Hypoxic Response Contributes to Altered Gene Expression and Precapillary Pulmonary Hypertension in Patients With Sickle Cell Disease

Abstract

Background We postulated that the hypoxic response in sickle cell disease (SCD) contributes to altered gene expression and pulmonary hypertension, a complication associated with early mortality. Methods and Results To identify genes regulated by the hypoxic response and not other effects of chronic anemia, we compared expression variation in peripheral blood mononuclear cells from 13 SCD subjects with hemoglobin SS genotype and 15 Chuvash polycythemia subjects (VHLR200W homozygotes with constitutive up-regulation of hypoxia inducible factors in the absence of anemia or hypoxia). At 5% false discovery rate, 1040 genes exhibited >1.15 fold change in both conditions; 297 were up-regulated and 743 down-regulated including MAPK8 encoding a mitogen-activated protein kinase important for apoptosis, T-cell differentiation and inflammatory responses. Association mapping with a focus on local regulatory polymorphisms in 61 SCD patients identified expression quantitative trait loci (eQTL) for 103 of these hypoxia response genes. In a University of Illinois SCD cohort the A allele of a MAPK8 eQTL, rs10857560, was associated with pre-capillary pulmonary hypertension defined as mean pulmonary artery pressure ≥25 and pulmonary capillary wedge pressure ≤15 mm Hg at right heart catheterization (allele frequency=0.66; OR=13.8, P=0.00036, n=238). This association was confirmed in an independent Walk-PHaSST cohort (allele frequency=0.65; OR=11.3, P=0.0025, n=519). The homozygous AA genotype of rs10857560 was associated with decreased MAPK8 expression and present in all 14 identified pre-capillary pulmonary hypertension cases among the combined 757 patients. Conclusions Our study demonstrates a prominent hypoxic transcription component in SCD and a MAPK8 eQTL associated with pre-capillary pulmonary hypertension.

Association of circulating transcriptomic profiles with mortality in sickle cell disease

“…Furthermore, pathway-based analysis of these transcriptomes clusters to signaling cascades known to be pathophysiologically relevant in SCD. 7,11,15,19,26,[33][34][35][36] Our data suggest that the transcriptome classifier is a biomarker that reflects disease severity as evidenced by abnormalities in important pathways that are driven by HbS polymerization and reflect the systemic nature of the complications of SCD. As such, FAIME analyses provide insights into the potential mechanistic and pathophysiological relevance of molecular clusters downstream of the inciting HgS polymerization event in SCD.…”

“…Seemingly heterogeneous pathways in porphyrin metabolism, bile secretion, and complement and coagulation cascades along with VEGF signaling and immune-mediated processes have all been shown to be directly relevant to SCD. 7,11,15,19,26,[33][34][35][36] Recently, meta-analysis of 4 published datasets of differentially regulated molecular pathways related to SCD demonstrated near identical pathways to those that are associated with survival in the current work including porphyrin metabolism, complement and coagulation cascades, VEGF signaling, and immune-mediated processes. 15 Another group evaluated differentially regulated genes by both RNAsequencing and conventional gene expression profiling in whole For personal use only.…”

“…15,[17][18][19]35,[37][38][39] Gene expression of PBMCs from patients with SCD have exhibited associations with iron homeostasis, inflammation, immunity, and the role or T cells, hypoxic response, and PH. 15,19,35 PBMCs comprise lymphocytes and monocytes and, occasionally, nucleated red blood cells. Cheadle et al 40 have reported an enrichment in erythroid-specific gene expression in PBMCs associated with disease severity in patients with idiopathic and sclerodermaassociated pulmonary arterial hypertension.…”

“…Evidence suggests that plasma concentrations of targeted proteins or changes in blood cells may be informative of disease presence, severity, and prognosis. 14 Changes in the peripheral blood transcriptome of patients with SCD have been well documented 7,[15][16][17][18][19][20] ; however, the ability of the transcriptome to predict outcomes has not been assessed. Given the established role of peripheral blood mononuclear cells (PBMCs) in inflammation and the utility of PBMC-derived gene expression in both diagnostic and prognostic aspects of other entities, [21][22][23][24][25] we hypothesized that PBMC gene expression profiling may be predictive of poor outcomes in patients with SCD.…”

Pulmonary Vascular and Ventricular Dysfunction in the Susceptible Patient (2015 Grover Conference Series)

“…Homozygosity for the A allele was present in all 14 of the patients with precapillary PH that we examined, suggesting that the dosage effect of the A allele on MAPK8 gene expression might contribute to the pathogenic mechanism of precapillary PH in SCD. 145 …”