Hepatocellular carcinoma (HCC) is a highly malignant tumor, according to the latest data from the National Cancer Center of China, liver cancer (mainly HCC) ranks second in the cancer mortality rate [1], which brings a great health burden to the people of the mainland. There is an urgent need to understand the pathogenesis of liver cancer and develop more effective treatment strategies.
Due to its unique location and blood supply, the liver is exposed to a large number of food antigens and microbial antigens from the intestine, in order to maintain the body's homeostasis and avoid excessive inflammation, the liver must maintain a balance between immune response and tolerance. If this balance is upset, inflammation, infection, or tumors may occur [2,3].
At the same time, the liver is also a metabolically active organ. For example, the liver is the central hub of bile acid metabolism, which not only plays an important role in the absorption and metabolism of lipids, but also acts as endocrine signaling molecules to regulate a variety of biological processes, including immune responses [4]. But at present, we do not know how the metabolism of the liver will affect the occurrence and development of tumors.
Recently, a research team led by Professor Ye Dan, Associate Professor Shi Yinghong and Associate Researcher Wang Pu of Huashan Hospital affiliated to Fudan University published the research results in the journal Journal of Hepatology[5].
They found that the expression of SIRT5 in human HCC tissues was significantly downregulated, and that low expression of SIRT5 was associated with a poor prognosis in patients. This is due to the fact that the lack of SIRT5 can cause an increase in primary bile acids, which can promote macrophage M2 polarization, creating an immunosuppressive microenvironment conducive to the occurrence and development of HCC.
The good news is that the use of the commonly used clinical drug cholestine (CHO) can chelate bile acids, reverse the M2 polarization of macrophages, and inhibit the growth of HCC.
Screenshot of the first page of the paper
The researchers analyzed public databases as well as clinical data and found that SIRT5 was significantly downregulated in HCC tissues, and that low expression of SIRT5 was associated with shorter survival in HCC patients. This suggests that SIRT5 may have tumor-suppressing effects.
Since more than 60% of HCC showed upregulation of YAP expression in oncogenes, the researchers divided the HCC patient data in the TPGA dataset into yap-ON and YAO-OFF based on the expression of YAP's target genes CTGF and CYR61, and found that the expression of SIRT5 was positively correlated with survival in YAP-ON patients, while there was no such correlation in YAP-OFF patients. These data suggest that downregulation of SIRT5 may be synergistic with oncogenes to promote the onset and development of HCC.
Downregulation of SIRT5 expression is associated with a poor prognosis in patients with HCC
In order to study the role of SIRT5 in the pathogenesis of HCC in vivo, the researchers introduced plasmids containing the oncogene YAP5SA or AKT1/NRasG12V into the liver of WT mice or SIRT5-/- mice by means of tail vein hypertension injection, and constructed a mouse liver cancer model. Experiments have found that SIRT5-/-MICE have more tumors, larger sizes, and shorter survival times in mice compared to WT mice. These data suggest that the deletion of SIRT5 in synergy with oncogenes promotes the development of HCC.
SIRT5 deficiency and oncogene synergistically promote the development of HCC
In order to further clarify that SIRT5 defects in hepatic parenchymal cells and oncogene expression are the causes of the development of HCC. The researchers inserted yap5SA and shRNA elements for SIRT5 in a single transposon at the same time, and transferred the constructed vector into the hepatic parenchymal cells of WT mice by high-pressure injection, and found that knocking down the expression of SIRT5 while transferring to the oncogene in the hepato parenchymal cells promoted the occurrence of HCC and shortened the survival time of mice.
On the other hand, if YAP5SA is introduced into SIRT5-/-mouse hepato parenchymal cells and SIRT5 overexpresses the plasmid, the occurrence of HCC is significantly inhibited, prolonging the survival of mice.
These results suggest that SIRT5 deficiency in hepatocytes (rather than other types of cells) can promote the development of HCC in synergistic oncogenes.
SIRT5 deficiency in hepatocytes promotes the development of HCC in synergistic oncogenes
In order to explore the mechanism of SIRT5 in the occurrence of HCC, the researchers carried out further research, and through cell line experiments, they found that SIRT5 defects did not affect the proliferation and migration ability of tumor cells themselves. This excludes the possibility that SIRT5 deficiency promotes HCC by enhancing hepatocyte tumorigenesis.
So what mechanism does SIRT5 deficiency promote tumorigenesis? The team analyzed the composition of immune cells in the tumor microenvironment and found that the number of M2 polarized macrophages and MDSCs in sirT5-/-mouse livers increased significantly, while the number of CD8+ T cells decreased significantly. This suggests that a deficiency in SIRT5 creates an immunosuppressive microenvironment conducive to the development of tumorigenesis.
