Endothelins inhibit the mineralization of osteoblastic MC3T3-E1 cells through the A-type endothelin receptor

Endothelin-1 differentially directs lineage specification of adipose- and bone marrow-derived mesenchymal stem cells

Blood vessels composed of endothelial cells (ECs) contact with mesenchymal stem cells (MSCs) in different tissues, suggesting possible interaction between these 2 types of cells. We hypothesized that endothelin-1 (ET1), a secreted paracrine factor of ECs, can differentially direct the lineages of adipose-derived stem cells (ASCs) and bone marrow-derived MSCs (BMSCs). Predifferentiated ASCs and BMSCs were treated with ET1 for 2 cell passages and then induced for multilineage differentiation. Our results showed that adipogenesis of ET1-pretreated ASCs and osteogenesis of ET1-pretreated BMSCs were increased compared to those of control cells. The effect of ET1 on enhancing adipogenesis of ASCs and osteogenesis of BMSCs was attenuated by blocking endothelin receptor type A (ETAR) and/or endothelin receptor type B (ETBR). Western blot analysis indicated that regulation by ET1 was mediated through activation of the protein kinase B and ERK1/2 signaling pathways. We analyzed subpopulations of ASCs and BMSCs with or without ETAR and/or ETBR, and we found that ETAR⁺/ETBR^- and ETAR^-/ETBR⁺ subpopulations of ASCs and those of BMSCs pretreated with ET1 were prone to turning into adipocytes and osteoblasts, respectively, after differentiation induction. Our findings provide insight into the differential regulation of MSC specification by ET1, which may help develop viable approaches for tissue regeneration.-Lee, M.-S., Wang, J., Yuan, H., Jiao, H., Tsai, T.-L., Squire, M. W., Li, W.-J. Endothelin-1 differentially directs lineage specification of adipose- and bone marrow-derived mesenchymal stem cells.

Endothelin but Not Angiotensin II May Mediate Hypertension-Induced Coronary Vascular Calcification in Chronic Kidney Disease

To understand the relationship between putative neurohormonal factors operative in hypertension and coronary artery calcification (CAC), the relevant cellular actions of angiotensin (Ang II) and endothelin-1 (ET-1) are reviewed. There is compelling evidence to implicate ET-1 in CAC. ET-1 increases phosphate transport with a 42 to 73% increase in V_max. Increased cellular phosphate may induce CAC through increased Ca x phosphate product, transformation of vascular smooth muscle cells into a bone-producing phenotype or cell apoptosis that releases procalcific substances. ET-1 is increased in several models of vascular calcification. ET-1 inhibits inhibitors of calcification, matrix Gla and osteoprotegerin, while enhancing pro-calcific factors such as BMP-2 and osteopontin. In contrast, Ang II inhibits phosphate transport decreasing V_max by 38% and increases matrix Gla. Ang II also stimulates bone resorption. Vascular calcification is reduced by ET-1 A receptor antagonists and to a greater extent than angiotensin receptor blockade although both agents reduce blood pressure.

Gap Junctions and Biophysical Regulation of Bone Cells

Communication between osteoblasts, osteoclasts, and osteocytes is integral to their ability to build and maintain the skeletal system and respond to physical signals. Various physiological mechanisms, including nerve communication, hormones, and cytokines, play an important role in this process. More recently, the important role of direct, cell-cell communication via gap junctions has been established. In this review, we demonstrate the integral role of gap junctional intercellular communication (GJIC) in skeletal physiology and bone cell mechanosensing.

Relationship between arterial calcification and bone loss in a new combined model rat by ovariectomy and vitamin D(3) plus nicotine

Epidemiological studies have reported an association between arterial calcification and bone loss after menopause. However, the underlying mechanism of the association remains unclear. Therefore, to explore the possible mechanisms of the association, we tried to develop a new combined model rat of ovariectomy (OVX, an animal model of osteoporosis) and vitamin D(3) plus nicotine (VDN rat, an animal model of arterial calcification). We tested them by using sham-operated control rats (SC), OVX control rats (OC), and OVX plus VDN-treated rats (OVN). Dissections were performed twice at 4 (4SC, 4OC, and 4OVN) and 8 (8SC, 8OC, and 8OVN) weeks after treatment. 8OVN showed bone loss and arterial calcification, although 8OC showed only bone loss. Moreover, arterial calcium content was associated with indexes of bone loss at 8 weeks. Thus, the OVN rat is considered a good model to examine the relationship of the two disorders after menopause. Additionally, the arterial endothelin-1 (ET-1, a potent regulator of arterial calcification) levels increased in both 4OVN and 8OVN, and the level was associated with arterial calcium content at 8 weeks. Furthermore, the arterial endothelial nitric oxide synthase (eNOS) protein, which is an enzyme that produces nitric oxide (an antiatherosclerotic substance), was significantly reduced in only 8OVN. Estrogens affect the alterations of the eNOS and ET-1 proteins. Therefore, we suggest that impairment of the ET-1- and NO-producing system in arterial tissue during periods of rapid bone loss by estrogen deficiency might be a mechanism of the relationship between the two disorders seen in postmenopausal women.

