Endogenous excess cortisol and glucocorticoid (GC) therapy are a major cause of secondary osteoporosis in humans. Intense bone resorption can also be observed in other vertebrates such as migratory teleost fish at the time of reproductive migration and during fasting when large amounts of calcium and phosphate are required. Using a primitive teleost, the European eel, as a model, we investigated whether cortisol could play an ancestral role in the induction of vertebral skeleton demineralization. Different histological and histomorphometric methods were performed on vertebral samples of control and cortisol-treated eels. We demonstrated that cortisol induced a significant bone demineralization of eel vertebrae, as shown by significant decreases of the mineral ratio measured by incineration, and the degree of mineralization measured by quantitative microradiography of vertebral sections. Histology and image analysis of ultrathin microradiographs showed the induction by cortisol of different mechanisms of bone resorption, including periosteocytic osteolysis and osteoclastic resorption. Specificity of cortisol action was investigated by comparison with the effects of sex steroids. Whereas, testosterone had no effect, estradiol induced vertebral skeleton demineralization, an effect related to the stimulated synthesis of vitellogenin (Vg), an oviparous specific phospho-calcio-lipoprotein. By contrast, the cortisol demineralization effect was not related to any stimulation of Vg. This study demonstrates GC-induced bone demineralization in an adult non-mammalian vertebrate, which undergoes natural bone resorption during its life cycle. Our data suggest that the stimulatory action of cortisol on bone loss may represent an ancestral and conserved endocrine regulation in vertebrates.
Miskal Sbaihi, Karine Rousseau, Sylvie Baloche, François Meunier, Martine Fouchereau-Peron and Sylvie Dufour
K A Staines, A S Pollard, I M McGonnell, C Farquharson and A A Pitsillides
Aberrant redeployment of the ‘transient’ events responsible for bone development and postnatal longitudinal growth has been reported in some diseases in what is otherwise inherently ‘stable’ cartilage. Lessons may be learnt from the molecular mechanisms underpinning transient chondrocyte differentiation and function, and their application may better identify disease aetiology. Here, we review the current evidence supporting this possibility. We firstly outline endochondral ossification and the cellular and physiological mechanisms by which it is controlled in the postnatal growth plate. We then compare the biology of these transient cartilaginous structures to the inherently stable articular cartilage. Finally, we highlight specific scenarios in which the redeployment of these embryonic processes may contribute to disease development, with the foresight that deciphering those mechanisms regulating pathological changes and loss of cartilage stability will aid future research into effective disease-modifying therapies.
Alessandra Bitto, Francesca Polito, Bruce Burnett, Robert Levy, Vincenzo Di Stefano, Mary Ann Armbruster, Herbert Marini, Letteria Minutoli, Domenica Altavilla and Francesco Squadrito
Glucocorticoid (GC)-induced osteoporosis (GIO) is the most important secondary cause of bone loss. Clinical evidence suggests a role for genistein (GEN) aglycone in the prevention of osteoporosis. We investigated whether GEN could prevent GIO as well as the development of osteonecrosis in the femoral head using an experimental rat model. A total of 28 female Sprague–Dawley rats were used in the study. GIO and osteonecrosis were induced by daily s.c. injections of 30 mg/kg of methylprednisolone (MP; n=7). Another group of animals (MP+GEN; n=7) concomitantly received MP (30 mg/kg per s.c.) and GEN aglycone (5 mg/kg per i.p.) for 60 days. Control animals were administered daily with vehicle (VEH) or GEN (5 mg/kg per i.p.) only. At the beginning and end of the treatment, animals were examined for bone mineral density (BMD) and bone mineral content (BMC). After killing, serum was collected to determine bone-alkaline phosphatase (b-ALP), carboxy-terminal collagen crosslink (CTX) and osteoprotegerin (OPG) levels. Femurs were removed and tested for breaking strength and bone histology analyzed for structural quality of the femoral neck. GEN aglycone prevented bone loss as measured by BMD and BMC. Moreover, GEN significantly increased the bone formation markers b-ALP and OPG, reduced the bone resorption marker CTX and statistically maintained comparable strength versus the VEH only group. Finally, histological scoring revealed a protective effect of GEN on bone structure statistically comparable with the VEH control animals. Results suggest that the GEN aglycone might be a preventive treatment for GIO and complications of osteonecrosis with long-term GC treatment.
