Vascular smooth muscle cell peroxisome proliferator-activated receptor-γ mediates pioglitazone-reduced vascular lesion formation - PubMed (original) (raw)

Vascular smooth muscle cell peroxisome proliferator-activated receptor-γ mediates pioglitazone-reduced vascular lesion formation

Milton Hamblin et al. Arterioscler Thromb Vasc Biol. 2011 Feb.

Abstract

Objective: Peroxisome proliferator-activated receptor-γ (PPARγ) has been reported to decrease vascular lesion formation. However, the critical role of vascular smooth muscle cell (VSMC) PPARγ in vascular lesion formation following transplantation is not well understood. In this study, we investigated the role of VSMC PPARγ-mediated signaling in transplantation-associated vascular lesion formation.

Methods and results: Carotid arteries from smooth muscle cell-selective PPARγ knockout (SMPG KO) and wild-type mice were transplanted to CBA/CaJ recipient mice. The recipient mice received a control diet or pioglitazone-containing diet. Pioglitazone reduced vascular lesion formation in transplanted wild-type, but not in SMPG KO carotid arteries. Histological analysis suggested that PPARγ attenuates vascular lesion formation through antiinflammatory signaling, as evidenced by the increase of intimal inflammatory cells and tumor necrosis factor-α expression in SMPG KO allografts. Intravital microscopy revealed increased inflammatory cell rolling and attachment to endothelial cells in small blood vessels of SMPG KO mice following cytokine stimulation. SMPG KO mice, as shown by Western blotting, have elevated vascular cell adhesion molecule-1 (VCAM-1) expression. Furthermore, immunohistochemistry demonstrated SMPG KO allografts have increased VCAM-1.

Conclusions: Loss of PPARγ in VSMC promotes transplantation-associated vascular lesion formation through increased VCAM-1 expression. VSMC PPARγ also mediates pioglitazone-reduced vascular lesion formation.

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Figures

Figure 1

Figure 1. Effects of VSMC PPARγ on vascular lesion formation

(A) Representative histological sections of carotid arteries from VSMC-selective PPARγ knockout (SMPG KO) and wild-type mice that were transplanted to CBA/CaJ recipient mice administered either a pioglitazone-treated diet or normal diet. Scale bars= 50 μm. Thin arrows demonstrate internal elastic layer and thick arrows demonstrate external elastic layer. (B) The effect of pioglitazone on the neointimal area of SMPG KO and wild-type mouse allografts. (C) The effect of pioglitazone on the neointimal area/medial area of SMPG KO and wild-type mouse allografts. n=6 for SMPG KO group and n=7 for wild-type group. Results are mean ± SEM. _P_-values < 0.05 were considered statistically significant.

Figure 2

Figure 2. VSMC PPARγ deletion increases inflammatory cell attachment

Representative hematoxylin and eosin staining of VSMC-selective PPARγ knockout (SMPG KO) and wild-type mouse carotid arteries that were transplanted to CBA/CaJ recipient mice fed a normal diet. Two weeks after transplantation, there was greater inflammatory cell accumulation in the lumens of SMPG KO allografts (B) compared with wild-type allografts (A). n=6 for SMPG KO group and n=7 for wild-type group. The inflammatory cell number for SMPG KO tissue was greater compared with the inflammatory cell number for wild-type tissue (C). Immunohistochemical staining for TNF-α expression revealed a greater area positive for cytokine expression in SMPG KO (E, F) compared with wild-type vessels (D, F). n=3 for each group in immunohistochemical study. Two slides per animal were analyzed for TNF-α expression. Scale bars= 50 μm. Results are mean ± SEM. _P_-values < 0.05 were considered statistically significant.

