Sirtuins: Key pieces in the host response to pathogens' puzzle

Sirtuin 2 inhibitor AGK2 exerts antiviral effects by inducing epigenetic suppression of hepatitis B virus covalently closed circular DNA through recruitment of repressive histone lysine methyltransferases and reduction of cccDNA

Chronic hepatitis B virus (HBV) infection continues to be a global health concern because current treatments such as interferon-α and nucleos(t)ide analogs cannot fully eliminate the virus due to persistence of covalently closed circular DNA (cccDNA) and integrated HBV DNA. Earlier research suggests that AGK2, a selective SIRT2 inhibitor, suppresses HBV replication by modifying key signaling pathways. This study aimed to further explore the anti-HBV effects of AKG2, particularly its effects on the epigenetic landscape of cccDNA. HBV-transfected and -infected cells were used to assess the impact of AGK2 on viral replication. Changes in SIRT2 expression and α-tubulin acetylation (SDS-PAGE-immunoblotting), core particle formation (native agarose gel electrophoresis and immunoblotting), HBV RNA (northern blotting) and DNA (Southern blotting) synthesis, and cccDNA levels (Southern blotting) were measured. Chromatin immunoprecipitation assays were performed to examine deposition of transcriptionally repressive epigenetic markers on cccDNA. AGK2 reduced expression of SIRT2, increased acetylated α-tubulin levels, and reduced synthesis of HBV RNA and DNA. Importantly, AGK2 also reduced cccDNA levels and increased deposition of repressive histone markers H4K20me1, H3K27me3, and H3K9me3 on cccDNA, mediated by histone lysine methyltransferases such as PR-Set7, EZH2, SETDB1, and SUV39H1. Additionally, there was a reduction in recruitment of RNA polymerase II and acetylated H3 to cccDNA, indicating that AGK2 enhances transcriptional repression. AGK2 suppresses HBV replication through direct antiviral actions, and by epigenetic modulation of cccDNA, indicating that using AGK2 to target SIRT2 and associated epigenetic regulators shows promise as a functional cure for chronic hepatitis B.

In silico approach reveals N-(5-phenoxythiophen-2-yl)-2-(arylthio)acetamides as promising selective SIRT2 inhibitors: the case of structural optimization of virtual screening-derived hits

Epigenetic modifications play an essential role in tumor suppression and promotion. Among the diverse range of epigenetic regulators, SIRT2, a member of NAD+-dependent protein deacetylates, has emerged as a crucial regulator of cellular processes, including cell cycle progression, DNA repair, and metabolism, impacting tumor growth and survival. In the present work, a series of N-(5-phenoxythiophen-2-yl)-2-(arylthio)acetamide derivatives were identified following a structural optimization of previously reported virtual screening hits, accompanied by enhanced SIRT2 inhibitory potency. Among the compounds, ST44 and ST45 selectively inhibited SIRT2 with IC50 values of 6.50 and 7.24 μM, respectively. The predicted binding modes of the two compounds revealed the success of the optimization run. Moreover, ST44 displayed antiproliferative effects on the MCF-7 human breast cancer cell line. Further, the contribution of SIRT2 inhibition in this effect of ST44 was supported by western blotting, affording an increased α-tubulin acetylation. Furthermore, molecular dynamics (MD) simulations and binding free energy calculations using molecular mechanics/generalized born surface area (MM-GBSA) method evaluated the accuracy of predicted binding poses and ligand affinities. The results revealed that ST44 exhibited a remarkable level of stability, with minimal deviations from its initial docking conformation. These findings represented a significant improvement over the virtual screening hits and may contribute substantially to our knowledge for further selective SIRT2 drug discovery.Communicated by Ramaswamy H. Sarma.

NAD+ Suppresses EV-D68 Infection by Enhancing Anti-Viral Effect of SIRT1

Enterovirus 68 (EV-D68) is a non-enveloped virus with a positive-sense single-stranded RNA genome that causes respiratory diseases and acute flaccid myelitis, posing significant threats to human health. However, an effective vaccine remains undeveloped. SIRT1, a nicotinamide adenine dinucleotide (NAD+)-dependent enzyme, plays a key role in cellular metabolism, but its interaction with NAD+ during viral infections is not well understood. In this study, through a metabolomics analysis, we demonstrate that EV-D68 infection influences cellular metabolism. Additionally, we show that NAD+ inhibits EV-D68 infection both in vivo and in vitro. EV-D68 reduces cellular NAD+ levels by regulating the expression of enzymes involved in NAD+ consumption and synthesis. Moreover, the infection increases the expression of sirtuin 1 (SIRT1), which inhibits EV-D68 replication in turn. Mechanistically, SIRT1 suppresses EV-D68 5'UTR-mediated translation, and the antiviral effect of SIRT1 on EV-D68 replication is enhanced by NAD+. Collectively, our findings highlight the critical role of NAD+ metabolism in EV-D68 infection and reveal the antiviral potential of SIRT1, providing valuable insights for the development of antiviral strategies.

