Objectives: Cerebral Malaria (CM) is a severe neurological complication of human malaria caused by the parasite Plasmodium falciparum and a leading cause of malarial deaths worldwide. Plasmodium berghei ANKA (PbA) induced experimental cerebral malaria (ECM), a murine disease model of CM is widely used to study the pathogenesis of CM. In ECM, CD8⁺ T cells migrate to the brain and induce the disruption of the blood brain barrier (BBB). However, the function of brain parenchymal cells especially the astrocytes, in ECM is not understood. In this study, we aim to understand how the deubiquitinating enzyme OTUD7b regulates astrocyte function in ECM.
Methods: Novel GFAP-Cre Otud7b^fl/fl conditional knock out mice were generated lacking OTUD7b in astrocytes. Otud7b^fl/fl and GFAP-Cre Otud7b^fl/fl mice were injected with PbA  infected RBCs and the disease progression was monitored. BBB integrity was investigated by Evans blue permeability assay. Brain pathology was analyzed by IHC. Intracerebral cytokines and chemokines were monitored by qRT-PCR. Activation of NF-κB and p38 MAPKs signalling pathways was analysed invitro by WB. The interaction partner of OTUD7b was identified by IP.
Results: Upon infection, all the Otud7b^fl/fl mice developed signs of ECM while 80% of GFAP-Cre Otud7b^fl/fl mice were protected. GFAP-Cre Otud7b^fl/fl mice displayed reduced brain pathology, had reduced intracerebral levels of the chemokine CXCL-10 and in turn harboured  reduced number of CD8⁺ T cells in the brain. Upon stimulation with iRBCs derived microvesicles invitro, OTUD7b^-/-astrocytes showed reduced activation of NF-κB and p38 MAPKs signalling pathways and reduced production of CXCL-10. Mechanistically, OTUD7b stabilizes TRAF6, by cleaving K48-linked polyubiquitin chains. The stabilized TRAF6 in turn induces CXCL-10 via the NF-κB pathway, which recruits pathogenic CD8⁺T cells to the brain and causes disruption of BBB and ECM.
Conclusions: Our study identifies OTUD7b as a promoter of neuro-inflammation in ECM and a potential therapeutic target.