Hyperactive lateral habenula mediates the comorbidity between rheumatoid arthritis and depression-like behaviors.

Rheumatoid arthritis (RA) patients have a high prevalence for depression. On the other hand, comorbid with depression is associated with worse prognosis for RA. However, little is known about the underlying mechanisms for the comorbidity between RA and depression. It remains to be elucidated which brain region is critically involved in the development of depression in RA, and whether alterations in the brain may affect pathological development of RA symptoms. Here, by combining clinical and animal model studies, we show that in RA patients, the level of depression is significantly correlated with the severity of RA disease activity and affects patients' quality of life. The collagen antibody-induced arthritis (CAIA) mouse model of RA also develops depression-like behaviors, accompanied by hyperactivity and alterations in gene expression reflecting cerebrovascular disruption in the lateral habenula (LHb), a brain region critical for processing negative valence. Importantly, inhibition of the LHb not only alleviates depression-like behaviors, but also results in rapid remission of RA symptoms and amelioration of RA-related pathological changes. Together, our study highlights a critical but previously overlooked contribution of hyperactive LHb to the comorbidity between RA and depression, suggesting that targeting LHb in conjunction with RA treatments may be a promising strategy for RA patients comorbid with depression.