Telomerase expression confers cardioprotection in the adult mouse heart after acute myocardial infarction

In the land of not-unhappiness: On the state-of-the-art of targeting aging and age-related diseases by biomedical research

The concept of the Land of Not-Unhappiness refers to the potential achievement of eliminating the pathologies of the aging process. To inform of how close we are to settling in the land, we summarize and review the achievements of research on anti-aging interventions over the last hundred years with a specific focus on strategies that slow down metabolism, compensate for aging-related losses, and target a broad range of age-related diseases. We critically evaluate the existing interventions labeled as "anti-aging," such as calorie restriction, exercise, stem cell administration, and senolytics, to provide a down-to-earth evaluation of their current applicability in counteracting aging. Throughout the text, we have maintained a light tone to make it accessible to non-experts in biogerontology, and provide a broad overview for those considering conducting studies, research, or seeking to understand the scientific basis of anti-aging medicine.

Telomerase is essential for cardiac differentiation and sustained metabolism of human cardiomyocytes

Telomeres as the protective ends of linear chromosomes, are synthesized by the enzyme telomerase (TERT). Critically short telomeres essentially contribute to aging-related diseases and are associated with a broad spectrum of disorders known as telomeropathies. In cardiomyocytes, telomere length is strongly correlated with cardiomyopathies but it remains ambiguous whether short telomeres are the cause or the result of the disease. In this study, we employed an inducible CRISPRi human induced pluripotent stem cell (hiPSC) line to silence TERT expression enabling the generation of hiPSCs and hiPSC-derived cardiomyocytes with long and short telomeres. Reduced telomerase activity and shorter telomere lengths of hiPSCs induced global transcriptomic changes associated with cardiac developmental pathways. Consequently, the differentiation potential towards cardiomyocytes was strongly impaired and single cell RNA sequencing revealed a shift towards a more smooth muscle cell like identity in the cells with the shortest telomeres. Poor cardiomyocyte function and increased sensitivity to stress directly correlated with the extent of telomere shortening. Collectively our data demonstrates a TERT dependent cardiomyogenic differentiation defect, highlighting the CRISPRi TERT hiPSCs model as a powerful platform to study the mechanisms and consequences of short telomeres in the heart and also in the context of telomeropathies.

Engineered Exosomes with Growth Differentiation Factor-15 Overexpression Enhance Cardiac Repair After Myocardial Injury

Background

Cardiac repair remains a thorny issue for survivors of acute myocardial infarction (AMI), due to the regenerative inertia of myocardial cells. Cell-free therapies, such as exosome transplantation, have become a potential strategy for myocardial injury. The aim of this study was to investigate the role of engineered exosomes in overexpressing Growth Differentiation Factor-15 (GDF-15) (GDF15-EVs) after myocardial injury, and their molecular mechanisms in cardiac repair.

Methods

H9C2 cells were transfected with GDF-15 lentivirus or negative control. The exosomes secreted from H9C2 cells were collected and identified. The cellular apoptosis and autophagy of H2O2-injured H9C2 cells were assessed by Western blotting, TUNEL assay, electron microscopy, CCK-8 and caspase 3/7 assay. A rat model of AMI was constructed by ligating the left anterior descending artery. The anti-apoptotic, pro-angiogenic effects of GDF15-EVs treatment, as well as ensuing functional and histological recovery were evaluated. Then, mRNA sequencing was performed to identify the differentially expressed mRNAs after GDF15-EVs treatment.

Results

GDF15-EVs inhibited apoptosis and promoted autophagy in H2O2 injured H9C2 cells. GDF15-EVs effectively decreased the infarct area and enhanced the cardiac function in rats with AMI. Moreover, GDF15-EVs hindered inflammatory cell infiltration, inhibited cell apoptosis, and promoted cardiac angiogenesis in rats with AMI. RNA sequence showed that telomerase reverse transcriptase (TERT) mRNA was upregulated in GDF15-EVs-treated H9C2 cells. AMPK signaling was activated after GDF15-EVs. Silencing TERT impaired the protective effects of GDF15-EVs on H2O2-injured H9C2 cells.

Conclusion

GDF15-EVs could fulfil their protective effects against myocardial injury by upregulating the expression of TERT and activating the AMPK signaling pathway. GDF15-EVs might be exploited to design new therapies for AMI.

Associations of measured and genetically predicted leukocyte telomere length with vascular phenotypes: a population-based study

Shorter leukocyte telomere length (LTL) is associated with cardiovascular dysfunction. Whether this association differs between measured and genetically predicted LTL is still unclear. Moreover, the molecular processes underlying the association remain largely unknown. We used baseline data of the Rhineland Study, an ongoing population-based cohort study in Bonn, Germany [56.2% women, age: 55.5 ± 14.0 years (range 30 - 95 years)]. We calculated genetically predicted LTL in 4180 participants and measured LTL in a subset of 1828 participants with qPCR. Using multivariable regression, we examined the association of measured and genetically predicted LTL, and the difference between measured and genetically predicted LTL (ΔLTL), with four vascular functional domains and the overall vascular health. Moreover, we performed epigenome-wide association studies of three LTL measures. Longer measured LTL was associated with better microvascular and cardiac function. Longer predicted LTL was associated with better cardiac function. Larger ΔLTL was associated with better microvascular and cardiac function and overall vascular health, independent of genetically predicted LTL. Several CpGs were associated (p < 1e-05) with measured LTL (n = 5), genetically predicted LTL (n = 8), and ΔLTL (n = 27). Genes whose methylation status was associated with ΔLTL were enriched in vascular endothelial signaling pathways and have been linked to environmental exposures, cardiovascular diseases, and mortality. Our findings suggest that non-genetic causes of LTL contribute to microvascular and cardiac function and overall vascular health, through an effect on the vascular endothelial signaling pathway. Interventions that counteract LTL may thus improve vascular function.

Cardiovascular aging: spotlight on mitochondria

Mitochondria are cellular organelles critical for ATP production and are particularly relevant to cardiovascular diseases including heart failure, atherosclerosis, ischemia-reperfusion injury, and cardiomyopathies. With advancing age, even in the absence of clinical disease, mitochondrial homeostasis becomes disrupted (e.g., redox balance, mitochondrial DNA damage, oxidative metabolism, and mitochondrial quality control). Mitochondrial dysregulation leads to the accumulation of damaged and dysfunctional mitochondria, producing excessive reactive oxygen species and perpetuating mitochondrial dysfunction. In addition, mitochondrial DNA, cardiolipin, and N-formyl peptides are potent activators of cell-intrinsic and -extrinsic inflammatory pathways. These age-related mitochondrial changes contribute to the development of cardiovascular diseases. This review covers the impact of aging on mitochondria and links these mechanisms to therapeutic implications for age-associated cardiovascular diseases.

Aging and atrial fibrillation: A vicious circle

Atrial fibrillation (AF) is the commonest sustained cardiac arrhythmia observed in clinical practice. Its prevalence increases dramatically with advancing age. This review article discusses the recent advances in studies investigating the relationship between aging and AF and the possible underlying mechanisms.

