Bone endothelial cells as estrogen targets

The role of estrogen and progesterone receptors in the rotator cuff disease: a retrospective cohort study

Background

Rotator cuff (RC) tears represent a common cause of shoulder pain and dysfunction in adults. The disease affects primarily women and occurs mainly in the postmenopausal period.

This study aimed to investigate immunohistochemically the presence of estrogen receptor-alpha (ER-⍺), estrogen receptor-beta (ER-β) and progesterone receptor (PR) in the supraspinatus tendon of patients with RC tendinopathy, searching for gender differences of expression. A secondary aim was to evaluate potential links between their expression and the typical histopathological findings of the ailment.

Methods

Biopsies of the supraspinatus tendon were collected intraoperatively from 15 postmenopausal women and 9 men undergoing RC surgery. Specimens were stained with Haematoxylin/Eosin, Masson-Goldner Trichrome, Alcian Blu and immunohistochemical stainings for ER-⍺, ER-β and PR were performed. Tendon alterations were evaluated with the Bonar histopathological scale. Statistical tests used in this study were the Spearman correlation coefficient and the Mann-Whitney U test.

Results

In the supraspinatus tendon, cells expressed ER-⍺ (p = 0.043), ER-β (p = 0.048) and PR (p = 0.004) with statistically significant differences related to age and sex of patients. Immunoreactivity was seen in the nuclei of tenocytes and vascular cells. Postmenopausal women’s samples showed a markedly higher expression of these receptors compared to their male counterpart. There was a positive correlation between the expression of ER-⍺ and ER-β (r = 0.59; p = 0.02) and between ER-β and PR (r = 0.72; p = 0.002) in women’s samples. Furthermore, in postmenopausal women the PR expression decreased with age (r = − 0.56; p = 0.027). Only in women, the ER-β expression positively correlated with the total Bonar histopathological score (p = 0.019) and the ER-β vascular expression positively correlated with ground substance alterations (p = 0.029).

Conclusions

These results reveal that ERs and PR are present in the supraspinatus tendon of patients with RC tears, suggesting a role of sex hormones in the pathogenesis of the disease.

Targeting Drug Delivery in the Elderly: Are Nanoparticles an Option for Treating Osteoporosis?

Nanoparticles bearing specific targeting groups can, in principle, accumulate exclusively at lesion sites bearing target molecules, and release therapeutic agents there. However, practical application of targeted nanoparticles in the living organism presents challenges. In particular, intravasally applied nanoparticles encounter physical and physiological barriers located in blood vessel walls, blocking passage from the blood into tissue compartments. Whereas small molecules can pass out of the blood, nanoparticles are too large and need to utilize physiological carriers enabling passage across endothelial walls. The issues associated with crossing blood-tissue barriers have limited the usefulness of nanoparticles in clinical applications. However, nanoparticles do not encounter blood-tissue barriers if their targets are directly accessible from the blood. This review focuses on osteoporosis, a disabling and common disease for which therapeutic strategies are limited. The target sites for therapeutic agents in osteoporosis are located in bone resorption pits, and these are in immediate contact with the blood. There are specific targetable biomarkers within bone resorption pits. These present nanomedicine with the opportunity to treat a major disease by use of simple nanoparticles loaded with any of several available effective therapeutics that, at present, cannot be used due to their associated side effects.

Biofabrication of vasculature in microphysiological models of bone

Bone contains a dense network of blood vessels that are essential to its homoeostasis, endocrine function, mineral metabolism and regenerative functions. In addition, bone vasculature is implicated in a number of prominent skeletal diseases, and bone has high affinity for metastatic cancers. Despite vasculature being an integral part of bone physiology and pathophysiology, it is often ignored or oversimplified inin vitrobone models. However, 3D physiologically relevant vasculature can now be engineeredin vitro, with microphysiological systems (MPS) increasingly being used as platforms for engineering this physiologically relevant vasculature. In recent years, vascularised models of bone in MPSs systems have been reported in the literature, representing the beginning of a possible technological step change in how bone is modelledin vitro. Vascularised bone MPSs is a subfield of bone research in its nascency, however given the impact of MPSs has had inin vitroorgan modelling, and the crucial role of vasculature to bone physiology, these systems stand to have a substantial impact on bone research. However, engineering vasculature within the specific design restraints of the bone niche is significantly challenging given the different requirements for engineering bone and vasculature. With this in mind, this paper aims to serve as technical guidance for the biofabrication of vascularised bone tissue within MPS devices. We first discuss the key engineering and biological considerations for engineering more physiologically relevant vasculaturein vitrowithin the specific design constraints of the bone niche. We next explore emerging applications of vascularised bone MPSs, and conclude with a discussion on the current status of vascularised bone MPS biofabrication and suggest directions for development of next generation vascularised bone MPSs.

Blood Vessels and Vascular Niches in Bone Development and Physiological Remodeling

Recent advances in our understanding of blood vessels and vascular niches in bone convey their critical importance in regulating bone development and physiology. The contribution of blood vessels in bone functions and remodeling has recently gained enormous interest because of their therapeutic potential. The mammalian skeletal system performs multiple functions in the body to regulate growth, homeostasis and metabolism. Blood vessels provide support to various cell types in bone and maintain functional niches in the bone marrow microenvironment. Heterogeneity within blood vessels and niches indicate the importance of specialized vascular niches in regulating skeletal functions. In this review, we discuss physiology of bone vasculature and their specialized niches for hematopoietic stem cells and mesenchymal progenitor cells. We provide clinical and experimental information available on blood vessels during physiological bone remodeling.

