[The role of expression of monocarboxylates of the first and fourth types (MCT1, MCT4) by tumor and stromal cells of prostate cancer in determining the prognosis and the efficiency of definitive treatment].

AIM: A search for new methods for diagnosing clinically significant prostate cancer is of importance due to the insufficient accuracy of modern methods in detecting aggressive tumors. One of the promising opportunities for the early diagnosis of clinically significant prostate cancer is the assessment of the glycolytic profile of the tumor by determining the expression of monocarboxylates (MCT) types 1 and 4 in tumor cells, as well as in adjacent stromal cells. MATERIALS AND METHODS: An analysis of patients of who underwent radical prostatectomy at the Institute of Urology and Reproductive Health of Sechenov University from 2015 to 2017 was carried out. The patients with histologically confirmed prostate adenocarcinoma were included in the study. Among them, the presence or absence of biochemical recurrence during the first year was studied. An immunohistochemical (IHC) study of postoperative specimen was performed to determine the expression of MCT1 and MCT4 by tumor and stromal cells. The correlation between the intensity of their expression and the risk of biochemical recurrence and the tumor characteristics was evaluated. RESULTS: High membrane expression of MCT1 directly correlated with high stromal expression of MCT4 (r=0.314, p<0.003). A significant direct correlation was found between the predominance of stromal expression of MCT4 over membrane expression and biochemical recurrence (r=0.403, p<0.001), as well as a high ISUP group (4 and 5) (r=0.294, p=0.005). CONCLUSIONS: Determination of the level of expression of type 1 and 4 monocarboxylate transporters in adenocarcinoma cells and tumor stromal cells can become an effective tool for risk stratification, and may also predict the biological behaviors of the prostate cancer and the efficiency of definitive treatment.

Identification of the HT-29 cell line as a model for investigating MCT1 transporters in sigmoid colon adenocarcinoma.

MCT1 transporters play a crucial role in the symbiotic relationship between humans and their colonic microbiome by facilitating the transport of bacteria-derived short chain fatty acids. Expression of colonic MCT1 transporters, localized in surface epithelial cells, is regulated by luminal butyrate levels. However, MCT1 also transports lactate and can be used by cancer cells to facilitate anaerobic glycolysis. Using immunolocalization techniques, this study investigated whether changes in MCT1 during cancer varied between different colonic regions. Whilst MCT1 abundance did not significantly change in transverse colon adenocarcinoma (P = 0.363, N = 6, paired T-Test), there was an increase in MCT1 in sigmoid colon adenocarcinoma (P = 0.010, N = 21, paired T-test). Using RT-PCR and western blotting, three human intestinal cell lines were tested for their suitability as a MCT1 cancer cell model. Experiments with Caco-2 cells confirmed that they modelled normal cells, with MCT1 only expressed after exposure to butyrate. In contrast, MCT1 was expressed in the absence of butyrate in both HCT-8 and HT-29 cell lines, with consistently high levels of MCT1 protein being present in HT-29 cells. Furthermore, butyrate treatment of HT-29 cells significantly decreased both MCT1 protein abundance (P < 0.001, N = 4, unpaired T-test) and glycosylation of its' chaperone protein, CD147 (P < 0.001, N = 4, unpaired T-test). These data suggest that (i) MCT1 transporter abundance increases in sigmoid colon adenocarcinoma, and (ii) HT-29 cells are an appropriate cell model with which to investigate MCT1 function in this disease.

Evidence of G-protein-coupled receptor and substrate transporter heteromerization at a single molecule level.