Upregulation of mitochondrial telomerase reverse transcriptase mediates the preventive effect of physical exercise on pathological cardiac hypertrophy via improving mitochondrial function and inhibiting oxidative stress

Physical exercise is a non-pharmacological intervention that helps prevent pathological cardiac hypertrophy. However, the underlying molecular mechanisms remain unclear. Telomerase reverse transcriptase (TERT) has non-telomeric functions such as protection against mitochondrial dysfunction and oxidative stress, and its myocardial expression is upregulated by physical exercise. Here, we found that physical exercise caused myocardial upregulation of mitochondrial TERT and sustenance during transverse aortic constriction (TAC)-induced cardiac hypertrophy. Overexpression of mitochondrial-targeted TERT (mito-TERT) via adeno-associated virus serotype 9 carrying the TERT-coding sequence fused with N-terminal mitochondrial-targeting sequence improved cardiac function and attenuated cardiac hypertrophy. Mechanistically, mito-TERT ameliorated mitochondrial dysfunction and oxidative stress, which were associated with improving the activity and subunit composition of complex I. Remarkably, the telomerase activator TA-65 also exhibited an antihypertrophic effect. Collectively, our results reveal a significant role for mito-TERT in mediating the antihypertrophic effect of physical exercise and demonstrate that TERT is a potential drug target for treating cardiac hypertrophy.

Long Telomeric Repeat-Containing RNA (TERRA): Biological Functions and Challenges in Vascular Aging and Disease

Telomere dysfunction is implicated in vascular aging and shorter leucocyte telomeres are associated with an increased risk of atherosclerosis, myocardial infarction, and heart failure. Another pathophysiological mechanism that explains the causal relationship between telomere shortening and atherosclerosis development focuses on the clonal hematopoiesis of indeterminate potential (CHIP), which represents a new and independent risk factor in atherosclerotic cardiovascular diseases. Since telomere attrition has a central role in driving vascular senescence, understanding telomere biology is essential to modulate the deleterious consequences of vascular aging and its cardiovascular disease-related manifestations. Emerging evidence indicates that a class of long noncoding RNAs transcribed at telomeres, known as TERRA for "TElomeric Repeat-containing RNA", actively participates in the mechanisms regulating telomere maintenance and chromosome end protection. However, the multiple biological functions of TERRA remain to be largely elucidated. In particular, the role of TERRA in vascular biology is surprisingly unknown. In this review, we discuss the current knowledge of TERRA and its roles in telomere biology. Additionally, we outline the pieces of evidence that exist regarding the relationship between TERRA dysregulation and disease. Finally, we speculate on how a comprehensive understanding of TERRA transcription in the cardiovascular system may provide valuable insights into telomere-associated vascular aging, offering great potential for new therapeutic approaches.

Distinct roles of telomerase activity in age-related chronic diseases: An update literature review

Although telomerase has low activity in somatic quiescent cells, it plays an significant roles in regenerative cells such as endothelial cells, hepatocytes, epithelial cells, and hemocytes. Telomerase activity and telomere length are critical factors in age-related chronic diseases as they are closely related to cell senescence. However, whether telomerase activity plays a key role in disease progression or whether the role of telomerase is unified among different diseases are unresolved. Considering that aging is the most important risk factor for neurodegenerative and metabolic diseases, this article will analyze the evidence, mechanism, and therapeutic potential of telomerase activity in several chronic disease, including type 2 diabetes, neurodegenerative diseases, atherosclerosis, heart failure and non-alcoholic fatty liver disease, in order to provide clues for the use of telomerase activity to target the treatment of age-related chronic diseases.

Novel Targets Regulating the Role of Endothelial Cells and Angiogenesis after Infarction: A RNA Sequencing Analysis

Endothelial cells (ECs) are a key target for cardioprotection due to their role in preserving cardiac microvasculature and homeostasis after myocardial infarction (MI). Our goal is to identify the genes involved in post-MI EC proliferation, EC apoptosis, and angiogenesis regulation via RNA-sequencing transcriptomic datasets. Using eight studies from the Gene Expression Omnibus, RNA-sequencing data from 92 mice submitted to different times of coronary ischemia or sham were chosen. Functional enrichment analysis was performed based on gene ontology biological processes (BPs). Apoptosis-related BPs are activated up to day 3 after ischemia onset, whereas endothelial proliferation occurs from day 3 onwards, including an overrepresentation of up to 37 genes. Endothelial apoptosis post-MI is triggered via both the extrinsic and intrinsic signaling pathways, as reflected by the overrepresentation of 13 and 2 specific genes, respectively. BPs implicated in new vessel formation are upregulated soon after ischemia onset, whilst the mechanisms aiming at angiogenesis repression can be detected at day 3. Overall, 51 pro-angiogenic and 29 anti-angiogenic factors displayed altered transcriptomic expression post-MI. This is the first study using RNA sequencing datasets to evaluate the genes participating in post-MI endothelium physiology and angiogenesis regulation. These novel data could lay the groundwork to advance understanding of the implication of ECs after MI.

Association of Longer Leukocyte Telomere Length With Cardiac Size, Function, and Heart Failure

Importance

Longer leukocyte telomere length (LTL) is associated with a lower risk of adverse cardiovascular outcomes. The extent to which variation in LTL is associated with intermediary cardiovascular phenotypes is unclear.

Objective

To evaluate the associations between LTL and a diverse set of cardiovascular imaging phenotypes.

Design, Setting, and Participants

This is a population-based cross-sectional study of UK Biobank participants recruited from 2006 to 2010. LTL was measured using a quantitative polymerase chain reaction method. Cardiovascular measurements were derived from cardiovascular magnetic resonance using machine learning. The median (IQR) duration of follow-up was 12.0 (11.3-12.7) years. The associations of LTL with imaging measurements and incident heart failure (HF) were evaluated by multivariable regression models. Genetic associations between LTL and significantly associated traits were investigated by mendelian randomization. Data were analyzed from January to May 2023.

Exposure

LTL.

Main Outcomes and Measures

Cardiovascular imaging traits and HF.

Results

Of 40 459 included participants, 19 529 (48.3%) were men, and the mean (SD) age was 55.1 (7.6) years. Longer LTL was independently associated with a pattern of positive cardiac remodeling (higher left ventricular mass, larger global ventricular size and volume, and higher ventricular and atrial stroke volumes) and a lower risk of incident HF (LTL fourth quartile vs first quartile: hazard ratio, 0.86; 95% CI, 0.81-0.91; P = 1.8 × 10-6). Mendelian randomization analysis suggested a potential causal association between LTL and left ventricular mass, global ventricular volume, and left ventricular stroke volume.

Conclusions and Relevance

In this cross-sectional study, longer LTL was associated with a larger heart with better cardiac function in middle age, which could potentially explain the observed lower risk of incident HF.

Modeling Duchenne Muscular Dystrophy Cardiomyopathy with Patients' Induced Pluripotent Stem-Cell-Derived Cardiomyocytes

Duchenne muscular dystrophy (DMD) is an X-linked progressive muscle degenerative disease caused by mutations in the dystrophin gene, resulting in death by the end of the third decade of life at the latest. A key aspect of the DMD clinical phenotype is dilated cardiomyopathy, affecting virtually all patients by the end of the second decade of life. Furthermore, despite respiratory complications still being the leading cause of death, with advancements in medical care in recent years, cardiac involvement has become an increasing cause of mortality. Over the years, extensive research has been conducted using different DMD animal models, including the mdx mouse. While these models present certain important similarities to human DMD patients, they also have some differences which pose a challenge to researchers. The development of somatic cell reprograming technology has enabled generation of human induced pluripotent stem cells (hiPSCs) which can be differentiated into different cell types. This technology provides a potentially endless pool of human cells for research. Furthermore, hiPSCs can be generated from patients, thus providing patient-specific cells and enabling research tailored to different mutations. DMD cardiac involvement has been shown in animal models to include changes in gene expression of different proteins, abnormal cellular Ca²⁺ handling, and other aberrations. To gain a better understanding of the disease mechanisms, it is imperative to validate these findings in human cells. Furthermore, with the recent advancements in gene-editing technology, hiPSCs provide a valuable platform for research and development of new therapies including the possibility of regenerative medicine. In this article, we review the DMD cardiac-related research performed so far using human hiPSCs-derived cardiomyocytes (hiPSC-CMs) carrying DMD mutations.

