Phosphate-induced autophagy counteracts vascular calcification by reducing matrix vesicle release. Kidney Int. 2013;83:1042-1051. [PMID: 23364520 DOI: 10.1038/ki.2012.482]

Exosomes, the message transporters in vascular calcification

Vascular calcification (VC) is caused by hydroxyapatite deposition in the intimal and medial layers of the vascular wall, leading to severe cardiovascular events in patients with hypertension, chronic kidney disease and diabetes mellitus. VC occurrences involve complicated mechanism networks, such as matrix vesicles or exosomes production, osteogenic differentiation, reduced cell viability, aging and so on. However, with present therapeutic methods targeting at VC ineffectively, novel targets for VC treatment are demanded. Exosomes are proven to participate in VC and function as initializers for mineral deposition. Secreted exosomes loaded with microRNAs are also demonstrated to modulate VC procession in recipient vascular smooth muscle cells. In this review, we targeted at the roles of exosomes during VC, especially at their effects on transporting biological information among cells. Moreover, we will discuss the potential mechanisms of exosomes in VC.

Role of AMPK in atherosclerosis via autophagy regulation

Atherosclerosis is characterized by the accumulation of lipids and deposition of fibrous elements in the vascular wall, which is the primary cause of cardiovascular diseases. Adenosine monophosphate-activated protein kinase (AMPK) is a metabolic sensor of energy metabolism that regulates multiple physiological processes, including lipid and glucose metabolism and the normalization of energy imbalances. Overwhelming evidence indicates that AMPK activation markedly attenuates atherosclerosis development. Autophagy inhibits cell apoptosis and inflammation and promotes cholesterol efflux and efferocytosis. Physiological autophagy is essential for maintaining normal cardiovascular function. Increasing evidence demonstrates that autophagy occurs in developing atherosclerotic plaques. Emerging evidence indicates that AMPK regulates autophagy via a downstream signaling pathway. The complex relationship between AMPK and autophagy has attracted the attention of many researchers because of this close relationship to atherosclerosis development. This review demonstrates the role of AMPK and autophagy in atherosclerosis. An improved understanding of this interrelationship will create novel preventive and therapeutic strategies for atherosclerosis.

Polysaccharide from Fuzi protects against Ox‑LDL‑induced calcification of human vascular smooth muscle cells by increasing autophagic activity

Polysaccharide from Fuzi (FPS) is a water‑soluble polysaccharide isolated from the traditional Chinese herbal medicine Fuzi. It has been demonstrated to protect hepatocytes against ischemia‑reperfusion injury through its potent antioxidant effects, and to attenuate starvation‑induced cytotoxicity in H9c2 cells by increasing autophagic activity. In the present study, Alizarin Red S staining was used to detect mineral deposition and reverse transcription‑quantitative polymerase chain reaction was used to detect the core binding factor α1 and smooth muscle 22α mRNA expression. To analyze autophagic activity, western blotting was used to detect microtubule‑associated protein 1A/1B light chain 3 and nucleoporin P62 expression. In addition, green fluorescent protein‑LC3 dots‑per‑cell was observed by fluorescence microscopy. It was demonstrated that oxidized low‑density lipoprotein (Ox‑LDL) could increase the calcification of human vascular smooth muscle cells (VSMCs) in a concentration‑dependent manner, and that FPS treatment had a significant protective effect against Ox‑LDL‑induced calcification of human VSMCs. Furthermore, FPS treatment alleviated the Ox‑LDL‑induced downregulation of autophagic activity, and the protective effect of FPS on Ox‑LDL‑induced calcification was attenuated by the autophagy inhibitor 3‑methyladenine. In conclusion, the present study demonstrated for the first time to the best of the authors' knowledge that FPS can protect against Ox‑LDL‑induced vascular calcification in human VSMCs, and that this likely occurs via the activation of autophagy. This supports the hypothesis that autophagy may be an endogenous protective mechanism counteracting vascular calcification, and that FPS may be used as a potential therapeutic for vascular calcification.

Sp1 Plays an Important Role in Vascular Calcification Both In Vivo and In Vitro

BACKGROUND

Vascular calcification and increased cardiovascular morbidity and mortality are closely related in patients with end-stage renal disease and diabetes mellitus. Specific protein 1 (Sp1) is a transactivation molecule that plays a crucial role in the regulation of apoptosis, fibrosis, angiogenesis, and other pathological disorders. There is evidence that specific protein 1 (Sp1) directly stimulates the transcription of bone morphogenetic protein 2 (BMP2) and that BMP2 plays a key role in the calcification process in the BMP2-expressing F9 cell model system. Here, we investigated whether Sp1 plays an important role in vascular calcification and its potential regulatory mechanism in vascular calcification.

METHODS AND RESULTS

In this study, vascular calcification was induced in male Wistar rats by administration of nicotine (25 mg/kg) and vitamin D3 (300 000 IU/kg). These rats were randomly selected for treatment with adenovirus harboring Sp1 knockdown gene or empty virus. The mechanism of Sp1 in vascular smooth muscle cells cultured in high phosphate medium was studied. Based on our findings, the Sp1 gene silencing or inhibition improved calcium deposition, which was partly achieved by inhibiting phenotype switch, apoptosis, and matrix vesicle release of vascular smooth muscle cells. Moreover, Sp1 can activate BMP2 transcription by binding to the Sp1-binding element of the BMP2 promoter.

CONCLUSIONS

Overall, elevated Sp1 exerts a pro-apoptotic effect, promoting BMP2 transcription and further accumulating vascular calcification. Proper and timely regulation of Sp1 expression may be a potential strategy for treatment of aging, end-stage renal disease, and diabetic-related macrovascular disease treatment.

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

BACKGROUND

Matrix vesicles (MVs) are released from hypertrophic chondrocytes and from mature osteoblasts, the cells responsible for endochondral and membranous ossification. Under pathological conditions, they can also be released from cells of non-skeletal tissues such as vascular smooth muscle cells. MVs are extracellular vesicles of approximately 100-300nm diameter harboring the biochemical machinery needed to induce mineralization.

SCOPE OF THE REVIEW

The review comprehensively delineates our current knowledge of MV biology and highlights open questions aiming to stimulate further research. The review is constructed as a series of questions addressing issues of MVs ranging from their biogenesis and functions, to biomimetic models. It critically evaluates experimental data including their isolation and characterization methods, like lipidomics, proteomics, transmission electron microscopy, atomic force microscopy and proteoliposome models mimicking MVs.

