Spine Metastases in Immunocompromised Mice after Intracardiac Injection of MDA-MB-231-SCP2 Breast Cancer Cells

Simple Summary

Breast cancer cells typically metastasize to bone, where their interaction with bone remodeling cell types enhances metastatic outgrowth and osteolytic bone destruction. The respective knowledge is largely based on xenograft models, where human breast cancer cells are injected into immunocompromised mice. Importantly, however, whereas skeletal analyses in these animals are usually restricted to hindlimb bones, human skeletal metastases are far more frequent in the spine. Therefore, our study addressed the question, if breast cancer cells injected into immunocompromised mice would also metastasize to the spine, and if this process is influenced by the amount of trabecular bone. We injected an established breast cancer cell line into immunocompromised mice with or without a transgene causing severe osteoporosis. Importantly, we found more tumor cell clusters of different size in spine sections than in femora, but the presence of the transgene did not affect their spreading and metastatic outgrowth.

Abstract

Breast cancer cells frequently metastasize to bone, where their interaction with bone remodeling cell types enhances osteolytic bone destruction. Importantly, however, whereas skeletal analyses of xenograft models are usually restricted to hindlimb bones, human skeletal metastases are far more frequent in the spine, where trabecular bone mass is higher compared to femur or tibia. Here, we addressed whether breast cancer cells injected into immunocompromised mice metastasize to the spine and if this process is influenced by the amount of trabecular bone. We also took advantage of mice carrying the Col1a1-Krm2 transgene, which display severe osteoporosis. After crossing this transgene into the immunocompromised NSG background we injected MDA-MB-231-SCP2 breast cancer cells and analyzed their distribution three weeks thereafter. We identified more tumor cells and clusters of different size in spine sections than in femora, which allowed influences on bone remodeling cell types to be analyzed by comparing tumor-free to tumor-burdened areas. Unexpectedly, the Col1a1-Krm2 transgene did not affect spreading and metastatic outgrowth of MDA-MB-231-SCP2 cells, suggesting that bone tumor interactions are more relevant at later stages of metastatic progression.

Decreased Trabecular Bone Mass in Col22a1-Deficient Mice

The bone matrix is constantly remodeled by the coordinated activities of bone-forming osteoblasts and bone-resorbing osteoclasts. Whereas type I collagen is the most abundant bone matrix protein, there are several other proteins present, some of them specifically produced by osteoblasts. In a genome-wide expression screening for osteoblast differentiation markers we have previously identified two collagen-encoding genes with unknown function in bone remodeling. Here we show that one of them, Col22a1, is predominantly expressed in bone, cultured osteoblasts, but not in osteoclasts. Based on this specific expression pattern we generated a Col22a1-deficient mouse model, which was analyzed for skeletal defects by µCT, undecalcified histology and bone-specific histomorphometry. We observed that Col22a1-deficient mice display trabecular osteopenia, accompanied by significantly increased osteoclast numbers per bone surface. In contrast, cortical bone parameters, osteoblastogenesis or bone formation were unaffected by the absence of Col22a1. Likewise, primary osteoblasts from Col22a1-deficient mice did not display a cell-autonomous defect, and they did not show altered expression of Rankl or Opg, two key regulators of osteoclastogenesis. Taken together, we provide the first evidence for a physiological function of Col22a1 in bone remodeling, although the molecular mechanisms explaining the indirect influence of Col22a1 deficiency on osteoclasts remain to be identified.

Piezo1 Inactivation in Chondrocytes Impairs Trabecular Bone Formation

The skeleton is a dynamic tissue continuously adapting to mechanical stimuli. Although matrix-embedded osteocytes are considered as the key mechanoresponsive bone cells, all other skeletal cell types are principally exposed to macroenvironmental and microenvironmental mechanical influences that could potentially affect their activities. It was recently reported that Piezo1, one of the two mechanically activated ion channels of the Piezo family, functions as a mechanosensor in osteoblasts and osteocytes. Here we show that Piezo1 additionally plays a critical role in the process of endochondral bone formation. More specifically, by targeted deletion of Piezo1 or Piezo2 in either osteoblast (Runx2Cre) or osteoclast lineage cells (Lyz2Cre), we observed severe osteoporosis with numerous spontaneous fractures specifically in Piezo1^Runx2Cre mice. This phenotype developed at an early postnatal stage and primarily affected the formation of the secondary spongiosa. The presumptive Piezo1^Runx2Cre osteoblasts in this region displayed an unusual flattened appearance and were positive for type X collagen. Moreover, transcriptome analyses of primary osteoblasts identified an unexpected induction of chondrocyte-related genes in Piezo1^Runx2Cre cultures. Because Runx2 is not only expressed in osteoblast progenitor cells, but also in prehypertrophic chondrocytes, these data suggested that Piezo1 functions in growth plate chondrocytes to ensure trabecular bone formation in the process of endochondral ossification. To confirm this hypothesis, we generated mice with Piezo1 deletion in chondrocytes (Col2a1Cre). These mice essentially recapitulated the phenotype of Piezo1^Runx2Cre animals, because they displayed early-onset osteoporosis with multiple fractures, as well as impaired formation of the secondary spongiosa with abnormal osteoblast morphology. Our data identify a previously unrecognized key function of Piezo1 in endochondral ossification, which, together with its role in bone remodeling, suggests that Piezo1 represents an attractive target for the treatment of skeletal disorders. © 2020 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Wnt1 is an Lrp5-independent bone-anabolic Wnt ligand

