Insulin-like growth factor-I promotes resistance of bovine preimplantation embryos to heat shock through actions independent of its anti-apoptotic actions requiring PI3K signaling.
For the bovine preimplantation embryo, insulin-like growth factor-I (IGF-I) is a survival factor that blocks the induction of apoptosis and reduces the decrease in development caused by heat shock. The first objective was to determine the signaling pathways whereby IGF-I acts to increase embryo cell number while inhibiting heat-shock induced apoptosis. Exposure of embryos to heat shock reduced cell number and increased percent apoptosis, but IGF-I increased cell number and blocked induction of apoptosis caused by heat shock. Actions of IGF-I to increase cell number were blocked by treatment with the mitogen activated protein kinase kinase (MAPKK) inhibitor PD 98059 whereas the phosphatidylinositol 3-kinase (PI3K) inhibitor LY 294002 had no effect. Conversely, LY 294002 but not PD 98059 blocked actions of IGF-I to inhibit induction of apoptosis caused by heat shock. The second objective was to determine whether IGF-I blocks effects of heat shock on development to the blastocyst stage by preventing apoptosis. Culture of embryos with IGF-I was effective in blocking the reduction in blastocyst development caused by heat shock-this action occurred even in the presence of LY 294002. Addition of another inhibitor of apoptosis, the caspase-3 inhibitor z-DEVD-fmk, did not mimic the protective effects of IGF-I on blastocyst development. Surprisingly, IGF-I was not effective in blocking the reduction in blastocyst development caused by heat shock when cultured with z-DEVD-fmk. In conclusion, the anti-apoptotic actions of IGF-I require PI3K signaling while actions to promote proliferation require MAPKK signaling. Moreover, actions of IGF-I to allow heat-shocked embryos to continue development to the blastocyst stage are independent of its anti-apoptotic effects.
Jousan
F Dean
FD
Department of Animal Sciences, University of Florida, Gainesville, Florida 32611-0910, USA.
Hansen
Peter J
PJ
D000818:Animals; D017209:Apoptosis; D001755:Blastocyst / Q000187:drug effects / Q000502:physiology*; D002417:Cattle; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005307:Fertilization in Vitro / Q000662:veterinary; D005419:Flavonoids / Q000494:pharmacology; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D006358:Hot Temperature; D020287:In Situ Nick-End Labeling; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D015398:Signal Transduction
D002867:Chromones; D004791:Enzyme Inhibitors; D005419:Flavonoids; D009025:Morpholines; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one