Background

The calcium binding protein S100A12 is highly upregulated in the serum and sputum of patients with allergic asthma and is suggested to be a biomarker and pathologic mediator of asthma.

Objective

To test the role of S100A12 in mediating airway inflammation in a mouse model of allergic lung inflammation.

Methods

Transgenic mice that express human S100A12 and wild type littermates were sensitized and challenged with ovalbumin and assessed for inflammation, lung structure and function.

Results

Following ovalbumin sensitization and challenge, S100A12 transgenic mice showed reduced peribronchial and perivascular inflammation, mucus production and eosinophilia as well as attenuated airway responsiveness to contractile agonist compared to wild type sensitized and challenged animals. This is explained, at least in part, by remodeled airways in S100A12 transgenic mice with thinning of the airway smooth muscle. S100A12 exposure induced Fas expression and activation of caspase 3 in cultured airway smooth muscle cells, suggesting that airway smooth muscle abnormalities observed in S100A12 transgenic mice may be mediated through myocyte apoptosis.

Conclusion and Clinical Relevance

S100A12 is one of the most abundant proteins found in the airways of human asthmatics, and it was postulated that S100A12 could mediate the inflammatory process. Our study shows for the first time that transgenic expression of S100A12 in the lung of mice does not exacerbate lung inflammation in a model of ovalbumin-induced allergic inflammation. We speculate that the high levels of S100/calgranulins found in BALF of asthmatics and of ovalbumin-treated transgenic S100A12 mice do not significantly mediate pulmonary inflammation.

Objective

The proinflammatory cytokine S100A12 is associated with coronary atherosclerotic plaque rupture. We previously generated transgenic mice with vascular smooth muscle–targeted expression of human S100A12 and found that these mice developed aortic aneurysmal dilation of the thoracic aorta. In the current study, we tested the hypothesis that S100A12 expressed in vascular smooth muscle in atherosclerosis-prone apolipoprotein E (ApoE)–null mice would accelerate atherosclerosis.

Methods and Results

ApoE-null mice with or without the S100A12 transgene were analyzed. We found a 1.4-fold increase in atherosclerotic plaque size and more specifically a large increase in calcified plaque area (45% versus 7% of innominate artery plaques and 18% versus 10% of aortic root plaques) in S100A12/ApoE-null mice compared with wild-type/ApoE-null littermates. Expression of bone morphogenic protein and other osteoblastic genes was increased in aorta and cultured vascular smooth muscle, and importantly, these changes in gene expression preceded the development of vascular calcification in S100A12/ApoE-null mice. Accelerated atherosclerosis and vascular calcification were mediated, at least in part, by oxidative stress because inhibition of NADPH oxidase attenuated S100A12-mediated osteogenesis in cultured vascular smooth muscle cells. S100A12 transgenic mice in the wild-type background (ApoE+/+) showed minimal vascular calcification, suggesting that S100A12 requires a proinflammatory/proatherosclerotic environment to induce osteoblastic differentiation and vascular calcification.

Conclusion

Vascular smooth muscle S100A12 accelerates atherosclerosis and augments atherosclerosis-triggered osteogenesis, reminiscent of features associated with plaque instability.

Background

The proinflammatory cytokine S100A12 (also known as EN-RAGE) is associated with cardiovascular morbidity and mortality in hemodialysis patients. In the cur- rent study, we tested the hypothesis that S100A12 expressed in vascular smooth muscle in nonatherosclerosis-prone C57BL/6J mice on normal rodent chow diet, but exposed to the metabolic changes of chronic kidney disease (CKD), would develop vascular disease resembling that observed in patients with CKD.

Methods

CKD was induced in S100A12 transgenic mice and wild-type littermate mice not expressing human S100A12 by surgical ligation of the ureters. The aorta was analyzed after 7 weeks of elevated BUN (blood urea nitrogen), and cultured aortic smooth muscle cells were studied.

Results

We found enhanced vascular medial calcification in S100A12tg mice subjected to CKD. Vascular calcification was mediated, at least in part, by activation of the receptor for S100A12, RAGE (receptor for advanced glycation endproducts), and by enhanced oxidative stress, since inhibition of NADPH-oxidase Nox1 and limited access of S100A12 to RAGE attenuated the calcification and gene expression of osteoblastic genes in cultured vascular smooth muscle cells.

Conclusion

S100A12 augments CKD-triggered osteogenesis in murine vasculature, reminiscent of features associated with enhanced vascular calcification in patients with chronic and end-stage kidney disease.

Atherosclerosis remains the leading cause of death in the western countries and represents a complex chronic inflammatory process whose regulation is dependent on a network of cytokine and chemokine signaling between key cells such as endothelial cells, monocytes, dendritic cells, lymphocytes and smooth muscle cells. This review focuses on the biology and function of S100 proteins and their receptor RAGE with respect to the multifactorial process leading to atherosclerosis, plaque rupture, and aortic wall remodeling.

Rationale

S100A12 is a small calcium binding protein that is a ligand of the Receptor for Advanced Glycation End products (RAGE). RAGE has been extensively implicated in inflammatory states such as atherosclerosis, but the role of S100A12 as its ligand is less clear.

Objective

To test the role of S100A12 in vascular inflammation, we generated and analyzed mice expressing human S100A12 in vascular smooth muscle under control of the SM22α promoter since S100A12 is not present in mice.

Methods and Results

Transgenic mice displayed pathologic vascular remodeling with aberrant thickening of the aortic media, disarray of elastic fibers, and increased collagen deposition, together with increased latent MMP-2 protein and reduction in smooth muscle stress fibers leading to a progressive dilatation of the aorta. In primary aortic smooth muscle cell cultures, we found that S100A12-mediates increased IL-6 production, activation of TGF β pathways and increased metabolic activity with enhanced oxidative stress. To correlate our findings to human aortic aneurysmal disease, we examined S100A12 expression in aortic tissue from patients with thoracic aortic aneurysm and found increased S100A12 expression in vascular smooth muscle cells.

Conclusion

S100A12 expression is sufficient to activate pathogenic pathways through the modulation of oxidative stress, inflammation and vascular remodeling in vivo.