Metformin ameliorates valve interstitial cell calcification by promoting autophagic flux

Calcific aortic valve disease (CAVD) is the most common heart disease of the developed world. It has previously been established that metformin administration reduces arterial calcification via autophagy; however, whether metformin directly regulates CAVD has yet to be elucidated. In the present study we investigated whether metformin alleviates valvular calcification through the autophagy-mediated recycling of Runx2. Calcification was reduced in rat valve interstitial cells (RVICs) by metformin treatment (0.5-1.5 mM) (P < 0.01), with a marked decrease in Runx2 protein expression compared to control cells (P < 0.05). Additionally, upregulated expression of Atg3 and Atg7 (key proteins required for autophagosome formation), was observed following metformin treatment (1 mM). Blocking autophagic flux using Bafilomycin-A1 revealed colocalisation of Runx2 with LC3 puncta in metformin treated RVICs (P < 0.001). Comparable Runx2 accumulation was seen in LC3 positive autolysosomes present within cells that had been treated with both metformin and hydroxychloroquine in combination (P < 0.001). Mechanistic studies employing three-way co-immunoprecipitation with Runx2, p62 and LC3 suggested that Runx2 binds to LC3-II upon metformin treatment in VICs. Together these studies suggest that the utilisation of metformin may represent a novel strategy for the treatment of CAVD.

TGF-β phospho antibody array identifies altered SMAD2, PI3K/AKT/SMAD, and RAC signaling contribute to the pathogenesis of myxomatous mitral valve disease

Background

TGFβ signaling appears to contribute to the pathogenesis of myxomatous mitral valve disease (MMVD) in both dogs and humans. However, little is known about the extent of the downstream signaling changes that will then affect cell phenotype and function in both species.

Objective

Identify changes in downstream signals in the TGFβ pathway in canine MMVD and examine the effects of antagonism of one significant signal (SMAD2 was selected).

Materials and methods

Canine cultures of normal quiescent valve interstitial cells (qVICs) and disease-derived activated myofibroblasts (aVICs) (n = 6) were examined for TGFβ signaling protein expression using a commercial antibody array. Significant changes were confirmed, and additional proteins of interest downstream in the TGFβ signaling pathway and markers of cell phenotype were examined (PRAS40, S6K, elF4E IRS-1, αSMA, and VIM), using protein immunoblotting. RT-PCR examined expression of gene markers of VIC activation (ACTA2, TAGLN, and MYH10; encoding the proteins αSMA, SM22, and Smemb, respectively). Attenuation of pSMAD2 in aVICs was examined using a combination of RNA interference technology (siRNA) and the SMAD7 (antagonizes SMAD2) agonist asiaticoside.

Results

The antibody array identified significant changes (P < 0.05) in 19 proteins, of which six were phosphorylated (p). There was increased expression of pSMAD2 and pRAC1 and decreased expression of pmTOR, pERK1/2, and pAKT1. Expression of pPRAS40 and pIRS-1 was increased, as was the mTOR downstream transcription factor pS6K, with increased expression of peIF4E in aVICs, indicating negative feedback control of the PI3K/AKT/mTOR pathway. SMAD2 antagonism by siRNA and the SMAD7 agonist asiaticoside decreased detection of pSMAD by at least 50%, significantly decreased expression of the aVIC gene markers ACTA2, TAGLN, and MYH10, and pαSMA, pAKT2, and pERK1, but had no effect on pS6K, pERK2, or pVIM expression in aVICs. SMAD2 antagonism transitioned diseased aVICs to normal qVICs, while maintaining a mesenchymal phenotype (VIM+) while concurrently affecting non-canonical TGFβ signaling.

Conclusion

MMVD is associated with changes in both the canonical and non-canonical TGFβ signaling pathway. Antagonism of SMAD2 transitions diseased-activated myofibroblasts back to a normal phenotype, providing data that will inform studies on developing novel therapeutics to treat MMVD in dogs and humans.

TGF-β-induced PI3K/AKT/mTOR pathway controls myofibroblast differentiation and secretory phenotype of valvular interstitial cells through the modulation of cellular senescence in a naturally occurring in vitro canine model of myxomatous mitral valve disease

PI3K/AKT/mTOR signalling contributes to several cardiovascular disorders. The aim of this study was to examine the PI3K/AKT/mTOR pathway in myxomatous mitral valve disease (MMVD). Double-immunofluorescence examined expression of PI3K and TGF-β1 in canine valves. Valve interstitial cells (VICs) from healthy or MMVD dogs were isolated and characterized. Healthy quiescent VICs (qVICs) were treated with TGF-β1 and SC-79 to induce activated myofibroblast phenotypes (aVICs). Diseased valve-derived aVICs were treated with PI3K antagonists and expression of RPS6KB1 (encoding p70 S6K) was modulated using siRNA and gene overexpression. SA-β-gal and TUNEL staining were used to identify cell senescence and apoptosis, and qPCR and ELISA to examine for senescence-associated secretory phenotype. Protein immunoblotting was used to examine expression of phosphorylated and total proteins. TGF-β1 and PI3K are highly expressed in mitral valve tissues. Activation of PI3K/AKT/mTOR and increased expression of TGF-β are found in aVICs. TGF-β transitions qVICs to aVICs by upregulation of PI3K/AKT/mTOR. Antagonism of PI3K/AKT/mTOR reverses aVIC myofibroblast transition by inhibiting senescence and promoting autophagy. Upregulation of mTOR/S6K induces transformation of senescent aVICs, with reduced capacity for apoptosis and autophagy. Selective knockdown of p70 S6K reverses cell transition by attenuating cell senescence, inhibiting apoptosis and improving autophagy. TGF-β-induced PI3K/AKT/mTOR signalling contributes to MMVD pathogenesis and plays crucial roles in the regulation of myofibroblast differentiation, apoptosis, autophagy and senescence in MMVD.

Increased PHOSPHO1 and alkaline phosphatase expression during the anabolic bone response to intermittent parathyroid hormone delivery

The administration of intermittent parathyroid hormone (iPTH) is anabolic to the skeleton. Recent studies with cultured osteoblasts have revealed that the expression of PHOSPHO1, a bone-specific phosphatase essential for the initiation of mineralisation, is regulated by PTH. Therefore, this study sought to determine whether the bone anabolic response to iPTH involves modulation of expression of Phospho1 and of other enzymes critical for bone matrix mineralisation. To mimic iPTH treatment, primary murine osteoblasts were challenged with 50 nM PTH for 6 h in every 48 h period for 8 days (4 cycles), 14 days (7 cycles) and 20 days (10 cycles) in total. The expression of both Phospho1 and Smpd3 was almost completely inhibited after 4 cycles, whereas 10 cycles were required to stimulate a similar response in Alpl expression. To explore the in vivo role of PHOSPHO1 in PTH-mediated osteogenesis, the effects of 14- and 28-day iPTH (80 µg/kg/day) administration was assessed in male wild-type (WT) and Phospho1-/- mice. The expression of Phospho1, Alpl, Smpd3, Enpp1, Runx2 and Trps1 expression was enhanced in the femora of WT mice following iPTH administration but remained unchanged in the femora of Phospho1-/- mice. After 28 days of iPTH administration, the anabolic response in the femora of WT was greater than that noted in Phospho1-/- mice. Specifically, cortical and trabecular bone volume/total volume, as well as cortical thickness, were increased in femora of iPTH-treated WT but not in iPTH-treated Phospho1-/- mice. Trabecular bone osteoblast number was also increased in iPTH-treated WT mice but not in iPTH-treated Phospho1-/-  mice. The increased levels of Phospho1, Alpl, Enpp1 and Smpd3 in WT mice in response to iPTH administration is consistent with their contribution to the potent anabolic properties of iPTH in bone. Furthermore, as the anabolic response to iPTH was attenuated in mice deficient in PHOSPHO1, this suggests that the osteoanabolic effects of iPTH are at least partly mediated via bone mineralisation processes.

