Monocarboxylic Acid Transporter Research Articles

Recent Advances In Developing Novel Anti-Cancer Drugs Targeting Tumor Hypoxic and Acidic Microenvironments.

Solid tumors often contain hypoxic microenvironments due to abnormal vasculatures and outweighing demands of oxygen. Cancer cells rely on anaerobic respiration, leading to sequential acidic microenvironments. Hypoxic and acidic microenvironments cause genetic instability and activate signaling pathways, contributing to cancer progression and therapy resistance, and have become targets for developing novel anti-cancer agents. This article reviews recent advances in the development of novel anti-cancer drugs targeting hypoxic and acidic microenvironments. Recent patents and published literature related to anti-cancer agents targeting tumor hypoxic and acidic microenvironments were searched and reviewed. Key termed used in the searching included cancer, anti-cancer drug, neoplasm, clinical trials, tumor microenvironment, hypoxic microenvironment, acidic microenvironment, hypoxia-inducible factors, hypoxia; metabolism; Warburg effect and aerobic glycolysis. A number of Hypoxia-Inducible Factor (HIF) inhibitors have been developed or discovered, but most of them have only exhibited indirect effects on HIFs, and a limited number of drugs are able to directly interfere with mRNA and protein of HIFs, the dimerization of α and β subunits, or the interaction between HIFs and its activators. The development of agents targeting acidic microenvironments focuses on V-ATPase, monocarboxylic acid transporters, Na+/H+ exchangers and carbonic anhydrases. Proton pump inhibitors as V-ATPase inhibitors have been applied in treating various tumors as an adjuvant therapy, but none of the other inhibitors has been approved for cancer treatment. Developing more specific agents, and seeking sensitive, applicable and accurate biomarkers may improve the efficacy of drugs targeting hypoxic and acidic microenvironments.

Propionate and butyrate induce gene expression of monocarboxylate transporter 4 and cluster of differentiation 147 in cultured rumen epithelial cells derived from preweaning dairy calves.

Short-chain fatty acids (SCFAs) are the main source of energy for postweaning ruminants. The monocarboxylic acid transporters, MCT1 and MCT4, are thought to contribute to the absorption of SCFAs from the surface of the rumen following weaning. The present study measured changes in MCT1 and MCT4 expression in ruminal epithelial cells isolated from male preweaning (22 to 34 d old, n = 6) and postweaning (55 to 58 d old, n = 8) calves after euthanasia and sought to examine whether SCFAs stimulate the expression of these transporters. In the current study, cluster of differentiation 147 (CD147) gene expression in the rumen was also investigated since CD147 has been considered to act as ancillary protein for MCT1 and MCT4 to express their correct function. The gene expression levels of MCT1, MCT4, and CD147 in the rumen were found to be significantly higher in postweaning calves than in preweaning calves. Strong MCT1 immunoreactivity was detected in both the stratum basale (SB) and the stratum spinosum (SS) in postweaning ruminal epithelium. Expression of MCT1 in preweaning calves was localized to a specific region of the SB and of the SS. MCT4-immunopositive cells were detected in the stratum corneum (SC) of the ruminal epithelium in postweaning calves. However, only a low level of signal was detected in the SC of preweaning animals. Furthermore, in vitro experiments, ruminal epithelial cells were incubated for 24 h with acetate (0.04, 0.4, and 4 mM), propionate (0.2, 2, and 20 mM), butyrate (0.1, 1, and 10 mM), or β-hydroxybutyrate (BHBA; 0.1, 1, and 10 mM), respectively. Both propionate and butyrate induced an increase in the gene expression levels of MCT4 and CD147, but did not affect MCT1 gene expression. There are no significant effects of acetate and BHBA treatment on these gene expressions. Taken together, these results suggest that an increase in MCT4 and CD147 gene expression in the ruminal epithelium of postweaning calves is likely to be due to the effects of propionate and butyrate derived from a solid-based diet, which may contribute to ruminal development following weaning.

