Expression Of Monocarboxylate Transporter 2 Research Articles

Effects of Fibroblast Growth Factor 21 on Lactate Uptake and Usage in Mice with Diabetes-Associated Cognitive Decline

Fibroblast growth factor 21 (FGF21) is an endocrine hormone that exerts beneficial effects on glucose and lipid metabolic homeostasis. However, the impact of FGF21 on type 1 diabetes-associated cognitive decline (DACD) and its mechanisms of action remain unclear. In this study, we aimed to evaluate the effects of FGF21 on lactate uptake and usage in a mouse model of streptozotocin-induced DACD. Six-week-old male C57BL/6 mice were divided into the control, diabetic, and FGF21 (which received 2mg/kg recombinant human FGF21) groups. At the end of the treatment period, learning and memory performance, nuclear magnetic resonance-based metabonomics, and expressions of various hippocampal protein were analyzed to determine the efficacy of FGF21. The results showed that compared to the control mice, the diabetic mice had reduced long-term memory performance after the hyperglycemic insult; decreased hippocampal levels of lactate dehydrogenase-B (LDH-B) activity, bioenergy metabolites, and monocarboxylate transporter 2 (MCT2); and increased lactate levels. Impaired phosphoinositide 3-kinase (PI3K) signaling was also observed in the diabetic mice. However, FGF21 treatment improved LDH-B activity, β-nicotinamide adenine dinucleotide, and ATP levels, and increased MCT2 expression and PI3K signaling pathway, which in turn improved the learning and memory defects. These findings demonstrated that the effects of FGF21 on DACD were associated with its ability to improve LDH-B-mediated lactate usage and MCT2-dependent lactate uptake. Further, these beneficial effects of FGF21 in the hippocampus were mediated by the PI3K signaling pathways.

MCT2 overexpression promotes recovery of cognitive function by increasing mitochondrial biogenesis in a rat model of stroke

ABSTRACT Monocarboxylate transporter 2 (MCT2) is the predominant monocarboxylate transporter expressed by neurons. MCT2 plays an important role in brain energy metabolism. Stroke survivors are at high risk of cognitive impairment. We reported previously that stroke-induced cognitive impairment was related to impaired energy metabolism. In the present study, we report that cognitive function was impaired after stroke in rats. We found that MCT2 expression, but not that of MCT1 or MCT4, was markedly decreased in the rat hippocampus at 7 and 28 days after transient middle cerebral artery occlusion (tMCAO). Moreover, MCT2 overexpression promoted recovery of cognitive function after stroke. The molecular mechanism underlying these effects may be related to an increase in adenosine monophosphate-activated protein kinase-mediated mitochondrial biogenesis induced by overexpression of MCT2. Our findings suggest that MCT2 activation ameliorates cognitive impairment after stroke.

유산소운동이 당뇨쥐 해마의 신경세포 LDH 동위효소, MCT2 및 GLUT3 단백질 발현에 미치는 영향

In the present study, the effects of aerobic exercise on expression of Lactate dehydrogenase (LDH) isozymes, Monocarboxylate transporter2 (MCT2) and Glucose transporter3 (GLUT3) in hippocampal neuron of Streptozotocin (STZ)-induced diabetic rats. The experimental animals were divided into three groups (n=10 in each group): the normal control group (CON), the diabetes mellitus group (DM), the diabetes and exercise group(DM-Ex). Animals in the exercise group were submitted to daily exercise in the water pool during 4weeks. Native polyacrylamide gel electrophoresis analysis for the purification of LDH isozyme was performed. Western blotting and immunohistochemistry analysis for the expression of MCT2 and GLUT3 was performed. Here in this study, LDH A4 and LDH A3B in DM were predominantly expressed compared to DM-Ex (p<.05), and LDH AB3 and LDH B4 in DM-Ex were predominantly expressed compared to DM (p<.05). MCT2 activity of DM and DM-Ex were significantly lower than that of CON (p<.05). MCT2 activity of DM-Ex was significantly higher than that of DM (p<.05). GLUT3 activity of DM and DM-Ex were significantly lower than that of CON (p<.05). GLUT3 activity of DM-Ex was significantly higher than that of DM (p<.05). The results of the present study indicate that aerobic exercise affects the production of ATP using lactic acid and the activity of neurons by adapting to the energy metabolic demands of diabetes in the hippocampal neurons.

