Publications by authors named "Jan Tuckermann"

134 Publications

The endothelium-bone axis in development, homeostasis and bone and joint disease.

Nat Rev Rheumatol 2021 Oct 3;17(10):608-620. Epub 2021 Sep 3.

Max Planck Institute for Molecular Biomedicine, Department of Tissue Morphogenesis, University of Münster, Faculty of Medicine, Münster, Germany.

Blood vessels form a versatile transport network that is best known for its critical roles in processes such as tissue oxygenation, metabolism and immune surveillance. The vasculature also provides local, often organ-specific, molecular signals that control the behaviour of other cell types in their vicinity during development, homeostasis and regeneration, and also in disease processes. In the skeletal system, the local vasculature is actively involved in both bone formation and resorption. In addition, blood vessels participate in inflammatory processes and contribute to the pathogenesis of diseases that affect the joints, such as rheumatoid arthritis and osteoarthritis. This Review summarizes the current understanding of the architecture, angiogenic growth and functional properties of the bone vasculature. The effects of ageing and pathological conditions, including arthritis and osteoporosis, are also discussed.
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http://dx.doi.org/10.1038/s41584-021-00682-3DOI Listing
October 2021

RSPO3 is important for trabecular bone and fracture risk in mice and humans.

Nat Commun 2021 08 13;12(1):4923. Epub 2021 Aug 13.

Sahlgrenska Osteoporosis Centre, Centre for Bone and Arthritis Research, Institute of Medicine, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden.

With increasing age of the population, countries across the globe are facing a substantial increase in osteoporotic fractures. Genetic association signals for fractures have been reported at the RSPO3 locus, but the causal gene and the underlying mechanism are unknown. Here we show that the fracture reducing allele at the RSPO3 locus associate with increased RSPO3 expression both at the mRNA and protein levels, increased trabecular bone mineral density and reduced risk mainly of distal forearm fractures in humans. We also demonstrate that RSPO3 is expressed in osteoprogenitor cells and osteoblasts and that osteoblast-derived RSPO3 is the principal source of RSPO3 in bone and an important regulator of vertebral trabecular bone mass and bone strength in adult mice. Mechanistic studies revealed that RSPO3 in a cell-autonomous manner increases osteoblast proliferation and differentiation. In conclusion, RSPO3 regulates vertebral trabecular bone mass and bone strength in mice and fracture risk in humans.
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http://dx.doi.org/10.1038/s41467-021-25124-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8363747PMC
August 2021

A guide to changing paradigms of glucocorticoid receptor function-a model system for genome regulation and physiology.

FEBS J 2021 Jul 2. Epub 2021 Jul 2.

Institute of Comparative Molecular Endocrinology (CME), Ulm University, Germany.

The glucocorticoid receptor (GR) is a bona fide ligand-regulated transcription factor. Cloned in the 80s, the GR has become one of the best-studied and clinically most relevant members of the nuclear receptor superfamily. Cooperative activity of GR with other transcription factors and a plethora of coregulators contribute to the tissue- and context-specific response toward the endogenous and pharmacological glucocorticoids (GCs). Furthermore, nontranscriptional activities in the cytoplasm are emerging as an additional function of GR. Over the past 40 years, the concepts of GR mechanisms of action had been constantly changing. Different methodologies in the pregenomic and genomic era of molecular biological research and recent cutting-edge technology in single-cell and single-molecule analysis are steadily evolving the views, how the GR in particular and transcriptional regulation in general act in physiological and pathological processes. In addition to the development of technologies for GR analysis, the use of model organisms provides insights how the GR in vivo executes GC action in tissue homeostasis, inflammation, and energy metabolism. The model organisms, namely the mouse, but also rats, zebrafish, and recently fruit flies carrying mutations of the GR became a major driving force to analyze the molecular function of GR in disease models. This guide provides an overview of the exciting research and paradigm shifts in the GR field from past to present with a focus on GR transcription factor networks, GR DNA-binding and single-cell analysis, and model systems.
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http://dx.doi.org/10.1111/febs.16100DOI Listing
July 2021

Sorting Nexin 10 as a Key Regulator of Membrane Trafficking in Bone-Resorbing Osteoclasts: Lessons Learned From Osteopetrosis.

Front Cell Dev Biol 2021 20;9:671210. Epub 2021 May 20.

Department of Immunology, The Weizmann Institute of Science, Rehovot, Israel.

Bone homeostasis is a complex, multi-step process, which is based primarily on a tightly orchestrated interplay between bone formation and bone resorption that is executed by osteoblasts and osteoclasts (OCLs), respectively. The essential physiological balance between these cells is maintained and controlled at multiple levels, ranging from regulated gene expression to endocrine signals, yet the underlying cellular and molecular mechanisms are still poorly understood. One approach for deciphering the mechanisms that regulate bone homeostasis is the characterization of relevant pathological states in which this balance is disturbed. In this article we describe one such "error of nature," namely the development of acute recessive osteopetrosis (ARO) in humans that is caused by mutations in sorting nexin 10 (SNX10) that affect OCL functioning. We hypothesize here that, by virtue of its specific roles in vesicular trafficking, SNX10 serves as a key selective regulator of the composition of diverse membrane compartments in OCLs, thereby affecting critical processes in the sequence of events that link the plasma membrane with formation of the ruffled border and with extracellular acidification. As a result, SNX10 determines multiple features of these cells either directly or, as in regulation of cell-cell fusion, indirectly. This hypothesis is further supported by the similarities between the cellular defects observed in OCLs form various models of ARO, induced by mutations in SNX10 and in other genes, which suggest that mutations in the known ARO-associated genes act by disrupting the same plasma membrane-to-ruffled border axis, albeit to different degrees. In this article, we describe the population genetics and spread of the original arginine-to-glutamine mutation at position 51 (R51Q) in SNX10 in the Palestinian community. We further review recent studies, conducted in animal and cellular model systems, that highlight the essential roles of SNX10 in critical membrane functions in OCLs, and discuss possible future research directions that are needed for challenging or substantiating our hypothesis.
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http://dx.doi.org/10.3389/fcell.2021.671210DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8173195PMC
May 2021

HAND2 is a novel obesity-linked adipogenic transcription factor regulated by glucocorticoid signalling.

