Comprehensive assessment of cellular senescence in the tumor microenvironment.

Cellular senescence (CS), a state of permanent growth arrest, is intertwined with tumorigenesis. Due to the absence of specific markers, characterizing senescence levels and senescence-related phenotypes across cancer types remain unexplored. Here, we defined computational metrics of senescence levels as CS scores to delineate CS landscape across 33 cancer types and 29 normal tissues and explored CS-associated phenotypes by integrating multiplatform data from ~20 000 patients and ~212 000 single-cell profiles. CS scores showed cancer type-specific associations with genomic and immune characteristics and significantly predicted immunotherapy responses and patient prognosis in multiple cancers. Single-cell CS quantification revealed intra-tumor heterogeneity and activated immune microenvironment in senescent prostate cancer. Using machine learning algorithms, we identified three CS genes as potential prognostic predictors in prostate cancer and verified them by immunohistochemical assays in 72 patients. Our study provides a comprehensive framework for evaluating senescence levels and clinical relevance, gaining insights into CS roles in cancer- and senescence-related biomarker discovery.

Targeting PDE4B (Phosphodiesterase-4 Subtype B) for Cardioprotection in Acute Myocardial Infarction via Neutrophils and Microcirculation.

BACKGROUND: Timely and complete restoration of blood flow is the most effective intervention for patients with acute myocardial infarction. However, the efficacy is limited by myocardial ischemia-reperfusion (MI/R) injury. PDE4 (phosphodiesterase-4) hydrolyzes intracellular cyclic adenosine monophosphate and it has 4 subtypes A-D. This study aimed to delineate the role of PDE4B (phosphodiesterase-4 subtype B) in MI/R injury. METHODS: Mice were subjected to 30-minute coronary artery ligation, followed by 24-hour reperfusion. Cardiac perfusion was assessed by laser Doppler flow. Vasomotor reactivities were determined in mouse and human coronary (micro-)arteries. RESULTS: Cardiac expression of PDE4B, but not other PDE4 subtypes, was increased in mice following reperfusion. PDE4B was detected primarily in endothelial and myeloid cells of mouse and human hearts. PDE4B deletion strikingly reduced infarct size and improved cardiac function 24-hour or 28-day after MI/R. PDE4B in bone marrow-derived cells promoted MI/R injury and vascular PDE4B further exaggerated this injury. Mechanistically, PDE4B mediated neutrophil-endothelial cell interaction and PKA (protein kinase A)-dependent expression of cell adhesion molecules, neutrophil cardiac infiltration, and release of proinflammatory cytokines. Meanwhile, PDE4B promoted coronary microcirculatory obstruction and vascular permeability in MI/R, without affecting flow restriction-induced thrombosis. PDE4B blockade increased flow-mediated vasodilatation and promoted endothelium-dependent dilatation of coronary arteries in a PKA- and nitric oxide-dependent manner. Furthermore, postischemia administration with piclamilast, a PDE4 pan-inhibitor, improved cardiac microcirculation, suppressed inflammation, and attenuated MI/R injury in mice. Incubation with sera from patients with acute myocardial infarction impaired acetylcholine-induced relaxations in human coronary microarteries, which was abolished by PDE4 inhibition. Similar protection against MI/R-related coronary injury was recapitulated in mice with PDE4B deletion or inhibition, but not with the pure vasodilator, sodium nitroprusside. CONCLUSIONS: PDE4B is critically involved in neutrophil inflammation and microvascular obstruction, leading to MI/R injury. Selective inhibition of PDE4B might protect cardiac function in patients with acute myocardial infarction designated for reperfusion therapy.

Transcriptional silencing of fetal hemoglobin expression by NonO.

