Monocarboxylate transporters 1 and 4: expression and regulation by PPARα in ovine ruminal epithelial cells

Abstract

In the intact rumen epithelium, isoforms 1 and 4 of the monocarboxylate transporter (MCT1 and MCT4) are thought to play key roles in mediating transcellular and intracellular permeation of short-chain fatty acids and their metabolites and in maintaining intracellular pH. We examined whether both MCT1 and MCT4 are expressed at mRNA and protein levels in ovine ruminal epithelial cells (REC) maintained in primary culture and whether they are regulated by peroxisome proliferator-activated receptor-α (PPARα). Because both transporters have been characterized to function coupled to protons, the influence of PPARα on the recovery of intracellular pH after l-lactate exposure was evaluated by spectrofluorometry. MCT1 and MCT4 were detected using immunocytochemistry both at the cell margins and intracellularly in cultured REC. To test regulation by PPARα, cells were exposed to WY 14.643, a selective ligand of PPARα, for 48 h. The subsequent qPCR analysis resulted in a dose-dependent upregulation of MCT1 and PPARα target genes, whereas response of MCT4 was not uniform. Protein expression of MCT1 and MCT4 quantified by Western blot analysis was not altered by WY 14.643 treatment. l-Lactate-dependent proton export was blocked almost completely by pHMB, a specific inhibitor of MCT1 and MCT4. However, l-lactate-dependent, pHMB-inhibited proton export in WY 14.643-treated cells was not significantly altered compared with cells not treated with WY 14.643. These data suggest that PPARα is particularly regulating MCT1 but not MCT4 expression. Extent of lactate-coupled proton export indicates that MCT1 is already working on a high level even under unstimulated conditions.

Ruminal epithelial cell proliferation and short-chain fatty acid transporters in vitro are associated with abundance of period circadian regulator 2 (PER2)

“…The proteins MCT1 and MCT4 are important SCFA transporters in ruminal epithelium; they transport intracellular SCFA − and metabolites of SCFA, including ketone bodies and lactate, into blood (Kirat et al, 2006). Activation of PPARA enhanced the abundance of MCT1 in ovine REC (Benesch et al, 2014), a response that seemed opposite to the present data for PPARA and MCT1. One possibility for this discrepancy is that PER2 might not modulate monocarboxylic acid transporter genes through regulating PPARA.…”

“…In nonruminants, evidence indicates that the central clock (also known as the master clock) is located in the suprachiasmatic nucleus of the hypothalamus and contains several single cell rhythm oscillators (Bell-Pedersen et al, 2005). Similar rhythm oscillators are also found in peripheral tissues such as liver, intestine, and retina (LeSauter et al, 1996;Matsumoto et al, 1996).…”

Evidence of In Vivo Absorption of Lactate and Modulation of Short Chain Fatty Acid Absorption from the Reticulorumen of Non-Lactating Cattle Fed High Concentrate Diets

“…However, ruminal butyrate infusions in vivo stimulated MCT4 expression [ 23 ], whereas the incubation of isolated ruminal epithelia with butyrate ex vivo stimulated both MCT4 and MCT1 expression [ 34 ], the same as did the feeding of 60% grain on DM basis in the rumen and colon in goats [ 33 ]. Furthermore, low ruminal pH is known to increase the production rates of conjugated linoleic acids [ 35 ] which, in turn, may increase MCT1 activity in the ruminal epithelium via PPAR-α signaling [ 36 ]. This strongly suggests that metabolites released from ruminal fermentation as well as biohydrogenation may induce an ability to absorb lactate; even though lactate concentrations are mostly very low in events of SARA due to its rapid utilization by ruminal bacteria [ 37 ].…”

Correlation of trans fatty acids with the severity of coronary artery disease lesions

“…Coronary artery atherosclerosis remains the leading cause of cardiovascular morbidity and mortality today in the word, and the association of circulating cholesterol or low-density lipoprotein-cholesterol (LDL-c) with atherosclerosis and coronary artery disease is well documented [ 1 ]. Moreover, a positive association between elevated circulating LDL levels and Trans fatty acid (Trans FA) intake has been shown in epidemiological studies [ 2 , 3 ]. Therefore, the potential for dietary Trans FA to alter or promote the relationship, between the LDL atherosclerosis and coronary artery disease is considerate the mechanism for the deleterious effects of Trans FAs on the cardiovascular system.…”