MAJOR CONCLUSIONS

MVs have a relatively well-defined function as initiators of mineralization. They bind to collagen and their composition reflects the composition of lipid rafts. We call attention to the as yet unclear mechanisms leading to the biogenesis of MVs, and how minerals form and when they are formed. We discuss the prospects of employing upcoming experimental models to deepen our understanding of MV-mediated mineralization and mineralization disorders such as the use of reconstituted lipid vesicles, proteoliposomes and, native sample preparations and high-resolution technologies.

GENERAL SIGNIFICANCE

MVs have been extensively investigated owing to their roles in skeletal and ectopic mineralization. MVs serve as a model system for lipid raft structures, and for the mechanisms of genesis and release of extracellular vesicles.

Phosphate stimulates myotube atrophy through autophagy activation: evidence of hyperphosphatemia contributing to skeletal muscle wasting in chronic kidney disease

Background

Accelerated muscle atrophy is associated with a three-fold increase in mortality in chronic kidney disease (CKD) patients. It is suggested that hyperphosphatemia might contribute to muscle wasting, but the underlying mechanisms remain unclear. Although evidence indicates that autophagy is involved in the maintenance of muscle homeostasis, it is not known if high phosphate levels can result in activation of autophagy, leading to muscle protein loss.

Methods

Immortalized rat L6 myotubes were exposed to a high concentration of phosphate, with or without autophagy inhibition. Myotube atrophy was examined by phase contrast microscopy. Autophagic activity was assessed by measuring the expression of microtubule-associated protein 1 light chain 3 (LC3) and p62 using quantitative real-time polymerase chain reaction and western blot.

Results

Phosphate induced cell atrophy in L6 myotubes in a dose- and time-dependent manner, and these responses were not associated with calcification or osteogenesis. Phosphate also dose- and time-dependently increased the LC3-II/LC3-I ratio. Inhibition of autophagy with wortmannin or knockdown of Atg5 significantly suppressed myotube atrophy caused by high phosphate concentration.

Conclusions

High phosphate concentration induces muscle cell atrophy through the activation of autophagy. Targeting autophagy could be a therapeutic strategy for preventing muscle wasting caused by hyperphosphatemia.

Inhibition of endo-lysosomal function exacerbates vascular calcification

Vascular calcification is a pathologic response to mineral imbalances and is prevalent in atherosclerosis, diabetes mellitus, and chronic kidney disease. When located in the media, it is highly associated with increased cardiovascular morbidity and mortality, particularly in patients on dialysis. Vascular calcification is tightly regulated and controlled by a series of endogenous factors. In the present study, we assess the effects of lysosomal and endosomal inhibition on calcification in vascular smooth muscle cells (VSMCs) and aortic rings. We observed that lysosomal function was increased in VSMCs cultured in calcification medium containing 3.5 mM inorganic phosphate (Pi) and 3 mM calcium (Ca²⁺) for 7 days. We also found that the lysosomal marker lysosome-associated membrane protein 2 was markedly increased and colocalized with osteogenic markers in calcified aortas from vitamin D₃-treated rats. Interestingly, both the lysosomal inhibitor chloroquine and the endosomal inhibitor dynasore dose-dependently enhanced Pi + Ca²⁺-mediated VSMC calcification. Inhibition of lysosomal and endosomal function also promoted osteogenic transformation of VSMCs. Additionally, lysosome inhibition increased Pi-induced medial calcification of aortic rings ex vivo. These data suggest that the endosome-lysosome system may play a protective role in VSMC and medial artery calcification.

Matrix vesicles induce calcification of recipient vascular smooth muscle cells through multiple signaling pathways

In patients with chronic kidney and end-stage renal diseases, the major risk factor for progression of arterial calcification is the presence of existing (baseline) calcification. Here, we tested whether calcification of arteries is extended from calcified vascular smooth muscle cells (VSMCs) to adjacent normal cells by matrix vesicle-induced alteration of cell signaling. Matrix vesicles isolated from VSMC of rats with chronic kidney disease were co-cultured with VSMCs from normal littermates. Endocytosis of vesicles by recipient cells was confirmed by confocal microscopy. The addition of cellular matrix vesicles with characteristics of exosomes and low fetuin-A content enhanced the calcification of recipient VSMC. Further, only cellular-derived matrix vesicles induced an increase in intracellular calcium ion concentration, NOX1 (NADPH oxidase) and the anti-oxidant superoxide dismutase-2 in recipient normal VSMC. The increase in intracellular calcium ion concentration was due to release from endoplasmic reticulum and partially attributed to the activation of both NOX1 and mitogen-activated protein kinase (MEK1 and Erk1/2) signaling, since inhibiting both pathways blocked the increase in intracellular calcium ion in recipient VSMC. In contrast, matrix vesicles isolated from the media had no effect on the intracellular calcium ion concentration or MEK1 signaling, and did not induce calcification. However, media matrix vesicles did increase Erk1/2, although not to the level of cellular matrix vesicles, and NOX1 expression. Blockade of NOX activity further inhibited the cellular matrix vesicle-induced accelerated calcification of recipient VSMC, suggesting a potential therapeutic role of such inhibition. Thus, addition of cellular-derived matrix vesicles from calcifying VSMC can accelerate calcification by inducing cell signaling changes and phenotypic alteration of recipient VSMC.

High magnesium prevents matrix vesicle-mediated mineralization in human bone marrow-derived mesenchymal stem cells via mitochondrial pathway and autophagy

Magnesium, as a physiological calcium antagonist, plays a vital role in the bone metabolism and the balance between magnesium and calcium is crucial in bone physiology. We recently demonstrated that matrix mineralization in human bone marrow-derived mesenchymal stem cells (hBMSCs) can be suppressed by high Mg²⁺ . However, a complete understanding of the mechanisms involved still remains to be elucidated. As mitochondrial calcium phosphate granules depletion manifests concurrently with the appearance of matrix vesicles (MVs) and autophagy are associated with matrix mineralization, we studied the effect of high extracellular Mg²⁺ on these pathways. Our results first demonstrated that high Mg²⁺ has a significant inhibitory effect on the generalization of extracellular mineral aggregates and the expression of collagen 1 along which the mineral crystals grow. Transmission electron microscope results showed that less amount of MVs were observed inside hBMSCs treated with high Mg²⁺ and high Mg²⁺ inhibited the release of MVs. In addition, high Mg²⁺ significantly suppressed mitochondrial Ca²⁺ accumulation. Autophagy is promoted as a response to osteogenesis of hBMSCs. High Mg²⁺ inhibited the level of autophagy upon osteogenesis and autophagy inhibitor 3-MA significantly suppressed mineralization. Exogenous ATP can reverse the inhibitory effect of high Mg²⁺ by increasing the level of autophagy. Taken together, our results indicate that high Mg²⁺ may modulate MVs-mediated mineralization via suppressing mitochondrial Ca²⁺ intensity and regulates autophagy of hBMSCs upon osteogenesis, resulting in decreased extracellular mineralized matrix deposition. Our results contribute to the understanding of the role of magnesium homeostasis in osteoporosis and the design of magnesium alloys.

