Nicotinamide Phosphoribosyltransferase in Smooth Muscle Cells Maintains Genome Integrity, Resists Aortic Medial Degeneration, and Is Suppressed in Human Thoracic Aortic Aneurysm Disease

Smooth-Muscle-Cell-Specific Deletion of CD38 Protects Mice from AngII-Induced Abdominal Aortic Aneurysm through Inhibiting Vascular Remodeling

Abdominal aortic aneurysm (AAA) is a serious vascular disease which is associated with vascular remodeling. CD38 is a main NAD+-consuming enzyme in mammals, and our previous results showed that CD38 plays the important roles in many cardiovascular diseases. However, the role of CD38 in AAA has not been explored. Here, we report that smooth-muscle-cell-specific deletion of CD38 (CD38SKO) significantly reduced the morbidity of AngII-induced AAA in CD38SKOApoe-/- mice, which was accompanied with a increases in the aortic diameter, medial thickness, collagen deposition, and elastin degradation of aortas. In addition, CD38SKO significantly suppressed the AngII-induced decreases in α-SMA, SM22α, and MYH11 expression; the increase in Vimentin expression in VSMCs; and the increase in VCAM-1 expression in smooth muscle cells and macrophage infiltration. Furthermore, we demonstrated that the role of CD38SKO in attenuating AAA was associated with the activation of sirtuin signaling pathways. Therefore, we concluded that CD38 plays a pivotal role in AngII-induced AAA through promoting vascular remodeling, suggesting that CD38 may serve as a potential therapeutic target for the prevention of AAA.

Transcriptome analysis reveals therapeutic potential of NAMPT in protecting against abdominal aortic aneurysm in human and mouse

Abdominal Aortic Aneurysm (AAA) is a life-threatening vascular disease characterized by the weakening and ballooning of the abdominal aorta, which has no effective therapeutic approaches due to unclear molecular mechanisms. Using single-cell RNA sequencing, we analyzed the molecular profile of individual cells within control and AAA abdominal aortas. We found cellular heterogeneity, with increased plasmacytoid dendritic cells and reduced endothelial cells and vascular smooth muscle cells (VSMCs) in AAA. Up-regulated genes in AAA were associated with muscle tissue development and apoptosis. Genes controlling VSMCs aberrant switch from contractile to synthetic phenotype were significantly enriched in AAA. Additionally, VSMCs in AAA exhibited cell senescence and impaired oxidative phosphorylation. Similar observations were made in a mouse model of AAA induced by Angiotensin II, further affirming the relevance of our findings to human AAA. The concurrence of gene expression changes between human and mouse highlighted the impairment of oxidative phosphorylation as a potential target for intervention. Nicotinamide phosphoribosyltransferase (NAMPT, also named VISFATIN) signaling emerged as a signature event in AAA. NAMPT was significantly downregulated in AAA. NAMPT-extracellular vesicles (EVs) derived from mesenchymal stem cells restored NAMPT levels, and offered protection against AAA. Furthermore, NAMPT-EVs not only repressed injuries, such as cell senescence and DNA damage, but also rescued impairments of oxidative phosphorylation in both mouse and human AAA models, suggesting NAMPT supplementation as a potential therapeutic approach for AAA treatment. These findings shed light on the cellular heterogeneity and injuries in AAA, and offered promising therapeutic intervention for AAA treatment.

Mapping microarchitectural degeneration in the dilated ascending aorta with ex vivo diffusion tensor imaging

Aims

Thoracic aortic aneurysms (TAAs) carry a risk of catastrophic dissection. Current strategies to evaluate this risk entail measuring aortic diameter but do not image medial degeneration, the cause of TAAs. We sought to determine if the advanced magnetic resonance imaging (MRI) acquisition strategy, diffusion tensor imaging (DTI), could delineate medial degeneration in the ascending thoracic aorta.

Methods and results

Porcine ascending aortas were subjected to enzyme microinjection, which yielded local aortic medial degeneration. These lesions were detected by DTI, using a 9.4 T MRI scanner, based on tensor disorientation, disrupted diffusion tracts, and altered DTI metrics. High-resolution spatial analysis revealed that fractional anisotropy positively correlated, and mean and radial diffusivity inversely correlated, with smooth muscle cell (SMC) and elastin content (P < 0.001 for all). Ten operatively harvested human ascending aorta samples (mean subject age 61.6 ± 13.3 years, diameter range 29-64 mm) showed medial pathology that was more diffuse and more complex. Nonetheless, DTI metrics within an aorta spatially correlated with SMC, elastin, and, especially, glycosaminoglycan (GAG) content. Moreover, there were inter-individual differences in slice-averaged DTI metrics. Glycosaminoglycan accumulation and elastin degradation were captured by reduced fractional anisotropy (R2 = 0.47, P = 0.043; R2 = 0.76, P = 0.002), with GAG accumulation also captured by increased mean diffusivity (R2 = 0.46, P = 0.045) and increased radial diffusivity (R2 = 0.60, P = 0.015).

Conclusion

Ex vivo high-field DTI can detect ascending aorta medial degeneration and can differentiate TAAs in accordance with their histopathology, especially elastin and GAG changes. This non-destructive window into aortic medial microstructure raises prospects for probing the risks of TAAs beyond lumen dimensions.

Selenoprotein deficiency disorder predisposes to aortic aneurysm formation

Aortic aneurysms, which may dissect or rupture acutely and be lethal, can be a part of multisystem disorders that have a heritable basis. We report four patients with deficiency of selenocysteine-containing proteins due to selenocysteine Insertion Sequence Binding Protein 2 (SECISBP2) mutations who show early-onset, progressive, aneurysmal dilatation of the ascending aorta due to cystic medial necrosis. Zebrafish and male mice with global or vascular smooth muscle cell (VSMC)-targeted disruption of Secisbp2 respectively show similar aortopathy. Aortas from patients and animal models exhibit raised cellular reactive oxygen species, oxidative DNA damage and VSMC apoptosis. Antioxidant exposure or chelation of iron prevents oxidative damage in patient's cells and aortopathy in the zebrafish model. Our observations suggest a key role for oxidative stress and cell death, including via ferroptosis, in mediating aortic degeneration.

Aortic regurgitation provokes phenotypic modulation of smooth muscle cells in the normal ascending aorta

BACKGROUND

Aortic complications are more likely to occur in patients with ascending aortic aneurysms and concomitant aortic regurgitation (AR). AR may have a negative influence on the aortic wall structure even in patients with tricuspid aortic valves and absence of aortic dilatation. It is unknown whether smooth muscle cell (SMC) changes are a feature of AR-associated aortic remodeling.

METHODS

Nondilated aortic samples were harvested intraoperatively from individuals with normal aortic valves (n = 10) or those with either predominant aortic stenosis (AS) (n = 20) or AR (n = 35). Tissue from each patient was processed for immunohistochemistry or used for the extraction of medial SMCs. Tissue and cells were stained for markers of SMC contraction (alpha-smooth muscle actin), synthesis (vimentin) and senescence (p16INK4A and p21Cip1 [p16/p21]). Replicative capacity was analyzed in cultured SMCs from AS- and AR-associated aortas. A subanalysis compared SMCs from individuals with either tricuspid aortic valves or bicuspid aortic valves to evaluate the effect of aortic valve morphology.

