Circadian time series proteomics reveals daily dynamics in cartilage physiology

OBJECTIVE

Cartilage in joints such as the hip and knee experiences repeated phases of heavy loading and low load recovery during the 24-h day/night cycle. Our previous work has shown 24 h rhythmic changes in gene expression at transcript level between night and day in wild type mouse cartilage which is lost in a circadian clock knock-out mouse model. However, it remains unknown to what extent circadian rhythms also regulate protein level gene expression in this matrix rich tissue.

METHODS

We investigated daily changes of protein abundance in mouse femoral head articular cartilage by performing a 48-h time-series LC-MS/MS analysis.

RESULTS

Out of the 1,177 proteins we identified across all time points, 145 proteins showed rhythmic changes in their abundance within the femoral head cartilage. Among these were molecules that have been implicated in key cartilage functions, including CTGF, MATN1, PAI-1 and PLOD1 & 2. Pathway analysis revealed that protein synthesis, cytoskeleton and glucose metabolism exhibited time-of-day dependent functions. Analysis of published cartilage proteomics datasets revealed that a significant portion of rhythmic proteins were dysregulated in osteoarthritis and/or ageing.

CONCLUSIONS

Our circadian proteomics study reveals that articular cartilage is a much more dynamic tissue than previously thought, with chondrocytes driving circadian rhythms not only in gene transcription but also in protein abundance. Our results clearly call for the consideration of circadian timing mechanisms not only in cartilage biology, but also in the pathogenesis, treatment strategies and biomarker detection in osteoarthritis.

Non-viral reprogramming of human nucleus pulposus cells with FOXF1 via extracellular vesicle delivery: an in vitro and in vivo study

Intervertebral disc (IVD) degeneration is characterized by decreased cellularity and proteoglycan synthesis and increased inflammation, catabolism, and neural/vascular ingrowth. Regenerative methods for IVD degeneration are largely cell-therapy-based or involve viral vectors, which are associated with mutagenesis and undesired immune responses. The present study used bulk electroporation and engineered extracellular vesicles (EVs) to deliver forkhead-box F1 (FOXF1) mRNA to degenerate human nucleus pulposus (NP) cells as a minimally invasive therapeutic strategy for IVD regeneration. Bulk electroporation was used to investigate FOXF1 effects on human NP cells during a 4-week culture in 3D agarose constructs. Engineered EV delivery of FOXF1 into human IVD cells in monolayer was determined, with subsequent in vivo validation in a pilot mouse IVD puncture model. FOXF1 transfection significantly altered gene expression by upregulating healthy NP markers [FOXF1, keratin 19 (KRT19)], decreasing inflammatory cytokines [interleukin (IL)-1β, -6], catabolic enzymes [metalloproteinase 13 (MMP13)] and nerve growth factor (NGF), with significant increases in glycosaminoglycan accumulation in human NP cells. Engineered EVs loaded with FOXF1 demonstrated successful encapsulation of FOXF1 cargo and effective uptake by human NP cells cultured in monolayer. Injection of FOXF1-loaded EVs into the mouse IVD in vivo resulted in a significant upregulation of FOXF1 and Brachyury, compared to controls at 7 d post-injection, with no evidence of cytotoxicity. This is the first study to demonstrate non-viral delivery of FOXF1 and reprogramming of human NP cells in vitro and mouse IVD cells in vivo. This strategy represents a non-addictive approach for treating IVD degeneration and associated back pain.

A review of techniques for visualising soft tissue microstructure deformation and quantifying strain Ex Vivo

Many biological tissues have a complex hierarchical structure allowing them to function under demanding physiological loading conditions. Structural changes caused by ageing or disease can lead to loss of mechanical function. Therefore, it is necessary to characterise tissue structure to understand normal tissue function and the progression of disease. Ideally intact native tissues should be imaged in 3D and under physiological loading conditions. The current published in situ imaging methodologies demonstrate a compromise between imaging limitations and maintaining the samples native mechanical function. This review gives an overview of in situ imaging techniques used to visualise microstructural deformation of soft tissue, including three case studies of different tissues (tendon, intervertebral disc and artery). Some of the imaging techniques restricted analysis to observational mechanics or discrete strain measurement from invasive markers. Full-field local surface strain measurement has been achieved using digital image correlation. Volumetric strain fields have successfully been quantified from in situ X-ray microtomography (micro-CT) studies of bone using digital volume correlation but not in soft tissue due to low X-ray transmission contrast. With the latest developments in micro-CT showing in-line phase contrast capability to resolve native soft tissue microstructure, there is potential for future soft tissue mechanics research where 3D local strain can be quantified. These methods will provide information on the local 3D micromechanical environment experienced by cells in healthy, aged and diseased tissues. It is hoped that future applications of in situ imaging techniques will impact positively on the design and testing of potential tissue replacements or regenerative therapies. LAY DESCRIPTION: The soft tissues in our bodies, such as tendons, intervertebral discs and arteries, have evolved to have complicated structures which deform and bear load during normal function. Small changes in these structures can occur with age and disease which then leads to loss of function. Therefore, it is important to image tissue microstructure in 3D and under functional conditions. This paper gives an overview of imaging techniques used to record the deformation of soft tissue microstructures. Commonly there are compromises between obtaining the best imaging result and retaining the samples native structure and function. For example, invasive markers and dissecting samples damages the tissues natural structure, and staining or clearing (making the tissue more transparent) can distort tissue structure. Structural deformation has been quantified from 2D imaging techniques (digital image correlation) to create surface strain maps which help identify local tissue mechanics. When extended to 3D (digital volume correlation), deformation measurement has been limited to bone samples using X-ray micro-CT. Recently it has been possible to image the 3D structure of soft tissue using X-ray micro-CT meaning that there is potential for internal soft tissue mechanics to be mapped in 3D. Future application of micro-CT and digital volume correlation will be important for soft tissue mechanics studies particularly to understand normal function, progression of disease and in the design of tissue replacements.

