Sirtuin 7 Regulates Nitric Oxide Production and Apoptosis to Promote Mycobacterial Clearance in Macrophages

Sirtuins as modulators of infection outcomes in the battle of host-pathogen dynamics

Sirtuins's central role in governing metabolic processes has been known for decades. However, over the past two decades, sirtuin functions have been linked to immune regulation and immunity. Sirtuins are NAD+ dependent protein deacylases involved in the regulation of several important biological processes ranging from energy homeostasis, metabolism, aging, apoptosis, autophagy, immunity, adipocyte, and muscle differentiation. Here, in this review, we discuss the role of sirtuins in several infectious diseases including viral, bacterial, and protozoan infections with detailed emphasis on bacterial-host interactions. We have aimed to explore both host and bacterial sirtuin functions contributing to the infection progression, host responses and their influence on the everlasting host-pathogen tug-of-war. In order to manipulate host pathways, pathogens such as intracellular bacteria have evolved parallelly and harbor bacterial sirtuins. The recent discoveries of bacterial sirtuins influencing the host-pathogen interaction outcomes pave the way for the discovery of potential therapeutic targets.

Host-directed therapy for tuberculosis

Current TB treatment regimens are hindered by drug resistance, numerous adverse effects, and long treatment durations, highlighting the need for 'me-better' treatment regimens. Host-directed therapy (HDT) has gained recognition as a promising approach in TB treatment. It allows the repurposing of existing drugs approved for other conditions and aims to enhance the effectiveness of existing anti-TB therapies, minimize drug resistance, decrease treatment duration, and adverse effects. By modulating the host immune response, HDT ameliorates immunopathological damage and improves overall outcomes by promoting autophagy, antimicrobial peptide production, and other mechanisms. It holds promise for addressing the challenges posed by multiple and extensively drug-resistant Mycobacterium tuberculosis strains, which are increasingly difficult to treat using conventional therapies. This article reviews various HDT candidates, including repurposed drugs, explores their underlying mechanisms such as autophagy promotion and inflammation reduction, while emphasizing their potential to improve TB treatment outcomes and outlining future research directions.

Development of a Genetically Encoded Sensor for Arginine

The amino acid l-arginine (Arg) plays important roles in multiple metabolic and physiological processes, and changes in its concentration have been implicated in pathological processes. While it is important to measure Arg levels in biological systems directly and in real-time, existing Arg sensors respond to l-ornithine or l-lysine. Here we report ArgS1, a new Arg sensor. It showed a concentration-dependent increase in the ratio Ex488/405 for Arg with an apparent affinity of ∼64 μM and with a dynamic range (ΔR/R0) of 3. ArgS1 responds to Arg in both the cytoplasm and the subcellular organelles. ArgS1 monitored Arg levels in MDA-MB-231 cells, a breast cancer cell line deficient in a key enzyme for Arg synthesis (arginino-succinate synthetase1, ASS1) and amenable to Arg depletion therapy. We found that Arg levels in MDA-MB-231 cells decreased after depletion of extracellular Arg with a concomitant decline in cell viability. When ASS1 was overexpressed in the cells, Arg levels increased and cell viability was also enhanced. Thus, ArgS1 is an effective tool for real-time monitoring of Arg in human cells over a dynamic range of physiological and pathological relevance.

Immune and Metabolic Mechanisms of Endothelial Dysfunction

Endothelial dysfunction is a strong prognostic factor in predicting the development of cardiovascular diseases. Dysfunctional endothelium loses its homeostatic ability to regulate vascular tone and prevent overactivation of inflammation, leading to vascular dysfunction. These functions are critical for vascular homeostasis and arterial pressure control, the disruption of which may lead to hypertension. Hypertension itself can also cause endothelial dysfunction, as endothelial cells are susceptible to haemodynamic changes. Although it is unclear which of those factors appear first, they create a vicious circle further damaging multiple organs, including the heart and vessels. There are also sex-specific differences in homeostatic functions of the endothelium regarding vessel tone regulation, which may contribute to differences in arterial blood pressure between men and women. Even more importantly, there are sex-differences in the development of endothelial dysfunction and vessel remodelling. Hence, an understanding of the mechanisms of endothelial dysfunction and its contribution to pathological vascular remodelling during hypertension is of critical importance. This review addresses immunological and metabolic aspects in mechanisms of endothelial dysfunction and the resulting mechanisms in vascular remodelling with respect to arterial hypertension, including the potential role of sex-specific differences.