Acupuncture up-regulates MCT2 expression of peri-ischemic cortex in middle cerebral artery occlusion rats

To observe the effect of manual acupuncture (MA)＋ electroacupuncture (EA) on changes of neurological function and expression of monocarboxylate transporter 2(MCT2)in cerebral ischemia (CI) rats, so as to explore its mechanism underlying improvement of ischemic cerebrovascular disease. Eighty male Wistar rats were equally randomized into four groups: normal control (normal), sham operation (sham), model and acupuncture. The CI model was induced by middle cerebral artery occlusion (MCAO) with a thread embolus. Manual acupuncture stimulation (mild twisting reinforcing-reducing method) was applied to "Baihui"(GV20)and "Fengfu"(GV16) for 10 min. EA (1 mA, 2 Hz /15 Hz) was respectively applied to bilateral "Quchi" (LI11) and "Zusanli"(ST36) for 20 min, once per day for 7 days. The neurological deficit severity was evaluated according to Zea Longa's methods. The activity of lactate dehydrogenase (LDH), fructose-6-phosphate kinase (PFK) and pyruvate kinase (PK) in the peri-ischemic cortex tissue was detected by enzymatic chemistry, and the expression of MCT2 detected by immunofluorescence histochemistry, Western blot and quantitative real-time PCR, separately. After CI and in comparison with the normal and sham groups, the Zea Longa's score, the fluorescence intensity and the expression level of MCT2 protein were significantly increased (P<0.01), and the activity of LDH, PFK and PK in the peri-ischemic cortex was significantly decreased in the model group (P<0.01). There was no significant change in the relative expression of MCT2 mRNA (P>0.05). Following the intervention and in comparison with the model group, the Zea Longa's score was considerably decreased in the acupuncture group (P<0.01), the activity of LDH, PFK and PK，and the expression levels of MCT2 protein and mRNA were considerably or further up-regulated in the acupuncture group (P<0.01, P<0.05). Acupuncture intervention can improve neurological function in CI rats, which is possibly related with its effects in up-regulating the expression of MCT2 and promoting the utilization of lactate in peri-ischemic cortex.

Curcumin Ameliorates Memory Deficits by Enhancing Lactate Content and MCT2 Expression in APP/PS1 Transgenic Mouse Model of Alzheimer's Disease.

Curcumin is a natural product with several anti-Alzheimer's disease (AD) neuroprotective properties. This study aimed to investigate the effects of curcumin on memory deficits, lactate content, and monocarboxylate transporter 2 (MCT2) in APP/PS1 mouse model of AD. APP/PS1 transgenic mice and wild-type (WT) C57BL/6J mice were used in the present study. Spatial learning and memory of the mice was detected using Morris water-maze test. Cerebral cortex and hippocampus lactate contents were detected using lactate assay. MCT2 expression in the cerebral cortex and hippocampus was examined by immunohistochemistry and Western blotting. Results showed that spatial learning and memory deficits were improved in curcumin-treated APP/PS1 mouse group compared with those in APP/PS1 mice group. Brain lactate content and MCT2 protein level were increased in curcumin-treated APP/PS1 mice than in APP/PS1 mice. In summary, our findings indicate that curcumin could ameliorate memory impairments in APP/PS1 mouse model of AD. This phenomenon may be at least partially due to its improving effect on the lactate content and MCT2 protein expression in the brain. Anat Rec, 302:332-338, 2019. © 2018 Wiley Periodicals, Inc.

