Hypoxia Triggers Osteochondrogenic Differentiation of Vascular Smooth Muscle Cells in an HIF-1 (Hypoxia-Inducible Factor 1)-Dependent and Reactive Oxygen Species-Dependent Manner.

Objective- Vascular calcification is associated with high risk of cardiovascular events and mortality. Osteochondrogenic differentiation of vascular smooth muscle cells (VSMCs) is the major cellular mechanism underlying vascular calcification. Because tissue hypoxia is a common denominator in vascular calcification, we investigated whether hypoxia per se triggers osteochondrogenic differentiation of VSMCs. Approach and Results- We studied osteochondrogenic differentiation of human aorta VSMCs cultured under normoxic (21% O2) and hypoxic (5% O2) conditions. Hypoxia increased protein expression of HIF (hypoxia-inducible factor)-1α and its target genes GLUT1 (glucose transporter 1) and VEGFA (vascular endothelial growth factor A) and induced mRNA and protein expressions of osteochondrogenic markers, that is, RUNX2 (runt-related transcription factor 2), SOX9 (Sry-related HMG box-9), OCN (osteocalcin) and ALP (alkaline phosphatase), and induced a time-dependent calcification of the extracellular matrix of VSMCs. HIF-1 inhibition by chetomin abrogated the effect of hypoxia on osteochondrogenic markers and abolished extracellular matrix calcification. Hypoxia triggered the production of reactive oxygen species, which was inhibited by chetomin. Scavenging reactive oxygen species by N-acetyl cysteine attenuated hypoxia-mediated upregulation of HIF-1α, RUNX2, and OCN protein expressions and inhibited extracellular matrix calcification, which effect was mimicked by a specific hydrogen peroxide scavenger sodium pyruvate and a mitochondrial reactive oxygen species inhibitor rotenone. Ex vivo culture of mice aorta under hypoxic conditions triggered calcification which was inhibited by chetomin and N-acetyl cysteine. In vivo hypoxia exposure (10% O2) increased RUNX2 mRNA levels in mice lung and the aorta. Conclusions- Hypoxia contributes to vascular calcification through the induction of osteochondrogenic differentiation of VSMCs in an HIF-1-dependent and mitochondria-derived reactive oxygen species-dependent manner.