Age-dependent expression of fibrosis-related genes and collagen deposition in the rat myocardium

The Senescent Heart-"Age Doth Wither Its Infinite Variety"

Cardiovascular diseases are a leading cause of morbidity and mortality world-wide. While many factors like smoking, hypertension, diabetes, dyslipidaemia, a sedentary lifestyle, and genetic factors can predispose to cardiovascular diseases, the natural process of aging is by itself a major determinant of the risk. Cardiac aging is marked by a conglomerate of cellular and molecular changes, exacerbated by age-driven decline in cardiac regeneration capacity. Although the phenotypes of cardiac aging are well characterised, the underlying molecular mechanisms are far less explored. Recent advances unequivocally link cardiovascular aging to the dysregulation of critical signalling pathways in cardiac fibroblasts, which compromises the critical role of these cells in maintaining the structural and functional integrity of the myocardium. Clearly, the identification of cardiac fibroblast-specific factors and mechanisms that regulate cardiac fibroblast function in the senescent myocardium is of immense importance. In this regard, recent studies show that Discoidin domain receptor 2 (DDR2), a collagen-activated receptor tyrosine kinase predominantly located in cardiac fibroblasts, has an obligate role in cardiac fibroblast function and cardiovascular fibrosis. Incisive studies on the molecular basis of cardiovascular aging and dysregulated fibroblast function in the senescent heart would pave the way for effective strategies to mitigate cardiovascular diseases in a rapidly growing elderly population.

Cardiac Molecular Analysis Reveals Aging-Associated Metabolic Alterations Promoting Glycosaminoglycans Accumulation Via Hexosamine Biosynthetic Pathway

Age is a prominent risk factor for cardiometabolic disease, and often leads to heart structural and functional changes. However, precise molecular mechanisms underlying cardiac remodeling and dysfunction resulting from physiological aging per se remain elusive. Understanding these mechanisms requires biological models with optimal translation to humans. Previous research demonstrated that baboons undergo age-related reduction in ejection fraction and increased heart sphericity, mirroring changes observed in humans. The goal of this study was to identify early cardiac molecular alterations that precede functional adaptations, shedding light on the regulation of age-associated changes. We performed unbiased transcriptomics of left ventricle (LV) samples from female baboons aged 7.5-22.1 years (human equivalent ~30-88 years). Weighted-gene correlation network and pathway enrichment analyses were performed to identify potential age-associated mechanisms in LV, with histological validation. Myocardial modules of transcripts negatively associated with age were primarily enriched for cardiac metabolism, including oxidative phosphorylation, tricarboxylic acid cycle, glycolysis, and fatty-acid β-oxidation. Transcripts positively correlated with age suggest upregulation of glucose uptake, pentose phosphate pathway, and hexosamine biosynthetic pathway (HBP), indicating a metabolic shift towards glucose-dependent anabolic pathways. Upregulation of HBP commonly results in increased glycosaminoglycan precursor synthesis. Transcripts involved in glycosaminoglycan synthesis, modification, and intermediate metabolism were also upregulated in older animals, while glycosaminoglycan degradation transcripts were downregulated with age. These alterations would promote glycosaminoglycan accumulation, which was verified histologically. Upregulation of extracellular matrix (ECM)-induced signaling pathways temporally coincided with glycosaminoglycan accumulation. We found a subsequent upregulation of cardiac hypertrophy-related pathways and an increase in cardiomyocyte width. Overall, our findings revealed a transcriptional shift in metabolism from catabolic to anabolic pathways that leads to ECM glycosaminoglycan accumulation through HBP prior to upregulation of transcripts of cardiac hypertrophy-related pathways. This study illuminates cellular mechanisms that precede development of cardiac hypertrophy, providing novel potential targets to remediate age-related cardiac diseases.

A defective mechanosensing pathway affects fibroblast-to-myofibroblast transition in the old male mouse heart

The cardiac fibroblast interacts with an extracellular matrix (ECM), enabling myofibroblast maturation via a process called mechanosensing. Although in the aging male heart, ECM is stiffer than in the young mouse, myofibroblast development is impaired, as demonstrated in 2-D and 3-D experiments. In old male cardiac fibroblasts, we found a decrease in actin polymerization, α-smooth muscle actin (α-SMA), and Kindlin-2 expressions, the latter an effector of the mechanosensing. When Kindlin-2 levels were manipulated via siRNA interference, young fibroblasts developed an old-like fibroblast phenotype, whereas Kindlin-2 overexpression in old fibroblasts reversed the defective phenotype. Finally, inhibition of overactivated extracellular regulated kinases 1 and 2 (ERK1/2) in the old male fibroblasts rescued actin polymerization and α-SMA expression. Pathological ERK1/2 overactivation was also attenuated by Kindlin-2 overexpression. In contrast, old female cardiac fibroblasts retained an operant mechanosensing pathway. In conclusion, we identified defective components of the Kindlin/ERK/actin/α-SMA mechanosensing axis in aged male fibroblasts.

Senescent cardiac fibroblasts: A key role in cardiac fibrosis

Cardiac fibroblasts are a cell population that controls the homeostasis of the extracellular matrix and orchestrates a damage response to maintain cardiac architecture and performance. Due to these functions, fibroblasts play a central role in cardiac fibrosis development, and there are large differences in matrix protein secretion profiles between fibroblasts from aged versus young animals. Senescence is a multifactorial and complex process that has been associated with inflammatory and fibrotic responses. After damage, transient cellular senescence is usually beneficial, as these cells promote tissue repair. However, the persistent presence of senescent cells within a tissue is linked with fibrosis development and organ dysfunction, leading to aging-related diseases such as cardiovascular pathologies. In the heart, early cardiac fibroblast senescence after myocardial infarction seems to be protective to avoid excessive fibrosis; however, in non-infarcted models of cardiac fibrosis, cardiac fibroblast senescence has been shown to be deleterious. Today, two new classes of drugs, termed senolytics and senostatics, which eliminate senescent cells or modify senescence-associated secretory phenotype, respectively, arise as novel therapeutical strategies to treat aging-related pathologies. However, further studies will be needed to evaluate the extent of the utility of senotherapeutic drugs in cardiac diseases, in which pathological context and temporality of the intervention must be considered.

