The glucocorticoid receptor in skeletal health and disease: insights from targeted knockout mice

Glucocorticoids are steroid hormones, secreted by the adrenals to regulate a range of metabolic, immunologic, and homeostatic functions. Due to their potent anti-inflammatory effects, synthetic glucocorticoids are widely used to treat inflammatory disorders. However, their use especially at high doses and over the long-term is associated with several unwanted side effects that compromises their intended use (e.g. glucocorticoid-induced osteoporosis and/or diabetes, myopathy, and skin atrophy). Both endogenous and synthetic glucocorticoids exert their effects through the glucocorticoid receptor, a transcription factor present in nearly all nucleated cells. Glucocorticoid receptor knockout mouse models have proved to be valuable tools in understanding how glucocorticoids contribute to skeletal health and disease. These models, described in this review, have helped to establish that the effects of glucocorticoids on the skeleton are multifaceted, cell specific and concentration dependent. Intriguingly, while endogenous glucocorticoids are essential for bone formation, high-dose exogenous glucocorticoids may induce bone loss. Additionally, the actions of endogenous glucocorticoids vary greatly depending on the disease microenvironment. For example, endogenous glucocorticoids have predominately beneficial anti-inflammatory effects in rheumatoid arthritis, but detrimental actions in osteoarthritis by driving cartilage loss and abnormal bone formation. Studies in tissue-specific knockout models provide important insights that will aid the development of new glucocorticoid therapeutics that can specifically target certain cell types to minimise unwanted effects from current glucocorticoid therapy.

Deletion of the chondrocyte glucocorticoid receptor attenuates cartilage degradation through suppression of early synovial activation in murine posttraumatic osteoarthritis

OBJECTIVE

Disruption of endogenous glucocorticoid signalling in bone cells attenuates osteoarthritis (OA) in aged mice, however, the role of endogenous glucocorticoids in chondrocytes is unknown. Here, we investigated whether deletion of the glucocorticoid receptor, specifically in chondrocytes, also alters OA progression.

DESIGN

Knee OA was induced by surgical destabilisation of the medial meniscus (DMM) in male 22-week-old tamoxifen-inducible glucocorticoid receptor knockout (chGRKO) mice and their wild-type (WT) littermates (n = 7-9/group). Mice were harvested 2, 4, 8 and 16 weeks after surgery to examine the spatiotemporal changes in molecular, cellular, and histological characteristics.

RESULTS

At all time points following DMM, cartilage damage was significantly attenuated in chGRKO compared to WT mice. Two weeks after DMM, WT mice exhibited increased chondrocyte and synoviocyte hypoxia inducible factor (HIF)-2α expression resulting in extensive synovial activation characterised by synovial thickening and increased interleukin-1 beta expression. At 2 and 4 weeks after DMM, WT mice displayed pronounced chondrocyte senescence and elevated catabolic signalling (reduced Yes-associated protein 1 (YAP1) and increased matrix metalloprotease [MMP]-13 expression). Contrastingly, at 2 weeks after DMM, HIF-2α expression and synovial activation were much less pronounced in chGRKO than in WT mice. Furthermore, chondrocyte YAP1 and MMP-13 expression, as well as chondrocyte senescence were similar in chGRKO-DMM mice and sham-operated controls.

CONCLUSION

Endogenous glucocorticoid signalling in chondrocytes promotes synovial activation, chondrocyte senescence and cartilage degradation by upregulation of catabolic signalling through HIF-2α in murine posttraumatic OA. These findings indicate that inhibition of glucocorticoid signalling early after injury may present a promising way to slow osteoarthritic cartilage degeneration.

What skills do New Zealand clinicians have to provide first trimester abortion in primary care and are they willing?

OBJECTIVE

To determine the skills and intentions of health practitioners in New Zealand to provide first trimester abortion care.New Zealand achieved abortion law reform in 2020, changing how abortion could be delivered and experienced by pregnant people. However, little has changed in the way abortion care is provided.

STUDY DESIGN

This survey, which was deployed to a range of health practitioners via regulatory bodies and professional groups, used an online free text and tick box survey. Questions included demographics, scope of practice, abortion care experience, philosophical perspective on abortion, and skills transferable to abortion care. Data was analysed using descriptive statistics and deductive and inductive thematic analysis.

