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Angiotensin II (Ang II), a potent mediator of vascular remodeling, can stimulate the synthesis of extracellular matrix in vascular cells. Recent studies indicate that connective tissue growth factor (CTGF) is involved in collagen synthesis. There is also increasing evidence that adventitial fibroblasts (AFs) are actively involved in vascular remodeling. However, whether collagen synthesis by AFs is mediated by CTGF, or whether it is relevant to Ang II, has not been studied. The present study was conducted to determine whether CTGF is expressed in AFs, and if so, whether the CTGF produced by AFs participates in collagen synthesis. The AFs were isolated from thoracic aorta of Wistar-Kyoto rats (WKY). The expression of CTGF was measured by Western blot or real-time PCR. Collagen synthesis was assessed by [(3)H]proline incorporation. Our results suggested that CTGF was expressed in AFs and secreted into medium. Ang II increased CTGF mRNA and protein expression in a time- and dose-dependent manner, with the maximal protein increase occurring at 24 h with an Ang II dose of 10(-7) mol/L, and this increase was inhibited by the Ang II receptor type 1 (AT(1)-R) antagonist losartan, but not by the Ang II receptor type 2 (AT(2)-R) antagonist PD123319. Ang II dose-dependently stimulated the incorporation of [(3)H]proline into cultured AFs, and this effect was inhibited by a CTGF antisense oligodeoxynucleotide. Overexpression of CTGF by pcDNA3.1(+)/CTGF increased [(3)H]proline incorporation in cultured AFs. The results demonstrated that, in cultured AFs, Ang II increased CTGF production via AT(1)-R, which could be mediators of collagen synthesis by Ang II. This finding suggests that CTGF might be a novel target for antifibrotic therapy in vascular diseases.

Phenotypic differentiation of adventitial fibroblasts into myofibroblasts is an essential feature of vascular remodeling. The present study was undertaken to test the hypothesis that reactive oxygen species (ROS) are involved in rat adventitial fibroblast differentiation to myofibroblast. Activation of alpha-smooth muscle actin (alpha-SMA) was used as a marker of myofibroblast. Angiotensin II increased intracellular ROS in adventitial fibroblasts that was completely inhibited by the free radical scavenger NAC, the NAD(P)H oxidase inhibitor DPI, and transfection of antisense gp91phox oligonucleotides. Myofibroblast differentiation was prevented by inhibition of ROS generation with DPI, NAC, and antisense gp91phox as shown by decreased expression of alpha-SMA. Angiotensin II rapidly induced phosphorylation of p38 MAPK and JNK, both of which were inhibited by DPI, NAC, antisense gp91phox, and the selective AT1 receptor antagonist, losartan. Inhibiting p38MAPK with SB202190 or JNK with SP600125 also reduced angiotensin II-induced alpha-SMA expression. These findings demonstrate that angiotensin II induces adventitial fibroblast differentiation to myofibroblast via a pathway that involves NADPH oxidase generation of ROS and activation of p38MAPK and JNK pathways.

1. In the present study, we compared the elastin and collagen content of thoracic aortic medial and adventitial layers from Wistar-kyoto (WKY) and spontaneously hypertensive rats (SHR). In addition, the effects of losartan, an angiotensin II receptor antagonist, and spironolactone, a mineralocorticoid receptor antagonist, on collagen and elastin content were determined. 2. Prehypertensive (4-week-old) and hypertensive (16-week-old) SHR were randomly divided into three groups treated with either 0.9% NaCl, losartan (20 mg/kg per day) or spironolactone (200 mg/kg per day). Prehypertensive and hypertensive SHR were treated for 12 and 16 weeks, respectively. Age-matched WKY rats were not treated with NaCl, losartan or spironolactone and served as the control group. 3. The medial and adventitial layers of the thoracic aorta were composed mainly of elastin and collagen, respectively, in both SHR and WKY rats. Compared with WKY rats, SHR exhibited greater collagen and elastin content in the media, but decreased collagen and elastin content in the adventitial layer. Both medial and adventitial collagen and elastin content increased significantly with age in both strains and was greater in 32-week-old rats compared with 16-week-old rats. Spironolactone treatment decreased collagen content in the media of thoracic aortas from prehypertensive SHR, whereas losartan decreased collagen content in the media of aortas from hypertensive SHR. In contrast, neither spironolactone nor losartan had any effect on adventitial collagen content in prehypertensive and hypertensive SHR. Medial collagen and elastin were positively related to pulse pressure (PP), but there was no correlation between adventitial mass or collagen content and PP or mean arterial pressure in untreated and treated SHR and WKY rats. 4. In conclusion, the composition of the medial and adventitial layers of the thoracic aorta differs and treatment of SHR with losartan and spironolactone decreases collagen content when delivered at the hypertensive or prehypertensive stage, respectively. However, neither drug has any effect on adventitial collagen content in SHR.