Modulation of Reactive Oxygen Species and Collagen Synthesis by Angiotensin II in Cardiac Fibroblasts

ABSTRACT

Angiotensin II increases the NAD(P)H-dependent superoxide anion production and the intracellular generation of reactive oxygen species in cardiac fibroblasts and apocynin, a NAD(P)H oxidase inhibitor, abrogates this rise. The membrane associated NAD(P)H oxidase complex is the predominant source of superoxide anion and reactive oxygen species generation in angiotensin II-stimulated adult cardiac fibroblasts. Inhibition of this NAD(P)H oxidase complex with apocynin completely blocks the angiotensin II-stimulated collagen production, collagen I and III protein and mRNA expression.

Superoxide anion production is also increased by the Cu,Zn-superoxide dismutase (SOD) inhibitor diethyldithiocarbamic acid (DETC) and decreased by the superoxide scavenger tempol in control and ANG II-treated fibroblasts. ANG II and DETC stimulate the collagen production and the collagen I and fibronectin content in fibroblasts. The SOD mimetics tempol and EUK-8 as well as polyethyleneglycol-SOD reduce the collagen production.

ANG II also decreases the activity and mRNA and protein expression of the mitochondrial antioxidants Mn-SOD and peroxiredoxin-3. Upon phosphorylation of Akt by ANG II, P-Akt is translocated from the cytoplasm to the nucleus and nuclear phosphorylation of FOXO3a by P-Akt leads to relocalisation of FOXO3a from the nucleus to the cytosol, resulting in a decrease in its transcriptional activity and in Mn-SOD expression. These data indicate that ANG II inactivates FOXO3a by activating Akt and this leads to a reduction in the expression of the antioxidant Mn-SOD. A role of SOD and the formed reactive oxygen species in the regulation and organization of collagen in cardiac fibroblasts is suggested.

Keywords:

Cardiac fibroblasts, angiotensin II, collagen, reactive oxygen species, superoxide dismutases, peroxiredoxins, FOXO3a.