Exercise-induced expression of monocarboxylate transporter 2 in the cerebellum and its contribution to motor performance

Monocarboxylate transporter 2 (MCT2) is an important component of the lactate transport system in neurons of the adult brain. Purkinje cells in the cerebellum have been shown to have high levels of MCT2, suggesting that this protein has a key function in energy metabolism and neuronal activities in these cells. However, it is not known whether inhibition of lactate transport via MCT2 in the cerebellum affects motor performance. To address this question, we examined motor performance in mice following the inhibition of lactate transport via MCT2 in the cerebellum using α-cyano-4-hydroxycinnamate (4-CIN). 4-CIN or saline was injected into the subarachnoidal space of the cerebellum of mice and motor performance was analyzed by a rotarod test both before and after injection. 4-CIN injection reduced retention time in the rotarod test by approximately 80% at 1h post-injection compared with pre-injection. No effect was observed at 2h post-injection or in mice treated with the vehicle control. Because we observed that MCT2 plays an important role in motor performance, we next investigated the effects of acute exercise on MCT2 transcription and protein levels in mice sampled pre-exercise and at 0 and 5h after 2h of treadmill running. We found a significant increase in MCT2 mRNA levels, but not of protein levels, in the cerebellum at 5h after exercise. Our results indicate that lactate transport via MCT2 in the cerebellum may play an important role in motor performance and that exercise can increase MCT2 expression at the transcriptional level.

Role of spinal monocarboxylate transporter-2 in development of acute inflammatory pain in mice

Objective To investigate the role of spinal monocarboxylate transporter-2 (MCT-2) in the development of acute inflammatory pain in mice. Methods Thirty-two male adult Kunming mice, weighing 20-25 g, were divided into 4 groups (n=8 each) using a random number table: control group (group C), inflammatory pain group (group IP), MCT-2 inhibitor α-cyano-4-hydroxy-cinnamate group (group 4-CIN), and dimethyl sulfoxide group (group D). In IP, 4-CIN and DMSO groups, the inflammatory pain was induced by injection of 5% formalin 10 μl into the plantar surface of the right hindpaw.At 30 min before formalin injection, the artificial cerebrospinal fluid, 4-CIN (100 μmol) and 10% DMSO 5 μl were injected intrathecally over 10 s in IP, 4-CIN and DMSO groups, respectively.Pain behavior was scored within 60 min after establishment of the model.The lumbar segment of the spinal cord was harvested at 60 min after establishment of the model for detection of the expression of MCT-2 by Western blot analysis. Results Compared with group C, the pain behavior score was significantly increased in phaseⅠand phase Ⅱ, and the expression of MCT-2 was up-regulated in IP, 4-CIN and DMSO groups (P 0.05). Conclusion Spinal MCT-2 is involved in the development of acute inflammatory pain in mice. Key words: Monocarboxylic acid transporters; Spinal cord; Inflammation; Pain

Localization of MCT2 at peroxisomes is associated with malignant transformation in prostate cancer.

Previous studies on monocarboxylate transporters expression in prostate cancer (PCa) have shown that monocarboxylate transporter 2 (MCT2) was clearly overexpressed in prostate malignant glands, pointing it out as a putative biomarker for PCa. However, its localization and possible role in PCa cells remained unclear. In this study, we demonstrate that MCT2 localizes mainly at peroxisomes in PCa cells and is able to take advantage of the peroxisomal transport machinery by interacting with Pex19. We have also shown an increase in MCT2 expression from non-malignant to malignant cells that was directly correlated with its peroxisomal localization. Upon analysis of the expression of several peroxisomal β-oxidation proteins in PIN lesions and PCa cells from a large variety of human prostate samples, we suggest that MCT2 presence at peroxisomes is related to an increase in β -oxidation levels which may be crucial for malignant transformation. Our results present novel evidence that may not only contribute to the study of PCa development mechanisms but also pinpoint novel targets for cancer therapy.

