Role of Macroautophagy in Mammalian Male Reproductive Physiology

Physiologically, autophagy is an evolutionarily conserved and self-degradative process in cells. Autophagy carries out normal physiological roles throughout mammalian life. Accumulating evidence shows autophagy as a mechanism for cellular growth, development, differentiation, survival, and homeostasis. In male reproductive systems, normal spermatogenesis and steroidogenesis need a balance between degradation and energy supply to preserve cellular metabolic homeostasis. The main process of autophagy includes the formation and maturation of the phagophore, autophagosome, and autolysosome. Autophagy is controlled by a group of autophagy-related genes that form the core machinery of autophagy. Three types of autophagy mechanisms have been discovered in mammalian cells: macroautophagy, microautophagy, and chaperone-mediated autophagy. Autophagy is classified as non-selective or selective. Non-selective macroautophagy randomly engulfs the cytoplasmic components in autophagosomes that are degraded by lysosomal enzymes. While selective macroautophagy precisely identifies and degrades a specific element, current findings have shown the novel functional roles of autophagy in male reproduction. It has been recognized that dysfunction in the autophagy process can be associated with male infertility. Overall, this review provides an overview of the cellular and molecular basics of autophagy and summarizes the latest findings on the key role of autophagy in mammalian male reproductive physiology.

Irisin/FNDC5: A participant in camel metabolism

The quantification, localization, production, function, and regulation of irisin/FNDC5 in camel species have not been previously studied. The objective of this study was to detect the irisin content in Arabian camel blood and tissues and study the gene expression of FNDC5 and PGC-1α in camel skeletal muscles and white adipose tissue depots under basal conditions. To monitor if exercise influences blood and tissue irisin protein levels as well as FNDC5 and PGC-1α gene expression levels, we analyzed irisin concentrations in the serum, skeletal muscles (soleus and gastrocnemius), and white adipose tissues (hump, subcutaneous, visceral, epididymal, and perirenal) in both control (n = 6) and exercised group (n = 6) using ELISA and determined the cellular localization of irisin/FNDC5 and the mRNA levels of FNDC5 and PGC-1α in skeletal muscles and adipose tissues via immunohistochemistry and real-time PCR, respectively. The possible regulatory roles of exercise on some hormones and metabolites as well as the detection of links between serum irisin and other circulating hormones (insulin, leptin, and cortisol) and metabolites (glucose, free fatty acids, triglycerides, and ATP) were explored for the first time in camels. Our results indicated that exercise induces tissue-specific regulation of the camel irisin, FNDC5, and PGC-1α levels, which subsequently regulates the circulating irisin level. Significant associations were detected between the levels of irisin/FNDC5/PGC-1α in camels and the metabolic and hormonal responses to exercise. Our study suggested that irisin regulates, or is regulated by, glucose, FFA, insulin, leptin, and cortisol in camels. The novel results of the present study will serve as baseline data for camels.

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.

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.

Monocarboxylate transporter genes in the mammary gland of lactating cows

This study is the first to examine the expression of the 14 monocarboxylate transporter genes (MCT1-MCT14) in the mammary gland of mammals. RT-PCR, Western blot, immunohistochemistry, and immunofluorescence confocal laser microscopy were applied in a comprehensive approach to assess the expression and cellular localization of MCTs in the mammary gland of lactating cattle. RT-PCR revealed the existence of nine MCT isoforms, namely MCT1, MCT2, MCT3, MCT4, MCT5, MCT8, MCT10, MCT13, and MCT14 in cow mammary gland. The amplified cDNA segments were confirmed by sequence analysis and deposited in the GenBank. Using the commercially available antibodies against MCT1-MCT8, Western blotting verified the protein expression of MCT1, MCT2, MCT3, MCT4, MCT5, and MCT8 in the cow mammary gland. The precise cellular localization of the identified MCT proteins showed that both MCT1 and MCT2 were basolaterally localized on the cow mammary alveolar epithelial cells. In contrast, MCT4 protein signal was expressed on the apical membrane of these alveolar epithelia. MCT8, however, was predominantly localized on the basolateral membranes of the lactocytes, along with its weak labeling on the apical membrane of the same cells. No immunoreactive staining for MCT3 and MCT5 proteins could be detected histochemically in lactating bovine mammary tissue. Additionally, we proved the colocalization of CD147 with both MCT1 and MCT4 on the boundaries of the cow mammary alveolar epithelia. The existence and localization pattern of MCT genes in the mammary gland of lactating cows suggest their possible involvement in the transport of essential elements required for milk synthesis and secretion.

