Golgi stress induces SIRT2 to counteract Shigella infection via defatty-acylation

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.

SIRT2-mediated ACSS2 K271 deacetylation suppresses lipogenesis under nutrient stress

De novo lipogenesis is associated with the development of human diseases such as cancer, diabetes, and obesity. At the core of lipogenesis lies acetyl coenzyme A (CoA), a metabolite that plays a crucial role in fatty acid synthesis. One of the pathways contributing to the production of cytosolic acetyl-CoA is mediated by acetyl-CoA synthetase 2 (ACSS2). Here, we reveal that when cells encounter nutrient stress, particularly a deficiency in amino acids, Sirtuin 2 (SIRT2) catalyzes the deacetylation of ACSS2 at the lysine residue K271. This results in K271 ubiquitination and subsequently proteasomal degradation of ACSS2. Substitution of K271 leads to decreased ubiquitination of ACSS2, increased ACSS2 protein level, and thus increased lipogenesis. Our study uncovers a mechanism that cells employ to efficiently manage lipogenesis during periods of nutrient stress.

Antibiotic target discovery by integrated phenotypic and activity-based profiling of electrophilic fragments

The emergence of antibiotic resistance necessitates the discovery of novel bacterial targets and antimicrobial agents. Here, we present a bacterial target discovery framework that integrates phenotypic screening of cysteine-reactive fragments with competitive activity-based protein profiling to map and functionally characterize the targets of screening hits. Using this approach, we identify β-ketoacyl-acyl carrier protein synthase III (FabH) and MiaA tRNA prenyltransferase as primary targets of a hit fragment, 10-F05, that confer bacterial stress resistance and virulence in Shigella flexneri. Mechanistic investigations elucidate that covalent C112 modification in FabH, an enzyme involved in bacterial fatty acid synthesis, results in its inactivation and consequent growth inhibition. We further demonstrate that irreversible C273 modification at the MiaA RNA-protein interaction interface abrogates substrate tRNA binding, attenuating resistance and virulence through decreased translational accuracy. Our findings underscore the efficacy of integrating phenotypic and activity-based profiling of electrophilic fragments to accelerate the identification and pharmacologic validation of new therapeutic targets.

Emerging roles of mitochondrial sirtuin SIRT5 in succinylation modification and cancer development

Succinylation represents an emerging class of post-translational modifications (PTMs), characterized by the enzymatic or non-enzymatic transfer of a negatively charged four-carbon succinyl group to the ϵ-amino group of lysine residues, mediated by succinyl-coenzyme A. Recent studies have highlighted the involvement of succinylation in various diseases, particularly cancer progression. Sirtuin 5 (SIRT5), a member of the sirtuin family, has been extensively studied for its robust desuccinylase activity, alongside its deacetylase function. To date, only a limited number of SIRT5 substrates have been identified. These substrates mediate diverse physiological processes such as glucose oxidation, fatty acid oxidation, ammonia detoxification, reactive oxygen species scavenging, anti-apoptosis, and inflammatory responses. The regulation of these activities can occur through either the same enzymatic activity acting on different substrates or distinct enzymatic activities targeting the same substrate. Aberrant expression of SIRT5 has been closely linked to tumorigenesis and disease progression; however, its role remains controversial. SIRT5 exhibits dual functionalities: it can promote tumor proliferation, metastasis, drug resistance, and metabolic reprogramming, thereby acting as an oncogene; conversely, it can also inhibit tumor cell growth and induce apoptosis, functioning as a tumor suppressor gene. This review aims to provide a comprehensive overview of the current research status of SIRT5. We discuss its structural characteristics and regulatory mechanisms, compare its functions with other sirtuin family members, and elucidate the mechanisms regulating SIRT5 activity. Specifically, we focus on the role of succinylation modification mediated by SIRT5 in tumor progression, highlighting how desuccinylation by SIRT5 modulates tumor development and delineating the underlying mechanisms involved.