Diabetologia 2021 Aug 20;64(8):1850-1865. Epub 2021 May 20.

Institute for Diabetes and Cancer (IDC); Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany.

Aims/hypothesis: Adipocytes are critical cornerstones of energy metabolism. While obesity-induced adipocyte dysfunction is associated with insulin resistance and systemic metabolic disturbances, adipogenesis, the formation of new adipocytes and healthy adipose tissue expansion are associated with metabolic benefits. Understanding the molecular mechanisms governing adipogenesis is of great clinical potential to efficiently restore metabolic health in obesity. Here we investigate the role of heart and neural crest derivatives-expressed 2 (HAND2) in adipogenesis.

Methods: Human white adipose tissue (WAT) was collected from two cross-sectional studies of 318 and 96 individuals. In vitro, for mechanistic experiments we used primary adipocytes from humans and mice as well as human multipotent adipose-derived stem (hMADS) cells. Gene silencing was performed using siRNA or genetic inactivation in primary adipocytes from loxP and or tamoxifen-inducible Cre-ERT2 mouse models with Cre-encoding mRNA or tamoxifen, respectively. Adipogenesis and adipocyte metabolism were measured by Oil Red O staining, quantitative PCR (qPCR), microarray, glucose uptake assay, western blot and lipolysis assay. A combinatorial RNA sequencing (RNAseq) and ChIP qPCR approach was used to identify target genes regulated by HAND2. In vivo, we created a conditional adipocyte Hand2 deletion mouse model using Cre under control of the Adipoq promoter (Hand2) and performed a large panel of metabolic tests.

Results: We found that HAND2 is an obesity-linked white adipocyte transcription factor regulated by glucocorticoids that was necessary but insufficient for adipocyte differentiation in vitro. In a large cohort of humans, WAT HAND2 expression was correlated to BMI. The HAND2 gene was enriched in white adipocytes compared with brown, induced early in differentiation and responded to dexamethasone (DEX), a typical glucocorticoid receptor (GR, encoded by NR3C1) agonist. Silencing of NR3C1 in hMADS cells or deletion of GR in a transgenic conditional mouse model results in diminished HAND2 expression, establishing that adipocyte HAND2 is regulated by glucocorticoids via GR in vitro and in vivo. Furthermore, we identified gene clusters indirectly regulated by the GR-HAND2 pathway. Interestingly, silencing of HAND2 impaired adipocyte differentiation in hMADS and primary mouse adipocytes. However, a conditional adipocyte Hand2 deletion mouse model using Cre under control of the Adipoq promoter did not mirror these effects on adipose tissue differentiation, indicating that HAND2 was required at stages prior to Adipoq expression.

Conclusions/interpretation: In summary, our study identifies HAND2 as a novel obesity-linked adipocyte transcription factor, highlighting new mechanisms of GR-dependent adipogenesis in humans and mice.

Data Availability: Array data have been submitted to the GEO database at NCBI (GSE148699).
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http://dx.doi.org/10.1007/s00125-021-05470-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8245394PMC
August 2021

An SNX10-dependent mechanism downregulates fusion between mature osteoclasts.

J Cell Sci 2021 05 11;134(9). Epub 2021 May 11.

Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel.

Homozygosity for the R51Q mutation in sorting nexin 10 (SNX10) inactivates osteoclasts (OCLs) and induces autosomal recessive osteopetrosis in humans and in mice. We show here that the fusion of wild-type murine monocytes to form OCLs is highly regulated, and that its extent is limited by blocking fusion between mature OCLs. In contrast, monocytes from homozygous R51Q SNX10 mice fuse uncontrollably, forming giant dysfunctional OCLs that can become 10- to 100-fold larger than their wild-type counterparts. Furthermore, mutant OCLs display reduced endocytotic activity, suggesting that their deregulated fusion is due to alterations in membrane homeostasis caused by loss of SNX10 function. This is supported by the finding that the R51Q SNX10 protein is unstable and exhibits altered lipid-binding properties, and is consistent with a key role for SNX10 in vesicular trafficking. We propose that OCL size and functionality are regulated by a cell-autonomous SNX10-dependent mechanism that downregulates fusion between mature OCLs. The R51Q mutation abolishes this regulatory activity, leading to excessive fusion, loss of bone resorption capacity and, consequently, to an osteopetrotic phenotype in vivo. This article has an associated First Person interview with the joint first authors of the paper.
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http://dx.doi.org/10.1242/jcs.254979DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8182410PMC
May 2021

Intact Glucocorticoid Receptor Dimerization Is Deleterious in Trauma-Induced Impaired Fracture Healing.

Front Immunol 2020 17;11:628287. Epub 2021 Feb 17.

Institute of Comparative Molecular Endocrinology, Ulm University, Ulm, Germany.

Following severe trauma, fracture healing is impaired because of overwhelming systemic and local inflammation. Glucocorticoids (GCs), acting the glucocorticoid receptor (GR), influence fracture healing by modulating the trauma-induced immune response. GR dimerization-dependent gene regulation is essential for the anti-inflammatory effects of GCs. Therefore, we investigated in a murine trauma model of combined femur fracture and thoracic trauma, whether effective GR dimerization influences the pathomechanisms of trauma-induced compromised fracture healing. To this end, we used mice with decreased GR dimerization ability (GR). The healing process was analyzed by cytokine/chemokine multiplex analysis, flow cytometry, gene-expression analysis, histomorphometry, micro-computed tomography, and biomechanical testing. GR mice did not display a systemic or local hyper-inflammation upon combined fracture and thorax trauma. Strikingly, we discovered that GR mice were protected from fracture healing impairment induced by the additional thorax trauma. Collectively and in contrast to previous studies describing the beneficial effects of intact GR dimerization in inflammatory models, we report here an adverse role of intact GR dimerization in trauma-induced compromised fracture healing.
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http://dx.doi.org/10.3389/fimmu.2020.628287DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7927427PMC
June 2021

PTPRJ promotes osteoclast maturation and activity by inhibiting Cbl-mediated ubiquitination of NFATc1 in late osteoclastogenesis.