G-protein-coupled receptors (GPCRs) can constitute complexes with non-GPCR integral membrane proteins, while such interaction has not been demonstrated at a single molecule level so far. We here investigated the potential interaction between the thyrotropin receptor (TSHR) and the monocarboxylate transporter 8 (MCT8), a member of the major facilitator superfamily (MFS), using fluorescence cross-correlation spectroscopy (FCCS). Both the proteins are expressed endogenously on the basolateral plasma membrane of the thyrocytes and are involved in stimulation of thyroid hormone production and release. Indeed, we demonstrate strong interaction between both the proteins which causes a suppressed activation of Gq/11 by TSH-stimulated TSHR. Thus, we provide not only evidence for a novel interaction between the TSHR and MCT8, but could also prove this interaction on a single molecule level. Moreover, this interaction forces biased signaling at the TSHR. These results are of general interest for both the GPCR and the MFS research fields.

Regulation of Monocarboxylic Acid Transporter 1 Trafficking by the Canonical Wnt/ß-Catenin Pathway in Rat Brain Endothelial Cells Requires Cross-talk with Notch Signaling.

The transport of monocarboxylate fuels such as lactate, pyruvate, and ketone bodies across brain endothelial cells is mediated by monocarboxylic acid transporter 1 (MCT1). Although the canonical Wnt/ß-catenin pathway is required for rodent blood-brain barrier development and for the expression of associated nutrient transporters, the role of this pathway in the regulation of brain endothelial MCT1 is unknown. Here we report expression of nine members of the frizzled receptor family by the RBE4 rat brain endothelial cell line. Furthermore, activation of the canonical Wnt/ß-catenin pathway in RBE4 cells via nuclear ß-catenin signaling with LiCl does not alter brain endothelialMct1mRNA but increases the amount of MCT1 transporter protein. Plasma membrane biotinylation studies and confocal microscopic examination of mCherry-tagged MCT1 indicate that increased transporter results from reduced MCT1 trafficking from the plasma membrane via the endosomal/lysosomal pathway and is facilitated by decreased MCT1 ubiquitination following LiCl treatment. Inhibition of the Notch pathway by the γ-secretase inhibitorN-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycinet-butyl ester negated the up-regulation of MCT1 by LiCl, demonstrating a cross-talk between the canonical Wnt/ß-catenin and Notch pathways. Our results are important because they show, for the first time, the regulation of MCT1 in cerebrovascular endothelial cells by the multifunctional canonical Wnt/ß-catenin and Notch signaling pathways.

Overexpression of reactive oxygen species scavenger enzymes is associated with a good prognosis in triple-negative breast cancer.

OBJECTIVE: The aim of this study was to investigate the expression of redox proteins in triple-negative breast cancer (TNBC), a breast cancer type which harbors an aggressive phenotype, and to demonstrate the relationships between the expression of reactive oxygen species (ROS) markers and clinical outcome. METHODS: From 2000 to 2005, we analyzed tissue samples from 135 cases of TNBC obtained from curative surgeries at the Severance Hospital, Seoul, South Korea. Immunochemical staining for redox proteins was performed. RESULTS: The median patient age was 48 (range 27-76) years. TNM staging was as follows: T1 (n = 52, 38.5%), T2 (n = 81, 60%), T3 (n = 2, 1.5%), N0 (n = 88, 65.2%), N1 (n = 35, 25.9%), N2 (n = 8, 5.9%) and N3 (n = 4, 3.0%). Median follow-up was 59 (range 12-99) months. The high-expression catalase group tended to have a lower N stage (p = 0.016), lower tumor recurrence (p = 0.02) as well as longer overall survival rates (p = 0.05). After adjusting for patient age as well as tumor and nodal stage, we found that primary breast cancers with high catalase expression levels did not have an improved clinical outcome. A high MTC4 expression in the stroma was strongly associated with increased manganese superoxide dismutase expression (p = 0.015) and a significantly longer overall survival (p = 0.032). CONCLUSION: Considering the lack of targeted molecules as well as molecular heterogeneity of TNBC, ROS markers may provide clues to clinical outcome in TNBC.

MCT8 is Downregulated by Short Time Iodine Overload in the Thyroid Gland of Rats.

