Rheologic and Vascular Modulators in Sickle Vaso-occlusion ABSTRACT Sickle cell disease (SCD) is characterized by episodes of painful vaso-occlusive crisis and multiple organ damage, severely compromising the quality of life in the affected individuals. Tissue hypoxia is of primary importance to the pathogenesis of SCD and its attendant complications. Chronic hypoxia is a predictable consequence of abnormal red cell rheology, sickling, hemolytic anemia and recurring vaso-occlusive episodes. In SCD, chronic tissue hypoxia and oxidative stress are likely to activate hypoxia inducible factor (HIF)-1?, a key protein regulating cellular responses to tissue hypoxia. HIF-1? activation and its potential stabilization in SCD (supported by our preliminary observation in transgenic sickle mice) will have both adverse (altered vascular tone) and beneficial (cytoprotective) consequences on microvascular regulation. We hypothesize that HIF-1? expression will be dependent not only on tissue oxygen tension, but also on nitric oxide (NO) bioavailability, carbon monoxide (CO) generation and increased oxidative stress (reperfusion injury). Also, the extent and duration of NO and CO signaling modulated by hemolytic rate and oxidant generation will regulate HIF-1? expression. HIF-1? up-regulates a variety of genes including those for vasoactive stimuli and it also confers protection against reperfusion injury although the role of this transcription factor remains unexplored in SCD. The objective of the proposed in vivo studies is to delineate the relative contribution of these likely mechanisms. In this resubmission, we will focus on the following interrelated aspects: i) examine the factors and mechanisms involved in the regulation of HIF-1? expression in SCD, ii) delineate the role of HIF-1? using HIF-1?-deficient sickle mice, and ii) investigate relative roles of hemolytic rate and oxidative stress in HIF-1 activation. We believe that the proposed studies constitute the first attempt to understand these aspects under in vivo conditions.
Under Specific Aim 1, we will test the hypothesis that intravascular sickling, tissue oxygen tension, reduced NO bioavailability and increased CO production will regulate HIF-1? expression and affect microvascular hemodynamics. Our preliminary studies show that activation of HIF-1? in transgenic sickle is associated with the induction of HO-1 and vascular endothelial growth factor (VEGF), a surrogate marker for HIF-1?. Moreover, we show that hypoxia induces marked activation of HIF-1? in vascular endothelial cells.
Under Specific Aim 2, we will test the hypothesis that, in SCD, HIF-1? activation will contribute to altered vascular tone and reactivity and confer cytoprotection against reperfusion injury by modulating expression of vasoactive/cytoprotective molecules (e.g., HO-1). We will investigate this aspect using bone marrow transplantation from sickle mice into mice partially deficient in HIF-1?, and by super induction of HIF-1?.
Under Specific Aim 3, we will test the hypothesis that, in SCD, hemolysis and oxidative stress have distinct effects on HIF-1? expression and microvascular regulation via NO-dependent mechanism. To explore our hypotheses, we will use state-of-the art transgenic sickle mouse models and mice deficient in HIF-1?, and combine intravital techniques with cellular and molecular analyses. The proposed in vivo studies are expected to provide insights into the adverse and beneficial effects of HIF-1? and NO in SCD, which may lead to new therapeutic strategies.

Public Health Relevance

Sickle cell disease (SCD) is characterized by episodes of painful vaso-occlusive crisis, multiple organ damage, and severely compromising quality of life in the affected individuals. Among African-Americans, sickle cell disease occurs at a rate of 1 per 400 births. Red cell sickling in small-diameter blood vessels is considered the ultimate event in the pathophysiology of vaso-occlusion (vessel blockage). In addition, SCD is characterized by tissue hypoxia that may trigger activation of adaptive mechanisms such as activation of hypoxia-inducible factor-1? (HIF-1?), while persistent hemolysis and oxidative stress will impair nitric oxide (NO) bioavailability and depletion of NO substrate, arginine. The proposed exploratory studies will focus on the role HIF-1? and NO in SCD. A better understanding of the role of in HIF-1? and NO and their interactions will allow us to design future studies with therapeutic implications.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL070047-08
Application #
8204645
Study Section
Hypertension and Microcirculation Study Section (HM)
Program Officer
Luksenburg, Harvey
Project Start
2002-04-01
Project End
2013-11-30
Budget Start
2011-12-01
Budget End
2013-11-30
Support Year
8
Fiscal Year
2012
Total Cost
$373,500
Indirect Cost
$148,500
Name
Albert Einstein College of Medicine
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
110521739
City
Bronx
State
NY
Country
United States
Zip Code
10461
Barabino, Gilda A; Platt, Manu O; Kaul, Dhananjay K (2010) Sickle cell biomechanics. Annu Rev Biomed Eng 12:345-67
Dasgupta, Trisha; Fabry, Mary E; Kaul, Dhananjay K (2010) Antisickling property of fetal hemoglobin enhances nitric oxide bioavailability and ameliorates organ oxidative stress in transgenic-knockout sickle mice. Am J Physiol Regul Integr Comp Physiol 298:R394-402
Kaul, Dhananjay K; Finnegan, Eileen; Barabino, Gilda A (2009) Sickle red cell-endothelium interactions. Microcirculation 16:97-111
Kaul, Dhananjay K; Zhang, Xiaoqin; Dasgupta, Trisha et al. (2008) Arginine therapy of transgenic-knockout sickle mice improves microvascular function by reducing non-nitric oxide vasodilators, hemolysis, and oxidative stress. Am J Physiol Heart Circ Physiol 295:H39-47
Kaul, D K (2008) Sickle red cell adhesion: many issues and some answers. Transfus Clin Biol 15:51-5
Finnegan, Eileen M; Barabino, Gilda A; Liu, Xiao-du et al. (2007) Small-molecule cyclic alpha V beta 3 antagonists inhibit sickle red cell adhesion to vascular endothelium and vasoocclusion. Am J Physiol Heart Circ Physiol 293:H1038-45
Kaul, Dhananjay K; Liu, Xiao-du; Zhang, Xiaoqin et al. (2006) Inhibition of sickle red cell adhesion and vasoocclusion in the microcirculation by antioxidants. Am J Physiol Heart Circ Physiol 291:H167-75
Kaul, Dhananjay K; Liu, Xiao-du; Zhang, Xiaoqin et al. (2006) Peptides based on alphaV-binding domains of erythrocyte ICAM-4 inhibit sickle red cell-endothelial interactions and vaso-occlusion in the microcirculation. Am J Physiol Cell Physiol 291:C922-30
Dasgupta, Trisha; Hebbel, Robert P; Kaul, Dhananjay K (2006) Protective effect of arginine on oxidative stress in transgenic sickle mouse models. Free Radic Biol Med 41:1771-80
Kaul, Dhananjay K; Liu, Xiao-du; Chang, Hee-Yoon et al. (2004) Effect of fetal hemoglobin on microvascular regulation in sickle transgenic-knockout mice. J Clin Invest 114:1136-45

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