Leptin promotes osteoblast differentiation and mineralization of primary cultures of vascular smooth muscle cells by inhibiting glycogen synthase kinase (GSK)-3β

PARP-2 acts on ILK signaling and pharmacological targeting of PARP-2 ameliorate endometriosis in a mouse model

Endometriosis, an endocrine disorder in reproductive-aged women with an occurrence of ∼10 %, gives rise to inflammation, pelvic pain, menstrual irregularity, infertility, etc. One study demonstrated the elevated plasma level of PARP during endometriosis. Thus, we studied the role of PARP-2 during endometriosis using human endometriotic tissue and cells along with an endometriosis mouse model. We found an increased expression level of PARP-2 in the endometriotic tissue from human endometriosis patients, likewise in the endometriotic cells, 12Z and mouse model. The expression level of PARP-2 was suppressed by progesterone (P4) in the immortalized human endometriotic cells (IHECs). However, the danazol (100 mg/kg body weight) treatment reduced the lesion size, but not the expression level of PARP-2 in the endometriotic lesion from the mouse model. PARP-2 inhibition by UPF-1069 (5 mg/kg b. wt.) treatment in the mouse model of endometriosis reduced the endometriotic lesion area. During ovulation and letrozole (1 mg/kg b.wt.) treatment in the endometriosis SD rat model, the expression level of PARP-2 was high. The cell aggregation, a spheroid formation assay using IHECs was reduced by PARP-2 inhibition. The inflammatory chemokines, CCL-11 and -22, GSK-3beta and ILK were downregulated in IHECs by PARP-2 inhibitor (10 μM). Transient overexpression of ILK in endometriotic cells showed reduced levels of PARP-2 and GSK-3beta. In conclusion, PARP-2 is upregulated in the endometriotic tissue in response to estradiol (E2) and inhibition of it pharmacologically reduced the IHECs congregation and the endometriotic lesion, possibly affecting the inflammatory response via ILK-GSK-3beta, in the mouse model and human endometriotic cells.

High-Density Lipoproteins from Coronary Artery Disease and Aortic Valve Stenosis Patients Differentially Regulate Gene Expression in a Model of Cardiac Adipocytes

Previous reports have described a statistical association between high-density lipoproteins (HDL) subclasses and the expression of genes coding for pro-calcifying proteins in the epicardial adipose tissue of patients with coronary artery disease (CAD) and aortic valvular stenosis (AVS). These results suggest a causal relationship between HDL and the regulation of gene expression in epicardial adipose tissue. However, there is no experimental evidence that supports this causal relationship. Therefore, we explored the effect of HDL isolated from CAD or AVS patients on the expression of OPN, BMP2, and BMP4, genes coding for proteins related to calcification, osteopontin, and bone morphogenetic proteins -2 and -4, respectively, and LEP, UCP, and PER, coding for leptin, uncoupling protein-1, and perilipin-2, respectively, proteins that confer phenotypic characteristics to adipocytes. The experiments were performed using a novel model of cardiac adipocytes differentiated in vitro from stromal cells of rabbit cardiac adipose tissue. AVS or CAD patients' HDL differentially modulated the expression of BMP4 and LEP, whereas HDL from both kinds of patients upregulated the OPN gene expression. A high concentration of triglycerides associated to small HDL and a higher concentration of phospholipids of large HDL from CAD patients than those from AVS individuals were the most remarkable structural differences. Finally, we demonstrated that cholesterol from reconstituted HDL was internalized to the adipocytes. The regulation of genes related to the secretory activity of cardiac adipocytes mediated by HDL has clinical implications as a potential therapeutic target for the prevention and treatment of CAD and AVS. In summary, the HDL isolated from the CAD and AVS patients differentially regulated gene expression in adipocytes by a mechanism that seems to be dependent on HDL lipid internalization to the cells and structural characteristics of the lipoproteins.

Advances in the mechanisms of vascular calcification in chronic kidney disease

Vascular calcification (VC) is common in patients with advanced chronic kidney disease (CKD).A series of factors, such as calcium and phosphorus metabolism disorders, uremic toxin accumulation, inflammation and oxidative stress and cellular senescence, cause osteoblast-like differentiation of vascular smooth muscle cells, secretion of extracellular vesicles, and imbalance of calcium regulatory factors, which together promote the development of VC in CKD. Recent advances in epigenetics have provided better tools for the investigation of VC etiology and new approaches for finding more accurate biomarkers. These advances have not only deepened our understanding of the pathophysiological mechanisms of VC in CKD, but also provided valuable clues for the optimization of clinical predictors and the exploration of potential therapeutic targets. The aim of this article is to provide a comprehensive overview of the pathogenesis of CKD VC, especially the new advances made in recent years, including the various key factors mentioned above. Through the comprehensive analysis, we expect to provide a solid theoretical foundation and research direction for future studies targeting the specific mechanisms of CKD VC, the establishment of clinical predictive indicators and the development of potential therapeutic strategies.