Electroacupuncture pretreatment ameliorates Golgi stress and the inflammation response against endotoxin-induced lung injury

BACKGROUND

Sepsis is a life-threatening condition involving organ dysfunction characterized by a generalized inflammatory syndrome, and the associated mortality rate is high. Electroacupuncture (EA) exerts benefits in endotoxemia-induced lung injury, mainly through lung inflammation reduction and cellular homeostasis, although the anti-inflammatory mechanisms underlying these benefits remain to be completely understood.

METHODS

Mice were pretreated with EA or sham EA therapy 5 days prior to the induction of endotoxemia through the administration of lipopolysaccharide (LPS) and cecal ligation and puncture (CLP). Histopathological changes, systemic inflammation and cell death in the lungs were assessed. Transmission electron microscopy was employed to visually identify the structure of the Golgi complex. We examined proteins involved in maintaining the structural integrity of the Golgi apparatus and proteins associated with Golgi stress. The potential molecular mechanisms were investigated through overexpression of CREB3.

RESULTS

EA pretreatment effectively rescued the lung from pathological changes, lung edema, cell apoptosis, and survival rate in septic mice, along with the improvement of physiological parameters. Endotoxemia strongly induces fragmented Golgi stacks, leading to fragmentation and disintegration of its shape, inducing cell apoptosis, and causing the outbreak of a large amount of inflammation in the lungs. EA therapy can significantly inhibit the fragmented process of Golgi stress to rescue the morphological changes and exert anti-inflammatory effects. And this protective effect may be related to downregulation of cAMP responsive element binding protein 3 (CREB3) and ADP-Ribosylation Factor 4 (ARF4), one of the key pathways involved in Golgi stress response. However, Sham EA (SEA) treatment did not substantially improve the fragmentation, stacking, and separation of Golgi organization, and inflammatory damage induced by endotoxin remains. This study discovered that overexpression of CREB3 may diminish the protective efficacy of EA.

CONCLUSION

Administering EA pretreatment at precisely selected acupoints notably improves the survival rate in mice challenged with endotoxemia and concurrently exerts a protective effect against inflammatory lung injury. This salutary impact is speculated to be mediated through the augmentation of the Golgi apparatus's stress response.

Candidate serum protein biomarkers for active pulmonary tuberculosis diagnosis in tuberculosis endemic settings

BACKGROUND

Identification of non-sputum diagnostic markers for tuberculosis (TB) is urgently needed. This exploratory study aimed to discover potential serum protein biomarkers for the diagnosis of active pulmonary TB (PTB).

METHOD

We employed Proximity Extension Assay (PEA) to measure levels of 92 protein biomarkers related to inflammation in serum samples from three patient groups: 30 patients with active PTB, 29 patients with other respiratory diseases with latent TB (ORD with LTBI+), and 29 patients with other respiratory diseases without latent TB (ORD with LTBI-). To understand the functional mechanisms associated with differentially expressed proteins, we performed Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. Least absolute shrinkage and selection operator (LASSO) regression was employed to identify potential TB diagnostic protein biomarkers. Network interactions among the identified candidate diagnostic markers were then analyzed, and their diagnostic performance was evaluated using logistic regression and receiver operating characteristic (ROC) analysis.

RESULT

The analysis revealed 37 differentially expressed proteins (DEPs) in the active PTB group compared to both ORD with LTBI + and ORD with LTBI- groups. Gene Ontology analysis indicated that these DEPs were primarily involved in the inflammatory response, while KEGG enrichment analysis highlighted the cytokine-cytokine receptor interaction pathway as the top significant hit. LASSO regression identified eight promising candidate protein biomarkers: IFN-gamma, LIF, uPA, CSF-1, SCF, SIRT2, 4E-BP1, and GDNF. The combined set of these eight proteins yielded an AUC of 0.943 for differentiating active PTB from ORD with LTBI+, and an AUC of 0.927 for distinguishing PTB from ORD with LTBI-.

