SARS-CoV-2 spike protein induces IL-18-mediated cardiopulmonary inflammation via reduced mitophagy

Cardiopulmonary complications are major drivers of mortality caused by the SARS-CoV-2 virus.Interleukin-18,an inflammasomeinduced cytokine,has emerged as a novel mediator of cardiopulmonary pathologies but its regulation via SARS-CoV-2 signaling remains unknown.Based on a screening panel,IL-18 was identified amongst 19 cytokines to stratify mortality and hospitalization burden in patients hospitalized with COVID-19.Supporting clinical data,administration of SARS-CoV-2 Spike 1(S1)glycoprotein or receptor-binding domain(RBD)proteins into human angiotensin-converting enzyme 2(hACE2)transgenic mice induced cardiac fibrosis and dysfunction associated with higher NF-κB phosphorylation(pNF-κB)and cardiopulmonary-derived IL-18 and NLRP3 expression.IL-18 inhibition via IL-18BP resulted in decreased cardiac pNF-κB and improved cardiac fibrosis and dysfunction in S1-or RBD-exposed hACE2 mice.Through in vivo and in vitro work,both S1 and RBD proteins induced NLRP3 inflammasome and IL-18 expression by inhibiting mitophagy and increasing mitochondrial reactive oxygenation species.Enhancing mitophagy prevented Spike protein-mediated IL-18 expression.Moreover,IL-18 inhibition reduced Spike protein-mediated pNF-κB and EC permeability.Overall,the link between reduced mitophagy and inflammasome activation represents a novel mechanism during COVID-19 pathogenesis and suggests IL-18 and mitophagy as potential therapeutic targets.

SNX17 regulates Notch pathway and pancreas development through the retromer-dependent recycling of Jag1

Background:Notch is one of the most important signaling pathways involved in cell fate determination.Activation of the Notch pathway requires the binding of a membrane-bound ligand to the Notch receptor in the adjacent cell which induces proteolytic cleavages and the activation of the receptor.A unique feature of the Notch signaling is that processes such as modification,endocytosis or recycling of the ligand have been reported to play critical roles during Notch signaling,however,the underlying molecular mechanism appears context-dependent and often controversial.Results:Here we identified SNX17 as a novel regulator of the Notch pathway.SNX17 is a sorting nexin family protein implicated in vesicular trafficking and we find it is specifically required in the ligand-expressing cells for Notch signaling.Mechanistically,SNX17 regulates the protein level of Jag1a on plasma membrane by binding to Jag1a and facilitating the retromer-dependent recycling of the ligand.In zebrafish,inhibition of this SNX17-mediated Notch signaling pathway results in defects in neurogenesis as well as pancreas development.Conclusions:Our results reveal that SNX17,by acting as a cargo-specific adaptor,promotes the retromer dependent recycling of Jag1a and Notch signaling and this pathway is involved in cell fate determination during zebrafish neurogenesis and pancreas development.