2024 Volume 47 Issue 4 Pages 764-770
L-Lactate transport via monocarboxylate transporters (MCTs) in the central nervous system, represented by the astrocyte-neuron lactate shuttle (ANLS), is crucial for the maintenance of brain functions, including memory formation. Previously, we have reported that MCT1 contributes to L-lactate transport in normal human astrocytes. Therefore, in this study, we aimed to identify transporters that contribute to L-lactate transport in human neurons. SH-SY5Y cells, which are used as a model for human neurons, were differentiated using all-trans-retinoic acid. L-Lactate uptake was measured using radiolabeled L-lactate, and the expression of MCT proteins was confirmed Western blotting. L-Lactate transport was pH-dependent and saturated at high concentrations. Kinetic analysis suggested that L-lactate uptake was biphasic. Furthermore, MCT1, 2 selective inhibitors inhibited L-lactate transport. In addition, the expression of MCT1 and 2 proteins, but not MCT4, was confirmed. In this study, we demonstrated that MCT1 and 2 are major contributors to L-lactate transport in differentiated human neuroblastoma SH-SY5Y cells from the viewpoint of kinetic analysis. These results lead to a better understanding of ANLS in humans, and further exploration of the factors that can promote MCT1 and 2 functions is required.
L-Lactate is an essential regulator of brain function. L-Lactate is the product of anaerobic metabolism and effluxes from the cell, whereas under aerobic conditions, it is also used for synthesizing acetyl-CoA for use in the tricarboxylic acid cycle. In the central nervous system, the astrocyte-neuron lactate shuttle (ANLS), in which L-lactate is released from astrocytes and taken up by neurons for energy metabolism, is important for brain energy metabolism.1) Additionally, L-lactate plays an important role in neuronal excitability, plasticity, and memory consolidation.2) Therefore, understanding the kinetics of L-lactate in the brain is important.
Monocarboxylate transporter (MCT)1, MCT2, and MCT4 are the major pH-dependent L-lactate transporters that are expressed in various organs, including the small intestine, skeletal muscle, lung, liver, and brain.3,4) In the brain, it has been reported that the knockdown of MCTs in rats impaired long-term memory formation.5) Interestingly, topical administration of L-lactate to the hippocampus restored long-term memory formation in MCT1 and MCT4 knockdown mice, but not in MCT2 knockdown mice, indicating that each isoform may have a different role. Thus, MCTs may affect brain function, and it is important to confirm their functional isoforms.
Several studies have been conducted on pH-dependent L-lactate transport in the central nervous system of rodents.6–8) It has been reported that MCT1 and MCT2 are expressed in the GT1-7 mouse hypothalamic GnRH neuronal cell line, and MCT1, MCT2 and MCT4 are expressed in hypothalamic primary cell culture of rats.8) Some reports have analyzed for the pH-dependent and concentration-dependent L-lactate uptake in neuronal cell lines of rodents,6–8) but it has not been clear which transporters are involved in the uptake of L-lactate. Kinetic analysis and expression characteristics have also been performed on cells other than neurons, and it is widely known that MCT1 contributes to the release of L-lactate from vascular endothelial cells and MCT1 or MCT4 from astrocytes.9) From the results of these studies in rodents, MCT isoforms with confirmed protein expression did not necessarily transport L-lactate in each tissue. In the human brain, MCT1 is expressed in vascular endothelial cells and astrocytes10); MCT2 is found in neurons in the white matter and gray matter and in some astrocytes11); and MCT4 is found in the basolateral cytoplasmic membrane of a small number of epithelial cells, astrocytes, and the capillary wall.12) We previously reported that MCT1 contributes to L-lactate transport in human astrocyte-derived cells (NHA) using kinetic analysis and inhibitory experiments.13) In the central nervous system, MCT2 is thought to play an important role in L-lactate transport because MCT2 is expressed in human neurons. However, there are no verification of L-lactate transport in human neurons, and the carriers of L-lactate remain unclear. Consequenly, we aimed to identify transporters that contribute to L-lactate transport in human neurons.
Differentiated SH-SY5Y human neuroblastoma cells are often used as human neuronal models.14) In this study, we performed a kinetic analysis to elucidate L-lactate transport carriers in human neuroblastoma SH-SY5Y cells.
[14C]-labeled L-lactic acid sodium salt (NEC599050UC) was purchased from PerkinElmer, Inc. (U.S.A.). All the compounds used were of the highest purity available.