Extracellular matrix fragmentation in young, healthy cartilaginous tissues

Although the composition and structure of cartilaginous tissues is complex, collagen II fibrils and aggrecan are the most abundant assemblies in both articular cartilage (AC) and the nucleus pulposus (NP) of the intervertebral disc (IVD). Whilst structural heterogeneity of intact aggrecan ( containing three globular domains) is well characterised, the extent of aggrecan fragmentation in healthy tissues is poorly defined. Using young, yet skeletally mature (18-30 months), bovine AC and NP tissues, it was shown that, whilst the ultrastructure of intact aggrecan was tissue-dependent, most molecules (AC: 95 %; NP: 99.5 %) were fragmented (lacking one or more globular domains). Fragments were significantly smaller and more structurally heterogeneous in the NP compared with the AC (molecular area; AC: 8543 nm2; NP: 4625 nm2; p < 0.0001). In contrast, fibrillar collagen appeared structurally intact and tissue-invariant. Molecular fragmentation is considered indicative of a pathology; however, these young, skeletally mature tissues were histologically and mechanically (reduced modulus: AC: ≈ 500 kPa; NP: ≈ 80 kPa) comparable to healthy tissues and devoid of notable gelatinase activity (compared with rat dermis). As aggrecan fragmentation was prevalent in neonatal bovine AC (99.5 % fragmented, molecular area: 5137 nm2) as compared with mature AC (95.0 % fragmented, molecular area: 8667 nm2), it was hypothesised that targeted proteolysis might be an adaptive process that modified aggrecan packing (as simulated computationally) and, hence, tissue charge density, mechanical properties and porosity. These observations provided a baseline against which pathological and/or age-related fragmentation of aggrecan could be assessed and suggested that new strategies might be required to engineer constructs that mimic the mechanical properties of native cartilaginous tissues.

Visualising the 3D microstructure of stained and native intervertebral discs using X-ray microtomography

Intervertebral disc degeneration (IVDD) is linked to low back pain. Microstructural changes during degeneration have previously been imaged using 2D sectioning techniques and 3D methods which are limited to small specimens and prone to inducing artefacts from sample preparation. This study explores micro computed X-ray tomography (microCT) methods with the aim of resolving IVD 3D microstructure whilst minimising sample preparation artefacts. Low X-ray absorption contrast in non-mineralised tissue can be enhanced using staining and phase contrast techniques. A step-wise approach, including comparing three stains, was used to develop microCT for bovine tail IVD using laboratory and synchrotron sources. Staining successfully contrasted collagenous structures; however not all regions were stained and the procedure induced macroscopic structural changes. Phase contrast microCT of chemically fixed yet unstained samples resolved the nucleus pulposus, annulus fibrosus and constituent lamellae, and finer structures including collagen bundles and cross-bridges. Using the same imaging methods native tissue scans were of slightly lower contrast but free from sample processing artefacts. In the future these methods may be used to characterise structural remodelling in soft (non-calcified) tissues and to conduct in situ studies of native loaded tissues and constructs to characterise their 3D mechanical properties.

Qualitative grading of disc degeneration by magnetic resonance in the lumbar and cervical spine: lack of correlation with histology in surgical cases

BACKGROUND

Clinically, magnetic resonance (MR) imaging is the most effective non-invasive tool for assessing IVD degeneration. Histological examination of the IVD provides a more detailed assessment of the pathological changes at a tissue level. However, very few reports have studied the relationship between these techniques. Identifying a relationship may allow more detailed staging of IVD degeneration, of importance in targeting future regenerative therapies.

OBJECTIVES

To investigate the relationship between MR and histological grading of IVD degeneration in the cervical and lumbar spine in patients undergoing discectomy.

METHODS

Lumbar (N = 99) and cervical (N = 106) IVD samples were obtained from adult patients undergoing discectomy surgery for symptomatic IVD herniation and graded to ascertain a histological grade of degeneration. The pre-operative MR images from these patients were graded for the degree of IVD (MR grade) and vertebral end-plate degeneration (Modic Changes, MC). The relationship between histological and MR grades of degeneration were studied.

RESULTS

In lumbar and cervical IVD the majority of samples (93%) exhibited moderate levels of degeneration (ie MR grades 3-4) on pre-operative MR scans. Histologically, most specimens displayed moderate to severe grades of degeneration in lumbar (99%) and cervical spine (93%). MR grade was weakly correlated with patient age in lumbar and cervical study groups. MR and histological grades of IVD degeneration did not correlate in lumbar or cervical study groups. MC were more common in the lumbar than cervical spine (e.g. 39 versus 20% grade 2 changes; p < 0.05), but failed to correlate with MR or histological grades for degeneration.

CONCLUSIONS

In this surgical series, the resected IVD tissue displayed moderate to severe degeneration, but there is no correlation between MR and histological grades using a qualitative classification system. There remains a need for a quantitative, non-invasive, pre-clinical measure of IVD degeneration that correlates with histological changes seen in the IVD.

The use of a novel bone allograft wash process to generate a biocompatible, mechanically stable and osteoinductive biological scaffold for use in bone tissue engineering

Fresh-frozen biological allograft remains the most effective substitute for the 'gold standard' autograft, sharing many of its osteogenic properties but, conversely, lacking viable osteogenic cells. Tissue engineering offers the opportunity to improve the osseointegration of this material through the addition of mesenchymal stem cells (MSCs). However, the presence of dead, immunogenic and potentially harmful bone marrow could hinder cell adhesion and differentiation, graft augmentation and incorporation, and wash procedures are therefore being utilized to remove the marrow, thereby improving the material's safety. To this end, we assessed the efficiency of a novel wash technique to produce a biocompatible, biological scaffold void of cellular material that was mechanically stable and had osteoinductive potential. The outcomes of our investigations demonstrated the efficient removal of marrow components (~99.6%), resulting in a biocompatible material with conserved biomechanical stability. Additionally, the scaffold was able to induce osteogenic differentiation of MSCs, with increases in osteogenic gene expression observed following extended culture. This study demonstrates the efficiency of the novel wash process and the potential of the resultant biological material to serve as a scaffold in bone allograft tissue engineering.

Identification of novel nucleus pulposus markers: Interspecies variations and implications for cell-based therapiesfor intervertebral disc degeneration

Mesenchymal stem-cell based therapies have been proposed as novel treatments for intervertebral disc degeneration, a prevalent and disabling condition associated with back pain. The development of these treatment strategies, however, has been hindered by the incomplete understanding of the human nucleus pulposus phenotype and by an inaccurate interpretation and translation of animal to human research. This review summarises recent work characterising the nucleus pulposus phenotype in different animal models and in humans and integrates their findings with the anatomical and physiological differences between these species. Understanding this phenotype is paramount to guarantee that implanted cells restore the native functions of the intervertebral disc. Cite this article: Bone Joint Res 2013;2:169-78.

Skeletal muscle contractile properties and proinflammatory cytokine gene expression in human endotoxaemia

Background

Muscle dysfunction associated with sepsis contributes to morbidity and mortality but the underlying mechanisms are unclear. This study examined whether muscle weakness relates to an intrinsic defect in contraction, or to central mechanisms associated with acute illness, and whether systemic endotoxaemia induces changes in gene expression for proinflammatory cytokines within human muscle in vivo.

Methods

In this experimental study, 12 healthy men received intravenous Escherichia coli lipopolysaccharide (LPS, 4 ng/kg) or saline (control). Voluntary and electrically stimulated quadriceps contraction, and tumour necrosis factor (TNF) α mRNA expression in quadriceps muscle biopsies were studied before and after the infusion.

