Sirtuin Inhibitors Research Articles

Syringaresinol attenuates Tau phosphorylation and ameliorates cognitive dysfunction induced by sevoflurane in aged rats.

Cognitive dysfunction following anesthesia with agents such as sevoflurane is a significant clinical problem, particularly in elderly patients. This study aimed to explore the protective effects of the phytochemical syringaresinol (SYR) against sevoflurane-induced cognitive deficits in aged Sprague-Dawley rats and to determine the underlying mechanisms involved. We assessed the impact of SYR on sevoflurane-induced cognitive impairment, glial activation, and neuronal apoptosis through behavioral tests (Morris water maze), immunofluorescence, Western blotting for key proteins involved in apoptosis and inflammation, and enzyme-linked immunosorbent assays for interleukin-1β, tumor necrosis factor-α, and interleukin-6. SYR treatment mitigated sevoflurane-induced cognitive decline, reduced microglial and astrocyte activation (decreased Iba-1 and GFAP expression), and countered neuronal apoptosis (reduced Bax, cleaved-caspase3, and cleaved-PARP expression). SYR also enhanced Sirtuin-1 (SIRT1) expression and reduced p-Tau phosphorylation; these effects were reversed by the SIRT1 inhibitor EX527. SYR exerts neuroprotective effects on sevoflurane-induced cognitive dysfunction by modulating glial activity, apoptotic signaling, and Tau phosphorylation through the SIRT1 pathway. These findings could inform clinical strategies to safeguard cognitive function in patients undergoing anesthesia.

Synergistic effect of genistein and adiponectin reduces fat deposition in chicken hepatocytes by activating the ERβ-mediated SIRT1-AMPK signaling pathway

Dietary supplementation with bioactive substances that can regulate lipid metabolism is an effective approach for reducing excessive fat deposition in chickens. Genistein (GEN) has the potential to alleviate fat deposition; however, the underlying mechanism of GEN's fat-reduction action in chickens remains unclear. Therefore, the present study aimed to explore the underlying mechanism of GEN on the reduction of fat deposition from a novel perspective: intercellular transmission of adipokine between adipocytes and hepatocytes. The findings showed that GEN enhanced the secretion of adiponectin (APN) in chicken adipocytes, and the enhancement effect of GEN was completely blocked when the cells were pretreated with inhibitors targeting estrogen receptor β (ERβ) or proliferator-activated receptor γ (PPARγ) signals, respectively. Furthermore, the results demonstrated that both co-treatment with GEN and APN or treatment with the medium supernatant (Med SUP) derived from chicken adipocytes treated with GEN significantly decreased the content of triglyceride and increased the protein levels of ERβ, Sirtuin 1 (SIRT1) and phosphor-AMP-activated protein kinase (p-AMPK) in chicken hepatocytes compared to the cells treated with GEN or APN alone. Moreover, the increase in the protein levels of SIRT1 and p-AMPK induced by GEN and APN co-treatment or Med SUP treatment were blocked in chicken hepatocytes pretreated with the inhibitor of ERβ signals. Importantly, the up-regulatory effect of GEN and APN co-treatment or Med SUP treatment on the protein level of p-AMPK was also blocked in chicken hepatocytes pretreated with a SIRT1 inhibitor; however, the increase in the protein level of SIRT1 induced by GEN and APN co-treatment or Med SUP treatment was not reversed when the hepatocytes were pretreated with an AMPK inhibitor. In conclusion, the present study demonstrated that GEN enhanced APN secretion by activating the ERβ-Erk-PPARγ signaling pathway in chicken adipocytes. Subsequently, adipocyte-derived APN synergized with GEN to activate the ERβ-mediated SIRT1-AMPK signaling pathway in chicken hepatocytes, ultimately reducing fat deposition. These findings provide substantial evidence from a novel perspective, supporting the potential use of GEN as a dietary supplement to prevent excessive fat deposition in poultry.

