Demyelination contributes to depression comorbidity in a rat model of chronic epilepsy via dysregulation of Olig2/LINGO-1 and disturbance of calcium homeostasis

Depression is the most common comorbidity among patients with epilepsy. Despite prior assumptions that antiepileptic drugs are to blame, more and more pathological studies have shown that latent neurological alterations associated with white matter injury and demyelination may underlie this link. However, whether disturbances in cerebral myelination contribute to the initiation of depression in epilepsy remains unclear. In the present study, we investigated the connection between demyelination disorders and the development of depression comorbidity in epilepsy. We first induced spontaneous recurrent epilepticus seizure (SRS) in young rats with pilocarpine. We then established depressive behaviors by recurrent forced swimming test and evaluate the depression state by sucrose preference test. The ratio of depression comorbidity in SRS rats was then calculated. Next, myelination in SRS-Depressed (SRS-D) rats was explored via PCR, western blotting, and immunohistochemistry for the key myelin promotion factor, Olig2 and inhibition factor, LINGO-1. Finally, in situ RNA hybridization of NCX3, one of the dominant Ca2+ extrusion proteins in oligodendrocytes (OLs) was performed to explore whether Ca2+ homeostasis of OLs was disturbed in epilepsy-induced hypoxic conditions and involved in the epilepsy-depression comorbidity. Our results revealed that one-quarter of the SRS rats displayed typical depressive behaviors, which were defined as SRS-D rats. In SRS-D rats, severe demyelination was also observed, accompanied with reduced expression of MBP, Olig2, and NCX3 and increased expression of LINGO-1 in the cingulate gyrus. In SRS-Non depressed rats, no significant changes were found from the control animals. This work provides new insights into the demyelination in epilepsy-depression comorbidity, which involves dysregulation of Olig2/LINGO-1 and disturbance of Ca2+ homeostasis.