Effects of elevated glucose levels on interactions of cardiac fibroblasts with the extracellular matrix.

Exposure of fibroblasts to high glucose levels promotes a fibrotic response characterized by increased expression of extracellular matrix components including interstitial collagens. Little is known about the effects of glucose levels on other aspects of fibroblast function. Fibroblasts in the myocardium are surrounded by an extensive extracellular matrix composed predominantly of type I collagen. Interactions between fibroblasts and the myocardial extracellular matrix are thought to affect heart function by altering ventricular diastolic properties. The purpose of the present study was to determine the effects of elevated glucose levels on the interactions between heart fibroblasts and the collagenous extracellular matrix. Studies were performed to determine the effects of relative glucose levels on the ability of fibroblasts to migrate on and contract a three-dimensional collagenous substratum. These experiments illustrated that exposure of cardiac fibroblasts to high glucose levels (25 mM) resulted in decreased migratory activity of fibroblasts on a collagen matrix and decreased fibroblast proliferation. In addition, high glucose stimulated collagen and collagen-binding integrin expression and contraction of three-dimensional collagen gels by cardiac fibroblasts. These studies illustrate that altered glucose levels induce important changes in the interactions of cardiac fibroblasts with the collagenous extracellular matrix.

17beta-estradiol modulation of angiotensin II-stimulated response in cardiac fibroblasts.

The ovarian hormone, 17beta-estradiol, has been suggested to play an important role in gender-specific differences in cardiovascular diseases. One possible cardioprotective mechanism involves the interaction between 17beta-estradiol and the renin-angiotensin system. Previous studies demonstrated that fibroblast function and gene expression are regulated by biochemical factors including growth factors, hormones, and cytokines, but little is known regarding the integration of these diverse signals. Therefore, the purpose of this study was to determine the ability of 17beta-estradiol to modulate angiotensin II (AngII) effects on integrin-induced collagen gel contraction, matrix metalloproteinase (MMP) activity and expression, and signal transduction pathways in isolated neonatal cardiac fibroblasts. 17beta-estradiol significantly attenuated AngII-stimulated collagen gel contraction and significantly diminished the effect of AngII on the expression of beta1 and not alpha1integrins. Active MMP-2 levels were decreased by AngII and addition of 17beta-estradiol resulted in further reductions. Relative MMP-2 mRNA levels showed essentially identical patterns to protein levels. 17beta-estradiol pretreatment increased AngII-mediated mitogen-activated protein (MAP) kinase p42/44 activation and slightly decreased p38 activation compared to non-pretreated fibroblasts. Simultaneous addition of 17beta-estradiol and AngII had little to no effect on AngII activation of p42/44 or p38 MAP kinase. The current studies demonstrate the inhibitory role of estrogen on AngII-induced fibroblast-mediated ECM remodeling, gene expression, and signal transduction. These studies begin to elucidate the mechanisms of estrogen effects on myocardial remodeling and function.