Nynrin preserves hematopoietic stem cell function by inhibiting the mitochondrial permeability transition pore opening (RNA-Seq for Nynrin cko HSC)

Mitochondria have recently been identified as a critical regulator for the homeostasis of hematopoietic stem cells (HSCs). However, the mechanism underlying HSC regulation still needs to be clarified. Here, we identify transcription factor Nynrin as a novel regulator of HSC maintenance through modulation of mitochondrial function. We demonstrate that Nynrin is highly expressed in HSC under steady and stress state. Nynrin knockout leads to significantly decreased long-term HSC frequency, markedly reduced HSC dormancy, and self-renewal capacity in steady-state and stress hematopoiesis. We observed abnormal mitochondrial metabolism and mitochondrial permeability transition pore (mPTP) opening in Nynrin-deficient HSCs. Notably, Nynrin-deficient HSCs are more compromised in tolerance of irradiation- and 5-fluorouracil-induced stresses and exhibit typical phenotypes of necrosis. In contrast, overexpression of Nynrin in HSC is resistant to the radiation. Mechanistically, Nynrin deletion induces transactivation of Ppif. Overexpression of cyclophilin D (CypD), the protein encoded by the Ppif gene, causes mPTP opening, mitochondrial swelling, ROS overinduction, and cell necrosis. Both blocking the function of CypD by using cyclosporin A (CsA) or reducing the expression of Ppif could inhibit Nynrin deficiency-induced mitochondrial metabolism enhancement and ROS overproduction, thereby evidently rescuing the impairment of HSCs in Nynrin mutant mice. Collectively, our data, for the first time, characterize Nynrin as a critical regulator of HSC function acting through the Ppif/mPTP mitochondria axis and highlight the importance of Nynrin in HSC maintenance. These data provide new insights into the mechanisms for controlling HSC fate.