Intracellular complement factor H protects neurons during CNS inflammation.

Neurodegeneration is a major driver of disability in multiple sclerosis (MS), the most common chronic inflammatory disease of the central nervous system (CNS)1. Retinal ganglion cells (RGCs), a heterogeneous neuronal population in the eye, undergo degeneration in MS and provide a model to study neuronal subtype-specific resilience to inflammatory injury2. However, the neuron-intrinsic mechanisms underlying differential vulnerability remain unclear. Here we identify a neuroprotective role for intracellular complement factor H (CFH) in neurons. Using single-nucleus RNA-sequencing analysis of RGCs from donors with MS and control individuals, we found that CFH expression was strongly correlated with intrinsic resilience to RGC degeneration. Mechanistically, CFH was induced in retinal and other CNS neurons in response to inflammatory and oxidative stress, where it limited reactive oxygen species accumulation and lipid peroxidation. CFH localized to the endoplasmic reticulum, a major site of lipid peroxidation during neuronal ferroptosis. Its protective activity was dependent on its C-terminal SCR20 domain, was independent of CFH secretion and was preserved in the absence of complement component C3. These findings reveal a non-canonical intracellular function of CFH in neurons. Together, our results identify CFH as a key mediator of neuronal resilience across the CNS in mice and humans and provide mechanistic insight into inflammatory neurodegeneration with implications for MS therapy and neuroprotection more broadly.