Sirtuin2 blockade inhibits replication of Human Immunodeficiency Virus-1 and Mycobacterium tuberculosis in macrophages and humanized mice

Coinfections with Mycobacterium tuberculosis (Mtb) and HIV-1 present a critical health challenge and require treatment for survival. We found that human M1 macrophages inhibit Mtb growth, while M2 macrophages, characterized by elevated Sirt2 expression, permit Mtb growth. Further, we found that HIV-1 augmented Sirt2 gene expression in MФs. Therefore, we explored the therapeutic potential of sirtuin-modulating drugs in MФs. Sirtinol, a Sirt2 inhibitor, significantly reduced HIV-1 growth in M0, M1, and M2-MФs by >1 log10 over 7 days. Conversely, individual doses of resveratrol and SRT1460, which activate Sirt1, did not affect HIV-1. However, their combination showed a strong synergistic inhibition of HIV-1. The combination of sirtinol with resveratrol was neither synergistic nor antagonistic. Sirtinol upregulated iNOS and ATG5 mRNA in HIV-1 infected MФs in a phenotype-dependent manner. In a humanized mouse model (Hu-NSG-SGM3) co-infected with Mtb H37Rv and the HIV-1 BAL strain, treatment with sirtinol alone, or in combination with combination antiretroviral therapy (cART), showed promising results; Sirtinol alone reduced Mtb growth, while its combination with cART effectively inhibited HIV-1 replication in the organs. We propose that Sirt2 blockade and Sirt1-activation represent a novel dual therapeutic strategy for treating HIV-1 and Mtb coinfections.

SIRT7 remodels the cytoskeleton via RAC1 to enhance host resistance to Mycobacterium tuberculosis

Phagocytosis of Mycobacterium tuberculosis (Mtb) followed by its integration into the matured lysosome is critical in the host defense against tuberculosis. How Mtb escapes this immune attack remains elusive. In this study, we unveiled a novel regulatory mechanism by which SIRT7 regulates cytoskeletal remodeling by modulating RAC1 activation. We discovered that SIRT7 expression was significantly reduced in CD14+ monocytes of TB patients. Mtb infection diminished SIRT7 expression by macrophages at both the mRNA and protein levels. SIRT7 deficiency impaired actin cytoskeleton-dependent macrophage phagocytosis, LC3II expression, and bactericidal activity. In a murine tuberculosis model, SIRT7 deficiency detrimentally impacted host resistance to Mtb, while Sirt7 overexpression significantly increased the host defense against Mtb, as determined by bacterial burden and inflammatory-histopathological damage in the lung. Mechanistically, we demonstrated that SIRT7 limits Mtb infection by directly interacting with and activating RAC1, through which cytoskeletal remodeling is modulated. Therefore, we concluded that SIRT7, in its role regulating cytoskeletal remodeling through RAC1, is critical for host responses during Mtb infection and proposes a potential target for tuberculosis treatment.IMPORTANCETuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains a significant global health issue. Critical to macrophages' defense against Mtb is phagocytosis, governed by the actin cytoskeleton. Previous research has revealed that Mtb manipulates and disrupts the host's actin network, though the specific mechanisms have been elusive. Our study identifies a pivotal role for SIRT7 in this context: Mtb infection leads to reduced SIRT7 expression, which, in turn, diminishes RAC1 activation and consequently impairs actin-dependent phagocytosis. The significance of our research is that SIRT7 directly engages with and activates Rac Family Small GTPase 1 (RAC1), thus promoting effective phagocytosis and the elimination of Mtb. This insight into the dynamic between host and pathogen in TB not only broadens our understanding but also opens new avenues for therapeutic development.