Effect of pectin feeding on monocarboxylate transporters in rat adrenal gland

We have recently proved the expression and localization of seven monocarboxylate transporters (MCT1, MCT2, MCT3, MCT4, MCT5, MCT7, and MCT8) in the rat adrenal gland. So far, there are no data reporting possible regulation of any MCT isoform in the adrenal gland. Pectin is a soluble dietary fiber that is known to exert a hypocholesterolemic effect and increases the short chain fatty acids production in the large intestine. This work aimed to study the effect of pectin feeding on the expression of MCTs (MCT1-MCT5, MCT7, and MCT8) and their cellular distribution in rat adrenal gland. Western blotting demonstrated significant increase in the expression levels of MCT1, MCT2, MCT4, MCT5, and MCT7 in pectin-fed rats in comparison with the controls. Immunohistochemistry revealed extended distribution and distinctive increase in the immunoreactivities of MCT1, MCT2, MCT4, MCT5, and MCT7 in the adrenal cortical zones, besides the increase in the immunoreactive intensity of MCT5 and MCT7 in the adrenal medulla of pectin-fed versus control rats. Interestingly, zona glomerulosa which did not show any reactivity for MCT1 or MCT2 in controls, exhibited marked immunopositivities for both MCT1 and MCT2 in pectin-fed rats. MCT3 and MCT8, however, did not show significant changes in their expression levels between pectin-fed and control rats. Our data is the first to describe the up regulation of various MCTs in rat adrenal gland under the influence of pectin feeding. This up regulation might be a compensatory response to the hypocholesterolemic effect of pectin in order to maximize the intracellular availability of acetate. This article suggests that monocarboxylate transporters have an important physiological role in the regulation of adrenal hormones as well as in cholesterol homeostasis.

Presence of ten isoforms of monocarboxylate transporter (MCT) family in the bovine adrenal gland

This study provides novel information regarding the existence and precise cellular localization of various monocarboxylate transporters (MCTs) in the mammalian adrenal gland. RT-PCR results revealed that 10 MCT isoforms, namely MCT1, MCT2, MCT3, MCT4, MCT5, MCT8, MCT9, MCT10, MCT13, and MCT14 are expressed in the bovine adrenal gland. MCTs (MCT1-MCT8) proteins were examined by Western blot analysis in the bovine adrenal gland. The precise cellular localization of six MCT isoforms (MCT1-MCT5 and MCT8) within the different zones of the adrenal gland has been determined by immunohistochemical and immunofluorescence confocal laser microscopy analyses. To gain insight on the species differences for the expression profiles of MCT isoforms in this vital organ, we also examined the expression and cellular localization of MCT1-MCT8 in the rat adrenal gland. Some discrepancies in MCTs profiles between cattle and rat have been observed in the different zones of the adrenal gland. The tissue distribution pattern of MCT isoforms in the steroid-secreting adrenal cortex and catecholamine-secreting adrenal medulla suggests that they may play distinct roles in the regulation of the different hormone biosynthesis in the adrenal gland. Also, it is possible that different MCT isoforms in adrenal gland can be differentially regulated under acute or chronic conditions. This report can form the basis for future research on the regulation of these transporters in the adrenal gland.

Dietary pectin up-regulates monocaboxylate transporter 1 in the rat gastrointestinal tract

This work was undertaken to study the effect of pectin feeding on the expression level, cellular localization and functional activity of monocarboxylate transporter 1 (MCT1) in the gastrointestinal tract of rats. The results indicated that MCT1 protein level was significantly increased along the entire length of the gastrointestinal tract of pectin-fed rats in comparison with control animals. Immunohistochemical analysis revealed an increase in MCT1 in the stratified squamous epithelia of the forestomach as well as in the basolateral membranes of the cells lining the gastric pit of the glandular stomach of pectin-fed rats when compared with control animals. The parietal cells, which showed barely any or no detectable MCT1 in the control group, exhibited a strong intensity of MCT1 on the basolateral membranes in pectin-fed rats. In the small intestine of pectin-fed rats, strong immunopositivity for MCT1 was detected in the brush border and basolateral membranes of the absorptive enterocytes lining the entire villi, while in control rats, weak reactivity was detected on the brush border membrane in a few absorptive enterocytes in the villus tip. In the large intestine of control animals, MCT1 was detected on the basolateral membranes of the epithelia lining the caecum and colon. This staining intensity was markedly increased in pectin-fed rats, along with the appearance of strong reactivity for MCT1 on the apical membranes of the surface and crypt epithelia of caecum and colon. Our results also showed that MCT1 co-localizes with its chaperone, basigin (CD147), in the rat gastrointestinal tract, and that the pectin feeding increased the expression of CD147. In vivo functional studies revealed an enhanced acetate absorption in the colon of pectin-fed in comparison with control animals. We conclude that MCT1 is up-regulated along the gastrointestinal tract of pectin-fed rats, which might represent an adaptive response to the increased availability of its substrates.

