Defining renal phenotype in Alström syndrome.

BACKGROUND: Alström syndrome (AS) is a rare autosomal recessive ciliopathy with a wide spectrum of clinical features, including cone-rod retinal dystrophy, neuronal deafness, severe insulin resistance and major organ failure. The characteristics of renal disease in the syndrome have not been systematically described. The aim of this study is to define the onset and progression of renal disease in AS. METHOD: Prospective observational cohort study. SETTING AND PARTICIPANTS: Thirty-two adult subjects from a national specialist clinic in UK and 86 subjects from an international AS registry were studied. OUTCOMES: First, an international registry cross-sectional study across all age groups to determine change in kidney function was performed. Secondly, a detailed assessment was carried out of adult AS patients with serial follow-up to determine incidence, aetiology and progression of renal disease. ANALYTICAL APPROACH: Generalized estimating equations were used to evaluate the relationship between age and estimated glomerular filtration rate (eGFR). Associations between patient factors and eGFR levels were then assessed in the adult AS cohort. RESULTS: The international registry study of the renal function of 118 subjects with AS (median age 21 years) showed a rapid decline with age, at an average of -16.7 and -10.9 mL/min/1.73 m2 per decade in males and females, respectively. In a UK national cohort of 32 patients with AS (median age 22 years), 20/32 (63%) had chronic kidney disease (CKD) Stage 3 or above based on eGFR <60 mL/min/1.73 m2 or evidence of albuminuria. Hyperuricaemia was noted in 25/32 (79%). Structural abnormalities such as nephrocalcinosis without hypercalcaemia and cysts were observed in 20/32 (63%) subjects. Lower urinary tract symptoms were frequent in 17/19 (70%) of AS patients. Histological evidence showed mixed tubulo-interstitial and glomerular disease. CONCLUSIONS: This is the first study to demonstrate that renal disease is the hallmark of AS, which starts early and progresses with age, leading to a high prevalence of advanced CKD at young age. AS should be considered in the differential diagnosis of rare genetic renal diseases.

Sharpin Controls Osteogenic Differentiation of Mesenchymal Bone Marrow Cells.

The cytosolic protein Sharpin is a component of the linear ubiquitin chain assembly complex, which regulates NF-κB signaling in response to specific ligands, such as TNF-α. Its inactivating mutation in chronic proliferative dermatitis mutation (Cpdm) mice causes multiorgan inflammation, yet this phenotype is not transferable into wild-type mice by hematopoietic stem cell transfer. Recent evidence demonstrated that Cpdm mice additionally display low bone mass, and that this osteopenia is corrected by Tnf deletion. Because the cellular mechanism underlying this pathology, however, was still undefined, we performed a thorough skeletal phenotyping of Cpdm mice on the basis of nondecalcified histology and cellular and dynamic histomorphometry. We show that the trabecular and cortical osteopenia in Cpdm mice is solely explained by impaired bone formation, whereas osteoclastogenesis is unaffected. Consistently, Cpdm primary calvarial cells display reduced osteogenic capacity ex vivo, and the same was observed with CD11b(-) bone marrow cells. Unexpectedly, short-term treatment of these cultures with TNF-α did not reveal an impaired molecular response in the absence of Sharpin. Instead, genome-wide and gene-specific expression analyses revealed that Cpdm mesenchymal cells display increased responsiveness toward TNF-α-induced expression of specific cytokines, such as CXCL5, IL-1ß, and IL-6. Therefore, our data not only demonstrate that the skeletal defects of Cpdm mice are specifically caused by impaired differentiation of osteoprogenitor cells, they also suggest that increased cytokine expression in mesenchymal bone marrow cells contributes to the inflammatory phenotype of Cpdm mice.

The phenotypic and molecular genetic spectrum of Alström syndrome in 44 Turkish kindreds and a literature review of Alström syndrome in Turkey.

