Noncollagenous Matrix Proteins Controlling Mineralization

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The soft tissues of the oral cavity are constantly subjected to microtrauma due to various factors. The gingiva in particular reacts to these beyond a point resulting in reactive hyperplastic lesions. Amongst these, the pyogenic granuloma and the peripheral ossifying fibroma are the most common clinical entities. Since they have a similar clinical presentation but diverse histomorphologic illustrations, it was advocated that there exists an interrelation between these two reactive fibrous overgrowths. Hence, this paper is intended to abolish the quandary in diagnosing peripheral ossifying fibroma and pyogenic granuloma.

Poly(ADP-Ribose) Links the DNA Damage Response and Biomineralization

Biomineralization of the extracellular matrix is an essential, regulated process. Inappropriate mineralization of bone and the vasculature has devastating effects on patient health, yet an integrated understanding of the chemical and cell biological processes that lead to mineral nucleation remains elusive. Here, we report that biomineralization of bone and the vasculature is associated with extracellular poly(ADP-ribose) synthesized by poly(ADP-ribose) polymerases in response to oxidative and/or DNA damage. We use ultrastructural methods to show poly(ADP-ribose) can form both calcified spherical particles, reminiscent of those found in vascular calcification, and biomimetically calcified collagen fibrils similar to bone. Importantly, inhibition of poly(ADP-ribose) biosynthesis in vitro and in vivo inhibits biomineralization, suggesting a therapeutic route for the treatment of vascular calcifications. We conclude that poly(ADP-ribose) plays a central chemical role in both pathological and physiological extracellular matrix calcification.

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Poly(ADP-ribose) is found close to ECM calcification in developing bone and arteries

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Poly(ADP-ribose) is produced in response to oxidative stress and delivered to the ECM

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Poly(ADP-ribose) forms dense liquid droplets with calcium ions

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Inhibiting PARP enzyme activity blocks calcification in vitro and in vivo

Contribution of biomimetic collagen-ligand interaction to intrafibrillar mineralization

Contemporary models of intrafibrillar mineralization mechanisms are established using collagen fibrils as templates without considering the contribution from collagen-bound apatite nucleation inhibitors. However, collagen matrices destined for mineralization in vertebrates contain bound matrix proteins for intrafibrillar mineralization. Negatively charged, high-molecular weight polycarboxylic acid is cross-linked to reconstituted collagen to create a model for examining the contribution of collagen-ligand interaction to intrafibrillar mineralization. Cryogenic electron microscopy and molecular dynamics simulation show that, after cross-linking to collagen, the bound polyelectrolyte caches prenucleation cluster singlets into chain-like aggregates along the fibrillar surface to increase the pool of mineralization precursors available for intrafibrillar mineralization. Higher-quality mineralized scaffolds with better biomechanical properties are achieved compared with mineralization of unmodified scaffolds in polyelectrolyte-stabilized mineralization solution. Collagen-ligand interaction provides insights on the genesis of heterogeneously mineralized tissues and the potential causes of ectopic calcification in nonmineralized body tissues.

Influences of Sex and Estrogen in Arterial and Valvular Calcification

Vascular and cardiac valvular calcification was once considered to be a degenerative and end stage product in aging cardiovascular tissues. Over the past two decades, however, a critical mass of data has shown that cardiovascular calcification can be an active and highly regulated process. While the incidence of calcification in the coronary arteries and cardiac valves is higher in men than in age-matched women, a high index of calcification associates with increased morbidity, and mortality in both sexes. Despite the ubiquitous portending of poor outcomes in both sexes, our understanding of mechanisms of calcification under the dramatically different biological contexts of sex and hormonal milieu remains rudimentary. Understanding how the critical context of these variables inform our understanding of mechanisms of calcification-as well as innovative strategies to target it therapeutically-is essential to advancing the fields of both cardiovascular disease and fundamental mechanisms of aging. This review will explore potential sex and sex-steroid differences in the basic biological pathways associated with vascular and cardiac valvular tissue calcification, and potential strategies of pharmacological therapy to reduce or slow these processes.

