TEP-1, a glial thioester protein is required for cilia organization and intraflagellar transport in ensheathed sensory neurons

Age-related macular degeneration (AMD), the leading cause of blindness in the elderly, is characterized by progressive degeneration of retinal photoreceptors. Traditional disease models suggest that defective repression of thioester protein C3 activity by complement factor H (CFH) is a major contributor to pathogenesis in AMD and a related disease, early-onset drusen maculopathy (EODM). Our previous study identified novel functions for human CFH and C. elegans CFH-1 in the maintenance of inversin compartment integrity in photoreceptors and mechanosensory neurons, indicating that CFH has a novel, evolutionarily conserved role in cilia compartment organization that is distinct from its established function in alternative complement pathway regulation. Here, we investigate the C. elegans thioester protein TEP-1, an ancestral relative of C3 and other members of the AMCOM family (C4, C5, CD109, and alpha-2-macroglobulin). TEP-1 localizes to select glial cell surfaces and regulates inversin compartment organization and intraflagellar transport (IFT) within the cilia of ensheathed sensory neurons. In addition to revealing a novel role for an AMCOM family member in sensory neuron structure and protein transport, the localization of C3 and CFH on human photoreceptors provides support for non-canonical models of AMD and EODM pathogenesis in which defects in cilia structure and protein transport contribute directly to the progressive photoreceptor dysfunction that characterizes these diseases.