Human fetal globin (γ-globin) genes are developmentally silenced after birth, and reactivation of γ-globin expression in adulthood ameliorates symptoms of hemoglobin disorders, such as sickle cell disease (SCD) and ß-thalassemia. However, the mechanisms by which γ-globin expression is precisely regulated are still incompletely understood. Here, we found that NonO (non-POU domain-containing octamer-binding protein) interacted directly with SOX6, and repressed the expression of γ-globin gene in human erythroid cells. We showed that NonO bound to the octamer binding motif, ATGCAAAT, of the γ-globin proximal promoter, resulting in inhibition of γ-globin transcription. Depletion of NonO resulted in significant activation of γ-globin expression in K562, HUDEP-2, and primary human erythroid progenitor cells. To confirm the role of NonO in vivo, we further generated a conditional knockout of NonO by using IFN-inducible Mx1-Cre transgenic mice. We found that induced NonO deletion reactivated murine embryonic globin and human γ-globin gene expression in adult ß-YAC mice, suggesting a conserved role for NonO during mammalian evolution. Thus, our data indicate that NonO acts as a novel transcriptional repressor of γ-globin gene expression through direct promoter binding, and is essential for γ-globin gene silencing.

Targeting senescent cells for vascular aging and related diseases.

Cardiovascular diseases are a serious threat to human health, especially in the elderly. Vascular aging makes people more susceptible to cardiovascular diseases due to significant dysfunction or senescence of vascular cells and maladaptation of vascular structure and function; moreover, vascular aging is currently viewed as a modifiable cardiovascular risk factor. To emphasize the relationship between senescent cells and vascular aging, we first summarize the roles of senescent vascular cells (endothelial cells, smooth muscle cells and immune cells) in the vascular aging process and inducers that contribute to cellular senescence. Then, we present potential strategies for directly targeting senescent cells (senotherapy) or preventively targeting senescence inducers (senoprevention) to delay vascular aging and the development of age-related vascular diseases. Finally, based on recent research, we note some important questions that still need to be addressed in the future.

Exploring Innovation with Scientific Thinking.

The mode of scientific thinking is undergoing rapid and profound changes. In the 21st century, macro and micro civilizations go parallel. A systematic and scientific methodology is required for the study of complex things. The thinking mode in modern medicine is gradually shifting from analytical, reductive thinking to holistic and systematic thinking. As such Western medicine and traditional Chinese medicine are gradually approaching the epistemology of health and disease state. The importance of scientific thinking in innovation has been expounded in this study. The development trends in medicine in the current era are analyzed, the importance of systems theory in the study of human bodies is discussed, and a new medical model named Novel Systems Medicine is proposed.

Metagenomic profiling of the pro-inflammatory gut microbiota in ankylosing spondylitis.

OBJECTIVE: Gut dysbiosis has been reported implicated in ankylosing spondylitis (AS), a common chronic inflammatory disease mainly affects sacroiliac joints and spine. Utilizing deep sequencing on the feces of untreated AS patients, our study aimed at providing an in-depth understanding of AS gut microbiota. METHODS: We analyzed the fecal metagenome of 85 untreated AS patients and 62 healthy controls by metagenomic shotgun sequencing, and 23 post-treatment feces of those AS patients were collected for comparison. Comparative analyses among different cohorts including AS, rheumatoid arthritis and Behcet's disease were performed to uncover some common signatures related to inflammatory arthritis. Molecular mimicry of a microbial peptide was also demonstrated by ELISpot assay. RESULTS: We identified AS-enriched species including Bacteroides coprophilus, Parabacteroides distasonis, Eubacterium siraeum, Acidaminococcus fermentans and Prevotella copri. Pathway analysis revealed increased oxidative phosphorylation, lipopolysaccharide biosynthesis and glycosaminoglycan degradation in AS gut microbiota. Microbial signatures of AS gut selected by random forest model showed high distinguishing accuracy. Some common signatures related to autoimmunity, such as Bacteroides fragilis and type III secretion system (T3SS), were also found. Finally, in vitro experiments demonstrated an increased amount of IFN-γ producing cells triggered by a bacterial peptide of AS-enriched species, mimicking type II collagen. CONCLUSIONS: These findings collectively indicate that gut microbiota was perturbed in untreated AS patients with diagnostic potential, and some AS-enriched species might be triggers of autoimmunity by molecular mimicry. Additionally, different inflammatory arthritis shared some common microbial signatures.

