The loss of photoreceptors is the defining characteristic of many
retinal degenerative diseases, but the mechanisms that regulate photoreceptor cell death are not fully understood. Here we have used the 661W cone photoreceptor cell line to ask whether exposure to the
terminal complement complex C5b-9 induces cell death and/or modulates the sensitivity of these cells to other cellular stressors. 661W cone photoreceptors were exposed to complete normal human serum following antibody blockade of CD59. Apoptosis induction was assessed morphologically, by flow cytometry, and on western blotting by probing for cleaved PARP and activated
caspase-3. Necroptosis was assessed by flow cytometry and
Sirtuin 2 inhibition using 2-cyano-3-[5-(2,5-dichlorophenyl)-2-furyl]-N-5-quinolinylacrylamide (AGK2). The sensitivity of 661W cells to
ionomycin,
staurosporine,
peroxide and
chelerythrine was also investigated, with or without prior formation of
C5b-9. 661W cells underwent apoptotic cell death following exposure to
C5b-9, as judged by
poly(ADP-ribose) polymerase 1 cleavage and activation of
caspase-3. We also observed apoptotic cell death in response to
staurosporine, but 661W cells were resistant to both
ionomycin and
peroxide. Interestingly,
C5b-9 significantly increased 661W sensitivity to
staurosporine-induced apoptosis and necroptosis. These studies show that low levels of
C5b-9 on 661W cells can induce apoptosis, and that
C5b-9 specifically sensitizes 661W cells to certain apoptotic and necroptotic pathways. Our observations provide new insight into the potential role of the
complement system in photoreceptor loss, with implications for the molecular aetiology of
retinal disease.