Alström syndrome (ALMS) is an autosomal recessive disease characterized by multiple organ involvement, including neurosensory vision and hearing loss, childhood obesity, diabetes mellitus, cardiomyopathy, hypogonadism, and pulmonary, hepatic, renal failure and systemic fibrosis. Alström Syndrome is caused by mutations in ALMS1, and ALMS1 protein is thought to have a role in microtubule organization, intraflagellar transport, endosome recycling and cell cycle regulation. Here, we report extensive phenotypic and genetic analysis of a large cohort of Turkish patients with ALMS. We evaluated 61 Turkish patients, including 11 previously reported, for both clinical spectrum and mutations in ALMS1. To reveal the molecular diagnosis of the patients, different approaches were used in combination, a cohort of patients were screened by the gene array to detect the common mutations in ALMS1 gene, then in patients having any of the common ALMS1 mutations were subjected to direct DNA sequencing or next-generation sequencing for the screening of mutations in all coding regions of the gene. In total, 20 distinct disease-causing nucleotide changes in ALMS1 have been identified, eight of which are novel, thereby increasing the reported ALMS1 mutations by 6% (8/120). Five disease-causing variants were identified in more than one kindred, but most of the alleles were unique to each single patient and identified only once (16/20). So far, 16 mutations identified were specific to the Turkish population, and four have also been reported in other ethnicities. In addition, 49 variants of uncertain pathogenicity were noted, and four of these were very rare and probably or likely deleterious according to in silico mutation prediction analyses. ALMS has a relatively high incidence in Turkey and the present study shows that the ALMS1 mutations are largely heterogeneous; thus, these data from a particular population may provide a unique source for the identification of additional mutations underlying Alström Syndrome and contribute to genotype-phenotype correlation studies.

Human apolipoprotein E isoforms differentially affect bone mass and turnover in vivo.

The primary role of apolipoprotein E (apoE) is to mediate the cellular uptake of lipoproteins. However, a new role for apoE as a regulator of bone metabolism in mice has recently been established. In contrast to mice, the human APOE gene is characterized by three common isoforms APOE ε2, ε3, and ε4 that result in different metabolic properties of the apoE isoforms, but it remains controversial whether the APOE polymorphism influences bone traits in humans. To clarify this, we investigated bone phenotypes of apoE knock-in (k.i.) mice, which express one human isoform each (apoE2 k.i., apoE3 k.i., apoE4 k.i.) in place of the mouse apoE. Analysis of 12-week-old female k.i. mice revealed increased levels of biochemical bone formation and resorption markers in apoE2 k.i. animals as compared to apoE3 k.i. and apoE4 k.i., with a reduced osteoprotegerin (OPG)/receptor activator of NF-κB ligand (RANKL) ratio in apoE2 k.i., indicating increased turnover with prevailing resorption in apoE2 k.i. Accordingly, histomorphometric and micro-computed tomography (µCT) analyses demonstrated significantly lower trabecular bone mass in apoE2 than in apoE3 and apoE4 k.i. animals, which was reflected by a significant reduction of lumbar vertebrae maximum force resistance. Unlike trabecular bone, femoral cortical thickness, and stability was not differentially affected by the apoE isoforms. To extend these observations to the human situation, plasma from middle-aged healthy men homozygous for ε2/ε2, ε3/ε3, and ε4/ε4 (n = 21, n = 80, n = 55, respectively) was analyzed with regard to bone turnover markers. In analogy to apoE2 k.i. mice, a lower OPG/RANKL ratio was observed in the serum of ε2/ε2 carriers as compared to ε3/ε3 and ε4/ε4 individuals (p = 0.02 for ε2/ε2 versus ε4/ε4). In conclusion, the current data strongly underline the general importance of apoE as a regulator of bone metabolism and identifies the APOE ε2 allele as a potential genetic risk factor for low trabecular bone mass and vertebral fractures in humans.

High bone mass in the STR/ort mouse results from increased bone formation and impaired bone resorption and is associated with extramedullary hematopoiesis.