RESULTS

128 respondents included doctors, nurses, midwives, counsellors, and social workers from a range of practice settings, the majority from primary health (51%). Most respondents indicated competency or proficiency in clinical skills relevant to provision of early medical abortion. However, practitioners were more likely to indicate "I do not have this skill" or "support required" for: calculating gestational age by bimanual examination (42%), LARC (implant and IUC) insertion (36%), undertake a pregnancy related consultation using tikanga best practice guidelines (19%).Analysis of qualitative data showed three main themes; (1) support for abortion access and for abortion provision in primary care (2) levels of intention to provide abortion (3) critical components for an action plan for abortion in primary care.

CONCLUSION

Abortion care in the community has support from health practitioners. They identified needs including development of clinical skills, funding, and wider sector support.

Osteoblastic glucocorticoid signaling exacerbates high-fat-diet- induced bone loss and obesity

Chronic high-fat diet (HFD) consumption not only promotes obesity and insulin resistance, but also causes bone loss through mechanisms that are not well understood. Here, we fed wild-type CD-1 mice either chow or a HFD (43% of energy from fat) for 18 weeks; HFD-fed mice exhibited decreased trabecular volume (-28%) and cortical thickness (-14%) compared to chow-fed mice. In HFD-fed mice, bone loss was due to reduced bone formation and mineral apposition, without obvious effects on bone resorption. HFD feeding also increased skeletal expression of sclerostin and caused deterioration of the osteocyte lacunocanalicular network (LCN). In mice fed HFD, skeletal glucocorticoid signaling was activated relative to chow-fed mice, independent of serum corticosterone concentrations. We therefore examined whether skeletal glucocorticoid signaling was necessary for HFD-induced bone loss, using transgenic mice lacking glucocorticoid signaling in osteoblasts and osteocytes (HSD2^OB/OCY-tg mice). In HSD2^OB/OCY-tg mice, bone formation and mineral apposition rates were not suppressed by HFD, and bone loss was significantly attenuated. Interestingly, in HSD2^OB/OCY-tg mice fed HFD, both Wnt signaling (less sclerostin induction, increased β-catenin expression) and glucose uptake were significantly increased, relative to diet- and genotype-matched controls. The osteocyte LCN remained intact in HFD-fed HSD2^OB/OCY-tg mice. When fed a HFD, HSD2^OB/OCY-tg mice also increased their energy expenditure and were protected against obesity, insulin resistance, and dyslipidemia. Therefore, glucocorticoid signaling in osteoblasts and osteocytes contributes to the suppression of bone formation in HFD-fed mice. Skeletal glucocorticoid signaling is also an important determinant of glucose uptake in bone, which influences the whole-body metabolic response to HFD.

Loss of the Vitamin D Receptor in Human Breast Cancer Cells Promotes Epithelial to Mesenchymal Cell Transition and Skeletal Colonization

Expression of the vitamin D receptor (VDR) is thought to be associated with neoplastic progression. However, the role of the VDR in breast cancer metastasis to bone and the molecular mechanisms underlying this process are unknown. Employing a rodent model (female Balb/c nu/nu mice) of systemic metastasis, we here demonstrate that knockdown of the VDR strongly increases the metastatic potential of MDA-MB-231 human breast cancer cells to bone, resulting in significantly greater skeletal tumor burden. Ablation of VDR expression promotes cancer cell mobility (migration) and invasiveness, thereby facilitating skeletal colonization. Mechanistically, these changes in tumor cell behavior are attributable to shifts in the expression of proteins involved in cell adhesion, proliferation, and cytoskeletal organization, patterns characteristic for epithelial-to-mesenchymal cell transition (EMT). In keeping with these experimental findings, analyses of human breast cancer specimens corroborated the association between VDR expression, EMT-typical changes in protein expression patterns, and clinical prognosis. Loss of the VDR in human breast cancer cells marks a critical point in oncogenesis by inducing EMT, promoting the dissemination of cancer cells, and facilitating the formation of tumor colonies in bone. © 2019 American Society for Bone and Mineral Research.

