Restricted diet delays accelerated ageing and genomic stress in DNA-repair-deficient mice.

Mice deficient in the DNA excision-repair gene Ercc1 (Ercc1∆/-) show numerous accelerated ageing features that limit their lifespan to 4-6 months. They also exhibit a 'survival response', which suppresses growth and enhances cellular maintenance. Such a response resembles the anti-ageing response induced by dietary restriction (also known as caloric restriction). Here we report that a dietary restriction of 30% tripled the median and maximal remaining lifespans of these progeroid mice, strongly retarding numerous aspects of accelerated ageing. Mice undergoing dietary restriction retained 50% more neurons and maintained full motor function far beyond the lifespan of mice fed ad libitum. Other DNA-repair-deficient, progeroid Xpg-/- (also known as Ercc5-/-) mice, a model of Cockayne syndrome, responded similarly. The dietary restriction response in Ercc1∆/- mice closely resembled the effects of dietary restriction in wild-type animals. Notably, liver tissue from Ercc1∆/- mice fed ad libitum showed preferential extinction of the expression of long genes, a phenomenon we also observed in several tissues ageing normally. This is consistent with the accumulation of stochastic, transcription-blocking lesions that affect long genes more than short ones. Dietary restriction largely prevented this declining transcriptional output and reduced the number of γH2AX DNA damage foci, indicating that dietary restriction preserves genome function by alleviating DNA damage. Our findings establish the Ercc1∆/- mouse as a powerful model organism for health-sustaining interventions, reveal potential for reducing endogenous DNA damage, facilitate a better understanding of the molecular mechanism of dietary restriction and suggest a role for counterintuitive dietary-restriction-like therapy for human progeroid genome instability syndromes and possibly neurodegeneration in general.

Statins and fibrates do not affect development of spontaneous cartilage damage in STR/Ort mice.

OBJECTIVE: Since statins and fibrates are capable of improving the metabolic profile of patients as well as decreasing inflammation, they are considered as potential drugs for preventing osteoarthritis (OA). The goal of the present study was to investigate the effect of these drugs in the STR/Ort spontaneous OA mouse model. DESIGN: Male STR/Ort mice received control diet or control diet containing two different dosages of simvastatin or fenofibrate or a combination of both. Mice were euthanized after 16 weeks of treatment at the age of 24 weeks. Serum analysis for metabolic and inflammatory markers, histologic OA grading and micro computed tomography (µCT) analysis of subchondral bone plate were performed. RESULTS: Simvastatin treatment did not have a statistically significant effect on any of the measured parameters. Fenofibrate treated mice gained less body weight (BW) and had lower serum amyloid A (SAA) levels, but higher Interleukin (IL)-1α and MIP1α than other mice. Mice treated with 200 mg/kg BW/day fenofibrate had less subchondral bone plate volume than control, but no statistically significant reduction in cartilage damage. In the combination treatment group, BW and SAA were lower than control. Overall, bodyweight, synovium membrane cell layers and SAA levels correlated to subchondral bone plate changes and subchondral bone plate changes correlated to cartilage damage. CONCLUSIONS: Statins and fibrates did not affect development of cartilage damage in the STR/Ort spontaneous OA mouse model. Fenofibrates however, had an effect on BW, serum inflammation markers and subchondral bone plate morphology.

Age-related skeletal dynamics and decrease in bone strength in DNA repair deficient male trichothiodystrophy mice.

Accumulation of DNA damage caused by oxidative stress is thought to be one of the main contributors of human tissue aging. Trichothiodystrophy (TTD) mice have a mutation in the Ercc2 DNA repair gene, resulting in accumulation of DNA damage and several features of segmental accelerated aging. We used male TTD mice to study the impact of DNA repair on bone metabolism with age. Analysis of bone parameters, measured by micro-computed tomography, displayed an earlier decrease in trabecular and cortical bone as well as a loss of periosteal apposition and a reduction in bone strength in TTD mice with age compared to wild type mice. Ex vivo analysis of bone marrow differentiation potential showed an accelerated reduction in the number of osteogenic and osteoprogenitor cells with unaltered differentiation capacity. Adipocyte differentiation was normal. Early in life, osteoclast number tended to be increased while at 78 weeks it was significantly lower in TTD mice. Our findings reveal the importance of genome stability and proper DNA repair for skeletal homeostasis with age and support the idea that accumulation of damage interferes with normal skeletal maintenance, causing reduction in the number of osteoblast precursors that are required for normal bone remodeling leading to a loss of bone structure and strength.

Pathophysiology of peri-articular bone changes in osteoarthritis.

Osteoarthritis (OA) is a disease that involves the entire joint, but its pathophysiology is not well described. Alterations in peri-articular bone are an integral part of the OA disease process and different aspects of bone changes have been described in different patient (sub)groups and animal models. In this review we will discuss the osteoarthritis pathophysiology from the perspective of periarticular bone changes, which can be considered at three hierarchical levels: the bone (or joint) shape, the subchondral bone architecture and its cellular and molecular phenotype. In this review we try to provide an overview of the current knowledge of peri-articular bone changes in OA and what it could possibly imply for the initiation of OA and its progression. This article is part of a Special Issue entitled "Osteoarthritis".