Results

Endotoxaemia induced transient weakness of voluntary quadriceps contraction, equivalent to a 7·8 (95 per cent confidence interval 2·1 to 13·5) per cent reduction in contractile force at 180 min (P = 0·027) and a 9·0 (5·2 to 12·8) per cent reduction at 300 min (P = 0·008). Electrically stimulated contraction was unaffected. LPS administration resulted in an apparent fibre-specific induction of TNF-α mRNA.

Conclusion

Endotoxaemia results in a reduction in voluntary muscle contractile force without an apparent defect in stimulated muscle contraction. Loss of volition may be a more important factor than intrinsic dysfunction in acute sepsis-associated human muscle weakness.

Human disc degeneration is associated with increased MMP 7 expression

During intervertebral disc (IVD) degeneration, normal matrix synthesis decreases and degradation of disc matrix increases. A number of proteases that are increased during disc degeneration are thought to be involved in its pathogenesis. Matrix metalloproteinase 7 (MMP 7) (Matrilysin, PUMP-1) is known to cleave the major matrix molecules found within the IVD, i.e., the proteoglycan aggrecan and collagen type II. To date, however, it is not known how its expression changes with degeneration or its exact location. We investigated the localization of MMP 7 in human, histologically graded, nondegenerate, degenerated and prolapsed discs to ascertain whether MMP 7 is up-regulated during disc degeneration. Samples of human IVD tissue were fixed in neutral buffered formalin, embedded in paraffin, and sections stained with hematoxylin and eosin to score the degree of morphological degeneration. Immunohistochemistry was performed to localize MMP 7 in 41 human IVDs with varying degrees of degeneration. We found that the chondrocyte-like cells of the nucleus pulposus and inner annulus fibrosus were MMP 7 immunopositive; little immunopositivity was observed in the outer annulus. Nondegenerate discs showed few immunopositive cells. A significant increase in the proportion of MMP 7 immunopositive cells was seen in the nucleus pulposus of discs classified as showing intermediate levels of degeneration and a further increase was seen in discs with severe degeneration. Prolapsed discs showed more MMP 7 immunopositive cells compared to nondegenerated discs, but fewer than those seen in cases of severe degeneration.

Connective tissue growth factor expression in human intervertebral disc: implications for angiogenesis in intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is strongly associated with chronic low back pain, one of the most common causes of morbidity in the West. While normal healthy IVD is avascular, angiogenesis is a constant feature of IVD degeneration and has been shown to be associated with in-growth of nerves. Connective tissue growth factor (CTGF) plays a pivotal role in angiogenesis. To investigate the expression of CTGF in both normal and degenerated IVD, 21 IVDs were obtained from patients at surgery or postmortem examination and grouped according to the severity of histological degeneration. The immunohistochemical expression of CTGF was correlated with the degree of degeneration. CD31 immunohistochemistry was used to correlate IVD degeneration with vasculature. Our results showed that CTGF is expressed in non-degenerated and degenerated human IVDs and increased expression of CTGF is associated with degenerated discs, particularly within areas of neovascularization. We suggest that CTGF may play a role in angiogenesis in the human degenerated IVD.

Quantum dots light up pathology

Quantum dots (QDs) are novel nanocrystal fluorophores with extremely high fluorescence efficiency and minimal photobleaching. They also possess a constant excitation wavelength together with sharp and symmetrical tunable emission spectra. These unique optical properties make them near-perfect fluorescent markers and there has recently been rapid development of their use for bioimaging. QDs can be conjugated to a wide range of biological targets, including proteins, antibodies, and nucleic acid probes, rendering them of particular interest to pathology researchers. They have been used in multiplex immunohistochemistry and in situ hybridization, which when combined with multispectral imaging, has enabled quantitative measurement of gene expression in situ. QDs have also been used for live in vivo animal imaging and are now being applied to an ever-increasing range of biological problems. These are detailed in this review, which also acts to outline the important advances that have been made in their range of applications. The relative novelty of QDs can present problems in their practical use and guidelines for their application are given.

Strategies for regeneration of the intervertebral disc

Low back pain resulting from degenerative disc disease is the most common cause of disability in the UK. Current low back pain treatments are aimed at either treating the symptoms of pain, or removing the source of pain itself, but do not address the biological basis of the disease. Our increasing understanding of the molecular biological basis for degenerative disc disease has enabled the development of strategies aimed at tackling the causes of degeneration. Here we review the progress that has been made in strategies using cells, biomaterials and growth factors aimed at regenerating the human intervertebral disc.

Investigation of the role of IL-1 and TNF in matrix degradation in the intervertebral disc

OBJECTIVE

To establish if IL-1 or TNF regulates matrix degradation in the non-degenerate or degenerate intervertebral disc (IVD).

METHODS

In situ zymography (ISZ) has been used to investigate the role of IL-1 and TNF in the matrix degradation characterizing symptomatic IVD degeneration. ISZ employed three substrates (gelatin, collagen II, casein) and four different challenges, IL-1beta, IL-1 receptor antagonist (IL-1Ra), TNF-alpha and anti-TNF.

RESULTS

We have shown for the first time that whilst IL-1beta will stimulate and IL-1 receptor antagonist will inhibit matrix degradation in intact human IVD tissue, neither TNF-alpha nor anti-TNF have any measurable effect on degradation of these matrices.

CONCLUSION

This study has addressed a current area of controversy in IVD biology, namely, whether either IL-1 or TNF or both are involved in driving matrix degradation. Our data indicate that IL-1 is a key cytokine mediating matrix degradation in the IVD and therefore a therapeutic target.

Morphology, mechanisms and pathology of musculoskeletal ageing

In general terms, the recognized alterations in circulating humoral factors (hormones, cytokines, growth factors) that occur in ageing, coupled with innate cellular senescence exaggerated by the slow turnover of many connective tissue cell populations and the age-associated alterations in matrix molecule cross-linking, predispose the elderly to altered connective tissue biology. These changes can be profound, leading to poor mobility, altered ability to withstand cold, weakness and an increased risk of falls, fractures and age-associated 'degenerative' diseases, such as osteoarthritis and osteoporosis. As understanding of the causes of altered connective tissue function with age increases, it is becoming clearer that many of the predisposing factors (growth hormone, cytokines, load/life style) are potential targets for improving quality of life in the elderly.