A Unified Model of Age-Related Cardiovascular Disease

Despite progress in biomedical technologies, cardiovascular disease remains the main cause of mortality. This is at least in part because current clinical interventions do not adequately take into account aging as a driver and are hence aimed at suboptimal targets. To achieve progress, consideration needs to be given to the role of cell aging in disease pathogenesis. We propose a model unifying the fundamental processes underlying most age-associated cardiovascular pathologies. According to this model, cell aging, leading to cell senescence, is responsible for tissue changes leading to age-related cardiovascular disease. This process, occurring due to telomerase inactivation and telomere attrition, affects all components of the cardiovascular system, including cardiomyocytes, vascular endothelial cells, smooth muscle cells, cardiac fibroblasts, and immune cells. The unified model offers insights into the relationship between upstream risk factors and downstream clinical outcomes and explains why interventions aimed at either of these components have limited success. Potential therapeutic approaches are considered based on this model. Because telomerase activity can prevent and reverse cell senescence, telomerase gene therapy is discussed as a promising intervention. Telomerase gene therapy and similar systems interventions based on the unified model are expected to be transformational in cardiovascular medicine.

Telomere Shortening in Hypertensive Heart Disease Depends on Oxidative DNA Damage and Predicts Impaired Recovery of Cardiac Function in Heart Failure

BACKGROUND

Heart failure (HF) coincides with cardiomyocyte telomere shortening. Arterial hypertension is the most prominent risk factor for HF. Both HF and arterial hypertension are associated with dysregulation of the neurohormonal axis. How neurohormonal activation is linked to telomere shortening in the pathogenesis of HF is incompletely understood.

METHODS

Cardiomyocyte telomere length was assessed in a mouse model of hypertensive HF induced by excess neurohormonal activation (AngII [angiotensin II] infusion, high salt diet, and uninephrectomy), in AngII-stimulated cardiomyocytes and in endomyocardial biopsies from patients with HF. Superoxide production, expression of NOX2 (NADPH oxidase 2) and PRDX1 (peroxiredoxin 1) and HDAC6 (histone deacetylase 6) activity were assessed.

RESULTS

Telomere shortening occurred in vitro and in vivo, correlating with both left ventricular (LV) dilatation and LV systolic function impairment. Telomere shortening coincided with increased superoxide production, increased NOX2 expression, increased HDAC6 activity, loss of the telomere-specific antioxidant PRDX1, and increased oxidative DNA-damage. NOX2 knockout prevented PRDX1 depletion, DNA-damage and telomere shortening confirming this enzyme as a critical source of reactive oxygen species. Cotreatment with the NOX inhibitor apocynin ameliorated hypertensive HF and telomere shortening. Similarly, treatment with the HDAC6 inhibitor tubastatin A, which increases PRDX1 bioavailability, prevented telomere shortening in adult cardiomyocytes. To explore the clinical relevance of our findings, we examined endomyocardial biopsies from an all-comer population of patients with HF with reduced ejection fraction. Here, cardiomyocyte telomere length predicted the recovery of cardiac function.

CONCLUSIONS

Cardiomyocyte telomere shortening and oxidative damage in heart failure with reduced ejection fraction induced by excess neurohormonal activation depends on NOX2-derived superoxide and may help to stratify HF therapy.

Noncanonical Role of Telomerase in Regulation of Microvascular Redox Environment With Implications for Coronary Artery Disease

Telomerase reverse transcriptase (TERT) (catalytic subunit of telomerase) is linked to the development of coronary artery disease (CAD); however, whether the role of nuclear vs. mitchondrial actions of TERT is involved is not determined. Dominant-negative TERT splice variants contribute to decreased mitochondrial integrity and promote elevated reactive oxygen species production. We hypothesize that a decrease in mitochondrial TERT would increase _mtDNA damage, promoting a pro-oxidative redox environment. The goal of this study is to define whether mitochondrial TERT is sufficient to maintain nitric oxide as the underlying mechanism of flow-mediated dilation by preserving _mtDNA integrity.Immunoblots and quantitative polymerase chain reaction were used to show elevated levels of splice variants α- and β-deletion TERT tissue from subjects with and without CAD. Genetic, pharmacological, and molecular tools were used to manipulate TERT localization. Isolated vessel preparations and fluorescence-based quantification of _mtH₂O₂ and NO showed that reduction of TERT in the nucleus increased flow induced NO and decreased _mtH₂O₂ levels, while prevention of mitochondrial import of TERT augmented pathological effects. Further elevated _mtDNA damage was observed in tissue from subjects with CAD and initiation of _mtDNA repair mechanisms was sufficient to restore NO-mediated dilation in vessels from patients with CAD. The work presented is the first evidence that catalytically active mitochondrial TERT, independent of its nuclear functions, plays a critical physiological role in preserving NO-mediated vasodilation and the balance of mitochondrial to nuclear TERT is fundamentally altered in states of human disease that are driven by increased expression of dominant negative splice variants.

The landscape of aging

Aging is characterized by a progressive deterioration of physiological integrity, leading to impaired functional ability and ultimately increased susceptibility to death. It is a major risk factor for chronic human diseases, including cardiovascular disease, diabetes, neurological degeneration, and cancer. Therefore, the growing emphasis on “healthy aging” raises a series of important questions in life and social sciences. In recent years, there has been unprecedented progress in aging research, particularly the discovery that the rate of aging is at least partly controlled by evolutionarily conserved genetic pathways and biological processes. In an attempt to bring full-fledged understanding to both the aging process and age-associated diseases, we review the descriptive, conceptual, and interventive aspects of the landscape of aging composed of a number of layers at the cellular, tissue, organ, organ system, and organismal levels.

A coalition to heal-the impact of the cardiac microenvironment

Heart regenerative medicine has been gradually evolving from a view of the heart as a nonregenerative organ with terminally differentiated cardiac muscle cells. Understanding the biology of the heart during homeostasis and in response to injuries has led to the realization that cellular communication between all cardiac cell types holds great promise for treatments. Indeed, recent studies highlight new disease-reversion concepts in addition to cardiomyocyte renewal, such as matrix- and vascular-targeted therapies, and immunotherapy with a focus on inflammation and fibrosis. In this review, we will discuss the cross-talk within the cardiac microenvironment and how specific therapies aim to target the hostile cardiac milieu under pathological conditions.

Telomere therapy for chronic kidney disease

Chronic kidney disease (CKD) is estimated to affect almost 10% of individuals worldwide and is one of the leading causes of morbidity and mortality. Renal fibrosis, a central pathway in CKD progression (irrespective of etiology), is associated with shortened or dysfunctional telomeres in animal studies. Telomeres are specialized nucleoprotein structures located at the chromosome end that maintain genomic integrity. The mechanisms of associations between telomere length and CKD have not yet been fully elucidated, however, CKD patients with shorter telomere length may have decreased renal function and a higher mortality rate. A plethora of ongoing research has focused on possible therapeutic applications of telomeres with the overall goal to preserve telomere length as a therapy to treat CKD.

