Cerebroretinal microangiopathy with calcifications and cysts: Characterization of the skeletal phenotype

Authors

Sanna Toiviainen-Salo, Tarja Linnankivi, Anne Saarinen, Mervi K. Mäyränpää, Riitta Karikoski, Outi Mäkitie

Abstract

Cerebral cysts and calcifications with leukoencephalopathy and retinal vascular abnormalities are diagnostic hallmarks of cerebroretinal microangiopathy with calcifications and cysts (CRMCC). Previous studies have suggested that skeletal involvement is also common, but its characteristics remain unknown. This study aimed to assess the skeletal phenotype in CRMCC. All Finnish patients with features consistent with CRMCC and for whom radiographs were available were included. Clinical information pertinent to the skeletal phenotype was collected from hospital records, and all plain radiographs were reviewed for skeletal features. Bone mineral density (BMD) was measured by DXA. In one patient, bone biopsies were obtained for bone histology and histomorphometric analyses. The LRP5 gene was analyzed for mutations by direct sequencing. Our results show that the skeletal phenotype in CRMCC includes (1) compromised longitudinal growth pre- and postnatally, (2) generalized osteopenia or early onset low turnover osteoporosis with fragility fractures, and (3) metaphyseal abnormalities that may lead to limb deformities such as short femoral neck or genua valga. DXA measurements in three patients showed low BMD, and bone biopsies in the fourth patient with pathological fractures and impaired fracture healing showed low-turnover osteoporosis, with reduced osteoclast and osteoblast activity. Direct sequencing of all LRP5 coding exons and exon–intron boundaries in six patients with CRMCC revealed no putative mutations. We conclude that the CRMCC-associated bone disease is characterized by low BMD and pathological fractures with delayed healing, metaphyseal changes, and short stature pre- and postnatally. LRP5 is not a disease-causing gene in CRMCC.

Link to Article

http://dx.doi.org/10.1002/ajmg.a.33994

Analysis of osteoarthritis in a mouse model of the progeroid human DNA repair syndrome trichothiodystrophy

Authors

Sander M. Botter, Michel Zar, Gerjo J. V. M van Osch, Harry van Steeg, Martijn E. T. Dollé, Jan H. J. Hoeijmakers, Harrie Weinans, and Johannes P. T. M. van Leeuwen

Abstract

The increasing average age in developed societies is paralleled by an increase in the prevalence of many age-related diseases such as osteoarthritis (OA), which is characterized by deformation of the joint due to cartilage damage and increased turnover of subchondral bone. Consequently, deficiency in DNA repair, often associated with premature aging, may lead to increased pathology of these two tissues. To examine this possibility, we analyzed the bone and cartilage phenotype of male and female knee joints derived from 52- to 104-week-old WT C57Bl/6 and trichothiodystrophy (TTD) mice, who carry a defect in the nucleotide excision repair pathway and display many features of premature aging. Using micro-CT, we found bone loss in all groups of 104-week-old compared to 52-week-old mice. Cartilage damage was mild to moderate in all mice. Surprisingly, female TTD mice had less cartilage damage, proteoglycan depletion, and osteophytosis compared to WT controls. OA severity in males did not significantly differ between genotypes, although TTD males had less osteophytosis. These results indicate that in premature aging TTD mice age-related changes in cartilage were not more severe compared to WT mice, in striking contrast with bone and many other tissues. This segmental aging character may be explained by a difference in vasculature and thereby oxygen load in cartilage and bone. Alternatively, a difference in impact of an anti-aging response, previously found to be triggered by accumulation of DNA damage, might help explain why female mice were protected from cartilage damage. These findings underline the exceptional segmental nature of progeroid conditions and provide an explanation for pro- and anti-aging features occurring in the same individual.

Link to Article

http://dx.doi.org/10.1007/s11357-010-9175-3

Decreased Bone Formation and Osteopenia in Lamin A/C-Deficient Mice

Authors

Wei Li, Li Sze Yeo, Christopher Vidal, Thomas McCorquodale, Markus Herrmann, Diane Fatkin, Gustavo Duque

Abstract

Age-related bone loss is associated with changes in bone cellularity with characteristically low levels of osteoblastogenesis. The mechanisms that explain these changes remain unclear. Although recent in vitro evidence has suggested a new role for proteins of the nuclear envelope in osteoblastogenesis, the role of these proteins in bone cells differentiation and bone metabolism in vivo remains unknown. In this study, we used the lamin A/C null (Lmna−/−) mice to identify the role of lamin A/C in bone turnover and bone structure in vivo. At three weeks of age, histological and micro computed tomography measurements of femurs in Lmna−/− mice revealed a significant decrease in bone mass and microarchitecture in Lmna−/− mice as compared with their wild type littermates. Furthermore, quantification of cell numbers after normalization with bone surface revealed a significant reduction in osteoblast and osteocyte numbers in Lmna−/− mice compared with their WT littermates. In addition, Lmna−/− mice have significantly lower osteoclast number, which show aberrant changes in their shape and size. Finally, mechanistic analysis demonstrated that absence of lamin A/C is associated with increase expression of MAN-1 a protein of the nuclear envelope closely regulated by lamin A/C, which also colocalizes with Runx2 thus affecting its capacity as osteogenic transcription factor. In summary, these data clearly indicate that the presence of lamin A/C is necessary for normal bone turnover in vivo and that absence of lamin A/C induces low bone turnover osteopenia resembling the cellular changes of age-related bone loss.

