Characterization of primary and restenotic atherosclerotic plaque from the superficial femoral artery: Potential role of Smad3 in regulation of SMC proliferation

Abstract

Objective: To characterize and compare primary and restenotic lesions of the superficial femoral artery and analyze the contribution of TGF-beta/Smad3 signaling to the pathophysiology of peripheral artery occlusive disease.

Methods and results: Immunohistochemical studies were performed on specimens retrieved from the superficial femoral artery of patients undergoing either atherectomy for primary atherosclerotic or recurrent disease after stenting and/or prior angioplasty. Immunohistochemical analysis revealed a significantly higher smooth muscle cell (SMC) content (alpha-actin+) and expression of Smad3 in restenotic lesions while primary lesions contained significantly more leukocytes (CD45+) and macrophages (CD68+). Further studies demonstrated colocalization of Smad3 with alpha-actin and PCNA, suggesting a role for Smad3 in the proliferation observed in restenotic lesions. To confirm a role for Smad3 in SMC proliferation, we both upregulated Smad3 via adenoviral mediated gene transfer (AdSmad3) and inhibited Smad3 through transfection with siRNA in human aortic SMCs, then assessed cell proliferation with tritiated thymidine. Overexpression of Smad3 enhanced whereas inhibition of Smad3 decreased cell proliferation.

Conclusion: Differences in cellular composition and cell proliferation in conjunction with the finding that Smad3 is expressed exclusively in restenotic disease suggest that TGF-beta, through Smad3 signaling, may play an essential role in SMC proliferation and the pathophysiology of restenosis in humans.

Figure 1. Immunohistochemical analysis of human atherosclerotic and restenotic lesions

Immuohistochemistry of primary atherosclerotic (n=5) and restenotic lesions (n=3). Representative sections are shown. Staining for (A) α-actin, (B) PCNA, (C) CD68, and (D) CD45. Magnification 400x. (E) Quantification of positive immunostaining in restenotic or primary atherosclerotic lesions expressed as a ratio of positive/total cells ± standard error (*p<0.001 restenotic compared to primary lesions).

Figure 2. Smad3 staining of human atherosclerotic and restenotic lesions

Smad3 staining of primary atherosclerotic lesions (n=5) and restenotic lesions (n=3). Representative sections are shown. Magnification 400x.

Figure 3. Colocalization of Smad3 with α-actin and PCNA

Double immunofluorescent staining of restonotic plaque. (A) Staining reveals a) nuclei (blue), b) nuclear Smad3 (green), c) α-actin (red), and d) colocalization (nuclear green surrounded by cytoplasmic red) (white arrows). (B) Staining reveals a) nuclei (blue), b) nuclear Smad3 (green), c) nuclear PCNA (red) and d) colocalization (yellow) (white arrows).

Figure 4. The effect of Smad3 on human SMC proliferation

(A) Western blotting of human aortic SMCs demonstrating the effects of Smad3 overexpression via AdSmad3 infection and Smad3 downregulation via transient tranfection with Smad3 siRNA. (B) ³H-thymidine incorporation in human aortic SMCs following overexpression or inhibition of Smad3 (n=3, *p<0.001 compared to AdLacZ or scrambled control).

Figure 5. The effect of Smad3 on SMC apoptosis

Vascular SMCs were infected with AdLacZ or AdSmad3, then lysed and analysed for apoptosis using ELISA. *p<0.05 compared to negative control.