Glutaminases as a Novel Target for SDHB-Associated Pheochromocytomas/Paragangliomas

SGLT2 inhibitor improves kidney function and morphology by regulating renal metabolism in mice with diabetic kidney disease

BACKGROUND

Diabetic kidney disease (DKD) is a secondary complication of diabetes mellitus and a leading cause of chronic kidney disease.

AIM

To investigate the impact of long-term canagliflozin treatment on DKD and elucidate its underlying mechanism.

METHODS

DKD model was established using high-fat diet and streptozotocin in male C57BL/6J mice (n = 30). Mice were divided into five groups and treated for 12 weeks. 1) normal control mice, 2) DKD model, 3) mice treated low-dose of canagliflozin, 4) high-dose of canagliflozin and 5) β-hydroxybutyrate. Mice kidney morphology and function were evaluated, and a metabolomics analysis was performed.

RESULTS

Canagliflozin treatment reduced blood creatinine and urine nitrogen levels and improved systemic insulin sensitivity and glucose tolerance in diabetic mice. Additionally, a decrease in histological lesions including collagen and lipid deposition in the kidneys was observed. β-hydroxybutyrate treatment did not yield a comparable outcome. The metabolomics analysis revealed that canagliflozin induced alterations in amino acid metabolism profiles in the renal tissue of diabetic mice.

CONCLUSION

Canagliflozin protects the kidneys of diabetic mice by increasing the levels of essential amino acids, promoting mitochondrial homeostasis, mitigating oxidative stress, and stimulating the amino acid-dependent tricarboxylic acid cycle.

Study on Mechanisms of Resistance to SDHI Fungicide Pydiflumetofen in Fusarium fujikuroi

Rice bakaenii disease (RBD) is a widespread and devastating disease mainly caused by Fusarium fujikuroi. Pydiflumetofen (Pyd) is a novel succinate dehydrogenase inhibitor (SDHI) with strong inhibitory activity against F. fujikuroi, but the mechanism of resistance to Pyd has not been well studied for this pathogen. Through fungicide adaption, a total of 12 Pyd-resistant mutants were obtained and the resistance level could be divided into three categories of high resistance (HR), moderate resistance (MR), and low resistance (LR) with resistance factors (RF) of 184.04-672.90, 12.63-42.49, and <10, respectively. Seven genotypes of point mutations in FfSdh genes (FfSdhBH248L, FfSdhBH248D, FfSdhBH248Y, FfSdhC2A83V, FfSdhC2H144Y, FfSdhDS106F, and FfSdhDE166K) were found in these mutants, among which genotype FfSdhBH248L and FfSdhC2A83V mutants showed HR, genotype FfSdhBH248D, FfSdhBH248Y, FfSdhC2H144Y, and FfSdhDE166K mutants showed MR, and genotype FfSdhDS106F mutants showed LR. Moreover, all the substitutions of amino acid point mutations including FfSdhBH248L/D/Y, FfSdhC2A83V,H144Y, and FfSdhDS106F,E166K conferring resistance to Pyd in F. fujikuroi were verified by protoplast transformation. Additionally, a positive cross-resistance was detected between Pyd and another SDHI fungicide penflufen, while no cross-resistance was detected between Pyd and phenamacril, prochloraz, azoxystrobin, carbendazim, or fludioxonil. Although pathogenicity of the mutants was increased compared with that of the wild-type parental strains, the mycelial growth rate and spore production levels of the resistant mutants were significantly decreased (P < 0.05), indicating significant fitness cost of resistance to Pyd in F. fujikuroi. Taken together, the risk of resistance to Pyd in F. fujikuroi might be moderate, and appropriate precautions against resistance development in natural populations should be taken into account when Pyd is used for the control of RBD.