Metabolites and metabolism in vascular calcification: links between adenosine signaling and the methionine cycle

The global population of individuals with cardiovascular disease is expanding, and a key risk factor for major adverse cardiovascular events is vascular calcification. The pathogenesis of cardiovascular calcification is complex and multifaceted, with external cues driving epigenetic, transcriptional, and metabolic changes that promote vascular calcification. This review provides an overview of some of the lesser understood molecular processes involved in vascular calcification and discusses the links between calcification pathogenesis and aspects of adenosine signaling and the methionine pathway; the latter of which salvages the essential amino acid methionine, but also provides the substrate critical for methylation, a modification that regulates the function and activity of DNA and proteins. We explore the complex and dynamic nature of osteogenic reprogramming underlying intimal atherosclerotic calcification and medial arterial calcification (MAC). Atherosclerotic calcification is more widely studied; however, emerging studies now show that MAC is a significant pathology independent from atherosclerosis. Furthermore, we emphasize metabolite and metabolic-modulating factors that influence vascular calcification pathogenesis. Although the contributions of these mechanisms are more well-define in relation to atherosclerotic intimal calcification, understanding these pathways may provide crucial mechanistic insights into MAC and inform future therapeutic approaches. Herein, we highlight the significance of adenosine and methyltransferase pathways as key regulators of vascular calcification pathogenesis.

Melanocortin-4 receptor in macrophages attenuated angiotensin II-induced abdominal aortic aneurysm in mice

Obesity is recognized as an independent risk factor for abdominal aortic aneurysm (AAA). While mutations in the melanocortin-4 receptor (MC4R) gene is the most common cause of obesity caused by mutations in a single gene, the link between MC4R function and vascular disease has still remained unclear. Here, by using melanocortin-4 receptor (MC4R) deficient mice, we confirmed MC4R deficiency promotes AAA and atherosclerosis. We demonstrated the contribution of two novel factors towards vascular vulnerability in this model: leptin signaling in vascular smooth muscle cells (VSMCs) and loss of MC4R signaling in macrophages. Leptin was shown to promote vascular vulnerability via PI3K-dependent upregulation of Spp1 expression in VSMC. Additionally, Ang II-induced AAA incidence was significantly reduced when MC4R gene expression was myeloid cell-specifically rescued in MC4R deficient (MC4RTB/TB) mice. Ex vivo analysis showed a suppression in NF-κB activity in bone marrow-derived macrophages from LysM(+);MC4RTB/TB mice compared to LysM(-);MC4RTB/TB mice, which exaggerates with endogenous MC4R ligand treatment; α-MSH. These results suggest that MC4R signaling in macrophages attenuates AAA by inhibiting NF-κB activity and subsequent vascular inflammation.

Leptin in Atherosclerosis: Focus on Macrophages, Endothelial and Smooth Muscle Cells

Increasing adipose tissue mass in obesity directly correlates with elevated circulating leptin levels. Leptin is an adipokine known to play a role in numerous biological processes including regulation of energy homeostasis, inflammation, vascular function and angiogenesis. While physiological concentrations of leptin may exhibit multiple beneficial effects, chronically elevated pathophysiological levels or hyperleptinemia, characteristic of obesity and diabetes, is a major risk factor for development of atherosclerosis. Hyperleptinemia results in a state of selective leptin resistance such that while beneficial metabolic effects of leptin are dampened, deleterious vascular effects of leptin are conserved attributing to vascular dysfunction. Leptin exerts potent proatherogenic effects on multiple vascular cell types including macrophages, endothelial cells and smooth muscle cells; these effects are mediated via an interaction of leptin with the long form of leptin receptor, abundantly expressed in atherosclerotic plaques. This review provides a summary of recent in vivo and in vitro studies that highlight a role of leptin in the pathogenesis of atherosclerotic complications associated with obesity and diabetes.

Association Between Liver Fat and Bone Density is Confounded by General and Visceral Adiposity in a Community-Based Cohort

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) is associated with low bone mineral density (BMD); however, it is not known whether early-stage NAFLD may be associated with BMD after accounting for BMI or visceral adipose tissue (VAT).

METHODS

This was a cross-sectional study of 3,462 Framingham Heart Study participants who underwent computed tomographic measurement of liver fat, VAT volume, volumetric spine BMD, vertebral cross-sectional area (CSA), and vertebral compressive strength. This study excluded heavy alcohol consumers. Multivariable linear regression models were used to assess the association between NAFLD and volumetric BMD, CSA, and vertebral compressive strength after accounting for covariates, including BMI or VAT.

RESULTS

A total of 2,253 participants (mean age, 51.2  [SD 10.7] years; 51.1% women) were included. In multivariable-adjusted models, positive associations between NAFLD and integral BMD, trabecular BMD, and vertebral compressive strength were observed. However, results were attenuated and no longer significant after additionally adjusting for BMI or VAT. NAFLD was observed to be weakly associated with a lower vertebral CSA in adjusted models.

CONCLUSIONS

In a community-based cohort, the associations between NAFLD and BMD and vertebral strength were confounded by BMI and VAT. However, NAFLD was associated with a reduced vertebral CSA in adjusted models.