p53 Regulates Mitochondrial Dynamics in Vascular Smooth Muscle Cell Calcification

Arterial calcification is an important characteristic of cardiovascular disease. It has key parallels with skeletal mineralization; however, the underlying cellular mechanisms responsible are not fully understood. Mitochondrial dynamics regulate both bone and vascular function. In this study, we therefore examined mitochondrial function in vascular smooth muscle cell (VSMC) calcification. Phosphate (Pi)-induced VSMC calcification was associated with elongated mitochondria (1.6-fold increase, p < 0.001), increased mitochondrial reactive oxygen species (ROS) production (1.83-fold increase, p < 0.001) and reduced mitophagy (9.6-fold decrease, p < 0.01). An increase in protein expression of optic atrophy protein 1 (OPA1; 2.1-fold increase, p < 0.05) and a converse decrease in expression of dynamin-related protein 1 (DRP1; 1.5-fold decrease, p < 0.05), two crucial proteins required for the mitochondrial fusion and fission process, respectively, were noted. Furthermore, the phosphorylation of DRP1 Ser637 was increased in the cytoplasm of calcified VSMCs (5.50-fold increase), suppressing mitochondrial translocation of DRP1. Additionally, calcified VSMCs showed enhanced expression of p53 (2.5-fold increase, p < 0.05) and β-galactosidase activity (1.8-fold increase, p < 0.001), the cellular senescence markers. siRNA-mediated p53 knockdown reduced calcium deposition (8.1-fold decrease, p < 0.01), mitochondrial length (3.0-fold decrease, p < 0.001) and β-galactosidase activity (2.6-fold decrease, p < 0.001), with concomitant mitophagy induction (3.1-fold increase, p < 0.05). Reduced OPA1 (4.1-fold decrease, p < 0.05) and increased DRP1 protein expression (2.6-fold increase, p < 0.05) with decreased phosphorylation of DRP1 Ser637 (3.20-fold decrease, p < 0.001) was also observed upon p53 knockdown in calcifying VSMCs. In summary, we demonstrate that VSMC calcification promotes notable mitochondrial elongation and cellular senescence via DRP1 phosphorylation. Furthermore, our work indicates that p53-induced mitochondrial fusion underpins cellular senescence by reducing mitochondrial function.

Metformin protects against vascular calcification through the selective degradation of Runx2 by the p62 autophagy receptor

Vascular calcification is associated with aging, type 2 diabetes, and atherosclerosis, and increases the risk of cardiovascular morbidity and mortality. It is an active, highly regulated process that resembles physiological bone formation. It has previously been established that pharmacological doses of metformin alleviate arterial calcification through adenosine monophosphate-activated protein kinase (AMPK)-activated autophagy, however the specific pathway remains elusive. In the present study we hypothesized that metformin protects against arterial calcification through the direct autophagic degradation of runt-related transcription factor 2 (Runx2). Calcification was blunted in vascular smooth muscle cells (VSMCs) by metformin in a dose-dependent manner (0.5-1.5 mM) compared to control cells (p < 0.01). VSMCs cultured under high-phosphate (Pi) conditions in the presence of metformin (1 mM) showed a significant increase in LC3 puncta following bafilomycin-A1 (Baf-A; 5 nM) treatment compared to control cells (p < 0.001). Furthermore, reduced expression of Runx2 was observed in the nuclei of metformin-treated calcifying VSMCs (p < 0.0001). Evaluation of the functional role of autophagy through Atg3 knockdown in VSMCs showed aggravated Pi-induced calcification (p < 0.0001), failure to induce autophagy (punctate LC3) (p < 0.001) and increased nuclear Runx2 expression (p < 0.0001) in VSMCs cultured under high Pi conditions in the presence of metformin (1 mM). Mechanistic studies employing three-way coimmunoprecipitation with Runx2, p62, and LC3 revealed that p62 binds to both LC3 and Runx2 upon metformin treatment in VSMCs. Furthermore, immunoblotting with LC3 revealed that Runx2 specifically binds with p62 and LC3-II in metformin-treated calcified VSMCs. Lastly, we investigated the importance of the autophagy pathway in vascular calcification in a clinical setting. Ex vivo clinical analyses of calcified diabetic lower limb artery tissues highlighted a negative association between Runx2 and LC3 in the vascular calcification process. These studies suggest that exploitation of metformin and its analogues may represent a novel therapeutic strategy for clinical intervention through the induction of AMPK/Autophagy Related 3 (Atg3)-dependent autophagy and the subsequent p62-mediated autophagic degradation of Runx2.

Increased PHOSPHO1 expression mediates cortical bone mineral density in renal osteodystrophy

Patients with advanced chronic kidney disease (CKD) often present with skeletal abnormalities, a condition known as renal osteodystrophy (ROD). While tissue non-specific alkaline phosphatase (TNAP) and PHOSPHO1 are critical for bone mineralization, their role in the etiology of ROD is unclear. To address this, ROD was induced in both WT and Phospho1 knockout (P1KO) mice through dietary adenine supplementation. The mice presented with hyperphosphatemia, hyperparathyroidism, and elevated levels of FGF23 and bone turnover markers. In particular, we noted that in CKD mice, bone mineral density (BMD) was increased in cortical bone (P < 0.05) but decreased in trabecular bone (P < 0.05). These changes were accompanied by decreased TNAP (P < 0.01) and increased PHOSPHO1 (P < 0.001) expression in WT CKD bones. In P1KO CKD mice, the cortical BMD phenotype was rescued, suggesting that the increased cortical BMD of CKD mice was driven by increased PHOSPHO1 expression. Other structural parameters were also improved in P1KO CKD mice. We further investigated the driver of the mineralization defects, by studying the effects of FGF23, PTH, and phosphate administration on PHOSPHO1 and TNAP expression by primary murine osteoblasts. We found both PHOSPHO1 and TNAP expressions to be downregulated in response to phosphate and PTH. The in vitro data suggest that the TNAP reduction in CKD-MBD is driven by the hyperphosphatemia and/or hyperparathyroidism noted in these mice, while the higher PHOSPHO1 expression may be a compensatory mechanism. Increased PHOSPHO1 expression in ROD may contribute to the disordered skeletal mineralization characteristic of this progressive disorder.

Cardiomyocytes disrupt pyrimidine biosynthesis in nonmyocytes to regulate heart repair

Various populations of cells are recruited to the heart after cardiac injury, but little is known about whether cardiomyocytes directly regulate heart repair. Using a murine model of ischemic cardiac injury, we demonstrate that cardiomyocytes play a pivotal role in heart repair by regulating nucleotide metabolism and fates of nonmyocytes. Cardiac injury induced the expression of the ectonucleotidase ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), which hydrolyzes extracellular ATP to form AMP. In response to AMP, cardiomyocytes released adenine and specific ribonucleosides that disrupted pyrimidine biosynthesis at the orotidine monophosphate (OMP) synthesis step and induced genotoxic stress and p53-mediated cell death of cycling nonmyocytes. As nonmyocytes are critical for heart repair, we showed that rescue of pyrimidine biosynthesis by administration of uridine or by genetic targeting of the ENPP1/AMP pathway enhanced repair after cardiac injury. We identified ENPP1 inhibitors using small molecule screening and showed that systemic administration of an ENPP1 inhibitor after heart injury rescued pyrimidine biosynthesis in nonmyocyte cells and augmented cardiac repair and postinfarct heart function. These observations demonstrate that the cardiac muscle cell regulates pyrimidine metabolism in nonmuscle cells by releasing adenine and specific nucleosides after heart injury and provide insight into how intercellular regulation of pyrimidine biosynthesis can be targeted and monitored for augmenting tissue repair.