Wolff-Chaikoff effect is characterized by the blockade of thyroid hormone synthesis and secretion due to iodine overload. However, the regulation of monocarboxylate transporter 8 during Wolff-Chaikoff effect and its possible role in the rapid reduction of T4 secretion by the thyroid gland remains unclear. Patients with monocarboxylate transporter 8 gene loss-of-function mutations and monocarboxylate transporter 8 knockout mice were shown to have decreased serum T4 levels, indicating that monocarboxylate transporter 8 could be involved in the secretion of thyroid hormones from the thyroid gland. Herein, we aimed to evaluate the regulation of monocarboxylate transporter 8 during the Wolff-Chaikoff effect and the escape from iodine overload, besides the importance of iodine organification for this regulation. Monocarboxylate transporter 8 mRNA and protein levels significantly decreased after 1 day of NaI administration to rats, together with decreased serum T4; while no alteration was observed in LAT2 expression. Moreover, both monocarboxylate transporter 8 expression and serum T4 was restored after 6 days of NaI. The inhibition of thyroperoxidase activity by methimazole prevented the inhibitory effect of NaI on thyroid monocarboxylate transporter 8 expression, suggesting that an active thyroperoxidase is necessary for MCT8 downregulation by iodine overload, similarly to other thyroid markers, such as sodium iodide symporter. Therefore, we conclude that thyroid monocarboxylate transporter 8 expression is downregulated during iodine overload and that the normalization of its expression parallels the escape phenomenon. These data suggest a possible role for monocarboxylate transporter 8 in the changes of thyroid hormones secretion during the Wolff-Chaikoff effect and escape.

A lactate shuttle system between tumour and stromal cells is associated with poor prognosis in prostate cancer.

BACKGROUND: In a malignant tumour, cancer cells are embedded in stromal cells, namely cancer-associated fibroblasts (CAFs). These CAFs are now accepted as important players in cancer dynamics, being involved in tumour growth and progression. Although there are various reports on the interaction between tumour and stromal cells, the clinico-pathological significance of this cross-talk is still largely unknown. In this study, we aimed to characterise the expression of key metabolic proteins involved in glucose transport, pyruvate/lactate shuttle system, glycolytic metabolism and fatty acid oxidation in CAFs and tumour cells in different stages of malignant transformation. We further aimed to contextualise the clinico-pathological significance of these protein expression profiles with reference to known prognostic indicators, including biochemical recurrence in pT stage. METHODS: Prostate tissues were obtained from 480 patients with a median age of 64 years following radical prostatectomy with no previous hormonal therapy. Tissues were analysed for the expression of several key metabolism-related proteins in glands and surrounding fibroblasts by immunohistochemistry. Reliable markers of prognosis such as pT stage and biochemical recurrence were assessed for each case. RESULTS: We observed that prostate cancer cells did not rely mainly on glycolytic metabolism, while there was a high expression of MCT4 and CAIX - in CAFs. This corroborates the hypothesis of the "Reverse Warburg effect" in prostate cancer, in which fibroblasts are under oxidative stress and express CAIX, an established hypoxia marker. We found that alterations in the expression of metabolism-related proteins were already evident in the early stages of malignant transformation, suggesting the continuing alteration of CAFs from an early stage. Additionally, and for the first time, we show that cases showing high MCT4 expression in CAFs with concomitant strong MCT1 expression in prostate cancer (PCa) cells are associated with poor clinical outcome, namely pT3 stage of the tumour. CONCLUSIONS: In summary, this work demonstrates for the first time the clinico-pathological significance of the lactate shuttle in prostate cancer. It also suggests that other alterations in CAFs may be useful prognostic factors, and further supports the use of MCT1/MCT4 as targets for PCa therapy.

Aberrant expression of monocarboxylate transporter 4 in tumour cells predicts an unfavourable outcome in patients with hepatocellular carcinoma.