Vascular Transcriptome Profiling Reveals Aging-Related Genes in Angiotensin â ¡-Induced Hypertensive Mouse Aortas.

Objective Angiotensin Ⅱ (Ang Ⅱ)-induced vascular damage is a major risk of hypertension. However, the underlying molecular mechanism of AngⅡ-induced vascular damage is still unclear. In this study, we explored the novel mechanism associated with Ang II-induced hypertension. Methods We treated 8- to 12-week-old C57BL/6J male mice with saline and Ang Ⅱ(0.72 mg/kg·d) for 28 days, respectively. Then the RNA of the media from the collected mice aortas was extracted for transcriptome sequencing. Principal component analysis was applied to show a clear separation of different samples and the distribution of differentially expressed genes was manifested by Volcano plot. Functional annotations including Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway were performed to reveal the molecular mechanism of Ang Ⅱ-induced hypertension. Finally, the differentially expressed genes were validated by using quantitative real-time PCR. Results The result revealed that a total of 773 genes, including 599 up-regulated genes and 174 down-regulated genes, were differentially expressed in the aorta of Ang Ⅱ-induced hypertension mice model. Functional analysis of differentially expressed genes manifested that various cellular processes may be involved in the Ang Ⅱ-induced hypertension, including some pathways associated with hypertension such as extracellular matrix, inflammation and immune response. Interestingly, we also found that the differentially expressed genes were enriched in vascular aging pathway, and further validated that the expression levels of insulin-like growth factor 1 and adiponectin were significantly increased (P<0.05). Conclusion We identify that vascular aging is involved in Ang Ⅱ-induced hypertension, and insulin-like growth factor 1 and adiponectin may be important candidate genes leading to vascular aging.

Protective Role of mPGES-1 (Microsomal Prostaglandin E Synthase-1)-Derived PGE2 (Prostaglandin E2) and the Endothelial EP4 (Prostaglandin E Receptor) in Vascular Responses to Injury.

OBJECTIVE: Deletion of mPGES-1 (microsomal prostaglandin E synthase-1)-an anti-inflammatory target alternative to COX (cyclooxygenase)-2-attenuates injury-induced neointima formation in mice. This is attributable to the augmented levels of PGI2 (prostacyclin)-a known restraint of the vascular response to injury, acting via IP (I prostanoid receptor). To examine the role of mPGES-1-derived PGE2 (prostaglandin E2) in vascular remodeling without the IP. APPROACH AND RESULTS: Mice deficient in both IP and mPGES-1 (DKO [double knockout] and littermate controls [IP KO (knockout)]) were subjected to angioplasty wire injury. Compared with the deletion of IP alone, coincident deletion of IP and mPGES-1 increased neointima formation, without affecting media area. Early pathological changes include impaired reendothelialization and increased leukocyte invasion in neointima. Endothelial cells (ECs), but not vascular smooth muscle cells, isolated from DKOs exhibited impaired cell proliferation. Activation of EP (E prostanoid receptor) 4 (and EP2, to a lesser extent), but not of EP1 or EP3, promoted EC proliferation. EP4 antagonism inhibited proliferation of mPGES-1-competent ECs, but not of mPGES-1-deficient ECs, which showed suppressed PGE2 production. EP4 activation inhibited leukocyte adhesion to ECs in vitro, promoted reendothelialization, and limited neointima formation post-injury in the mouse. Endothelium-restricted deletion of EP4 in mice suppressed reendothelialization, increased neointimal leukocytes, and exacerbated neointimal formation. CONCLUSIONS: Removal of the IP receptors unmasks a protective role of mPGES-1-derived PGE2 in limiting injury-induced vascular hyperplasia. EP4, in the endothelial compartment, is essential to promote reendothelialization and restrain neointimal formation after injury. Activating EP4 bears therapeutic potential to prevent restenosis after percutaneous coronary intervention.