MiR-29a Increase in Aging May Function as a Compensatory Mechanism Against Cardiac Fibrosis Through SERPINH1 Downregulation

Deregulation of microRNA (miRNA) profile has been reportedly linked to the aging process, which is a dominant risk factor for many pathologies. Among the miRNAs with documented roles in aging-related cardiac diseases, miR-18a, -21a, -22, and -29a were mainly associated with hypertrophy and/or fibrosis; however, their relationship to aging was not fully addressed before. The purpose of this paper was to evaluate the variations in the expression levels of these miRNAs in the aging process. To this aim, multiple organs were harvested from young (2–3-months-old), old (16–18-months-old), and very old (24–25-months-old) mice, and the abundance of the miRNAs was evaluated by quantitative real-time (RT)-PCR. Our studies demonstrated that miR-21a, miR-22, and miR-29a were upregulated in the aged heart. Among them, miR-29a was highly expressed in many other organs, i.e., the brain, the skeletal muscle, the pancreas, and the kidney, and its expression was further upregulated during the natural aging process. Western blot, immunofluorescence, and xCELLigence analyses concurrently indicated that overexpression of miR-29a in the muscle cells decreased the collagen levels as well as cell migration and proliferation. Computational prediction analysis and overexpression studies identified SERPINH1, a specific chaperone of procollagens, as a potential miR-29a target. Corroborating to this, significantly downregulated SERPINH1 levels were found in the skeletal muscle, the heart, the brain, the kidney, and the pancreas harvested from very old animals, thereby indicating the role of the miR-29a-SERPINH1 axis in the aging process. In vitro analysis of miR-29a effects on fibroblast and cardiac muscle cells pointed toward a protective role of miR-29a on aging-related fibrosis, by reducing cell migration and proliferation. In conclusion, our study indicates an adaptive increase of miR-29 in the natural aging process and suggests its role as a transcriptional repressor of SERPINH1, with a potential therapeutic value against adverse matrix remodeling and aging-associated tissue fibrosis.

Transforming growth factor-β in myocardial disease

Transforming growth factor-β (TGFβ) isoforms are upregulated and activated in myocardial diseases and have an important role in cardiac repair and remodelling, regulating the phenotype and function of cardiomyocytes, fibroblasts, immune cells and vascular cells. Cardiac injury triggers the generation of bioactive TGFβ from latent stores, through mechanisms involving proteases, integrins and specialized extracellular matrix (ECM) proteins. Activated TGFβ signals through the SMAD intracellular effectors or through non-SMAD cascades. In the infarcted heart, the anti-inflammatory and fibroblast-activating actions of TGFβ have an important role in repair; however, excessive or prolonged TGFβ signalling accentuates adverse remodelling, contributing to cardiac dysfunction. Cardiac pressure overload also activates TGFβ cascades, which initially can have a protective role, promoting an ECM-preserving phenotype in fibroblasts and preventing the generation of injurious, pro-inflammatory ECM fragments. However, prolonged and overactive TGFβ signalling in pressure-overloaded cardiomyocytes and fibroblasts can promote cardiac fibrosis and dysfunction. In the atria, TGFβ-mediated fibrosis can contribute to the pathogenic substrate for atrial fibrillation. Overactive or dysregulated TGFβ responses have also been implicated in cardiac ageing and in the pathogenesis of diabetic, genetic and inflammatory cardiomyopathies. This Review summarizes the current evidence on the role of TGFβ signalling in myocardial diseases, focusing on cellular targets and molecular mechanisms, and discussing challenges and opportunities for therapeutic translation.

Imaging tools for assessment of myocardial fibrosis in humans: the need for greater detail

Myocardial fibrosis is recognized as a key pathological process in the development of cardiac disease and a target for future therapeutics. Despite this recognition, the assessment of fibrosis is not a part of routine clinical practice. This is primarily due to the difficulties in obtaining an accurate assessment of fibrosis non-invasively. Moreover, there is a clear discrepancy between the understandings of myocardial fibrosis clinically where fibrosis is predominately studied with comparatively low-resolution medical imaging technologies like MRI compared with the basic science laboratories where fibrosis can be visualized invasively with high resolution using molecularly specific fluorescence microscopes at the microscopic and nanoscopic scales. In this article, we will first review current medical imaging technologies for assessing fibrosis including echo and MRI. We will then highlight the need for greater microscopic and nanoscopic analysis of human tissue and how this can be addressed through greater utilization of human tissue available through endomyocardial biopsies and cardiac surgeries. We will then describe the relatively new field of molecular imaging that promises to translate research findings to the clinical practice by non-invasively monitoring the molecular signature of fibrosis in patients.

Exogenous Hydrogen Sulfide Ameliorates Diabetic Myocardial Fibrosis by Inhibiting Cell Aging Through SIRT6/AMPK Autophagy

Stress aging of myocardial cells participates in the mechanism of myocardial fibrosis (MF). Previous studies have shown that hydrogen sulfide (H₂S) can improve MF, however the specific internal mechanism remains still unclear. Therefore, this study aims to explore whether H₂S can improve myocardial cell aging induced by high glucose and myocardial fibrosis in diabetic rats by activating autophagy through SIRT6/AMPK. We observed that HG (high glucose, 33 mM) induced down-regulation of endogenous H₂S-producing enzyme CSE protein expression, increased cell senescence, down-regulation of autophagy-related proteins Beclin1, Atg5, Atg12, Atg16L1, and inhibition of SIRT6/AMPK signaling pathway in H9c2 cardiomyocytes. H₂S (NaHS: 400 μM) could up-regulate CSE protein expression, inhibit cell senescence, activate autophagy and SIRT6/AMPK signaling pathway. On the contrary, no above phenomena was achieved upon addition of CSE inhibitor PAG (dl-propargylglycine: mmol/L). In order to further elucidate the relationship between H₂S and SIRT6/AMPK signaling pathway, dorsomorphin dihydrochloride (Dor), an inhibitor of AMPK signaling pathway, was added to observe the reversal of H₂S’s inhibitory effect on myocardial cell aging. At the same, streptozotocin (STZ; 40 mg/kg) was injected intraperitoneally to build an animal model of diabetic SD rats. The results showed that myocardial collagen fibers were significantly deposited, myocardial tissue senescent cells were significantly increased and the expression of CSE protein was down-regulated, while SIRT6/AMPK signaling pathway and cell autophagy were significantly inhibited. H₂S-treated (NaHS; 56 μmol/kg) could significantly reverse the above phenomenon. In conclusion, these findings suggest that exogenous H₂S can inhibit myocardial cell senescence and improve diabetic myocardial fibrosis by activating CSE and autophagy through SIRT6/AMPK signaling pathway.

