The universal NF-kappaB inhibitor a20 protects from transplant vasculopathy by differentially affecting apoptosis in endothelial and smooth muscle cells

Abstract

Transplant vasculopathy (TV) is an accelerated form of atherosclerosis resulting in chronic rejection of vascularized allografts. The causes of TV are multifactorial and integrate at the level of the vascular wall, leading to a phenotypic switch of endothelial cells (ECs) and smooth muscle cells (SMCs). A20 is a NF-kappaB-dependent stress response gene in ECs and SMCs with potent anti-inflammatory effect in both cell types through blockade of NF-kappaB. A20 expression in ECs and SMCs correlates with the absence of TV in rat kidney allografts and long-term functioning human kidney allografts. We demonstrate that A20 protects ECs from tumor necrosis factor, Fas, and natural killer cell-mediated apoptosis by inhibiting proteolytic cleavage of caspase 8. A20 also safeguards ECs from complement-mediated necrosis. Hence, effectively shutting down cell death pathways initiated by inflammatory and immune offenders associated with TV. In contrast, A20 sensitizes SMCs to cytokine and Fas-mediated apoptosis through a novel nitric oxide (NO)-dependent mechanism. The unexpected proapoptotic effect of A20 in SMCs translates in vivo by the regression of established neointimal carotid lesions following balloon angioplasty in rats. Antedating apoptosis of SMCs, expression of the inducible NO synthase increases in A20-expressing neointimal SMCs, corroborating the involvement of NO in causing the proapoptotic effect of A20 in SMCs. Combined anti-inflammatory and anti- or proapoptotic functions of A20 in ECs and SMCs respectively qualify the positive effect of A20 upon vascular remodeling and healing. We propose that A20-based therapies may be effective in prevention and treatment of TV.

Figure 1

Evaluation of I/M ratio on H&E stained rat carotid arteries sections at 28+14 days following balloon angioplasty demonstrates regression of neointima in rAd.A20 transduced vessels as compared to NT and rAd.β-gal transduced vessels. Arrows define the Intima (I) (100X).

Figure 2

Significant iNOS immunostaining is detected in rAd.A20 transduced vessels at day 28+1, antedating increased TUNEL positive cells at day 28+3 within the neointima of these vessels. Representative sections are shown (400X).