Manganese induces neuroinflammation through SPON1-mediated activation of ERK1/2/NF-κB pathway

Excessive accumulation of manganese (Mn) can cause neuroinflammation, impairing cognitive function. SPON1, a secreted glycoprotein in the extracellular matrix, is implicated in neuroinflammation, but its role in activating pro-inflammatory pathways in Mn-induced neuroinflammation remains unclear. This study employed in vivo and in vitro models to investigate Mn neuroinflammation. The expression levels of SPON1 and the ERK1/2/NF-κB pathway associated with inflammation were measured in male C57BL/6 mice after gavage of Mn at different doses (0, 25, 50, 100 mg/kg) for 12 weeks. SPON1 levels were measured after primary hippocampal neurons, primary cortical neurons, neuroblastoma cells (N2a), and microglial cells (BV2) were exposed to various concentrations of Mn for 24 h. We observed that in vivo Mn exposure significantly decreased SPON1 expression in the cortex but not in the hippocampus. Similarly, in vitro experiments demonstrated that Mn exposure significantly reduced SPON1 levels in primary cortical neurons, N2a, and BV2. In addition, Mn exposure increased the expression levels of ERK1/2 and NF-κB pathway proteins in the mouse cortex. Because BV2 cells are susceptible to inflammatory signals, they were chosen to elucidate how SPON1 induces neuroinflammation during Mn exposure. SPON1 knockdown increases the expression of inflammatory factors, whereas SPON1 overexpression inhibits the activation of the ERK1/2/NF-κB pathway and reduces inflammatory factor levels. In summary, these results suggest that Mn may affect the activation of ERK1/2/NF-κB pathway and the expression of inflammatory factors by inhibiting SPON1, ultimately promoting neuroinflammation.