Molecular mechanism of ruminal epithelial inflammatory damage in sheep with subacute acidosis

Abstract

Background The long-term feeding of high-concentrate diets to ruminants will damage the structure and function of their rumen flora, leading to changes in the gastrointestinal patterns of digestive nutrients and metabolic factors, and causing subacute rumen acidosis (SARA). Methods 28 small-tailed Han sheep were randomly selected and divided into three groups, namely the control group, SARA model group, and treatment group. The control group was fed low concentrate fodder, the model group was fed high concentrate fodder, and the treatment group was fed the HC first and then the LC after successfully establishing the model (n = 9). Results SARA-model sheep had high concentrations of lipopolysaccharide (LPS) in their rumen fluid and blood, whereas tumor necrosis factor-α (TNF-α) was significantly elevated in the rumen fluid, with no difference in the blood. The levels of inflammation-related proteins, namely cyclooxygenase-2 (COX-2), interleukin-6 (IL-6), TNF-α, and Toll-like receptor-4 (TLR-4), were significantly increased in the rumen epithelium of SARA-model sheep. Phosphorylation levels of nuclear transcription factor-κB (NF-κB) and mitogen-activated protein kinases (MAPKs) in the SARA group were significantly higher than those in the control and treatment groups. The phosphorylation levels of NF-κB and MAPKs inflammatory mediators and protein levels of inflammatory factors in the SARA-model sheep rumen abdominal sac were significantly higher than those in the rumen dorsal sac. The expression of tight junction proteins ZO-1, occludin, claudin-1 and claudin-4 decreased compared with that in the control group. The expression of light chain 3 (LC-3) increased in rumen epithelium of SARA sheep, while the trend of autophagy substrate sequestosome-1 (P62) was opposite to that of LC-3. Conclusions These results indicate that SARA leads to a high concentration of ruminal LPS, which significantly increases the expression and synthesis of pro-inflammatory cytokines in the rumen epithelium, through the over-activation of NF-κB and MAPK inflammatory pathways, thereby inducing rumenitis, damaging the integrity of rumen epithelium; moreover, damage to the rumen abdominal sac is more serious than that to the rumen dorsal sac. In the process of rumen gastritis, autophagy is involved in the regulation and inhibition of the inflammatory response.