The HLA-B27 transgenic rat, a model of spondyloarthritis, has decreased bone mineral density and increased RANKL to osteoprotegerin mRNA ratio

Bone Involvement in Rheumatoid Arthritis and Spondyloartritis: An Updated Review

Several rheumatologic diseases are primarily distinguished by their involvement of bone tissue, which not only serves as a mere target of the condition but often plays a pivotal role in its pathogenesis. This scenario is particularly prominent in chronic inflammatory arthritis such as rheumatoid arthritis (RA) and spondyloarthritis (SpA). Given the immunological and systemic nature of these diseases, in this review, we report an overview of the pathogenic mechanisms underlying specific bone involvement, focusing on the complex interactions that occur between bone tissue's own cells and the molecular and cellular actors of the immune system, a recent and fascinating field of interest defined as osteoimmunology. Specifically, we comprehensively elaborate on the distinct pathogenic mechanisms of bone erosion seen in both rheumatoid arthritis and spondyloarthritis, as well as the characteristic process of aberrant bone formation observed in spondyloarthritis. Lastly, chronic inflammatory arthritis leads to systemic bone involvement, resulting in systemic bone loss and consequent osteoporosis, along with increased skeletal fragility.

The risk of osteoporosis in patients with ankylosing spondylitis-A large retrospective matched cohort study

BACKGROUND

Ankylosing spondylitis (AS) is associated with increased bone turnover and systemic inflammation. Osteoporosis is common but frequently underappreciated in AS, studies regarding the incidence of osteoporosis in AS are limited and based on small cohorts. The aim of this study is to assess the risk of osteoporosis in patients with AS compared to matched controls.

METHODS

A population based retrospective cohort study using data retrieved from a large electronic medical record in Israel, the Clalit health services. Included patients that were diagnosed with AS from January 2002 to December 2018 were followed for development of osteoporosis. The incidence of osteoporosis was compared between AS and controls and a logistic regression model was used to assess the interaction between AS and osteoporosis.

RESULTS

The study included 5476 AS patients, and 27,657 age- and sex-frequency matched controls. The incidence of osteoporosis in AS patients was significantly higher than controls (4.7% vs 2.8%, p<0.001) in the whole cohort as well as when stratified by sex. Osteoporosis developed earlier in patients with AS versus controls (4.1 vs 5.2 years, p<0.001). In multivariate analysis and after adjustment to several potential confounders, AS was found to independently associated with osteoporosis (HR 1.83, 95%CI 1.58-2.11, p<0.0001).

CONCLUSIONS

Our study confirms the higher incidence and earlier development of osteoporosis in patients with AS. Such finding highlights the increased need of awareness and earlier detection of such comorbidity allowing prompt treatment to prevent undesired sequalae including increased risk of fractures.

Prevalence and Factors of Osteoporosis and High Risk of Osteoporotic Fracture in Patients with Ankylosing Spondylitis: A Multicenter Comparative Study of Bone Mineral Density and the Fracture Risk Assessment Tool

Background: We investigated the prevalence of and the factors associated with a high risk of osteoporotic fractures in Korean patients with ankylosing spondylitis (AS). Methods: This was a multicenter, retrospective study including 219 AS patients from five university hospitals; the control group was selected by matching age and sex with those of the AS patients. The fracture risk was evaluated based on bone mineral density (BMD) measured by dual-energy X-ray absorptiometry and the fracture risk assessment tool (FRAX) with/without BMD. Results: The mean age of the patients was 47.6 years, and 144 (65.8%) patients were men. According to the WHO criteria and FRAX with/without BMD, the candidates for pharmacological treatment were 44 (20.1%), 20 (13.2%), and 23 (15.1%) patients, respectively, significantly more than those in the healthy control group. Among them, the proportion of patients receiving osteoporosis treatment was 39.1–75%. In logistic regression analysis, menopause was an independent factor for the high risk of fracture according to the WHO criteria and FRAX with/without BMD. C-reactive protein level (odds ratio (OR) 3.8 and OR 6) and glucocorticoid use (OR 1.5 and OR 1.7) were associated with a high risk of osteoporotic fracture based on FRAX without BMD and osteoporosis diagnosed according to the WHO criteria. Conclusions: Our study suggests that both FRAX and WHO criteria may be complementary for treatment decisions to reduce osteoporotic fractures in patients with AS.