RESULTS

In aortic tissue samples, AR was associated with decreased alpha-smooth muscle actin and increased vimentin, p16 and p21 compared with normal aortic valves and AS. In cell culture, SMCs from AR-aortas had decreased alpha-smooth muscle actin and increased vimentin compared with SMCs from AS-aortas. AR-associated SMCs had increased p16 and p21 expression, and they reached senescence earlier than SMCs from AS-aortas. In AR, SMC changes were more pronounced with the presence of a bicuspid aortic valve.

CONCLUSIONS

AR itself negatively influences SMC phenotype in the ascending aortic wall. This AR-specific effect is independent of aortic diameter and aortic valve morphology, although it is more pronounced with bicuspid aortic valves. These findings provide insight into the mechanisms of AR-related aortic remodeling, and they provide a model for studying SMC-specific therapies in culture.

Nicotinamide Mononucleotide Alleviates Angiotensin II-Induced Human Aortic Smooth Muscle Cell Senescence in a Microphysiological Model

ABSTRACT

The occurrence and development of aortic aneurysms are accompanied by senescence of human aortic smooth muscle cells (HASMCs). Because the mechanism of HASMC senescence has not been fully elucidated, the efficacy of various antisenescence treatments varies. Decreased nicotinamide adenine dinucleotide (NAD + ) levels are one of the mechanisms of cell senescence, and there is a lack of evidence on whether increasing NAD + levels could alleviate HASMC senescence and further retard the progression of aortic aneurysms.We constructed an HASMC-based organ-on-a-chip microphysiological model. RNA sequencing was performed on cell samples from the vehicle control and angiotensin II groups to explore biological differences. We detected cellular senescence markers and NAD + levels in HASMC-based organ-on-a-chip. Subsequently, we pretreated HASMC using the synthetic precursor of NAD + , nicotinamide mononucleotide, and angiotensin II treatment, and used rhythmic stretching to investigate whether nicotinamide mononucleotide could delay HASMC senescence.The HASMC-based organ-on-a-chip model can simulate the biomechanical microenvironment of HASMCs in vivo, and the use of angiotensin II in the model replicated senescence in HASMCs. The senescence of HASMCs was accompanied by downregulation of the expression level of nicotinamide phosphoribosyltransferase and NAD + . Pretreatment with nicotinamide mononucleotide significantly increased the NAD + level and alleviated the senescence of HASMCs, but did not change the expression level of nicotinamide phosphoribosyltransferase.Our study provides a complementary research platform between traditional cell culture and animal experiments to explore HASMC senescence in aortic aneurysms. Furthermore, it provides evidence for NAD + boosting therapy in the clinical treatment of aortic aneurysms.

Interactions between Intestinal Homeostasis and NAD+ Biology in Regulating Incretin Production and Postprandial Glucose Metabolism

The intestine has garnered attention as a target organ for developing new therapies for impaired glucose tolerance. The intestine, which produces incretin hormones, is the central regulator of glucose metabolism. Glucagon-like peptide-1 (GLP-1) production, which determines postprandial glucose levels, is regulated by intestinal homeostasis. Nicotinamide phosphoribosyltransferase (NAMPT)-mediated nicotinamide adenine dinucleotide (NAD⁺) biosynthesis in major metabolic organs such as the liver, adipose tissue, and skeletal muscle plays a crucial role in obesity- and aging-associated organ derangements. Furthermore, NAMPT-mediated NAD⁺ biosynthesis in the intestines and its upstream and downstream mediators, adenosine monophosphate-activated protein kinase (AMPK) and NAD⁺-dependent deacetylase sirtuins (SIRTs), respectively, are critical for intestinal homeostasis, including gut microbiota composition and bile acid metabolism, and GLP-1 production. Thus, boosting the intestinal AMPK-NAMPT-NAD⁺-SIRT pathway to improve intestinal homeostasis, GLP-1 production, and postprandial glucose metabolism has gained significant attention as a novel strategy to improve impaired glucose tolerance. Herein, we aimed to review in detail the regulatory mechanisms and importance of intestinal NAMPT-mediated NAD⁺ biosynthesis in regulating intestinal homeostasis and GLP-1 secretion in obesity and aging. Furthermore, dietary and molecular factors regulating intestinal NAMPT-mediated NAD⁺ biosynthesis were critically explored to facilitate the development of new therapeutic strategies for postprandial glucose dysregulation.

Identification and Analysis of Hub Genes and Immune Cells Associated with the Formation of Acute Aortic Dissection

Background

Acute type A aortic dissection (AAD) is a catastrophic disease with high mortality, but the pathogenesis has not been fully elucidated. This study is aimed at identifying hub genes and immune cells associated with the pathogenesis of AAD.

Methods

The datasets were downloaded from Gene Expression Omnibus (GEO). Gene Set Enrichment Analysis (GSEA), gene set variation analysis (GSVA), and differential analysis were performed. The differentially expressed genes (DEGs) were intersected with specific genes collected from MSigDB. The gene function and pathway enrichment analysis were also performed on intersecting genes. The key modules were selected by weighted gene coexpression network analysis (WGCNA). Hub genes were identified by least absolute shrinkage and selection operator (LASSO) analysis and were verified in the metadataset. The immune cell infiltration was analyzed by CIBERSORT, and the relationship between hub genes and immune cells was performed by Pearson's correlation analysis. The single-cell RNA sequencing (scRNA-seq) dataset was used to verify the differences in DNA damage and repair signaling pathways and hub genes in different cell types.

Results

The results of GSEA and GSVA indicated that DNA damage and repair processes were activated in the occurrence of AAD. The gene function and pathway enrichment analysis on differentially expressed DNA damage- and repair-related genes showed that these genes were mainly involved in the regulation of the cell cycle process, cellular response to DNA damage stimulus, response to wounding, p53 signaling pathway, and cellular senescence. Three key modules were identified by WGCNA. Five genes were screened as hub genes, including CDK2, EIF4A1, GLRX, NNMT, and SLCO2A1. Naive B cells and Gamma delta T cells (γδ T cells) were decreased in AAD, but monocytes and M0 macrophages were increased. scRNA-seq analysis included that DNA damage and repair processes were activated in smooth muscle cells (SMCs), tissue stem cells, and monocytes in the aortic wall of patients with AAD.

Conclusions

Our results suggested that DNA damage- and repair-related genes may be involved in the occurrence of AAD by regulating many biological processes. The hub genes and immune cells reported in this study also increase the understanding of AAD.

Age-dependent phenotypic modulation of smooth muscle cells in the normal ascending aorta

Objectives

Ascending aortic aneurysms are associated with pre-existing conditions, including connective tissue disorders (i.e., Marfan syndrome) and bicuspid aortic valves. The underlying mechanisms remain uncertain. Even less is known regarding ascending aortic aneurysms in individuals with normal (i.e., tricuspid) aortic valves (TAV), and without known aneurysm-associated disorders. Regardless of etiology, the risk of aortic complications increases with biological age. Phenotypic modulation of smooth muscle cells (SMCs) is a feature of ascending aortic aneurysms, whereby contractile SMCs are replaced with synthetic SMCs that are capable of degrading the aortic wall. We asked whether age itself causes dysfunctional SMC phenotype modulation, independent of aortic dilatation or pre-existing aneurysm-associated diseases.

Methods

Non-dilated ascending aortic samples were obtained intra-operatively from 40 patients undergoing aortic valve surgery (range: 20-82 years old, mean: 59.1 ± 15.2). Patients with known genetic diseases or aortic valve malformations were excluded. Tissue was divided, and a portion was formalin-fixed and immunolabeled for alpha-smooth muscle actin (ASMA), a contractile SMC protein, and markers of synthetic (vimentin) or senescent (p16/p21) SMCs. Another fragment was used for SMC isolation (n = 10). Cultured SMCs were fixed at cell passage 2 and stained for phenotype markers, or were cultured indefinitely to determine replicative capacity.