Abstract CT252: Nicotinamide in combination with EGFR-TKIs for the treatment of stage IV lung adenocarcinoma with EGFR mutations: A randomized double-blind (Phase IIb) trial

Abstract Background: RUNX3 is a tumor suppressor gene, which is inactivated in approximately 70% of lung adenocarcinomas. Nicotinamide, a sirtuin inhibitor, has demonstrated potential in re-activating epigenetically silenced RUNX3 in cancer cells. This study assessed the therapeutic benefits of combining nicotinamide with first-generation EGFR-TKIs for patients with stage IV lung cancer carrying EGFR mutations. Patients and Methods: We assessed the impact of nicotinamide on carcinogen-induced lung adenocarcinomas in mice and observed that nicotinamide increased RUNX3 levels and inhibited lung cancer growth. Subsequently, 110 consecutive patients with stage IV lung cancer who had EGFR mutations were recruited: 70 females (63.6%) and 84 never-smokers (76.4%). The patients were randomly assigned to receive either nicotinamide (1 g/day, n = 55) or placebo (n = 55). The primary and secondary endpoints were progression-free survival (PFS) and overall survival (OS), respectively. Results: After a median follow-up of 54.3 months, the nicotinamide group exhibited a median PFS of 12.7 months (95% CI, 10.4-18.3), while the placebo group had a PFS of 10.9 months (9.0-13.2; p = 0.2). The median OS was similar in the two groups (31.0 months with nicotinamide vs. 29.4 months with placebo; p = 0.2). Notably, subgroup analyses revealed a significant reduction in mortality risk for females (p = 0.01) and never-smokers (p = 0.03) treated with nicotinamide. Conclusion: The addition of nicotinamide with EGFR-TKIs demonstrated potential improvements in PFS and OS, with notable survival benefits for female patients and those who had never smoked. (ClinicalTrials.gov Identifier: NCT02416739) Citation Format: Cheol-Kyu Park, Hyung-Joo Oh, Suk-Chul Bae, In-Jae Oh, Kyoung-Mi Jung, Da-Mi Kim, Jung-Won Lee, Chang Kyun Kang, Il Yeong Park, Young-Chul Kim. Nicotinamide in combination with EGFR-TKIs for the treatment of stage IV lung adenocarcinoma with EGFR mutations: A randomized double-blind (Phase IIb) trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT252.

Water-soluble 4-(dimethylaminomethyl)heliomycin exerts greater antitumor effects than parental heliomycin by targeting the tNOX-SIRT1 axis and apoptosis in oral cancer cells.

The antibiotic heliomycin (resistomycin), which is generated from Streptomyces resistomycificus, has multiple activities, including anticancer effects. Heliomycin was first described in the 1960s, but its clinical applications have been hindered by extremely low solubility. A series of 4-aminomethyl derivatives of heliomycin were synthesized to increase water solubility; studies showed that they had anti-proliferative effects, but the drug targets remained unknown. In this study, we conducted cellular thermal shift assays (CETSA) and molecular docking simulations to identify and validate that heliomycin and its water-soluble derivative, 4-(dimethylaminomethyl)heliomycin (designated compound 4-dmH) engaged and targeted with sirtuin-1 (SIRT1) in p53-functional SAS and p53-mutated HSC-3 oral cancer cells. We further addressed the cellular outcome of SIRT1 inhibition by these compounds and found that, in addition to SIRT1, the water-soluble 4-dmH preferentially targeted a tumor-associated NADH oxidase (tNOX, ENOX2). The direct binding of 4-dmH to tNOX decreased the oxidation of NADH to NAD+ which diminished NAD+-dependent SIRT1 deacetylase activity, ultimately inducing apoptosis and significant cytotoxicity in both cell types, as opposed to the parental heliomycin-induced autophagy. We also observed that tNOX and SIRT1 were both upregulated in tumor tissues of oral cancer patients compared to adjacent normal tissues, suggesting their clinical relevance. Finally, the better therapeutic efficacy of 4-dmH was confirmed in tumor-bearing mice, which showed greater tNOX and SIRT1 downregulation and tumor volume reduction when treated with 4-dmH compared to heliomycin. Taken together, our in vitro and in vivo findings suggest that the multifaceted properties of water-soluble 4-dmH enable it to offer superior antitumor value compared to parental heliomycin, and indicated that it functions through targeting the tNOX-NAD+-SIRT1 axis to induce apoptosis in oral cancer cells.