Loss of Endothelial CXCR7 Impairs Vascular Homeostasis and Cardiac Remodeling After Myocardial Infarction: Implications for Cardiovascular Drug Discovery.

BACKGROUND: Genome-wide association studies identified the association of the CXCL12 genetic locus (which encodes the chemokine CXCL12, also known as stromal cell-derived factor 1) with coronary artery disease and myocardial infarction (MI). Unlike CXCR4, the classic receptor for CXCL12, the function of CXCR7 (the most recently identified receptor) in vascular responses to injury and in MI remains unclear. METHODS: Tissue expression of CXCR7 was examined in arteries from mice and humans. Mice that harbored floxed CXCR7 and Cdh5-promoter driven CreERT2 were treated with tamoxifen to induce endothelium-restricted deletion of CXCR7. The resulting conditional knockout mice and littermate controls were studied for arterial response to angioplasty wire injury and cardiac response to coronary artery ligation. The role of CXCR7 in endothelial cell proliferation and angiogenesis was determined in vitro with cells from mice and humans. The effects of adenoviral delivery of CXCR7 gene and pharmacological activation of CXCR7 were evaluated in mice subjected to MI. RESULTS: Injured arteries from both humans and mice exhibited endothelial CXCR7 expression. Conditional endothelial CXCR7 deletion promoted neointimal formation without altering plasma lipid levels after endothelial injury and exacerbated heart functional impairment after MI, with increased both mortality and infarct sizes. Mechanistically, the exacerbated responses in vascular and cardiac remodeling are attributable to the key role of CXCR7 in promoting endothelial proliferation and angiogenesis. Impressively, the impaired post-MI cardiac remodeling occurred with elevated levels of CXCL12, which was previously thought to mediate cardiac protection by exclusively engaging its cognate receptor, CXCR4. In addition, both CXCR7 gene delivery via left ventricular injection and treatment with a CXCR7 agonist offered cardiac protection after MI. CONCLUSIONS: CXCR7 represents a novel regulator of vascular homeostasis that functions in the endothelial compartment with sufficient capacity to affect cardiac function and remodeling after MI. Activation of CXCR7 may have therapeutic potential for clinical restenosis after percutaneous coronary intervention and for heart remodeling after MI.

Tryptophan-Derived 3-Hydroxyanthranilic Acid Contributes to Angiotensin II-Induced Abdominal Aortic Aneurysm Formation in Mice In Vivo.

BACKGROUND: Abnormal amino acid metabolism is associated with vascular disease. However, the causative link between dysregulated tryptophan metabolism and abdominal aortic aneurysm (AAA) is unknown. METHODS: Indoleamine 2,3-dioxygenase (IDO) is the first and rate-limiting enzyme in the kynurenine pathway of tryptophan metabolism. Mice with deficiencies in both apolipoprotein e (Apoe) and IDO (Apoe-/-/IDO-/-) were generated by cross-breeding IDO-/- mice with Apoe-/- mice. RESULTS: The acute infusion of angiotensin II markedly increased the incidence of AAA in Apoe-/- mice, but not in Apoe-/-/IDO-/- mice, which presented decreased elastic lamina degradation and aortic expansion. These features were not altered by the reconstitution of bone marrow cells from IDO+/+ mice. Moreover, angiotensin II infusion instigated interferon-γ, which induced the expression of IDO and kynureninase and increased 3-hydroxyanthranilic acid (3-HAA) levels in the plasma and aortas of Apoe-/- mice, but not in IDO-/- mice. Both IDO and kynureninase controlled the production of 3-HAA in vascular smooth muscle cells. 3-HAA upregulated matrix metallopeptidase 2 via transcription factor nuclear factor-κB. Furthermore, kynureninase knockdown in mice restrained 3-HAA, matrix metallopeptidase 2, and resultant AAA formation by angiotensin II infusion. Intraperitoneal injections of 3-HAA into Apoe-/- and Apoe-/-/IDO-/- mice for 6 weeks increased the expression and activity of matrix metallopeptidase 2 in aortas without affecting metabolic parameters. Finally, human AAA samples had stronger staining with the antibodies against 3-HAA, IDO, and kynureninase than those in adjacent nonaneurysmal aortic sections of human AAA samples. CONCLUSIONS: These data define a previously undescribed causative role for 3-HAA, which is a product of tryptophan metabolism, in AAA formation. Furthermore, these findings suggest that 3-HAA reduction may be a new target for treating cardiovascular diseases.