Results

In whole tissue, ASMA decreased (R² = 0.47, P < 0.0001), while vimentin increased (R² = 0.33, P = 0.02) with age. In cultured SMCs, ASMA decreased (R² = 0.35, P = 0.03) and vimentin increased (R² = 0.25, P = 0.04) with age. p16 (R² = 0.34, P = 0.02) and p21 (R² = 0.29, P = 0.007) also increased with age in SMCs. Furthermore, the replicative capacity of SMCs from older patients was decreased compared to that of younger patients (P = 0.03).

Conclusion

By investigating non-dilated aortic samples from individuals with normal TAVs, we found that age itself has a negative impact on SMCs in the ascending aortic wall, whereby SMCs switched from the contractile phenotype to maladaptive synthetic or senescent states with increased age. Therefore, based on our findings, modification of SMC phenotype should be studied as a therapeutic consideration against aneurysms in the future, regardless of etiology.

Telomere Length: Implications for Atherogenesis

PURPOSE OF REVIEW

The purpose of the study is to explore the evidence linking telomere length with atherosclerotic ischemic disease.

RECENT FINDINGS

There has been a recent expansion in strategies for measuring telomere length, including analyzing genome sequence data and capitalizing on genomic loci that associate with telomere length. These, together with more established approaches, have been used to generate a more complete picture of telomere length relationships with ischemic disease. Whereas earlier meta-analyses suggested an association between short leukocyte telomeres and ischemic disease, several recent large population studies now provide particularly compelling data, including an association with cardiovascular mortality. In addition, whether short leukocyte telomeres might be causally related to ischemic disease has been interrogated using Mendelian randomization strategies, which point to shorter leukocyte telomeres as a determining risk factor. Importantly however, the wide, interindividual variability in telomere length still means that a single assessment of leukocyte telomere length in an individual does not reliably report on a biological aging process. In this regard, recent multi-tissue analyses of telomere length dynamics are providing both new mechanistic insights into how telomere length and shortening rates may participate in atherogenesis and risk prediction opportunities. The balance of evidence indicates that short leukocyte telomeres confer a risk for atherosclerotic cardiovascular disease. Moreover, an integrated analysis of telomere lengths in leukocytes and other tissues may provide a window into individualized telomere dynamics, raising new prospects for risk management.

A novel 6-metabolite signature for prediction of clinical outcomes in type 2 diabetic patients undergoing percutaneous coronary intervention

Background

Outcome prediction tools for patients with type 2 diabetes mellitus (T2DM) undergoing percutaneous coronary intervention (PCI) are lacking. Here, we developed a machine learning-based metabolite classifier for predicting 1-year major adverse cardiovascular events (MACEs) after PCI among patients with T2DM.

Methods

Serum metabolomic profiling was performed in a nested case–control study of 108 matched pairs of patients with T2DM occurring and not occurring MACEs at 1 year after PCI, then the matched pairs were 1:1 assigned into the discovery and internal validation sets. External validation was conducted using targeted metabolite analyses in an independent prospective cohort of 301 patients with T2DM receiving PCI. The function of candidate metabolites was explored in high glucose-cultured human aortic smooth muscle cells (HASMCs).

Results

Overall, serum metabolome profiles differed between diabetic patients with and without 1-year MACEs after PCI. Through VSURF, a machine learning approach for feature selection, we identified the 6 most important metabolic predictors, which mainly targeted the nicotinamide adenine dinucleotide (NAD⁺) metabolism. The 6-metabolite model based on random forest and XGBoost algorithms yielded an area under the curve (AUC) of ≥ 0.90 for predicting MACEs in both discovery and internal validation sets. External validation of the 6-metabolite classifier also showed good accuracy in predicting MACEs (AUC 0.94, 95% CI 0.91–0.97) and target lesion failure (AUC 0.89, 95% CI 0.83–0.95). In vitro, there were significant impacts of altering NAD⁺ biosynthesis on bioenergetic profiles, inflammation and proliferation of HASMCs.

Conclusion

The 6-metabolite model may help for noninvasive prediction of 1-year MACEs following PCI among patients with T2DM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-022-01561-1.

Patient-derived microphysiological model identifies the therapeutic potential of metformin for thoracic aortic aneurysm

Background

Thoracic aortic aneurysm (TAA) is the permanent dilation of the thoracic aortic wall that predisposes patients to lethal events such as aortic dissection or rupture, for which effective medical therapy remains scarce. Human-relevant microphysiological models serve as a promising tool in drug screening and discovery.

Methods

We developed a dynamic, rhythmically stretching, three-dimensional microphysiological model. Using patient-derived human aortic smooth muscle cells (HAoSMCs), we tested the biological features of the model and compared them with native aortic tissues. Drug testing was performed on the individualized TAA models, and the potentially effective drug was further tested using β-aminopropionitrile-treated mice and retrospective clinical data.

Findings

The HAoSMCs on the model recapitulated the expressions of many TAA-related genes in tissue. Phenotypic switching and mitochondrial dysfunction, two disease hallmarks of TAA, were highlighted on the microphysiological model: the TAA-derived HAoSMCs exhibited lower alpha-smooth muscle actin expression, lower mitochondrial membrane potential, lower oxygen consumption rate and higher superoxide accumulation than control cells, while these differences were not evidently reflected in two-dimensional culture flasks. Model-based drug testing demonstrated that metformin partially recovered contractile phenotype and mitochondrial function in TAA patients’ cells. Mouse experiment and clinical investigations also demonstrated better preserved aortic microstructure, higher nicotinamide adenine dinucleotide level and lower aortic diameter with metformin treatment.

Interpretation

These findings support the application of this human-relevant microphysiological model in studying personalized disease characteristics and facilitating drug discovery for TAA. Metformin may regulate contractile phenotypes and metabolic dysfunctions in diseased HAoSMCs and limit aortic dilation.

Funding

This work was supported by grants from National Key R&D Program of China (2018YFC1005002), National Natural Science Foundation of China (82070482, 81771971, 81772007, 51927805, and 21734003), the Science and Technology Commission of Shanghai Municipality (20ZR1411700, 18ZR1407000, 17JC1400200, and 20YF1406900), Shanghai Municipal Science and Technology Major Project (2017SHZDZX01), and Shanghai Municipal Education Commission (Innovation Program 2017-01-07-00-07-E00027). Y.S.Z. was not supported by any of these funds; instead, the Brigham Research Institute is acknowledged.

MiR-186-5p Downregulates NAMPT and Functions as a Potential Therapeutic Target for Sepsis-Induced Coagulation Disorders

Purpose

Present study is aimed to explore the role of miR-186-5p in sepsis-induced coagulation disorders and molecular mechanisms.

Methods

Thirty-four sepsis patients and 34 respiratory infection/pneumonia patients were selected in the present study. Polymicrobial sepsis model was created by cecal ligation and puncture (CLP). The mRNA expression was detected by qRT-PCR. Western blot was utilized to measure protein expression. Thromborel S Reagent was applied to measure the prothrombin time (PT). Platelet count of blood was measured via LH 780. ELISA kits were utilized to evaluate the fibrinogen and PAI-1 concentration.