Link to Article

http://dx.doi.org/10.1371/journal.pone.0019313

Nuclear NAC Influences Bone Matrix Mineralization and Osteoblast Maturation In Vivo

Authors

Thomas Meury, Omar Akhouayri, Toghrul Jafarov, Vice Mandic, and René St-Arnaud

Abstract

Nascent-polypeptide-associated complex and coactivator alpha (NAC) is a protein shuttling between the nucleus and the cytoplasm. Upon phosphorylation at residue serine 43 by integrin-linked kinase, NAC is translocated to the nuclei of osteoblasts, where it acts as an AP-1 coactivator to increase osteocalcin gene transcription. To determine the physiological role of nuclear NAC, we engineered a knock-in mouse model with a serine-to-alanine mutation at position 43 (S43A). The S43A mutation resulted in a decrease in the amount of nuclear NAC with reduced osteocalcin gene promoter occupancy, leading to a significant decrease in osteocalcin gene transcription. The S43A mutant bones also expressed decreased levels of 1(I) collagen mRNA and as a consequence had significantly less osteoid tissue. Transient transfection assays and chromatin immunoprecipitation confirmed the 1(I) collagen gene as a novel NAC target. The reduced quantity of bone matrix in S43A mutant bones was mineralized faster, as demonstrated by the significantly reduced mineralization lag time, producing a lower volume of immature, woven-type bone characterized by poor lamellation and an increase in the number of osteocytes. Accordingly, the expression of the osteocyte differentiation marker genes DMP-1 (dentin matrix protein 1), E11, and SOST (sclerostin) was increased. The accelerated mineralization phenotype was cell autonomous, as osteoblasts isolated from the calvaria of S43A mutant mice mineralized their matrix faster than did wild-type cells. Thus, inhibition of NAC nuclear translocation results in an osteopenic phenotype caused by reduced expression of osteocalcin and type I collagen, accelerated mineralization, and immature woven-bone formation.

Link to Article

http://dx.doi.org/10.1128/mcb.00378-09

Altered bone composition in children with vertebral fracture

Authors

Inari S Tamminen, Mervi K Mäyränpää, Mikael J Turunen, Hanna Isaksson, Outi Mäkitie, Jukka S Jurvelin, Heikki Kröger

Abstract

Primary osteoporosis in children often leads to vertebral fractures but it remains unknown whether these fractures associate with changes in bone composition. This study aimed to determine the differences in bone composition in fracture-prone children with and without vertebral fractures, as assessed by Fourier transform infrared spectroscopic imaging (FTIRI) and bone histomorphometry. Iliac crest bone biopsies (n = 24) were obtained from children who were suspected of primary osteoporosis based on evidence from the fracture history and/or low bone mineral density (BMD) in DXA. Vertebral morphology was determined by radiography. Bone biopsies were analyzed using histomorphometry and FTIRI. Phosphate-to-amide I, carbonate-to-phosphate, carbonate-to-amide I, and cross-link ratios (collagen maturity) were calculated. Children with (n = 14) and without (n = 10) vertebral fracture were compared. Low cancellous bone volume (BV/TV) was detected by histomorphometry in 36% of the children with vertebral fracture, and bone turnover rate was abnormal in 64% of them. Children with vertebral fractures had lower carbonate-to-phosphate ratio (p < 0.05) and higher collagen maturity (p < 0.05) than children without vertebral fracture. The children with low BV/TV in biopsy showed lower carbonate-to-amide I ratio (p < 0.05) than the children with normal bone volume. This study showed changes in bone composition among fracture-prone children who had sustained a vertebral fracture. The observed changes in bone composition in these children might contribute to their greater propensity to sustain vertebral fractures.

Link to Article

http://dx.doi.org/10.1002/jbmr.409

Evaluation of an anorganic bovine-derived mineral with P-15 hydrogel bone graft: preliminary study in a rabbit cranial bone model

Authors

Sérgio Matos, Fernando Guerra, Jack T. Krauser, Helena Figueiredo, João Pedro Marcelino, Mariano Sanz

Abstract

The present investigation aimed to assess the bone-regenerative potential of two formulations of anorganic bovine-derived mineral bound to a P-15 (ABM/P-15) bone graft – the particulate and the hydrogel forms – in a delayed healing rabbit cranial defect model. Ten adult male New Zealand White rabbits were used to create two 8 mm transcortical cranial defects per rabbit and each one received randomly the test material (ABM/P-15 carboxymethyl cellulose (CMC)-hydrogel graft), the standard control material (ABM/P-15 particulate graft) or remained empty as a negative control. The defects were allowed to heal for 2 and 4 weeks. Qualitative and quantitative histological outcomes were assessed on undecalcified sections. In the defects grafted with the test material, at both time points, there was a marked random migration of the bone substitute particles. As a consequence, the space maintenance provision was lost and new bone formation was reduced compared with the control particulate graft material. The histomorphometric analysis showed that the control material attained better results, with an average of 13.8 ± 1.9% and 18.2 ± 4.4% of new bone at 2 and 4 weeks, compared with 8.5 ± 2.4% and 13 ± 2.9% for the test material. These differences were significant at 2 weeks (P≤0.05), but not at 4 weeks (P>0.05). Additionally, there was a significant difference in the total area of mineralized tissue (new bone plus particles), favoring the standard control over the test material: 43.2 ± 14.4% vs. 14.2 ± 5.3% at 2 weeks and 56.9 ± 4.2% vs. 24.2 ± 9.6% at 4 weeks, respectively. The test ABM/P-15 CMC-hydrogel graft material behaved in this animal model by migration of the graft particles, what determined an unpredictable osseoconduction and, consequently, a decreased quality and quantity of bone regeneration as compared with the osseopromotive behavior exhibited by the standard particulate form of the ABM/P-15 control graft. It is therefore suggested to restrain the application of the hydrogel graft form in non-contained anatomical bone defects.

Link to Article

http://dx.doi.org/10.1111/j.1600-0501.2011.02179.x