Expression of Netosis Regulators and Correlation with Inflammatory and Coagulation Biomarkers in Sickle Cell Anemia Patients

Introduction: Sickle cell anemia (SCA) is a multi-systemic disease characterized by inflammation and chronic hemolysis. SCA is also associated with an increased risk of venous thromboembolism (VTE), with recent evidence suggesting that coagulation activation could also be involved in the pathogenesis of progressive organ failure in this condition. The generation of neutrophil extracellular traps, also termed NETosis, has been associated with the pathogenesis of VTE, and is also part of the immunothrombosis process. Furthermore, biomarkers of NETosis have been demonstrated in both animal models and SCA patients. NETosis is a complex process that involves the orchestrated participation of several proteins such as peptidyl arginine deaminase (PADI4), neutrophil elastase (ELANE) and myeloperoxidase (MPO). PADI4 mediates histone critulination, an essential step for NETosis, so that inhibition of PADI4 could be considered a potential therapeutic strategy for conditions in which NETosis play a relevant pathogenic role. Although attractive, investment in this strategy requires a more detailed knowledge of the role of PADI4 in pathogenesis of SCA. Objetives: in this study, we aimed to evaluate the expression of PADI4, ELANE, and MPO in steady state SCA patients, and to correlate these results with markers of inflammation and coagulation activation. Methods: mRNA was obtained from isolated neutrophils, and gene expression of PADI4, ELANE, and MPO were measured by qPCR in 54 steady state SCA patients and 40 healthy volunteers matched by age and geographic origin. Gene expressions levels were then correlated with inflammatory mediators and D-dimer. Results: no significant difference could be observed in the expression of PADI4 (0.55 vs 0.49; P = 0.42) and MPO (0.29 vs 0.39; P = 0.88) between healthy volunteers and patients respectively. In contrast, ELANE was up-regulated when patients compared with controls (1.46 vs 0.16; P <0.0001). PADI4 expression did not correlate with any biomarker of inflammation or coagulation (P>0.05). Interestingly, both ELANE and MPO were positively correlated with D-dimer (R=0.4; P=0.004 and R=0.32; P=0.004, respectively), and Von Willebrand factor (R=0.27; P=0.04 and R=0.30; P=0.04, respectively). ELANE was also correlated with TNF-α (R=0.30; P=0.03). Conclusion: gene expression of ELANE, but not PADI4 is up-regulated in steady state SCA patients, with both ELANE and MPO presenting significant associations with D-dimer and other biomarkers of inflammatory activation. Additional studies are ongoing to evaluate PADI4 expression and activity, both in steady state and during acute episodes in SCA. A more detailed evaluation of the role of PADI4 in the pathogenesis of SCA is warranted for the proper design of clinical trials based on PADI4 inhibition.