Targeted metabolomics detects a putatively diagnostic signature in plasma and dried blood spots from head and neck paraganglioma patients

Head and neck paragangliomas (HNPGLs), rare chemoresistant tumors curable only with surgery, are strongly influenced by genetic predisposition, hence patients and relatives require lifetime follow-up with MRI and/or PET-CT because of de novo disease risk. This entails exposure to electromagnetic/ionizing radiation, costs, and organizational challenges, because patients and relatives are scattered far from reference centers. Simplified first-line screening strategies are needed. We employed flow injection analysis tandem mass spectrometry, as used in newborn metabolic screening, to compare the plasma metabolic profile of HNPGL patients (59 samples, 56 cases) and healthy controls (24 samples, 24 cases). Principal Component Analysis (PCA) and Partial Least Discriminant Analysis (PLS-DA) highlighted a distinctive HNPGL signature, likely reflecting the anaplerotic conversion of the TCA cycle to glutaminolysis and catabolism of branched amino acids, DNA damage and deoxyadenosine (dAdo) accumulation, impairment of fatty acid oxidation, switch towards the Warburg effect and proinflammatory lysophosphatidylcholines (LPCs) signaling. Statistical analysis of the metabolites that most impacted on PLS-DA was extended to 10 acoustic neuroma and 2 cholesteatoma patients, confirming significant differences relative to the HNPGL plasma metabolomic profile. The best confusion matrix from the ROC curve built on 2 metabolites, dAdo and C26:0-LPC, provided specificity of 94.29% and sensitivity of 89.29%, with positive and negative predictive values of 96.2% and 84.6%, respectively. Analysis of dAdo and C26:0-LPC levels in dried venous and capillary blood confirmed that dAdo, likely deriving from 2'-deoxy-ATP accumulated in HNPGL cells following endogenous genotoxic damage, efficiently discriminated HNPGL patients from healthy controls and acoustic neuroma/cholesteatoma patients on easily manageable dried blood spots.

Genetics of Pheochromocytomas and Paragangliomas Determine the Therapeutical Approach

Pheochromocytomas and paragangliomas are the most heritable endocrine tumors. In addition to the inherited mutation other driver mutations have also been identified in tumor tissues. All these genetic alterations are clustered in distinct groups which determine the pathomechanisms. Most of these tumors are benign and their surgical removal will resolve patient management. However, 5–15% of them are malignant and therapeutical possibilities for them are limited. This review provides a brief insight about the tumorigenesis associated with pheochromocytomas/paragangliomas in order to present them as potential therapeutical targets.

Loss of SDHB Induces a Metabolic Switch in the hPheo1 Cell Line toward Enhanced OXPHOS

BACKGROUND

Enzymes of tricarboxylic acid (TCA) have recently been recognized as tumor suppressors. Mutations in the SDHB subunit of succinate dehydrogenase (SDH) cause pheochromocytomas and paragangliomas (PCCs/PGLs) and predispose patients to malignant disease with poor prognosis.

METHODS

Using the human pheochromocytoma cell line (hPheo1), we knocked down SDHB gene expression using CRISPR-cas9 technology.

RESULTS

Microarray gene expression analysis showed that >500 differentially expressed gene targets, about 54%, were upregulated in response to SDHB knock down. Notably, genes involved in glycolysis, hypoxia, cell proliferation, and cell differentiation were up regulated, whereas genes involved in oxidative phosphorylation (OXPHOS) were downregulated. In vitro studies show that hPheo1 proliferation is not affected negatively and the cells that survive by shifting their metabolism to the use of glutamine as an alternative energy source and promote OXPHOS activity. Knock down of SDHB expression results in a significant increase in GLUD1 expression in hPheo1 cells cultured as monolayer or as 3D culture. Analysis of TCGA data confirms the enhancement of GLUD1 in SDHB mutated/low expressed PCCs/PGLs.

CONCLUSIONS

Our data suggest that the downregulation of SDHB in PCCs/PGLs results in increased GLUD1 expression and may represent a potential biomarker and therapeutic target in SDHB mutated tumors and SDHB loss of activity-dependent diseases.

