Cross-platform validation of neurotransmitter release impairments in schizophrenia patient-derived NRXN1-mutant neurons

Significance Heterozygous NRXN1 deletions predispose to schizophrenia and other neurodevelopmental disorders. Engineered heterozygous NRXN1 deletions impair neurotransmitter release in human neurons, suggesting a synaptic pathophysiological mechanism. In a multicenter effort to test the generality and robustness of this pivotal observation, we used, at two laboratories, independent analyses of patient-derived and newly engineered human neurons with heterozygous NRXN1 deletions. Schizophrenia patient-derived neurons with NRXN1 deletions exhibited the same major decrease in neurotransmitter release and an increase in CASK protein as engineered human neurons with NRXN1 deletions. Strikingly, engineered mouse Nrxn1-deficient neurons derived by the same method displayed no such phenotype, suggesting a human-specific role for NRXN1. Thus, heterozygous NRXN1 deletions robustly impair synaptic function in human neurons, enabling future drug discovery efforts. Heterozygous NRXN1 deletions constitute the most prevalent currently known single-gene mutation associated with schizophrenia, and additionally predispose to multiple other neurodevelopmental disorders. Engineered heterozygous NRXN1 deletions impaired neurotransmitter release in human neurons, suggesting a synaptic pathophysiological mechanism. Utilizing this observation for drug discovery, however, requires confidence in its robustness and validity. Here, we describe a multicenter effort to test the generality of this pivotal observation, using independent analyses at two laboratories of patient-derived and newly engineered human neurons with heterozygous NRXN1 deletions. Using neurons transdifferentiated from induced pluripotent stem cells that were derived from schizophrenia patients carrying heterozygous NRXN1 deletions, we observed the same synaptic impairment as in engineered NRXN1-deficient neurons. This impairment manifested as a large decrease in spontaneous synaptic events, in evoked synaptic responses, and in synaptic paired-pulse depression. Nrxn1-deficient mouse neurons generated from embryonic stem cells by the same method as human neurons did not exhibit impaired neurotransmitter release, suggesting a human-specific phenotype. Human NRXN1 deletions produced a reproducible increase in the levels of CASK, an intracellular NRXN1-binding protein, and were associated with characteristic gene-expression changes. Thus, heterozygous NRXN1 deletions robustly impair synaptic function in human neurons regardless of genetic background, enabling future drug discovery efforts.