WNT1 mutations in humans are associated with a new form of osteogenesis imperfecta and with early-onset osteoporosis, suggesting a key role of WNT1 in bone mass regulation. However, the general mode of action and the therapeutic potential of Wnt1 in clinically relevant situations such as aging remain to be established. Here, we report the high prevalence of heterozygous WNT1 mutations in patients with early-onset osteoporosis. We show that inactivation of Wnt1 in osteoblasts causes severe osteoporosis and spontaneous bone fractures in mice. In contrast, conditional Wnt1 expression in osteoblasts promoted rapid bone mass increase in developing young, adult, and aged mice by rapidly increasing osteoblast numbers and function. Contrary to current mechanistic models, loss of Lrp5, the co-receptor thought to transmit extracellular WNT signals during bone mass regulation, did not reduce the bone-anabolic effect of Wnt1, providing direct evidence that Wnt1 function does not require the LRP5 co-receptor. The identification of Wnt1 as a regulator of bone formation and remodeling provides the basis for development of Wnt1-targeting drugs for the treatment of osteoporosis.

Deficiency of sphingosine-1-phosphate receptor 3 does not affect the skeletal phenotype of mice lacking sphingosine-1-phosphate lyase

Albeit osteoporosis is one of the most prevalent disorders in the aged population, treatment options stimulating the activity of bone-forming osteoblasts are still limited. We and others have previously identified sphingosine-1-phosphate (S1P) as a bone remodeling coupling factor, which is released by bone-resorbing osteoclasts to stimulate bone formation. Moreover, S1pr3, encoding one of the five known S1P receptors (S1P3), was found differentially expressed in osteoblasts, and S1P3 deficiency corrected the moderate high bone mass phenotype of a mouse model (deficient for the calcitonin receptor) with increased S1P release from osteoclasts. In the present study we addressed the question, if S1P3 deficiency would also influence the skeletal phenotype of mice lacking S1P-lyase (encoded by Sgpl1), which display markedly increased S1P levels due to insufficient degradation. Consistent with previous reports, the majority of Sgpl1-deficient mice died before or shortly after weaning, and this lethality was not influenced by additional S1P3 deficiency. At 3 weeks of age, Sgpl1-deficient mice displayed increased trabecular bone mass, which was associated with enhanced osteoclastogenesis and bone resorption, but also with increased bone formation. Most importantly however, none of the skeletal parameters assessed by μCT, histomorphometry and serum analyses were significantly influenced by additional S1P3 deficiency. Taken together, our findings fully support the concept that S1P is a potent osteoanabolic molecule, although S1P3 is not the sole receptor mediating this influence. Since S1P receptors are considered excellent drug targets, it is now required to screen for the impact of other family members on bone formation.

Th17 cell frequency is associated with low bone mass in primary sclerosing cholangitis

BACKGROUND & AIMS

Osteoporotic fractures are a major cause of morbidity and reduced quality of life in patients with primary sclerosing cholangitis (PSC), a progressive bile duct disease of unknown origin. Although it is generally assumed that this pathology is a consequence of impaired calcium homeostasis and malabsorption, the cellular and molecular causes of PSC-associated osteoporosis are unknown.

METHODS

We determined bone mineral density by dual-X-ray absorptiometry and assessed bone microstructure by high-resolution peripheral quantitative computed tomography in patients with PSC. Laboratory markers of liver and bone metabolism were measured, and liver stiffness was assessed by FibroScan. We determined the frequency of Th17 cells by the ex vivo stimulation of peripheral blood mononuclear cells in a subgroup of 40 patients with PSC. To investigate the potential involvement of IL-17 in PSC-associated bone loss, we analyzed the skeletal phenotype of mice lacking Abcb4 and/or Il-17.

