Hypoxia-induced expression of C1q, a subcomponent of the complement system, in cultured rat PC12 cells

This study investigated the effect of exposure to hypoxia on the expression of C1q mRNA and protein in cultured PC12 cells. PC12 cells expressed neither C1q mRNA nor protein before hypoxia. However, the cells expressed C1q mRNA immediately after hypoxia, and then A, B, and C chains of C1q and higher molecular weight C1q proteins during reoxygenation. Under the same experimental conditions, cell membrane disintegration began during hypoxia, whereas DNA fragmentation initiated during reoxygenation later than C1q protein expression. These results suggest that in response to hypoxia, PC12 cells per se express C1q mRNA and protein in the early phase before initiation of DNA fragmentation in the absence of any influence of other cellular components. These findings may be relevant for the pathogenesis and treatment of stroke.