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Morag J Young Baker Heart and Diabetes Institute, Prahran, Australia
Hudson Institute of Medical Research, Clayton, Australia

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Colin D Clyne Hudson Institute of Medical Research, Clayton, Australia

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Karen E Chapman The University/BHF Centre for Cardiovascular Science, The University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh, UK

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Coronavirus disease (COVID-19) is caused by a new strain of coronavirus, the severe acute respiratory syndrome coronavirus 2 or SARS-CoV-2. At the time of writing, SARS-CoV-2 has infected over 5 million people worldwide. A key step in understanding the pathobiology of the SARS-CoV-2 was the identification of -converting enzyme 2 (ACE2) as the receptor for SARS-CoV-2 to gain entry into host cells. ACE2 is an established component of the ‘protective arm’ of the renin-angiotensin-aldosterone-system (RAAS) that opposes ACE/angiotensin II (ANG II) pressor and tissue remodelling actions. Identification of ACE2 as the entry point for SARS-CoV-2 into cells quickly focused attention on the use of ACE inhibitors (ACEi), angiotensin receptor blockers (ARB) and mineralocorticoid receptor antagonists (MRA) in patients with hypertension and cardiovascular disease given that these pharmacological agents upregulate ACE2 expression in target cells. ACE2 is cleaved from the cells by metalloproteases ADAM10 and ADAM17. Steroid hormone receptors regulate multiple components of the RAAS and may contribute to the observed variation in the incidence of severe COVID-19 between men and women, and in patients with pre-existing endocrine-related disease. Moreover, glucocorticoids play a critical role in the acute and chronic management of inflammatory disease, independent of any effect on RAAS activity. Dexamethasone, a synthetic glucocorticoid, has emerged as a life-saving treatment in severe COVID-19. This review will examine the endocrine mechanisms that control ACE2 and discusses the impact of therapies targeting the RAAS, glucocorticoid and other endocrine systems for their relevance to the impact of SARS-CoV-2 infection and the treatment and recovery from COVID-19-related critical illness.

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Clement K M Ho Prostate Research Group, Endocrinology Unit, Clinical Biochemistry, University of Edinburgh Cancer Research Centre, Western General Hospital, 4th floor MRC Human Genetics Building, Crewe Road South, Edinburgh EH4 2XU, UK
Prostate Research Group, Endocrinology Unit, Clinical Biochemistry, University of Edinburgh Cancer Research Centre, Western General Hospital, 4th floor MRC Human Genetics Building, Crewe Road South, Edinburgh EH4 2XU, UK

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Jyoti Nanda Prostate Research Group, Endocrinology Unit, Clinical Biochemistry, University of Edinburgh Cancer Research Centre, Western General Hospital, 4th floor MRC Human Genetics Building, Crewe Road South, Edinburgh EH4 2XU, UK

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Karen E Chapman Prostate Research Group, Endocrinology Unit, Clinical Biochemistry, University of Edinburgh Cancer Research Centre, Western General Hospital, 4th floor MRC Human Genetics Building, Crewe Road South, Edinburgh EH4 2XU, UK

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Fouad K Habib Prostate Research Group, Endocrinology Unit, Clinical Biochemistry, University of Edinburgh Cancer Research Centre, Western General Hospital, 4th floor MRC Human Genetics Building, Crewe Road South, Edinburgh EH4 2XU, UK

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Oestrogens have been implicated as a cause of benign prostatic hyperplasia (BPH). Previous animal studies led to the hypothesis that oestrogens can stimulate prostate growth, resulting in hyperplasia of the gland. In humans, the precise role of oestrogens in BPH pathogenesis is currently unclear. We investigated the direct effects of oestradiol on the proliferation of BPH-derived prostate cells in culture. Oestradiol (10−7 and 10−6 M) moderately increased the proliferation of stromal cells in culture; this stimulation was antagonised by anti-oestrogen ICI 182 780, indicating an oestrogen receptor (ER)-mediated mechanism. By contrast, oestradiol had no effects on the proliferation of epithelial cells in culture. Parameters that can determine the response of stromal cells to oestrogens, including expression of the two ER subtypes and aromatase activity, were investigated. ERβ expression in stromal cells in culture was demonstrated by immunohistochemistry and western blot analysis, and was confirmed by semi-quantitative RT-PCR showing higher expression of ERβ than ERα mRNA in stromal cells. Aromatase, the enzyme that converts androgen precursors to oestrogens, was also examined. Aromatase mRNA and activity were detected in stromal, but not epithelial cells in culture, suggesting a mechanism whereby oestrogen concentrations can be regulated in the BPH stroma. Taken together, these findings support the hypothesis that oestrogens play a role in the pathogenesis of BPH, a disease characterised predominantly by stromal overgrowth.