Cardiac tissue remodeling in healthy aging: the road to pathology

This review aims to highlight the normal physiological remodeling that occurs in healthy aging hearts, including changes that occur in contractility, conduction, valve function, large and small coronary vessels, and the extracellular matrix. These "normal" age-related changes serve as the foundation that supports decreased plasticity and limited ability for tissue remodeling during pathophysiological states such as myocardial ischemia and heart failure. This review will identify populations at greater risk for poor tissue remodeling in advanced age along with present and future therapeutic strategies that may ameliorate dysfunctional tissue remodeling in aging hearts.

The Extracellular Matrix in Ischemic and Nonischemic Heart Failure

The ECM (extracellular matrix) network plays a crucial role in cardiac homeostasis, not only by providing structural support, but also by facilitating force transmission, and by transducing key signals to cardiomyocytes, vascular cells, and interstitial cells. Changes in the profile and biochemistry of the ECM may be critically implicated in the pathogenesis of both heart failure with reduced ejection fraction and heart failure with preserved ejection fraction. The patterns of molecular and biochemical ECM alterations in failing hearts are dependent on the type of underlying injury. Pressure overload triggers early activation of a matrix-synthetic program in cardiac fibroblasts, inducing myofibroblast conversion, and stimulating synthesis of both structural and matricellular ECM proteins. Expansion of the cardiac ECM may increase myocardial stiffness promoting diastolic dysfunction. Cardiomyocytes, vascular cells and immune cells, activated through mechanosensitive pathways or neurohumoral mediators may play a critical role in fibroblast activation through secretion of cytokines and growth factors. Sustained pressure overload leads to dilative remodeling and systolic dysfunction that may be mediated by changes in the interstitial protease/antiprotease balance. On the other hand, ischemic injury causes dynamic changes in the cardiac ECM that contribute to regulation of inflammation and repair and may mediate adverse cardiac remodeling. In other pathophysiologic conditions, such as volume overload, diabetes mellitus, and obesity, the cell biological effectors mediating ECM remodeling are poorly understood and the molecular links between the primary insult and the changes in the matrix environment are unknown. This review article discusses the role of ECM macromolecules in heart failure, focusing on both structural ECM proteins (such as fibrillar and nonfibrillar collagens), and specialized injury-associated matrix macromolecules (such as fibronectin and matricellular proteins). Understanding the role of the ECM in heart failure may identify therapeutic targets to reduce geometric remodeling, to attenuate cardiomyocyte dysfunction, and even to promote myocardial regeneration.

Extracellular matrix roles in cardiorenal fibrosis: Potential therapeutic targets for CVD and CKD in the elderly

Whereas hypertension, diabetes, and dyslipidemia are age-related risk factors for cardiovascular disease (CVD) and chronic kidney disease (CKD), aging alone is an independent risk factor. With advancing age, the heart and kidney gradually but significantly undergo inflammation and subsequent fibrosis, which eventually results in an irreversible decline in organ physiology. Through cardiorenal network interactions, cardiac dysfunction leads to and responds to renal injury, and both facilitate aging effects. Thus, a comprehensive strategy is needed to evaluate the cardiorenal aging network. Common hallmarks shared across systems include extracellular matrix (ECM) accumulation, along with upregulation of matrix metalloproteinases (MMPs) including MMP-9. The wide range of MMP-9 substrates, including ECM components and inflammatory cytokines, implicates MMP-9 in a variety of pathological and age-related processes. In particular, there is strong evidence that inflammatory cell-derived MMP-9 exacerbates cardiorenal aging. This review explores the potential therapeutic targets against CVD and CKD in the elderly, focusing on ECM and MMP roles.

Engineering cardiac microphysiological systems to model pathological extracellular matrix remodeling

Many cardiovascular diseases are associated with pathological remodeling of the extracellular matrix (ECM) in the myocardium. ECM remodeling is a complex, multifactorial process that often contributes to declines in myocardial function and progression toward heart failure. However, the direct effects of the many forms of ECM remodeling on myocardial cell and tissue function remain elusive, in part because conventional model systems used to investigate these relationships lack robust experimental control over the ECM. To address these shortcomings, microphysiological systems are now being developed and implemented to establish direct relationships between distinct features in the ECM and myocardial function with unprecedented control and resolution in vitro. In this review, we will first highlight the most prominent characteristics of ECM remodeling in cardiovascular disease and describe how these features can be mimicked with synthetic and natural biomaterials that offer independent control over multiple ECM-related parameters, such as rigidity and composition. We will then detail innovative microfabrication techniques that enable precise regulation of cellular architecture in two and three dimensions. We will also describe new approaches for quantifying multiple aspects of myocardial function in vitro, such as contractility, action potential propagation, and metabolism. Together, these collective technologies implemented as cardiac microphysiological systems will continue to uncover important relationships between pathological ECM remodeling and myocardial cell and tissue function, leading to new fundamental insights into cardiovascular disease, improved human disease models, and novel therapeutic approaches.

