Monocyte/Macrophage Regulation of Vascular Calcification In Vitro

Abstract

Background-Calcification is a common complication of atherosclerosis and other chronic inflammatory processes that involves infiltration of monocytes and accumulation of macrophages. Methods and Results-To determine whether these cells modulate vascular calcification in vitro, calcifying vascular cells (CVCs), a subpopulation of osteoblast-like cells derived from the artery wall, were cocultured with human peripheral blood monocytes for 5 days. Results showed that alkaline phosphatase (ALP) activity, a marker of osteoblastic differentiation, was significantly greater in cocultures than in cultures of CVCs or monocytes alone. Both ALP activity and matrix mineralization increased in proportion to the number of monocytes added. Activation of monocyte/macrophages (M/Ms) by oxidized LDL further increased ALP activity in cocultures. However, neither conditioned medium from oxidized-LDL-activated M/Ms or transwell coculture had this effect on CVCs, which suggests a need for cell-to-cell contact. In contrast, conditioned medium from lipopolysaccharide-activated M/Ms increased ALP activity of CVCs. ELISA showed that lipopolysaccharide-activated M/Ms secreted tumor necrosis factor-␣, and neutralizing antibody to tumor necrosis factor-␣ attenuated the induction of ALP activity by the conditioned media. Conclusions-These

Cell-specific effects of TNF-α and IL-1β on alkaline phosphatase: implication for syndesmophyte formation and vascular calcification

“…The data presented above indicate that TNF-a and IL-1b decrease TNAP expression and activity in chondrocytes and entheseal chondrocyte-like cells, and therefore might exert inhibitory effects on ectopic bone formation during AS. This is in marked contrast with the published effects of TNF-a on TNAP expression and activity in VSMCs 22,23 and on vascular calcification in diabetic mice. 24 In this context, we aimed at deciphering the mechanisms responsible for the different Cell-specific effects of TNF-a on TNAP P Lencel et al effect of TNF-a on TNAP in chondrocytes and VSMCs.…”

“…19,20 Recently, we showed that TNF-a and IL-1b stimulate TNAP expression and activity independently of the master osteoblast transcription factor RUNX2, and hypothesized that these cytokines may be able to induce calcification in tissues enriched in a fibrillar collagen, such as the entheseal fibro-cartilage. 21 This hypothesis was conceivable since TNF-a stimulates TNAP expression in vascular smooth muscle cells (VSMCs), 22,23 and since blockade of TNF-a with infliximab specifically inhibits vascular calcification in the LdlrÀ/À diabetes mellitus mouse model, without reducing obesity, hypercholesterolemia or hyperglycemia. 24 In this hypothesis, cytokines may stimulate ectopic collagen calcification by the mere stimulation of TNAP activity, and this calcified matrix, may in turn induce the ossification process, in the arterial wall, 25 and in entheseal fibro-cartilage during AS.…”

Msx2 promotes cardiovascular calcification by activating paracrine Wnt signals

“…In our models, high-fat diets are necessary to induce robust vascular calcification (ref. 14 and data not shown); thus, some diet-regulated metabolic parameter, potentially a phospholipid or oxidized sterol (6,8,51), synergizes with Msx2-Wnt signaling to drive medial calcification. Of note, surgical resection of the adventitia reduces segmental medial artery calcification (43); whether this arises from loss of adventitial pro-osteogenic paracrine signals, reductions in the vascular osteoprogenitor pool, or a combination of both is unknown.…”

“…Since adventitial myofibroblasts are migratory (40), cells mobilized via proliferative expansion of the tunica adventitia may robustly calcify in the environment of the tunica media. However, Demer and colleagues have identified a subpopulation of resident cells in the tunica media -the CVC -that express pericytic myofibroblast markers, elaborate ALP, and deposit minerals in response to oxidized sterols and monocyte inflammatory signals (2,6,50,51). Since CVCs represent 10-30% of the medial cell population (50), the relative contribution of media versus adventitial osteogenic progenitors to mural calcification has yet to be established.…”

Collagens in the progression and complications of atherosclerosis

“…Rather, they are potential sources of proatherogenic factors such as cytokines and reactive oxygen species, which appear to exacerbate calcification in a paracrine manner. 129 Towler and colleagues have illustrated the osteogenic potential of adventitial aortic myofibroblasts in Ldlr -/-mice. 130 Watson and colleagues reported that calcifying CVCs in vitro produced an ECM rich in type I collagen and that exposure to type I collagen stimulated robust calcification by otherwise slowlymineralizing cells.…”