Abstract-The myocardium of the failing heart undergoes a number of structural alterations, most notably hypertrophy of cardiac myocytes and an increase in extracellular matrix proteins, often seen as primary fibrosis. Connective tissue growth factor (CTGF) is a key molecule in the process of fibrosis and therefore seems an attractive therapeutic target. Regulation of CTGF expression at the promoter level has been studied extensively, but it is unknown how CTGF transcripts are regulated at the posttranscriptional level. Here we provide several lines of evidence to show that CTGF is importantly regulated by 2 major cardiac microRNAs (miRNAs), miR-133 and miR-30. First, the expression of both miRNAs was inversely related to the amount of CTGF in 2 rodent models of heart disease and in human pathological left ventricular hypertrophy. Second, in cultured cardiomyocytes and fibroblasts, knockdown of these miRNAs increased CTGF levels. Third, overexpression of miR-133 or miR-30c decreased CTGF levels, which was accompanied by decreased production of collagens. Fourth, we show that CTGF is a direct target of these miRNAs, because they directly interact with the 3Ј untranslated region of CTGF. Taken together, our results indicate that miR-133 and miR-30 importantly limit the production of CTGF. We also provide evidence that the decrease of these 2 miRNAs in pathological left ventricular hypertrophy allows CTGF levels to increase, which contributes to collagen synthesis. In conclusion, our results show that both miR-133 and miR-30 directly downregulate CTGF, a key profibrotic protein, and thereby establish an important role for these miRNAs in the control of structural changes in the extracellular matrix of the myocardium.

Diseases caused by mutations in lamins A and C (laminopathies) suggest a crucial role for A-type lamins in different cellular processes. Laminopathies mostly affect tissues of mesenchymal origin. As transforming growth factor-beta1 (TGF-beta1) signalling impinges on the retinoblastoma protein (pRB) and SMADs, we tested the hypothesis that lamins modulate cellular responses to TGF-beta1 signalling, via the regulation of these transcription factors in mesenchymal cells. Here, we report that A-type lamins are essential for the inhibition of fibroblast proliferation by TGF-beta1. TGF-beta1 dephosphorylated pRB through PP2A, both of which, we show, are associated with lamin A/C. In addition, lamin A/C modulates the effect of TGF-beta1 on collagen production, a marker of mesenchymal differentiation. Our findings implicate lamin A/C in control of gene activity downstream of TGF-beta1, via nuclear phosphatases such as PP2A. This biological function provides a novel explanation for the observed mesenchymal dysfunction in laminopathies.

Abstract-Cardiac hypertrophy can lead to heart failure (HF), but it is unpredictable which hypertrophied myocardium will progress to HF. We surmised that apart from hypertrophy-related genes, failure-related genes are expressed before the onset of failure, permitting molecular prediction of HF. Hearts from hypertensive homozygous renin-overexpressing (Ren-2) rats that had progressed to early HF were compared by microarray analysis to Ren-2 rats that had remained compensated. To identify which HF-related genes preceded failure, cardiac biopsy specimens were taken during compensated hypertrophy and we then monitored whether the rat progressed to HF or remained compensated. Among 48 genes overexpressed in failing hearts, we focused on thrombospondin-2 (TSP2). TSP2 was selectively overexpressed only in biopsy specimens from rats that later progressed to HF. Moreover, expression of TSP2 was increased in human hypertrophied hearts with decreased (0.19Ϯ0.01) versus normal ejection fraction (0.11Ϯ0. [arbitrary units]; PϽ0.05).Angiotensin II induced fatal cardiac rupture in 70% of TSP2 knockout mice, with cardiac failure in the surviving mice; this was not seen in wild-type mice. In TSP2 knockout mice, angiotensin II increased matrix metalloproteinase (MMP)-2 and MMP-9 activity by 120% and 390% compared with wild-type mice (PϽ0.05). In conclusion, we identify TSP2 as a crucial regulator of the integrity of the cardiac matrix that is necessary for the myocardium to cope with increased loading and that may function by its regulation of MMP activity. This suggests that expression of TSP2 marks an early-stage molecular program that is activated uniquely in hypertrophied hearts that are prone to fail. Key Words: extracellular matrix Ⅲ hypertrophy Ⅲ microarray Ⅲ myocardium H ypertension causes cardiac hypertrophy, one of the most important risk factors for heart failure (HF). However, not all hypertrophied hearts will ultimately fail. 1,2 This suggests that additional mechanisms, besides those that cause hypertrophy, are recruited during progression from compensated hypertrophy to failure. Possibly, failure-prone forms of left ventricular hypertrophy are already discernible on a molecular level at early stages, before transition toward overt HF has occurred. If failure-prone hypertrophied hearts would indeed express distinct molecular signs of their propensity to transgress to failure, this property would provide an opportunity to identify these failure-prone hearts at an early stage in the disease process.Although recent studies have reported many molecular and cellular changes underlying cardiac hypertrophy, 3,4 the additional factors that contribute to HF have remained elusive. In a hypothesis-driven search for mechanisms that characterize failing hypertrophied hearts, Boluyt et al documented the upregulation of genes encoding extracellular matrix components in spontaneously hypertensive rats with HF. 5-8 However, it is not clear whether the overexpression of these genes preceded the overt clinical syndrome of HF, or whethe...