Astrocyte RNA degradation and cognitive function

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PROJECT SUMMARY Despite its putative link to many mental illnesses, Nonsense-Mediated mRNA Decay (NMD) represents a relatively unexplored mechanism for regulating mRNA stability in brain function. NMD functions in a tissue-, cell type- and cell-state specific manner and modulates stability of selective mRNAs to fine-tune transcript abundance. There is dearth of knowledge regarding the identity of such NMD target RNAs, particularly in cells in their normal in vivo context. A particularly large gap in the field is the cell-specific function and targets of NMD in vivo. Our recent work has established that neuronal NMD regulates GLUR1 signaling and is required for proper synaptic plasticity, cognition, and local protein synthesis in dendrites, providing fundamental insight into the neuron-specific function of NMD within the brain. To date, no study has reported a specific function for NMD nor identified NMD substrates within glial cells in the brain. Astroglial control of synaptic activity translates into regulation of cognition making astrocytes a novel therapeutic target to treat cognitive dysfunctions. However, the mechanisms through which astrocytes regulate neuronal function are not well understood. Currently, it is not known whether mRNA degradation in astrocytes contribute to the regulation of synaptic plasticity and behavior. The goal of this application is to determine the contribution of astrocytic NMD to synaptic plasticity and cognitive performance. Several predicted ‘canonical’ and ‘atypical’ NMD targets are expressed in astrocytes. Our gene ontology analysis of these predicted NMD targets identified molecular function enrichment for Ca2+ signaling. Consistent with this, we have found that disruption of NMD in astrocytes resulted in elevated Ca2+ activity in vitro. Dynamic Ca2+ transients in astrocytes have been suggested to control proper basal synaptic transmission and modulate hippocampal LTP. We have also found that conditional ablation of NMD in astrocytes impaired memory in the adult mice. Based on the published literature and our preliminary studies, we hypothesize that NMD regulates Ca2+ activity in astrocytes, and astrocytic NMD is required for proper cognitive function and behavior in the adult brain. To test this hypothesis, we propose to determine 1) whether NMD is required for different aspects of learning and memory 2) the effects of astrocytic NMD ablation on neurons (e.g., assessing neuronal network connectivity and synaptic plasticity) and 3) functional deficits of NMD-deficient astrocytes (i.e., by assessing Ca2+ activity in vivo) and in vivo NMD targets in astrocytes. We will use a combination of techniques including an inducible-genetic mouse model, behavioral assays, electrophysiology, live-animal Ca2+ imaging by two-photon microscopy, stereotaxic viral labeling, Multielectrode Array Assay, in vivo RNAseq/bioinformatics, and in vivo HITS-CLIP. The successful completion of this research will provide a coherent view of how cell-specific mRNA degradation underlies the highly regulated synaptic and cognitive function in the mammalian brain and might be valuable for providing new insights into the astrocytic mechanisms of synaptic dysfunction and neurocognitive diseases.