Homocysteine induces COX-2 expression in macrophages through ROS generated by NMDA receptor-calcium signaling pathways

Abstract

Homocysteine (Hcy) at elevated levels is a putative risk factor for many cardiovascular disorders including atherosclerosis. In the present study, we investigated the effect of Hcy on the expression of cyclooxygenase (COX)-2 in murine macrophages and the mechanisms involved. Hcy increased the expression of COX-2 mRNA and protein in dose- and time-dependent manners, but did not affect COX-1 expression. Hcy-induced COX-2 expression was attenuated not only by the calcium chelators, EGTA and BAPTA-AM, but also by an antioxidant, N-acetylcysteine. Calcium chelators also attenuated Hcy-induced reactive oxygen species (ROS) production in macrophages, indicating that Hcy-induced COX-2 expression might be mediated through ROS generated by calcium-dependent signaling pathways. In another series of experiments, Hcy increased the intracellular concentration of calcium in a dose-dependent manner, which was attenuated by MK-801, an N-methyl-D-aspartate (NMDA) receptor inhibitor, but not by bicuculline, a gamma-aminobutyric acid receptor inhibitor. Molecular inhibition of NMDA receptor using small interfering RNA also attenuated Hcy-induced increases in intracellular calcium. Furthermore, both ROS production and Hcy-induced COX-2 expression were also inhibited by MK-801 as well as by molecular inhibition of NMDA receptor. Taken together, these findings suggest that Hcy enhances COX-2 expression in murine macrophages by ROS generated via NMDA receptor-mediated calcium signaling pathways.

Functional plasticity of the N-methyl-d-aspartate receptor in differentiating human erythroid precursor cells

“…Recently, we have shown that NMDARs in RBCs show a high degree of basal activity when in the circulation (18). Additionally, glutamate levels within the bone marrow may be regulated by controlled secretion of this amino acid from megakaryocytes and macrophages (3, 22, 32, 39). The close association of bone marrow and glutamatergic nerve endings may further contribute to the alterations in glutamate levels promoting erythropoiesis and increasing RBC production.…”

Inhibition of NMDAR Reduces Bladder Hypertrophy and Improves Bladder Function in Cyclophosphamide Induced Cystitis

“…14,15 In addition to neuronal expression of NMDAR, recent studies showed that NMDAR activity is also present in peripheral tissues, including macrophages, bone marrow and the cardiovascular system. 16,17 The effects of central and peripheral NMDAR are often differentiated using the specific antagonists MK-801 and D-AP5. MK-801 is used to block overall NMDAR activity for its ability to cross the blood-brain barrier 18,19 and D-AP5 is used to study the role of peripheral NMDAR.…”

Monoacylglycerol lipase inhibitor protects primary cultured neurons against homocysteine-induced impairments in rat caudate nucleus through COX-2 signaling

“…Hcy induced COX-2 expression in macrophages, hepatic cell, as well as in the primary cultured CN neurons, which was hazardous to the function of cells [14,22,38]. Previous findings showed that the direct application of 2-AG or elevation of endogenous 2-AG by URB602 protects the hippocampal and CN neurons through suppression of cyclooxygenase-2 (COX-2) expression, which is provoked by pro-inflammatory IL-1β and LPS, excitotoxic glutamate and kainic acid and β-amyloid, via a CB1 receptor-dependent NF-κB signaling pathway [12,25,41].…”