Src kinase as a mediator of convergent molecular abnormalities leading to NMDAR hypoactivity in schizophrenia

Abstract

Numerous investigations support decreased glutamatergic signaling as a pathogenic mechanism of schizophrenia: yet molecular underpinnings for such dysregulation are largely unknown. In the postmortem dorsolateral prefrontal cortex, we found striking decreases in tyrosine phosphorylation of N-methyl-D aspartate (NMDA) receptor subunit 2 (GluN2), which is critical for neuroplasticity. The decreased GluN2 activity in schizophrenia may not be due to downregulation of NMDA receptors since MK-801 binding and NMDA receptor complexes in the PSD were in fact increased in schizophrenia cases. At the post-receptor level, however, we found striking reductions in the protein kinase C, Pyk 2 and Src kinase activity, which in tandem can decrease GluN2 activation. Given that Src serves as a hub of various signaling mechanisms impacting GluN2 phosphorylation, we postulated that Src hypoactivity may result from convergent alterations of various schizophrenia susceptibility pathways and thus mediate their impacts on NMDA receptor signaling. Indeed, the DLPFC of schizophrenia cases exhibit increased PSD-95 and erbB4 and decreased RPTPa and dysbindin-1, each of which reduces Src activity via protein interaction with Src. To test genomic underpinnings for Src hypoactivity, we examined genome wide association study results, incorporating 13,394 cases and 34,676 controls, which yielded no significant association of individual variants of Src and its direct regulators with schizophrenia. However, a wider protein-protein interaction based network centered on Src, showed significant enrichment of gene-level associations with schizophrenia compared to other psychiatric illnesses. Our results together demonstrate striking decreases in NMDA receptor signaling at the post-receptor level and propose Src as a nodal point of convergent dysregulations impacting NMDA receptor pathway via protein-protein associations.

Abnormal N-acetylglucosaminyltransferase expression in prefrontal cortex in schizophrenia

“…Protein folding, trafficking, localization, and recycling are all affected by glycosylation (Dennis et al, 2009; Helenius & Aebi, 2004; Ohtsubo & Marth, 2006; Parodi, 2000), and alterations of these processes in schizophrenia may be linked to abnormalities of glycosylation pathways. Multiple studies have found abnormal subcellular distribution of neurotransmitter receptors and transporters as well as other synaptic proteins in the brain in schizophrenia (Thompson et al, 1998; Talbot et al, 2011; Deo et al, 2012; Hammond et al, 2010; Kristiansen et al, 2010; Shan et al, 2014; Banerjee et al, 2014; Mueller et al, 2015). Interestingly, several studies have shown that neurotransmitter receptors containing abnormally N-glycosylated subunits exhibit abnormal subcellular distribution in schizophrenia brain.…”

Sociability Deficits and Altered Amygdala Circuits in Mice Lacking Pcdh10, an Autism Associated Gene

“…50 mg amygdala (5 animals were pooled into three samples of 50 mgs in each group, transgenic or wild types) were fractionated into various subcellular fractions using methods previously described (41,42). Protein extracts including PSD fractions were size fractionated in 7.5% Tris Glycine (Biorad, Hercules, CA) gels and western blotted with the following antibodies: PCDH10 (rat OL-protocadherin, clone 5G10, cat# MABT20, Millipore, Billerica, MA); β-actin (mouse, cat# A2228, Sigma, St. Louis, MO); PSD-95 (mouse, cat# 75-028, NeuroMab, Davis, CA); and GLUN1 (goat, cat# sc-1467) GLUN2A (goat, cat# sc-1468), and SRC (mouse, cat# sc-5266), all from Santa Cruz Biotechnology, Dallas, TX).…”

“…Sample sizes for experiments were chosen based on adequately powered sample sizes used for the same types of data published by our research group and others (22,39,42–46). No animals were excluded from the analysis of behavior, VSDi, spine analysis, and biochemistry.…”

The NMDA Receptor and Schizophrenia

“…This same meta-analysis found no consistent statistically significant changes in cortical mRNA and protein expression of GluN2 (A, B, D) or GluN3A subunits in schizophrenia, with the exception of reduced GluN2C mRNA in the PFC (Catts et al, 2015; Weickert et al, 2013). In the postsynaptic density fraction obtained from human post-mortem dorsolateral PFC tissue, there is a marked reduction in the activity of signaling cascades downstream of the NMDAR in schizophrenia, despite an apparent increase in NMDAR density and GluN1 expression (Banerjee et al, 2015). In the hippocampus, there have been several reports of reduced GluN1 levels selectively in the dentate gyrus of patients with schizophrenia (X.…”