Background

Intervertebral disc degeneration (DD) is a complex age-related condition that constitutes the main risk factor for disabling back pain. DD is assessed using different traits extracted from MR imaging (MRI), normally combined to give summary measures (e.g. Pfirmann score). The aetiology of DD is poorly understood and despite its high heritability (75%), the precise genetic predisposition is yet to be defined. Genome wide association study (GWAS) is used to discover genetic variants associated with a disease or phenotype. It tests variants across the whole genome. It requires large samples to provide adequate but unfortunately there is poor availability of spine imaging data due to the high cost of MRI. We have adopted new methods to examine different MRI traits independently and use the information of those traits to boost GWAS power using specialized statistical software for jointly analyse correlated traits.

For many decades, we have viewed osteoarthritis (OA) as a homogeneous disease characterised by “wear and tear”. However, this view has been challenged recently and it is now clear that OA is a heterogeneous and low-grade inflammatory disease with multiple aetiologies and phenotypes. Each of these different phenotypes may be identified and targeted differently, opening up multiple pathways for therapeutic intervention. Combining imaging and carefully selected panels of biochemical markers can achieve enhanced patient stratification and lead to better-designed clinical trials. Analyses of observational studies and clinical trial datasets are underway to understand better the phenotypes responsible for why people develop OA and why, prognostically, they have differences in terms of disease progression. The aim of this presentation is to discuss the underlying mechanisms involved in common OA phenotypes, with a particular focus on low-grade inflammation and metabolic alterations. Aberrant cellular metabolism has been implicated in the pathogenesis of OA and this talk will summarise the current state of knowledge on the role of impaired metabolism in the cells of the osteoarthritic joint and highlight areas for future research, such as the potential to target metabolic pathways and mediators therapeutically.

Introduction

Pain related to knee osteoarthritis (OA) is a complex phenomenon that cannot be fully explained by radiographic disease severity. We hypothesized that pain phenotypes are likely to be derived from a confluence of factors across multiple domains: knee OA pathology, psychology, and neurophysiological pain processing. The purpose of this study was to identify distinct phenotypes of knee OA, using measures from the proposed domains.

Although osteoarthritis (OA) is characterized by articular cartilage damage, synovial inflammation is a prominent feature contributing to disease progression. In addition to synovial tissue resident macrophages, infiltrating macrophages and monocytes, their lineage precursors, may also contribute to pathological processes. In mice, peripheral blood monocytes may be categorized according to pro-inflammatory/classical and patrolling/non-classical subsets. The aim of this study was to identify profiles of peripheral blood monocyte subsets as well as different synovial macrophage phenotypes during disease development. OA was induced in knees of C57BL/6 mice by destabilization of the medial meniscus (DMM). Blood was harvested from the facial vein 7 days prior to and 1, 7, 14, 28, and 56 days post induction of OA. Separate mice were sham-operated as a control. Monocyte subsets and synovial macrophage populations were identified by flow cytometry. Levels of classical monocytes were significantly higher at day 14 (p<0.001) and day 28 (p=0.031) in peripheral blood of DMM-operated mice compared to control. Furthermore, the percentage of non-classical monocytes was significantly lower in DMM-mice at day 14 (p=0.026). At day 56 post OA-induction, an increase in total synovial macrophages (CD11b+F4/80+ cells) was observed between DMM and sham operated knees (p=0.021). The ratio between pro-inflammatory (CD11b+F4/80+CD86+) and tissue repair (CD11b+F4/80+CD206+) synovial macrophage subsets tended to be higher in DMM knees, however this finding was not statistically significant (p>0.05). In light of the present findings, further investigation is required to elucidate the relationship of peripheral blood monocyte subsets to synovial inflammation and features of OA pathogenesis.

Hyaline cartilage and immature nucleus pulposus possess similar macromolecules in their extracellular matrix, and there is no unique molecular marker to distinguish the two tissues. We show that in normal disc (fifteen to twenty-five years old), the GAG to hydroxyproline ratio (proteoglycan to collagen ratio) within the nucleus pulposus is approximately 28:1. However, the GAG to hydroxyproline ratio within hyaline cartilage of the same group is 2.5:1. This information is important in identifying stem cell conversion to a nucleus pulposus cell phenotype rather than a chondrocyte phenotype for tissue engineering of intervertebral disc.