FEBS J 2021 08 5;288(15):4702-4723. Epub 2021 Mar 5.

Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot, Israel.

Bone-resorbing osteoclasts (OCLs) are multinucleated phagocytes, whose central roles in regulating bone formation and homeostasis are critical for normal health and development. OCLs are produced from precursor monocytes in a multistage process that includes initial differentiation, cell-cell fusion, and subsequent functional and morphological maturation; the molecular regulation of osteoclastogenesis is not fully understood. Here, we identify the receptor-type protein tyrosine phosphatase PTPRJ as an essential regulator specifically of OCL maturation. Monocytes from PTPRJ-deficient (JKO) mice differentiate and fuse normally, but their maturation into functional OCLs and their ability to degrade bone are severely inhibited. In agreement, mice lacking PTPRJ throughout their bodies or only in OCLs exhibit increased bone mass due to reduced OCL-mediated bone resorption. We further show that PTPRJ promotes OCL maturation by dephosphorylating the M-CSF receptor (M-CSFR) and Cbl, thus reducing the ubiquitination and degradation of the key osteoclastogenic transcription factor NFATc1. Loss of PTPRJ increases ubiquitination of NFATc1 and reduces its amounts at later stages of osteoclastogenesis, thereby inhibiting OCL maturation. PTPRJ thus fulfills an essential and cell-autonomous role in promoting OCL maturation by balancing between the pro- and anti-osteoclastogenic activities of the M-CSFR and maintaining NFATc1 expression during late osteoclastogenesis.
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http://dx.doi.org/10.1111/febs.15778DOI Listing
August 2021

A physiological glucocorticoid rhythm is an important regulator of brown adipose tissue function.

Mol Metab 2021 05 3;47:101179. Epub 2021 Feb 3.

Department of Medicine, Division of Endocrinology, Leiden University Medical Center, Leiden, the Netherlands; Einthoven Laboratory for Experimental Vascular Medicine, Leiden University Medical Center, Leiden, the Netherlands. Electronic address:

Objective: Brown adipose tissue (BAT) displays a strong circadian rhythm in metabolic activity, but it is unclear how this rhythm is regulated. As circulating levels of corticosterone coincide with the rhythm of triglyceride-derived fatty acid (FA) uptake by BAT, we investigated whether corticosterone regulates BAT circadian rhythm.

Methods: Corticosterone levels were flattened by implanting mice with subcutaneous corticosterone-releasing pellets, resulting in constant circulating corticosterone levels.

Results: Flattened corticosterone rhythm caused a complete loss of circadian rhythm in triglyceride-derived fatty acid uptake by BAT. This effect was independent of glucocorticoid receptor expression in (brown) adipocytes and was not caused by deregulation of clock gene expression or overexposure to glucocorticoids, but rather seemed mediated by reduced sympathetic innervation of BAT. In a mouse model of hyperlipidemia and metabolic syndrome, long-term experimental flattening of corticosterone - and thus rhythm in BAT function - resulted in adiposity.

Conclusions: This study highlights that a physiological rhythm in glucocorticoids is an important regulator of BAT function and essential for the maintenance of metabolic health.
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http://dx.doi.org/10.1016/j.molmet.2021.101179DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7907824PMC
May 2021

Leukemia inhibitory factor treatment attenuates the detrimental effects of glucocorticoids on bone in mice.

Bone 2021 04 9;145:115843. Epub 2021 Jan 9.

Institute of Comparative Molecular Endocrinology, University of Ulm, Ulm, Germany; Clinics of the Ludwig Maximilians University Munich, Munich, Germany. Electronic address:

Glucocorticoids (GCs) are widely used drugs for the treatment of inflammatory and autoimmune diseases. However, a severe side effect induced by long-term GC therapy is osteoporosis. Leukemia inhibitory factor (LIF) - a glycoprotein 130 (gp130) dependent cytokine and member of the interleukin-6 cytokine family - is an activator protein 1 (AP-1) target gene that may be involved in one of the mechanisms underlying GC-induced bone loss. Indeed, we previously reported that the mRNA expression level of LIF was enhanced upon osteogenic differentiation, but was significantly decreased in GC-treated osteoblasts. In this study, we show that in vitro LIF treatment rescues the decreased early osteogenic differentiation and mineralization of GC-treated osteoblasts. Furthermore, we also demonstrate that in vivo LIF treatment protects against GC-mediated trabecular bone loss by decreasing the loss of both trabecular bone formation and osteoblast numbers. This protection appears to be conferred by LIF rescuing GC decreased activity of Stat3, MAPK, and Akt signaling pathways. Thus, the specific targeting of LIF signaling may represent a new therapeutic strategy to prevent GC-induced trabecular bone loss.
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http://dx.doi.org/10.1016/j.bone.2021.115843DOI Listing
April 2021

Impact of downstream effects of glucocorticoid receptor dysfunction on organ function in critical illness-associated systemic inflammation.

Intensive Care Med Exp 2020 Dec 18;8(Suppl 1):37. Epub 2020 Dec 18.

Institute of Comparative Molecular Endocrinology (CME), Ulm University, Ulm, Germany.

Glucocorticoids (GCs) are stress hormones that regulate developmental and physiological processes and are among the most potent anti-inflammatory drugs to suppress chronic and acute inflammation. GCs act through the glucocorticoid receptor (GR), a ubiquitously expressed ligand-activated transcription factor, which translocates into the nucleus and can act via two different modes, as a GR monomer or as a GR dimer. These two modes of action are not clearly differentiated in practice and may lead to completely different therapeutic outcomes. Detailed aspects of GR mechanisms are often not taken into account when GCs are used in different clinical scenarios. Patients, with critical illness-related corticosteroid insufficiency, treated with natural or synthetic GCs are still missing a clearly defined therapeutic strategy. This review discusses the different modes of GR function and its importance on organ function in vivo.
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http://dx.doi.org/10.1186/s40635-020-00325-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7746781PMC
December 2020

Inhibition of 11β-HSD1 Expression by Insulin in Skin: Impact for Diabetic Wound Healing.

J Clin Med 2020 Nov 28;9(12). Epub 2020 Nov 28.

