The Inverse Relationship Between Osteoporosis and Osteoarthritis

Pattern of thoracic osteophytes development and the association between calcification of the aorta and thoracic osteophytes: CT study

INTRODUCTION

Our aim was use state-of-the-art computed tomography (CT) to assess the prevalence and size of osteophytes in the thoracic spine; the effect of the thoracic aorta on osteophyte development; and the relationship between thoracic aortic calcification and osteophytes.

METHODS

Thoracic CT scans of 100 individuals taken at the T4-T12 spinal levels were examined to determine the numbers and sizes of osteophytes on the right/left side of the vertebrae. Calcific deposits in the thoracic aorta (TAC) at each thoracic vertebral level were assessed. The mean length of the thoracic osteophytes on each side, the total thoracic osteophyte score (TTOS), and the numbers of osteophytes were calculated.

RESULTS

The sample comprised 44 males/56 females (mean age 66.45 ± 9.37). TAC was observed in 54 subjects. Osteophytes were significantly larger on the right side than the left at each spinal level. The largest osteophytes on both sides were at the T9, T10, and T11 levels. After adjustment for age, no significant association was found between sex and TTOS on the left (F = 0.277, p = .600) or right (F = 3.856, p = .052). The right TTOS was significantly associated with TAC after adjustment for age and sex (p = .018).

CONCLUSIONS

Osteophytes in the thoracic spine are prevalent in older adults, with number and size increasing with age in both sexes. Osteophytes are significantly less prominent on the left side than the right, probably because of the proximity of the aorta. TTOS and TAC occurred in the same individuals after adjustment for age and sex, suggesting a possible common etiology.

Epigenetic regulation of interleukin-8, an inflammatory chemokine, in osteoarthritis

OBJECTIVE

To determine whether altered IL8 methylation status is associated with increased expression of IL8 in human osteoarthritic (OA) chondrocytes.

METHODS

IL8 expression levels and the percentage CpG methylation in human chondrocytes were quantified by qRT-PCR and pyrosequencing in OA patients and in non-OA osteoporotic controls. The effect of CpG methylation on IL8 promoter activity was determined using a CpG-free vector; co-transfections with expression vectors encoding nuclear factor-kappa B (NF-κB), AP-1 and C/EBP were subsequently undertaken to analyse for IL8 promoter activity in response to changes in methylation status.

RESULTS

IL8 expression in OA patients was 37-fold higher than in osteoporotic controls. Three CpG sites in the IL8 promoter were significantly demethylated in OA patients. Multiple regression analysis revealed that the degree of methylation of the CpG site located at -116-bp was the strongest predictor of IL8 expression. In vitro DNA methylation was noted to decrease IL8 promoter basal activity. Furthermore, NF-κB, AP-1 and C/EBP strongly enhanced IL8 promoter activity whilst DNA methylation inhibited the effects of these three transcription factors.

CONCLUSIONS

The present study demonstrates the key role of DNA methylation status on the expression of IL8 in human chondrocytes. We demonstrate a quantitative relationship between percentage methylation and gene expression within clinical samples. These studies provide direct evidence linking the activation of IL8, DNA demethylation and the induction of the OA process with important therapeutic implications therein for patients with this debilitating disease.

Molecular changes in articular cartilage and subchondral bone in the rat anterior cruciate ligament transection and meniscectomized models of osteoarthritis

Background

Osteoarthritis (OA) is a debilitating, progressive joint disease.

Methods

Similar to the disease progression in humans, sequential events of early cartilage degradation, subchondral osteopenia followed by sclerosis, and late osteophyte formation were demonstrated in the anterior cruciate ligament transection (ACLT) or ACLT with partial medial meniscectomy (ACLT + MMx) rat OA models. We describe a reliable and consistent method to examine the time dependent changes in the gene expression profiles in articular cartilage and subchondral bone.

