Age-related Decline In BubR1 Impairs Adult Hippocampal Neurogenesis

Objective: Aging can induce the decline of adult hippocampal neurogenesis,and finally result in cognitive dysfunction.Age is a major risk factor in neurodegenerative disorders associated with cognitive impairments.In both humans and mice,the hippocampus is one of two neurogenic niches where newborn neurons arising from neural stem cells are constantly generated throughout life in a process termed adult hippocampal neurogenesis.Deficits in this process are observed with aging and are believed to underlie age-related cognitive deficits.However,the molecular identity governing such impairments is not fully understood.Emerging evidence demonstrates that decline in the mitotic checkpoint kinase BubR1 level occurs with natural aging and induces progeroid features in both mice and children with mosaic variegated aneuploidy syndrome.Whether BubR1 contributes to age-related deficits in hippocampal neurogenesis is yet to be determined.A mitotic checkpoint kinase,BubR1,has emerged as a key genetic factor in age-related pathology and lifespan.Whether BubR1 also regulates age-related changes in adult hippocampal neurogenesis is unknown.Method: We decide to divide our experiments into three parts.The first part is that we want to observe expression of BubR1 from in vivo and in vitro with immunofluorescence method,and determine the location of BubR1.And at the same time,We want to know the change with different types of neuro progenitor cells,and especially the change during the postmitotic stage.For the second part,with the help of the immunofluorescence method and Ed U i.p.,we want to learn the effect of BubR1 on the neural proliferation process,and make sure whether the change of numbers of newborn neurons from BubR1H/H can induce the decline of the increasing number of progenitor cells.At the last one,based on previous study,we plan to perform stereology retrovirus/lentivirus injection,Ed U i.p.,immunofluorescence method and some other experiments to study the effect of BubR1 on maturation and dendrite formation.Results: In the first part,we found BubR1 is expressed in the postnatal mouse dentate gyrus,which was relatively higher in the SGZ than the dentate granule layer.In addition,BubR1 is expressed in radial glial-like NSCs,and reduced in an age-dependent manner.Derived from isolated neural progenitors in vitro,immunostaining of BubR1 showed localization in the cytoplasm and dendrites.For the second part,we showed a significant reduction in activated RGCs,IPCs,and neuroblasts in the BubR1H/H mice,quiescent RGCs were not statistically different in the BubR1H/H mice.Furthermore,this decrease in newborn cells was exacerbated in BubR1H/H mice in an age-dependent manner.BubR1H/H mice exhibited a significant decrease in the density of mature newborn neurons.However,survival of newborn cells was not affected with BubR1 insufficiency.The last part,we found a significant increase in the percentage of immature neurons with a concurrent decrease of mature neurons in BubR1H/H mice.At the same time,GFP+ newborn neurons at 14-day post-injection exhibited decreased primary dendrite length,total dendrite length,total branch number,and branch point number with sh RNA-BubR1 expression compared to sh RNA-control.Furthermore,these morphological alterations(excluding total branch number)observed in BubR1 knockdown were significantly rescued in BubR1 overexpression mice.Conclusion: A large body of evidence suggests that age-related deficits in hippocampal neurogenesis contribute to cognitive decline.Activated RGCs,IPCs,and neuroblasts are highly vulnerable to BubR1 insufficiency,but quiescent RGCs are less vulnerable.Deficits seen in BubR1H/H mice were not due to early developmental dysfunction.Taken together,these results suggest an essential and adult-specific role for BubR1 in regulating neural progenitor proliferation in vivo.The reduction in adult hippocampal neurogenesis in BubR1H/H mice results mainly from a decrease in of neural progenitor proliferation rather than affecting survival.Impaired dendrite morphogenesis is indeed mediated through BubR1 in a cell-autonomous manner.Thus,these results suggest BubR1 is required for proper maturation and morphogenesis and support a critical post-mitotic function of BubR1 in vivo.Our identification of BubR1 as a new and critical regulator controlling sequential steps across adult hippocampal neurogenesis raises the possibility that BubR1 may be a key mediator regulating aging-related hippocampal pathology.