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Jethro S Johnson Computational Genomics Analysis and Training, Medical Research Council-Functional Genomics Unit, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK

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Monica N Opiyo University/BHF Centre for Cardiovascular Science, Queen’s Medical Research Institute, Edinburgh, UK

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Marian Thomson Edinburgh Genomics, Ashworth Laboratories, University of Edinburgh, Edinburgh, UK

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Karim Gharbi Edinburgh Genomics, Ashworth Laboratories, University of Edinburgh, Edinburgh, UK

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Jonathan R Seckl University/BHF Centre for Cardiovascular Science, Queen’s Medical Research Institute, Edinburgh, UK

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Andreas Heger Computational Genomics Analysis and Training, Medical Research Council-Functional Genomics Unit, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK

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Karen E Chapman University/BHF Centre for Cardiovascular Science, Queen’s Medical Research Institute, Edinburgh, UK

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The enzyme 11β-hydroxysteroid dehydrogenase (11β-HSD) interconverts active glucocorticoids and their intrinsically inert 11-keto forms. The type 1 isozyme, 11β-HSD1, predominantly reactivates glucocorticoids in vivo and can also metabolise bile acids. 11β-HSD1-deficient mice show altered inflammatory responses and are protected against the adverse metabolic effects of a high-fat diet. However, the impact of 11β-HSD1 on the composition of the gut microbiome has not previously been investigated. We used high-throughput 16S rDNA amplicon sequencing to characterise the gut microbiome of 11β-HSD1-deficient and C57Bl/6 control mice, fed either a standard chow diet or a cholesterol- and fat-enriched ‘Western’ diet. 11β-HSD1 deficiency significantly altered the composition of the gut microbiome, and did so in a diet-specific manner. On a Western diet, 11β-HSD1 deficiency increased the relative abundance of the family Bacteroidaceae, and on a chow diet, it altered relative abundance of the family Prevotellaceae. Our results demonstrate that (i) genetic effects on host–microbiome interactions can depend upon diet and (ii) that alterations in the composition of the gut microbiome may contribute to the aspects of the metabolic and/or inflammatory phenotype observed with 11β-HSD1 deficiency.

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Alistair I Freeman
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Helen L Munn
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Val Lyons
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Alexander Dammermann
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Jonathan R Seckl
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Karen E Chapman
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The level of expression of the glucocorticoid receptor (GR) is the principal determinant of glucocorticoid sensitivity in most cells. GR levels are permanently ‘set’ in a tissue-specific manner in response to the perinatal environment, an effect we have previously shown to relate to differential expression of tissue-enriched alternative promoters/exons 1 of the GR gene. In adult animals, GR levels are dynamically regulated around the ‘set point’ by glucocorticoids themselves, with glucocorticoids down-regulating GR mRNA in most cells and tissues. Here we have examined whether autoregulation of GR mRNA by glucocorticoids involves differential promoter regulation. We show that, in contrast to tissue-specific programming of GR mRNA levels, autoregulation of GR mRNA in vivo does not involve differential regulation of variant exon 1-containing GR mRNAs in that the major variants are down-regulated to a similar extent by glucocorticoid treatment. Consistent with this, transfections of reporter constructs showed that the majority of GR promoters, which are contained within a 4.4 kb region upstream of exon 2, are similarly regulated by glucocorticoids, with two regions of the promoter redundantly required for glucocorticoid regulation. Thus transcriptional autoregulation can occur in adult tissues around the set point established by promoter selection in early life.

