Cardiac myocyte-specific overexpression of human GTP cyclohydrolase I protects against acute cardiac allograft rejection

Abstract

Alp NJ, Pieper GM. Cardiac myocyte-specific overexpression of human GTP cyclohydrolase I protects against acute cardiac allograft rejection. Am J Physiol Heart Circ Physiol 299: H88 -H96, 2010. First published April 23, 2010; doi:10.1152/ajpheart.00203.2010 is the rate-limiting enzyme for tetrahydrobiopterin (BH 4) synthesis. Decreases in GTPCH activity and expression have been shown in late stages of acute cardiac rejection, suggesting a deficit in BH4. We hypothesized that increasing intracellular levels of BH4 by cardiac myocyte-targeted overexpression of GTPCH would diminish acute cardiac allograft rejection. Transgenic mice overexpressing GTPCH in the heart were generated and crossed on C57BL6 background. Wild-type and transgenic mouse donor hearts were transplanted into BALB/c recipient mice. Left ventricular (LV) function, histological rejection, BH4 levels, and inflammatory cytokine gene expression (mRNA) were examined. Expression of human GTPCH was documented by PCR, Western analysis, and function by a significant (P Ͻ 0.001) increase in cardiac BH4 levels. GTPCH transgene decreased histological rejection (46%; P Ͻ 0.003) and cardiac myocyte injury (eosin autofluorescence; 56%; P Ͻ 0.0001) independent of changes in inflammatory cytokine expression or nitric oxide content. GTPCH transgene decreased IL-2 (88%; P Ͻ 0.002), IL-1R2 (42%; P Ͻ 0.0001), and programmed cell death-1 (67%; P Ͻ 0.0001) expression, whereas it increased fms-like tyrosine kinase 3 (156%; P Ͻ 0.0001) and stromal-derived factor-1 (2; 190%; P Ͻ 0.0001) expression. There was no difference in ejection fraction or fractional shortening; however, LV mass was significantly increased (P Ͻ 0.05) only in wild-type grafts. The decreases in LV mass, cardiac injury, and histological rejection support a protective role of cardiac GTPCH overexpression and increased BH4 synthesis in cardiac allografts. The mechanism of the decreased rejection appears related to decreased T cell proliferation and modulation of immune function by higher expression of genes involved in hematopoietic/stromal cell development and recruitment.tetrahydrobiopterin; rejection; stromal-derived factor 1; left ventricular mass; guanosine 5=-triphosphate cyclohydrolase TETRAHYDROBIOPTERIN (BH 4 ) is a cofactor for only a few known enzymes including three isoforms of nitric oxide (NO) synthases (NOS), four aromatic amino acid hydroxylases, and glyceryl ether monoxygenase (25,30). Synthesis of BH 4 is regulated by the expression of the key enzyme GTP cyclohydrolase I (GTPCH). The discovery of nuclear localization of GTPCH and other proteins involved in BH 4 synthesis (5) coupled with earlier findings that the mitogenic action of BH 4 in various cells is independent of changes in catecholamine and NO synthesis (1) suggests potentially new unknown roles of BH 4 . Thus there is new awareness of the potential regulation of GTPCH/BH 4 for a vast array of biological processes far beyond that regulating NO and catecholamine synthesis including cell proliferation, cell division, apoptosis,...

Increasing tetrahydrobiopterin in cardiomyocytes adversely affects cardiac redox state and mitochondrial function independently of changes in NO production

“…In our previous studies, we found a significant increase in BH 4 and its metabolites in the heart, reaching a total of about 100-fold higher levels than those found in wild type heart. This accumulation did not alter plasma biopterin levels [22] and, as shown in this study, it did not alter endogenous liver concentrations either indicating that increased GTPCH expression resulting in increased levels of BH 4 has tissue-specific activity. Here we confirmed that increasing cardiomyocyte GTPCH results in an incremental accumulation in both BH 4 and BH 2 in the heart.…”

“…Enhanced GTPCH activity in transgenic hearts (mGCH) was previously shown by specific detection of high GTPCH protein expression and increased BH 4 levels that were several-fold higher than those detected in hearts from wild type mice [22]. To assess the persistence of this increase, we analyzed BH 4 in left ventricle (LV) in hearts from normal growing mGCH at different ages and compared these changes with those found in hearts from age-matched, wild type animals.…”

“…This observation raised the possibility that cardiomyocytes do not mediate NO-regulated responses to cytokines in the adult heart, and that increased GTPCH/NO are better explained by stimulation of other cell types in the heart and/or due to infiltrating inflammatory cells [20,21]. To clarify this idea, we generated a mouse model expressing GTPCH gene in a cardiomyocyte-specific manner (mGCH) [22]. Analysis of the transgenic mouse heart confirmed an increased expression of GTPCH protein together with high BH 4 production.…”

“…Notably, this model showed that increased BH 4 production protected the heart against acute allograft rejection as shown by decreased histological rejection, cardiac injury and cell death. These responses however were not linked to NO surge but to changes in IL-2 and stromal derived factor-1 expression levels [22]. Another model for the cardioprotective activity of cardiomyocyte-targeted BH 4 was indicated in a hyperglycemic model of ischemic preconditioning (IPC) [23].…”

Role of Stromal Cell-Derived Factor-1 in Patients With Non-ST Elevation Acute Coronary Syndrome

“…30) Notably, SDF-1 appears to be actively involved in the pathophysiology of cardiac ischemia-reperfusion injury by promotion of antiapoptotic effects and increase of myocardial STAT3 activation in cardiomyocytes. 31) In cultured cardiomyocytes, SDF-1 expression is strongly upregulated by several factors, including GTP cyclohydrolase I, 32) heme oxygenase-1, 33) hypoxia-inducible factor 1alpha 34) and inflammatory cytokines. 35,36) Together, these experimental data suggest that SDF-1 may provide insight into a distinct pathophysiological axis in ACS.…”