Osteoblast-specific deficiency of ectonucleotide pyrophosphatase or phosphodiesterase-1 engenders insulin resistance in high-fat diet fed mice

Supraphysiological levels of the osteoblast-enriched mineralization regulator ectonucleotide pyrophosphatase or phosphodiesterase-1 (NPP1) is associated with type 2 diabetes mellitus. We determined the impact of osteoblast-specific Enpp1 ablation on skeletal structure and metabolic phenotype in mice. Female, but not male, 6-week-old mice lacking osteoblast NPP1 expression (osteoblast-specific knockout [KO]) exhibited increased femoral bone volume or total volume (17.50% vs. 11.67%; p < .01), and reduced trabecular spacing (0.187 vs. 0.157 mm; p < .01) compared with floxed (control) mice. Furthermore, an enhanced ability of isolated osteoblasts from the osteoblast-specific KO to calcify their matrix in vitro compared to fl/fl osteoblasts was observed (p < .05). Male osteoblast-specific KO and fl/fl mice showed comparable glucose and insulin tolerance despite increased levels of insulin-sensitizing under-carboxylated osteocalcin (195% increase; p < .05). However, following high-fat-diet challenge, osteoblast-specific KO mice showed impaired glucose and insulin tolerance compared with fl/fl mice. These data highlight a crucial local role for osteoblast NPP1 in skeletal development and a secondary metabolic impact that predominantly maintains insulin sensitivity.

Mitochondrial Dysfunction: Cause or Consequence of Vascular Calcification?

Mitochondria are crucial bioenergetics powerhouses and biosynthetic hubs within cells, which can generate and sequester toxic reactive oxygen species (ROS) in response to oxidative stress. Oxidative stress-stimulated ROS production results in ATP depletion and the opening of mitochondrial permeability transition pores, leading to mitochondria dysfunction and cellular apoptosis. Mitochondrial loss of function is also a key driver in the acquisition of a senescence-associated secretory phenotype that drives senescent cells into a pro-inflammatory state. Maintaining mitochondrial homeostasis is crucial for retaining the contractile phenotype of the vascular smooth muscle cells (VSMCs), the most prominent cells of the vasculature. Loss of this contractile phenotype is associated with the loss of mitochondrial function and a metabolic shift to glycolysis. Emerging evidence suggests that mitochondrial dysfunction may play a direct role in vascular calcification and the underlying pathologies including (1) impairment of mitochondrial function by mineral dysregulation i.e., calcium and phosphate overload in patients with end-stage renal disease and (2) presence of increased ROS in patients with calcific aortic valve disease, atherosclerosis, type-II diabetes and chronic kidney disease. In this review, we discuss the cause and consequence of mitochondrial dysfunction in vascular calcification and underlying pathologies; the role of autophagy and mitophagy pathways in preventing mitochondrial dysfunction during vascular calcification and finally we discuss mitochondrial ROS, DRP1, and HIF-1 as potential novel markers and therapeutic targets for maintaining mitochondrial homeostasis in vascular calcification.

Ex vivo 18F-fluoride uptake and hydroxyapatite deposition in human coronary atherosclerosis

Early microcalcification is a feature of coronary plaques with an increased propensity to rupture and to cause acute coronary syndromes. In this ex vivo imaging study of coronary artery specimens, the non-invasive imaging radiotracer, ¹⁸F-fluoride, was highly selective for hydroxyapatite deposition in atherosclerotic coronary plaque. Specifically, coronary ¹⁸F-fluoride uptake had a high signal to noise ratio compared with surrounding myocardium that makes it feasible to identify coronary mineralisation activity. Areas of ¹⁸F-fluoride uptake are associated with osteopontin, an inflammation-associated glycophosphoprotein that mediates tissue mineralisation, and Runt-related transcription factor 2, a nuclear protein involved in osteoblastic differentiation. These results suggest that ¹⁸F-fluoride is a non-invasive imaging biomarker of active coronary atherosclerotic mineralisation.

PHOSPHO1 is a skeletal regulator of insulin resistance and obesity

BACKGROUND

The classical functions of the skeleton encompass locomotion, protection and mineral homeostasis. However, cell-specific gene deletions in the mouse and human genetic studies have identified the skeleton as a key endocrine regulator of metabolism. The bone-specific phosphatase, Phosphatase, Orphan 1 (PHOSPHO1), which is indispensable for bone mineralisation, has been recently implicated in the regulation of energy metabolism in humans, but its role in systemic metabolism remains unclear. Here, we probe the mechanism underlying metabolic regulation by analysing Phospho1 mutant mice.

RESULTS

Phospho1^-/- mice exhibited improved basal glucose homeostasis and resisted high-fat-diet-induced weight gain and diabetes. The metabolic protection in Phospho1^-/- mice was manifested in the absence of altered levels of osteocalcin. Osteoblasts isolated from Phospho1^-/- mice were enriched for genes associated with energy metabolism and diabetes; Phospho1 both directly and indirectly interacted with genes associated with glucose transport and insulin receptor signalling. Canonical thermogenesis via brown adipose tissue did not underlie the metabolic protection observed in adult Phospho1^-/- mice. However, the decreased serum choline levels in Phospho1^-/- mice were normalised by feeding a 2% choline rich diet resulting in a normalisation in insulin sensitivity and fat mass.

CONCLUSION

We show that mice lacking the bone mineralisation enzyme PHOSPHO1 exhibit improved basal glucose homeostasis and resist high-fat-diet-induced weight gain and diabetes. This study identifies PHOSPHO1 as a potential bone-derived therapeutic target for the treatment of obesity and diabetes.

Expression of Calcification and Extracellular Matrix Genes in the Cardiovascular System of the Healthy Domestic Sheep (Ovis aries)

The maintenance of a healthy cardiovascular system requires expression of genes that contribute to essential biological activities and repression of those that are associated with functions likely to be detrimental to cardiovascular homeostasis. Vascular calcification is a major disruption to cardiovascular homeostasis, where tissues of the cardiovascular system undergo ectopic calcification and consequent dysfunction, but little is known about the expression of calcification genes in the healthy cardiovascular system. Large animal models are of increasing importance in cardiovascular disease research as they demonstrate more similar cardiovascular features (in terms of anatomy, physiology and size) to humans than do rodent species. We used RNA sequencing results from the sheep, which has been utilized extensively to examine calcification of prosthetic cardiac valves, to explore the transcriptome of the heart and cardiac valves in this large animal, in particular looking at expression of calcification and extracellular matrix genes. We then examined genes implicated in the process of vascular calcification in a wide array of cardiovascular tissues and across multiple developmental stages, using RT-qPCR. Our results demonstrate that there is a balance between genes that promote and those that suppress mineralization during development and across cardiovascular tissues. We show extensive expression of genes encoding proteins involved in formation and maintenance of the extracellular matrix in cardiovascular tissues, and high expression of hematopoietic genes in the cardiac valves. Our analysis will support future research into the functions of implicated genes in the development of valve calcification, and increase the utility of the sheep as a large animal model for understanding ectopic calcification in cardiovascular disease. This study provides a foundation to explore the transcriptome of the developing cardiovascular system and is a valuable resource for the fields of mammalian genomics and cardiovascular research.