Metabolic Determinants in Cardiomyocyte Function and Heart Regenerative Strategies

Heart disease is the leading cause of mortality in developed countries. The associated pathology is characterized by a loss of cardiomyocytes that leads, eventually, to heart failure. In this context, several cardiac regenerative strategies have been developed, but they still lack clinical effectiveness. The mammalian neonatal heart is capable of substantial regeneration following injury, but this capacity is lost at postnatal stages when cardiomyocytes become terminally differentiated and transit to the fetal metabolic switch. Cardiomyocytes are metabolically versatile cells capable of using an array of fuel sources, and the metabolism of cardiomyocytes suffers extended reprogramming after injury. Apart from energetic sources, metabolites are emerging regulators of epigenetic programs driving cell pluripotency and differentiation. Thus, understanding the metabolic determinants that regulate cardiomyocyte maturation and function is key for unlocking future metabolic interventions for cardiac regeneration. In this review, we will discuss the emerging role of metabolism and nutrient signaling in cardiomyocyte function and repair, as well as whether exploiting this axis could potentiate current cellular regenerative strategies for the mammalian heart.

Dexmedetomidine attenuates hypoxia-induced cardiomyocyte injury by promoting telomere/telomerase activity: Possible involvement of ERK1/2-Nrf2 signaling pathway

Dexmedetomidine (Dex), an α2-adrenergic receptor (α2-AR) agonist, possesses cardioprotection against ischaemic/hypoxic injury, but the exact mechanism is not fully elucidated. Since telomere/telomerase dysfunction is involved in myocardial ischemic damage, the present study aimed to investigate whether Dex ameliorates cobalt chloride (CoCl_2; a hypoxia mimic agent in vitro)-induced the damage of H9c2 cardiomyocytes by improving telomere/telomerase dysfunction and further explored the underlying mechanism focusing on ERK1/2-Nrf2 signaling pathway. Result showed that Dex increased cell viability, decreased apoptosis, and reduced cardiomyocyte hypertrophy as illustrated by the decreases in cell surface area and the biomarker levels for cardiac hypertrophy including atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and myosin heavy chain β (β-MHC) mRNA and protein in CoCl₂ -exposed H9c2 cells. Intriguingly, Dex increased the telomere length and telomerase activity as well as telomere reverse transcriptase (TERT) protein and mRNA levels in H9c2 cells exposed to CoCl₂ , indicating that Dex promotes telomere/telomerase function under hypoxia. In addition, Dex remarkably diminished the ROS generation, reduced MDA content, and increased antioxidative signaling as evidenced by the increases in SOD and GSH-Px activities. Furthermore, Dex increased the ratio of P-ERK1/2/T-ERK1/2 and P-Nrf2/T-Nrf2 and enhanced Nrf2 nuclear translocation in CoCl₂ -subjected H9c2 cells, suggesting that Dex promotes the activation of the ERK1/2-Nrf2 signaling pathway. These novel findings indicated that Dex attenuates myocardial ischemic damage and reduces myocardial hypertrophy by promoting telomere/telomerase function, which may be associated with the activation of the ERK1/2-Nrf2 signaling pathway in vitro. This article is protected by copyright. All rights reserved.

Telomere dysfunction in ageing and age-related diseases

Ageing organisms accumulate senescent cells that are thought to contribute to body dysfunction. Telomere shortening and damage are recognized causes of cellular senescence and ageing. Several human conditions associated with normal ageing are precipitated by accelerated telomere dysfunction. Here, we systematize a large body of evidence and propose a coherent perspective to recognize the broad contribution of telomeric dysfunction to human pathologies.

Neonatal injury models: integral tools to decipher the molecular basis of cardiac regeneration

Myocardial injury often leads to heart failure due to the loss and insufficient regeneration of resident cardiomyocytes. The low regenerative potential of the mammalian heart is one of the main drivers of heart failure progression, especially after myocardial infarction accompanied by large contractile muscle loss. Preclinical therapies for cardiac regeneration are promising, but clinically still missing. Mammalian models represent an excellent translational in vivo platform to test drugs and treatments for the promotion of cardiac regeneration. Particularly, short-lived mice offer the possibility to monitor the outcome of such treatments throughout the life span. Importantly, there is a short period of time in newborn mice in which the heart retains full regenerative capacity after cardiac injury, which potentially also holds true for the neonatal human heart. Thus, in vivo neonatal mouse models of cardiac injury are crucial to gain insights into the molecular mechanisms underlying the cardiac regenerative processes and to devise novel therapeutic strategies for the treatment of diseased adult hearts. Here, we provide an overview of the established injury models to study cardiac regeneration. We summarize pioneering studies that demonstrate the potential of using neonatal cardiac injury models to identify factors that may stimulate heart regeneration by inducing endogenous cardiomyocyte proliferation in the adult heart. To conclude, we briefly summarize studies in large animal models and the insights gained in humans, which may pave the way toward the development of novel approaches in regenerative medicine.

Gene Therapy Strategies Targeting Aging-Related Diseases

Rapid advancements have taken place in gene therapy technology. However, effective methods for treating aging- or age-related chronic diseases, which are often closely related to genes or even multiple genes, are still lacking. The path to developing cures is winding, while gene therapy that targets genes related to aging represents an exciting research direction with tremendous potential. Among aging-related genes, some candidates have been studied at different levels, from cell to organismal levels (e.g., mammalian models) with different methods, from overexpression to gene editing. The TERT and APOE have even entered the stage of clinical trials. Even those displaying only a preliminary association with diseases have potential applications. This article discusses the foundations and recent breakthroughs in the field of gene therapy, providing a summary of current mainstream strategies and gene therapy products with clinical and preclinical applications. Finally, we review representative target genes and their potential for treating aging or age-related diseases.

Potential Therapies to Protect the Aging Heart Against Ischemia/Reperfusion Injury

Despite important advances in the treatment of myocardial infarction that have significantly reduced mortality, there is still an unmet need to limit the infarct size after reperfusion injury in order to prevent the onset and severity of heart failure. Multiple cardioprotective maneuvers, therapeutic targets, peptides and drugs have been developed to effectively protect the myocardium from reperfusion-induced cell death in preclinical studies. Nonetheless, the translation of these therapies from laboratory to clinical contexts has been quite challenging. Comorbidities, comedications or inadequate ischemia/reperfusion experimental models are clearly identified variables that need to be accounted for in order to achieve effective cardioprotection studies. The aging heart is characterized by altered proteostasis, DNA instability, epigenetic changes, among others. A vast number of studies has shown that multiple therapeutic strategies, such as ischemic conditioning phenomena and protective drugs are unable to protect the aged heart from myocardial infarction. In this Mini-Review, we will provide an updated state of the art concerning potential new cardioprotective strategies targeting the aging heart.

Innate Mechanisms of Heart Regeneration

Heart regeneration is a remarkable process whereby regrowth of damaged cardiac tissue rehabilitates organ anatomy and function. Unfortunately, the human heart is highly resistant to regeneration, which creates a shortage of cardiomyocytes in the wake of ischemic injury, and explains, in part, why coronary artery disease remains a leading cause of death worldwide. Luckily, a detailed blueprint for achieving therapeutic heart regeneration already exists in nature because several lower vertebrate species successfully regenerate amputated or damaged heart muscle through robust cardiomyocyte proliferation. A growing number of species are being interrogated for cardiac regenerative potential, and several commonalities have emerged between those animals showing high or low innate capabilities. In this review, we provide a historical perspective on the field, discuss how regenerative potential is influenced by cardiomyocyte properties, mitogenic signals, and chromatin accessibility, and highlight unanswered questions under active investigation. Ultimately, delineating why heart regeneration occurs preferentially in some organisms, but not in others, will uncover novel therapeutic inroads for achieving cardiac restoration in humans.