Cell Culture and DifferentiationThe SH-SY5Y cells were purchased from KAC Co., Ltd. (Japan). SH-SY5Y cells were routinely cultured in Dulbecco’s modified Eagle’s medium (DMEM)/Ham F-12 (Nacalai Tesque, Japan) supplemented with 15% fetal bovine serum, 1% penicillin–streptomycin antibiotic (Sigma-Aldrich, U.S.A.), and 1% MEM nonessential amino acids (Gibco, U.S.A.). The medium was changed every 2 d and passaged when subconfluent. No more than 25 passages were used in any experiment. As a differentiated condition, cells were seeded at the appropriate density, cultured for 2 d, and the medium was replaced with Neurobasal™-A Medium containing 10 µM all-trans-retinoic acid (Wako, Japan), B-27™ Supplement (Gibco, Thermo Fisher, U.S.A.), GlutaMAX Supplement (Gibco, Thermo Fisher) and 1% penicillin–streptomycin antibiotic. Thereafter, the medium was replaced every 2 d and used for various experiments 7 d after seeding. We examined whether this manipulation resulted in changes in cell morphology and mRNA levels of differentiation markers.
RT-PCR and Quantitative Real-Time PCR (qPCR)Total RNA was extracted using ISOGEN II (Nippon Gene, Tokyo, Japan). cDNA was synthesized from the total RNA using ReverTra Ace (TOYOBO, Japan). qPCR was performed using KAPA SYBR Fast qPCR kit (Kapa Biosystems, U.S.A.) and LightCycler® 480 System II (Loche, U.S.A.). To determine the housekeeping genes for the normalization of gene expression levels, we investigated the mRNA level changes of several commonly used genes (Supplementary Fig. 1). Thus, we decided to use 18S ribosomal RNA (rRNA), which shows no changes during differentiation, as a housekeeping gene. The primer sequences used for qPCR amplification are listed in Supplementary Table 1. The qPCR thermocycling protocol was as follows: 40 cycles of denaturation at 95 °C for 5 s; annealing at 57 °C for 20 s; and extension at 72 °C for 1 s. The software calculated the relative amount of the target and housekeeping genes based on threshold cycles.
[14C]-L-Lactate UptakeThe SH-SY5Y cells were differentiated and cultured until they reached confluence. The measurement of L-lactate uptake was performed as previously described with minor modification.13) Briefly, SH-SY5Y cells were plated and cultured as described in Cell culture and differentiation section. After washing, the cells were pre-incubated with the 0.5 mL of Hank’s balanced salt saline (HBSS) buffer (25 mM D-glucose, 137 mM NaCl, 5.4 mM KCl, 0.34 mM Na2HPO4, 0.44 mM KH2PO4, 1.3 mM CaCl2, 0.81 mM MgSO4, 4.2 mM NaHCO3, 10 mM Good’s buffer), adjusted to pH 5.5 at 37 °C for 10 min. N-(2-Hydroxyethyl)piperazine-N′-2-ethanesulfonic acid (HEPES) was used for pH 8.0–7.0 HBSS buffer, MES was used for pH 7.0–5.5 HBSS buffer and HOMOPIPES was used for pH 5.0 HBSS buffer. After pre-incubation, HBSS buffer containing [14C]-labeled L-lactate of 0.64 µM was incubated at 37 °C. After removal of the added HBSS buffer, cells were washed twice with 1000 µL of HBSS buffer adjusted to pH 7.4 to stop reactions. In addition, AR-C155858 and AZD3965 were pre-incubated for 10 min, and AZD0095 and atorvastatin for 5 min because it takes time to show inhibitory effects or to match the incubation time used in a previous study.15,16) After cells were lysed by adding 500 µL of 0.2 N NaOH -1% sodium dodecyl sulfate (SDS) solution, 3 mL of Ultima Gold™ scintillation cocktail (PerkinElmer, Inc.) was added, and a liquid scintillation counter was used to quantify [14C]-L-lactic acid sodium salt using a liquid scintillation counter. All uptake values were corrected for protein content. Protein concentration was determined using a Pierce® BCA Protein Assay Kit (Thermo Scientific), in accordance with the manufacturer’s instructions.