Results

MiR-186-5p expression was lower and nicotinamide phosphoribosyltransferase (NAMPT) mRNA expression was higher in sepsis patients in contrast to control group. Coagulation time was markedly prolonged and platelet count was markedly decreased in CLP mice. In addition, fibrinogen concentration was obviously lower and PAI-1 concentration was obviously higher in CLP mice. MiR-186-5p mimic obviously decreased coagulation time and PAI-1 concentration, while raised platelet count and fibrinogen concentration. Targetscan predicted miR-186-5p might directly regulates NAMPT, and luciferase reporter assay verified this prediction. In addition, miR-186-5p mimic obviously inhibited the mRNA expression of NAMPT. Knockdown of NAMPT improved coagulation dysfunction in sepsis. Overexpression of NAMPT reversed the improvement effect of miR-186-5p on coagulation dysfunction. MiR-186-5p mimic markedly inhibited NF-κB pathway.

Conclusion

MiR-186-5p inhibited sepsis-induced coagulation disorders via targeting NAMPT and inactivating NF-κB pathway.

NAD+ and Vascular Dysfunction: From Mechanisms to Therapeutic Opportunities

Nicotinamide adenine dinucleotide (NAD+) is an essential and pleiotropic coenzyme involved not only in cellular energy metabolism, but also in cell signaling, epigenetic regulation, and post-translational protein modifications. Vascular disease risk factors are associated with aberrant NAD+ metabolism. Conversely, the therapeutic increase of NAD+ levels through the administration of NAD+ precursors or inhibitors of NAD+-consuming enzymes reduces chronic low-grade inflammation, reactivates autophagy and mitochondrial biogenesis, and enhances oxidative metabolism in vascular cells of humans and rodents with vascular pathologies. As such, NAD+ has emerged as a potential target for combatting age-related cardiovascular and cerebrovascular disorders. This review discusses NAD+-regulated mechanisms critical for vascular health and summarizes new advances in NAD+ research directly related to vascular aging and disease, including hypertension, atherosclerosis, coronary artery disease, and aortic aneurysms. Finally, we enumerate challenges and opportunities for NAD+ repletion therapy while anticipating the future of this exciting research field, which will have a major impact on vascular medicine.

Therapeutic Potential of Emerging NAD+-Increasing Strategies for Cardiovascular Diseases

Cardiovascular diseases are the leading cause of death worldwide. Aging and/or metabolic stress directly impact the cardiovascular system. Over the last few years, the contributions of altered nicotinamide adenine dinucleotide (NAD+) metabolism to aging and other pathological conditions closely related to cardiovascular diseases have been intensively investigated. NAD+ bioavailability decreases with age and cardiometabolic conditions in several mammalian tissues. Compelling data suggest that declining tissue NAD+ is commonly related to mitochondrial dysfunction and might be considered as a therapeutic target. Thus, NAD+ replenishment by either genetic or natural dietary NAD+-increasing strategies has been recently demonstrated to be effective for improving the pathophysiology of cardiac and vascular health in different experimental models, as well as human health, to a lesser extent. Here, we review and discuss recent experimental evidence illustrating that increasing NAD+ bioavailability, particularly by the use of natural NAD+ precursors, may offer hope for new therapeutic strategies to prevent and treat cardiovascular diseases.

Vascular Smooth Muscle Cells in Aortic Aneurysm: From Genetics to Mechanisms

Aortic aneurysm, including thoracic aortic aneurysm and abdominal aortic aneurysm, is the second most prevalent aortic disease following atherosclerosis, representing the ninth-leading cause of death globally. Open surgery and endovascular procedures are the major treatments for aortic aneurysm. Typically, thoracic aortic aneurysm has a more robust genetic background than abdominal aortic aneurysm. Abdominal aortic aneurysm shares many features with thoracic aortic aneurysm, including loss of vascular smooth muscle cells (VSMCs), extracellular matrix degradation and inflammation. Although there are limitations to perfectly recapitulating all features of human aortic aneurysm, experimental models provide valuable tools to understand the molecular mechanisms and test novel therapies before human clinical trials. Among the cell types involved in aortic aneurysm development, VSMC dysfunction correlates with loss of aortic wall structural integrity. Here, we discuss the role of VSMCs in aortic aneurysm development. The loss of VSMCs, VSMC phenotypic switching, secretion of inflammatory cytokines, increased matrix metalloproteinase activity, elevated reactive oxygen species, defective autophagy, and increased senescence contribute to aortic aneurysm development. Further studies on aortic aneurysm pathogenesis and elucidation of the underlying signaling pathways are necessary to identify more novel targets for treating this prevalent and clinical impactful disease.

Nicotinamide effects on the metabolism of human fibroblasts and keratinocytes assessed by quantitative, label-free fluorescence imaging

Alterations in metabolism are central to the aging process. Therefore, understanding the subcellular functional and structural changes associated with metabolic aging is critical. Current established methods for exploring cell metabolism either require the use of exogenous agents or are destructive to the tissue or cells. Two-photon excited fluorescence (TPEF) imaging has emerged as a method for monitoring subtle metabolic changes non-invasively. In this study, we use TPEF imaging to acquire high-resolution fluorescence images from two coenzymes, NAD(P)H (reduced form of nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide), within human fibroblasts and keratinocytes in response to B3 (a nicotinamide precursor) supplementation and/or UV irradiation, without addition of exogenous labels. In addition, multi-parametric analysis methods are used to extract functional information of cellular metabolism, including cellular redox state, NAD(P)H fluorescence lifetime, and mitochondrial organization. Our results demonstrate that such optical metabolic assessments can serve as sensitive, label-free, non-destructive reporters of known effects of B3 to maintain and in some cases even enhance the respiratory function of mitochondria, while lowering oxidative damage. Thus, TPEF imaging, supported by highly-quantitative analysis, can serve as a tool to understand aging-dependent metabolic changes as well as the effect of actives on human epidermal and dermal cells.

Diseases of the Aorta and Kidney Disease: Conclusions from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference

Chronic kidney disease (CKD) is an independent risk factor for the development of abdominal aortic aneurysm (AAA), as well as for cardiovascular and renal events and all-cause mortality following surgery for AAA or thoracic aortic dissection. In addition, the incidence of acute kidney injury (AKI) after any aortic surgery is particularly high, and this AKI per se is independently associated with future cardiovascular events and mortality. On the other hand, both development of AKI after surgery and the long-term evolution of kidney function differ significantly depending on the type of AAA intervention (open surgery vs. the various subtypes of endovascular repair). Current knowledge regarding AAA in the general population may not be always applicable to CKD patients, as they have a high prevalence of co-morbid conditions and an elevated risk for periprocedural complications. This summary of a Kidney Disease: Improving Global Outcomes Controversies Conference group discussion reviews the epidemiology, pathophysiology, diagnosis, and treatment of Diseases of the Aorta in CKD and identifies knowledge gaps, areas of controversy, and priorities for future research.

The role of senescence in the pathogenesis of atrial fibrillation: A target process for health improvement and drug development

Cellular senescence is a state of growth arrest that occurs after cells encounter various stresses. Senescence contributes to tumour suppression, embryonic development, and wound healing. It impacts on the pathology of various diseases by secreting inflammatory chemokines, immune modulators and other bioactive factors. These secretory biosignatures ultimately cause inflammation, tissue fibrosis, immunosenescence and many ageing-related diseases such as atrial fibrillation (AF). Because the molecular mechanisms underpinning AF development remain unclear, current treatments are suboptimal and have serious side effects. In this review, we summarize recent results describing the role of senescence in AF. We propose that senescence factors induce AF and have a causative role. Hence, targeting senescence and its secretory phenotype may attenuate AF.

