Progression of intestinal permeability changes and alpha‐synuclein expression in a mouse model of Parkinson's disease

Abstract

Parkinson’s disease (PD) is a multifocal degenerative disorder for which there is no cure. The majority of cases are sporadic with unknown etiology. Recent data indicate that untreated patients with de novo PD have increased colonic permeability and that both de novo and premotor patients have pathological expression of α-synuclein (α-syn) in their colon. Both endpoints potentially can serve as disease biomarkers and even may initiate PD events through gut-derived, lipopolysaccharide (LPS)-induced neuronal injury. Animal models could be ideal for interrogating the potential role of the intestines in the pathogenesis of PD; however, few current animal models of PD encompass these nonmotor features. We sought to establish a progressive model of PD that includes the gastrointestinal (GI) dysfunction present in human patients. C57/BL6 mice were systemically administered one dose of either LPS (2.5 mg/kg) or saline and were sacrificed in monthly intervals (n=5 mice for 5 months) to create a time-course. Small and large intestinal permeability was assessed by analyzing the urinary output of orally ingested sugar probes through capillary column gas chromatography. α-Syn expression was assessed by counting the number of mildly, moderately, and severely affected myenteric ganglia neurons throughout the GI tract, and the counts were validated by quantitative optical density measurements. Nigrostriatal integrity was assessed by tyrosine hydroxylase immunohistochemistry stereology and densitometry. LPS caused an immediate and progressive increase in α-syn expression in the large intestine but not in the small intestine. Intestinal permeability of the whole gut (large and small intestines) progressively increased between months 2 and 4 after LPS administration but returned to baseline levels at month 5. Selective measurements demonstrated that intestinal permeability in the small intestine remained largely intact, suggesting that gut leakiness was predominately in the large intestine. Phosphorylated serine 129-α-syn was identified in a subset of colonic myenteric neurons at months 4 and 5. Although these changes were observed in the absence of nigrostriatal degeneration, an abrupt but insignificant increase in brainstem α-syn was observed that paralleled the restoration of permeability. No changes were observed over time in controls. LPS, an endotoxin used to model PD, causes sequential increases in α-syn immunoreactivity, intestinal permeability, and pathological α-syn accumulation in the colon in a manner similar to that observed in patients with PD. These features are observed without nigrostriatal degeneration and incorporate PD features before the motor syndrome. This allows for the potential use of this model in testing neuroprotective and disease-modifying therapies, including intestinal-directed therapies to fortify intestinal barrier integrity.

A Role for Neuronal Alpha-Synuclein in Gastrointestinal Immunity

“…A recent report that individuals with PD have increased intestinal permeability suggests another mechanism, in addition to infection, that might provoke the expression (or accumulation) of αS within the ENS 25,26 , namely the exposure of the ENS to commensal microbes. In another study, orally administered E. coli producing curli protein, a protein that facilitates bacterial attachment to epithelial cells and subsequent invasion, enhanced αS deposition in plexi in the gut and in hippocampus and striatum in aged Fischer 344 rats (which spontaneously accumulate αS within their ENS as they age 27 ) as compared to rats exposed to mutant bacteria lacking the capacity to produce curli or to rats exposed to vehicle 3 .…”

Gut Microbiota Dysfunction as Reliable Non-invasive Early Diagnostic Biomarkers in the Pathophysiology of Parkinson's Disease: A Critical Review

“…Symptoms like constipation, dysbiosis, altered intestinal permeability and enteric accumulation of a-synuclein co-exist with the inflammation in the GI tract. [72][73][74][75] Persistant inflammation in the gut leads to systemic inflammation and ultimately neuroinflammation. Recent studies have reported that gut inflammation and oxidative stress do exist in patients with PD.…”

“…The GI inflammation is associated with symptoms like constipation, intestinal permeability, dysbiosis, and higher levels of pathogenic enteric a-synuclein (together characterized as GI dysfunction) that appear more than two decades before the onset of motor symptoms. [72][73][74][75] Also, studies have reported that PD patients show inflammation and oxidative stress in the gut.…”

Influence of Commensal Microbiota on the Enteric Nervous System and Its Role in Neurodegenerative Diseases

“…Characteristic deposition of α-synuclein in human PD patients [51] and altered patterns of phospho-α-synuclein aggregates [52] as well as elevated total intestinal permeability [53] have been reported. Together with the fact that SNP within peptidoglycan-recognizing protein genes are associated with PD [54] and that systemic application of LPS leads to an immediate and progressive increase in α-synuclein expression in the large intestine of mice [55], the gut itself might have the potential to contribute to disease progression in PD rather than merely reflecting pathology in a non-CNS organ.…”