Figure 3

Figure 3. VSMC PPARγ deletion increases monocyte adhesion in vivo

Intravital microscopy was used for in vivo detection of monocytes labeled with rhodamine 6G. (A) Visualization of monocytes adhering to the venular endothelium of vascular smooth muscle cell PPARγ knockout (SMPG KO) and wild-type mice four hours after a 1 mg/kg lipopolysaccharide (LPS) injection. (B) Mice deficient in VSMC PPARγ displayed increases in the number of monocytes rolling on venular endothelium per minute in both saline- and LPS-treated studies. (C) LPS-injected SMPG KO mice demonstrated a significantly greater number of cells adhering to venular endothelium per minute versus wild-type mice. Data are representative of 6 separate experiments. Arrows represent rhodamine 6G-stained monocytes.

Figure 4

Figure 4. PPARγ affects VCAM-1 levels in VSMC

(A) Western Blot analysis revealed elevated VCAM-1 expression in thoracic arteries of eight-week-old smooth muscle cell-selective PPARγ knockout (SMPG KO) mice. n=3 for each pooled sample. (B, C) SMPG KO allografts, as shown by immunohistochemical staining, demonstrated a greater area of positive for VCAM-1 at two and four weeks after transplantation. n=3 animals for each group in immunohistochemical study. Two slides per animal were analyzed for VCAM-1 expression. (D) PPARγ overexpression by adenovirus (Ad-PPARγ) resulted in decreased VCAM-1 expression in rat aortic smooth muscle cells (RASMC) stimulated with 10 ng/ml hIL-1. In contrast, adenoviral PPARγ knockdown elevated VCAM-1 expression in hIL-1-stimulated cells. Ad-GFP was utilized as a control. (E) The addition of pioglitazone decreased hIL-1-induced increases in RASMC VCAM-1 expression. Results are mean ± SEM. _P_-values < 0.05 were considered statistically significant. Data are representative of 3 separate experiments.

Figure 5

Figure 5. PPARγ knockdown increases NF-κB activation in VSMC

(A) Western Blot analysis of cytosolic and nuclear p65 levels in hIL-stimulated (10 ng/ml) rat aortic smooth muscle cells (RASMC). PPARγ overexpression reduced while PPARγ knockdown increased nuclear p65 levels. Neither PPARγ overexpression nor PPARγ RNAi had any significant effect on cytosolic p65 levels. (B) Western Blot analysis of RASMC nuclear fractions showed PPARγ knockdown increased phosphorylation of both IkappaB kinase (IKK) and IkappaBalpha (IκBα). Ad-GFP served as an adenovirus control. Results are mean ± SEM. _P_-values < 0.05 were considered statistically significant. Data are representative of 3 separate experiments.

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References

    1. Hamblin M, Chang L, Fan Y, Zhang J, Chen YE. PPARs and the cardiovascular system. Antioxid Redox Signal. 2009;11:1415–1452. - PMC - PubMed
    1. Hamblin M, Chang L, Zhang J, Chen YE. The role of peroxisome proliferator-activated receptor gamma in blood pressure regulation. Curr Hypertens Rep. 2009;11:239–245. - PubMed
    1. Duan SZ, Ivashchenko CY, Russell MW, Milstone DS, Mortensen RM. Cardiomyocyte-specific knockout and agonist of peroxisome proliferator-activated receptor-gamma both induce cardiac hypertrophy in mice. Circ Res. 2005;97:372–379. - PubMed
    1. Ding G, Fu M, Qin Q, Lewis W, Kim HW, Fukai T, Bacanamwo M, Chen YE, Schneider MD, Mangelsdorf DJ, Evans RM, Yang Q. Cardiac peroxisome proliferator-activated receptor gamma is essential in protecting cardiomyocytes from oxidative damage. Cardiovasc Res. 2007;76:269–279. - PubMed
    1. Chawla A, Boisvert WA, Lee CH, Laffitte BA, Barak Y, Joseph SB, Liao D, Nagy L, Edwards PA, Curtiss LK, Evans RM, Tontonoz P. A PPAR gamma-LXR-ABCA1 pathway in macrophages is involved in cholesterol efflux and atherogenesis. Mol Cell. 2001;7:161–171. - PubMed

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