Department of Dermatology, Venereology and Allergology, Faculty of Medicine, Leipzig University, Johannisallee 30, 04103 Leipzig, Germany.

Chronic, non-healing wounds impose a great burden on patients, professionals and health care systems worldwide. Diabetes mellitus (DM) and obesity are globally highly prevalent metabolic disorders and increase the risk for developing chronic wounds. Glucocorticoids (GCs) are endogenous stress hormones that exert profound effects on inflammation and repair systems. 11-beta-hydroxysteroid dehydrogenase 1 (11β-HSD1) is the key enzyme which controls local GC availability in target tissues such as skin. Since treatment with GCs has detrimental side effects on skin integrity, causing atrophy and delayed wound healing, we asked whether the dysregulated expression of 11β-HSD1 and consequently local GC levels in skin contribute to delayed wound healing in obese, diabetic db/db mice. We found increased expression of 11β-HSD1 during disturbed wound healing and in the healthy skin of obese, diabetic db/db mice. Cell analysis revealed increased expression of 11β-HSD1 in fibroblasts, myeloid cells and dermal white adipose tissue from db/db mice, while expression in keratinocytes was unaffected. Among diabetes- and obesity-related factors, insulin and insulin-like growth factor 1 down-regulated 11β-HSD1 expression in fibroblasts and myeloid cells, while glucose, fatty acids, TNF-α and IL-1β did not affect it. Insulin exerted its inhibitory effect on 11β-HSD1 expression by activating PI3-kinase/Akt-signalling. Consequently, the inhibitory effect of insulin is attenuated in fibroblasts from insulin-resistant db/db mice. We conclude that insulin resistance in obesity and diabetes prevents the down-regulation of 11β-HSD1, leading to elevated endogenous GC levels in diabetic skin, which could contribute to impaired wound healing in patients with DM.
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http://dx.doi.org/10.3390/jcm9123878DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7760287PMC
November 2020

RNF40 exerts stage-dependent functions in differentiating osteoblasts and is essential for bone cell crosstalk.

Cell Death Differ 2021 02 8;28(2):700-714. Epub 2020 Sep 8.

Institute of Comparative Molecular Endocrinology, University of Ulm, Helmholtzstrasse 8/1, 89081, Ulm, Germany.

The role of histone ubiquitination in directing cell lineage specification is only poorly understood. Our previous work indicated a role of the histone 2B ubiquitin ligase RNF40 in controlling osteoblast differentiation in vitro. Here, we demonstrate that RNF40 has a stage-dependent function in controlling osteoblast differentiation in vivo. RNF40 expression is essential for early stages of lineage specification, but is dispensable in mature osteoblasts. Paradoxically, while osteoblast-specific RNF40 deletion led to impaired bone formation, it also resulted in increased bone mass due to impaired bone cell crosstalk. Loss of RNF40 resulted in decreased osteoclast number and function through modulation of RANKL expression in OBs. Mechanistically, we demonstrate that Tnfsf11 (encoding RANKL) is an important target gene of H2B monoubiquitination. These data reveal an important role of RNF40-mediated H2B monoubiquitination in bone formation and remodeling and provide a basis for exploring this pathway for the treatment of conditions such as osteoporosis or cancer-associated osteolysis.
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http://dx.doi.org/10.1038/s41418-020-00614-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7862367PMC
February 2021

Author Correction: Glucocorticoids suppress Wnt16 expression in osteoblasts in vitro and in vivo.

Sci Rep 2020 Jun 4;10(1):9344. Epub 2020 Jun 4.

Division of Endocrinology, Diabetes, and Bone Diseases, Department of Medicine III, Technische Universität Dresden, Dresden, Germany.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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http://dx.doi.org/10.1038/s41598-020-65962-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7271193PMC
June 2020

The Role of Glucocorticoid Receptor and Oxytocin Receptor in the Septic Heart in a Clinically Relevant, Resuscitated Porcine Model With Underlying Atherosclerosis.

Front Endocrinol (Lausanne) 2020 14;11:299. Epub 2020 May 14.

Ulm University Medical Center, Institute for Anesthesiological Pathophysiology and Process Engineering, Ulm, Germany.

The pathophysiology of sepsis-induced myocardial dysfunction is not resolved to date and comprises inflammation, barrier dysfunction and oxidative stress. Disease-associated reduction of tissue cystathionine-γ-lyase (CSE) expression, an endogenous HS-producing enzyme, is associated with oxidative stress, barrier dysfunction and organ injury. CSE-mediated cardio-protection has been suggested to be related the upregulation of oxytocin receptor (OTR). CSE can also mediate glucocorticoid receptor (GR) signaling, which is important for normal heart function. A sepsis-related loss of cardiac CSE expression associated with impaired organ function has been reported previously. The aim of this current study was to investigate the role of cardiac GR and OTR after polymicrobial sepsis in a clinically relevant, resuscitated, atherosclerotic porcine model. Anesthetized and instrumented FBM (Familial Hypercholesterolemia Bretoncelles Meishan) pigs with high fat diet-induced atherosclerosis underwent poly-microbial septic shock ( = 8) or sham procedure ( = 5), and subsequently received intensive care therapy with fluid and noradrenaline administration for 24 h. Cardiac protein expression and mRNA levels were analyzed. Systemic troponin, a marker of cardiac injury, was significantly increased in septic animals in contrast to sham, whereas OTR and GR expression in septic hearts were reduced, along with a down-regulation of anti-inflammatory GR target genes and the antioxidant transcription factor NRF2. These results suggest a potential interplay between GR, CSE, and OTR in sepsis-mediated oxidative stress, inflammation and cardiac dysfunction.
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http://dx.doi.org/10.3389/fendo.2020.00299DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7239997PMC
May 2021

PPARδ-mediated mitochondrial rewiring of osteoblasts determines bone mass.

Sci Rep 2020 05 21;10(1):8428. Epub 2020 May 21.

Department of Internal Medicine 3, Rheumatology and Immunology, Friedrich Alexander University Erlangen-Nurnberg and Universitätsklinikum Erlangen, Erlangen, Germany.