Results

Local regulation of matrix degradation markers was demonstrated by a significant increase in mRNA levels of aggrecanase-1 and MMP-13 as early as the first week post-surgery, and expression remained elevated throughout the 10 week study. Immunohistochemistry confirmed MMP-13 expression in differentiated chondrocytes and synovial fibroblasts at week-2 and cells within osteophytes at week-10 in the surgically-modified-joints. Concomitant increases in chondrocyte differentiation markers, Col IIA and Sox 9, and vascular invasion markers, VEGF and CD31, peaked around week-2 to -4, and returned to Sham levels at later time points in both models. Indeed, VEGF-positive cells were found in the deep articular chondrocytes adjacent to subchondral bone. Osteoclastic bone resorption markers, cathepsin K and TRAP, were also elevated at week-2. Confirming bone resorption is an early local event in OA progression, cathepsin K positive osteoclasts were found invading the articular cartilage from the subchondral region at week 2. This was followed by late disease events, including subchondral sclerosis and osteophyte formation, as demonstrated by the upregulation of the osteoanabolic markers runx2 and osterix, toward week-4 to 6 post-surgery.

Conclusions

In summary, this study demonstrated the temporal and cohesive gene expression changes in articular cartilage and subchondral bone using known markers of OA progression. The findings here support genome-wide profiling efforts to elucidate the sequential and complex regulation of the disease.

Expression of ADAMTS-4 by chondrocytes in the surface zone of human osteoarthritic cartilage is regulated by epigenetic DNA de-methylation

The two major aggrecanases involved in osteoarthritis (OA) are ADAMTS-4 and ADAMTS-5. Knock-out studies suggested that ADAMTS-5, but not ADAMTS-4, is the major aggrecanase in murine OA. However, studies of human articular cartilage suggest that ADAMTS-4 also contributes to aggrecan degradation in human OA. This study investigated ADAMTS-4 in human OA. While ADAMTS-4 was virtually absent in control cartilage, numerous ADAMTS-4 immuno-positive chondrocytes were present in OA cartilage and their numbers increased with disease severity. RT-PCR confirmed expression, especially in the surface zone. DNA methylation was lost at specific CpG sites in the ADAMTS-4 promoter in OA chondrocytes, suggesting that the increased gene expression was more than a simple up-regulation, but involved loss of DNA methylation at specific CpG sites, resulting in a heritable and permanent expression of ADAMTS-4 in OA chondrocytes. These results suggest that ADAMTS-4 is epigenetically regulated and plays a role in aggrecan degradation in human OA.

Are bone losers distinguishable from bone formers in a skeletal series? Implications for adult age at death assessment methods

Clinical studies indicate that genetic factors play a crucial role in primary osteoarthritis and osteoporosis. In addition, it has been suggested that these two diseases are inversely related. Within a population, one can find two sub-groups: the "bone formers" and the "bone losers". The changes to the joint surfaces used to assess adult age at death are related to the loss of bone substance and to bone formation (osteophytes). The modification of these indicators with age differs between bone formers and bone losers. Therefore, age-at-death assessment methods should make use of two standards, one for each sub-group. A preliminary study examining the possibility of distinguishing those who lose cortical bone from those who show signs of bony formation was conducted on a series of skeletons from Portugal, dating to the end of 19th century and the beginning of the 20th. Bone loss was evaluated using the cortical index (CI) of the second metacarpal on X-rays. The presence of osteophytes on dry bones was assessed macroscopically. Our study indicates that females' CI decreases with age, whereas the presence of osteophytes is strongly related to age in both sexes. But we have failed to find the inverse relationship between osteophytes and bone loss. Our study, however, shows that within a population, some individuals are not likely to develop osteophytes.

Association between the abnormal expression of matrix-degrading enzymes by human osteoarthritic chondrocytes and demethylation of specific CpG sites in the promoter regions

OBJECTIVE

To investigate whether the abnormal expression of matrix metalloproteinases (MMPs) 3, 9, and 13 and ADAMTS-4 by human osteoarthritic (OA) chondrocytes is associated with epigenetic "unsilencing."