Monocarboxylate transporter 2 (MCT2) as putative biomarker in prostate cancer

Monocarboxylate transporter 2 (MCT2) is a transmembrane protein involved in the transport of monocarboxylates such as pyruvate and lactate. In a previous study we described overexpression of MCT2 in prostate carcinoma raising the hypothesis of using MCT2 as a possible biomarker in prostate cancer. With the present study we aimed to compare the pattern of expression of MCT2 and alpha-methylacyl-CoA racemase (AMACR), in prostate carcinoma, PIN lesions, non-neoplastic prostate tissue, and normal prostate and compare their sensitivity and specificity. Also, we wanted to evaluate the value of using MCT2 in combination with AMACR and the negative markers 34βE12 or p63 to detect prostate cancer. A total of 349 cases, including prostate carcinoma, non-neoplastic prostate tissue and PIN lesions, from radical prostatectomies were examined by immunohistochemistry for AMACR, MCT2, p63, and 34βE12, using tissue microarrays (TMAs). Normal prostate from radical cystoprostatectomy was also studied. Our study revealed that MCT2, similarly to AMACR, was consistently expressed in prostate cancer regardless of the Gleason score. In combination with AMACR and p63 or 34βE12, MCT2 helped to improve the diagnosis of prostate carcinoma. Also, overexpression of MCT2 as well as AMACR in PIN lesions may indicate the involvement of these two proteins in prostate cancer initiation. We provided evidence for the presence of MCT2 in prostate cancer, selectively labeling malignant glands. Importantly, assessment of MCT2 together with AMACR, along with the negative markers, highly increases the accuracy in prostate cancer diagnosis.

The inhibition of monocarboxylate transporter 2 (MCT2) by AR-C155858 is modulated by the associated ancillary protein

In mammalian cells, MCTs (monocarboxylate transporters) require association with an ancillary protein to enable plasma membrane expression of the active transporter. Basigin is the preferred binding partner for MCT1, MCT3 and MCT4, and embigin for MCT2. In rat and rabbit erythrocytes, MCT1 is associated with embigin and basigin respectively, but its sensitivity to inhibition by AR-C155858 was found to be identical. Using RT (reverse transcription)–PCR, we have shown that Xenopus laevis oocytes contain endogenous basigin, but not embigin. Co-expression of exogenous embigin was without effect on either the expression of MCT1 or its inhibition by AR-C155858. In contrast, expression of active MCT2 at the plasma membrane of oocytes was significantly enhanced by co-expression of exogenous embigin. This additional transport activity was insensitive to inhibition by AR-C155858 unlike that by MCT2 expressed with endogenous basigin that was potently inhibited by AR-C155858. Chimaeras and C-terminal truncations of MCT1 and MCT2 were also expressed in oocytes in the presence and absence of exogenous embigin. L-Lactate Km values for these constructs were determined and revealed that the TM (transmembrane) domains of an MCT, most probably TM7–TM12, but not the C-terminus, are the major determinants of L-lactate affinity, whereas the associated ancillary protein has little or no effect. Inhibitor titrations of lactate transport by these constructs indicated that embigin modulates MCT2 sensitivity to AR-C155858 through interactions with both the intracellular C-terminus and TMs 3 and 6 of MCT2. The C-terminus of MCT2 was found to be essential for its expression with endogenous basigin.

