KNOCKDOWN OF CONNEXIN43 POTENTIATES ANTIDEPRESSANT EFFECT ON BRAIN-DERIVED NEUROTROPHIC FACTOR EXPRESSION IN PRIMARY CULTURED ASTROCYTES

Abstract Background The number of depression patients is increasing, which is one of the society problems in the world. In general, antidepressants affect through the increase of monoamine concentration at synaptic cleft. Although antidepressants upregulate monoamine level immediately after administration, several months are required for the manifestation of antidepressant effect in patients of depression, suggesting the other mechanism which is independent with monoamine. Moreover, the therapeutic satisfaction is very low because antidepressant drugs are not effective for one-third of patients and the most appropriate drug for each patient is different. Therefore, the development of biomarker to assess the efficacy of antidepressants is needed. Connexin43 (Cx43) is highly expressed in astrocytes, which is the most abundant glia cells in the brain, and contributes to not only intercellular molecular transportation but also intracellular signaling. It is demonstrated that Cx43 expression is reduced in the prefrontal cortex and hippocampus of depressive patients, suggesting that Cx43 may be involved in the pathology of depression. Our previous study showed that Cx43 expression in hippocampus was negatively correlated with the antidepressant effect of amitriptyline in the depressive model mice. In addition, we demonstrated that amitriptyline increases brain-derived neurotrophic factor (BDNF) expression in primary cultured astrocytes. However, the significance of Cx43 reduction for the antidepressant effect and the influence of Cx43 downregulation for BDNF expression by antidepressant drug in the astrocytes are still uncovered. Aims & Objectives The current study examined whether amitriptyline potentiates BDNF expression in astrocytes with reduced Cx43 expression, and the mechanism of this potentiation. Method Primary cultured astrocytes were prepared from the cerebral cortex of neonatal Wistar rats. The expression of Cx43 was downregulated by RNA interference. The expression of mRNA and protein were measured by real-time PCR and western blotting, respectively. Results Downregulation of Cx43 potentiated the amitriptyline-induced BDNF expression in cultured astrocytes. This potentiation was significantly suppressed by the blockade of LPA1/3 receptors, Src tyrosine kinase, and extracellular signal-regulated kinase (ERK). Discussion & Conclusion The current study revealed that reduced Cx43 expression potentiates the amitriptyline-induced BDNF expression in cortical astrocytes. In addition, LPA1/3-mediated Src-ERK signaling is crucial in the potentiation of amitriptyline-induced BDNF expression in Cx43-downregulated astrocytes. These results indicate the downregulation of Cx43 observed in the depressive patients might contribute to therapeutic effect of antidepressants.