Declining cognitive function is a hallmark feature of the aging process in the elderly population. Since aging is the major risk factor for many leading causes of death, including dementias such as Alzheimer's disease (AD), novel targets and strategies are needed as this population grows in the US and beyond. Though the conventional view has held that plasticity is limited in the aged brain, emerging data has challenged this notion, revealing that factors present within young blood are restorative for aged tissues throughout the body while suggesting links between the systemic environment and aging- and Alzheimer's- related changes in the brain. Aged mice sharing young blood via the parabiosis model or through plasma transfer exhibit improved synaptic plasticity, dendritic spine number, and cognitive performance, which led me to explore novel brain activities for systemic protein factors that may have relevance for AD. Our recently published work uncovered tissue inhibitor of metalloproteinases 2 (TIMP2), a protein enriched in developmentally-early human and young mouse plasma versus aged plasma that plays a surprisingly central role in regulating synaptic plasticity within the hippocampus. I showed that treatment with TIMP2 significantly revitalizes hippocampal function, as assessed by gene expression, long-term potentiation, and memory performance in hippocampal-dependent behavioral tasks. Moreover, removing TIMP2 from hippocampal slices dramatically reduced LTP and its loss in plasma ablated cognitive improvements conferred by young plasma. This work has nonetheless left many fundamental questions open related to TIMP2's function within the hippocampus, and its role in Alzheimer's disease remains unexplored. Recent work shows significantly reduced TIMP2 levels in AD patients with vascular changes in CSF and altered levels of TIMP2 target MMP2 in plasma; our preliminary data support a perturbation of TIMP2 metabolism in plasma in mouse models of AD pathology. We also find that TIMP2 expression decreases within dentate gyrus mossy cells important for the LTP response. In this work, we will probe the mechanism by which CNS TIMP2 directly regulates hippocampal function and the extent to which TIMP2 regulates hippocampal function in AD via changes in synaptic integrity as well as amyloid-? (A?)-dependent mechanisms. We hypothesize that TIMP2 regulates synaptic function in the normal hippocampus and is restorative in the context of AD pathology, primarily by acting to maintain synaptic integrity. We will address this hypothesis in three major aims: (1) To assess functional effects in mice in which hippocampal TIMP2 has been targeted and to evaluate the contribution of its source in mossy cells to plasticity, (2) to assess the role of canonical and putative TIMP2 targets within the hippocampus, (3) and to investigate the role of TIMP2 and related pathways in amyloid-independent and amyloid-dependent mechanisms of AD pathology.
Our aims will interrogate the function of TIMP2, a novel molecule with pro- plasticity roles in the hippocampus, having implications for development and creation of AD therapies.
Aging, a strong risk factor for Alzheimer's disease, causes detrimental changes in the hippocampus, which is a key brain region responsible for learning and memory function. This proposal investigates how TIMP2, a protein revealed to be elevated in young blood, acts within the central nervous system to facilitate hippocampal synaptic function on a gene expression, cellular, and cognitive level in the context of Alzheimer's disease pathology. Creating insight into this mechanism will inform therapies targeting facets of Alzheimer's disease, while also providing insights into how other secreted proteins within the hippocampus influence cognitive function.