Mitochondrial Telomerase Reverse Transcriptase Protects from Myocardial Ischemia/reperfusion Injury by Improving Complex I Composition and Function

Background: The catalytic subunit of telomerase, Telomerase Reverse Transcriptase (TERT) has protective functions in the cardiovascular system. TERT is not only present in the nucleus, but also in mitochondria. However, it is unclear whether nuclear or mitochondrial TERT is responsible for the observed protection and appropriate tools are missing to dissect this. Methods: We generated new mouse models containing TERT exclusively in the mitochondria (mitoTERT mice) or the nucleus (nucTERT mice) to finally distinguish between the functions of nuclear and mitochondrial TERT. Outcome after ischemia/reperfusion, mitochondrial respiration in the heart as well as cellular functions of cardiomyocytes, fibroblasts, and endothelial cells were determined. Results: All mice were phenotypically normal. While respiration was reduced in cardiac mitochondria from TERT-deficient and nucTERT mice, it was increased in mitoTERT animals. The latter also had smaller infarcts than wildtype mice, whereas nucTERT animals had larger infarcts. The decrease in ejection fraction after one, two and four weeks of reperfusion was attenuated in mitoTERT mice. Scar size was also reduced and vascularization increased. Mitochondrial TERT protected a cardiomyocyte cell line from apoptosis. Myofibroblast differentiation, which depends on complex I activity, was abrogated in TERT-deficient and nucTERT cardiac fibroblasts and completely restored in mitoTERT cells. In endothelial cells, mitochondrial TERT enhanced migratory capacity and activation of endothelial NO synthase. Mechanistically, mitochondrial TERT improved the ratio between complex I matrix arm and membrane subunits explaining the enhanced complex I activity. In human right atrial appendages, TERT was localized in mitochondria and there increased by remote ischemic preconditioning. The Telomerase activator, TA-65 evoked a similar effect in endothelial cells, thereby increasing their migratory capacity, and enhanced myofibroblast differentiation. Conclusions: Mitochondrial, but not nuclear TERT, is critical for mitochondrial respiration and during ischemia/reperfusion injury. Mitochondrial TERT improves complex I subunit composition. TERT is present in human heart mitochondria, and remote ischemic preconditioning increases its level in those organelles. TA-65 has comparable effects ex vivo and improves migratory capacity of endothelial cells and myofibroblast differentiation. We conclude that mitochondrial TERT is responsible for cardioprotection and its increase could serve as a therapeutic strategy.

Telomere Attrition and Clonal Hematopoiesis of Indeterminate Potential in Cardiovascular Disease

Clinical evidence suggests that conventional cardiovascular disease (CVD) risk factors cannot explain all CVD incidences. Recent studies have shown that telomere attrition, clonal hematopoiesis of indeterminate potential (CHIP), and atherosclerosis (telomere-CHIP-atherosclerosis, TCA) evolve to play a crucial role in CVD. Telomere dynamics and telomerase have an important relationship with age-related CVD. Telomere attrition is associated with CHIP. CHIP is commonly observed in elderly patients. It is characterized by an increase in blood cell clones with somatic mutations, resulting in an increased risk of hematological cancer and atherosclerotic CVD. The most common gene mutations are DNA methyltransferase 3 alpha (DNMT3A), Tet methylcytosine dioxygenase 2 (TET2), and additional sex combs-like 1 (ASXL1). Telomeres, CHIP, and atherosclerosis increase chronic inflammation and proinflammatory cytokine expression. Currently, their epidemiology and detailed mechanisms related to the TCA axis remain incompletely understood. In this article, we reviewed recent research results regarding the development of telomeres and CHIP and their relationship with atherosclerotic CVD.

Exercise training increases telomerase reverse transcriptase gene expression and telomerase activity: A systematic review and meta-analysis

Telomeres protect genomic stability and shortening is one of the hallmarks of ageing. Telomerase reverse transcriptase (TERT) is the major protein component of telomerase, which elongates telomeres. Given that short telomeres are linked to a host of chronic diseases and the therapeutic potential of telomerase-based therapies as treatments and a strategy to extend lifespan, lifestyle factors that increase TERT gene expression and telomerase activity could attenuate telomere attrition and contribute to healthy biological ageing. Physical activity and maximal aerobic fitness are associated with telomere maintenance, yet the molecular mechanisms remain unclear. Therefore, the purpose of this systematic review and meta-analysis was to identify the influence of a single bout of exercise and long-term exercise training on TERT expression and telomerase activity. A search of human and rodent trials using the PubMed, Scopus, Science Direct and Embase databases was performed. Based on findings from the identified and eligible trials, both a single bout of exercise (n; standardised mean difference [95%CI]: 5; SMD: 1.19 [0.41-1.97], p = 0.003) and long-term exercise training (10; 0.31 [0.03-0.60], p = 0.03) up-regulates TERT and telomerase activity in non-cancerous somatic cells. As human and rodent studies were included in the meta-analyses both exhibited heterogeneity (I² = 55-87%, p < 0.05). Endurance athletes also exhibited increased leukocyte TERT and telomerase activity compared to their inactive counterparts. These findings suggest exercise training as an inexpensive lifestyle factor that increases TERT expression and telomerase activity. Regular exercise training could attenuate telomere attrition through a telomerase-dependent mechanism and ultimately extend health-span and longevity.

Growth differentiation factor 11 attenuates cardiac ischemia reperfusion injury via enhancing mitochondrial biogenesis and telomerase activity

It has been reported that growth differentiation factor 11 (GDF11) protects against myocardial ischemia/reperfusion (IR) injury, but the underlying mechanisms have not been fully clarified. Considering that GDF11 plays a role in the aging/rejuvenation process and that aging is associated with telomere shortening and cardiac dysfunction, we hypothesized that GDF11 might protect against IR injury by activating telomerase. Human plasma GDF11 levels were significantly lower in acute coronary syndrome patients than in chronic coronary syndrome patients. IR mice with myocardial overexpression GDF11 (oe-GDF11) exhibited a significantly smaller myocardial infarct size, less cardiac remodeling and dysfunction, fewer apoptotic cardiomyocytes, higher telomerase activity, longer telomeres, and higher ATP generation than IR mice treated with an adenovirus carrying a negative control plasmid. Furthermore, mitochondrial biogenesis-related proteins and some antiapoptotic proteins were significantly upregulated by oe-GDF11. These cardioprotective effects of oe-GDF11 were significantly antagonized by BIBR1532, a specific telomerase inhibitor. Similar effects of oe-GDF11 on apoptosis and mitochondrial energy biogenesis were observed in cultured neonatal rat cardiomyocytes, whereas GDF11 silencing elicited the opposite effects to oe-GDF11 in mice. We concluded that telomerase activation by GDF11 contributes to the alleviation of myocardial IR injury through enhancing mitochondrial biogenesis and suppressing cardiomyocyte apoptosis.

Three-dimensional quantitative assessment of myocardial infarction via multimodality fusion imaging: methodology, validation, and preliminary clinical application

Background

The precise assessment of myocardial infarction (MI) is crucial both for therapeutic interventions in old MI and the development of new and effective techniques to repair injured myocardium. A novel method was developed to assess left ventricular (LV) quantitatively infarction through three-dimensional (3D) multimodality fusion based on computed tomography angiography (CTA) and technetium-99m methoxyisobutylisonitrile (^99mTc-MIBI) single-photon emission computed tomography (SPECT) images. This study sought to develop a 3D quantitative method for MI for pre-clinical study and clinical application.

