Sirtuin5 contributes to colorectal carcinogenesis by enhancing glutaminolysis in a deglutarylation-dependent manner

Defective Endothelial Glutaminolysis Contributes to Impaired Angiogenesis and Poor Ischemic Tissue Repair in Diabetes

It has been demonstrated that glutamine is a key player in boosting endothelial cell (EC) proliferation. However, despite its importance, the role of endothelial glutaminolysis in diabetes remains largely unexplored. Our research aimed to investigate the function of glutaminolysis in ECs within the context of diabetes and to evaluate the potential therapeutic effects of salvianolic acid B (SalB) and α-ketoglutarate (α-KG) on diabetic vascular complications. Histological analysis of skin wounds in diabetic patients revealed delayed restoration of vascularization and collagen synthesis during wound healing, accompanied by decreased glutaminase 1 (GLS1) expression and reduced colocalization with the EC marker platelet-endothelial cell adhesion molecule-1 (CD31). Additionally, a significant decline in GLS1 activity and expression was observed in ECs isolated from diabetic hearts. In vitro studies using cultured ECs demonstrated that exposure to high glucose and high fat (HGHF) reduced GLS1 expression and suppressed glutaminolysis, impairing EC proliferation and tube formation. These adverse effects were mitigated by treatment with SalB or supplementation with α-KG plus nonessential amino acids (NEAAs). Among diabetic mice subjected to myocardial ischemia/reperfusion (MI/R), SalB administration or α-KG supplementation promoted myocardial revascularization and improved cardiac dysfunction. Notably, endothelial-specific GLS1 deletion in mice blocked the beneficial effects afforded by SalB but not those afforded by α-KG. Furthermore, SalB administration accelerated angiogenesis and cutaneous wound healing in diabetic mice, and these influences were removed by pharmacological inhibition of GLS1 using bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl) ethyl sulfide (BPTES) or genetic deletion of endothelial GLS1. These findings indicate that defective endothelial glutaminolysis contributes to impaired angiogenesis and poor ischemic tissue repair in diabetes. Improving endothelial glutaminolysis by treatment with SalB or metabolic supplementation with α-KG promotes angiogenesis and ischemic tissue repair in diabetic mice, emphasizing the possibility of GLS1 as a treatment target.

SIRT5: a potential target for discovering bioactive natural products

Silent information regulator 5 (SIRT5) is the fifth member of the sirtuin family, which is mainly expressed in mitochondrial matrix. SIRT5 plays a key role in metabolism and antioxidant responses, and is an important regulator for maintaining intracellular homeostasis. Given its involvement in multiple cellular processes, dysregulation of SIRT5 activity is associated with a variety of diseases. This review explores the structural characteristics of SIRT5 that influence its substrate specificity, highlights recent research advances, and summarizes its four key enzymatic activities along with their corresponding substrates in disease contexts. We also discuss the natural products that modulate SIRT5 activity and identify potential targets of SIRT5 through virtual docking, which may provide new therapeutic avenues. Although the mechanism of SIRT5 in diseases needs to be further elucidated and deglutathionylation activities are still at an early stage, targeting SIRT5 and its substrates holds significant promise for the development of novel therapeutics.

Crosstalk between metabolism and epigenetics during macrophage polarization

Macrophage polarization is a dynamic process driven by a complex interplay of cytokine signaling, metabolism, and epigenetic modifications mediated by pathogens. Upon encountering specific environmental cues, monocytes differentiate into macrophages, adopting either a pro-inflammatory (M1) or anti-inflammatory (M2) phenotype, depending on the cytokines present. M1 macrophages are induced by interferon-gamma (IFN-γ) and are characterized by their reliance on glycolysis and their role in host defense. In contrast, M2 macrophages, stimulated by interleukin-4 (IL-4) and interleukin-13 (IL-13), favor oxidative phosphorylation and participate in tissue repair and anti-inflammatory responses. Metabolism is tightly linked to epigenetic regulation, because key metabolic intermediates such as acetyl-coenzyme A (CoA), α-ketoglutarate (α-KG), S-adenosylmethionine (SAM), and nicotinamide adenine dinucleotide (NAD+) serve as cofactors for chromatin-modifying enzymes, which in turn, directly influences histone acetylation, methylation, RNA/DNA methylation, and protein arginine methylation. These epigenetic modifications control gene expression by regulating chromatin accessibility, thereby modulating macrophage function and polarization. Histone acetylation generally promotes a more open chromatin structure conducive to gene activation, while histone methylation can either activate or repress gene expression depending on the specific residue and its methylation state. Crosstalk between histone modifications, such as acetylation and methylation, further fine-tunes macrophage phenotypes by regulating transcriptional networks in response to metabolic cues. While arginine methylation primarily functions in epigenetics by regulating gene expression through protein modifications, the degradation of methylated proteins releases arginine derivatives like asymmetric dimethylarginine (ADMA), which contribute directly to arginine metabolism-a key factor in macrophage polarization. This review explores the intricate relationships between metabolism and epigenetic regulation during macrophage polarization. A better understanding of this crosstalk will likely generate novel therapeutic insights for manipulating macrophage phenotypes during infections like tuberculosis and inflammatory diseases such as diabetes.

Glutamate dehydrogenase 1-catalytic glutaminolysis feedback activates EGFR/PI3K/AKT pathway and reprograms glioblastoma metabolism

BACKGROUND

Glutamine is an important nutrient for cancer cell growth that provides biological sources for nucleic acid and fatty acid synthesis, but the role of glutaminolysis in signal transduction and glioblastoma (GBM) progression remains little known.

METHODS

Knockdown and overexpression cells were obtained to explore the functional roles of glutamate dehydrogenase 1 (GDH1) in cell proliferation, tumor formation, and aerobic glycolysis. RNA-seq, Chromatin immunoprecipitation, luciferase assay, and western blot were performed to verify the regulation of the EGFR-AKT pathway by the GDH1 (also known as GLUD1) and KDM6A. Metabolite-level measurements and Seahorse Assay were performed to assess the functional role of GHD1 in reprogramming glycolysis.

RESULTS

Here, we report that GDH1 catalytic glutaminolysis is essential for GBM cell line proliferation and brain tumorigenesis even in high-glucose conditions. Glutamine is metabolized through glutaminolysis to produce α-ketoglutarate (α-KG). We demonstrate that glutamine in combination with leucine activates mammalian TORC1 by enhancing glutaminolysis and α-KG production. α-KG increases the transcription of PDPK1 by reducing the suppressive histone modification H3K27me3 and then promotes the activation of the PI3K/AKT/mTOR pathway. This transcriptional activation induced by α-KG requires histone demethylase KDM6A, which is a 2-oxoglutarate oxygenase that plays an important role in converting α-KG to succinate. Furthermore, we show that GDH1-catalytic glutaminolysis also increases the expression of HK2 and promotes glycolysis in high-glucose conditions dependent on KDM6A-mediated demethylation of H3K27.

CONCLUSIONS

These findings suggest a novel function of glutaminolysis in the regulation of signal transduction and metabolism reprogramming and provide further evidence for the unique role of glutaminolysis in GBM progression.

Activation and inhibition of sirtuins: From bench to bedside

The sirtuin family comprises seven NAD+-dependent enzymes which catalyze protein lysine deacylation and mono ADP-ribosylation. Sirtuins act as central regulators of genomic stability and gene expression and control key processes, including energetic metabolism, cell cycle, differentiation, apoptosis, and aging. As a result, all sirtuins play critical roles in cellular homeostasis and organism wellness, and their dysregulation has been linked to metabolic, cardiovascular, and neurological diseases. Furthermore, sirtuins have shown dichotomous roles in cancer, acting as context-dependent tumor suppressors or promoters. Given their central role in different cellular processes, sirtuins have attracted increasing research interest aimed at developing both activators and inhibitors. Indeed, sirtuin modulation may have therapeutic effects in many age-related diseases, including diabetes, cardiovascular and neurodegenerative disorders, and cancer. Moreover, isoform selective modulators may increase our knowledge of sirtuin biology and aid to develop better therapies. Through this review, we provide critical insights into sirtuin pharmacology and illustrate their enzymatic activities and biological functions. Furthermore, we outline the most relevant sirtuin modulators in terms of their modes of action, structure-activity relationships, pharmacological effects, and clinical applications.