Gonadal Hormones and Bone

In both sexes, estrogen is one of the most essential hormones for maintaining bone integrity. Also, especially in men, androgen has beneficial effects on bone independent of estrogen. However, estrogen replacement therapy for postmenopausal women increases the risk of developing breast cancer and endometrial cancer, and androgen replacement therapy for partial androgen deficiency of the aging male increases the risk of developing prostate cancer. Various mechanisms have been proposed on the effects of gonadal hormones on bone, such as effects through cytokines including IL-6 and effects on the OPG/RANKL ratio. In addition, large amounts of new information deriving from high-throughput gene expression analysis raise the possibility of multiple other effects on bone cells. Both estrogen and androgen exert their effects via the estrogen receptor (ER) or the androgen receptor (AR), which belongs to the nuclear receptor superfamily. Compounds such as selective estrogen receptor modulators (SERMs) and selective androgen receptor modulators (SARMs) also bind ER and AR, respectively. However, SERMs and SARMs alter the ER or AR structure differently from estrogen or androgen, resulting in other downstream gene responses. As a result they can exert favorable effects on bone while suppressing the undesirable actions of estrogen and androgen. Elucidation of ER and AR ligand-specific and tissue-specific gene regulation mechanisms will also provide information on the signal transduction mechanisms of other nuclear receptors and will be valuable for the development of new therapeutic agents.

Mechanical, hormonal and metabolic influences on blood vessels, blood flow and bone

Bone tissue is highly vascularized due to the various roles bone blood vessels play in bone and bone marrow function. For example, the vascular system is critical for bone development, maintenance and repair and provides O₂, nutrients, waste elimination, systemic hormones and precursor cells for bone remodeling. Further, bone blood vessels serve as egress and ingress routes for blood and immune cells to and from the bone marrow. It is becoming increasingly clear that the vascular and skeletal systems are intimately linked in metabolic regulation and physiological and pathological processes. This review examines how agents such as mechanical loading, parathyroid hormone, estrogen, vitamin D and calcitonin, all considered anabolic for bone, have tremendous impacts on the bone vasculature. In fact, these agents influence bone blood vessels prior to influencing bone. Further, data reveal strong associations between vasodilator capacity of bone blood vessels and trabecular bone volume, and poor associations between estrogen status and uterine mass and trabecular bone volume. Additionally, this review highlights the importance of the bone microcirculation, particularly the vascular endothelium and NO-mediated signaling, in the regulation of bone blood flow, bone interstitial fluid flow and pressure and the paracrine signaling of bone cells. Finally, the vascular endothelium as a mediator of bone health and disease is considered.

The role of angiogenesis in implant dentistry part II: The effect of bone-grafting and barrier membrane materials on angiogenesis

BACKGROUND

In implant dentistry, bone substitute materials and barrier membranes are used in different treatments including guided bone regeneration (GBR), socket preservation, alveolar ridge augmentation, maxillary sinus elevation, and filling bony defects around the inserted dental implant. One of the most important factors in prognosis of treatments using these materials is the growth of new blood vessels in applied areas. Present review was performed to evaluate the effect of the bone-grafting and barrier membrane materials on angiogenesis events.

MATERIAL AND METHODS

An electronic search was performed in PubMed, MEDLINE, and EMBASE databases via OVID using the keywords mentioned in the PubMed and MeSH headings regarding the role of angiogenesis in implant dentistry from January 2000-April 2014.

RESULTS

Of the 5,622 articles identified in our initial search results, only 33 met the inclusion criteria set for this review. Among bone substitute materials the autogenous bone-grafts, and among the barrier membranes the collagenous membranes, had the highest angiogenic potentials. Other bone-grafting materials or membranes were mostly used with pro-angiogenic factors to enhance their angiogenic properties.

CONCLUSIONS

Angiogenesis is one of the key factors, which plays a critical role in success rate of GBR technique and is seriously considered in manufacturing bone-grafting and barrier membrane materials. However, there is still lack of clinical and in-vivo studies addressing the effect of angiogenesis in treatments using bone-grafting and barrier membrane materials.

Bone vascularization in normal and disease conditions

Bone vasculature is essential for many processes, such as skeletal development and growth, bone modeling and remodeling, and healing processes. Endothelium is an integral part of bone tissue, expressing a physiological paracrine function via growth factors and chemokines release, and interacting with several cellular lines. Alterations of the complex biochemical interactions between vasculature and bone cells may lead to various clinical manifestations. Two different types of pathologies result: a defect or an excess of bone vasculature or endothelium metabolism. Starting from the molecular basis of the interactions between endothelial and bone cells, the Authors present an overview of the recent acquisitions in the physiopathology of the most important clinical patterns, and the modern therapeutic strategies for their treatments.

In vitro models for the evaluation of angiogenic potential in bone engineering

Blood vessels have a fundamental role both in skeletal homeostasis and in bone repair. Angiogenesis is also important for a successful bone engineering. Therefore, scaffolds should be tested for their ability to favour endothelial cell adhesion, proliferation and functions. The type of endothelial cell to use for in vitro assays should be carefully considered, because the properties of these cells may depend on their source. Morphological and functional relationships between endothelial cells and osteoblasts are evaluated with co-cultures, but this model should still be standardized, particularly for distinguishing the two cell types. Platelet-rich plasma and recombinant growth factors may be useful for stimulating angiogenesis.

The relationship between menstrual cycle phase and anterior cruciate ligament injury: a case-control study of recreational alpine skiers

BACKGROUND

Female athletes suffer a greater incidence of anterior cruciate ligament tears compared with male athletes when participating in common sports; however, very little is known about the factors that explain this disparity.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

Female recreational alpine skiers with an anterior cruciate ligament rupture and age-matched control skiers provided a serum sample and self-reported menstrual history data immediately after injury. Both serum concentrations of progesterone and menstrual history were then used to group subjects into either preovulatory or postovulatory phases of the menstrual cycle.

