The Role of Glucocorticoids in Bone Metabolism
Glucocorticoids are potent anti-inflammatory steroids that are highly effective in the treatment of diseases such as rheumatoid arthritis, asthma, inflammatory bowel disease, malignancies and in organ transplantation. While the beneficial effects of glucocorticoids are hard to overestimate, their application is limited by numerous adverse (side) effects such as osteoporosis, muscle wasting, diabetes and skin atrophy.
The members of the Bone Research Program have a long-standing interest in the effects of glucocorticoids on bone, both under physiological and pathological conditions. Using cutting-edge techniques such as knock-out, overexpression and gene therapy models, we are investigating the molecular actions of endogenous and exogenous glucocorticoids on bone and beyond. One of the models we have been using extensively is characterised by a transgene that results in the inactivation of glucocorticoids in the bone forming cells (‘osteoblast’) only. The transgene directs these cells to produce an enzyme known as 11beta-hydroxysteroid dehydrogenase type 2, which converts active cortisol into inactive cortisone. This model allows us to study the actions of glucocorticoids on osteoblasts and dissect these from the effects on other cell types. In addition, we have established a range of cell-targeted glucocorticoid receptor (GR) knock-out models, generating GR-deficient connective tissue (fibroblasts), bone forming (osteoblasts), cartilage (chondrocytes) and fat cells (adipocytes). Using these models in vitro and in vivo, we are currently working on the following research projects:
- Effects of exogenous glucocorticoids on bone, fat and muscle metabolism.
- Endogenous glucocorticoids and ageing.
- Endogenous glucocorticoids and wnt signaling in bone development.
- Endogenous glucocorticoids in immune arthritis.
- The glucocorticoid-receptor and its role in skeletal biology
Effects of exogenous glucocorticoids on bone, fat and energy metabolism
S Gasparini, H Henneicke, S Kim, C Jørgensen, H Bräuner-Osborne, H Zhou, MJ Seibel
The bone-related effects of exogenous glucocorticoids, particularly when given at pharmacological (therapeutic) levels, are of major interest. Glucocorticoid-induced osteoporosis is the most frequent form of secondary osteoporosis and remains an unsolved medical problem. However, glucocorticoids affect not only bone but also many other systems, including glucose and lipid (i.e. systemic energy metabolism). Surprisingly, some of these effects seem to be mediated through bone, which makes the skeleton an even more interesting target of research. To study these questions in more detail, we have developed a method of long-term glucocorticoid treatment that enables us to deliver a sustained pharmacological dose of glucocorticoids and hence simulate chronic exogenous glucocorticoid excess (Steroids 74: 245-249, 2009). Using this method in models where osteoblastic glucocorticoid signalling has been interrupted, we established that the osteoblast is the main skeletal target of glucocorticoid action (Bone 49: 733-42, 2011). To our surprise, we also found that the osteoblast mediates not only the deleterious effects of glucocorticoids on bone but also those on systemic energy metabolism. Very recently, we demonstrated that osteoblasts play a central role in the pathogenesis of glucocorticoid-induced diabetes and obesity (J Clin Invest 122: 4172-89, 2012). We established that targeted disruption of glucocorticoid signalling in osteoblasts results in preservation of osteoblastic osteocalcin release, while at the same time preventing the development of insulin resistance, glucose intolerance and obesity in glucocorticoid-treated mice. Nearly identical effects were achieved when we replaced osteocalcin in glucocorticoid-treated animals via gene therapy.
Moreover, replacement of osteocalcin resulted in clearance of hepatic lipid deposits and improved phosphorylation of the insulin receptor, despite treatment with high-dose glucocorticoids. These data suggests that the effects of glucocorticoids on systemic energy metabolism are mediated, in significant parts, through their actions on bone cells. We are currently in the process of identifying the mechanisms that govern the changes in bone, fat, muscle and fuel metabolism induced by exogenous glucocorticoids.
Interaction of Exogenous Glucocorticoids and Sex Steroids in Metabolic Dysfunction
S Gasparini, H Henneicke, S Kim, M Swarbrick, D Handelsman, H Zhou, MJ Seibel
Glucocorticoid excess is associated with adverse metabolic effects which often limits their therapeutic use, thus a greater understanding of the mechanisms underlying these side effects is paramount. As male rodents have been shown to respond more robustly to the anti-inflammatory effects of glucocorticoids, we aimed to determine whether there are also sex differences in the metabolic response to glucocorticoids.
We have now observed that mice have a strong dichotomy in their metabolic response to excess glucocorticoids, with males being more sensitive than females. Our data indicate that androgens potentiate the adverse metabolic side effects of excess glucocorticoids.