Traction force microscopy of engineered cardiac tissues

Cardiac tissue development and pathology have been shown to depend sensitively on microenvironmental mechanical factors, such as extracellular matrix stiffness, in both in vivo and in vitro systems. We present a novel quantitative approach to assess cardiac structure and function by extending the classical traction force microscopy technique to tissue-level preparations. Using this system, we investigated the relationship between contractile proficiency and metabolism in neonate rat ventricular myocytes (NRVM) cultured on gels with stiffness mimicking soft immature (1 kPa), normal healthy (13 kPa), and stiff diseased (90 kPa) cardiac microenvironments. We found that tissues engineered on the softest gels generated the least amount of stress and had the smallest work output. Conversely, cardiomyocytes in tissues engineered on healthy- and disease-mimicking gels generated significantly higher stresses, with the maximal contractile work measured in NRVM engineered on gels of normal stiffness. Interestingly, although tissues on soft gels exhibited poor stress generation and work production, their basal metabolic respiration rate was significantly more elevated than in other groups, suggesting a highly ineffective coupling between energy production and contractile work output. Our novel platform can thus be utilized to quantitatively assess the mechanotransduction pathways that initiate tissue-level structural and functional remodeling in response to substrate stiffness.

Cardiac fibrosis in the ageing heart: Contributors and mechanisms

Cardiac fibrosis refers to an excessive deposition of extracellular matrix (ECM) in cardiac tissue. Fibrotic tissue is stiffer and less compliant, resulting in subsequent cardiac dysfunction and heart failure. Cardiac fibrosis in the ageing heart may involve activation of fibrogenic signalling and inhibition of anti-fibrotic signalling, leading to an imbalance of ECM turnover. Excessive accumulation of ECM such as collagen in older patients contributes to progressive ventricular dysfunction. Overexpression of collagen is derived from various sources, including higher levels of fibrogenic growth factors, proliferation of fibroblasts and cellular transdifferentiation. These may be triggered by factors, such as oxidative stress, inflammation, hypertension, cellular senescence and cell death, contributing to age-related fibrotic cardiac remodelling. In this review, we will discuss the fibrogenic contributors in age-related cardiac fibrosis, and the potential mechanisms by which fibrogenic processes can be interrupted for therapeutic intent.

The impact of aging on cardiac extracellular matrix

Age-related changes in cardiac homeostasis can be observed at the cellular, extracellular, and tissue levels. Progressive cardiomyocyte hypertrophy, inflammation, and the gradual development of cardiac fibrosis are hallmarks of cardiac aging. In the absence of a secondary insult such as hypertension, these changes are subtle and result in slight to moderate impaired myocardial function, particularly diastolic function. While collagen deposition and cross-linking increase during aging, extracellular matrix (ECM) degradation capacity also increases due to increased expression of matrix metalloproteinases (MMPs). Of the MMPs elevated with cardiac aging, MMP-9 has been extensively evaluated and its roles are reviewed here. In addition to proteolytic activity on ECM components, MMPs oversee cell signaling during the aging process by modulating cytokine, chemokine, growth factor, hormone, and angiogenic factor expression and activity. In association with elevated MMP-9, macrophage numbers increase in an age-dependent manner to regulate the ECM and angiogenic responses. Understanding the complexity of the molecular interactions between MMPs and the ECM in the context of aging may provide novel diagnostic indicators for the early detection of age-related fibrosis and cardiac dysfunction.

Aging and the cardiac collagen matrix: Novel mediators of fibrotic remodelling

Cardiovascular disease is a leading cause of death worldwide and there is a pressing need for new therapeutic strategies to treat such conditions. The risk of developing cardiovascular disease increases dramatically with age, yet the majority of experimental research is executed using young animals. The cardiac extracellular matrix (ECM), consisting predominantly of fibrillar collagen, preserves myocardial integrity, provides a means of force transmission and supports myocyte geometry. Disruptions to the finely balanced control of collagen synthesis, post-synthetic deposition, post-translational modification and degradation may have detrimental effects on myocardial functionality. It is now well established that the aged heart is characterized by fibrotic remodelling, but the mechanisms responsible for this are incompletely understood. Furthermore, studies using aged animal models suggest that interstitial remodelling with disease may be age-dependent. Thus with the identification of new therapeutic strategies targeting fibrotic remodelling, it may be necessary to consider age-dependent mechanisms. In this review, we discuss remodelling of the cardiac collagen matrix as a function of age, whilst highlighting potential novel mediators of age-dependent fibrotic pathways.

Interactions of Short-Term and Chronic Treadmill Training With Aging of the Left Ventricle of the Heart

With aging, there is a decline in cardiac function accompanying increasing risk of arrhythmias. These effects are likely to be mechanistically associated with age-associated changes in calcium regulation within cardiac myocytes. Previous studies suggest that lifelong exercise can potentially reduce age-associated changes in the heart. Although exercise itself is associated with changes in cardiac function, little is known about the interactions of aging and exercise with respect to myocyte calcium regulation. To investigate this, adult (12 months) and old (24 months) C57/Bl6 mice were trained using moderate-intensity treadmill running. In response to 10 weeks’ training, comparable cardiac hypertrophic responses were observed, although aging independently associated with additional cardiac hypertrophy. Old animals also showed increased L- and T-type calcium channels, the sodium–calcium exchange, sarcoendoplasmic reticulum calcium ATPase, and collagen (by 50%, 92%, 66%, 88%, and 113% respectively). Short-term exercise training increased D-type and T-type calcium channels in old animals only, whereas an increase in sodium–calcium exchange was seen only in adult animals. Long-term (12 months) training generally opposed the effects of aging. Significant hypertrophy remained in long-term trained old animals, but levels of sarcoendoplasmic reticulum calcium ATPase, sodium–calcium exchange, and collagen were not significantly different from those found in the adult trained animals.