MK Lindberg, Z Weihua, N Andersson, S Moverare, H Gao, O Vidal, M Erlandsson, S Windahl, G Andersson, DB Lubahn, H Carlsten, K Dahlman-Wright, JA Gustafsson and C Ohlsson
Estrogen exerts a variety of important physiological effects, which have been suggested to be mediated via the two known estrogen receptors (ERs), alpha and beta. Three-month-old ovariectomized mice, lacking one or both of the two estrogen receptors, were given estrogen subcutaneously (2.3 micro g/mouse per day) and the effects on different estrogen-responsive parameters, including skeletal effects, were studied. We found that estrogen increased the cortical bone dimensions in both wild-type (WT) and double ER knockout (DERKO) mice. DNA microarray analysis was performed to characterize this effect on cortical bone and it identified four genes that were regulated by estrogen in both WT and DERKO mice. The effect of estrogen on cortical bone in DERKO mice might either be due to remaining ERalpha activity or represent an ERalpha/ERbeta-independent effect. Other effects of estrogen, such as increased trabecular bone mineral density, thymic atrophy, fat reduction and increased uterine weight, were mainly ERalpha mediated.
J. W. M. Chow, J. M. Lean, T. Abe and T. J. Chambers
We have previously demonstrated that administration of oestrogen, at doses sufficient to raise serum concentrations to those seen in late pregnancy, increases trabecular bone formation in the metaphysis of adult rats. To determine whether prostaglandins (PGs), which have been shown to induce osteogenesis in vivo, play a role in the induction of bone formation by oestrogen, 13-week-old female rats were given daily doses of 4 mg 17β-oestradiol (OE2)/kg for 17 days, alone or with indomethacin (1 mg/kg). The rats were also given double fluorochrome labels and at the end of the experiment tibias were subjected to histomorphometric assessment. Treatment with OE2 suppressed longitudinal bone growth and increased uterine wet weight, as expected, and neither response was affected by indomethacin. Oestrogen also induced a threefold increase in trabecular bone formation in the proximal tibial metaphysis, which resulted in a substantial increase in trabecular bone volume. As previously observed, the increase in bone formation was predominantly due to an increase in osteoblast recruitment (as judged by an increase in the percentage of bone surface showing double fluorochrome labels), with only a minor increase in the activity of mature osteoblasts (as judged by the mineral apposition rate). Indomethacin abolished the increase in osteoblastic recruitment, but the activity of mature osteoblastic cells remained high. The bone formation rate and bone volume remained similar to controls. The results suggest that PG production may be necessary for the increased osteoblastic recruitment induced by oestrogen, but not to mediate the effects of oestrogen on the activity of mature osteoblasts.
Journal of Endocrinology (1992) 133, 189–195
A. Goulding and E. Gold
Prolonged administration of LHRH agonist suppresses pituitary gonadotrophin secretion, thereby lowering blood oestrogen. This study was undertaken to compare the osteopaenic effects of bilateral ovariectomy and chronic administration of the LHRH agonist, buserelin, in the rat. Four groups of animals which had their skeletons labelled with 45Ca were studied for 4 weeks. Group 1 underwent a sham-ovariectomy, group 2 were surgically ovariectomized, group 3 were given buserelin by daily s.c. injection and group 4 were given a continuous infusion of buserelin by osmotic minipump. Plasma concentrations of oestradiol were measured weekly. Bone resorption was assessed by measuring the urinary excretion of 45Ca and hydroxyproline and determining bone 45Ca content.
Ovariectomy and buserelin treatments lowered blood oestradiol, increased biochemical indices of bone resorption and decreased femur and total body calcium and 45Ca values. The degree of oesteopaenia elicited by ovariectomy and buserelin treatment was similar. Bone responses to s.c. buserelin and to continuous buserelin infusion were alike. We attribute evidence of increases in bone resorption and induction of osteopaenia with buserelin treatment to hypo-oestrogenism.
We have shown for the first time by bone analysis that buserelin induces osteopaenia as effectively as bilateral ovariectomy. This appears to be the first demonstration in the rat that long-term administration of LHRH agonist influences bone. Administration of buserelin provides a new way of inducing oestrogen-deficiency osteopaenia in the rat without removing the ovaries.
Journal of Endocrinology (1989) 121, 293–298
J Jeyabalan, M Shah, B Viollet and C Chenu
There is increasing evidence that osteoporosis, similarly to obesity and diabetes, could be another disorder of energy metabolism. AMP-activated protein kinase (AMPK) has emerged over the last decade as a key sensing mechanism in the regulation of cellular energy homeostasis and is an essential mediator of the central and peripheral effects of many hormones on the metabolism of appetite, fat and glucose. Novel work demonstrates that the AMPK signaling pathway also plays a role in bone physiology. Activation of AMPK promotes bone formation in vitro and the deletion of α or β subunit of AMPK decreases bone mass in mice. Furthermore, AMPK activity in bone cells is regulated by the same hormones that regulate food intake and energy expenditure through AMPK activation in the brain and peripheral tissues. AMPK is also activated by antidiabetic drugs such as metformin and thiazolidinediones (TZDs), which also impact on skeletal metabolism. Interestingly, TZDs have detrimental skeletal side effects, causing bone loss and increasing the risk of fractures, although the role of AMPK mediation is still unclear. These data are presented in this review that also discusses the potential roles of AMPK in bone as well as the possibility for AMPK to be a future therapeutic target for intervention in osteoporosis.
