P.1.017 - New link between inflammation and schizophrenia: IgG with nuclease activity

Abstract

Introduction Schizophrenia is known to be associated with the disorganization of neurotransmission processes in the brain as well as immunological disturbances [1]. Inflammation in the perinatal period can lead to a violation of synaptic plasticity and pruning of synapses in the adulthood [2]. Also, microRNAs play an important role in neuronal development. The microRNA expression profiles in the circulation and brain are altered in schizophrenia. It is shown that a change in the levels of microRNAs in the blood serum or brain leads to a violation of behavior [3]. We have shown that the formation of catalytic antibodies (abzymes) is one of the signs of immune system pathology. Catalytic antibodies hydrolyzing DNA were detected in the serum of patients with schizophrenia [4]. We assume that antibodies hydrolyzing the circulating regulatory nucleic acids can play a role in schizophrenia pathogenesis. Objectives To investigate a) microRNA-hydrolyzing activity of IgG antibodies from the serum of patients with schizophrenia; b) correlation of the microRNA-hydrolyzing activity level with clinical features of the disease; c) the cytotoxicity of isolated IgG on the human neuroblastoma cell culture IMR-32. Materials and Methods In our study, 35 patients with a verified diagnosis of simple or paranoid schizophrenia and 20 healthy donors were included. The average age in the group of patients was 35.8±8.9 years, duration of disease – 9.1±5.4 years. Electrophoretically and immunologically homogeneous IgGs were obtained by affinity chromatography of the serum proteins under conditions removing non-specifically bound proteins. The microRNA-hydrolyzing activity of IgG was detected by the level of hydrolysis of two neuro-specific fluorescently labeled microRNAs (miR-137 and miR-219a-2-3p). The products of the hydrolysis were analyzed by PAGE under denaturing conditions using laser scanner. Cytotoxicity of antibodies on human neuroblastoma cell culture IMR-32 was studied using MTT-test. Statistical analysis was carried out using the Pearson’s correlation in the Statistica 10 software. Results We have shown for the first time that IgG from all schizophrenia patients possesses microRNA-hydrolyzing activity. Using strict criteria, we proved that the observed activity is an intrinsic property of IgGs in schizophrenia. Interestingly, the microRNA-hydrolyzing activity level on miR-137 is strongly negatively correlated with the disease duration (R=–0.879). The activity decreased with increasing duration of the disease. Also, the level of RNase activity on miR-219a-2-3p was positively correlated with the values of the General Psychopathology PANSS scale and the PANSS Total score (R>0.8). It was shown that the RNase activity is metal-dependent. The kinetic parameters of nuclease reactions catalyzed by IgG were significantly lower than that for native enzymes. Besides, we detected the major hydrolysis sites of two neuro-specific microRNAs. Also, we show that IgG from schizophrenia patients with nuclease activity reduced the survival rate neuroblastoma IMR-32 cell culture by 10-28%. Conclusion We propose that immunological disorders can play an important role in schizophrenia, especially in the prodromal period. The environment and genetic predisposition can lead to inflammation and the formation of antibodies hydrolyzing the microRNAs. These antibodies can contribute to changes in the level of circulating microRNAs and schizophrenia development.