Cyclic nucleotide phosphodiesterase 1C contributes to abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is characterized by aorta dilation due to wall degeneration, which mostly occurs in elderly males. Vascular aging is implicated in degenerative vascular pathologies, including AAA. Cyclic nucleotide phosphodiesterases, by hydrolyzing cyclic nucleotides, play critical roles in regulating vascular structure remodeling and function. Cyclic nucleotide phosphodiesterase 1C (PDE1C) expression is induced in dedifferentiated and aging vascular smooth muscle cells (SMCs), while little is known about the role of PDE1C in aneurysm. We observed that PDE1C was not expressed in normal aorta but highly induced in SMC-like cells in human and murine AAA. In mouse AAA models induced by Angiotensin II or periaortic elastase, PDE1C deficiency significantly decreased AAA incidence, aortic dilation, and elastin degradation, which supported a causative role of PDE1C in AAA development in vivo. Pharmacological inhibition of PDE1C also significantly suppressed preestablished AAA. We showed that PDE1C depletion antagonized SMC senescence in vitro and/or in vivo, as assessed by multiple senescence biomarkers, including senescence-associated β-galactosidase activity, γ-H2AX foci number, and p21 protein level. Interestingly, the role of PDE1C in SMC senescence in vitro and in vivo was dependent on Sirtuin 1 (SIRT1). Mechanistic studies further showed that cAMP derived from PDE1C inhibition stimulated SIRT1 activation, likely through a direct interaction between cAMP and SIRT1, which leads to subsequent up-regulation of SIRT1 expression. Our findings provide evidence that PDE1C elevation links SMC senescence to AAA development in both experimental animal models and human AAA, suggesting therapeutical significance of PDE1C as a potential target against aortic aneurysms.

NAD+ homeostasis in human health and disease

Depletion of nicotinamide adenine dinucleotide (NAD+ ), a central redox cofactor and the substrate of key metabolic enzymes, is the causative factor of a number of inherited and acquired diseases in humans. Primary deficiencies of NAD+ homeostasis are the result of impaired biosynthesis, while secondary deficiencies can arise due to other factors affecting NAD+ homeostasis, such as increased NAD+ consumption or dietary deficiency of its vitamin B3 precursors. NAD+ depletion can manifest in a wide variety of pathological phenotypes, ranging from rare inherited defects, characterized by congenital malformations, retinal degeneration, and/or encephalopathy, to more common multifactorial, often age-related, diseases. Here, we discuss NAD+ biochemistry and metabolism and provide an overview of the etiology and pathological consequences of alterations of the NAD+ metabolism in humans. Finally, we discuss the state of the art of the potential therapeutic implications of NAD+ repletion for boosting health as well as treating rare and common diseases, and the possibilities to achieve this by means of the different NAD+ -enhancing agents.

Senescence-induced inflammation: an important player and key therapeutic target in atherosclerosis

Inflammation is a hallmark and potent driver of pathological vascular remodelling in atherosclerosis. However, current anti-inflammatory therapeutic strategies have shown mixed results. As an alternative perspective on the conundrum of chronic inflammation emerging evidence points towards a small subset of senescent cells as a critical player and central node driving atherosclerosis. Senescent cells belonging to various cell types are a dominant and chronic source of a large array of pro-inflammatory cytokines and various additional plaque destabilizing factors, being involved with various aspects of atherosclerosis pathogenesis. Antagonizing these key agitators of local chronic inflammation and plaque instability may provide a causative and multi-purpose therapeutic strategy to treat atherosclerosis. Anti-senescence treatment options with translational potential are currently in development. However, several questions and challenges remain to be addressed before these novel treatment approaches may enter the clinical setting.

Extracellular Tuning of Mitochondrial Respiration Leads to Aortic Aneurysm

Supplemental Digital Content is available in the text.

Background:

Marfan syndrome (MFS) is an autosomal dominant disorder of the connective tissue caused by mutations in the FBN1 (fibrillin-1) gene encoding a large glycoprotein in the extracellular matrix called fibrillin-1. The major complication of this connective disorder is the risk to develop thoracic aortic aneurysm. To date, no effective pharmacologic therapies have been identified for the management of thoracic aortic disease and the only options capable of preventing aneurysm rupture are endovascular repair or open surgery. Here, we have studied the role of mitochondrial dysfunction in the progression of thoracic aortic aneurysm and mitochondrial boosting strategies as a potential treatment to managing aortic aneurysms.

Methods:

Combining transcriptomics and metabolic analysis of aortas from an MFS mouse model (Fbn1^c1039g/+) and MFS patients, we have identified mitochondrial dysfunction alongside with mtDNA depletion as a new hallmark of aortic aneurysm disease in MFS. To demonstrate the importance of mitochondrial decline in the development of aneurysms, we generated a conditional mouse model with mitochondrial dysfunction specifically in vascular smooth muscle cells (VSMC) by conditional depleting Tfam (mitochondrial transcription factor A; Myh11-Cre^ERT2Tfam^flox/flox mice). We used a mouse model of MFS to test for drugs that can revert aortic disease by enhancing Tfam levels and mitochondrial respiration.

Results:

The main canonical pathways highlighted in the transcriptomic analysis in aortas from Fbn1^c1039g/+ mice were those related to metabolic function, such as mitochondrial dysfunction. Mitochondrial complexes, whose transcription depends on Tfam and mitochondrial DNA content, were reduced in aortas from young Fbn1^c1039g/+ mice. In vitro experiments in Fbn1-silenced VSMCs presented increased lactate production and decreased oxygen consumption. Similar results were found in MFS patients. VSMCs seeded in matrices produced by Fbn1-deficient VSMCs undergo mitochondrial dysfunction. Conditional Tfam-deficient VSMC mice lose their contractile capacity, showed aortic aneurysms, and died prematurely. Restoring mitochondrial metabolism with the NAD precursor nicotinamide riboside rapidly reverses aortic aneurysm in Fbn1^c1039g/+ mice.

Conclusions:

Mitochondrial function of VSMCs is controlled by the extracellular matrix and drives the development of aortic aneurysm in Marfan syndrome. Targeting vascular metabolism is a new available therapeutic strategy for managing aortic aneurysms associated with genetic disorders.

CTRP13 Mitigates Abdominal Aortic Aneurysm Formation via NAMPT1

Abdominal aortic aneurysm (AAA) is a life-threatening cardiovascular disease characterized by localized dilation of the abdominal aorta. C1q/tumor necrosis factor (TNF)-related protein-13 (CTRP13) is a secreted adipokine that plays important roles in the cardiovascular system. However, the functional role of CTRP13 in the formation and development of AAA has yet to be explored. In this study, we determined that serum CTRP13 levels were significantly downregulated in blood samples from patients with AAA and in rodent AAA models induced by Angiotensin II (Ang II) in ApoE^-/- mice or by CaCl₂ in C57BL/6J mice. Using two distinct murine models of AAA, CTRP13 was shown to effectively reduce the incidence and severity of AAA in conjunction with reduced aortic macrophage infiltration, expression of proinflammatory cytokines (interleukin-6 [IL-6], TNF-α, and monocyte chemoattractant protein 1 [MCP-1]), and vascular smooth muscle cell (SMC) apoptosis. Mechanistically, nicotinamide phosphoribosyl-transferase 1 (NAMPT1) was identified as a new target of CTRP13. The decreased in vivo and in vitro expression of NAMPT1 was markedly reversed by CTRP13 supplementation in a ubiquitination-proteasome-dependent manner. NAMPT1 knockdown further blocked the beneficial effects of CTRP13 on vascular inflammation and SMC apoptosis. Overall, our study reveals that CTRP13 management may be an effective treatment for preventing AAA formation.

