TLR2 Potentiates SR-Marco-Mediated Neuroinflammation by Interacting with the SRCR Domain

Abstract

Microglial activation-induced neuroinflammation is critical in the pathogenesis of neurodegenerative diseases. Activated microglia are regulated mainly by innate pattern recognition receptors (PRRs) on their surface, of which macrophage receptor with collagenous structure (Marco) is a well-characterized scavenger receptor constitutively expressed on specific subsets of macrophages, including microglia. Increasing evidence has shown that Marco is involved in the pathogenesis of a range of inflammatory processes. However, research on the role of Marco in regulating neuroinflammation has reported conflicting results. In the present study, we examined the role Marco played in triggering neuroinflammation and its underlying mechanisms. The results demonstrated that silencing the Marco gene resulted in a significantly reduced neuroinflammatory response and vice versa. α-Syn stimulation in Marco overexpressing cells induced a pronounced inflammatory response, suggesting that Marco alone could trigger an inflammatory response. We also found that TLR2 significantly promoted Marco-mediated neuroinflammation, indicating TLR2 was an important co-receptor of Marco. Knocking down the TLR2 gene in microglia and mouse substantia nigra resulted in decreased expression of Marco. Subsequent mechanistic studies showed that deleting the SRCR domain of Marco resulted in disruption of the inflammatory response and the interaction between TLR2 and Marco. This suggested that TLR2 binds directly to the SRCR domain of Marco and regulates Marco-mediated neuroinflammation. In summary, this investigation revealed that TLR2 could potentiate Marco-mediated neuroinflammation by interacting with the SRCR domain of Marco, providing a new target for inhibiting neuroinflammation in neurodegenerative diseases.

Keywords: Macrophage receptor with collagenous structure; Microglia; Neuroinflammation; SRCR domain; Toll-like receptor 2.