Model systems in SDHx-related pheochromocytoma/paraganglioma

Pheochromocytoma (PHEO) and paraganglioma (PGL) (together PPGL) are tumors with poor outcomes that arise from neuroendocrine cells in the adrenal gland, and sympathetic and parasympathetic ganglia outside the adrenal gland, respectively. Many follow germline mutations in genes coding for subunits of succinate dehydrogenase (SDH), a tetrameric enzyme in the tricarboxylic acid (TCA) cycle that both converts succinate to fumarate and participates in electron transport. Germline SDH subunit B (SDHB) mutations have a high metastatic potential. Herein, we review the spectrum of model organisms that have contributed hugely to our understanding of SDH dysfunction. In Saccharomyces cerevisiae (yeast), succinate accumulation inhibits alpha-ketoglutarate-dependent dioxygenase enzymes leading to DNA demethylation. In the worm Caenorhabditis elegans, mutated SDH creates developmental abnormalities, metabolic rewiring, an energy deficit and oxygen hypersensitivity (the latter is also found in Drosophila melanogaster). In the zebrafish Danio rerio, sdhb mutants display a shorter lifespan with defective energy metabolism. Recently, SDHB-deficient pheochromocytoma has been cultivated in xenografts and has generated cell lines, which can be traced back to a heterozygous SDHB-deficient rat. We propose that a combination of such models can be efficiently and effectively used in both pathophysiological studies and drug-screening projects in order to find novel strategies in PPGL treatment.

Analytical Performance of NGS-Based Molecular Genetic Tests Used in the Diagnostic Workflow of Pheochromocytoma/Paraganglioma

Next Generation Sequencing (NGS)-based methods are high-throughput and cost-effective molecular genetic diagnostic tools. Targeted gene panel and whole exome sequencing (WES) are applied in clinical practice for assessing mutations of pheochromocytoma/paraganglioma (PPGL) associated genes, but the best strategy is debated. Germline mutations of at the least 18 PPGL genes are present in approximately 20-40% of patients, thus molecular genetic testing is recommended in all cases. We aimed to evaluate the analytical and clinical performances of NGS methods for mutation detection of PPGL-associated genes. WES (three different library preparation and bioinformatics workflows) and an in-house, hybridization based gene panel (endocrine-onco-gene-panel- ENDOGENE) was evaluated on 37 (20 WES and 17 ENDOGENE) samples with known variants. After optimization of the bioinformatic workflow, 61 additional samples were tested prospectively. All clinically relevant variants were validated with Sanger sequencing. Target capture of PPGL genes differed markedly between WES platforms and genes tested. All known variants were correctly identified by all methods, but methods of library preparations, sequencing platforms and bioinformatical settings significantly affected the diagnostic accuracy. The ENDOGENE panel identified several pathogenic mutations and unusual genotype-phenotype associations suggesting that the whole panel should be used for identification of genetic susceptibility of PPGL.

From Metabolism to Genetics and Vice Versa: The Rising Role of Oncometabolites in Cancer Development and Therapy

Over the last decades, the study of cancer metabolism has returned to the forefront of cancer research and challenged the role of genetics in the understanding of cancer development. One of the major impulses of this new trend came from the discovery of oncometabolites, metabolic intermediates whose abnormal cellular accumulation triggers oncogenic signalling and tumorigenesis. These findings have led to reconsideration and support for the long-forgotten hypothesis of Warburg of altered metabolism as oncogenic driver of cancer and started a novel paradigm whereby mitochondrial metabolites play a pivotal role in malignant transformation. In this review, we describe the evolution of the cancer metabolism research from a historical perspective up to the oncometabolites discovery that spawned the new vision of cancer as a metabolic disease. The oncometabolites' mechanisms of cellular transformation and their contribution to the development of new targeted cancer therapies together with their drawbacks are further reviewed and discussed.