SIRT2 Acts as a Cardioprotective Deacetylase in Pathological Cardiac Hypertrophy.

BACKGROUND: Pathological cardiac hypertrophy induced by stresses such as aging and neurohumoral activation is an independent risk factor for heart failure and is considered a target for the treatment of heart failure. However, the mechanisms underlying pathological cardiac hypertrophy remain largely unknown. We aimed to investigate the roles of SIRT2 in aging-related and angiotensin II (Ang II)-induced pathological cardiac hypertrophy. METHODS: Male C57BL/6J wild-type and Sirt2 knockout mice were subjected to the investigation of aging-related cardiac hypertrophy. Cardiac hypertrophy was also induced by Ang II (1.3 mg/kg/d for 4 weeks) in male C57BL/6J Sirt2 knockout mice, cardiac-specific SIRT2 transgenic (SIRT2-Tg) mice, and their respective littermates (8 to ≈12 weeks old). Metformin (200 mg/kg/d) was used to treat wild-type and Sirt2 knockout mice infused with Ang II. Cardiac hypertrophy, fibrosis, and cardiac function were examined in these mice. RESULTS: SIRT2 protein expression levels were downregulated in hypertrophic hearts from mice. Sirt2 knockout markedly exaggerated cardiac hypertrophy and fibrosis and decreased cardiac ejection fraction and fractional shortening in aged (24-month-old) mice and Ang II-infused mice. Conversely, cardiac-specific SIRT2 overexpression protected the hearts against Ang II-induced cardiac hypertrophy and fibrosis and rescued cardiac function. Mechanistically, SIRT2 maintained the activity of AMP-activated protein kinase (AMPK) in aged and Ang II-induced hypertrophic hearts in vivo as well as in cardiomyocytes in vitro. We identified the liver kinase B1 (LKB1), the major upstream kinase of AMPK, as the direct target of SIRT2. SIRT2 bound to LKB1 and deacetylated it at lysine 48, which promoted the phosphorylation of LKB1 and the subsequent activation of LKB1-AMPK signaling. Remarkably, the loss of SIRT2 blunted the response of AMPK to metformin treatment in mice infused with Ang II and repressed the metformin-mediated reduction of cardiac hypertrophy and protection of cardiac function. CONCLUSIONS: SIRT2 promotes AMPK activation by deacetylating the kinase LKB1. Loss of SIRT2 reduces AMPK activation, promotes aging-related and Ang II-induced cardiac hypertrophy, and blunts metformin-mediated cardioprotective effects. These findings indicate that SIRT2 will be a potential target for therapeutic interventions in aging- and stress-induced cardiac hypertrophy.

Age-Associated Sirtuin 1 Reduction in Vascular Smooth Muscle Links Vascular Senescence and Inflammation to Abdominal Aortic Aneurysm.