SIRT5-mediated GLS and GDH desuccinylation attenuates the autophagy of bovine mammary epithelial cells induced by ammonia

Sirtuin 5 (SIRT5) in mitochondria possesses a strong capacity for lysine desuccinylation, involving in various biological processes. Our previous research demonstrated that NH3 regulated autophagy dependent on SIRT5 in bovine mammary epithelial cells (bMECs). Interestingly, we discovered that SIRT5 reduced the content of NH3 and glutamate by inhibiting GLS activity in bMECs, the ratio of ADP/ATP also declined. In this study, we identified that SIRT5 interacted with endogenous GLS and GDH through Co-IP assay, but had no effect on endogenous GLS and GDH expression. SIRT5 made the succinylation levels of GLS and GDH significantly declined and resulted in the reduction of GLS and GDH activity. Next, the content of ammonia and glutamate, as well as the related autophagy markers were measured, we found that SIRT5 affected the glutamine metabolism, which attenuated ammonia release in MAC-T cells, accompanying with cellular autophagy decline, reducing the formation of autophagosome. Deletion of SIRT5 gene in MAC-T cells by means of CRISPR-cas9, we found the content of NH3 and glutamate increased, as well as autophagy promoted, which could be alleviated by SIRT5 overexpression. SIRT5 KO also resulted in increase of succinylation of GLS and GDH, as well as autophagy response in bMECs. Furthermore, SIRT5 promoted the maintenance of mitochondria homeostasis. Mechanistically, SIRT5 reduced ammonia release by modulating the succinylation levels and enzymatic activities of GLS and GDH in mitochondria and promoted the maintenance of mitochondria homeostasis, as well as further attenuated ammonia-stimulated autophagy in bovine mammary epithelial cells.

Metformin combined with CB-839 specifically inhibits KRAS-mutant ovarian cancer

KRAS mutations can cause metabolic reprogramming in ovarian cancer, leading to an increased metastatic capacity. This study investigated the metabolic reprogramming changes induced by KRAS mutations in ovarian cancer and the mechanism of action of metformin combined with a glutaminase 1 inhibitor (CB-839). KRAS-mutant ovarian cancer accounted for 14% of ovarian cancers. The expression of glucose metabolism-related (PFKFB3, HK2, GLUT1, and PDK2) and glutamine metabolism-related enzymes (GLS1 and ASCT2) was elevated in KRAS-mutant ovarian cancer cells compared with that in wild-type cells. KRAS-mutant cells had a higher aerobic oxidative capacity than did wild-type cells. Metformin inhibited proliferation, the expression of glucose metabolism-related enzymes, and the aerobic oxidative capacity of KRAS-mutant cells compared with those of control cells. Furthermore, it enhanced the expression of glutamine metabolism-related enzymes in KRAS-mutant cells. Metformin combined with CB-839 inhibited the proliferation and aerobic oxidation of KRAS-mutant cells to a greater extent than that observed in wild-type cells. Additionally, the inhibitory effects of metformin and CB-839 in the KRAS-mutant ovarian cancer NOD-SCID mouse model were significantly stronger than those in the drug-alone group. KRAS mutations lead to enhanced glucose and glutamine metabolism in ovarian cancer cells, which was inhibited by metformin combined with CB-839.

Moxibustion Alleviates Inflammation via SIRT5-mediated Post-translational Modification and Macrophage Polarization

Macrophage polarisation is influenced by Sirtuin5 (SIRT5), which is crucial for regulating anti-inflammatory processes. Moxibustion, a traditional Chinese medicine therapy, exerts anti-inflammatory effects by altering the succinate/α-ketoglutarate (α-KG) ratio, an indicator of the M1 to M2 macrophage shift. Glutamate dehydrogenase 1 (GLUD1), a key enzyme involved in α-KG production, is desuccinylated by SIRT5. Currently, the potential influence of moxibustion on SIRT5-GLUD1-α-KG-mediated macrophage polarization in inflammatory diseases remains unexplored. C57BL/6 J and Sirt5 knockout mice were used as complete Freund's adjuvant (CFA)-induced adjuvant arthritis models. Moxibustion and acupoint injections of MC3482 were administered. Paw capacity asssays and ELISA were performed to quantify inflammatory effects and the expression of succinate, and α-KG expressions. Flow cytometry (FCM) and immunofluorescence were used to assesss the expression of M1- and M2-like macrophages. LC-MS/MS-based proteomic analysis was performed, and GLUD1 was identified desuccinylated protein associated with SIRT5. Western blotting and immunoprecipitation (IP) were used to detect SIRT5, GLUD1, and succinylated GLUD1expressions. Moxibustion and the SIRT5-mediated desuccinylation inhibitor MC3482 decreased inflammation by increasing the number of M2 macrophages and reducing the number of M1 macrophage in the CFA model. The potential mechanism may be related to the effects of moxibustion and SIRT5 inhibition, which inverted succinate and α-KG levels in the CFA group, resulting in low succinate, high α-KG, and increased GLUD1 succinylation after treatment. These findings suggest that the anti-inflammatory effects moxibustion are related to the impact of macrophage conversion after SIRT5-mediated post-translational modification.

Tumor Metabolic Reprogramming and Ferroptosis: The Impact of Glucose, Protein, and Lipid Metabolism

Ferroptosis, a novel form of cell death discovered in recent years, is typically accompanied by significant iron accumulation and lipid peroxidation during the process. This article systematically elucidates how tumor metabolic reprogramming affects the ferroptosis process in tumor cells. The paper outlines the basic concepts and physiological significance of tumor metabolic reprogramming and ferroptosis, and delves into the specific regulatory mechanisms of glucose metabolism, protein metabolism, and lipid metabolism on ferroptosis. We also explore how complex metabolic changes in the tumor microenvironment further influence the response of tumor cells to ferroptosis. Glucose metabolism modulates ferroptosis sensitivity by influencing intracellular energetic status and redox balance; protein metabolism, involving amino acid metabolism and protein synthesis, plays a crucial role in the initiation and progression of ferroptosis; and the relationship between lipid metabolism and ferroptosis primarily manifests in the generation and elimination of lipid peroxides. This review aims to provide a new perspective on how tumor cells regulate ferroptosis through metabolic reprogramming, with the ultimate goal of offering a theoretical basis for developing novel therapeutic strategies targeting tumor metabolism and ferroptosis.

Sirtuin insights: bridging the gap between cellular processes and therapeutic applications

The greatest challenges that organisms face today are effective responses or detection of life-threatening environmental changes due to an obvious semblance of stress and metabolic fluctuations. These are associated with different pathological conditions among which cancer is most important. Sirtuins (SIRTs; NAD+-dependent enzymes) are versatile enzymes with diverse substrate preferences, cellular locations, crucial for cellular processes and pathological conditions. This article describes in detail the distinct roles of SIRT isoforms, unveiling their potential as either cancer promoters or suppressors and also explores how both natural and synthetic compounds influence the SIRT function, indicating promise for therapeutic applications. We also discussed the inhibitors/activators tailored to specific SIRTs, holding potential for diseases lacking effective treatments. It may uncover the lesser-studied SIRT isoforms (e.g., SIRT6, SIRT7) and their unique functions. This article also offers a comprehensive overview of SIRTs, linking them to a spectrum of diseases and highlighting their potential for targeted therapies, combination approaches, disease management, and personalized medicine. We aim to contribute to a transformative era in healthcare and innovative treatments by unraveling the intricate functions of SIRTs.

Advances in research on the relationship between mitochondrial function and colorectal cancer: a bibliometric study from 2013 to 2023

The study provides a thorough examination of literature from 2013 to 2023, delving into the intricate relationship between mitochondrial function and colorectal cancer (CRC). It offers a concise overview of the current landscape and emerging trends in this rapidly evolving research area. The findings indicate a consistent rise in annual publications, reflecting growing interest and significant potential in the field. China emerges as the leading contributor, followed by the United States and India. However, despite China's dominance in output, its average citation rate is lower than that of the US, which leads in citations per publication, highlighting a noticeable disparity. In the realm of research institutions, Shanghai Jiao Tong University and China Medical University are identified as major contributors, yet the potential for inter-institutional collaboration remains largely untapped, suggesting avenues for future synergy. Internationally, China-US collaborations are particularly robust, fostering cross-border knowledge exchange. Hyun Jin Won and Li Wei are recognized as prolific authors, while Ahmedin Jemal is an influential co-cited scholar, noted for his seminal contributions. Keyword analysis reveals research focus areas, such as the complex CRC tumor microenvironment, molecular mechanisms of oxidative stress, and key multidrug resistance pathways. It also highlights the promising potential of mitochondria-targeted therapies and nanomolecular technologies in clinical practice, signaling their growing significance in addressing complex health challenges. The study underscores the imperative to validate complex mitochondrial mechanisms and signaling pathways in CRC, with a particular emphasis on translating these insights into drug targets for clinical trials. Advancing this research is expected to refine and enhance CRC treatment strategies. Additionally, it highlights the urgency of validating mitochondrial complexities in CRC, advocating for collaborative efforts to link these mechanisms with tailored therapeutic interventions for clinical testing. This integrated approach promises significant advancements in developing effective, targeted CRC treatments, ultimately improving patient outcomes.