The Role of Secondary Calciprotein Particles in the Mineralisation Paradox of Chronic Kidney Disease

Mineralisation paradox is prevalent in chronic kidney disease and ageing where increased vascular calcification is accompanied by reduced bone mineralisation and osteopenia. Secondary calciprotein particles (CPP2), colloidal nanoparticles containing hydroxyapatite crystal stabilised by a protein shell, have been implicated in vascular calcification in chronic kidney disease. Here, we describe the effect of CPP2 on osteoblasts and vascular smooth muscle cells (VSMC) mineralisation in an in vitro model system. The mineralisation paradox can be simulated in vitro by the addition of phosphate ions (Pi, 3 mM) and CPP2 (10 µg/ml of Ca equivalent). Pi alone induced osteoblast mineralisation but had no effect on VSMC mineralisation. CPP2 alone had no effect on mineralisation in either cell line, but when combined with elevated Pi, reduced osteoblast-like mineralisation (P < 0.001) whilst induced VSMC mineralisation (P < 0.001). These results suggest that in an in vitro system the synergistic interaction between Pi and CPP2 could mimic the mineralisation paradox, and may provide a potential mechanistic link to explain these clinical observations.

Nano-Hydroxyapatite Stimulation of Gene Expression Requires Fgf Receptor, Phosphate Transporter, and Erk1/2 Signaling

Hydroxyapatite (HAp) is critical to health both as the main structural material of the skeleton and storage material of calcium and phosphate. Nanosized HAp (nHAp) is naturally produced by mineralizing cells during bone formation and remodeling and is the main constituent of the skeleton. As such, HAp is currently being investigated as a therapeutic biomaterial for orthopedic and dental purposes. Recent studies have suggested that extracellular nHAp can influence osteoblast lineage commitment and cell function through changes in gene expression; however, the mechanisms remain to be elucidated. Here, the cellular and molecular mechanism by which rod-shaped nHAp (10 × 100 nm) stimulates gene expression in preosteoblast bone marrow stromal cells was investigated. Electron microscopy detected a rapid and stable interaction of nHAp with the cell membrane, which correlated with a strong stimulation of the Erk1/2 signaling pathway. Results also identified the requirement of the Fgf receptor signaling and phosphate-transporters for nHAp regulated gene expression whereas a calcium-sensing receptor inhibitor had no effect. Collectively, the study uncovers novel signaling pathways and cellular events specifically stimulated by and required for the cellular response to free extracellular HAp. The results provide insight into the osteoblastic response to HAp relevant to functional mineralization and pathological calcification and could be used in the development of biomaterials for orthopedic purposes.

Dietary potassium regulates vascular calcification and arterial stiffness

Vascular calcification is a risk factor that predicts adverse cardiovascular complications of several diseases including atherosclerosis. Reduced dietary potassium intake has been linked to cardiovascular diseases such as hypertension and incidental stroke, although the underlying molecular mechanisms remain largely unknown. Using the ApoE-deficient mouse model, we demonstrated for the first time to our knowledge that reduced dietary potassium (0.3%) promoted atherosclerotic vascular calcification and increased aortic stiffness, compared with normal (0.7%) potassium-fed mice. In contrast, increased dietary potassium (2.1%) attenuated vascular calcification and aortic stiffness. Mechanistically, reduction in the potassium concentration to the lower limit of the physiological range increased intracellular calcium, which activated a cAMP response element-binding protein (CREB) signal that subsequently enhanced autophagy and promoted vascular smooth muscle cell (VSMC) calcification. Inhibition of calcium signals and knockdown of either CREB or ATG7, an autophagy regulator, attenuated VSMC calcification induced by low potassium. Consistently, elevated autophagy and CREB signaling were demonstrated in the calcified arteries from low potassium diet-fed mice as well as aortic arteries exposed to low potassium ex vivo. These studies established a potentially novel causative role of dietary potassium intake in regulating atherosclerotic vascular calcification and stiffness, and uncovered mechanisms that offer opportunities to develop therapeutic strategies to control vascular disease.

Neuroprotective effect of 5-aminolevulinic acid against low inorganic phosphate in neuroblastoma SH-SY5Y cells

PiT-1 (encoded by SLC20A1) and PiT-2 (encoded by SLC20A2) are type-III sodium-dependent phosphate cotransporters (NaPiTs). Recently, SLC20A2 mutations have been found in patients with idiopathic basal ganglia calcification (IBGC), and were predicted to bring about an inability to transport Pi from the extracellular environment. Here we investigated the effect of low Pi loading on the human neuroblastoma SH-SY5Y and the human glioblastoma A172 cell lines. The results show a different sensitivity to low Pi loading and differential regulation of type-III NaPiTs in these cells. We also examined whether 5-aminolevulinic acid (5-ALA) inhibited low Pi loading-induced neurotoxicity in SH-SY5Y cells. Concomitant application of 5-ALA with low Pi loading markedly attenuated low Pi-induced cell death and mitochondrial dysfunction via the induction of HO-1 by p38 MAPK. The findings provide us with novel viewpoints to understand the pathophysiology of IBGC, and give a new insight into the clinical prevention and treatment of IBGC.

Inflammation and premature aging in advanced chronic kidney disease

Systemic inflammation in end-stage renal disease is an established risk factor for mortality and a catalyst for other complications, which are related to a premature aging phenotype, including muscle wasting, vascular calcification, and other forms of premature vascular disease, depression, osteoporosis, and frailty. Uremic inflammation is also mechanistically related to mechanisms involved in the aging process, such as telomere shortening, mitochondrial dysfunction, and altered nutrient sensing, which can have a direct effect on cellular and tissue function. In addition to uremia-specific causes, such as abnormalities in the phosphate-Klotho axis, there are remarkable similarities between the pathophysiology of uremic inflammation and so-called "inflammaging" in the general population. Potentially relevant, but still somewhat unexplored in this respect, are abnormal or misplaced protein structures, as well as abnormalities in tissue homeostasis, which evoke danger signals through damage-associated molecular patterns, as well as the senescence-associated secretory phenotype. Systemic inflammation, in combination with the loss of kidney function, can impair the resilience of the body to external and internal stressors by reduced functional and structural tissue reserves, and by impairing normal organ crosstalk, thus providing an explanation for the greatly increased risk of homeostatic breakdown in this population. In this review, the relationship between uremic inflammation and a premature aging phenotype, as well as potential causes and consequences, are discussed.

