Unraveling the Pathogenesis of Zika Virus: Insights and Implications
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Chapter 1: Introduction to Zika Virus Pathogenicity
Zika virus has led to a significant public health crisis in Brazil, with over 1,600 infants born with microcephaly between September 2015 and April 2016. The rapid emergence of Zika’s pathogenicity, particularly within Brazil, remains poorly understood. Notably, a single nucleotide substitution (M-F37L) has been identified as pivotal, transforming a partially attenuated strain (DN-1) into a pathogenic variant. This mutation notably reduces the size and weight of progeny but does not correlate with differences in viremia.
Section 1.1: Key Discoveries in Zika Research
Recent investigations uncovered that a solitary nucleotide alteration in the Membrane protein—from phenylalanine to leucine at position 37—enhances Zika virulence in vivo. This change converts the attenuated strain (DN1) into a pathogenic one in both interferon knockout mice (A129 mice) and congenital mouse models. This observation led to further exploration of the host responses triggered by the M-F37L mutation compared to the DN-1 strain.
Section 1.2: Transcriptomic Analysis of Zika Strains
A microarray analysis was conducted on MRC5 cells infected with various Zika strains, including wild-type strains from both Asian and African lineages, the M-F37L strain, and several attenuated variants. This analysis allowed for a comparison of the transcriptomic responses elicited by these strains. Principal component analysis (PCA) indicated that the pathogenic M-F37L and wild-type strains clustered distinctly from both the uninfected controls and the attenuated strains. Importantly, all pathogenic strains activated pathways associated with inflammation, apoptosis, mitochondrial alterations, and cell cycle regulation.
Chapter 2: Mitochondrial Function and Metabolic Profiling
The first video titled "Understanding the Pathogenesis of the Emerging Zika Virus with Michael Diamond, MD, PhD" provides valuable insights into the mechanisms driving Zika virus pathogenicity.
We further examined gene signatures using Gene-set Enrichment Analysis (GSEA), which revealed that mitochondrial-related pathways were notably impacted between the M-F37L and DN1 strains. This prompted an investigation into the mitochondrial characteristics of these Zika strains. Given the mitochondria's crucial role in cellular metabolism, we also assessed the metabolic profiles of cells infected with various Zika virus strains.
The second video titled "Zika Virus (Genus Flavivirus)" elaborates on the classification and implications of the Zika virus.
Our efforts focused on optimizing the Seahorse Extracellular Flux assay to evaluate the effects of Zika virus infection on mitochondrial numbers and functionality. The published protocol yields consistent results across experimental replicates, enabling us to accurately characterize mitochondrial phenotypes post-infection. The results from the mitochondrial and glycolytic stress tests indicated a decline in both oxidative phosphorylation and glycolysis in the pathogenic Zika strains.
Section 2.1: Exploring Therapeutic Interventions
Collaborating with colleagues from SMART-MIT, mass spectrometry analyses demonstrated that the host's metabolic processes were redirected towards the pentose phosphate pathway in the M-F37L strain. This shift resulted in diminished substrates available for mitochondrial metabolism, leading to increased production of reactive oxygen species and heightened inflammation.
These intriguing results prompted us to investigate potential therapeutic strategies to mitigate mitochondrial dysfunction caused by pathogenic Zika virus infection. We tested pyruvate supplementation to bypass the pentose phosphate pathway and directly feed into the citric acid cycle. Remarkably, pyruvate treatment restored mitochondrial metabolism and suppressed transcriptomic signatures related to inflammation and apoptosis. Furthermore, pre-treatment with ethyl pyruvate partially alleviated the pathogenic effects of wild-type Zika strains in A129 mice.
Overall, our findings underscore a critical aspect of Zika virus pathogenesis: metabolic disruption that impairs mitochondrial functions, thus exacerbating inflammation and cell death.
Conclusion: Future Directions
Numerous questions remain unanswered. Can nutritional interventions alleviate the impact of Zika? Are genetic mutations in the Membrane region directly linked to increased virulence? How do pathogenic strains manipulate host resources to favor viral replication? A comprehensive understanding of these issues is crucial for preparing for future Zika virus outbreaks.
This research was conducted at Duke-NUS Medical School and published in Cell Reports. Special acknowledgments to Clement Yau, John Low, and Eng Eong Ooi for their invaluable contributions.