Targeting sirtuins for cancer therapy: epigenetics modifications and beyond

Sirtuins (SIRTs) are well-known as nicotinic adenine dinucleotide+(NAD+)-dependent histone deacetylases, which are important epigenetic enzymes consisting of seven family members (SIRT1-7). Of note, SIRT1 and SIRT2 are distributed in the nucleus and cytoplasm, while SIRT3, SIRT4 and SIRT5 are localized in the mitochondria. SIRT6 and SIRT7 are distributed in the nucleus. SIRTs catalyze the deacetylation of various substrate proteins, thereby modulating numerous biological processes, including transcription, DNA repair and genome stability, metabolism, and signal transduction. Notably, accumulating evidence has recently underscored the multi-faceted roles of SIRTs in both the suppression and progression of various types of human cancers. Crucially, SIRTs have been emerging as promising therapeutic targets for cancer therapy. Thus, in this review, we not only present an overview of the molecular structure and function of SIRTs, but elucidate their intricate associations with oncogenesis. Additionally, we discuss the current landscape of small-molecule activators and inhibitors targeting SIRTs in the contexts of cancer and further elaborate their combination therapies, especially highlighting their prospective utility for future cancer drug development.

SIRT5 exacerbates eosinophilic chronic rhinosinusitis by promoting polarization of M2 macrophage

BACKGROUND

Previous studies implied that local M2 polarization of macrophage promoted mucosal edema and exacerbated TH2 type inflammation in chronic rhinosinusitis with nasal polyps (CRSwNP). However, the specific pathogenic role of M2 macrophages and the intrinsic regulators in the development of CRS remains elusive.

OBJECTIVE

We sought to investigate the regulatory role of SIRT5 in the polarization of M2 macrophages and its potential contribution to the development of CRSwNP.

METHODS

Real-time reverse transcription-quantitative PCR and Western blot analyses were performed to examine the expression levels of SIRT5 and markers of M2 macrophages in sinonasal mucosa samples obtained from both CRS and control groups. Wild-type and Sirt5-knockout mice were used to establish a nasal polyp model with TH2 inflammation and to investigate the effects of SIRT5 in macrophage on disease development. Furthermore, in vitro experiments were conducted to elucidate the regulatory role of SIRT5 in polarization of M2 macrophages.

RESULTS

Clinical investigations showed that SIRT5 was highly expressed and positively correlated with M2 macrophage markers in eosinophilic polyps. The expression of SIRT5 in M2 macrophages was found to contribute to the development of the disease, which was impaired in Sirt5-deficient mice. Mechanistically, SIRT5 was shown to enhance the alternative polarization of macrophages by promoting glutaminolysis.

CONCLUSIONS

SIRT5 plays a crucial role in promoting the development of CRSwNP by supporting alternative polarization of macrophages, thus providing a potential target for CRSwNP interventions.

Pyruvate dehydrogenase complex E1 subunit α crotonylation modulates cocaine-associated memory through hippocampal neuron activation

Neuronal activation is required for the formation of drug-associated memory, which is critical for the development, persistence, and relapse of drug addiction. Nevertheless, the metabolic mechanisms underlying energy production for neuronal activation remain poorly understood. In the study, a large-scale proteomics analysis of lysine crotonylation (Kcr), a type of protein posttranslational modification (PTM), reveals that cocaine promoted protein Kcr in the hippocampal dorsal dentate gyrus (dDG). We find that Kcr is predominantly discovered in a few enzymes critical for mitochondrial energy metabolism; in particular, pyruvate dehydrogenase (PDH) complex E1 subunit α (PDHA1) is crotonylated at the lysine 39 (K39) residue through P300 catalysis. Crotonylated PDHA1 promotes pyruvate metabolism by activating PDH to increase ATP production, thus providing energy for hippocampal neuronal activation and promoting cocaine-associated memory recall. Our findings identify Kcr of PDHA1 as a PTM that promotes pyruvate metabolism to enhance neuronal activity for cocaine-associated memory.

Roles of Sirtuins in Hearing Protection

Hearing loss is a health crisis that affects more than 60 million Americans. Currently, sodium thiosulfate is the only drug approved by the Food and Drug Administration (FDA) to counter hearing loss. Sirtuins were proposed as therapeutic targets in the search for new compounds or drugs to prevent or cure age-, noise-, or drug-induced hearing loss. Sirtuins are proteins involved in metabolic regulation with the potential to ameliorate sensorineural hearing loss. The mammalian sirtuin family includes seven members, SIRT1-7. This paper is a literature review on the sirtuins and their protective roles in sensorineural hearing loss. Literature search on the NCBI PubMed database and NUsearch included the keywords 'sirtuin' and 'hearing'. Studies on sirtuins without relevance to hearing and studies on hearing without relevance to sirtuins were excluded. Only primary research articles with data on sirtuin expression and physiologic auditory tests were considered. The literature review identified 183 records on sirtuins and hearing. After removing duplicates, eighty-one records remained. After screening for eligibility criteria, there were forty-eight primary research articles with statistically significant data relevant to sirtuins and hearing. Overall, SIRT1 (n = 29) was the most studied sirtuin paralog. Over the last two decades, research on sirtuins and hearing has largely focused on age-, noise-, and drug-induced hearing loss. Past and current studies highlight the role of sirtuins as a mediator of redox homeostasis. However, more studies need to be conducted on the involvement of SIRT2 and SIRT4-7 in hearing protection.

Analysis of the Expression and Prognostic Value of SIRTs in Hepatocellular Carcinoma

Purpose

This study contributes to the evolving understanding of the pivotal involvement of Sirtuins (SIRTs) in various human cancers, with a particular focus on elucidating their expression patterns and clinical relevance within the context of hepatocellular carcinoma (HCC). The investigation involves a comprehensive analysis of mRNA expression and prognostic implications associated with distinct SIRTs in HCC.

Patients and Methods

Initial data pertaining to SIRT expression in HCC patients were collated from publicly accessible databases. Subsequently, the expression levels of select members of the SIRT family were validated using clinicopathological specimens from HCC patients. Additionally, HCC tissue microarray was employed to scrutinize the correlation between SIRT7 expression and HCC prognosis.

Results

The findings indicated a substantial upregulation of SIRT2, SIRT3, SIRT4, SIRT6, and SIRT7 in HCC tissues. Survival analysis underscored a pronounced association between elevated mRNA levels of SIRT3, SIRT6, and SIRT7 and an adverse prognosis for HCC patients. Particularly, SIRT7 emerged as a potential independent risk factor for poor prognosis in HCC patients. Examination of the HCC tissue microarray revealed heightened expression of SIRT7 in 68 cases (54.8%) of HCC tissues. Multivariate analysis established high SIRT7 expression as an independent risk factor for diminished Disease-Free Survival (DFS) and Overall Survival (OS) in HCC patients.

Conclusion

The aberrant expression of SIRT7 presents itself may be as a novel biomarker for predicting the prognosis of HCC patients.

Metabolic heterogeneity in tumor microenvironment - A novel landmark for immunotherapy

The surrounding non-cancer cells and tumor cells that make up the tumor microenvironment (TME) have various metabolic rhythms. TME metabolic heterogeneity is influenced by the intricate network of metabolic control within and between cells. DNA, protein, transport, and microbial levels are important regulators of TME metabolic homeostasis. The effectiveness of immunotherapy is also closely correlated with alterations in TME metabolism. The response of a tumor patient to immunotherapy is influenced by a variety of variables, including intracellular metabolic reprogramming, metabolic interaction between cells, ecological changes within and between tumors, and general dietary preferences. Although immunotherapy and targeted therapy have made great strides, their use in the accurate identification and treatment of tumors still has several limitations. The function of TME metabolic heterogeneity in tumor immunotherapy is summarized in this article. It focuses on how metabolic heterogeneity develops and is regulated as a tumor progresses, the precise molecular mechanisms and potential clinical significance of imbalances in intracellular metabolic homeostasis and intercellular metabolic coupling and interaction, as well as the benefits and drawbacks of targeted metabolism used in conjunction with immunotherapy. This offers insightful knowledge and important implications for individualized tumor patient diagnosis and treatment plans in the future.