Autophagy negatively regulates pro-osteogenic activity in human aortic valve interstitial cells

BACKGROUND

Autophagy is a physiological process that plays an important role in maintaining cellular functions. When aortic valve interstitial cells (AVICs) are stimulated with inflammatory or mechanical stress, one response is elevated pro-osteogenic activity. We hypothesized that autophagy is important in the prevention or regulation of this pro-osteogenic activity in AVICs.

MATERIALS AND METHODS

AVICs were isolated. Autophagy activity was examined and its role in AVIC's pro-osteogenic activity was determined using chemical inhibitors and genetic techniques. The pro-osteogenic biomarker bone morphogenetic protein 2 (BMP-2) and alkaline phosphatase (ALP) were analyzed by immunoblotting and calcium deposition assay.

RESULTS

Human AVICs from normal aortic valve donors displayed significantly higher autophagic activity than those from calcified aortic valve donors as indicated by lower protein levels of light chain 3-II. Suppression of autophagy by 3-methyladenine, bafilomycin, or knockdown of Atg7 gene induced the expression of BMP-2 and ALP, increased ALP activity, and calcium deposit formation in normal AVICs. Conversely, upregulation of autophagy with rapamycin or overexpression of Atg7 gene decreased the levels of BMP-2 and ALP in diseased AVICs.

CONCLUSIONS

Our data showed that autophagy negatively regulates the pro-osteogenic activity in human AVICs, suggesting that upregulation of autophagy may prevent the progression of calcific aortic valve disease.

Activation of the Nrf2-ARE Signaling Pathway Prevents Hyperphosphatemia-Induced Vascular Calcification by Inducing Autophagy in Renal Vascular Smooth Muscle Cells

This study investigates the effect of nuclear factor erythroid 2-related factor 2-antioxidant response element (Nrf2-ARE) signaling pathway in vascular calcification (VC) via inducing Autophagy in renal vascular smooth muscle cells (VSMCs). VSMCs were assigned into six experimental groups: the normal control, high phosphorus, si-negative control (si-NC), Nrf2-siRNA, over-expressed Nrf2, and negative control (NC) groups. RT-PCR was applied to detect the mRNA expressions of the desired Nrf2-ARE signaling pathway-related genes (Nrf2, NQO-1, HO-1, γ-GCS). The protein products of these genes: apoptosis-related genes (LC3I and LC3II), osteogenic marker proetins (Runt-related transcription factor 2) Runx2 and BMP2 were all detected by Western blotting. Autophagosomes in VSMCs were observed under a transmission electron microscope. We discovered an increased calcium ion concentration and upregulated Runx2, BMP2, Nrf2, HO-1, γ-GCS, NQO-1, and LC3II/LC3I expressions in the high phosphorous, si-NC and Nrf2-siRNA, and NC groups, compared with the normal control group. Compared to the high phosphorus and si-NC groups, higher levels of Runx2 and BMP2 but decreased Nrf2, HO-1, γ-GCS, NQO-1, and LC3II/LC3I expressions were detected in the Nrf2-siRNA group. The high phosphorus, si-NC and over-expressed Nrf2 experimental groups all had increased Nrf2, NQO-1, HO-1, γ-GCS, and LC3II/LC3I expressions as well as high numbers of autophagosomes compared with the normal control group. Finally, we detected a lower amount of autophagosomes presence and Nrf2, NQO-1, HO-1 γ-GCS, and LC3II/LC3 protein expression of Nrf2-siRNA group than that of the high phosphorus and si-NC groups. Activation of Nrf2-ARE signaling pathway may prevent hyperphosphatemia-induced VC by inducing autophagy in VSMCs. J. Cell. Biochem. 118: 4708-4715, 2017. © 2017 Wiley Periodicals, Inc.

Oestrogen Inhibits Arterial Calcification by Promoting Autophagy

Arterial calcification is a major complication of cardiovascular disease. Oestrogen replacement therapy in postmenopausal women is associated with lower levels of coronary artery calcification, but its mechanism of action remains unclear. Here, we show that oestrogen inhibits the osteoblastic differentiation of vascular smooth muscle cells (VSMCs) in vitro and arterial calcification in vivo by promoting autophagy. Through electron microscopy, GFP–LC3 redistribution, and immunofluorescence analyses as well as measurement of the expression of the autophagosome marker light-chain I/II (LC3I/II) and autophagy protein 5 (Atg5), we show that autophagy is increased in VSMCs by oestrogen in vitro and in vivo. The inhibitory effect of oestrogen on arterial calcification was counteracted by 3-methyladenine (3MA) or knockdown of Atg5 and was increased by rapamycin. Furthermore, the inhibitory effect of oestrogen on arterial calcification and the degree of autophagy induced by oestrogen were blocked by a nonselective oestrogen receptor (ER) antagonist (ICI 182780), a selective oestrogen receptor alpha (ERα) antagonist (MPP), and ERα-specific siRNA. Our data indicate that oestrogen inhibits the osteoblastic differentiation of VSMCs by promoting autophagy through the ERα signalling pathway in vitro and arterial calcification in vivo by increasing autophagy. Our findings provide new insights into the mechanism by which oestrogen contributes to vascular calcification in vitro and in vivo.

Roles of platelet-derived growth factor in vascular calcification

Vascular calcification (VC) is prevalent in aging, and patients with hypertension, chronic kidney disease (CKD), or diabetes. VC is regarded as an active and complex process that involves multiple mechanisms responsible for calcium deposition in vessel wall. In light of the complicated pathogenesis of VC, effective therapy for ameliorating VC is limited. Thus, it is urgent to explore the potential mechanisms and find new targets for the therapy of VC. Platelet-derived growth factor (PDGF), a potent mitogen, and chemoattractant have been found to disturb the vascular homeostasis by inducing inflammation, oxidative stress, and phenotype transition, all of which accelerate the process of VC. The aim of current review is to present a review about the roles of PDGF in affecting VC and to establish a potential target for treating VC.

