Identification and treatment of abdominal aortic aneurysm (AAA) remain among the most prominent challenges in vascular medicine. MicroRNAs (miRNAs) are crucial regulators of cardiovascular pathology and represent intriguing targets to limit AAA expansion. Here we show, by using two established murine models of AAA disease along with human aortic tissue and plasma analysis, that miR-24 is a key regulator of vascular inflammation and AAA pathology. In vivo and in vitro studies reveal chitinase 3-like 1 (Chi3l1) to be a major target and effector under the control of miR-24, regulating cytokine synthesis in macrophages as well as their survival, promoting aortic smooth muscle cell migration and cytokine production, and stimulating adhesion molecule expression in vascular endothelial cells. We further show that modulation of miR-24 alters AAA progression in animal models, and that miR-24 and CHI3L1 represent novel plasma biomarkers of AAA disease progression in humans.

Background Stiffening of the aortic wall is a phenomenon consistently observed in age and in abdominal aortic aneurysm (AAA). However, its role in AAA pathophysiology is largely undefined. Methods and Results Using an established murine elastase-induced AAA model, we demonstrate that segmental aortic stiffening (SAS) precedes aneurysm growth. Finite element analysis (FEA) reveals that early stiffening of the aneurysm-prone aortic segment leads to axial (longitudinal) wall stress generated by cyclic (systolic) tethering of adjacent, more compliant wall segments. Interventional stiffening of AAA-adjacent aortic segments (via external application of surgical adhesive) significantly reduces aneurysm growth. These changes correlate with reduced segmental stiffness of the AAA-prone aorta (due to equalized stiffness in adjacent segments), reduced axial wall stress, decreased production of reactive oxygen species (ROS), attenuated elastin breakdown, and decreased expression of inflammatory cytokines and macrophage infiltration, as well as attenuated apoptosis within the aortic wall. Cyclic pressurization of segmentally stiffened aortic segments ex vivo increases the expression of genes related to inflammation and extracellular matrix (ECM) remodeling. Finally, human ultrasound studies reveal that aging, a significant AAA risk factor, is accompanied by segmental infrarenal aortic stiffening. Conclusions The present study introduces the novel concept of segmental aortic stiffening (SAS) as an early pathomechanism generating aortic wall stress and triggering aneurysmal growth, thereby delineating potential underlying molecular mechanisms and therapeutic targets. In addition, monitoring SAS may aid the identification of patients at risk for AAA.

Key Words: RANKL Ⅲ vascular calcification Ⅲ BMP-2 Ⅲ MGP Ⅲ estrogen V ascular calcification is one of the major complications of cardiovascular disease and an independent risk factor for myocardial infarction and cardiac death, 1 among other outcomes. Arterial calcification is also associated with osteoporosis, especially in postmenopausal women. 2 Recent evidence strongly suggests the biological linkages on both disease mechanisms based on the presence of bone-related proteins 3 and bone-related cells at the site of calcification. 4 Accordingly, a triad of key proteins in bone metabolism has emerged as new players in cardiovascular diseases: RANK (the receptor activator of nuclear factor B), the RANK ligand (RANKL), and osteoprotegerin (OPG).In bone, RANKL and OPG are expressed in osteoblasts, and the receptor RANK is expressed in osteoclast cells. The major role of RANKL in bone is the stimulation of osteoclast activity 5 and inhibition of osteoclast apoptosis. 6 RANKL binds not only to RANK but also to OPG,7,8 which is secreted as a soluble protein that lacks transmembrane and cytoplasmic domains. Because of this peculiarity of a decoy receptor, the major biological action described for OPG has been through the binding to RANKL and consequent inhibition of RANK stimulation, then decreasing the osteoclast differentiation and activity in bone. 7,8 OPG-deficient mice develop severe osteoporosis resulting from marked increase in osteoclast activation, and interestingly two-thirds of the animals have profound vascular medial calcification. 9 Similar to OPG-deficient mouse phenotype, postmenopausal women also have high incidence of osteoporosis and vascular calcification, 10 which suggests that RANK-RANKL system may work not only in osteoporosis but also in arterial calcification.

Rationale Accelerated arterial stiffening is a major complication of diabetes with no specific therapy available up to date. Objective The present study investigates the role of the osteogenic transcription factor Runx2 as a potential mediator and therapeutic target of aortic fibrosis and aortic stiffening in diabetes. Methods and Results Using a murine model of type 2 diabetes (db/db mice) we identify progressive structural aortic stiffening that precedes the onset of arterial hypertension. At the same time, Runx2 is aberrantly upregulated in the medial layer of db/db aortae as well as in thoracic aortic samples from type 2 diabetic patients. Vascular smooth muscle-specific overexpression of Runx2 in transgenic mice increases expression of its target genes, Col1a1 and Col1a2, leading to medial fibrosis and aortic stiffening. Interestingly, increased Runx2 expression per se is not sufficient to induce aortic calcification. Using in vivo and in vitro approaches, we further demonstrate that Runx2 expression in diabetes is regulated via a redox-sensitive pathway that involves a direct interaction of NF-κB with the Runx2 promoter. Conclusion In conclusion this study highlights Runx2 as a previously unrecognized inducer of vascular fibrosis in the setting of diabetes, promoting arterial stiffness irrespective of calcification.