Noradrenaline enhances the expression of the neuronal monocarboxylate transporter MCT2 by translational activation via stimulation of PI3K/Akt and the mTOR/S6K pathway

Monocarboxylate transporter 2 (MCT2) expression is up-regulated by noradrenaline (NA) in cultured cortical neurons via a putative but undetermined translational mechanism. Western blot analysis showed that p44/p42 mitogen-activated protein kinase (MAPK) was rapidly and strongly phosphorylated by NA treatment. NA also rapidly induced serine/threonine protein kinase from AKT virus (Akt) phosphorylation but to a lesser extent than p44/p42 MAPK. However, Akt activation persisted over a longer period. Similarly, NA induced a rapid and persistent phosphorylation of mammalian target of rapamycin (mTOR), a kinase implicated in the regulation of translation in the central nervous system. Consistent with activation of the mTOR/S6 kinase pathway, phosphorylation of the ribosomal S6 protein, a component of the translation machinery, could be observed upon treatment with NA. In parallel, it was found that the NA-induced increase in MCT2 protein was almost completely blocked by LY294002 (phosphoinositide 3-kinase inhibitor) as well as by rapamycin (mTOR inhibitor), while mitogen-activated protein kinase kinase and p38 MAPK inhibitors had much smaller effects. Taken together, these data reveal that NA induces an increase in neuronal MCT2 protein expression by a mechanism involving stimulation of phosphoinositide 3-kinase/Akt and translational activation via the mTOR/S6 kinase pathway. Moreover, considering the role of NA in synaptic plasticity, alterations in MCT2 expression as described in this study might represent an adaptation to face energy demands associated with enhanced synaptic transmission.

Induction of Monocarboxylate Transporter 2 Expression and Ketone Transport following Traumatic Brain Injury in Juvenile and Adult Rats

Based on recent work demonstrating age-dependent ketogenic neuroprotection after traumatic brain injury (TBI), it was hypothesized that the neuroprotection among early post-weaned animals was related to induced cerebral transport of ketones after injury. Regional changes in monocarboxylate transporter 2 (MCT2) were acutely examined with immunohistochemistry after sham surgery or controlled cortical impact injury among postnatal day 35 and adult rats. Both ages showed elevated MCT2 expression in the ipsilateral cerebral vasculature after TBI. Using Western blotting, MCT2 expression was 80–88% greater in microvessels isolated from postnatal day 35 rats at all time points relative to adults. The increased MCT2 expression was temporally correlated with an age-related increase in cerebral uptake of ketones, when ketones were made available after injury.

Vagal complex monocarboxylate transporter-2 expression during hypoglycemia

Astrocytic provision of lactate provision to neurons may be a critical indicator of substrate fuel availability in metabolic sensing sites in the brain, including the hindbrain dorsal vagal complex. We examined the hypothesis that vagal complex monocarboxylate transporter protein levels are gender dependent and estrogen dependent, and that estrogen influences adaptation of these protein responses during repeated insulin-induced hypoglycemia. Western blot analyses showed that male and estrogen-treated ovariectomized female rats exhibit opposite changes in monocarboxylate transporter-2 levels after one insulin injection, as well as divergent patterns of adaptation to this metabolic challenge. The data suggest that sex differences in hypoglycemic patterns in vagal complex lactate transport may underlie disparate signaling of cellular energy imbalance.

Developmental and hormonal regulation of the monocarboxylate transporter 2 (MCT2) expression in the mouse germ cells.

During spermatogenesis, postmeiotic germ cells utilize lactate produced by Sertoli cells as an energy metabolite. While the hormonal regulation of lactate production in Sertoli cells has been relatively well established, the transport of this energy substrate to the germ cells, particularly via the monocarboxylate transporters (MCTs), as well as the potential endocrine control of such a process remain to be characterized. Here, we report the developmentally and hormonally regulated expression of MCT2 in the testis. At Day 18, MCT2 starts to be expressed in germ cells as detected by Northern blot. The mRNA are translated into protein (40 kDa) in elongating spermatids. Ultrastructural analysis demonstrated that MCT2 protein is localized to the outer face of the cell membrane of spermatid tails. MCT2 mRNA levels are under the control of the endocrine, specifically follicle-stimulating hormone (FSH) and testosterone, and paracrine systems. Indeed, a 35-day-old rat hypophysectomy resulted in an 8-fold increase in testicular MCT2 mRNA levels. Conversely, FSH and LH administration to the hypophysectomized rats reduced MCT2 mRNA levels to the basal levels observed in intact animals. The decrease in MCT2 mRNA levels was confirmed in vitro using isolated seminiferous tubules incubated with FSH or testosterone. FSH or testosterone inhibited in a dose-dependent manner MCT2 mRNA levels with maximal inhibitory doses of 2.2 ng/ml and 55.5 ng/ml for FSH and testosterone, respectively. In addition to the endocrine control, TNFalpha and TGFbeta also exerted an inhibitory effect on MCT2 mRNA levels with a maximal effect at 10 ng/ml and 6.6 ng/ml for TGFbeta and TNFalpha, respectively. Together with previous studies, the present data reinforce the concept that among the key functions of the endocrine/paracrine systems in the testis is the control of the energy metabolism occurring in the context of Sertoli cell-germ cell metabolic cooperation where lactate is produced in somatic cells and transported to germ cells via, at least, MCT2.