Bone turnover, which is determined by osteoclast-mediated bone resorption and osteoblast-mediated bone formation, represents a highly energy consuming process. The metabolic requirements of osteoblast differentiation and mineralization, both essential for regular bone formation, however, remain incompletely understood. Here we identify the nuclear receptor peroxisome proliferator-activated receptor (PPAR) δ as key regulator of osteoblast metabolism. Induction of PPARδ was essential for the metabolic adaption and increased rate in mitochondrial respiration necessary for the differentiation and mineralization of osteoblasts. Osteoblast-specific deletion of PPARδ in mice, in turn, resulted in an altered energy homeostasis of osteoblasts, impaired mineralization and reduced bone mass. These data show that PPARδ acts as key regulator of osteoblast metabolism and highlight the relevance of cellular metabolic rewiring during osteoblast-mediated bone formation and bone-turnover.
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http://dx.doi.org/10.1038/s41598-020-65305-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7242479PMC
May 2020

Massive osteopetrosis caused by non-functional osteoclasts in R51Q SNX10 mutant mice.

Bone 2020 07 8;136:115360. Epub 2020 Apr 8.

Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel. Electronic address:

The R51Q mutation in sorting nexin 10 (SNX10) was shown to cause a lethal genetic disease in humans, namely autosomal recessive osteopetrosis (ARO). We describe here the first R51Q SNX10 knock-in mouse model and show that mice homozygous for this mutation exhibit massive, early-onset, and widespread osteopetrosis. The mutant mice exhibit multiple additional characteristics of the corresponding human disease, including stunted growth, failure to thrive, missing or impacted teeth, occasional osteomyelitis, and a significantly-reduced lifespan. Osteopetrosis in this model is the result of osteoclast inactivity that, in turn, is caused by absence of ruffled borders in the mutant osteoclasts and by their inability to secrete protons. These results confirm that the R51Q mutation in SNX10 is a causative factor in ARO and provide a model system for studying this rare disease.
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http://dx.doi.org/10.1016/j.bone.2020.115360DOI Listing
July 2020

CD163 expression defines specific, IRF8-dependent, immune-modulatory macrophages in the bone marrow.

J Allergy Clin Immunol 2020 11 19;146(5):1137-1151. Epub 2020 Mar 19.

Institute of Immunology, University of Muenster, Muenster, Germany. Electronic address:

Background: Scavenger receptor CD163 is exclusively expressed on monocytes/macrophages and is widely used as a marker for alternatively activated macrophages. However, the role of CD163 is not yet clear.

Objectives: We sought to examine the function of CD163 in steady-state as well as in sterile and infectious inflammation.

Methods: Expression of CD163 was analyzed under normal and inflammatory conditions in mice. Functional relevance of CD163 was investigated in models of inflammation in wild-type and CD163 mice.

Results: We describe a subpopulation of bone marrow-resident macrophages (BMRMs) characterized by a high expression of CD163 and functionally distinct from classical bone marrow-derived macrophages. Development of CD163 BMRMs is strictly dependent on IFN regulatory factor-8. CD163 BMRMs show a specific transcriptome and cytokine secretion pattern demonstrating a specific immunomodulatory profile of these cells. Accordingly, CD163 mice show a stronger inflammation in allergic contact dermatitis, indicating a regulatory role of CD163. However, CD163 mice are highly susceptible to S aureus infections, demonstrating the relevance of CD163 for antimicrobial defense as well.

Conclusions: Our data indicate that anti-inflammatory and immunosuppressive mechanisms are not necessarily associated with a decreased antimicrobial activity. In contrast, our data define a novel macrophage population that controls overwhelming inflammation on one hand but is also necessary for an effective control of infections on the other hand.
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http://dx.doi.org/10.1016/j.jaci.2020.02.034DOI Listing
November 2020

Impaired Glucocorticoid Receptor Dimerization Aggravates LPS-Induced Circulatory and Pulmonary Dysfunction.

Front Immunol 2019 23;10:3152. Epub 2020 Jan 23.

Institute of Comparative Molecular Endocrinology (CME), Ulm University, Ulm, Germany.

Sepsis, that can be modeled by LPS injections, as an acute systemic inflammation syndrome is the most common cause for acute lung injury (ALI). ALI induces acute respiratory failure leading to hypoxemia, which is often associated with multiple organ failure (MOF). During systemic inflammation, the hypothalamus-pituitary-adrenal axis (HPA) is activated and anti-inflammatory acting glucocorticoids (GCs) are released to overcome the inflammation. GCs activate the GC receptor (GR), which mediates its effects via a GR monomer or GR dimer. The detailed molecular mechanism of the GR in different inflammatory models and target genes that might be crucial for resolving inflammation is not completely identified. We previously observed that mice with attenuated GR dimerization (GR) had a higher mortality in a non-resuscitated lipopolysaccharide (LPS)- and cecal ligation and puncture (CLP)-induced inflammation model and are refractory to exogenous GCs to ameliorate ALI during inflammation. Therefore, we hypothesized that impaired murine GR dimerization (GR) would further impair organ function in LPS-induced systemic inflammation under human like intensive care management and investigated genes that are crucial for lung function in this setup. Anesthetized GR and wildtype (GR) mice were challenged with LPS (10 mg·kg, intraperitoneal) and underwent intensive care management ("lung-protective" mechanical ventilation, crystalloids, and norepinephrine) for 6 h. Lung mechanics and gas exchange were assessed together with systemic hemodynamics, acid-base status, and mitochondrial oxygen consumption (JO). Western blots, immunohistochemistry, and real time quantitative polymerase chain reaction were performed to analyze lung tissue and inflammatory mediators were analyzed in plasma and lung tissue. When animals were challenged with LPS and subsequently resuscitated under intensive care treatment, GR mice had a higher mortality compared to GR mice, induced by an increased need of norepinephrine to achieve hemodynamic targets. After challenge with LPS, GR mice also displayed an aggravated ALI shown by a more pronounced impairment of gas exchange, lung mechanics and increased osteopontin (Opn) expression in lung tissue. Impairment of GR dimerization aggravates systemic hypotension and impairs lung function during LPS-induced endotoxic shock in mice. We demonstrate that the GR dimer is an important mediator of hemodynamic stability and lung function, possibly through regulation of Opn, during LPS-induced systemic inflammation.
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http://dx.doi.org/10.3389/fimmu.2019.03152DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6990631PMC
November 2020

A Jack of All Trades: Impact of Glucocorticoids on Cellular Cross-Talk in Osteoimmunology.

