Increased Serum MMP-9 in Long-COVID May Reflect Activation of Microglia by SARS-CoV-2 Spike Protein (preprint)

Long-COVID is a major health concern because many patients develop chronic neuropsychiatric symptoms, but the precise pathogenesis is unknown. Matrix metalloproteinase-9 (MMP-9) can disrupt neuronal connectivity and was elevated in patients with COVID-19. MMP-9 was measured in the serum of long COVID patients and healthy controls, as well as in the supernatant fluid of cultured human SV-40 microglia, by commercial ELISA. Results were analyzed with one-way ANOVA. MMP-9 in the serum of Long-COVID patients and supernatant fluid from cultured human microglia stimulated by recombinant SARS-CoV-2 Spike protein was assayed by ELISA. MMP-9 was significantly elevated in the serum of Long-COVID patients compared to healthy controls. Moreover, cultured human microglia released MMP-9 when stimulated by Spike protein. In conclusion, MMP-9 may contribute to the development of Long-COVID and serve both as a prognostic biomarker and as target for treatment.

Recombinant SARS-CoV-2 Spike Protein and its Receptor Binding Domain stimulate release of different pro-inflammatory mediators via activation of distinct receptors on human microglia cells (preprint)

SARS-CoV-2 infects cells via its spike (S) protein binding to its surface receptor Angiotensin Converting Enzyme 2 (ACE2) on target cells and results in acute symptoms involving especially the lungs known as COVID-19. However, increasing evidence indicates that SARS-CoV-2 infection produces neuroinflammation associated with neurological, neuropsychiatric, and cognitive symptoms persists well past the resolution of the infection, known as post-COVID-19 sequalae or Long-COVID. The neuroimmune mechanism(s) involved in Long-COVID have not been adequately characterized. In this study, we show that recombinant SARS-CoV-2 full-length S protein stimulates release of pro-inflammatory IL-1b, CXCL8, IL-6 and MMP-9 from cultured human microglia via TLR4 receptor activation. Instead, recombinant receptor-binding domain (RBD) stimulates release of TNF-α, IL-18 and S100B via ACE2 signaling. These results provide evidence that SARS-CoV-2 spike protein contributes to neuroinflammation through different mechanisms that may be involved in CNS pathologies associated with Long-COVID.