A novel postsynaptic density protein: the monocarboxylate transporter MCT2 is co-localized with δ-glutamate receptors in postsynaptic densities of parallel fiber-Purkinje cell synapses

Confocal immunofluorescence microscopy showed strong monocarboxylate transporter 2 (MCT2) labeling of Purkinje cell bodies and punctate labeling in the molecular layer. By immunogold cytochemistry, it could be demonstrated that the MCT2 immunosignal was concentrated at postsynaptic densities of parallel fiber-Purkinje cell synapses. The distribution of MCT2 transporters within the individual postsynaptic densities mimicked that of the delta2 glutamate receptor, as shown by use of two different gold-particle sizes. The MCT2 distribution was also compared with the distributions of other monocarboxylate transporters (MCT1 and MCT4). The MCT1 immunolabeling was localized in the endothelial cells, while MCT4 immunogold particles were associated with glial profiles, including those abutting the synaptic cleft of the parallel fiber-spine synapses. The postsynaptic density (PSD) molecules identified so far can be divided into five classes: receptors, their anchoring molecules, molecules involved in signal transduction, ion channels, and attachment proteins. Here, we provide evidence that this list of molecules must now be extended to comprise an organic molecule transporter: the monocarboxylate transporter MCT2. The present data suggest that MCT2 has specific transport functions related to the synaptic cleft and that this transporter may allow an influx of lactate derived from perisynaptic glial processes. The expression of MCT2 in synaptic membranes may allow energy supply to be tuned to the excitatory drive.

2. A novel postsynaptic density protein: the monocarboxylate transporter MCT2is colocalized with glutamate receptors in postsynaptic densities of parallel fiber-Purkinje cell synapses

Confocal immunofluorescence microscopy showed strong monocarboxylate transporter 2 (MCT2) labeling of Purkinje cell bodies and punctate labeling in the molecular layer. By immunogold cytochemistry, it could be demonstrated that the MCT2 immunosignal was concentrated at postsynaptic densities of parallel fiber–Purkinje cell synapses. The distribution of MCT2 transporters within the individual postsynaptic densities mimicked that of the δ2 glutamate receptor, as shown by use of two different gold-particle sizes. The MCT2 distribution was also compared with the distributions of other monocarboxylate transporters (MCT1 and MCT4). The MCT1 immunolabeling was localized in the endothelial cells, while MCT4 immunogold particles were associated with glial profiles, including those abutting the synaptic cleft of the parallel fiber-spine synapses. The postsynaptic density (PSD) molecules identified so far can be divided into five classes: receptors, their anchoring molecules, molecules involved in signal transduction, ion channels, and attachment proteins. Here, we provide evidence that this list of molecules must now be extended to comprise an organic molecule transporter: the monocarboxylate transporter MCT2. The present data suggest that MCT2 has specific transport functions related to the synaptic cleft and that this transporter may allow an influx of lactate derived from perisynaptic glial processes. The expression of MCT2 in synaptic membranes may allow energy supply to be tuned to the excitatory drive.