Discovery of Novel N-Acylhydrazone Derivatives as Potent Inhibitors of Sirtuin-1

AbstractSIRT1 enzyme is a key family member of Silent Information Regulators (Sirtuins), which catalyze the deacetylation of proteins. Therefore, developing new SIRT1 inhibitors has potential application in treating cancer disease and age-related metabolic disorders. In this study, we synthesized a series of N-acylhydrazone (NAH) derivatives and performed high-throughput screening of their inhibitory activity against the recombinant SIRT1 protein by a luminescent assay. Using in silico screening, we identified a new NAH derivative that features both selectivity and a high binding affinity towards the active pocket of SIRT1 that are comparable to known inhibitors such as Ex527 and Sirtinol. Such high binding affinity makes the new derivatives promising alternatives to the available inhibitors and holds promise for developing better-targeted drugs against SIRT1 activity.

The effect of quercetin on adipogenesis, lipolysis, and apoptosis in 3T3-L1 adipocytes: The role of SIRT1 pathways.

Lipotoxicity, caused by adipocyte triglyceride over-accumulation, contributes to obesity-related comorbidities such as hypertension, type 2 diabetes, coronary heart disease, respiratory dysfunction, and osteoarthritis. This study focuses on determining how sirtuin-1 (SIRT-1) mediates quercetin's (QCT) effect on 3T3-L1 adipocytes. Key aspects of this study include preventing adipogenesis, inducing lipolysis, and stimulating adipocyte apoptosis. 3T3-L1 adipocytes underwent treatment with varying QCT doses, lipopolysaccharide (LPS), and the SIRT-1 inhibitor EX-527, followed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide [MTT] assay for cell viability assessment. Furthermore, quantitative real-time polymerase chain reaction measured mRNA expression levels of adipogenesis markers (fatty acid synthase [FASN] and peroxisome proliferator-activated receptor gamma [PPARγ]), lipolysis markers (adipose triglyceride lipase [ATGL] and hormone-sensitive lipase [HSL]), and apoptosis markers (B-cell lymphoma2 [Bcl-2], Bcl-2 Associated -X-protein [BAX] and Caspase-3). The data showed that LPS+QCT significantly reduced cell viability in a dose- and time-dependent manner, unaffected by LPS+QCT+EX-527. Treatment with LPS+QCT did not affect FASN and PPARγ expression but significantly increased ATGL and HSL mRNA expression compared with LPS alone. Interestingly, EX-527 reversed the effects of LPS+QCT on lipogenesis and lipolysis markers completely. QCT enhanced apoptosis in a SIRT-1 independent pattern. The data suggest that QCT suppresses adipogenesis while increasing lipolysis via SIRT-1. However, QCT's effects on apoptosis appear to be independent of SIRT-1. These findings provide further evidence for QCT's effects on adipocytes, particularly its interaction with SIRT-1.

A dual recognition-based strategy employing Ni-modified metal-organic framework for in situ screening of SIRT1 inhibitors from Chinese herbs

Sirtuin1 (SIRT1), an NAD+-dependent histone deacetylase, plays a crucial role in regulating molecular signaling pathways. Recently, inhibition of SIRT1 rather than its activation shows the therapeutic potential for central nervous system disorder, however, the discovered SIRT1 inhibitors remains limited. In this work, a dual recognition-based strategy was developed to screen SIRT1 inhibitors from natural resources in situ. This approach utilized a Ni-modified metal-organic framework (Ni@Tyr@UiO-66-NH2) along with cell lysate containing an engineered His-tagged SIRT1 protein, eliminating the need for purified proteins, pure compounds, and protein immobilization. The high-performance Ni@Tyr@UiO-66-NH2 was synthesized by modifying the surface of UiO-66-NH2 with Ni2+ ions to specifically capture His-tagged SIRT1 while persevering its enzyme activity. By employing dual recognition, in which Ni@Tyr@UiO-66-NH2 recognized SIRT1 and SIRT1 recognized its ligands, the process of identifying SIRT1 inhibitors from complex matrix was vastly streamlined. The developed method allowed the efficient discovery of 16 natural SIRT1 inhibitors from Chinese herbs. Among them, 6 compounds were fully characterized, and suffruticosol A was found to have an excellent IC50 value of 0.95 ± 0.12 μM. Overall, an innovative dual recognition-based strategy was proposed to efficiently identify SIRT1 inhibitors in this study, offering scientific clues for the development of drugs targeting CNS disorders.