The miR-26a/SIRT6/HIF-1α axis regulates glycolysis and inflammatory responses in host macrophages during Mycobacterium tuberculosis infection

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis. Here, a macrophage infection model was used to unravel the role of the histone deacetylase sirtuin 6 (SIRT6) in Mtb-triggered regulation of the innate immune response. Mtb infection downregulated microRNA-26a and upregulated its target SIRT6. SIRT6 suppressed glycolysis and expression of HIF-1α-dependent glycolytic genes during infection. In addition, SIRT6 regulated the levels of intracellular succinate which controls stabilization of HIF-1α, as well as the release of interleukin (IL)-1β. Furthermore, SIRT6 inhibited inducible nitric oxide synthase (iNOS) and proinflammatory IL-6 but augmented anti-inflammatory arginase expression. The miR-26a/SIRT6/HIF-1α axis therefore regulates glycolysis and macrophage immune responses during Mtb infection. Our findings link SIRT6 to rewiring of macrophage signaling pathways facilitating dampening of the antibacterial immune response.

Quantitative analysis of the lysine acetylome reveals the role of SIRT3-mediated HSP60 deacetylation in suppressing intracellular Mycobacterium tuberculosis survival

Protein acetylation and deacetylation are key epigenetic modifications that regulate the initiation and development of several diseases. In the context of infection with Mycobacterium tuberculosis (M. tb), these processes are essential for host-pathogen interactions and immune responses. However, the specific effects of acetylation and deacetylation on cellular functions during M. tb infection are not fully understood. This study employed Tandem Mass Tag (TMT) labeling for quantitative proteomic profiling to examine the acetylproteome (acetylome) profiles of noninfected and M. tb-infected macrophages. We identified 715 acetylated peptides from 1,072 proteins and quantified 544 lysine acetylation sites (Kac) in 402 proteins in noninfected and M. tb-infected macrophages. Our research revealed a link between acetylation events and metabolic changes during M. tb infection. Notably, the deacetylation of heat shock protein 60 (HSP60), a key chaperone protein, was significantly associated with this process. Specifically, the deacetylation of HSP60 at K96 by sirtuin3 (SIRT3) enhances macrophage apoptosis, leading to the elimination of intracellular M. tb. These findings underscore the pivotal role of the SIRT3-HSP60 axis in the host immune response to M. tb. This study offers a new perspective on host protein acetylation and suggests that targeting host-directed therapies could be a promising approach for tuberculosis immunotherapy.

IMPORTANCE

Protein acetylation is crucial for the onset, development, and outcome of tuberculosis (TB). Our study comprehensively investigated the dynamics of lysine acetylation during M. tb infection, shedding light on the intricate host-pathogen interactions that underlie the pathogenesis of tuberculosis. Using an advanced quantitative lysine proteomics approach, different profiles of acetylation sites and proteins in macrophages infected with M. tb were identified. Functional enrichment and protein-protein network analyses revealed significant associations between acetylated proteins and key cellular pathways, highlighting their critical role in the host response to M. tb infection. Furthermore, the deacetylation of HSP60 and its influence on macrophage-mediated clearance of M. tb underscore the functional significance of acetylation in tuberculosis pathogenesis. In conclusion, this study provides valuable insights into the regulatory mechanisms governing host immune responses to M. tb infection and offers promising avenues for developing novel therapeutic interventions against TB.

Targeting Macrophages: Therapeutic Approaches in Diabetic Kidney Disease

Diabetes is not solely a metabolic disorder but also involves inflammatory processes. The immune response it incites is a primary contributor to damage in target organs. Research indicates that during the initial phases of diabetic nephropathy, macrophages infiltrate the kidneys alongside lymphocytes, initiating a cascade of inflammatory reactions. The interplay between macrophages and other renal cells is pivotal in the advancement of kidney disease within a hyperglycemic milieu. While M1 macrophages react to the inflammatory stimuli induced by elevated glucose levels early in the disease progression, their subsequent transition to M2 macrophages, which possess anti-inflammatory and tissue repair properties, also contributes to fibrosis in the later stages of nephropathy by transforming into myofibroblasts. Comprehending the diverse functions of macrophages in diabetic kidney disease and regulating their activity could offer therapeutic benefits for managing this condition.

