Identification of host genetic factors involved in cerebral malaria resistance: from mouse to human

Malaria is a parasitic (Plasmodium spp.) blood infection that affects over 300 million people annually and has applied strong selective pressure on the human genome in endemic areas. Several protein variants in erythrocyte and immune cells have been associated with protection against uncomplicated and severe disease including malarial anemia and cerebral malaria. We have used an unbiased forward genetic approach to compare inbred mice that display differential susceptibility to P. berghei ANKA infection as a means to study genetic determinants of experimental cerebral malaria. Susceptible C57BL/6 mice display early appearance of neurological symptoms and uniform lethality prior to day 12 post-infection, while resistant BALB/c mice succumb to anemia much later in infection without developing significant cerebral pathology. We used quantitative trait locus (QTL) mapping in F2 mice derived from C57BL/6 and BALB/c parental strains, and localized this difference to a 10-20Mb region of chromosome 19 (LOD = 4.69, p<0.05), which we termed Berr5. Comparing brain RNA expression profiles following infection suggested the interferon-induced proteins with tetratricopeptide repeats gene cluster (Ifit1-3) or Fas as candidate genes underlying differential survival. Berr5 also overlapped with three other infection and inflammatory QTLs supporting a model where upregulation of inflammatory molecules may be critical to cerebral malaria pathology. Independently, we also report that BXH2 mice carrying a mutation in Interferon Regulatory Factor 8 (Irf8R294C) are completely resistant to cerebral malaria. Using microarray transcript profiling and chromatin immunoprecipitation coupled to sequencing (ChIP-Seq), we found that 92 of the 125 genes upregulated by infection in susceptible controls contained an IRF8 binding site, and further identified a core subset of 53 genes which were also regulated in response to Mycobacterium tuberculosis. Response of these genes in infected BXH2 mice is significantly blunted and therefore, this list may represent key drivers of the pathological response. Third, having previously shown that mutations in pyruvate kinase cause susceptibility to blood stage malaria in vivo (P. chabaudi) and in culture (P. falciparum), we investigated whether loss-of-function variants in human PKLR may be retained in human populations living in malaria-endemic areas. As a first step we sequenced all coding regions of PKLR in 384 geographically diverse human samples. We observed high diversity in African samples and identified 12 putatively loss-of-function alleles, translating to a mutant allele carrier frequency of 1.5%. Additional analyses revealed a slight, but significant deviation from neutral evolution in both Pakistan and Sub-Saharan Africa, consistent with the possibility that PKLR deficiency may offer some advantage, possibly by modulating malarial infection.Chaque année, 300 millions de personnes sont victimes du paludisme, une infection parasitaire (Plasmodium spp.) du sang, qui s'est aussi révélé la source d'une forte pression sélective sur le génome humain dans les régions endémiques. Plusieurs variants de protéines chez les cellules immunitaires et les érythrocytes ont été associés à un effet protecteur contre la progression et certains symptômes sévères du paludisme, telles anémie et atteintes cérébrales. Par approche génétique directe, nous avons comparé certaines souches de souris démontrant différents degrés de susceptibilité à l'infection par P. berghei ANKA afin d'étudier les facteurs génétiques liés au neuropaludisme en laboratoire. La souris C57BL/6 (susceptible) présente très tôt des symptômes neurologiques et succombe généralement avant le 12ième jour suivant l'infection, alors que la souris BALB/c (résistante) cèdera beaucoup plus tard à la maladie des suites d'une anémie. Nous avons adopté une stratégie par cartographie de loci à caractère quantitatif (QTLs) chez les souris F2 obtenues à partir des souches parentales C57BL/6 et BALB/c. Nous y avons distingué un locus de 10-20Mb sur le chromosome 19 (LOD = 4.69, p