Alkaline phosphatase: a novel treatment target for cardiovascular disease in CKD

Cardiovascular disease is the main cause of early death in the settings of chronic kidney disease (CKD), type 2 diabetes mellitus (T2DM), and ageing. Cardiovascular events can be caused by an imbalance between promoters and inhibitors of mineralization, which leads to vascular calcification. This process is akin to skeletal mineralization, which is carefully regulated and in which isozymes of alkaline phosphatase (ALP) have a crucial role. Four genes encode ALP isozymes in humans. Intestinal, placental and germ cell ALPs are tissue-specific, whereas the tissue-nonspecific isozyme of ALP (TNALP) is present in several tissues, including bone, liver and kidney. TNALP has a pivotal role in bone calcification. Experimental overexpression of TNALP in the vasculature is sufficient to induce vascular calcification, cardiac hypertrophy and premature death, mimicking the cardiovascular phenotype often found in CKD and T2DM. Intestinal ALP contributes to the gut mucosal defence and intestinal and liver ALPs might contribute to the acute inflammatory response to endogenous or pathogenic stimuli. Here we review novel mechanisms that link ALP to vascular calcification, inflammation, and endothelial dysfunction in kidney and cardiovascular diseases. We also discuss new drugs that target ALP, which have the potential to improve cardiovascular outcomes without inhibiting skeletal mineralization.

A novel role of cellular interactions in vascular calcification

A series of clinical trials have confirmed the correlation between vascular calcification (VC) and cardiovascular events and mortality. However, current treatments have little effects on the regression of VC. Potent and illustrative mechanisms have been proven to exist in both bone metabolism and VC, indicating that these two processes share similarities in onset and progression. Multiple osteoblast-like cells and signaling pathways are involved in the process of VC. In this review, we summarized the roles of different osteoblast-like cells and we emphasized on how they communicated and interacted with each other using different signaling pathways. Further studies are needed to uncover the underlying mechanisms and to provide novel therapies for VC.

Ghrelin improves vascular autophagy in rats with vascular calcification

BACKGROUNDS

This study aimed to investigate whether ghrelin ameliorated vascular calcification (VC) through improving autophagy.

METHODS

VC model was induced by nicotine plus vitamin D₃ in rats and β-glycerophosphate in vascular smooth muscle cell (VSMC). Calcium deposition was detected by von Kossa staining or alizarin red S staining. ALP activity was also detected. Western blot was used to assess the protein expression.

RESULTS

Ghrelin treatment attenuated the elevation of calcium deposition and ALP activity in VC model both in vivo and in vitro. Interesting, the protein levels of autophagy markers, LC3 and beclin1 were significantly upregulated by ghrelin in VC model. An autophagy inhibitor, 3-methyladenine blocks the ameliorative effect of ghrelin on VC. Furthermore, protein expressions of phosphate-AMPK were increased by ghrelin treatment both in calcified aorta and VSMC. The effect of ghrelin on autophagy induction and VC attenuation was prevented by AMPK inhibitor, compound C.

CONCLUSIONS

Our results suggested that ghrelin improved autophagy through AMPK activation, which was resulted in VC amelioration. These data maybe throw light on prevention and therapy of VC.

Systems biological understanding of the regulatory network and the possible therapeutic strategies for vascular calcification

Since there is no precise therapy for treating vascular calcification by directly targeting the vascular wall, we aim to unveil novel drug targets through mining the molecular effect of a high phosphate environment on vascular cells through computational methods. Here, we hypothesize that manipulation of the vascular pathogenic network by small molecule therapeutics predicted from prior knowledge might offer great promise. With this, we intend to understand the publicly available transcriptomic data of vascular smooth muscle cells and endothelial cells exposed to the high phosphate induced vascular calcification milieu and to re-examine the above published experiments for reasons different from those examined in the previous studies through multilevel systems biological understanding. Hence, in this study the differentially expressed genes were subjected to both upstream and downstream network analysis through multiple standalone software and web servers. To provide an insight into causal signaling, we simultaneously predicted upstream regulatory layers through transcription factor and kinome enrichment analysis. Moreover the possible systems pharmacological choices were presented in three ways as (1) drug induced expression modulation, (2) drugs that interact with upstream and downstream regulatory targets, (3) possible natural product therapeutics from target-compound relationship. Furthermore for validating the current study we have specifically evaluated the preventive effect of two predicted natural compounds in a bovine aortic calcification model. The overall observation predicts a few novel mechanisms that might be involved in vascular dysfunction and calcification in both cell types. Also, the systems pharmacological investigation provides clues for the possible therapeutic options along with validation. In conclusion, the current study indicates that reanalysis of transcriptomic data propels us to reposition the approved drugs and use natural compounds as novel therapeutic agents for vascular calcification.

Dorsomorphin homologue 1, a highly selective small-molecule bone morphogenetic protein inhibitor, suppresses medial artery calcification

BACKGROUND

Medial artery calcification develops in diabetes, chronic kidney disease, and as part of the aging process. It is associated with increased morbidity and mortality in vascular patients. Bone morphogenetic proteins (BMPs) have previously been implicated in the initiation and progression of vascular calcification. We thus evaluated whether dorsomorphin homologue 1 (DMH1), a highly selective BMP inhibitor, could attenuate vascular calcification in vitro and in an organ culture model of medial calcification.

METHODS

Confluent human aortic smooth muscle cells (SMCs) were cultured in calcification medium containing 3.0 mM inorganic phosphate (Pi) for 7 days with or without DMH1. Medial calcification was assessed using an aortic organ culture model. Calcification was visualized by alizarin red S staining, and calcium concentration was assessed by an o-cresolphthalein complexone calcium assay. Osteogenic cell and vascular SMC markers were determined by Western blot, quantitative reverse transcription polymerase chain reaction, and immunohistochemical staining.

RESULTS

DMH1 reduced Pi-induced calcium deposition in human SMCs. It also antagonized human recombinant BMP2-induced calcium accumulation. Western blot further revealed that DMH1 was able to block Pi-mediated upregulation of the osteoblast markers osterix and alkaline phosphatase and downregulation of the SMC markers smooth muscle myosin heavy chain and SM22α as well as p-Smad1/5/8, suggesting that DMH1 may regulate SMC osteogenic differentiation through the BMP/Smad1/5/8 signaling pathway. Finally, using an ex vivo aortic ring organ culture model, we observed that DMH1 reduces Pi-induced aortic medial calcification.

CONCLUSIONS

The selective BMP inhibitor DMH1 can inhibit calcium accumulation in vascular SMCs and arterial segments exposed to elevated phosphate levels. Such small molecules may have clinical utility in reducing medial artery calcification in our population of vascular patients.