Downregulation of MCT4 for lactate exchange promotes the cytotoxicity of NK cells in breast carcinoma

Monocarboxylate transporter‐4 (MCT4), a monocarboxylic acid transporter, demonstrates significantly increased expression in the majority of malignancies. We performed an experiment using BALB/C mice, and our results showed that ShMCT4 transfection or the pharmaceutic inhibition of MCT4 with 7acc1 strengthens the activity of NK cells. The results of a calcein assay revealed that the cytotoxicity of NK cells was strengthened via inhibition of MCT4. In addition, ELISA testing showed that the content of perforin and CD107a was increased, and PCR amplification and immunoblotting revealed that the expression of NKG2D and H60 was upregulated after the inhibition of MCT4. Further, we observed an elevated pH value, decreased extracellular lactate flow, and attenuated tumor growth. Therefore, we concluded that the inhibition of MCT4 enhanced the cytotoxicity of NK cells by blocking lactate flux and reversing the acidified tumor microenvironment. In addition to these findings, we also discovered that MCT4 depletion may have a pronounced impact on autophagy, which was surmised by observing that the inhibition of autophagy (3MA) pulled the enhanced cytotoxicity of NK cells downwards. Together, these data suggest that the key effect of MCT4 depletion on NK cells probably utilizes inductive autophagy as a compensatory metabolic mechanism to minimize the acidic extracellular microenvironment associated with lactate export in tumors.

Altered gene transcription linked to astrocytes and oligodendrocytes in frontal cortex in Creutzfeldt-Jakob disease

ABSTRACTTargeted expression of genes coding for proteins specific to astrocytes, oligodendrocytes and myelin was performed in frontal cortex area 8 of Creutzfeldt-Jakob disease methionine/methionine and valine/valine (CJD MM1 and VV2, respectively) compared with controls. GFAP (glial fibrillary acidic protein) mRNA was up-regulated whereas SLC1A2 (solute carrier family 1 member 2, coding for glutamate transporter 1: GLT1), AQ4 (aquaporin 4), MPC1 (mitochondrial pyruvate carrier 1) and UCP5 (mitochondrial uncoupled protein 5) mRNAs were significantly down-regulated in CJD MM1 and CJD VV2, and GJA1 (connexin 43) in CJD VV2. OLIG1 and OLIG2 (oligodendocyte transcription factor 1 and 2, respectively), SOX10 (SRY-Box10) and oligodendroglial precursor cell (OPC) marker NG2 (neuronal/glial antigen) 2 were preserved, but GALC (coding for galactosylceramidase), SLC2A1 (solute carrier family 2 member 1: glucose transporter member 1: GLUT1) and MCT1 (monocarboxylic acid transporter 1) mRNA expression levels were significantly reduced in CJD MM1 and CJD VV2. Expression levels of most genes linked to myelin were not altered in the cerebral cortex in CJD. Immunohistochemistry to selected proteins disclosed individual variations but GFAP, Olig-2, AQ4 and GLUT1 correlated with mRNA levels, whereas GLT1 was subjected to individual variations. However, MPC1, UCP5 and MCT1 decrease was more closely related to the respective reduced neuronal immunostaining. These observations support the idea that molecular deficits linked to energy metabolism and solute transport in astrocytes and oligodendrocytes, in addition to neurons, are relevant in the pathogenesis of cortical lesions in CJD.

Beta-hydroxybutyrate (3-OHB) can influence the energetic phenotype of breast cancer cells, but does not impact their proliferation and the response to chemotherapy or radiation

