IGF-II Promotes Stemness of Neural Restricted Precursors

Abstract

Insulin-like growth factor (IGF)-I and IGF-II regulate brain development and growth through the IGF type 1 receptor (IGF-1R). Less appreciated is that IGF-II, but not IGF-I, activates a splice variant of the insulin receptor (IR) known as IR-A. We hypothesized that IGF-II exerts distinct effects from IGF-I on neural stem/progenitor cells (NSPs) via its interaction with IR-A. Immunofluorescence revealed high IGF-II in the medial region of the subventricular zone (SVZ) comprising the neural stem cell niche, with IGF-II mRNA predominant in the adjacent choroid plexus. The IGF-1R and the IR isoforms were differentially expressed with IR-A predominant in the medial SVZ, whereas the IGF-1R was more abundant laterally. Similarly, IR-A was more highly expressed by NSPs, whereas the IGF-1R was more highly expressed by lineage restricted cells. In vitro, IGF-II was more potent in promoting NSP expansion than either IGF-I or standard growth medium. Limiting dilution and differentiation assays revealed that IGF-II was superior to IGF-I in promoting stemness. In vivo, NSPs propagated in IGF-II migrated to and took up residence in periventricular niches while IGF-I-treated NSPs predominantly colonized white matter. Knockdown of IR or IGF-1R using shRNAs supported the conclusion that the IGF-1R promotes progenitor proliferation, whereas the IR is important for self-renewal. Q-PCR revealed that IGF-II increased Oct4, Sox1, and FABP7 mRNA levels in NSPs. Our data support the conclusion that IGF-II promotes the self-renewal of neural stem/progenitors via the IR. By contrast, IGF-1R functions as a mitogenic receptor to increase precursor abundance.

Insulin receptor isoform switching in intestinal stem cells, progenitors, differentiated lineages and tumors: evidence that IR-B limits proliferation

“…IR-A was the predominant isoform in the undifferentiated, cycling IESCs and rapidly dividing progenitors in the crypt, whereas IR-B expression was increased in Sox9-EGFP High cells enriched for post-mitotic EEC and Sox9-EGFP Negative IECs enriched for other post-mitotic, differentiated lineages, including enterocytes. Our findings are consistent with studies in other tissues where IR-A levels were higher in progenitor cells, including white pre-adipocytes, osteoblast precursors and neural progenitors compared with differentiated cells (Avnet et al, 2012;Serrano et al, 2005;Ziegler et al, 2012).…”

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

“…Whereas the lineage of NSCs within the SVZ as well as the generation and migration of NSP progeny has been an area of intense focus, the niche microenvironment has only recently been studied in detail. The notion that the CSF and IGFs, in particular, play an integral role in the NSC niche has only garnered attention recently (1,2,19). The CSF stimulates the growth of neurospheres in an IGF-IIdependent manner.…”

“…Quantitative Real-time PCR-Q-PCR was performed as described in Ziegler et al (1), with ␤-actin and Quantitech realtime primers for BMI-1, Hes5, Id2, and Axin 2 (QT00165298, QT00268044, QT01038870, and 01547672).…”

“…A recent study suggested that IGF-2R promotes memory consolidation in vivo (18); which is connected to the maintenance of hippocampal neurogenesis. In our prior study defining IGF-II function in NSC self-renewal, we investigated effects of IGF-II through IR or IGF-1R but did not analyze potential IGF-II actions through the IGF-2R (1). Thus, we first tested the F19L analog, which has a phenylalanine substitution at amino acid 19 for leucine and has greater than 6-fold higher binding affinity for IGF-2R than wild type IGF-II while binding the IGF-1R and IR-A with affinities similar to IGF-II (Table 1).…”

“…Indeed, the IGF system has been largely overlooked as a critical signaling pathway that is required to propagate neural stem cells (NSCs) in culture. Recent studies have determined IGF-II is involved in NSC proliferation and maintenance in the subventricular zone (SVZ) (1,2).…”