Ligand-based design and synthesis of new trityl histamine and trityl cysteamine derivatives as SIRT2 inhibitors for cancer therapy

The relentless pursuit of novel therapeutic agents against cancer has led to the identification of multiple molecular targets, among which Sirtuin 2 (SIRT2) has garnered significant attention. This study presents an extensive SAR study of our reported trityl scaffold-based SIRT2 inhibitors. This study encompasses a range of different medicinal chemistry approaches to improve the activity of the lead compounds TH-3 and STCY1. The rationally designed and synthesized structures were confirmed using NMR and high-resolution mass spectroscopy before performing SIRT2 inhibition assay, NCI60 cytotoxicity test, and cell cycle analysis. Indeed, our strategies afforded hitherto unreported SIRT2 inhibitors with high activity, particularly 2a, 4a, 7c, and 7f. Remarkably, the presence of a lipophilic para substitution on the phenyl group of a freely rotating or a locked trityl moiety enhanced activity SIRT2 inhibition. Concomitantly, the synthesized compounds showed prominent activity against different cancer lines from the NCI60 assay. Of interest, compound 7c stands out as a potent and highly selective antiproliferative agent against leukemia and colon cancer panels. Furthermore, 7c treatment resulted in cell cycle arrest in MCF-7 cells at G2 phase and did not cause in vitro DNA cleavage.

Current Trends in Sirtuin Activator and Inhibitor Development.

Sirtuins are NAD+-dependent protein deacylases and key metabolic regulators, coupling the cellular energy state with selective lysine deacylation to regulate many downstream cellular processes. Humans encode seven sirtuin isoforms (Sirt1-7) with diverse subcellular localization and deacylase targets. Sirtuins are considered protective anti-aging proteins since increased sirtuin activity is canonically associated with lifespan extension and decreased activity with developing aging-related diseases. However, sirtuins can also assume detrimental cellular roles where increased activity contributes to pathophysiology. Modulation of sirtuin activity by activators and inhibitors thus holds substantial potential for defining the cellular roles of sirtuins in health and disease and developing therapeutics. Instead of being comprehensive, this review discusses the well-characterized sirtuin activators and inhibitors available to date, particularly those with demonstrated selectivity, potency, and cellular activity. This review also provides recommendations regarding the best-in-class sirtuin activators and inhibitors for practical research as sirtuin modulator discovery and refinement evolve.

SIRT1-Rab7 axis attenuates NLRP3 and STING activation through late endosomal-dependent mitophagy during sepsis-induced acute lung injury.

Acute lung injury (ALI) is a leading cause of mortality in patients with sepsis due to proinflammatory endothelial changes and endothelial permeability defects. Mitochondrial dysfunction is recognized as a critical mediator in the pathogenesis of sepsis-induced ALI. Although mitophagy regulation of mitochondrial quality is well recognized, little is known about its role in lung ECs during sepsis-induced ALI. Sirtuin 1 (SIRT1) is a histone protein deacetylase involved in inflammation, mitophagy, and cellular senescence. Here, the authors show a type of late endosome-dependent mitophagy that inhibits NLRP3 and STING activation through SIRT1 signaling during sepsis-induced ALI. C57BL/6J male mice with or without administration of the SIRT1 inhibitor EX527 in the CLP model and lung ECs in vitro were developed to identify mitophagy mechanisms that underlie the cross-talk between SIRT1 signaling and sepsis-induced ALI. SIRT1 deficient mice exhibited exacerbated sepsis-induced ALI. Knockdown of SIRT1 interfered with mitophagy through late endosome Rab7, leading to the accumulation of damaged mitochondria and inducing excessive mitochondrial reactive oxygen species (mtROS) generation and cytosolic release of mitochondrial DNA (mtDNA), which triggered NLRP3 inflammasome and the cytosolic nucleotide sensing pathways (STING) over-activation. Pharmacological inhibition of STING and NLRP3 i n vivo or genetic knockdown in vitro reversed SIRT1 deficiency mediated endothelial permeability defects and endothelial inflammation in sepsis-induced ALI. Moreover, activation of SIRT1 with SRT1720 in vivo or overexpression of SIRT1 in vitro protected against sepsis-induced ALI. These findings suggest that SIRT1 signaling is essential for restricting STING and NLRP3 hyperactivation by promoting endosomal-mediated mitophagy in lung ECs, providing potential therapeutic targets for treating sepsis-induced ALI.

