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BioMed Research International
Volume 2015 (2015), Article ID 359537, 12 pages
http://dx.doi.org/10.1155/2015/359537
Research Article

Hypoxia Induces a Metabolic Shift and Enhances the Stemness and Expansion of Cochlear Spiral Ganglion Stem/Progenitor Cells

1Department of Otolaryngology-Head and Neck Surgery, Tri-Service General Hospital, National Defense Medical Center, No. 325, Section 2, Cheng-Kung Road, Taipei 114, Taiwan
2Department of Otolaryngology, Auditory Medical Center, Cheng Hsin General Hospital, No. 45, Cheng Hsin Street, Taipei 112, Taiwan
3Graduate Institute of Medical Sciences, National Defense Medical Center, No. 161, Section 6, Minquan East Road, Taipei 114, Taiwan
4Medical Research Center, Cardinal Tien Hospital, No. 362, Zhongzheng Road, Xindian District, New Taipei City 23148, Taiwan
5Graduate Institute of Microbiology and Immunology, National Defense Medical Center, No. 161, Section 6, Minquan East Road, Taipei 114, Taiwan
6Laboratory Animal Center, National Defense Medical Center, No. 161, Section 6, Minquan East Road, Taipei 114, Taiwan

Received 28 August 2014; Accepted 3 October 2014

Academic Editor: Chung-Feng Hwang

Copyright © 2015 Hsin-Chien Chen et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Previously, we demonstrated that hypoxia (1% O2) enhances stemness markers and expands the cell numbers of cochlear stem/progenitor cells (SPCs). In this study, we further investigated the long-term effect of hypoxia on stemness and the bioenergetic status of cochlear spiral ganglion SPCs cultured at low oxygen tensions. Spiral ganglion SPCs were obtained from postnatal day 1 CBA/CaJ mouse pups. The measurement of oxygen consumption rate, extracellular acidification rate (ECAR), and intracellular adenosine triphosphate levels corresponding to 20% and 5% oxygen concentrations was determined using a Seahorse XF extracellular flux analyzer. After low oxygen tension cultivation for 21 days, the mean size of the hypoxia-expanded neurospheres was significantly increased at 5% O2; this correlated with high-level expression of hypoxia-inducible factor-1 alpha (Hif-1α), proliferating cell nuclear antigen (PCNA), cyclin D1, Abcg2, nestin, and Nanog proteins but downregulated expression of p27 compared to that in a normoxic condition. Low oxygen tension cultivation tended to increase the side population fraction, with a significant difference found at 5% O2 compared to that at 20% O2. In addition, hypoxia induced a metabolic energy shift of SPCs toward higher basal ECARs and higher maximum mitochondrial respiratory capacity but lower proton leak than under normoxia, where the SPC metabolism was switched toward glycolysis in long-term hypoxic cultivation.