Research progress on Sirtuins (SIRTs) family modulators

Sirtuins (SIRTs) represent a class of nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylases that exert a crucial role in cellular signal transduction and various biological processes. The mammalian sirtuins family encompasses SIRT1 to SIRT7, exhibiting therapeutic potential in counteracting cellular aging, modulating metabolism, responding to oxidative stress, inhibiting tumors, and improving cellular microenvironment. These enzymes are intricately linked to the occurrence and treatment of diverse pathological conditions, including cancer, autoimmune diseases, and cardiovascular disorders. Given the significance of histone modification in gene expression and chromatin structure, maintaining the equilibrium of the sirtuins family is imperative for disease prevention and health restoration. Mounting evidence suggests that modulators of SIRTs play a crucial role in treating various diseases and maintaining physiological balance. This review delves into the molecular structure and regulatory functions of the sirtuins family, reviews the classification and historical evolution of SIRTs modulators, offers a systematic overview of existing SIRTs modulation strategies, and elucidates the regulatory mechanisms of SIRTs modulators (agonists and inhibitors) and their clinical applications. The article concludes by summarizing the challenges encountered in SIRTs modulator research and offering insights into future research directions.

Histidine re-sensitizes pediatric acute lymphoblastic leukemia to 6-mercaptopurine through tetrahydrofolate consumption and SIRT5-mediated desuccinylation

Despite progressive improvements in the survival rate of pediatric B-cell lineage acute lymphoblastic leukemia (B-ALL), chemoresistance-induced disease progression and recurrence still occur with poor prognosis, thus highlighting the urgent need to eradicate drug resistance in B-ALL. The 6-mercaptopurine (6-MP) is the backbone of ALL combination chemotherapy, and resistance to it is crucially related to relapse. The present study couples chemoresistance in pediatric B-ALL with histidine metabolism deficiency. Evidence was provided that histidine supplementation significantly shifts the 6-MP dose-response in 6-MP-resistant B-ALL. It is revealed that increased tetrahydrofolate consumption via histidine catabolism partially explains the re-sensitization ability of histidine. More importantly, this work provides fresh insights into that desuccinylation mediated by SIRT5 is an indispensable and synergistic requirement for histidine combination therapy against 6-MP resistance, which is undisclosed previously and demonstrates a rational strategy to ameliorate chemoresistance and protect pediatric patients with B-ALL from disease progression or relapse.

Ferroptosis in cancer: From molecular mechanisms to therapeutic strategies

Ferroptosis is a non-apoptotic form of regulated cell death characterized by the lethal accumulation of iron-dependent membrane-localized lipid peroxides. It acts as an innate tumor suppressor mechanism and participates in the biological processes of tumors. Intriguingly, mesenchymal and dedifferentiated cancer cells, which are usually resistant to apoptosis and traditional therapies, are exquisitely vulnerable to ferroptosis, further underscoring its potential as a treatment approach for cancers, especially for refractory cancers. However, the impact of ferroptosis on cancer extends beyond its direct cytotoxic effect on tumor cells. Ferroptosis induction not only inhibits cancer but also promotes cancer development due to its potential negative impact on anticancer immunity. Thus, a comprehensive understanding of the role of ferroptosis in cancer is crucial for the successful translation of ferroptosis therapy from the laboratory to clinical applications. In this review, we provide an overview of the recent advancements in understanding ferroptosis in cancer, covering molecular mechanisms, biological functions, regulatory pathways, and interactions with the tumor microenvironment. We also summarize the potential applications of ferroptosis induction in immunotherapy, radiotherapy, and systemic therapy, as well as ferroptosis inhibition for cancer treatment in various conditions. We finally discuss ferroptosis markers, the current challenges and future directions of ferroptosis in the treatment of cancer.

OXCT1 functions as a succinyltransferase, contributing to hepatocellular carcinoma via succinylating LACTB

Metabolic reprogramming is an important feature of cancers that has been closely linked to post-translational protein modification (PTM). Lysine succinylation is a recently identified PTM involved in regulating protein functions, whereas its regulatory mechanism and possible roles in tumor progression remain unclear. Here, we show that OXCT1, an enzyme catalyzing ketone body oxidation, functions as a lysine succinyltransferase to contribute to tumor progression. Mechanistically, we find that OXCT1 functions as a succinyltransferase, with residue G424 essential for this activity. We also identified serine beta-lactamase-like protein (LACTB) as a main target of OXCT1-mediated succinylation. Extensive succinylation of LACTB K284 inhibits its proteolytic activity, resulting in increased mitochondrial membrane potential and respiration, ultimately leading to hepatocellular carcinoma (HCC) progression. In summary, this study establishes lysine succinyltransferase function of OXCT1 and highlights a link between HCC prognosis and LACTB K284 succinylation, suggesting a potentially valuable biomarker and therapeutic target for further development.

Integrated analysis of necroptosis related gene signature to predict clinical outcomes, immune status and drug sensitivity in lower grade Glioma

Background

The treatment of lower grade gliomas (LGG) is currently the most challenging dilemma in the management of intracranial tumors. Necroptosis is a type of programmed cell death that is closely associated with tumor progression, However, the role of necroptosis related genes in LGG is not yet well elucidated.

Methods

Online databases were used to obtain gene expression and clinical information. After gene differential expression analysis, a risk score model based on prognostic differentially expressed necroptosis-related genes (DENGs) were constructed to predict prognosis for LGG patients. The validity of the risk score model was then assessed with Kaplan-Meier survival curve. The prognostic DENGs included in the risk score model were then subjected to gene expression analysis, functional enrichment analysis, consensus clustering analysis, and single cell sequencing analysis. Finally, we investigated the correlation of the risk score and immune infiltration in LGG tumor microenvironment and drug sensitivity for LGG patients in different risk groups.

Results

A survival risk score model was constructed based on seven prognostic DENGs, which demonstrated satisfactory performance in predicting the prognosis of LGG patients. According to functional enrichment analyses, these seven DENGs may play a regulatory role in LGG tumorigenesis through several immune and metabolic pathways. LGG patients could be categorized into two clusters with distinct prognosis and clinicopathologic characteristics based on the expression of seven DENGs. Single-cell sequencing analysis demonstrated that the DENG signature was differentially expressed in various types of cells in LGG and may play a vital role in oncogenesis. Additionally, drug sensitivity analysis suggested that the seven-gene signature could guide clinical medication for LGG patients.

Conclusion

Our study developed a reliable necroptosis-related signature to predict the prognosis of LGG patients. This gene signature may also help estimate immune status and anti-cancer drug sensitivity in LGG patients. Our findings may pave the way to enhance our understanding of necroptosis in LGG.

SIRT5-mediated ME2 desuccinylation promotes cancer growth by enhancing mitochondrial respiration

Mitochondrial malic enzyme 2 (ME2), which catalyzes the conversion of malate to pyruvate, is frequently upregulated during tumorigenesis and is a potential target for cancer therapy. However, the regulatory mechanism underlying ME2 activity is largely unknown. In this study, we demonstrate that ME2 is highly expressed in human colorectal cancer (CRC) tissues, and that ME2 knockdown inhibits the proliferation of CRC cells. Furthermore, we reveal that ME2 is succinylated and identify Sirtuins 5 (SIRT5) as an ME2 desuccinylase. Glutamine deprivation directly enhances the interaction of SIRT5 with ME2 and thus promotes SIRT5-mediated desuccinylation of ME2 at lysine 346, activating ME2 enzymatic activity. Activated ME2 significantly enhances mitochondrial respiration, thereby counteracting the effects of glutamine deprivation and supporting cell proliferation and tumorigenesis. Additionally, the levels of succinylated ME2 at K346 and SIRT5 in CRC tissues, which are negatively correlated, are associated with patient prognosis. These observations suggest that SIRT5-catalyzed ME2 desuccinylation is a key signaling event through which cancer cells maintain mitochondrial respiration and promote CRC progression under glutamine deficiency conditions, offering the possibility of targeting SIRT5-mediated ME2 desuccinylation for CRC treatment.