Beyond mineralisation: metabolic functions for matrix mineralisation regulators

The physiological mineralisation of skeletal tissues, as well as the pathological mineralisation of soft tissues involves a fine balance between regulators that either promote or inhibit the process. In recent years, several studies have advocated a non-skeletal role for some of these mineralisation regulators in a range of human diseases, including diabetes, cardiovascular disease, obesity and neurodegenerative disease. This is an emerging area of interest and the functional roles and mechanisms of action of these various endocrine factors, phosphatases and phosphodiesterase's in important pathologies are the focus of this review. Mechanistic insight of the pathways through which these acknowledged regulators of skeletal mineralisation act beyond the skeleton has the potential to identify druggable targets for commonly experienced morbidities, notably those related to metabolism and metabolic syndrome.

Osteocalcin Regulates Arterial Calcification Via Altered Wnt Signaling and Glucose Metabolism

Arterial calcification is an important hallmark of cardiovascular disease and shares many similarities with skeletal mineralization. The bone-specific protein osteocalcin (OCN) is an established marker of vascular smooth muscle cell (VSMC) osteochondrogenic transdifferentiation and a known regulator of glucose metabolism. However, the role of OCN in controlling arterial calcification is unclear. We hypothesized that OCN regulates calcification in VSMCs and sought to identify the underpinning signaling pathways. Immunohistochemistry revealed OCN co-localization with VSMC calcification in human calcified carotid artery plaques. Additionally, 3 mM phosphate treatment stimulated OCN mRNA expression in cultured VSMCs (1.72-fold, p < 0.001). Phosphate-induced calcification was blunted in VSMCs derived from OCN null mice (Ocn ^-/- ) compared with cells derived from wild-type (WT) mice (0.37-fold, p < 0.001). Ocn ^-/- VSMCs showed reduced mRNA expression of the osteogenic marker Runx2 (0.51-fold, p < 0.01) and the sodium-dependent phosphate transporter, PiT1 (0.70-fold, p < 0.001), with an increase in the calcification inhibitor Mgp (1.42-fold, p < 0.05) compared with WT. Ocn ^-/- VSMCs also showed reduced mRNA expression of Axin2 (0.13-fold, p < 0.001) and Cyclin D (0.71 fold, p < 0.01), markers of Wnt signaling. CHIR99021 (GSK3β inhibitor) treatment increased calcium deposition in WT and Ocn ^-/- VSMCs (1 μM, p < 0.001). Ocn ^-/- VSMCs, however, calcified less than WT cells (1 μM; 0.27-fold, p < 0.001). Ocn ^-/- VSMCs showed reduced mRNA expression of Glut1 (0.78-fold, p < 0.001), Hex1 (0.77-fold, p < 0.01), and Pdk4 (0.47-fold, p < 0.001). This was accompanied by reduced glucose uptake (0.38-fold, p < 0.05). Subsequent mitochondrial function assessment revealed increased ATP-linked respiration (1.29-fold, p < 0.05), spare respiratory capacity (1.59-fold, p < 0.01), and maximal respiration (1.52-fold, p < 0.001) in Ocn ^-/- versus WT VSMCs. Together these data suggest that OCN plays a crucial role in arterial calcification mediated by Wnt/β-catenin signaling through reduced maximal respiration. Mitochondrial dynamics may therefore represent a novel therapeutic target for clinical intervention. © 2019 American Society for Bone and Mineral Research.

Autophagy as a novel therapeutic target in vascular calcification

The autophagy pathway is a key regulator of cellular metabolism and homeostasis, and plays a critical role in maintaining normal vascular cell function. It is well recognised that autophagy can regulate endothelial cell homeostasis, vascular smooth muscle cell (VSMC) phenotype transition, and calcium (Ca²⁺) homeostasis in VSMCs. Emerging evidence has demonstrated that autophagy directly protects against vascular calcification (VC). Crosstalk between endosomes, dysfunctional mitochondria, autophagic vesicles and Ca²⁺ and phosphate (Pi) enriched matrix vesicles (MVs) may underpin the pathogenesis of VC. In this review, we summarize the current experimental evidence in understanding how autophagy maintains normal vascular cell function and its protective role against vascular calcification. We also discuss the underlying molecular and cellular mechanisms through which autophagy inhibits vascular calcification. Pharmacological modulation of autophagy may offer an exciting new strategy for the treatment of vascular calcification.

Differing calcification processes in cultured vascular smooth muscle cells and osteoblasts

Arterial medial calcification (AMC) is the deposition of calcium phosphate mineral, often as hydroxyapatite, in the medial layer of the arteries. AMC shares some similarities to skeletal mineralisation and has been associated with the transdifferentiation of vascular smooth muscle cells (VSMCs) towards an osteoblast-like phenotype. This study used primary mouse VSMCs and calvarial osteoblasts to directly compare the established and widely used in vitro models of AMC and bone formation. Significant differences were identified between osteoblasts and calcifying VSMCs. First, osteoblasts formed large mineralised bone nodules that were associated with widespread deposition of an extracellular collagenous matrix. In contrast, VSMCs formed small discrete regions of calcification that were not associated with collagen deposition and did not resemble bone. Second, calcifying VSMCs displayed a progressive reduction in cell viability over time (≤7-fold), with a 50% increase in apoptosis, whereas osteoblast and control VSMCs viability remained unchanged. Third, osteoblasts expressed high levels of alkaline phosphatase (TNAP) activity and TNAP inhibition reduced bone formation by to 90%. TNAP activity in calcifying VSMCs was ∼100-fold lower than that of bone-forming osteoblasts and cultures treated with β-glycerophosphate, a TNAP substrate, did not calcify. Furthermore, TNAP inhibition had no effect on VSMC calcification. Although, VSMC calcification was associated with increased mRNA expression of osteoblast-related genes (e.g. Runx2, osterix, osteocalcin, osteopontin), the relative expression of these genes was up to 40-fold lower in calcifying VSMCs versus bone-forming osteoblasts. In summary, calcifying VSMCs in vitro display some limited osteoblast-like characteristics but also differ in several key respects: 1) their inability to form collagen-containing bone; 2) their lack of reliance on TNAP to promote mineral deposition; and, 3) the deleterious effect of calcification on their viability.

A novel fluorescein-bisphosphonate based diagnostic tool for the detection of hydroxyapatite in both cell and tissue models

A rapid and efficient method for the detection of hydroxyapatite (HAP) has been developed which shows superiority to existing well-established methods. This fluorescein-bisphosphonate probe is highly selective for HAP over other calcium minerals and is capable of detecting lower levels of calcification in cellular models than either hydrochloric acid-based calcium leaching assays or the Alizarin S stain. The probe has been shown to be effective in both in vitro vascular calcification models and in vitro bone calcification models. Moreover we have demonstrated binding of this probe to vascular calcification in rat aorta and to areas of microcalcification, in human vascular tissue, beyond the resolution of computed tomography in human atherosclerotic plaques. Fluorescein-BP is therefore a highly sensitive and specific imaging probe for the detection of vascular calcification, with the potential to improve not only ex vivo assessments of HAP deposition but also the detection of vascular microcalcification in humans.

Spermine increases acetylation of tubulins and facilitates autophagic degradation of prion aggregates

Autolysosomal dysfunction and unstable microtubules are hallmarks of chronic neurodegenerative diseases associated with misfolded proteins. Investigation of impaired protein quality control and clearance systems could therefore provide an important avenue for intervention. To investigate this we have used a highly controlled model for protein aggregation, an in vitro prion system. Here we report that prion aggregates traffic via autolysosomes in the cytoplasm. Treatment with the natural polyamine spermine clears aggregates by enhancing autolysosomal flux. We demonstrated this by blocking the formation of mature autophagosomes resulting in accumulation of prion aggregates in the cytoplasm. Further we investigated the mechanism of spermine’s mode of action and we demonstrate that spermine increases the acetylation of microtubules, which is known to facilitate retrograde transport of autophagosomes from the cellular periphery to lysosomes located near the nucleus. We further report that spermine facilitates selective autophagic degradation of prion aggregates by binding to microtubule protein Tubb6. This is the first report in which spermine and the pathways regulated by it are applied as a novel approach towards clearance of misfolded prion protein and we suggest that this may have important implication for the broader family of protein misfolding diseases.