Front Immunol 2019 17;10:2460. Epub 2019 Oct 17.

Institute of Comparative Molecular Endocrinology (CME), University of Ulm, Ulm, Germany.

Glucocorticoids (GCs) are known to have a strong impact on the immune system, metabolism, and bone homeostasis. While these functions have been long investigated separately in immunology, metabolism, or bone biology, the understanding of how GCs regulate the cellular cross-talk between innate immune cells, mesenchymal cells, and other stromal cells has been garnering attention rather recently. Here we review the recent findings of GC action in osteoporosis, inflammatory bone diseases (rheumatoid and osteoarthritis), and bone regeneration during fracture healing. We focus on studies of pre-clinical animal models that enable dissecting the role of GC actions in innate immune cells, stromal cells, and bone cells using conditional and function-selective mutant mice of the GC receptor (GR), or mice with impaired GC signaling. Importantly, GCs do not only directly affect cellular functions, but also influence the cross-talk between mesenchymal and immune cells, contributing to both beneficial and adverse effects of GCs. Given the importance of endogenous GCs as stress hormones and the wide prescription of pharmaceutical GCs, an improved understanding of GC action is decisive for tackling inflammatory bone diseases, osteoporosis, and aging.
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http://dx.doi.org/10.3389/fimmu.2019.02460DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6811614PMC
November 2020

Glucocorticoids employ the monomeric glucocorticoid receptor to potentiate vitamin D and parathyroid hormone-induced osteoclastogenesis.

FASEB J 2019 12 14;33(12):14394-14409. Epub 2019 Nov 14.

Center for Bone and Arthritis Research, Institute for Medicine, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden.

Glucocorticoid (GC) therapy decreases bone mass and increases the risk of fractures. We investigated interactions between the GC dexamethasone (DEX) and the bone resorptive agents 1,25(OH)-vitamin D (D3) and parathyroid hormone (PTH) on osteoclastogenesis. We observed a synergistic potentiation of osteoclast progenitor cell differentiation and formation of osteoclasts when DEX was added to either D3- or PTH-treated mouse bone marrow cell (BMC) cultures. Cotreatment of DEX with D3 or PTH increased gene encoding calcitonin receptor (), acid phosphatase 5, tartrate resistant (), cathepsin K (), and TNF superfamily member 11 () mRNA, receptor activator of NF-κB ligand protein (RANKL), numbers of osteoclasts on plastic, and pit formation and release of C-terminal fragment of type I collagen from cells cultured on bone slices. Enhanced RANKL protein expression caused by D3 and DEX was absent in BMC from mice in which the GC receptor (GR) was deleted in stromal cells/osteoblasts. Synergistic interactions between DEX and D3 on RANKL and osteoclast formation were present in BMC from mice with attenuated GR dimerization. These data demonstrate that the GR cooperates with D3 and PTH signaling, causing massive osteoclastogenesis, which may explain the rapid bone loss observed with high dosages of GC treatment.-Conaway, H. H., Henning, P., Lie, A., Tuckermann, J., Lerner, U. H. Glucocorticoids employ the monomeric glucocorticoid receptor to potentiate vitamin D and parathyroid hormone-induced osteoclastogenesis.
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http://dx.doi.org/10.1096/fj.201802729RRRDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6894088PMC
December 2019

Despite Genetic Iron Overload, -Hemochromatosis Mice Do Not Show Bone Loss.

JBMR Plus 2019 Sep 26;3(9):e10206. Epub 2019 Jul 26.

Institute of Comparative Molecular Endocrinology, University of Ulm Ulm Germany.

One of the most prevalent genetic iron overload disorders in Caucasians is caused by mutations in the gene. Both patients and -mouse models develop a progressive accumulation of iron in the parenchymal cells of various tissues, eventually resulting in liver cirrhosis, hepatocellular carcinoma, cardiomyopathies, hypogonadism, and other pathologies. Clinical data and preclinical models have brought considerable attention to the correlation between iron overload and the development of osteoporosis in hemochromatosis. Our study critically challenges this concept. We show that systemic iron overload, at the degree present in mice, does not associate with the microarchitecture impairment of long bones, thus excluding a negative effect of iron overload on bone integrity. We further reveal that Hfe actions in osteoblasts and osteoclasts are dispensable for the maintenance of bone and iron homeostasis in mice under steady-state conditions. We conclude that, despite systemic iron overload, mice present normal physiological bone homeostasis. © 2019 The Authors. in published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.
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http://dx.doi.org/10.1002/jbm4.10206DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6808227PMC
September 2019

mir-124-5p Regulates Phagocytosis of Human Macrophages by Targeting the Actin Cytoskeleton via the ARP2/3 Complex.

Front Immunol 2019 4;10:2210. Epub 2019 Oct 4.

Institute of Microbiology and Biotechnology, University of Ulm, Ulm, Germany.

Phagocytosis is a cellular process crucial for recognition and removal of apoptotic cells and foreign particles, subsequently initiating appropriate immune responses. The process of phagocytosis is highly complex and involves major rearrangements of the cytoskeleton. Due to its complexity and importance for tissue homoeostasis and immune responses, it is tightly regulated. Over the last decade, microRNAs (miRNAs) have emerged as important regulators of biological pathways including the immune response by fine-tuning expression of gene regulatory networks. In order to identify miRNAs implicated in the regulation of phagocytosis, a systematic screening of all currently known, human miRNAs was performed using THP-1 macrophage-like cells and serum-opsonized latex beads. Of the total of 2,566 miRNAs analyzed, several led to significant changes in phagocytosis. Among these, we validated miR-124-5p as a novel regulator of phagocytosis. Transfection with miR-124-5p mimics reduced the number of phagocytic cells as well as the phagocytic activity of phorbol-12-myristate-13-acetate (PMA)-activated THP-1 cells and differentiated primary human macrophages. analysis suggested that miR-124-5p targets genes involved in regulation of the actin cytoskeleton. Transcriptional analyses revealed that expression of genes encoding for several subunits of the ARP2/3 complex, a crucial regulator of actin polymerization, is reduced upon transfection of cells with miR-124-5p. Further analyses identified potential binding motifs for miR-124-5p in the mRNAs of these genes. Luciferase reporter assays using these binding motifs indicate that at least two of the genes ( and ) are direct targets of miR-124-5p. Moreover, ARPC3 and ARPC4 protein levels were significantly reduced following miR-124-5p transfection. Collectively, the presented results suggest that miR-124-5p regulates phagocytosis in human macrophages by directly targeting expression of components of the ARP2/3 complex.
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http://dx.doi.org/10.3389/fimmu.2019.02210DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6787173PMC
November 2020

Fighting the Fire: Mechanisms of Inflammatory Gene Regulation by the Glucocorticoid Receptor.

