Regulation of munc18-1 and syntaxin-1A interactive partners in schizophrenia prefrontal cortex: down-regulation of munc18-1a isoform and 75 kDa SNARE complex after antipsychotic treatment

Abstract

Munc18-1 and syntaxin-1 are crucial interacting molecules for synaptic membrane fusion and neurotransmitter release. Contrasting abnormalities of several proteins of the exocytotic machinery, including the formation of SNARE (synaptobrevin, SNAP-25 and syntaxin-1) complexes, have been reported in schizophrenia. This study quantified in the dorsolateral prefrontal cortex (PFC, Brodmann area 9) the immunocontent of munc18-1a/b isoforms, syntaxin-1A, other presynaptic proteins (synaptotagmin, synaptophysin), and SNARE complexes, as well as the effects of psychoactive drug exposure, in schizophrenia (SZ, n=24), non-schizophrenia suicide (SD, n=13) and major depression (MD, n=15) subjects compared to matched controls (n=39). SZ was associated with normal expression of munc18-1a/b and increased syntaxin-1A (+44%). The presence of antipsychotic drugs reduced the basal content of munc18-1a isoform (-23%) and synaptobrevin (-32%), and modestly reduced that of up-regulated syntaxin-1A (-16%). Munc18-1a and syntaxin-1A protein expression correlated positively in controls but showed a markedly opposite pattern in SZ, regardless of antipsychotic treatment. Thus, the ratio of syntaxin-1A to munc18-1a showed a net increase in SZ (+53/114%). The SNARE complex (75 kDa) was found unaltered in antipsychotic-free and reduced (-28%) in antipsychotic-treated SZ subjects. None of these abnormalities were observed in SD and MD subjects, unexposed or exposed to psychoactive drugs. The results reveal some exocytotic dysfunctions in SZ that are probably related to an imbalance of the interaction between munc18-1a and SNARE (mainly syntaxin-1A) complex. Moreover, antipsychotic drug treatment is associated with lower content of key proteins of the exocytotic machinery, which could result in a destabilization/impairment of neurosecretion.

Cyclin-dependent kinase-5 and p35/p25 activators in schizophrenia and major depression prefrontal cortex: basal contents and effects of psychotropic medications

“…The study design was approved by the Ethical Committee of Clinical Investigation (CEIC, Spain) and developed in accordance with the guidelines of the University of the Balearic Islands. Caucasian subjects who had died of various causes were subjected to a retrospective search for previous psychiatric diagnoses (DSM-IV) and medications as described (Gil-Pisa et al 2012 ;Urigü en et al 2009). Healthy controls (no evidence of psychiatric or neurological disorder) and subjects with SZ or MD were included in the study.…”

“…Healthy controls (no evidence of psychiatric or neurological disorder) and subjects with SZ or MD were included in the study. These SZ and MD subjects had been used in a previous study that revealed alterations of key proteins of the exocytotic machinery in PFC (Brodmann's area 9 ; BA9) of SZ subjects (Gil-Pisa et al 2012). Subjects with SZ or MD [psychotropic-free : SZ(x) or MD(x); psychotropic-treated : SZ(+) or MD(+)] were matched to control subjects for post-mortem interval (PMI), brain pH, gender and age at death (Table 1 ; see Gil-Pisa et al 2012 for individual features including causes of death and blood/urine levels of psychotropic drugs, which are also reported in the present study as Supplementary Tables S1 and S2).…”

“…In a recent study, syntaxin-1A was found increased and munc18-1a unchanged in SZ prefrontal cortex (PFC), and both proteins were downregulated by antipsychotic drug treatment (Gil-Pisa et al 2012). In contrast, munc18-1 and syntaxin-1A were unaltered in PFC of major depression (MD) subjects, regardless of antidepressant drug treatment (Gil-Pisa et al 2012). Given the regulatory role of CDK5 in neurosecretion and munc18rsyntaxin-1A interaction, this study investigated the basal status of CDK5 and activators p35/p25 in post-mortem PFC of well-characterized subjects with SZ or MD, as well as the effects of psychotropic medications.…”

“…CDK5 activation requires the cofactor p35, a noncyclin regulatory protein, and/or p25, a p35 active product (Kusakawa et al 2000 ;Tsai et al 1994). Over the past decade, the synaptic hypothesis of schizophrenia (SZ) and major depressive disorder has revealed dysfunctions of neuroplasticity (Eastwood, 2004 ;Nissen et al 2010) and neurosecretion (Gil-Pisa et al 2012 ;Johnson et al 2008), which might involve the participation of CDK5 and activators. Thus, the pharmacological or genetic inhibition of CDK5 activity was shown to potentiate presynaptic function in neurons, indicating that this kinase normally acts as a strong suppressor of neurotransmitter release (Kim & Ryan, 2010).…”

“…CDK5/p35 was reported to bind and phosphorylate munc18, which can then regulate munc18rsyntaxin-1A interaction in nerve endings (Fletcher et al 1999 ;Shuang et al 1998). In a recent study, syntaxin-1A was found increased and munc18-1a unchanged in SZ prefrontal cortex (PFC), and both proteins were downregulated by antipsychotic drug treatment (Gil-Pisa et al 2012). In contrast, munc18-1 and syntaxin-1A were unaltered in PFC of major depression (MD) subjects, regardless of antidepressant drug treatment (Gil-Pisa et al 2012).…”