Role of Uremic Toxins in Early Vascular Ageing and Calcification

In patients with advanced chronic kidney disease (CKD), the accumulation of uremic toxins, caused by a combination of decreased excretion secondary to reduced kidney function and increased generation secondary to aberrant expression of metabolite genes, interferes with different biological functions of cells and organs, contributing to a state of chronic inflammation and other adverse biologic effects that may cause tissue damage. Several uremic toxins have been implicated in severe vascular smooth muscle cells (VSMCs) changes and other alterations leading to vascular calcification (VC) and early vascular ageing (EVA). The above mentioned are predominant clinical features of patients with CKD, contributing to their exceptionally high cardiovascular mortality. Herein, we present an update on pathophysiological processes and mediators underlying VC and EVA induced by uremic toxins. Moreover, we discuss their clinical impact, and possible therapeutic targets aiming at preventing or ameliorating the harmful effects of uremic toxins on the vasculature.

Zhuang-Gu-Fang Treats Osteoporosis in Ovariectomized Rats by Increasing the Osteogenesis-Related Factors Leptin, Ghrelin, and PYY

Zhuang-Gu-Fang is a Chinese medicinal compound mixture, which is mainly composed of traditional remedies like the Epimedium Herb, Astragalus, and Eucommia among many others. The study is aimed at investigating the therapeutic effect of Zhuang-Gu-Fang in ovariectomized rats. Fifty six-month-old Wistar rats were randomly selected and divided into 5 groups (n = 10), namely, model group, positive group, low-dose Chinese medicine group, medium-dose group, and high-dose group. Another 10 sham operation Wistar rats were taken as a negative control group. After 3 months of intervention, the bone mineral density (BMD), procollagen type I N-peptide (PINP), beta C-terminal cross-linked telopeptides of type I collagen carboxyl-terminal peptide (β-CTX), Leptin, Ghrelin, and Peptide YY (PYY) of each group were measured. Besides, the ultrastructure of bone structure and osteoblasts was also observed by transmission electron microscopy. Western blot method was used to detect the expression levels of Leptin and Ghrelin in bone tissue, and RT-PCR detected the mRNA expression levels of Leptin and Ghrelin. BMD test indicated that Zhuang-Gu-Fang could effectively prevent the loss of tibia bone in ovariectomized rats. Histomorphology analysis showed that Zhuang-Gu-Fang could preserve trabecular bone structure integrity and improve osteoblast ultrastructure. Notably, the study found out that Zhuang-Gu-Fang worked through balancing the bone metabolism via increasing bone formation/resorption ratio. Additionally, Zhuang-Gu-Fang highlighted the recovery effects in multiple levels of osteogenesis- and osteanagenesis-related factors Leptin, Ghrelin, and PYY. Conclusively, the study proved the therapeutic potential of the Zhuang-Gu-Fang for postmenopausal osteoporosis (PMOP) and further revealed that its therapeutic effect was related to the balance of bone metabolism and the recovery effects of bone-related factors Leptin, Ghrelin, and PYY.

Uremic Toxins and Vascular Calcification-Missing the Forest for All the Trees

The cardiorenal syndrome relates to the detrimental interplay between the vascular system and the kidney. The uremic milieu induced by reduced kidney function alters the phenotype of vascular smooth muscle cells (VSMC) and promotes vascular calcification, a condition which is strongly linked to cardiovascular morbidity and mortality. Biological mechanisms involved include generation of reactive oxygen species, inflammation and accelerated senescence. A better understanding of the vasotoxic effects of uremic retention molecules may reveal novel avenues to reduce vascular calcification in CKD. The present review aims to present a state of the art on the role of uremic toxins in pathogenesis of vascular calcification. Evidence, so far, is fragmentary and limited with only a few uremic toxins being investigated, often by a single group of investigators. Experimental heterogeneity furthermore hampers comparison. There is a clear need for a concerted action harmonizing and standardizing experimental protocols and combining efforts of basic and clinical researchers to solve the complex puzzle of uremic vascular calcification.

The Role of Sclerostin in Bone and Ectopic Calcification

Sclerostin, a 22-kDa glycoprotein that is mainly secreted by the osteocytes, is a soluble inhibitor of canonical Wnt signaling. Therefore, when present at increased concentrations, it leads to an increased bone resorption and decreased bone formation. Serum sclerostin levels are known to be increased in the elderly and in patients with chronic kidney disease. In these patient populations, there is a high incidence of ectopic cardiovascular calcification. These calcifications are strongly associated with cardiovascular morbidity and mortality. Although data are still controversial, it is likely that there is a link between ectopic calcification and serum sclerostin levels. The main question, however, remains whether sclerostin exerts either a protective or deleterious role in the ectopic calcification process.

