MicroRNA-18 and microRNA-19 regulate CTGF and TSP-1 expression in age-related heart failure.

To understand the process of cardiac aging, it is of crucial importance to gain insight into the age-related changes in gene expression in the senescent failing heart. Age-related cardiac remodeling is known to be accompanied by changes in extracellular matrix (ECM) gene and protein levels. Small noncoding microRNAs regulate gene expression in cardiac development and disease and have been implicated in the aging process and in the regulation of ECM proteins. However, their role in age-related cardiac remodeling and heart failure is unknown. In this study, we investigated the aging-associated microRNA cluster 17-92, which targets the ECM proteins connective tissue growth factor (CTGF) and thrombospondin-1 (TSP-1). We employed aged mice with a failure-resistant (C57Bl6) and failure-prone (C57Bl6 × 129Sv) genetic background and extrapolated our findings to human age-associated heart failure. In aging-associated heart failure, we linked an aging-induced increase in the ECM proteins CTGF and TSP-1 to a decreased expression of their targeting microRNAs 18a, 19a, and 19b, all members of the miR-17-92 cluster. Failure-resistant mice showed an opposite expression pattern for both the ECM proteins and the microRNAs. We showed that these expression changes are specific for cardiomyocytes and are absent in cardiac fibroblasts. In cardiomyocytes, modulation of miR-18/19 changes the levels of ECM proteins CTGF and TSP-1 and collagens type 1 and 3. Together, our data support a role for cardiomyocyte-derived miR-18/19 during cardiac aging, in the fine-tuning of cardiac ECM protein levels. During aging, decreased miR-18/19 and increased CTGF and TSP-1 levels identify the failure-prone heart.

The extent of coronary atherosclerosis is associated with increasing circulating levels of high sensitive cardiac troponin T.

OBJECTIVE: This study explored the relationship between coronary atherosclerotic plaque burden and quantifiable circulating levels of troponin measured with a recently introduced high sensitive cardiac troponin T (hs-cTnT) assay. METHODS AND RESULTS: Cardiac patients suspected of having coronary artery disease (CAD) but without acute coronary syndrome were studied. Cardiac troponin T levels were assessed using the fifth-generation hs-cTnT assay. All patients (n=615) underwent cardiac computed tomographic angiography (CCTA). On the basis of CCTA, patients were classified as having no CAD or mild (<50% lesion), moderate (50% to 70% lesion), severe (>70% lesion), or multivessel CAD (multiple >70% lesions). As a comparison, high-sensitivity C-reactive protein levels were measured. Progressively increasing hs-cTnT levels were found in patients with mild (median, 4.5 ng/L), moderate (median, 5.5 ng/L), severe (median, 5.7 ng/L), and multivessel (median, 8.6 ng/L) CAD compared with patients without CAD (median, 3.7 ng/L) (all P<0.01). For high-sensitivity C-reactive protein and N-terminal pro-B-type natriuretic peptide, no such relationship was observed. In patients without CAD, 11% showed hs-cTnT levels in the highest quartile, compared with 62% in the multivessel disease group (P<0.05). Multivariance analysis identified hs-cTnT as an independent risk factor for the presence of CAD. CONCLUSIONS: In patients without acute coronary syndrome, even mild CAD is associated with quantifiable circulating levels of hs-cTnT.

Syndecan-1 amplifies angiotensin II-induced cardiac fibrosis.

Syndecan-1 (Synd1) is a transmembrane heparan sulfate proteoglycan that functions as a coreceptor for various growth factors and modulates signal transduction. The present study investigated whether Synd1, by affecting growth factor signaling, may play a role in hypertension-induced cardiac fibrosis and dysfunction. Expression of Synd1 was increased significantly in mouse hearts with angiotensin II-induced hypertension, which was spatially related to cardiac fibrosis. Angiotensin II significantly impaired fractional shortening and induced cardiac fibrosis in wild-type mice, whereas these effects were blunted in Synd1-null mice. Angiotensin II significantly increased cardiac expression of connective tissue growth factor and collagen type I and III in wild-type mice, which was blunted in Synd1-null mice. These findings were confirmed in vitro, where angiotensin II induced the expression of both connective tissue growth factor and collagen I in fibroblasts. The absence of Synd1 in either Synd1-null fibroblasts, after knockdown of Synd1 by short hairpin RNA, or after inhibition of heparan sulfates by protamine attenuated this increase, which was associated with reduced phosphorylation of Smad2. In conclusion, loss of Synd1 reduces cardiac fibrosis and dysfunction during angiotensin II-induced hypertension.