Western BlottingSH-SY5Y cell proteins were extracted using radio immunoprecipitation assay (RIPA) buffer (Cell Signaling Technology, U.S.A.), according to the manufacturer’s instructions. Equal amounts of protein (10 µg) were separated using 10% SDS-polyacrylamide gel electrophoresis (PAGE) and transferred to polyvinylidene fluoride (PVDF) membranes. PVDF membranes were blocked with 1% fat-free dry milk for 1 h, followed by incubation with primary antibodies against MCT1 (sc-365501, Santa Cruz Biotechnology, U.S.A.), (1/200), MCT2 (ab198272, Abcam, U.K.), (1/1000), MCT4 (22787-1-AP, Proteintech Group, U.S.A.), (1/1000), and β-actin (ab179467, Abcam, U.K.), (1/5000) in both 0.5% fat-free dry milk in phosphate-buffered saline containing Tween 20 (PBS-T) at 4 °C overnight. Membranes were washed with PBS-T and incubated with secondary goat anti-mouse immunoglobulin G (IgG)1-HRP antibody (1070-05, Southern Biotech, U.S.A.) (1/4000) or mouse anti-rabbit IgG-HRP (sc-2357, Santa Cruz Biotechnology, U.S.A.) (1/4000) in both 0.5% fat-free dry milk in PBS-T for 1 h at room temperature. Membranes were washed again with PBS-T, developed with ECL Prime Western blotting Detection Reagent (Cytiva, U.S.A.), and visualized using an Image Quant LAS 4000 mini.
Small Interfering RNA (siRNA) TransfectionThe siRNA transfection was optimized using Lipofectamine RNAiMAX (Thermo Fisher Scientific). According to the previous study,17) the cells were treated by forward transfection to a final siRNA concentration of 7.5 nM on days 1 and 6 after seeding. The medium was replaced 24 h after each transfection. Stealth RNA interference (RNAi) Negative Control Medium GC Duplex was used as the negative control siRNA and HSS185929 was used as the MCT1 siRNA.
Data AnalysisAll data are expressed as mean ± standard error. Significant differences between the two groups of data were evaluated using the Student’s t-test. Dunnett’s method was used for multiple comparisons with the controls. Statistical significance was set at p-value <0.05 or 0.01. Curve fitting was performed to fit the following equation by nonlinear regression analysis using SigmaPlot 14.5 (Systat Software, U.S.A.):
 |
where V is the substrate uptake rate, [S] is the substrate concentration in the medium, Vmax1 and Vmax2 are the maximum uptakes, and Km1 and Km2 are the Michaelis–Menten constants in phases 1 and 2, respectively.
Tau and NeuroD1 are known differentiation markers in SH-SY5Y cells.18) The previous report showed that the mRNA level of Tau was increased while that of NeuroD1 was decreased during cell differentiation. In this study, the mRNA levels of these markers in differentiated SH-SY5Y cells were significantly altered compared to those in undifferentiated SH-SY5Y cells, as previously reported (Fig. 1A). In addition, the mRNA levels of genes involved in the glycolytic pathway were evaluated because it has been shown that during differentiation, there is a shift from the glycolytic pathway to oxidative phosphorylation.19) The mRNA levels of hexokinase-2 (HK2), lactate dehydrogenase A (LDHA), glucose transporter 1 (GLUT1), and MCT1 significantly decreased (Fig. 1B). Furthermore, c-MYC, which is involved in the decreased expression of glycolytic pathway-related genes during differentiation,19) was significantly downregulated (Fig. 1C). Based on these results, the SH-SY5Y cells were considered to have differentiated properly.
mRNA levels were quantified via RT-qPCR and normalized to 18S rRNA levels. (A) Neuronal markers. (B) Glycolysis-related genes. (C) c-MYC. Data are presented as the means with standard error (S.E.) of four independent experiments. *; p < 0.05, compared with undifferentiated cells. **; p < 0.01, compared with undifferentiated cells.
The time dependence of L-lactate uptake in differentiated SH-SY5Y cells was examined. The results showed that L-lactate uptake increased linearly for up to 5 min (Supplementary Fig. 2); therefore, the uptake time was set to 5 min.
Lactate transport carriers exist not only in MCTs but also in sodium-coupled monocarboxylate transporters (SMCTs), which are sodium dependent.3) Therefore, we examined the driving force of L-lactate transport. Although L-lactate uptake without sodium tended to increase, no significant differences in L-lactate uptake in SH-SY5Y cells was observed with or without sodium (Fig. 2A). The sodium and/or proton carriers other than MCTs may be indirectly involved in L-lactate uptake in SH-SY5Y cells without sodium. In contrast, as proton concentration increased, L-lactate uptake increased (Fig. 2B). The Hill coefficient for the pH dependence returned to 1.1 ± 0.22. The data were fitted to the Henderson–Hasselbälch equation, and the pKa was calculated to be 6.3 ± 0.14 (Fig. 2C).
