Macrophage-stimulated microRNA expression in mural cells promotes transplantation-induced neointima formation

Abstract

In this study, we tested the possibility that macrophages might contribute to neointima formation by stimulating microRNA expressions in mural cells. Thoracic aortas from F344 rats were transplanted into recipient Lewis rats. Clodronate liposome was used for in vivo macrophage depletion. Using miR-21 as a prototypic example of vascular enriched microRNA, we showed that macrophage depletion reduced the expression level of miR-21, which was upregulated in the allograft. This effect of macrophage depletion was accompanied by attenuations in neointimal hyperplasia and transplantation-induced vascular inflammation. Using in vitro assays, we identified that macrophages might stimulate miR-21 expression in smooth muscle cells and adventitial fibroblasts via the release of tumor necrosis factor-α. We also showed that silencing of miR-21 suppressed tumor necrosis factor-induced proliferation, migration, and inflammatory responses in mural cells. Our results suggest that macrophage may promote transplantation-induced neointima formation by stimulating miR-21 expression in vascular mural cells, which promotes mural cell proliferation, migration and/or inflammation. Moreover, we have established that tumor necrosis factor-α has a major role in mediating this paracrine process.

Adventitial Activation in the Pathogenesis of Injury-Induced Arterial Remodeling

“…21,26 Moreover, our results have demonstrated that targeting adventitial macrophage accumulation and activation may effectively repress transplantation-induced arterial remodeling. 32 It is suggested that activation of the tunica adventitia may have crucial implications in the pathogenesis of transplant vasculopathy (Figure 1). Further investigations are warranted to clarify whether inhibiting adventitial NADPH oxidase and the process of neovascularization may represent new strategies for preventing this disease.…”

“…Moreover, treating transplanted vessels with miR-21 antagomir induced a significant reduction in the development of neointima and significantly reduced the inflammatory responses in both media and adventitia. 32 Using in vitro assays, macrophages were found to stimulate miR-21 expression in smooth muscle cells and adventitial fibroblasts via the release of tumor necrosis factor-a, whereas silencing of miR-21 expression attenuated tumor necrosis factoreinduced proliferation, migration, and inflammation in smooth muscle cells and fibroblasts. 32 More important, it was confirmed that systemic depletion of macrophages concomitantly repressed the vascular miR-21 expression and ameliorated transplantation-induced neointimal remodeling.…”

“…32 Using in vitro assays, macrophages were found to stimulate miR-21 expression in smooth muscle cells and adventitial fibroblasts via the release of tumor necrosis factor-a, whereas silencing of miR-21 expression attenuated tumor necrosis factoreinduced proliferation, migration, and inflammation in smooth muscle cells and fibroblasts. 32 More important, it was confirmed that systemic depletion of macrophages concomitantly repressed the vascular miR-21 expression and ameliorated transplantation-induced neointimal remodeling. These observations suggest that adventitial macrophages may promote transplant vasculopathy by regulating miRNA expressions in vascular mural cells via paracrine factors, and this process may represent a novel mechanism underlying the pathogenesis of transplant vasculopathy.…”

“…27 Similarly, we and others have shown that systemic depletion of endogenous macrophages suppressed the development of transplant vasculopathy. 31,32 It has been recognized that the initial phases of adventitial inflammatory cell infiltration are similar in both acute arterial injuries and chronic vascular diseases, like atherosclerosis. 9 Mechanistically, monocytes/macrophages can secrete various cytokines and proinflammatory factors, including ILs, tumor necrosis factor-a, transforming growth factor-b, and platelet-derived growth factor.…”

“…36 The expression of miR-21 in adventitia and media is increased over time after aorta transplantation. 32 Adventitial fibroblasts isolated from the transplanted aorta were cultured, and an increased expression of miR-21 was observed in comparison to cells isolated from sham vessels. Moreover, treating transplanted vessels with miR-21 antagomir induced a significant reduction in the development of neointima and significantly reduced the inflammatory responses in both media and adventitia.…”