The use of therapeutic drug monitoring in the management of protease inhibitor-related toxicity

The aim of this project was to determine whether therapeutic drug monitoring (TDM) and subsequent dose modification is effective in the management of protease inhibitor (PI)-associated toxicity. A retrospective case-notes review of patients who had had TDM for suspected antiretroviral drug toxicity from November 2000 to March 2002 was carried out. This identified six symptomatic patients in whom high plasma drug levels of a PI had been found and subsequent dose modification was associated with improvement/resolution of symptoms. In 5/6 patients viral loads were below the level of detection prior to TDM and remained so after dose reduction of PI. TDM-directed dose modification of PI enables patients to continue effective regimens of highly active antiretroviral therapy, thus avoiding the need to switch the regimen.

Training and other predictors of personal protective equipment use in Australian grain farmers using pesticides

OBJECTIVES

To investigate patterns of use of personal protective equipment (PPE) to reduce pesticide exposure in a sample of Australian farmers and also to assess the influence of possible predictive factors.

METHODS

A cross-sectional survey of 1102 farmers recruited through the Victorian Farmers Federation (VFF) was conducted. A written questionnaire was filled out by participants at VFF meetings attended by a visiting research assistant. Participants answered questions about frequency of pesticide use and PPE items they usually used when doing two different pesticide-related tasks, mixing and application, of each of four classes of pesticides. They also answered questions about personal characteristics, farm characteristics, farming activities, career and health.

RESULTS

Nearly all surveyed farmers had ever used pesticides, and over 87% had used Herbicides or Animal Health Products in the previous 12 months. Non-use of PPE was frequently reported, with up to 10-40% of farmers routinely using no PPE at all when using pesticides. Across all pesticide classes, PPE use was higher for pesticide mixing than for application. In multivariate analyses PPE use appeared to be most strongly associated with younger age and farm chemical training.

CONCLUSIONS

PPE use across all pesticide classes was poor, indicating the possibility of clinically significant pesticide exposure in many farmers. Given that PPE use was found to be associated with farm chemical training, the authors suggest that training is likely to be an important intervention for reducing farmers' pesticide exposure. Poor uptake of farm chemical training by farmers and the aging farming workforce are causes for concern in the light of these findings.

The introduction of a daily telephone advice service: how is it used and is it worth the effort?

Improving access to medical advice by telephone may reduce unnecessary consultations, limit interruptions through the day and provide a more flexible service to meet patient needs. We advertised and introduced a daily advice line for patients and found that it was used appropriately and to mutual benefit.

Acid hydrolase activities in B cell chronic lymphocytic leukaemia lymphocytes: correlation of cytochemical reactions with immunological phenotype

The cytochemical reactions of 5 acid hydrolases, alpha-naphthyl acetate esterase (ANAE), acid phosphatase (AP), beta-glucuronidase, beta-glucosaminidase and dipeptidylaminopeptidase IV (DAP IV) were investigated in lymphocytes from 30 patients with B cell chronic lymphocytic leukaemia (B-CLL). Based on ANAE and AP reactivities, 4 cytochemically distinctive subgroups were identified: Group 1: AP and ANAE less than 50% positive lymphocytes (5 cases); Group 2: AP greater than 50%, ANAE less than 50% positive lymphocytes (11 cases); Group 3: AP less than 50%, ANAE greater than 50% positive lymphocytes (7 cases); Group 4: AP and ANAE greater than 50% positive lymphocytes (7 cases). beta-Glucuronidase displayed similar patterns of reactivity to AP. beta-Glucosaminidase activity was observed in the majority of lymphocytes in most patients, whereas DAP IV activity was present in less than 20% of lymphoid cells. The study failed to establish any relationship between cytochemical grouping and patients' clinical status, peripheral lymphocyte counts, E or mouse rosette values, light or heavy chain cellular immunoglobulin (Ig) class. Attempts to correlate acid hydrolase and Ig heavy chain isotype expression, putative markers of B cell maturation, were unsuccessful and indicate that within the narrow spectrum of B cell differentiation seen in B-CLL these characteristics are unrelated.