BackgroundKetogenic diets (KDs) or short-term fasting are popular trends amongst supportive approaches for cancer patients. Beta-hydroxybutyrate (3-OHB) is the main physiological ketone body, whose concentration can reach plasma levels of 2–6 mM during KDs or fasting. The impact of 3-OHB on the biology of tumor cells described so far is contradictory. Therefore, we investigated the effect of a physiological concentration of 3 mM 3-OHB on metabolism, proliferation, and viability of breast cancer (BC) cells in vitro.MethodsSeven different human BC cell lines (BT20, BT474, HBL100, MCF-7, MDA-MB 231, MDA-MB 468, and T47D) were cultured in medium with 5 mM glucose in the presence of 3 mM 3-OHB at mild hypoxia (5% oxygen) or normoxia (21% oxygen). Metabolic profiling was performed by quantification of the turnover of glucose, lactate, and 3-OHB and by Seahorse metabolic flux analysis. Expression of key enzymes of ketolysis as well as the main monocarboxylic acid transporter MCT2 and the glucose-transporter GLUT1 was analyzed by RT-qPCR and Western blotting. The effect of 3-OHB on short- and long-term cell proliferation as well as chemo- and radiosensitivity were also analyzed.Results3-OHB significantly changed the oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) in BT20 cells resulting in a more oxidative energetic phenotype. MCF-7 and MDA-MB 468 cells had increased ECAR only in response to 3-OHB, while the other three cell types remained uninfluenced. All cells expressed MCT2 and GLUT1, thus being able to uptake the metabolites. The consumption of 3-OHB was not strongly linked to mRNA overexpression of key enzymes of ketolysis and did not correlate with lactate production and glucose consumption. Neither 3-OHB nor acetoacetate did interfere with proliferation. Further, 3-OHB incubation did not modify the response of the tested BC cell lines to chemotherapy or radiation.ConclusionsWe found that a physiological level of 3-OHB can change the energetic profile of some BC cell lines. However, 3-OHB failed to influence different biologic processes in these cells, e.g., cell proliferation and the response to common breast cancer chemotherapy and radiotherapy. Thus, we have no evidence that 3-OHB generally influences the biology of breast cancer cells in vitro.

BSG and MCT1 Genetic Variants Influence Survival in Multiple Myeloma Patients.

Multiple myeloma (MM) is a haematologic malignancy characterized by the presence of atypical plasma cells. Basigin (BSG, CD147) controls lactate export through the monocarboxylic acid transporter 1 (MCT1, SLC16A1) and supports MM survival and proliferation. Additionally, BSG is implicated in response to treatment with immunomodulatory drugs (thalidomide and its derivatives). We investigated the role of single nucleotide polymorphisms (SNPs) in the gene coding for BSG and SLC16A1 in MM. Following an in silico analysis, eight SNPs (four in BSG and four in SLC16A1) predicted to have a functional effect were selected and analyzed in 135 MM patients and 135 healthy individuals. Alleles rs4919859 C, rs8637 G, and haplotype CG were associated with worse progression-free survival (p = 0.006, p = 0.017, p = 0.002, respectively), while rs7556664 A, rs7169 T and rs1049434 A (all in linkage disequilibrium (LD), r2 > 0.98) were associated with better overall survival (p = 0.021). Similar relationships were observed in thalidomide-treated patients. Moreover, rs4919859 C, rs8637 G, rs8259 A and the CG haplotype were more common in patients in stages II–III of the International Staging System (p < 0.05), while rs8259 A correlated with higher levels of β-2-microglobulin and creatinine (p < 0.05). Taken together, our results show that BSG and SLC16A1 variants affect survival, and may play an important role in MM.

Activity-dependent neuronal Klotho enhances astrocytic aerobic glycolysis

Mutations of the β-glucuronidase protein α-Klotho have been associated with premature aging, and altered cognitive function. Although highly expressed in specific areas of the brain, Klotho functions in the central nervous system remain unknown. Here, we show that cultured hippocampal neurons respond to insulin and glutamate stimulation by elevating Klotho protein levels. Conversely, AMPA and NMDA antagonism suppress neuronal Klotho expression. We also provide evidence that soluble Klotho enhances astrocytic aerobic glycolysis by hindering pyruvate metabolism through the mitochondria, and stimulating its processing by lactate dehydrogenase. Pharmacological inhibition of FGFR1, Erk phosphorylation, and monocarboxylic acid transporters prevents Klotho-induced lactate release from astrocytes. Taken together, these data suggest Klotho is a potential new player in the metabolic coupling between neurons and astrocytes. Neuronal glutamatergic activity and insulin modulation elicit Klotho release, which in turn stimulates astrocytic lactate formation and release. Lactate can then be used by neurons and other cells types as a metabolic substrate.

