Non-activatable Mutant of Inhibitor of Kappa B Kinase Α (ikkα) Exerts Vascular Site-Specific Effects on Atherosclerosis in Apoe-deficient Mice

Background and aims: IKK alpha is an important regulator of gene expression. As IKK alpha kinase inactivity in bone marrow-derived cells does not affect atherosclerosis, we here investigate the impact of a whole body-IKK alpha kinase inactivity on atherosclerosis. Methods: Apolipoprotein E (Apoe)-deficient mice homozygous for an activation-resistant Ikk alpha-mutant (Ikk alpha(AA/AA)Apoe(-/-)) and Ikk alpha(+/+)Apoe(-/-) controls received a Western-type diet. Atherosclerotic lesion size and cellular content were analyzed using histology and immunofluorescence. Vascular protein expression and IKK alpha kinase activity were quantified by Luminex multiplex immuno-assay and ELISA. Results: A vascular site-specific IKK alpha expression and kinase activation profile was revealed, with higher total IKK alpha protein levels in aortic root but increased IKK alpha phosphorylation, representing activated IKK alpha, in the aortic arch. This was associated with a vascular site-specific effect of Ikk alpha(AA/AA) knock-in on atherosclerosis: in the aortic root, Ikk alpha(AA/AA) knock-in decreased lesion size by 22.0 +/- 7.7% (p < 0.01), reduced absolute lesional smooth muscle cell numbers and lowered pro-atherogenic MMP2. In contrast, Ikk alpha(AA/AA) knock-in increased lesion size in the aortic arch by 43.7 +/- 20.1% (p < 0.001), increased the abundance of lesional smooth muscle cells in brachiocephalic artery as main arch side branch and elevated MMP2. A similar profile was observed for MMP3. No effects were observed on necrotic core or collagen deposition in atherosclerotic lesions, nor on absolute lesional macrophage numbers. Conclusions: A non-activatable IKK alpha kinase differentially affects atherosclerosis in aortic root vs. aortic arch/brachiocephalic artery, associated with a differential vascular IKK alpha expression and kinase activation profile as well as with a vascular site-dependent impact on lesional smooth muscle cell accumulation and protein expression profiles.