Inhibition of arterial medial calcification and bone mineralization by extracellular nucleotides: The same functional effect mediated by different cellular mechanisms

Arterial medial calcification (AMC) is thought to share some outward similarities to skeletal mineralization and has been associated with the transdifferentiation of vascular smooth muscle cells (VSMCs) to an osteoblast-like phenotype. ATP and UTP have previously been shown to inhibit bone mineralization. This investigation compared the effects of extracellular nucleotides on calcification in VSMCs with those seen in osteoblasts. ATP, UTP and the ubiquitous mineralization inhibitor, pyrophosphate (PP_i ), dose dependently inhibited VSMC calcification by ≤85%. Culture of VSMCs in calcifying conditions was associated with an increase in apoptosis; treatment with ATP, UTP, and PP_i reduced apoptosis to levels seen in non-calcifying cells. Extracellular nucleotides had no effect on osteoblast viability. Basal alkaline phosphatase (TNAP) activity was over 100-fold higher in osteoblasts than VSMCs. ATP and UTP reduced osteoblast TNAP activity (≤50%) but stimulated VSMC TNAP activity (≤88%). The effects of extracellular nucleotides on VSMC calcification, cell viability and TNAP activity were unchanged by deletion or inhibition of the P2Y₂ receptor. Conversely, the actions of ATP/UTP on bone mineralization and TNAP activity were attenuated in osteoblasts lacking the P2Y₂ receptor. Ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) hydrolyses ATP and UTP to produce PP_i . In both VSMCs and osteoblasts, deletion of NPP1 blunted the inhibitory effects of extracellular nucleotides suggesting involvement of P2 receptor independent pathways. Our results show that although the overall functional effect of extracellular nucleotides on AMC and bone mineralization is similar there are clear differences in the cellular mechanisms mediating these actions.

Suppressor of cytokine signaling 2 (Socs2) deletion protects bone health of mice with DSS-induced inflammatory bowel disease

Individuals with inflammatory bowel disease (IBD) often present with poor bone health. The development of targeted therapies for this bone loss requires a fuller understanding of the underlying cellular mechanisms. Although bone loss in IBD is multifactorial, the altered sensitivity and secretion of growth hormone (GH) and insulin-like growth factor-1 (IGF-1) in IBD is understood to be a critical contributing mechanism. The expression of suppressor of cytokine signaling 2 (SOCS2), a well-established negative regulator of GH signaling, is stimulated by proinflammatory cytokines. Therefore, it is likely that SOCS2 expression represents a critical mediator through which proinflammatory cytokines inhibit GH/IGF-1 signaling and decrease bone quality in IBD. Using the dextran sodium sulfate (DSS) model of colitis, we reveal that endogenously elevated GH function in the Socs2^−/− mouse protects the skeleton from osteopenia. Micro-computed tomography assessment of DSS-treated wild-type (WT) mice revealed a worsened trabecular architecture compared to control mice. Specifically, DSS-treated WT mice had significantly decreased bone volume, trabecular thickness and trabecular number, and a resulting increase in trabecular separation. In comparison, the trabecular bone of Socs2-deficient mice was partially protected from the adverse effects of DSS. The reduction in a number of parameters, including bone volume, was less, and no changes were observed in trabecular thickness or separation. This protected phenotype was unlikely to be a consequence of improved mucosal health in the DSS-treated Socs2^−/− mice but rather a result of unregulated GH signaling directly on bone. These studies indicate that the absence of SOCS2 is protective against bone loss typical of IBD. This study also provides an improved understanding of the relative effects of GH/IGF-1 signaling on bone health in experimental colitis, information that is essential before these drugs are explored as bone protective agents in children and adults with IBD.

Summary: Using a mouse model of inflammatory bowel disease, this article provides an improved understanding of the relative effects of GH/IGF-1 on bone health in experimental colitis.

Comparative Transcriptomic Profiling and Gene Expression for Myxomatous Mitral Valve Disease in the Dog and Human

Myxomatous mitral valve disease is the single most important mitral valve disease in both dogs and humans. In the case of the dog it is ubiquitous, such that all aged dogs will have some evidence of the disease, and for humans it is known as Barlow's disease and affects up to 3% of the population, with an expected increase in prevalence as the population ages. Disease in the two species show many similarities and while both have the classic myxomatous degeneration only in humans is there extensive fibrosis. This dual pathology of the human disease markedly affects the valve transcriptome and the difference between the dog and human is dominated by changes in genes associated with fibrosis. This review will briefly examine the comparative valve pathology and then, in more detail, the transcriptomic profiling and gene expression reported so far for both species.

Skeletal energy homeostasis: a paradigm of endocrine discovery

Throughout the last decade, significant developments in cellular, molecular and mouse models have revealed major endocrine functions of the skeleton. More recent studies have evolved the interplay between bone-specific hormones, the skeleton, marrow adipose tissue, muscle and the brain. This review focuses on literature from the last decade, addressing the endocrine regulation of global energy metabolism via the skeleton. In addition, we will highlight several recent studies that further our knowledge of new endocrine functions of some organs; explore remaining unanswered questions; and, finally, we will discuss future directions for this more complex era of bone biology research.

Culture of Murine Embryonic Metatarsals: A Physiological Model of Endochondral Ossification

The fundamental process of endochondral ossification is under tight regulation in the healthy individual so as to prevent disturbed development and/or longitudinal bone growth. As such, it is imperative that we further our understanding of the underpinning molecular mechanisms involved in such disorders so as to provide advances towards human and animal patient benefit. The mouse metatarsal organ explant culture is a highly physiological ex vivo model for studying endochondral ossification and bone growth as the growth rate of the bones in culture mimic that observed in vivo. Uniquely, the metatarsal organ culture allows the examination of chondrocytes in different phases of chondrogenesis and maintains cell-cell and cell-matrix interactions, therefore providing conditions closer to the in vivo situation than cells in monolayer or 3D culture. This protocol describes in detail the intricate dissection of embryonic metatarsals from the hind limb of E15 murine embryos and the subsequent analyses that can be performed in order to examine endochondral ossification and longitudinal bone growth.

The Expression of PHOSPHO1, nSMase2 and TNAP is Coordinately Regulated by Continuous PTH Exposure in Mineralising Osteoblast Cultures

Sustained exposure to high levels of parathyroid hormone (PTH), as observed in hyperparathyroidism, is catabolic to bone. The increase in the RANKL/OPG ratio in response to continuous PTH, resulting in increased osteoclastogenesis, is well established. However, the effects of prolonged PTH exposure on key regulators of skeletal mineralisation have yet to be investigated. This study sought to examine the temporal expression of PHOSPHO1, TNAP and nSMase2 in mineralising osteoblast-like cell cultures and to investigate the effects of continuous PTH exposure on the expression of these enzymes in vitro. PHOSPHO1, nSMase2 and TNAP expression in cultured MC3T3-C14 cells significantly increased from day 0 to day 10. PTH induced a rapid downregulation of Phospho1 and Smpd3 gene expression in MC3T3-C14 cells and cultured hemi-calvariae. Alpl was differentially regulated by PTH, displaying upregulation in cultured MC3T3-C14 cells and downregulation in hemi-calvariae. PTH was also able to abolish the stimulatory effects of bone morphogenic protein 2 (BMP-2) on Smpd3 and Phospho1 expression. The effects of PTH on Phospho1 expression were mimicked with the cAMP agonist forskolin and blocked by the PKA inhibitor PKI (5-24), highlighting a role for the cAMP/PKA pathway in this regulation. The potent down-regulation of Phospho1 and Smpd3 in osteoblasts in response to continuous PTH may provide a novel explanation for the catabolic effects on the skeleton of such an exposure. Furthermore, our findings support the hypothesis that PHOSPHO1, nSMase2 and TNAP function cooperatively in the initiation of skeletal mineralisation.