Specific Inhibitors of Mitochondrial Deacylase Sirtuin 4 Endowed with Cellular Activity

Sirtuins are NAD+-dependent protein lysine deacylases implicated in aging-related diseases. Mammalian Sirtuin 4 (Sirt4) is located in mitochondria and a potential therapeutic target for cancer and metabolic diseases, but no potent and selective Sirt4 inhibitors have been reported. Here, we describe the identification of potent Sirt4-specific small-molecule inhibitors. Testing hits from a target-based virtual screen revealed 12 active compounds. A focused screen based on two top compounds, followed by structure-assisted design of derivatives, yielded four first-in-class potent Sirt4 inhibitors. Kinetic analyses indicate compound competition with the acyl peptide substrate, consistent with the docking models and implicating Sirt4's unique acyl binding site. The compounds indeed show preference for Sirt4 over other isoforms, with one of them (69) being highly isoform selective, and they are active in cells. Our results provide first lead compounds and mechanistic insights for optimization toward Sirt4-specific inhibitors useful as experimental tools and potential therapeutics.

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.

Myeloid-Specific SIRT6 Deletion Protects Against Particulate Matter (PM2.5)-Induced Airway Inflammation

Purpose

Particulate matter (PM_2.5) is a common risk factor for airway inflammation. Alveolar macrophages play a critical role in airway inflammation. Sirtuin 6 (SIRT6) is a class Ill histone deacetylase that exerts an anti-inflammatory effect in airway diseases. However, the role of SIRT6 on PM2.5-induced airway inflammation in macrophages remains unclear. We aimed to determine whether SIRT6 protects against PM_2.5-induced airway inflammation in macrophages.

Methods

The effect of SIRT6 on PM_2.5-induced airway inflammation was assessed by using THP1 cells or bone marrow-derived macrophages (BMDMs) exposed to PM_2.5 in vitro and myeloid cell-specific SIRT6 conditional knockout mice (Sirt6^fl/fl-LysMCre) in vivo.

Results

PM2.5 increased SIRT6 expression in THP1 cells, but SIRT6 gene silencing decreased PM2.5 induced inflammatory cytokines in THP1 cells. Moreover, the expression of SIRT6 and inflammatory cytokines was also decreased in BMDMs with myeloid-specific deletion of SIRT6 after stimulation of PM_2.5. In vivo, Sirt6^fl/fl-LysMCre mice substantially decreased airway inflammation in response to PM_2.5 exposure.

Conclusion

Our results revealed that SIRT6 promotes the PM_2.5-induced airway inflammation in macrophages and indicated that inhibition of SIRT6 in macrophages may represent therapeutic strategy for airway disorders induced by airborne particulate pollution.

Sirtuin-dependent metabolic and epigenetic regulation of macrophages during tuberculosis

Macrophages are the preeminent phagocytic cells which control multiple infections. Tuberculosis a leading cause of death in mankind and the causative organism Mycobacterium tuberculosis (MTB) infects and persists in macrophages. Macrophages use reactive oxygen and nitrogen species (ROS/RNS) and autophagy to kill and degrade microbes including MTB. Glucose metabolism regulates the macrophage-mediated antimicrobial mechanisms. Whereas glucose is essential for the growth of cells in immune cells, glucose metabolism and its downsteam metabolic pathways generate key mediators which are essential co-substrates for post-translational modifications of histone proteins, which in turn, epigenetically regulate gene expression. Herein, we describe the role of sirtuins which are NAD+-dependent histone histone/protein deacetylases during the epigenetic regulation of autophagy, the production of ROS/RNS, acetyl-CoA, NAD+, and S-adenosine methionine (SAM), and illustrate the cross-talk between immunometabolism and epigenetics on macrophage activation. We highlight sirtuins as emerging therapeutic targets for modifying immunometabolism to alter macrophage phenotype and antimicrobial function.