Rodent Models of Spondyloarthritis Have Decreased White and Bone Marrow Adipose Tissue Depots

Bone marrow adipose tissue (BMAT) has recently been recognized as a distinct fat depot with endocrine functions. However, if and how it is regulated by chronic inflammation remains unknown. Here, we investigate the amount of white fat and BMAT in HLA-B27 transgenic rats and curdlan-challenged SKG mice, two well-established models of chronic inflammatory spondyloarthritis (SpA). Subcutaneous and gonadal white adipose tissue and BMAT was reduced by 65-70% and by up to 90% in both experimental models. Consistently, B27 rats had a 2-3-fold decrease in the serum concentrations of the adipocyte-derived cytokines adiponectin and leptin as well as a 2-fold lower concentration of triglycerides. The bone marrow of B27 rats was further characterized by higher numbers of neutrophils, lower numbers of erythroblast precursors, and higher numbers of IL-17 producing CD4⁺ T cells. IL-17 concentration was also increased in the serum of B27 rats. Using a cell culture model, we show that high levels of IL-17 in the serum of B27 rats negatively impacted adipogenesis (-76%), an effect that was reversed in the presence of neutralizing anti-IL-17 antibody. In summary, these findings show BMAT is severely reduced in two experimental models of chronic inflammatory SpA and suggest that IL-17 is involved in this process.

Role of HLA-B27 in the comorbidities observed in Axial Spondyloarthritis: Data from COMOSPA

OBJECTIVE

To analyze the potential association between the presence of HLA-B27 and the different comorbidities observed in Axial Spondyloarthritis patients.

METHODS

A comparative cross-sectional study including Axial Spondyloarthritis patients from COMOSPA registry. COMOSPA is a worldwide registry that includes a wide set of anthropometric and clinical variables from 3984 patients with Spondyloarthritis. The registry also includes the most frequent comorbidities observed in Spondyloarthitis such as obesity, hypertension, diabetes, hyperlipidemia, heart ischemic disease, stroke, renal failure, neoplasms, peptic ulcer, diverticulitis, chronic obstructive pulmonary disease, and the presence of osteoporosis. A descriptive analysis and a multiple logistic regression model was performed including all variables assessed.

RESULTS

2370 patients fulfilled ASAS criteria of Axial Spondyloarthritis patients and were included in the study. 1858 (78.4%) of them were HLA-B27 positive. HLA-B27 positive Axial Spondyloarthritis patients presented significantly higher percentage of male sex, longer disease duration, higher percentage of definite Ankylosing Spondylitis, higher CRP levels, and were also more frequent tobacco consumers and excessive alcohol intakers compared to the negatives. However, disease activity measured by BASDAI, BASFI and ASDAS-CRP were all significantly higher in the HLA-B27 negative patients compared to the positive ones. The only association observed between any comorbidity and presence of HLA-B27 genotype was the presence of osteoporosis, even after adjusting in the multivariate analysis for all variables assessed.

CONCLUSION

The association observed between the HLA-B27 genotype and the presence of osteoporosis in Axial Spondyloarthritis patients could be of great relevance given the impact of osteoporosis in the phenotypical frame of these patients.

Mechanisms Underlying Bone Loss Associated with Gut Inflammation

Patients with gastrointestinal diseases frequently suffer from skeletal abnormality, characterized by reduced bone mineral density, increased fracture risk, and/or joint inflammation. This pathological process is characterized by altered immune cell activity and elevated inflammatory cytokines in the bone marrow microenvironment due to disrupted gut immune response. Gastrointestinal disease is recognized as an immune malfunction driven by multiple factors, including cytokines and signaling molecules. However, the mechanism by which intestinal inflammation magnified by gut-residing actors stimulates bone loss remains to be elucidated. In this article, we discuss the main risk factors potentially contributing to intestinal disease-associated bone loss, and summarize current animal models, illustrating gut-bone axis to bridge the gap between intestinal inflammation and skeletal disease.