Niacin protects against abdominal aortic aneurysm formation via GPR109A independent mechanisms: role of NAD+/nicotinamide

AIMS

Chronic adventitial and medial infiltration of immune cells play an important role in the pathogenesis of abdominal aortic aneurysms (AAAs). Nicotinic acid (niacin) was shown to inhibit atherosclerosis by activating the anti-inflammatory G protein-coupled receptor GPR109A [also known as hydroxycarboxylic acid receptor 2 (HCA2)] expressed on immune cells, blunting immune activation and adventitial inflammatory cell infiltration. Here, we investigated the role of niacin and GPR109A in regulating AAA formation.

METHODS AND RESULTS

Mice were supplemented with niacin or nicotinamide, and AAA was induced by angiotensin II (AngII) infusion or calcium chloride (CaCl2) application. Niacin markedly reduced AAA formation in both AngII and CaCl2 models, diminishing adventitial immune cell infiltration, concomitant inflammatory responses, and matrix degradation. Unexpectedly, GPR109A gene deletion did not abrogate the protective effects of niacin against AAA formation, suggesting GPR109A-independent mechanisms. Interestingly, nicotinamide, which does not activate GPR109A, also inhibited AAA formation and phenocopied the effects of niacin. Mechanistically, both niacin and nicotinamide supplementation increased nicotinamide adenine dinucleotide (NAD+) levels and NAD+-dependent Sirt1 activity, which were reduced in AAA tissues. Furthermore, pharmacological inhibition of Sirt1 abrogated the protective effect of nicotinamide against AAA formation.

CONCLUSION

Niacin protects against AAA formation independent of GPR109A, most likely by serving as an NAD+ precursor. Supplementation of NAD+ using nicotinamide-related biomolecules may represent an effective and well-tolerated approach to preventing or treating AAA.

Phylogenic Determinants of Cardiovascular Frailty, Focus on Hemodynamics and Arterial Smooth Muscle Cells

The evolution of the circulatory system from invertebrates to mammals has involved the passage from an open system to a closed in-parallel system via a closed in-series system, accompanying the increasing complexity and efficiency of life’s biological functions. The archaic heart enables pulsatile motion waves of hemolymph in invertebrates, and the in-series circulation in fish occurs with only an endothelium, whereas mural smooth muscle cells appear later. The present review focuses on evolution of the circulatory system. In particular, we address how and why this evolution took place from a closed, flowing, longitudinal conductance at low pressure to a flowing, highly pressurized and bifurcating arterial compartment. However, although arterial pressure was the latest acquired hemodynamic variable, the general teleonomy of the evolution of species is the differentiation of individual organ function, supported by specific fueling allowing and favoring partial metabolic autonomy. This was achieved via the establishment of an active contractile tone in resistance arteries, which permitted the regulation of blood supply to specific organ activities via its localized function-dependent inhibition (active vasodilation). The global resistance to viscous blood flow is the peripheral increase in frictional forces caused by the tonic change in arterial and arteriolar radius, which backscatter as systemic arterial blood pressure. Consequently, the arterial pressure gradient from circulating blood to the adventitial interstitium generates the unidirectional outward radial advective conductance of plasma solutes across the wall of conductance arteries. This hemodynamic evolution was accompanied by important changes in arterial wall structure, supported by smooth muscle cell functional plasticity, including contractility, matrix synthesis and proliferation, endocytosis and phagocytosis, etc. These adaptive phenotypic shifts are due to epigenetic regulation, mainly related to mechanotransduction. These paradigms actively participate in cardio-arterial pathologies such as atheroma, valve disease, heart failure, aneurysms, hypertension, and physiological aging.

Targeting Molecular Mechanism of Vascular Smooth Muscle Senescence Induced by Angiotensin II, A Potential Therapy via Senolytics and Senomorphics

Cardiovascular disease (CVD) is a prevalent issue in the global aging population. Premature vascular aging such as elevated arterial stiffness appears to be a major risk factor for CVD. Vascular smooth muscle cells (VSMCs) are one of the essential parts of arterial pathology and prone to stress-induced senescence. The pervasiveness of senescent VSMCs in the vasculature increases with age and can be further expedited by various stressing events such as oxidative stress, mitochondria dysfunction, endoplasmic reticulum stress, and chronic inflammation. Angiotensin II (AngII) can induce many of these responses in VSMCs and is thus considered a key regulator of VSMC senescence associated with CVD. Understanding the precise mechanisms and consequences of senescent cell accumulation may uncover a new generation of therapies including senolytic and senomorphic compounds against CVD. Accordingly, in this review article, we discuss potential molecular mechanisms of VSMC senescence such as those induced by AngII and the therapeutic manipulations of senescence to control age-related CVD and associated conditions such as by senolytic.

The Role of Sirtuin-1 in the Vasculature: Focus on Aortic Aneurysm

Sirtuin-1 (SirT1) is a nicotinamide adenine dinucleotide-dependent deacetylase and the best characterized member of the sirtuins family in mammalians. Sirtuin-1 shuttles between the cytoplasm and the nucleus, where it deacetylates histones and non-histone proteins involved in a plethora of cellular processes, including survival, growth, metabolism, senescence, and stress resistance. In this brief review, we summarize the current knowledge on the anti-oxidant, anti-inflammatory, anti-apoptotic, and anti-senescence effects of SirT1 with an emphasis on vascular diseases. Specifically, we describe recent research advances on SirT1-mediated molecular mechanisms in aortic aneurysm (AA), and how these processes relate to oxidant stress and the heme-oxygenase (HO) system. HO-1 and HO-2 catalyze the rate-limiting step of cellular heme degradation and, similar to SirT1, HO-1 exerts beneficial effects in the vasculature through the activation of anti-oxidant, anti-inflammatory, anti-apoptotic, and anti-proliferative signaling pathways. SirT1 and HO-1 are part of an integrated system for cellular stress tolerance, and may positively interact to regulate vascular function. We further discuss sex differences in HO-1 and SirT1 activity or expression, and the potential interactions between the two proteins, in relation to the progression and severity of AA, as well as the ongoing efforts for translational applications of SirT1 activation and HO-1 induction in the treatment of cardiovascular diseases including AA.

Targeting senescent cells to attenuate cardiovascular disease progression

Cardiovascular disease (CVD) is the most common disease to increase as life expectancy increases. Most high-profile pharmacological treatments for age-related CVD have led to inefficacious results, implying that novel approaches to treating these pathologies are needed. Emerging data have demonstrated that senescent cardiovascular cells, which are characterized by irreversible cell cycle arrest and a distinct senescence-associated secretory phenotype, accumulate in aged or diseased cardiovascular systems, suggesting that they may impair cardiovascular function. This review discusses the evidence implicating senescent cells in cardiovascular ageing, the onset and progression of CVD, and the molecular mechanisms underlying cardiovascular cell senescence. We also review eradication of senescent cardiovascular cells by small-molecule-drug-mediated apoptosis and immune cell-mediated efferocytosis and toxicity as promising and precisely targeted therapeutics for CVD prevention and treatment.

