#5885 hypoxia induces complement activation on human kidney epithelial cells

Abstract Background and Aims Ischemia-reperfusion injury is an inevitable event associated with kidney transplantation (Tx) and has a major impact on short- and long-term graft survival. Proximal tubular epithelial cells are both a source of complement during Tx and a target of complement activation. The normal kidney has a capacity to protect itself from complement activation through cellular expression of complement regulatory proteins. In this study we investigated whether hypoxia and reoxygenation increase C3 deposition and alter complement regulatory protein expression (CD46, CD59 and CD55). Method In vitro, HKC-8 renal proximal tubular epithelial cells were subjected to 24h of hypoxia (1% O2) and then reoxygenated for 4h (O2 = 21%) in the presence of 40% normal human serum. qRT-PCR was used to estimate the level of VEGF-A (as a positive control), C3, CD46, CD59 and CD55 expression. Similar analysis was performed in untreated, normoxic cells. Immunofluorescence staining was used to determine C3 deposition on the cell surface and intensity quantified by ImageJ. Experiments were repeated three times. Results qRT-PCR analysis of HKC-8 cells in hypoxia revealed significant increases in the expression of VEGF-A after 24h (p = 0.0113). C3 expression following hypoxia and reoxygenation increased insignificantly. Increased expression of CD59 with the presence of serum was observed in epithelial cells (p = 0.026). However, no significant change was seen in the expression of CD55 and CD46. Reoxygenation in human serum led to significantly greater deposition of C3 on hypoxic cells compared with normoxic HKC-8 cells (Figure 1, 2). Conclusion Our preliminary data suggests that hypoxia and reoxygenation significantly increases C3 deposition on the proximal tubular cell surface. CD59, as one of the regulators of complement activation is upregulated at mRNA level after hypoxia followed by 4h reperfusion in the presence of serum. These data demonstrate that hypoxia and reoxygenation activate complement system with upregulation of CD59 as a cell defence. However, expression of CD46 and CD55 do not change. Further study is needed to identify the impact of hypoxia on complement regulation in primary epithelial cells and kidney tissues.