María A. Alonso

Trend in hip fracture epidemiology over a 14-year period in a Spanish population

Spain lacks detailed data on hip fracture trends despite being the country with the greatest increase in the pensioner-to-provider ratio in Europe. We reproduced a study on hip fracture incidence in a region of northern Spain (Cantabria) carried out 14 years ago to determine whether a secular trend to change is taking place. If such a trend could be found, our objective was to determine whether the effect is solely due to ageing or whether additional variables are involved. We assessed the incidence of hip fracture in patients aged ≥50 years through clinical records from Emergency Units and Orthopedic Surgical Units of all hospitals in the region of Cantabria in 1988 and 2002. A total of 318 new cases of hip fracture were recorded in 1988 and 490 in 2002 (54% increase; p<0.001). No significant changes were noticed following an adjustment for age. Women accounted for the increase in crude hip fracture incidence [246 women and 72 men suffered a hip fracture in 1988 compared to 404 women and 86 men in 2002 (64% increase in women and 19% increase in men; p<0.005 and not significant, respectively)]. The female:male ratio was 3.4 in 1988 versus 4.7 in 2002; following age-adjustment, no significant changes were found (1.8 in 1988 and 1.9 in 2002). The increase in crude hip fracture incidence was greater at cervical (versus trochanteric) sites. Patient residence, time of the year, site of fracture, kind of injury, previous contralateral hip fracture, length of stay, and peri-operative mortality did not differ significantly. In conclusion, a crude hip fracture incidence increase of about 50% in the northern Spanish region of Cantabria has taken place over the last 14 years. This effect does not persist after adjustments have been made for age. The crude rate increase occurred mainly at the expense of women, with a more noticeable rise in cervical fractures as opposed to trochanteric lesions.

Aromatase expression in osteoarthritic and osteoporotic bone

OBJECTIVE Estrogen deprivation is a central mechanism in the development of osteoporosis with aging. Results from recent studies also suggest the involvement of estrogens in the pathophysiology of osteoarthritis (OA). Aromatization of androgenic precursors in peripheral tissue is the main source of estrogens in postmenopausal women and in men. However, the importance of aromatase expression in bone is a subject of controversy. This study was undertaken to determine aromatase expression in bone samples from patients with hip fracture and patients with OA. METHODS We studied 104 patients with hip fracture (n = 60) or primary hip OA (n = 44). Aromatase expression was determined in trabecular bone samples from the femoral neck and in osteoblast cultures grown by the primary explant technique (n = 62), using real-time reverse transcriptase-polymerase chain reaction. RESULTS Aromatase RNA was detected in bone samples at levels similar to those found in adipose tissue. Transcript levels were significantly lower in bone tissue samples obtained from patients with OA than in those obtained from patients with fracture (P = 0.00001). Likewise, primary cultures of osteoblast cells from OA patients revealed lower aromatase expression than those of cells from fracture patients (P = 0.012). Results were independent of age or sex differences. CONCLUSION Our findings indicate that the aromatase gene is expressed in bone tissue in high amounts, similar to those found in adipose tissue, but transcript levels are lower in tissue samples and osteoblast cultures from patients with OA than in those from patients with hip fracture. Since estrogens may help to prevent local cartilage degradation, it can be speculated that such a reduced expression of aromatase could facilitate the development of OA.

Role of BMPs in the regulation of sclerostin as revealed by an epigenetic modifier of human bone cells

Sclerostin, encoded by the SOST gene, is specifically expressed by osteocytes. However osteoblasts bear a heavily methylated SOST promoter and therefore do not express SOST. Thus, studying the regulation of human SOST is challenged by the absence of human osteocytic cell lines. Herein, we explore the feasibility of using the induction of SOST expression in osteoblasts by a demethylating agent to study the mechanisms underlying SOST transcription, and specifically, the influence of bone morphogenetic proteins (BMPs). Microarray analysis and quantitative PCR showed that AzadC up-regulated the expression of several BMPs, including BMP-2, BMP-4 and BMP-6, as well as several BMP downstream targets. Recombinant BMP-2 increased the transcriptional activity of the SOST promoter cloned into a reporter vector. Likewise, exposing cells transfected with the vector to AzadC also resulted in increased transcription. On the other hand, inhibition of the canonical BMP signaling blunted the effect of AzadC on SOST. These results show that the AzadC-induced demethylation of the SOST promoter in human osteoblastic cells may be a valuable tool to study the regulation of SOST expression. As a proof of concept, it allowed us to demonstrate that BMPs stimulate SOST expression by a mechanism involving BMPR1A receptors and downstream Smad-dependent pathways.

Contribution of genetic and epigenetic mechanisms to Wnt pathway activity in prevalent skeletal disorders.

We reported previously that the expression of Wnt-related genes is lower in osteoporotic hip fractures than in osteoarthritis. We aimed to confirm those results by analyzing β-catenin levels and explored potential genetic and epigenetic mechanisms involved. β-Catenin gene expression and nuclear levels were analyzed by real time PCR and confocal immunofluorescence. Increased nuclear β-catenin was found in osteoblasts isolated from patients with osteoarthritis (99 ± 4 units vs. 76 ± 12, p=0.01, n=10), without differences in gene transcription, which is consistent with a post-translational down-regulation of β-catenin and decreased Wnt pathway activity. Twenty four single nucleotide polymorphisms (SNPs) of genes showing differential expression between fractures and osteoarthritis (WNT4, WNT10A, WNT16 and SFRP1) were analyzed in DNA isolated from blood of 853 patients. The genotypic frequencies were similar in both groups of patients, with no significant differences. Methylation of Wnt pathway genes was analyzed in bone tissue samples (15 with fractures and 15 with osteoarthritis) by interrogating a CpG-based methylation array. Six genes showed significant methylation differences between both groups of patients: FZD10, TBL1X, CSNK1E, WNT8A, CSNK1A1L and SFRP4. The DNA demethylating agent 5-deoxycytidine up-regulated 8 genes, including FZD10, in an osteoblast-like cell line, whereas it down-regulated other 16 genes. In conclusion, Wnt activity is reduced in patients with hip fractures, in comparison with those with osteoarthritis. It does not appear to be related to differences in the allele frequencies of the Wnt genes studied. On the other hand, methylation differences between both groups could contribute to explain the differences in Wnt activity.