Characterisation of matrix vesicles in skeletal and soft tissue mineralisation

The importance of matrix vesicles (MVs) has been repeatedly highlighted in the formation of cartilage, bone, and dentin since their discovery in 1967. These nano-vesicular structures, which are found in the extracellular matrix, are believed to be one of the sites of mineral nucleation that occurs in the organic matrix of the skeletal tissues. In the more recent years, there have been numerous reports on the observation of MV-like particles in calcified vascular tissues that could be playing a similar role. Therefore, here, we review the characteristics MVs possess that enable them to participate in mineral deposition. Additionally, we outline the content of skeletal tissue- and soft tissue-derived MVs, and discuss their key mineralisation mediators that could be targeted for future therapeutic use.

Large animal models of cardiovascular disease

The human cardiovascular system is a complex arrangement of specialized structures with distinct functions. The molecular landscape, including the genome, transcriptome and proteome, is pivotal to the biological complexity of both normal and abnormal mammalian processes. Despite our advancing knowledge and understanding of cardiovascular disease (CVD) through the principal use of rodent models, this continues to be an increasing issue in today's world. For instance, as the ageing population increases, so does the incidence of heart valve dysfunction. This may be because of changes in molecular composition and structure of the extracellular matrix, or from the pathological process of vascular calcification in which bone-formation related factors cause ectopic mineralization. However, significant differences between mice and men exist in terms of cardiovascular anatomy, physiology and pathology. In contrast, large animal models can show considerably greater similarity to humans. Furthermore, precise and efficient genome editing techniques enable the generation of tailored models for translational research. These novel systems provide a huge potential for large animal models to investigate the regulatory factors and molecular pathways that contribute to CVD in vivo. In turn, this will help bridge the gap between basic science and clinical applications by facilitating the refinement of therapies for cardiovascular disease.

Increased linear bone growth by GH in the absence of SOCS2 is independent of IGF-1

Growth hormone (GH) signaling is essential for postnatal linear bone growth, but the relative importance of GHs actions on the liver and/or growth plate cartilage remains unclear. The importance of liver derived insulin like‐growth factor‐1 (IGF‐1) for endochondral growth has recently been challenged. Here, we investigate linear growth in Suppressor of Cytokine Signaling‐2 (SOCS2) knockout mice, which have enhanced growth despite normal systemic GH/IGF‐1 levels. Wild‐type embryonic ex vivo metatarsals failed to exhibit increased linear growth in response to GH, but displayed increased Socs2 transcript levels (P < 0.01). In the absence of SOCS2, GH treatment enhanced metatarsal linear growth over a 12 day period. Despite this increase, IGF‐1 transcript and protein levels were not increased in response to GH. In accordance with these data, IGF‐1 levels were unchanged in GH‐challenged postnatal Socs2^‐/‐ conditioned medium despite metatarsals showing enhanced linear growth. Growth‐plate Igf1 mRNA levels were not elevated in juvenile Socs2^‐/‐ mice. GH did however elevate IGF‐binding protein 3 levels in conditioned medium from GH challenged metatarsals and this was more apparent in Socs2^‐/‐ metatarsals. GH did not enhance the growth of Socs2^‐/‐ metatarsals when the IGF receptor was inhibited, suggesting that IGF receptor mediated mechanisms are required. IGF‐2 may be responsible as IGF‐2 promoted metatarsal growth and Igf2 expression was elevated in Socs2^‐/‐ (but not WT) metatarsals in response to GH. These studies emphasise the critical importance of SOCS2 in regulating GHs ability to promote bone growth. Also, GH appears to act directly on the metatarsals of Socs2^‐/‐ mice, promoting growth via a mechanism that is independent of IGF‐1. J. Cell. Physiol. 9999: 2796–2806, 2015. © 2015 Wiley Periodicals, Inc.

Effects of etidronate on the Enpp1⁻/⁻ mouse model of generalized arterial calcification of infancy

Generalized arterial calcification of infancy (GACI) is an autosomal recessive disorder of spontaneous infantile arterial and periarticular calcification which is attributed to mutations in the ectonucleotide pyrophosphatase/phosphodiesterase 1 (Enpp1) gene. Whilst the bisphosphonate, etidronate, is currently used off-label for the treatment for GACI, recent studies have highlighted its detrimental effects on bone mineralisation. In the present study, we used the Enpp1-/- mouse model of GACI to examine the effects of etidronate treatment (100 µg/kg), on vascular and skeletal calcification. Micro-computed tomography (µCT) analysis revealed a significant decrease in trabecular bone mass, as reflected by the decrease in trabecular bone volume/tissue volume (BV/TV; %), trabecular thickness, trabecular separation, trabecular number and pattern factor (P<0.05) in the Enpp1-/- mice in comparison to the wild-type (WT) mice. Mechanical testing revealed that in the WT mice, treatment with etidronate significantly improved work to fracture and increased work post-failure (P<0.05, in comparison to the vehicle-treated WT mice). This significant increase, however, was not observed in the Enpp1-/- mice. Treatment with etidronate had no effect on bone parameters in the WT mice; however, the Enpp1-/- mice displayed an increased structural model index (SMI; P<0.05). We used a recently developed 3D µCT protocol to reconstruct and quantify the extensive aortic calcification in Enpp1-/- mice in comparison to the WT mice. However, treatment with etidronate did not prevent de novo calcification, and did not arrest the progression of established calcification of the aorta.

Endocrine role of bone: recent and emerging perspectives beyond osteocalcin

Recent developments in endocrinology, made possible by the combination of mouse genetics, integrative physiology and clinical observations have resulted in rapid and unanticipated advances in the field of skeletal biology. Indeed, the skeleton, classically viewed as a structural scaffold necessary for mobility, and regulator of calcium-phosphorus homoeostasis and maintenance of the haematopoietic niche has now been identified as an important regulator of male fertility and whole-body glucose metabolism, in addition to the classical insulin target tissues. These seminal findings confirm bone to be a true endocrine organ. This review is intended to detail the key events commencing from the elucidation of osteocalcin (OC) in bone metabolism to identification of new and emerging candidates that may regulate energy metabolism independently of OC.

Mineralisation of collagen rich soft tissues and osteocyte lacunae in Enpp1(-/-) mice

Ecto-nucleotide pyrophosphatase/phosphodiesterases (NPPs) hydrolyse nucleotide triphosphates to the corresponding nucleotide monophosphates and the mineralisation inhibitor, pyrophosphate (PPi). This study examined the role of NPP1 in osteocytes, osteoclasts and cortical bone, using a mouse model lacking NPP1 (Enpp1(-/-)). We used microcomputed tomography (μCT) to investigate how NPP1 deletion affects cortical bone structure; excised humerus bones from 8, 15 and 22-week old mice were scanned at 0.9 μm. Although no changes were evident in the cortical bone of 8-week old Enpp1(-/-) mice, significant differences were observed in older animals. Cortical bone volume was decreased 28% in 22-week Enpp1(-/-) mice, whilst cortical porosity was reduced 30% and 60% at 15 and 22-weeks, respectively. This was accompanied by up to a 15% decrease in closed pore diameter and a 55% reduction in the number of pores. Cortical thickness was reduced up to 35% in 15 and 22-week Enpp1(-/-) animals and the endosteal diameter was increased up to 23%. Thus, the cortical bone from Enpp1(-/-) mice was thinner and less porous, with a larger marrow space. Scanning electron microscopy (SEM) revealed a decrease in the size and number of blood vessel channels in the cortical bone as well as a 40% reduction in the mean plan area of osteocyte lacunae. We noted that the number of viable osteocytes isolated from the long bones of Enpp1(-/-) mice was decreased ≤50%. In contrast, osteoclast formation and resorptive activity were unaffected by NPP1 deletion. μCT and histological analysis of Enpp1(-/-) mice also revealed calcification of the joints and vertebrae as well as soft tissues including the whisker follicles, ear pinna and trachea. This calcification worsened as the animals aged. Together, these data highlight the key role of NPP1 in regulating calcification of both soft and skeletal tissues.