WNT/β-catenin signaling promotes VSMCs to osteogenic transdifferentiation and calcification through directly modulating Runx2 gene expression

Arterial medial calcification (AMC) is prevalent in patients with chronic kidney disease (CKD) and contributes to elevated risk of cardiovascular events and mortality. Vascular smooth muscle cells (VSMCs) to osteogenic transdifferentiation (VOT) in a high-phosphate environment is involved in the pathogenesis of AMC in CKD. WNT/β-catenin signaling is indicated to play a crucial role in osteogenesis via promoting Runx2 expression in osteoprogenitor cells, however, its role in Runx2 regulation and VOT remains incompletely clarified. In this study, Runx2 was induced and β-catenin was activated by high-phosphate in VSMCs. Two forms of active β-catenin, dephosphorylated on Ser37/Thr41 and phosphorylated on Ser675 sites, were upregulated by high-phosphate. Activation of β-catenin, through ectopic expression of stabilized β-catenin, inhibition of GSK-3β, or WNT-3A protein, induced Runx2 expression, whereas blockade of WNT/β-catenin signaling with Porcupine (PORCN) inhibitor or Dickkopf-1 (DKK1) protein inhibited Runx2 induction by high-phosphate. WNT-3A promoted osteocalcin expression and calcium deposition in VSMCs, whereas DKK1 ameliorated calcification of VSMCs induced by high-phosphate. Two functional T cell factor (TCF)/lymphoid enhancer-binding factor binding sites were identified in the promoter region of Runx2 gene in VSMCs, which interacted with TCF upon β-catenin activation. Site-directed mutation of each of them attenuated Runx2 response to β-catenin, and deletion or destruction of both of them completely abolished this responsiveness. In the aortic tunica media of rats with chronic renal failure, followed by AMC, Runx2 and β-catenin was induced, and the Runx2 mRNA level was positively associated with the abundance of phosphorylated β-catenin (Ser675). Collectively, our study suggested that high-phosphate may activate WNT/β-catenin signaling through different pathways, and the activated WNT/β-catenin signaling, through direct downstream target Runx2, could play an important role in promoting VOT and AMC.

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.

Where do we stand on vascular calcification?

Vascular disease, such as atherosclerosis and diabetic vasculopathy, is frequently complicated by vascular calcification. Previously believed to be an end-stage process of unregulated mineral precipitation, it is now well established to be a multi-faceted disease influenced by the characteristics of its vascular location, the origins of calcifying cells and numerous regulatory pathways. It reflects the fundamental plasticity of the vasculature that is gradually being revealed by progress in vascular and stem cell biology. This review provides a brief overview of where we stand in our understanding of vascular calcification, facing the challenge of translating this knowledge into viable preventive and therapeutic strategies.

Autophagy: A double-edged sword in intervertebral disk degeneration

Autophagy is a homeostatic mechanism through which intracellular damaged organelles and proteins are degraded and recycled in response to increased metabolic demands or stresses. Although primarily cytoprotective, dysfunction of autophagy is often associated with many degenerative diseases, including intervertebral disc (IVD) degeneration (IDD). As a main contributing factor to low back pain, IDD is the pathological basis for various debilitating spinal diseases. Either higher or lower levels of autophagy are observed in degenerative IVD cells. Despite the precise role of autophagy in disc degeneration that is still controversial, with difference from protection to aggravation, targeting autophagy has shown promise for mitigating disc degeneration. In the current review, we summarize the changes of autophagy in degenerative IVD cells and mainly discuss the relationship between autophagy and IDD. With continued efforts, modulation of the autophagic process could be a potential and attractive therapeutic strategy for degenerative disc disease.

Effects of donor age and proliferative aging on the phenotype stability of rat aortic smooth muscle cells

Age-related effects of the vascular wall have been associated with several hemodynamic dysfunctions, including medial vascular calcification. Vascular aging has been traditionally addressed using proliferative senescence of vascular smooth muscle cells (VSMC) in vitro, which induces osteoblastic transition and favors calcification in vitro. In this work, we have analyzed the relationship between organismal aging and proliferative senescence by comparing the proliferative aging of VSMC obtained from young, mature, and old rats (2-, 12-, and 24-month cell lines [CL], respectively). VSMC proliferated to more than 100 cumulative population doublings (CPD) without evidence of proliferative senescence, most likely as a consequence of telomerase induction. The apoptosis rate increased with CPD in all three CL, but the oxidation status of the cells was not modified. The magnitude of all gene expression changes caused by CPD was higher than the magnitude of the changes caused by donor age: the expressions of VSMC markers α-actin and SM22α decreased, while the expressions of transcription factors Msx2 and Runx2 and of bone morphogenetic protein-2 increased. Treatment of the cells with 2 mmol/L Pi revealed that the intensity of the effect of CPD on calcium deposition was greater than the effect of donor age. In conclusion, the proliferative lifespan of VSMC magnifies the effect of donor age on the osteoblastic transition of VSMC, therefore suggesting that in vivo vascular aging changes can be less dramatic than what is shown by in vitro aging.

Matrix vesicles: Are they anchored exosomes?

Numerous studies have documented that matrix vesicles are unique extracellular membrane-bound microparticles that serve as initial sites for mineral formation in the growth plate and most other vertebrate mineralizing tissues. Microparticle generation is not confined to hard tissues, as cells in soft tissues generate similar structures; numerous studies have shown that a common type of extracellular particle, termed an exosome, a product of the endosomal pathway, shares many characteristics of matrix vesicles. Indeed, analyses of size, morphology and lipid and protein content indicate that matrix vesicles and exosomes are homologous structures. Such a possibility impacts our understanding of the biogenesis, processing and function of matrix vesicles (exosomes) in vertebrate hard tissues and explains in part how cells control the earliest stages of mineral deposition. Moreover, since exosomes influence a spectrum of functions, including cell-cell communication, it is suggested that this type of microparticle may provide a mechanism for the transfer of signaling molecules between cells within the growth plate and thereby regulate endochondral bone development and formation.

7-Ketocholesterol-induced lysosomal dysfunction exacerbates vascular smooth muscle cell calcification via oxidative stress

Vascular calcification is known to reduce the elasticity of aorta. Several studies have suggested that autophagy-lysosomal pathway (ALP) in vascular smooth muscle cells (VSMCs) is associated with vascular calcification. A major component of oxidized low-density lipoproteins, 7-ketocholesterol (7-KC), has been reported to promote inorganic phosphorus (Pi)-induced vascular calcification and induce ALP. The aim of this study was to unravel the relationship between ALP and the progression of calcification by 7-KC. Calcification of human VSMCs was induced by Pi stimulation in the presence or absence of 7-KC. FACS analysis showed that 7-KC-induced apoptosis at a high concentration (30 μM), but not at a low concentration (15 μM). Interestingly, 7-KC promoted calcification in VSMCs regardless of apoptosis. Immunoblotting and immunostaining showed that 7-KC inhibits not only the fusion of autophagosomes and lysosomes but also causes a swell of lysosomes with the reduction of cathepsin B and D. Moreover, lysosomal protease inhibitors exacerbated the apoptosis-independent calcification by 7-KC although inhibition of autophagosome formation by Atg5 siRNA did not. Finally, the 7-KC-induced progression of calcification was alleviated by the treatment with antioxidant. Taken together, our data showed that 7-KC promotes VSMC calcification through lysosomal-dysfunction-dependent oxidative stress.