CONCLUSION

We have identified eight protein markers that reliably differentiate active PTB from ORD irrespective of LTBI presence. Further large-scale validation and translation of these protein markers into a user-friendly and affordable point-of-care test hold the potential to significantly enhance TB control in high-burden regions.

The Biosynthesis and Applications of Protein Lipidation

Protein lipidation dramatically affects protein structure, localization, and trafficking via remodeling protein-membrane and protein-protein interactions through hydrophobic lipid moieties. Understanding the biosynthesis of lipidated proteins, whether natural ones or mimetics, is crucial for reconstructing, validating, and studying the molecular mechanisms and biological functions of protein lipidation. In this Perspective, we first provide an overview of the natural enzymatic biosynthetic pathways of protein lipidation in mammalian cells, focusing on the enzymatic machineries and their chemical linkages. We then discuss strategies to biosynthesize protein lipidation in mammalian cells by engineering modification machineries and substrates. Additionally, we explore site-specific protein lipidation biosynthesis in vitro via enzyme-mediated ligations and in vivo primarily through genetic code expansion strategies. We also discuss the use of small molecule tools to modulate the process of protein lipidation biosynthesis. Finally, we provide concluding remarks and discuss future directions for the biosynthesis and applications of protein lipidation.

SIRT6 in Regulation of Mitochondrial Damage and Associated Cardiac Dysfunctions: A Possible Therapeutic Target for CVDs

Cardiovascular diseases (CVDs) can be described as a global health emergency imploring possible prevention strategies. Although the pathogenesis of CVDs has been extensively studied, the role of mitochondrial dysfunction in CVD development has yet to be investigated. Diabetic cardiomyopathy, ischemic-reperfusion injury, and heart failure are some of the CVDs resulting from mitochondrial dysfunction Recent evidence from the research states that any dysfunction of mitochondria has an impact on metabolic alteration, eventually causes the death of a healthy cell and therefore, progressively directing to the predisposition of disease. Cardiovascular research investigating the targets that both protect and treat mitochondrial damage will help reduce the risk and increase the quality of life of patients suffering from various CVDs. One such target, i.e., nuclear sirtuin SIRT6 is strongly associated with cardiac function. However, the link between mitochondrial dysfunction and SIRT6 concerning cardiovascular pathologies remains poorly understood. Although the Role of SIRT6 in skeletal muscles and cardiomyocytes through mitochondrial regulation has been well understood, its specific role in mitochondrial maintenance in cardiomyocytes is poorly determined. The review aims to explore the domain-specific function of SIRT6 in cardiomyocytes and is an effort to know how SIRT6, mitochondria, and CVDs are related.

Post-translational targeting of Rab35 by the effector IcsB of Shigella determines intracellular bacterial niche formation

Escape from the bacterial-containing vacuole (BCV) is a key step of Shigella host cell invasion. Rab GTPases subverted to in situ-formed macropinosomes in the vicinity of the BCV have been shown to promote its rupture. The involvement of the BCV itself has remained unclear. We demonstrate that Rab35 is non-canonically entrapped at the BCV. Stimulated emission depletion imaging localizes Rab35 directly on the BCV membranes before vacuolar rupture. The bacterial effector IcsB, a lysine Nε-fatty acylase, is a key regulator of Rab35-BCV recruitment, and we show post-translational acylation of Rab35 by IcsB in its polybasic region. While Rab35 and IcsB are dispensable for the first step of BCV breakage, they are needed for the unwrapping of damaged BCV remnants from Shigella. This provides a framework for understanding Shigella invasion implicating re-localization of a Rab GTPase via its bacteria-dependent post-translational modification to support the mechanical unpeeling of the BCV.

