PhD defense of Dana MACHMOUCHI on November 19th 2024

Dana MACHMOUCHI will defend her PhD thesis on November 19, 2024, at 9:30 a.m. (metropolitan time), 12:30 p.m. (Reunion time), in the POLENYK amphitheater at the University of Reunion Island, Moufia, Saint-Denis.

Exploring the Pathogenic Mechanisms of West African Zika Virus: Viral Replication and Host Interaction

Abstract: The Zika virus (ZIKV), historically confined to Africa and Asia, has become a significant global health concern, particularly following the recent outbreaks in the Americas, which were associated with severe congenital malformations and neurological disorders. While much of the research focus has been on the Asian/American ZIKV genotype, there is mounting evidence that African ZIKV strains could pose an equally, if not more, severe threat to public health, especially in terms of fetal pathogenicity. This thesis aims to enhance our understanding of the molecular mechanisms underlying the pathogenicity of contemporary ZIKV strains from West Africa, with a particular focus on the roles of nonstructural proteins in viral replication, immune evasion, and the host cell stress response. To achieve this, we generated an infectious molecular clone, GUINEA-18, from a ZIKV strain (ZIKV-15555) isolated in Guinea in 2018. This clone represents a contemporary strain of the African ZIKV lineage. We conducted a comparative analysis using the well-characterized infectious molecular clone of the historical African ZIKV strain MR766, designated as MR766MC. The replication properties of both viral clones were examined in different cell lines, including VeroE6, A549, and HCM3 cells. Our findings revealed that the GUINEA-18 clone exhibited a slower replication rate, reduced cytotoxicity, and a lower ability to activate the host’s innate immune system compared to the MR766MC strain. This suggests that contemporary West African ZIKV strains may interact differently with host cells compared to their historical counterparts. To dissect the molecular basis for these differences, we constructed chimeric viruses by swapping nonstructural protein-coding regions between GUINEA-18 and MR766MC. Our results highlighted the critical roles of NS1 to NS4B proteins in determining the replication efficiency and pathogenicity of the virus. Among these, NS4B emerged as a key player in modulating the replication properties of the GUINEA-18 strain. Additionally, we discovered that GUINEA-18 has developed an efficient mechanism to inhibit the assembly of cytoplasmic stress granules (SGs) in A549 cells, a cellular defense mechanism typically triggered in response to viral infection. The ability of GUINEA-18 to block SG formation was largely dependent on the NS1 to NS4B proteins, underscoring their importance in the virus’s strategy to evade host defenses. Building on these findings, the thesis further investigates the role of the NS1 protein in the pathogenicity of contemporary West African ZIKV strains. Through protein sequence alignment, we identified seven amino acid substitutions in the NS1 protein of GUINEA-18 compared to the NS1 protein of the historical MR766 strain. Functional analyses of these mutations revealed that the contemporary NS1 protein (NS1CWA) is more efficiently secreted and exhibits a different subcellular localization compared to the NS1 protein of MR766 (NS1MR766). This altered behavior of NS1CWA was found to significantly enhance viral replication and cytotoxicity while simultaneously reducing the activation of innate immune responses in infected cells. A chimeric MR766 virus containing NS1CWA demonstrated these enhanced pathogenic traits, further emphasizing the pivotal role of NS1 in the virulence of contemporary West African ZIKV strains. In conclusion, this thesis provides a comprehensive analysis of the molecular determinants that contribute to the replication and pathogenicity of contemporary West African ZIKV strains. The research underscores the critical roles of NS1 to NS4B proteins, particularly NS1 and NS4B, in these processes. The findings raise important questions about the potential risks associated with currently circulating ZIKV strains in sub- Saharan Africa and highlight the need for ongoing surveillance and research to better understand the public health implications of these viral strains. Through this work, we contribute valuable insights that could inform future strategies for the management and prevention of ZIKV-associated diseases, particularly in regions where the African lineage of the virus is prevalent.

Keywords : Zika virus, West African ZIKV, NS1 protein, NS4B protein, viral replication, immune evasion, cytotoxicity, stress granules, molecular clone, GUINEA-18, MR766, pathogenicity, viral determinants.

Members of the jury
Nathalie Dejucq-Rainsford : Directrice de Recherche Inserm (IRSET Inserm) – Rapporteuse
Yves Rouillé, Directeur de Recherche CNRS (Institut Pasteur de Lille) – Rapporteur
Marie-Pierre Courageot, Maîtresse de Conférences à l’Université de Reims – Examinatrice
Nathalie Chazal, Professeure à l’Université de Montpellier – Examinatrice & Présidente du jury
Philippe Desprès, Professeur à l’Université de La Réunion – Directeur de Thèse
Alain Kohl, Professeur à Liverpool School of Tropical Medicine – Co-Directeur de Thèse