Involvement of the adaptor protein 3 complex in lignocellulase secretion in Neurospora crassa revealed by comparative genomic screening

BACKGROUND

Lignocellulase hypersecretion has been achieved in industrial fungal workhorses such as Trichoderma reesei, but the underlying mechanism associated with this process is not well understood. Although previous comparative genomic studies have revealed that the mutagenic T. reesei strain RUT-C30 harbors hundreds of mutations compared with its parental strain QM6a, how these mutations actually contribute to the hypersecretion phenotype remains to be elucidated.

RESULTS

In this study, we systematically screened gene knockout (KO) mutants in the cellulolytic fungus Neurospora crassa, which contains orthologs of potentially defective T. reesei RUT-C30 mutated genes. Of the 86 deletion mutants screened in N. crassa, 12 exhibited lignocellulase production more than 25% higher than in the wild-type (WT) strain and 4 showed nearly 25% lower secretion. We observed that the deletion of Ncap3m (NCU03998), which encodes the μ subunit of the adaptor protein 3 (AP-3) complex in N. crassa, led to the most significant increase in lignocellulase secretion under both Avicel and xylan culture conditions. Moreover, strains lacking the β subunit of the AP-3 complex, encoded by Ncap3b (NCU06569), had a similar phenotype to ΔNcap3m, suggesting that the AP-3 complex is involved in lignocellulase secretion in N. crassa. We also found that the transcriptional abundance of major lignocellulase genes in ΔNcap3m was maintained at a relatively higher level during the late stage of fermentation compared with the WT, which might add to the hypersecretion phenotype. Finally, we found that importation of the T. reesei ap3m ortholog Trap3m into ΔNcap3m can genetically restore secretion of lignocellulases to normal levels, which suggests that the effect of the AP-3 complex on lignocellulase secretion is conserved in cellulolytic ascomycetes.

CONCLUSIONS

Using the model cellulolytic fungus N. crassa, we explored potential hypersecretion-related mutations in T. reesei strain RUT-C30. Through systematic genetic screening of 86 corresponding orthologous KO mutants in N. crassa, we identified several genes, particularly those encoding the AP-3 complex that contribute to lignocellulase secretion. These findings will be useful for strain improvement in future lignocellulase and biomass-based chemical production.

Nano-hydroxyapatite modulates osteoblast lineage commitment by stimulation of DNA methylation and regulation of gene expression

Hydroxyapatite (HA) is the primary structural component of the skeleton and dentition. Under biological conditions, HA does not occur spontaneously and therefore must be actively synthesized by mineralizing cells such as osteoblasts. The mechanism(s) by which HA is actively synthesized by cells and deposited to create a mineralized matrix are not fully understood and the consequences of mineralization on cell function are even less well understood. HA can be chemically synthesized (HAp) and is therefore currently being investigated as a promising therapeutic biomaterial for use as a functional scaffold and implant coating for skeletal repair and dental applications. Here we investigated the biological effects of nano-HAp (10 × 100 nm) on the lineage commitment and differentiation of bone forming osteoblasts. Exposure of early stage differentiating osteoblasts resulted in dramatic and sustained changes in gene expression, both increased and decreased, whereas later stage osteoblasts were much less responsive. Analysis of the promoter region one of the most responsive genes, alkaline phosphatase, identified the stimulation of DNA methylation following cell exposure to nano-HAp. Collectively, the results reveal the novel epigenetic regulation of cell function by nano-HAp which has significant implication on lineage determination as well as identifying a novel potential therapeutic use of nanomaterials.

The role of fetuin-A in mineral trafficking and deposition

Calcium and phosphate are the principle ions involved in the deposition of mineral in the human body. Inhibitors of mineralisation are essential for the prevention of ectopic mineral precipitation and deposition. In the past decade, through in vitro, in vivo and clinical observation studies, we have come to appreciate the importance of fetuin-A (Fet-A), a circulating glycoprotein, in preventing ectopic calcium phosphate mineralisation. Moreover, the detection of Fet-A-containing mineral complex, termed calciprotein particles (CPPs), has provided new ways to assess an individual's calcific risk. The pathophysiological significance of CPPs in disease states is yet to be defined, but it provides an exciting avenue to further our understanding of the development of ectopic mineralisation.

The role of autophagy in vascular biology

There is increasing interest in the role of autophagic flux in maintaining normal vessel wall biology and a growing suspicion that autophagic dysregulation may be a common pathway through which vascular aging and associated pathologies develop. Within endothelial and smooth muscle cells, diverse but important triggers that range from oxidized lipids to β-amyloid seem to stimulate autophagosome formation potently. In addition, emerging evidence links autophagy to a wide array of vascular processes ranging from angiogenesis to calcification of the vessel wall. Alterations in autophagic flux are also increasingly being implicated in disease processes that include both atherosclerosis and pulmonary hypertension. Finally, recent insights point toward an important role of autophagy in the paracrine regulation of vasoactive substances from the endothelium. Here, we review the progress in understanding how autophagy can contribute to vascular biology and the emerging strategies to target this process for therapeutic benefit.

Autophagy: an emerging therapeutic target in vascular diseases

Autophagy is a cellular catabolic process responsible for the destruction of long-lived proteins and organelles via lysosome-dependent pathway. This process is of great importance in maintaining cellular homeostasis, and deregulated autophagy has been implicated in the pathogenesis of a wide range of diseases. A growing body of evidence suggests that autophagy can be activated in vascular disorders such as atherosclerosis. Autophagy occurs under basal conditions and mediates homeostatic functions in cells but in the setting of pathological states up-regulated autophagy can exert both protective and detrimental functions. Therefore, the precise role of autophagy and its relationship with the progression of the disease need to be clarified. This review highlights recent findings regarding autophagy activity in vascular cells and its potential contribution to vascular disorders with a focus on atherogenesis. Finally, whether the manipulation of autophagy represents a new therapeutic approach to treat or prevent vascular diseases is also discussed.

