AQP9 Is a Prognostic Factor for Kidney Cancer and a Promising Indicator for M2 TAM Polarization and CD8+ T-Cell Recruitment

Abstract

BackgroundIt is undeniable that the tumor microenvironment (TME) plays an indispensable role in the progression of kidney renal clear cell carcinoma (KIRC). However, the precise mechanism of activities in TME is still unclear.Methods and ResultsUsing the CIBERSORT and ESTIMATE calculation methods, the scores of the two main fractions of tumor-infiltrating immune cells (TICs) from The Cancer Genome Atlas (TCGA) database of 537 KIRC patients were calculated. Subsequently, differentially expressed genes (DEGs) were drawn out by performing an overlap between Cox regression analysis and protein–protein interaction (PPI) network. Aquaporin 9 (AQP9) was identified as a latent predictor through the process. Following research revealed that AQP9 expression was positively correlated with the pathological characteristics (TNM stage) and negatively connected with survival time. Then, by performing gene set enrichment analysis (GSEA), it can be inferred that genes with high expression level of AQP9 were mainly enriched in immune-related activities, while low AQP9 group was associated with functions of cellular metabolism. Further studies have shown that regulatory T cells (Tregs), macrophages M2, macrophages M0, CD4+ T cells, and neutrophils were positively correlated with AQP9 expression. While the levels of mast cells, natural killer (NK) cells, and CD8+ T cells are negatively correlated with AQP9. The result of multiple immunohistochemistry (mIHC) suggests a negative relevance between AQP9 and CD8+ T cells and reveals a trend of consistent change on AQP9 and M2 macrophages.ConclusionThe expression level of AQP9 may be helpful in predicting the prognosis of patients with KIRC, especially to the TME state transition, the mechanism of which is possibly through lipid metabolism and P53, Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathways that affect M2 polarization. AQP9 was associated with the expression levels of M2, tumor-associated macrophages (TAMs), and the recruitment of CD8+ T cells in tumor environment. The research result indicates that AQP9 may be an obstacle to maintain the immune activity of TME.

Abnormal expression and the significant prognostic value of aquaporins in clear cell renal cell carcinoma

“…In addition, JIng JB et al showed that the protein expression level of AQP9 was significantly increased in ccRCC, the expression level of AQP9 increased with the pathological stage of the tumor. At the same time, AQP9 was associated with the expression of macrophages and the inhibition of the recruitment of NK and CD8+T cells in the tumor microenvironment [56]. These experimental results can further confirm our results.…”

“…Jing JB et al explored the expression of AQP9 which was consistent with ours, and they also analyzed the relationship between AQP9 and tumor environment. The results showed that in ccRCC, AQP9 promoted tumor-associated macrophage polarization, inhibited the recruitment of natural killer (NK) cells and CD8+ T cells by inhibiting P53 and activating the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway, and ultimately stimulated a reorientation of the tumor microenvironment in ccRCC toward tumor-friendly directions [56]. Combining the above analyses of AQP1 and AQP9, we may guess that AQP1 is the tumor suppressor gene of ccRCC while AQP9 is the proto-oncogene of ccRCC.…”

The Multifaceted Role of Aquaporin-9 in Health and Its Potential as a Clinical Biomarker

“…Overall, the expression of AQP9 in humans appears to be more selective than in mice, with hepatocytes and neutrophils being by far the major expression sites in normal human tissues. Through the use of Aqp9 -KO cells, AQP9 protein expression has been verified in hepatocytes [ 53 , 77 , 78 , 79 ], immune cells, including neutrophils [ 80 , 81 ], macrophages [ 82 ], CD8+ T-cells [ 83 , 84 ], stratum granulosum of the epidermis [ 75 ], principal cells of the epididymis, and vas deferens [ 77 ], bone marrow dendritic cells [ 37 ], and a limited population of neuronal cells [ 58 , 76 , 85 ].…”

“…In macrophages, AQP9 was shown to be required in phagocytosis promoted by the Pseudomonas aeruginosa lasI/rhlI quorum sensing genes as its expression was strongly increased and the related protein was redistributed to the leading and trailing regions after macrophages were infected with the pathogen [ 82 ]. Involvement of AQP9 in macrophage M2 polarization has been recently shown in the progression of kidney renal clear cell carcinoma [ 84 ]. In CD8+ T cells, AQP9 was required for longevity and fast response to rechallenge [ 83 ], and to cell locomotion in reaching the tumor microenvironment [ 84 ].…”

“…Involvement of AQP9 in macrophage M2 polarization has been recently shown in the progression of kidney renal clear cell carcinoma [ 84 ]. In CD8+ T cells, AQP9 was required for longevity and fast response to rechallenge [ 83 ], and to cell locomotion in reaching the tumor microenvironment [ 84 ].…”