PAK1 Protein Expression in the Auditory Cortex of Schizophrenia Subjects

Abstract

Deficits in auditory processing are among the best documented endophenotypes in schizophrenia, possibly due to loss of excitatory synaptic connections. Dendritic spines, the principal post-synaptic target of excitatory projections, are reduced in schizophrenia. p21-activated kinase 1 (PAK1) regulates both the actin cytoskeleton and dendritic spine density, and is a downstream effector of both kalirin and CDC42, both of which have altered expression in schizophrenia. This study sought to determine if there is decreased auditory cortex PAK1 protein expression in schizophrenia through the use of quantitative western blots of 25 schizophrenia subjects and matched controls. There was no significant change in PAK1 level detected in the schizophrenia subjects in our cohort. PAK1 protein levels within subject pairs correlated positively with prior measures of total kalirin protein in the same pairs. PAK1 level also correlated with levels of a marker of dendritic spines, spinophilin. These latter two findings suggest that the lack of change in PAK1 level in schizophrenia is not due to limited sensitivity of our assay to detect meaningful differences in PAK1 protein expression. Future studies are needed to evaluate whether alterations in PAK1 phosphorylation states, or alterations in protein expression of other members of the PAK family, are present in schizophrenia.

Large-scale generation of human iPSC-derived neural stem cells/early neural progenitor cells and their neuronal differentiation

“…Human postmortem cortex gray matter homogenates previously prepared from 3 normal subjects were obtained. 31 20 mg of iPSC-derived neurons proteins or human cortex gray matter tissue homogenate were mixed with 20 mg of a stable isotope labeled neuronal proteome standard, separated by electrophoresis on a 4-12% gradient SDSpoly-acrylamide gel, and subject to on-gel digestion as previously described. 32 Liquid Chromatograph -Selected Reaction Monitoring analyses were conducted on a TSQ Quantum triple stage quadrupole mass spectrometer (ThermoFisher Scientific) with an Ultimate 3000 HPLC (Dionex) and a PicoChip Column (New Objective).…”

Dendritic spine alterations in schizophrenia

“…Although the magnitude of the increase was modest, it was present in 20/26 (77%) subject pairs evaluated. In contrast, total levels of kalrin-5, kalirin-12, and PAK1 were not affected [78;79]. Finding altered kalirin-9 in schizophrenia is supported by prior reports that rare missense mutations located within the region of the KALRN gene shared only by kalirin-9 and -12 have been associated with risk for schizophrenia [80].…”

“…This latter principal was further highlighted by the observation that the effect of global knockout of kalirin isoforms on dendritic spine loss varies by cortical region and developmental age, presumably reflecting age and regional variation in the background of molecules signaling to the actin cytoskeleton [76;77]. Perhaps not surprisingly, then, when Deo et al evaluated protein levels of 4 kalirin isoforms, kalirin-5, -7, -9, and -12 in primary auditory cortex, a region in which dendritic spine loss has also been found in schizophrenia [78;79], levels of kalirin-7 were not altered in the schizophrenia subjects. Whether the differences in findings for kalirin-7 protein between Deo et al [78] and Rubio et al [71] result from regional variations in disease-related effects must at present await further attempted replications, as differences in the cohorts studied is also a plausible source of the discrepancy.…”

“…Spinophilin recruits the RhoA GEF, Lfc, to spines [83] and targets protein phosphatase 1 to glutamate receptors [82] and to actin [84]. No change In spinophilin protein expression in prefrontal and auditory cortex [79;85] and both increased [86] and unchanged [87] expression of spinophilin mRNA in prefrontal cortex have been found in subjects with schizophrenia. However, because spinophilin is predominantly expressed in dendritic spines in cerebral cortex [88], spine loss may mask any increase in spinophilin levels within spines when gray matter homogenates are studied.…”

Will the Treatment Protocols for Schizophrenia be Changing Soon?

“…Those with schizophrenia not only show performance decrements on short term memory tasks, but they have difficulty detecting motion (Kantrowitz & Javitt, 2010), distinguishing pure tones (Deo et al, 2013), distinguishing prosodic changes, and understanding the meaning of words when they are used in a metaphorical sense (Kantrowitz & Javitt, 2010), and recognizing sarcasm (Kantrowitz, Hoptman, Leitman, Silipo, & Javitt, 2013). Indeed, as a group, those with schizophrenia score one standard deviation below average on measures of cognitive function (van Os & Kapur, 2009).…”