Affinity Prediction of Shikonins Towards Sirtuins and the Requisite Structural Motifs for the Selective Inhibition of SIRT2 and SIRT3

Background: Shikonin and alkannin derivatives have various pharmacological activities with unknown mechanisms of action. Sirtuins are key intracellular enzymes involved in the cell cycle and metabolism and are ideal targets of therapeutic agents. Some evidence based on recent studies indicates that shikonins are possible modulators of sirtuins. Objective: In this study, an extensive computational workflow was utilized to assess the affinity of 27 different derivatives of shikonins towards SIRT1-6 as possible molecular targets. Methods: Molecular docking and dynamics simulation studies were performed, followed by MMPBSA analysis, and the results were compared with standard and selective sirtuin inhibitors. Subsequently, the scaffold hopping approach was used to find novel and more drug-like structures. Accordingly, the pharmacophoric features of 3,4-(Methylenedioxy)cinnamoyl alkannin in SIRT2 and SIRT3 were extracted and used for screening PubChem and Mcule databases. Results: The results indicated that 3,4-(Methylenedioxy)cinnamoyl alkannin is a potent SIRT2 and SIRT3 inhibitor and even more potent than the standard sirtuin inhibitors AGK2 and selisistat. The results successfully revealed some privileged fragments for the selective inhibition of SIRT2 and SIRT3. Conclusion: An indole or benzimidazole fragment linked to basic nitrogen through an amide would be an ideal structural feature for SIRT2 inhibition, and 3-methyl-2H-pyrazolo[3,4-b]pyridine was found to be a privileged fragment for optimal inhibition of SIRT3.

Metformin alleviates junctional epithelium senescence via the AMPK/SIRT1/autophagy pathway in periodontitis induced by hyperglycemia

The junctional epithelium (JE) serves a crucial protective role in the periodontium. High glucose-related aging results in accelerated barrier dysfunction of the gingival epithelium, which may be associated with diabetic periodontitis. Metformin, an oral hypoglycemic therapeutic, has been proposed as a anti-aging agent. This study aimed to clarify the effect of metformin on diabetic periodontitis and explore its mechanism in ameliorating senescence of JE during hyperglycemia. The db/db mice was used as a diabetic model mice and alterations in the periodontium were observed by hematoxylin-eosin staining and immunohistochemistry. An ameloblast-like cell line (ALC) was cultured with high glucose to induce senescence. Cellular senescence and oxidative stress were evaluated by SA-β-gal staining and Intracellular reactive oxygen species (ROS) levels. Senescence biomarkers, P21 and P53, and autophagy markers, LC3-II/LC3-I, were measured by western blotting and quantitative real-time PCR. To construct a stable SIRT1 (Sirtuin 1) overexpression cell line, we transfected ALCs with lentiviral vectors overexpressing the mouse SIRT1 gene. Cellular senescence was increased in the JE of db/db mice and the periodontium was destroyed, which could be alleviated by metformin. Moreover, oxidative stress and cellular senescence in a high glucose environment were reduced by metformin in in-vitro assays. The autophagy inhibitor 3-MA and SIRT1 inhibitor EX-527 could dampen the effects of metformin. Overexpression of SIRT1 resulted in increased autophagy and decreased oxidative stress and cellular senescence. Meanwhile, AMPK (AMP-activated protein kinase) inhibition reversed the anti-senescence effects of metformin. Overall, these results suggest that metformin alleviates periodontal damage in db/db mice and cellular senescence in ALCs under high glucose conditions via the AMPK/SIRT1/autophagy pathway.

Metformin Attenuates Manganese-Induced Oxidative Stress in N27-A Dopaminergic Neuronal Cells.