RESULTS

Unlike in patients with primary biliary cholangitis, bone loss in patients with PSC was not associated with disease duration or liver fibrosis. However, we observed a significant negative correlation between the bone resorption biomarker deoxypyridinoline and bone mineral density in the PSC cohort, indicating increased bone resorption. Importantly, the frequency of Th17 cells in peripheral blood was positively correlated with the urinary deoxypyridinoline level and negatively correlated with bone mass. We observed that Abcb4-deficient mice displayed a low-bone-mass phenotype, which was corrected by an additional Il-17 deficiency or anti-IL-17 treatment, whereas the liver pathology was unaffected.

CONCLUSIONS

Our findings demonstrate that an increased frequency of Th17 cells is associated with bone resorption in PSC. Whether antibody-based IL-17 blockade is beneficial against bone loss in patients with PSC should be addressed in future studies.

LAY SUMMARY

Primary sclerosing cholangitis (PSC) is a cholestatic liver disease characterized by progressive bile duct destruction. One serious complication of PSC is reduced bone mass resulting in increased fracture risk. Herein, we demonstrate that Th17 cells mediate bone loss in PSC by inducing bone resorption, which suggests that antibody-based IL-17 blockade might be beneficial for the treatment of bone loss in affected patients.

The Lysosomal Protein Arylsulfatase B Is a Key Enzyme Involved in Skeletal Turnover

Skeletal pathologies are frequently observed in lysosomal storage disorders, yet the relevance of specific lysosomal enzymes in bone remodeling cell types is poorly defined. Two lysosomal enzymes, ie, cathepsin K (Ctsk) and Acp5 (also known as tartrate-resistant acid phosphatase), have long been known as molecular marker proteins of differentiated osteoclasts. However, whereas the cysteine protease Ctsk is directly involved in the degradation of bone matrix proteins, the molecular function of Acp5 in osteoclasts is still unknown. Here we show that Acp5, in concert with Acp2 (lysosomal acid phosphatase), is required for dephosphorylation of the lysosomal mannose 6-phosphate targeting signal to promote the activity of specific lysosomal enzymes. Using an unbiased approach we identified the glycosaminoglycan-degrading enzyme arylsulfatase B (Arsb), mutated in mucopolysaccharidosis type VI (MPS-VI), as an osteoclast marker, whose activity depends on dephosphorylation by Acp2 and Acp5. Similar to Acp2/Acp5^-/- mice, Arsb-deficient mice display lysosomal storage accumulation in osteoclasts, impaired osteoclast activity, and high trabecular bone mass. Of note, the most prominent lysosomal storage accumulation was observed in osteocytes from Arsb-deficient mice, yet this pathology did not impair production of sclerostin (Sost) and Fgf23. Because the influence of enzyme replacement therapy (ERT) on bone remodeling in MPS-VI is still unknown, we additionally treated Arsb-deficient mice by weekly injection of recombinant human ARSB from 12 to 24 weeks of age. We found that the high bone mass phenotype of Arsb-deficient mice and the underlying bone cell deficits were fully corrected by ERT in the trabecular compartment. Taken together, our results do not only show that the function of Acp5 in osteoclasts is linked to dephosphorylation and activation of lysosomal enzymes, they also provide an important proof-of-principle for the feasibility of ERT to correct bone cell pathologies in lysosomal storage disorders. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

Loss of menin in osteoblast lineage affects osteocyte-osteoclast crosstalk causing osteoporosis

During osteoporosis bone formation by osteoblasts is reduced and/or bone resorption by osteoclasts is enhanced. Currently, only a few factors have been identified in the regulation of bone integrity by osteoblast-derived osteocytes. In this study, we show that specific disruption of menin, encoded by multiple endocrine neoplasia type 1 (Men1), in osteoblasts and osteocytes caused osteoporosis despite the preservation of osteoblast differentiation and the bone formation rate. Instead, an increase in osteoclast numbers and bone resorption was detected that persisted even when the deletion of Men1 was restricted to osteocytes. We demonstrate that isolated Men1-deficient osteocytes expressed numerous soluble mediators, such as C-X-C motif chemokine 10 (CXCL10), and that CXCL10-mediated osteoclastogenesis was reduced by CXCL10-neutralizing antibodies. Collectively, our data reveal a novel role for Men1 in osteocyte–osteoclast crosstalk by controlling osteoclastogenesis through the action of soluble factors. A role for Men1 in maintaining bone integrity and thereby preventing osteoporosis is proposed.