Deficiency of the bone mineralization inhibitor NPP1 protects mice against obesity and diabetes

The emergence of bone as an endocrine regulator has prompted a re-evaluation of the role of bone mineralization factors in the development of metabolic disease. Ectonucleotide pyrophosphatase/phosphodiesterase-1 (NPP1) controls bone mineralization through the generation of pyrophosphate, and levels of NPP1 are elevated both in dermal fibroblast cultures and muscle of individuals with insulin resistance. We investigated the metabolic phenotype associated with impaired bone metabolism in mice lacking the gene that encodes NPP1 (Enpp1^−/− mice). Enpp1^−/− mice exhibited mildly improved glucose homeostasis on a normal diet but showed a pronounced resistance to obesity and insulin resistance in response to chronic high-fat feeding. Enpp1^−/− mice had increased levels of the insulin-sensitizing bone-derived hormone osteocalcin but unchanged insulin signalling within osteoblasts. A fuller understanding of the pathways of NPP1 could inform the development of novel therapeutic strategies for treating insulin resistance.

Direct stimulation of bone mass by increased GH signalling in the osteoblasts of Socs2-/- mice

The suppressor of cytokine signalling (Socs2(-/-))-knockout mouse is characterised by an overgrowth phenotype due to enhanced GH signalling. The objective of this study was to define the Socs2(-/-) bone phenotype and determine whether GH promotes bone mass via IGF1-dependent mechanisms. Despite no elevation in systemic IGF1 levels, increased body weight in 4-week-old Socs2(-/-) mice following GH treatment was associated with increased cortical bone area (Ct.Ar) (P<0.01). Furthermore, detailed bone analysis of male and female juvenile and adult Socs2(-/-) mice revealed an altered cortical and trabecular phenotype consistent with the known anabolic effects of GH. Indeed, male Socs2(-/-) mice had increased Ct.Ar (P<0.05) and thickness associated with increased strength. Despite this, there was no elevation in hepatic Igf1 expression, suggesting that the anabolic bone phenotype was the result of increased local GH action. Mechanistic studies showed that in osteoblasts and bone of Socs2(-/-) mice, STAT5 phosphorylation was significantly increased in response to GH. Conversely, overexpression of SOCS2 decreased GH-induced STAT5 signalling. Although an increase in Igf1 expression was observed in Socs2(-/-) osteoblasts following GH, it was not evident in vivo. Igf1 expression levels were not elevated in response to GH in 4-week-old mice and no alterations in expression was observed in bone samples of 6-week-old Socs2(-/-) mice. These studies emphasise the critical role of SOCS2 in controlling the local GH anabolic bone effects. We provide compelling evidence implicating SOCS2 in the regulation of GH osteoblast signalling and ultimately bone accrual, which maybe via mechanisms that are independent of IGF1 production in vivo.

Optimisation of the differing conditions required for bone formation in vitro by primary osteoblasts from mice and rats

The in vitro culture of calvarial osteoblasts from neonatal rodents remains an important method for studying the regulation of bone formation. The widespread use of transgenic mice has created a particular need for a reliable, simple method that allows the differentiation and bone‑forming activity of murine osteoblasts to be studied. In the present study, we established such a method and identified key differences in optimal culture conditions between mouse and rat osteoblasts. Cells isolated from neonatal rodent calvariae by collagenase digestion were cultured for 14‑28 days before staining for tissue non-specific alkaline phosphatase (TNAP) and bone mineralisation (alizarin red). The reliable differentiation of mouse osteoblasts, resulting in abundant TNAP expression and the formation of mineralised 'trabecular‑shaped' bone nodules, occurred only following culture in α minimum essential medium (αMEM) and took 21‑28 days. Dexamethasone (10 nM) inhibited bone mineralisation in the mouse osteoblasts. By contrast, TNAP expression and bone formation by rat osteoblasts were observed following culture in both αMEM and Dulbecco's modified Eagle's medium (DMEM) after approximately 14 days (although ~3‑fold more effectively in αMEM) and was strongly dependent on dexamethasone. Both the mouse and rat osteoblasts required ascorbate (50 µg/ml) for osteogenic differentiation and β‑glycerophosphate (2 mM) for mineralisation. The rat and mouse osteoblasts showed similar sensitivity to the well‑established inhibitors of mineralisation, inorganic pyrophosphate (PPi) and adenosine triphosphate (ATP; 1‑100 µM). The high efficiency of osteogenic differentiation observed following culture in αMEM, compared with culture in DMEM possibly reflects the richer formulation of the former. These findings offer a reliable technique for inducing mouse osteoblasts to form bone in vitro and a more effective method for culturing bone‑forming rat osteoblasts.

A protective role for FGF-23 in local defence against disrupted arterial wall integrity?

Increasing interest is focusing on the role of the FGF-23/Klotho axis in mediating vascular calcification. However, the underpinning mechanisms have yet to be fully elucidated. Murine VSMCs were cultured in calcifying medium for a 21 d period. FGF-23 mRNA expression was significantly up-regulated by 7d (1.63-fold; P<0.001), with a concomitant increase in protein expression. mRNA and protein expression of both FGFR1 and Klotho were confirmed. Increased FGF-23 and Klotho protein expression was also observed in the calcified media of Enpp1(-/-) mouse aortic tissue. Reduced calcium deposition was observed in calcifying VSMCs cultured with recombinant FGF-23 (10 ng/ml; 28.1% decrease; P<0.01). Calcifying VSMCs treated with PD173074, an inhibitor of FGFR1 and FGFR3, showed significantly increased calcification (50 nM; 87.8% increase; P<0.001). FGF-23 exposure induced phosphorylation of ERK1/2. Treatment with FGF-23 in combination with PD98059, an ERK1/2 inhibitor, significantly increased VSMC calcification (10 μM; 41.3% increase; P<0.01). Use of FGF-23 may represent a novel therapeutic strategy for inhibiting vascular calcification.

Pharmacological inhibition of PHOSPHO1 suppresses vascular smooth muscle cell calcification

Medial vascular calcification (MVC) is common in patients with chronic kidney disease, obesity, and aging. MVC is an actively regulated process that resembles skeletal mineralization, resulting from chondro-osteogenic transformation of vascular smooth muscle cells (VSMCs). Here, we used mineralizing murine VSMCs to study the expression of PHOSPHO1, a phosphatase that participates in the first step of matrix vesicles-mediated initiation of mineralization during endochondral ossification. Wild-type (WT) VSMCs cultured under calcifying conditions exhibited increased Phospho1 gene expression and Phospho1(-/-) VSMCs failed to mineralize in vitro. Using natural PHOSPHO1 substrates, potent and specific inhibitors of PHOSPHO1 were identified via high-throughput screening and mechanistic analysis and two of these inhibitors, designated MLS-0390838 and MLS-0263839, were selected for further analysis. Their effectiveness in preventing VSMC calcification by targeting PHOSPHO1 function was assessed, alone and in combination with a potent tissue-nonspecific alkaline phosphatase (TNAP) inhibitor MLS-0038949. PHOSPHO1 inhibition by MLS-0263839 in mineralizing WT cells (cultured with added inorganic phosphate) reduced calcification in culture to 41.8% ± 2.0% of control. Combined inhibition of PHOSPHO1 by MLS-0263839 and TNAP by MLS-0038949 significantly reduced calcification to 20.9% ± 0.74% of control. Furthermore, the dual inhibition strategy affected the expression of several mineralization-related enzymes while increasing expression of the smooth muscle cell marker Acta2. We conclude that PHOSPHO1 plays a critical role in VSMC mineralization and that "phosphatase inhibition" may be a useful therapeutic strategy to reduce MVC.

