Hypoxia Inducible Factor-2α Regulates the Development of Retinal Astrocytic Network by Maintaining Adequate Supply of Astrocyte Progenitors

Abstract

Here we investigate the role of hypoxia inducible factor (HIF)-2α in coordinating the development of retinal astrocytic and vascular networks. Three Cre mouse lines were used to disrupt floxed Hif-2α, including Rosa26CreERT2, Tie2Cre, and GFAPCre. Global Hif-2α disruption by Rosa26CreERT2 led to reduced astrocytic and vascular development in neonatal retinas, whereas endothelial disruption by Tie2Cre had no apparent effects. Hif-2α deletion in astrocyte progenitors by GFAPCre significantly interfered with the development of astrocytic networks, which failed to reach the retinal periphery and were incapable of supporting vascular development. Perplexingly, the abundance of strongly GFAP+ mature astrocytes transiently increased at P0 before they began to lag behind the normal controls by P3. Pax2+ and PDGFRα+ astrocytic progenitors and immature astrocytes were dramatically diminished at all stages examined. Despite decreased number of astrocyte progenitors, their proliferation index or apoptosis was not altered. The above data can be reconciled by proposing that HIF-2α is required for maintaining the supply of astrocyte progenitors by slowing down their differentiation into non-proliferative mature astrocytes. HIF-2α deficiency in astrocyte progenitors may accelerate their differentiation into astrocytes, a change which greatly interferes with the replenishment of astrocyte progenitors due to insufficient time for proliferation. Rapidly declining progenitor supply may lead to premature cessation of astrocyte development. Given that HIF-2α protein undergoes oxygen dependent degradation, an interesting possibility is that retinal blood vessels may regulate astrocyte differentiation through their oxygen delivery function. While our findings support the consensus that retinal astrocytic template guides vascular development, they also raise the possibility that astrocytic and vascular networks may mutually regulate each other's development, mediated at least in part by HIF-2α.

Retinal Proteoglycans Act as Cellular Receptors for Basement Membrane Assembly to Control Astrocyte Migration and Angiogenesis

“…Here, we showed that astrocyte-specific deletion of PDGFRα resulted in arrest of astrocytes migration, which further prevented retinal angiogenesis. This result was also consistent with previous reports that genetic ablation of HIF-2α or Tlx in astrocytes abolished retinal vasculature (Duan et al, 2014; Uemura et al, 2006), suggesting that the astrocytic network is indeed indispensable for retinal angiogenesis. Taken together, these observations suggest that, other than secreting VEGF, astrocyte must also play additional roles in endothelial cell migration.…”

Astrocytes follow ganglion cell axons to establish an angiogenic template during retinal development

“…Because the glial network is present first, and because it resembles the vascular plexus that will later form (Figure A), it has been proposed that astrocytes provide a template that guides angiogenesis. Several lines of evidence support this notion (Duan, Takeda, & Fong, ; Fruttiger et al, ; Gnanaguru et al, ; Uemura, Kusuhara, Wiegand, Yu, & Nishikawa, ), including a recent study demonstrating that astrocytes are critical for onset of retinal angiogenesis (Tao & Zhang, ). However, in this study, the complete removal of astrocytes led to a complete failure of vascular development, leaving open the question of how vessel pattern might develop in the absence of an astrocyte template.…”

High expression of HIF-2α and its anti-radiotherapy effect in lung cancer stem cells

“…Real-time PCR was performed with a SYBR Premix EX Taq kit (Takara Dalian, Dalian, China) on an ABI Prism 7500 real-time PCR system (Applied Biosystems, Life Technologies, Carlsbad, CA, USA), with human GAPDH as the internal control. The following primers were used for qPCR analyses: HIF-2α (5'-AGTTCTGGCTCCTGCAAGAA-3', 5'-AGTTCTGGC TCCTGCAAGAA-3' (Duan et al, 2014); GAPDH (5'-CGGAGTCAACGGATTTGGTCGTAT-3', 5'-TGCTAAGCAGTTGGTGGTGCAGGA-3').…”