Expression of complement regulators and receptors on human NT2-N neurons—Effect of hypoxia and reoxygenation

Abstract

Complement activation can cause tissue damage in cerebral stroke by the release of biologically potent activation products and impaired function of regulatory proteins. We investigated the constitutive and hypoxia–reoxygenation-dependent expression of complement receptor 1 (CD35), membrane cofactor protein (CD46), decay-accelerating factor (CD55), protectin (CD59), and complement C3a and C5a receptors (C3aR and C5aR) on human NT2-N neurons. The effect of hypoxia–reoxygenation on C3d-deposition on neurons and endothelial cells was also investigated. NT2-N neurons were examined by cellular enzyme-linked immunosorbent assay and immunofluorescence microscopy. Endothelial cells were examined by flow cytometry. Three hours 1% or 0.1% hypoxia and 21 h reoxygenation with 50% AB-serum were used to investigate the effect of hypoxia–reoxygenation on regulators and C3d-deposition. NT2-N neurons expressed significant amounts of CD59 (Clone H19/Clone BRIC229: p = 0.000006/ p = 0.000003), CD46 ( p = 0.00006), CD55 ( p = 0.003) and C3aR ( p = 0.00003). CD35 and C5aR were not significantly expressed. There were no effects of hypoxia–reoxygenation on any of the regulators or receptors after 1% hypoxia and reoxygenation. However, CD55 ( p = 0.02) was down-regulated after 0.1% hypoxia and subsequent reoxygenation with AB-serum. There were no difference observed in the C3d-deposition during hypoxia–reoxygenation in either neurons or endothelial cells. In conclusion, human NT2-N neurons constitutively express C3aR, CD46, CD55 and, in particular, CD59. The cells may respond to locally produced C3a and, at the same time, be well protected against complement attack. Although severe hypoxia–reoxygenation may down-regulate CD55 expression, it does not seem to influence C3d-deposition.