Sirtuins in macrophage immune metabolism: A novel target for cardiovascular disorders

Sirtuins (SIRT1-SIRT7), as a family of NAD+-dependent protein modifying enzymes, have various catalytic functions, such as deacetylases, dealkalylases, and deribonucleases. The Sirtuins family is directly or indirectly involved in pathophysiological processes such as glucolipid metabolism, oxidative stress, DNA repair and inflammatory response through various pathways and assumes an important role in several cardiovascular diseases such as atherosclerosis, myocardial infarction, hypertension and heart failure. A growing number of studies supports that metabolic and bioenergetic reprogramming directs the sequential process of inflammation. Failure of homeostatic restoration leads to many inflammatory diseases, and that macrophages are the central cells involving the inflammatory response and are the main source of inflammatory cytokines. Regulation of cellular metabolism has emerged as a fundamental process controlling macrophage function, but its exact signaling mechanisms remain to be revealed. Understanding the precise molecular basis of metabolic control of macrophage inflammatory processes may provide new approaches for targeting immune metabolism and inflammation. Here, we provide an update of studies in cardiovascular disease on the function and role of sirtuins in macrophage inflammation and metabolism, as well as drug candidates that may interfere with sirtuins, pointing to future prospects in this field.

Targeting succinylation-mediated metabolic reprogramming as a potential approach for cancer therapy

Metabolic reprogramming is a common hallmark of cancers and involves alterations in many metabolic pathways during tumor initiation and progression. However, the cancer-specific modulation of metabolic reprogramming requires further elucidation. Succinylation, a newly identified protein posttranslational modification (PTM), participates in many cellular processes by transferring a succinyl group to a residue of the target protein, which is related to various pathological disorders including cancers. In recent years, there has been a gradual increase in the number of studies on the regulation of tumors by protein succinylation. Notably, accumulating evidence suggests that succinylation can mediate cancer cell metabolism by altering the structure or activity of metabolism-related proteins and plays vital roles in metabolic reprogramming. Furthermore, some antitumor drugs have been linked to succinylation-mediated tumor-associated metabolism. To better elucidate lysine succinylation mediated tumor metabolic reprogramming, this review mainly summarizes recent studies on the regulation and effects of protein succinylation in tumors, focusing on the metabolic regulation of tumorigenesis and development, which will provide new directions for cancer diagnosis as well as possible therapeutic targets.

Canagliflozin reduces chemoresistance in hepatocellular carcinoma through PKM2-c-Myc complex-mediated glutamine starvation

Cisplatin (CPT) is one of the standard treatments for hepatocellular carcinoma (HCC). However, its use is limits as a monotherapy due to drug resistance, and the underlying mechanism remains unclear. To solve this problem, we tried using canagliflozin (CANA), a clinical drug for diabetes, to reduce chemoresistance to CPT, and the result showed that CANA could vigorously inhibit cell proliferation and migration independent of the original target SGLT2. Mechanistically, CANA reduced aerobic glycolysis in HCC by targeting PKM2. The downregulated PKM2 directly bound to the transcription factor c-Myc in the cytoplasm to form a complex, which upregulated the level of phosphorylated c-Myc Thr58 and promoted the ubiquitination and degradation of c-Myc. Decreased c-Myc reduced the expression of GLS1, a key enzyme in glutamine metabolism, leading to impaired glutamine utilization. Finally, intracellular glutamine starvation induced ferroptosis and sensitized HCC to CPT. In conclusion, our study showed that CANA re-sensitized HCC to CPT by inducing ferroptosis through dual effects on glycolysis and glutamine metabolism. This is a novel mechanism to increase chemosensitivity, which may provide compatible chemotherapy drugs for HCC.

Degradation of HIF-1α induced by curcumol blocks glutaminolysis and inhibits epithelial-mesenchymal transition and invasion in colorectal cancer cells

Colorectal cancer (CRC) has high morbidity and mortality. Epithelial-mesenchymal transition (EMT) is associated with CRC progression and metastasis. Glutaminolysis is essential for malignancy of cancer cells. Here, we examined the effects of curcumol on CRC EMT. We observed that curcumol suppressed invasion and migration in human CRC cells associated with upregulation of epithelial markers E-cadherin and Zonula occludens 1 and downregulation of mesenchymal markers N-cadherin and Vimentin as well as EMT-related transcription factors Snail and Twist. Curcumol increased intracellular levels of glutamine but decreased intracellular levels of glutamate, α-ketoglutarate, ATP, glutathione, and tricarboxylic acid cycle metabolites, suggesting interruption of glutaminolysis. Next, curcumol repressed glutaminase 1 (Gls1) mRNA and protein expression, and overexpression of Gls1 promoted EMT and abolished curcumol effects on CRC cell EMT. Molecular examinations showed that curcumol stimulated protein degradation of hypoxia-inducible factor-1α (HIF-1α) and prevented its nuclear accumulation in CRC cells. HIF-1α agonist deferoxamine (DFO) promoted HIF-1α binding to Gls1 promoter and increased Gls1 expression but abolished curcumol's inhibitory effects on Gls1 expression. DFO also enhanced EMT and invasion and migration in CRC cells and eliminated curcumol effects. Furthermore, mouse CRC models were established with in vivo overexpression of HIF-1α and Gls1. Curcumol effectively inhibited CRC growth, metastasis, and EMT in mice, which was abrogated by overexpression of HIF-1α or Gls1. Altogether, stimulation of HIF-1α degradation was required for curcumol to disrupt EMT and repress invasion and migration in CRC cells through inhibiting Gls1-mediated glutaminolysis. Curcumol could be a promising candidate for intervention of CRC metastasis. • Curcumol inhibits EMT and blocks glutaminolysis in CRC cells. • Inhibition of Gls1 is required for curcumol blockade of glutaminolysis and EMT. • Curcumol induces HIF-1α degradation leading to inhibition of Gls1 and blockade of glutaminolysis and EMT. • Curcumol suppresses CRC growth and metastasis via inhibiting HIF-1α, glutaminolysis and EMT in mice.

Quercetin inhibits DNA damage responses to induce apoptosis via SIRT5/PI3K/AKT pathway in non-small cell lung cancer

SIRT5 is a mitochondrial NAD+ -dependent lysine deacylase. Downregulation of SIRT5 has been linked to several primary cancers and DNA damage. In clinical therapy for non-small cell lung cancer (NSCLC), the Feiyiliu Mixture (FYLM) is an experience and effective Chinese herb prescription. And we found that quercetin is an important ingredient in the FYLM. However, whether quercetin regulates DNA damage repair (DDR) and induces apoptosis through SIRT5 in NSCLC remains unknown. The present study revealed that quercetin directly binds to SIRT5 and inhibits the phosphorylation of PI3K/AKT through the interaction between SIRT5 and PI3K, thus inhibiting the repair process of homologous recombination (HR) and non-homologous end-joining (NHEJ) in NSCLC, which raise mitotic catastrophe and apoptosis. Our study provided a novel mechanism of action of quercetin in the treatment of NSCLC.

SIRT5 Activation and Inorganic Phosphate Binding Reduce Cancer Cell Vitality by Modulating Autophagy/Mitophagy and ROS

Cancer cells show increased glutamine consumption. The glutaminase (GLS) enzyme controls a limiting step in glutamine catabolism. Breast tumors, especially the triple-negative subtype, have a high expression of GLS. Our recent study demonstrated that GLS activity and ammonia production are inhibited by sirtuin 5 (SIRT5). We developed MC3138, a selective SIRT5 activator. Treatment with MC3138 mimicked the deacetylation effect mediated by SIRT5 overexpression. Moreover, GLS activity was regulated by inorganic phosphate (Pi). Considering the interconnected roles of GLS, SIRT5 and Pi in cancer growth, our hypothesis is that activation of SIRT5 and reduction in Pi could represent a valid antitumoral strategy. Treating cells with MC3138 and lanthanum acetate, a Pi chelator, decreased cell viability and clonogenicity. We also observed a modulation of MAP1LC3B and ULK1 with MC3138 and lanthanum acetate. Interestingly, inhibition of the mitophagy marker BNIP3 was observed only in the presence of MC3138. Autophagy and mitophagy modulation were accompanied by an increase in cytosolic and mitochondrial reactive oxygen species (ROS). In conclusion, our results show how SIRT5 activation and/or Pi binding can represent a valid strategy to inhibit cell proliferation by reducing glutamine metabolism and mitophagy, leading to a deleterious accumulation of ROS.

