No abstract

Zika virus (ZIKV) is a flavivirus with teratogenic effects on the fetal brain, but the spectrum of brain injury is unknown, particularly when ultrasound imaging is normal. In a pregnant pigtail macaque (Macaca nemestrina) model, we demonstrate that ZIKV injury to the fetal brain was significant even in the absence of microcephaly and is clinically challenging to detect. A common and subtle injury pattern was identified including: 1) periventricular T2-hyperintense foci and loss of fetal non-cortical brain volume, 2) injury to the ependymal epithelium with underlying gliosis, and 3) loss of late fetal neuronal progenitor cells in the subventricular zone (temporal cortex) and subgranular zone (dentate gyrus, hippocampus) with dysmorphic granule neuron patterning. Attenuation of fetal neurogenic output demonstrates potentially significant teratogenic effects of congenital ZIKV infection even without microcephaly. All children exposed to ZIKV in utero should be followed long-term for neurocognitive deficits, regardless of head size at birth.

Pyroptosis is an inflammatory form of programmed cell death following cellular damage or infection. It is a lytic process driven by gasdermin D-mediated cellular permeabilization and presumed osmotic forces thought to induce swelling and rupture. We found that pyroptotic cells do not spontaneously rupture in culture but lose mechanical resilience. As a result, cells were susceptible to rupture by extrinsic forces, such as shear stress or compression. Cell analyses revealed that all major cytoskeleton components were disrupted during pyroptosis and that sensitivity to rupture was calpaindependent and linked with cleavage of vimentin and loss of intermediate filaments. Moreover, while release of lactate dehydrogenase (LDH), HMGB1, and IL-1β occurred without rupture, rupture was required for release of large inflammatory stimuli-ASC specks, mitochondria, nuclei, and bacteria. Importantly, supernatants from ruptured cells were more immunostimulatory than those from nonruptured cells. These observations reveal undiscovered cellular events occurring during pyroptosis, define the mechanisms driving pyroptotic rupture, and highlight the immunologic importance of this event.

In recent years, Asian lineage Zika virus (ZIKV) strains emerged to cause pandemic outbreaks associated with a high rate of congenital ZIKV syndrome (CZVS). The reasons for the enhanced spread and severe disease caused by newly emerging strains are not fully understood. Here we compared viral sequences, viral replication, and innate immune signaling induction of three different ZIKV strains derived from African and Asian lineages and West Nile virus, another flavivirus. We found pronounced differences in activation of innate immune signaling and inhibition of viral replication across ZIKV strains. The newly emerged Asian ZIKV strain Brazil Fortaleza 2015, which is associated with a higher rate of neurodevelopmental disorders like microcephaly, induced much weaker and delayed innate immune signaling in infected cells. However, superinfection studies to assess control of innate immune signaling induced by Sendai virus argue against an active block of IRF3 activation by the Brazilian strain of ZIKV and rather suggest an evasion of detection by host cell pattern recognition receptors. Compared to the Asian strain FSS13025 isolated in Cambodia, both ZIKV Uganda MR766 and ZIKV Brazil Fortaleza appear less sensitive to the interferon-induced antiviral response. ZIKV infection studies of cells lacking the different RIG-I-like receptors identified RIG-I as the major cytosolic pattern recognition receptor for detection of ZIKV. IMPORTANCE Zika Virus (ZIKV), discovered in 1947, is divided into African and Asian lineages. Pandemic outbreaks caused by currently emerging Asian lineage strains are accompanied by high rates of neurological disorders and exemplify the global health burden associated with this virus. Here we compared virological and innate immunological aspects of two ZIKV strains from the Asian lineage, an emerging Brazilian strain and a less-pathogenic Cambodian strain, and the prototypic African lineage ZIKV strain from Uganda. Compared to the replication of other ZIKV strains, the replication of ZIKV Brazil was less sensitive to the antiviral actions of interferon (IFN), while infection with this strain induced weaker and delayed innate immune responses in vitro. Our data suggest that ZIKV Brazil directs a passive strategy of innate immune evasion that is reminiscent of a stealth virus. Such strain-specific properties likely contribute to differential pathogenesis and should be taken into consideration when choosing virus strains for future molecular studies.