Plasmodium-infected erythrocytes (pRBC) induce endothelial cell apoptosis via a heme-mediated signaling pathway

Abstract

Heme is cytotoxic to the plasmodium parasite, which converts it to an insoluble crystalline form called hemozoin (malaria pigment) in erythrocytes during replication. The increased serum levels of free heme cause tissue damage, activation of microvascular endothelial and glial cells, focal inflammation, activation of apoptotic pathways, and neuronal tissue damage. Several hypotheses have been proposed to explain how these causative factors exacerbate fatal malaria. However, none of them fully explain the detailed mechanisms leading to the high morbidity and mortality associated with malaria. We have previously reported that heme-induced brain microvascular endothelial cell (HBVEC) apoptosis is a major contributor to severe malaria pathogenesis. Here, we hypothesized that heme (at clinically relevant levels) induces inflammation and apoptosis in HBVEC, a process that is mediated by independent proinflammatory and proapoptotic signaling pathways. In this study, we determined the key signaling molecules associated with heme-mediated apoptosis in HBVEC in vitro using RT2 profiler polymerase chain reaction array technology and confirmed results using immunostaining techniques. While several expressed genes in HBVEC were altered upon heme stimulation, we determined that the apoptotic effects of heme were mediated through p73 (tumor protein p73). The results provide an opportunity to target heme-mediated apoptosis therapeutically in malaria-infected individuals.

Heme-mediated apoptosis and fusion damage in BeWo trophoblast cells

“…We recently found that expressions of several genes were altered when HBVECs underwent apoptosis induced by hemestimulation. Among these genes, tumor protein p73 was one of the significant mediators of the apoptotic effects15. In BeWo cells, we observed a similar p 73 gene regulated apoptosis of trophoblasts induced by heme (Fig.…”

Mesenchymal stromal cells protect against vascular damage and depression-like behavior in mice surviving cerebral malaria

“…We observed BBB disruption at days 6 and 7 post-infection and a higher level of LDH release when HMEC cells were stimulated with heme, indicating increased cell death due to heme from the presence of PbA-infected red cells in the brain. Heme is produced by malaria trophozoites during intra-erythrocytic development and has an important role in the pathophysiology of cerebral malaria [ 20 , 21 ]. Increased levels of free heme contribute to inflammation, tissue damage, and BBB dysfunction [ 22 , 23 ] and lead to apoptosis of brain endothelial cells in vitro [ 20 ].…”

“…Heme is produced by malaria trophozoites during intra-erythrocytic development and has an important role in the pathophysiology of cerebral malaria [ 20 , 21 ]. Increased levels of free heme contribute to inflammation, tissue damage, and BBB dysfunction [ 22 , 23 ] and lead to apoptosis of brain endothelial cells in vitro [ 20 ]. Increased number of leukocytes and platelets at the site of parasite sequestration in the brain and upregulation of chemokines and cytokines are present in malaria patients [ 24 , 25 ] and in murine models of cerebral malaria [ 26 , 27 ].…”

Modelling heme-mediated brain injury associated with cerebral malaria in human brain cortical organoids

“…We previously demonstrated that heme induced endothelial cell apoptosis through Signal Transducer and Activator of Transcription 3 (STAT3) and its target gene Matrix Metalloproteinase 3 ( MMP3 ) signaling 68 . In addition, heme upregulated the Tumor Protein p73 (TP73) levels in human brain endothelial cells in vitro ; depletion of TP73 inhibited heme-induced apoptosis 22 . Furthermore, depletion of circulating endothelial progenitor cells during malaria pathogenesis is a function of heme-induced apoptosis mediated by CXCL-10 induction and toll-like receptor (TLR) activation 66 .…”

“…The role of HCM-induced hemolysis, methemoglobin and free heme in HCM pathogenesis was recently highlighted in mice and in cross-sectional studies in humans 20 . HCM increased hemolysis due to intra-erythrocytic (iRBC) parasite proliferation results in blood-brain barrier (BBB) dysfunction, release of free heme into the brain parenchyma, widespread edema, petechial hemorrhages, neuronal injury, hemiparesis in young adults 21 and death 22 .…”