Targeting central immune signaling enhances the effects of methylphenidate in alleviating apathy-like behavior in 5xFAD mice.

Alzheimer's disease (AD) is frequently accompanied by neuropsychiatric symptoms (NPS), among which apathy, one of the most prevalent and burdensome, accelerates cognitive decline and disease progression, yet its molecular underpinnings remain unclear. Our previous RNA-sequencing of AD subjects revealed abnormal immune gene expression uniquely associated with apathy. In this study, we investigated whether these changes are also linked to apathy-like behavior in 5xFAD mice, and whether administration of C3a receptor antagonist SB290157, alone or with methylphenidate, modifies these behaviors. We first validated the expression of apathy-related immune hub genes identified in human AD in the prefrontal cortex (PFC) of 16-month-old 5xFAD mice using RT-qPCR. Separate cohorts of similarly aged 5xFAD and WT mice then received SB290157 and/or methylphenidate for two weeks. Results indicate that increased immune-related genes, including Tyrobp, C3, C3ar, C1qa, C1qb, and C1qc expression, were strongly correlated with apathy-like behavior in 5xFAD mice. Combined SB290157 and methylphenidate treatment significantly improved nest-building behavior, reduced C3 and C3ar protein expression, as well as restored dendritic spine density in the PFC. Our results confirm complement-mediated immune dysregulation is linked to apathy and suggest that co-targeting complement and catecholaminergic pathways may offer a novel therapeutic strategy for alleviating apathy in AD.