Zika Virus Depletes Neural Progenitors in Human Cerebral Organoids through Activation of the Innate Immune Receptor TLR3

Abstract

Emerging evidence from the current outbreak of Zika virus (ZIKV) indicates a strong causal link between Zika and microcephaly. To investigate how ZIKV infection leads to microcephaly, we used human embryonic stem cell-derived cerebral organoids to recapitulate early stage, first trimester fetal brain development. Here we show that a prototype strain of ZIKV MR766 efficiently infects organoids and causes a decrease in overall organoid size that correlates with the kinetics of viral copy number. The innate immune receptor Toll-Like-Receptor 3 (TLR3) was upregulated after ZIKV infection of human organoids and mouse neurospheres and TLR3 inhibition reduced the phenotypic effects of ZIKV infection. Pathway analysis of gene expression changes during TLR3 activation highlighted 41 genes also related to neuronal development, suggesting a mechanistic connection to disrupted neurogenesis. Together, therefore, our findings identify a link between ZIKV-mediated TLR3 activation, perturbed cell fate and a reduction in organoid volume reminiscent of microcephaly.

Vulnerability of primitive human placental trophoblast to Zika virus

“…The likely involvement of ZIKV in neurological disease is consistent with its ability to infect and replicate within human cortical neuronal progenitor cells and slow their growth (9,10), infect human neurospheres and brain organoids (9,(11)(12)(13), and colonize the developing brain of mouse fetuses injected directly with the virus (14). Importantly, an African lineage strain (MR766) of ZIKV from Uganda (ZIKV U ) is as at least as capable of infecting human neural progenitor cells in vitro as strains of Asian origin (10,12,13,15), even though there is no indication that the former causes brain developmental abnormalities in infants.…”

Características de la estructura molecular de las proteínas E del virus Zika y E1 del virus de la rubeola. Posibles implicaciones en el neurotropismo y en las alteraciones del sistema nervioso

“…Dicho neurotropismo diferencial durante el desarrollo se ha observado en estudios recientes en ratones, los cuales evidenciaron altos grados de infección por el ZIKV en el cerebro, la médula espinal (6,46) y las células epiteliales (44,46). Aunque no se sabe por qué algunas células epiteliales y neuronales son más propensas a la infección por el ZIKV que otras (por ejemplo, las neuronas progenitoras lo son más que las corticales maduras) (5,8,47), se podrían presentar diferentes mecanismos de entrada mediados por distintos tipos de receptores (por ejemplo, Axl o TAR), así como tasas de infección diferentes debido a cambios en el grado de expresión de factores del huésped requeridos para la entrada (por ejemplo, TLR3), la replicación o el ensamblaje del ZIKV (42). Además, las diferencias específicas del tipo celular en los programas de defensa intrínseca de las células también podrían explicar la variación en la infección por el ZIKV en distintos tipos de células epiteliales y neurales (47,48).…”

Translational potential of human brain organoids

“…Several research groups applied the brain organoid model to study Zika infection, a current epidemic that has been strongly linked to newborn microcephaly 35, 46, 47, 48, 49, 50. These studies have provided evidence that human neural stem cells are selectively vulnerable35, 48 and more susceptible to premature differentiation50 upon Zika virus infection, providing a molecular explanation for the observed microcephaly.…”

“…These studies have provided evidence that human neural stem cells are selectively vulnerable35, 48 and more susceptible to premature differentiation50 upon Zika virus infection, providing a molecular explanation for the observed microcephaly. A further study suggested activation of innate immune responses as a possible mechanism for Zika‐induced neuroprogenitor cell death 47. In addition, organoid model has been used to identify putative receptor proteins mediating Zika entry into the nervous system 49.…”