BACKGROUND & AIMS: The tumour cell microenvironment, which includes local oxygen saturation, pericellular pH and stromal cells, can modulate tumour progression. This study determined the prognostic impact of infiltrating tumour-associated macrophages and the expression of monocarboxylate transporter 4 (MCT4) and glypican 3 (GPC3) in hepatocellular carcinoma (HCC) clinical specimens. METHODS: A total of 225 cases of resected HCC were subjected to immunohistochemical analyses of CD68, CD204, MCT4 and GPC3. Immunoreactivities and other common clinicopathological parameters were subjected to univariate prognostic analyses for overall survival (OS, n = 225) and disease-free survival (DFS, n = 222). All variables with prognostic impact were further analysed in multivariate analysis. RESULTS: Increased intratumoural infiltration of CD204-positive or MCT4-positive macrophages suggested shorter OS (P = 0.015 or P = 0.001 respectively), but DFS was not altered. The GPC3 score (with an emphasis on circumferential immunoreactivity) was correlated with shorter OS and DFS. Aberrant expression of MCT4 in HCC cells was observed in a subset of HCC cases (21%, 47/225). In those cases, significantly poorer OS (P < 0.0001) and DFS (P = 0.0003) were observed, and there was a positive correlation with the intratumoural infiltration of CD204- or MCT4-positive macrophages and the GPC3 score. Multivariate analysis showed that aberrant MCT4 expression in HCC cells was an independent prognostic factor for shorter OS (P = 0.018) and DFS (P = 0.006) after resection of HCC. CONCLUSION: Aberrant expression of MCT4 in carcinoma cells serves as a novel, independent prognostic factor for HCC, indicating a poorer patient outcome.

Lactate transporters in the context of prostate cancer metabolism: what do we know?

Metabolic changes during malignant transformation have been noted for many years in tumours. Otto Warburg first reported that cancer cells preferentially rely on glycolysis for energy production, even in the presence of oxygen, leading to the production of high levels of lactate. The crucial role of lactate efflux and exchange within the tumour microenvironment drew attention to monocarboxylate transporters (MCTs). MCTs have been recognized as promising targets in cancer therapy, and their expression was described in a large variety of tumours; however, studies showing how these isoforms contribute to the acquisition of the malignant phenotype are scarce and still unclear regarding prostate cancer. In this review, we focus on the role for MCTs in cell metabolism, supporting the development and progression of prostate cancer, and discuss the exploitation of the metabolic nature of prostate cancer for therapeutic and diagnostic purposes.

Maternal obesity-associated disruption of polarized lactate transporter MCT4 expression in human placenta.

Maternal obesity is associated with an increased risk of adverse pregnancy outcomes including stillbirth, and their etiology is thought to be related to placental and fetal hypoxia. In this study, we sought to investigate the levels of lactate in maternal and umbilical cord blood, a well characterized biomarker for hypoxia, and expression of plasma membrane lactate transporter MCT1 and MCT4 in the placental syncytiotrophoblast (STB), which are responsible for lactate uptake and extrusion, respectively, from pregnant women with a diagnosis of obesity following a Cesarean delivery at term. With use of approaches including immunofluorescence staining, Western blot, RT-qPCR and ELISA, our results revealed that in controls the expression of MCT1 was equally observed between basal (fetal-facing, BM) and microvillous (maternal-facing, MVM) membrane of the STB, whereas MCT4 was predominantly expressed in the MVM but barely detected in the BM. However, obese patients demonstrated significant decreased MCT4 abundance in the MVM coupled with concurrent elevated expression in the BM. We also found a linear trend toward decreasing MCT4 expression ratio of MVM to BM with increasing maternal pre-pregnancy BMI. Furthermore, our data showed that the lactate ratios of fetal cord arterial to maternal blood were remarkably reduced in obese samples compared to their normal counterparts. Collectively, these results suggest that the loss of polarization of lactate transporter MCT4 expression in placental STB leading to disruption of unidirectional lactate transport from the fetal to the maternal compartment may constitute part of mechanisms linking maternal obesity and pathogenesis of stillbirth.

