C1q-dependent clearance of alpha-synuclein allows macrophages to transiently limit enteric synucleinopathy in male mice

Deposition of misfolded α-synuclein (αsyn) in the enteric nervous system (ENS) is found in multiple neurodegenerative diseases. It is hypothesized that ENS synucleinopathy contributes to both the pathogenesis and non-motor morbidity in Parkinson’s Disease (PD), but the cellular and molecular mechanisms that shape enteric histopathology and dysfunction are poorly understood. Here, we employ a fibrillar injection model of enteric synucleinopathy in male mice and demonstrate that ENS-resident macrophages, which play a critical role in maintaining ENS homeostasis, initially respond to enteric neuronal αsyn pathology by upregulating machinery for complement-mediated engulfment. Pharmacologic depletion of ENS-macrophages or genetic deletion of C1q enhanced enteric neuropathology. Conversely, C1q deletion ameliorated gut dysfunction, indicating that complement partially mediates αsyn-induced gut dysfunction. However, this C1q-dependent clearance mechanism diminished over time and its failure temporally correlated with the further increase in ENS pathology. These findings highlight the importance of enteric neuron-macrophage interactions in removing toxic protein aggregates that putatively shape the gastrointestinal manifestations of PD. Misfolded α-synuclein in the gut contributes to Parkinsons’s disease pathogenesis and gut symptoms. Gut macrophages clear α-synuclein via C1q–complement pathways; loss of this response worsens neuropathology and improves gut function, implicating neuroimmune crosstalk.