Lactic acid induces lactate transport and glycolysis/OXPHOS interconversion in glioblastoma

doi:10.1016/j.bbrc.2018.06.092

Biochemical and Biophysical Research Communications

Volume 503, Issue 2, 5 September 2018, Pages 888-894

https://doi.org/10.1016/j.bbrc.2018.06.092 Get rights and content

Highlights

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Lactic acidosis induces lactate transportation and reuse.
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Under glucose-deprived condition, lactic acidosis could keep cell growth and maintain ATP content to resist cell death through glycolysis/ OXPHOS inter-conversion in U251 cell.
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Different region of tumor tissue has diverse glucose metabolic way to adapt adverse microenvironment and maintain proliferation and progression in GMB.

Abstract

The Warburg effect is a dominant phenotype of most tumor cells. Recent reports have shown that the Warburg effect can be reprogrammed by the tumor microenvironment. Lactic acidosis and glucose deprivation are the common adverse microenvironments in solid tumor. The metabolic reprogramming induced by lactic acid and glucose deprivation remains to be elucidated in glioblastoma. Here, we show that, under glucose deprivation, lactic acid can preserve high ATP levels and resist cell death in U251 cells. At the same time, we find that MCT1 and MCT4 are significantly highly expressed. The metabolic regulation factor HIF-1α decreased and C-MYC increased. Nuclear respiratory factor 1 (NRF1) and oxidative phosphorylation (OXPHOS)-related proteins (NDUFB8, ND1) are all distinctly increased. Therefore, lactic acid can induce lactate transport and convert the dominant Warburg effect to OXPHOS. Through bioinformatics analysis, the high expression of HIF-1α, MCT1 or MCT4 indicate a poor prognosis in glioblastoma. In addition, in glioblastoma tissue, HIF-1α, MCT4 and LDH are highly expressed in the interior region, and their expression is decreased in the lateral region. MCT1 can not be detected in the interior region and is highly expressed in the lateral region. Hence, different regions of glioblastoma have diverse energy metabolic pathways. Glycolysis occurs mainly in the interior region and OXPHOS in the lateral region. In general, lactic acid can induce regional energy metabolic reprogramming and assist tumor cells to adapt and resist adverse microenvironments. This study provides new ideas for furthering understanding of the metabolic features of glioblastoma. It may promote the development of new therapeutic strategies in GBM.

Introduction

Most tumor cells use glycolysis rather than oxidative phosphorylation (OXPHOS) as the main energy metabolic pathway to produce ATP. Although glycolysis is far less efficient than OXPHOS for ATP generation, tumor cells display abnormally high glycolytic rates in order to preserve high ATP levels [1,2]. The excessive conversion of glucose to lactate, even with ample oxygen in tumor cells, is called the Warburg effect [3].

As a consequence of heightened glycolysis, lactate levels can be up to 40 mM in tumors; otherwise, the physiological concentration of lactate is between 1.8 mM and 2 mM in normal tissue [4]. Hence, lactic acidosis generally exists in solid tumor microenvironments. High levels of lactic acid were initially considered to be merely an indicator of the glycolytic flux. However, some evidence has indicated that lactic acid may directly contribute to tumor growth, metastasis and angiogenesis [5]. Besides, clinical studies have demonstrated that patients with high levels of lactate showed poor prognoses and bad overall survival rates of head and neck cancer and non-small cell lung cancer [6,7].

Additionally, due to rapid proliferation, disorganized vasculature and dysfunctional capillary, glucose deprivation is also a common condition in most solid tumors. Hence, lactic acidosis and glucose deprivation are the common adverse microenvironments in solid tumors [8]. In vitro, tumor cells undergo apoptosis when tumor cells are cultured in a glucose-deprived medium [9]. However, solid tumors plainly resist glucose deprivation in vivo. This indicates that the tumor microenvironment may contain factors that allow cancer cells to resist glucose deprivation-induced apoptosis. Hui et al. have reported that tumors can use lactate as a fuel in lung tumors and the contribution of lactate to the TCA cycle in vivo exceeds that of glucose [10]. High concentrations of lactic acid may provide a necessary fuel source for glucose-deprived tumors to avoid apoptosis.