(A) The uptake of L-lactate (0.64 µM) by differentiated SH-SY5Y cells was measured in the presence of 140 mM sodium and sodium-free. Data are means with S.E. of three independent experiments. No statistical significance was observed. (B, C) Uptake of L-lactate (0.64 µM) by differentiated SH-SY5Y cells was measured following 5 min incubation in the presence of increasing concentrations of H+ (0.032–10 µM). Data are presented as means ± S.E. of three independent experiments. (B) The Hill equation. (C) The Henderson–Hasselbälch equation.
We evaluated MCT expression in differentiated SH-SY5Y cells. HepG2 cells, which have been shown to express MCT1, MCT2, and MCT4,20) were used as a positive control. Bands for MCT1 and 2, but not for MCT4, were detected compared to HepG2 cells (Fig. 3). Transfection of MCT1 siRNA reduced the signal of the larger molecular weight of the MCT1 band (Supplementary Fig. 3A).
Western blot of differentiated SH-SY5Y and HepG2 cells showing MCT1 (40–48 kDa), MCT2 (52 kDa), MCT4 (42–45 kDa), and β-actin (42 kDa).
The uptake rate increased in an L-lactate concentration-dependent manner and was saturated at high concentrations (Fig. 4). The inset in Fig. 4 shows the Eadie–Hofstee plot, which suggests that L-lactate transport was biphasic. Kinetic parameters were calculated using Eadie–Hofstee plot. Km1, Vmax1 or Km2, and Vmax2 were estimated to be 0.32 mM, 12 nmol/mg protein/min or 1.0 mM, and 23 nmol/mg protein/min, respectively.
L-Lactate (0.01–10 mM) uptake by differentiated SH-SY5Y cells was measured by subtracting the value in HEPES buffer (pH 7.4) at 37 °C for 5 min from the value in MES buffer (pH 5.5) at 37 °C for 5 min. The inset shows the Eadie–Hofstee plot of the data after subtraction of non-saturable L-lactate uptake. V denotes L-lactate uptake rate, while S denotes L-lactate concentration. Data are means ± S.E. of three independent experiments.
The effects of various MCT inhibitors on L-lactate uptake are shown in Table 1. First, L-lactate transport was inhibited by α-cyano-4-hydroxycinnamic acid (CHC), a classic non-selective inhibitor of MCTs.21) AZD0095, an MCT4-selective inhibitor,22) had no effect on L-lactate transport. In contrast, L-lactate uptake was strongly inhibited by 10 nM AR-C155858, a selective MCT1/2 inhibitor with Ki values (MCT1: 2.3 nM, MCT2: < 10 nM).23) AZD3965 greatly inhibited L-lactate uptake at 20 nM, which is the MCT2 Ki value, but not at 2 nM, which is close to the MCT1 Ki value.24) In addition, incubation with pyruvate, a substrate of MCT1 and 2,21) reduced L-lactate uptake by approximately 20% at 0.1 mM, which is close to the MCT2 Km value, and by approximately 70% at 1 mM, which is close to that of MCT1. L-Lactate uptake is also reduced by 5-oxoproline, a selective substrate of MCT1, which is not a substrate of MCT4.13) Furthermore, atorvastatin, which was reported to be selective for MCT2,16) inhibited L-lactate transport at a concentration of 10 µM, which implies no inhibitory activity on MCT1.
