Glycine N-methyltransferase inhibits aristolochic acid nephropathy by increasing CYP3A44 and decreasing NQO1 expression in female mouse hepatocytes

Unveiling correlations between aristolochic acids and liver cancer: spatiotemporal heterogeneity phenomenon

Aristolochic acids are a class of naturally occurring compounds in Aristolochiaceae that have similar structural skeletons and chemical properties. Exposure to aristolochic acids is a risk factor for severe kidney disease and urinary system cancer. However, the carcinogenicity of aristolochic acids to the liver, which is the main site of aristolochic acid metabolism, is unclear. Although the characteristic fingerprint of aristolochic acid-induced mutations has been detected in the liver and aristolochic acids are known to be hepatotoxic, whether aristolochic acids can directly cause liver cancer is yet to be verified. This review summarizes the findings of long-term carcinogenicity studies of aristolochic acids in experimental animals. We propose that spatiotemporal heterogeneity in the carcinogenicity of these phytochemicals could explain why direct evidence of aristolochic acids causing liver cancer has never been found in adult individuals. We also summarized the reported approaches to mitigate aristolochic acid-induced hepatotoxicity to better address the associated global safety issue and provide directions and recommendations for future investigation.

The oncogenic mechanisms of the Janus kinase-signal transducer and activator of transcription pathway in digestive tract tumors

Digestive tract tumors are heterogeneous and involve the dysregulation of multiple signaling pathways. The Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway plays a notable role in the oncogenesis of digestive tract tumors. Typically activated by pro-inflammatory cytokines, it regulates important biological processes, such as cell growth, differentiation, apoptosis, immune responses, and inflammation. The aberrant activation of this pathway manifests in different forms, including mutations in JAKs, overexpression of cytokine receptors, and sustained STAT activation, and contributes to promoting the malignant characteristics of cancer cells, including uncontrolled proliferation, resistance to apoptosis, enhanced invasion and metastasis, angiogenesis, acquisition of stem-like properties, and drug resistance. Numerous studies have shown that aberrant activation of the JAK-STAT pathway is closely related to the development and progression of digestive tract tumors, contributing to tumor survival, angiogenesis, changes in the tumor microenvironment, and even immune escape processes. In addition, this signaling pathway also affects the sensitivity of digestive tract tumors to chemotherapy and targeted therapy. Therefore, it is crucial to comprehensively understand the oncogenic mechanisms underlying the JAK-STAT pathway in order to develop effective therapeutic strategies against digestive tract tumors. Currently, several JAK-STAT inhibitors are undergoing clinical and preclinical trials as potential treatments for various human diseases. However, further investigation is required to determine the role of this pathway, as well as the effectiveness and safety of its inhibitors, especially in the context of digestive tract tumors. In this review, we provide an overview of the structure, classic activation, and negative regulation of the JAK-STAT pathway. Furthermore, we discuss the pathogenic mechanisms of JAK-STAT signaling in different digestive tract tumors, with the aim of identifying potential novel therapeutic targets. Video Abstract.

TNF- α from the Proximal Nephron Exacerbates Aristolochic Acid Nephropathy

Key Points

Proximal tubular TNF aggravates kidney injury and fibrogenesis in aristolochic acid nephropathy. Tubular TNF disrupts the cell cycle in injured tubular epithelial cells. TNF-mediated toxic renal injury is independent of systemic immune responses.

Background

Aristolochic acid nephropathy (AAN) presents with tubular epithelial cell (TEC) damage and tubulointerstitial inflammation. Although TNF-α regulates cell apoptosis and inflammatory responses, the effects of tubular TNF in the progression of AAN require elucidation.

Methods

Floxed TNF mice on the 129/SvEv background were crossed with PEPCK-Cre mice to generate PEPCK-Cre + TNF flox/flox (TNF PTKO) mice or bred with Ksp-Cre mice to generate KSP-Cre + TNF flox/flox (TNF DNKO) mice. TNF PTKO, TNF DNKO, and wild-type controls (Cre negative littermates) were subjected to acute and chronic AAN.