Matrix elasticity regulates the optimal cardiac myocyte shape for contractility

Concentric hypertrophy is characterized by ventricular wall thickening, fibrosis, and decreased myocyte length-to-width aspect ratio. Ventricular thickening is considered compensatory because it reduces wall stress, but the functional consequences of cell shape remodeling in this pathological setting are unknown. We hypothesized that decreases in myocyte aspect ratio allow myocytes to maximize contractility when the extracellular matrix becomes stiffer due to conditions such as fibrosis. To test this, we engineered neonatal rat ventricular myocytes into rectangles mimicking the 2-D profiles of healthy and hypertrophied myocytes on hydrogels with moderate (13 kPa) and high (90 kPa) elastic moduli. Actin alignment was unaffected by matrix elasticity, but sarcomere content was typically higher on stiff gels. Microtubule polymerization was higher on stiff gels, implying increased intracellular elastic modulus. On moderate gels, myocytes with moderate aspect ratios (∼7:1) generated the most peak systolic work compared with other cell shapes. However, on stiffer gels, low aspect ratios (∼2:1) generated the most peak systolic work. To compare the relative contributions of intracellular vs. extracellular elasticity to contractility, we developed an analytical model and used our experimental data to fit unknown parameters. Our model predicted that matrix elasticity dominates over intracellular elasticity, suggesting that the extracellular matrix may potentially be a more effective therapeutic target than microtubules. Our data and model suggest that myocytes with lower aspect ratios have a functional advantage when the elasticity of the extracellular matrix decreases due to conditions such as fibrosis, highlighting the role of the extracellular matrix in cardiac disease.

Urinary proteome analysis in hypertensive patients with left ventricular diastolic dysfunction

AIMS

Despite the significant heart failure (HF) burden on society, easily applicable screening techniques, particularly for the early detection of asymptomatic left ventricular (LV) dysfunction, are lacking. The present study aimed to identify and test a set of urinary polypeptides that may indicate early LV diastolic dysfunction as defined by echocardiography in hypertensive patients in a cross-sectional case-control study nested within the FLEMish study on ENvironment, Genes and Health Outcome (FLEMENGHO).

METHODS AND RESULTS

To identify potentially discriminating urinary biomarkers for LV diastolic dysfunction, we applied capillary electrophoresis coupled to mass spectrometry. In the discovery set, we compared 19 hypertensive patients with asymptomatic LV diastolic dysfunction with 19 healthy controls. In the absence of adjustment for multiple testing, 85 urinary peptides were different between cases and controls at a P-value of <0.033. With adjustment for multiple testing, three potential biomarkers remained significantly different between cases and controls (P ≤ 0.02). We combined the 85 potential biomarkers in a high-dimensional model (classifier), which we applied in a blinded manner to an independent test set of 16 hypertensive patients with symptomatic HF and 16 healthy controls. Upon unblinding, the area under the receiver operating characteristic curve (AUC) of the HF classification was 0.84 (95% CI: 0.70-0.98; P= 0.001).

CONCLUSION

In asymptomatic hypertensive patients with LV diastolic dysfunction, we identified a set of urinary polypeptides specific for essential hypertension with LV diastolic dysfunction that subsequently distinguished hypertensive patients with overt HF from healthy controls.

Molecular mechanisms of cardiomyocyte aging

Western societies are rapidly aging, and cardiovascular diseases are the leading cause of death. In fact, age and cardiovascular diseases are positively correlated, and disease syndromes affecting the heart reach epidemic proportions in the very old. Genetic variations and molecular adaptations are the primary contributors to the onset of cardiovascular disease; however, molecular links between age and heart syndromes are complex and involve much more than the passage of time. Changes in CM (cardiomyocyte) structure and function occur with age and precede anatomical and functional changes in the heart. Concomitant with or preceding some of these cellular changes are alterations in gene expression often linked to signalling cascades that may lead to a loss of CMs or reduced function. An understanding of the intrinsic molecular mechanisms underlying these cascading events has been instrumental in forming our current understanding of how CMs adapt with age. In the present review, we describe the molecular mechanisms underlying CM aging and how these changes may contribute to the development of cardiovascular diseases.

Age-dependent alterations in fibrillar collagen content and myocardial diastolic function: role of SPARC in post-synthetic procollagen processing

Advanced age, independent of concurrent cardiovascular disease, can be associated with increased extracellular matrix (ECM) fibrillar collagen content and abnormal diastolic function. However, the mechanisms causing this left ventricular (LV) remodeling remain incompletely defined. We hypothesized that one determinant of age-dependent remodeling is a change in the extent to which newly synthesized procollagen is processed into mature collagen fibrils. We further hypothesized that secreted protein acidic and rich in cysteine (SPARC) plays a key role in the changes in post-synthetic procollagen processing that occur in the aged myocardium. Young (3 mo old) and old (18-24 mo old) wild-type (WT) and SPARC-null mice were studied. LV collagen content was measured histologically by collagen volume fraction, collagen composition was measured by hydroxyproline assay as soluble collagen (1 M NaCl extractable) versus insoluble collagen (mature cross-linked), and collagen morphological structure was examined by scanning electron microscopy. SPARC expression was measured by immunoblot analysis. LV and myocardial structure and function were assessed using echocardiographic and papillary muscle experiments. In WT mice, advanced age increased SPARC expression, myocardial diastolic stiffness, fibrillar collagen content, and insoluble collagen. In SPARC-null mice, advanced age also increased myocardial diastolic stiffness, fibrillar collagen content, and insoluble collagen but significantly less than those seen in WT old mice. As a result, insoluble collagen and myocardial diastolic stiffness were lower in old SPARC-null mice (1.36 +/- 0.08 mg hydroxyproline/g dry wt and 0.04 +/- 0.005) than in old WT mice (1.70 +/- 0.10 mg hydroxyproline/g dry wt and 0.07 +/- 0.005, P < 0.05). In conclusion, the absence of SPARC reduced age-dependent alterations in ECM fibrillar collagen and diastolic function. These data support the hypothesis that SPARC plays a key role in post-synthetic procollagen processing and contributes to the increase in collagen content found in the aged myocardium.

Cardiac rupture after myocardial infarction: new insights from murine models

Cardiac rupture after a myocardial infarction is an uncommon event with devastating consequences. Although the clinical features of rupture have been described, the genetic and molecular influences on this outcome in patients are less certain. In mice, at least 17 genetic models have been developed that enhance or suppress the likelihood of rupture postmyocardial infarction. The purpose of this review is to describe these recent advances, recognizing that nearly all of the information has been obtained from mouse models of free wall rupture. Although it is probable that the same genetic determinants apply to septal and papillary muscle rupture, the possibility remains that there are unique modulators of risk for rupture at differing anatomic sites within the heart. It is likely that the candidate genes also influence rupture in humans, although this conclusion must be confirmed. The mouse models will be helpful to direct future proteomic and genomic studies in patients and may already suggest certain fundamental pathways. For example, the essential role of collagen production and stabilization postmyocardial infarction may direct therapies to enhance collagen cross-linking and limit its degradation as a strategy to reduce rates of rupture and enhance myocardial healing.