Bone biology and physiology: implications for novel osteoblastic osteosarcoma treatments?

Healthy bone undergoes a continuous cycle of bone resorption by osteoclasts and formation by osteoblasts. These processes are in turn regulated by developmental sequences involved in differentiation of bone marrow puripotent mesenchymal cells into osteoblasts and mononuclear hemaotpoitic stem cells into osteoclasts. A variety of growth factors and receptors are involved in these maturation sequences. Osteoblast proliferation and inhibition, for example, are highly dependent not only on such factors as bone morphogenic protein and core binding factor a1 (CBFa1), but on intracellular levels of calcium and cAMP. Therefore, agents that affect concentrations of these two compounds may hypothetically play a role in osteoblastic osteosarcoma treatment. Osteoblast proliferation is also under neural control; in particular, the activity of the N-methyl-d-aspartate (NMDA) and alpha adrenergic 1 receptors. Antagonists to these receptors may also hypothetically play a role in osteoblastic osteosarcoma therapy. This article reviews the basic science supporting the putative roles of common, relatively safe but disparate agents-ranging from caffeine and theophylline to dextromethorphan and econazole-in the potential treatment of osteoblastic osteosarcoma.

Endothelin1-induced Ca(2+) mobilization is altered in calvarial osteoblastic cells of Cx43(+/- ) mice

During bone remodeling, osteoblastic (OB) cells have a central role leading to the production of extracellular matrix and its subsequent mineralization. As revealed by human physiopathologies, the OB differentiation process is essential for the control of calcium metabolism and normal bone formation. Moreover, accumulating data in the field of bone development suggest that connexin 43 (Cx43)-mediated gap junctional communication plays an important role in OB differentiation and function. Since Ca(2+) has a central role in OB physiology, the aim of the present study was to investigate the hypothetical involvement of Cx43 in OB calcium homeostasis. We performed measurements of intracellular calcium activity ([Ca(2+)]( i )) by a cytofluorimetric method using Fluo-4 as a calcium indicator and endothelin-1 (ET-1) as a physiological calcium-mobilizing factor on cultured OB cells isolated from calvaria of Cx43(+/-) and Cx43(+/+) mice. Partial deletion of the Cx43 gene induced a significant decrease in the [Ca(2+)]( i ) rise elicited by ET-1. This reduction was not correlated to a decrease or a modification of ET receptor subtype expression as assessed by real-time reverse-transcription polymerase chain reaction. Pharmacological investigations led us to demonstrate that the significant difference in [Ca(2+)]( i ) peak amplitude during the ET-1 action was associated with decreased calcium influx involving L-type voltage-sensitive calcium channels, whereas calcium release from intracellular stores and implication of phospholipase C were not affected by the reduced expression of Cx43. In conclusion, our data demonstrate for the first time that the Cx43 level of expression and/or function is able to modulate the [Ca(2+)]( i ) mobilization in OB cells.

Comparison of plasma endothelin levels between osteoporotic, osteopenic and normal subjects

Background

It has been demonstrated that endothelins (ET) have significant roles in bone remodeling, metabolism and physiopathology of several bone diseases. We aimed to investigate if there was any difference between the plasma ET levels of osteoporotic patients and normals.

Methods

86 patients (70 women and 16 men) with a mean age of 62.6 (ranges: 51–90) years were included in this study. Patients were divided into groups of osteoporosis, osteopenia and normal regarding reported T scores of DEXA evaluation according to the suggestions of World Health Organization. According to these criteria 19, 43 and 24 were normal, osteopenic and osteoporotic respectively. Then total plasma level of ET was measured in all patients with monoclonal antibody based sandwich immunoassay (EIA) method. One-way analysis of variance test was used to compare endothelin values between normals, osteopenics and osteoporotics.

Results

Endothelin total plasma level in patients was a mean of 98.36 ± 63.96, 100.92 ± 47.2 and 99.56 ± 56.6 pg/ml in osteoporotic, osteopenic and normal groups respectively. The difference between groups was not significant (p > 0.05).

Conclusion

No significant differences in plasma ET levels among three groups of study participants could be detected in this study.