JJ Smink, JG Koster, MG Gresnigt, R Rooman, JA Koedam and SC Van Buul-Offers
Glucocorticoid (GC) treatment in childhood can lead to suppression of longitudinal growth as a side effect. The actions of GCs are thought to be mediated in part by impaired action of the insulin-like growth factors (IGF-I and IGF-II) and their binding proteins (IGFBP-1 to -6). We have studied the effects of GCs on IGF and IGFBP expression at the local level of the growth plate, using non-radioactive in situ hybridization. We treated 3-week-old normal mice for 4 weeks with dexamethasone (DXM). We also treated human IGF-II (hIGF-II) transgenic mice in order to investigate whether IGF-II could protect against the growth retarding effect of this GC. DXM treatment resulted in general growth retardation in both mice strains, however, only in normal mice was tibial length decreased. In both normal and hIGF-II trangenic mice, the total width of the growth plate was not affected, whereas the width of the proliferative zone decreased as a result of the DXM treatment. Additionally, only in normal mice, the width of the hypertrophic zone thickened. Only expression of IGF-I, IGF-II and IGFBP-2 could be detected in the growth plates of 7-week-old normal mice. IGFBP-1, -3, -4, -5 and -6 mRNAs were not detected. DXM treatment of normal mice induced a significant 2.4-fold increase in the number of cells expressing IGF-I mRNA, whereas IGF-II and IGFBP-2 mRNA levels were not affected. In hIGF-II transgenic mice, IGF-I mRNA levels were significantly increased, while endogenous IGF-II and IGFBP-2 mRNAs were unaffected, compared to normal animals. DXM treatment of the hIGF-II transgenic mice induced a further increase of IGF-I mRNA expression, to a similar extent as in DXM-treated normal mice. The increase of IGF-I due to DXM treatment in normal mice might be a reaction in order to minimize the GC-induced growth retardation. Another possibility could be that the increase of IGF-I would contribute to the GC-induced growth retardation by accelerating the differentiation of chondrocytes, resulting in accelerated ossification. In the growth plates of hIGF-II transgenic mice, the higher basal level of IGF-I, might be responsible for the observed partial protection against the adverse effects of GCs on bone.
K. W. Kan and R. L. Cruess
In order to assess glucocorticoid actions on fetal cartilage development, [3H]dexamethasone binding site levels in fetal bovine cartilaginous tissues from long bones were measured, using a whole cell assay at 37 °C. Displaceable [3H]dexamethasone binding in epiphysial growth cartilage was maximal (16·2 fmol/106 cells) in fetuses of 10–15 cm crown–rump length (CR), and declined to 22% of the maximum in fetuses of 20–30 cm CR. Subsequently, [3H]dexamethasone binding rose to a plateau (13·0 fmol/106 cells) in fetuses of 30–80 cm CR and declined in those of 80–100 cm CR. When measured in growth plate cartilage, [3H]dexamethasone binding was significantly higher in fetuses of 40–80 cm CR (39 fmol/106 cells) than in those of 80–100 cm CR. There was no significant change of [3H]dexamethasone binding affinities in epiphysial chondrocytes of 5–100 cm CR fetuses or in growth plate chondrocytes of 40–100 cm CR fetuses.
These results demonstrate that fetal cartilaginous tissues during development possess varying cellular levels of glucocorticoid binding and may thus have temporal changes in sensitivity to glucocorticoid hormones.
J. Endocr. (1986) 110, 257–262
D. N. KALU, CARMEL HILLYARD and G. V. FOSTER
The effect of glucagon on bone was studied in rats. Urinary hydroxyproline excretion and incorporation of [3H]proline into bone hydroxyproline were used as indices of bone collagen breakdown and formation respectively. Parathyroid extract (15 USP units/rat/h, i.v.), infused into thyroparathyroidectomized animals, increased urinary hydroxyproline excretion. This increase was nullified by simultaneous administration of glucagon (50 μg/rat/h, i.v.). Rats treated with glucagon for 12 days (30 μg/100 g/day, s.c.) excreted slightly less hydroxyproline in their urine than controls. In both intact and thyroparathyroidectomized rats, glucagon (10 μg/100 g/h, s.c.) decreased incorporation of [3H]proline into bone. Similar results were obtained in nephrectomized rats, evidence that changes produced by glucagon were not solely due to alterations in proline pool size caused by increased renal excretion. From these data it is concluded that: (1) glucagon can inhibit bone resorption (the effect being slight in normal rats, but easily demonstrable in parathyroid hormone-treated thyroparathyroidectomized rats), (2) release of endogenous calcitonin is not required to produce this effect, (3) parathyroid hormone and glucagon may act on the same target cell in bone, (4) inhibition of skeletal resorption may contribute to glucagon-induced hypocalcaemia, and (5) the hormone possibly decreases bone formation. Since pharmacological doses of glucagon were used in our studies, the relationship of the observations made to the physiological role of glucagon is unknown.