title: 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.
authors.affiliation: Department of Biochemistry, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei, Taiwan Center for Reproductive Medicine and Sciences, Taipei Medical University Hospital, Taipei, Taiwan.
authors.forename: Y-H
authors.initials: YH
authors.lastname: Huang
authors.affiliation: School of Pharmacy, College of Pharmacy, Taipei Medical University, Taipei, Taiwan.
authors.forename: M-H
authors.initials: MH
authors.lastname: Lin
authors.affiliation: Department of Biochemistry, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei, Taiwan.
authors.forename: P-C
authors.initials: PC
authors.lastname: Wang
authors.affiliation: Department of Biochemistry, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.
authors.forename: Y-C
authors.initials: YC
authors.lastname: Wu
authors.affiliation: Department of Biochemistry, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.
authors.forename: H-L
authors.initials: HL
authors.lastname: Chiang
authors.affiliation: Department of Biochemistry, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei, Taiwan.
authors.forename: Y-L
authors.initials: YL
authors.lastname: Wang
authors.affiliation: Department of Biochemistry, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.
authors.forename: J-H
authors.initials: JH
authors.lastname: Chang
authors.affiliation: Department of Pharmacology, College of Medicine, National Taiwan University, No.1, Section 1, Je-Ai Rd, Taipei, Taiwan.
authors.forename: Y-K
authors.initials: YK
authors.lastname: Huang
authors.affiliation: Department of Pharmacology, College of Medicine, National Taiwan University, No.1, Section 1, Je-Ai Rd, Taipei, Taiwan.
authors.forename: S-Y
authors.initials: SY
authors.lastname: Gu
authors.affiliation: Graduate Institute of Clinical Genomics, College of Medicine, National Taiwan University, Taipei, Taiwan Division of Endocrinology and Infertility, Department of Obstetrics and Gynecology, College of Medicine, National Taiwan University, Taipei Medical University, Taipei, Taiwan.
authors.forename: H-N
authors.initials: HN
authors.lastname: Ho
authors.affiliation: Department of Pharmacology, College of Medicine, National Taiwan University, No.1, Section 1, Je-Ai Rd, Taipei, Taiwan tyling@ntu.edu.tw.
authors.forename: T-Y
authors.initials: TY
authors.lastname: Ling
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics* / Q000378:metabolism; D015687:Cell Hypoxia / Q000235:genetics; D049109:Cell Proliferation; D002478:Cells, Cultured; D025461:Feedback, Physiological; D018507:Gene Expression Regulation, Developmental; D005854:Germ Cells / Q000166:cytology / Q000378:metabolism*; D008297:Male; D051379:Mice; D050814:Octamer Transcription Factor-3 / Q000235:genetics* / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D019009:Proto-Oncogene Proteins c-kit / Q000235:genetics / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D013737:Testis / Q000166:cytology / Q000378:metabolism; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D050814:Octamer Transcription Factor-3; D019869:Phosphatidylinositol 3-Kinases; D019009:Proto-Oncogene Proteins c-kit; D017526:Receptor, IGF Type 1; D058570:TOR Serine-Threonine Kinases; D000099162:Endothelial PAS Domain-Containing Protein 1; C494174:Pou5f1 protein, mouse; C546843:mTOR protein, mouse
keywords: germline; niche growth factor; oxygen tension; self-renewal; tissue-specific stem cells