Hyaluronan Regulates Neuronal and Immune Function in the Rat Small Intestine and Colonic Microbiota after Ischemic/Reperfusion Injury

Abstract

Background: Intestinal ischemia and reperfusion (IRI) injury induces acute and long-lasting damage to the neuromuscular compartment and dysmotility. This study aims to evaluate the pathogenetic role of hyaluronan (HA), a glycosaminoglycan component of the extracellular matrix, as a modulator of the enteric neuronal and immune function and of the colonic microbiota during in vivo IRI in the rat small intestine. Methods: mesenteric ischemia was induced in anesthetized adult male rats for 60 min, followed by 24 h reperfusion. Injured, sham-operated and non-injured animals were treated with the HA synthesis inhibitor, 4-methylumbelliferone (4-MU 25 mg/kg). Fecal microbiota composition was evaluated by Next Generation Sequencing. Neutrophil infiltration, HA homeostasis and toll like receptor (TLR2 and TLR4) expression in the small intestine were evaluated by immunohistochemical and biomolecular approaches (qRT-PCR and Western blotting). Neuromuscular responses were studied in vitro, in the absence and presence of the selective TLR2/4 inhibitor, Sparstolonin B (SsnB 10, 30 µM). Results: 4-MU significantly reduced IRI-induced enhancement of potentially harmful Escherichia and Enterococcus bacteria. After IRI, HA levels, neutrophil infiltration, and TLR2 and TLR4 expression were significantly enhanced in the muscularis propria, and were significantly reduced to baseline levels by 4-MU. In the injured, but not in the non-injured and sham-operated groups, SsnB reduced both electrical field-stimulated (EFS, 0.1–40 Hz) contractions and EFS-induced (10 Hz) non-cholinergic non-adrenergic relaxations. Conclusions: enhanced HA levels after intestinal IRI favors harmful bacteria overgrowth, increases neutrophil infiltration and promotes the upregulation of bacterial target receptors, TLR2 and TLR4, in the muscularis propria, inducing a pro-inflammatory state. TLR2 and TLR4 activation may, however, underlay a provisional benefit on excitatory and inhibitory neuronal pathways underlying peristalsis.

Intestinal barrier function in the naked mole-rat: an emergent model for gastrointestinal insights

“…Notably, the histological features of the NMRs small intestine and colon more closely resemble those of bigger rodents, such as rats (69) and guinea pigs (70,71). This is of particular interest because the altered intestinal architecture found in NMRs would not completely explain the increased ileum tissue integrity (reflected as increased in TEER) observed in these animals compared to mice.…”

Intestinal barrier function in the naked mole-rat: an emergent model for gastrointestinal insights

“…Notably, the histological features of the NMRs small intestine and colon more closely resemble those of bigger rodents, such as rats (69) and guinea pigs (70,71). This is of particular interest because the altered intestinal architecture found in NMRs would not completely explain the increased ileum tissue integrity (reflected as increased in TEER)…”

Neutrophil extracellular traps drive intestinal microvascular endothelial ferroptosis by impairing Fundc1-dependent mitophagy

“…The occurrence of I/R in intestinal tissues can stimulate the release of reactive oxygen species and associated inflammatory mediators, instigating the aggregation and activation of neutrophils within the intestine [ 46 ]. The persistence of activated neutrophils could exacerbate local intestinal damage, culminating in the impairment of the gut barrier and translocation of intestinal bacteria and endotoxins [ 47 , 48 ]. Our prior research on rats revealed that II/R injury could result in intestinal inflammation and a reduction in the levels of tight junction proteins [ 16 ].…”