Immune Clearance of Senescent Cells to Combat Ageing and Chronic Diseases

Senescent cells are generally characterized by permanent cell cycle arrest, metabolic alteration and activation, and apoptotic resistance in multiple organs due to various stressors. Excessive accumulation of senescent cells in numerous tissues leads to multiple chronic diseases, tissue dysfunction, age-related diseases and organ ageing. Immune cells can remove senescent cells. Immunaging or impaired innate and adaptive immune responses by senescent cells result in persistent accumulation of various senescent cells. Although senolytics-drugs that selectively remove senescent cells by inducing their apoptosis-are recent hot topics and are making significant research progress, senescence immunotherapies using immune cell-mediated clearance of senescent cells are emerging and promising strategies to fight ageing and multiple chronic diseases. This short review provides an overview of the research progress to date concerning senescent cell-caused chronic diseases and tissue ageing, as well as the regulation of senescence by small-molecule drugs in clinical trials and different roles and regulation of immune cells in the elimination of senescent cells. Mounting evidence indicates that immunotherapy targeting senescent cells combats ageing and chronic diseases and subsequently extends the healthy lifespan.

Cellular Senescence in Arterial Diseases

Cell-proliferation potency is limited, as cells cannot proceed through the cell cycle continually. Instead, they eventually show an irreversible arrest of proliferation, commonly referred to as cellular senescence. Following the initial discovery of this phenomenon by Hayflick et al., studies have indicated that cells are also destined to undergo aging. In addition to the irreversible termination of proliferation, senescent cells are characterized by a flattened and enlarged morphology. Senescent cells become pro-inflammatory and contribute to the initiation and maintenance of sustained chronic sterile inflammation. Aging is associated with the accumulation of senescent cells in the cardiovascular system, and in general these cells are considered to be pathogenic because they mediate vascular remodeling. Recently, genetic and pharmacological approaches have enabled researchers to eliminate senescent cells both in vitro and in vivo. The term “senolysis” is now used to refer to the depletion of senescent cells, and evidence indicates that senolysis contributes to the reversal of age-related pathogenic phenotypes without the risk of tumorigenesis. The concept of senolysis has opened new avenues in research on aging, and senolysis may be a promising therapeutic approach for combating age-related disorders, including arterial diseases.

Nicotinamide phosphoribosyltransferase aggravates inflammation and promotes atherosclerosis in ApoE knockout mice

Nicotinamide phosphoribosyltransferase (Nampt) is the rate-limiting enzyme of nicotinamide adenine dinucleotide (NAD) salvage biosynthesis in mammals, and is involved in fundamental physiological processes and pathophysiology of many diseases. Thus far, however, the role of Nampt in atherosclerosis development is still in debate. In this study, we crossed global Nampt transgenic mice (Nampt-Tg) with a well-established atherosclerosis animal model (ApoE knockout mice, ApoE^-/-) to generate ApoE^-/-;Nampt-Tg mice and investigated the effects of Nampt overexpression on atherosclerosis development in ApoE^-/- mice. Both ApoE^-/- and ApoE^-/-;Nampt-Tg mice were fed with a pro-atherosclerotic high-fat diet (HFD) for 16 weeks. Their serum lipid contents and atherosclerotic lesion were assessed. The results showed that there was no significant difference in body weight or serum levels of glucose, total cholesterol, triglycerides, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol between the two strains of mice, but ApoE^-/-;Nampt-Tg mice had a significantly higher level of serum non-esterified fatty acid. Compared with ApoE^-/- mice, ApoE^-/-;Nampt-Tg mice displayed significantly increased atherosclerotic lesion area and thickness, lower collagen content, decreased collagen I/III ratio (collagen immaturation), increased number of apoptotic cells, and enhanced activities of caspase-3, caspase-8, and caspase-9. Moreover, macrophage infiltration (F4/80 staining), tumor necrosis factor signaling, and chemokines expression (ICAM-1 and CXCR-4) were all activated in aortic atherosclerotic plaque of ApoE^-/-;Nampt-Tg mice compared with ApoE^-/- mice. Our results provide in vivo evidence that Nampt transgene aggravates atherosclerotic inflammation and promotes atherosclerosis development in ApoE^-/- mice.

Smooth muscle cell and arterial aging: basic and clinical aspects

Arterial aging engages a plethora of key signalling pathways that act in concert to induce vascular smooth muscle cell (VSMC) phenotypic changes leading to vascular degeneration and extracellular matrix degradation responsible for alterations of the mechanical properties of the vascular wall. This review highlights proof-of-concept examples of components of the extracellular matrix, VSMC receptors which connect extracellular and intracellular structures, and signalling pathways regulating changes in mechanotransduction and vascular homeostasis in aging. Furthermore, it provides a new framework for understanding how VSMC stiffness and adhesion to extracellular matrix contribute to arterial stiffness and how interactions with endothelial cells, platelets, and immune cells can regulate vascular aging. The identification of the key players of VSMC changes operating in large and small-sized arteries in response to increased mechanical load may be useful to better elucidate the causes and consequences of vascular aging and associated progression of hypertension, arteriosclerosis, and atherosclerosis.

Role of endothelial NAD+ deficiency in age-related vascular dysfunction

Age-related alterations in endothelium and the resulting vascular dysfunction critically contribute to a range of pathological conditions associated with old age. To develop therapies rationally that improve vascular health and thereby increase health span and life span in older adults, it will be essential to understand the cellular and molecular mechanisms contributing to vascular aging. Preclinical studies in model organisms demonstrate that NAD+ availability decreases with age in multiple tissues and that supplemental NAD+ precursors can ameliorate many age-related cellular impairments. Here, we provide a comprehensive overview of NAD+-dependent pathways [including the NAD+-using silent information regulator-2-like enzymes and poly(ADP-ribose) polymerase enzymes] and the potential consequences of endothelial NAD+ deficiency in vascular aging. The multifaceted vasoprotective effects of treatments that reverse the age-related decline in cellular NAD+ levels, as well as their potential limitations, are discussed. The preventive and therapeutic potential of NAD+ intermediates as effective, clinically relevant interventions in older adults at risk for ischemic heart disease, vascular cognitive impairment, and other common geriatric conditions and diseases that involve vascular pathologies (e.g., sarcopenia, frailty) are critically discussed. We propose that NAD+ precursors [e.g., nicotinamide (Nam) riboside, Nam mononucleotide, niacin] should be considered as critical components of combination therapies to slow the vascular aging process and increase cardiovascular health span.

Seno-destructive smooth muscle cells in the ascending aorta of patients with bicuspid aortic valve disease

Background

Ascending aortic aneurysms constitute an important hazard for individuals with a bicuspid aortic valve (BAV). However, the processes that degrade the aortic wall in BAV disease remain poorly understood.

Methods

We undertook in situ analysis of ascending aortas from 68 patients, seeking potentially damaging cellular senescence cascades. Aortas were assessed for senescence-associated-ß-galactosidase activity, p16^Ink4a and p21 expression, and double-strand DNA breaks. The senescence-associated secretory phenotype (SASP) of cultured-aged BAV aortic smooth muscle cells (SMCs) was evaluated by transcript profiling and consequences probed by combined immunofluorescence and circular polarization microscopy. The contribution of p38 MAPK signaling was assessed by immunostaining and blocking strategies.

Findings

We uncovered SMCs at varying depths of cellular senescence within BAV- and tricuspid aortic valve (TAV)-associated aortic aneurysms. Senescent SMCs were also abundant in non-aneurysmal BAV aortas but not in non-aneurysmal TAV aortas. Multivariable analysis revealed that BAV disease independently associated with SMC senescence. Furthermre, SMC senescence was heightened at the convexity of aortas associated with right-left coronary cusp fusion. Aged BAV SMCs had a pronounced collagenolytic SASP. Moreover, senescent SMCs in the aortic wall were enriched with surface-localized MMP1 and surrounded by weakly birefringent collagen fibrils. The senescent-collagenolytic SMC phenotype depended on p38 MAPK signaling, which was chronically activated in BAV aortas.

