Red Blood Cell Proteomics: Challenges in biomarker discovery for clinical applications

Abstract

Introduction This thesis describes the application of mass-spectrometry-based approaches on the cytosolic red blood cell (RBC) proteome in gaining improved understanding and insight into the metabolic effects and mechanisms of rare hereditary RBC defects that result in hemolytic anemia. Whilst the responsible mutation or molecular defects resulting in RBC enzymopathies may readily be identified using complementary techniques such as next‐generation sequencing, the particular challenge that we address in these studies is in understanding and linking together the observed physiological presentation to the respective RBC metabolic pathways that are affected. In chapter 2, we review the challenges faced when performing mass spectrometry based proteomics on RBCs as an in‐depth discussion following this general introduction. Here we explore the unmet need to understand rare hemolytic anemias and further detail recent approaches and attempts by experts in the field at solving the well‐known dynamic range problem in RBC proteome analysis. Successes and limitations in using more traditional approaches for biomarker discovery in red blood cell based disorders are also reviewed. Chapter 3 describes the discovery of a potential biomarker that could lead to more comprehensive diagnosis in hereditary non‐spherocytic hemolytic anemia (HNSHA). We sought to use validated quantitative proteomics on the RBC cytosolic proteome of a number of patients with pyrimidine 5’ nucleotidase deficiency. These findings are important in shedding more insight on the pathophysiology i.e. red cell clearance, in pyrimidine 5’ nucleotidase deficiency anemia, and further demonstrate the potential benefit of coupling quantitative proteomics strategies with currently established and routine HNSHA diagnosis procedures. In chapter 4, a similar approach is applied in MS‐based quantification of the enzymatic changes in RBCs obtained from a unique family in which the entire members are affected by a genetic mutation in PIEZO1 protein which is responsible for causing hereditary xerocytosis. In this family only the male members demonstrated physiological characteristics of hereditary xerocytosis, while the female member is asymptomatic. We thus used comparative proteomics to explore the downstream effects of molecular defects in PIEZO1 on RBC function. From our findings we further explore the broad effects of hereditary xerocytosis on RBC energy metabolism, which would be complementary in understanding interrelated protein function in the RBC cytosol. Summary By increasing our understanding on the diagnosis, pathophysiology and molecular basis of RBC enzymopathies, such as in the studies described in this thesis, we can establish robust diagnostic approaches that lead to correct and timely identification of hereditary hemolytic anemias. To a patient suffering from prolonged hemolytic anemia of unknown origin, finally being able to understand the cause and development of their illness may be beneficial in providing peace of mind. More importantly, a better understanding of specific diagnoses would allow for the development of tailored disease treatment regimens which would mitigate possible complications and also allow for appropriate genetic counseling.