RESULTS

Analysis of serum concentrations of progesterone revealed that alpine skiers in the preovulatory phase of the menstrual cycle were significantly more likely to tear their anterior cruciate ligaments than were skiers in the postovulatory phase (odds ratio, 3.22; 95% confidence interval, 1.09-9.52; P = .027). Analysis of menstrual history data found similar results, but the difference was not statistically significant (odds ratio, 2.38; 95% confidence interval, 0.86-6.54; P = .086).

CONCLUSION

The likelihood of sustaining an anterior cruciate ligament injury does not remain constant during the menstrual cycle; instead, the risk of suffering an anterior cruciate ligament disruption is significantly greater during the preovulatory phase of the menstrual cycle compared with the postovulatory phase.

CLINICAL RELEVANCE

Phase of menstrual cycle may be one of the risk factors that influence knee ligament injury among female alpine skiers. The findings from this study should be considered in subsequent studies designed to identify persons at risk for anterior cruciate ligament injury and to develop intervention strategies.

Characteristic distribution of immunoreaction for estrogen receptor alpha in rat ameloblasts

Estrogen has a diverse function, including cell proliferation and differentiation via estrogen receptors (ER), which have been reported to be the case in various tissues in addition to female reproductive organs. A recent immunocytochemical study has reported the expression of ERalpha, a subtype of ER, in rat odontoblasts, suggesting an involvement of estrogen in the differentiation of tooth-forming cells. However, there is no information on the ERalpha immunoexpression in ameloblasts. The present study was therefore undertaken to examine the localization of ERalpha immunoreaction in rat ameloblasts during amelogenesis. A computer-assisted quantitative analysis under a confocal laser scanning microscope was employed to demonstrate the stage-specific localization pattern of ERalpha immunoreaction. Immunohistochemistry of the rat enamel organ revealed ERalpha expression as nuclear localization in ameloblasts, stratum intermedium, stellate reticulum, and papillary layer, in addition to mature and immature odontoblasts. The ratio of immunopositive nuclei to total nuclei (immunopositive ratio) in ameloblasts was high at the apical loop region and gradually declined at the presecretory stage to zero at the secretory stage with statistically significant difference. The ERalpha immunolabeling pattern exhibited a periodic change at the maturation stage proper with constant higher labeling in ruffle-ended ameloblasts than in smooth-ended ameloblasts. The positive ratio was then followed by a statistically significant increase in immunolabeling thereafter. This stage-specific immunolabeling pattern during amelogenesis suggests a possible role of ERalpha in ameloblast proliferation and differentiation.

The effect of estradiol and progesterone on knee and ankle joint laxity

BACKGROUND

Female athletes suffer a higher incidence of anterior cruciate ligament injuries compared to their male counterparts, and they appear to be at increased risk for these injuries when they have increased anterior-posterior knee laxity and at specific phases of the menstrual cycle. Although the mechanism by which these factors combine to increase injury risk is unclear, studies suggest that cyclic variations in joint laxity produced by hormone fluctuation during the menstrual cycle predispose an athlete to increased risk of ligamentous injury. Little is known about whether joint laxity varies cyclically during the menstrual cycle and if so, whether it is modulated by cyclic variations of estradiol (E2) and progesterone (P4).

HYPOTHESIS

Increased serum estradiol (E2) and progesterone (P4) levels are associated with increased ankle and knee joint laxity.

STUDY DESIGN

Cohort study. Level of evidence, 2.

METHODS

Ankle laxity, anterior-posterior knee laxity, and serum concentrations of estradiol (E2) and progesterone (P4) were measured during the menstrual cycle in women and at corresponding time intervals in men (controls). Ankle laxity was measured from stress radiographs and included anterior talar translation relative to the tibia and talar tilt relative to the tibia; anterior-posterior knee laxity was measured with the KT-1000 arthrometer.

RESULTS

Women had greater knee and ankle laxity values compared to men. There was, however, no change in knee and ankle laxity over the normal menstrual cycle in women and no change over time in men. There was no relationship between estradiol and progesterone fluctuation and ankle and knee joint laxity.

CONCLUSIONS

Knee and ankle joint laxities are greater for women compared to men; however, the cyclic estradiol and progesterone fluctuations that occur during the menstrual cycle do not produce cyclic fluctuations of joint laxity. Studies using joint laxity to identify a subject at risk for ligamentous injury need only consider making measurements at a specific point in time, such as during a preseason screening evaluation.

Expression of estrogen receptor alpha (ER alpha) in the rat temporomandibular joint

Numerous epidemiological studies have pointed out a higher frequency of temporomandibular disorder (TMD) in women than in men, which indicates the involvement of a sex hormone, such as estrogen, in the pathogenesis of TMD. Although estrogen is known to play pivotal roles in osteoarthrosis or rheumatoid arthritis in systemic joints, there have been few reports about the role of estrogen in the temporomandibular joint (TMJ). The effect of estrogen is generally mediated by the estrogen receptors (ERs) ER alpha (the predominant type) and ER beta. In this study we examined the expression of ER alpha protein and mRNA in the TMJ of adult male rats by immunocytochemistry and in situ hybridization histochemistry. Intense ER alpha immunoreactivity was localized in the synovial lining cells, stromal cells in the articular disc, and chondrocytes in the TMJ. These ER alpha-immunopositive synovial lining cells are characteristic of cytoplasmic processes identified with confocal and immunoelectron microscopy, which indicates that they are synovial type B cells. In situ hybridization histochemistry confirmed intense signals for ER alpha in the synovial lining cells and the sublining fibroblasts at mRNA levels. The nuclei of chondrocytes showed an intense immunoreaction for ER alpha in the maturative and hypertrophic layers of the articular cartilage. In addition to the nuclear localization of ER alpha, a weak immunoreaction appeared in the cytoplasm of some ER alpha-positive cells. These findings support the hypothesis that TMJ tissue-at least in the male rat-has the potential to be an estrogen target tissue.

