Purpose: To investigate the role of protein kinases on programmed cell death of developing retinal cells. Methods: Explants of neonatal rat retinae were kept in vitro either with or without inhibitors of protein synthesis, in the presence of various activators or inhibitors of protein kinases. Apoptosis was assessed in sections of the histotypical explants by either morphological criteria or using a modified TUNEL method. Results: The axotomized ganglion cells degenerate within 1-2 days in the explants. Inhibition of protein synthesis with either cycloheximide or anisomycin prevented apoptosis of ganglion cells, while inducing apoptosis in mitotic and early postmitotic cells in the neuroblastic layer. 2-AP, an inhibitor of MAP kinase, mimicked both these effects. TPA and bisindolylmaleimide, respectively an activator and an inhibitor of PKC, had no effect. In turn, activation of adenylyl-cyclase with either forskolin or 8-Br-cAMP selectively blocked apoptosis induced in the neuroblastic layer by protein synthesis inhibition. 8-Br-cGMP had little or no effect. Activation of adenyl-cyclase was effective up to 18 hours following the start of protein synthesis inhibition. HA-1004, an inhibitor of protein kinase A reverted this effect. Conclusion: The data indicate that a cAMP-dependent protein kinase selectively modulates a program of apoptosis continuously blocked by anti-apoptotic proteins. In addition, MAP kinase appears to be involved in the control of retinal apoptosis.
