With an ever-aging population and an estimated prevalence of Alzheimer disease of 5.7 million people in the United States alone, the impetus for more targeted treatments for age-related cognitive disorders is greater now than ever. Neuroplasticity, the ability of neural networks to adapt and remodel given experience, dwindles with age, providing possible mechanistic insights into this decline. An important layer of neuroplasticity, unique to a couple of discrete areas of the adult mammalian brain, is the addition of newly-generated neurons into existing circuits, a process known as neurogenesis. While the existence and importance of adult hippocampal neurogenesis in young adults has been well-established, we know very little about hippocampal neurogenesis in aging brains. Importantly, hippocampal neurogenesis continues into old age although there is a substantial decline in the number of newborn neurons. For example, in 26-month-old rodents, ~1000 proliferating cells could be detected per day, although only half that detected in 5-month-old adult rats. A recent study demonstrated that thousands of new neurons could be detected in the aged adult human dentate gyrus, and further, that in patients with Alzheimer disease, newborn neurons were fewer in number and exhibited delayed maturation. As a starting point, we ask why neurogenesis declines in the aging brain. Based on our preliminary studies, we found that biased circuit activity may regulate hippocampal neurogenesis in the aging brain. During screening of potential molecules biasing circuit activity, we found that one sphingolipid signaling is active in interneurons and becomes less active in the aging brain. We propose to genetically intervene this signaling to study its role in regulating neurogenesis in the aging brain. Lastly, we determine how biased circuit activity regulates hippocampal neurogenesis. Our results will not only provide mechanistic insights into the understanding of neurogenesis in the aging brain it also provides a possible strategy to intervene aging circuit activity to regulate neurogenesis.
Disease, degeneration or aging of the nervous system are among the greatest public health concerns in the United States and are generally considered irreparable, often causing catastrophic damage to the functional capacity of the individual. Now, however, characterization of neural stem cells residing within specific germinal centers of the brain and in cell culture raises hope that functional regeneration of nervous tissue may be feasible, if we learn to exploit neurogenesis for clinical benefit. The research proposal here aims to study how existing brain cells control the integration of new members derived from endogenous neural stem cells in aging brains. If successful, this proposal will lead to advanced understanding of neural stem cell biology, possibly leading to the development of new drugs for repair and regeneration of the nervous system.