Role of vascular factors in osteoporosis

Osteoporosis is a silent epidemic in the world today. With the increase in the elderly population, there will be an increase in the prevalence of osteoporosis, and so the need for focused preventive strategies should become a public health priority. Prophylactic therapy and risk-factor reduction is important, as this is likely to be cost effective. There are scientific observations that point out that vascular dysfunction seen with aging may be related to the pathogenesis of osteoporosis. Here we review this relationship from a different angle. We think aggressive control of vascular risk factors in addition to the known existing osteoporosis risk factors may help to reduce the morbidity and mortality associated with this disease.

Bone growth stimulators. New tools for treating bone loss and mending fractures

In the new millennium, humans will be traveling to Mars and eventually beyond with skeletons that respond to microgravity by self-destructing. Meanwhile in Earth's aging populations growing numbers of men and many more women are suffering from crippling bone loss. During the first decade after menopause all women suffer an accelerating loss of bone, which in some of them is severe enough to result in "spontaneous" crushing of vertebrae and fracturing of hips by ordinary body movements. This is osteoporosis, which all too often requires prolonged and expensive care, the physical and mental stress of which may even kill the patient. Osteoporosis in postmenopausal women is caused by the loss of estrogen. The slower development of osteoporosis in aging men is also due at least in part to a loss of the estrogen made in ever smaller amounts in bone cells from the declining level of circulating testosterone and is needed for bone maintenance as it is in women. The loss of estrogen increases the generation, longevity, and activity of bone-resorbing osteoclasts. The destructive osteoclast surge can be blocked by estrogens and selective estrogen receptor modulators (SERMs) as well as antiosteoclast agents such as bisphosphonates and calcitonin. But these agents stimulate only a limited amount of bone growth as the unaffected osteoblasts fill in the holes that were dug by the now suppressed osteoclasts. They do not stimulate osteoblasts to make bone--they are antiresorptives not bone anabolic agents. (However, certain estrogen analogs and bisphosphates may stimulate bone growth to some extent by lengthening osteoblast working lives.) To grow new bone and restore bone strength lost in space and on Earth we must know what controls bone growth and destruction. Here we discuss the newest bone controllers and how they might operate. These include leptin from adipocytes and osteoblasts and the statins that are widely used to reduce blood cholesterol and cardiovascular damage. But the main focus of this article is necessarily the currently most promising of the anabolic agents, the potent parathyroid hormone (PTH) and certain of its 31- to 38-aminoacid fragments, which are either in or about to be in clinical trial or in the case of Lilly's Forteo [hPTH-(1-34)] tentatively approved by the Food and Drug Administration for treating osteoporosis and mending fractures.

The effect of in vivo mechanical loading on estrogen receptor alpha expression in rat ulnar osteocytes

The presence of estrogen receptor alpha (ER alpha) in osteocytes was identified immunocytochemically in transverse sections from 560 to 860 microm distal to the midshaft of normal neonatal and adult male and female rat ulnas (n = 3 of each) and from adult male rat ulnas that had been exposed to 10 days of in vivo daily 10-minute periods of cyclic loading producing peak strains of either -3000 (n = 3) or -4000 microstrain (n = 5). Each animal ambulated normally between loading periods, and its contralateral ulna was used as a control. In animals in which limbs were subject to normal locomotor loading alone, 14 +/- 1.2% SEM of all osteocytes in each bone section were ER alpha positive. There was no influence of either gender (p = 0.725) or age (p = 0.577) and no interaction between them (p = 0.658). In bones in which normal locomotion was supplemented by short periods of artificial loading, fewer osteocytes expressed ER alpha (7.5 +/- 0.91% SEM) than in contralateral control limbs, which received locomotor loading alone (14 +/- 1.68% SEM; p = 0.01; median difference, 6.43; 95% CI, 2.60, 10.25). The distribution of osteocytes expressing ER alpha was uniform across all sections and thus did not reflect local peak strain magnitude. This suggests that osteocytes respond to strain as a population, rather than as individual strain-responsive cells. These data are consistent with the hypothesis that ER alpha is involved in bone cells' responses to mechanical strain. High strains appear to decrease ER alpha expression. In osteoporotic bone, the high strains assumed to accompany postmenopausal bone loss may reduce ER alpha levels and therefore impair the capacity for appropriate adaptive remodeling.

Effects of oophorectomy on functional properties of resistance arteries isolated from the cancellous bone of the rabbit femur

Information is sparse concerning the effect of oophorectomy (OOX) on bone vascularization and blood flow of possible significance for altered remodeling. Whether OOX affects functional characteristics of isolated bone resistance arteries was investigated. Ring preparations (diameter approximately 250 microm) of small femoral bone arteries from oophorectomized and sham-operated rabbits were mounted on a myograph six weeks postoperatively. Cumulative concentration response curves were obtained for various agonists at a normalized lumen diameter. Oophorectomy did not significantly influence lumen diameter, maximal response to high potassium, or maximal response to high potassium and 10(-5) M noradrenaline. However, OOX significantly increased the maximal response to noradrenaline (OOX 2.14 +/- 0.36 N/m, Sham 1.25 +/- 0.14 N/m) and endothelin-1 (OOX 1.76 +/- 0.32, Sham 0.95 +/- 0.15) in metaphyseal arteries. Moreover, the corresponding maximal active pressure for the agonists was significantly increased. OOX did not influence endothelial function assessed by the effects of acetylcholine or substance P. The functional responses of diaphyseal arteries were unaffected by OOX. The study demonstrates regional differences in the effects of OOX on small arteries of importance for control of vascular resistance in bone which suggests a relation between altered vascular function after ovarian hormonal withdrawal and the changes in bone turnover associated with osteoporosis.