Mycobacterium tuberculosis-macrophage interaction: Molecular updates

Mycobacterium tuberculosis (Mtb), the causative agent of Tuberculosis (TB), remains a pathogen of great interest on a global scale. This airborne pathogen affects the lungs, where it interacts with macrophages. Acidic pH, oxidative and nitrosative stressors, and food restrictions make the macrophage's internal milieu unfriendly to foreign bodies. Mtb subverts the host immune system and causes infection due to its genetic arsenal and secreted effector proteins. In vivo and in vitro research have examined Mtb-host macrophage interaction. This interaction is a crucial stage in Mtb infection because lung macrophages are the first immune cells Mtb encounters in the host. This review summarizes Mtb effectors that interact with macrophages. It also examines how macrophages control and eliminate Mtb and how Mtb manipulates macrophage defense mechanisms for its own survival. Understanding these mechanisms is crucial for TB prevention, diagnosis, and treatment.

Hesperetin, a Promising Dietary Supplement for Preventing the Development of Calcific Aortic Valve Disease

BACKGROUND

No effective therapeutic agents for calcific aortic valve disease (CAVD) are available currently. Dietary supplementation has been proposed as a novel treatment modality for various diseases. As a flavanone, hesperetin is widely abundant in citrus fruits and has been proven to exert protective effects in multiple diseases. However, the role of hesperetin in CAVD remains unclear.

METHODS

Human aortic valve interstitial cells (VICs) were isolated from aortic valve leaflets. A mouse model of aortic valve stenosis was constructed by direct wire injury (DWI). Immunoblotting, immunofluorescence staining, and flow cytometry were used to investigate the roles of sirtuin 7 (Sirt7) and nuclear factor erythroid 2-related factor 2 (Nrf2) in hesperetin-mediated protective effects in VICs.

RESULTS

Hesperetin supplementation protected the mice from wire-injury-induced aortic valve stenosis; in vitro, hesperetin inhibited the lipopolysaccharide (LPS)-induced activation of NF-κB inflammatory cytokine secretion and osteogenic factors expression, reduced ROS production and apoptosis, and abrogated LPS-mediated injury to the mitochondrial membrane potential and the decline in the antioxidant levels in VICs. These benefits of hesperetin may have been obtained by activating Nrf2-ARE signaling, which corrected the dysfunctional mitochondria. Furthermore, we found that hesperetin could directly bind to Sirt7 and that the silencing of Sirt7 decreased the effects of hesperetin in VICs and potently abolished the ability of hesperetin to increase Nrf2 transcriptional activation.

CONCLUSIONS

Our work demonstrates that hesperetin plays protective roles in the aortic valve through the Sirt7-Nrf2-ARE axis; thus, hesperetin might be a potential dietary supplement that could prevent the development of CAVD.

Resistance and Susceptibility Immune Factors at Play during Mycobacterium tuberculosis Infection of Macrophages

Tuberculosis (TB), caused by infection with Mycobacterium tuberculosis (M.tb), is responsible for >1.5 million deaths worldwide annually. Innate immune cells, especially macrophages, are the first to encounter M.tb, and their response dictates the course of infection. During infection, macrophages exert a variety of immune factors involved in either controlling or promoting the growth of M.tb. Research on this topic has been performed in both in vitro and in vivo animal models with discrepant results in some cases based on the model of study. Herein, we review macrophage resistance and susceptibility immune factors, focusing primarily on recent advances in the field. We include macrophage cellular pathways, bioeffector proteins and molecules, cytokines and chemokines, associated microbiological factors and bacterial strains, and host genetic factors in innate immune genes. Recent advances in mechanisms underlying macrophage resistance and susceptibility factors will aid in the successful development of host-directed therapeutics, a topic emphasized throughout this review.