Hypoxia Signaling in Cancer: From Basics to Clinical Practice

Cancer hypoxia, recognized as one of the most important hallmarks of cancer, affects gene expression, metabolism and ultimately tumor biology-related processes. Major causes of cancer hypoxia are deficient or inappropriate vascularization and systemic hypoxia of the patient (frequently induced by anemia), leading to a unique form of genetic reprogramming by hypoxia induced transcription factors (HIF). However, constitutive activation of oncogene-driven signaling pathways may also activate hypoxia signaling independently of oxygen supply. The consequences of HIF activation in tumors are the angiogenic phenotype, a novel metabolic profile and the immunosuppressive microenvironment. Cancer hypoxia and the induced adaptation mechanisms are two of the major causes of therapy resistance. Accordingly, it seems inevitable to combine various therapeutic modalities of cancer patients by existing anti-hypoxic agents such as anti-angiogenics, anti-anemia therapies or specific signaling pathway inhibitors. It is evident that there is an unmet need in cancer patients to develop targeted therapies of hypoxia to improve efficacies of various anti-cancer therapeutic modalities. The case has been opened recently due to the approval of the first-in-class HIF2α inhibitor.

Three Dimensional Cell Culturing for Modeling Adrenal and Pituitary Tumors

In vitro monolayer conditions are not able to reproduce the complexity of solid tumors, still, there is scarce information about the 3D cell culture models of endocrine tumor types. Therefore, our aim was to develop in vitro 3D tumor models by different methodologies for adrenocortical carcinoma (H295R), pituitary neuroendocrine tumor (RC-4B/C and GH3) and pheochromocytoma (PC-12). Various methodologies were tested. Cell biological assays (cell viability, proliferation and live cell ratio) and steroid hormone production by HPLC-MS/MS method were applied to monitor cellular well-being. Cells in hanging drops and embedded in matrigel formed multicellular aggregates but they were difficult to handle and propagate for further experiments. The most widely used methods: ultra-low attachment plate (ULA) and spheroid inducing media (SFDM) were not the most viable 3D model of RC-4B/C and GH3 cells that would be suitable for further experiments. Combining spheroid generation with matrigel scaffold H295R 3D models were viable for 7 days, RC-4B/C and GH3 3D models for 7–10 days. ULA and SFDM 3D models of PC-12 cells could be used for further experiments up to 4 days. Higher steroid production in 3D models compared to conventional monolayer culture was detected. Endocrine tumor cells require extracellular matrix as scaffold for viable 3D models that can be one reason behind the lack of the usage of endocrine 3D cultures. Our models help understanding the pathogenesis of endocrine tumors and revealing potential biomarkers and therapeutic targets. They could also serve as an excellent platform for preclinical drug test screening.

Targeting YTHDF1 effectively re-sensitizes cisplatin-resistant colon cancer cells by modulating GLS-mediated glutamine metabolism

Colorectal cancer (CRC) has a high mortality rate and poor prognosis. Despite chemotherapeutic agents such as cisplatin, which has achieved a better prognosis and survival rate against cancer, drug resistance leads to significant challenges. Accumulating evidence suggests that YTHDF1, the N ⁶-methyladenosine (m6A) "reader," is an important regulator in tumor progresses. Herein, we report that YTHDF1 was significantly upregulated in human colon tumors and cell lines. Overexpression of YTHDF1 decreased the cisplatin sensitivity of colon cancer cells. From the established cisplatin-resistant CRC cell line (LoVo CDDP R), we detected that YTHDF1 was significantly upregulated in cisplatin-resistant CRC cells. Intriguingly, RNA sequencing (RNA-seq) results revealed that glutamine metabolism enzymes were clearly upregulated in LoVo CDDP R cells. Glutamine uptake, that is, glutaminase (GLS) activity, was upregulated in LoVo CDDP R cells. Furthermore, bioinformatics analysis indicated that the 3' UTR of GLS1 contained a putative binding motif of YTHDF1, and an interaction was further validated by a protein-RNA interaction assay (RNA immunoprecipitation [RIP]). Furthermore, we demonstrated that YTHDF1 promoted protein synthesis of GLS1. Inhibiting GLS1 effectively synergizes with cisplatin to induce colon cancer cell death. Finally, that YTHDF1 mediated cisplatin through the GLS1-glutamine metabolism axis was validated by an in vivo xenograft mouse model. In summary, our study reveals a new mechanism for YTHDF1-promoted cisplatin resistance, contributing to overcoming chemoresistant colon cancers.