Alterations of bone mineral density, bone microarchitecture and strength in patients with ankylosing spondylitis: a cross-sectional study using high-resolution peripheral quantitative computerized tomography and finite element analysis

Introduction

Ankylosing spondylitis (AS) is an inflammatory disease associated with new bone formation and an increased risk of osteoporosis and fractures. The negative effects of AS on bone microarchitecture and strength are unclear. Thus, we conducted an observational study to analyze the effect of AS on bone microarchitecture and strength.

Methods

Patients with AS (n = 53) and non-AS subjects (n = 85) were recruited for the study. All subjects underwent clinical evaluation, DXA and high-resolution peripheral quantitative CT scans (HRpQCT).

Results

The AS patients were aged 44 ± 12 (mean ± standard deviation) years and had a median disease duration of 17 (interquartile range: 7–27) years. They were found to have lower cortical, trabecular and total vBMD at the distal radius and tibia than non-AS subjects on multivariable regression analysis. Cortical parameters such as cortical thickness and porosity, and bone strength parameters such bone stiffness and stress as estimated by finite element analysis (FEA) in AS patients were significantly worse than that of-non-AS subjects. Among patients with AS, male sex, mSASSS greater than zero and HLA-B27 negative status were associated with worse bone microarchitecture.

Conclusions

Patients with AS have worse bone mineral density, microarchitecture and strength when compared to non-AS subjects. More research is needed to understand the mechanisms underlying bone pathology in AS and to assess the effect of treatments such as TNF inhibitors on bone quality and fracture risk.

Inflammation, bone loss and fracture risk in spondyloarthritis

Osteoporosis (ie, low bone mineral density) is common in ankylosing spondylitis, related to both systemic inflammation and decreased mobility. Vertebral fracture risk is increased; acute back pain in these patients is not always a flare-up of the disease, as it can be related to bone complications. Intervertebral disc fractures in the ankylosed spine are associated with severe neurological complications. As expected from pathophysiology, treatments effective against inflammation have a positive effect on bone, and prospective open studies have shown that tumour-necrosis-factor blockers can improve bone mineral density at the spine and the hip. There is so far no evidence of a decreased risk of fractures with such treatment.

Loss of bone strength in HLA-B27 transgenic rats is characterized by a high bone turnover and is mainly osteoclast-driven

OBJECTIVE

Although osteopenia is frequent in spondyloarthritis (SpA), the underlying cellular mechanisms and association with other symptoms are poorly understood. This study aimed to characterize bone loss during disease progression, determine cellular alterations, and assess the contribution of inflammatory bowel disease (IBD) to bone loss in HLA-B27 transgenic rats.

METHODS

Bones of 2-, 6-, and 12-month-old non-transgenic, disease-free HLA-B7 and disease-associated HLA-B27 transgenic rats were examined using peripheral quantitative computed tomography, μCT, and nanoindentation. Cellular characteristics were determined by histomorphometry and ex vivo cultures. The impact of IBD was determined using [21-3 x 283-2]F1 rats, which develop arthritis and spondylitis, but not IBD.

RESULTS

HLA-B27 transgenic rats continuously lost bone mass with increasing age and had impaired bone material properties, leading to a 3-fold decrease in bone strength at 12 months of age. Bone turnover was increased in HLA-B27 transgenic rats, as evidenced by a 3-fold increase in bone formation and a 6-fold increase in bone resorption parameters. Enhanced osteoclastic markers were associated with a larger number of precursors in the bone marrow and a stronger osteoclastogenic response to RANKL or TNFα. Further, IBD-free [21-3 x 283-2]F1 rats also displayed decreased total and trabecular bone density.

CONCLUSIONS

HLA-B27 transgenic rats lose an increasing amount of bone density and strength with progressing age, which is primarily mediated via increased bone remodeling in favor of bone resorption. Moreover, IBD and bone loss seem to be independent features of SpA in HLA-B27 transgenic rats.

