Lack of Hypoxia-Inducible Factor-1α Impairs Midbrain Neural Precursor Cells Involving Vascular Endothelial Growth Factor Signaling

Abstract

Oxygen tension is critical for proliferation of human and murine midbrain-derived neural precursor cells (mNPCs). Here, we conditionally inactivated the hypoxia-responsive transcription factor hypoxia-inducible factor-1α (HIF-1α) in murine NPCs to determine its role in proliferation, survival, and dopaminergic differentiationin vitroas well as survival of murine dopaminergic neuronsin vivo. HIF-1α conditional knock-out (HIF-1α CKO) mNPCs showed midbrain-specific impairment of survival and proliferation. Dopaminergic differentiation of HIF-1α CKO mNPCsin vitrowas markedly reduced. Expression of vascular endothelial growth factor (VEGF) mRNA was reduced in HIF-1α CKO mNPCs, whereas erythropoietin signaling was not affected. Treatment of HIF-1α CKO mNPCs with 50 ng/ml VEGF partially recovered proliferation and dopaminergic differentiationin vitro. In substantia nigra (SN) of adult HIF-1α CKO mice, protein levels of dopaminergic marker molecules such as tyrosine hydroxylase (TH) and aldehyde dehydrogenase were reduced by 41 and 61%, respectively. The cell survival marker Bcl-2 was reduced by 58% while caspase-3 was activated. Nonbiased stereological cell counts of TH-positive neurons in SN of young adult HIF-1α CKO mice revealed a reduction of 31% compared with cre/wt mice (in which the wild- typeHif1aallele is expressed in parallel with the Cre recombinase allele). However, we found no impairment of striatal dopamine concentrations or locomotor behavior. In conclusion, HIF-1α seems to be a transcription factor relevant to the development and survival of substantia nigra dopaminergic neurons involving VEGF signaling.

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