Role of SIRT5 in the analgesic effectiveness of moxibustion at ST36 in mice with inflammatory pain

Sirtuine5 (SIRT5) is an important molecule involved in the pathology of inflammatory diseases. To investigate the impact of SIRT5 on the analgesic effectiveness of moxibustion, we established a complete Freund's adjuvant- (CFA-) induced inflammatory pain in mice model. Moxibustion was applied at the Zusanli (ST36) acupoint in mice with inflammatory pain. The analgesic effectiveness was evaluated by thermal hyperalgesia and mechanical allodynia tests in the right paws after CFA injection. The expression of inflammatory cytokines, including the pro-inflammatory factors IL-1β and TNF-α, and the anti-inflammatory factors IL-4 and TGF-β expressions, was evaluated using by ELISA. Furthermore, SIRT5 was evaluated by immunofluorescence and western blotting. The results showed that, compared with the CFA group, both thermal and mechanical pain thresholds increased with moxibustion and the SIRT5 inhibitor MC3482 intervention at ST36. Additionally, compared to the CFA-induced group, the inflammatory mediators, including IL-1β and TNF-α, decreased, while the anti-inflammatory cytokines IL-4 and TGF-β increased with moxibustion and MC3482 ST36 acupoint injection. Western blot results showed a decreased expression of SIRT5 at the ST36 site with moxibustion and MC3482 injection, compared to the CFA-induced group. SIRT5 expression in the right paw of mice injected with moxibustion and MC3482 was higher than that in the CFA-induced group. This study revealed that SIRT5 expression is involved in moxibustion analgesia and may be a potential mediator in the regulation of analgesia.

Orchestration of Mitochondrial Function and Remodeling by Post-Translational Modifications Provide Insight into Mechanisms of Viral Infection

The regulation of mitochondria structure and function is at the core of numerous viral infections. Acting in support of the host or of virus replication, mitochondria regulation facilitates control of energy metabolism, apoptosis, and immune signaling. Accumulating studies have pointed to post-translational modification (PTM) of mitochondrial proteins as a critical component of such regulatory mechanisms. Mitochondrial PTMs have been implicated in the pathology of several diseases and emerging evidence is starting to highlight essential roles in the context of viral infections. Here, we provide an overview of the growing arsenal of PTMs decorating mitochondrial proteins and their possible contribution to the infection-induced modulation of bioenergetics, apoptosis, and immune responses. We further consider links between PTM changes and mitochondrial structure remodeling, as well as the enzymatic and non-enzymatic mechanisms underlying mitochondrial PTM regulation. Finally, we highlight some of the methods, including mass spectrometry-based analyses, available for the identification, prioritization, and mechanistic interrogation of PTMs.

Mitochondrial remodeling in colorectal cancer initiation, progression, metastasis, and therapy: A review

Colorectal cancer (CRC) is a major health concern with multifactorial pathophysiology representing intense therapeutic challenges. It is well known that deregulation of spatiotemporally-controlled signaling pathways and their metabolic reprogramming effects play a pivotal role in the development and progression of CRC. As such, the mitochondrial role in CRC initiation gained a lot of attention recently, as it is considered the powerhouse that regulates the bioenergetics in CRC. In addition, the crosstalk between microRNAs (miRNAs) and mitochondrial dysfunction has become a newfangled passion for deciphering CRC molecular mechanisms. This review sheds light on the relationship between different signaling pathways involved in metabolic reprogramming and their therapeutic targets, alterations in mitochondrial DNA content, mitochondrial biogenesis, and mitophagy, and the role of polymorphisms in mitochondrial genes as well as miRNAs regulating mitochondrial proteins in CRC initiation, progression, metastasis, and resistance to various therapies.

The Role of NAD+, SIRTs Interactions in Stimulating and Counteracting Carcinogenesis

The World Health Organization has identified oncological diseases as one of the most serious health concerns of the current century. Current research on oncogenesis is focused on the molecular mechanisms of energy-biochemical reprogramming in cancer cell metabolism, including processes contributing to the Warburg effect and the pro-oncogenic and anti-oncogenic roles of sirtuins (SIRTs) and poly-(ADP-ribose) polymerases (PARPs). However, a clear understanding of the interaction between NAD⁺, SIRTs in cancer development, as well as their effects on carcinogenesis, has not been established, and literature data vary greatly. This work aims to provide a summary and structure of the available information on NAD⁺, SIRTs interactions in both stimulating and countering carcinogenesis, and to discuss potential approaches for pharmacological modulation of these interactions to achieve an anticancer effect.

Emerging Roles of SIRT5 in Metabolism, Cancer, and SARS-CoV-2 Infection

Sirtuin 5 (SIRT5) is a predominantly mitochondrial enzyme catalyzing the removal of glutaryl, succinyl, malonyl, and acetyl groups from lysine residues through a NAD+-dependent deacylase mechanism. SIRT5 is an important regulator of cellular homeostasis and modulates the activity of proteins involved in different metabolic pathways such as glycolysis, tricarboxylic acid (TCA) cycle, fatty acid oxidation, electron transport chain, generation of ketone bodies, nitrogenous waste management, and reactive oxygen species (ROS) detoxification. SIRT5 controls a wide range of aspects of myocardial energy metabolism and plays critical roles in heart physiology and stress responses. Moreover, SIRT5 has a protective function in the context of neurodegenerative diseases, while it acts as a context-dependent tumor promoter or suppressor. In addition, current research has demonstrated that SIRT5 is implicated in the SARS-CoV-2 infection, although opposing conclusions have been drawn in different studies. Here, we review the current knowledge on SIRT5 molecular actions under both healthy and diseased settings, as well as its functional effects on metabolic targets. Finally, we revise the potential of SIRT5 as a therapeutic target and provide an overview of the currently reported SIRT5 modulators, which include both activators and inhibitors.

Metabolic reprogramming in colorectal cancer: regulatory networks and therapy

With high prevalence and mortality, together with metabolic reprogramming, colorectal cancer is a leading cause of cancer-related death. Metabolic reprogramming gives tumors the capacity for long-term cell proliferation, making it a distinguishing feature of cancer. Energy and intermediate metabolites produced by metabolic reprogramming fuel the rapid growth of cancer cells. Aberrant metabolic enzyme-mediated tumor metabolism is regulated at multiple levels. Notably, tumor metabolism is affected by nutrient levels, cell interactions, and transcriptional and posttranscriptional regulation. Understanding the crosstalk between metabolic enzymes and colorectal carcinogenesis factors is particularly important to advance research for targeted cancer therapy strategies via the investigation into the aberrant regulation of metabolic pathways. Hence, the abnormal roles and regulation of metabolic enzymes in recent years are reviewed in this paper, which provides an overview of targeted inhibitors for targeting metabolic enzymes in colorectal cancer that have been identified through tumor research or clinical trials.

Pyrazolone derivatives as potent and selective small-molecule SIRT5 inhibitors

Sirtiun 5 (SIRT5) is a NAD+-dependent protein lysine deacylase. It is emerging as a promising target for the development of drugs to treat cancer and metabolism-related diseases. In this study, we screened 5000 compounds and identified a hit compound 14 bearing a pyrazolone functional group as a novel SIRT5-selective inhibitor. Structure-based optimization of 14 resulted in compound 47 with an IC50 value of 0.21 ± 0.02 μM and a 100-fold improved potency. Compound 47 showed substantial selectivity for SIRT5 over SIRT1-3 and SIRT6. Biochemical studies suggest that 47 does not occupy the NAD + -binding pocket and acts as a substrate-competitive inhibitor. The identified potent and selective SIRT5 inhibitors allow further studies as research tools and therapeutic agents.

Targeting epigenetic regulation for cancer therapy using small molecule inhibitors

Cancer cells display pervasive changes in DNA methylation, disrupted patterns of histone posttranslational modification, chromatin composition or organization and regulatory element activities that alter normal programs of gene expression. It is becoming increasingly clear that disturbances in the epigenome are hallmarks of cancer, which are targetable and represent attractive starting points for drug creation. Remarkable progress has been made in the past decades in discovering and developing epigenetic-based small molecule inhibitors. Recently, epigenetic-targeted agents in hematologic malignancies and solid tumors have been identified and these agents are either in current clinical trials or approved for treatment. However, epigenetic drug applications face many challenges, including low selectivity, poor bioavailability, instability and acquired drug resistance. New multidisciplinary approaches are being designed to overcome these limitations, e.g., applications of machine learning, drug repurposing, high throughput virtual screening technologies, to identify selective compounds with improved stability and better bioavailability. We provide an overview of the key proteins that mediate epigenetic regulation that encompass histone and DNA modifications and discuss effector proteins that affect the organization of chromatin structure and function as well as presently available inhibitors as potential drugs. Current anticancer small-molecule inhibitors targeting epigenetic modified enzymes that have been approved by therapeutic regulatory authorities across the world are highlighted. Many of these are in different stages of clinical evaluation. We also assess emerging strategies for combinatorial approaches of epigenetic drugs with immunotherapy, standard chemotherapy or other classes of agents and advances in the design of novel epigenetic therapies.