Sex steroids and bone

Sex steroids are essential for skeletal development and the maintenance of bone health throughout adult life, and estrogen deficiency at menopause is a major pathogenetic factor in the development of osteoporosis in postmenopausal women. The mechanisms by which the skeletal effects of sex steroids are mediated remain incompletely understood, but in recent years there have been considerable advances in our knowledge of how estrogens and, to a lesser extent androgens, influence bone modeling and remodeling in health and disease. New insights into estrogen receptor structure and function, recent discoveries about the development and activity of osteoclasts, and lessons learned from human and animal genetic mutations have all contributed to increased understanding of the skeletal effects of estrogen, both in males and females. Studies of untreated and treated osteoporosis in postmenopausal women have also contributed to this knowledge and have provided unequivocal evidence for the potential of high-dose estrogen therapy to have anabolic skeletal effects. The development of selective estrogen receptor modulators has provided a new approach to the prevention of osteoporosis and other major diseases of menopause and has implications for the therapeutic use of other steroid hormones, including androgens. Further elucidation of the mechanisms by which sex steroids affect bone thus has the potential to improve the clinical management not only of osteoporosis, both in men and women, but also of a number of other diseases related to sex hormone status.

Localized expression of aromatase in human vascular tissues

The atheroprotective effects of estrogen are well established and the presence of an estrogen receptor in vascular tissues has recently been reported. Therefore, we investigated the localization of the estrogen-producing enzyme aromatase in vascular tissues to assess the possible contribution of endocrine, paracrine, and autocrine modes of action. Aromatase was found in human vascular smooth muscle cells (SMCs) but not in endothelial cells on in situ hybridization. These observations were further supported by quantitative analysis of aromatase mRNA and the activity in 15 human vascular specimens. Only trace levels of expression were detected in the 3 infants examined, whereas 0.0088 to 0.0806 amol/ microg RNA of aromatase mRNA and 12.9 to 122.3 fmol. h-1. mg-1 protein of the activity were detected in 12 of the adult individuals. The switching of tissue-specific exon 1 of the human aromatase gene was also observed in some cases. Aromatase was found to be expressed only in cultured SMCs and not in cultured endothelial cells of human aorta and pulmonary artery and to be regulated through dexamethasone and the signaling pathways of protein kinase A and C. Study results revealed the localized expression of aromatase in vascular SMCs, which indicated a possible direct action of locally produced estrogen in an autocrine or paracrine manner, with possible cross talk between smooth muscle and endothelial cells.

17beta-estradiol induces apoptosis in the preosteoclastic FLG 29.1 cell line

Although compelling data have demonstrated the effectiveness of estrogen replacement therapy for the treatment of accelerated bone loss in postmenopausal osteoporosis and ovariectomized animals, the mechanisms by which estrogens reduce bone resorption remain to be elucidated. To address this issue, in the present study we investigated whether estrogens were able to induce programmed cell death or apoptosis in osteoclast precursors. To this purpose, a preosteoclastic cell line (FLG 29.1) was cultured in the absence or presence of nanomolar concentrations of 17beta-estradiol (17betaE2). Using time-lapse videomicroscopy, it was shown that 17betaE2 induced FLG 29.1 cell apoptosis in a dose- and time-dependent manner. Furthermore, a significant increase in the activity of caspase 3 enzyme and in the number of nuclei undergoing DNA fragmentation was observed in FLG 29.1 cells treated with 17betaE2 compared to untreated cells. Finally, transmission electron microscopy of the treated cells showed typical apoptotic morphology. These data indicate that 17betaE2 is able to promote in vitro apoptosis in preosteoclastic cells and suggest that estrogenic molecules may exert in vivo a direct role in negatively modulating the pool of undifferentiated bone marrow cells capable ultimately of maturing into osteoclasts.

Bone hyperemia precedes disuse-induced intracortical bone resorption

An in vivo model was used to determine whether bone hyperemia precedes increased intracortical porosity induced by disuse. Twenty-four adult male roosters (age 1 yr) were randomly assigned to intact-control, 7-days-sham-surgery, 7-days-disuse, and 14-days-disuse groups. Disuse was achieved by isolating the left ulna diaphysis from physical loading via parallel metaphyseal osteotomies. The right ulna served as an intact contralateral control. Colored microspheres were used to assess middiaphyseal bone blood flow. Bone blood flow was symmetric between the left and right ulnae of the intact-control and sham-surgery groups. After 7 days of disuse, median (+/-95% confidence interval) standardized blood flow was significantly elevated compared with the contralateral bone (6.5 +/- 5.2 vs. 1.0 +/- 0.8 ml x min-1 x 100 g-1; P = 0.03). After 14 days of disuse, blood flow was also elevated but to a lesser extent. Intracortical porosity in the sham-surgery and 7-days-disuse bones was not elevated compared with intact-control bones. At 14 days of disuse, the area of intracortical porosity was significantly elevated compared with intact control bones (0.015 +/- 0.02 vs. 0. 002 +/- 0.002 mm2; P = 0.03). We conclude that disuse induces bone hyperemia before an increase in intracortical porosity. The potential interaction between bone vasoregulation and bone cell dynamics remains to be studied.

Tumor growth of FGF or VEGF transfected MCF-7 breast carcinoma cells correlates with density of specific microvessels independent of the transfected angiogenic factor

We have previously shown that fibroblast growth factor (FGF)-1-, FGF-4-, or vascular endothelial growth factor (VEGF/VPF)-transfected MCF-7 breast carcinoma cells growing as tumors in nude mice are tamoxifen resistant and/or estrogen independent. These transfectants provide opportunity for study of in situ tumor-induced angiogenesis promoted by the individual angiogenic factors under growth-promoting versus growth-inhibiting hormonal conditions. In the present study, vessels in tumors harvested at varying times after tumor cell injection were immunohistochemically highlighted and vessel morphology and topography were scored on a scale of 0 to 4 by blinded observers. In tumors produced by all cell lines under all growth-promoting hormonal conditions, there was significantly increased abundance (P < 0.05) of edge-associated and intratumor microvessels, but not of stromally located microvessels, when compared with tumor nodules harvested under growth-inhibiting conditions, regardless of the identity of the angiogenic factor or the hormonal treatment. Image analysis of bromodeoxyuridine (BrdU)-labeled nuclei of tumors produced by all cell lines under all hormonal conditions harvested at early time points showed that mean labeling indices were highest for hormonal conditions that produced the most robust growth in that particular cell line, implying that a high BrdU labeling index is a predictor of future tumor growth in individual tumors. These results confirm previous studies that established the importance of neovascularization for tumor growth and provide validation for use of these cell lines to study the process of angiogenesis in vivo. Study of gene expression in endothelial cells in edge-associated or intratumor vessels using this model might reveal mechanisms important in tumor-induced angiogenesis in human breast cancer.

