All ETDs from UAB

Advisory Committee Chair

James H Meador-Woodruff

Advisory Committee Members

Sarah Clinton

Rita Cowell

Anne Theibert

Scott Wilson

Document Type

Dissertation

Date of Award

2014

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Although the glutamate hypothesis of schizophrenia posits altered glutamatergic transmission is occurring in this illness, the precise mechanisms be-hind these proposed changes in schizophrenia brain remain elusive. Recent evidence from our laboratory supports a model of altered forward trafficking of glutamate receptors to synaptic membranes in schizophrenia, which could contribute to changes in neurotransmission. The AMPA subtype of ionotropic glutamate receptor (AMPAR), is the main facilitator of fast, excitatory neurotransmission in the brain, and changes in AMPAR number at synapses may control synaptic strength and plasticity. One mechanism that could alter AMPAR trafficking to synapses is abnormal expression of AMPAR auxiliary proteins, such as the transmembrane AMPAR regulatory proteins (TARPs) or Cornichon homologues (CNIHs). These proteins coassemble with AMPARs in endoplasmic reticulum (ER), and traffic AMPARs from the ER to synapses. We measured TARP and CNIH protein expression in brain homogenates from anterior cingulate cortex (ACC) and found increased protein expression for TARP γ-3 and γ-5, and decreased expression for γ-2, γ-4, γ-7, γ-8, and CNIH-2 in schizophrenia, consistent with other reports of diminished AMPAR trafficking. To test if fewer AMPARs were being trafficked to synapses in schizophrenia, we developed a strategy to isolate and enrich synapses from ACC and measured AMPAR, TARP, and CNIH expression in this fraction. We found decreased expression of the AMPAR subunit GluA1 at synapses in schizophrenia, which corresponded to fewer GluA1 subunits in a fraction enriched for ER, and decreased total protein levels in homogenates. We found no changes in subcellular protein expression for TARP or CNIH proteins, but ratios of GluA1 to AMPAR, TARP, and CNIH proteins were decreased in schizophrenia, suggesting that early processing of these complexes may be disrupted at ER, and may be hindering the trafficking of GluA1-containing receptors to the synapse. We also evaluated NMDAR subunit expression and found no intracellular changes. Taken together, these studies demonstrate a reliable method for the isolation of synapses in postmortem tissue, and provide evidence that altered regulation of receptor trafficking and early processing may be an underlying mechanism contributing to glutamate dysregulation in schizophrenia.

Share

COinS