Severe malaria kills about 900,000 children a year and impairs brain function in some survivors. Human CM (HCM) is a severe form of malaria characterized by sequestration of parasitized red blood cells (pRBCs) in cerebral micro-circulation and induction of inflammatory mediators which cause impaired consciousness with unarousable coma. We reported [PLoS One, 2012;7(3):e34280)] that excess production of heme, a by-product of Plasmodium berghei-damaged erythrocytes during infection, is a major cause of inflammation, loss of blood brain barrier (BBB) integrity and tissue damage associated with fatal experimental cerebral malaria (ECM) . Excess free heme induces up-regulation of STAT3 and CXCL10 whereas up-regulation of HO-1, an essential enzyme in heme catabolism, limits sequestration of pRBC, induction of inflammatory mediators and brain tissue damage caused by ECM. Following a screen for agents that attenuate ECM, we identified Neuregulin- 1(NRG-1), a 8 kDa peptide currently undergoing clinical trials for use against traumatic brain injury, that attenuates mortality, limits sequestration of pRBC, induces anti-inflammatory mediators and reduces brain tissue damage in ECM when delivered intravenously or intra-peritoneally at 5g/kg (J Neuro,2014:11:9). NRG- 1 mediated attenuation of mortality was via perturbation of expression of a network of pro-inflammatory and anti-inflammatory factors during ECM pathogenesis. We observed that ECM resistant mice (BALB/c) constitutively expressed higher levels of NRG-1 in brain tissue than ECM susceptible (C57BL/6) mice. In human malaria, serum NRG-1 was higher in mild malaria cases but lowest in fatal HCM indicating a possible inhibitory role of infection on endogenous serum NRG-1 production. Expression of NRG-1 in brain tissue, on the other hand, was dependent on expression of ErbB4, a NRG-1 receptor, in damaged brain regions. Since NRG-1 negatively regulates STAT3 and CXCL10 (a key biological determinant of fatal ECM) and positively regulates HO-1, our goal is to functionally assess the key pathways perturbed by NRG-1 to attenuate ECM and HCM pathogenesis. Our main hypothesis is that NRG-1 attenuates CM mortality by down regulating CXCL10 and STAT3 activation and up regulating HO-1. The proposed study focuses on the mechanism by which NRG- 1 regulates the heme-STAT3-CXCL10-HO-1 system to protect against fatal ECM.
Three specific aims are proposed.
Specific Aim 1 : will test the hypothesis that NRG-1 is essential for protection of brain microvascular endothelium and blood-brain barrier (BBB) against heme-induced damage in human CM pathogenesis.
Specific Aim 2 : will test the hypothesis that NRG-1 is essential for protection against ECM-induced CNS damage and neurobehavioral outcomes via heme-STAT3-CXCL10-HO-1 signaling pathway.
Specific Aim 3 : will test the hypothesis that NRG-1 attenuates severe HCM by restoring integrity of human blood-brain barrier. Understanding the protective effect of NRG-1 against CM pathogenesis and mortality will provide opportunities for discovery of a new class of small molecule adjunctive therapeutics and interventions against fatal CM.
Most adjunctive treatments developed to date against severe malaria have not reduced fatal outcomes mainly because the treatments focus on clearance of circulating parasites but ignores deleterious parasite and host factors that appear early after infection or remain after treatment. We were first to report that heme-activated STAT3 and CXCL10 signaling during Plasmodium infection mediates pathogenesis of fatal cerebral malaria (CM) and that Neuregulin-1 (NRG-1), a potent anti-inflammatory/cytoprotective factor, significantly attenuates experimental cerebral malaria (ECM)- associated mortality via down-regulation of STAT3 and CXCL10 and up-regulation of HO-1. The proposed study will clarify the role of NRG-1 in attenuation of ECM and human cerebral malaria (HCM) and mechanisms mediating its function.
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