Bone mineral density in patients with symptoms suggestive of spondyloarthritis

Patients with axial spondyloarthritis (axSpA) have an increased risk of osteoporosis related to inflammation. We evaluate the performance of low bone mineral density (BMD) in diagnosis of axSpA for patients with symptoms suggestive of the disease. A low BMD (T ≤ -2) could be an additional tool for the diagnosis of axSpA.

INTRODUCTION

Diagnosis of axial spondyloarthritis (axSpA) can be challenging, especially in the absence of radiographic abnormalities. Patients with axSpA have an increased risk of osteoporosis related to inflammation. This study evaluated the performance of low bone mineral density (BMD) in diagnosis of axSpA for patients with symptoms suggestive of the disease.

METHODS

Medical files of patients that visited a tertiary centre for symptoms suggestive of axSpA were reviewed. Two hundred and sixty-seven patients were classified in confirmed axSpA or unconfirmed axSpA according to the diagnosis of a senior rheumatologist. BMD measurements results and percentage of patients with a low BMD (T ≤ -2) at either spine or hip were compared between the two groups. Diagnostic performances of low BMD (specificity, sensitivity, positive, negative predictive values and positive likelihood ratio (LR+)) were assessed.

RESULTS

Compared to patients with unconfirmed axSpA (n = 74), patients with confirmed axSpA (n = 193) had similar age, were more frequently male, with positive HLA B27, higher disease duration and higher C-reactive protein (CRP). Low BMD was more frequent at spine and hip, in patients with confirmed (40.3%) than unconfirmed axSpA (24.6%, p = 0.021). The LR+ of low BMD for an axSpA diagnosis was 2.60 and 3.12 at the spine and hip. In the subgroup of patients without any radiographic abnormalities (n = 128), the LR+ of low BMD for an axSpA diagnosis was 2.90 and 2.54 at the spine and hip.

CONCLUSION

In patients with symptoms suggestive of axSpA, a low BMD (T ≤ -2) could be an additional tool for the diagnosis of axSpA.

Altered bone material properties in HLA-B27 rats include reduced mineral to matrix ratio and altered collagen cross-links

Spondyloarthropathy and inflammatory bowel disease (IBD), which includes ulcerative colitis and Crohn's disease, are often associated with severe osteopenia/osteoporosis in both children and adults. HLA-B27 transgenic rats present a phenotype that includes severe colitis and severely accelerated alveolar bone loss. The purpose of this study was to evaluate long bone density status, systemic bone metabolic markers, and intrinsic bone material properties in HLA-B27 transgenic (TG) rats, and compare them with those of age- and sex-matched wild-type (WT) animals. The results indicate that in the HLA-B27 rat, an animal susceptible to both alveolar bone loss (ABL) and long bone osteopenia, there is a statistically significant negative correlation between ABL and long bone bone mineral density (BMD), as well as mineral/matrix ratio at active bone-forming trabecular surfaces. The TG animals had a lower mineral/matrix ratio and higher relative proteoglycan and advanced glycation end product (ϵ-N-Carboxymethyl-L-lysine) content and pyridinoline/divalent collagen cross-link ratio compared with WT. These results may provide better understanding of the interrelationship between osteoporosis and oral bone loss, the underlying causes of the inferior bone strength in the HLA-B27 transgenic animals, and could prove to be a useful model in the elucidation of the pathophysiology of spondyloarthropathy and IBD-associated osteopenia/osteoporosis and in the evaluation of pharmacological intervention(s) against such conditions.

HLA-B27 alters the response to tumor necrosis factor α and promotes osteoclastogenesis in bone marrow monocytes from HLA-B27-transgenic rats

OBJECTIVE

To determine whether HLA-B27 expression alters the response of bone marrow monocytes from HLA-B27/human β2 -microglobulin-transgenic (B27-Tg) rats to tumor necrosis factor α (TNFα) and, if so, whether this affects the cells involved in bone homeostasis.

METHODS

Bone marrow monocytes were treated with RANKL or with TNFα to promote osteoclast formation. Osteoclasts were quantified by counting. Gene expression was measured using quantitative polymerase chain reaction analysis, and protein was detected by enzyme-linked immunosorbent assay, immunoblotting, or immunofluorescence. Effects of endogenously produced cytokines on osteoclast formation were determined with neutralizing antibodies.