Preliminary Study on Composition and Microstructure of Calcification in Craniopharyngiomas

To analyze the element composition and microstructure of calcification in craniopharyngiomas and to explore the differences among differing degrees of calcification, 50 consecutive patients with craniopharyngioma were selected. X-ray diffraction analysis and energy-dispersive X-ray spectroscopy analysis were performed on the calcified plaques isolated from the tumor specimens. All calcified plaques were constituted of hydroxyapatite crystals and some amorphous materials. The main elements for the analysis were calcium, phosphate, carbon, and oxygen. There were significant differences among groups of differing degrees of calcification in the percentage composition of calcium, phosphorus, and carbon (P < 0.05), in which the element content of calcium and phosphorus had a positive correlation with the extent of calcification (rp = 0.745 and 0.778, respectively, P < 0.01), while the element content of carbon had a negative correlation with the extent of calcification (rp =−0.526, P <0.01). The calcium, phosphorus, and carbon content are different in calcified plaques with different extents of calcification. The element content of calcium, phosphorus, and carbon influences the degree of calcification.

Osteopontin expression in reactive lesions of gingiva

Reactive proliferations of the gingiva comprise lesions such as pyogenic granuloma (PG), inflammatory fibroepithelial hyperplasia (IFH), peripheral ossifying fibroma (POF), and peripheral giant cell lesion. Osteopontin (OPN) has a dual role, it promotes mineralization when it is bound to solid substrate, and on the other hand, it inhibits mineralization when it is seen in association with solution. Objectives The study aimed to evaluate the expression of osteopontin in normal gingival tissue and different types of focal reactive proliferations of gingival tissue, and its role in the development of calcification within it. Material and Methods The presence and distribution of osteopontin was assessed using immunohistochemistry in five cases of normal gingival tissue and 30 cases of focal reactive proliferations of gingiva. Results There was no expression of osteopontin in normal subjects. Few cases of pyogenic granuloma, inflammatory fibroepithelial hyperplasia, and all the cases of peripheral ossifying fibroma showed positivity for osteopontin in the inflammatory cells, stromal cells, extracellular matrix, and in the calcifications. Conclusion The expression of osteopontin in all the cases of peripheral ossifying fibroma speculates that the majority of the cases of peripheral ossifying fibroma originate from the periodontal ligament cells. The treatment modalities for peripheral ossifying fibroma should differ from other focal reactive proliferations of gingiva.

Microcalcifications in atherosclerotic lesion of apolipoprotein E-deficient mouse

Evidence is accumulating that calcium-rich microdeposits in the vascular wall might play a crucial role in the onset and progression of atherosclerosis. Here we investigated an atherosclerotic lesion of the carotid artery in an established murine model, i.e. the apolipoprotein E-deficient (APOE(-/-) ) mouse to identify (i) the presence of microcalcifications, if any, (ii) the elemental composition of microcalcifications with special reference to calcium/phosphorus mass ratio and (iii) co-localization of increased concentrations of iron and zinc with microcalcifications. Atherosclerosis was induced by a flow-divider placed around the carotid artery resulting in low and high shear-stress regions. Element composition was assessed with a proton microprobe. Microcalcifications, predominantly present in the thickened intima of the low shear-stress region, were surrounded by areas with normal calcium levels, indicating that calcium-precipitation is a local event. The diameter of intimal microcalcifications varied from 6 to 70 μm. Calcium/phosphorus ratios of microcalcifications varied from 0.3 to 4.8, mainly corresponding to the ratio of amorphous calcium-phosphate. Increased iron and zinc concentrations commonly co-localized with microcalcifications. Our findings indicate that the atherosclerotic process in the murine carotid artery is associated with locally accumulated calcium, iron and zinc. The calcium-rich deposits resemble amorphous calcium phosphate rather than pure hydroxyapatite. We propose that the APOE(-/-) mouse, in which atherosclerosis was evoked by a flow-divider, offers a useful model to investigate the pathophysiological significance of accumulation of elements such as calcium, iron and zinc.

