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Abstract Background Plasma gelsolin (pGSN) is an important part of the blood actin buffer that prevents negative consequences of possible F-actin deposition in the microcirculation and has various functions during host immune response. Recent reports reveal that severe COVID-19 correlates with reduced levels of pGSN. Therefore, using an in vitro system, we investigated whether pGSN could attenuate increased permeability of the blood–brain barrier (BBB) during its exposure to the portion of the SARS-CoV-2 spike protein containing the receptor binding domain (S1 subunit). Materials and methods Two- and three-dimensional models of the human BBB were constructed using the human cerebral microvascular endothelial cell line hCMEC/D3 and exposed to physiologically relevant shear stress to mimic perfusion in the central nervous system (CNS). Trans-endothelial electrical resistance (TEER) as well as immunostaining and Western blotting of tight junction (TJ) proteins assessed barrier integrity in the presence of the SARS-CoV-2 spike protein and pGSN. The IncuCyte Live Imaging system evaluated the motility of the endothelial cells. Magnetic bead-based ELISA was used to determine cytokine secretion. Additionally, quantitative real-time PCR (qRT-PCR) revealed gene expression of proteins from signaling pathways that are associated with the immune response. Results pGSN reversed S1-induced BBB permeability in both 2D and 3D BBB models in the presence of shear stress. BBB models exposed to pGSN also exhibited attenuated pro-inflammatory signaling pathways (PI3K, AKT, MAPK, NF-κB), reduced cytokine secretion (IL-6, IL-8, TNF-α), and increased expression of proteins that form intercellular TJ (ZO-1, occludin, claudin-5). Conclusion Due to its anti-inflammatory and protective effects on the brain endothelium, pGSN has the potential to be an alternative therapeutic target for patients with severe SARS-CoV-2 infection, especially those suffering neurological complications of COVID-19. 

Abstract Cellular mechanics encompass both mechanical properties that resist forces applied by the external environment and internally generated forces applied at the location of cell–cell and cell–matrix junctions. Here, the authors demonstrate that microindentation of cellular domes formed by cell monolayers that locally lift off the substrate provides insight into both aspects of cellular mechanics in multicellular structures. Using a modified Hertz contact equation, the force–displacement curves generated by a micro‐tensiometer are used to measure an effective dome stiffness. The results indicate the domes are consistent with the Laplace–Young relationship for elastic membranes, regardless of biochemical modulation of the RhoA‐ROCK signaling axis. In contrast, activating RhoA, and inhibiting ROCK both alter the relaxation dynamics of the domes deformed by the micro‐tensiometer, revealing an approach to interrogate the role of RhoA‐ROCK signaling in multicellular mechanics. A finite element model incorporating a Mooney–Rivlin hyperelastic constitutive equation to describe monolayer mechanics predicts effective stiffness values that are consistent with the micro‐tensiometer measurements, verifying previous measurements of the response of cell monolayers to tension. Overall, these studies establish microindentation of fluid‐filled domes as an avenue to investigate the contribution of cell‐generated forces to the mechanics of multicellular structures.