Coexpression of MCT1 and MCT4 in ALK-positive Anaplastic Large Cell Lymphoma: Diagnostic and Therapeutic Implications.

In solid tumors, glycolytic cancer or stromal cells export lactates through monocarboxylate transporter (MCT) 4, while oxidative cancer or stromal cells take up lactates as metabolic fuels or signaling molecules through MCT1. CD147 acts as a chaperone of MCT1 or MCT4. Unlike solid tumors, malignant lymphomas have a peculiar tumor microenvironment. To investigate the metabolic phenotype of malignant lymphoma associated with lactate transport, we analyzed immunohistochemical expressions of MCT1, MCT4, and CD147 in 247 cases of various malignant lymphomas. Surprisingly, both MCT1 and MCT4 were diffusely expressed on tumor cell membranes in all cases (11/11, 100%) of anaplastic lymphoma kinase (ALK) (+) anaplastic large cell lymphoma (ALCL). In contrast, only MCT1 was diffusely expressed in tumor cells of ALK(-) ALCL, as well as in B-cell, natural killer/T-cell, T-cell, and classic Hodgkin lymphomas. In these lymphomas, MCT4 expression was mostly localized to adjacent stromal cells. The pattern of diffuse membranous MCT1 and partial MCT4 expressions in tumor cells was observed in 1 case each of peripheral T-cell lymphoma (1/15, 6.7%) and multiple myeloma (1/34, 2.9%). CD147 was diffusely expressed in all types of lymphoma tumor and/or stromal cells. In conclusion, ALK(+) ALCL has a unique metabolism showing high coexpression of MCT1 and MCT4 in tumor cells. Because only ALK(+) ALCL overexpresses MCT4, immunostaining for MCT4 together with ALK is very useful for differential diagnosis from ALK(-) ALCL or peripheral T-cell lymphoma. Moreover, dual targeting against MCT1 and MCT4 would be an appropriate therapeutic approach for ALK(+) ALCL.

Cellular expression of monocarboxylate transporters in the female reproductive organ of mice: implications for the genital lactate shuttle.

The present study examined the cellular localization of monocarboxylate transporters (MCTs), glucose transporters (GLUTs), and some glycolysis-related molecules in the murine female genital tract to demonstrate existence of lactate/pyruvate-dependent energy systems. MCT1, a major MCT subtype, was localized selectively in the ovarian granulosa, oviductal-ciliated cells, and vaginal epithelium; all localizations were associated with intense expressions of glycolytic enzymes. MCT1 was localized in the cell membrane of granulosa cells, including fine processes extending from cumulus cells toward oocytes. The cumulus cells and oocytes showed intense signals for lactate dehydrogenase (LDH)-A and -B, respectively. The basolateral membrane of oviductal-ciliated cells expressed MCT4 as well as MCT1, while adjacent non-ciliated cells contained an intense immunoreactivity for aldolase-C, a glycolytic enzyme. The expression of GLUTs in the ovary was generally weak with an intense expression of GLUT1 only in some vascular endothelia. The oviductal epithelium expressed GLUT1 and GLUT3, respectively, in the basolateral and apical membrane of non-ciliated cells. In the vagina, the basal layers of epithelium were immunolabeled for MCT1 with the entire length of cell membrane, and expressed abundantly both GLUT1 and LDH-A. The findings correspond well with the rich existence of lactate in the genital fluids and strongly suggest the active transport of lactate/pyruvate in the female reproductive tract, which provides favorable conditions for oocytes, sperms, and zygotes.

lncRNA SLC16A1-AS1 as a novel prognostic biomarker in non-small cell lung cancer.