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Zoi Michailidou Endocrine Unit, Queen’s Medical Research Institute, Centre for Cardiovascular Sciences, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, UK
Departments of Clinical Biochemistry and Medicine, Cambridge Institute for Medical Research, Addenbrooke’s Hospital, Cambridge CB2 2XY, UK

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Anthony P Coll Endocrine Unit, Queen’s Medical Research Institute, Centre for Cardiovascular Sciences, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, UK
Departments of Clinical Biochemistry and Medicine, Cambridge Institute for Medical Research, Addenbrooke’s Hospital, Cambridge CB2 2XY, UK

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Christopher J Kenyon Endocrine Unit, Queen’s Medical Research Institute, Centre for Cardiovascular Sciences, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, UK
Departments of Clinical Biochemistry and Medicine, Cambridge Institute for Medical Research, Addenbrooke’s Hospital, Cambridge CB2 2XY, UK

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Nicholas M Morton Endocrine Unit, Queen’s Medical Research Institute, Centre for Cardiovascular Sciences, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, UK
Departments of Clinical Biochemistry and Medicine, Cambridge Institute for Medical Research, Addenbrooke’s Hospital, Cambridge CB2 2XY, UK

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Stephen O’Rahilly Endocrine Unit, Queen’s Medical Research Institute, Centre for Cardiovascular Sciences, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, UK
Departments of Clinical Biochemistry and Medicine, Cambridge Institute for Medical Research, Addenbrooke’s Hospital, Cambridge CB2 2XY, UK

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Jonathan R Seckl Endocrine Unit, Queen’s Medical Research Institute, Centre for Cardiovascular Sciences, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, UK
Departments of Clinical Biochemistry and Medicine, Cambridge Institute for Medical Research, Addenbrooke’s Hospital, Cambridge CB2 2XY, UK

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Karen E Chapman Endocrine Unit, Queen’s Medical Research Institute, Centre for Cardiovascular Sciences, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, UK
Departments of Clinical Biochemistry and Medicine, Cambridge Institute for Medical Research, Addenbrooke’s Hospital, Cambridge CB2 2XY, UK

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Proopiomelanocortin (POMC) deficiency causes severe obesity through hyperphagia of hypothalamic origin. However, low glucocorticoid levels caused by adrenal insufficiency mitigate against insulin resistance, hyperphagia and fat accretion in Pomc−/−mice. Upon exogenous glucocorticoid replacement, corticosterone-supplemented (CORT) Pomc−/− mice show exaggerated responses, including excessive fat accumulation, hyperleptinaemia and insulin resistance. To investigate the peripheral mechanisms underlying this glucocorticoid hypersensitivity, we examined the expression levels of key determinants and targets of glucocorticoid action in adipose tissue and liver. Despite lower basal expression of 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), which generates active glucocorticoids within cells, CORT-mediated induction of 11β-HSD1 mRNA levels was more pronounced in adipose tissues of Pomc−/−mice. Similarly, CORT treatment increased lipoprotein lipase mRNA levels in all fat depots in Pomc−/− mice, consistent with exaggerated fat accumulation. Glucocorticoid receptor (GR) mRNA levels were selectively elevated in liver and retroperitoneal fat of Pomc−/− mice but were corrected by CORT in the latter depot. In liver, CORT increased phosphoenolpyruvate carboxykinase mRNA levels specifically in Pomc−/− mice, consistent with their insulin-resistant phenotype. Furthermore, CORT induced hypertension in Pomc−/−mice, independently of adipose or liver renin–angiotensin system activation. These data suggest that CORT-inducible 11β-HSD1 expression in fat contributes to the adverse cardiometabolic effects of CORT in POMC deficiency, whereas higher GR levels may be more important in liver.

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Katie J Mylonas University/BHF Centre for Cardiovascular Science, University of Edinburgh, Queen’s Medical Research Institute, Edinburgh, UK

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Neil A Turner Division of Cardiovascular & Diabetes Research, Leeds Institute of Cardiovascular & Metabolic Medicine (LICAMM), School of Medicine, University of Leeds, Leeds, UK

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Sumia A Bageghni Division of Cardiovascular & Diabetes Research, Leeds Institute of Cardiovascular & Metabolic Medicine (LICAMM), School of Medicine, University of Leeds, Leeds, UK

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Christopher J Kenyon University/BHF Centre for Cardiovascular Science, University of Edinburgh, Queen’s Medical Research Institute, Edinburgh, UK

