miRNA-221 and miRNA-222 synergistically function to promote vascular calcification.

Vascular calcification shares many similarities with skeletal mineralisation and involves the phenotypic trans-differentiation of vascular smooth muscle cells (VSMCs) to osteoblastic cells within a calcified environment. Various microRNAs (miRs) are known to regulate cell differentiation; however, their role in mediating VSMC calcification is not fully understood. miR-microarray analysis revealed the significant down-regulation of a range of miRs following nine days in culture, including miR-199b, miR-29a, miR-221, miR-222 and miR-31 (p < 0.05). Subsequent studies investigated the specific role of the miR-221/222 family in VSMC calcification. Real-time quantitative polymerase chain reaction data confirmed the down-regulation of miR-221 (32.4%; p < 0.01) and miR-222 (15.7%; p < 0.05). VSMCs were transfected with mimics of miR-221 and miR-222, individually and in combination. Increased calcium deposition was observed in the combined treatment (two-fold; p < 0.05) but not in individual treatments. Runx2 and Msx2 expression was increased during calcification, but no difference in expression was observed following transfection with miR mimics. Interestingly, miR-221 and miR-222 mimics induced significant changes in ectonucleotide phosphodiesterase 1 (Enpp1) and Pit-1 expression, suggesting that these miRs may modulate VSMC calcification through cellular inorganic phosphate and pyrophosphate levels.

New insights into NPP1 function: lessons from clinical and animal studies.

The recent elucidation of rare human genetic disorders resulting from mutations in ectonucleotide pyrophosphotase/phosphodiesterase (ENPP1), also known as plasma cell membrane glycoprotein 1 (PC-1), has highlighted the vital importance of this molecule in human health and disease. Generalised arterial calcification in infants (GACI), a frequently lethal disease, has been reported in recessive inactivating mutations in ENPP1. Recent findings have also linked hypophosphataemia to a lack of NPP1 function. A number of human genetic studies have indicated that NPP1 is a vital regulator that influences a wide range of tissues through various signalling pathways and when disrupted can lead to significant pathology. The function of Enpp1 has been widely studied in rodent models, where both the mutant tiptoe walking (ttw/ttw) mouse and genetically engineered Enpp1(-/-) mice show significant alterations in skeletal and soft tissue mineralisation, calcium/phosphate balance and glucose homeostasis. These models therefore provide important tools with which to study the potential mechanisms underpinning the human diseases associated with altered NPP1. This review will focus on the recent advances in our current knowledge of the actions of NPP1 in relation to bone disease, cardiovascular pathologies and diabetes. A fuller understanding of the mechanisms through which NPP1 exerts its pathological effects may stimulate the development of novel therapeutic strategies for patients at risk from the devastating clinical outcomes associated with disrupted NPP1 function.

MEPE is a novel regulator of growth plate cartilage mineralization.

Matrix extracellular phosphoglycoprotein (MEPE) belongs to the SIBLING protein family which play key roles in biomineralization. Although the growth plates of MEPE-overexpressing mice display severe morphological disruption, the expression and function of MEPE in growth plate matrix mineralization remains largely undefined. Here we show MEPE and its cleavage product, the acidic serine aspartate-rich MEPE-associated motif (ASARM) peptide, to be localised to the hypertrophic zone of the growth plate. We also demonstrate that the phosphorylated (p)ASARM peptide inhibits ATDC5 chondrocyte matrix mineralization. Stable MEPE-overexpressing ATDC5 cells also had significantly reduced matrix mineralization in comparison to the control cells. Interestingly, we show that the addition of the non-phosphorylated (np)ASARM peptide promoted mineralization in the ATDC5 cells. The peptides and the overexpression of MEPE did not affect the differentiation of the ATDC5 cells. For a more physiologically relevant model, we utilized the metatarsal organ culture model. We show the pASARM peptide to inhibit mineralization at two stages of development, as shown by histological and µCT analysis. Like in the ATDC5 cells, the peptides did not affect the differentiation of the metatarsals indicating that the effects seen on mineralization are direct, as is additionally confirmed by no change in alkaline phosphatase activity or mRNA expression. In the metatarsal organ cultures, the pASARM peptide also reduced endothelial cell markers and vascular endothelial growth factor mRNA expression. Taken together these results show MEPE to be an important regulator of growth plate chondrocyte matrix mineralization through its cleavage to an ASARM peptide.

The role of cellular senescence during vascular calcification: a key paradigm in aging research.

Vascular calcification has severe clinical consequences and is considered an accurate predictor of future adverse cardiovascular events. Vascular calcification refers to the deposition of calcium phosphate mineral, most often hydroxyapatite, in arteries. Extensive calcification of the vascular system is a key characteristic of aging. In this article, we outline the mechanisms governing vascular calcification and highlight its association with cellular senescence. This review discusses the molecular mechanisms of cellular senescence and its affect on calcification of vascular cells, the relevance of phosphate regulation and the function of FGF23 and Klotho proteins. The association of vascular calcification and cellular senescence with the rare human aging disorder Hutchison-Gilford Progeria Syndrome (HGPS) is highlighted and the mouse models used to try to determine the underlying pathways are discussed. By understanding the pathways involved in these processes novel drug targets may be elucidated in an effort to reduce the effects of cellular aging as a risk factor in cardiovascular disease.

MOVAS-1 cell line: a new in vitro model of vascular calcification.

Vascular calcification has severe clinical consequences in a number of diseases, including diabetes, atherosclerosis and end-stage renal disease. The in vitro calcification of primary mouse, human and bovine vascular smooth muscle cells (VSMCs) is commonly employed to examine the mechanisms of vascular calcification. However, to date, no published studies have utilised a murine cell line to investigate this process. In the present study, we aimed to determine whether the mouse VSMC line MOVAS-1 can calcify in vitro. We established that the calcification of MOVAS-1 cells can be induced in the presence of calcifying medium (containing ß-glycerophosphate and ascorbic acid), as detected by Alizarin Red and von Kossa staining, and quantification of calcium deposition and alkaline phosphatase activity. We also showed that the time course of MOVAS-1 calcification is comparable to that of the primary murine aortic VSMCs, establishing the MOVAS-1 cells as a feasible and relevant model. Significant increases in the mRNA expression profile of key genes associated with vascular calcification (Ocn, Akp2 and PiT-1) were observed in MOVAS-1 cells cultured under calcifying conditions, with similar changes in expression in murine aortic VSMCs. Furthermore, a significant reduction in calcification was observed in MOVAS-1 cells following treatment with levamisole and etidronate, known inhibitors of calcification. In conclusion, we demonstrated that the MOVAS-1 line is a reliable, convenient and economical system in which to investigate vascular calcification in vitro, and will make a useful contribution to increasing our understanding of this pathological process.