Methods

Three months after the MI models were established in 20 minipigs, CTA and SPECT images were acquired separately, which were then aligned automatically with the constraints of the shape and the whole heart and LV myocardium position. Infarct ratios were quantified based on the 3D fusion images. The quantitative assessment was then experimentally validated via an ex vivo histology analysis using triphenyl-tetrazolium-chloride staining and subsequently applied to post-MI patients (n=8).

Results

The location of an infarct identified by the SPECT was consistent with that identified by an ex vivo heart in a 3D space. Infarct size determined by CTA-SPECT was correlated with infarct size assessed by triphenyl-tetrazolium-chloride pathology {27.6% [interquartile range (IQR) 17.1-34.7%] vs. 24.1% (IQR 14.7-32.5%), r²=0.99, P<0.01}. In clinical cases, the CTA-SPECT 3D fusion quantitative results were significantly correlated with the quantitative perfusion SPECT results (r=0.976, P<0.01).

Conclusions

The proposed 3D fusion quantitative assessment method provides reliable and intuitive evaluations of infarction. This novel quantification technique enables whole heart quantification for the pre-operation evaluation and post-diagnosis management of old MI patients. It could also be applied to the design of 3D-printed cardiac patches.

Progress in cardiac research - from rebooting cardiac regeneration to a complete cell atlas of the heart

We review some of the important discoveries and advances made in basic and translational cardiac research in 2020. For example, in the field of myocardial infarction (MI), new aspects of autophagy and the importance of eosinophils were described. Novel approaches such as a glycocalyx mimetic were used to improve cardiac recovery following MI. The strategy of 3D bio-printing was shown to allow the fabrication of a chambered cardiac organoid. The benefit of combining tissue engineering with paracrine therapy to heal injured myocardium is discussed. We highlight the importance of cell-to cell communication, in particular the relevance of extracellular vesicles such as exosomes, which transport proteins, lipids, non-coding RNAs and mRNAs and actively contribute to angiogenesis and myocardial regeneration. In this rapidly growing field, new strategies were developed to stimulate the release of reparative exosomes in ischaemic myocardium. Single-cell sequencing technology is causing a revolution in the study of transcriptional expression at cellular resolution, revealing unanticipated heterogeneity within cardiomyocytes, pericytes and fibroblasts, and revealing a unique subpopulation of cardiac fibroblasts. Several studies demonstrated that exosome- and non-coding RNA-mediated approaches can enhance human induced pluripotent stem cell (iPSC) viability and differentiation into mature cardiomyocytes. Important details of the mitochondrial Ca2+ uniporter and its relevance were elucidated. Novel aspects of cancer therapeutic-induced cardiotoxicity were described, such as the novel circular RNA circITCH, which may lead to novel treatments. Finally, we provide some insights into the effects of SARS-CoV-2 on the heart.

Meteorin-like/Meteorin-β protects heart against cardiac dysfunction

Meteorin-like/Meteorin-β (Metrnl/Metrnβ) is a secreted protein produced by skeletal muscle and adipose tissue that exerts metabolic actions that improve glucose metabolism. The role of Metrnβ in cardiac disease is completely unknown. Here, we show that Metrnβ-null mice exhibit asymmetrical cardiac hypertrophy, fibrosis, and enhanced signs of cardiac dysfunction in response to isoproterenol-induced cardiac hypertrophy and aging. Conversely, adeno-associated virus-mediated specific overexpression of Metrnβ in the heart prevents the development of cardiac remodeling. Furthermore, Metrnβ inhibits cardiac hypertrophy development in cardiomyocytes in vitro, indicating a direct effect on cardiac cells. Antibody-mediated blockage of Metrnβ in cardiomyocyte cell cultures indicated an autocrine action of Metrnβ on the heart, in addition to an endocrine action. Moreover, Metrnβ is highly produced in the heart, and analysis of circulating Metrnβ concentrations in a large cohort of patients reveals that it is a new biomarker of heart failure with an independent prognostic value.

Novel aspects of age-protection by spermidine supplementation are associated with preserved telomere length

Ageing provokes a plethora of molecular, cellular and physiological deteriorations, including heart failure, neurodegeneration, metabolic maladaptation, telomere attrition and hair loss. Interestingly, on the molecular level, the capacity to induce autophagy, a cellular recycling and cleaning process, declines with age across a large spectrum of model organisms and is thought to be responsible for a subset of age-induced changes. Here, we show that a 6-month administration of the natural autophagy inducer spermidine in the drinking water to aged mice is sufficient to significantly attenuate distinct age-associated phenotypes. These include modulation of brain glucose metabolism, suppression of distinct cardiac inflammation parameters, decreased number of pathological sights in kidney and liver and decrease of age-induced hair loss. Interestingly, spermidine-mediated age protection was associated with decreased telomere attrition, arguing in favour of a novel cellular mechanism behind the anti-ageing effects of spermidine administration.

Estrogen is required for maintaining the quality of cardiac stem cells

Compared to the age-matched men, the incidence of cardiovascular diseases is lower in premenopausal but higher in postmenopausal women, suggesting the cardio-protective role of estrogen in females. Although cardiac stem cells (CSCs) express estrogen receptors, yet the effects of estrogen on CSCs remain unclear. In this study, we investigated the potential role of estrogen in maintaining the quality of CSCs by in vivo and in vitro experiments. For the in vivo study, estrogen deficiency was induced by ovariectomy in 6-weeks-old C57BL/6 female mice, and then randomly given 17β-estradiol (E₂) replacements at a low dose (0.01 mg/60 days) and high dose (0.18 mg/60 days), or vehicle treatment. All mice were killed 2 months after treatments, and heart tissues were collected for ex vivo expansion of CSCs. Compared to age-matched healthy controls, estrogen deficiency slightly decreased the yield of CSCs with significantly lower telomerase activity and more DNA damage. Interestingly, E₂ replacements at low and high doses significantly increased the yield of CSCs and reversed the quality impairment of CSCs following estrogen deficiency. For the in vitro study, twice-passaged CSCs from the hearts of adult healthy female mice were cultured with the supplement of 0.01, 0.1, and 1 μM E₂ in the medium for 3 days. We found that E₂ supplement increased c-kit expression, increased proliferative activity, improved telomerase activity, and reduced DNA damage of CSCs in a dose-dependent manner. Our data suggested the potential role of estrogen in maintaining the quality of CSCs, providing new insight into the cardio-protective effects of estrogen.

Age-Related Pathways in Cardiac Regeneration: A Role for lncRNAs?

Aging imposes a barrier for tissue regeneration. In the heart, aging leads to a severe rearrangement of the cardiac structure and function and to a subsequent increased risk of heart failure. An intricate network of distinct pathways contributes to age-related alterations during healthy heart aging and account for a higher susceptibility of heart disease. Our understanding of the systemic aging process has already led to the design of anti-aging strategies or to the adoption of protective interventions. Nevertheless, our understanding of the molecular determinants operating during cardiac aging or repair remains limited. Here, we will summarize the molecular and physiological alterations that occur during aging of the heart, highlighting the potential role for long non-coding RNAs (lncRNAs) as novel and valuable targets in cardiac regeneration/repair.