Effects of aging and cyclosporin a on collagen turnover in human gingiva

Background:

We aimed at characterizing the aging gingiva analyzing: i) collagen content and turnover in human gingival tissues and fibroblasts obtained from healthy young and aging subjects. ii) the effect of cyclosporin A administration in human cultured gingival fibroblasts obtained from aging compared to young subjects.

Methods:

Morphological analysis was performed on haematoxylin-eosin and Sirius red stained paraffin-embedded gingival biopsies from young and aging healthy subjects. The expression of the main genes and proteins involved in collagen turnover were determined by real time PCR, dot blot and SDS-zymography on cultured young and aging gingival fibroblasts, and after cyclosporin A administration.

Results:

Our results suggest that in healthy aged people, gingival connective tissue is characterized by a similar collagen content and turnover. Collagen turnover pathways are similarly affected by cyclosporin A treatment in young and aging gingival fibroblasts.

Conclusions:

Cyclosporin A administration affects gingival collagen turnover pathways in young and aging fibroblasts at the same extent, suggesting that during aging cyclosporin A administration is not related to relevant collagen turnover modifications.

The human urinary proteome reveals high similarity between kidney aging and chronic kidney disease

Aging induces morphological changes of the kidney and reduces renal function. We analyzed the low molecular weight urinary proteome of 324 healthy individuals from 2-73 years of age to gain insight on human renal aging. We observed age-related modification of secretion of 325 out of over 5000 urinary peptides. The majority of these changes were associated with renal development before and during puberty, while 49 peptides were related to aging in adults. We therefore focussed the remainder of the study on these 49 peptides. The majority of these 49 peptides were also markers of chronic kidney disease, suggesting high similarity between aging and chronic kidney disease. Blinded evaluation of samples from healthy volunteers and diabetic nephropathy patients confirmed both the correlation of biomarkers with aging and with renal disease. Identification of a number of these aging-related peptides led us to hypothesize that reduced proteolytic activity is involved in human renal aging. Finally, among the 324 supposedly healthy individuals, some had urinary aging-related peptide excretion patterns typical of an individual significantly older than their actual age. In conclusion, these aging-related biomarkers may allow noninvasive detection of renal lesions in healthy persons and show high resemblance between human aging and chronic kidney disease. This similarity has to be taken into account when searching for biomarkers of renal disease.

Age-related atrial fibrosis

Many age-related diseases are associated with, and may be promoted by, cardiac fibrosis. Transforming growth factor (TGF)-beta, hypoxia-induced factor (HIF), and the matrix metalloproteinase (MMP) system have been implicated in fibrogenesis. Thus, we investigated whether age is related to these systems and to atrial fibrosis. Right atrial appendages (RAA) obtained during heart surgery (n = 115) were grouped according to patients' age (<50 years, 51-60 years, 61-70 years, or >70 years). Echocardiographic ejection fractions (EF) and fibrosis using Sirius-red-stained histological sections were determined. TGF-beta was determined by quantitative RT-PCR and hypoxia-related factors [HIF1 alpha, the vascular endothelial growth factor (VEGF)-receptor, CD34 (a surrogate marker for microvessel density), the factor inhibiting HIF (FIH), and prolyl hydroxylase 3 (PHD 3)] were detected by immunostaining. MMP-2 and -9 activity were determined zymographically, and mRNA levels of their common tissue inhibitor TIMP-1 were determined by RT-PCR. Younger patients (<50 years) had significantly less fibrosis (10.1% +/- 4.4% vs 16.6% +/- 8.3%) than older individuals (>70 years). While HIF1 alpha, FIH, the VEGF-receptor, and CD34 were significantly elevated in the young, TGF-beta and PHD3 were suppressed in these patients. MMP-2 and -9 activity was found to be higher while TIMP-1 levels were lower in older patients. Statistical analysis proved age to be the only factor influencing fibrogenesis. With increasing age, RAAs develop significantly more fibrosis. An increase of fibrotic and decrease of hypoxic signalling and microvessel density, coupled with differential expression of MMPs and TIMP-1 favouring fibrosis may have helped promote atrial fibrogenesis.

Adaptive response of the heart to long-term anemia induced by iron deficiency

Anemia is common in patients with chronic heart failure and an independent predictor of poor prognosis. Chronic anemia leads to left ventricular (LV) hypertrophy and heart failure, but its molecular mechanisms remain largely unknown. We investigated the mechanisms, including the molecular signaling pathway, of cardiac remodeling induced by iron deficiency anemia (IDA). Weanling Sprague-Dawley rats were fed an iron-deficient diet for 20 wk to induce IDA, and the molecular mechanisms of cardiac remodeling were evaluated. The iron-deficient diet initially induced severe anemia, which resulted in LV hypertrophy and dilation with preserved systolic function associated with increased serum erythropoietin (Epo) concentration. Cardiac STAT3 phosphorylation and VEGF gene expression increased by 12 wk of IDA, causing angiogenesis in the heart. Thereafter, sustained IDA induced upregulation of cardiac hypoxia inducible factor-1alpha gene expression and maintained upregulation of cardiac VEGF gene expression and cardiac angiogenesis; however, sustained IDA promoted cardiac fibrosis and lung congestion, with decreased serum Epo concentration and cardiac STAT3 phosphorylation after 20 wk of IDA compared with 12 wk. Upregulation of serum Epo concentration and cardiac STAT3 phosphorylation is associated with a beneficial adaptive mechanism of anemia-induced cardiac hypertrophy, and later decreased levels of these molecules may be critical for the transition from adaptive cardiac hypertrophy to cardiac dysfunction in long-term anemia. Understanding the mechanism of cardiac maladaptation to anemia may lead to a new strategy for treatment of chronic heart failure with anemia.

