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The tight junction proteins in sheep rumen maintain two separated compartments between the ruminal milieu and
the animal. This separation helps avoiding the adsorption of noxes while ensuring an efficient transport of solutes
like SCFA. Little is known about the modulation of tight junction proteins in the rumen. Since butyrate is already
known as a powerful modulator of genes in the rumen and other organs, we hypothesized that butyrate would
also affect ruminal tight junctions. Furthermore, butyrate can activate gene expression pathways that are similar
to those stimulated by hypoxia (1). Vice versa, hypoxic condition can affect the normal tight junction pattern in
mice brains (2) and human upper respiratory airways (3). Therefore, the central question of the present study was
whether butyrate and hypoxia can affect the mRNA expression of selected tight junction proteins in sheep rumen.
Methods: Six sheep were fed on a hay-only diet of for fifteen days. After stunning and exsanguination, about 20 x
20 cm of tissue was removed from the ventral ruminal sac after opening of the abdominal wall. The muscular and
serosal layers were stripped from the epithelia and epithelial pieces were mounted in the Ussing chambers.
Ruminal epithelia were incubated for six hours with three different buffer solutions. A buffer solution without SCFA
and gassed with 100% oxygen was used as a control. A second group received bilaterally a buffer solution
enriched with 50 mM of Na-n-butyrate and gassed with 100% of oxygen. A third group received a buffer solution
without SCFA that was gassed with 100% nitrogen to induce hypoxia. Subsequently total RNA was extracted and
converted to cDNA. RT-qPCR was used to compare the mRNA expression of claudin-1, -4, -7, -17 and occludin.
Results: The mRNA expression of claudin-4, -7 and -17 was similar for all groups. Claudin-1 mRNA expression
was increased in the tissues incubated with 50 mM n-butyrate, as well as in tissues subjected to hypoxia (P <
0.05). Occludin mRNA expression was higher only for the tissues incubated under hypoxic conditions.
Conclusion: Hypoxia and incubation with high n-butyrate concentrations both up-regulated the mRNA expression
of the tight junction-tightening protein claudin-1 while hypoxia additionally increased the expression of occludin.
The precise functional relevance of these transcriptional changes has to be evaluated in further studies because
it has been shown earlier that the applied incubation conditions induce an acute increase in epithelial
conductance (1) instead of a decrease.