Date Published: February 15, 2018
Publisher: Public Library of Science
Author(s): Charles Arama, Issa Diarra, Bourèma Kouriba, Francine Sirois, Olesya Fedoryak, Mahamadou A. Thera, Drissa Coulibaly, Kirsten E. Lyke, Christopher V. Plowe, Michel Chrétien, Ogobara K. Doumbo, Majambu Mbikay, Hiroyoshi Ariga.
Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) is a hepatic secretory protein which promotes the degradation of low-density lipoprotein receptors leading to reduced hepatic uptake of plasma cholesterol. Non-synonymous single-nucleotide polymorphisms in its gene have been linked to hypo- or hyper- cholesterolemia, depending on whether they decrease or increase PCSK9 activity, respectively. Since the proliferation and the infectivity of Plasmodium spp. partially depend on cholesterol from the host, we hypothesize that these PCSK9 genetic polymorphisms could influence the course of malaria infection in individuals who carry them. Here we examined the frequency distribution of one dominant (C679X) and two recessive (A443T, I474V) hypocholesterolemic polymorphisms as well as that of one recessive hypercholesterolemic polymorphism (E670G) among healthy and malaria-infected Malian children.
Dried blood spots were collected in Bandiagara, Mali, from 752 age, residence and ethnicity-matched children: 253 healthy controls, 246 uncomplicated malaria patients and 253 severe malaria patients. Their genomic DNA was extracted and genotyped for the above PCSK9 polymorphisms using Taqman assays. Associations of genotype distributions and allele frequencies with malaria were evaluated.
The minor allele frequency of the A443T, I474V, E670G, and C679X polymorphisms in the study population sample was 0.12, 0.20, 0.26, and 0.02, respectively. For each polymorphism, the genotype distribution among the three health conditions was statistically insignificant, but for the hypercholesterolemic E670G polymorphism, a trend towards association of the minor allele with malaria severity was observed (P = 0.035). The association proved to be stronger when allele frequencies between healthy controls and severe malaria cases were compared (Odd Ratio: 1.34; 95% Confidence Intervals: 1.04–1.83); P = 0.031).
Carriers of the minor allele of the E670G PCSK9 polymorphism might be more susceptible to severe malaria. Further investigation of the cholesterol regulating function of PCSK9 in the pathophysiology of malaria is needed.
Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) is a secretory glycoprotein discovered in 2003 and initially termed Neural Apoptosis-Regulated Convertase 1 (NARC-1) . It belongs to the family of proprotein convertases, the serine endoproteinases involved in the proteolytic activation of a variety of secretory precursor proteins [2, 3]. Its gene is located on human chromosome 1. It was the segregation of missense mutations at its locus with autosomal dominant hypercholesterolemia (ADH) that led to the identification of its function in cholesterol metabolism .
A total of 752 DNA samples were genotyped for the rs28362263 (G>A), rs562556 (A>G), rs505151 (A>G), and rs28362286 (C>A) SNPs leading to A443T, I474V, E670G, and C679X PCSK9 polymorphisms, respectively. Their genotype distribution in this population sample did not deviate from HWE and their MAFs were 0.12, 0.20, 0.26, and 0.022, respectively (see Table 1).
The E670G polymorphism is located in the cysteine/histidine-rich domain C-terminal domain (CHRD) of PCSK9. This domain is required for the LDLR-degrading activity of the protein . The substitution of the charged Glu by a neutral Glycine at position 670 increases this activity presumably by altering CHRD conformation. The E670G polymorphism has been associated with hypercholesterolemia and increased risk of coronary artery disease . In adults, for unknown reasons, the association with high plasma cholesterol appears to be male-gender specific . In our children study, homozygous carriers of the minor allele, were mostly males and there were more of them among severe malaria patients than among healthy controls. These observations call for further studies that include lipid profiling to verify whether E670G-linked chronic hypercholesterolemia is indeed associated with a greater risk of severe malaria. In patients under septic shock, the GOF 670G variation was associated with greater blood levels of pro-inflammatory cytokines and greater mortality . In mice, increased PCSK9 activity was linked to inflammation and septic shock lethality; its deficiency reversed these adverse outcomes [36, 37]. Therefore it is possible that the E670G polymorphism contributes to the inflammatory responses that commonly accompany and sometimes aggravate malaria [38, 39].
Data presented in this preliminary report support the notion that PCSK9 activity could affect susceptibility to malaria. This finding should be corroborated by prospectively studying a larger population sample. It should be pointed out that sub-Saharan Africans commonly carry more than one non-synonymous LOF and GOF PCSK9 SNPs in various combinations . In the present cohort, 17.6% of subjects carried two of the four SNPs examined. In such cases, the resultant phenotype could be difficult to predict unless they are correlated with cholesterolemia. A substantial deviation from normal cholesterolemia in the absence of malaria may be a valid predictor of susceptibility or resistance to it. Furthermore, induction of normocholesterolemia with anti-PCSK9 drugs in hypercholesterolemic individuals could be useful for anti-malaria prophylaxis and therapy.