Intestinal Macrophages Modulate Brain Synucleinopathy in Parkinson's Disease

Emerging evidence suggests that Parkinson's disease (PD) may have its origin in the enteric nervous system (ENS), from where alpha-synuclein (aS) pathology spreads to the brain. Decades before the onset of motor symptoms, PD patients suffer from constipation and present with circulating T cells responsive to aS, suggesting that peripheral immune responses initiated in the ENS may be involved in the early stages of PD. However, cellular mechanisms that trigger aS pathology in the ENS and its spread along the gut-brain axis remain elusive. Here, we demonstrate that muscularis macrophages (ME-Macs), housekeepers of ENS integrity and intestinal homeostasis, modulate aS pathology and neurodegeneration in models of PD. ME-Macs contain misfolded aS, adopt a signature reflecting endolysosomal dysfunction, and modulate the expansion of T cells that travel from the ENS to the brain via the dura mater as aS pathology progresses. Directed ME-Mac depletion leads to reduced aS pathology in the ENS and CNS, prevents T cell expansion, and mitigates neurodegeneration and motor dysfunction, suggesting a role for ME-Macs as early cellular initiators of aS pathology along the gut-brain axis. Understanding these mechanisms could pave the way for early-stage biomarkers in PD. Overall design: In this study, single-cell RNA sequencing was performed on duodenal muscularis externa from wild-type and 3KL a-synuclein transgenic mice to capture transcriptional changes associated with a-synuclein pathology. 4 biologically independent samples were analyzed per genotype, each consisting of pooled tissue from 4 mice to ensure reproducibility. Macrophages and T cells were isolated from the muscularis externa and profiled in parallel to assess their transcriptional states and potential interactions. The design allowed direct comparison between disease and control conditions, with quality control and clustering used to define distinct cell populations. Main variable: genotype (WT vs 3KL).