Expression of monocarboxylate transporter 1 (MCT1) in the dog intestine

In this study, the expression and distribution of monocarboxyolate transporter 1 (MCT1) along the intestines (duodenum, jejunum, ileum, cecum, colon and rectum) of dogs were investigated at both the mRNA and protein levels. The expression of MCT1 protein and its distribution were confirmed by Western blotting and immunohistochemical staining using the antibody for MCT1. We identified mRNA coding for MCT1 and a 43-kDa band of MCT1 protein in all regions from the duodenum to the rectum. Immunoreactive staining for MCT1 was also observed in epithelial cells throughout the intestines. MCT1 immunoreactivity was greater in the large intestine than in the small intestine. MCT1 protein was predominantly expressed on the basolateral membranes along intestinal epithelial cells, suggesting that MCT1 may play an important role in lactate efflux and transport of short-chain fatty acids (SCFAs) to the bloodstream across the basolateral membranes of the dog intestine.

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.

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 (MCT1) plays a direct role in short-chain fatty acids absorption in caprine rumen

Despite the importance of short-chain fatty acids (SCFA) in maintaining the ruminant physiology, the mechanism of SCFA absorption is still not fully studied. The goal of this study was to elucidate the possible involvement of monocarboxylate transporter 1 (MCT1) in the mechanism of SCFA transport in the caprine rumen, and to delineate the precise cellular localization and the level of MCT1 protein along the entire caprine gastrointestinal tract. RT-PCR revealed the presence of mRNA encoding for MCT1 in all regions of the caprine gastrointestinal tract. Quantitative Western blot analysis showed that the level of MCT1 protein was in the order of rumen >/= reticulum > omasum > caecum > proximal colon > distal colon > abomasum > small intestine. Immunohistochemistry and immunofluorescence confocal analyses revealed widespread immunoreactive positivities for MCT1 in the caprine stomach and large intestine. Amongst the stratified squamous epithelial cells of the forestomach, MCT1 was predominantly expressed on the cell boundaries of the stratum basale and stratum spinosum. Double-immunofluorescence confocal laser-scanning microscopy confirmed the co-localization of MCT1 with its ancillary protein, CD147 in the caprine gastrointestinal tract. In vivo and in vitro functional studies, under the influence of the MCT1 inhibitors, p-chloromercuribenzoate (pCMB) and p-chloromercuribenzoic acid (pCMBA), demonstrated significant inhibitory effect on acetate and propionate transport in the rumen. This study provides evidence, for the first time in ruminants, that MCT1 has a direct role in the transepithelial transport and efflux of the SCFA across the stratum spinosum and stratum basale of the forestomach toward the blood side.

Monocarboxylate transporter 1 (MCT1) mediates transport of short-chain fatty acids in bovine caecum

The present study was undertaken to investigate the functional role of monocarboxylate transporter 1 (MCT1) in the ruminant large intestine. Messenger RNA encoding for MCT1 was verified by reverse transcriptase-polymerase chain reaction in caecum, proximal colon and distal colon of adult cattle. Both immunohistochemistry and confocal laser microscopy verified that the MCT1 protein was abundant in the surface epithelium of the large intestine, and the amount decreased from the opening of the crypt to its base. In the immunopositive cells, MCT1 was primarily localized in the basolateral membranes of epithelium lining the large intestine. Western blotting indicated that the levels of MCT1 protein were highest in the caecum, followed by proximal colon and then distal colon. In vitro studies were conducted to elucidate the possible involvement of MCT1 in the transport of short-chain fatty acids (SCFA) across the isolated mucosal sheets of cattle caecum using the Ussing chamber technique. Acetate absorption was found to be pH dependent, and the rate of acetate absorption increased as pH decreased. The serosal application of the MCT1 inhibitor 'p-chloromercuribenzoic acid (pCMB)' significantly reduced the transport of acetate across the caecal epithelium of cows. In addition, the transport of acetate was significantly reduced in the presence of its analogue, propionate, indicating that acetate and propionate compete for binding to the same transporter. The results show that MCT1 is a major route for SCFA efflux across the basolateral membrane of bovine large intestine and that it could play a role in the regulation of intracellular pH.

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.