RESULTS

TNFα treatment enhanced osteoclast formation 2.5-fold in HLA-B27-expressing cells as compared to wild-type or to HLA-B7/human β2 -microglobulin-expressing monocytes. TNFα induced ∼4-fold up-regulation of HLA-B27, which was associated with the accumulation of misfolded heavy chains, binding of the endoplasmic reticulum (ER) chaperone BiP, and activation of an ER stress response, which was not seen with HLA-B7. No differences were seen with RANKL-induced osteoclastogenesis. Enhanced interleukin-1α (IL-1α) production from ER-stressed bone marrow monocytes from B27-Tg rats was found to be necessary and sufficient for enhanced osteoclast formation. However, bone marrow monocytes from B27-Tg rats also produced more interferon-β (IFNβ), which attenuated the effect of IL-1α on osteoclast formation.

CONCLUSION

HLA-B27-induced ER stress alters the response of bone marrow monocytes from B27-Tg rats to TNFα, which is associated with enhanced production of IL-1α and IFNβ, cytokines that exhibit opposing effects on osteoclast formation. The altered response of cells expressing HLA-B27 to proinflammatory cytokines suggests that this class I major histocompatibility complex allele may contribute to the pathogenesis of spondyloarthritis and its unique phenotype through downstream effects involving alterations in bone homeostasis.

Circulating Levels of Soluble Receptor Activator of NF- κ B Ligand and Matrix Metalloproteinase 3 (and Their Antagonists) in Asian Indian Patients with Ankylosing Spondylitis

Background. Bone loss in ankylosing spondylitis may be related to inflammation. Data from previous studies on circulating levels of sRANKL, OPG, MMP3, and TIMP is inconsistent; thus this study is planned to look at this aspect in Asian Indian patients. Methods. Cross-sectional study included patients with ankylosing spondylitis and age- and gender-similar controls. Serum levels of sRANKL, OPG, MMP-3, and TIMP-1 were measured by ELISA. Results. Included 85 patients (M : F = 82 : 3) having mean age (±SD) 33.0 ± 10.0 years and disease duration 11.3 ± 7.3 years. BASDAI, BASFI, BASMI, and ESR were 4.0 ± 2.2, 3.9 ± 2.8, 3.0 ± 2.8, and 59.2 ± 31.2, respectively. Patients had higher mean (±SD) OPG level (649.7 ± 286.8, 389.3 ± 244.8 pg/mL, P < 0.001). However, there was no difference in sRANKL (349.2 ± 872.0, 554.7 ± 1850.1, P = ns). Serum MMP-3 (91.4 ± 84.7, 55.9 ± 37.1 ng/mL, P < 0.01) and TIMP-1 (520.6 ± 450.7, 296.5 ± 114.2 ng/mL, P < 0.001) levels were higher in patients; however, there was no difference in MMP-3/TIMP-1 ratio. Conclusion. Circulating levels of OPG were higher; however, there was no difference in sRANKL in Asian Indian ankylosing spondylitis patients. Although both MMP-3 and TIMP-1 were raised, their ratio was not different from that of controls.

Deletion of estrogen receptor beta accelerates early stage of bone healing in a mouse osteotomy model

This study examined the role of estrogen receptor (ER) beta during mouse femoral fracture healing by employing ER knockout (KO) mice. The fracture healing in KO mice was enhanced in the early stage of neovascularization and the middle stage of endochondral ossification.

INTRODUCTION

This study was conducted to examine the role of ER beta during fracture healing.

METHODS

Female ERbeta knockout (KO) mice (18 weeks old) and age-matched female wild-type (WT) mice underwent open osteotomy on the right femur. They were sacrificed at 1, 2, 4 and 6 weeks post-fracture. The sera and callus samples were subjected to the following analyses: micro-computed tomography (CT)-based angiography, micro-CT evaluation, histological examination, histomorphometry examination, real-time polymerase chain reaction (PCR) analysis, biochemical marker, and mechanical testing.