Human umbilical vein endothelial cells lack expression of the estrogen receptor

Estrogens may influence the expression of various cytokines, adhesion molecules, von Willebrand factor and prostacyclin produced by endothelial cells. However, reports concerning expression of the estrogen receptor in endothelial cells are controversial. Primary human umbilical vein endothelial cells (HUV-EC), the non continuous human umbilical vein endothelial cell line HUV-EC-C (ATCC CRL 1730) and endothelial cells from 10 frozen umbilical cords were analyzed for the expression of the estrogen receptor. Immunological studies using estrogen receptor specific antibodies failed to detect the expression of the receptor in all human umbilical vein endothelial cells tested. No estrogen receptor transcripts were found in primary HUV-EC or HUV-EC-C by reverse transcriptase-polymerase chain reaction. Weak hybridization signals were detected when the PCR amplicons were hybridized with estrogen receptor cDNA sequences as a probe. In vitro protein-DNA interaction studies revealed no complexes between a fully consensus estrogen response element and HUV-EC-C extracts. Finally, transient transfection studies in HUV-EC-C could not demonstrate 17beta-estradiol-induced transcription of the beta-galactosidase reporter gene linked to a consensus estrogen response element. These observations suggest that human umbilical vein endothelial cells lack the estrogen receptor.

Effect of Steroid Hormones and Retinoids on the Formation of Capillary-Like Tubular Structures of Human Microvascular Endothelial Cells in Fibrin Matrices Is Related to Urokinase Expression

Angiogenesis, the formation of new capillary blood vessels, is a feature of a variety of pathological processes. To study the effects of a specific group of hormones (all ligands of the steroid/retinoid/thyroid hormone receptor superfamily) on the angiogenic process in humans, we have used a model system in which human microvascular endothelial cells from foreskin (hMVEC) are cultured on top of a human fibrin matrix in the presence of basic fibroblast growth factor and tumor necrosis factor-α. This model mimics the in vivo situation where fibrin appears to be a common component of the matrix present at sites of chronic inflammation and tumor stroma. Our results show that testosterone and dexamethasone are strong inhibitors and all-trans retinoic acid (at-RA) and 9-cis retinoic acid (9-cis RA) are potent stimulators of the formation of capillary-like tubular structures. These effects are mediated by their respective nuclear hormone receptors as demonstrated by the use of specific synthetic receptor agonists and antagonists. 17β-estradiol, progesterone, and 1,25-dihydroxyvitamin D3 did not affect or only weakly affected in vitro angiogenesis, which may be related to the lack of significant nuclear receptor expression. Although hMVEC express both thyroid hormone receptors α and β, no effect of thyroid hormone on tube formation was found. The effects of testosterone, dexamethasone,at-RA, and 9-cis RA on tube formation were accompanied by parallel changes in urokinase-type plasminogen activator (u-PA) expression, at both mRNA and antigen levels. Exogenous suppletion of the medium with single chain u-PA enhances tube formation in our in vitro model, whereas quenching of u-PA activity (but not of tissue-type plasminogen activator activity) or of u-PA binding to u-PA receptor by specific antibodies suppressed basal and retinoid-stimulated tube formation. Moreover, addition of scu-PA to testosterone- or dexamethasone-treated hMVEC restored the suppressed angiogenic activity for a substantial part. Aprotinin, an inhibitor of plasmin activity, completely inhibited tube formation, indicating that the proteolytic properties of the u-PA/u-PA receptor complex are crucial in this process. Our results show that steroid hormones (testosterone and dexamethasone) and retinoids have strong, but opposite effects on tube formation in a human in vitro model reflecting pathological angiogenesis in the presence of fibrin and inflammatory mediators. These effects can be explained by hormone-receptor–mediated changes in u-PA expression, resulting in enhanced local proteolytic capacity of the u-PA/u-PA receptor complex.

© 1998 by The American Society of Hematology.

Effect of Steroid Hormones and Retinoids on the Formation of Capillary-Like Tubular Structures of Human Microvascular Endothelial Cells in Fibrin Matrices Is Related to Urokinase Expression