Preamplification techniques for real-time RT-PCR analyses of endomyocardial biopsies

Background

Due to the limited RNA amounts from endomyocardial biopsies (EMBs) and low expression levels of certain genes, gene expression analyses by conventional real-time RT-PCR are restrained in EMBs. We applied two preamplification techniques, the TaqMan^® PreAmp Master Mix (T-PreAmp) and a multiplex preamplification following a sequence specific reverse transcription (SSRT-PreAmp).

Results

T-PreAmp encompassing 92 gene assays with 14 cycles resulted in a mean improvement of 7.24 ± 0.33 Ct values. The coefficients for inter- (1.89 ± 0.48%) and intra-assay variation (0.85 ± 0.45%) were low for all gene assays tested (<4%). The PreAmp uniformity values related to the reference gene CDKN1B for 91 of the investigated gene assays (except for CD56) were -0.38 ± 0.33, without significant differences between self-designed and ABI inventoried Taqman^® gene assays. Only two of the tested Taqman^® ABI inventoried gene assays (HPRT-ABI and CD56) did not maintain PreAmp uniformity levels between -1.5 and +1.5. In comparison, the SSRT-PreAmp tested on 8 self-designed gene assays yielded higher Ct improvement (9.76 ± 2.45), however was not as robust regarding the maintenance of PreAmp uniformity related to HPRT-CCM (-3.29 ± 2.40; p < 0.0001), and demonstrated comparable intra-assay CVs (1.47 ± 0.74), albeit higher inter-assay CVs (5.38 ± 2.06; p = 0.01). Comparing EMBs from each 10 patients with dilated cardiomyopathy (DCM) and inflammatory cardiomyopathy (DCMi), T-PreAmp real-time RT-PCR analyses revealed differential regulation regarding 27 (30%) of the investigated 90 genes related to both HPRT-CCM and CDKN1B. Ct values of HPRT and CDKN1B did not differ in equal RNA amounts from explanted DCM and donor hearts.

Conclusion

In comparison to the SSRT-PreAmp, T-PreAmp enables a relatively simple workflow, and results in a robust PreAmp of multiple target genes (at least 92 gene assays as tested here) by a mean Ct improvement around 7 cycles, and in a lower inter-assay variance in RNA derived from EMBs. Preliminary analyses comparing EMBs from DCM and DCMi patients, revealing differential regulation regarding 30% of the investigated genes, confirm that T-PreAmp is a suitable tool to perform gene expression analyses in EMBs, expanding gene expression investigations with the limited RNA/cDNA amounts derived from EMBs. CDKN1B, in addition to its function as a reference gene for the calculation of PreAmp uniformity, might serve as a suitable housekeeping gene for real-time RT-PCR analyses of myocardial tissues.

Aldosterone Antagonism Fails to Attenuate Age-Associated Left Ventricular Fibrosis

Collagen accumulates disproportionately in cardiac remodeling induced by hypertension and associated with advancing age. Spironolactone (Spiro), an aldosterone antagonist, attenuates the accumulation of collagen induced by hypertension. It was hypothesized that Spiro would attenuate the age-associated increase in percent collagen in the heart. Female Fisher 344 rats at 3 months (Y), 12 months (M), and 21 months (O) of age were treated with Spiro (30 mg/kg/d) or vehicle (Veh) for 2 months, yielding six groups: Y-Veh, Y-Spiro, M-Veh, M-Spiro, O-Veh, and O-Spiro. Hearts were harvested for immunoblotting, RNA blotting, and biochemical analysis. Percent collagen in the left ventricle and septum was greatest in the oldest rats. Spiro did not significantly attenuate the age-associated increase in collagen fraction or the age-associated increases in expression of atrial natriuretic factor and beta-myosin heavy chain messenger RNA. Chronic aldosterone antagonism does not attenuate the age-associated increase in collagen fraction in the female Fisher 344 rat heart.

Preservation of coronary reserve by ivabradine-induced reduction in heart rate in infarcted rats is associated with decrease in perivascular collagen

We tested the hypothesis that chronically reducing the heart rate in infarcted middle-aged rats using ivabradine (IVA) would induce arteriolar growth and attenuate perivascular collagen and, thereby, improve maximal perfusion and coronary reserve in the surviving myocardium. Myocardial infarction (MI) was induced in 12-mo-old male Sprague-Dawley rats, which were then treated with either IVA (10.5 mg.kg(-1).day(-1); MI + IVA) or placebo (MI) via intraperitoneal osmotic pumps for 4 wk. Four weeks of IVA treatment limited the increase in left ventricular end-diastolic pressure and the decrease in ejection fraction but did not affect the size of the infarct, the magnitude of myocyte hypertrophy, or the degree of arteriolar and capillary growth. However, treatment reduced interstitial and periarteriolar collagen in the surviving myocardium of MI + IVA rats. The reduced periarteriolar collagen content was associated with improvement in maximal myocardial perfusion and coronary reserve. Although the rates of proliferation of periarteriolar fibroblasts were similar in the MI and MI + IVA groups, the expression levels of the AT(1) receptor and transforming growth factor (TGF)-beta(1) in the myocardium, as well as the plasma level of the ANG II peptide, were lower in treated rats 14 days after MI. Therefore, our data reveal that improved maximal myocardial perfusion and coronary reserve in MI + IVA rats are most likely the result of reduced periarteriolar collagen rather than enhanced arteriolar growth.

Age-dependent changes in contraction and regional myocardial myosin heavy chain isoform expression in rats

The goals of this study were to measure the relative levels of the alpha- and beta-isoforms of myosin heavy chain (MHC-alpha and MHC-beta, respectively) in multiple, specific regions of the adult rat heart and to determine whether age-dependent changes in isoform levels in different regions are uniform. Relative amounts of MHC-alpha and MHC-beta were determined in right and left atria and left ventricular (LV) Purkinje fibers (PF), papillary muscles, trabeculae, and endo-, mid-, and epicardial regions at 2, 5, 10, 16, and 21 mo. PFs contained substantial amounts of myosin and were striated and capable of generating force and shortening on activation. Levels of MHC-beta increased in all LV compartments with age, especially between 2 and 5 mo. There was more MHC-beta in PFs than other LV sites. There were regional differences in the level of MHC-beta throughout the LV at all ages, and the rates of change within regions differed. Ca(2+)-activated tension in PFs and trabeculae was compared at 2 and 22 mo. PF tension was less than trabecula tension, and this difference may be explained by differences in MHC content. V(max) and tension-generating ability in PFs decreased with age. Maximal tension generated by trabeculae did not change during aging. A large proportion of the increase in the level of MHC-beta that is normally associated with aging occurs at a relatively early age in rat LV. PFs, with their small diameters and short diffusion distance, should be considered for skinned multicellular myocardial studies.

