Reduction of Sphingosine Kinase 1 Phosphorylation and Activity in Plasmodium-Infected Erythrocytes

Abstract

Sphingosine-1-phosphate (S1P), a bioactive lipid mediator is involved in an array of biological processes and linked to pathological manifestations. Erythrocyte is known as the major reservoir for S1P as they lack S1P-degrading enzymes (S1P lyase and S1P phosphohydrolase) and harbor sphingosine kinase-1 (SphK-1) essential for sphingosine conversion to S1P. Reduced S1P concentration in serum was correlated with disease severity in patients with Plasmodium falciparum and Plasmodium vivax infections. Herein, we aimed to identify the underlying mechanism and contribution of host erythrocytes toward depleted S1P levels in Plasmodium-infected patients vs. healthy individuals. The level and activity of SphK-1 were measured in vitro in both uninfected and cultured P. falciparum-infected erythrocytes. Infected erythrocytes demonstrated a significant decrease in SphK-1 level in a time-dependent manner. We found that 10-42 h post invasion (hpi), SphK1 level was predominantly reduced to ∼50% in rings, trophozoites, and schizonts compared to uninfected erythrocytes. We next analyzed the phosphorylation status of SphK-1, a modification responsible for its activity and S1P production, in both uninfected control and Plasmodium-infected erythrocytes. Almost ∼50% decrease in phosphorylation of SphK-1 was observed that could be corroborated with significant reduction in the production and release of S1P in infected erythrocytes. Serum S1P levels were studied in parallel in P. falciparum (N = 15), P. vivax (N = 36)-infected patients, and healthy controls (N = 6). The findings revealed that S1P concentration was significantly depleted in uncomplicated malaria cases and was found to be lowest in complicated malaria and thrombocytopenia in both P. falciparum and P. vivax-infected groups ( * * p < 0.01). The lower serum S1P level could be correlated with the reduced platelet count defining the role of S1P level in platelet formation. In conclusion, erythrocyte SphK-1 and S1P levels were studied in Plasmodium-infected individuals and erythrocytes that helped in characterizing the complications associated with malaria and thrombocytopenia, providing insights into the contribution of host erythrocyte biology in malaria pathogenesis. Finally, this study proposes the use of S1P and its analog as a novel adjunct therapy for malaria complications.

Sphingosine 1-Phosphate in Malaria Pathogenesis and Its Implication in Therapeutic Opportunities

“…It is possible that poor intracellular S1P in parasite infected RBC may favor its binding with un-infected RBCs in rosette for auxiliary S1P to the growing parasite through trans-cellular transportation. In a recent study, the observation of time dependent decrease in SPHK1 activity in infected RBC in vitro culture of falciparum parasite without affecting normal RBC (Sah et al, 2020 ) supports a possible acquisition of S1P from nearby uninfected cells. Investigation on this aspect would thus be helpful in better understanding on involvement of S1P in rosette formation and subsequent complicacy in severe malaria.…”

“…A significant decrease in SPHK-1 phosphorylation and activity were observed in a time-dependent manner in falciparum-infected erythrocytes compared to uninfected RBCs. (Sah et al, 2020) 2 Human Erythrocytes Intracellular parasitic growth was assessed upon pharmacological inhibition of host cell SPHK1 in falciparum infected RBCs…”

“…Also hemoglobin and platelet levels were highly reduced in CM (Finney et al, 2011) 9 Human S1P levels in serum of adult Indian malaria patients (falciparum and vivax infected) were compared to healthy controls S1P level was significantly less in malaria patients compared to healthy control. Complicated malaria patients had the lowest S1P level, and platelet count positively correlated with S1P level (Sah et al, 2020) (Continued) Human Autopsied patients who died with P. falciparum malaria were categorized into PE and Non-PE group, and cellular expression of SPHK-1 and S1PR-3 were investigated using immune histochemistry.…”

“…been documented due to the lack of phosphorylation (Sah et al, 2020). Recently, GPCR proteins such as bradykinin receptors and muscarinic M3 receptor were shown to induce SPHK1 translocation to membrane (ter Braak et al, 2009;Bruno et al, 2018) and thus their inhibition would be provocative of future research.…”

“…Inhibition of SPHK1 phosphorylation at serine 225 has enabled reduced translocation to membrane resulting into deregulated S1P in Leishmaniasis infected macrophages (Arish et al, 2018 ). Reduced SPHK1 activity in falciparum infected RBCs has also been documented due to the lack of phosphorylation (Sah et al, 2020 ). Recently, GPCR proteins such as bradykinin receptors and muscarinic M3 receptor were shown to induce SPHK1 translocation to membrane (ter Braak et al, 2009 ; Bruno et al, 2018 ) and thus their inhibition would be provocative of future research.…”