Results

Deletion of TNF in the proximal but not distal nephron attenuated kidney injury, renal inflammation, and tubulointerstitial fibrosis after acute or chronic aristolochic acid (AA) exposure. The TNF PTKO mice did not have altered numbers of infiltrating myeloid cells in AAN kidneys. Nevertheless, kidneys from AA-treated TNF PTKO mice had reduced levels of proteins involved in regulated cell death, higher proportions of TECs in the G0/G1 phase, and reduced TEC proportions in the G2/M phase. Pifithrin-α , which restores the cell cycle, abrogated differences between the wild-type and PTKO cohorts in G2/M phase arrest of TECs and kidney fibrosis after AA exposure.

Conclusions

TNF from the proximal but not the distal nephron propagates kidney injury and fibrogenesis in AAN in part by inducing G2/M cell cycle arrest of TECs.

High-fat diet plus HNF1A variant promotes polyps by activating β-catenin in early-onset colorectal cancer

The incidence of early-onset colorectal cancer (EO-CRC) is rising and is poorly understood. Lifestyle factors and altered genetic background possibly contribute. Here, we performed targeted exon sequencing of archived leukocyte DNA from 158 EO-CRC participants, which identified a missense mutation at p.A98V within the proximal DNA binding domain of Hepatic Nuclear Factor 1 α (HNF1AA98V, rs1800574). The HNF1AA98V exhibited reduced DNA binding. To test function, the HNF1A variant was introduced into the mouse genome by CRISPR/Cas9, and the mice were placed on either a high-fat diet (HFD) or high-sugar diet (HSD). Only 1% of the HNF1A mutant mice developed polyps on normal chow; however, 19% and 3% developed polyps on the HFD and HSD, respectively. RNA-Seq revealed an increase in metabolic, immune, lipid biogenesis genes, and Wnt/β-catenin signaling components in the HNF1A mutant relative to the WT mice. Mouse polyps and colon cancers from participants carrying the HNF1AA98V variant exhibited reduced CDX2 and elevated β-catenin proteins. We further demonstrated decreased occupancy of HNF1AA98V at the Cdx2 locus and reduced Cdx2 promoter activity compared with WT HNF1A. Collectively, our study shows that the HNF1AA98V variant plus a HFD promotes the formation of colonic polyps by activating β-catenin via decreasing Cdx2 expression.

An insight on microbial degradation of benzo[a]pyrene: current status and advances in research

Benzo[a]pyrene (BaP) is a high molecular weight polycyclic aromatic hydrocarbon produced as a result of incomplete combustion of organic substances. Over the years, the release of BaP in the atmosphere has increased rapidly, risking human lives. BaP can form bonds with DNA leading to the formation of DNA adducts thereby causing cancer. Therefore addressing the problem of its removal from the environment is quite pertinent though it calls for a very cumbersome and tedious process owing to its recalcitrant nature. To resolve such issues many efforts have been made to develop physical and chemical technologies of BaP degradation which have neither been cost-effective nor eco-friendly. Microbial degradation of BaP, on the other hand, has gained much attention due to added advantage of the high level of microbial diversity enabling great potential to degrade the substance without impairing environmental sustainability. Microorganisms produce enzymes like oxygenases, hydrolases and cytochrome P450 that enable BaP degradation. However, microbial degradation of BaP is restricted due to several factors related to its bio-availability and soil properties. Technologies like bio-augmentation and bio-stimulation have served to enhance the degradation rate of BaP. Besides, advanced technologies such as omics and nano-technology have opened new doors for a better future of microbial degradation of BaP and related compounds.

Nuclear localization dictates hepatocarcinogenesis suppression by glycine N-methyltransferase

BACKGROUND

GNMT (glycine N-methyltransferase) is a tumor suppressor gene, but the mechanisms mediating its suppressive activity are not entirely known.

