¹Masaryk University, Psychiatry, Brno, Czech Republic, ²University hospital Brno, Psychiatry, Brno, Czech Republic, ³Masaryk University, Histology and Embryology, Brno, Czech Republic

Background: Very little is known about the mechanism of action of clozapine, and it is unclear what part of its complex receptor profile accounts for its unique efficacy in treatment-resistant schizophrenia. Its relatively lower effect on dopamine mechanisms suggests the importance of non-dopaminergic processes. This is also indicated by the profile of very rare mutations with a high effect size on the risk of schizophrenia, which largely involves glutamatergic neurotransmission. Cellular models derived from human induced pluripotent cells (hiPSCs) are a suitable tool for studying the biological processes associated with the effect of psychotropic drugs in mental illnesses.

Aims & Objectives: Evaluation of possible effects of clozapine on the glutamatergic system in lines of derived pyramidal neurons and astrocytes from patients with pharmacoresistant schizophrenia responding to clozapine treatment (TRS-CLZ+).

Method: We developed pyramidal neuron and astrocyte lines derived from hiPSCs from 3 TRS-CLZ+ and 2 healthy subjects. We assessed neuronal activity using calcium imaging, electrophysiology, and NMDA currents under native conditions and after glutamate exposure, without and with co-culture with CLZ. D-serine levels were assessed in astrocyte culture. We assessed the detection of changes in the expression of genes associated with the glutamate system using RNA sequencing before and after CLZ exposure. Differentially expressed genes related to glutamate system were detected.

Results: Cultivation with CLZ increased the number of calcium pulses in PN after glutamate administration and restored it ot the levels seen in lines from healthy subjects. Moreover, it led to increase of NMDA currents. It also led to the increase of expression of GRIN2A, GRIN2B, GRIA2, and GRM5 genes in PN. In astrocytes, lower intracellular glutamate levels were observed, as well as reduced levels of D-serine. The D-serin levels significantly increased after cultivation with CLZ.

Discussion & Conclusions: Clozapine demonstrated its ability to normalize the glutamate-induced activity of pyramidal neurons with the improvement of their NMDA currents, findings that were reflected at the level of gene expression of glutamate system related genes. Moreover, clozapine was also able to increase the levels of NMDA co-agonist D-serin in astrocytes showing that both cellular types are involved in glutamate dysfunction in treatment resistant schizophrenia and response to CLZ. It is, however, unclear, what is the mechanism of these CLZ effects and further research of biological processes related to the improvement of NMDA function by CLZ is needed.
Supported by Ministry of Health of the Czech Republic, grant nr. NW24-04-00158.