Long non-coding RNAs (lncRNAs) have proved to act as crucial biomarkers in tumors. Novel biomarkers in non-small cell lung cancer (NSCLC) need to be investigated badly. To identify the differentially expressed lncRNAs between NSCLC tissue and adjacent tissue, microarray analysis was performed. lncRNA SLC16A1-AS1 was significantly less expressed in NSCLC tissue than that in adjacent tissue. Gain-of-function experiments was performed to determine the biological functions of SLC16A1-AS. In situhybridization and survival analysis were applied in lung cancer tissue samples to determine the prognostic role of SLC16A1-AS1. It was showed that SLC16A1-AS1 was remarkably downregulated in NSCLC tissues and cell lines. Functionally, SLC16A1-AS1 overexpression could inhibit the viability and proliferation of lung cancer cell, block the cell cycle and promote cell apoptosis in vitro which may result from reduced phosphorylation of rat sarcoma (RAS)/ proto-oncogene serine/threonine-protein kinase (RAF)/ mitogen-activated protein kinase kinase (MEK)/ extracellular regulated protein kinases (ERK) pathway caused by elevated expression of SLC16A1-AS1. Clinical sample analysis showed that SLC16A1-AS1 had a favorable impact on the overall survival and progression-free survival of patients with NSCLC. Our results suggested that SLC16A1-AS1 may act as a potential biomarker for patients with NSCLC.

SLC1A1, SLC16A9, and CNTN3 Are Potential Biomarkers for the Occurrence of Colorectal Cancer.

BACKGROUND: This study is aimed at identifying unknown clinically relevant genes involved in colorectal cancer using bioinformatics analysis. METHODS: Original microarray datasets GSE107499 (ulcerative colitis), GSE8671 (colorectal adenoma), and GSE32323 (colorectal cancer) were downloaded from the Gene Expression Omnibus. Common differentially expressed genes were filtered from the three datasets above. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses were performed, followed by construction of a protein-protein interaction network to identify hub genes. Kaplan-Meier survival analysis and TIMER database analysis were used to screen the genes related to the prognosis and tumour-infiltrating immune cells of colorectal cancer. Receiver operating characteristic curves were used to assess whether the genes could be used as markers for the diagnosis of ulcerative colitis, colorectal adenoma, and colorectal cancer. RESULTS: A total of 237 differentially expressed genes common to the three datasets were identified, of which 60 were upregulated, 125 were downregulated, and 52 genes that were inconsistently up- and downregulated. Common differentially expressed genes were mainly enriched in the cellular component of extracellular exosome and integral component of membrane categories. Eight hub genes, i.e., CXCL3, CXCL8, CEACAM7, CNTN3, SLC1A1, SLC16A9, SLC4A4, and TIMP1, were related to the prognosis and tumour-infiltrating immune cells of colorectal cancer, and these genes have diagnostic value for ulcerative colitis, colorectal adenoma, and colorectal cancer. CONCLUSION: Three novel genes, CNTN3, SLC1A1, and SLC16A9 were shown to have diagnostic value with respect to the occurrence of colorectal cancer and should be verified in future studies.

Cellular expression of a monocarboxylate transporter (MCT1) in the mammary gland and sebaceous gland of mice.

Proton-coupled monocarboxylate transporters (MCTs) are essential for the transport of lactate, ketone bodies, and other monocarboxylates through the plasma membrane, but the direction and substrates of transporting in loco remain unclear. The present study examined the expression and subcellular localization of MCTs in lipogenic organs. An in situ hybridization survey of major MCT subtypes detected an intense expression of MCT1 mRNA in the mammary gland, Harderian gland, and sebaceous gland. The MCT1 immunoreactivity was found baso-laterally in acinar cells of the mammary and Harderian glands. Alveolar cells of sebaceous glands in the skin, eyelids, and penis contained the membrane-associated MCT1 immunoreactivity along the entire length of the cell surface at the margin of alveoli. These MCT1-expressing exocrine glands possessed more abundant transcripts of acetyl-CoA carboxylase-1, a key enzyme for lipogenesis, than did representative lipogenetic organs such as the liver. Since the secretions from these glands contain fat as a major product, the cellular localization of MCT1 suggests the involvement of the transporter in the uptake of lactate, acetate, and other monocarboxylates for production of medium- and long-chain fatty acids.