Interpretation

We have identified a cellular senescence-collagen destruction axis in at-risk ascending aortas. This novel “seno-destructive” SMC phenotype could open new opportunities for managing BAV aortopathy.

Fund

Canadian Institutes of Health Research, Lawson Health Research Institute, Heart and Stroke Foundation of Ontario/Barnett-Ivey Chair.

NAD+ Deficiency Is a Common Central Pathological Factor of a Number of Diseases and Aging: Mechanisms and Therapeutic Implications

Increasing evidence has indicated critical roles of nicotinamide adenine dinucleotide, oxidized form (NAD⁺) in various biological functions. NAD⁺ deficiency has been found in models of a number of diseases such as cerebral ischemia, myocardial ischemia, and diabetes, and in models of aging. Applications of NAD⁺ or other approaches that can restore NAD⁺ levels are highly protective in these models of diseases and aging. NAD⁺ produces its beneficial effects by targeting at multiple pathological pathways, including attenuating mitochondrial alterations, DNA damage, and oxidative stress, by modulating such enzymes as sirtuins, glyceraldehyde-3-phosphate dehydrogenase, and AP endonuclease. These findings have suggested great therapeutic and nutritional potential of NAD⁺ for diseases and senescence. Recent Advances: Approaches that can restore NAD⁺ levels are highly protective in the models of such diseases as glaucoma. The NAD⁺ deficiency in the diseases and aging results from not only poly(ADP-ribose) polymerase-1 (PARP-1) activation but also decreased nicotinamide phosphoribosyltransferase (Nampt) activity and increased CD38 activity. Significant biological effects of extracellular NAD⁺ have been found. Increasing evidence has suggested that NAD⁺ deficiency is a common central pathological factor in a number of diseases and aging. Critical Issues and Future Directions: Future studies are required for solidly establishing the concept that "NAD⁺ deficiency is a common central pathological factor in a number of disease and aging." It is also necessary to further investigate the mechanisms underlying the NAD⁺ deficiency in the diseases and aging. Preclinical and clinical studies should be conducted to determine the therapeutic potential of NAD⁺ for the diseases and aging.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Changes in aortic reactivity associated with the loss of equilibrative nucleoside transporter 1 (ENT1) in mice

Slc29a1 encodes for equilibrative nucleoside transporter subtype 1 (ENT1), the primary mechanism of adenosine transfer across cell membranes. Previous studies showed that tissues isolated from Slc29a1-null mice are relatively resistant to injury caused by vascular ischemia-reperfusion. To determine if there are similar changes in the microvasculature, and investigate underlying mechanism, we examined aortas isolated from wildtype and Slc29a1-null mice. Aorta macrostructure and gene expression were examined histologically and by qPCR, respectively. Wire myography was used to assess the contractile properties of isolated thoracic aortic rings and their response to adenosine under both normoxic and hypoxic conditions. In vivo haemodynamic parameters were assessed using the tail-cuff method. Slc29a1-null mice had significantly (P<0.05) increased plasma adenosine (2.75-fold) and lower blood pressure (~15% ↓) than wild-type mice. Aortas from Slc29a1-null mice were stiffer with a smaller circumference (11% ↓), and had an enhanced contractile response to KCl and receptor-mediated stimuli. Blockade of ENT1 with nitrobenzylthioinosine significantly enhanced (by ~3.5-fold) the response of aorta from wild-type mice to phenylephrine, but had minimal effect on aortas from Slc29a1-null mice. Adenosine enhanced phenylephrine-mediated constriction in the wild-type tissue under both normoxic (11.7-fold) and hypoxic (3.6-fold) conditions, but had no effect on the Slc29a1-null aortic aorta. In conclusion, aortas from Slc29a1-null mice respond to hypoxic insult in a manner comparable to wild-type tissues that have been pharmacologically preconditioned with adenosine. These data also support a role for ENT1 in the regulation of the protective effects of adenosine on contractile function in elastic conduit arteries such as thoracic aorta.

Proinflammatory Arterial Stiffness Syndrome: A Signature of Large Arterial Aging

Age-associated structural and functional remodeling of the arterial wall produces a productive environment for the initiation and progression of hypertension and atherosclerosis. Chronic aging stress induces low-grade proinflammatory signaling and causes cellular proinflammation in arterial walls, which triggers the structural phenotypic shifts characterized by endothelial dysfunction, diffuse intimal-medial thickening, and arterial stiffening. Microscopically, aged arteries exhibit an increase in arterial cell senescence, proliferation, invasion, matrix deposition, elastin fragmentation, calcification, and amyloidosis. These characteristic cellular and matrix alterations not only develop with aging but can also be induced in young animals under experimental proinflammatory stimulation. Interestingly, these changes can also be attenuated in old animals by reducing low-grade inflammatory signaling. Thus, mitigating age-associated proinflammation and arterial phenotype shifts is a potential approach to retard arterial aging and prevent the epidemic of hypertension and atherosclerosis in the elderly.

Vascular Senescence in Cardiovascular and Metabolic Diseases

In mammals, aging is associated with accumulation of senescent cells. Stresses such as telomere shortening and reactive oxygen species induce “cellular senescence”, which is characterized by growth arrest and alteration of the gene expression profile. Chronological aging is associated with development of age-related diseases, including heart failure, diabetes, and atherosclerotic disease, and studies have shown that accumulation of senescent cells has a causative role in the pathology of these age-related disorders. Endothelial cell senescence has been reported to develop in heart failure and promotes pathologic changes in the failing heart. Senescent endothelial cells and vascular smooth muscle cells are found in atherosclerotic plaque, and studies indicate that these cells are involved in progression of plaque. Diabetes is also linked to accumulation of senescent vascular endothelial cells, while endothelial cell senescence per se induces systemic glucose intolerance by inhibiting skeletal muscle metabolism. A close connection between derangement of systemic metabolism and cellular senescence is also well recognized. Aging is a complex phenomenon, and there is no simple approach to understanding the whole process. However, there is accumulating evidence that cellular senescence has a central role in the development and progression of various undesirable aspects of aging. Suppression of cellular senescence or elimination of senescent cells reverses phenotypic changes of aging in several models, and proof-of-concept has been established that inhibiting accumulation of senescent cells could become a next generation therapy for age-related disorders. It is clear that cellular senescence drives various pathological changes associated with aging. Accordingly, further investigation into the role of this biological process in age-related disorders and discovery of senolytic compounds are important fields for future exploration.

NAD+ in Aging: Molecular Mechanisms and Translational Implications

The coenzyme NAD+ is critical in cellular bioenergetics and adaptive stress responses. Its depletion has emerged as a fundamental feature of aging that may predispose to a wide range of chronic diseases. Maintenance of NAD+ levels is important for cells with high energy demands and for proficient neuronal function. NAD+ depletion is detected in major neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases, cardiovascular disease and muscle atrophy. Emerging evidence suggests that NAD+ decrements occur in various tissues during aging, and that physiological and pharmacological interventions bolstering cellular NAD+ levels might retard aspects of aging and forestall some age-related diseases. Here, we discuss aspects of NAD+ biosynthesis, together with putative mechanisms of NAD+ action against aging, including recent preclinical and clinical trials.