Arabidopsis thaliana sirtuins control proliferation and glutamate dehydrogenase activity

Sirtuins are part of a gene family of NAD-dependent deacylases that act on histone and non-histone proteins and control a variety of activities in all living organisms. Their roles are mainly related to energy metabolism and include lifetime regulation, DNA repair, stress resistance, and proliferation. A large amount of knowledge concerning animal sirtuins is available, but data about their plant counterparts are scarce. Plants possess few sirtuins that have, like in animals, a recognized role in stress defense and metabolism regulation. However, engagement in proliferation control, which has been demonstrated for mammalian sirtuins, has not been reported for plant sirtuins so far. In this work, srt1 and srt2 Arabidopsis mutant seedlings have been used to evaluate in vivo the role of sirtuins in cell proliferation and regulation of glutamate dehydrogenase, an enzyme demonstrated to be involved in the control of cell cycle in SIRT4-defective human cells. Moreover, bioinformatic analyses have been performed to elucidate sequence, structure, and function relationships between Arabidopsis sirtuins and between each of them and the closest mammalian homolog. We found that cell proliferation and GDH activity are higher in mutant seedlings, suggesting that both sirtuins exert a physiological inhibitory role in these processes. In addition, mutant seedlings show plant growth and root system improvement, in line with metabolic data. Our data also indicate that utilization of an easy to manipulate organism, such as Arabidopsis plant, can help to shed light on the molecular mechanisms underlying the function of genes present in interkingdom species.

The sirtuin family in health and disease

Sirtuins (SIRTs) are nicotine adenine dinucleotide(+)-dependent histone deacetylases regulating critical signaling pathways in prokaryotes and eukaryotes, and are involved in numerous biological processes. Currently, seven mammalian homologs of yeast Sir2 named SIRT1 to SIRT7 have been identified. Increasing evidence has suggested the vital roles of seven members of the SIRT family in health and disease conditions. Notably, this protein family plays a variety of important roles in cellular biology such as inflammation, metabolism, oxidative stress, and apoptosis, etc., thus, it is considered a potential therapeutic target for different kinds of pathologies including cancer, cardiovascular disease, respiratory disease, and other conditions. Moreover, identification of SIRT modulators and exploring the functions of these different modulators have prompted increased efforts to discover new small molecules, which can modify SIRT activity. Furthermore, several randomized controlled trials have indicated that different interventions might affect the expression of SIRT protein in human samples, and supplementation of SIRT modulators might have diverse impact on physiological function in different participants. In this review, we introduce the history and structure of the SIRT protein family, discuss the molecular mechanisms and biological functions of seven members of the SIRT protein family, elaborate on the regulatory roles of SIRTs in human disease, summarize SIRT inhibitors and activators, and review related clinical studies.

Sirtuin5 protects colorectal cancer from DNA damage by keeping nucleotide availability

In our previous study, we reported that sirtuin5 (SIRT5), a member of the NAD⁺-dependent class III histone deacetylase family, is highly expressed in colorectal cancer (CRC). Herein we show that SIRT5 knockdown impairs the production of ribose-5-phosphate, which is essential for nucleotide synthesis, resulting in continuous and irreparable DNA damage and consequently leading to cell cycle arrest and enhanced apoptosis in CRC cells. These SIRT5 silencing-induced effects can be reversed by nucleoside supplementation. Mechanistically, SIRT5 activates transketolase (TKT), a key enzyme in the non-oxidative pentose phosphate pathway, in a demalonylation-dependent manner. Furthermore, TKT is essential for SIRT5-induced malignant phenotypes of CRC both in vivo and in vitro. Altogether, SIRT5 silencing induces DNA damage in CRC via post-translational modifications and inhibits tumor growth, suggesting that SIRT5 can serve as a promising target for CRC treatment.

SIRT5 is a proviral factor that interacts with SARS-CoV-2 Nsp14 protein

SARS-CoV-2 non-structural protein Nsp14 is a highly conserved enzyme necessary for viral replication. Nsp14 forms a stable complex with non-structural protein Nsp10 and exhibits exoribonuclease and N7-methyltransferase activities. Protein-interactome studies identified human sirtuin 5 (SIRT5) as a putative binding partner of Nsp14. SIRT5 is an NAD-dependent protein deacylase critical for cellular metabolism that removes succinyl and malonyl groups from lysine residues. Here we investigated the nature of this interaction and the role of SIRT5 during SARS-CoV-2 infection. We showed that SIRT5 interacts with Nsp14, but not with Nsp10, suggesting that SIRT5 and Nsp10 are parts of separate complexes. We found that SIRT5 catalytic domain is necessary for the interaction with Nsp14, but that Nsp14 does not appear to be directly deacylated by SIRT5. Furthermore, knock-out of SIRT5 or treatment with specific SIRT5 inhibitors reduced SARS-CoV-2 viral levels in cell-culture experiments. SIRT5 knock-out cells expressed higher basal levels of innate immunity markers and mounted a stronger antiviral response, independently of the Mitochondrial Antiviral Signaling Protein MAVS. Our results indicate that SIRT5 is a proviral factor necessary for efficient viral replication, which opens novel avenues for therapeutic interventions.

Elucidation of an mTORC2-PKC-NRF2 pathway that sustains the ATF4 stress response and identification of Sirt5 as a key ATF4 effector

Proliferating cancer cells are dependent on glutamine metabolism for survival when challenged with oxidative stresses caused by reactive oxygen species, hypoxia, nutrient deprivation and matrix detachment. ATF4, a key stress responsive transcription factor, is essential for cancer cells to sustain glutamine metabolism when challenged with these various types of stress. While it is well documented how the ATF4 transcript is translated into protein as a stress response, an important question concerns how the ATF4 message levels are sustained to enable cancer cells to survive the challenges of nutrient deprivation and damaging reactive oxygen species. Here, we now identify the pathway in triple negative breast cancer cells that provides a sustained ATF4 response and enables their survival when encountering these challenges. This signaling pathway starts with mTORC2, which upon sensing cellular stresses arising from glutamine deprivation or an acute inhibition of glutamine metabolism, initiates a cascade of events that triggers an increase in ATF4 transcription. Surprisingly, this signaling pathway is not dependent on AKT activation, but rather requires the mTORC2 target, PKC, which activates the transcription factor Nrf2 that then induces ATF4 expression. Additionally, we identify a sirtuin family member, the NAD⁺-dependent de-succinylase Sirt5, as a key transcriptional target for ATF4 that promotes cancer cell survival during metabolic stress. Sirt5 plays fundamental roles in supporting cancer cell metabolism by regulating various enzymatic activities and by protecting an enzyme essential for glutaminolysis, glutaminase C (GAC), from degradation. We demonstrate that ectopic expression of Sirt5 compensates for knockdowns of ATF4 in cells exposed to glutamine deprivation-induced stress. These findings provide important new insights into the signaling cues that lead to sustained ATF4 expression as a general stress-induced regulator of glutamine metabolism, as well as highlight Sirt5 an essential effector of the ATF4 response to metabolic stress.

Loss of SIRT5 promotes bile acid-induced immunosuppressive microenvironment and hepatocarcinogenesis

BACKGROUND & AIMS

The liver is a metabolically active organ and is also 'tolerogenic', exhibiting sophisticated mechanisms of immune regulation that prevent pathogen attacks and tumorigenesis. How metabolism impacts the tumor microenvironment (TME) in hepatocellular carcinoma (HCC) remains understudied.

METHODS

We investigated the role of the metabolic regulator SIRT5 in HCC development by conducting metabolomic analysis, gene expression profiling, flow cytometry and immunohistochemistry analyses in oncogene-induced HCC mouse models and human HCC samples.

RESULTS

We show that SIRT5 is downregulated in human primary HCC samples and that Sirt5 deficiency in mice synergizes with oncogenes to increase bile acid (BA) production, via hypersuccinylation and increased BA biosynthesis in the peroxisomes of hepatocytes. BAs act as a signaling mediator to stimulate their nuclear receptor and promote M2-like macrophage polarization, creating an immunosuppressive TME that favors tumor-initiating cells (TICs). Accordingly, high serum levels of taurocholic acid correlate with low SIRT5 expression and increased M2-like tumor-associated macrophages (TAMs) in HCC patient samples. Finally, administration of cholestyramine, a BA sequestrant and FDA-approved medication for hyperlipemia, reverses the effect of Sirt5 deficiency in promoting M2-like polarized TAMs and liver tumor growth.