We here describe the novel high bone mass phenotype in STR/ort mice that leads to increased bone masses of cortical and trabecular bone and is associated with elevated osteoblast activity and impaired osteoclast function alike. Comparison of STR/ort and C57BL/6 mice reveals an increase in trabecular bone volumes of the vertebrae and at femoral metaphysis. In the females, this difference is significant as early as 2 months of age and at 9 months the females by far exceed their age matched males in all parameters measured. The increase in cortical bone mass at femoral diaphysis results from an apposition to the endosteal surface, it is significant for both sexes as early as 1 month of age and leads to bone marrow compression and extramedullary hematopoiesis. Altered activities of both, the osteoblast and the osteoclast contribute to the high bone mass and collectively this phenotype supports a multifactorial pathogenesis. Moreover, the spontaneous development of osteoarthritis in male STR/ort mice is suggestive of a tight correlation between trabecular bone mass and the development of degenerative changes of the articular cartilage.

Osteopetrosis, osteopetrorickets and hypophosphatemic rickets differentially affect dentin and enamel mineralization.

Osteopetrosis (OP) is an inherited disorder of defective bone resorption, which can be accompanied by impaired skeletal mineralization, a phenotype termed osteopetrorickets (OPR). Since individuals with dysfunctional osteoclasts often develop osteomyelitis of the jaw, we have analyzed, if dentin and enamel mineralization are differentially affected in OP and OPR. Therefore, we have applied non-decalcified histology and quantitative backscattered electron imaging (qBEI) to compare the dental phenotypes of Src(-/-), oc/oc and Hyp(-/0) mice, which serve as models for OP, OPR and hypophosphatemic rickets, respectively. While both, Src(-/-) and oc/oc mice, were characterized by defects of molar root formation, only oc/oc mice displayed a severe defect of dentin mineralization, similar to Hyp(-/0) mice. Most importantly, while enamel thickness was not affected in either mouse model, the calcium content within the enamel phase was significantly reduced in oc/oc, but not in Src(-/-) or Hyp(-/0) mice. Taken together, these data demonstrate that dentin and enamel mineralization are differentially affected in Src(-/-) and oc/oc mice. Moreover, since defects of dental mineralization may trigger premature tooth decay and thereby osteomyelitis of the jaw, they further underscore the importance of discriminating between OP and OPR in the respective individuals.

Pharmacological estrogen administration causes a FSH-independent osteo-anabolic effect requiring ER alpha in osteoblasts.

Postmenopausal osteoporosis is characterized by declining estrogen levels, and estrogen replacement therapy has been proven beneficial for preventing bone loss in affected women. While the physiological functions of estrogen in bone, primarily the inhibition of bone resorption, have been studied extensively, the effects of pharmacological estrogen administration are still poorly characterized. Since elevated levels of follicle-stimulating hormone (FSH) have been suggested to be involved in postmenopausal bone loss, we investigated whether the skeletal response to pharmacological estrogen administration is mediated in a FSH-dependent manner. Therefore, we treated wildtype and FSHß-deficicent (Fshb(-/-)) mice with estrogen for 4 weeks and subsequently analyzed their skeletal phenotype. Here we observed that estrogen treatment resulted in a significant increase of trabecular and cortical bone mass in both, wildtype and Fshb(-/-) mice. Unexpectedly, this FSH-independent pharmacological effect of estrogen was not caused by influencing bone resorption, but primarily by increasing bone formation. To understand the cellular and molecular nature of this osteo-anabolic effect we next administered estrogen to mouse models carrying cell specific mutant alleles of the estrogen receptor alpha (ERα). Here we found that the response to pharmacological estrogen administration was not affected by ERα inactivation in osteoclasts, while it was blunted in mice lacking the ERα in osteoblasts or in mice carrying a mutant ERα incapable of DNA binding. Taken together, our findings reveal a previously unknown osteo-anabolic effect of pharmacological estrogen administration, which is independent of FSH and requires DNA-binding of ERα in osteoblasts.

Stress fractures in elderly patients.