RESULTS

Micro-CT-based angiography showed that the total vessel volume at the fracture site was larger in the KO group than the WT group at 1 and 2 weeks post-fracture. Micro-CT analysis revealed that the callus volume was significantly higher in the KO group from week 2 to week 4 post-fracture when compared with the WT group consistent with the histological data. Analysis of biochemical markers indicated that circulating P1NP levels in the KO mice were significantly higher than in the WT mice from week 2 to week 4 and that temporal expression of circulating C-terminal telopeptide of type I collagen (CTX) levels was also higher in the KO mice than in the WT mice. These results were consistent with quantitative real-time PCR analysis. The ultimate load, stiffness, and energy to failure were significantly higher in the KO mice than in the WT mice at week 4.

CONCLUSIONS

The fracture healing in KO mice was enhanced in the early stage of neovascularization and the middle stage of endochondral ossification, but not by the end of healing. Blockade of ERbeta can be considered as another therapeutic strategy for osteoporotic fracture and non-union fracture.

Impaired bone healing pattern in mice with ovariectomy-induced osteoporosis: A drill-hole defect model

OBJECTIVE

To establish a drill-hole defect model in osteoporotic mouse femur by comparing temporal cortical bone healing pattern between OVX-induced osteoporotic bone and sham-operated bone.

METHODS

3-month-old female C57BL/6 mice were randomly divided into an ovariectomy group (OVX) and a sham-operated group (Sham). At 6 weeks post-surgery, 7 mice from each group were sacrificed to examine the distal femur and femoral shaft by both micro-CT and mechanical testing for confirming established osteoporosis induced by OVX. In the remaining mice, a cortical bone defect 0.8mm in diameter was created on the mid-diaphysis of the right femur. The local repair process at days 0, 3, 7, 10, 14 and 21 after creation of the drill-hole was in vivo monitored by high-resolution micro-CT scanning. At each time point, each animal was scanned four times and was removed from the scanner between scans to determine reproducibility. Mice were sacrificed at each time point (n=12 at days 0, 3, 7, 10 and 14; n=20 at day 21). Before sacrifice, sera were collected to examine expression of bone formation marker P1NP (procollagen type I N-terminal propeptide) and bone resorption marker CTX (C-terminal telopeptide of type I collagen). After sacrifice, callus samples were collected and subjected to the following analyses: micro-CT-based angiography; histological examination; immunohistochemical staining to determine estrogen receptor expression; quantitative real-time PCR analysis of collagen type I, collagen type II, collagen type X, osteocalcin, tartrate-resistant acid phosphatase, estrogen receptor alpha (ER alpha) and estrogen receptor beta (ER beta) gene expression; and three-point mechanical testing.

RESULTS

At 6 weeks post-surgery, OVX mice had significantly lower bone mass, impaired bone micro architecture and compromised mechanical properties compared to the Sham mice. In vivo micro-CT analysis revealed that the bone volume fraction in the defect region was significantly lower in the OVX group from day 10 to day 21 post-injury as compared to the Sham group, and was significantly lower in the intra-medulla region in the OVX group from day 7 to day 14 as compared to the Sham group, consistent with the histological data. Analysis of bone biochemical markers indicated that circulating P1NP levels normalized by baseline in the OVX mice were significantly lower than in the Sham mice from day 7 to day 10, and that temporal expression of circulating CTX levels normalized by baseline was also lower in the OVX mice as compared to the Sham mice. These results were consistent with quantitative real-time PCR analysis. ER alpha mRNA expression was significantly lower in the OVX mice, whereas ER beta mRNA expression was significantly higher in the OVX mice as compared to the Sham mice at all time points examined, consistent with immunohistochemical staining. The restoration of femoral mechanical property, determined based on ultimate load and energy-to-failure, was significantly lower in the OVX mice than in the Sham mice. In addition, in vivo micro-CT scanning for quantifying new bone formation in the defect site was highly reproducible in this model.

CONCLUSION

The bone healing of the drill-hole defect was impaired in mice with OVX-induced osteoporosis. The present study provides a model to investigate the functional role of specific gene in osteoporotic bone healing and may facilitate development of novel therapeutic strategies for promoting osteoporotic bone healing.

