Therapeutic Targets in Acute Chest Syndrome

SUMMARY This project is aimed at improving the health of individuals who have sickle cell disease (SCD) by defining a potential pro-survival factor of acute chest syndrome (ACS), and exploring whether this factor can be developed as a molecular therapeutic. ACS is the leading pulmonary complication and a common cause of premature death

in SCD. There is no specific treatment for ACS despite decades of intensive research, and so it continues to be a major clinical problem in SCD, particularly, in Africa. We recently discovered that extracellular heme triggers ACS in an inflammatory process involving toll-like receptor 4 signaling. A growing number of experimental,

clinical and genomics studies support this model of ACS pathogenesis in which extracellular heme triggers the acute lung injury. In this new R01 project, we test the novel idea that children express supra-physiological levels of heme oxygenase-1 (HO-1), the rate-limiting heme degradation enzyme. We posit that the high-level HO-1 in

children enhances their ability to clear excess heme from the blood circulation to improve their overall outcome from ACS. In pilot studies, we found that replenishing HO-1 in the plasma of adult SCD mice improved ACS survival. These prior research provide a strong rationale to understand how endogenous HO-1 production is

regulated in SCD, and to test whether a recombinant HO-1 will be efficacious in treating ACS in a preclinical model. Thus, in Aim #1, we will quantify blood HO-1 expression in patients and transgenic mice with SCD, and examine whether HO-1 expression in peripheral blood mononuclear cells is influenced by miR-494 expression

and methylation of a highly conserved CpG site in HMOX1 the HO-1 gene. We will over-express and knock- down miR-494 in human peripheral blood mononuclear cells, and knock-out HO-1 activity in peripheral blood mononuclear cells of transgenic SCD mice, to determine the direct effects of these genetic/epigenetic alterations

on HO-1 concentration in the plasma. We will perform whole genome next generation sequencing of SCD children with extreme levels of blood HO-1 level to identify novel whole genome sequence (WGS) variants that influence activity of this enzyme independent of age, miR-494 and HMOX1 methylation. In Aim #2, we will study

a large cohort of SCD patients in Ghana to assess for the first time whether baseline blood HO-1 level, miR-494 level, HMOX1 methylation and WGS variants influence ACS risk. In Aim #3, we will use functional genomics to test the importance of HO-1 expression in blood cells in improving ACS survival, and test the efficacy of a novel

truncated recombinant HO-1 molecule to rescue transgenic SCD mice from ACS. Data from this project has the potential to fundamentally change our understanding of how the body naturalizes the danger posed by circulating heme on organ function. In addition, it may provide a mechanism to explain the markedly variable ACS outcome

in children and adults, with a tangible therapeutic strategy that can be implemented expeditiously using our novel HO-1 biologic.