Angiogenesis, the formation of new capillary blood vessels, is a feature of a variety of pathological processes. To study the effects of a specific group of hormones (all ligands of the steroid/retinoid/thyroid hormone receptor superfamily) on the angiogenic process in humans, we have used a model system in which human microvascular endothelial cells from foreskin (hMVEC) are cultured on top of a human fibrin matrix in the presence of basic fibroblast growth factor and tumor necrosis factor-α. This model mimics the in vivo situation where fibrin appears to be a common component of the matrix present at sites of chronic inflammation and tumor stroma. Our results show that testosterone and dexamethasone are strong inhibitors and all-trans retinoic acid (at-RA) and 9-cis retinoic acid (9-cis RA) are potent stimulators of the formation of capillary-like tubular structures. These effects are mediated by their respective nuclear hormone receptors as demonstrated by the use of specific synthetic receptor agonists and antagonists. 17β-estradiol, progesterone, and 1,25-dihydroxyvitamin D3 did not affect or only weakly affected in vitro angiogenesis, which may be related to the lack of significant nuclear receptor expression. Although hMVEC express both thyroid hormone receptors α and β, no effect of thyroid hormone on tube formation was found. The effects of testosterone, dexamethasone,at-RA, and 9-cis RA on tube formation were accompanied by parallel changes in urokinase-type plasminogen activator (u-PA) expression, at both mRNA and antigen levels. Exogenous suppletion of the medium with single chain u-PA enhances tube formation in our in vitro model, whereas quenching of u-PA activity (but not of tissue-type plasminogen activator activity) or of u-PA binding to u-PA receptor by specific antibodies suppressed basal and retinoid-stimulated tube formation. Moreover, addition of scu-PA to testosterone- or dexamethasone-treated hMVEC restored the suppressed angiogenic activity for a substantial part. Aprotinin, an inhibitor of plasmin activity, completely inhibited tube formation, indicating that the proteolytic properties of the u-PA/u-PA receptor complex are crucial in this process. Our results show that steroid hormones (testosterone and dexamethasone) and retinoids have strong, but opposite effects on tube formation in a human in vitro model reflecting pathological angiogenesis in the presence of fibrin and inflammatory mediators. These effects can be explained by hormone-receptor–mediated changes in u-PA expression, resulting in enhanced local proteolytic capacity of the u-PA/u-PA receptor complex.

© 1998 by The American Society of Hematology.

Localization of estrogen-receptor-related antigen in human odontoblasts

Estrogen receptors have been demonstrated in many osteogenic cell lines. Recently, we showed that estrogen deficiency induced by ovariectomy caused enhanced dentin formation in adult rats, suggesting that estrogen receptors may be present in dental tissues. Nothing is known about estrogen receptors in human teeth. We used immunohistochemical staining and immuno-blotting to demonstrate the presence of estrogen receptors in human pulp and/or the pulpo-dentinal border. Unerupted human wisdom teeth were surgically removed, frozen in liquid nitrogen, and prepared for immunological studies. Western blot analysis with monoclonal antibodies specific for human estrogen-receptor-related antigens demonstrated an approximately 29-kDa clear double band in the material scraped from the predentin-odontoblast border and in the fluid that emerged into the pulpal chamber, evidently from the odontoblasts. A weaker double band was also present in pulpal tissue samples. By immunohistochemical staining, estrogen-receptor-related antigens were visualized in the predentinal-odontoblast region and in the pulpal blood vessels. Our results suggest the presence of estrogen receptors in human teeth, and thus the previously reported enhancement of the dentin formation in rats after ovariectomy may be mediated via these receptors.

Endothelium-dependent vasodilatation produced by the L-arginine/nitric oxide pathway in normal and ischemic bone

We used an experimental model of the perfused isolated rabbit tibia to investigate the vasodilatation produced by nitric oxide in the circulation of bone. Tibiae were perfused at a constant flow rate while the perfusion pressure was monitored continuously. Perfusion pressure was raised by the addition of noradrenaline to the perfusate, and dose responses were measured for bolus doses of acetylcholine and sodium nitroprusside. N omega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthesis, was then added to the perfusate at a concentration of 10(-4) M, and the dose responses to acetylcholine and sodium nitroprusside were repeated. Measurements were performed on groups of bones after 0, 6, 12, and 24 hours of normothermic ischemia (n 5, 4, 6, and 9, respectively). Both acetylcholine and sodium nitroprusside produced significant vasodilatation after 0 and 6 hours' ischemia, but no significant response was observed after 12 or 24 hours of ischemia. The vasodilatation produced by acetylcholine was significantly attenuated when L-NAME was added to the perfusate, but the vasodilatation produced by sodium nitroprusside remained unchanged. These findings confirm endothelial production of NO by stimulation of muscarinic receptors on the endothelial cells in bone and indicate that vasodilatation via the L-arginine/NO pathway remains viable for 6 hours after normothermic ischemia.

Calcifying subpopulation of bovine aortic smooth muscle cells is responsive to 17 beta-estradiol

BACKGROUND

Arterial calcification, common in atherosclerosis, is associated with an increased risk of clinical events such as myocardial infarction. We previously identified a subpopulation of bovine aortic medial cells, calcifying vascular cells (CVCs), that have osteoblastic characteristics and form bone mineral in vitro in the form of calcified nodules. To assess whether estrogen modulates arterial calcification as well as bone calcification, we tested CVCs for estrogen receptors and for the effect of 17 beta-estradiol on formation of calcified nodules, calcium content, alkaline phosphatase activity, and osteocalcin concentration in the culture medium.

METHODS AND RESULTS

Estrogen receptor immunoreactivity was identified in the cytoplasm and the perinuclear region of CVCs by immunocytochemistry. CVCs were treated with 17 beta-estradiol at concentrations of 0, 5, and 10 nmol/L. Twenty-one days of 17 beta-estradiol treatment resulted in a significantly increased number of calcified nodules, visualized by von Kossa staining, as well as increased calcium content of the cultures. Increases in alkaline phosphatase activity, a marker for early osteoblastic differentiation, and secreted osteocalcin, a marker for late osteoblastic differentiation, were enhanced in cells treated with 17 beta-estradiol compared with control cells.

CONCLUSIONS

These results suggest that 17 beta-estradiol promotes osteoblastic differentiation and calcification in vascular cells and that estrogen may play a regulatory role in arterial calcification.

Expression of an estrogen receptor by human coronary artery and umbilical vein endothelial cells

BACKGROUND

Premenopausal women have much lower susceptibility to coronary artery disease than do men or postmenopausal women. It has been proposed that estrogen plays a role in cardioprotection, but little information is available regarding the mechanism by which estrogen may help to protect the vasculature. Here, we describe an estrogen receptor (ER) in human coronary artery and umbilical vein endothelial cells.