METHODS

Cartilage was obtained from the femoral heads of 16 patients with OA and 10 control patients with femoral neck fracture. Chondrocytes with abnormal enzyme expression were immunolocalized. DNA was extracted, and the methylation status of the promoter regions of MMPs 3, 9, and 13 and ADAMTS-4 was analyzed with methylation-sensitive restriction enzymes, followed by polymerase chain reaction amplification.

RESULTS

Very few chondrocytes from control cartilage expressed the degrading enzymes, whereas all clonal chondrocytes from late-stage OA cartilage were immunopositive. The overall percentage of non-methylated sites was increased in OA patients (48.6%) compared with controls (20.1%): 20% versus 4% for MMP-13, 81% versus 47% for MMP-9, 57% versus 30% for MMP-3, and 48% versus 0% for ADAMTS-4. Not all CpG sites were equally susceptible to loss of methylation. Some sites were uniformly methylated, whereas in others, methylation was generally absent. For each enzyme, there was 1 specific CpG site where the demethylation in OA patients was significantly higher than that in controls: at -110 for MMP-13, -36 for MMP-9, -635 for MMP-3, and -753 for ADAMTS-4.

CONCLUSION

This study provides the first evidence that altered synthesis of cartilage-degrading enzymes by late-stage OA chondrocytes may have resulted from epigenetic changes in the methylation status of CpG sites in the promoter regions of these enzymes. These changes, which are clonally transmitted to daughter cells, may contribute to the development of OA.

Menopausal status, hormone replacement therapy use and risk of self-reported physician-diagnosed osteoarthritis in women attending menopause clinics in Italy

OBJECTIVE

In order to offer data on the association between menopausal status, hormone replacement therapy use and risk of self-reported physician-diagnosed osteoarthritis (OA) in women around menopause, we analyzed information collected in the framework of a large epidemiological study conducted in Italy.

METHODS

Since 1997, a large cross sectional study has been conducting on the characteristics of women around menopause attending a network of first level outpatients menopause clinics in Italy for general counseling about menopause or treatment of menopausal symptoms. Eligible for the study were women consecutively observed at the participating centers. Up to March 2000, a total of 42464 women (mean age 53 years) were observed. Women were asked, using the same questionnaire, about their general characteristics and habits, and if they suffer of OA diagnosed by a physician requiring medical or surgical treatment.

RESULTS

A total of 12521 women reported OA. The risk of OA increased with body mass index (BMI), the odds ratio, OR, being for BMI>or equal to 27 versus <24, 1.56 (95%CI 1.47-1.64). The risk increased with a history of osteoporosis/osteopenia (OR 1.65, 95%CI 1.57-1.74) and was lower in more educated women (OR high school/university degree vs. primary school degree 0.79, 95%CI 0.75-0.84). Considering menopausal status, women in spontaneous or surgical menopause were, at increased risk of OA (OR 1.13, 95%CI 1.07-1.21, and 1.18, 95%CI 1.08-1.28, respectively, in women in surgical and spontaneous menopause). No clear relationship, however, emerged with age at menopause. Ever hormonal replacement therapy users were at decreased risk of OA, the OR being for ever users in comparison with never 0.73 (95%CI 0.69-0.78).

CONCLUSION

This analysis gives some epidemiological support to the hypothesis that estrogen deficiency may increased the risk of OA.

