Wip1 regulates proliferation of adult neural progenitors through P53 dependent G2 cell cycle control

Abstract

Adult neurogenesis, the continual generation of new neurons from adult neural stem/progenitor cells (NPCs) in brain, represents the life-long regeneration capacity and holds great promise for cell replacement therapy to neurodegenerative diseases in elderly. The regenerative capacity of NPCs decline with aging, however, the intrinsic regulations of NPCs, especially those mediating aging of NPCs, remain poorly defined. This study shows that Wip1 phosphatase, previously studied in oncogenesis, functions as a crucial physiological regulator in adult neurogenesis during aging. In the forebrain, Wip1 deficiency resulted in a 90% decrease in new cell formation in adult olfactory bulb, accompanied by aberrantly decreased amplification of NPCs, stem cell frequency and self-renewal. Similarly, adult neurogenesis in hippocampus was also diminished upon knocking out Wip1. At cellular level, Wip1 knockout (ko) NPCs exhibited a prolonged cell cycle, an accumulation at G2 to M phase transition and elevated expression of cell cycle inhibitors p21 and Reprimo. Two observations suggested that Wip1 regulates NPCs through p53, which are the phosphorylation level of p53 was up-regulated in Wip1 ko NPCs in vivo and in vitro, and transcriptions of p21 and Reprimo was p53-dependent in NPCs. Furthermore, the impaired M-phase entry and amplification of Wip1-null NPCs were both reversed in Wip1/p53 double-null genotype to that comparable to p53-null genotype. Functional rescues by Wip1/p53 double null genotype were reproduced in vivo with the number of NPCs and neuroblasts. Present data demonstrate that Wip1 regulates the generation of new neural cells in adult olfactory bulb specifically through p53-dependent M phase entry of the cell cycle of NPCs. The implication of Wip1/p53 pathway on aging of NPCs was analyzed by real-time PCR and immunostaining. During aging, the number of NPCs was down-xvi regulated, which correlated with a marked down-regulation of Wip1 and a drastic up-regulation of p53 phosphorylation. Based on these data, Wip1/p53 regulation was proposed to mediate the aging process of NPCs. This study led to the identification of the important function of Wip1/p53 pathway in adult neurogenesis which possibly mediates aging of NPCs.