Association Between Serum Leptin Level and Calcific Aortic Valve Disease

Background The pathophysiological process of calcific aortic valve disease (CAVD) is similar to that of atherosclerosis. Leptin accelerates the process of atherosclerosis. We sought to examine the relationship between leptin and CAVD. Methods and Results Serum leptin was measured in 397 consecutive patients undergoing standard transthoracic echocardiography and Doppler flow imaging. Multiple logistic regression analyses were used to assess the association between leptin and CAVD. Western blotting was performed to detect the expression of phosphorylated and total extracellular signal-regulated kinase. Serum leptin (median) was higher in 200 patients with CAVD than that in 197 non-CAVD controls (20.07 versus 9.03 ng/mL; P<0.01). Leptin correlated positively with age (r=0.37, P<0.01) and negatively with estimated glomerular filtration rate (r=-0.37, P<0.01). Multivariate analysis indicated that elevated leptin was an independent determinant for the presence of CAVD (P<0.01). Receiver-operating characteristic curve analysis of leptin to detect the presence of CAVD showed that the area under the curve was 0.74 (95% CI, 0.69-0.79; P<0.01). The diagnostic value of leptin for the detection of CAVD was higher among younger patients (aged ≤65 years) or those with at least mildly reduced renal function (estimated glomerular filtration rate ≤82.06 mL/min per 1.73 m²). The activation of extracellular signal-regulated kinase 1/2 was stronger in calcific aortic valves than in normal aortic valves. Conclusions Elevated leptin is associated with the presence of CAVD, especially among younger patients or those with renal dysfunction.

Energy-Dense Diets and Mineral Metabolism in the Context of Chronic Kidney Disease⁻Metabolic Bone Disease (CKD-MBD)

The aim of this paper is to review current knowledge about the interactions of energy-dense diets and mineral metabolism in the context of chronic kidney disease–metabolic bone disease (CKD-MBD). Energy dense-diets promote obesity and type II diabetes, two well-known causes of CKD. Conversely, these diets may help to prevent weight loss, which is associated with increased mortality in advanced CKD patients. Recent evidence indicates that, in addition to its nephrotoxic potential, energy-dense food promotes changes in mineral metabolism that are clearly detrimental in the context of CKD-MBD, such as phosphorus (P) retention, increased concentrations of fibroblast growth factor 23, decreased levels of renal klotho, and reduction in circulating concentrations of calcitriol. Moreover, in uremic animals, a high fat diet induces oxidative stress that potentiates high P-induced vascular calcification, and these extraskeletal calcifications can be ameliorated by oral supplementation of vitamin E. In conclusion, although energy-dense foods may have a role in preventing undernutrition and weight loss in a small section of the CKD population, in general, they should be discouraged in patients with renal disease, due to their impact on P load and oxidative stress.

Novel insights into the relationship between nonalcoholic fatty liver disease and osteoporosis

Excess fat deposition and insulin resistance are considered the main risk factors for nonalcoholic fatty liver disease (NAFLD), and therefore, not surprisingly, the global prevalence of NAFLD increases in parallel with both obesity and type 2 diabetes. Although deterioration of bone homeostasis in patients with NAFLD is commonly observed, its etiology has not been fully elucidated yet. It was shown in several studies that bone tissue seems to be independently associated with NAFLD. A mechanistic perspective puts the liver at the center of mutual interdependencies obviously involving adipose tissue and muscles and also the bone matrix and bone cells, which are relatively novel. In this review, various pathophysiological mechanisms and possible mediating molecules that may interplay between NAFLD and bone tissue are described. Chronic inflammation, vitamin D3, growth hormone, insulin-like growth factor 1, osteopontin, fetuin-A, irisin, osteocalcin, and osteoprotegerin from osteoblasts have been proposed as mediators of mutual interactions among the skeleton, fatty tissue, and liver. Although to date there are still many issues that have not been elucidated, growing evidence suggests that screening and surveillance of bone mineral density in patients with NAFLD should be considered in future strategies and guidelines for NAFLD management.

Role of PKB/SGK-dependent phosphorylation of GSK-3α/β in vascular calcification during cholecalciferol overload in mice

Medial vascular calcification is a highly regulated process involving osteo-/chondrogenic transdifferentiation of vascular smooth muscle cells. Both, protein kinase B (PKB) and serum- and glucocorticoid-inducible kinase 1 (SGK1) are involved in the intracellular signaling of vascular calcification and both phosphorylate and inactivate glycogen synthase kinase 3 (GSK-3). The present study explored whether PKB/SGK-dependent phosphorylation of GSK-3α/β is involved in vascular calcification. Experiments were performed in Gsk-3α/β double knockin mice lacking functional PKB/SGK phosphorylation sites (gsk-3^KI) and corresponding wild-type mice (gsk-3^WT) following high-dosed cholecalciferol treatment as well as ex vivo in aortic ring explants from gsk-3^KI and gsk-3^WT mice treated without and with phosphate. In gsk-3^WT mice, high-dosed cholecalciferol induced vascular calcification and aortic osteo-/chondrogenic signaling, shown by increased expression of osteogenic markers Msx2, Cbfa1 and tissue-nonspecific alkaline phosphatase (Alpl). All these effects were suppressed in aortic tissue from gsk-3^KI mice. Cholecalciferol decreased aortic Gsk-3α/β phosphorylation (Ser^21/9) in gsk-3^WT mice, while no phosphorylation was observed in gsk-3^KI mice. Moreover, the mRNA expression of type III sodium-dependent phosphate transporter (Pit1) and plasminogen activator inhibitor 1 (Pai1) was increased following cholecalciferol treatment in aortic tissue of gsk-3^WT mice, effects again blunted in gsk-3^KI mice. In addition, phosphate treatment induced mineral deposition and osteogenic markers expression in aortic ring explants from gsk-3^WT mice, effects reduced in aortic ring explants from gsk-3^KI mice. In conclusion, vascular PKB/SGK-dependent phosphorylation of GSK-3α/β contributes to the osteoinductive signaling leading to vascular calcification.

