COVID-19 pandemic caused by SARS-CoV-2 infection is a public health emergency. COVID-19 typically exhibits respiratory illness. Unexpectedly, emerging clinical reports indicate that neurological symptoms continue to rise, suggesting detrimental effects of SARS-CoV-2 on the central nervous system (CNS). Here, we show that a Düsseldorf isolate of SARS-CoV-2 enters 3D human brain organoids within two days of exposure. Using COVID-19 convalescent serum, we identified that SARS-CoV-2 preferably targets soma of cortical neurons but not neural stem cells, the target cell type of ZIKA virus. Imaging cortical neurons of organoids reveal that SARS-CoV-2 exposure is associated with missorted Tau from axons to soma, hyperphosphorylation, and apparent neuronal death. Surprisingly, SARS-CoV-2 co-localizes specifically with Tau phosphorylated at Threonine-231 in the soma, indicative of early neurodegeneration-like effects. Our studies, therefore, provide initial insights into the impact of SARS-CoV-2 as a neurotropic virus and emphasize that brain organoids could model CNS pathologies of COVID-19.
Bilirubin-induced neurological damage (BIND) has been a subject of studies for decades, yet the molecular mechanisms at the core of this damage remain largely unknown. Throughout the years, many in vivo chronic bilirubin encephalopathy models, such as the Gunn rat and transgenic mice, have further elucidated the molecular basis of bilirubin neurotoxicity as well as the correlations between high levels of unconjugated bilirubin (UCB) and brain damage. Regardless of being invaluable, these models cannot accurately recapitulate the human brain and liver system; therefore, establishing a physiologically recapitulating in vitro model has become a prerequisite to unveil the breadth of complexities that accompany the detrimental effects of UCB on the liver and developing human brain. Stem-cell-derived 3D brain organoid models offer a promising platform as they bear more resemblance to the human brain system compared to existing models. This review provides an explicit picture of the current state of the art, advancements, and challenges faced by the various models as well as the possibilities of using stem-cell-derived 3D organoids as an efficient tool to be included in research, drug screening, and therapeutic strategies for future clinical applications.
Bilirubin induced neurological damage (BIND), which is also known as Kernicterus, occurs as a consequence of defects in the bilirubin conjugation machinery, thus resulting in unconjugated bilirubin (UCB) to cross the blood brain barrier (BBB) and accumulation. Severe hyperbilirubinemia can be caused by a mutation within the UGT1A1 encoding gene. This mutation has a direct contribution towards bilirubin conjugation leading to Kernicterus as a symptom of Crigler Najjar Syndromes (CNS1, CNS2) and Gilbert syndrome, which results in permanent neurological sequelae. In this comparative study, we used human induced pluripotent stem cells (hiPSCs) derived 3D-brain organoids to model BIND in vitro and unveil the molecular basis of the detrimental effects of UCB in the developing human brain. hiPSC derived from healthy and CNS patients were differentiated into day 20 brain organoids, these were then stimulated with 200nM UCB. Analyses at 24 and 72 hrs post-treatment point at UCB induced neuro-inflammation in both cell lines. Transcriptome and associated KEGG and Gene Ontology analyses unveiled activation of distinct inflammatory pathways such as cytokine cytokine receptor interaction, MAPK signaling, calcium signaling, NFkB activation. Furthermore, both mRNA expression and secretome analysis confirmed an upregulation of proinflammatory cytokines such as IL6 and IL8 upon UCB stimulation. In summary, this novel study has provided insights into how a human iPSC derived 3D-brain organoid model can serve as a prospective platform for studying the etiology of BIND Kernicterus.
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