RATIONALE: Uncontrolled growth of abdominal aortic aneurysms (AAAs) is a life-threatening vascular disease without an effective pharmaceutical treatment. AAA incidence dramatically increases with advancing age in men. However, the molecular mechanisms by which aging predisposes individuals to AAAs remain unknown. OBJECTIVE: In this study, we investigated the role of SIRT1 (Sirtuin 1), a class III histone deacetylase, in AAA formation and the underlying mechanisms linking vascular senescence and inflammation. METHODS AND RESULTS: The expression and activity of SIRT1 were significantly decreased in human AAA samples. SIRT1 in vascular smooth muscle cells was remarkably downregulated in the suprarenal aortas of aged mice, in which AAAs induced by angiotensin II infusion were significantly elevated. Moreover, vascular smooth muscle cell-specific knockout of SIRT1 accelerated angiotensin II-induced formation and rupture of AAAs and AAA-related pathological changes, whereas vascular smooth muscle cell-specific overexpression of SIRT1 suppressed angiotensin II-induced AAA formation and progression in Apoe-/- mice. Furthermore, the inhibitory effect of SIRT1 on AAA formation was also proved in a calcium chloride (CaCl2)-induced AAA model. Mechanistically, the reduction of SIRT1 was shown to increase vascular cell senescence and upregulate p21 expression, as well as enhance vascular inflammation. Notably, inhibition of p21-dependent vascular cell senescence by SIRT1 blocked angiotensin II-induced nuclear factor-κB binding on the promoter of monocyte chemoattractant protein-1 and inhibited its expression. CONCLUSIONS: These findings provide evidence that SIRT1 reduction links vascular senescence and inflammation to AAAs and that SIRT1 in vascular smooth muscle cells provides a therapeutic target for the prevention of AAA formation.

The Paraoxonase Gene Cluster Protects Against Abdominal Aortic Aneurysm Formation.

OBJECTIVE: Abdominal aortic aneurysm (AAA) is a life-threatening vascular pathology, the pathogenesis of which is closely related to oxidative stress. However, an effective pharmaceutical treatment is lacking because the exact cause of AAA remains unknown. Here, we aimed at delineating the role of the paraoxonases (PONs) gene cluster (PC), which prevents atherosclerosis through the detoxification of oxidized substrates, in AAA formation. APPROACH AND RESULTS: PC transgenic (Tg) mice were crossed to an Apoe-/- background, and an angiotensin II-induced AAA mouse model was used to analyze the effect of the PC on AAA formation. Four weeks after angiotensin II infusion, PC-Tg Apoe-/- mice had a lower AAA incidence, smaller maximal abdominal aortic external diameter, and less medial elastin degradation than Apoe-/- mice. Importantly, PC-Tg Apoe-/- mice exhibited lower aortic reactive oxidative species production and oxidative stress than did the Apoe-/- control mice. As a consequence, the PC transgene alleviated angiotensin II-induced arterial inflammation and suppressed arterial extracellular matrix degradation. Specifically, on angiotensin II stimulation, PC-Tg vascular smooth muscle cells exhibited lower levels of reactive oxidative species production and a decrease in the activities and expression levels of matrix metalloproteinase-2 and matrix metalloproteinase-9. Moreover, PC-Tg serum also enhanced vascular smooth muscle cell oxidative stress resistance and further decreased the expression levels of matrix metalloproteinase-2 and matrix metalloproteinase-9, indicating that circulatory and vascular smooth muscle cell PC members suppress oxidative stress in a synergistic manner. CONCLUSIONS: Our findings reveal, for the first time, a protective role of the PC in AAA formation and suggest PONs as promising targets for AAA prevention.

The long noncoding RNA Gm15055 represses Hoxa gene expression by recruiting PRC2 to the gene cluster.