PURPOSE: The purpose of this study was to investigate specific risk factors, common fracture locations and possible sex-specific differences in elderly patients with stress fractures. METHODS: This analysis enrolled 105 patients (83 women, 22 men) with stress fractures. For the analysis of possible risk factors related to increasing age, data from 82 patients (67 women, 15 men) aged 40 years and older (mean age of 57.4 ± 11.0 years) were compared with that from a younger control group [23 patients (16 women, seven men), mean age 28.4 ± 6.7 years]. Bone mineral density (BMD) was determined using dual-energy X-ray absorptiometry bone densitometry (DXA) and blood samples were taken. RESULTS: A total of 211 stress fractures were found. Of these, 177 were found in the study group, of which 90.4 % were located in the lower limb. Lumbar and femoral BMD was significantly lower in elderly patients; however, the BMD of most patients was within the osteopenic or normal range. Within the study group, a total of 83.8 % had a vitamin D insufficiency (<30 µg/l); 75.5 % were not engaged in regular physical activity more than once a week. Overweight patients within the study group had significantly more stress fractures compared to normal weight patients (2.6 ± 1.7 vs. 1.9 ± 1.1, p<0.05). CONCLUSIONS: A similar contribution of risk factors has been found for stress fractures in elderly patients and younger controls of the general population. Stress fracture incidence seems to be rather multifactorial and not based on osteoporotic changes alone. A balanced calcium and vitamin D metabolism seems to be of paramount importance for stress fracture prevention in elderly patients.

Application of ex vivo micro-computed tomography for assessment of in vivo fluorescence and plain radiographic imaging for monitoring bone metastases and osteolytic lesions.

The intracardiac injection model is a commonly used in vivo model to test therapeutic response in bone metastases. However, few studies have critically compared the performance of different imaging methods in terms of sensitivity and quantitative assessment of osteolytic lesions. We performed in vivo optical and plain radiographic imaging of bone metastases followed by high-sensitivity ex vivo micro-computed tomography (micro-CT) imaging. This approach allowed for quantitative assessment of in vivo imaging techniques using fluorescence and plain radiography. Comparison of lesions detected in vivo by fluorescent optical imaging with ex vivo micro-CT revealed that the limited spatial resolution of fluorescent optical imaging may underestimate the number of bone metastases. Radiography was compared with micro-CT for the detection of osteolytic lesions. When using dichotomous yes/no grading, there was a 64% agreement in detection of osteolytic lesions. When subjective semiquantitative grading methods were used to assess the extent of osteolytic lesions, a positive association between the micro-CT grades and the square root of the radiography-based grades was observed (p < 0.05). Micro-CT also showed a significant association with fluorescent optical values; however, no such association was observed between lesion scores based on radiographs and those based on fluorescent imaging. The findings reveal an approximate two-fold sensitivity for micro-CT compared to plain radiography in the detection of osteolytic lesions. Significant associations between micro-CT-based osteolytic lesion grade and tumor growth characterized by increased fluorescent area document the value of these two techniques for the assessment of osteolytic bone metastases.

Control of bone formation by the serpentine receptor Frizzled-9.

Although Wnt signaling in osteoblasts is of critical importance for the regulation of bone remodeling, it is not yet known which specific Wnt receptors of the Frizzled family are functionally relevant in this process. In this paper, we show that Fzd9 is induced upon osteoblast differentiation and that Fzd9(-/-) mice display low bone mass caused by impaired bone formation. Our analysis of Fzd9(-/-) primary osteoblasts demonstrated defects in matrix mineralization in spite of normal expression of established differentiation markers. In contrast, we observed a reduced expression of chemokines and interferon-regulated genes in Fzd9(-/-) osteoblasts. We also identified the ubiquitin-like modifier Isg15 as one potential downstream mediator of Fzd9 in these cells. Importantly, our molecular analysis further revealed that canonical Wnt signaling is not impaired in the absence of Fzd9, thus explaining the absence of a bone resorption phenotype. Collectively, our results reveal a previously unknown function of Fzd9 in osteoblasts, a finding that may have therapeutic implications for bone loss disorders.

