Enteric Alpha-synuclein inclusions, colonic inflammation, increased mucosal permeability and alterations of Bowel neuromuscular functiond precede central neurodegeneration in a transgenic mouse model of Parkinson's disease

Introduction. Gastrointestinal dysfunctions represent one of the most common non-motor symptoms of Parkinson's disease (PD). Several lines of evidence suggest that enteric accumula- tion of α-synuclein (αS) inclusions (a hallmark of PD) and colonic inflammation could contribute to bowel motor dysfunctions since the earliest stages of PD. However, current knowledge does not allow to establish a clear relationship between altered mucosal permeabil- ity, enteric inflammation, bowel dysmotility and PD pathology. This study examined concom- itantly enteric αS accumulation, mucosal permeability, bowel inflammation and in vitro colonic motor activity in a transgenic model of PD, before onset of neurodegeneration in the CNS. Methods. PrP human A53T αS transgenic (Tg) mice, Line G2-3 develop a progres- sive PD-like neurological and motor deficiency after 9 months of age, accompanied by neuronal degeneration and pathological accumulation of aggregated αS in the central nervous system (CNS). Animals were sacrificed at the age of 3, 6 and 9 months, in order to evaluate the presence and timing of enteric αS inclusions, alterations of intestinal mucosal barrier and colonic inflammation since the very early phases of the disease, before the overt develop- ment of CNS dysfunction. Blood samples were collected to evaluate circulating lipopolysac- charide (LPS) levels (an indirect index of intestinal permeability) by ELISA assay; then distal colon was excised and processed for: 1) expression and aggregation of αS (western blot); 2) tissue tumor necrosis factor (TNF) and interleukin-1beta (IL-1β) (ELISA). Colonic longitu- dinal and circular muscle preparations were set up in organ baths with Krebs solution, and connected to isometric transducers to record contractions elicited by electrical stimulation (ES, 10 Hz, 0.5 ms, 30 mA). Results: An accumulation of insoluble and aggregated αS was present in the enteric neurons of the distal colon in Tg mice since 3 months of age, as compared with controls. In addition, at 3, 6 and 9 months of age Tg mice displayed a significant elevation of circulating LPS along with increased colonic TNF and IL-1β levels. Electrically evoked contractions in longitudinal and circular muscle preparations were impaired in Tg mice at 3, 6 and 9 months of age, as compared with controls. Conclusion. The present findings suggest that a concomitance of enteric αS accumulation, altered mucosal permeability, bowel inflammation and impaired colonic motor activity represent early events in PD, occurring before the onset of CNS neurodegeneration. These changes could contribute to the pathogenesis of intestinal motor dysfunctions known to be associated with PD in humans.