Matrix synthesis and degradation in human intervertebral disc degeneration

Degeneration of the intervertebral disc has been implicated in chronic low back pain. Type II collagen and proteoglycan (predominantly aggrecan) content is crucial to proper disc function, particularly in the nucleus pulposus. In degeneration, synthesis of matrix molecules changes, leading to an increase in the synthesis of collagens type I and III and a decreased production of aggrecan. Linked to this is an increased expression of matrix-degrading molecules including MMPs (matrix metalloproteinases) and the aggrecanases, ADAMTS (a disintegrin and metalloprotease with thrombospondin motifs) 1, 4, 5, 9 and 15, all of which are produced by native disc cells. Importantly, we have found that there is a net increase in these molecules, over their natural inhibitors [TIMP-1 (tissue inhibitor of metalloproteinases-1), 2 and 3], suggesting a deregulation of the normal homoeostatic mechanism. Growth factors and cytokines [particularly TNFalpha (tumour necrosis factor alpha) and IL-1 (interleukin 1)] have been implicated in the regulation of this catabolic process. Our work has shown that in degenerate discs there is an increase in IL-1, but no corresponding increase in the inhibitor IL-1 receptor antagonist. Furthermore, treatment of human disc cells with IL-1 leads to a decrease in matrix gene expression and increased MMP and ADAMTS expression. Inhibition of IL-1 would therefore be an important therapeutic target for preventing/reversing disc degeneration.

Intervertebral disc biology, degeneration and novel tissue engineering and regenerative medicine therapies

Degeneration of the intervertebral disc (IVD) is a major cause of low back pain affecting a large percentage of the population at some point in their lives. Consequently IVD degeneration and its associated low back pain has a huge socio-economic impact and places a burden on health services world-wide. Current treatments remove the symptoms without treating the underlying problem and can result in reoccurrence in the same or adjacent discs. Tissue engineering offers hope that new therapies can be developed which can regenerate the IVD. Combined with this, development of novel biomaterials and an increased understanding of mesenchymal stem cell and IVD cell biology mean that tissue engineering of the IVD may soon become a reality. However for any regenerative medicine approach to be successful there must first be an understanding of the biology of the tissue and the pathophysiology of the disease process. This review covers these key areas and gives an overview of the recent developments in the fields of biomaterials, cell biology and tissue engineering of the IVD.

Contribution of VCAF-positive cells to neovascularization and calcification in atherosclerotic plaque development

Calcification of the vessel wall is a regulated process with many similarities to osteogenesis. Progenitor cells may play a role in this process. Previously, we identified a novel gene, Vascular Calcification Associated Factor (VCAF), which was shown to be important in pericyte osteogenic differentiation. The aim of this study was to determine the localization and expression pattern of VCAF in human cells and tissues. Immunohistochemical analysis of seven atherosclerotic arteries confirmed VCAF protein expression within calcified lesions. In addition, individual VCAF-positive cells were detected within the intima and adventitia in areas where sporadic 3G5-positive pericytes were localized. Furthermore, VCAF-positive cells were identified in newly formed microvessels in association with CD34-positive/CD146-positive/c-kit-positive cells as well as in intact CD31-positive endothelium in internal mammary arteries. Western blot analysis confirmed the presence of VCAF (18 kD) in protein lysates extracted from human smooth muscle cells, endothelial cells, macrophages, and osteoblasts. In fracture callus samples from three patients, VCAF was detected in osteoblasts and microvessels. This study demonstrates the presence of VCAF in neovessels and raises the possibility that VCAF could be a new marker for vascular progenitor cells involved in a number of differentiation pathways. These data may have implications for the prevention or treatment of vascular disease.

Comparison of gene-expression profiles in parallel bone marrow and peripheral blood samples in acute myeloid leukaemia by real-time polymerase chain reaction

BACKGROUND

Gene signatures (Indicator genes) in bone marrow that provide more precise prognostication in haematological malignancy have been identified by microarray expression studies. It would be beneficial to measure these diagnostic signatures in peripheral blood.

AIMS

To determine the degree of correspondence of gene expression for a set of Indicator genes between bone marrow and peripheral blood in acute myeloid leukaemia (AML).

METHODS

Parallel bone marrow aspirate and peripheral blood samples were obtained from 19 patients diagnosed with AML and mononuclear cells isolated from both sample types. mRNA was globally amplified by polyadenylated real-time polymerase chain reaction (polyA RT-PCR); the expression of 15 AML Indicator genes, identified from previous microarray studies, was measured by RT-PCR. All values were normalised to the mean expression of three housekeeping genes (IF2-beta, GAP and RbS9) and were statistically compared using SPSS software.

RESULTS

No significant difference in expression between bone marrow and peripheral blood was observed for 10 of the genes (leptin receptor, CD33, adipsin, proteoglycan 1, MB-1, cyclin D3, hSNF2b, proteasome iota, HkrT-1 and E2A), indicating its possible use in monitoring disease activity in peripheral blood samples, whereas c-myb, HOXA9, LYN, cystatin c and LTC4s showed significantly different expression between bone marrow and peripheral blood samples.

CONCLUSION

These results indicate a possible use for the method in monitoring AML in peripheral blood by RT-PCR measurement of Indicator genes. In addition, the initial use of polyA PCR facilitates translation to very small clinical samples, including fractionated cell populations, of particular importance for monitoring haematological malignancy.

Hypoxia inducible factor-1 and facilitative glucose transporters GLUT1 and GLUT3: putative molecular components of the oxygen and glucose sensing apparatus in articular chondrocytes

Articular cartilage is an avascular connective tissue in which the availability of oxygen and glucose is significantly lower than synovial fluid and plasma. Glucose is an important metabolic fuel and structural precursor that plays a key role in the synthesis of extracellular matrix macromolecules in articular cartilage. However, glucose concentrations in cartilage can fluctuate depending on age, physical activity and endocrine status. Chondrocytes are glycolytic cells and must be able to sense the quantities of oxygen and glucose available to them in the extracellular matrix and respond appropriately by adjusting cellular metabolism. Consequently chondrocytes must have the capacity to survive in an extracellular matrix with limited nutrients and low oxygen tensions. The molecular mechanisms responsible for allowing chondrocytes to adapt to these harsh environmental conditions are poorly understood. In this article we present a novel "dual" model of oxygen and glucose sensing in chondrocytes based on recent experimental data. This model incorporates the hypoxia-inducible factor alpha (HIF-1alpha) as an oxygen sensor and the hypoxia responsive facilitative glucose transporters, GLUT1 and GLUT3 as putative components of the glucose sensing apparatus in chondrocytes. Recent studies have shown that GLUT1 and GLUT3 are both expressed in chondrocytes and their HIF-1alpha-mediated transcription may be dually stimulated in response to hypoxia and low glucose conditions which in turn promote anaerobic glycolysis in favor of oxidative phosphorylation. This working model provides, for the first time, a unifying hypothesis to explain how chondrocytes might sense and respond to low oxygen tensions and alterations in extracellular glucose.

