SARS-CoV-2 spike protein induces inflammation via TLR2-dependent activation of the NF-κB pathway

Abstract

The pathogenesis of COVID-19 is associated with a hyperinflammatory response; however, the precise mechanism of SARS-CoV-2-induced inflammation is poorly understood. Here we investigated direct inflammatory functions of major structural proteins of SARS-CoV-2. We observed that spike (S) protein potently induced inflammatory cytokines and chemokines including IL-6, IL-1b, TNFa, CXCL1, CXCL2, and CCL2, but not IFNs in human and mouse macrophages. No such inflammatory response was observed in response to membrane (M), envelope (E), and nucleocapsid (N) proteins. When stimulated with extracellular S protein, human and mouse lung epithelial cells also produced inflammatory cytokines and chemokines. Interestingly, epithelial cells expressing S protein intracellularly were non-inflammatory, but elicited an inflammatory response in macrophages when co-cultured. Biochemical studies revealed that S protein triggers inflammation via activation of the NF-kB pathway in a MyD88-dependent manner. Further, such an activation of the NF-kB pathway was abrogated in Tlr2-deficient macrophages. Consistently, administration of S protein induced IL-6, TNF-a, and IL-1b in wild-type, but not Tlr2-deficient mice. Notably, upon recognition of S protein, TLR2 dimerizes with TLR1 or TLR6 to activate the NF-kB pathway. Together these data reveal a mechanism for the cytokine storm during SARS-CoV-2 infection and suggest that TLR2 could be a potential therapeutic target for COVID-19.

Evidence for investigating GSK-3 inhibitors as potential therapeutics for severe COVID-19

“…In summary, in line with other recent studies [ 4 , 10 ] we have found evidence that SARS-CoV-2 S and S2 proteins induce cytokine expression, in particular the chemokine CXCL10. Under the conditions tested, we found that two clinically relevant GSK-3 inhibitors and COB-187, a novel GSK-3 inhibitor, attenuate S and S2 induction of CXCL10.…”

“…Khan et al [ 4 ] provided evidence that S, but not M, E nor N protein induces cytokine (including chemokine) expression by THP-1 macrophages and human peripheral blood mononuclear cells and that this induction occurs via TLR2 and a NF-kB, MyD88-dependent pathway. Zheng et al [ 5 ] reported that the E protein, but not S, induces the production of proinflammatory cytokines by mouse bone marrow-derived macrophages.…”

Cytokine Elevation in Severe COVID-19 From Longitudinal Proteomics Analysis: Comparison With Sepsis

“…Importantly, IL-6 has also been reported to play an important role in controlling inflammatory cytokines ( 29 , 30 ) and to be protective in hyperoxia-induced lung damage ( 31 , 32 ). In COVID-19, the spike protein of SARS-CoV-2 induces the production of IL-6 by both macrophages and lung epithelial cells ( 33 ). The excess or continuous production of IL-6—as seen in lethal sepsis—can be harmful.…”

The Role of TLR2 in Infectious Diseases Caused by Mycobacteria: From Cell Biology to Therapeutic Target

“…TLR2 is not only investigated as a promising therapeutic target for mycobacterial infectious diseases, but also for other diseases (see Figure 4 ). In recent studies, TLR2 was reported to be a potential therapeutic target for COVID-19 [ 180 , 181 , 182 , 183 ]. A spike (S) protein is a main structural protein of SARS-CoV-2, which induces the inflammatory responses that are dependent on TLR2 [ 180 ].…”

“…In recent studies, TLR2 was reported to be a potential therapeutic target for COVID-19 [ 180 , 181 , 182 , 183 ]. A spike (S) protein is a main structural protein of SARS-CoV-2, which induces the inflammatory responses that are dependent on TLR2 [ 180 ]. Since death and severe cases of COVID-19 are associated with a hyper-inflammatory response [ 184 ], TLR2 antagonists can be tested for their capacity to alleviate the hyper-inflammatory response in SARS-CoV-2 infection or S protein stimulation.…”