Short-term activation of liver X receptors inhibits osteoblasts but long-term activation does not have an impact on murine bone in vivo.

Liver X receptors (LXRs) are nuclear receptors that play a crucial role in the transcriptional control of lipid metabolism. Pharmacological LXR activation is an attractive concept for the treatment of atherosclerosis. Genetic LXR deficiency in mice has been shown to have an effect on bone turnover and structure and LXR activation is known to influence the osteogenic differentiation of bone marrow stromal cells. Therefore, therapeutic pharmacological LXR activation may have relevant effects on bone. Here, using two synthetic LXR ligands, T0901317 and GW3965, we investigated the effect of LXR activation on murine osteoblasts and the influence of long-term LXR activation on bone in vivo in mice. Short term (48 h) in vitro treatment of primary murine osteoblasts with T0901317 resulted in a dose-dependent decrease of osteocalcin and alkaline phosphatase mRNA and protein. In vivo, a 6-day treatment of C57BL/6J mice with T0901317 led to a 40% reduction of serum osteocalcin concentrations. Long-term (12-week) oral administration of T0901317 or GW3965 influenced the expression of established LXR target genes in liver and intestine, but did not alter trabecular and cortical bone structure or bone turnover as determined by total skeleton radiography, histomorphometric analysis of lumbar vertebral trabecular bone, micro CT analysis of femur cortical bone and biochemical determination of bone formation and resorption markers. We conclude that short-term pharmacological LXR activation has the potential to profoundly influence osteoblast function, but that long-term LXR activation in vivo has no adverse effects on the murine skeleton.

Negative regulation of bone formation by the transmembrane Wnt antagonist Kremen-2.

Wnt signalling is a key pathway controlling bone formation in mice and humans. One of the regulators of this pathway is Dkk1, which antagonizes Wnt signalling through the formation of a ternary complex with the transmembrane receptors Krm1/2 and Lrp5/6, thereby blocking the induction of Wnt signalling by the latter ones. Here we show that Kremen-2 (Krm2) is predominantly expressed in bone, and that its osteoblast-specific over-expression in transgenic mice (Col1a1-Krm2) results in severe osteoporosis. Histomorphometric analysis revealed that osteoblast maturation and bone formation are disturbed in Col1a1-Krm2 mice, whereas bone resorption is increased. In line with these findings, primary osteoblasts derived from Col1a1-Krm2 mice display a cell-autonomous differentiation defect, impaired canonical Wnt signalling and decreased production of the osteoclast inhibitory factor Opg. To determine whether the observed effects of Krm2 on bone remodeling are physiologically relevant, we analyzed the skeletal phenotype of 24 weeks old Krm2-deficient mice and observed high bone mass caused by a more than three-fold increase in bone formation. Taken together, these data identify Krm2 as a regulator of bone remodeling and raise the possibility that antagonizing KRM2 might prove beneficial in patients with bone loss disorders.

Increased trabecular bone formation in mice lacking the growth factor midkine.

Midkine (Mdk) and pleiotrophin (Ptn) comprise a family of heparin-binding growth factors known primarily for their effects on neuronal cells. Since transgenic mice overexpressing Ptn have been reported to display increased bone density, we have previously analyzed Ptn-deficient mice but failed to detect any abnormality of skeletal development and remodeling. Together with the finding that Mdk expression increases in the course of primary osteoblast differentiation, we reasoned that Mdk, rather than Ptn, could play a physiologic role in bone formation. Here, we show that Mdk-deficient mice display an increased trabecular bone volume at 12 and 18 months of age, accompanied by cortical porosity. Histomorphometric quantification demonstrated an increased bone-formation rate compared with wild-type littermates, whereas bone resorption was differentially affected in trabecular and cortical bone of Mdk-deficient mice. To understand the effect of Mdk on bone formation at the molecular level, we performed a genome-wide expression analysis of primary osteoblasts and identified Ank and Enpp1 as Mdk-induced genes whose decreased expression in Mdk-deficient osteoblasts may explain, at least in part, the observed skeletal phenotype. Finally, we performed ovariectomy and observed bone loss only in wild-type but not in Mdk-deficient animals. Taken together, our data demonstrate that Mdk deficiency, at least in mice, results in an increased trabecular bone formation, thereby raising the possibility that Mdk-specific antagonists might prove beneficial in osteoporosis therapy.

