Sel1L/Hrd1 ER associated degradation (ERAD) preserves Hematopoietic stem cells (HSC) quiescence and self-renewal
ERAD deficiency via Sel1L knockout leads to accumulation of Rheb and activation of mTOR, which leads to HSC proliferation and activation
Hematopoietic stem cells (HSC) self-renew to sustain stem cell pools and differentiate to generate all types of blood cells. HSCs remain in quiescence to sustain their long-term self-renewal potential. It remains unclear whether protein quality control is required for stem cells in quiescence when RNA content, protein synthesis, and metabolic activities are profoundly reduced. Here, we report that protein quality control via endoplasmic reticulum associated degradation (ERAD) governs the function of quiescent hematopoietic stem cells (HSCs). The Sel1L/Hrd1 ERAD genes are enriched in the quiescent and inactive HSCs, and conditional knockout of Sel1L in hematopoietic tissues drives HSCs to hyper-proliferation, which leads to complete loss of HSC self-renewal and HSC depletion. Mechanistically, ERAD deficiency via Sel1L knockout leads to activation of mTOR signalling. Furthermore, we identify Rheb, an activator of mTOR, as a novel protein substrate of Sel1L/Hrd1 ERAD, which accumulates upon Sel1L deletion and HSC activation. Importantly, inhibition of mTOR, or Rheb, rescues HSC defects in Sel1L knockout mice. Protein quality control via ERAD is, therefore, a critical checkpoint that governs HSC quiescence and self-renewal by Rheb-mediated restriction of mTOR activity.