Association between MKL1 rs6001946 and schizophrenia in a Han Chinese population

Identification of a Predictive Model for Schizophrenia Based on SNPs in a Chinese Population

Background

Schizophrenia is a devastating mental disease with high heritability. A growing number of susceptibility genes associated with schizophrenia, as well as their corresponding SNPs loci, have been revealed by genome-wide association studies. However, using SNPs as predictors of disease and diagnosis remains difficult. Here, we aimed to uncover susceptibility SNPs in a Chinese population and to construct a prediction model for schizophrenia.

Methods

A total of 210 participants, including 70 patients with schizophrenia, 70 patients with bipolar disorder, and 70 healthy controls, were enrolled in this study. We estimated 14 SNPs using published risk loci of schizophrenia, and used these SNPs to build a model for predicting schizophrenia via comparison of genotype frequencies and regression. We evaluated the efficacy of the diagnostic model in schizophrenia and control patients using ROC curves and then used the 70 patients with bipolar disorder to evaluate the model's differential diagnostic efficacy.

Results

5 SNPs were selected to construct the model: rs148415900, rs71428218, rs4666990, rs112222723 and rs1716180. Correlation analysis results suggested that, compared with the risk SNP of 0, the risk SNP of 3 was associated with an increased risk of schizophrenia (OR = 13.00, 95% CI: 2.35-71.84, p = 0.003). The ROC-AUC of this prediction model for schizophrenia was 0.719 (95% CI: 0.634-0.804), with the greatest sensitivity and specificity being 60% and 80%, respectively. The ROC-AUC of the model in distinguishing between schizophrenia and bipolar disorder was 0.591 (95% CI: 0.497-0.686), with the greatest sensitivity and specificity being 60% and 55.7%, respectively.

Conclusion

The SNP risk score prediction model had good performance in predicting schizophrenia. To the best of our knowledge, previous studies have not applied SNP-based models to differentiate between cases of schizophrenia and other mental illnesses. It could have several potential clinical applications, including shaping disease diagnosis, treatment, and outcomes.

SRF depletion in early life contributes to social interaction deficits in the adulthood

Alterations in social behavior are core symptoms of major developmental neuropsychiatric diseases such as autism spectrum disorders or schizophrenia. Hence, understanding their molecular and cellular underpinnings constitutes the major research task. Dysregulation of the global gene expression program in the developing brain leads to modifications in a number of neuronal connections, synaptic strength and shape, causing unbalanced neuronal plasticity, which may be important substrate in the pathogenesis of neurodevelopmental disorders, contributing to their clinical outcome. Serum response factor (SRF) is a major transcription factor in the brain. The behavioral influence of SRF deletion during neuronal differentiation and maturation has never been studied because previous attempts to knock-out the gene caused premature death. Herein, we generated mice that lacked SRF from early postnatal development to precisely investigate the role of SRF starting in the specific time window before maturation of excitatory synapses that are located on dendritic spine occurs. We show that the time-controlled loss of SRF in neurons alters specific aspects of social behaviors in SRF knock-out mice, and causes deficits in developmental spine maturation at both the structural and functional levels, including downregulated expression of the AMPARs subunits GluA1 and GluA2, and increases the percentage of filopodial/immature dendritic spines. In aggregate, our study uncovers the consequences of postnatal SRF elimination for spine maturation and social interactions revealing novel mechanisms underlying developmental neuropsychiatric diseases.

Loss of serum response factor in mature neurons in the dentate gyrus alters the morphology of dendritic spines and hippocampus-dependent behavioral tasks

Serum response factor (SRF) is a major transcription factor that regulates the expression of several plasticity-associated genes in the brain. Although the developmental expression of SRF in excitatory neurons is crucial for establishing proper hippocampal circuitry, no substantial evidence of its role in unstimulated mature neurons has been provided. The present study used time-controlled, conditional SRF knockout mice and found that the lack of SRF in adult neurons led to decreased actin levels and inactivation of the actin-severing protein cofilin 1 through its increase in phosphorylation at Ser3. The augmentation of cofilin 1 phosphorylation correlated with an alteration of dendritic spine morphology in the dentate gyrus, which was reflected by an increase in the number of spines that clustered into the long-spine category. The changes in spine morphology coincided with a lower amplitude and frequency of miniature excitatory postsynaptic currents. Moreover, SRF knockout animals were hyperactive and exhibited impairments in hippocampus-dependent behaviors, such as digging, marble burying, and nesting. Altogether, our data indicate that the adult deletion of neuronal SRF leads to alterations of spine morphology and function and hippocampus-dependent behaviors. Thus, SRF deletion in adult neurons recapitulates some aspects of morphological, electrophysiological, and behavioral changes that are observed in such psychiatric disorders as schizophrenia and autism spectrum disorders.

Synaptic localisation of SRF coactivators, MKL1 and MKL2, and their role in dendritic spine morphology

The megakaryoblastic leukaemia (MKL) family are serum response factor (SRF) coactivators, which are highly expressed in the brain. Accordingly, MKL plays important roles in dendritic morphology, neuronal migration, and brain development. Further, nucleotide substitutions in the MKL1 and MKL2 genes are found in patients with schizophrenia and autism spectrum disorder, respectively. Thus, studies on the precise synaptic localisation and function of MKL in neurons are warranted. In this study, we generated and tested new antibodies that specifically recognise endogenously expressed MKL1 and MKL2 proteins in neurons. Using these reagents, we biochemically and immunocytochemically show that MKL1 and MKL2 are localised at synapses. Furthermore, shRNA experiments revealed that postsynaptic deletion of MKL1 or MKL2 reduced the percentage of mushroom- or stubby-type spines in cultured neurons. Taken together, our findings suggest that MKL1 and MKL2 are present at synapses and involved in dendritic spine maturation. This study may, at least in part, contribute to better understanding of the molecular mechanisms underlying MKL-mediated synaptic plasticity and neurological disorders.