The effects of lanthanum carbonate and calcium carbonate on bone abnormalities in patients with end-stage renal disease

BACKGROUND

Renal osteodystrophy is a common complication of end-stage renal disease (ESRD) and is a major cause of morbidity in patients with ESRD. High serum levels of phosphorus, calcium and parathyroid hormone are associated with the development of this disease. The effects on bone of treatment with lanthanum carbonate, a new phosphate binder, and calcium carbonate were assessed in patients with ESRD.

METHODS

This was an open-label, multicenter, parallel-group study. Patients were recruited within 12 weeks of commencing dialysis. Following screening, phosphate binder administration was stopped, tetracycline labeling administered and a transiliac bone biopsy taken. After randomization to lanthanum carbonate or calcium carbonate, patients were titrated to an optimum dose for 8 weeks and maintained at this dose for 44 weeks. The bone was then labeled and a second biopsy taken. Biopsy samples were analyzed histomorphometrically.

RESULTS

Paired bone biopsies from 33 lanthanum carbonate- and 30 calcium carbonate-treated patients were suitable for analysis. None of the patients on either treatment developed osteomalacia. Assessment of activation frequency changes showed that 41% of biopsies from lanthanum carbonate-treated patients moved towards normal (observed values at the follow-up biopsy were closer to expected values than were the baseline values, so patients were considered to be improved) compared with 23% of calcium carbonate-treated patients (p = 0.15).

CONCLUSIONS

This study indicates that there was no evidence of aluminum-like toxicity with lanthanum carbonate after 1 year of treatment in ESRD patients commencing dialysis, and there appeared to be a beneficial effect on bone-cell function and activity compared with calcium carbonate.

Degeneration of intervertebral discs: current understanding of cellular and molecular events, and implications for novel therapies

Recent advances in surgical techniques have made it possible to study the changes that are known as degeneration of the intervertebral disc (IVD) in greater depth than ever before. This is an important area of study because degeneration of the lumbar IVDs is associated, perhaps causally, with low back pain: one of the most common and debilitating conditions in the western world. The term degeneration implies an inevitable progression that is characteristic of wear-and-tear-associated conditions. However, modern research on human tissue has shown that this is not the case. Here, disruption of the micro-anatomy that is described as degeneration is an active process, which is probably regulated by locally produced cytokines. This one observation opens up the possibility of inhibiting or even reversing the processes of degeneration. The immediate question is how can the slowly progressive changes of degeneration be treated, particularly as connective tissue repair is thought to be a slow and highly regulated process. In this review, the possibility of using gene therapy as a single-shot, long-lasting therapeutic strategy is discussed, together with an outline of developments in this area to date.

Apoptosis of terminal hypertrophic chondrocytes in an in vitro model of endochondral ossification

It is widely accepted that growth plate chondrocytes undergo apoptosis when they reach the terminal hypertrophic stage of their differentiation during the process of endochondral ossification in vivo. In this report, an established chondrocyte cell culture model of mammalian endochondral ossification was utilized to investigate the fate of chondrocytes after they had entered hypertrophy in vitro. Fetal bovine epiphyseal chondrocytes were treated with the demethylating agent, 5-azacytidine, for 48 h and then cultured under azacytidine-depleted conditions. There was evidence for apoptosis in azacytidine-treated cells, as demonstrated by nuclear condensation and fragmentation (days 27 and 35) using transmission electron microscopy, and the detection of exposed phosphatidylserine on the plasma membrane surface of apoptotic chondrocytes (day 27) using fluorescence-labelled annexin V. Treated cultures on days 10 and 20 and untreated cultures at all corresponding time-points showed no morphological characteristics of apoptosis. In situ hybridization studies of treated cultures revealed that expression of the apoptotic suppressor, bcl-2, remained consistently high throughout the culture period, whilst the apoptotic inducer, bax, was not expressed until day 23. Quantification of these data showed a gradual shift in the ratio of the expression level of bcl-2 and bax in favour of bax with time in culture, particularly from day 23 onwards. Taken together, the results indicate that azacytidine-treated epiphyseal chondrocytes entered terminal hypertrophy from day 23 onwards in culture and died by apoptosis. This study confirms this culture system as a successful recapitulation of the entire mammalian chondrocyte differentiation pathway, including apoptosis. The culture model will prove valuable for studies of the apoptotic fate of terminally differentiated chondrocytes in the growth plate with a view to providing a better understanding of the underlying mechanisms of skeletal malformations and other pathological disorders such as osteoarthritis.

Adipocytic proportion of bone marrow is inversely related to bone formation in osteoporosis

AIMS

Preliminary studies have suggested that there is an increase in adipocytic tissue in osteoporotic (OP) bone, supporting in vitro evidence for a switch in differentiation of stromal cells from the osteoblastic to the adipocytic lineage. To investigate this the variation of the ratio of adipose tissue to haemopoietic/stromal tissue in OP bone was measured.

METHODS

The ratio of adipocytic to haemopoietic/stromal tissue (A/H) was measured by semi-automated image analysis in iliac crest biopsies from 127 patients with osteoporosis (84 female patients, 48 male patients; mean age, 55 years; range, 5-80). Fourteen patients with normal histomorphometric data (nine women; five men; mean age, 48 years; range 21-70) acted as controls.

RESULTS

The ratio of A/H was higher in OP bone than in the normal controls (OP mean 43.06% v normal mean 22.4%; p < 0.001). Multiple regression analysis showed that 98.5% of the variability in the A/H ratio was the result of age and several measures of bone formation, including cancellous wall thickness, osteoid volume, cancellous thickness, cortical wall thickness, cancellous apposition rate, and bone formation rate, together with cancellous separation (each significant at p < 0.001). Those with the greatest effect on the A/H ratio (in decreasing order) were cancellous apposition rate, osteoid volume, and age.

CONCLUSIONS

Cancellous apposition rate, osteoid volume, and age were associated with the increase in the proportion of adipose tissue present in OP bone. Of these, cancellous apposition rate reflects osteoblast activity, indicating that the increase in the volume of adipose tissue in osteoporosis is associated with reduced bone formation, supporting the postulated switch in differentiation of stromal cells from the osteoblastic to the adipocytic pathway in osteoporosis.

Nerve growth factor expression and innervation of the painful intervertebral disc

Following a previous description of nociceptive nerve fibre growth into usually aneural inner parts of painful intervertebral disc (IVD), this study has investigated whether nociceptive nerve ingrowth into painful IVD is stimulated by local production of neurotrophins. Immunohistochemistry and in situ hybridization have been used to investigate expression of the candidate neurotrophin, nerve growth factor (NGF), and its high- and low-affinity receptors trk-A and p75, respectively, in painful IVD excised for the management of low back pain. IVD from patients with back pain were of two types: those that when examined by discography reproduced the patient symptoms (pain level IVD) and those that did not (non-pain level IVD). Microvascular blood vessels accompanied nerve fibres growing into pain level IVD and these expressed NGF. The adjacent nerves expressed the high-affinity NGF receptor trk-A. These vessels entered the normally avascular IVD through the discal end plates. NGF expression was not identified in non-pain level or control IVD. Some non-pain level IVD had vessels within them, which entered through the annulus fibrosus. These did not express NGF nor did nerves accompany them. These findings show that nociceptive nerve ingrowth into painful IVD is causally linked with NGF production by blood vessels growing into the IVD, from adjacent vertebral bodies.