Front Immunol 2019 7;10:1859. Epub 2019 Aug 7.

Department of Biology, Institute for Comparative Molecular Endocrinology, University of Ulm, Ulm, Germany.

For many decades, glucocorticoids have been widely used as the gold standard treatment for inflammatory conditions. Unfortunately, their clinical use is limited by severe adverse effects such as insulin resistance, cardiometabolic diseases, muscle and skin atrophies, osteoporosis, and depression. Glucocorticoids exert their effects by binding to the Glucocorticoid Receptor (GR), a ligand-activated transcription factor which both positively, and negatively regulates gene expression. Extensive research during the past several years has uncovered novel mechanisms by which the GR activates and represses its target genes. Genome-wide studies and mouse models have provided valuable insight into the molecular mechanisms of inflammatory gene regulation by GR. This review focusses on newly identified target genes and GR co-regulators that are important for its anti-inflammatory effects in innate immune cells, as well as mutations within the GR itself that shed light on its transcriptional activity. This research progress will hopefully serve as the basis for the development of safer immune suppressants with reduced side effect profiles.
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http://dx.doi.org/10.3389/fimmu.2019.01859DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6693390PMC
October 2020

Glucocorticoids Shape Macrophage Phenotype for Tissue Repair.

Front Immunol 2019 9;10:1591. Epub 2019 Jul 9.

Institut NeuroMyoGène, Université Claude Bernard Lyon 1, Univ Lyon, CNRS UMR 5310, INSERM U1217, Lyon, France.

Inflammation is a complex process which is highly conserved among species. Inflammation occurs in response to injury, infection, and cancer, as an allostatic mechanism to return the tissue and to return the organism back to health and homeostasis. Excessive, or chronic inflammation is associated with numerous diseases, and thus strategies to combat run-away inflammation is required. Anti-inflammatory drugs were therefore developed to switch inflammation off. However, the inflammatory response may be beneficial for the organism, in particular in the case of sterile tissue injury. The inflammatory response can be divided into several parts. The first step is the mounting of the inflammatory reaction itself, characterized by the presence of pro-inflammatory cytokines, and the infiltration of immune cells into the injured area. The second step is the resolution phase, where immune cells move toward an anti-inflammatory phenotype and decrease the secretion of pro-inflammatory cytokines. The last stage of inflammation is the regeneration process, where the tissue is rebuilt. Innate immune cells are major actors in the inflammatory response, of which, macrophages play an important role. Macrophages are highly sensitive to a large number of environmental stimuli, and can adapt their phenotype and function on demand. This change in phenotype in response to the environment allow macrophages to be involved in all steps of inflammation, from the first mounting of the pro-inflammatory response to the post-damage tissue repair.
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http://dx.doi.org/10.3389/fimmu.2019.01591DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6632423PMC
October 2020

Osteoblast-derived NOTUM reduces cortical bone mass in mice and the locus is associated with bone mineral density in humans.

FASEB J 2019 10 15;33(10):11163-11179. Epub 2019 Jul 15.

Department of Internal Medicine and Clinical Nutrition, Institute of Medicine, Centre for Bone and Arthritis Research at the Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.

Osteoporosis is a common skeletal disease, affecting millions of individuals worldwide. Currently used osteoporosis treatments substantially reduce vertebral fracture risk, whereas nonvertebral fracture risk, mainly caused by reduced cortical bone mass, has only moderately been improved by the osteoporosis drugs used, defining an unmet medical need. Because several wingless-type MMTV integration site family members (WNTs) and modulators of WNT activity are major regulators of bone mass, we hypothesized that NOTUM, a secreted WNT lipase, might modulate bone mass an inhibition of WNT activity. To characterize the possible role of endogenous NOTUM as a physiologic modulator of bone mass, we developed global, cell-specific, and inducible -inactivated mouse models. expression was high in the cortical bone in mice, and conditional inactivation revealed that osteoblast lineage cells are the principal source of NOTUM in the cortical bone. Osteoblast lineage-specific inactivation increased cortical bone thickness an increased periosteal circumference. Inducible inactivation in adult mice increased cortical bone thickness as a result of increased periosteal bone formation, and silencing of expression in cultured osteoblasts enhanced osteoblast differentiation. Large-scale human genetic analyses identified genetic variants mapping to the locus that are strongly associated with bone mineral density (BMD) as estimated with quantitative ultrasound in the heel. Thus, osteoblast-derived NOTUM is an essential local physiologic regulator of cortical bone mass effects on periosteal bone formation in adult mice, and genetic variants in the locus are associated with BMD variation in adult humans. Therapies targeting osteoblast-derived NOTUM may prevent nonvertebral fractures.-Movérare-Skrtic, S., Nilsson, K. H., Henning, P., Funck-Brentano, T., Nethander, M., Rivadeneira, F., Coletto Nunes, G., Koskela, A., Tuukkanen, J., Tuckermann, J., Perret, C., Souza, P. P. C., Lerner, U. H., Ohlsson, C. Osteoblast-derived NOTUM reduces cortical bone mass in mice and the locus is associated with bone mineral density in humans.
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http://dx.doi.org/10.1096/fj.201900707RDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6766646PMC
October 2019

Identification of mineralocorticoid receptor target genes in the mouse hippocampus.

J Neuroendocrinol 2019 08 14;31(8):e12735. Epub 2019 Jun 14.

