Insulin-like growth factor-I prevents hypoxia-inducible factor-1 alpha-dependent G1/S arrest by activating cyclin E/cyclin-dependent kinase2 via the phoshatidylinositol-3 kinase/AKT/forkhead box O1/Cdkn1b pathway in porcine granulosa cells†

Abstract

As the follicle develops, the thickening of the granulosa compartment leads to progressively deficient supply of oxygen in granulosa cells (GCs) due to the growing distances from the follicular vessels. These conditions are believed to cause hypoxia in GCs during folliculogenesis. Upon hypoxic conditions, several types of mammalian cells have been reported to undergo cell cycle arrest. However, it remains unclear whether hypoxia exerts any impact on cell cycle progression of GCs. On the other hand, although the GCs may live in a hypoxic environment, their mitotic capability appears to be unaffected in growing follicles. It thus raises the question whether there are certain intraovarian factors that might overcome the inhibitory effects of hypoxia. The present study provides the first evidence suggesting that cobalt chloride (CoCl2)-mimicked hypoxia prevented G1-to-S cell cycle progression in porcine GCs. In addition, we demonstrated that the inhibitory effects of CoCl2 on GCs cell cycle are mediated through hypoxia-inducible factor-1 alpha/FOXO1/Cdkn1b pathway. Moreover, we identified insulin-like growth factor-I (IGF-I) as an intrafollicular factor required for cell cycle recovery by binding to IGF-I receptor in GCs suffering CoCl2 stimulation. Further investigations confirmed a role of IGF-I in preserving G1/S progression of CoCl2-treated GCs via activating the cyclin E/cyclin-dependent kinase2 complex through the phoshatidylinositol-3 kinase/protein kinase B (AKT)/FOXO1/Cdkn1b axis. Although the present findings were based on a hypoxia mimicking model by using CoCl2, our study might shed new light on the regulatory mechanism of GCs cell cycle upon hypoxic stimulation.

Multiple roles of hypoxia in bovine corpus luteum

“…Luteinization is the process by which the follicular granulosa and theca cells are transformed into luteal cells. It begins in the developing follicle, whose interior is under hypoxic conditions [7][8][9][10].…”

“…Luteinization is the process by which the follicular granulosa and theca cells are transformed into luteal cells. It begins in the developing follicle, whose interior is under hypoxic conditions [ 7 , 8 , 9 , 10 ]. Moderate hypoxia, such as the hypoxia in the peri-ovulatory follicles, has been shown to stimulate P4 production in granulosa cells (GCs) [ 11 , 12 , 13 ].…”

FOXO1 mediates hypoxia-induced G0/G1 arrest in ovarian somatic granulosa cells by activating the TP53INP1-p53-CDKN1A pathway

“…As one type of stress, hypoxia has been suggested to induce cell cycle arrest at G0/G1 phase and to block G1-to-S transition (Gardner et al, 2001). According to our previous studies, chemical-simulated hypoxia in primary cultured GCs could arrest cells at the G1/S boundary (Li et al, 2020). However, current evidence does not indicate whether and how real hypoxia acts on regulating GC cell cycle in vivo.…”

“…1I). Among the top 20 enriched pathways, we paid greater attention to FOXO1 signalling, because our previous studies suggested FOXO1 to be a crucial mediator of the stress response in ovarian GCs (Li et al, 2020;Shen et al, 2018Shen et al, , 2017Shen et al, , 2012Shen et al, , 2014, and FOXO1 is the only FOXO family member present in our transcriptomic data.…”

“…Interestingly, transcriptome sequencing in porcine large antral follicles revealed gene pathways associated with hypoxia (Munakata et al, 2016). Moreover, our earlier study showed that cobalt chloride (CoCl 2 ), a hypoxia-mimicking agent, could inhibit cell cycle progression in cultured GCs (Li et al, 2020). This prompted us to investigate whether hypoxia is actually involved in the regulation of the cell cycle in ovarian GCs during folliculogenesis.…”