Endogenous Glucocorticoids and Wnt signaling in bone development
C Fong-Yee, C Dunstan, D Chen (USA), MJ Seibel, H Zhou
We have discovered a novel mechanism by which glucocorticoids regulate mature osteoblastic control of mesenchymal progenitor lineage commitment, via Wnt signalling pathways (J Biol Chem 283: 1936-45, 2008). Consequently, we identified that blocking glucocorticoid signalling in osteoblasts delayed development of the skull in newborn mice and is thus required for the normal development of calvarial bone structures (Development 136: 427-436, 2009). In collaboration with Prof Di Chen (University of Rochester, USA) we are investigating the interaction of glucocorticoid and Wnt signaling in osteoblastic control of mesenchymal lineage commitment. In the long term, we hope that these studies will lead to strategies for the prevention of the detrimental effects of cortisone on bone.
Endogenous Glucocorticoids and Ageing
H Henneicke, S Kim, M Swarbrick, M Cooper, MJ Seibel, H Zhou
Ageing is associated with well characterised changes in body composition and energy metabolism. These include central obesity, glucose intolerance or diabetes, loss of muscle mass and osteoporosis. Interestingly, however, many of these changes are also key features of glucocorticoid-induced metabolic disease. We therefore reasoned that there could be a mechanistic link between glucocorticoid actions on bone and the changes in body composition and fuel metabolism seen with ageing.
We have now observed that targeted abrogation of osteoblastic glucocorticoid-signalling in mice almost completely prevents the age-related changes in body weight and fat mass seen in aged animals with normal glucocorticoid signalling in bone forming cells. It therefore appears that the changes in body composition occurring with age are related to the actions of endogenous glucocorticoids on osteoblasts. As these findings may have implications for our understanding of ageing in general, we aim to identify the mechanisms that link the skeletal actions of endogenous glucocorticoids with changes in body composition, body weight and systemic energy metabolism during ageing.
Endogenous Glucocorticoids and Diet-induced Bone, Fat and Metabolic Dysregulation
S Kim, H Henneicke, M Swarbrick, MJ Seibel, H Zhou
Overconsumption of energy-dense diets has become a major public health challenge due its causal association with obesity, diabetes and poor skeletal health. However, most animal studies that examine diet-induced obesity and diabetes have focused solely on very high-energy high-fat feeding and thus, we aimed to determine whether these adverse health outcomes are due to the high-energy density or high-fat component of diets. Further, we have previously shown that disruption of glucocorticoid signaling in bone protects mice from the adverse metabolic side effects of exogenous glucocorticoids hence, we also aimed to investigate whether abrogating glucocorticoid signaling in bone can protect from diet-induced metabolic disturbances.
We have now observed that high-energy feeding, regardless of dietary fat content induced obesity, hyperglycaemia and insulin insensitivity. Both high-energy diets induced significant bone loss. Surprisingly, targeted abrogation of osteoblastic glucocorticoid-signalling in mice almost completely prevents the high-fat or high-energy diets induced bone and metabolic dysfunction. These data indicates that high-energy density rather than high dietary fat content is a major driver of metabolic dysfunction. Importantly, these effects appear to be mediated by glucocorticoid signaling in osteoblasts and osteocytes. We are currently in the process of identifying the mechanisms that govern the link the skeletal actions of endogenous glucocorticoids with changes in bone, fat and systemic energy metabolism induced by high-energy or high-fat diets.
Endogenous Glucocorticoids in Osteoarthritis
J Tu, C Little, M Cooper, MJ Seibel, H Zhou
Osteoarthritis is one of the most common chronic diseases worldwide. With the rise in life expectancy the prevalence of degenerative joint disease has increased continuously and across all ethnicities. It is estimated that by the age 65 years, 80% of people have radiographic evidence of osteoarthritis. Treatments for osteoarthritis are primarily prescribed to reduce symptoms with no medical interventions known to effectively prevent or delay the development of degenerative joint disease. Intra-articular glucocorticoid injection is one of treatments used for decades for pain relief. Recently, a clinical study report that Intra-articular glucocorticoid injection resulted in significantly greater cartilage volume loss and no significant difference in knee pain when compare to intra-articular saline placebo osteoarthritis group (McAlindon et al., JAMA, 2017).
We investigated the impact of endogenous glucocorticoids in a murine model of surgically induced osteoarthritis. We made the observation that the surgically induced osteoarthritis was attenuated when glucocorticoid signalling was disrupted in osteoblasts/osteocytes. Our finding opens up new areas of research. The critical role of endogenous glucocorticoids in the pathogenesis of osteoarthritis has never been recognised before. Our findings allow for an innovative approach to a very old but unsolved problem of great medical and social significance. We plan to elucidate how glucocorticoids regulate osteoblast, osteocyte and chondrocyte function to promote the development of degenerative joint damage. We are currently investigating precise mechanisms by which endogenous glucocorticoids promote the progression of osteoarthritis as these hitherto unrecognised functions of endogenous glucocorticoids may open up new avenues for the prevention and treatment of human osteoarthritis.