ADAMTS5-/- mice have less subchondral bone changes after induction of osteoarthritis through surgical instability: implications for a link between cartilage and subchondral bone changes.

OBJECTIVE: Osteoarthritis (OA) is characterized by damaged articular cartilage and changes in subchondral bone. Previous work demonstrated aggrecanase-2 deficient (ADAMTS5-/-) mice to be protected from cartilage damage induced by joint instability. This study analyzed whether this protective effect on cartilage is also reflected in the subchondral bone structure. METHODS: Right knee joints from 10-week old male wild type (WT) and ADAMTS5-/- mice received transection of the medial meniscotibial ligament to induce OA, whereas left knees were left unoperated. After 8 weeks knee joints were scanned by micro-CT. The proximal tibia was selected for further analysis. Histology was performed to evaluate cartilage damage and osteoclast presence. RESULTS: ADAMTS5-/- joints had a significantly thinner subchondral plate and less epiphyseal trabecular bone compared to WT joints. Histology confirmed previous findings that ADAMTS5-/- mice have significantly less cartilage damage than WT in the instability-induced OA model. Although the subchondral bone plate became significantly thicker at the medial tibial plateau in operated joints of both genotypes, the percentage increase was significantly smaller in ADAMTS5-/- mice (WT: 20.7+/-4.7%, ADAMTS5-/-: 8.3+/-1.2% compared to the left unoperated control joint). In ADAMTS5-/- animals a significant decrease was found in both Oc.N./BS and Oc.S./BS. Finally, in WT but not in ADAMTS5-/- mice a significant correlation was found between medial subchondral bone plate thickness and cartilage damage at the medial tibial plateau. CONCLUSION: ADAMTS5-/- joints that were protected from cartilage damage showed minor changes in the subchondral bone structure, in contrast to WT mice where substantial changes were found. This finding suggests links between the process of cartilage damage and subchondral bone changes in instability-induced OA.

Cartilage damage pattern in relation to subchondral plate thickness in a collagenase-induced model of osteoarthritis.

OBJECTIVE: To see how initial differences in subchondral bone phenotype influence the development of cartilage damage and changes in subchondral bone architecture in an osteoarthritis (OA)-induced mouse model. METHOD: Intra-articular collagenase injections (right knee joint) and saline controls (left knee joint) were applied in the knees of two mouse strains known to have either a low or a high bone mass phenotype: the low bone mass C57Bl/6 mice with a thin subchondral bone plate and high bone mass C3H/HeJ mice with a thick subchondral bone plate. The ages of the mice were 16 and 30 weeks, with n=8 per group. The collagenase injection induced an osteoarthritic phenotype that was evaluated 4 weeks later in the tibia using histological analyses and micro-computed tomography (micro-CT). RESULTS: Both strains developed cartilage damage in the collagenase-injected right knee joints to a comparable extent, however, the spatial distribution of cartilage damage differed significantly: C57Bl/6 mice had most damage at the postero-lateral side, whereas in C3H/HeJ mice the postero-medial region was the most affected. Spontaneous cartilage damage was found in the saline-injected left control knees of C57Bl/6 mice, but in C3H/HeJ mice spontaneous cartilage damage was virtually absent. In both strains the subchondral bone plate of collagenase-injected joints became thinner, independent of the site of cartilage damage. TRAP-positive osteoclasts were observed underneath the subchondral bone plate, in line with the observed decreased thickness. No link was found between subchondral bone plate thickness and cartilage damage in the collagenase-injected joints. The subchondral trabecular architecture only changed in the high bone mass C3H/HeJ mice, with thinning of trabeculae and increased trabecular spacing. CONCLUSION: Thinning of the subchondral bone plate was found as a common observation 4 weeks after OA had been induced in two strains of mice having either a high or low bone phenotype, but no relation was found with the amount of cartilage damage. In addition, this study shows that different strains of mice can react differently to instability-induced OA with respect to the spatial arrangement of cartilage damage and changes in subchondral trabecular structure.

Quantification of subchondral bone changes in a murine osteoarthritis model using micro-CT.

In the past few years there has been a considerable interest in the role of bone in osteoarthritis. Despite the increasing evidence of the involvement of bone in osteoarthritis, it remains very difficult to attribute the cause or effect of changes in subchondral bone to the process of osteoarthritis. Although osteoarthritis in mice provides a useful model to study changes in the subchondral bone, detailed quantification of these changes is lacking. Therefore, the goal of this study was to quantify subchondral bone changes in a murine osteoarthritis model by use of micro-computed tomography (micro-CT). We induced osteoarthritis-like characteristics in the knee joints of mice using collagenase injections, and after four weeks we calculated various 3D morphometric parameters in the epiphysis of the proximal tibia. The collagenase injections caused cartilage damage, visible in histological sections, particularly on the medial tibial plateau. Micro-CT analysis revealed that the thickness of the subchondral bone plate was decreased both at the lateral and the medial side. The trabecular compartment demonstrated a small but significant reduction in bone volume fraction compared to the contralateral control joints. Trabeculae in the collagenase-injected joints were thinner but their shape remained rod-like. Furthermore, the connectivity between trabeculae was reduced and the trabecular spacing was increased. In conclusion, four weeks after induction of osteoarthritis in the murine knee subtle but significant changes in subchondral bone architecture could be detected and quantified in 3D with micro-CT analysis.