an irreversible transition from a quiescent to a pre-senescent state that results in the loss of muscle regeneration in sarcopenia; furthermore, increased expression of p16INK4a is identified as a common feature of senescent satellite cells. One of the properties crucial to the function of adult mammalian stem cells is the capacity to remain in a quiescent state for prolonged periods — and to respond when the need to regenerate arises. Loss of skeletal muscle mass and function are common features of advanced ageing in humans, associated with a loss of regenerative capacity of the skeletal muscle stem cells, known as satellite cells. Pura Munoz-Canoves and colleagues show that ageing satellite cells undergo an irreversible transition from quiescence to a pre-senescence state associated with increased expression of p16INK4a, a tumour-suppressor protein that has been identified as a marker for senescence. Repression of p16INK4a during adult life is shown to maintain satellite cells in a reversible quiescence state that allows muscle regeneration; p16INK4a is dysregulated in human geriatric satellite cells and the potential for muscle regeneration is lost.

Geriatric muscle stem cells switch reversible quiescence into senescence

Single-cell sequencing reveals dissociation-induced gene expression in tissue subpopulations

Adult skeletal muscle in mammals is a stable tissue under normal circumstances but has remarkable ability to repair after injury. Skeletal muscle regeneration is a highly orchestrated process invol...

Satellite Cells and the Muscle Stem Cell Niche

Diminished regenerative capacity of skeletal muscle occurs during adulthood. We identified a reduction in the intrinsic capacity of mouse adult satellite cells to contribute to muscle regeneration and repopulation of the niche. Gene expression analysis identified higher expression of JAK-STAT signaling targets in 3-week [corrected] 18-month-old mice [corrected]. Knockdown of Jak2 or Stat3 significantly stimulated symmetric satellite stem cell divisions on cultured myofibers. Genetic knockdown of Jak2 or Stat3 expression in prospectively isolated satellite cells markedly enhanced their ability to repopulate the satellite cell niche after transplantation into regenerating tibialis anterior muscle. Pharmacological inhibition of Jak2 and Stat3 activity similarly stimulated symmetric expansion of satellite cells in vitro and their engraftment in vivo. Intramuscular injection of these drugs resulted in a marked enhancement of muscle repair and force generation after cardiotoxin injury. Together these results reveal age-related intrinsic properties that functionally distinguish satellite cells and suggest a promising therapeutic avenue for the treatment of muscle-wasting diseases.

/pdf/inhibition-of-jak-stat-signaling-stimulates-adult-satellite-4vx8uhzscr.pdf

Inhibition of JAK-STAT signaling stimulates adult satellite cell function

http://www.kumc.edu/Documents/msctc/Price%20FD,%20Biochim%20Biophys%20Acta.%202007%20.pdf

Feodor D. Price

Papers

Satellite Cells and the Muscle Stem Cell Niche

Inhibition of JAK-STAT signaling stimulates adult satellite cell function

Stem cell based therapies to treat muscular dystrophy

Genome-wide RNA-Seq of Human Motor Neurons Implicates Selective ER Stress Activation in Spinal Muscular Atrophy

The Solution Structure of the C-terminal Domain of TonB and Interaction Studies with TonB Box Peptides