Metformin is an anti-diabetic drug that exerts protective effects against neurodegenerative diseases. In this study, we investigated the protective effects of metformin against manganese (Mn)-induced cytotoxicity associated with Parkinson's disease-like symptoms in N27-A dopaminergic (DA) cells. Metformin (0.1-1 mM) suppressed Mn (0.4 mM)-induced cell death in a concentration-dependent manner. Metformin pretreatment effectively suppressed the Mn-mediated increase in the levels of oxidative stress markers, such as reactive oxygen species (ROS) and thiobarbituric acid reactive substances. Moreover, metformin restored the levels of the antioxidants, superoxide dismutase, intracellular glutathione, and glutathione peroxidase, which were reduced by Mn. Metformin (0.5 mM) significantly attenuated the decrease in sirtuin-1 (SIRT1) and peroxisome proliferator activated receptor gamma coactivator-1 alpha levels, which were increased by Mn (0.4 mM). In addition, metformin inhibited the expression of microRNA-34a, which directly targeted SIRT1. Metformin also inhibited the loss of Mn-induced mitochondrial membrane potential (ΔΨm) and activation of the apoptosis marker, caspase-3. Furthermore, metformin-mediated inhibition of ROS generation and caspase-3 activation, recovery of ΔΨm, and restoration of cell viability were partially reversed by the SIRT1 inhibitor, Ex527. These results suggest that metformin may protects against Mn-induced DA neuronal cell death mediated by oxidative stress and mitochondrial dysfunction possibly via the regulation of SIRT1 pathway.

Nobiletin Ameliorates Aging of Chicken Ovarian Prehierarchical Follicles by Suppressing Oxidative Stress and Promoting Autophagy.

With the increase in the age of laying chickens, the aging of follicles is accelerated, and the reproductive ability is decreased. Increased oxidative stress and mitochondrial malfunction are indispensable causes of ovarian aging. In this study, the physiological condition of prehierarchical small white follicles (SWFs) was compared between D280 high-producing chickens and D580 aging chickens, and the effect of a plant-derived flavonoid nobiletin (Nob), a natural antioxidant, on senescence of SWFs granulosa cells (SWF-GCs) was investigated. The results showed that Nob treatment activated cell autophagy by activating the AMP-activated protein kinase (AMPK) and Sirtuin-1 (SIRT1) pathways in D-galactose (D-gal)-generated senescent SWF-GCs, restoring the expression of proliferation-related mRNAs and proteins. In addition, the expression of inflammation-related protein NF-κB was significantly enhanced in aging GCs that were induced by D-gal. Nob supplementation significantly increased the antioxidant capacity and decreased the expression of several genes associated with cell apoptosis. Furthermore, Nob promoted activation of PINK1 and Parkin pathways for mitophagy and alleviated mitochondrial edema. Either the AMPK inhibitor dorsomorphin (Compound C) or SIRT1 inhibitor selisistat (EX-527) attenuated the effect of Nob on mitophagy. The protective effect of Nob on natural aging, GC proliferation, and elimination of the beneficial impact on energy regulation of naturally aging ovaries was diminished by inhibition of Nob-mediated autophagy. These data suggest that Nob treatment increases the expression of mitophagy-related proteins (PINK1 and Parkin) via the AMPK/SIRT1 pathways to prevent ovarian aging in the laying chickens.

CM1, a Chrysin Derivative, Protects from Endotoxin-Induced Lethal Shock by Regulating the Excessive Activation of Inflammatory Responses.

