Alcohol modulation of cardiac matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs favors collagen accumulation.

BACKGROUND: Chronic alcohol consumption has been shown in human and animal studies to result in collagen accumulation, myocardial fibrosis, and heart failure. Cardiac fibroblasts produce collagen and regulate extracellular matrix (ECM) homeostasis through the synthesis and activity of matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs), with the balance of MMPs/TIMPs determining the rate of collagen turnover. Dynamic changes of MMP and TIMP expression were reported in alcohol-induced hepatic fibrosis; however, the effect of alcohol on MMP/TIMP balance in the heart and cardiac fibroblasts is unknown. We hypothesized that alcohol exposure alters cardiac fibroblast MMP and TIMP expression to promote collagen accumulation in the heart. METHODS: Cardiac fibroblasts isolated from adult rats were cultured in the presence of alcohol (12.5 to 200 mM) for 48 hours. MMP, TIMP, and collagen type I and III expression were assayed by Western blot analysis. Hydroxyproline (HPro) was used as a marker of collagen production. The in vivo cardiac effects of ethanol (EtOH) were determined using rats exposed to EtOH vapor for 2 weeks, resulting in blood alcohol levels of 150 to 200 mg/dl. Cardiac collagen volume fraction (CVF), as well as MMP, TIMP, and collagen expression, was assessed. RESULTS: EtOH-exposed rats exhibited up-regulation of TIMP-1, TIMP-3 and TIMP-4 in the heart, with no significant increases in MMPs. Cardiac fibroblasts exhibited transformation to a profibrotic phenotype following exposure to alcohol. These changes were reflected by increased α-smooth muscle actin and collagen I and III expression, as well as increased collagen secretion. In vivo EtOH exposure also produced fibrosis, indicated by increased CVF and expression of collagens. CONCLUSIONS: Alcohol exposure modulates cardiac fibroblast MMP/TIMP expression favoring a profile associated with collagen accumulation. Our data suggest that this disrupted MMP/TIMP profile may contribute to the development of myocardial fibrosis and cardiac dysfunction resulting from chronic alcohol abuse.

TNF-α increases cardiac fibroblast lysyl oxidase expression through TGF-ß and PI3Kinase signaling pathways.

TNF-α is a proinflammatory cytokine that is upregulated in many cardiac diseases. The increase of TNF-α expression affects both heart function and the structure of the extracellular matrix. Lysyl oxidase (LOX) is a key enzyme responsible for the maturation of extracellular matrix proteins, including collagens type I and III. In this study, we investigated the regulation of LOX expression and activity by TNF-α using adult rat cardiac fibroblasts. Our results indicate that TNF-α has a dichotomous effect on LOX expression by cardiac fibroblasts. Low dose TNF-α (1-5 ng/ml) decreased LOX expression, whereas higher doses (10-30 ng/ml) increased expression. The higher dose TNF-α effect on LOX expression was attenuated by the inhibition of PI3Kinase/Akt pathway. TGF-ß1 signaling played a significant role in mediating the TNF-α effect. TNF-α increased the expression of TGF-ß, and TGF-ß receptors type I and II, and also stimulated Smad3 phosphorylation. Inhibition of TGF-ß receptor I or Smad3 prevented increased LOX expression by TNF-α. These findings indicate that TNF-α stimulated LOX expression may play an important role in progressive cardiac fibrosis.

Induction of cardiac fibroblast lysyl oxidase by TGF-ß1 requires PI3K/Akt, Smad3, and MAPK signaling.

Lysyl oxidase (LOX) is a key extracellular enzyme responsible for the post-translational modification of collagens I and III to form mature fibrillar collagen. Increased expression of LOX is associated with fibrosis and cardiac dysfunction, yet little is known about the regulation of LOX in the heart. In this study, the cell signaling pathways responsible for the regulation of LOX expression by transforming growth factor (TGF)-ß1 were assessed. Adult cardiac fibroblasts were isolated from male Sprague-Dawley rat hearts by enzymatic digestion. Fibroblasts were grown in DMEM with 10% FBS until approximately 80% confluent, growth arrested for 24h, and then treated with TGF-ß1 (0-10 ng/ml), in the absence or presence of inhibitors of (1) PI3K (wortmannin), (2) Smad3 (SIS3), (3) p38-MAPK (PD169316), (4) JNK (SP600125) and (5) ERK1/2 (PD98059). TGF-ß1 treatment significantly upregulated LOX mRNA and protein expression in cardiac fibroblasts, as well as activity in the cell-conditioned media. Concomitant increases in collagen types I and III, and bone morphogenic protein (BMP-1) expression were found in response to TGF-ß1. The increase of LOX protein in response to TGF-ß1 was prevented by inhibitors of PI3K, Smad3, p38-MAPK, JNK and ERK1/2. Blockade of PI3K also decreased TGF-ß1 induced phosphorylation of Smad3, suggesting that the PI3K/Akt and Smad pathways may be integrated in TGF-ß1 signaling. Further studies are warranted to address the regulation of LOX in the normal and diseased heart, and how this critical extracellular enzyme may be targeted for clinical benefit.