Seven Novel Genes Related to Cell Proliferation and Migration of VHL-Mutated Pheochromocytoma

Pheochromocytoma, as a neuroendocrine tumor with the highest genetic correlation in all types of tumors, has attracted extensive attention. Von Hipper Lindau (VHL) has the highest mutation frequency among the genes associated with pheochromocytoma. However, the effect of VHL on the proteome of pheochromocytoma remains to be explored. In this study, the VHL knockdown (VHL-KD) PC12 cell model was established by RNA interference (shRNA). We compared the proteomics of VHL-KD and VHL-WT PC12 cell lines. The results showed that the expression of 434 proteins (VHL shRNA/WT > 1.3) changed significantly in VHL-KD-PC12 cells. Among the 434 kinds of proteins, 83 were involved in cell proliferation, cell cycle and cell migration, and so on. More importantly, among these proteins, we found seven novel key genes, including Connective Tissue Growth Factor (CTGF), Syndecan Binding Protein (SDCBP), Cysteine Rich Protein 61 (CYR61/CCN1), Collagen Type III Alpha 1 Chain (COL3A1), Collagen Type I Alpha 1 Chain (COL1A1), Collagen Type V Alpha 2 Chain (COL5A2), and Serpin Family E Member 1 (SERPINE1), were overexpressed and simultaneously regulated cell proliferation and migration in VHL-KD PC12 cells. Furthermore, the abnormal accumulation of HIF2α caused by VHL-KD significantly increased the expression of these seven genes during hypoxia. Moreover, cell-counting, scratch, and transwell assays demonstrated that VHL-KD could promote cell proliferation and migration, and changed cell morphology. These findings indicated that inhibition of VHL expression could promote the development of pheochromocytoma by activating the expression of cell proliferation and migration associated genes.

Succinate Dehydrogenase and Ribonucleic Acid Networks in Cancer and Other Diseases

Simple Summary

Although the dysfunction of the succinate dehydrogenase complex in mitochondria leads to cancer and other diseases due to aberrant metabolic reactions and signaling pathways, it is not well known how the succinate dehydrogenase complex is regulated. Our review highlights that non-coding ribonucleic acids (RNAs), RNA editing enzymes, and RNA modifying enzymes regulate expressions and functions of the succinate dehydrogenase complex. This research will provide new strategies for treating succinate dehydrogenase-relevant diseases in a clinic.

Abstract

Succinate dehydrogenase (SDH) complex connects both the tricarboxylic acid (TCA) cycle and the electron transport chain (ETC) in the mitochondria. However, SDH mutation or dysfunction-induced succinate accumulation results in multiple cancers and non-cancer diseases. The mechanistic studies show that succinate activates hypoxia response and other signal pathways via binding to 2-oxoglutarate-dependent oxygenases and succinate receptors. Recently, the increasing knowledge of ribonucleic acid (RNA) networks, including non-coding RNAs, RNA editors, and RNA modifiers has expanded our understanding of the interplay between SDH and RNA networks in cancer and other diseases. Here, we summarize recent discoveries in the RNA networks and their connections to SDH. Additionally, we discuss current therapeutics targeting SDH in both pre-clinical and clinical trials. Thus, we propose a new model of SDH–RNA network interaction and bring promising RNA therapeutics against SDH-relevant cancer and other diseases.