Angiotensin II up-regulates monocarboxylate transporters expression in the rat adrenal gland.

Angiotensin II (Ang II) is a major regulator of aldosterone secretion in the adrenal zona glomerulosa because it up-regulates the expression of a large number of genes involved in aldosterone biosynthesis. The transport of acetate across adrenocortical cells is a crucial step in the de novo synthesis of cholesterol, the steroid precursor of aldosterone. However, whether Ang II can affect this transport remains unknown. The current study aims to investigate the effect of in vivo infusion of Ang II on monocarboxylate transporters (MCT1, MCT2, and MCT4) gene expression in the rat adrenal gland. Immunohistochemical analysis and real-time PCR were used to examine the expression of MCTs at the protein and mRNA levels, respectively. The immunohistochemical analysis showed that higher numbers of cells expressed MCT1, MCT2, and MCT4 proteins in the zona glomerulosa and zona fasiculata of the adrenal cortex of Ang II-infused rats. Furthermore, real-time PCR indicated that in vivo infusion of Ang II increased the mRNA levels of MCT1, MCT2, and MCT4 in the rat adrenal gland. MCT up-regulation might maximize the intracellular transport of acetate in response to the stimulatory effect of Ang II on aldosterone secretion by the adrenal zona glomerulosa..

Regional and cellular distribution of monocarboxylate transporters 13 and 14 in the cattle gastrointestinal tract.

Understanding of the basic function of orphan transporters can only be achieved by examining their cellular location. This study is the first to describe the precise cellular localization of the orphan monocarboxylate transporters (MCT13) and (MCT14) in the physiologically distinct regions of the gastrointestinal tract of mammals. The present study demonstrated conclusively the regional distribution and relative expression levels of MCT13 and MCT14 on both mRNA and protein levels in the cattle gastrointestinal tract. The mRNA expression levels of MCT13 and MCT14 in the rumen, abomasum, jejunum, cecum, and proximal colon of cattle were examined using quantitative real time—PCR analysis. The precise cellular location of MCT13 and MCT14 along each part of the cattle stomach and intestine was carried out by immunohistochemistry. The data reveal distinct regional distribution in gene expression profiles of both MCT13 and MCT14 along the cattle gastrointestinal tract. Our study might be beneficial in future research to understand their physiological role in the ruminant gastrointestinal tract.

Expression of monocarboxylate transporter 1 in oral and ocular canine melanocytic tumors.

Solid tumors are composed of a heterogeneous population of cells surviving in various concentrations of oxygen. In a hypoxic environment, tumor cells generally up-regulate glycolysis and, therefore, generate more lactate that must be expelled from the cell through proton transporters to prevent intracellular acidosis. Monocarboxylate transporter 1 (MCT1) is a major proton transporter in mammalian cells that transports monocarboxylates, such as lactate and pyruvate, together with a proton across the plasma membrane. Melanocytic neoplasia occurs frequently in dogs, but the prognosis is highly site-dependent. In this study, 50 oral canine melanomas, which were subdivided into 3 histologic subtypes, and 17 ocular canine melanocytic neoplasms (14 melanocytomas and 3 melanomas) were used to examine and compare MCT1 expression. Immunohistochemistry using a polyclonal chicken anti-rat MCT1 antibody showed that most oral melanoma exhibited cell membrane staining, although there were no significant differences observed among the 3 histologic subtypes. In contrast, the majority of ocular melanocytic tumors were not immunoreactive. Additionally, we documented the presence of a 45-kDa band in cell membrane protein Western blots, and sequencing of a reverse transcriptase polymerase chain reaction band of expected size confirmed its identity as a partial canine MCT1 transcript in 3 oral tumors. Increased MCT1 expression in oral melanomas compared with ocular melanocytic tumors may reflect the very different biology between these tumors in dogs. These results are the first to document canine MCT1 expression in canine tumors and suggest that increased MCT1 expression may provide a potential therapeutic target for oral melanoma.

Monocarboxylate transporter 1 (MCT1) in the liver of pre-ruminant and adult bovines.

This study investigated the distribution and expression of monocarboxylate transporter 1 (MCT1) in the livers of pre-ruminant calves and adult bovines (bulls and cows), using different molecular biological techniques. Reverse transcription-polymerase chain reaction (RT-PCR) verified the presence of mRNA encoding for MCT1 in both pre-ruminant and adult bovine livers. Immunohistochemically, MCT1 was clearly demonstrated on the sinusoidal surfaces of bovine hepatocytes but its expression varied widely between pre-ruminants and adult bovines. In pre-ruminants, a faint hepatocellular expression of MCT1 was observed in a few hepatocytes, whereas an intense immunoreactive staining for MCT1 was shown in the majority of adult bovine hepatocytes. Western blot analysis also confirmed the results of the immunohistochemistry. Quantitative immunoblotting, as estimated by densitometric analysis, showed that the level of MCT1 in the liver of adult bovines was 8-9-fold greater (P<0.01) than that in pre-ruminant calf livers although no significant differences were detected between bulls and cows. The results demonstrated that MCT1 may play a crucial role in the transport of propionate in bovine liver, suggesting that MCT1 expression may be influenced by developmental and metabolic regulations.

Monocarboxylate transporter 1 gene expression in the ovine gastrointestinal tract.

In this study, we investigated the tissue distribution and expression of monocarboxylate transporter 1 (MCT1) along the gastrointestinal tract of sheep. Western blot analysis suggested the presence of MCT1 as a 43-kDa protein in immunoblots of membranes from the various tissues examined. The results of Western blotting were further confirmed by immunohistochemical studies, which revealed intense immunoreactivity for the MCT1 protein in the forestomach (rumen, reticulum and omasum) and large intestine (caecum, proximal and distal colon). Moderate reactivity, however, was detected in the abomasum, while no immunoreactivity could be seen in any regions of the small intestine examined. Furthermore, MCT1 was expressed at the mRNA level as determined by reverse transcriptase polymerase chain reaction (RT-PCR), which showed a band of the expected size (300 bp) in all tissues examined. From these results we concluded that MCT1 protein is highly expressed and distributed in the stomach and large intestine of sheep suggesting that MCT1 may play a significant role in the transport of short chain fatty acids and their metabolites in the gastrointestinal tract of ruminants.

Expression and distribution of monocarboxylate transporter 1 (MCT1) in the gastrointestinal tract of calves.

In the present study the expression and distribution of monocarboxylate transporter 1 (MCT1) along the gastrointestinal tract (rumen, reticulum, omasum, abomasum, duodenum, jejunum, ileum, cecum and colon) of calves were investigated on both mRNA and protein levels. The expression of MCT1 protein and its distribution were determined by Western blotting and immunohistochemical staining, respectively by using antibody for MCT1. MCT1 protein was visualized as a 43-kDa band on immunoblots of the membrane proteins prepared from the various regions examined, and it was more highly expressed in forestomach and large intestine than in abomasum and small intestine. With the use of reverse transcriptase-polymerase chain reaction, mRNA encoding for MCT1 was demonstrated in the different tissues examined. The immunohistochemical study confirmed the Western blot findings and showed strong MCT1 immunopositive staining in the stratified squamous epithelia of the forestomach as well as the epithelial cells lining the digestive tract in the cecum, proximal colon, and distal colon. The results suggest that MCT1 may play a role in the transport of SCFA and their metabolites in the gastrointestinal tract of bovines.