Golgi Stress Response: New Insights into the Pathogenesis and Therapeutic Targets of Human Diseases

The Golgi apparatus modifies and transports secretory and membrane proteins. In some instances, the production of secretory and membrane proteins exceeds the capacity of the Golgi apparatus, including vesicle trafficking and the post-translational modification of macromolecules. These proteins are not modified or delivered appropriately due to insufficiency in the Golgi function. These conditions disturb Golgi homeostasis and induce a cellular condition known as Golgi stress, causing cells to activate the 'Golgi stress response,' which is a homeostatic process to increase the capacity of the Golgi based on cellular requirements. Since the Golgi functions are diverse, several response pathways involving TFE3, HSP47, CREB3, proteoglycan, mucin, MAPK/ETS, and PERK regulate the capacity of each Golgi function separately. Understanding the Golgi stress response is crucial for revealing the mechanisms underlying Golgi dynamics and its effect on human health because many signaling molecules are related to diseases, ranging from viral infections to fatal neurodegenerative diseases. Therefore, it is valuable to summarize and investigate the mechanisms underlying Golgi stress response in disease pathogenesis, as they may contribute to developing novel therapeutic strategies. In this review, we investigate the perturbations and stress signaling of the Golgi, as well as the therapeutic potentials of new strategies for treating Golgi stress-associated diseases.

New insights into the role of the Golgi apparatus in the pathogenesis and therapeutics of human diseases

The Golgi apparatus is an essential cellular organelle that mediates homeostatic functions, including vesicle trafficking and the post-translational modification of macromolecules. Its unique stacked structure and dynamic functions are tightly regulated, and several Golgi proteins play key roles in the functioning of unconventional protein secretory pathways triggered by cellular stress responses. Recently, an increasing number of studies have implicated defects in Golgi functioning in human diseases such as cancer, neurodegenerative, and immunological disorders. Understanding the extraordinary characteristics of Golgi proteins is important for elucidating its associated intracellular signaling mechanisms and has important ramifications for human health. Therefore, analyzing the mechanisms by which the Golgi participates in disease pathogenesis may be useful for developing novel therapeutic strategies. This review articulates the structural features and abnormalities of the Golgi apparatus reported in various diseases and the suspected mechanisms underlying the Golgi-associated pathologies. Furthermore, we review the potential therapeutic strategies based on Golgi function.

Sirtuins at the Crossroads between Mitochondrial Quality Control and Neurodegenerative Diseases: Structure, Regulation, Modifications, and Modulators

Sirtuins (SIRT1-SIRT7), a family of nicotinamide adenine dinucleotide (NAD⁺)-dependent enzymes, are key regulators of life span and metabolism. In addition to acting as deacetylates, some sirtuins have the properties of deacylase, decrotonylase, adenosine diphosphate (ADP)-ribosyltransferase, lipoamidase, desuccinylase, demalonylase, deglutarylase, and demyristolyase. Mitochondrial dysfunction occurs early on and acts causally in the pathogenesis of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD). Sirtuins are implicated in the regulation of mitochondrial quality control, which is highly associated with the pathogenesis of neurodegenerative diseases. There is growing evidence indicating that sirtuins are promising and well-documented molecular targets for the treatment of mitochondrial dysfunction and neurodegenerative disorders by regulating mitochondrial quality control, including mitochondrial biogenesis, mitophagy, mitochondrial fission/fusion dynamics, and mitochondrial unfolded protein responses (mtUPR). Therefore, elucidation of the molecular etiology of sirtuin-mediated mitochondrial quality control points to new prospects for the treatment of neurodegenerative diseases. However, the mechanisms underlying sirtuin-mediated mitochondrial quality control remain obscure. In this review, we update and summarize the current understanding of the structure, function, and regulation of sirtuins with an emphasis on the cumulative and putative effects of sirtuins on mitochondrial biology and neurodegenerative diseases, particularly their roles in mitochondrial quality control. In addition, we outline the potential therapeutic applications for neurodegenerative diseases of targeting sirtuin-mediated mitochondrial quality control through exercise training, calorie restriction, and sirtuin modulators in neurodegenerative diseases.