Modulation of vH⁺-ATPase is part of the functional adaptation of sheep rumen epithelium to high-energy diet

Abstract

Ruminal vacuolar H(+)-ATPase (vH(+)-ATPase) activity is regulated by metabolic signals. Thus, we tested whether its localization, expression, and activity were changed by different feeding. Young male sheep (n = 12) were either fed hay ad libitum (h) or hay ad libitum plus additional concentrate (h/c) for 2 wk. The vH(+)-ATPase B subunit signal was predominantly found in the cell membrane and cytosol of rumen epithelial cells (REC) with basal/parabasal phenotype. The elevated number (threefold) of these cells in rumen mucosa of h/c-fed sheep reflects a high proliferative capacity and, explains the 2.3-fold increase of the total number of vH(+)-ATPase-expressing REC. However, in accordance with a 58% reduction of the vH(+)-ATPase B subunit mRNA expression in h/c-fed sheep, its protein amount per single REC was decreased. Using the fluorescent probe BCECF and selective inhibitors (foliomycin, amiloride), the contribution of vH(+)-ATPase and Na(+)/H(+) exchanger to intracellular pH (pH(i)) regulation was investigated. REC isolated from h/c-fed sheep keep their pH(i) at a significantly higher level (6.91 ± 0.03 vs. 6.74 ± 0.05 in h-fed sheep). Foliomycin or amiloride decreased pH(i) by 0.16 ± 0.02 and 0.57 ± 0.04 pH units when applied to REC from h-fed sheep, but the effects were markedly reduced (-88 and -33%) after concentrate feeding. Nevertheless, we found that REC proliferation rate and [cAMP](i) were reduced after foliomycin-induced vH(+)-ATPase inhibition. Our results provide the first evidence for a role of vH(+)-ATPase in regulation of REC proliferation, most probably by linking metabolically induced pH(i) changes to signaling pathways regulating this process.

Downregulation of Cellular Protective Factors of Rumen Epithelium in Goats Fed High Energy Diet

“…Upregulation of ATPB in the epithelium of goats in response to energy supply supports the findings of Bondzio et al [8], who have identified ATP5G (ATP synthase subunit gamma) to be up-regulated in sheep fed a concentrate supplemented diet, and suggests an increased energy requirement during enhanced proliferation of germinative epithelial cell layers of the rumen [47] or an increase of electrochemical gradients in response to energy supply [12]. On the other hand, the study demonstrated downregulation of other two enzymes involved in energy metabolism such as NDKB and TPI in response to high energy supply.…”

Butyrate and Subacute Ruminal Acidosis Affect Abundance of Membrane Proteins Involved With Proton and Short Chain Fatty Acid Transport in the Rumen Epithelium of Dairy Cows

“…In other studies, higher inclusion of dietary concentrates increased MCT1 protein abundance, both when compared to an all-forage diet (Kuzinski and Rontgen, 2011) and in unrestricted access as compared to restricted access, despite similar SCFA concentrations (Koho et al, 2011). In our study, the increase in MCT1 and NHE3 on epithelial cells appears to be primarily aimed at maintain-ing intracellular pH.…”

Review: Exogenous butyrate: implications for the functional development of ruminal epithelium and calf performance

“…triphosphatase (vH + -ATPase), a sensor of substrate and energy availability participating in H + translocation across limiting membranes and of the peroxisome proliferatoractivated receptor isoform-α (PPARα) involved in energy homeostasis and in cell cycle, has been estimated in proliferated epithelial cells in rumen with higher butyrate concentrations (Kuzinski et al, 2012;Naeem et al, 2012;Connor et al, 2013). The process of cell division is connected with pHi changes which are induced metabolically (Madshus, 1988).…”

“…The butyrateinduced acid load in the ruminal epithelial cells stimulates the activities of proteins involved in the pHi recovery to the values of cell homeostasis. These pH-homeostatic mechanisms include membrane-bound transporters belonging to the solute-carrier family, isoforms of (monocarboxylate transporter (MCT)), sodium-proton exchangers (NHEs) and also P-type cation transport adenosine triphosphatases (Graham et al, 2007;Kuzinski et al, 2012). It has been recognized that an increasing ruminal concentration of butyrate stimulates the activities of proton-linked monocarboxylate transporter isoform 1 (MCT1) and/or isoform 4 (MCT4) in transporting carboxylic acids in the ruminal epithelial cells in calves (Laarman et al, 2012), goats (Yan et al, 2014) and lambs (Malhi et al, 2013).…”

“…The full activity of NHEs has been recognized as a key transport element required for Na + /K + -ATPase and vH + -ATPase functions in the regulation of pHi homeostasis (Albrecht et al, 2008). Activities of these both enzymes in the rumen epithelium are positively affected by an increasing ruminal concentration of butyrate in goats and lambs (Kuzinski et al, 2012;Yan et al, 2014). Butyrate exerts a positive effect on the pHi-homeostatic mechanisms allowing butyrate to pass from the rumen in the ruminal epithelial cells and butyrate metabolites into the capillary bed.…”