Disruption of Major Histocompatibility Complex Class I Cytoplasmic Domain's Protein-Protein Interactions in Mouse Hippocampus

Abstract

Major Histocompatibility Complex Class I (MHCI) proteins are known for their role in the adaptive immune system, but there is a growing body of evidence that indicates MHCI contributes to non-immune, essential processes in the healthy brain. These include studies implicating MHCI in the regulation of synaptic plasticity and synaptic transmission. Neurons lacking MHCI display increased N-methyl-D-aspartate receptor (NMDAR)-mediated currents, but the molecular mechanism behind this process is still unclear. Previous work in our lab suggests that recombinant peptides derived from the cytoplasmic domain of MHCI (MHCICD), when delivered into single neurons, can block endogenous MHCI’s inhibitory effects on NMDARs, mimicking the effects of MHCI-deficiency. However, these original peptides could not cross cell membranes, and had to be infused into individual neurons via a micropipette. In order to investigate MHCICD’s function in larger neuronal populations, I created a fusion construct of the cytoplasmic domain of MHCI gene H2-K with a cell penetrating peptide derived from the HIV protein TAT, which allows the construct to cross cell membranes. I investigated the effects of cell-permeant MHCICD in two contexts. First, I examined the effect of the fusion peptide on ischemic excitotoxicity in vitro. We observed that peptide treatment was neuroprotective in cultured hippocampal neurons, and that this neuroprotection was specific to ischemic cell death. Second, I studied the effect of the fusion peptide on homeostatic synaptic scaling. In both wildtype (WT) and MHCI-deficient neurons, peptide treatment prevented scaling up of the size of the postsynaptic density in response to chronic activity blockade, and scaled down the basal size of the postsynaptic density. This thesis created a novel tool to study MHCICD’s function in a broader in vitro setting with temporal specificity.