The microbiome determines organ damage development in sickle cell disease

Project Summary: Sickle cell disease (SCD) is the most common inherited blood disorder in the United States, affecting 70,000- 100,000 Americans. SCD is caused by a mutation in the β-globin gene that leads to significant deformation of the red blood cell (RBC) membrane and promotes RBC adhesion to other cells, inducing vaso-occlusive episodes (VOE). Chronic SCD is accompanied by progressive, systemic multi-organ dysfunction and costs over $475 million annually in hospital admissions. Our recent work demonstrates that the depletion of microbiota in SCD mice by antibiotics reduces organ damage and iron overload. Our preliminary data show that organ damage is significantly improved in germ-free SCD mice compared to specific-pathogen-free SCD mice, confirming the importance of microbiota in organ damage development. Analysis by 16S rDNA sequencing uncovered a candidate bacterium—Enterococcus gallinarum (E. gallinarum)—that may promote organ damage in SCD mice. Additionally, we demonstrate that SCD mice fed an iron-restricted diet exhibit significant reversal of organ damage compared with SCD mice fed a control diet. In the current application, we propose a 5-year experimental plan to advance our understanding of the microbiota-mediated effects on SCD disease progression and to test the manipulation of microbiota as a potential novel SCD treatment. In Specific Aim 1, we will confirm whether E. gallinarum functions as a pathogenic bacterium to influence the progression of organ damage in SCD mice. Additionally, we will investigate whether an E. gallinarum–specific vaccine reduces organ damage burden in SCD mice. We will explore the microbiota- related mechanisms that induce organ damage in SCD mice. Specifically, we will study how microbiota can bypass the gut barrier by analyzing relevant gut permeability parameters such as tight junction and mucus layer integrity. We hypothesize that once E. gallinarum translocates from the portal vein to the liver, it upregulates T helper 17 (Th17) cells that recruit other inflammatory cells to induce the organ damage seen in SCD mice. In Specific Aim 2, we will explore the role of dietary iron in gut microbiota survival and whether dietary iron is involved in disrupting gut barrier integrity in SCD mice. These proposed studies, focused on strategies of microbiota manipulation in SCD, will allow us to identify the key microbial species that contribute to SCD pathophysiology and potentially provide novel, cost-effective approaches for managing SCD’s life-long complications.