Cellular and molecular mechanisms of abnormal calcification following ischemia-reperfusion injury in human liver transplantation

Recent studies suggest a possible link between calcification and ischemia-reperfusion injury following liver transplantation. Histological staining, immunolabeling, and biochemical and electron microscopy analyses were applied to assess the possible mechanism(s) of calcification in liver tissue. Although light microscopy studies did not reveal the presence of large necrotic or apoptotic areas, electron microscopy showed the presence of membrane-bound vacuolar structures in hepatocytes, indicative of cell damage. Myofibroblasts were abundant in regions surrounding and within calcification. In these precalcified and calcified areas, myofibroblasts expressed bone-specific matrix proteins, such as osteopontin, type 1 collagen and bone sialoprotein. In addition, transforming growth factor beta (TGFbeta)-1 and BMP2, two growth factors implicated in osteoblast differentiation, and Runx2 and Msx2, two transcription factors targets of TGFbeta-1 and BMP2, were also expressed in these myofibroblasts. These data suggest that liver calcification following transplantation may be a consequence of precipitation of hydroxylapatite emanating from necrotic or apoptotic hepatocytes associated with proliferation of myofibroblasts expressing bone-specific matrix proteins.

A Case of Massive Dystrophic Cardiac Calcinosis With Increased Bone Resorption Markers: A Novel Pathophysiologic Link?

We report a 72-year-old man who presented to our emergency room with congestive heart failure that was resistant to initial medical therapy. He had suffered from anterior myocardial infarction 20 years prior. Echocardiography and computed tomography revealed marked cardiac calcification including myocardium, chordal structures, mitral annulus, and aortic valve. Neither chronic renal insufficiency nor hypercalcemia were present in our patient. Bone resorption markers were increased and bone mineral density was consistent with severe osteoporosis. We suggested a novel mechanism, that increased bone resorption may lead to accumulation of calcium into avascular tissues in the heart (ie, chordal structures, mitral annulus, aortic valve, and fibronecrotic myocardium) especially in the setting of high left ventricular end-diastolic pressure. Dystrophic cardiac calcinosis, an age-related cardiomyopathy, is associated with elevated bone resorption markers and it may cause alterations in cellular calcium hemostasis with initiation of deleterious events leading to aggravate dilated and restrictive cardiomyopathy and may result in intractable congestive heart failure. The implication of this case report needs to be reemphasized.

Extensive induction of important mediators of fibrosis and dystrophic calcification in desmin-deficient cardiomyopathy

Mice lacking the intermediate filament protein desmin demonstrate abnormal mitochondria behavior, disruption of muscle architecture, and myocardial degeneration with extensive calcium deposits and fibrosis. These abnormalities are associated with cardiomyocyte hypertrophy, cardiac chamber dilation and eventually with heart failure. In an effort to elucidate the molecular mechanisms leading to the observed pathogenesis, we have analyzed gene expression changes in cardiac tissue using differential display polymerase chain reaction and cDNA atlas array methods. The most substantial changes were found in genes coding the small extracellular matrix proteins osteopontin and decorin that are dramatically induced in the desmin-null myocardium. We further analyzed their expression pattern both at the RNA and protein levels and we compared their spatial expression with the onset of calcification. Extensive osteopontin localization is observed by immunohistochemistry in the desmin-null myocardium in areas with massive myocyte death, as well as in hypercellular regions with variable degrees of calcification and fibrosis. Osteopontin is consistently co-localized with calcified deposits, which progressively are transformed to psammoma bodies surrounded by decorin, especially in the right ventricle. These data together with the observed up-regulation of transforming growth factor-beta1 and angiotensin-converting enzyme, could explain the extensive fibrosis and dystrophic calcification observed in the heart of desmin-null mice, potentially crucial events leading to heart failure.