Abstract
Epidermal growth factor (EGF) and glucagon-like peptides (GLP) modulate the tight junctions (TJ) of the intestinal epithelial barrier (EB) of monogastric animals. This work tried to elucidate whether GLP-1, GLP-2 and EGF can affect the EB of the rumen. Ovine ruminal epithelia were incubated in Ussing chambers for 7hr with 25 or 250nM of either GLP-1 or GLP-2 on the serosal side, with 2.5nM of EGF on the serosal side or with 0.25 or 2.5nM EGF on the mucosal side. No treatment affected tissue conductance. Short-circuit current (Isc ) was affected by time and treatment and their interactions. Only 250nM of either GLP-1 or GLP-2 decreased Isc in certain periods compared with 25nM GLP-1 or 0.25nM mucosally applied EGF; however, not when compared to control epithelia. Fluorescein flux rates (Jfluor ) of ruminal epithelia were affected by treatment, time and time×treatment interaction. The time×treatment interaction was based on an increase in Jfluor between the first and last hour in epithelia incubated with 25nM GLP-1 or GLP-2 and in epithelia incubated with EGF. After 7hr incubation, claudin-7 mRNA expression was downregulated in all treatments. Claudin-1 mRNA was upregulated after incubation with 2.5nM EGF on the serosal side, claudin-4 mRNA was downregulated by 2.5nM EGF on the mucosal side, and occludin mRNA was increased after incubation with 250nM GLP-2. The protein abundance of all tested TJ proteins was not influenced by treatment. We conclude that GLP-1, GLP-2, and EGF have no obvious acute effects on the EB of ruminal epithelia under simulated physiological conditions ex vivo. However, by decreasing the mRNA expression of claudin-7 and partly affecting other TJ proteins, they may modulate EB in the longer term or under certain conditions.
Highlights
The epithelial barrier (EB) of the rumen provides effective protection against free noxious agents in the ruminal milieu (Aschenbach et al, 2019; Penner, Steele, Aschenbach, & McBride, 2011)
Epithelia incubated with 250 nM glucagon‐like peptides (GLP)‐2 showed claudin‐1 and claudin‐4 mRNA expression similar to control epithelia (Figure 1); occludin mRNA expression was upregulated above the level of Control and all other treatments (p < .05)
Epithelia incubated with 2.5 nM epidermal growth factor (EGF) on the mucosal side showed claudin‐1 and occludin mRNA expression similar to control epithelia, but claudin‐4 mRNA expression was lower than control epithelia and epithelia incubated with glucagon‐like peptide‐1 (GLP‐1) or serosally applied EGF (p < .05)
Summary
The epithelial barrier (EB) of the rumen provides effective protection against free noxious agents in the ruminal milieu (Aschenbach et al, 2019; Penner, Steele, Aschenbach, & McBride, 2011) It can become ineffective under pathological conditions, e.g., when luminal accumulation of short‐chain fatty acids and protons challenge key epithelial functions (Aschenbach & Gabel, 2000; Greco et al, 2018; Meissner et al, 2017). Epidermal growth factor (EGF) has potential to improve the EB of different epithelia (Lamb‐Rosteski, Kalischuk, Inglis, & Buret, 2008; Ogawa et al, 2012) It is normally released from a variety of tissues; the release into saliva being of proposed relevance for the RE (Onaga et al, 2006). EGF may reach the RE from both the luminal and blood side
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