Clinical effects of CD33 and MPC-1 on the prognosis of multiple myeloma treated with bortezomib.

In the present study, the effects of immunophenotyping on the prognoses of patients with MM treated with bortezomib as induction therapy were investigated. A total of 118 patients with MM were examined, and the prognostic significance of the immunophenotyping and other factors were investigated. Immature and plasmablastic cell types and high-risk cytogenesis were more frequently observed in patients with CD33+ and MPC-1-. CD33+ and MPC-1- have potential as prognostic factors and correlated with lower progression-free survival and overall survival in a Kaplan-Meier analysis. Moreover, the present results demonstrated that at the relapse of disease, the percentage of CD33 increased (median 48.7%) and MPC-1 decreased (median 14.1%), respectively, therefore, both of these antigens may be associated with the refractory disease status. The present study showed that the expression of CD33 and MPC-1 in neoplastic plasma cells from patients with MM was associated with patient prognosis independent of other prognostic factors.

Cloning and functional characterization of human SMCT2 (SLC5A12) and expression pattern of the transporter in kidney.

Recently, we cloned two Na(+)-coupled lactate transporters from mouse kidney, a high-affinity transporter (SMCT1 or slc5a8) and a low-affinity transporter (SMCT2 or slc5a12). Here we report on the cloning and functional characterization of human SMCT2 (SLC5A12) and compare the immunolocalization patterns of slc5a12 and slc5a8 in mouse kidney. The human SMCT2 cDNA codes for a protein consisting of 618 amino acids. When expressed in mammalian cells or Xenopus oocytes, human SMCT2 mediates Na(+) -coupled transport of lactate, pyruvate and nicotinate. The affinities of the transporter for these substrates are lower than those reported for human SMCT1. Several non-steroidal anti-inflammatory drugs inhibit human SMCT2-mediated nicotinate transport, suggesting that NSAIDs interact with the transporter as they do with human SMCT1. Immunofluorescence microscopy of mouse kidney sections with an antibody specific for SMCT2 shows that the transporter is expressed predominantly in the cortex. Similar studies with an anti-SMCT1 antibody demonstrate that SMCT1 is also expressed mostly in the cortex. Dual-labeling of SMCT1 and SMCT2 with 4F2hc (CD98), a marker for basolateral membrane of proximal tubular cells in the S1 and S2 segments of the nephron, shows that both SMCT1 and SMCT2 are expressed in the apical membrane of the tubular cells. These studies also show that while SMCT2 is broadly expressed along the entire length of the proximal tubule (S1/S2/S3 segments), the expression of SMCT1 is mostly limited to the S3 segment. These studies suggest that the low-affinity transporter SMCT2 initiates lactate absorption in the early parts of the proximal tubule followed by the participation of the high-affinity transporter SMCT1 in the latter parts of the proximal tubule.

Expression, cellular localization, and functional role of monocarboxylate transporter 4 (MCT4) in the gastrointestinal tract of ruminants.

