Effects of insulin-like growth factors I and II on tumour-necrosis-factor-alpha-induced apoptosis in early murine embryos

The proposition that members of the insulin-like growth factor superfamily act as rescue factors from apoptosis in murine preimplantation embryos was tested. The cytokine tumour necrosis factor alpha (TNFalpha) was used to induce apoptosis. Zygotes were cultured for 5 days to the blastocyst stage in the presence or absence of TNFalpha and in the presence or absence of the insulin-like growth factors, IGF-I or IGF-II. Tumour necrosis factor alpha significantly increased the percentage of apoptotic cells and reduced the total cell count in Day 5 blastocysts. When IGF-I or IGF-II were added to the culture medium in the presence of TNFalpha, the cell number and apoptotic dead cell index (DCI) were restored to control values. Insulin-like growth factor-I alone had a greater effect on total cell number than IGF-II alone, but did not significantly decrease the apoptotic DCI. In contrast, IGF-II significantly reduced the number of apoptotic cells. This study shows that IGFs may play a role as apoptotic survival factors in the early mouse embryo.