The processes of a single adult microglia are estimated to make about 300 contacts per hour with neighboring synapses, neuron cell bodies, glia, and vascular endfeet in a healthy brain. It is presumed that during these brief contacts, microglia are receiving and locally responding to signals by releasing soluble factors (trophic and cytokine) and phagocytizing debris, apoptotic cells, and inappropriate synapses. A fascinating question in the field is how microglia can orchestrate the simultaneous, but often heterogenous responses at each of their separate processes, especially considering the transport of protein machinery (e.g. lysosomal components during phagocytosis) that are necessary. Neurons, which also respond to contacts from up tens to thousands of inputs are known to utilize RNA binding proteins (RBPs) to direct local protein translation to ribosomes within their dendrites, which is necessary for certain forms of long term potentiation and long term depression. It is currently unknown whether microglia translate mRNAs within their distal processes, and if so, whether there is a mechanism for localizing specific transcripts to specific sites. Given the number and diversity of contacts that microglial distal processes make, I hypothesize that microglia also utilize local translation to direct protein machinery to specific distal sites. In this proposal, I will interrogate this hypothesis through localization of ribosomes and localization and identification of RNA transcripts within microglial perisynaptic, distal processes. Analysis of data within recent microglial transcriptomic studies have identified high levels of the RBP, quaking (QK) and several RNA transcripts containing the QK binding motif. QK is known to regulate local mRNA translation within the distal processes of astrocytes and oligodendrocytes. Additionally, several of these transcripts have known roles in microglial synaptic remodeling, including cathepsin S. I further hypothesize that QK is necessary for the localization of specific microglial transcripts and that QK-RNA binding is necessary for proper microglial developmental synaptic pruning. In this proposal, I plan to identify targets of QK binding within microglia and determine if QK knock-down alters their localization. Finally, I will determine if QK knock-down alters microglial function through analysis of microglial synapse pruning. The goal of this proposal is to acquire mechanistic knowledge into how microglia regulate localization and translation of mRNA transcripts in response to extrinsic local cues during synaptic remodeling. Through this proposal, I hope to define novel mechanisms of microglial mRNA localization during the critical period of synaptic pruning, which may ultimately provide insight into several diseases where synaptic remodeling is altered, including Alzheimer?s disease, autism, schizophrenia, and others.
The goal of this proposal is to acquire mechanistic knowledge into how microglia regulate localization and translation of mRNA transcripts in response to extrinsic local cues during synaptic remodeling.