Involvement of GSK3/β-catenin in the action of extracellular ATP on differentiation of primary cultures from rat calvaria into osteoblasts

Modulation of purinergic receptors play an important role in the regulation of osteoblasts differentiation and bone formation. In this study, we investigated the involvement of the GSK3/βcatenin signaling in the action of ATPγ-S on osteogenic differentiation of primary cell cultures from rat calvaria. Our results indicate that the cell treatment with 10 or 100 µM ATPγ-S for 96 h increase the cytoplasmic levels of β-catenin and its translocation to nucleus respect to control. A similar effect was observed after cell treatment with the GSK3 inhibitor LiCl (10 mM). Cell treatments with 4-10 mM LiCl significantly stimulated ALP activity respect to control at 4 and 7 days, suggesting that inhibition of GSK-3 mediates osteoblastic differentiation of rat calvarial cells. Effects comparison between ATP and LiCl shown that ALP activity was significantly increased by 10 µM ATPγ-S and decreased by 10 mM LiCl at 10 day of treatment, respect to control, suggesting that the effect of ATPγ-S was less potent but more persistent than of LiCl in stimulating this osteogenic marker in calvarial cells. Cell culture mineralization was significantly increased by treatment with 10 µM ATPγ-S and decreased by 10 mM LiCl, respect to control. In together, these results suggest that GSK3 inhibition is involved in ATPγ-S action on rat calvarial cell differentiation into osteoblasts at early steadies. In addition such inhibition by LiCl appear promote osteoblasts differentiation at beginning but has a deleterious effect on its function at later steadies as the extracellular matrix mineralization.

The association of serum adiponectin with abdominal aortic calcification in Japanese male hemodialysis patients: a cross-sectional observational study

The negative relation of serum adiponectin to atherosclerosis becomes a positive association in patients with chronic kidney disease (CKD). We conducted a small-scale cross-sectional observational study, in 101 Japanese male hemodialysis patients, to examine the relationship of serum adiponectin and leptin to abdominal aortic calcification (AAC). The presence of AAC was evaluated from simple X-ray radiographs of the left lateral abdomen. Serum adiponectin was significantly higher in AAC-positive patients [18.8 (13.0-28.1) μg/mL] than in AAC-negative patients [15.4 (8.9-22.8) μg/mL] (p = 0.03), whereas serum leptin did not differ significantly between the two groups. Multiple logistic regression analysis showed that log adiponectin, but not log leptin, was independently and significantly associated in a positive manner with AAC (odds ratio: 16.31, 95% confidence interval: 1.70-156.41, p = 0.02), after adjustment for age, body weight, percentage body fat, hemodialysis duration, prevalence of diabetes mellitus, and other risk factors. In conclusion, we found a positive and independent association of serum adiponectin with AAC in male hemodialysis patients, indicating that the reversed association between serum adiponectin and atherosclerosis in patients with CKD dose not result from increased serum adiponectin due to the impaired urinary secretion.

Leptin induces osteoblast differentiation of human valvular interstitial cells via the Akt and ERK pathways

AIMS

Calcific aortic valve disease (CAVD) affects 2-6% of the population over 65 years, and age, gender, smoking, overweight, dyslipidemia, diabetes contribute to the development of this disease. CAVD results, in part, from the osteoblast differentiation of human valvular interstitial cells (VICs). This study aims to elucidate the effects of leptin on osteoblast phenotype of VICs and the signalling pathways involved.

METHODS

Patients who underwent aortic valve replacement for CAVD (n = 43) were included in this study. Patients with coronary artery disease (CAD) without CAVD (n = 129) were used as controls.

RESULTS

Patients with CAVD had higher serum leptin concentrations than CAD patients (p = 0.002). Leptin was found in calcific aortic valves, with higher concentrations in calcified versus non-calcified zones (p = 0.01). Chronic leptin stimulation of human VICs enhanced alkaline phosphatase (ALP) activity and ALP, BMP-2 and RUNX2 expression and decreased osteopontin expression. Moreover, inhibiting Akt or ERK during leptin stimulation lowered the expression of osteoblast markers in VIC.

CONCLUSIONS

Taken together, these findings indicate that leptin plays a critical role in CAVD development by promoting osteoblast differentiation of human aortic VICs in an Akt- and ERK-dependent manner. This study highlights the role of leptin in CAVD development, and further studies are needed to determine whether reducing circulating leptin levels or blocking leptin actions on VICs is efficient to slow CAVD progression.

Leptin Overexpression in Bone Marrow Stromal Cells Promotes Periodontal Regeneration in a Rat Model of Osteoporosis

BACKGROUND

Osteoporosis is associated with widespread periodontitis and impaired periodontal healing. However, there is a lack of information about the outcomes of regenerative approaches under the influence of osteoporosis. This study investigates the effect of leptin (LEP) overexpression on the regenerative potential of bone marrow stromal cells (BMSCs) in an osteoporotic rat periodontal fenestration defect model.