METHODS

We investigated the oncosuppressive mechanisms of GNMT in human hepatocellular carcinoma (HCC). GNMT mRNA and protein levels were evaluated by quantitative RT-PCR and immunoblotting. GNMT effect in HCC cell lines was modulated through GNMT cDNA induced overexpression or anti-GNMT siRNA transfection.

RESULTS

GNMT was expressed at low level in human HCCs with a better prognosis (HCCB) while it was almost absent in fast-growing tumors (HCCP). In HCCB, the nuclear localization of the GNMT protein was much more pronounced than in HCCP. In Huh7 and HepG2 cell lines, GNMT forced expression inhibited the proliferation and promoted apoptosis. At the molecular level, GNMT overexpression inhibited the expression of CYP1A (Cytochrome p450, aromatic compound-inducible), PREX2 (Phosphatidylinositol-3,4,5-trisphosphate-dependent Rac exchange factor 2), PARP1 [Poly (ADP-ribose) polymerase 1], and NFKB (nuclear factor-kB) genes. By chromatin immunoprecipitation, we found GNMT binding to the promoters of CYP1A1, PREX2, PARP1, and NFKB genes resulting in their strong inhibition. These genes are implicated in hepatocarcinogenesis, and are involved in the GNMT oncosuppressive action.

CONCLUSION

Overall, the present data indicate that GNMT exerts a multifaceted suppressive action by interacting with various cancer-related genes and inhibiting their expression.

Carnosine alleviates diabetic nephropathy by targeting GNMT, a key enzyme mediating renal inflammation and fibrosis

Diabetic nephropathy (DN) is a common microvascular complication of diabetes and the main cause of end-stage nephropathy (ESRD). Inflammation and fibrosis play key roles in the development and progression of diabetic nephropathy. By using in vivo and in vitro DN models, our laboratory has identified the protective role of carnosine (CAR) on renal tubules. Our results showed that carnosine restored the onset and clinical symptoms as well as renal tubular injury in DN. Furthermore, carnosine decreased kidney inflammation and fibrosis in DN mice. These results were consistent with high glucose (HG)-treated mice tubular epithelial cells (MTECs). Using web-prediction algorithms, cellular thermal shift assay (CETSA) and molecular docking, we identified glycine N-methyltransferase (GNMT) as a carnosine target. Importantly, we found that GNMT, a multiple functional protein that regulates the cellular pool of methyl groups by controlling the ratio of S-adenosylmethionine (SAM) to S-adenosylhomocysteine (SAH), was down-regulated significantly in the serum of Type 1 DM patients and renal tissues of DN mice. Moreover, using cultured TECs, we confirmed that the increased GNMT expression by transient transfection mimicked the protective role of carnosine in reducing inflammation and fibrosis. Conversely, the inhibition of GNMT expression abolished the protective effects of carnosine. In conclusion, carnosine might serve as a promising therapeutic agent for DN and GNMT might be a potential therapeutic target for DN.

Mitoquinone alleviates vincristine-induced neuropathic pain through inhibiting oxidative stress and apoptosis via the improvement of mitochondrial dysfunction