Tissue engineering of intervertebral discs (IVDs) using mesenchymal stem cells (MSCs) induced to differentiate into a disc-cell phenotype has been considered as an alternative treatment for disc degeneration. Since there is no unique marker for disc tissue, and because cartilage and immature nucleus pulposus (NP) possess similar macromolecules in their extracellular matrix, it is currently difficult to recognize MSC conversion to a disc cell. In this study, we compare the proteoglycan to collagen ratio in the NP of normal disc to that of the hyaline cartilage of the endplate within the same group of individuals.

To distinguish between a normal NP and hyaline cartilage phenotype for tissue engineering of IVDs.

Human lumbar spine specimens were harvested from fresh cadavers, aged twelve week to seventy-nine year. Discs and endplates were examined for total collagen using the hydroxyproline assay and glycosaminoglycan (GAG) content using a standard assay.

In a mature disc with no degeneration (fifteen to twentyfive years), the GAG to hydroxyproline ratio within the NP is approximately 28:1. However, the ratio within the hyaline cartilage endplate of the same group is 2.5:1.

A high proteoglycan to collagen ratio can be used to distinguish NP cells from chondrocytes. The lower NP collagen content is probably responsible for its gelatinous nature rather than the firm texture of hyaline cartilage, and this is essential for normal disc function. This information is crucial in identifying a NP-like phenotype when MSCs are induced to differentiate into a disc cell as opposed to a chondrocyte, for tissue engineering of IVDs.

Introduction

Iliac crest bone marrow aspirate (ICBMA) is frequently cited as the ‘gold-standard’ source of MSCs. MSCs have been shown to reside within the intramedullary (IM) cavities of long-bones [Nelea, 2005] however a comparative assessment with ICBMA has not yet been performed and the phenotype of the latter compartment MSCs remains undefined in their native environment.

Aims

Patient-reported outcome measures have become an important part of routine care. The aim of this study was to determine if Patient-Reported Outcomes Measurement Information System (PROMIS) measures can be used to create patient subgroups for individuals seeking orthopaedic care.

Introduction. Aseptic loosening, the clinical endpoint of osteolysis, remains the leading cause of total hip arthroplasty (THA) failure, and is caused by a host response to wear debris that varies between individuals. Although several candidate gene studies have identified loci associated with osteolysis susceptibility, there have been no systematic studies at genome-wide level. We aimed to identify risk loci associated with osteolysis by conducting a genome-wide association study. Methods. 3,706 Caucasian European patients following THA were studied. The discovery cohort comprising 894 patients (317 with osteolysis) were genotyped using the Illumina-610 beadchip followed by 1000 Genome-based imputation covering 10 million single nucleotide polymorphisms (SNPs). Phenotypes were transformed to normality where required, regressed on important covariates and z-standardised. Following quality control, osteolysis case-control analysis and a quantitative trait association analysis for time to prosthesis failure were undertaken. Index SNPs p<9×10. −4. were taken forward for replication in a second cohort comprising 2,812 subjects (834 osteolysis cases) recruited from the Norwegian arthroplasty registry. Genotyping was undertaken using Sequenom MassARRAY iPLEX Gold assay and association analyses undertaken using logistic and linear regression. Summary statistics were combined in a fixed-effects meta-analysis framework. Results. The strongest signal associated with time to prosthesis failure lay within DEFB129 gene. The signal index SNP, rs6105394, approached genome wide significance at p=5.75×10. −7. Two signals in the susceptibility analysis also approached genome-wide significance, 1 within CAMK4 (rs306105, OR 0.41, p=6.54×10. −7. ) and 1 upstream of PLNXA2 (rs11119057, OR 0.96, p=6.44×10. −7. ). Following meta-analysis, the strongest signal in the susceptibility analysis remained that within CAMK4 (rs306105, p=3.79×10. −4. ). The strongest signal associated with time to failure was just upstream of CNTN3 (rs1374879, p=2.15×10. −5. ). Discussion. We have identified promising loci associated with osteolysis and time to prosthesis failure although not at genome-wide significance (p<5×10. −8. ). In order to further validate these loci, larger genome wide association analysis is required

Aims

Mendelian randomization (MR) is considered to overcome the bias of observational studies, but there is no current meta-analysis of MR studies on rheumatoid arthritis (RA). The purpose of this study was to summarize the relationship between potential pathogenic factors and RA risk based on existing MR studies.