Drugs Targeting Sirtuin 2 Exhibit Broad-Spectrum Anti-Infective Activity

Direct-acting anti-infective drugs target pathogen-coded gene products and are a highly successful therapeutic paradigm. However, they generally target a single pathogen or family of pathogens, and the targeted organisms can readily evolve resistance. Host-targeted agents can overcome these limitations. One family of host-targeted, anti-infective agents modulate human sirtuin 2 (SIRT2) enzyme activity. SIRT2 is one of seven human sirtuins, a family of NAD+-dependent protein deacylases. It is the only sirtuin that is found predominantly in the cytoplasm. Multiple, structurally distinct SIRT2-targeted, small molecules have been shown to inhibit the replication of both RNA and DNA viruses, as well as intracellular bacterial pathogens, in cell culture and in animal models of disease. Biochemical and X-ray structural studies indicate that most, and probably all, of these compounds act as allosteric modulators. These compounds appear to impact the replication cycles of intracellular pathogens at multiple levels to antagonize their replication and spread. Here, we review SIRT2 modulators reported to exhibit anti-infective activity, exploring their pharmacological action as anti-infectives and identifying questions in need of additional study as this family of anti-infective agents advances to the clinic.

Symmetrical 2,7-disubstituted 9H-fluoren-9-one as a novel and promising scaffold for selective targeting of SIRT2

Sirtuin 2 (SIRT2) belongs to the family of silent information regulators (sirtuins), which comprises nicotinamide adenine dinucleotide (NAD+)-dependent protein lysine deacetylases. With a distribution across numerous tissues and organs of the human body, SIRT2 is involved in a wide range of physiological and pathological processes, such as regulating the cell cycle, energy metabolism, DNA repair, and tumorigenesis. Aberrant expression of SIRT2 has been closely associated with particular etiologies of human diseases, positioning SIRT2 as a promising therapeutic target. Herein, we detail the design overview and findings of novel symmetrical 2,7-disubstituted 9H-fluoren-9-one derivatives targeting SIRT2. SG3 displayed the most potent SIRT2-selective inhibitory profile, with an IC50 value of 1.95 μ M $\mu {\rm{M}}$ , and reduced the cell viability of human breast cancer MCF-7 cells accompanied by hyperacetylation of α-tubulin. Finally, molecular docking, molecular dynamics simulations, and binding free energy calculations using molecular mechanics/generalized born surface area method were performed to verify the binding ability of SG3 to SIRT2. Taken together, these results could enhance our understanding of the structural elements necessary for inhibiting SIRT2 and shed light on the mechanism of inhibition.

Structure-Function Insights into the Dual Role in Nucleobase and Nicotinamide Metabolism and a Possible Use in Cancer Gene Therapy of the URH1p Riboside Hydrolase

The URH1p enzyme from the yeast Saccharomyces cerevisiae has gained significant interest due to its role in nitrogenous base metabolism, particularly involving uracil and nicotinamide salvage. Indeed, URH1p was initially classified as a nucleoside hydrolase (NH) with a pronounced preference for uridine substrate but was later shown to also participate in a Preiss-Handler-dependent pathway for recycling of both endogenous and exogenous nicotinamide riboside (NR) towards NAD+ synthesis. Here, we present the detailed enzymatic and structural characterisation of the yeast URH1p enzyme, a member of the group I NH family of enzymes. We show that the URH1p has similar catalytic efficiencies for hydrolysis of NR and uridine, advocating a dual role of the enzyme in both NAD+ synthesis and nucleobase salvage. We demonstrate that URH1p has a monomeric structure that is unprecedented for members of the NH homology group I, showing that oligomerisation is not strictly required for the N-ribosidic activity in this family of enzymes. The size, thermal stability and activity of URH1p towards the synthetic substrate 5-fluoruridine, a riboside precursor of the antitumoral drug 5-fluorouracil, make the enzyme an attractive tool to be employed in gene-directed enzyme-prodrug activation therapy against solid tumours.

Human Umbilical Cord Mesenchymal-Stem-Cell-Derived Extracellular Vesicles Reduce Skin Inflammation In Vitro

The protective roles of extracellular vesicles derived from human umbilical cord mesenchymal stem cells against oxazolone-induced damage in the immortalized human keratinocyte cell line HaCaT were investigated. The cells were pretreated with or without UCMSC-derived extracellular vesicles 24 h before oxazolone exposure. The pretreated UVMSC-EVs showed protective activity, elevating cell viability, reducing intracellular ROS, and reducing the changes in the mitochondrial membrane potential compared to the cells with a direct oxazolone treatment alone. The UCMSC-EVs exhibited anti-inflammatory activity via reducing the inflammatory cytokines IL-1β and TNF-α. A mechanism study showed that the UCMSC-EVs increased the protein expression levels of SIRT1 and P53 and reduced P65 protein expression. It was concluded that UVMSC-EVs can induce the antioxidant defense systems of HaCaT cells and that they may have potential as functional ingredients in anti-aging cosmetics for skin care.