METHODS AND RESULTS

Human umbilical vein endothelial cells and human coronary artery endothelial cells were cultured in hormone-free medium for 48 hours before experiments. Estradiol (3.7 nmol/L) added to cultures promoted proliferation by a mechanism that is inhibited by the specific ER antagonist ICI182,780. Estradiol-treated cells incorporated twice the [3H]thymidine of hormone-free cells; this increase was prevented by ICI182,780. Endothelial cells from both sources stained in a nuclear pattern with an ER-specific antibody. Ribonuclease protection assay detected mRNA for the ER. Ligand-binding studies estimated 2 x 10(4) to 8 x 10(4) receptors per cell and a Kd of approximately 5 nmol/L. Interaction of ERs with a consensus estrogen response element was shown by an electrophoretic mobility shift assay. In addition, an antibody against the ER supershifted the protein-DNA complex.

CONCLUSIONS

These studies define the presence of an ER in human coronary artery and umbilical vein endothelial cells. They support the hypothesis that cardioprotective effects of estrogen are mediated, at least in part, through a classic steroid hormone receptor mechanism.

17 beta-estradiol increases calcium content in fetal mouse parietal bones cultured in serum-free medium only at physiological concentrations

Using a bone organ culture system that shows mineralization in vitro, we investigated whether 17 beta-estradiol dose-dependently increases calcium content in cultured calvarial bones in serum-free medium. Fetal mouse parietal bones (3 x 3 mm) were cultured in phenol red-free BGJ medium containing phosphate (3-4 mmol/L), calcium (1-1.25 mmol/L), insulin (6 micrograms/ML), and transferrin (6 micrograms/mL) for 4-5 days. Under these culture conditions, the calcium content of the cultured bones (at dissection 34.0 +/- 4.6 micrograms/bone [mean +/- SD], n = 50) increased by 15-20 micrograms during 4-5 days of culture. 17 beta-Estradiol increased the calcium content significantly at 10(-12) to 10(-11) mol/L, but not at lower (10(113) mol/L) or higher (10(-10) to 10(-9) mol/L) concentrations. 17 alpha-Estradiol had no effect. The stimulatory effect of 17 beta-estradiol was completely inhibited by the antiestrogen agent ICI-182,780. The anabolic effect of 17 beta-estradiol was elicited not only in bones from females but also in those from males. 17 beta-Estradiol had no significant effect on 45Ca release from prelabeled parietal bones. Furthermore, light- and electron-microscopic examinations revealed that bone mineralization proceeded through formation of matrix vesicles, without any metastatic or dystrophic calcification. These in vitro findings suggest that 17 beta-estradiol elicits small, but reproducible, direct effects on calcium content in the parietal bones not only in female but also in male fetal mice at physiological-free E2 concentrations (10(-12)-10(-11) mol/L), which is attainable in serum of normal human subjects. In contrast to in vivo studies, pharmacological doses of 17 beta-estradiol had no anabolic effect on parietal bones. The mechanism of such a biphasic effect of estrogens remains to be elucidated.

Primary immunolocalization of estrogen and progesterone target cells in the human anterior cruciate ligament

To identify estrogen and progesterone target cells in the human anterior cruciate ligament immunohistochemical localization of both estrogen and progesterone receptors was performed in 17 specimens of human anterior cruciate ligament. All ligament specimens were obtained at surgery. Thirteen specimens were from women, and four were from men: the average age was 57 years (range, 18-78 years). Eleven specimens (from nine women and two men) came from total knee replacements for osteoarthritis of the knee: three (from two women and one man), from reconstructions of the anterior cruciate ligament: two (both from women), from medial meniscectomies; and one (from a man), from an amputation secondary to chondrosarcoma of the pelvis. An immunoperoxidase method using monoclonal antibodies to the estrogen and progesterone receptors was employed to identify estrogen and progesterone target cells in the anterior cruciate ligament. Staining of both receptors was demonstrable in 14 specimens and in the remaining three specimens less than 15% of the cells were stained. Both estrogen and progesterone receptors were localized to synoviocytes in the synovial lining, fibroblasts in the anterior cruciate ligament stroma and cells in the blood vessel walls of the ligament. This demonstration of receptors for estrogen and progesterone in the cells of anterior cruciate ligament suggests that female sex hormones may have an effect on its structure and composition.

Functional estrogen receptors in a human preosteoclastic cell line

The primary biological effect of the estrogen estradiol-17 beta (17 beta E2) on bone is to decrease bone resorption. However, whether 17 beta E2 affects osteoclast differentiation or function directly or through its action on osteoblasts is unclear. To investigate this question we examined the human preosteoclastic cell line FLG 29.1 for evidence of functional estrogen receptors (ERs). Southern blotting of reverse transcription-PCR amplification products with a 32P-labeled cDNA probe for the human ER mRNA demonstrated that FLG 29.1 cells express ER mRNA. Binding of [3H]17 beta E2 to nuclear ERs was steroid specific with approximately 400 saturable, high affinity (Kd approximately 1 nM) binding sites per cell nucleus. Nuclear ERs covalently labeled with [3H]tamoxifen aziridine showed an apparent molecular weight of 65,000 by SDS/PAGE and Western blotting with the D75 monoclonal antibody to human ER. Pretreatment of cells with 0.1, 1.0, or 10 nM 17 beta E2 induced a dose- and time-dependent specific binding of progesterone to FGL 29.1 cells, and stimulation of the cells with 10 nM and 100 nM 17 beta E2 significantly (P < 0.05) reduced cell proliferation. Transcriptional activity of the ER gene was detected by transient transfection of cells with the pERE-BLCAT plasmid containing the estrogen response element for the vitellogenin A2 gene and the bacterial chloramphenicol acetyltransferase reporter gene. Treatment of FLG 29.1 cells with 10 nM 17 beta E2 increased chloroamphenicol acetyltransferase expression from 5- to 29-fold compared to controls. These observations suggest a potential role for estrogen in osteoclastogenesis.