Association of aromatase and estrogen receptor gene polymorphisms with hip fractures.

SummaryTwo polymorphisms of the aromatase and estrogen receptor genes appeared to interact to influence the risk of hip fractures in women.IntroductionAllelic variants of the aromatase gene have been associated with bone mineral density and vertebral fractures. Our objective was to analyze the relationship between two polymorphisms of the aromatase and estrogen receptor genes and hip fractures.MethodsWe studied 498 women with hip fractures and 356 controls. A C/G polymorphism of the aromatase gene and a T/C polymorphism of the estrogen receptor α gene were analyzed using Taqman assays. Aromatase gene expression was determined in 43 femoral neck samples by real-time RT-PCR.ResultsThere were no significant differences in the overall distribution of genotypes between the fracture and control groups. However, among women with a TT genotype of the estrogen receptor, the CC aromatase genotype was more frequent in women with fractures than in controls (39 vs. 23%, p = 0.009). Thus, women homozygous for T alleles of estrogen receptor and C alleles of aromatase were at increased risk of fracture (odds ratio 2.0; 95% confidence interval 1.2–3.4). The aromatase polymorphism was associated with RNA levels in bone tissue, which were three times lower in samples with a CC genotype (p = 0.009).ConclusionsThese common polymorphisms of the aromatase and estrogen receptor genes appear to interact, influencing the risk of hip fractures in women.

Differential analysis of genome-wide methylation and gene expression in mesenchymal stem cells of patients with fractures and osteoarthritis

ABSTRACT Insufficient activity of the bone-forming osteoblasts leads to low bone mass and predisposes to fragility fractures. The functional capacity of human mesenchymal stem cells (hMSCs), the precursors of osteoblasts, may be compromised in elderly individuals, in relation with the epigenetic changes associated with aging. However, the role of hMSCs in the pathogenesis of osteoporosis is still unclear. Therefore, we aimed to characterize the genome-wide methylation and gene expression signatures and the differentiation capacity of hMSCs from patients with hip fractures. We obtained hMSCs from the femoral heads of women undergoing hip replacement due to hip fractures and controls with hip osteoarthritis. DNA methylation was explored with the Infinium 450K bead array. Transcriptome analysis was done by RNA sequencing. The genomic analyses revealed that most differentially methylated loci were situated in genomic regions with enhancer activity, distant from gene bodies and promoters. These regions were associated with differentially expressed genes enriched in pathways related to hMSC growth and osteoblast differentiation. hMSCs from patients with fractures showed enhanced proliferation and upregulation of the osteogenic drivers RUNX2/OSX. Also, they showed some signs of accelerated methylation aging. When cultured in osteogenic medium, hMSCs from patients with fractures showed an impaired differentiation capacity, with reduced alkaline phosphatase activity and poor accumulation of a mineralized matrix. Our results point to 2 areas of potential interest for discovering new therapeutic targets for low bone mass disorders and bone regeneration: the mechanisms stimulating MSCs proliferation after fracture and those impairing their terminal differentiation.

Haplotypes of intron 4 of the estrogen receptor alpha gene and hip fractures: a replication study in Caucasians

BackgroundDespite their great impact, few genetic association studies have used hip fractures as an endpoint. However, the association of two polymorphisms on intron 4 of estrogen receptor alpha (ESR1) with hip fractures was recently reported in a Chinese population. The aim of this study was to investigate whether such association is also present in Caucasians.MethodsWe analyzed those two SNPs and another neighbour SNP located on the exon 4 of ESR1 in 787 patients with hip fractures and 953 controls from Spain.ResultsThe allelic frequencies differed markedly from those reported in Asian populations. Nevertheless, haplotypes including the rs3020314 and rs1884051 loci in intron 4 showed a significant association with hip fractures (omnibus test p = 0.006 in the whole group and 0.00005 in women). In the sex-stratified analysis, the association was significant in females, but not in males. In women, the CA haplotype appeared to have a protective influence, being present in 6.5% of the controls, but only in 3% of patients with fractures (odds ratio 0.39; 95% confidence interval 0.26-0.59; estimated population preventive fraction 3.5%). The inclusion of the rs1801132 SNP of exon 4 further increased the statistical significance of the association (odds ratio 0.17; 95% CI 0.08-0.37; p = 0.00001). Each SNP appeared to contribute independently to the association. No genotype-related differences in gene expression were found in 42 femoral bone samples.ConclusionsThis study confirms the association of some polymorphisms in the region of exon 4/intron 4 of ESR1 and hip fractures in women. However, there are marked differences in allele frequencies between Asian and Caucasian populations.

Análisis comparativo del epigenoma del tejido óseo y de osteoblastos primarios

), and in those located in genes involved in bone metabolism. However, some of the loci (7-8%) deviated from this general tendency and showed differences in methylation greater than 20%. Conclusions: These results indicate that the methylation data obtained in cultures are not necessarily a true reflection of that which occurs in tissues, which means that care should be taken when extrapolating such results to an in vivo situation.