SIRT5 deficiency promotes an increase in the number of M2 macrophages
Because the substrate of SIRT5 includes a variety of metabolically related enzymes, the researchers performed a metabolomics analysis of the livers of SIRT5-/- and WT mice injected with YAP5SA at high pressure. The results showed that SIRT5-/-mice were modulated in the liver bile acid biosynthesis pathway. Although there was no significant change in the content of total bile acids in the liver of SIRT5-/-mice, the proportion of T-CA (bile acid and bile acid binding product with taurine) in bile acid was significantly increased, and the concentration of T-CA in sirt5-/-mouse serum was also significantly higher than that in WT mice.
To explore whether SIRT5 deficiencies affect the tumor microenvironment through T-CA, the researchers conducted in vitro co-culture experiments as well as macrophage polarization experiments, and found that T-CA can promote macrophage M2 polarization, and this role relies on T-CA's nuclear receptor FXR. These data suggest that SIRT5-deficient liver cells can promote macrophage M2 polarization by increasing the content of T-CA.
SIRT5 deficiency promotes an increase in T-CA and promotes macrophage M2 polarization
Since T-CA can cause immunosuppression and promote the development of HCC, can neutralizing T-CA reverse immunosuppression and thus inhibit tumor growth?
To figure this out, the researchers used the commonly used clinical cholestylamine treatment to treat mice introduced into YAP5SA. Cholestamine therapy not only effectively reduced the T-CA levels in the liver and serum of mice, but also significantly reduced the number of MDSCs and M2 polarized macrophages in SIRT5-/- mice (rather than SIRT5+/+ mice), and reduced the number and weight of tumor nodules. This suggests that the use of cholestamine chelating T-CA can effectively reverse the immunosuppression caused by MDSC and M2 polarized macrophages and inhibit tumor growth.
Cholestylamine therapy reverses immunosuppression and reduces tumor burden
The above findings in mice revealed in mice that SIRT5 deficiency increases liver as well as serum T-CA levels, and T-CA promotes macrophage M2 polarization causing immunosuppression to promote tumor growth. In order to explore whether the same mechanism exists in human HCC patients, the researchers analyzed the transcriptome data of HCC patients in the TCGA database and the clinical specimens of HCC patients, and found that the expression of SIRT5 gene was significantly inversely correlated with TAM and M2 macrophage marker genes.
Moreover, compared with healthy people, the serum T-CA level of HCC patients was significantly increased, and there was a positive correlation between high serum T-CA and the number of tumor local TAM and M2 macrophages. These data suggest that the mechanisms found in mice are similarly present in patients with HCC.
Serum T-CA concentrations in patients with HCC were positively correlated with M2 macrophage markers
Overall, the results of this study reveal the mechanism by which the low expression of SIRT5 increases T-CA content in HCC, which in turn leads to tumor immune evasion, and also proposes a potential therapeutic strategy for the treatment of HCC patients with approved cholestylamine, which is of great significance for HCC patients with low expression of SIRT5 or high serum T-CA. It is expected that further clinical trials will explore the therapeutic effect of cholestylamine on HCC, thus bringing hope to the majority of HCC patients.
This study mechanism summarizes
At the same time, we also want to know whether the anticholeamine chelating bile hydrochloride reversal immunosuppressive effect can have a synergistic effect with immunotherapy such as PD-1/PD-L1 inhibitors and improve the efficacy.
bibliography:
1. Rongshou Zheng, Siwei Zhang, Hongmei Zeng, Shaoming Wang, Kexin Sun, Ru Chen, Li Li, Wenqiang Wei, Jie He,Cancer incidence and mortality in China, 2016,Journal of the National Cancer Center,2022, doi:10.1016/j.jncc.2022.02.002.
2. Crispe IN. The liver as a lymphoid organ. Annu Rev Immunol. 2009;27:147-163. doi:10.1146/annurev.immunol.021908.132629
3. Wangensteen KJ, Chang KM. Multiple Roles for Hepatitis B and C Viruses and the Host in the Development of Hepatocellular Carcinoma. Hepatology. 2021;73 Suppl 1(Suppl 1):27-37. doi:10.1002/hep.31481
4. Fiorucci S, Biagioli M, Zampella A, Distrutti E. Bile Acids Activated Receptors Regulate Innate Immunity. Front Immunol. 2018;9:1853. Published 2018 Aug 13. doi:10.3389/fimmu.2018.01853
5. Sun R, Zhang Z, Bao R, et al. Loss of SIRT5 promotes bile acid-induced immunosuppressive microenvironment and hepatocarcinogenesis. J Hepatol. 2022; S0168-8278(22)00139-8. doi:10.1016/j.jhep.2022.02.030
Responsible editor 丨IoTalker