TSPO ligands stimulate ZnPPIX transport and ROS accumulation leading to the inhibition of P. falciparum growth in human blood

Abstract

After invading red blood cells (RBCs), Plasmodium falciparum (Pf) can export its own proteins to the host membrane and activate endogenous channels that are present in the membrane of RBCs. This transport pathway involves the Voltage Dependent Anion Channel (VDAC). Moreover, ligands of the VDAC partner TranSlocator PrOtein (TSPO) were demonstrated to inhibit the growth of the parasite. We studied the expression of TSPO and VDAC isoforms in late erythroid precursors, examined the presence of these proteins in membranes of non-infected and infected human RBCs, and evaluated the efficiency of TSPO ligands in inhibiting plasmodium growth, transporting the haem analogue Zn-protoporphyrin-IX (ZnPPIX) and enhancing the accumulation of reactive oxygen species (ROS). TSPO and VDAC isoforms are differentially expressed on erythroid cells in late differentiation states. TSPO2 and VDAC are present in the membranes of mature RBCs in a unique protein complex that changes the affinity of TSPO ligands after Pf infection. TSPO ligands dose-dependently inhibited parasite growth, and this inhibition was correlated to ZnPPIX uptake and ROS accumulation in the infected RBCs. Our results demonstrate that TSPO ligands can induce Pf death by increasing the uptake of porphyrins through a TSPO2–VDAC complex, which leads to an accumulation of ROS.

Activated Microglia in the Brain: Mitochondrial and Cell Membrane-Associated Targets for Positron Emission Tomography

“…This should offer not only new information on the physiological and pathophysiological role of TSPO in inflammatory diseases but also on potential protective mechanisms in infectious diseases like malaria [66].…”

“…Later reports described a TSPO2 isoform in the plasma membrane during differentiation of erythrocytes [66].…”

TSPO2 translocates 5‐aminolevulinic acid into human erythroleukemia cells

“…Moreover, PK 11195 reduced the amount of coproporphyrin but not the PPIX ( Figure 1E). We performed western blots of K562 cell lysate to characterise TSPO2 ( Figure 1F) that was previously described to be localised in RBC plasma membrane and erythroid cells [Fan et al, 2009;An et al, 2014;Marginedas-Freixa et al, 2016]. TSPO2 has a molecular weight about 19 kDa and was mostly observed as a trimer (above standard of 55 kDa).…”

“…Then, cells were fixed by 3% paraformaldehyde for 15 min, quenched for 10 min in 20 mM glycine, permeabilised for 20 min in 0.1% saponin, and blocked in PBS containing 3% BSA and 0.1% saponin for 20 min at room temperature. Primary antibody anti-hTSPO2 (1/200) [Marginedas-Freixa et al, 2016] was added in the same blocking buffer for 1 h. Cells were washed three times in PBS and incubated for 1 h with anti-rabbit Alexa 488 (1/200) and Hoechst dye (1/1000). After three washes, cells were mounted with mounting medium GB Mount (GBI labs).…”

“…TSPO is expressed both at the plasma and outer mitochondrial membranes [Papadopoulos et al, 2006]. Recent data show that isoform 2 of TSPO (TSPO2) is present in the plasma membrane of mature red blood cells (RBC) and expressed on erythroid cells in late differentiation states [Fan et al, 2009;An et al, 2014;Marginedas-Freixa et al, 2016]. The aim of this study was, therefore, to determine the role played by TSPO in ALA incorporation in human erythroleukemia cells.…”