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 importance of the SIBLING family of proteins on skeletal mineralisation and bone remodelling

The small integrin-binding ligand N-linked glycoprotein (SIBLING) family consists of osteopontin, bone sialoprotein, dentin matrix protein 1, dentin sialophosphoprotein and matrix extracellular phosphoglycoprotein. These proteins share many structural characteristics and are primarily located in bone and dentin. Accumulating evidence has implicated the SIBLING proteins in matrix mineralisation. Therefore, in this review, we discuss the individual role that each of the SIBLING proteins has in this highly orchestrated process. In particular, we emphasise how the nature and extent of their proteolytic processing and post-translational modification affect their functional role. Finally, we describe the likely roles of the SIBLING proteins in clinical disorders of hypophosphataemia and their potential therapeutic use.

Mechanisms and clinical consequences of vascular calcification

Vascular calcification has severe clinical consequences and is considered an accurate predictor of future adverse cardiovascular events, including myocardial infarction and stroke. Previously vascular calcification was thought to be a passive process which involved the deposition of calcium and phosphate in arteries and cardiac valves. However, recent studies have shown that vascular calcification is a highly regulated, cell-mediated process similar to bone formation. In this article, we outline the current understanding of key mechanisms governing vascular calcification and highlight the clinical consequences. By understanding better the molecular pathways and genetic circuitry responsible for the pathological mineralization process novel drug targets may be identified and exploited to combat and reduce the detrimental effects of vascular calcification on human health.

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 β-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.

Inflammatory cytokines and the GH/IGF-I axis: novel actions on bone growth

Longitudinal bone growth is a tightly regulated process that relies on complex synchronized mechanisms at the growth plate. Chronic paediatric inflammatory diseases are well accepted to lead to growth retardation and this is likely due to raised inflammatory cytokine levels and reduced growth hormone (GH)/insulin-like growth factor-1 (IGF-I) signalling. The precise cellular mechanisms responsible for this inhibition are unclear and therefore in this article, we will review the potential interactions between inflammatory cytokines and the GH/IGF-I axis in the regulation of bone growth. In particular, we will emphasis the potential contribution of the suppressors of cytokine signalling (SOCS) proteins, and in particular SOCS2, in mediating this process.

Inflammatory cytokines in juvenile idiopathic arthritis: effects on physical growth and the insulin-like-growth factor axis

OBJECTIVE

To investigate the relationship between markers of inflammation with physical growth and systemic markers of GH secretion in JIA.

DESIGN

This is a cross sectional prospective study of patients with JIA recruited during therapeutic arthrocentesis of 17 children with JIA (F,10): 8 oligoarticular (OJIA) and 9 polyarticular (PJIA).

RESULTS

Median adjusted height (AHt) SDS was -0.3 (-2.2 to 1.6). Serum ALS SDS (median -1.3, range -2.7 to -0.6) was reduced compared with serum IGFBP-3 SDS (median -0.5, range -7.7 to 2.3) and IGF-1 SDS (median -0.2, range -0.5 to 0.5). Log serum IL5 (95% CI -3.25, -0.81) and log serum IL15 (95% CI -9.58, -4.10) were independent factors associated with AHt SDS. Inflammatory cytokines individually showed no association with IGF-1, IGFBP-1, -2, -3 and ALS.

CONCLUSION

Children with JIA and mild degree of growth retardation show decreased ALS and IGFBP-3. Cytokines did not show an association to systemic markers of GH secretion. However, this study reports the novel, preliminary association between serum levels of IL5 and IL15 and the extent of short stature.

Cytokine profiling and in vitro studies of murine bone growth using biological fluids from children with juvenile idiopathic arthritis

OBJECTIVE

Growth retardation in children with chronic inflammatory disease may be partly due to direct effects of pro-inflammatory cytokines on the growth plate and requires further investigation.

DESIGN

This study assessed the cytokine concentrations in serum and synovial fluid (SF) in juvenile idiopathic arthritis (JIA), and determined the effect of the biological fluid on cultured murine metatarsal growth.

PATIENTS

Serum and SF were obtained from four children attending for arthrocentesis (child A, systemic; children B, C and D, oligoarticular). In addition, serum samples were obtained from four more children (children E and F, polyarticular; child G, oligoarticular).

MEASUREMENTS

Anthropometry, cytokine levels and longitudinal bone growth were assessed.

RESULTS

Cytokines were elevated to a variable extent in the samples. Although all serum samples were associated with reduced metatarsal growth, only SF from child A and child B reduced metatarsal growth. Metatarsals treated with child A's SF showed reduced proliferation, reduced proliferative and mineralizing zone width, and increased hypertrophic zone width. Tumour necrosis factor (TNF)-alpha, interleukin (IL)-1beta and IL-6 concentrations were elevated in child A's SF. However, SF exposure with neutralizing antibodies to these cytokines or IGF-1 did not improve metatarsal growth.

CONCLUSION

SF and serum JIA samples can impair bone growth at the growth plate. In synovial fluid, the effect is variable but resistant to treatment with IL-1beta, IL-6 and TNF-alpha specific antibodies and IGF-1, suggesting that other factors in this biological fluid may also have an effect on longitudinal growth through IGF-1-independent mechanisms.

A Comparison of Breast Muscle Characteristics in Three Broiler Great-Grandparent Lines

Genetic selection of broiler chickens has led to a gross overdevelopment of the broiler breast muscle pectoralis major. This may have resulted in increased myopathy and detrimental effects on meat quality. The present study examined 3 commercial great-grandparent lines (lines A, B, and C). Lines A and B are female lines, and line C is a male line. The mean BW of line C (2.7 kg) was significantly greater than those of lines A and B (both 2.3 kg). However, the mean breast yield of both lines B and C (8.9 and 8.7%, respectively) was significantly greater than that of line A (6.9%). Line B therefore matched the meat yield of line A while maintaining a high reproductive capacity. The mean breast fillet weight of line A (169 g) was significantly lower than lines B (207 g) and C (235 g). No differences were observed between lines in either mean fiber size or amount of connective tissue. Therefore, additional fibers must provide the additional weight in the breast fillet of lines B and C, compared with A. Plasma creatine kinase activity, a commonly used marker of muscle damage, was significantly higher in line A (1368 IU/L) than in lines B (995 IU/L) and C (982 IU/L). However, qualitative evaluations of muscle pathology revealed no differences among lines. Selection for increased embryonic muscle fiber number, rather than for increased radial fiber growth, could improve growth potential and may also alleviate muscle damage.

Cytokine actions in growth disorders associated with pediatric chronic inflammatory diseases (review)

Growth disorders are commonly observed in children suffering from chronic inflammatory diseases such as Juvenile Idiopathic Arthritis (JIA) and Inflammatory Bowel Disease (IBD). These disorders range from general growth retardation to local acceleration of growth in the affected limb and are associated with the increased production of pro-inflammatory cytokines. In this article, we review how cytokines influence child growth by exerting a local effect at the level of the growth plate, and through systemic effects throughout the whole body.