Metabolomic Profiling Identifies Hypoxia-Induced Imbalanced Lands' Cycle Promotes Sickling and Disease Progression

Sickle cell disease (SCD) is a prevalent hemolytic genetic disorder with high morbidity and mortality affecting millions of individuals worldwide. Although it is well accepted that deoxygenation and polymerization of sickle hemoglobin (HbS) are initial triggers for sickling, it has been known for more than three decades that abnormal membrane lipid organization and composition are found in sickle erythrocyte. Early studies showed some lipids are altered in sickle erythrocytes, however, no studies have identified overall membrane lipid alteration and functional role of those altered specific lipids in SCD. Using unbiased metabolomic profiling, we found that lysophospholipids (LPLs), particularly lysophosphocholines (LysoPCs), were significantly elevated inside erythrocytes of mice with SCD due to imbalanced Lands' cycle. Lands' cycle containing two concerted enzymes: phospholipases A₂ (PLA2s) and lysophospholipid acyltransferases (LPLATs) was initially discovered in 1958. However, its function and cellular regulation in membrane homeostasis in SCD remain unrecognized prior to our metabolomics screening. Here, we demonstrated that enhancing imbalanced Lands' cycle promotes a process of sickling and disease progression in mice by inducing LysoPC content inside erythrocytes. Significantly, correcting impaired Lands' cycle reduced LysoPC levels within erythrocytes and attenuated sickling and disease progression in mice. Mechanistically, we revealed that hypoxia-mediated MEK/ERK activation underlies imbalanced Lands' cycle by preferentially inducing activity of PLA2 but not LPCAT1 in mouse sickle erythrocytes. Additionally, the detrimental role of impaired Lands' cycle-induced LysoPC production in sickling via MEK/ERK-dependent activation of PLA2 in SCD patients mirrors our mouse finding. Overall, our studies have identified a pathological role of imbalanced Lands' cycle in SCD, revealed molecular basis regulating Lands' cycle and immediately provided novel therapeutic possibilities for the disease.