Epilepsy is often comorbid with psychiatric illnesses, including anxiety and depression. Despite the high incidence of psychiatric comorbidities in people with epilepsy, few studies address the underlying mechanisms. Stress can trigger epilepsy and depression. Evidence from human and animal studies support that hypothalamic-pituitary-adrenal (HPA) axis dysfunction may contribute to both disorders as well as their comorbidity (Kanner, 2003). Here, we investigate if HPA axis dysfunction may influence epilepsy outcomes and psychiatric comorbidities. We generated a novel mouse model ( Kcc2 / Crh KO mice) lacking the K + /Cl - co-transporter, KCC2, in corticotropin-releasing hormone (CRH) neurons, which exhibit stress- and seizure-induced HPA axis hyperactivation (Melon et al., 2018). We used the Kcc2 / Crh KO mice to examine the impact on epilepsy outcomes, including seizure frequency/burden, comorbid behavioral deficits, and SUDEP risk. We found sex differences in HPA axis dysfunction's effect on chronically epileptic KCC2/Crh KO mice seizure burden, vulnerability to comorbid behavioral deficits, and SUDEP. Suppressing HPA axis hyperexcitability in this model using pharmacological or chemogenetic approaches decreased SUDEP incidence, suggesting that HPA axis dysfunction may contribute to SUDEP. Altered neuroendocrine markers were present in SUDEP cases compared to people with epilepsy or individuals without epilepsy. Together, these findings implicate HPA axis dysfunction in the pathophysiological mechanisms contributing to psychiatric comorbidities in epilepsy and SUDEP. Significance Statement Our work provides new insight into a potential novel pathophysiological mechanism contributing to psychiatric illnesses and SUDEP in epilepsy patients, implicating HPA axis dysfunction in negative outcomes associated with epilepsy. This study is the first to link HPA axis dysfunction to SUDEP risk. Chronically epileptic male mice with exaggerated HPA axis dysfunction had increased SUDEP incidence. The translational relevance of these findings is supported by neuroendocrine abnormalities observed in postmortem samples from individuals that died of SUDEP. These data suggest that neuroendocrine mechanisms should be further explored in psychiatric comorbidities in epilepsy and SUDEP risk. Further, neuroendocrine markers may be a biomarker for SUDEP risk.

Hypothalamic-pituitary-adrenal axis dysfunction elevates SUDEP risk in a sex-specific manner