Expression of chondrocyte markers by cells of normal and degenerate intervertebral discs

AIMS

To investigate the phenotype of cells in normal and degenerate intervertebral discs by studying the expression of molecules characteristic of chondrocytes in situ.

METHODS

Human intervertebral discs taken at surgery were graded histologically, and classified on this basis as normal or degenerate. Eighteen of each type were selected, and in situ hybridisation was performed for the chondrocytic markers Sox9 and collagen II using (35)S labelled cDNA probes. Aggrecan was located by immunohistochemistry, using the monoclonal antibody HAG7E1, and visualised with an avidin-biotin peroxidase system.

RESULTS

In the normal discs, strong signals for Sox9 and collagen II mRNA, and strong staining for the aggrecan protein were seen for the cells of the nucleus pulposus (NP), but reactions were weak or absent over the cells of the annulus fibrosus (AF). In degenerate discs, the Sox9 and collagen II mRNA signals remained visible over the cells of the NP and were again absent in the AF. Aggrecan staining was not visible in the NP cells, and was again absent in the AF.

CONCLUSIONS

Cells of the normal NP showed expression of all three markers, clearly indicating a chondrocytic phenotype. In degeneration, there was evidence of a loss of aggrecan synthesis, which may contribute to the pathogenesis of disc degeneration. AF cells showed no evidence of a chondrocytic phenotype in either normal or degenerate discs.

Current understanding of cellular and molecular events in intervertebral disc degeneration: implications for therapy

Until recently, material removed from the intervertebral disc (IVD) at surgery consisted either of 'loose bodies' from the centre of the IVD or discal tissue displaced (prolapsed) into the intervertebral root or spinal canals. This material is best regarded as a by-product of disc degeneration and therefore not representative of the disease process itself. Recent advances in surgical techniques, particularly anterior fusion, in which large segments of the anterior part of the IVD are excised with the anatomical relationships between different components intact, have generated material that can be investigated with modern molecular and cell biological techniques. This is an important area of study because degeneration of the lumbar IVDs is associated, perhaps causally, with low back pain, one of the most common and debilitating conditions in the West. 'Degeneration' carries implications of inevitable progression of wear-and-tear associated conditions. Modern research on human IVD tissue has shown that this is far from the case and that disruption of the micro-anatomy described as degeneration is an active process, regulated by locally produced molecules. The exciting consequence of this observation is the possibility of being able to inhibit or even reverse the processes of degeneration using targeted therapy.

E-cadherin and beta-catenin are down-regulated in prostatic bone metastases

OBJECTIVE

To determine the E-cadherin and beta-catenin expression phenotype in untreated primary prostate cancer and corresponding bone metastases.

MATERIALS AND METHODS

Paired bone metastasis and primary prostate specimens were obtained from 14 men with untreated metastatic prostate carcinoma. The tumours were histologically graded by an independent pathologist. Expression of mRNA for E-cadherin and beta-catenin was detected within the tumour cells using in-situ hybridization with a 35S-labelled cDNA probe. The expression of E-cadherin and beta-catenin were graded as uniform, heterogeneous or negative.

RESULTS

The mRNA for E-cadherin was expressed in 13 of 14 primary carcinomas and 11 bone metastases; beta-catenin was expressed by 13 and nine, respectively. Of the primary tumours, nine expressed E-cadherin and beta-catenin uniformly; in contrast, all metastases had down-regulated E-cadherin and/or beta-catenin.

CONCLUSIONS

The down-regulation of E-cadherin and beta-catenin are a feature of the metastatic phenotype, which may be a significant factor in the genesis of bone metastases. However, this does not appear to be reflected in the expression of these molecules in the primary tumours.

Parathyroid hormone related peptide and receptor expression in paired primary prostate cancer and bone metastases

Parathyroid hormone-related peptide is a regulatory protein implicated in the pathogenesis of bone metastases, particularly in breast carcinoma. Parathyroid hormone-related peptide is widely expressed in primary prostate cancers but there are few reports of its expression in prostatic metastases. The aim of this study was to examine the expression of parathyroid hormone-related peptide and its receptor in matched primary and in bone metastatic tissue from patients with untreated adenocarcinoma of the prostate. Eight-millimetre trephine iliac crest bone biopsies containing metastatic prostate cancer were obtained from 14 patients from whom matched primary tumour tissue was also available. Histological grading was performed by an independent pathologist. The cellular location of mRNA for parathyroid hormone-related peptide and parathyroid hormone-related peptide receptor was identified using in situ hybridization with (35)S-labelled probe. Expression of parathyroid hormone-related peptide and its receptor was described as uniform, heterogenous or negative within the tumour cell population. Parathyroid hormone-related peptide expression was positive in 13 out of 14 primary tumours and in all 14 metastases. Receptor expression was evident in all 14 primaries and 12 out of 14 metastases. Co-expression of parathyroid hormone-related peptide and parathyroid hormone-related peptide receptor was common (13 primary tumours, 12 metastases). The co-expression of parathyroid hormone-related peptide and its receptor suggest that autocrine parathyroid hormone-related peptide mediated stimulation may be a mechanism of escape from normal growth regulatory pathways. The high frequency of parathyroid hormone-related peptide expression in metastases is consistent with a role in the pathogenesis of bone metastases.

Moderation of iodoacetate-induced experimental osteoarthritis in rats by matrix metalloproteinase inhibitors

OBJECTIVE

To determine the effect of matrix metalloproteinase (MMP) inhibitors in mono-iodoacetate-induced arthritis in rats.

DESIGN

The ability of compounds to inhibit MMPs in vitro was assessed kinetically using a quenched fluorescent substrate. Rats were injected with iodoacetate intraarticularly in one knee joint and damage to the tibial plateau was evaluated from digitized images captured using an image analyser and by histology. Collagenase and gelatinase activity in cartilage from iodoacetate injected knees were evaluated using(3)H-rat type I collagen and gelatin zymography, respectively.

RESULTS

Collagenase and gelatinase activity significantly increased in the knee cartilage of rats injected with iodoacetate with peak activity by day 7. Three MMP inhibitors were examined for their efficacy in the rat iodoacetate-induced arthritis model. Significant (P< 0.05) inhibition of cartilage damage was observed in animals treated orally with 35 mg/kg b.i.d. of the three different MMP inhibitors. Inhibition of cartilage damage by the MMP inhibitors ranged from 36-42%.

