Calcitonin Gene Related Peptide Mediates Gut Alpha Synuclein Aggregation in a Mouse Model of Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative disorder defined by the accumulation of misfolded alpha synuclein (aSyn) protein in the brain and periphery, including the gastrointestinal (GI) tract. Prodromal PD symptoms include constipation and visceral pain, physiological processes that are regulated by enteric neuronal calcitonin gene related peptide (CGRP). Previous work utilizing a rotenone model of PD revealed increased aSyn in CGRP+ myenteric neurons, and elevated apical crypt CGRP immunoreactivity. Therefore, we hypothesize that CGRP is a potential mediator of aSyn aggregation in the myenteric plexus. To further investigate CGRPs role in enteric aSyn accumulation, this study used transgenic hA53T aSyn mice overexpressing human aSyn to generate organotypic slices of proximal colon. Slices were treated ex vivo with 10µM vehicle [dimethylsulfoxide (DMSO)] or 2µM CGRP for 24 h. Immunohistochemistry against aSyn and the pan-neuronal marker protein gene-product (PGP) 9.5 allowed quantification of aSyn co-localization with myenteric PGP9.5+ neurons. Treatment with CGRP increased the percentage of PGP9.5+ myenteric neuronal area that contained aSyn immunoreactivity in both A53T and wild-type (WT) animals (F(2, 21) = 18.39, p < 0.05). In WT mice, aSyn was increased by 1048% in CGRP treated slices (vehicle 1.8 +/- 0.33; CGRP 20.5 +/- 2) and by 235% (vehicle 9.4 +/- 1.3; CGRP 31.5 +/- 6.2) in A53T animals. aSyn levels in both A53T and WT mice increased to similar levels following CGRP treatment. Using an enzyme-linked immunosorbent assay, stool CGRP levels were found positively correlated with age in A53T mice (Spearman’s rho = 0.886, p < 0.5), but not in WT mice (Spearman’s rho = 0.198, p > 0.5) with no differences observed in homogenized colon tissue. This suggests that CGRP is released as aSyn accumulates and disease progresses in A53T mice, rather than being retained in the gut wall. This study demonstrates a key role for CGRP in facilitating aSyn aggregation in the myenteric plexus, an effect present regardless of whether the animal already had pre-existing aSyn accumulation and PD pathology (e.g., A53T animals). Understanding the mechanistic role of enteric CGRP in mediating peripheral aSyn accumulation would offer valuable insights into the GI symptomology of prodromal PD. National Institute of Mental Health (NIMH), “Sex Differences in Major Depression: Impact of Prenatal-Immune and Autonomic Dysregulation” (ORWH NIMH U54-MH118919) This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.