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Christopher I White University/BHF Centre for Cardiovascular Science, University of Edinburgh, Queen’s Medical Research Institute, Edinburgh, UK

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Kieran McGregor University/BHF Centre for Cardiovascular Science, University of Edinburgh, Queen’s Medical Research Institute, Edinburgh, UK

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Robert A Kimmitt University/BHF Centre for Cardiovascular Science, University of Edinburgh, Queen’s Medical Research Institute, Edinburgh, UK

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Richard Sulston University/BHF Centre for Cardiovascular Science, University of Edinburgh, Queen’s Medical Research Institute, Edinburgh, UK

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Valerie Kelly University/BHF Centre for Cardiovascular Science, University of Edinburgh, Queen’s Medical Research Institute, Edinburgh, UK

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Brian R Walker University/BHF Centre for Cardiovascular Science, University of Edinburgh, Queen’s Medical Research Institute, Edinburgh, UK

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Karen E Porter Division of Cardiovascular & Diabetes Research, Leeds Institute of Cardiovascular & Metabolic Medicine (LICAMM), School of Medicine, University of Leeds, Leeds, UK

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Karen E Chapman University/BHF Centre for Cardiovascular Science, University of Edinburgh, Queen’s Medical Research Institute, Edinburgh, UK

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Gillian A Gray University/BHF Centre for Cardiovascular Science, University of Edinburgh, Queen’s Medical Research Institute, Edinburgh, UK

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We have previously demonstrated that neutrophil recruitment to the heart following myocardial infarction (MI) is enhanced in mice lacking 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) that regenerates active glucocorticoid within cells from intrinsically inert metabolites. The present study aimed to identify the mechanism of regulation. In a mouse model of MI, neutrophil mobilization to blood and recruitment to the heart were higher in 11β-HSD1-deficient (Hsd11b1 / ) relative to wild-type (WT) mice, despite similar initial injury and circulating glucocorticoid. In bone marrow chimeric mice, neutrophil mobilization was increased when 11β-HSD1 was absent from host cells, but not when absent from donor bone marrow-derived cells. Consistent with a role for 11β-HSD1 in ‘host’ myocardium, gene expression of a subset of neutrophil chemoattractants, including the chemokines Cxcl2 and Cxcl5, was selectively increased in the myocardium of Hsd11b1 / mice relative to WT. SM22α-Cre directed disruption of Hsd11b1 in smooth muscle and cardiomyocytes had no effect on neutrophil recruitment. Expression of Cxcl2 and Cxcl5 was elevated in fibroblast fractions isolated from hearts of Hsd11b1 / mice post MI and provision of either corticosterone or of the 11β-HSD1 substrate, 11-dehydrocorticosterone, to cultured murine cardiac fibroblasts suppressed IL-1α-induced expression of Cxcl2 and Cxcl5. These data identify suppression of CXCL2 and CXCL5 chemoattractant expression by 11β-HSD1 as a novel mechanism with potential for regulation of neutrophil recruitment to the injured myocardium, and cardiac fibroblasts as a key site for intracellular glucocorticoid regeneration during acute inflammation following myocardial injury.

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Zhenguang Zhang University/BHF Centre for Cardiovascular Science, The Queen’s Medical Research Institute, The University of Edinburgh, Edinburgh, UK

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Agnes E Coutinho University/BHF Centre for Cardiovascular Science, The Queen’s Medical Research Institute, The University of Edinburgh, Edinburgh, UK

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Tak Yung Man University/BHF Centre for Cardiovascular Science, The Queen’s Medical Research Institute, The University of Edinburgh, Edinburgh, UK

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Tiina M J Kipari Centre for Genomic and Experimental Medicine, MRC Institute of Genetic and Molecular Medicine, The University of Edinburgh, Western General Hospital, Edinburgh, UK

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Patrick W F Hadoke University/BHF Centre for Cardiovascular Science, The Queen’s Medical Research Institute, The University of Edinburgh, Edinburgh, UK

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Donald M Salter Centre for Genomic and Experimental Medicine, MRC Institute of Genetic and Molecular Medicine, The University of Edinburgh, Western General Hospital, Edinburgh, UK

