SARS-CoV-2 S Protein Subunit 1 Elicits Ca2+ Influx - Dependent Ca2+ Signals in Pancreatic Stellate Cells and Macrophages In Situ.

Abstract

The S protein subunit 1 (S1) of SARS-CoV-2 is known to be responsible for the binding of the virus to host cell receptors, but the initial intracellular signalling steps following receptor activation of cells in the exocrine pancreas are unknown. Using an intact live mouse pancreatic lobule preparation, we observed that S1 elicited Ca2+ signals in stellate cells and macrophages, but not in the dominant acinar cells. The Ca2+ signals occurred mostly in the form of repetitive Ca2+ spikes. The probability of observing Ca2+ signals depended on the S1 concentration. The threshold was close to 70 nM, whereas at 600 nM, all cells responded. The SARS-Cov-2 nucleocapsid protein did not elicit any Ca2+ signals in any of the three cell types tested. The S1-induced Ca2+ signals in stellate cells started much faster (122 ± 37s) than those in macrophages (468 ± 68s). Furthermore, the interleukin-18 binding protein (IL-18BP) abolished the responses in macrophages without affecting the Ca2+ signals in stellate cells. The S1-elicited Ca2+ signals were completely dependent on the presence of external Ca2+ and were abolished by a selective inhibitor (CM4620) of Orai1 Ca2+ Release Activated Ca2+ channels. SARS-CoV-2 may contribute to acute pancreatitis, an often fatal inflammatory human disease. The S1-elicited Ca2+ signals we have observed in the pancreatic stellate cells and endogenous macrophages may play an important part in the development of the inflammatory process.