Joost J. Leenders

miR-133 and miR-30 Regulate Connective Tissue Growth Factor. Implications for a Role of MicroRNAs in Myocardial Matrix Remodeling

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 3′ 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.

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.

Regulation of Cardiac Gene Expression by KLF15, a Repressor of Myocardin Activity

Pathological forms of left ventricular hypertrophy (LVH) often progress to heart failure. Specific transcription factors have been identified that activate the gene program to induce pathological forms of LVH. It is likely that apart from activating transcriptional inducers of LVH, constitutive transcriptional repressors need to be removed during the development of cardiac hypertrophy. Here, we report that the constitutive presence of Krüppel-like factor 15 (KLF15) is lost in pathological hypertrophy and that this loss precedes progression toward heart failure. We show that transforming growth factor-β-mediated activation of p38 MAPK is necessary and sufficient to decrease KLF15 expression. We further show that KLF15 robustly inhibits myocardin, a potent transcriptional activator. Loss of KLF15 during pathological LVH relieves the inhibitory effects on myocardin and stimulates the expression of serum response factor target genes, such as atrial natriuretic factor. This uncovers a novel mechanism where activated p38 MAPK decreases KLF15, an important constitutive transcriptional repressor whose removal seems a vital step to allow the induction of pathological LVH.

Tapping the brake on cardiac growth-endogenous repressors of hypertrophic signaling.

Cardiac hypertrophy is considered an early hallmark during the clinical course of heart failure and an important risk factor for cardiac morbidity and mortality. Although hypertrophy of individual cardiomyocytes in response to pathological stimuli has traditionally been considered as an adaptive response required to sustain cardiac output, accumulating evidence from studies in patients and animal models suggests that in most instances hypertrophy of the heart also harbors maladaptive aspects. Major strides have been made in our understanding of the pathways that convey pro-hypertrophic signals from the outside of the cell to the nucleus. In recent years it also has become increasingly evident that the heart possesses a variety of endogenous feedback mechanisms to counterbalance this growth response. These repressive mechanisms are of particular interest since they may provide valuable therapeutic options. In this review we summarize currently known endogenous repressors of pathological cardiac growth as they have been studied by gene targeting in mice. Many of the repressors that function in signal transduction appear to regulate calcineurin (e.g. PICOT, calsarcin, RCAN) and JNK signaling (e.g. CDC42, MKP-1) and some will be described in greater detail in this review. In addition, we will focus on factors such as Kruppel-like factors (KLF4, KLF15 and KLF10) and histone deacetylases (HDACs), which constitute a relevant group of nuclear proteins that repress transcription of the hypertrophic gene program in cardiomyocytes.

Repression of cardiac hypertrophy by KLF15: Underlying mechanisms and therapeutic implications

The Kruppel-like factor (KLF) family of transcription factors regulates diverse cell biological processes including proliferation, differentiation, survival and growth. Previous studies have shown that KLF15 inhibits cardiac hypertrophy by repressing the activity of pivotal cardiac transcription factors such as GATA4, MEF2 and myocardin. We set out this study to characterize the interaction of KLF15 with putative other transcription factors. We first show that KLF15 interacts with myocardin-related transcription factors (MRTFs) and strongly represses the transcriptional activity of MRTF-A and MRTF-B. Second, we identified a region within the C-terminal zinc fingers of KLF15 that contains the nuclear localization signal. Third, we investigated whether overexpression of KLF15 in the heart would have therapeutic potential. Using recombinant adeno-associated viruses (rAAV) we have overexpressed KLF15 specifically in the mouse heart and provide the first evidence that elevation of cardiac KLF15 levels prevents the development of cardiac hypertrophy in a model of Angiotensin II induced hypertrophy.

Prognostic value of circulating microRNAs on heart failure-related morbidity and mortality in two large diverse cohorts of general heart failure patients

Small studies suggested circulating microRNAs (miRNAs) as biomarkers for heart failure (HF). However, standardized approaches and quality assessment for measuring circulating miRNAs are not uniformly established, and most studies have been small, so that results are inconsistent. We used a standardized data handling protocol, optimized for circulating miRNA qPCRs to remove noise and used it to assess which circulating miRNAs robustly add prognostic information in patients with HF.

Lysosomal integral membrane protein 2 is a novel component of the cardiac intercalated disc and vital for load-induced cardiac myocyte hypertrophy

Schroen et al. 2007. J. Exp. Med. doi:10.1084/jem.20070145 [OpenUrl][1][Abstract/FREE Full Text][2] [1]: {openurl}?query=rft_id%253Dinfo%253Adoi%252F10.1084%252Fjem.20070145%26rft_id%253Dinfo%253Apmid%252F17485520%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%