Early IKKb-dependent anabolic and fibrotic signatures govern vascular smooth muscle cells fate and abdominal aortic aneurysm development

Aims Abdominal aortic aneurysm (AAA) is a complex aortic disease define by a dilatation of the infrarenal aorta and the most common form of aneurysm in humans. Whereas inflammation contribute to AAA development, quenching vascular inflammation using classical pharmacological approaches or inhibiting the immune system does not influence the progression of AAA in humans indicating the lack of a complete picture on the molecular events that drive this aortopathy. This study was designed to comprehend the earliest molecular indicators, aiming to pinpoint a biological target associated with the latter. Methods and results Using ApoE-deficient mice fed with a standard diet and infused with Angiotensin II (Ang II), we conducted bulk RNA-sequencing analysis on suprarenal (SRA) regions obtained from both unchallenged and challenged WT mice, specifically examining responses 24 hours after Ang II infusion to capture the initial phases of aortic stress response. We further created a unique model of hyperlipidemic mice in which the expression of IKK can be conditionally (via tamoxifen injection) suppressed in vascular SMCs (CreERT2 under the control of the Acta2 promoter). The development of AAA was evaluated using in situ examination and quantified using RT-qPCR, immunohistochemistry and fluorescence microscopy. Cultured vascular SMC were exposed to the selective IKK inhibitor MLN120b and the expression levels of phenotypic markers KLF4, -Catenin and CTGF were addressed using cellular extracts and immunoblot analysis. Results RNASeq data support the presence of early anabolic events in SRA regions detailing activation of the mTORC1 pathway, which paralleled cellular processes including mitochondria, ribosome and sterol biosynthesis and the Unfolded Protein Response (UPR). Conditional deletion of the Ikbkb gene in vascular SMCs significantly reduces the incidence of SRA lesions as well as the rate of aneurysm ruptures in animals exposed to Ang II. In situ analysis further demonstrated that the protection conferred by the lack of IKK expression in vascular SMC is associated with reduced inflammatory response, the preservation of the contractile over the degradative vascular SMC phenotypes and the absence of anabolic and fibrotic signatures. Conclusion Our data not only reinforce the major roles play by vascular SMC in the rapid adaptation leading to the deleterious remodeling of the vascular wall and aortic lesions but also support a paradigm aiming at repositioning the efforts focusing on anabolic rather than inflammatory events. We used a transgenic homozygous mouse model referred to as SMA-CreERT2IkkbFlox/FloxApoE-/- in which IKKb expression can be temporally and selectively prevented in ApoE-/- vascular SMCs on a C57BL6 background (referred as KO). Wild-type and KO mice were treated with saline or angiotensin II (Ang II) (500 to 1000 ng/min/kg) s.c. with constant infusion using osmotic pumps for 24 h. Total RNA from the suprarenal aorta was extracted using the RNeasy Mini Kit (No. 74106, Qiagen).