Systemic Rather Than Local Heme Oxygenase-1 Overexpression Improves Cardiac Allograft Outcomes in a New Transgenic Mouse

Abstract

Heme oxygenase-1 (HO-1), a rate-limiting enzyme in heme catabolism, exhibits potent antioxidant and anti-inflammatory properties. We developed HO-1 transgenic (Tg) mice using a rat HO-1 genomic transgene under the control of the endogenous promoter. Transgene expression was demonstrated by RT-PCR in all studied tissues, and a modest HO-1 overexpression was documented by Western, ELISA, and enzyme activity assays. To assess the effect of local vs systemic HO-1 in the acute rejection response, we used Tg mice as organ donors or recipients of MHC-incompatible heart grafts. In the local HO-1 overexpression model, Tg allografts survived 10.5 ± 0.7 days (n = 10), compared with 6.5 ± 0.4 days (n = 6) for wild-type donor controls (p = 0.0001). In the systemic HO-1 overexpression model, Tg recipients maintained allografts for 26.8 ± 3.4 days (n = 10), compared with 6.3 ± 0.1 days (n = 12) in wild-type controls (p = 0.00009). Inhibition of HO activity by treatment with tin protoporphyrin blunted survival advantage in Tg mice and resulted in acute graft rejection (n = 3). Increased carboxyhemoglobin levels were consistently noted in Tg mice. Comparisons of grafts at day 4 indicated that HO-1 overexpression was inversely associated with vasculitis/inflammatory cell infiltrate in both models. Hearts transplanted into Tg recipients showed decreased CD4+ lymphocyte infiltration and diminished immune activation, as judged by CD25 expression. Thus, although local and systemic HO-1 overexpression improved allograft outcomes, systemic HO-1 led to a more robust protection and resulted in a significant blunting of host immune activation. This Tg mouse provides a valuable tool to study mechanisms by which HO-1 exerts beneficial effects in organ transplantation.

Heme Oxygenase-1 Promoter Polymorphism Protects Liver Allograft

“…In spite of our findings in clinical liver transplantation, HO-1 was shown to modulate inflammatory responses in a transgenic mouse model [20]. We speculate that in the mice, the HO-1 expression levels are much higher than the intrinsic HO-1 in human stressed liver cells.…”

Carbon Monoxide Produced by Heme Oxygenase-1 Suppresses T Cell Proliferation via Inhibition of IL-2 Production

“…It has been reported that HO-1-deficient mice contract a progressive chronic inflammatory disease, demonstrated by enlarged spleen and lymph nodes, high peripheral white blood cell counts, and high splenic and lymph node CD4 ϩ :CD8 ϩ T cell ratios with numerous activated CD4 ϩ T cells (4,5). It has also been reported that splenocytes isolated from HO-1-overexpressing mice tend to display lower proliferation indices against allogeneic stimulation in both CD4 ϩ and CD8 ϩ subsets and markedly increased allotransplant survival by inhibiting infiltrations of inflammatory cells and CD4 ϩ T cells (29). The administration of a HO-1 inducer to normal mice results in suppressions of T cell-mediated cytotoxicity and Th1-mediated cytokine production and decreases in the lymphoproliferative alloresponse and differentiation of CTLs (30).…”

ERK5 Activation Inhibits Inflammatory Responses via Peroxisome Proliferator-activated Receptor δ (PPARδ) Stimulation

“…The cytoprotective role of HO-1 has been observed recently in many kinds of cells including skeletal muscle (37), cardiomyocytes (38), hepatocytes (39,40), as well as in vascular endothelial cells (16,41). Several mechanisms could be responsible for the cytoprotective action of the HO-1.…”