Skeletal analysis and comparison of bog bodies from Northern European peat bogs.

Although numerous bodies were deposited in Western European bogs in the past centuries, few were found and underwent archeological analysis. No studies comparing skeletal structure and mineralization of bog bodies from different ages have been performed to this day. Therefore, the aim of this study was to analyze and compare skeletal features and specifics of the human remains of three bog bodies from the Iron and Middle Ages found in Northern European peat bogs. Demineralization due to the acidic environment in peat bogs was comparably pronounced in all three bodies. Still, the macroscopic state of skeletal preservation was excellent. In addition to contact radiography, we used peripheral quantitative computed tomography to measure cortical bone mineral density. The conservation of skeletal three-dimensional microstructural elements was assessed by high-resolution microcomputed tomography analysis. These techniques revealed severe differences in bone mineral density and enabled us to determine handedness in all three bodies. Additionally, unique skeletal features like intravital bone lesions, immobilization osteoporosis, and Harris lines were found. A deformity of the left femoral head was observed which had the typical appearance of an advanced stage of Legg-Calve-Perthes disease. This study gives detailed insight into the skeletal microstructure and microarchitecture of 800- to 2,700-year-old bog bodies. Skeletal analysis enables us to draw conclusions not only concerning changes in the acidic environment of the bog, but also serves as a diagnostic tool to unravel life circumstances and diseases suffered by humans in the Iron and Middle Ages.

Impaired gastric acidification negatively affects calcium homeostasis and bone mass.

Activation of osteoclasts and their acidification-dependent resorption of bone is thought to maintain proper serum calcium levels. Here we show that osteoclast dysfunction alone does not generally affect calcium homeostasis. Indeed, mice deficient in Src, encoding a tyrosine kinase critical for osteoclast activity, show signs of osteopetrosis, but without hypocalcemia or defects in bone mineralization. Mice deficient in Cckbr, encoding a gastrin receptor that affects acid secretion by parietal cells, have the expected defects in gastric acidification but also secondary hyperparathyroidism and osteoporosis and modest hypocalcemia. These results suggest that alterations in calcium homeostasis can be driven by defects in gastric acidification, especially given that calcium gluconate supplementation fully rescues the phenotype of the Cckbr-mutant mice. Finally, mice deficient in Tcirg1, encoding a subunit of the vacuolar proton pump specifically expressed in both osteoclasts and parietal cells, show hypocalcemia and osteopetrorickets. Although neither Src- nor Cckbr-deficient mice have this latter phenotype, the combined deficiency of both genes results in osteopetrorickets. Thus, we find that osteopetrosis and osteopetrorickets are distinct phenotypes, depending on the site or sites of defective acidification.

Brief communication: Two and three-dimensional analysis of bone mass and microstructure in a bog body from the Iron Age.

Human remains from peat bogs, called "bog bodies," have yielded valuable insights into human history because of their excellent preservation of soft tissue. On the other hand, the acidic environment of the peat leads to an extensive demineralization of skeletal elements, complicating their analysis. We studied the skeleton of the bog body "Moora" dated to approximately 650 B.C. Nondestructive evaluation of the bone was made using contact X-rays, peripheral quantitative computed tomography (pQCT) analysis, multislice computed tomography (CT) and high resolution micro computed tomography (microCT) imaging. Two thousand seven hundred years in the acidic environment of the bog led to a loss of 92.7% of bone mineral density. Despite this demineralization and in contrast to other bog bodies, the spatial structure of the bones of "Moora" is exceptionally well preserved. We found Harris lines and were able to obtain the first three-dimensional data on the trabecular microstructure of the bone of a young woman from the early Iron Age.