Sepsis, a leading cause of death worldwide, is a harmful inflammatory condition that is primarily caused by an endotoxin released by Gram-negative bacteria. Effective targeted therapeutic strategies for sepsis are lacking. In this study, using an in vitro and in vivo mouse model, we demonstrated that CM1, a derivative of the natural polyphenol chrysin, exerts an anti-inflammatory effect by inducing the expression of the ubiquitin-editing protein TNFAIP3 and the NAD-dependent deacetylase sirtuin 1 (SIRT1). Interestingly, CM1 attenuated the Toll-like receptor 4 (TLR4)-induced production of inflammatory cytokines by inhibiting the extracellular-signal-regulated kinase (ERK)/MAPK and nuclear factor kappa B (NF-κB) signalling pathways. In addition, CM1 induced the expression of TNFAIP3 and SIRT1 on TLR4-stimulated primary macrophages; however, the anti-inflammatory effect of CM1 was abolished by the siRNA-mediated silencing of TNFAPI3 or by the genetic or pharmacologic inhibition of SIRT1. Importantly, intravenous administration of CM1 resulted in decreased susceptibility to endotoxin-induced sepsis, thereby attenuating the production of pro-inflammatory cytokines and neutrophil infiltration into the lung compared to control mice. Collectively, these findings demonstrate that CM1 has therapeutic potential for diverse inflammatory diseases, including sepsis.

Deacetylase Sirtuin 1 mitigates type I IFN- and type II IFN-induced signaling and antiviral immunity.

Type I and type II IFNs are important immune modulators in both innate and adaptive immunity. They transmit signaling by activating JAK-STAT pathways. Sirtuin 1 (SIRT1), a class III NAD+-dependent deacetylase, has multiple functions in a variety of physiological processes. Here, we characterized the novel functions of SIRT1 in the regulation of type I and type II IFN-induced signaling. Overexpression of SIRT1 inhibited type I and type II IFN-induced interferon-stimulated response element activation. In contrast, knockout of SIRT1 promoted type I and type II IFN-induced expression of ISGs and inhibited viral replication. Treatment with SIRT1 inhibitor EX527 had similar positive effects. SIRT1 physically associated with STAT1 or STAT3, and this interaction was enhanced by IFN stimulation or viral infection. By deacetylating STAT1 at K673 and STAT3 at K679/K685/K707/K709, SIRT1 downregulated the phosphorylation of STAT1 (Y701) and STAT3 (Y705). Sirt1+/- primary peritoneal macrophages and Sirt1+/- mice exhibited enhanced IFN-induced signaling and antiviral activity. Thus, SIRT1 is a novel negative regulator of type I and type II IFN-induced signaling through its deacetylase activity.IMPORTANCESIRT1 has been reported in the precise regulation of antiviral (RNA and DNA) immunity. However, its functions in type I and type II IFN-induced signaling are still unclear. In this study, we deciphered the important functions of SIRT1 in both type I and type II IFN-induced JAK-STAT signaling and explored the potential acting mechanisms. It is helpful for understanding the regulatory roles of SIRT1 at different levels of IFN signaling. It also consolidates the notion that SIRT1 is an important target for intervention in viral infection, inflammatory diseases, or even interferon-related therapies.

Human cytomegalovirus modulates mTORC1 to redirect mRNA translation within quiescently infected monocytes.

Human cytomegalovirus (HCMV) utilizes peripheral blood monocytes as a means to systemically disseminate throughout the host. Following viral entry, HCMV stimulates non-canonical Akt signaling leading to the activation of mTORC1 and the subsequent translation of select antiapoptotic proteins within infected monocytes. However, the full extent to which the HCMV-initiated Akt/mTORC1 signaling axis reshapes the monocyte translatome is unclear. We found HCMV entry alone was able to stimulate widescale changes to mRNA translation levels and that inhibition of mTOR, a component of mTORC1, dramatically attenuated HCMV-induced protein synthesis. Although monocytes treated with normal myeloid growth factors also exhibited increased levels of translation, mTOR inhibition had no effect, suggesting HCMV activation of mTOR stimulates the acquisition of a unique translatome within infected monocytes. Indeed, polyribosomal profiling of HCMV-infected monocytes identified distinct prosurvival transcripts that were preferentially loaded with ribosomes when compared to growth factor-treated cells. Sirtuin 1 (SIRT1), a deacetylase that exerts prosurvival effects through regulation of the PI3K/Akt pathway, was found to be highly enriched following HCMV infection in an mTOR-dependent manner. Importantly, SIRT1 inhibition led to the death of HCMV-infected monocytes while having minimal effect on uninfected cells. SIRT1 also supported a positive feedback loop to sustain Akt/mTORC1 signaling following viral entry. Taken together, HCMV profoundly reshapes mRNA translation in an mTOR-dependent manner to enhance the synthesis of select factors necessary for the survival of infected monocytes.IMPORTANCEHuman cytomegalovirus (HCMV) infection is a significant cause of morbidity and mortality among the immunonaïve and immunocompromised. Peripheral blood monocytes are a major cell type responsible for disseminating the virus from the initial site of infection. In order for monocytes to mediate viral spread within the host, HCMV must subvert the naturally short lifespan of these cells. In this study, we performed polysomal profiling analysis, which demonstrated HCMV to globally redirect mRNA translation toward the synthesis of cellular prosurvival factors within infected monocytes. Specifically, HCMV entry into monocytes induced the translation of cellular SIRT1 to generate an antiapoptotic state. Defining the precise mechanisms through which HCMV stimulates survival will provide insight into novel anti-HCMV drugs able to target infected monocytes.