Association between Alzheimer's disease pathogenesis and early demyelination and oligodendrocyte dysfunction.

The APPSwe/PSEN1dE9 (APP/PS1) transgenic mouse model is an Alzheimer's disease mouse model exhibiting symptoms of dementia, and is commonly used to explore pathological changes in the development of Alzheimer's disease. Previous clinical autopsy and imaging studies suggest that Alzheimer's disease patients have white matter and oligodendrocyte damage, but the underlying mechanisms of these have not been revealed. Therefore, the present study used APP/PS1 mice to assess cognitive change, myelin loss, and corresponding changes in oligodendrocytes, and to explore the underlying mechanisms. Morris water maze tests were performed to evaluate cognitive change in APP/PS1 mice and normal C57BL/6 mice aged 3 and 6 months. Luxol fast blue staining of the corpus callosum and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) for myelin basic protein (MBP) mRNA were carried out to quantify myelin damage. Immunohistochemistry staining for NG2 and qRT-PCR for monocarboxylic acid transporter 1 (MCT1) mRNA were conducted to assess corresponding changes in oligodendrocytes. Our results demonstrate that compared with C57BL/6 mice, there was a downregulation of MBP mRNA in APP/PS1 mice aged 3 months. This became more obvious in APP/PS1 mice aged 6 months accompanied by other abnormalities such as prolonged escape latency in the Morris water maze test, shrinkage of the corpus callosum, upregulation of NG2-immunoreactive cells, and downregulation of MCT1 mRNA. These findings indicate that the involvement of early demyelination at 3 months and the oligodendrocyte dysfunction at 6 months in APP/PS1 mice are in association with Alzheimer's disease pathogenesis.

Transcriptomics reveal an integrative role for maternal thyroid hormones during zebrafish embryogenesis

Thyroid hormones (THs) are essential for embryonic brain development but the genetic mechanisms involved in the action of maternal THs (MTHs) are still largely unknown. As the basis for understanding the underlying genetic mechanisms of MTHs regulation we used an established zebrafish monocarboxylic acid transporter 8 (MCT8) knock-down model and characterised the transcriptome in 25hpf zebrafish embryos. Subsequent mapping of differentially expressed genes using Reactome pathway analysis together with in situ expression analysis and immunohistochemistry revealed the genetic networks and cells under MTHs regulation during zebrafish embryogenesis. We found 4,343 differentially expressed genes and the Reactome pathway analysis revealed that TH is involved in 1681 of these pathways. MTHs regulated the expression of core developmental pathways, such as NOTCH and WNT in a cell specific context. The cellular distribution of neural MTH-target genes demonstrated their cell specific action on neural stem cells and differentiated neuron classes. Taken together our data show that MTHs have a role in zebrafish neurogenesis and suggest they may be involved in cross talk between key pathways in neural development. Given that the observed MCT8 zebrafish knockdown phenotype resembles the symptoms in human patients with Allan-Herndon-Dudley syndrome our data open a window into understanding the genetics of this human congenital condition.

Lactate Promotes Synthetic Phenotype in Vascular Smooth Muscle Cells.

The phenotypes of vascular smooth muscle cells (vSMCs) comprise a continuum bounded by predominantly contractile and synthetic cells. Some evidence suggests that contractile vSMCs can assume a more synthetic phenotype in response to ischemic injury, but the mechanisms that activate this phenotypic switch are poorly understood. To determine whether lactate, which increases in response to regional ischemia, may promote the synthetic phenotype in vSMCs. Experiments were performed with vSMCs that had been differentiated from human induced pluripotent stem cells and then cultured in glucose-free, lactate-enriched (L+) medium or in standard (L-) medium. Compared with the L- medium, the L+ medium was associated with significant increases in synthetic vSMC marker expression, proliferation, and migration and with significant declines in contractile and apoptotic activity. Furthermore, these changes were accompanied by increases in the expression of monocarboxylic acid transporters and were generally attenuated both by the blockade of monocarboxylic acid transporter activity and by transfection with iRNA for NDRG (N-myc downstream regulated gene). Proteomics, biomarker, and pathway analyses suggested that the L+ medium tended to upregulate the expression of synthetic vSMC markers, the production of extracellular proteins that participate in tissue construction or repair, and the activity of pathways that regulate cell proliferation and migration. Observations in hypoxia-cultured vSMCs were similar to those in L+-cultured vSMCs, and assessments in a swine myocardial infarction model suggested that measurements of lactate levels, lactate-dehydrogenase levels, vSMC proliferation, and monocarboxylic acid transporter and NDRG expression were greater in the ischemic zone than in nonischemic tissues. These results demonstrate for the first time that vSMCs assume a more synthetic phenotype in a microenvironment that is rich in lactate. Thus, mechanisms that link glucose metabolism to vSMC phenotypic switching could play a role in the pathogenesis and treatment of cardiovascular disease.