Stress reactivity elicits a tissue-specific reduction in telomere length in aging zebrafish (Danio rerio)

Individual differences in personality are associated with variation in healthy aging. Health behaviours are often cited as the likely explanation for this association; however, an underlying biological mechanism may also exist. Accelerated leukocyte telomere shortening is implicated in multiple age-related diseases and is associated with chronic activation of the hypothalamus-pituitary-adrenal (HPA) axis, providing a link between stress-related personality differences and adverse health outcomes. However, the effects of the HPA axis are tissue specific. Thus, leukocyte telomere length may not accurately reflect telomere length in disease-relevant tissues. Here, we examined the correlation between stress reactivity and telomere length in heart and brain tissue in young (6-9 month) and aging (18 month) zebrafish. Stress reactivity was assessed by tank diving and through gene expression. Telomere length was assessed using quantitative PCR. We show that aging zebrafish have shorter telomeres in both heart and brain. Telomere length was inversely related to stress reactivity in heart but not brain of aging individuals. These data support the hypotheses that an anxious predisposition contributes to accelerated telomere shortening in heart tissue, which may have important implications for our understanding of age-related heart disease, and that stress reactivity contributes to age-related telomere shortening in a tissue-specific manner.

GDF15 as a biomarker of ageing

The ageing process is accompanied by the gradual development of chronic systemic inflammation (inflamm-ageing). Growth differentiation factor 15 (GDF15) is associated with inflammation and known to be a stress-induced factor. The present study aimed to explore the association of GDF15 with ageing. In this cross-sectional study, serum GDF15, hematological parameters, and biomedical parameters were determined in 120 healthy individuals (23-83 years old, males). Three telomere related parameters, including telomere length, telomerase activity, and the expression of human telomerase reverse transcriptase (hTERT) mRNA were also quantified. Our results showed that the older group has a higher levels of GDF15 and lower expression of hTERT mRNA, and PBMC telomerase activity (p < 0.001). In individuals with high GDF15 levels, they were older, and presented with the lower level of hTERT mRNA and T/S ratio (p < 0.01). Spearman correlation analysis shows that GDF15 positively correlated with age (r = 0.664, p < 0.001), and negatively correlated with telomere length (r = -0.434, p < 0.001), telomerase activity (r = -0.231, p = 0.012), and hTERT mRNA (r = -0.206, p = 0.024). Furthermore, in multivariate regression analysis, GDF15 levels showed a statistically significant linear and negative relationship with PBMC telomerase activity (β-coefficient = -0.583, 95% CI -1.044 to -0.122, p = 0.014), telomere length (β-coefficient = -0.200, 95% CI -0.305 to -0.094, p < 0.001), and hTERT mRNA (β-coefficient = -0.207, 95% CI -0.312 to -0.102, p < 0.001) after adjusting for confounders. These results support that circulating GDF15 is the potential biomarker of ageing that may influence the risk and progression of multiple ageing conditions.

Telomerase therapy attenuates cardiotoxic effects of doxorubicin

Doxorubicin is one of the most potent chemotherapeutic agents. However, its clinical use is restricted due to the severe risk of cardiotoxicity, partially attributed to elevated production of reactive oxygen species (ROS). Telomerase canonically maintains telomeres during cell division but is silenced in adult hearts. In non-dividing cells such as cardiomyocytes, telomerase confers pro-survival traits, likely owing to the detoxification of ROS. Therefore, we hypothesized that pharmacological overexpression of telomerase may be used as a therapeutic strategy for the prevention of doxorubicin-induced cardiotoxicity. We used adeno-associated virus (AAV)-mediated gene therapy for long-term expression of telomerase in in vitro and in vivo models of doxorubicin-induced cardiotoxicity. Overexpression of telomerase protected the heart from doxorubicin-mediated apoptosis and rescued cardiac function, which was accompanied by preserved cardiomyocyte size. At the mechanistic level, we observed altered mitochondrial morphology and dynamics in response to telomerase expression. Complementary in vitro experiments confirmed the anti-apoptotic effects of telomerase overexpression in human induced pluripotent stem cell-derived cardiomyocytes after doxorubicin treatment. Strikingly, elevated levels of telomerase translocated to the mitochondria upon doxorubicin treatment, which helped to maintain mitochondrial function. Thus, telomerase gene therapy could be a novel preventive strategy for cardiotoxicity by chemotherapy agents such as the anthracyclines.

Telomeres and telomerase in risk assessment of cardiovascular diseases

Telomeres are repetitive nucleoprotein structures located at the ends of chromosomes. Reduction in the number of repetitions causes cell senescence. Cells with high proliferative potential age with each replication cycle. Post-mitotic cells (e.g. cardiovascular cells) have a different aging mechanism. During the aging of cardiovascular system cells, permanent DNA damage occurs in the telomeric regions caused by mitochondrial dysfunction, which is a phenomenon independent of cell proliferation and telomere length. Mitochondrial dysfunction is accompanied by increased production of reactive oxygen species and development of inflammation. This phenomenon in the cells of blood vessels can lead to atherosclerosis development. Telomere damage in cardiomyocytes leads to the activation of the DNA damage response system, histone H2A.X phosphorylation, p53 activation and p21 and p16 protein synthesis, resulting in the SASP phenotype (senescence-associated secretory phenotype), increased inflammation and cardiac dysfunction. Cardiovascular cells show the activity of the TERT subunit of telomerase, an enzyme that prevents telomere shortening. It turns out that disrupting the activity of this enzyme can also contribute to the formation of cardiovascular diseases. Measurements of telomere length according to the "blood-muscle" model may help in the future to assess the risk of cardiovascular complications in people undergoing cardiological procedures, as well as to assess the effectiveness of some drugs.

Aging impairs alveolar epithelial type II cell function in acute lung injury

Morbidity and mortality rates in acute lung injury (ALI) increase with age. As alveolar epithelial type II cells (AE2) are crucial for lung function and repair, we hypothesized that aging promotes senescence in AE2 and contributes to the severity and impaired regeneration in ALI. ALI was induced with 2.5 μg lipopolysaccharide/g body weight in young (3 mo) and old (18 mo) mice that were euthanized 24 h, 72 h, and 10 days later. Lung function, pulmonary surfactant activity, stereology, cell senescence, and single-cell RNA sequencing analyses were performed to investigate AE2 function in aging and ALI. In old mice, surfactant activity was severely impaired. A 60% mortality rate and lung function decline were observed in old, but not in young, mice with ALI. AE2 of young mice adapted to injury by increasing intracellular surfactant volume and proliferation rate. In old mice, however, this adaptive response was compromised, and AE2 of old mice showed signs of cell senescence, increased inflammatory signaling, and impaired surfactant metabolism in ALI. These findings provide evidence that ALI promotes a limited proliferation rate, increased inflammatory response, and surfactant dysfunction in old, but not in young, mice, supporting an impaired regenerative capacity and reduced survival rate in ALI with advancing age.

Telomerase activation in the treatment of aging or degenerative diseases: a systematic review

Telomeres are protective structures that are shortened during the lifetime, resulting in aging and degenerative diseases. Subjects experiencing aging and degenerative disorders present smaller telomeres than young and healthy ones. The size of these structures can be stabilized by telomerase, an enzyme which is inactive in adult tissues but functional in fetal and newborn tissues and adult testes and ovaries. The aim of this study was to perform a systematic review to evaluate the effect of telomerase activation in the treatment of degenerative and aging disorders. We accomplished the search using the Pubmed interface for papers published from September 1985 to April 16th, 2020. We found twenty one studies that matched our eligibility criteria. I concluded that telomerase is probably a potential and safe treatment for aging and degenerative diseases, demonstrating neither side effects nor risk of cancer in the selected studies. Further studies in humans are needed to confirm safety and efficiency of this treatment.