Glycation end-product cross-link breaker reduces collagen and improves cardiac function in aging diabetic heart

Aging and diabetes mellitus (DM) both affect the structure and function of the myocardium, resulting in increased collagen in the heart and reduced cardiac function. As part of this process, hyperglycemia is a stimulus for the production of advanced glycation end products (AGEs), which covalently modify proteins and impair cell function. The goals of this study were first to examine the combined effects of aging and DM on hemodynamics and collagen types in the myocardium in 12 dogs, 9-12 yr old, and second to examine the effects of the AGE cross-link breaker phenyl-4,5-dimethylthazolium chloride (ALT-711) on myocardial collagen protein content, aortic stiffness, and left ventricular (LV) function in the aged diabetic heart. The alloxan model of DM was utilized to study the effects of DM on the aging heart. DM induced in the aging heart decreased LV systolic function (LV ejection fraction fell by 25%), increased aortic stiffness, and increased collagen type I and type III protein content. ALT-711 restored LV ejection fraction, reduced aortic stiffness and LV mass with no reduction in blood glucose level (199 +/- 17 mg/dl), and reversed the upregulation of collagen type I and type III. Myocardial LV collagen solubility (%) increased significantly after treatment with ALT-711. These data suggest that an AGE cross-link breaker may have a therapeutic role in aged patients with DM.

Adenosine A1 and A2A receptor cross-talk during ageing in the rat myocardium

Adenosine (Ado), a naturally occurring autacoid, exerts cardioprotective effects against myocardial ischemia and reperfusion injury, through activation of its receptors type 1 (A1) and 2A (A2A). Since ageing involves a complex change in these effects, we evaluated A1 and A2A gene expression in left (LV) and right ventricle (RV) from 2-, 5-, 12-, and 21-month-old Sprague-Dawley rats. LV end-diastolic (EDD) and end-systolic (ESD) internal dimensions (mm) and LV fractional shortening (FS, %) were measured by M-mode echocardiography. Senescence was associated with a reduction in FS (42+/-1, 38+/-2, 39+/-2 and 35+/-2, in 2-, 5-, 12- and 21-month-old rats; p<0.02) and increases in EDD (7.5+/-0.2, 8.1+/-0.2, 8.5+/-0.2 and 8.8+/-0.2; p<0.001) and ESD (4.2+/-0.1, 4.4+/-0.2, 4.7+/-0.2 and 5.1+/-0.2; p=0.002). Ado A1 mRNA levels were highest in 12 and 21-month-old animals in both ventricles (LV: p<0.001; RV: p=0.001). By contrast, Ado A2A gene expression was lower in the aged LV (p<0.001), but higher in the aged RV (p<0.001). These modifications of Ado receptor gene expression and especially the increase in A1 receptor mRNA may partially explain the stronger antiadrenergic effects of Ado in the senescent heart.

Studies of prevention, treatment and mechanisms of heart failure in the aging spontaneously hypertensive rat

The spontaneously hypertensive rat (SHR) is an animal model of genetic hypertension which develops heart failure with aging, similar to man. The consistent pattern of a long period of stable hypertrophy followed by a transition to failure provides a useful model to study mechanisms of heart failure with aging and test treatments at differing phases of the disease process. The transition from compensated hypertrophy to failure is accompanied by changes in cardiac function which are associated with altered active and passive mechanical properties of myocardial tissue; these events define the physiologic basis for cardiac decompensation. In examining the mechanism for myocardial tissue dysfunction, studies have demonstrated a central role for neurohormonal activation, and specifically the renin-angiotensin-aldosterone system. Pharmacologic attenuation of this system at differing points in the course of the process suggests that prevention but not reversal of myocardial tissue dysfunction is possible. The roles of the extracellular matrix, apoptosis, intracellular calcium, beta-adrenergic stimulation, microtubules, and oxygen supply-demand relationships in ultimately mediating myocardial tissue dysfunction are reviewed. Studies suggest that while considerable progress has been made in understanding and treating the transition to failure, our current state of knowledge is limited in scope and we are not yet able to define specific mechanisms responsible for tissue dysfunction. It will be necessary to integrate information on the roles of newly discovered, and as yet undiscovered, genes and pathways to provide a clearer understanding of maladaptive remodeling seen with heart failure. Understanding the mechanism for tissue dysfunction is likely to result in more effective treatments for the prevention and reversal of heart failure with aging. It is anticipated that the SHR model will assist us in reaching these important goals.

Age-related left ventricular function in the mouse: analysis based on in vivo pressure-volume relationships

Our study compared left ventricular (LV) function between senescent and young adult mice through in situ pressure-volume loop analysis. Two groups of mice (n = 9 each), 6-mo-old and 16-mo-old (senescent) mice, were anesthetized with urethan and alpha-chloralose, and their LV were instrumented with a Millar 1.4-Fr conductance micromanometer catheter for the acquisition of the pressure-volume loops. The senescent mice had a significantly decreased contractile function related to load-dependent parameters, including stroke volume index, ejection fraction, cardiac output index, stroke work index, and maximum derivative of change in systolic pressure over time. The load-independent parameters, preload recruitable stroke work and the slope (end-systolic volume elastance) of the end-systolic pressure-volume relationship, were significantly decreased in the senescent mice. Heart rate and arterial elastance were not different between the two groups; however, the ventricular-to-vascular coupling ratio (ratio of elastance of artery to end-systolic volume elastance) was increased by threefold in the senescent mice (P < 0. 001). Thus there were significant decreases in contractile function in the senescent mouse heart that appeared to be related to reduced mechanical efficiency but not related to arterial elastance.