Quantum Dot Mimetics of SARS-CoV-2 for Understanding Origins of Neurologic Disease Associated with Long Covid

Colloidal semiconductor quantum dots (QDs) are exceptional fluorescent probes for bioimaging applications; their enhanced photophysical properties, such as photostability and brightness, compared to conventional fluorophores are essential for achieving high-resolution precision. Additionally, the synthetic tunability of QD emission makes them viable candidates for multiplexed imaging and various biosensing applications. However, conventional applications of fluorescent probes, including QDs, investigate biomolecular interactions by conjugation of a biomolecule to the probe. While such material design is functionally justifiable for single proteins, such designs are incompatible with probing the function of more complex structures such as protein aggregates or virus particles in a manner that is representative of their native environment.<br/><br/>Thus, to study the physiochemical interactions relevant to SARS-CoV-2 mediated disease in the central nervous system (CNS), we have constructed a QD biomimetic for SARS-CoV-2 (COVID-QDs) with a focus on achieving high structural fidelity to native virus particles. The COVID-QDs act as a proxy for SARS-CoV-2 virus particles by accurately mimicking the general shape, size, and surface density of spike proteins. Specifically, the COVID-QDs were constructed by linking SARS-CoV-2 spike (S) proteins to polymeric phospholipid chains that formed a micellar envelope around the QDs; this forms a decorated capsid-like structure in native virus particles. By ensuring structural fidelity, we are able to fluorescently probe the physicochemical interactions between COVID-QDs and various cell types in a context that better reflects the native function of SARS-CoV-2.<br/><br/>We found that the COVID-QDs mediate dysfunction in a model system for the neurovascular unit, comprising endothelial cells, neurons, and glia. Interestingly, by correlating fluorescent micrographs, acquired by structured illumination, with functional biological assays, we have determined that the COVID-QDs primarily bind to the endothelial cells, leading to increased inflammation and leakage. This functional modulation of the endothelial cells by the COVID-QDs subsequently results in inflammation of the neuroglia underneath the endothelial monolayer. Our data shows that the dysfunction of the neural cell types is not mediated by direct interaction with COVID-QDs that have migrated through the endothelial monolayer. These results add to a body of evidence indicating that the neurological effects associated with COVID-19 are primarily driven by inflammation through virus particle-mediated dysregulation of the endothelium. Furthermore, we have identified a potential small molecule that could reverse the effects of the COVID-QDs, leading to inhibition of inflammation in both the monolayer and the CNS.