Osteoporosis in inflammatory joint diseases

Rheumatoid arthritis (RA) and ankylosing spondylitis (AS) are two inflammatory joint diseases characterized by bone complications including osteoporosis. In RA, periarticular bone loss, bone erosions, and systemic osteoporosis are observed, with an increased risk of fractures. Determinants of fractures are underlying conditions (as RA has a female preponderance and an increased prevalence with age), severity of the disease, and use of glucocorticoids. However, bone loss can occur even in glucocorticoid-naive patients. Prospective data show that the optimal control of inflammation in RA is associated with decrease in structural damage and bone loss. RA illustrates the role of inflammation on bone resorption. In AS, osteoporosis is an early event and vertebral fracture risk is increased. Bone loss is related mainly to inflammation, as the disease can occur in young male adult populations, and glucocorticoids are not used in this disease. However, AS is characterized by progressive stiffness and ankylosis of the spine and illustrates also the potential role of inflammation on local bone formation.

Advances in the understanding of mineral and bone metabolism in inflammatory bowel diseases

Chronic inflammatory disorders such as inflammatory bowel diseases (IBDs) affect bone metabolism and are frequently associated with the presence of osteopenia, osteoporosis, and increased risk of fractures. Although several mechanisms may contribute to skeletal abnormalities in IBD patients, inflammation and inflammatory mediators such as TNF, IL-1β, and IL-6 may be the most critical. It is not clear whether the changes in bone metabolism leading to decreased mineral density are the result of decreased bone formation, increased bone resorption, or both, with varying results reported in experimental models of IBD and in pediatric and adult IBD patients. New data, including our own, challenge the conventional views, and contributes to the unraveling of an increasingly complex network of interactions leading to the inflammation-associated bone loss. Since nutritional interventions (dietary calcium and vitamin D supplementation) are of limited efficacy in IBD patients, understanding the pathophysiology of osteopenia and osteoporosis in Crohn's disease and ulcerative colitis is critical for the correct choice of available treatments or the development of new targeted therapies. In this review, we discuss current concepts explaining the effects of inflammation, inflammatory mediators and their signaling effectors on calcium and phosphate homeostasis, osteoblast and osteoclast function, and the potential limitations of vitamin D used as an immunomodulator and anabolic hormone in IBD.

Autosomal recessive mental retardation, deafness, ankylosis, and mild hypophosphatemia associated with a novel ANKH mutation in a consanguineous family

CONTEXT

Mutations in ANKH cause the highly divergent conditions familial chondrocalcinosis and craniometaphyseal dysplasia. The gene product ANK is supposed to regulate tissue mineralization by transporting pyrophosphate to the extracellular space.

OBJECTIVE

We evaluated several family members of a large consanguineous family with mental retardation, deafness, and ankylosis. We compared their skeletal, metabolic, and serological parameters to that of the autosomal recessive progressive ankylosis (ank) mouse mutant, caused by a loss-of-function mutation in the murine ortholog Ank.

PARTICIPANTS

The studied patients had painful small joint soft-tissue calcifications, progressive spondylarthropathy, osteopenia, mild hypophosphatemia, mixed hearing loss, and mental retardation.

RESULTS

After mapping the disease gene to 5p15, we identified the novel homozygous ANK missense mutation L244S in all patients. Although L244 is a highly conserved amino acid, the mutated ANK protein was detected at normal levels at the plasma membrane in primary patient fibroblasts. The phenotype was highly congruent with the autosomal recessive progressive ankylosis (ank) mouse mutant. This indicates a loss-of-function effect of the L244S mutation despite normal ANK protein expression. Interestingly, our analyses revealed that the primary step of joint degeneration is fibrosis and mineralization of articular soft tissues. Moreover, heterozygous carriers of the L244S mutation showed mild osteoarthritis without metabolic alterations, pathological calcifications, or central nervous system involvement.

CONCLUSION

Beyond the description of the first human progressive ankylosis phenotype, our results indicate that ANK influences articular soft tissues commonly involved in degenerative joint disorders. Furthermore, this human disorder provides the first direct evidence for a role of ANK in the central nervous system.