CONCLUSION

MMP inhibitors are partially protective against cartilage and subchondral bone damage induced by iodoacetate. These results support an important role for MMPs in mediating the joint damage in this model of arthritis.

Dual colour FISH in paraffin wax embedded bone trephines for identification of numerical and structural chromosomal abnormalities in acute myeloid leukaemia and myelodysplasia

AIMS/BACKGROUND

The advent of new treatments for haematological malignancies has led to the need for a correlation between cytogenetic and morphological abnormalities. This study aimed to achieve this by the application of interphase cytogenetics to marrow trephine sections, a technique not previously reported for formalin fixed, paraffin wax embedded trephine biopsies.

METHODS

Dual colour fluorescence in situ hybridisation (FISH) was used to detect numerical and structural abnormalities in routinely processed paraffin wax embedded trephine biopsies. Three cases with t(8;21) and three with t(15;17) were analysed, together with a case of trisomy 8. Chromosome specific probes were hybridised with sections and disclosed by fluorescein isothiocyanate and rhodamine/Texas red labelled antidigoxigenin and antibiotin amplification; translocations were identified by colocalisation of probes using a double wavelength bypass filter.

RESULTS

A translocation signal was present in 12% and 11.5% of the cells counted in the t(8;21) and t(15;17) cases, respectively, but in none of the normal controls (p < 0.001). In the case of trisomy 8, 9% of the cells counted contained three hybridisation signals for chromosome 8, whereas no cell contained more than two in the normal control (p < 0.001).

CONCLUSIONS

This technique is useful for archived routinely processed material, enabling it to be used as a research tool but also, and perhaps more importantly, in clinical practice.

Osteoporosis in men: a cellular endocrine perspective of an increasingly common clinical problem

Although it has been accepted that osteoporosis is common in women, only recently have we become aware that it is also widespread in men; one in twelve men in the UK have osteoporosis. In many cases, there are recognisable causes for their osteoporosis, but a significant proportion (approximately one third) of these men have idiopathic disease. A major problem is that these cases are difficult to treat. An important therapeutic strategy would be to identify men at risk from osteoporosis sufficiently early, so that they can begin preventative measures. Moreover, development of novel means of treating these men would be an important clinical advance. With the emphasis on osteoporosis in women, however, the cellular and molecular basis for male idiopathic osteoporosis (MIO) is still poorly understood. Nevertheless, there are some aspects of skeletal regulation which may be specific for men and which could form the basis for addressing these problems. Thus, the importance of oestrogen in maintaining the adult skeleton in men as well as women implies that bone cells in men can respond to low levels of the hormone. Both oestrogen receptor (ER) alpha and beta are expressed in bone in vivo, which may be important for oestrogen action on bone in men. Furthermore, in osteoporosis generally, there is increasing evidence for defective osteoblast differentiation such that there is a surfeit of adipocytes over osteoblasts. A low peak bone mass is a powerful risk factor for osteoporosis in later life; bone formation and, by implication, osteoblast differentiation, is key to the mechanism by which it is accrued. GH and IGFs are important for regulating osteoblast differentiation. Evidence now suggests that they are associated with bone mineral density, particularly in men. The genes for ERs, GH and IGF-I might be useful candidates with which we can begin to detect men at risk from osteoporosis. Furthermore, the mechanisms by which oestrogen, GH and IGF-I regulate the male skeleton could provide the basis for developing novel means of treating MIO.

Localization of estrogen receptor beta protein expression in adult human bone

Evidence suggests that the newly described estrogen receptor beta (ER-beta) may be important for estrogen (17beta-estradiol) action on the skeleton, but its cellular localization in adult human bone requires clarification. We addressed this by using indirect immunoperoxidase with a novel affinity purified polyclonal antibody to human ER-beta, raised to hinge domain (D) sequences from the human receptor. Bone was demineralized in 20% EDTA and all biopsy specimens were formalin-fixed and wax-embedded. Vigorous retrieval was essential for ER-beta detection. In sections (5 microm) of benign prostate hyperplasia, used as positive control, clear nuclear immunoreactivity was seen in glandular epithelial cells, with a 1:500 dilution of ER-beta40. For bone sections, optimal antibody dilutions were 1:100-1:250. We found that in normal bone (from graft operations), in fracture callus from both men and women (>25 years old), pagetic bone, osteophytes, and secondary hyperparathyroid bone, all from older patients, ER-beta was expressed clearly in osteoclast nuclei, with little cytoplasmic immunoreactivity. Nuclear immunoreactivity was still prominent in osteoclasts, with antibody diluted 1:500, although it faded in other cells. Osteoblasts, in areas of active bone formation or bone remodeling, also expressed ER-beta, as did some osteocytes. However, hypertrophic chondrocytes were negative, unlike mesenchymal cells, adjacent to the osteogenesis. Megakaryocytes and some capillary blood vessels cells were receptor positive. All ER-beta expression was blocked totally by preincubation of antibody with antigen. We conclude that ER-beta is expressed in cells of osteoblast lineage and in osteoclasts. The latter appear relatively abundant in this receptor and this might provide a means for direct action of estrogen on osteoclasts.

A novel cell culture model of chondrocyte differentiation during mammalian endochondral ossification

Endochondral ossification (EO) occurs in the growth plate where chondrocytes pass through discrete stages of proliferation, maturation, hypertrophy, and calcification. We have developed and characterized a novel bovine cell culture model of EO that mirrors these events and will facilitate in vitro studies on factors controlling chondrocyte differentiation. Chondrocytes derived from the epiphyses of long bones of fetal calves were treated with 5-azacytidine (aza-C) for 48 h. Cultures were maintained subsequently without aza-C and harvested at selected time points for analyses of growth and differentiation status. A chondrocytic phenotype associated with an extensive extracellular matrix rich in proteoglycans and collagen types II and VI was observed in aza-C-treated and -untreated cultures. aza-C-treated cultures were characterized by studying the expression of several markers of chondrocyte differentiation. Parathyroid hormone-related protein (PTHrP) and its receptor, both markers of maturation, were expressed at days 5-9. Type X collagen, which is restricted to the stage of hypertrophy, was expressed from day 11 onward. Hypertrophy was confirmed by a 14-fold increase in cell size by day 15 and an increased synthesis of alkaline phosphatase during the hypertrophic period (days 14-28). The addition of PTHrP to aza-C-treated cultures at day 14 led to the down-regulation of type X collagen by 6-fold, showing type X collagen expression is under the control of PTHrP as in vivo. These findings show that aza-C can induce fetal bovine epiphyseal chondrocytes to differentiate in culture in a manner consistent with that which occurs during the EO process in vivo.