METHODS

Rat BMSCs were transfected with adenoviruses harboring the human (h)LEP gene. Cell proliferation and osteogenic differentiation were evaluated. A β-tricalcium phosphate scaffold seeded with transfected cells was implanted into nude mice to investigate ectopic osteogenesis and into an osteoporotic rat defect to study periodontal regeneration. Regenerated periodontal and bone-like tissues were analyzed by histologic methods.

RESULTS

hLEP overexpression induced osteogenic differentiation of BMSCs as evidenced by the upregulation of osteogenesis-related genes such as Runt-related transcription factor 2, alkaline phosphatase (ALP), and collagen Type I, as well as increased ALP activity and enhanced mineralization. Mice implanted with hLEP-BMSC-containing scaffolds showed more extensive formation of bone-like tissue than those in other groups. Periodontal defects were also filled to a greater degree when treated with hLEP-BMSCs and contained cementum and a well-organized periodontal ligament after 10 and 28 days.

CONCLUSION

hLEP overexpression in BMSCs can stimulate periodontal regeneration in osteoporotic conditions and might be a promising strategy for periodontal regeneration in patients with osteoporosis.

Nonalcoholic fatty liver disease and decreased bone mineral density: is there a link?

PURPOSE

Liver diseases are associated with decreased bone mineral density (BMD) and evidence suggests that nonalcoholic fatty liver disease (NAFLD) affects several extra-hepatic organs, interacting with the regulation of multiple endocrine and metabolic pathways. This review focuses on the rapidly expanding body of evidence that supports a strong association between NAFLD and the risk of decreased BMD, expression of low bone mass (osteoporosis), or reduced mineralization (osteomalacia).

METHODS

We identified studies by searching PubMed for original articles published in English through March 2015 using the keywords "nonalcoholic fatty liver disease" or "fatty liver" combined with "bone mineral density", "osteoporosis", or "osteomalacia".

RESULTS

Recent cross-sectional and case-control studies involving both adults and children have consistently shown that patients with NAFLD exhibit a greater prevalence of decreased BMD compared with age-, sex-, and body mass index-matched healthy controls. Accumulating clinical and experimental evidence suggests that NAFLD may contribute to the pathophysiology of low BMD, possibly through the direct contribution of NAFLD to whole-body and hepatic insulin resistance and/or the systemic release of multiple pro-inflammatory, pro-coagulant, and pro-fibrogenic mediators.

CONCLUSIONS

Although more research is needed before firm conclusions can be drawn, it appears that there is a non-chance, statistical association between NAFLD and low BMD. This finding argues for more careful monitoring and evaluation of BMD among patients with NAFLD. The potential contribution of NAFLD itself to the development and progression of decreased BMD warrants further study.

Increased osteogenesis in osteoporotic bone marrow stromal cells by overexpression of leptin

Osteoporosis leads to increased bone fractures and net bone loss, in part because of the dysfunction of bone marrow stromal cells (BMSCs). Leptin is an adipokine that plays important roles in many biological processes, including the regulation of the actions of mesenchymal stem cells. Our aim is to investigate the osteogenic effects of leptin in osteoporotic BMSCs in vitro and in vivo. The leptin gene was transferred into BMSCs isolated from osteoporotic rats by using recombinant adenoviruses. Once the gene and protein expression of leptin had been confirmed, MTT assays were performed; leptin overexpression was confirmed not to affect the viability of osteoporotic BMSCs. However, alkaline phosphatase (ALP) activity measurements, Alizarin red staining and analyses by quantitative real-time reverse transcription with the polymerase chain reaction revealed that leptin upregulated ALP activity, mineral deposition and the mRNA levels of runt-related transcription factor 2, ALP and collagen type І. Lastly, the effects of leptin on osteogenic differentiation were assessed in vivo. Cells transfected with leptin exhibited increased osteogenic differentiation and enhanced formation of bone-like structures. This study thus reveals, for the first time, that the overexpression of leptin in osteoporotic BMSCs (1) enhances their capacity to differentiate into osteoblasts and to form bone-like tissue and (2) might be a useful skeletal regenerative therapy in osteoporotic patients.

The hunger games of skeletal metabolism

Gastrointestinal peptides and adipokines are critical signalling molecules involved in controlling whole-body energy homeostasis. These circulating hormones regulate a variety of biological responses such as hunger, satiety and glucose uptake. In vivo experiments have established that these hormones also regulate bone metabolism, while associations between these hormones and bone mass have been observed in human clinical studies. With a focus on recent research, this review aims to describe the roles that gastrointestinal peptides (ghrelin, peptide YY, glucose-dependent insulinotropic polypeptide, glucagon-like peptide 1 and glucagon-like peptide 2) and adipokines (leptin and adiponectin) have in bone metabolism and to examine their effects on bone in situations of altered metabolism, such as obesity. As the prevalence of obesity continues to increase, there is a growing interest in understanding the interactions between nutritional regulators from the gut and adipose tissue and their influence on bone mass.