Abstract TP32: Sirtuin 3 Regulation of Mitochondrial Dynamics and Neuronal Apoptosis During Ischemia/Reperfusion

Ischemic stroke occurs when the blood supply to the brain is interrupted, reducing the access of affected tissue to oxygen and glucose. The lack of oxygen inhibits the electron transport chain, leading to intracellular ATP deficiency, cellular damage, and death. The restoration of blood flow, known as reperfusion, allows the reintroduction of oxygen but may cause increased oxidative stress, as it hyperactivates the electron transport chain and thus induces excessive production of reactive oxygen species (ROS), leading to further cell death. One potential therapeutic target for reperfusion injury is Sirtuin 3 (SIRT3), which mediates the deacetylation of enzymes that are responsible for the reduction of ROS, leading to protection against oxidative stress. This study aims to understand the role of SIRT3 on ischemia and reperfusion-induced neuronal apoptosis. Primary neurons were isolated from wildtype mice postnatal day 0-1 and cultured for 14 days. The neurons underwent 2-hour oxygen-glucose deprivation mimicking stroke, followed by reperfusion. The neurons were then lysed, and western blots were done to analyze changes in protein levels. The western blots show that SIRT3 levels significantly decline over 1-6 hours post-reperfusion (n≥3, p<0.05), and TOM20, a mitochondrial protein, declines at 1 hour post-reperfusion(n≥3, p<0.05), indicating mitophagy. In addition, the cleavage of caspase-3 significantly increases at 4 hours post-reperfusion (n=3, p<0.05), implying apoptosis. Our data suggests that SIRT3 plays a crucial role in the mitochondrial metabolism of neurons and could be a potential target for reperfusion therapy. Future experiments would examine the effects of a SIRT3 activator and inhibitor on cell apoptosis.

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.

Opportunities and Difficulties in the Repurposing of HDAC Inhibitors as Antiparasitic Agents

Ongoing therapy for human parasite infections has a few known drugs but with serious side effects and the problem of drug resistance, impelling us to discover novel drug candidates with newer mechanisms of action. Universally, this has boosted the research in the design and development of novel medicinal agents as antiparasitic drugs with a novel mode of action. Histone deacetylase inhibitors (HDACis) are used in a vast variety of diseases due to their anti-inflammatory properties. Drug repurposing strategies have already approved HDACis as cancer therapeutics and are now under investigation for many parasitic infections. Along with the expression of the gene, histone deacetylase (HDAC) enzymes also act as a slice of great multi-subunit complexes, targeting many non-histones, changing systemic and cellular levels signaling, and producing different cell-based specified effects. Zinc (Zn2+)- and nicotinamide adenine dinucleotide (NAD+)-dependent HDACs of parasites play pivotal roles in the alteration of gene expression of parasites. Some of them are already known to be responsible for the survival of several parasites under odd circumstances; thus, targeting them for therapeutic interventions will be novel for potential antiparasitic targets. This point of view outlines the knowledge of both class-I and class-II HDACis and sirtuin inhibitors that emerged to be the key players in the treatment of human parasitic disorders like Leishmaniasis, Schistosomiasis, Malaria, Trypanosomiasis, and Toxoplasmosis. This review also focuses on repurposing opportunities and challenges in HDAC inhibitors that are preceded by their clinical development as potent new antiparasitic drugs.