Rsk2, the Kinase Mutated in Coffin-Lowry Syndrome, Controls Cementum Formation

The ribosomal S6 kinase RSK2 is essential for osteoblast function, and inactivating mutations of RSK2 cause osteopenia in humans with Coffin-Lowry syndrome (CLS). Alveolar bone loss and premature tooth exfoliation are also consistently reported symptoms in CLS patients; however, the pathophysiologic mechanisms are unclear. Therefore, aiming to identify the functional relevance of Rsk2 for tooth development, we analyzed Rsk2-deficient mice. Here, we show that Rsk2 is a critical regulator of cementoblast function. Immunohistochemistry, histology, micro-computed tomography imaging, quantitative backscattered electron imaging, and in vitro assays revealed that Rsk2 is activated in cementoblasts and is necessary for proper acellular cementum formation. Cementum hypoplasia that is observed in Rsk2-deficient mice causes detachment and disorganization of the periodontal ligament and was associated with significant alveolar bone loss with age. Moreover, Rsk2-deficient mice display hypomineralization of cellular cementum with accumulation of nonmineralized cementoid. In agreement, treatment of the cementoblast cell line OCCM-30 with a Rsk inhibitor reduces formation of mineralization nodules and decreases the expression of cementum markers. Western blot analyses based on antibodies against Rsk1, Rsk2, and an activated form of the 2 kinases confirmed that Rsk2 is expressed and activated in differentiating OCCM-30 cells. To discriminate between periodontal bone loss and systemic bone loss, we additionally crossed Rsk2-deficient mice with transgenic mice overexpressing the osteoanabolic transcription factor Fra1. Fra1 overexpression clearly increases systemic bone volume in Rsk2-deficient mice but does not protect from alveolar bone loss. Our results indicate that cell autonomous cementum defects are causing early tooth loss in CLS patients. Moreover, we identify Rsk2 as a nonredundant regulator of cementum homeostasis, alveolar bone maintenance, and periodontal health, with all these features being independent of Rsk2 function in systemic bone formation.

Impaired bone remodeling and its correction by combination therapy in a mouse model of mucopolysaccharidosis-I

Mucopolysaccharidosis-I (MPS-I) is a lysosomal storage disease (LSD) caused by inactivating mutations of IDUA, encoding the glycosaminoglycan-degrading enzyme α-l-iduronidase. Although MPS-I is associated with skeletal abnormalities, the impact of IDUA deficiency on bone remodeling is poorly defined. Here we report that Idua-deficient mice progressively develop a high bone mass phenotype with pathological lysosomal storage in cells of the osteoblast lineage. Histomorphometric quantification identified shortening of bone-forming units and reduced osteoclast numbers per bone surface. This phenotype was not transferable into wild-type mice by bone marrow transplantation (BMT). In contrast, the high bone mass phenotype of Idua-deficient mice was prevented by BMT from wild-type donors. At the cellular level, BMT did not only normalize defects of Idua-deficient osteoblasts and osteocytes but additionally caused increased osteoclastogenesis. Based on clinical observations in an individual with MPS-I, previously subjected to BMT and enzyme replacement therapy (ERT), we treated Idua-deficient mice accordingly and found that combining both treatments normalized all histomorphometric parameters of bone remodeling. Our results demonstrate that BMT and ERT profoundly affect skeletal remodeling of Idua-deficient mice, thereby suggesting that individuals with MPS-I should be monitored for their bone remodeling status, before and after treatment, to avoid long-term skeletal complications.

[Using statistics of tuberculosis clinics and hospitals in the social and epidemiological history of the "white plague" in the late nineteenth and early twentieth centuries]

During the late XIXth and the beginning of the XXth centuries, the struggle against tuberculosis is a strong reason to redefine health as social gaming, and not as individual gaming anymore. Here the number of actors increases on the market of medical cares, involving some tensions. This paper compares (by the means of death causes statistics) people affected and treated in a local hospital, and those treated in the antitubercular health centres from the province of Liège. It studies the respective contribution of hospital records and statistics list of health centres to the historical epidemiology of the "white plague" and to social history of the health.

[Health and citizenship in contemporary Belgium]

We summarize the relations between the development of health policies and the definition of citizenship in Belgium during the 19th and 20th centuries. In the limited scope of the present article we describe the main developments and offer a plausible introduction to subsequent studies. We aim to show that thanks to the scientific study of the changes that took place during two centuries, we can understand the reasons why there are currently so many contradictions in health policy. It is hoped that our findings will help us to better understand the present and prepare for the future.