CONCLUSIONS

This study uncovers a novel function of SIRT5 in orchestrating BA metabolism to prevent tumor immune evasion and suppress HCC development. Our results also suggest a potential strategy of using clinically proven BA sequestrants for the treatment of patients with HCC, especially those with decreased SIRT5 and abnormally high BAs.

LAY SUMMARY

Hepatocellular caricinoma (HCC) development is closely linked to metabolic dysregulation and an altered tumor microenvironment. Herein, we show that loss of the metabolic regulator Sirt5 promotes hepatocarcinogenesis, which is associated with abnormally elevated bile acids and subsequently an immunosuppressive microenvironment that favors HCC development. Targeting this mechanism could be a promising clinical strategy for HCC.

The histone deacetylase SIRT6 promotes glycolysis through the HIF-1α/HK2 signaling axis and induces erlotinib resistance in non-small cell lung cancer

Erlotinib is a first-generation epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI). Overcoming erlotinib resistance is crucial to improve the survival of advanced non-small cell lung cancer (NSCLC) patients with sensitive EGFR mutations. It is also an important clinical problem that urgently needs a solution. In this study, we explored strategies to overcome erlotinib resistance from the perspective of energy metabolism. SIRT6 is a histone deacetylase. Here, we found that high expression of SIRT6 is associated with poor prognosis of lung adenocarcinoma, especially in EGFR-mutated NSCLC patients. The next cell experiment found that SIRT6 expression increased in erlotinib-resistant cells, and SIRT6 expression was negatively correlated with the sensitivity of NSCLC to erlotinib. Inhibition of SIRT6 promoted erlotinib-induced apoptosis in erlotinib-resistant cells, and glycolysis in drug-resistant cells was also inhibited. Functional studies have shown that SIRT6 increases glycolysis through the HIF-1α/HK2 signaling axis in drug-resistant cells and inhibits the sensitivity of NSCLC cells to erlotinib. In addition, the HIF-1α blocker PX478-2HCL attenuated the glycolysis and erlotinib resistance induced by SIRT6. More importantly, we confirmed the antitumor effect of SIRT6 inhibition combined with erlotinib in NSCLC-bearing mice. Our findings indicate that the cancer metabolic pathway regulated by SIRT6 may be a new target for attenuating NSCLC erlotinib resistance and has potential as a biomarker or therapeutic target to improve outcomes in NSCLC patients.

Therapeutic Potential and Activity Modulation of the Protein Lysine Deacylase Sirtuin 5

Sirtiun 5 (SIRT5) is a NAD+-dependent protein lysine deacylase primarily located in mitochondria. SIRT5 displays an affinity for negatively charged acyl groups and mainly catalyzes lysine deglutarylation, desuccinylation, and demalonylation while possessing weak deacetylase activity. SIRT5 substrates play crucial roles in metabolism and reactive oxygen species (ROS) detoxification, and SIRT5 activity is protective in neuronal and cardiac physiology. Moreover, SIRT5 exhibits a dichotomous role in cancer, acting as context-dependent tumor promoter or suppressor. Given its multifaceted activity, SIRT5 is a promising target in the design of activators or inhibitors that might act as therapeutics in many pathologies, including cancer, cardiovascular disorders, and neurodegeneration. To date, few cellular-active peptide-based SIRT5 inhibitors (SIRT5i) have been described, and potent and selective small-molecule SIRT5i have yet to be discovered. In this perspective, we provide an outline of SIRT5's roles in different biological settings and describe SIRT5 modulators in terms of their mode of action, pharmacological activity, and structure-activity relationships.

Sirtuin 4 Inhibits Prostate Cancer Progression and Metastasis by Modulating p21 Nuclear Translocation and Glutamate Dehydrogenase 1 ADP-Ribosylation

Protein posttranslational modification regulates several biological mechanisms, including tumor progression. In this study, we show that the mitochondrial Sirtuin 4 (SIRT4), which has ADP-ribosylation activity, plays a role in prostate cancer (PCa) progression. Firstly, SIRT4 expression was verified in PCa tissues and cell lines by quantitative real-time PCR (qRT-PCR) and western blotting. Subsequently, we established stable PC-3 and 22rv1 cells that overexpressed SIRT4 and knocked down SIRT4, respectively. The functions of SIRT4 in PCa were explored through various phenotype experiments. The mechanism underlying the functions of SIRT4 was investigated through western blotting, immunoprecipitation, immunofluorescence, and nuclear and cytoplasmic extraction assays. We revealed that SIRT4 inhibited cell progression both in vivo and in vitro. Mechanistically, on the one hand, SIRT4 promoted the ADP-ribosylation of glutamate dehydrogenase 1 to inhibit the glutamine metabolism pathways. On the other hand, SIRT4 inhibited the phosphorylation of AKT, thereby affecting p21 phosphorylation and its cellular localization for cell cycle arrest. In conclusion, our study indicates that SIRT4 is directly associated with PCa progression and could be a novel target for PCa therapy.

Arginine methylation of MTHFD1 by PRMT5 enhances anoikis resistance and cancer metastasis

Metastasis accounts for the major cause of cancer-related mortality. How disseminated tumor cells survive under suspension conditions and avoid anoikis is largely unknown. Here, using a metabolic enzyme-centered CRISPR-Cas9 genetic screen, we identified methylenetetrahydrofolate dehydrogenase, cyclohydrolase and formyltetrahydrofolate synthetase 1 (MTHFD1) as a novel suppressor of anoikis. MTHFD1 depletion obviously restrained the capacity of cellular antioxidant defense and inhibited tumor distant metastasis. Mechanistically, MTHFD1 was found to bind the protein arginine methyltransferase 5 (PRMT5) and then undergo symmetric dimethylation on R173 by PRMT5. Under suspension conditions, the interaction between MTHFD1 and PRMT5 was strengthened, which increased the symmetric dimethylation of MTHFD1. The elevated methylation of MTHFD1 largely augmented its metabolic activity to generate NADPH, therefore leading to anoikis resistance and distant organ metastasis. Therapeutically, genetic depletion or pharmacological inhibition of PRMT5 declined tumor distant metastasis. And R173 symmetric dimethylation status was associated with metastasis and prognosis of ESCC patients. In conclusion, our study uncovered a novel regulatory role and therapeutic implications of PRMT5/MTHFD1 axis in facilitating anoikis resistance and cancer metastasis.

Osmundacetone modulates mitochondrial metabolism in non-small cell lung cancer cells by hijacking the glutamine/glutamate/α-KG metabolic axis

BACKGROUND

Osmundacetone (OSC) is a bioactive phenolic compound isolated from Phellinus igniarius and that was shown to exert cytotoxic effects on cancer cells in our previous work. The antiproliferative impact of OSC on non-small cell lung cancer (NSCLC) and the underlying mechanisms, however, have not been studied.

PURPOSE

This study aimed to explore the antiproliferative effect of OSC on NSCLC cells and the mechanisms involved.

METHODS

Cell viability, colony formation and cell cycle distribution were measured following exposure to OSC in vitro. The anticancer activity of OSC was also examined using a xenograft growth assay in vivo. Furthermore, serum metabolomics analysis by GC-MS was done to detect alterations in the metabolic profile. Next, expression of GLS1 and GLUD1, the key enzymes in glutamine metabolism, was evaluated using RT-PCR and western blot. α-KG and NADH metabolites were assessed by ELISA. Mitochondrial functions and morphology were evaluated using the JC-1 probe and transmission electron microscopy, respectively. The ATP production rate in mitochondria of cells with OSC treatment was determined using a Seahorse XFe24 Analyzer.

RESULTS

OSC selectively reduced the proliferation of A549 and H460 cells. OSC triggered G2/M cell cycle arrest and decreased the cell clone formation. A mouse xenograft model revealed that OSC inhibited tumor growth in vivo. Findings of serum metabolomics analyses indicated that the anticancer function of OSC was related to disorders of glutamine metabolism. Such a speculation was further verified by the expression level of GLUD1, which was downregulated by OSC treatment. Concentrations of the related metabolites α-KG and NADH were reduced in response to OSC treatment. Moreover, OSC led to disorganization of the mitochondrial ultrastructure and a decrease in mitochondrial membrane potential. OSC also decreased ATP production via oxidative phosphorylation (OXPHOS) but did not affect glycolysis in NSCLC cells.

CONCLUSION

The key role of OSC in mitochondrial energy metabolism in NSCLC cells is to suppress tumor development and cell proliferation downregulating GLUD1 to inhibit the glutamine/glutamate/α-KG metabolic axis and OXPHOS. It indicats that OSC might be a potential natural agent for personalized medicine and an anticancer metabolic modulator in NSCLC chemotherapy.