Plasmodium falciparum impairs Ang-1 secretion by pericytes in a 3D brain microvessel model
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Disruption of the vascular protective angiopoietin-Tie axis is common in cerebral malaria (CM) patients, who display elevated angiopoietin-2 (Ang-2) and reduced angiopoietin-1 (Ang-1) blood concentrations. The role of pericytes in CM pathogenesis remains unexplored, despite being a major source of brain Ang-1 secretion and evidence of pericyte damage observed in CM postmortem samples. Here we engineered a human 3D microfluidics-based brain microvessel model containing the minimal cellular components to replicate the angiopoietin-Tie axis, human primary brain microvascular endothelial cells and pericytes. This model replicated pericyte vessel coverage and ultrastructural interactions present in the brain microvasculature. When exposed to P. falciparum -iRBC egress products, 3D brain microvessels presented decreased Ang-1 secretion, increased vascular permeability, and minor ultrastructural changes in pericyte morphology. Notably, P. falciparum -mediated barrier disruption was partially reversed after pre-treatment with recombinant Ang-1 and the Tie-2 activator, AKB-9778. Our approach suggests a novel mechanistic role of pericytes in CM pathogenesis and highlights the potential of therapeutics that target the angiopoietin-Tie axis to rapidly counteract vascular dysfunction caused by P. falciparum .
The paper explained
Problem
Cerebral malaria (CM) is a severe complication of Plasmodium falciparum infection, resulting in the majority of ∼600000 malarial deaths annually. Despite anti-malarial drug administration upon hospitalization, fatality rates still range from 15-25% and many survivors suffer long term neurological disabilities. A common dysregulated vascular pathway identified in CM patients is the angiopoietin-Tie axis. Treatments that restore this vascular homeostatic pathway appear as a potential avenue for adjunctive therapies in experimental rodent CM models. Nevertheless, the use of rodent CM models for therapeutic discovery is not ideal, given that P. falciparum pathogenesis is species-specific. Therefore, the development of novel and advanced human 3D microvascular models offers new avenues to study disease pathogenesis and explore potential adjunctive CM treatments.
Results
In this study, we generate a 3D human brain microvasculature model that reproduces in vivo interactions between two key cell types necessary to reproduce the protective angiopoietin-Tie axis: human brain endothelial cells and pericytes. Addition of P. falciparum -infected red blood cell (iRBC) egress products causes vascular disruption and hampers the release of the vascular protective factor, angiopoietin-1, from brain pericytes. 18-hour pre-treatment of Ang-1 for 18h prevents iRBC egress product-induced vascular disruption. A short pre-treatment of the microvessels with AKB-9778, a downstream pharmaceutical inducer of angiopoietin-Tie axis activity currently in phase II clinical trial for diabetic retinopathy, partially restores vascular integrity. Our study highlights the role of pericytes in CM and the therapeutic potential of interventions that restore the angiopoietin-Tie2 axis as adjunctive CM treatments.
Impact
Our study demonstrates the potential of bioengineered vascular models to recapitulate dysregulated pathways previously characterized in malaria patients, and in providing a physiologically-relevant platform to test adjunctive therapies. The use of the 3D brain microvascular model has enhanced our understanding of the mechanisms behind CM pathogenesis, uncovering a previously unappreciated effect of P. falciparum on brain pericytes, linking angiopoietin-Tie axis dysregulation and microvasculature disruption. These findings pave the way for the identification of novel, fast-acting therapeutics, such as AKB-9778, to restore vascular integrity in CM patients.