This is the first study to determine the precise cellular localization of monocarboxylate transporter 4 (MCT4), along with its co-existence with its chaperone, CD147 in the ruminant gastrointestinal tract. Quantitative Western blot analysis demonstrated that the abundance of MCT4 protein was in the order of forestomach > large intestine > abomasum >or= small intestine. Immunohistochemistry and immunofluorescence confocal laser microscopy showed that MCT4 in the forestomach was confined to the cell membranes of strata corneum and granulosum, while diffuse cytoplasmic staining for MCT4 was visualized in strata spinosum and basale. In the epithelium cells lining the abomasum, MCT4 immunoreactive positivities were predominantly localized on the basolateral membranes. In the small intestine, MCT4 was localized at the brush borders and the basolateral membranes of the epithelial cells lining the villi, however it was mostly found on the apical membranes of the crypt cells. In the large intestine, the immunoreactivity for MCT4 differed between the surface epithelium and the crypts; in the surface epithelium, MCT4 was mainly localized at the apical membranes, whereas in the crypts it was predominantly expressed on the basolateral membranes of the lining epithelial cells. MCT4 was remarkably co-existed with CD147 along the bovine gastrointestinal tract. Our results suggest that MCT4 can play an important role in the transport of SCFA. The study also explored the potential functional collaboration between MCT1 and MCT4 and provided new insights into the mechanisms that mediate the transport of SCFA and other monocarboxylates in the different segments of the ruminant gastrointestinal tract.

Sensitive reduction in 14C-acetate uptake in a short-term ischemic rat brain.

14C-acetate is preferentially taken up by astrocytes, and is a useful tool for measurement of glial metabolism. The aim of this study was to determine the effects of short-term ischemia on 14C-acetate uptake in the rat brain. The middle cerebral artery was occluded for 3, 10, or 30 minutes. Five minutes after reperfusion, rats were injected with 14C-acetate and decapitated 5 minutes later. Radioactivity concentrations in striatum and cerebral cortex were determined by autoradiography. Cerebral blood flow was also measured using 14C-iodoamphetamine. Neuronal cell death was measured by Nissl staining, and expression of monocarboxylate transporter-1 was examined by immunohistochemical staining. A significant reduction of 14C-acetate uptake was observed in striatum by 3 minutes of occlusion. The degree of reduction of 14C-acetate uptake and reduction area were increased with occlusion period. In contrast, within the same region the regional blood flow was increased by 10 minutes of occlusion, suggesting that uptake of 14C-acetate was independent of blood flow. No neural cell death was detected, and no significant alteration of monocarboxylate transporter-1 expression was observed by 30 minutes of occlusion. These results indicate that 14C-acetate uptake is a sensitive marker for glial metabolism in the ischemic rat brain.

Monocarboxylate transporter 8 expression in the human placenta: the effects of severe intrauterine growth restriction.

Thyroid hormones (THs) are essential for normal fetal development, with even mild perturbation in maternal thyroid status in early pregnancy being associated with neurodevelopmental delay in children. Transplacental transfer of maternal THs is critical, with increasing evidence suggesting a role for 3,3',5-tri-iodothyronine (T3) in development and function of the placenta itself, as well as in development of the central nervous and other organ systems. Intrauterine growth restriction (IUGR) is associated with fetal hypothyroxinaemia, a factor that may contribute to neurodevelopmental delay. The recent description of monocarboxylate transporter 8 (MCT8) as a powerful and specific TH membrane transporter, and the association of MCT8 mutations with profound neurodevelopmental delay, led us to explore MCT8 expression in placenta. We describe the expression of MCT8 in normal human placenta throughout gestation, and in normal third-trimester placenta compared with that associated with IUGR using quantitative reverse transcriptase PCR. MCT8 mRNA was detected in placenta from early first trimester, with a significant increase with advancing gestation (P=0.007). In the early third trimester, MCT8 mRNA was increased in IUGR placenta compared with normal samples matched for gestational age (P<0.05), but there was no difference between IUGR and normal placenta in the late third trimester. Western immunoblotting findings in IUGR and normal placentae were in accord with mRNA data. MCT8 immunostaining was demonstrated in villous cytotrophoblast and syncytiotrophoblast as well as extravillous trophoblast cells from the first trimester onwards with increasingly widespread immunoreactivity seen with advancing gestation. In conclusion, expression of MCT8 in placenta from early gestation is compatible with an important role in TH transport during fetal development and a specific role in placental development. Altered expression in placenta associated with IUGR may reflect a compensatory mechanism attempting to increase T3 uptake by trophoblast cells.