Regulation of mRNA transcripts and DNA synthesis in the rat heart following intravenous injection of transforming growth factor beta 1

Temporary fatigue and altered extracellular matrix in skeletal muscle during progression of heart failure in rats

Patients with congestive heart failure (CHF) experience increased skeletal muscle fatigue. The mechanism underlying this phenomenon is unknown, but a deranged extracellular matrix (ECM) might be a contributing factor. Hence, we examined ECM components and regulators in a rat postinfarction model of CHF. At various time points during a 3.5 mo-period after induction of CHF in rats by left coronary artery ligation, blood, interstitial fluid (IF), and muscles were sampled. Isoflurane anesthesia was employed during all surgical procedures. IF was extracted by wicks inserted intermuscularly in a hind limb. We measured cytokines in plasma and IF, whereas matrix metalloproteinase (MMP) activity and collagen content, as well as the level of glycosaminoglycans and hyaluronan were determined in hind limb muscle. In vivo fatigue protocols of the soleus muscle were performed at 42 and 112 days after induction of heart failure. We found that the MMP activity and collagen content in the skeletal muscles increased significantly at 42 days after induction of CHF, and these changes were time related to increased skeletal muscle fatigability. These parameters returned to sham levels at 112 days. VEGF in IF was significantly lower in CHF compared with sham-operated rats at 3 and 10 days, but no difference was observed at 112 days. We conclude that temporary alterations in the ECM, possibly triggered by VEGF, are related to a transient development of skeletal muscle fatigue in CHF.

Regulation of matrix metalloproteinases by cytokines and reactive oxygen/nitrogen species in the myocardium

Dysregulation of the myocardial extracellular matrix contributes to abnormal cardiac muscle function. Changes in the balance between matrix deposition and matrix degradation by matrix metalloproteinases (MMPs) can lead to cardiac fibrosis and dilation. In this review, we discuss the regulation of MMPs, their endogenous inhibitors (TIMPs) and collagen synthesis by inflammatory cytokines and reactive oxygen/nitrogen species (ROS/RNS). Inflammatory cytokines, such as interleukin-1beta and tumor necrosis factor-alpha, and ROS activate mitogen-activated protein kinases and stress-responsive protein kinases in cardiac cells. In non-cardiac tissues, inflammatory cytokine activation of these kinases is redox sensitive, suggesting ROS may also be involved in cytokine signaling in the heart. Subsequent activation of transcription factors including AP-1, Ets, and nuclear factor kappa-B leads to increased transcription of MMPs. ROS also directly activate MMPs post-translationally. In addition, inflammatory cytokines and ROS lead to decreased TIMP levels and collagen synthesis. Work in animal models suggests that inhibition of inflammatory cytokine or ROS signaling leads to less myocardial remodeling. Further study of the signaling of regulation of the cardiac extracellular matrix may lead to new approaches for the treatment of myocardial remodeling and failure.

Transforming growth factor beta-1 attenuates endothelin-1-induced functions in neonatal cardiac myocytes

In the present study we characterized a "crosstalk" mechanism between transforming growth factor beta-1 (TGF beta-1) and endothelin-1 (ET1) signaling pathways in neonatal cardiac myocytes. A 5 minute pretreatment with 1 ng/ml concentrations of TGF beta-1 attenuated ET1-induced negative chronotropic effects and translocation of the alpha, delta and varepsilonPKC isozymes to the particulate cell fraction. We found no effect of TGF beta-1 on responses induced by the P(2) purinergic agonist ATP or phorbol ester. Treatment of cardiac myocytes with acidic fibroblast growth factor (aFGF) did not alter ET1- or ATP-mediated effects on contraction rate or translocation of PKC isozymes to the particulate fraction. Our studies suggest that TGF beta-1 may act as a negative modulator of ET1- but not ATP- or phorbol ester-induced PKC isozyme signaling events in neonatal cardiac myocytes. A better understanding of the complex ET1 and TGF beta-1 signaling mechanisms in neonatal heart cells should enhance our knowledge regarding the interplay between these pathways.

Cytokine expression increases in nonmyocytes from rats with postinfarction heart failure

Growing evidence suggests that cardiac nonmyocyte cells may play an important regulatory role in the response to myocardial overload and injury via altered expression of paracrine products, such as cytokines and growth factors, but information concerning the cell-specific changes in the expression of these substances in heart-failure models is limited. Therefore, cardiac nonmyocytes were isolated from rats 1 day and 1 and 6 wk after left coronary artery ligation with resulting hemodynamic evidence of heart failure and in sham-operated control animals. mRNAs for tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta, IL-6, transforming growth factors (TGF)-beta1 and TGF-beta3, and type I and type III collagen were measured by Northern analyses. The temporal and quantitative relationships between the expression of these cytokines and collagen and myocyte hypertrophy were determined. mRNA expression of IL-1beta was increased by 1.3-fold at 1 day and 1 wk, and expression of TNF-alpha, IL-1beta, IL-6, TGF-beta1, and TGF-beta3 were increased by 1.4- to 2.1-fold at the 1-wk time point before returning toward baseline at 6 wk. There were significant correlations between the expression of these cytokines and the expression of types I and III collagen, which also peaked at 1 wk. Myocyte hypertrophy was seen first at 6 wk. These observations are consistent with a hypothesis that nonmyocyte cells play a regulatory role in the extracellular matrix changes during postinfarction remodeling and highlight the importance of examining cell-specific changes in gene expression and elucidating the role of cell-to-cell interactions within the myocardium.

Insulin-like growth factor II induces DNA synthesis in fetal ventricular myocytes in vitro

Insulin-like growth factor II (IGF2) belongs to a family of growth factors that includes insulin and insulin-like growth factor I (IGF1). Although the accumulating evidence indicates that IGF1 is involved in regulating proliferation of ventricular myocytes, the role of IGF2 is less clear. To gain more insight into the functions of IGF2, rat ventricular expression of IGF2 mRNA at four developmental stages was examined by Northern analysis. An abundant IGF2 mRNA of approximately 3.8 kb was detected in fetal ventricles. It was dramatically decreased in neonatal ventricles and became undetectable in juvenile and adult ventricles. Similar expression patterns of the mRNA encoding IGF1 receptor and IGF2 receptor were observed. Since the results of Northern analysis strongly suggest the importance of IGF2 in regulating proliferation of fetal rat ventricular myocytes, the effects of an exogenous IGF2 on DNA synthesis in cultured rat ventricular myocytes were determined. DNA synthesis, which was monitored by measuring 5-bromo-2'-deoxyuridine (BrdU) and [3H]thymidine incorporation, was increased by twofold to threefold in IGF2-stimulated fetal ventricular myocytes, whereas no change in BrdU or [3H]thymidine incorporation was observed in neonatal ventricular myocytes. Instead, IGF2 seemed to induce hypertrophy in neonatal ventricular myocytes. An antisense oligonucleotide against rat IGF2 mRNA was able to significantly reduce BrdU incorporation, and this effect was quantitatively reversed by the addition of exogenous IGF2. Reversion by exogenous IGF2 was abolished by a monoclonal antibody against IGF1 receptor. In conclusion, our results suggest that IGF2 directly regulates proliferation of fetal rat ventricular myocytes in a paracrine/autocrine fashion.