Insulin- like Growth Factor- II ( IGF- II) and IGF- II Analogs with Enhanced Insulin Receptor- a Binding Affinity Promote Neural Stem Cell Expansion*

Background: IGF-II promotes neural stem cell (NSC) proliferation and self-renewal. Results: IGF-II analogs are useful for elucidating the receptors responsible for NSC expansion. Conclusion: F19A expands NSCs via IR-A. Significance: IGF-II promotes stemness of NSCs via the IR-A and not through activation of either the IGF-1R or the IGF-2R. The objective of this study was to employ genetically engineered IGF-II analogs to establish which receptor(s) mediate the stemness promoting actions of IGF-II on mouse subventricular zone neural precursors. Neural precursors from the subventricular zone were propagated in vitro in culture medium supplemented with IGF-II analogs. Cell growth and identity were analyzed using sphere generation and further analyzed by flow cytometry. F19A, an analog of IGF-II that does not bind the IGF-2R, stimulated an increase in the proportion of neural stem cells (NSCs) while decreasing the proportion of the later stage progenitors at a lower concentration than IGF-II. V43M, which binds to the IGF-2R with high affinity but which has low binding affinity to the IGF-1R and to the A isoform of the insulin receptor (IR-A) failed to promote NSC growth. The positive effects of F19A on NSC growth were unaltered by the addition of a functional blocking antibody to the IGF-1R. Altogether, these data lead to the conclusion that IGF-II promotes stemness of NSCs via the IR-A and not through activation of either the IGF-1R or the IGF-2R.