LOX-1 Mediates Inflammatory Activation of Microglial Cells Through the p38-MAPK/NF-κB Pathways Under Hypoxic-Ischemic Conditions

Abstract

Background: Microglial cells play an important role in the immune system in the brain. Activated microglial cells are not only injurious but also neuroprotective. We confirmed marked lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) expression in microglial cells in pathological lesions in the neonatal hypoxic-ischemic encephalopathy model brain. LOX-1 is known to be an activator of cytokines and chemokines through intracellular pathways. Here, we investigated a novel role of LOX-1 in microglial cells under hypoxic and ischemic conditions. Methods: We isolated primary rat microglial cells from 3-day-old Sprague-Dawley rat brains and confirmed that the isolated cells showed more than 98% Iba-1 positive with immunocytochemistry. We performed oxygen glucose deprivation (OGD) treatment of primary rat microglial cells as an in vitro model of nHIE. Then, we evaluated the expression levels of LOX-1, cytokines and chemokines with or without siRNA and inhibitors, compared with no OGD-treated cells. In addition, we analyzed reactive oxygen species and cell viability.Results: We found that defects in oxygen and nutrition induced LOX-1 expression and led to the production of inflammatory mediators, such as the cytokines IL-1β, IL-6 and TNF-α, the chemokines CCL2, CCL5 and CCL3 and reactive oxygen/nitrile species. Then, the LOX-1 signal transduction pathway was blocked by inhibitors, LOX-1 siRNA, the p38-MAPK inhibitor SB203580 and the NF-κB inhibitor BAY11-7082 suppressed the production of the inflammatory mediators. Moreover, we demonstrated that LOX-1 in microglial cells was autonomously overexpressed by positive feedback of the intracellular LOX-1 pathway. Conclusion: The hypoxic/ischemic conditions of microglial cells induced LOX-1 expression and activated immune system. We revealed one of the LOX-1 signaling pathways in microglia and provide a hint of a new treatment strategy for nHIE. It was speculated that Microglial cells are known to contribute to various neurological diseases. Hypoxic and ischemic brain injuries result in lifelong neurological and mental deficiency. LOX-1 and its related molecules or chemicals may be major therapeutic candidates.