FoxO maintains a genuine muscle stem-cell quiescent state until geriatric age

Tissue regeneration declines with ageing but little is known about whether this arises from changes in stem-cell heterogeneity. Here, in homeostatic skeletal muscle, we identify two quiescent stem-cell states distinguished by relative CD34 expression: CD34High, with stemness properties (genuine state), and CD34Low, committed to myogenic differentiation (primed state). The genuine-quiescent state is unexpectedly preserved into later life, succumbing only in extreme old age due to the acquisition of primed-state traits. Niche-derived IGF1-dependent Akt activation debilitates the genuine stem-cell state by imposing primed-state features via FoxO inhibition. Interventions to neutralize Akt and promote FoxO activity drive a primed-to-genuine state conversion, whereas FoxO inactivation deteriorates the genuine state at a young age, causing regenerative failure of muscle, as occurs in geriatric mice. These findings reveal transcriptional determinants of stem-cell heterogeneity that resist ageing more than previously anticipated and are only lost in extreme old age, with implications for the repair of geriatric muscle.
The authors acknowledge funding from MINECO-Spain (grant no. RTI2018-096068), ERC2016-AdG-741966, LaCaixa-HEALTH-HR17-00040, MDA, UPGRADE-H2020-825825, AFM and DPP-Spain to P.M.-C; María-de-Maeztu-Program for Units of Excellence to UPF (grant no. MDM-2014-0370) and the Severo-Ochoa-Program for Centers of Excellence to CNIC (grant no. SEV-2015-0505). This work was also supported by NIAMS IRP through NIH grants nos AR041126 and AR041164 to V.S. and utilized computational resources of the NIH HPC Biowulf cluster (http://hpc.nih.gov); ASI, Ricerca Finalizzata, Ateneo Sapienza to A.M.; AIRC (grant no. 23257); ASI (grant no. MARS-PRE, DC-VUM-2017-006); H2020-MSCA-RISE-2014 (645648) to M.S. and a FNR core grant (grant no. C15/BM/10397420) to A.d.S. L.G.P. was partially supported by an FPI fellowship and an EMBO fellowship (grant no. ALTF 420-2017); and S.C., X.H. and V.M. by FI, Severo-Ochoa and PFI Fellowships (Spain), respectively.