Effects of hypoxia inducible factors on pluripotency in human iPS cells

Abstract

A hypoxic condition is known to contribute to pluripotency. In the present article, the effects of transcription factors were first assessed regarding the proliferation and differentiation of human induced pluripotent stem (iPS) cells under hypoxic conditions using cell morphology and real-time polymerase chain reaction (RT-PCR). Morphology evaluations and RT-PCR revealed that the colony formation was promoted and the expression of pluripotent markers was increased under hypoxic conditions. In addition, the function of hypoxia inducible factors (HIFs) in human iPS cells under hypoxic conditions was evaluated in relation to the morphology and the expression of pluripotency markers by siRNA and RT-PCR. The HIF-2α silencing group showed a reduction in the colony size of human iPS cells and a statistically significant reduction in the expression of undifferentiation markers compared to the control group. Furthermore, the expression of HIF-2α was decreased when signal transducer and activator of transcription 3 (STAT3) was suppressed by its inhibitor, Stattic or S31 201. The inhibition using Stattic did not produce colony formation. The expression of pluripotent markers was also decreased using Stattic or S31 201. This study indicates that the HIF-2α expression in human iPS cells was activated under hypoxic conditions, similarly to that in murine iPS cells, and that HIF-2α among HIFs is the most effective compound for maintaining the pluripotency of human iPS cells. Furthermore, the STAT3 signal pathway regulates the expression of HIF-2α.

Oxygen as a Master Regulator of Human Pluripotent Stem Cell Function and Metabolism

“…However, the effect of low oxygen tension on such parameters as cell growth and the expression of pluripotency markers differs among various studies, as summarized in Table 1. Most of the available data show accelerated cell growth under hypoxic conditions [19,20,37,40] and enhanced expression of pluripotency markers, OCT4, SOX2, NANOG [20,40,48]. Our own results stayed in line with these observations, supporting the beneficial role of a low oxygen condition in the maintenance of pluripotency in hiPSCs (Figure 2).…”

“…It has been demonstrated that physiological hypoxia (3-5% O 2 ) supports an undifferentiated state of hPSCs, and decreases the rate of spontaneous differentiation, which can be observed as areas of flattened and enlarged cells with translucent cytoplasm localized at the periphery of the colonies. Such areas are smaller or absent under hypoxic conditions, compared to normoxia (21% O 2 ) [19,20,36,40,46]. Importantly, hypoxia was crucial to the maintenance of inactivated X chromosomes in hESCs, which is an indicator of naïve pluripotency [47].…”

“…While each of the niche components can strongly influence SC physiology, a growing body of evidence supports the crucial effect of oxygen concentration on various types of SCs, including mesenchymal SCs, hematopoietic SCs, and neural SCs [30][31][32][33][34]. Similarly, oxygen has been indicated as a master regulator of PSC functions, influencing cellular reprogramming, differentiation, genetic stability, and the maintenance of pluripotency [20,[35][36][37][38].…”

“…Importantly, the functions and activity of hiPSCs might be strongly influenced by the cellular microenvironment. Accordingly, oxygen tension seems to be one of the key factors modulating cellular metabolism and pluripotency [19][20][21][22].…”

Differentiation of Induced Pluripotent Stem Cells towards Mesenchymal Stromal Cells is Hampered by Culture in 3D Hydrogels

“…For instance, it has been demonstrated that the high degree of cross-linking inside a polymer network decreases diffusion of water, ions, and small molecules which might interfere with cell growth 59 . Furthermore, oxygen pressure has been shown to be an influencing factor in the differentiation process of stem cells 60,61 . However, as the fibrin gels that we generated were very thin (1–2 mm in depth), it is unlikely that the cells inside fibrin gel experienced severe hypoxic conditions.…”