2′-Hydroxycinnamaldehyde targets low-density lipoprotein receptor-related protein-1 to inhibit lipopolysaccharide-induced microglial activation

2′-Hydroxycinnamaldehyde (HCA) isolated from the stem bark of Cinnamomum cassia and its derivative 2′-benzoyloxycinnamaldehyde (BCA) were reported to have anti-angiogenic, anti-proliferative, and anti-inflammatory effects in several human cancer cells and RAW 264.7 macrophage cells. However, effects of HCA/BCA on the neuroinflammation have not been investigated. In the present study, a potential anti-neuroinflammatory effect of HCA/BCA was assessed in lipopolysaccharide (LPS)-stimulated microglial cultures and microglia/neuroblastoma cocultures. Nitric oxide production, inflammatory gene expression, and signaling pathways were investigated. HCA/BCA significantly decreased the production of nitric oxide and tumor necrosis factor-alpha (TNF-α) in microglial cells. HCA/BCA also attenuated the expression of inducible nitric oxide synthase (iNOS) and pro-inflammatory cytokines such as interleukin-1β (IL-1β) and TNF-α at mRNA level via blockade of ERK, JNK, p38 MAPK, and NF-κB activation. Moreover, HCA/BCA was neuroprotective by reducing microglia-mediated neuroblastoma cell death in a microglia-neuroblastoma co-culture. Affinity chromatography and LC-MS/MS analysis identified low-density lipoprotein receptor-related protein 1 (LRP1) as a potential molecular target of HCA in microglial cells. Based on the studies using the receptor-associated protein (RAP) that blocks a ligand binding to LRP1 and the siRNA-mediated LRP1 gene silencing, we were able to conclude that HCA inhibited LPS-induced microglial activation via LRP1. Our results suggest that HCA/BCA be anti-inflammatory and neuroprotective in the CNS by targeting LRP1, and may have a therapeutic potential against neuroinflammatory diseases.