Endogenous Glucocorticoids in Immune Arthritis
J Tu, J Tuckermann, F Buttgereit, C Little, M Cooper, MJ Seibel, H Zhou
Synthetic glucocorticoids are of great importance in the treatment of rheumatoid arthritis (RA) and other inflammatory rheumatic diseases. The role of endogenous glucocorticoid action in contributing to the susceptibility and/or severity of RA remains to be elucidated. While investigating the role of endogenous glucocorticoids in immune-mediated arthritis, we made the surprising observation that arthritis was attenuated when glucocorticoid signalling was disrupted in osteoblasts. These unexpected observations suggest that endogenous glucocorticoids modulate the local inflammatory response through direct effects on osteoblasts (Arthritis & Rheum 60:1998-2007, 2009).
In collaboration with Prof Frank Buttgereit (Berlin, Germany), Prof Jan Tuckermann (Ulm, Germany) and Prof Mark Cooper (Sydney) we are currently investigating the mechanisms behind our observations. In particular, we are focussing on the cells in the joints such as osteoblasts, chondrocytes and synovial fibroblasts.
The role of the Vitamin D receptor in malignant bone disease
Y Zheng, K Horas, C Fong-Yee, H Zhou, MJ Seibel
Breast cancer and prostate cancer each have a particular preference to form secondary tumours (metastases) in bone. Breast cancer metastases to bone are associated with bone destruction (‘lytic lesions’) which frequently cause significant pain, pathological fractures and hypercalcaemia. Metastases from prostate cancer usually induce high bone formation, resulting in ‘sclerotic’ or ‘osteoblastic’ lesions which consist of disorganised bone and also can cause severe pain and pathological fractures. In both breast and prostate cancers, the tumour cells ‘enslave’ the resident bone cells (osteoblasts and osteoclasts) to destroy the surrounding normal bone. It has been proposed that the destruction of normal bone leads to the release of growth factors stored in the bone matrix that help the cancer cells to grow faster, thus creating a vicious cycle that contributes to the survival and expansion of bone metastases.
The BRP is particularly interested in how the bone microenvironment and its behaviour affect tumour growth in bone. One way of doing this is to manipulate bone remodelling rates and observe how changes in bone turnover impact the ability of cancer cells to target bone and to establish destructive tumours. For example, anti-resorptive treatments inhibit tumour growth in bone indirectly through effects on osteoclasts, rather than directly through effects on tumour cells (Bone 2007). Furthermore, we demonstrated for the first time that dietary calcium insufficiency strongly promotes tumour growth in bone, mainly through a PTH-mediated increase in bone turnover (Cancer Research 2007; Clin Exp Metastasis 2008). In further research, we found that vitamin D deficiency has similar effects on the growth of breast or prostate cancer in bone (Cancer Research 2010, Bone 2010, The Prostate 2011). While the accelerated destructive process is in part due to an increase in osteoclast mediated bone resorption, our results also suggest that vitamin D, and in particular the vitamin D receptor itself exert direct control over breast and prostate cancer progression in primary and secondary tumours (Bone Research 2017). Results of these studies may have clinical implications as vitamin D deficiency contributes to the risk of developing breast cancer and prostate and to its progression to metastatic disease.
Effects of FSH on Bone Structure and Metabolism
S Kim, H Zhou, DJ Handelsman, MJ Seibel
In collaboration with Dr Charles Allan and Prof David Handelsman (Andrology), we are studying the phenotype of female transgenic mice over expressing human FSH. We have determined that these mice develop high bone density. This study shows for the first time an apparent anabolic effect of human FSH on mouse bone (Allan et al., PNAS 2010). Further studies are planned to investigate in more detail the mechanism for the bone changes in these mice.
In addition to basic research, the Bone Research Program has a strong clinical research arm. Most of this research happens at the academic section of the Department of Endocrinology & Metabolism, which is part of both Concord Hospital (Sydney Local Health District) and the ANZAC Institute’s Bone Research Program.
The Concord Fracture Liaison Service: A world-class research and clinical program for secondary fracture prevention
K Ganda and MJ Seibel
Despite the availability of effective treatments that greatly reduce the risk of re-fracture, most patients with incident osteoporotic fractures are neither investigated nor treated for their underlying condition. World-wide, over 70% of people with osteoporotic fractures go undiagnosed and untreated. This appalling situation led us to implement the “Concord Fracture Liaison Service” at Concord Hospital in 2005, with the aim to significantly improve the care of people with osteoporosis. This patient-focussed service includes targeted case-finding, systematic assessment and evaluation, and pharmacological and non-pharmacological treatment as indicated. Other components include patient self-management education programs and support systems, exercise and nutritional advice, care coordination and access to specialised health professionals.