| Treatment | % of control |
|---|---|
| CHC 30 µM | 63.6 ± 6.33* |
| CHC 100 µM | 50.0 ± 5.29* |
| CHC 200 µM | 53.2 ± 8.74* |
| CHC 1 mM | 28.1 ± 3.12** |
| AZD0095 10 µM | 99.9 ± 0.09 |
| AR-C155858 10 nM | 12.0 ± 3.12** |
| AZD3965 2 nM | 104 ± 11.9 |
| AZD3965 20 nM | 26.8 ± 3.23** |
| Pyruvate 0.1 mM | 77.3 ± 2.20* |
| Pyruvate 1 mM | 37.2 ± 6.38** |
| 5-Oxoproline 10 mM | 32.4 ± 2.74** |
| Atorvastatin 10 µM | 52.6 ± 6.77** |
L-Lactate uptake (0.64 µM) by differentiated SH-SY5Y cells was measured in the presence of various substrates and inhibitors (30, 100, 200 µM, and 1 mM α-Cyano-4-hydroxycinnamic acid (CHC); 10 µM AZD0095; 10 nM AR-C155858; 2 and 20 nM AZD3965; 0.1 and 1 mM Pyruvate; 10 mM 5-Oxoproline; 10 µM Atorvastatin) in MES buffer (pH 5.5) at 37 °C for 5 min. For 10 nM AR-C155858, 2 and 20 nM AZD3965, 10 min pre-incubation, for 10 µM AZD0095 and 10 µM Atorvastatin, 5 min pre-incubation was performed because it is known that it takes time to show the inhibitory effect. Data are means ± S.E. of three independent experiments. *; p < 0.05 compared with Control. **; p < 0.01 compared with Control.
L-Lactate transport in the central nervous system is involved in a variety of functions, such as memory formation. In rodents, it has been reported that L-lactate was released from astrocytes via MCT1 or MCT4 and flowed into neurons via MCT2.9) However, the transporters involved in L-lactate uptake by human neuronal cells remain unclear. Therefore, we performed functional analysis of L-lactate uptake in SH-SY5Y cells, a commonly used model of human neurons. To the best of our knowledge, this is the first report of the kinetic analysis of L-lactate uptake using human neuron-like cells.
First, we measured the mRNA levels of various genes to assess neuron-like differentiation in SH-SY5Y cells. Tau is involved in microtubules stabilization and NeuroD1 is related to differentiation induction. These markers exhibit inversely correlated behavior during SH-SY5Y cells differentiation.18) This study showed that the mRNA level of Tau was increased and that of NeuroD1 was decreased, consistent with the previous report. Moreover, c-MYC expression was reported to be downregulated during the differentiation of neural progenitor cells to neurons, and the mRNA expression of genes involved in the glycolytic pathway was found to be decreased in a study using human iPS cells.19) In the present study, a similar decrease in the mRNA levels was observed (Figs. 1B, C). In addition, we observed morphological changes in which the cell body became shapelier, and neurites became more elongated than in undifferentiated cells (Supplementary Fig. 4). Based on the above points, we considered that differentiation proceeded adequately and that the cells were appropriate as a neuron-like model for further examination.
L-Lactate transporters include MCTs and SMCTs. SMCTs have two subtypes, SMCT1 and SMCT2, which transport L-lactate and pyruvate, respectively, with sodium as the driving force. SMCT1 has been reported to be expressed in rodent neurons and to transport L-lactate.25) SMCT2 has been reported to localize to astrocytes, Müller cells, and glial cells of the retina,26) but there are no reports of its localization in other brain regions. In this study, L-lactate uptake did not change in the presence or absence of sodium (Fig. 2A) and SMCT1 and SMCT2 mRNA expression was not observed (data not shown), suggesting that the sodium gradient was unlikely to be involved in L-lactate uptake in SH-SY5Y cells. In contrast, L-lactate transport increased with decreasing extracellular pH. The Hill coefficient was calculated to be 1.1 ± 0.21, and the pKa was calculated to be 6.3 ± 0.14, which is close to the calculated value in previous studies of MCT transporter characteristic.13,27) This is consistent with the characteristics of MCT1, 2, and 4, which transport L-lactate in a pH-dependent (Figs. 2B, C).3) MCTs are the transporters with the highest affinity in the order of MCT2, MCT1, and MCT4, with Km values of 0.32 ± 0.02, 1.0 ± 0.1 and 3.4 ± 0.4 mM, respectively, at pH 5.5.28–30) In this study, L-lactate transport was biphasic in pH 5.5 (Fig. 3), with Km values calculated as 0.32 mM and 1.0 mM, which were close to previous reports.