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Jonathan R Seckl University/BHF Centre for Cardiovascular Science, The Queen’s Medical Research Institute, The University of Edinburgh, Edinburgh, UK

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Karen E Chapman University/BHF Centre for Cardiovascular Science, The Queen’s Medical Research Institute, The University of Edinburgh, Edinburgh, UK

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11β-Hydroxysteroid dehydrogenase-1 (11β-HSD1) predominantly converts inert glucocorticoids into active forms, thereby contributing to intracellular glucocorticoid levels. 11β-HSD1 is dynamically regulated during inflammation, including in macrophages where it regulates phagocytic capacity. The resolution of inflammation in some disease models including inflammatory arthritis is impaired by 11β-HSD1 deficiency or inhibition. However, 11β-HSD1 deficiency/inhibition also promotes angiogenesis, which is beneficial in mouse models of surgical wound healing, myocardial infarction or obesity. The cell types responsible for the anti-inflammatory and anti-angiogenic roles of 11β-HSD1 have not been characterised. Here, we generated Hsd11b1 MKO mice with LysM-Cre mediated deletion of Hsd11b1 to investigate whether 11β-HSD1 deficiency in myeloid phagocytes is pro-angiogenic and/or affects the resolution of inflammation. Resolution of inflammatory K/BxN-induced arthritis was impaired in Hsd11b1 MKO mice to a similar extent as in mice globally deficient in 11β-HSD1. This was associated with >2-fold elevation in levels of the endothelial marker Cdh5 mRNA, suggesting increased angiogenesis in joints of Hsd11b1 MKO mice following arthritis. A pro-angiogenic phenotype was confirmed by measuring angiogenesis in subcutaneously implanted polyurethane sponges, in which Hsd11b1 MKO mice showed 20% greater vessel density than their littermate controls, associated with higher expression of Cdh5. Thus, 11β-HSD1 deficiency in myeloid phagocytes promotes angiogenesis. Targeting 11β-HSD1 in macrophages may be beneficial in tissue repair.

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Rachel V Richardson University/BHF Centre for Cardiovascular Science, University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh, UK

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Emma J Batchen University/BHF Centre for Cardiovascular Science, University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh, UK

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Adrian J W Thomson Edinburgh Preclinical Imaging, University of Edinburgh, Edinburgh, UK

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Rowan Darroch University/BHF Centre for Cardiovascular Science, University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh, UK

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Xinlu Pan University/BHF Centre for Cardiovascular Science, University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh, UK

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Eva A Rog-Zielinska University/BHF Centre for Cardiovascular Science, University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh, UK

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Wiktoria Wyrzykowska University/BHF Centre for Cardiovascular Science, University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh, UK

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Kathleen Scullion University/BHF Centre for Cardiovascular Science, University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh, UK

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Emad A S Al-Dujaili Dietetics, Nutrition, and Biological Sciences Department, Queen Margaret University, Musselburgh, UK

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Mary E Diaz University/BHF Centre for Cardiovascular Science, University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh, UK

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Carmel M Moran University/BHF Centre for Cardiovascular Science, University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh, UK
Edinburgh Preclinical Imaging, University of Edinburgh, Edinburgh, UK

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Christopher J Kenyon University/BHF Centre for Cardiovascular Science, University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh, UK

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Gillian A Gray University/BHF Centre for Cardiovascular Science, University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh, UK

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Karen E Chapman University/BHF Centre for Cardiovascular Science, University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh, UK

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Corticosteroids directly affect the heart and vasculature and are implicated in the pathogenesis of heart failure. Attention is focussed upon the role of the mineralocorticoid receptor (MR) in mediating pro-fibrotic and other adverse effects of corticosteroids upon the heart. In contrast, the role of the glucocorticoid receptor (GR) in the heart and vasculature is less well understood. We addressed this in mice with cardiomyocyte and vascular smooth muscle deletion of GR (SMGRKO mice). Survival of SMGRKO mice to weaning was reduced compared with that of littermate controls. Doppler measurements of blood flow across the mitral valve showed an elongated isovolumetric contraction time in surviving adult SMGRKO mice, indicating impairment of the initial left ventricular contractile phase. Although heart weight was elevated in both genders, only male SMGRKO mice showed evidence of pathological cardiomyocyte hypertrophy, associated with increased myosin heavy chain-β expression. Left ventricular fibrosis, evident in both genders, was associated with elevated levels of mRNA encoding MR as well as proteins involved in cardiac remodelling and fibrosis. However, MR antagonism with spironolactone from birth only modestly attenuated the increase in pro-fibrotic gene expression in SMGRKO mice, suggesting that elevated MR signalling is not the primary driver of cardiac fibrosis in SMGRKO mice, and cardiac fibrosis can be dissociated from MR activation. Thus, GR contributes to systolic function and restrains normal cardiac growth, the latter through gender-specific mechanisms. Our findings suggest the GR:MR balance is critical in corticosteroid signalling in specific cardiac cell types.