Abstract 1895: A conserved E2F1-activated gene regulatory network encompassing monocarboxylic acid transporter-1, its co-operating antisense lncRNA SLC16A1-AS1 and their common downstream targets mediates bladder cancer invasiveness

Abstract AIM: The therapeutic arsenal against muscle-invasive bladder cancer (BC) is poor, leading to fatal outcomes and necessitating next-generation targeted therapeutics. A causative event of BC progression is activation of the gene regulatory networks (GRN) of the transcription factor E2F1. LncRNAs are emerging integral components of the E2F1-regulated GRNs, but their implication in BC progression is unknown. Our study focuses on lncRNAs that participate in E2F1-activated GRNs underlying BC progression and the therapeutic exploitation thereof. METHODS: We applied bioinformatics on BC patient cohorts to identify clinically relevant lncRNAs upregulated in invasive stages. Of those, the E2F1-responsive lncRNAs were defined by subjecting T24 clones inducibly overexpressing E2F1 to HTA2.0 RNA arrays. Candidates in close proximity to oncogenes/tumor-suppressors were further selected, based on an emerging “guilt-by-association” rule of lncRNA biology. LncRNAs were qPCR-validated and E2F1-transactivation was shown by ChIP and reporter assays. The SLC16A1-AS1 lncRNA was functionally characterized by CRISPR/Cas9 knockout in invasive BC cells, followed by migration/invasion/metabolic assays, transcriptomics and mice in vivo experimentation. SLC16A1-AS1 homologues across species were predicted by comparative genomics. RESULTS: Our pipeline unveiled SLC16A1-AS1 lncRNA located nearby and antisense to SLC16A1 protein-coding gene. SLC16A1 synthesizes the membrane-bound Monocarboxylic Acid Transporter-1 (MCT1), a key metabolic regulator that mediates lactate uptake and glycolytic flux and favors BC invasiveness; while SLC16A1-AS1 function was unknown to date. SLC16A1 and SLC16A1-AS1 present a ‘head-to-head’ gene arrangement, with a bidirectional E2F1-responsive promoter. This ‘operon-like’ gene cluster is conserved across mammals, implying functional relevance of MCT1/E2F1/SLC16A1-AS1. In invasive BC cells, E2F1 transactivates SLC16A1-AS1, which remains in the nucleus exerting gene regulatory functions, as well as MCT1, which localizes in the cytoplasm to control lactate flux. SLC16A1-AS1 induces EMT-independent invasiveness by regulating expression of downstream cell migration-related targets which are co-modulated by MCT1. CONCLUSIONS: MCT1 and SLC16A1-AS1 constitute a composite, E2F1-responsive functional unit, co-operatively regulating common cell-migration related downstream targets. Their conserved gene arrangement, which ensures simultaneous transcription upon E2F1 upregulation, could facilitate co-ordination between metabolism reprogramming and cell migration to establish aggressive phenotypes. Combining SLC16A1-AS1 suppression with formulated MCT1 inhibitors might provide a therapeutic basis against progressive BC. Citation Format: Berdien A. Jansen, Stella Logotheti, Dirk Heckl, Jan-Henning Klusmann, Dirk Kozcan, Laila Taher, Georg Fuellen, David Engelmann, Brigitte Pützer. A conserved E2F1-activated gene regulatory network encompassing monocarboxylic acid transporter-1, its co-operating antisense lncRNA SLC16A1-AS1 and their common downstream targets mediates bladder cancer invasiveness [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1895. doi:10.1158/1538-7445.AM2017-1895

