Transcriptional Activation by Hypoxia and Low-Density Lipoprotein Loading in Cultured Vascular Smooth Muscle Cells

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Aim: The aim of this study was to investigate transcriptional activation in vascular SMC cultured under hypoxic conditions and high low-density lipoprotein (LDL) levels.
Methods: We cultured vascular SMC under hypoxic conditions and high LDL levels, and RNA expression profiles for more than 5800 were analyzed by DNA microarray. We performed promoter sequence analysis of genes induced by the combination of hypoxia and high LDL level conditions.
Results: In human coronary arterial SMC, the combination of hypoxia and high LDL level conditions induced the expression of 40 genes. Genes induced during the first 24 hours were known to be involved in inflammation, while late genes induced during 48 to 72 hours were composed primarily of genes involved in lipid and/or glucose metabolism. Promoter sequence analysis of these genes revealed that 39 of the 40 genes possessed multiple hypoxic response elements (HRE). The most induced gene in the combination of hypoxia and high LDL level conditions was the leptin gene. Functional analysis of the 3kb leptin promoter revealed that HRE at-166 mediated transcriptional activation by hypoxia, but 3kb reporter constructs can not reproduce the additive affect of LDL under hypoxia.
Conclusion: These results support the hypothesis that an HRE-mediated mechanism may be involved in transcriptional activation during lipid deposition in vascular SMC induced by hypoxia and LDL loading, but additional mechanisms may be involved in the synergistic action induced by LDL.