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Andrea Lovdel University/BHF Centre for Cardiovascular Science, The University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh BioQuarter, Edinburgh, UK

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Karla J Suchacki University/BHF Centre for Cardiovascular Science, The University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh BioQuarter, Edinburgh, UK

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Fiona Roberts University/BHF Centre for Cardiovascular Science, The University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh BioQuarter, Edinburgh, UK

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Richard J Sulston University/BHF Centre for Cardiovascular Science, The University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh BioQuarter, Edinburgh, UK

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Robert J Wallace Department of Orthopaedics, The University of Edinburgh, Edinburgh, UK

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Benjamin J Thomas University/BHF Centre for Cardiovascular Science, The University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh BioQuarter, Edinburgh, UK

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Rachel M B Bell University/BHF Centre for Cardiovascular Science, The University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh BioQuarter, Edinburgh, UK

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Iris Pruñonosa Cervera University/BHF Centre for Cardiovascular Science, The University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh BioQuarter, Edinburgh, UK

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Gavin J Macpherson Department of Orthopaedic Surgery, Royal Infirmary of Edinburgh, Edinburgh, UK

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Nicholas M Morton University/BHF Centre for Cardiovascular Science, The University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh BioQuarter, Edinburgh, UK
Centre for Systems Health and Integrated Metabolic Research, Department of Biosciences, School of Science and Technology, Nottingham Trent University, Nottingham, UK

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Natalie Z M Homer University/BHF Centre for Cardiovascular Science, The University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh BioQuarter, Edinburgh, UK

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Karen E Chapman University/BHF Centre for Cardiovascular Science, The University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh BioQuarter, Edinburgh, UK

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William P Cawthorn University/BHF Centre for Cardiovascular Science, The University of Edinburgh, The Queen’s Medical Research Institute, Edinburgh BioQuarter, Edinburgh, UK

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Bone marrow adipose tissue (BMAT) comprises >10% of total adipose mass in healthy humans. It increases in diverse conditions, including ageing, obesity, osteoporosis, glucocorticoid therapy, and notably, during caloric restriction (CR). BMAT potentially influences skeletal, metabolic, and immune functions, but the mechanisms of BMAT expansion remain poorly understood. Our hypothesis is that, during CR, excessive glucocorticoid activity drives BMAT expansion. The enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) amplifies glucocorticoid activity by catalysing intracellular regeneration of active glucocorticoids from inert 11-keto forms. Mice lacking 11β-HSD1 resist metabolic dysregulation and bone loss during exogenous glucocorticoid excess; thus, we hypothesised that 11β-HSD1 knockout mice would also resist excessive glucocorticoid action during CR, thereby restrining BMAT expansion and bone loss. To test this, we first confirmed that 11β-HSD1 is expressed in mouse and human bone marrow. We then investigated the effects of CR in male and female control and 11β-HSD1 knockout mice from 9 to 15 weeks of age. CR increased Hsd11b1 mRNA in adipose tissue and bone marrow. Deletion of Hsd11b1 did not alter bone or BMAT characteristics in mice fed a control diet and had little effect on tibial bone microarchitecture during CR. Notably, Hsd11b1 deletion attenuated the CR-induced increases in BMAT and prevented increases in bone marrow corticosterone in males but not females. This was not associated with suppression of glucocorticoid target genes in bone marrow. Instead, knockout males had increased progesterone in plasma and bone marrow. Together, our findings show that knockout of 11β-HSD1 prevents CR-induced BMAT expansion in a sex-specific manner and highlights progesterone as a potential new regulator of bone marrow adiposity.

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