Association of two gene polymorphisms with osteoarthritis secondary to hip dysplasia

Two adjacent genes on the 12q chromosome, the alpha 1 chain of Type II collagen, and the vitamin D receptor, have been considered potentially related to the pathophysiology of osteoarthritis. Two restriction fragment length polymorphisms were detected in 50 healthy donors and in 143 patients having a total hip replacement for idiopathic osteoarthritis or osteoarthritis secondary to developmental hip dysplasia. The polymorphic sites of Type II collagen and vitamin D receptor were amplified by polymerase chain reaction, and the products were digested with PvuII and BsmI restriction enzymes, respectively. The results showed that medical history and clinical characteristics, including gender, familial history of osteoarthritis, other hip prosthesis, and how early in life implantation was done did not seem to be connected to a particular genotype. Significant results were found by assessing the two groups of diseases that led to hip arthroplasty, suggesting a possible link between some haplotypes and the risk of severe osteoarthritis in patients with hip dysplasia. These results indicate that genetic markers could contribute to the understanding of the natural history of this disease.

Interrelationship between bone aging traits and basic anthropometric characteristics

Using plain hand radiographs, the age dependence of various bone-aging traits (bone mineral density [BMD], cortical index [CI], osteoarthritis [OA], and osseographic [OSS] scores) was evaluated to test whether the correlation among these traits is an individual- or population-based phenomenon. In addition, the effect of anthropometric features on variation of bone-aging traits was estimated. The study included 1,295 individuals from Chuvasha, Russia, 18 to 89 years. BMD was measured from the compact compartment of the middle and distal phalanges of both 3(rd) fingers. The CI of the II-IV metacarpal bones and II-IV proximal phalanges was obtained. The development of OA was based on the standard Kellgren and Lawrence grading scheme for 28 hand joints. OSS score, a surrogate measure that takes into account different kinds of bone changes, was also obtained for each individual. Body weight and height, eight skinfold thicknesses on the trunk and extremities, and breadths of the long bones were measured. Sex-based univariate analyses and multivariate statistical analysis showed the following: 1) Age dependence was defined more strongly in "OA-linked" compared to "osteoporosis (OP)-linked" traits; 2) While "OP-linked" bone-aging traits correlated with age differently between sexes, "OA-linked" traits did not; 3) The strong interrelationship between OA-linked and OP-linked traits in both sexes became very weak and statistically insignificant (P > 0.10) after adjustment for age. Thus, OA and OP conditions in the same individual develop independently and probably reflect different underlying physiological mechanisms. 4) Anthropometric characteristics were significantly correlated with bone-aging traits, but correlations were low (r < 0.20). Thus, the contribution of anthropometric characteristics to the rate and pattern of bone aging of the hand was to relatively small.

More knee joint osteoarthritis (OA) in mice after inactivation of one allele of type II procollagen gene but less OA after lifelong voluntary wheel running exercise

OBJECTIVE

To investigate the incidence and severity of osteoarthritis (OA) and the effects of voluntary wheel running in normal mice and mice carrying either a targeted inactivation of one allele, heterozygous 'knockout', of Col2a1 gene or both alleles, homozygous 'knockout', of Col11a2 gene.

METHODS

Mice lived until 15 months of age in individual cages. Running activity was recorded around the clock. OA changes were evaluated from serial knee joint sections by light microscopy.

RESULTS

Heterozygous inactivation of Col2a1 gene coding for type II procollagen made the cartilage more susceptible to OA. At 15 months of age, OA prevalence was 60-90% in knockouts and 20-45% in normal controls (P < 0.01-0.001). Unexpectedly, a reduction of OA due to wheel running was observed in both knockout strains (P< 0.05-0.01). This effect was most evident in the femoral condyles. Incidence of OA in runners was approximately 50-85% of that in sedentary littermates. OA prevalence was higher in normal control and runner mice with high body weight. Running did not affect OA development in normal mice.

CONCLUSION

Heterozygous knockout of Col2a1 gene increased the OA prevalence in mice. Lifelong voluntary wheel running had a protective effect against OA in both knockout mice lines. The reason for this remains unknown. Reduction of OA may result from the reorganization and strengthening of the articular cartilage collagen network and/or adjacent muscles due to running, or lower body weight. Increased compliance of the articular cartilage and bones of the knockout mice may also contribute to the reduction of OA in exercised animals.