Einthoven Laboratory, Division of Endocrinology, Department of Medicine, Leiden University Medical Center, Leiden, The Netherlands.

Brain mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs) respond to the same glucocorticoid hormones but can have differential effects on cellular function. Several lines of evidence suggest that MR-specific target genes must exist and might underlie the distinct effects of the receptors. The present study aimed to identify MR-specific target genes in the hippocampus, a brain region where MR and GR are co-localised and play a role in the stress response. Using genome-wide binding of both receptor types, we previously identified MR-specific, MR-GR overlapping and GR-specific putative target genes. We now report altered gene expression levels of such genes in the hippocampus of forebrain MR knockout (fbMRKO) mice, killed at the time of their endogenous corticosterone peak. Of those genes associated with MR-specific binding, the most robust effect was a 50% reduction in Jun dimerization protein 2 (Jdp2) mRNA levels in fbMRKO mice. Down-regulation was also observed for the MR-specific Nitric oxide synthase 1 adaptor protein (Nos1ap) and Suv3 like RNA helicase (Supv3 l1). Interestingly, the classical glucocorticoid target gene FK506 binding protein 5 (Fkbp5), which is associated with MR and GR chromatin binding, was expressed at substantially lower levels in fbMRKO mice. Subsequently, hippocampal Jdp2 was confirmed to be up-regulated in a restraint stress model, posing Jdp2 as a bona fide MR target that is also responsive in an acute stress condition. Thus, we show that MR-selective DNA binding can reveal functional regulation of genes and further identify distinct MR-specific effector pathways.
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http://dx.doi.org/10.1111/jne.12735DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6771480PMC
August 2019

A miR-29a-driven negative feedback loop regulates peripheral glucocorticoid receptor signaling.

FASEB J 2019 05 11;33(5):5924-5941. Epub 2019 Feb 11.

Institute for Diabetes and Cancer (IDC), Helmholtz Center Munich, Neuherberg, Germany.

The glucocorticoid receptor (GR) represents the crucial molecular mediator of key endocrine, glucocorticoid hormone-dependent regulatory circuits, including control of glucose, protein, and lipid homeostasis. Consequently, aberrant glucocorticoid signaling is linked to severe metabolic disorders, including insulin resistance, obesity, and hyperglycemia, all of which also appear upon chronic glucocorticoid therapy for the treatment of inflammatory conditions. Of note, long-term glucocorticoid exposure under these therapeutic conditions typically induces glucocorticoid resistance, requiring higher doses and consequently triggering more severe metabolic phenotypes. However, the molecular basis of acquired glucocorticoid resistance remains unknown. In a screen of differential microRNA expression during glucocorticoid-dependent adipogenic differentiation of human multipotent adipose stem cells, we identified microRNA 29a (miR-29a) as one of the most down-regulated transcripts. Overexpression of miR-29a impaired adipogenesis. We found that miR-29a represses GR in human adipogenesis by directly targeting its mRNA, and downstream analyses revealed that GR mediates most of miR-29a's anti-adipogenic effects. Conversely, miR-29a expression depends on GR activation, creating a novel miR-29-driven feedback loop. miR-29a and GR expression were inversely correlated both in murine adipose tissue and in adipose tissue samples obtained from human patients. In the latter, miR-29a levels were additionally strongly negatively correlated with body mass index and adipocyte size. Importantly, inhibition of miR-29 in mice partially rescued the down-regulation of GR during dexamethasone treatment. We discovered that, in addition to modulating GR function under physiologic conditions, pharmacologic glucocorticoid application in inflammatory disease also induced miR-29a expression, correlating with reduced GR levels. This effect was abolished in mice with impaired GR function. In summary, we uncovered a novel GR-miR-29a negative feedback loop conserved between mice and humans, in health and disease. For the first time, we elucidate a microRNA-related mechanism that might contribute to GR dysregulation and resistance in peripheral tissues.-Glantschnig, C., Koenen, M., Gil-Lozano, M., Karbiener, M., Pickrahn, I., Williams-Dautovich, J., Patel, R., Cummins, C. L., Giroud, M., Hartleben, G., Vogl, E., Blüher, M., Tuckermann, J., Uhlenhaut, H., Herzig, S., Scheideler, M. A miR-29a-driven negative feedback loop regulates peripheral glucocorticoid receptor signaling.
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http://dx.doi.org/10.1096/fj.201801385RRDOI Listing
May 2019

Phosphorylation of the phosphatase PTPROt at Tyr is a molecular switch that controls osteoclast activity and bone mass in vivo.

Sci Signal 2019 01 8;12(563). Epub 2019 Jan 8.

Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel.

Bone resorption by osteoclasts is essential for bone homeostasis. The kinase Src promotes osteoclast activity and is activated in osteoclasts by the receptor-type tyrosine phosphatase PTPROt. In other contexts, however, PTPROt can inhibit Src activity. Through in vivo and in vitro experiments, we show that PTPROt is bifunctional and can dephosphorylate Src both at its inhibitory residue Tyr and its activating residue Tyr Whereas wild-type and PTPROt knockout mice exhibited similar bone masses, mice in which a putative C-terminal phosphorylation site, Tyr, in endogenous PTPROt was replaced with phenylalanine had increased bone mass and reduced osteoclast activity. Osteoclasts from the knock-in mice also showed reduced Src activity. Experiments in cultured cells and in osteoclasts derived from both mouse strains demonstrated that the absence of phosphorylation at Tyr caused PTPROt to dephosphorylate Src at the activating site pTyr In contrast, phosphorylation of PTPROt at Tyr enabled PTPROt to recruit Src through Grb2 and to dephosphorylate Src at the inhibitory site Tyr, thus stimulating Src activity. We conclude that reversible phosphorylation of PTPROt at Tyr is a molecular switch that selects between its opposing activities toward Src and maintains a coherent signaling output, and that blocking this phosphorylation event can induce physiological effects in vivo. Because most receptor-type tyrosine phosphatases contain potential phosphorylation sites at their C termini, we propose that preventing phosphorylation at these sites or its consequences may offer an alternative to inhibiting their catalytic activity to achieve therapeutic benefit.
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http://dx.doi.org/10.1126/scisignal.aau0240DOI Listing
January 2019
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