The Hox genes encode transcription factors that determine embryonic pattern formation. In embryonic stem cells, the Hox genes are silenced by PRC2. Recent studies have reported a role for long noncoding RNAs in PRC2 recruitment in vertebrates. However, little is known about how PRC2 is recruited to the Hox genes in ESCs. Here, we used stable knockdown and knockout strategies to characterize the function of the long noncoding RNAGm15055 in the regulation of Hoxa genes in mouse ESCs. We found that Gm15055 is highly expressed in mESCs and its expression is maintained by OCT4.Gm15055 represses Hoxa gene expression by recruiting PRC2 to the cluster and maintaining the H3K27me3 modification on Hoxa promoters. A chromosome conformation capture assay revealed the close physical association of the Gm15055 locus to multiple sites at the Hoxa gene cluster in mESCs, which may facilitate the in cis targeting of Gm15055RNA to the Hoxa genes. Furthermore, an OCT4-responsive positive cis-regulatory element is found in the Gm15055 gene locus, which potentially regulates both Gm15055 itself and the Hoxa gene activation. This study suggests how PRC2 is recruited to the Hoxa locus in mESCs, and implies an elaborate mechanism for Hoxa gene regulation in mESCs.

Epigenetic Regulation of Vascular Aging and Age-Related Vascular Diseases.

Vascular aging refers to the structural and functional defects that occur in the aorta during the aging process and is characterized by increased vascular cell senescence, vascular dyshomeostasis, and vascular remodeling. Vascular aging is a major risk factor for vascular diseases. However, the current understanding of the biological process of vascular aging and age-related diseases is insufficient. Epigenetic regulation can influence gene expression independently of the gene sequence and mainly includes DNA methylation, histone modifications, and RNA-based gene regulation. Epigenetic regulation plays important roles in many physiological and pathophysiological processes and may explain some gaps in our knowledge regarding the interaction between genes and diseases. In this review, we summarize recent advances in the understanding of the epigenetic regulation of vascular aging and age-related diseases in terms of vascular cell senescence, vascular dyshomeostasis, and vascular remodeling. Moreover, the possibility of targeting epigenetic regulation to delay vascular aging and treat age-related vascular diseases is also discussed.

SIRT4 accelerates Ang II-induced pathological cardiac hypertrophy by inhibiting manganese superoxide dismutase activity.

AIMS: Oxidative stress contributes to the development of cardiac hypertrophy and heart failure. One of the mitochondrial sirtuins, Sirt4, is highly expressed in the heart, but its function remains unknown. The aim of the present study was to investigate the role of Sirt4 in the pathogenesis of pathological cardiac hypertrophy and the molecular mechanism by which Sirt4 regulates mitochondrial oxidative stress. METHODS AND RESULTS: Male C57BL/6 Sirt4 knockout mice, transgenic (Tg) mice exhibiting cardiac-specific overexpression of Sirt4 (Sirt4-Tg) and their respective controls were treated with angiotensin II (Ang II, 1.1 mg/kg/day). At 4 weeks, hypertrophic growth of cardiomyocytes, fibrosis and cardiac function were analysed. Sirt4 deficiency conferred resistance to Ang II infusion by significantly suppressing hypertrophic growth, and the deposition of fibrosis. In Sirt4-Tg mice, aggravated hypertrophy and reduced cardiac function were observed compared with non-Tg mice following Ang II treatment. Mechanistically, Sirt4 inhibited the binding of manganese superoxide dismutase (MnSOD) to Sirt3, another member of the mitochondrial sirtuins, and increased MnSOD acetylation levels to reduce its activity, resulting in elevated reactive oxygen species (ROS) accumulation upon Ang II stimulation. Furthermore, inhibition of ROS with manganese 5, 10, 15, 20-tetrakis-(4-benzoic acid) porphyrin, a mimetic of SOD, blocked the Sirt4-mediated aggravation of the hypertrophic response in Ang II-treated Sirt4-Tg mice. CONCLUSIONS: Sirt4 promotes hypertrophic growth, the generation of fibrosis and cardiac dysfunction by increasing ROS levels upon pathological stimulation. These findings reveal a role of Sirt4 in pathological cardiac hypertrophy, providing a new potential therapeutic strategy for this disease.

