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: IKKα is an important regulator of gene expression. As IKKα kinase inactivity in bone marrow-derived cells does not affect atherosclerosis, we here investigate the impact of a whole body-IKKα kinase inactivity on atherosclerosis.

Methods: Apolipoprotein E (Apoe)-deficient mice homozygous for an activation-resistant Ikkα-mutant (IkkαApoe) and IkkαApoe controls received a Western-type diet. Atherosclerotic lesion size and cellular content were analyzed using histology and immunofluorescence. Vascular protein expression and IKKα kinase activity were quantified by Luminex multiplex immuno-assay and ELISA.

Results: A vascular site-specific IKKα expression and kinase activation profile was revealed, with higher total IKKα protein levels in aortic root but increased IKKα phosphorylation, representing activated IKKα, in the aortic arch. This was associated with a vascular site-specific effect of Ikkα knock-in on atherosclerosis: in the aortic root, Ikkα 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, Ikkα 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 IKKα kinase differentially affects atherosclerosis in aortic root vs. aortic arch/brachiocephalic artery, associated with a differential vascular IKKα expression and kinase activation profile as well as with a vascular site-dependent impact on lesional smooth muscle cell accumulation and protein expression profiles.