Late life targeting of the IGF 1 receptor improves healthspan and lifespan in female mice Nature Communications Specific insulin IGF1 hybrid receptor activation assay reveals IGF1 as a more potent ligand than insulin Scientific Reports Frontiers Sheep recombinant IGF 1 promotes organ specific growth in fetal sheep Insulin like growth factor 1 stimulates retinal cell proliferation via activation of multiple signaling pathways ScienceDirect