Sodium nitrate co-supplementation does not exacerbate low dose metronomic doxorubicin-induced cachexia in healthy mice

The purpose of this study was to determine whether (1) sodium nitrate (SN) treatment progressed or alleviated doxorubicin (DOX)-induced cachexia and muscle wasting; and (2) if a more-clinically relevant low-dose metronomic (LDM) DOX treatment regimen compared to the high dosage bolus commonly used in animal research, was sufficient to induce cachexia in mice. Six-week old male Balb/C mice (n = 16) were treated with three intraperitoneal injections of either vehicle (0.9% NaCl; VEH) or DOX (4 mg/kg) over one week. To test the hypothesis that sodium nitrate treatment could protect against DOX-induced symptomology, a group of mice (n = 8) were treated with 1 mM NaNO₃ in drinking water during DOX (4 mg/kg) treatment (DOX + SN). Body composition indices were assessed using echoMRI scanning, whilst physical and metabolic activity were assessed via indirect calorimetry, before and after the treatment regimen. Skeletal and cardiac muscles were excised to investigate histological and molecular parameters. LDM DOX treatment induced cachexia with significant impacts on both body and lean mass, and fatigue/malaise (i.e. it reduced voluntary wheel running and energy expenditure) that was associated with oxidative/nitrostative stress sufficient to induce the molecular cytotoxic stress regulator, nuclear factor erythroid-2-related factor 2 (NRF-2). SN co-treatment afforded no therapeutic potential, nor did it promote the wasting of lean tissue. Our data re-affirm a cardioprotective effect for SN against DOX-induced collagen deposition. In our mouse model, SN protected against LDM DOX-induced cardiac fibrosis but had no effect on cachexia at the conclusion of the regimen.

Long noncoding RNA in cardiac aging and disease

Cardiovascular diseases (CVDs) are the main cause of morbidity and mortality in Western society and present an important age-related risk. With the constant rise in life expectancy, prevalence of CVD in the population will likely increase further. New therapies, especially in the elderly, are needed to combat CVD. This review is focused on the role of long noncoding RNA (lncRNA) in CVD. RNA sequencing experiments in the past decade showed that most RNA does not code for protein, but many RNAs function as ncRNA. Here, we summarize the recent findings of lncRNA regulation in the diseased heart. The potential use of these RNAs as biomarkers of cardiac disease prediction is also discussed.

Low-Level Nanog Expression in the Regulation of Quiescent Endothelium

Supplemental Digital Content is available in the text.

Nanog is expressed in adult endothelial cells (ECs) at a low-level, however, its functional significance is not known. The goal of our study was to elucidate the role of Nanog in adult ECs using a genetically engineered mouse model system.

Telomerase gene therapy ameliorates the effects of neurodegeneration associated to short telomeres in mice

Neurodegenerative diseases associated with old age such as Alzheimer’s disease present major problems for society, and they currently have no cure. The telomere protective caps at the ends of chromosomes shorten with age, and when they become critically short, they can induce a persistent DNA damage response at chromosome ends, triggering secondary cellular responses such as cell death and cellular senescence. Mice and humans with very short telomeres owing to telomerase deficiencies have an earlier onset of pathologies associated with loss of the regenerative capacity of tissues. However, the effects of short telomeres in very low proliferative tissues such as the brain have not been thoroughly investigated. Here, we describe a mouse model of neurodegeneration owing to presence of short telomeres in the brain as the consequence of telomerase deficiency. Interestingly, we find similar signs of neurodegeneration in very old mice as the consequence of physiological mouse aging. Next, we demonstrate that delivery of telomerase gene therapy to the brain of these mice results in amelioration of some of these neurodegeneration phenotypes. These findings suggest that short telomeres contribute to neurodegeneration diseases with aging and that telomerase activation may have a therapeutic value in these diseases.

Cardiomyocyte ageing and cardioprotection: consensus document from the ESC working groups cell biology of the heart and myocardial function

Advanced age is a major predisposing risk factor for the incidence of coronary syndromes and comorbid conditions which impact the heart response to cardioprotective interventions. Advanced age also significantly increases the risk of developing post-ischaemic adverse remodelling and heart failure after ischaemia/reperfusion (IR) injury. Some of the signalling pathways become defective or attenuated during ageing, whereas others with well-known detrimental consequences, such as glycoxidation or proinflammatory pathways, are exacerbated. The causative mechanisms responsible for all these changes are yet to be elucidated and are a matter of active research. Here, we review the current knowledge about the pathophysiology of cardiac ageing that eventually impacts on the increased susceptibility of cells to IR injury and can affect the efficiency of cardioprotective strategies.

The molecular biomarkers of vascular aging and atherosclerosis: telomere length and mitochondrial DNA4977 common deletion

Age is the dominant risk factor for the most prevalent atherosclerotic vascular diseases, including coronary artery disease, myocardial infarction, cerebrovascular disease and stroke. In human, telomere erosion and mitochondrial DNA (mtDNA) damage play a central role in the mechanisms leading to cellular aging decline. This review summarizes the most relevant findings on the role of telomere shortening and the common mtDNA⁴⁹⁷⁷ deletion in the progression and evolution of atherosclerosis by combining insight from experimental models and human clinical studies. The current evidence shows a link between telomere erosion and compromised mitochondrial function and provides a new perspective regarding their potential role as clinical biomarkers and therapeutic targets.

Overexpression of the histidine triad nucleotide-binding protein 2 protects cardiac function in the adult mice after acute myocardial infarction

AIM

To explore the role of the histidine triad nucleotide-binding 2 (HINT2) protein in heart failure.

METHODS

Neonatal mouse ventricle myocytes (NMVMs) and myocardial infarction-induced heart failure mice were used for in vitro or in vivo experiments. Adenovirus (ADV) and adeno-associated virus serum type 9 (AAV9) vectors were used to regulate HINT2 expression. The expression of HINT2 was determined by quantifying the mRNA and protein levels. Cell survival was analysed using the CCK-8 kit and TUNEL staining. Mitochondrial function was determined by the mitochondrial membrane potential and oxygen consumption rates. AAV9-HINT2 was injected 24 h post-myocardial infarction following which transthoracic echocardiography and histological analyses were performed after 4 weeks. Positron emission tomography tomography-computed tomography (PET/CT) and targeted metabolomics analyses were used to explore the metabolic status in vivo. NAD levels were measured using a colorimetric kit. Computer-simulated rigid body molecular docking was performed using AUTODOCK4. Molecule binding kinetics assays were performed using biolayer interferometry.

RESULTS

HINT2 was down-regulated in NMVMs in hypoxia. ADV-HINT2-induced HINT2 overexpression improved NMVM survival after exposure to hypoxia. Mitochondrial function was preserved in the ADV-HINT2 group under hypoxic conditions. In vivo experiments showed that cardiac function and metabolic status was preserved by HINT2 overexpression. HINT2 overexpression restored mitochondrial NAD levels; this was dependent on nicotinamide mononucleotide (NMN). Using computer-simulated molecular docking analysis and biolayer interferometry, we observed that HINT2 potentially binds and associates with NMN.

CONCLUSION

HINT2 overexpression protects cardiac function in adult mice after myocardial infarction by maintaining mitochondrial NAD homeostasis.