Effect of protein restriction followed by realimentation on growth, nutrient digestibility, ruminal parameters, and transporter gene expression in lambs

We report the effects of a protein-restricted diet and realimentation with a milk replacer (MR) and starter on the growth, digestibility, fermentation, and expression of the genes involved in volatile fatty acid (VFA) absorption in the lamb ruminal epithelium. Sixteen newborn twin Hu lamb pairs were used. Each pair was fed the MR and starter with a normal protein level (NPL, 250 and 210g/kg, respectively) or a low protein level (LPL, 190 and 150g/kg, respectively) from 15 to 60days of age (restriction period). Then, all lambs were fed the starter containing 210g crude protein/kg diet from 61 to 90days of age (realimentation period). Intake was measured daily, and body weight was measured at 15, 60, and 90days of age. Digestibility trials were carried out from 51 to 60 and from 81 to 90days of age with four lambs randomly selected from each group. Eight lambs from each group were slaughtered on 60 and 90days of age before morning feeding, and their ruminal fermentation parameters were measured. The expression levels of the genes involved in VFA absorption in ruminal epitheliums were measured. During the restriction period, feed intake did not differ between the groups (P=0.116). The final body weight (P=0.006) and the average daily gain (ADG; P=0.003) was greater, while the feed conversion ratio (P=0.011) was lower in the NPL group. No difference was observed in dry matter (P=0.894) and organic matter (P=0.495) digestibility, or the N retention/N intake (P=0.607). The ruminal pH of the lambs fed the LPL diets was greater (P=0.012). A decrease in ammonia content (P=0.023) and the total VFA concentration (P<0.001) was found in the LPL lambs. The molecular acetate content was greater in the LPL group (P=0.002), but that of propionate was lower (P=0.034). Protein restriction decreased the mRNA abundance of the transporters, anion exchanger 2 (P=0.019) and was downregulated in adenoma (P=0.025), Na+/H+ exchanger 1 (P=0.017), 2 (P=0.025), and 3 (P=0.037). After realimentation, body weight (P=0.006) and ADG (P=0.013) were lower in the lambs fed the LPL diet. The feed conversion ratio (P=0.301) was the same in the two groups. Lambs fed a LPL diet had a greater N retention/N intake (P=0.031). No difference was determined in the ruminal pH or the total VFA concentration between the groups (P=0.572). A greater mRNA level of monocarboxylic acid transporter 4 (P=0.021) and Na+/H+ exchanger 2 (P=0.049) was observed in the LPL group. These results suggest that realimentation partially recovers nutrient requirements and ruminal function, but lambs subjected to protein restriction still physically lag behind those continuously fed the NPL diet, indicating a permanent effect on later growth owing to nutrient restriction during very early life.

Uptake of perfluorooctanoic acid by Caco-2 cells: Involvement of organic anion transporting polypeptides

The mechanism underlying the intestinal absorption of perfluorooctanoic acid (PFOA) was investigated using Caco-2 cells. The uptake of PFOA from the apical membrane of Caco-2 cells was fast, and pH, temperature, and concentration dependent, but Na+ independent. Coincubation with sulfobromophthalein (BSP), glibenclamide, estron-3-sulfate, cyclosporine A or rifamycin SV, which are typical substrates or inhibitors of organic anion transporting polypeptides (OATPs), significantly decreased the uptake of PFOA. However, coincubation with probenecid or p-aminohippuric acid, typical substrates of organic anion transporters, did not decrease the uptake of PFOA. Furthermore, coincubation with l-lactic acid or benzoic acid, substrates of monocarboxylic acid transporters, did not decrease PFOA uptake. The relationship between the initial uptake of PFOA and its concentration was saturable, suggesting the involvement of a carrier-mediated process. The calculated Km and uptake clearance (Vmax/Km) values for PFOA were 8.3μM and 55.0μL/mg protein/min, respectively. This clearance value was about 3-fold greater than that of the non-saturable uptake clearance (Kd: 18.1μL/mg protein/min). Lineweaver–Burk plots revealed that BSP competitively inhibits the uptake of PFOA, with a Ki value of 23.1μM. These results suggest that the uptake of PFOA from the apical membranes of Caco-2 cells could be, at least in part, mediated by OATPs along with BSP.

