The most important contribution of our study to ZIKV

The most important contribution of our study to ZIKV research is the finding of ZIKV-mediated impairment of hNSC neuronal differentiation in a cell-strain-dependent manner. Specifically, ZIKV infection significantly reduced neuronal differentiation of K054 and K048 strains but not G010. Both RNA sequencing and qRT-PCR also confirm the similar trend of reduction in the expression of neuron-specific TUBB3 gene. This cell-strain-dependent impairment is unlikely related to the initial derivation of hNSC strains from different human gestational weeks: K048 at the week 9, and both K054 and G010 at 13. First, it is known that there are no significant developmental milestones between gestational weeks 9 and 13 (Stiles and Jernigan, 2010). Second, K054 and G010 were both derived from week 13 but respond differently to ZIKV in terms of neuronogenesis. On the other hand, both K054 and K048 showed significant reduction in the number of differentiated neurons despite being derived from different developmental stages. Third, the cell-strain-dependent impairment of neuronal differentiation is unlikely due to the long-term culture (passage 22) of hNSCs. Previous studies indicate that some hNSC strains, when cultured long-term in vitro, extensively accumulate chromosomal 7 and 19 trisomy that may affect neuronal differentiation (Sareen et al., 2009). However, our cytogenetic analyses identified only minimal if any chromosomal trisomy in all cell strains. Finally, the cell-strain-dependent neuronal deficit is unlikely attributed to ZIKV-induced apoptosis. This is because that K054 cells, although having a higher apoptotic sglt than K048, showed a smaller reduction of neurons than K048. Furthermore, the low rates (<1.7%) of apoptotic cell death in K048 and K054 do not match the magnitude of neuronal reduction (>33%) caused by ZIKV infection. Interestingly, this cell-strain-dependent neuronal impairment seems well correlated with the ZIKV-induced alteration of global gene expression pattern; i.e., K054 and K048 share similar changes in transcriptome and neuronal phenotype that are distinct from G010. It remains to be determined what gene(s) is/are responsible for ZIKV-induced and cell-strain-dependent reduction of neuronal differentiation. One of the most obvious differences detected by transcriptome analyses is that K054 and K048 but not G010 share similar patterns in the innate immune response, including interferons, cytokines, and complements. A recent study also shows that cranial neural crest cells produce cytokines associated with decreased neurogenesis following infection with either MR-766 or H/PF/2013 ZIKV strains (Bayless et al., 2016). In addition, the findings related to downregulation of the Histone 1 gene family in K048 and K054 but not G010 also warrant further investigation due to the broad implications of histone modifications. Further studies with additional hNSC strains and ZIKV viral strains are required to investigate the correlation of these findings and the underlying mechanisms as to how different genetic backgrounds contribute to the cell-strain-dependent neuronal deficits following ZIKV infection.
Experimental Procedures
Author Contributions
Introduction Parkinson\'s disease (PD) is a progressive neurodegenerative disorder currently affecting 4% of the population >80 years and whose prevalence is expected to double by 2030 (de Lau and Breteler, 2006). Multiple neurotransmitter systems are involved in the neurodegeneration of PD, but the loss of substantia nigra dopaminergic neurons is responsible for the dominant early motor features. The pathological hallmark of PD is the accumulation and aggregation of α-synuclein and the deposition of Lewy bodies. A heterogeneous range of etiologically and pathogenically relevant factors have been identified for PD, and it is likely that the neurodegeneration and clinical manifestations of the disease are the end result of multiple aberrant pathways (Schapira and Jenner, 2011). Several single gene defects have been identified in familial and apparently sporadic PD (Volta et al., 2015). Numerically the most important genetic risk factor for PD is the presence of mutations of the glucocerebrosidase gene GBA1 (Sidransky et al., 2009). Although precise estimates vary between populations, approximately 5%–10% of PD patients carry GBA1 mutations, their presence increasing the risk for PD in any one individual by 20–30 times (Beavan and Schapira, 2013).