TNAP stimulates vascular smooth muscle cell trans-differentiation into chondrocytes through calcium deposition and BMP-2 activation: Possible implication in atherosclerotic plaque stability

Abstract

Atherosclerotic plaque calcification varies from early, diffuse microcalcifications to a bone-like tissue formed by endochondral ossification. Recently, a paradigm has emerged suggesting that if the bone metaplasia stabilizes the plaques, microcalcifications are harmful. Tissue-nonspecific alkaline phosphatase (TNAP), an ectoenzyme necessary for mineralization by its ability to hydrolyze inorganic pyrophosphate (PP), is stimulated by inflammation in vascular smooth muscle cells (VSMCs). Our objective was to determine the role of TNAP in trans-differentiation of VSMCs and calcification. In rodent MOVAS and A7R5 VSMCs, addition of exogenous alkaline phosphatase (AP) or TNAP overexpression was sufficient to stimulate the expression of several chondrocyte markers and induce mineralization. Addition of exogenous AP to human mesenchymal stem cells cultured in pellets also stimulated chondrogenesis. Moreover, TNAP inhibition with levamisole in mouse primary chondrocytes dropped mineralization as well as the expression of chondrocyte markers. VSMCs trans-differentiated into chondrocyte-like cells, as well as primary chondrocytes, used TNAP to hydrolyze PP, and PP provoked the same effects as TNAP inhibition in primary chondrocytes. Interestingly, apatite crystals, associated or not to collagen, mimicked the effects of TNAP on VSMC trans-differentiation. AP and apatite crystals increased the expression of BMP-2 in VSMCs, and TNAP inhibition reduced BMP-2 levels in chondrocytes. Finally, the BMP-2 inhibitor noggin blocked the rise in aggrecan induced by AP in VSMCs, suggesting that TNAP induction in VSMCs triggers calcification, which stimulates chondrogenesis through BMP-2. Endochondral ossification in atherosclerotic plaques may therefore be induced by crystals, probably to confer stability to plaques with microcalcifications.

Vascular Calcification—New Insights into Its Mechanism

“…BMP2 suppresses VSMC proliferation through p21 inhibition, followed by cell cycle arrest [181,182]. Intimal hyperplasia, induced by balloon injury, is reduced by BMP2 [183], which also effects loss of SMC markers, and acquisition of osteoblastic profile gene expression, including Msx2, alkaline phosphatase(ALP), OPN, and others [171,[184][185][186].…”

Matrix vesicles from chondrocytes and osteoblasts: Their biogenesis, properties, functions and biomimetic models

“…Key osteogenic markers, including TNAP, PHOSPHO1 and P i T1 also play a critical role in regulating the process of VSMC mineralization [201–203]. VSMC-driven arterial mineralization is aided by an additional mechanism in patients with CKD.…”

Pyrocarbon versus cobalt-chromium in the context of spherical interposition implants: an in vitro study on cultured chondrocytes

“…TNAP is an enzyme necessary for mineralisation of the extracellular matrix and it is present in calcified tissues (Balcerzak et al, 2003). An important TNAP activity, which can be measured in the cell lysate, reflects usually a high rate of mineralisation (Balcerzak et al, 2003;Fakhry et al, 2017). A significant decrease of this enzymatic activity in cultured chondrocytes was observed on both PyC and CoCr, in comparison to the plastic control (Fig.…”