Thrombospondins in the heart: potential functions in cardiac remodeling.

Cardiac remodeling after myocardial injury involves inflammation, angiogenesis, left ventricular hypertrophy and matrix remodeling. Thrombospondins (TSPs) belong to the group of matricellular proteins, which are non-structural extracellular matrix proteins that modulate cell-matrix interactions and cell function in injured tissues or tumors. They interact with different matrix and membrane-bound proteins due to their diverse functional domains. That the expression of TSPs strongly increases during cardiac stress or injury indicates an important role for them during cardiac remodeling. Recently, the protective properties of TSP expression against heart failure have been acknowledged. The current review will focus on the biological role of TSPs in the ischemic and hypertensive heart, and will describe the functional consequences of TSP polymorphisms in cardiac disease.

Absence of thrombospondin-2 causes age-related dilated cardiomyopathy.

BACKGROUND: The progressive shift from a young to an aged heart is characterized by alterations in the cardiac matrix. The present study investigated whether the matricellular protein thrombospondin-2 (TSP-2) may affect cardiac dimensions and function with physiological aging of the heart. METHODS AND RESULTS: TSP-2 knockout (KO) and wild-type mice were followed up to an age of 60 weeks. Survival rate, cardiac function, and morphology did not differ at a young age in TSP-2 KO compared with wild-type mice. However, >55% of the TSP-2 KO mice died between 24 and 60 weeks of age, whereas <10% of the wild-type mice died. In the absence of TSP-2, older mice displayed a severe dilated cardiomyopathy with impaired systolic function, increased cardiac dilatation, and fibrosis. Ultrastructural analysis revealed progressive myocyte stress and death, accompanied by an inflammatory response and replacement fibrosis, in aging TSP-2 KO animals, whereas capillary or coronary morphology or density was not affected. Importantly, adeno-associated virus-9 gene-mediated transfer of TSP-2 in 7-week-old TSP-2 KO mice normalized their survival and prevented dilated cardiomyopathy. In TSP-2 KO animals, age-related cardiomyopathy was accompanied by increased matrix metalloproteinase-2 and decreased tissue transglutaminase-2 activity, together with impaired collagen cross-linking. At the cardiomyocyte level, TSP-2 deficiency in vivo and its knockdown in vitro decreased the activation of the Akt survival pathway in cardiomyocytes. CONCLUSIONS: TSP-2 expression in the heart protects against age-dependent dilated cardiomyopathy.

Absence of SPARC results in increased cardiac rupture and dysfunction after acute myocardial infarction.

The matricellular protein SPARC (secreted protein, acidic and rich in cysteine, also known as osteonectin) mediates cell-matrix interactions during wound healing and regulates the production and/or assembly of the extracellular matrix (ECM). This study investigated whether SPARC functions in infarct healing and ECM maturation after myocardial infarction (MI). In comparison with wild-type (WT) mice, animals with a targeted inactivation of SPARC exhibited a fourfold increase in mortality that resulted from an increased incidence of cardiac rupture and failure after MI. SPARC-null infarcts had a disorganized granulation tissue and immature collagenous ECM. In contrast, adenoviral overexpression of SPARC in WT mice improved the collagen maturation and prevented cardiac dilatation and dysfunction after MI. In cardiac fibroblasts in vitro, reduction of SPARC by short hairpin RNA attenuated transforming growth factor beta (TGF)-mediated increase of Smad2 phosphorylation, whereas addition of recombinant SPARC increased Smad2 phosphorylation concordant with increased Smad2 phosphorylation in SPARC-treated mice. Importantly, infusion of TGF-beta rescued cardiac rupture in SPARC-null mice but did not significantly alter infarct healing in WT mice. These findings indicate that local production of SPARC is essential for maintenance of the integrity of cardiac ECM after MI. The protective effects of SPARC emphasize the potential therapeutic applications of this protein to prevent cardiac dilatation and dysfunction after MI.

Increased expression of syndecan-1 protects against cardiac dilatation and dysfunction after myocardial infarction.