The structure of the FLS is simple. Patients 45 years or older presenting to Concord Hospital with a fracture are being screened to determine whether the fracture had resulted from inadequate trauma. Patients deemed to have suffered a fragility fracture then undergo a standardized series of assessments and investigations, including a medical history, physical examination, bone mineral density (BMD) scan, thoracolumbar spine radiographs and specific blood and urine tests. Multidisciplinary resources were used as appropriate, including involvement of other specialists, Physiotherapy, Dietetics, nursing teams, Social/ Allied Health Services at Concord Hospital. Patients diagnosed with osteoporosis were educated about their condition, the risks and benefits of available treatments, and the need for long-term adherence with their management plan. Patients were offered evidence-based pharmacologic and non-pharmacologic interventions as indicated. All patients had access to government-subsidized medications approved in Australia for the secondary prevention of osteoporotic fractures. Patients were reviewed 3 months after their initial visit, and annually thereafter. Annual follow-up visits included an assessment of medication compliance and adverse effects, a physical examination and follow-up questionnaire, together with serial BMD scans and selected laboratory tests. The FLS worked in close co-operation with chronic care services, primary care, community-based lifestyle services and homecare services which are an integral part of the service.
Outcome data analysed after 4 years, evaluated re-fracture rates in people who underwent standard care (i.e. non FLS care) compared to those managed by the FLS. The analysis included 403 patients (246 in the intervention and 157 in the control group). Both groups had similar baseline characteristics, with no differences in socioeconomic status, clinical risk factors, or the frequency of prevalent osteoporotic fractures (Osteoporosis Intl. 2011). Figure 1 demonstrates the incidence of re-fracture between the two groups: There were 10 (4.1%) new fractures in patients managed by the FLS, and 31 (19.7%) new fractures in the control group (p< 0.001). Thus, the risk of suffering a further fracture over four years was reduced by 80% in the intervention group. In those who suffered a new fracture, the time to re-fracture was significantly longer in the FLS group (26 vs. 16 months). The effect of the intervention was independent of age, gender and fracture type. Thus, the key factor achieving the re-fractures in the MTF group was the intervention itself.
As an outpatient service, the Concord FLS is sustainable with relatively little support. On a wider scale, the Concord FLS is cost-efficient on the basis of greatly reduced cost for treating re-fractures. Health economic modelling demonstrates the cost per QALY delivered ranges between AUD 19,500 and 33,600, well below the $50,000 mark – the commonly accepted Australian threshold indicating health economic cost-effectiveness. This has been published in Osteoporosis International, the leading journal in the field of clinical osteoporosis care (Osteoporosis Intl. 2012).
The Concord Fracture Liaison Service has provided tangible improvements in osteoporosis care to the community, as demonstrated by clinically relevant outcome measures (re-fracture rates). This model of care is not only cost-effective, but applicable to any health care network. In recognition of the innovative achievements of this service, Concord Hospital and the Sydney Local Health District have received both the Baxter Award 2012 and the NSW Premier’s Award 2012.
The Concord Health in Ageing Men Project (CHAMP)
Epidemiological studies on ageing have tended to focus on women, a phenomenon recognized by sociologists as the feminization of ageing. However, a large percentage of older people are men. For example, in Australia, 44% of those aged 65 and over are male, as are 39% of those aged 75 years and over. Furthermore, the 5–7 year shorter life expectancy for men than women and higher death rates at all ages, including older ages, suggest that more detailed study of the health of older men is essential.
The Concord Health and Ageing in Men Project (CHAMP) was established to investigate health in old men, defined as age 70 years and over. There is no upper age limit for recruitment into CHAMP. The initial chief investigators were Robert Cumming, David Handelsman, Markus Seibel, Helen Creasey, Philip Sambrook, Louise Waite, Vasi Naganathan and David Le Couteur. The study has been funded through several projects grants by the National Health and Medical Research Council of Australia, with additional funding from other competitive sources. Recruitment of study subjects occurred during 2005 and 2006, with the first follow-up assessments in early 2007. Since then, there were two further assessments, producing a wealth of cross-sectional and prospective longitudinal data. Since its inception in 2005, the team has published over 30 original reports on topics relevant to the ageing of older men, including pain, depression and quality of life; psychotropic drug use and alcohol drinking; polypharmacy; ethnicity and falls; the prevalence and treatment of osteoporosis in older Australian men; factors affecting bone loss, muscle strength and fractures, socioeconomic status and bone health; urinary incontinence; frailty and use of health resources, to name a few.