Emerging regulators of vascular smooth muscle cell function in the development and progression of atherosclerosis

After a period of relative senescence in the field of vascular smooth muscle cell (VSMC) research with particular regards to atherosclerosis, the last few years has witnessed a resurgence, with extensive research re-assessing potential molecular mechanisms and pathways that modulate VSMC behaviour within the atherosclerotic-prone vessel wall and the atherosclerotic plaque itself. Attention has focussed on the pathological contribution of VSMC in plaque calcification; systemic and local mediators such as inflammatory molecules and lipoproteins; autocrine and paracrine regulators which affect cell-cell and cell to matrix contacts alongside cytoskeletal changes. In this brief focused review, recent insights that have been gained into how a myriad of recently identified factors can influence the pathological behaviour of VSMC and their subsequent contribution to atherosclerotic plaque development and progression has been discussed. An overriding theme is the mechanisms involved in the alterations of VSMC function during atherosclerosis.

Adipocyte induced arterial calcification is prevented with sodium thiosulfate

BACKGROUND

Calcification can occur in fat in multiple clinical conditions including in the dermis, breasts and in the abdomen in calciphylaxis. All of these are more common in patients with advanced kidney disease. Clinically, hyperphosphatemia and obesity are risk factors. Thus we tested the hypothesis that adipocytes can calcify in the presence of elevated phosphorus and/or that adipocytes exposed to phosphorus can induce vascular smooth muscle cell (VSMC) calcification.

METHODS

3T3-L1 preadipocytes were induced into mature adipocytes and then treated with media containing high phosphorus. Calcification was assessed biochemically and PCR performed to determine the expression of genes for osteoblast and adipocyte differentiation. Adipocytes were also co-cultured with bovine VSMC to determine paracrine effects, and the efficacy of sodium thiosulfate was determined.

RESULTS

The results demonstrated that high phosphorus induced the calcification of differentiated adipocytes with increased expression of osteopontin, the osteoblast transcription factor Runx2 and decreased expression of adipocyte transcription factors peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT-enhancer-binding protein α (CEBPα), indicating that high phosphorus led to a phenotypic switch of adipocytes to an osteoblast like phenotype. Sodium thiosulfate, dose dependently decreased adipocyte calcification and inhibited adipocyte induced increase of VSMC calcification. Co-culture studies demonstrated that adipocytes facilitated VSMC calcification partially mediated by changes of secretion of leptin and vascular endothelial growth factor (VEGF) from adipocytes.

CONCLUSION

High phosphorus induced calcification of mature adipocytes, and adipocytes exposed to elevated phosphorus can induce calcification of VSMC in a paracrine manner. Sodium thiosulfate inhibited this calcification and decreased the secretin of leptin and VEGF from adipocytes. These results suggest that adipocyte exposure to elevated phosphorus may be a pathogenic factor in calcification observed in the skin in calciphylaxis and other diseases.

Vitamin E protection of obesity-enhanced vascular calcification in uremic rats

This study aimed to determine the extent of extraskeletal calcification in uremic Zucker rats, by comparing obese and lean phenotypes, and to evaluate the influence of vitamin E (VitE) on the development of calcifications in both uremic rats and human vascular smooth muscle cells (HVSMCs) cultured in vitro. Zucker rats of lean and obese phenotypes with normal renal function [control (C); C-lean and C-obese groups] and with uremia [5/6 nephrectomy (Nx); Nx-lean and Nx-obese groups] and uremic rats treated with VitE (Nx-lean + VitE and Nx-obese + VitE groups) were studied. Uremic groups were subjected to Nx, fed a 0.9% phosphorus diet, and treated with calcitriol (80 ng/kg ip). The aortic calcium concentration was significantly higher ( P < 0.05) in Nx-obese rats (10.0 ± 2.1 mg/g tissue) than in Nx-lean rats (3.6 ± 1.3 mg/g tissue). A decrease in plasma glutathione peroxidase activity was observed in Nx-obese rats compared with Nx-lean rats (217.2 ± 18.2 vs. 382.3 ± 15.5 nmol·min−1·ml−1, P < 0.05). Treatment with VitE restored glutathione peroxidase activity and reduced the aortic calcium concentration to 4.6 ± 1.3 mg/g tissue. The differences in mineral deposition between Nx-lean, Nx-obese, Nx-lean + VitE, and Nx-obese + VitE rats were also evidenced in other soft tissues. In HVSMCs incubated with high phosphate, VitE also prevented oxidative stress and reduced calcium content, bone alkaline phosphatase, and gene expression of core-binding factor-α1. In conclusion, uremic obese rats develop more severe calcifications than uremic lean rats and VitE reduces oxidative stress and vascular calcifications in both rats and cultures of HVSMCs.