BACKGROUND: The cell-associated proteoglycan syndecan-1 (Synd1) closely regulates inflammation and cell-matrix interactions during wound healing and tumorigenesis. The present study investigated whether Synd1 may also regulate cardiac inflammation, matrix remodeling, and function after myocardial infarction (MI). METHODS AND RESULTS: First, we showed increased protein and mRNA expression of Synd1 from 24 hours on, reaching its maximum at 7 days after MI and declining thereafter. Targeted deletion of Synd1 resulted in increased inflammation and accelerated, yet functionally adverse, infarct healing after MI. In concordance, adenoviral gene expression of Synd1 protected against exaggerated inflammation after MI, mainly by reducing transendothelial adhesion and migration of leukocytes, as shown in vitro. Increased inflammation in the absence of Synd1 resulted in increased monocyte chemoattractant protein-1 expression, increased activity of matrix metalloproteinase-2 and -9, and decreased activity of tissue transglutaminase, associated with increased collagen fragmentation and disorganization. Exaggerated inflammation and adverse matrix remodeling in the absence of Synd1 increased cardiac dilatation and impaired systolic function, whereas gene overexpression of Synd1 reduced inflammation and protected against cardiac dilatation and failure. CONCLUSIONS: Increased expression of Synd1 in the infarct protects against exaggerated inflammation and adverse infarct healing, thereby reducing cardiac dilatation and dysfunction after MI in mice.

Imatinib attenuates end-organ damage in hypertensive homozygous TGR(mRen2)27 rats.

Imatinib specifically inhibits receptor tyrosine kinase signaling and is clinically used to treat leukemia. Receptor tyrosine kinases not only mediate tumor growth but also initiate adverse signaling in heart failure. We investigated whether imatinib, by inhibiting the platelet-derived growth factor receptor-beta (PDGFRbeta), prevents cardiac and renal damage in TGR(mRen2)27 (Ren2) rats. Eight-week-old male homozygous Ren2 and Sprague Dawley rats were treated either with imatinib (30 mg/kg; STI-571) or placebo for 8 weeks (Ren2 n=12 for each group; Sprague Dawley n=6 for each group). Imatinib did not affect blood pressure or left ventricular (LV) hypertrophy in both groups. Imatinib attenuated the decline in fractional shortening (imatinib versus Ren2 placebo 45+/-4.5% versus 32+/-3%; n=7-11; P<0.05) and in diastolic function in Ren2 rats (baseline diastolic dP/dt corrected for systolic blood pressure Ren2 imatinib versus Ren2 placebo 38.6+/-0.67 versus 35.3+/-0.41 [1 . s(-1)]; n=7-11; P<0.05). This was associated with decreased cardiac fibrosis and decreased activation of PDGFRbeta and extracellular signal-regulated kinase 1/2. Renal microvascular hypertrophy and perivascular fibrosis in Ren2 rats were significantly decreased by imatinib. In vitro, imatinib blocked angiotensin II-induced activation of the PDGFRbeta and significantly decreased fibroblast proliferation and collagen production. In conclusion, imatinib did not affect LV hypertrophy but attenuated the decline in cardiac function and reduced renal microvascular damage associated with reduced activation of the PDGFRbeta. The simultaneous improvement in both heart and kidneys suggests that inhibition of the PDGFRbeta has broad protective effects that may provide novel avenues for a blood pressure-independent protection against end-organ damage.

Matricellular proteins in the heart: possible role during stress and remodeling.

Matricellular proteins are extracellular matrix proteins that modulate cell-matrix interactions and cell function, and do not seem to have a direct structural role. The family includes tenascin-C (TN-C), tenascin-X (TN-X), osteonectin, osteopontin, thrombospondin-1 (TSP1) and thrombospondin-2 (TSP2). Expression of matricellular proteins is high during embryogenesis, but almost absent during normal postnatal life. Interestingly, it re-appears in response to injury. Left ventricular remodeling is a complicated process that occurs in the stressed heart, and is still not completely understood. Several members of the matricellular protein family, like tenascin-C, osteopontin, and osteonectin are up-regulated after cardiac injury. Therefore, this group of proteins may have crucial functions in the heart coping with stress. This review will focus on the expression, regulation and function of these matricellular proteins, and will discuss the crucial functions that these proteins might exert during remodeling of the stressed heart.