<i>Prdm16</i> is a critical regulator of adult long-term hematopoietic stem cell quiescence.

Abstract

Regulation of quiescence is critical for the maintenance of adult hematopoietic stem cells (HSCs). Disruption of transcription factor gene <i>Prdm16</i> during mouse embryonic development has been shown to cause a severe loss of fetal liver HSCs; however, the underlying mechanisms and the function of <i>Prdm16</i> in adult HSCs remain unclear. To investigate the role of <i>Prdm16</i> in adult HSCs, we generated a novel conditional knockout mouse model and deleted <i>Prdm16</i> in adult mouse hematopoietic system using the IFN-inducible <i>Mx1-Cre</i> Our results show that <i>Prdm16</i> deletion in the adult mouse hematopoietic system has a less severe effect on HSCs, causing a gradual decline of adult HSC numbers and a concomitant increase in the multipotent progenitor (MPP) compartment. <i>Prdm16</i> deletion in the hematopoietic system following transplantation produced the same phenotype, indicating that the defect is intrinsic to adult HSCs. This HSC loss was also exacerbated by stress induced by 5-fluorouracil injections. Annexin V staining showed no difference in apoptosis between wild-type and knockout adult HSCs. In contrast, Bromodeoxyuridine analysis revealed that loss of <i>Prdm16</i> significantly increased cycling of long-term HSCs (LT-HSCs) with the majority of the cells found in the S to G2/M phase. Consistently, RNA sequencing analysis of mouse LT-HSCs with and without <i>Prdm16</i> deletion showed that <i>Prdm16</i> loss induced a significant decrease in the expression of several known cell cycle regulators of HSCs, among which <i>Cdkn1a</i> and <i>Egr1</i> were identified as direct targets of <i>Prdm16</i> Our results suggest that <i>Prdm16</i> preserves the function of adult LT-HSCs by promoting their quiescence.