Hypoxia inducible factor 2α/insulin-like growth factor receptor signal loop supports the proliferation and Oct-4 maintenance of mouse germline stem cells

Abstract

Hypoxia inducible factor 2α (HIF-2α) is critical for primordial germ cell (PGC) survival as knockout of HIF-2α (HIF-2α(-/-)) decreases both expression of Oct-4 and PGC number in genital ridge. Hypoxia is known to stabilize HIF-2α protein from proteasomal degradation. However, little is known about the hypoxia-associated endocrinal signaling in HIF-2α expression. The current work demonstrates a role for an endocrine insulin-like growth factor-I receptor (IGF-IR)-PI3K/Akt-mTOR-HIF-2α regulatory loop in the proliferation and Oct-4 maintenance of PGC-like alkaline phosphatase positive mouse germline stem cells (AP(+)GSCs). We found that hypoxia greatly increased the cell proliferation and the levels of nuclear Oct-4/HIF-2α protein of AP(+)GSCs. The hypoxic-AP(+)GSCs presented stronger stemness ability for germ cell differentiation than normoxic, with expressions of c-KIT (differentiation germ cell marker), VASA (differentiation germ cell marker) and SCP3 (meiotic marker) using a renal capsule transplantation assay. Meanwhile, hypoxia significantly increased the expression levels of secreted-IGF-I and IGF-IR. The IGF-I dose dependently increased the HIF-2α expression levels in AP(+)GSCs; and, the inhibition of IGF-IR by RNA interference (shIGF-IR) or LY294002 (PI3K inhibitor)/Rapamycin (mTOR inhibitor) effectively suppressed the IGF-I- and/or hypoxia-induced HIF-2α and Oct-4 expression, suggesting that the IGF-IR and its downstream Akt/mTOR signaling are involved in the IGF-I/hypoxia effects. Additionally, knockdown of HIF-2α dramatically suppressed Oct-4 and IGF-IR protein levels in AP(+)GSC cells. In conclusion, the present study demonstrates a regulatory loop of IGF-IR-PI3K/Akt-mTOR-HIF-2α in proliferation and Oct-4 maintenance of PGC-like AP(+)GSCs under hypoxia. This finding provides insights into the niche endocrinology underlying early germ cell development.

An injectable non-cross-linked hyaluronic-acid gel containing therapeutic spheroids of human adipose-derived stem cells

“…It could be induced by spheroidal structure and high-density culture gel environment. We have learned that the spheroid center has a lower oxygen tension than the outer layers 10, 14 , and hypoxia can mediate or regulate the expression of NANOG and OCT-4 34–36 . In HA ASC spheroids, we found a NANOG-negative surface zone and a NANOG-positive core zone of spheroids (Fig.…”

The Homeobox Transcription Factor RHOX10 Drives Mouse Spermatogonial Stem Cell Establishment

“…Indeed, T is known to promote the generation of PGCs (Aramaki et al, 2013). Other Rhox10 -regulated genes encode factors driving ProSG/SSC proliferation and/or survival, including Erbb3 , which encodes a receptor tyrosine kinase that has been implicated in driving ProSG proliferation (Toyoda-Ohno et al, 1999) and Epas1 , which encodes a hypoxia-induced transcription factor that supports proliferation of germline stem cell cultures (Huang et al, 2014). …”

Function of insulin‑like growth factor 1 receptor in cancer resistance to chemotherapy (Review)

“…Specifically, nuclear IGF1R interferes with Wnt signaling, which upregulates ABC drug transporters and modulates drug responses (99). Regarding the tumor microenvironment, activating IGF1R results in stabilizing hypoxia-inducible factor (HIF)-1α and HIF-2α, and the upregulation of vascular endothelial growth factor (100). A previous study demonstrated that overexpressing HIF-1α increased the expression of Bcl-2, decreased the expression of BAX, and induced the expression of MDR1 and MRP1 (101).…”