Figure 6
From: Hypoxia-mediated impaired erythrocyte Lands’ Cycle is pathogenic for sickle cell disease
Imbalanced Lands’ cycles is seen in SCD patients and contributes to hypoxia-induced sickling by preferentially inducing PLA2 activity in MEK/ERK-dependent manner.
(a,b) Measurement of PLA2 activity (a) and LPCAT activity (b) in the erythrocytes from healthy volunteers (control, n = 15) and patients with SCD (n = 22). (c–f) LysoPC content (c), PC content (d), the ratio of LysoPC/PC (e) and the percentage of LysoPC/PL (f) were quantified in the erythrocytes of controls and individuals with SCD. Error bars, SEM; n = 8. *P < 0.05 versus control, **P < 0.01 versus control. (g) Quantification of blood smear of human SCD erythrocytes treated with DMSO or different dosage of cPLA2 inhibitors, MAFP and Pyrrophenone or LPCAT inhibitor, CI-976 under 4% oxygen condition for 2 hours, respectively. (h) Quantification of blood smears of human SCD erythrocytes treated with methanol (vehicle) or different concentrations of LysoPC under 4% oxygen conditions for 2 hours. Error bars, SEM; n = 6. *P < 0.05, **P < 0.01 versus controls. (i) Measurement of PLA2 activity in human SCD erythrocytes treated with DMSO or two different MEK inhibitors, PD98059 (20 μM) and U0126 (10 μM) under hypoxic condition, respectively. (j) Quantification of blood smear analysis of human SCD erythrocytes treated with DMSO or two different MEK inhibitors. Data are represented as the mean percentages of sickled cells ± SEM (n = 6). *P < 0.05 versus SCD Tg mice treated with DMSO under normoxia. **P < 0.05 relative to DMSO-treated group under hypoxia condition. (k) Working Model: hypoxia preferentially induced elevation of activity of erythrocyte cPLA2 but not LPACT1 via MEK/ERK signaling cascade results in increased generation of erythrocyte LysoPLs and free fatty acids, in particular LysoPC and AA and subsequently increased release of AA to the circulation in SCD. Under hypoxia, increased erythrocyte membrane LysoPC and deoxygenated HbS work together to promote sickling. Moreover, elevated circulating AA leads to increased production of multiple inflammatory mediators including leukotrienes and prostaglandins. As such, imbalanced erythrocyte Lands’ cycle-mediated elevated LysoPC and AA are pathogenic to induce sickling, inflammation and tissue damage. Thus, correcting impaired Lands’ cycle is a novel therapeutic approach for SCD management.