Chemotherapy drugs such as vincristine (Vin) could cause neuropathic pain. However, it is still lack of ideal therapeutic strategy to treat it. Mitochondrial dysfunction has been involved in the pathogenesis of neuropathic pain. The mitochondrial-targeted antioxidant, mitoquinone (MitoQ), is able to modify mitochondrial signaling, showing beneficial effects on various diseases. In the study, we investigated whether MitoQ could regulate Vin-induced neuropathic pain, and the underlying molecular mechanisms. The results showed that MitoQ significantly improved Vin-induced pain hypersensitivity and glial activation in mice. In addition, Vin resulted in severe oxidative stress in spinal cord tissues of mice, which were inhibited by MitoQ treatment through improving Nrf2 (NF-E2-related factor 2) expression in nuclear. Also, MitoQ treatment dose-dependently reduced the expression of pro-inflammatory cytokines, indicating its anti-inflammatory effects. Importantly, Vin stimulation contributed to mitochondrial fission, as evidenced by the increased expression of phosphorylated Drp1 (dynamin related protein 1) and Fis (mitochondrial fission protein 1), whereas mitochondrial fussion was inhibited. However, these effects were notably abrogated by MitoQ, subsequently improving mitochondrial dysfunction. Moreover, neuron death evoked by Vin was significantly rescued by MitoQ treatment. We also observed significantly reduced expression of cleaved Caspase-3 and Bax expression in spinal cord of MitoQ-treated mice with Vin stimulation. In contrast, anti-apoptotic factor Bcl-2 protein levels decreased by Vin were restored by MitoQ. The process of Cyto-c release from mitochondria triggered by Vin was effectively inhibited in mice treated with MitoQ. These in vivo results were further verified in the primary neurons using the in vitro and ex vivo experiments. Furthermore, MitoQ treatment alleviated axonal degeneration and mitochondria dysfunction induced by Vin. Thus, mitoquinone could alleviate vincristine-induced neuropathic pain by inhibiting oxidative stress and apoptosis via the improvement of mitochondrial dysfunction.

Aristolochic Acid-Induced Nephrotoxicity: Molecular Mechanisms and Potential Protective Approaches

Aristolochic acid (AA) is a generic term that describes a group of structurally related compounds found in the Aristolochiaceae plants family. These plants have been used for decades to treat various diseases. However, the consumption of products derived from plants containing AA has been associated with the development of nephropathy and carcinoma, mainly the upper urothelial carcinoma (UUC). AA has been identified as the causative agent of these pathologies. Several studies on mechanisms of action of AA nephrotoxicity have been conducted, but the comprehensive mechanisms of AA-induced nephrotoxicity and carcinogenesis have not yet fully been elucidated, and therapeutic measures are therefore limited. This review aimed to summarize the molecular mechanisms underlying AA-induced nephrotoxicity with an emphasis on its enzymatic bioactivation, and to discuss some agents and their modes of action to reduce AA nephrotoxicity. By addressing these two aspects, including mechanisms of action of AA nephrotoxicity and protective approaches against the latter, and especially by covering the whole range of these protective agents, this review provides an overview on AA nephrotoxicity. It also reports new knowledge on mechanisms of AA-mediated nephrotoxicity recently published in the literature and provides suggestions for future studies.

Tumor suppressor gene glycine N-methyltransferase and its potential in liver disorders and hepatocellular carcinoma

Glycine N-methyltransferase is a protein with many functions. In addition to catalyzing the production of sarcosine in the one carbon metabolism pathway, it plays a role in the detoxification of environmental carcinogens such as benzo[a]pyrene, aflatoxin B1, and aristocholic acid. There is also increasing evidence suggesting a role of GNMT deficiency in liver carcinogenesis. In this review, we discuss the role of GNMT in the detoxification of xenobiotics and the mechanism of GNMT suppression during liver tumorigenesis. The protective role of GNMT in the liver allows GNMT to not only serve as a marker of liver disease, but also potentially be applied in the treatment of liver disorders and hepatocellular carcinoma. We describe the potential use of GNMT in gene therapy and we introduce the development of a GNMT promoter reporter assay that can be used to screen medicinal drugs and herbal libraries for natural compounds with anti-cancer properties.

Predominant global glomerulosclerosis in patients of upper urinary tract urothelial carcinoma with pre-existing renal function impairment is a predictor of poor renal outcomes

Background

Incidence of renal dysfunction and risks of progression to end-stage renal disease (ESRD) were reported higher in upper urinary tract urothelial carcinoma (UTUC) than in renal cell carcinoma (RCC) patients after unilateral nephrectomy.

