Endothelial dysfunction accompanied by the loss of endothelial cell phenotype plays an essential role in
cardiovascular diseases. Here, we report that knockdown of
biliverdin reductase (BVR), the
enzyme of the
heme degradation pathway converting
biliverdin to
bilirubin, shifts endothelial phenotype of the primary human aortic endothelial cells (HAECs) to mesenchymal-like one. It is reflected by the loss of endothelial markers and angiogenic response, with concomitant acquiring of mesenchymal markers, increased migratory capacity and
metalloproteinase activity. BVR-deficiency induces the activity of Nrf2
transcription factor and increases
heme oxygenase-1 (HO-1) level, which is accompanied by the reduction of cellular
heme content, increase in a free
iron fraction and oxidative stress. Accordingly, the phenotype of BVR-deficient cells can be mimicked by
hemin or
iron overload. Depletion of HO-1 in BVR-deficient ECs abrogates the increase in intracellular free
iron and oxidative stress, preventing the loss of endothelial markers. Treatment of BVR-deficient cells with
bilirubin does not rescue the endothelial phenotype of HAECs. Unlike BLVRA
mRNA level, the expression of HMOX1, HMOX1:BLVRA ratio and HO-1
protein level positively correlate with
abdominal aortic aneurysm size in clinical samples. Collectively, the non-enzymatic activity of BVR contributes to the maintenance of healthy endothelial phenotype through the prevention of HO-1-dependent
iron-overload, oxidative stress and subsequent endothelial-to-mesenchymal transition (EndMT).