The Elastic Lamellae of Devitalized Arteries Calcify When Incubated in Serum

Abstract

Objective-To determine whether serum contains an activity that induces artery calcification. Methods and Results-The elastic lamellae of devitalized rat aortas calcify rapidly in rat or bovine serum, or in human serum provided [Pi] Ն2 mmol/L. This calcification is attributable to a potent serum calcification factor (SCF), one that causes devitalized aortas to calcify when incubated in DMEM containing as little as 1.5% serum but not in DMEM alone. The SCF that initiates medial elastin calcification has the same 50-to 150-kDa size and protease sensitivity as the SCF shown previously to initiate calcification of type I collagen. Our working hypothesis is that the same SCF initiates calcification of collagen and elastin, and that this SCF arises from sites of normal bone mineralization and, like alkaline phosphatase, is released into general circulation. The SCF does not initiate medial elastin calcification in living arteries, which suggests that vascular cells may prevent this calcification. This hypothesis is supported by the observations that living arteries secrete the calcification inhibitor matrix Gla protein (MGP); that inactivation of MGP with warfarin causes living arteries to calcify; and that addition of MGP to medium containing warfarin prevents this calcification. Key Words: medial artery calcification Ⅲ elastic lamellae Ⅲ serum calcification factor Ⅲ matrix Gla protein Ⅲ devitalized and living arteries T wo major types of arterial calcification have been observed in human patients. 1,2 One affects the intimal layer of arteries and occurs within atherosclerotic plaques. The other involves the artery media and initially occurs within the elastic lamellae. This second type of vascular calcification is common in patients with chronic kidney disease and in patients with diabetes mellitus. Each type of arterial calcification has different physiological consequences, with clearcut evidence for adverse hemodynamic changes attributable to medial wall calcification but not to atherosclerotic plaque calcification, and the possible contribution of atherosclerotic plaque calcification to plaque rupture and subsequent thrombosis, an issue that does not apply to medial wall calcification. Conclusion-TheOur long-term goal is to understand the mechanisms that initiate calcification of the elastic lamellae of the artery media and the mechanisms that inhibit this calcification. In the course of our investigations, we became intrigued with the evidence for an association between bone metabolism and artery calcification, 3 an association that led us to propose that medial artery calcification is linked to bone resorption. One prediction of this hypothesis is that inhibitors of bone resorption should inhibit artery calcification. 3 In previous studies, we tested this prediction using 3 different types of bone resorption inhibitors, each with an entirely different mode of action on the osteoclast, the amino bisphosphonates alendronate and ibandronate, 3-5 the cytokine osteoprotegerin, 6 and the V-H ϩ -ATPase inhibitor SB...

Matrix Gla protein is involved in elastic fiber calcification in the dermis of pseudoxanthoma elasticum patients

“…It has been repeatedly shown that MGP, although it is a circulating protein, acts as inhibitor of the extracellular matrix calcification in the vicinity of cells expressing the protein. 12,34,37 Therefore, our findings that PXE fibroblasts express lower amount of the g-carboxylated form of MGP compared to controls may suggest that calcification of elastic fibers, at least in the dermis of PXE patients, might depend on local scarce availability of the active carboxylated form of MGP. 26 This hypothesis is in agreement with data obtained on transgenic animals showing that local, and not systemic, expression of MGP inhibits extracellular matrix calcification, 34 and with findings showing that only living smooth muscle cells producing MGP are able to prevent calcification of aortic rings in organ culture.…”

“…This is in agreement with recent observations that mature MGP is synthesized by cells in periphery, 34 where it would exert local inhibition of ectopic calcification. 12,34,37 In conclusion, impaired maturation of MGP would be part of the metabolic alterations of PXE fibroblasts and could play a relevant role in time-dependent stability of elastic fibers in PXE.…”

“…26 This hypothesis is in agreement with data obtained on transgenic animals showing that local, and not systemic, expression of MGP inhibits extracellular matrix calcification, 34 and with findings showing that only living smooth muscle cells producing MGP are able to prevent calcification of aortic rings in organ culture. 37 How to reconcile ABCC6 mutations in PXE with impaired expression and maturation of MGP is an open question. In the absence of knowledge on the physiological role of the membrane transporter responsible for PXE, we approach the problem of clinical manifestations in PXE by trying to understand the mechanisms of elastic fiber calcification, to identify cells involved and to characterize alterations of connective tissue metabolism relevant for the progression of disease.…”

Common Genetic Variants of MGP Are Associated With Calcification on the Arterial Wall but Not With Calcification Present in the Atherosclerotic Plaques

“…The ability of MGP to inhibit crystal growth depends on the presence of Gla residues, which could bind calcium in both solution and calcium salt crystals. 34,35 But the degree of γ-carboxylation required for MGP to inhibit calcification in humans is not known. In addition to being carboxylated, MGP can also undergo a posttranslational phosphorylation, which is also thought to contribute to its functionality.…”

Aortic Msx2-Wnt Calcification Cascade Is Regulated by TNF-α–Dependent Signals in Diabetic Ldlr −/− Mice

“…34 Thus, disease pathobiology and histological characteristics will differ depending on the mechanisms used to initiate vascular calcium deposition. In early lesions of the Ldlr Ϫ/Ϫ mouse, arterial calcium deposition visualized by Alizarin red staining is overlapping yet distinct from that seen with von Kossa stain for phosphate deposition (unpublished observations); similar observations were noted almost 40 years ago by Puchtler et al in studies of early human atherosclerotic lesions.…”