Osteoclastogenic Differentiation of Macrophages in the Development of Abdominal Aortic Aneurysms

Arterial calcification is common and contributes to the pathogenesis of occlusive vascular disease. Similar to the dynamics of bone, it is a tightly controlled process that maintains a balance between osteogenesis and osteolysis. However, whether calcium homeostasis plays a role in the development of aneurysms has not been explored. We hypothesized that macrophages differentiate into osteoclasts in aneurysmal arteries and that protease byproducts contribute to aneurysm pathophysiology.

We performed histological and immunohistochemical analyses and showed that macrophages positive for several osteoclast markers, including tartrate acid phosphatase, occur in great numbers in the human aneurysmal aorta, but very few occur in the human stenotic aorta and none in the nondiseased human aorta. Moreover, in situ zymography showed elevated protease activity in these cells compared with undifferentiated macrophages. Tumor necrosis factor-α and calcium phosphate stimulated this osteoclastogenic differentiation process through nuclear factor-κB, mitogen-activated protein kinases, and intracellular calcium signaling but not the receptor activator of the nuclear factor-κB ligand. Inhibition of osteoclastogenic differentiation by bisphosphonate inhibits aneurysm development in a mouse model.

These results suggest that differentiation of macrophages into osteoclasts contributes to the pathophysiology of aneurysmal disease.