Mitochondrial Sirtuins in cardiometabolic diseases.

Mitochondria are heterogeneous and essentially contribute to cellular functions and tissue homeostasis. Mitochondrial dysfunction compromises overall cell functioning, tissue damage, and diseases. The advances in mitochondrion biology increase our understanding of mitochondrial dynamics, bioenergetics, and redox homeostasis, and subsequently, their functions in tissue homeostasis and diseases, including cardiometabolic diseases (CMDs). The functions of mitochondria mainly rely on the enzymes in their matrix. Sirtuins are a family of NAD+-dependent deacylases and ADP-ribosyltransferases. Three members of the Sirtuin family (SIRT3, SIRT4, and SIRT5) are located in the mitochondrion. These mitochondrial Sirtuins regulate energy and redox metabolism as well as mitochondrial dynamics in the mitochondrial matrix and are involved in cardiovascular homeostasis and CMDs. In this review, we discuss the advances in our understanding of mitochondrial Sirtuins in mitochondrion biology and CMDs, including cardiac remodeling, pulmonary artery hypertension, and vascular dysfunction. The potential therapeutic strategies by targetting mitochondrial Sirtuins to improve mitochondrial function in CMDs are also addressed.

PML4 facilitates erythroid differentiation by enhancing the transcriptional activity of GATA-1.

Promyelocytic leukemia protein (PML) has been implicated as a participant in multiple cellular processes including senescence, apoptosis, proliferation, and differentiation. Studies of PML function in hematopoietic differentiation previously focused principally on its myeloid activities and also indicated that PML is involved in erythroid colony formation. However, the exact role that PML plays in erythropoiesis is essentially unknown. In this report, we found that PML4, a specific PML isoform expressed in erythroid cells, promotes endogenous erythroid genes expression in K562 and primary human erythroid cells. We show that the PML4 effect is GATA binding protein 1 (GATA-1) dependent using GATA-1 knockout/rescued G1E/G1E-ER4 cells. PML4, but not other detected PML isoforms, directly interacts with GATA-1 and can recruit it into PML nuclear bodies. Furthermore, PML4 facilitates GATA-1 trans-activation activity in an interaction-dependent manner. Finally, we present evidence that PML4 enhances GATA-1 occupancy within the globin gene cluster and stimulates cooperation between GATA-1 and its coactivator p300. These results demonstrate that PML4 is an important regulator of GATA-1 and participates in erythroid differention by enhancing GATA-1 trans-activation activity.

Sox2 Deacetylation by Sirt1 Is Involved in Mouse Somatic Reprogramming.

Mouse somatic cells can be reprogrammed into induced pluripotent stem cells by defined factors known to regulate pluripotency, including Oct4, Sox2, Klf4, and c-Myc. Together with Oct4, Sox2 plays a major role as a master endogenous pluripotent genes trigger in reprogramming. It has been reported that Sirtuin 1 (Sirt1), a member of the Sirtuin family of NAD(+) -dependent protein deacetylases, is involved in embryonic stem cell antioxidation, differentiation, and individual development. However, as a deacetylation enzyme, whether Sirt1 influences reprogramming through its post-translational modification function remains unknown. In this study, we provide evidence that deacetylation of Sox2 by Sirt1 is required for reprogramming. We found that a low level of Sox2 acetylation could significantly increase reprogramming efficiency. Furthermore, we found that Sox2 can be deacetylated by Sirt1 in an Oct4-mediated manner. Compared with wild-type cells, Sirt1-null mouse embryonic fibroblasts exhibit decreased reprogramming efficiency, and overexpression of Sirt1 rescues this defect. In addition, Sirt1 functions in the regulation of reprogramming through deacetylating Sox2. Taken together, we have identified a new regulatory role of Sirt1 in reprogramming and provided a link between deacetylation events and somatic cell reprogramming. Stem Cells 2015;33:2135-2147.