Drosophila Innate Immunity Involves Multiple Signaling Pathways and Coordinated Communication Between Different Tissues

The innate immune response provides the first line of defense against invading pathogens, and immune disorders cause a variety of diseases. The fruit fly Drosophila melanogaster employs multiple innate immune reactions to resist infection. First, epithelial tissues function as physical barriers to prevent pathogen invasion. In addition, macrophage-like plasmatocytes eliminate intruders through phagocytosis, and lamellocytes encapsulate large particles, such as wasp eggs, that cannot be phagocytosed. Regarding humoral immune responses, the fat body, equivalent to the mammalian liver, secretes antimicrobial peptides into hemolymph, killing bacteria and fungi. Drosophila has been shown to be a powerful in vivo model for studying the mechanism of innate immunity and host-pathogen interactions because Drosophila and higher organisms share conserved signaling pathways and factors. Moreover, the ease with which Drosophila genetic and physiological characteristics can be manipulated prevents interference by adaptive immunity. In this review, we discuss the signaling pathways activated in Drosophila innate immunity, namely, the Toll, Imd, JNK, JAK/STAT pathways, and other factors, as well as relevant regulatory networks. We also review the mechanisms by which different tissues, including hemocytes, the fat body, the lymph gland, muscles, the gut and the brain coordinate innate immune responses. Furthermore, the latest studies in this field are outlined in this review. In summary, understanding the mechanism underlying innate immunity orchestration in Drosophila will help us better study human innate immunity-related diseases.

Sirtuins: Research advances on the therapeutic role in acute kidney injury

BACKGROUND

Acute kidney injury (AKI), a common multidisciplinary diagnostic clinical critical illness, eventually causes end-stage renal disease (ESRD). Although many clinical measures have been taken to prevent or treat AKI, high morbidity and death rates were recorded. Therefore, in-depth pathogenesis study and search for new therapeutic targets are in demand. Interestingly, the suirtuins family showed a significant protective effect in AKI. Sirtuins (SIRT1-7) is a family of seven proteins with NAD⁺-dependent type III histone deacetylase activity. Sirtuins family members were involved by AKI, and regulation of sirtuins activities significantly improved AKI-induced renal injury. Therefore, the therapeutic role and molecular mechanisms of the sirtuins family in AKI has important research implications for clinical applications or basic research.

PURPOSE

This review summarizes recent advances in the roles and functions of the sirtuins family, discusses their therapeutic effects on AKI and related molecular mechanisms, and the mechanisms of action of small molecule specific activators or inhibitors sirtuins in the prevention and treatment of AKI were discussed.

METHODS

The data in this review were retrieved from various scientific databases (PubMed, Google scholar, Science Direct, and Web of Science), till December 2021. The keywords were used as follows: "Sirtuins", "Acute kidney injury", "AKI", "Sirtuins modulators" and "Histone deacetylation". The retrieved data followed PRISMA criteria (preferred reporting items for systematic review).

RESULTS

Growing evidence indicates that members of the sirtuins family regulate the development and progression of different renal diseases, including AKI, through anti-inflammation, antioxidation, anti-apoptotic, and maintenance of mitochondrial homeostasis. The molecular mechanism of Sirtuins family on AKI mainly regulated NF-κB, JNK/ERK, and AMPK/mTOR signaling pathways, upregulated the expression of PGC-1α, HO-1, NRF2, Bcl-2, OPA1, and AMPK, and downregulated the expression of NRLP3, IL-1β, TNF-α, IL-6, ROS, MFF, Drp1, Bax, ERK, and mTOR. In addition, the active ingredients of herbs (resveratrol, thujaplicins, huperzine, and curcumin) could activate the activity of SIRT1 or SIRT3, thereby improving AKI. Meanwhile, the synthetic Sirtuins inhibitor (AK-1) inhibited SIRT2 activity, thus alleviating AKI. In the future, more specific modulators will remain needed to enhance the clinical therapeutic role of the Sirtuins family in AKI.

CONCLUSION

The sirtuins family is a promising type III histone deacetylase for AKI treatment. This review will provide insight into sirtuins family's therapeutic role in AKI and promote the clinical use of sirtuins modulators in AKI.