Metabolic remodelling defines cellular subtypes of human neuronal progenitors and their susceptibility to zika virus replication
Keywords: neuronal progenitors
Zika congenital syndrome
Zika virus
neuronal metabolism
immunometabolism

Maternal infections by Zika virus (ZIKV) during the first trimester of pregnancy result in either abortion or severe damage to the developing brain in 8-12% of cases. However, the route of ZIKV to the developing brain remains unclear. Emerging work suggests ZIKV replication imposes energetic demands on the developing brain that overwrite the highly orchestrated energetic processes required for normal cellular growth, proliferation, and differentiation. Energetic dysfunction could be attributed as the main cause for ZIKV-induced detrimental brain damage in new-borns yet, there is no clear evidence on the altered energetic pathway(s) and/or substrate(s) required to sustain ZIKV replication.
The work presented in this thesis showed the characterization of 2D in vitro cultures of cortical neuronal progenitor cells (hi-NPCs) and tissue-resident-like macrophages (hiPSC-MPh) derived from human pluripotent stem cells as models of the early fetal brain to better understand the pathogenesis of ZIKV. Analysis of the preferred energetic pathway in hi-NPCs distinguished two distinct subtypes of brain progenitors resembling populations with characteristics of quiescent radial-glia-like cells or proliferative intermediate neuronal progenitors. ZIKV infection in hi-NPCs revealed a subtype-specific permissibility to infection with metabolic implications resulting in reprogramming towards an increased cytosolic glucose metabolism. This was not observed in hiPSC-MPh as these cells showed less permissibility to ZIKV infection than hi-NPCs yet, the low rates of viral production in hiPSC-MPh were sufficient to disseminate virions to hi-NPCs, highlighting a potential route for maternal-fetal transmission of ZIKV. Further analysis using immune-metabolic compromised RSAD2-KO hiPSC-MPh showed that cytosolic glycolysis may underlie mechanisms for high rates of ZIKV replication. However, more research and validation of the current results are required to clearly elucidate whether energy intermediates can diminish ZIKV replication for potential therapeutics. These were not explored in detail due to the disruptions caused by the COVID-19 pandemic, instead this thesis includes an isolated chapter on SARS-CoV-2 because of the change in research projects.
The small research on SARS-CoV-2 hypothesises that macrophages do not negatively contribute to severe COVID-19 by the triggering the cytokine storm but have a dual role by decreasing SARS-CoV-2 replication kinetics by the degradation of circulating virions. Herein, I showed that macrophages, both peripheral (MDM) and hiPSC-MPh, were not productively infected by SARS-CoV-2 virions after direct (cell-free) or indirect exposure (cell-to-cell transfer). Instead, these cells phagocytized virions for phagolysosome degradation and decreased the viral replication kinetics by reducing the amount of output virions that can infect susceptible cells. This suggested a potential protective role of macrophages against the dissemination of SARS-CoV-2 within infected tissues.