We further investigated the effects of several MCT inhibitors on MCT isoforms that contribute to L-lactate uptake by differentiated SH-SY5Y cells (Table 1). First, L-lactate uptake was inhibited by CHC, a classic non-selective MCT inhibitor.21) This suggested that MCTs are involved in L-lactate transport in differentiated SH-SY5Y cells. In addition, AZD0095, MCT4 selective inhibitor,22) did not affect L-lactate uptake. In contrast, with MCT1, 2 selective inhibitors, L-lactate transport was greatly inhibited by exposure to sufficient doses. 2 nM AZD3965, with the Ki value of MCT1,24) did not inhibit L-lactate transport. Since the Ki value was calculated from experiments in Xenopus laevis oocytes, higher concentrations than the Ki value may be required to show an inhibitory effect on L-lactate uptake in SH-SY5Y cells. It was also possible that MCT2, which has a high affinity for L-lactate transport, was preferentially utilized. Moreover, 20 nM AZD3965 has the Ki value of MCT2,24) and L-lactate transport is inhibited by approximately 70%. In addition, 10 µM atorvastatin, a concentration that inhibits MCT2 but not MCT1,16) inhibited L-lactate transport. The Km value of MCT1 for 5-oxoproline is reported to be less than 10 mM,27) and that of MCT2 for 5-oxoproline has not been reported to date. We observed that 10 mM 5-oxoproline inhibited the uptake of L-lactate in SH-SY5Y cells by more than 50%. This indicates that MCT1 at least contributes to L-lactate transport, although it is not known whether 5-oxoproline inhibits MCT2. Furthermore, 0.1 mM pyruvate, which competitively inhibits L-lactate, has a Km value of MCT2,21) but L-lactate transport was inhibited by only approximately 20%. Since both L-lactate and pyruvate are common substrates of MCT1 and MCT2, pyruvate at low concentrations may not have shown an inhibitory effect on MCT2. Therefore, it is difficult to conclude whether L-lactate transport is involved only in MCT2. We conducted the siRNA transfection on SH-SY5Y cells to confirm the contribution of MCT1 and MCT2 to L-lactate transport. The transfection of MCT1 siRNA markedly decreased the protein expression of MCT1 but not that of MCT2. In this condition, L-lactate uptake in SH-SY5Y cells significantly decreased (Supplementary Fig. 3). Because we could not obtain effective siRNA that decreases the expression of MCT2 in the SH-SY5Y cells, further studies of MCT2 siRNA transfection in these cells are needed. Based on the results of the kinetic analysis, inhibitory experiments, and MCT1 siRNA transfection, we concluded that both MCT1 and MCT2 are involved in L-lactate transport in SH-SY5Y cells. This is consistent with the result that MCT1 and MCT2 proteins were expressed (Fig. 3).
In this study, we used SH-SY5Y cells, which are often used as a model for neurons. Previous reports have suggested that MCT1 primarily contributes to L-lactate transport in differentiated SH-SY5Y cells because the protein expression levels of MCT1 were maintained, and those of MCT2 were decreased between pre- and post-differentiation.31) These changes of the protein expression of MCTs are consistent with our results confirmed by Western blotting (data not shown). Other reports have indicated that MCT2 is important in the central nervous system of humans.32) However, these reports did not verify the carriers involved in L-lactate transport by kinetic analysis. In this study, we performed the kinetic analysis of L-lactate uptake in differentiated SH-SY5Y cells and the inhibitory experiments by using atorvastatin, which has a selective inhibitory effect on MCT2. We demonstrated that both MCT1 and MCT2 contribute to L-lactate transport in differentiated human neuroblastoma SH-SY5Y cells for the first time, which is consistent with the results in rodent cells.8) However, it remains uncertain whether both MCT1 and MCT2 contribute to L-lactate transport in actual neurons because the SH-SY5Y cells were derived from cancer cells. When further optimal neural models are established in the future, it is necessary to perform the analysis of L-lactate transport in those models. Moreover, neurons are suggested to receive L-lactate from surrounding astrocytes and microglia in the ANLS hypothesis. It is desirable to evaluate the transporters contributing to L-lactate uptake by co-culturing human neurons with astrocytes and microglia.
In conclusion, we revealed that MCT1 and MCT2 are mainly responsible for L-lactate uptake in differentiated human neuroblastoma SH-SY5Y cells. L-Lactate transport in the brain plays an important role in memory formation. Furthermore, an evaluation of the relationship between the expression of MCT1, MCT2 and memory formation capacity, and a search for factors that may modulate the expression of MCT1 and MCT2 should be conducted.
This work was supported by the Japan Society for the Promotion of Science KAKENHI (Grant Number: 20K07171) (provided to M. K.) and the Kobayashi Foundation (provided to M. K.).
The authors declare no conflict of interest.
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