PROJECT 4-NPTX2 and Adaptation to Cognitive Aging

Project 4 examines the role of NPTX2 and homeostatic scaling in age-related cognitive decline. NPTX2 is an immediate early gene expressed by pyramidal neurons and mediates activity-dependent homeostatic strengthening of inhibitory circuits by adaptively strengthening excitatory drive of parvalbumin interneurons (PV-IN). This PPG has examined the effect of aging on cognition using outbred Long-Evans rats and has documented increased pyramidal neuron excitability and reduced PV-IN circuit inhibition that are associated with cognitive decline. Preliminary studies further reveal reduced NPTX2 expression in Aged-Impaired rats and rescue of circuit deficits by NPTX2 transgene expression. Here, we build on these observations and examine the hypothesis that failure of NPTX2 homeostatic mechanisms contribute to age-related cognitive decline. Aim 1 will test the hypotheses that NPTX2 loss-of-function (LOF) accelerates age-related cognitive decline while NPTX2 gain-of-function (GOF) delays or prevents age-related cognitive decline. A conditional NPTX2 LOF model uses a newly developed NPTX2f/f rat together with virus-mediated delivery of Cre to delete NPTX2 at 11 m and together with Core B details the impact on cognitive behavior. In a reciprocal set of experiments, we create NPTX2 GOF models using two distinct approaches that include virus mediated NPTX2 transgene and oligonucleotide mediated NPTX2 mRNA stabilization. The impact of GOF on cognitive behavior is evaluated in collaboration with Core B. Aim 2 examines molecular and cellular mechanisms mediating dynamic targeting of NPTX2 to excitatory synapses. Studies use state-of-the-art proximity labeling methods to identify proteins involved in synaptic NPTX2 exocytosis and shedding. Aim 3 uses in vivo 2-photon imaging to examine the hypothesis that age-related cognitive deficits are associated with disruption of a critical phase of homeostatic scaling that mediates activity-dependent NPTX2 exocytosis and shedding. Analyses examine diurnal changes in synaptic NPTX2 in association with waking behaviors and sleep comparing Young, Aged-Impaired and Aged-Unimpaired rats. We also test the effect of levetiracetam in Aged-Impaired rats. Studies in Aims 1 and 3 include both male and female rats. The Aims are highly synergistic with other Projects and together will reveal fundamental mechanisms of aging, cognitive resilience and cognitive decline.