Phosphate uptake-independent signaling functions of the type III sodium-dependent phosphate transporter, PiT-1, in vascular smooth muscle cells

Vascular calcification (VC) is prevalent in chronic kidney disease and elevated serum inorganic phosphate (Pi) is a recognized risk factor. The type III sodium-dependent phosphate transporter, PiT-1, is required for elevated Pi-induced osteochondrogenic differentiation and matrix mineralization in vascular smooth muscle cells (VSMCs). However, the molecular mechanism(s) by which PiT-1 promotes these processes is unclear. In the present study, we confirmed that the Pi concentration required to induce osteochondrogenic differentiation and matrix mineralization of mouse VSMCs was well above that required for maximal Pi uptake, suggesting a signaling function of PiT-1 that was independent of Pi transport. Elevated Pi-induced signaling via ERK1/2 phosphorylation was abrogated in PiT-1 deficient VSMCs, but could be rescued by wild-type (WT) and a Pi transport-deficient PiT-1 mutant. Furthermore, both WT and transport-deficient PiT-1 mutants promoted osteochondrogenic differentiation as measured by decreased SM22α and increased osteopontin mRNA expression. Finally, compared to vector alone, expression of transport-deficient PiT-1 mutants promoted VSMC matrix mineralization, but not to the extent observed with PiT-1 WT. These data suggest that both Pi uptake-dependent and -independent functions of PiT-1 are important for VSMC processes mediating vascular calcification.

Aging and uremia: Is there cellular and molecular crossover?

Many observers have noted that the morphological changes that occur in chronic kidney disease (CKD) patients resemble those seen in the geriatric population, with strikingly similar morbidity and mortality profiles and rates of frailty in the two groups, and shared characteristics at a pathophysiological level especially in respect to the changes seen in their vascular and immune systems. However, whilst much has been documented about the shared physical characteristics of aging and uremia, the molecular and cellular similarities between the two have received less attention. In order to bridge this perceived gap we have reviewed published research concerning the common molecular processes seen in aging subjects and CKD patients, with specific attention to altered proteostasis, mitochondrial dysfunction, post-translational protein modification, and senescence and telomere attrition. We have also sought to illustrate how the cell death and survival pathways apoptosis, necroptosis and autophagy are closely interrelated, and how an understanding of these overlapping pathways is helpful in order to appreciate the shared molecular basis behind the pathophysiology of aging and uremia. This analysis revealed many common molecular characteristics and showed similar patterns of cellular dysfunction. We conclude that the accelerated aging seen in patients with CKD is underpinned at the molecular level, and that a greater understanding of these molecular processes might eventually lead to new much needed therapeutic strategies of benefit to patients with renal disease.

Autophagy in Vascular Disease

Autophagy is a reparative, life-sustaining process by which cytoplasmic components are sequestered in double-membrane vesicles and degraded on fusion with lysosomal compartments. Growing evidence reveals that basal autophagy is an essential in vivo process mediating proper vascular function. Moreover, autophagy is stimulated by many stress-related stimuli in the arterial wall to protect endothelial cells and smooth muscle cells against cell death and the initiation of vascular disease, in particular atherosclerosis. Basal autophagy is atheroprotective during early atherosclerosis but becomes dysfunctional in advanced atherosclerotic plaques. Little is known about autophagy in other vascular disorders, such as aneurysm formation, arterial aging, vascular stiffness, and chronic venous disease, even though autophagy is often impaired. This finding highlights the need for pharmacological interventions with compounds that stimulate the prosurvival effects of autophagy in the vasculature. A large number of animal studies and clinical trials have indicated that oral or stent-based delivery of the autophagy inducer rapamycin or derivatives thereof, collectively known as rapalogs, effectively inhibit the basic mechanisms that control growth and destabilization of atherosclerotic plaques. Other autophagy-inducing drugs, such as spermidine or add-on therapy with widely used antiatherogenic compounds, including statins and metformin, are potentially useful to prevent vascular disease with minimal adverse effects.

Vascular calcification is coupled with phenotypic conversion of vascular smooth muscle cells through Klf5-mediated transactivation of the Runx2 promoter

Both Klf5 (Krüppel-like factor 5) and Runx2 are involved in phenotypic switching of VSMC (vascular smooth muscle cells). However, the potential link between Klf5 and Runx2 in mediating vascular calcification remains unclear. The aim of the present study was to elucidate the actual relationship between Klf5 and Runx2 in mediating VSMC calcification. We found that high Pi (phosphate) increased the expression of Klf5, which is accompanied by loss of SM α-actin and SM22α (smooth muscle 22 α), as well as gain of Runx2 expression. Overexpression of Klf5 increased, while knockdown of Klf5 decreased, Runx2 expression and calcification. Further study showed that Klf5 bound directly to the Runx2 promoter and activated its transcription. Klf5 was also induced markedly in the calcified aorta of adenine-induced uremic rats. In conclusion, we demonstrate a critical role for Klf5-mediated induction of Runx2 in high Pi -induced VSMC calcification.

Vascular calcification: Mechanisms of vascular smooth muscle cell calcification

Vascular calcification is highly prevalent and, when present, is associated with major adverse cardiovascular events. Vascular smooth muscle cells play an integral role in mediating vessel calcification by undergoing differentiation to osteoblast-like cells and generating matrix vesicles that serve as a nidus for calcium-phosphate deposition in the vessel wall. Once believed to be a passive process, it is now recognized that vascular calcification is a complex and highly regulated process that involves activation of cellular signaling pathways, circulating inhibitors of calcification, genetic factors, and hormones. This review will examine several of the key mechanisms linking vascular smooth muscle cells to vessel calcification that may be targeted to reduce vessel wall mineralization and, thereby, reduce cardiovascular risk.

Chronic kidney disease and premature ageing

Chronic kidney disease (CKD) shares many phenotypic similarities with other chronic diseases, including heart failure, chronic obstructive pulmonary disease, HIV infection and rheumatoid arthritis. The most apparent similarity is premature ageing, involving accelerated vascular disease and muscle wasting. We propose that in addition to a sedentary lifestyle and psychosocial and socioeconomic determinants, four major disease-induced mechanisms underlie premature ageing in CKD: an increase in allostatic load, activation of the 'stress resistance response', activation of age-promoting mechanisms and impairment of anti-ageing pathways. The most effective current interventions to modulate premature ageing-treatment of the underlying disease, optimal nutrition, correction of the internal environment and exercise training-reduce systemic inflammation and oxidative stress and induce muscle anabolism. Deeper mechanistic insight into the phenomena of premature ageing as well as early diagnosis of CKD might improve the application and efficacy of these interventions and provide novel leads to combat muscle wasting and vascular impairment in chronic diseases.