PPM1D and depressive disorder: Since depressive illness and stress are closely linked to cellular senescence22, 23, our findings that Wip1 deficiency either in Wip1 null mice or in CUMS-exposed mice increased cellular senescence in hippocampus, a key brain structure in the pathophysiology of depression24, 25, extend our knowledge to understand the regulatory role of Wip1 in mediating brain cellular senescence and depression.