Leptin promotes the osteoblastic differentiation of vascular smooth muscle cells from female mice by increasing RANKL expression

Arterial calcification is a complex and active regulated process, which results from a process of osteoblastic differentiation of vascular smooth muscle cells (VSMCs). Leptin, the product of the ob gene, mainly regulates food intake and energy expenditure and recently has been considered to be correlated with the arterial calcification. However, the mechanisms of the effects of leptin on osteoblastic differentiation of VSMCs are unknown. We used calcifying vascular smooth muscle cells (CVSMCs) as a model to investigate the relationship between leptin and the osteoblastic differentiation of CVSMCs and the signaling pathways involved. Our experiments demonstrated that leptin could increase expression of receptor activator of nuclear factor-κB ligand (RANKL) and bone morphogenetic protein 4 (BMP4), as well as alkaline phosphatase (ALP) activity, runt-related transcription factor 2 expression, calcium deposition, and the formation of mineralized nodules in CVSMCs. Suppression of RANKL with small interfering RNA abolished the leptin-induced ALP activity and BMP4 expression in CVSMCs. Leptin could activate the ERK1/2 and phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. Furthermore, pretreatment with the ERK inhibitor PD98059 and the PI3K inhibitor LY294002 abolished leptin-induced RANKL expression and blocked the promotion of ALP activity of CVSMCs. Silencing of the leptin receptor OB-Rb with small interfering RNA abolished leptin-induced activation of ERK and Akt and the expression of RANKL and reversed the effects of leptin on ALP activity. Meanwhile, addition of Noggin (the BMP4 inhibitor) blunted the effect of leptin on ALP activity. These results show that leptin can promote osteoblastic differentiation of CVSMCs by the OB-Rb/ERK1/2/RANKL-BMP4 and OB-Rb/PI3K/Akt/RANKL-BMP4 pathways.

Comparison of pro-inflammatory cytokines and bone metabolism mediators around titanium and zirconia dental implant abutments following a minimum of 6 months of clinical function

OBJECTIVES

Dental implant abutments are fundamental prosthetic components within dentistry that require optimal biocompatibility. The primary aim of this cross-sectional study was to preliminarily assess differences in the pro-inflammatory cytokine and bone metabolism mediator protein expression in the peri-implant crevicular fluid (PICF) adjacent to transmucosal abutments.

MATERIAL AND METHODS

Abutments were fabricated from either titanium or zirconia in patients previously receiving single-tooth implant therapy. All subjects sampled in this study had an identical implant system and implant-abutment connection. Participants (n = 46) had an average time of clinical function for 22 months (6.2-72.8 months, ±SD 17 months) and received a clinical and radiographic examination of the implant site at the time of PICF sampling using a paper strip-based sampling technique. Cytokine, chemokine, and bone metabolism mediator quantities (picograms/30 s) were determined using a commercial 22-multiplexed fluorescent bead-based immunoassay instrument. A total of 19 pro-inflammatory cytokines and seven bone metabolism mediators were evaluated.

RESULTS

Multivariable analyses provided no evidence of a group (titanium or zirconia), gender, or age effect with regard to the expression of pro-inflammatory mediators evaluated. Significant (P = 0.022) differences were observed for the bone mediator leptin, with titanium abutments demonstrating significantly elevated levels in comparison with zirconia. Osteopontin demonstrated a significant (P = 0.0044) correlation with age of the subjects.

CONCLUSIONS

No significant differences in pro-inflammatory cytokine or bone metabolism mediator profiles were observed biochemically, with the exception of leptin, for the abutment biomaterials of titanium or zirconia The molecular PICF findings support the observed clinical biocompatibility of both titanium and zirconia abutments.

Adiponectin is a candidate biomarker of lower extremity bone density in men with chronic spinal cord injury

Adipose tissue is a major regulator of bone metabolism and in the general population obesity is associated with greater bone mineral density (BMD). However, bone-fat interactions are multifactorial, and may involve pathways that influence both bone formation and resorption with competing effects on the skeleton. One such pathway involves adipocyte production of adipokines that regulate bone metabolism. In this study we determined the association between BMD, walking status, and circulating adipokines (adiponectin and leptin) in 149 men with chronic spinal cord injury (SCI). Although adipokine levels did not vary significantly based on walking status, there was a significant inverse association between adiponectin and BMD in wheelchair users independent of body composition. We found no association between adiponectin and BMD in the walkers and no association between leptin and BMD in either group. These findings suggest that for subjects with chronic SCI, walking may mitigate the effect of adiponectin mediated bone loss. For wheelchair users, adipose-derived adiponectin may contribute to SCI-induced osteoporosis because the osteoprotective benefits of obesity appear to require mechanical loading during ambulation.

Interactions among bone, liver, and adipose tissue predisposing to diabesity and fatty liver

Growing epidemiological evidence connects obesity and its complications, including metabolic syndrome, diabetes, and nonalcoholic fatty liver disease (NAFLD) to reduced bone health and osteoporosis. Parallel to human studies, experimental data disclosed a complex network of interaction among adipose tissue, the liver, and the bone, which reciprocally modulate the function of each other. The main mediators of such crosstalk include hormonal/cytokine signals from the bone (osteopontin, osteocalcin, and osteoprotegerin), the liver (fetuin-A), and adipose tissue [leptin, tumor necrosis factor-α (TNF-α), and adiponectin]. Dysregulation of this network promotes the development of diabesity, NAFLD, and osteoporosis. We will review recent advances in understanding the mechanisms of bone-liver-adipose tissue interaction predisposing to obesity, diabetes, NAFLD, and osteoporosis and their potential clinical implications.