To reveal the underlying mechanism that AKR1B10 facilitates the Warburg metabolism, we employed RNA-seq in PC9-BrM3 cells with or without AKR1B10 silence (BrM3-shNC/shAKR1B10). The Pearson correlation coefficient analysis indicated good reproducibility of RNA-seq data (Additional file
5: Fig. S2A). We used the absolute values of log
2FoldChange > 0.5 and padj < 0.05 as the screening criteria to identify differential genes, and then mapped and enriched the downregulated differential genes in KEGG pathways. The pathway of pyruvate metabolism, which contains the glycolytic metabolism from pyruvate to lactate, was found enriched in BrM3-shAKR1B10 group compared with BrM3-shNC (Fig.
5A), and the exact differential genes enriched in the pyruvate metabolism were lactate dehydrogenases (LDHA, LDHB) (Fig.
5B), of which LDHA has a higher affinity for pyruvate, facilitating glycolytic process by preferentially converting pyruvate to lactate [
28]. qPCR and western blotting verified that AKR1B10 silence leads to the downregulation of LDHA while overexpression of AKR1B10 caused the increased LDHA (Fig.
5C, D), revealing the mechanism on the regulation of AKR1B10 on the Warburg metabolism. Also, AKR1B10 displayed a similar regulatory effect on LDHB (Additional file
5: Fig. S2C). To demonstrate that the AKR1B10-LDHA regulatory axis is the main pathway of AKR1B10-enhanced glycolysis, we further administered GSK2837808A, a potent and selective LDHA inhibitor, in PC9 cells overexpressing AKR1B10 (PC9-OE) and then assess the cellular lactate level, the results showed that GSK2837808A remarkably attenuated the increased lactate level caused by AKR1B10 overexpression in PC9 cells (Fig.
5E). Staining of brain tumors isolated from mice after intracranial injection also verified that the expression of LDHA was significantly decreased in BrM3-shAKR1B10 group, compared with BrM3-shNC group (Fig.
5F). We further collected the metastasectomy surgical specimens from lung cancer BM patients (n = 29) and assessed the correlation between AKR1B10 and LDHA expression by IHC staining, the data showed a significant positive correlation between AKR1B10 and LDHA (Fig.
5G, H), indicating the existence of AKR1B10-LDHA regulatory axis in lung cancer BM. According to the staining results, we categorised patients with AKR1B10 expression IRS score ≥ 6 as the high expression group (n = 20) while patients with AKR1B10 expression IRS score < 6 (n = 9) as the low expression group, and performed the survival analysis which showed that those patients with high AKR1B10 expression had a shorter overall survival (OS) (Additional file
5: Fig. S2D). Besides, phosphoinositide 3-kinase (PI3K) pathway, a key link modulates the multidrug resistance of cancers [
29], was also enriched in the BrM3-shAKR1B10 group compared with BrM3-shNC (Fig.
5A, Additional file
5: Fig. S2B). Since a recent study notably defined the association between glycolysis and PI3K pathway that glycolysis constantly enhanced PI3K pathway to control T cell immunity [
30], we confirmed the effects of glycolysis on PI3K in BrM3 cells by treating the cells with 2-DG. The results of western blotting showed that inhibition of glycolysis resulted in the significant suppression of PI3K pathway (Additional file
5: Fig. S2E). To summarize, the results suggested that AKR1B10 promotes the production of lactate by increasing the LDHA expression.