Brain metabolism in health, aging, andneurodegeneration.

Brain cells normally respond adaptively to bioenergetic challenges resulting from ongoing activity in neuronal circuits, and from environmental energetic stressors such as food deprivation and physical exertion. At the cellular level, such adaptive responses include the "strengthening" of existing synapses, the formation of new synapses, and the production of new neurons from stem cells. At the molecular level, bioenergetic challenges result in the activation of transcription factors that induce the expression of proteins that bolster the resistance of neurons to the kinds of metabolic, oxidative, excitotoxic, and proteotoxic stresses involved in the pathogenesis of brain disorders including stroke, and Alzheimer's and Parkinson's diseases. Emerging findings suggest that lifestyles that include intermittent bioenergetic challenges, most notably exercise and dietary energy restriction, can increase the likelihood that the brain will function optimally and in the absence of disease throughout life. Here, we provide an overview of cellular and molecular mechanisms that regulate brain energy metabolism, how such mechanisms are altered during aging and in neurodegenerative disorders, and the potential applications to brain health and disease of interventions that engage pathways involved in neuronal adaptations to metabolic stress.

Crucial genes at the onset of lactation revealed by transcriptome screening of Domestic Yak mammary gland

At the onset of lactation, there are three distinct stages of mammary tissue development and function including mammogenesis, colostrogenesis, and lactogenesis. The mechanism of the transition from colostrogenesis to lactogenesis of Maiwa Yak is still unknown. In this study, mammary tissues from three Maiwa Yaks were collected at 1 and 30 d after parturition for transcriptome exploration using Affymetrix Bovine Genome Arrays. Comparing 1 and 30 d results, a total of 517 annotated differentially expressed genes (DEGs) were identified at the criteria of a P ≤ 0.05. The ratio of up-regulated genes to the down-regulated ones was around 1:2 (more specifically, 164:353). To depict the profile of DEGs, a dynamic impact approach (DIA) was used to analyse the microarray data based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. GO terms “fatty acid transport” and “monocarboxylic acid transport” were significantly induced during the colostrum period. The strongly impacted KEGG pa...

Long-range atmospheric transport of volatile monocarboxylic acids with Asian dust over a high mountain snow site, central Japan

Abstract. To understand the long-range transport of monocarboxylic acids from the Asian continent to the Japanese islands, we collected snowpack samples from a pit sequence (depth ca. 6 m) at the Murodo-Daira snowfield near the summit of Mt. Tateyama, central Japan, in 2009 and 2011. Snow samples (n = 16) were analyzed for normal (C1–C10), branched chain (iC4–iC6), aromatic (benzoic and toluic acid isomers), and hydroxyl (glycolic and lactic) monocarboxylic acids, together with inorganic ions and dissolved organic carbon (DOC). Acetic acid (C2) was found to be a dominant species (average 125 ng g−1), followed by formic acid (C1) (85.7 ng g−1) and isopentanoic acid (iC5) (20.0 ng g−1). We found a strong correlation (r = 0.88) between formic plus acetic acids and non-sea-salt Ca2+ that is a proxy of Asian dust. Contributions of total monocarboxylic acids to DOC in 2009 (21.2 ± 11.6 %) were higher than that in 2011 (3.75 ± 2.62 %), being consistent with higher intensity of Asian dust in 2009 than in 2011. Formic plus acetic acids also showed a positive correlation (r = 0.90) with benzoic acid that is a tracer of automobile exhaust, indicating that monocarboxylic acids and their precursors are largely emitted from anthropogenic sources in China and/or secondarily produced in the atmosphere by photochemical processing. In addition, the ratio of formic plus acetic acids to nss–Ca2+ (0.27) was significantly higher than those (0.00036–0.0018) obtained for reference dust materials of Chinese loess deposits from the Tengger and Gobi deserts. This result suggests that volatile and semi-volatile organic acids are adsorbed on the alkaline dust particles during long-range atmospheric transport. Entrainment of organic acids by dusts is supported by a good correlation (r = 0.87) between formic plus acetic acids and pH of melt snow samples. Our study suggests that Asian alkaline dusts may be a carrier of volatile monocarboxylic acids.

