Analysis of the effect of aging on the response to hypoxia by cDNA microarray Hyungsoo Kim a , Dong-Ki Lee b , Ji-Woong Choi a , Jin-Soo Kim b , Sang Chul Park a,c , Hong-Duk Youn a, * a Department of Biochemistry and Molecular Biology, Cancer Research Institute, Seoul National University College of Medicine, 28 Yongon-dong, Chongro-gu, Seoul 110-799, South Korea b Toolgen Inc., Jeonmin-dong, Yusung-gu, Daejon 305-390, South Korea c The Aging and Apoptosis Research Center, Seoul National University College of Medicine, 199-1 Dongsoong-dong, Chongro-gu, Seoul 110-510, South Korea Received 28 May 2003; received in revised form 30 June 2003; accepted 30 June 2003 Abstract Little is known about the detail of hypoxia-responsive gene expression patterns in advanced age, even though aging is thought to be partially associated with a decreased response to hypoxia. In the present study, we identified several hypoxia-inducible genes and investigated the effect of aging on hypoxic gene expression profiles using cDNA microarray analysis of young/old human diploid fibroblasts. Of 7458 genes in the microarray, we found that genes involved in angiogenesis, defense against oxidative stress, and transcription regulation are severely impaired in senescent cell, which is consistent with the fact that aged cells have attenuated responses to various stimuli. # 2003 Elsevier Ireland Ltd. All rights reserved. Keywords: Aging; Hypoxia; cDNA microarray; Hypoxia-inducible factor; Angiogenesis 1. Introduction Aging is characterized by a deleterious and progres- sive decline in physiological efficiency. Since multiple factors are involved in the aging progress, it is still difficult to collectively understand the global network involved. Nonetheless, it is known that the aging process primarily occurs due to an altered gene expression by the loss or the altered activities of gene regulatory molecules (Roy et al., 2002). In particular, an aged organism is susceptible to various age-related diseases including vascular diseases and shows impaired angio- genesis under hypoxic conditions, which result from the reduced induction of vascular endothelial growth factor (VEGF) (Rivard et al., 1999), a potent hypoxia-targeted angiogenesis stimulator (Shweiki et al., 1992). Hypoxia, a limited cellular oxygen tension, is impor- tant for the regulation of the expressions of essential genes under specific developmental or physiological conditions: energy metabolism, proliferation, survival/ apoptosis, erythropoiesis and angiogenesis (Semenza, 2001). Hypoxia-inducible factor-1 (HIF-1) is a basic / helix /loop  /helix protein and forms heterodimer com- posed of a constitutively expressed HIF-1b subunit and an O 2 -regulated HIF-1a subunit (Wang et al., 1995). In the normoxic cells, HIF-1a protein, which is hydro- xylated at proline residues in its oxygen-dependent degradation (ODD) domain by O 2 -regulated prolyl hydroxylases, is subjected to ubiquitination and subse- quent proteosomal degradation by von Hippel  /Lindau (VHL) tumor suppressor protein. However, under hypoxic conditions, HIF-1a escapes from the degrada- tion pathway, and forms a heterodimeric active complex that binds to hypoxia-responsive recognition element (HRE), which leads to the induction of hypoxia- responsive genes such as erythropoietin (EPO), VEGF, and the genes required for metabolic adaptation to an * Corresponding author. Tel.:  /82-2-3668-7450; fax:  /82-2-744- 4534. E-mail address: hdyoun@snu.ac.kr (H.-D. Youn). Mechanisms of Ageing and Development 124 (2003) 941  /949 www.elsevier.com/locate/mechagedev 0047-6374/03/$ - see front matter # 2003 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/S0047-6374(03)00166-0