Methods

Totally 193 renal cancer patients, including 132 UTUC and 61 RCC, were studied to clarify whether the pathological changes of the kidney remnant removed from nephrectomy and the clinical factors might predict the risk of ESRD. Renal tubulointerstitial (TI) score and global glomerulosclerosis (GGS) rate were examined by one pathologist and two nephrologists independently under same histopathological criteria.

Results

The glomerular filtration rates at the time of surgery were lower in UTUC than RCC groups (p < 0.001). Average GGS score and average TI rate were higher in UTUC than in RCC groups (p < 0.001; p < 0.001). Competitive risk factor analysis revealed that abnormal GGS rate not related to age, predominant in UTUC with pre-existing renal function impairment, was a histopathological predictor of poor renal outcomes (creatinine doubling or ESRD) within 5 years in UTUC patients.

Conclusion

Pre-existing renal function and pathological change of kidney remnant in both UTUC and RCC have the value for prediction of renal outcomes.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5414-x) contains supplementary material, which is available to authorized users.

Utilizing proteomic approach to identify nuclear translocation related serine kinase phosphorylation site of GNMT as downstream effector for benzo[a]pyrene

Glycine N-methyltransferase (GNMT) protein is highly expressed in certain tissues, such as liver, pancreas, and prostate. GNMT serves multiple roles which include a methyl group transfer enzyme and a liver tumor suppressor. Benzo(a)pyrene (BaP), a family member of polycyclic aromatic hydrocarbon (PAH), is a known environmental carcinogen found in coal tar, tobacco smoke, barbecued food and incomplete combustion of auto fuel. BaP recruits cytochrome P450 to transform itself into benzo(a)pyrene-7,8-diol-9,10-epoxide (B(a) PDE), which covalently interacts with DNA causing tumorigenesis. BaP can be detoxified through GNMT and induces GNMT translocation into the cellular nucleus. GNMT translocation is accompanied by phosphorylation, but the role of phosphorylation in GNMT remains to be explored. Using liquid chromatography coupled with tandem mass spectrometry, this study identified serine 9 of GNMT as the phosphorylation site upon BaP treatment. When serine 9 was mutated and lost the capability to be phosphorylated, the occurrence of BaP-induced GNMT nuclear translocation was dramatically decreased. Also, this mutant from of GNMT lost the ability of phosphorylation and increased cytochrome P450 1A1 (Cyp1a) expression upon BaP treatment. In addition, protein kinase C (PKC) and c-Jun NH2-terminal kinase (JNK) may be required for such phosphorylation. Further characterization of phosphorylated GNMT for its link to BaP may bring new insights into chemical detoxification.

MicroRNA-224 down-regulates Glycine N-methyltransferase gene expression in Hepatocellular Carcinoma

Glycine N-methyltransferase (GNMT) is a tumor suppressor for HCC. It is down-regulated in HCC, but the mechanism is not fully understood. MicroRNA-224 (miR-224) acts as an onco-miR in HCC. This study is the first to investigate miR-224 targeting the coding region of GNMT transcript. The GNMT-MT plasmid containing a miR-224 binding site silent mutation of the GNMT coding sequence can escape the suppression of miR-224 in HEK293T cells. Expression of both exogenous and endogenous GNMT was suppressed by miR-224, while miR-224 inhibitor enhanced GNMT expression. miR-224 counteracts the effects of GNMT on the reduction of cell proliferation and tumor growth. The levels of miR-224 and GNMT mRNA showed a significant inverse relationship in tumor specimens from HCC patients. Utilizing CCl4-treated hepatoma cells and mice as a cell damage of inflammatory or liver injury model, we observed that the decreased expression levels of GNMT were accompanied with the elevated expression levels of miR-224 in hepatoma cells and mouse liver. Finally, hepatic AAV-mediated GNMT also reduced CCl4-induced miR-224 expression and liver fibrosis. These results indicated that AAV-mediated GNMT has potential liver protection activity. miR-224 can target the GNMT mRNA coding sequence and plays an important role in GNMT suppression during liver tumorigenesis.