Fluid transport by the cornea endothelium is dependent on buffering lactic acid efflux.

Maintenance of corneal hydration is dependent on the active transport properties of the corneal endothelium. We tested the hypothesis that lactic acid efflux, facilitated by buffering, is a component of the endothelial fluid pump. Rabbit corneas were perfused with bicarbonate-rich (BR) or bicarbonate-free (BF) Ringer of varying buffering power, while corneal thickness was measured. Perfusate was collected and analyzed for lactate efflux. In BF with no added HEPES, the maximal corneal swelling rate was 30.0 ± 4.1 μm/h compared with 5.2 ± 0.9 μm/h in BR. Corneal swelling decreased directly with [HEPES], such that with 60 mM HEPES corneas swelled at 7.5 ± 1.6 μm/h. Perfusate [lactate] increased directly with [HEPES]. Similarly, reducing the [HCO3 (-)] increased corneal swelling and decreased lactate efflux. Corneal swelling was inversely related to Ringer buffering power (β), whereas lactate efflux was directly related to β. Ouabain (100 μM) produced maximal swelling and reduction in lactate efflux, whereas carbonic anhydrase inhibition and an monocarboxylic acid transporter 1 inhibitor produced intermediate swelling and decreases in lactate efflux. Conversely, 10 μM adenosine reduced the swelling rate to 4.2 ± 0.8 μm/h and increased lactate efflux by 25%. We found a strong inverse relation between corneal swelling and lactate efflux (r = 0.98, P < 0.0001). Introducing lactate in the Ringer transiently increased corneal thickness, reaching a steady state (0 ± 0.6 μm/h) within 90 min. We conclude that corneal endothelial function does not have an absolute requirement for bicarbonate; rather it requires a perfusing solution with high buffering power. This facilitates lactic acid efflux, which is directly linked to water efflux, indicating that lactate flux is a component of the corneal endothelial pump.

The transport mechanism of monocarboxylate transporter on spinosin in Caco-2 cells

Objectives: The aim of this study was to determine the uptake mechanism of spinosin (SPI) by the monocarboxylic acid transporters (MCTs) in Caco-2 cells. Methods: The Caco-2 cells were pretreated with various monocarboxylic acids, and the uptake of spinosin from Caco-2 cells was measured by High Performance Liquid Chromatography (HPLC). Key findings: Preloading of various monocarboxylic acids enhanced the uptake of SPI, especially salicylic acid (a substrate of MCTs) had a 23.4 times increase in SPI uptake, indicating that the monocarboxylic acid transporters had an efflux effect on SPI uptake and salicylic acid had a strong inhibition on SPI efflux in Caco-2 cells. At the same time, the uptake of SPI through Caco-2 cells was Na+- and temperature-dependent, pretreatment without Na+ significantly increased the uptake of SPI by 1.85 times and incubated at low temperature (4°C) SPI uptake increased 20% than that of 37°C. Furthermore, SPI was transported mainly via a carrier-mediated transport: [Vmax=5.364μg/mg protein, Km=657.0μg/mL]. Conclusion: The uptake of spinosin (SPI) in Caco-2 cells was mainly regulated by the monocarboxylic acid transporters along with Salicylic acid.

Regulation of Monocarboxylic Acid Transporter 1 Trafficking by the Canonical Wnt/β-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/β-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/β-catenin pathway in RBE4 cells via nuclear β-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/β-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/β-catenin and Notch signaling pathways.

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