Recent reports have also shown that the Warburg effect, the hallmark of tumors, is variable. The metabolic pathway of tumor cells can be affected by the tumor microenvironment [11]. So, apart from its use as a fuel, it remains unclear whether lactic acid may be able to induce a change in the energy metabolic pathways of tumor cells and how tumor cells could more efficiently utilize lactic acid to adapt to adverse microenvironments.

Glioblastoma (GBM), the most common and malignant brain cancer, is characterized by prominent cellular heterogeneity, high-speed proliferation, extensive invasion of brain tissue and almost inevitable recurrence [12]. Prior studies have reported that malignant brain tumors show intensive glycolysis, lactic acidosis and glucose deprivation [12]. Glioblastoma may be a preferable material in which to explore the role of lactic acid in the tumor microenvironment. Hence, under glucose-deprived conditions, U251 was treated with lactic acid. We subsequently detected a change in the cell cycle, cell growth, cell ATP content and the relative abundance of metabolic molecules.

This research will be of significance in understanding the metabolic mechanism used by tumor cells to survive and resist adverse microenvironments, which could contribute to the clinical treatment of GBM.

Section snippets

Cell lines, cell culture and reagents

U251 cell line was purchased from the Kunming cell bank of the Chinese Academy of Science. The cells were cultured at 37 °C, 5% CO₂ in high glucose Dulbecco's modified Eagle's medium (DMEM, Gibco) supplemented with 10% fetal bovine serum (FBS, BI), 100 U/ml penicillin (Gibco) and 100 U/ml streptomycin (Gibco).

Tumor samples

Glioblastoma tissue samples were collected during surgical procedures at the Department of Pathology, the People's Hospital of Dali (Dali, China). These samples were composed of

Lactic acid promotes cell growth and increases ATP levels in U251 cells

Proliferated tumor cells are characterized by the Warburg effect. As an outcome of the high rate of glycolysis, lactic acidosis is a common condition in solid tumors. To explore the energy metabolic change in U251 cells, which exhibit a classical Warburg effect under lactic acidosis [13], we treated U251 cells with 0–30 mM lactic acid for 48 h. The results showed that under lactic acidosis, especially in the 15-mM lactic acid condition, the cell growth was significantly increased, and the ATP

Discussion

In the last century, Otto Warburg proposed that tumor cells depend on glycolysis and glycolysis is the main source of energy in both aerobic and anaerobic conditions [3]. The increase in glucose uptake and the enhancement of glycolysis is a metabolic hallmark of tumor cells [14]. Hypoxia-inducible factor 1 (HIF-1) is the most important regulation molecular for up-regulating glycolysis [15]. It can inhibit glucose carbon to flow into the TCA cycle and accelerate the conversion of pyruvate into

Conflict of interest

None.

Acknowledgements

All work in this manuscript was financially supported by the National Natural Science Foundation of China (no. 31760331, 31260276, 31160237, 81271330, 81360310, 31106237, 31471187, 31171215, 31601155) and Yunnan Province Science and Technology Innovation Team (2011CI123).

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¹: Authors contributed equally.

View full text

Lactic acid induces lactate transport and glycolysis/OXPHOS interconversion in glioblastoma

Highlights

Abstract

Introduction

Section snippets

Cell lines, cell culture and reagents

Tumor samples

Lactic acid promotes cell growth and increases ATP levels in U251 cells

Discussion

Conflict of interest

Acknowledgements

Cell

Semin. Radiat. Oncol.

Int. J. Radiat. Oncol. Biol. Phys.

Canc. Cell

Cell Metabol.

Cell Metabol.

Canc. Cell

Cell Rep.

Glucose metabolism in cancer cells

Curr. Opin. Clin. Nutr. Metab. Care

On the origin of cancer cells

Science

Multiple biological activities of lactic acid in cancer: influences on tumor growth, angiogenesis and metastasis

Curr. Pharmaceut. Des.

Lactic acid promotes cell growth and increases ATP levels in U251 cells