Metabotropic glutamate receptor 5 binding and protein expression in schizophrenia and following antipsychotic drug treatment

Abstract

Metabotropic glutamate receptor 5 (mGluR5) has been identified as a potential therapeutic target for schizophrenia, primarily due to its ability to indirectly modulate glutamatergic signalling through the NMDA receptor (NMDAR). Despite its potential, molecular studies characterising mGluR5 in schizophrenia are limited. We therefore aimed to determine if the mGluR5 binding site or protein levels were altered in schizophrenia or by current antipsychotics. Using in-situ radioligand binding and immunoblot, we measured [3H]MPEP binding to mGluR5 and mGluR5 protein density in the post-mortem dorsolateral prefrontal cortex (DLPFC; BA46) of 37 schizophrenia and 37 matched control subjects. Subsequently, we measured [3H]MPEP binding in rat brains following typical (haloperidol) or atypical (olanzapine) antipsychotic treatment (n = 6/group). Subjects with schizophrenia showed no significant alteration in mGluR5 binding density or mGluR5 protein levels. Furthermore, mGluR5 binding in the rat cortex, thalamus, hippocampus and striatum was unaltered by short-, medium-and long-term antipsychotic treatment. Our data suggests that there are no alterations in mGluR5 in schizophrenia subjects. The lack of alteration in mGluR5 binding and protein in schizophrenia is advantageous because its ability to modulate the NMDAR is potentially unhindered, thereby supporting the development of novel antipsychotic agents that work through the mGluR5/NMDAR complex. ', Schizophrenia Research, vol. 146,[1][2][3] AbstractMetabotropic glutamate receptor 5 (mGluR5) has been identified as a potential therapeutic target for schizophrenia, primarily due to its ability to indirectly modulate glutamatergic signalling through the NMDA receptor (NMDAR). Despite its potential, molecular studies characterising mGluR5 in schizophrenia are limited. We therefore aimed to determine if the mGluR5 binding site or protein levels were altered in schizophrenia or by current antipsychotics. Using in-situ radioligand binding and immunoblot, we measured [ 3 H]MPEP binding to mGluR5 and mGluR5 protein density in post-mortem dorsolateral prefrontal cortex (DLPFC; BA46) of 37 schizophrenia subjects (including 7 schizoaffective) and 37 matched controls. Subsequently, we measured [ 3 H]MPEP binding in rat brains following typical (haloperidol) or atypical (olanzapine) antipsychotic treatment (n=6/group). Subjects with schizophrenia (n=30) showed no significant alteration in mGluR5 binding density or mGluR5 protein levels. However subjects with schizoaffective disorder (n=7) displayed a trend towards reduced mGluR5 binding (20%) compared to schizophrenia subjects (p=0.079), suggesting different underlying biochemistry of the disorder. In schizoaffective subjects of depressive subtype (n=4), mGluR5 binding was reduced by 39% compared to controls (p=0.022). Furthermore, mGluR5 binding in the rat cortex, thalamus, hippocampus and striatum was unaltered by short-, medium-and long-term antipsychotic treatment. Our data suggests that there are diagnostic specific alte...

Alterations of mGluR5 and its endogenous regulators Norbin, Tamalin and Preso1 in schizophrenia: towards a model of mGluR5 dysregulation

“…There was no effect of gender or hemisphere on mGluR5 mRNA expression. We have previously reported no change in mGluR5 monomer levels in this cohort in DLPFC [17]. However, mGluR5 dimer expression was 53.5% higher in schizophrenia subjects compared to controls (F 1,70 =8.688, p<0.001; co-varying for freezer storage time, which correlated with dimer levels [ Table S2]: F 1,69 =44.808, p<0.001).…”

“…After one week of acclimatization, rats were distributed into 9 treatment groups (3 treatments x 3 treatment-durations; n=6/group), as described previously [17]. Animals were fed prepared food pellets 3 times/day at 8 hour intervals, containing either: (1) typical antipsychotic, haloperidol (0.1mg/kg body weight; daily total 0.3mg/kg), (2) atypical antipsychotic, olanzapine (1mg/kg body weight; daily total 3mg/kg), (3) vehicle control (empty food pellets), for short term (8 days), medium term (15 days) and long term (35 days) durations.…”

“…The following polyclonal antibodies were used: mGluR5 (ABCAM ab27190 [17]), Tamalin (ABCAM ab30576 [32]), Preso1 (Santa Cruz sc-242862 [16,27]) and Norbin (ABCAM ab130507). Immunoblotting was performed as described previously [17], with minor modifications optimized for the measurement of each protein of interest (Table 1). Samples were loaded at 5µg and 10µg for all proteins assessed in human and rat brain samples respectively.…”

“…As mGluR5 was detected at two molecular weights, mGluR5 dimer and total (sum of monomer and dimer) levels are reported. We have previously reported only mGluR5 monomer levels [17]; total and dimer measures in this study were analyzed from the same experimental run. Norbin (79kDa) and Tamalin (96kDa) proteins were identified as single bands at the expected molecular weights in the human DLPFC (Fig.…”

Differential effects of short- and long-term antipsychotic treatment on the expression of neuregulin-1 and ErbB4 receptors in the rat brain

“…It is important that the drug dosages used in this study have been used previously and have been shown to be pharmacologically and behaviourally effective (Assié et al, 2006;Deng et al, 2007;Han et al, 2009a;WestonGreen et al, 2011). It should also be noted that female rats were used in this study, because our previous studies have shown that female rats are a suitable model for investigating pharmacological effects of antipsychotics (Han et al, 2009a;Han et al, 2009b;Han et al, 2008;Lian et al, 2013Lian et al, , 2014bMatosin et al, 2013). Furthermore, rats were closely housed in a room occupied by only female rats in this study.…”