Subtractive hybridization--genetic takeaways and the search for meaning

Gene expression profiling relies on mRNA extraction from defined cell systems, which in the case of pathological processes necessarily results in the use of small quantities of tissues, sometimes as little as a few cells. This obviates the use of many systems of gene expression profiling and is best carried out using cDNA amplified by poly(A) reverse transcription polymerase chain reaction, which is capable of generating material representative of all the expressed genes in samples as small as one cell. Analysis of this material using subtractive hybridization compares the genes expressed at different stages of a biological/pathological process allowing identification of the all the genes upregulated during the process. The identification of the genes present is not dependent on their prior description or on the choice of genes used in a screen and as such the method is ideal for identifying novel genes or unsuspected genes. We have used the method to identify genes involved in normal osteoblastic differentiation and in Paget's disease of bone and it has been widely used to study normal differentiation and pathological processes in a number of systems. The method, its applications and its relationship with the other methods of gene expression profiling are reviewed.

Down-regulation of human osteoblast PTH/PTHrP receptor mRNA in end-stage renal failure

BACKGROUND

Resistance to the action of parathyroid hormone (PTH) has been demonstrated in end-stage renal failure and is considered to be important in the pathogenesis of secondary hyperparathyroidism. The mechanism of resistance is unknown. However, altered regulation of cellular PTH/PTH-related protein (PTH/PTHrP) receptor (PTH1R) has been assumed to be important.

METHODS

We have used in situ hybridization to examine PTH1R mRNA expression by osteoblasts in human bone and have compared the expression in high- and low-turnover renal bone disease, high-turnover nonrenal bone disease (healing fracture callus and Pagetic bone), and normal bone. Bone biopsies were formalin fixed, ethylenediaminetetraacetic acid decalcified, and paraffin wax embedded. A 1.8 kb PTH1R cDNA probe, labeled with 35S, was used, and the hybridization signal was revealed by autoradiography. The density of signal over osteoblasts was quantitated using a semiautomated Leica image analysis software package.

RESULTS

The mean density of PTH1R mRNA signal over osteoblasts in renal high-turnover bone was only 36% of that found in nonrenal high-turnover bone (P < 0.05) and 51% of that found in normal bone (P < 0.05). Osteoblast PTH1R mRNA signal in adynamic bone from individuals with diabetes mellitus was 28% of normal bone (P < 0.05) and 54% of that found in renal high-turnover bone (P < 0.05).

CONCLUSIONS

These results demonstrate a down-regulation of osteoblast PTH1R mRNA in end-stage renal failure in comparison to normal and high-turnover bone from otherwise healthy individuals, and provide an insight into the mechanisms of "skeletal resistance" to the actions of PTH.

Preliminary report of impaired oestrogen receptor-alpha expression in bone, but no involvement of androgen receptor, in male idiopathic osteoporosis

In western countries, osteoporosis affects at least 1 in 12 of all adult males and a third of osteoporotic men have idiopathic disease (MIO). Both oestrogen and testosterone are now known to be important to the male skeleton. As normal oestrogen levels have been found in younger MIO cases, it is hypothesized that, in bone, their responses to gonadal steroids may be defective, through impaired receptor expression. This study therefore compared oestrogen receptor (ER)-alpha and androgen receptor (AR) expression, by indirect immunofluorescence and semi-quantitative image analysis, in undecalcified fresh frozen bone sections from MIO patients (33-56 years), age-matched control men (n=7), and, for reference, ovarian steroid-replete (n=7) and -deficient women (n=6). In normal men, 23%+/-SEM 6% osteoblasts and 14%+/-SEM 2% osteocytes expressed ERalpha protein, similar to hormone-replete women. Although receptor expression decreased in hormone-deficient women, loss of ERalpha protein in MIO patients was more severe (1%+/-SEM 0.5% osteocytes, 2%+/-SEM 1% osteoblasts expressed receptor). In all four groups, there was little osteocyte AR expression, but in the women, a proportion of osteoblasts were receptor-positive. Deficient osteoblast and osteocyte ERalpha protein expression could explain the bone loss in these MIO patients.

Expression of the imprinted tumour-suppressor gene H19 is tightly regulated during normal haematopoiesis and is reduced in haematopoietic precursors of patients with the myeloproliferative disease polycythaemia vera

cDNA subtraction was employed to uncover differences in gene expression between myeloproliferative polycythaemia vera (PV) and normal haematopoietic precursors. Following cDNA subtraction using mRNAs isolated from PV and normal CD34+/CD33- bone-marrow cells, expression of the tumour suppressor H19 was found to be low or absent in the PV sample. Low levels of H19 expression in PV patients were confirmed by in situ hybridization. Using semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) to examine expression in the pluripotent haematopoietic cell line FDCP-mix and single bone-marrow precursors, unambiguous IGF2 and H19 expression was demonstrated in normal haematopoietic precursors. Examination of individual bone-marrow precursors revealed that all IGF2-expressing haematopoietic precursors also co-expressed H19, indicating that H19 and IGF2 may be co-ordinately regulated during haematopoiesis. Analysis of FDCP-mix undergoing differentiation and single pluripotent and committed bone-marrow precursors revealed that the pattern of H19 expression coincided with the commitment to a single lineage. Taken together, these observations demonstrate that H19 and IGF2 are specifically expressed during haematopoiesis and that low levels of H19 expression are associated with PV and may contribute to the pathology of the disease.

Cellular mechanisms of renal osteodystrophy

Renal osteodystrophy affects all patients with end-stage renal failure, resulting in significant skeletal and extra-skeletal morbidity. The patterns of disease seen in bone are the result of changes in calcium, phosphate, parathyroid hormone (PTH), and vitamin D metabolism, as well as the effects of uremia. Standard histological techniques, however, give little insight into the altered biological activity or mechanisms of disease at the cellular level. In order to examine the cellular abnormalities in renal bone disease we have performed a series of in situ hybridization studies to examine renal bone cell expression of genes for PTH receptor (PTHR1), transforming growth factor beta (TGF-beta) and insulin growth factor 1 (IGF-I). PTHR1 mRNA was expressed predominantly by osteoblasts, but also by resorbing osteoclasts, suggesting that these cells may be stimulated directly by PTH. Semi-quantitative analysis of gene expression showed down-regulation of PTHR1 mRNA by osteoblasts in renal bone compared with normal, fracture and Pagetic bone. This may be important in the pathogenesis of skeletal resistance seen in end-stage renal failure, altering the "threshold" at which PTH has its effects on bone cells. TGF-beta and IGF-I mRNA expression was also decreased, suggesting that synthesis of these factors, postulated to be mediators of PTH, is also downregulated.

The distribution of type VI collagen in the developing tissues of the bovine femoral head

Type VI collagen appears central to the maintenance of tissue integrity. In adult articular cartilage, type VI collagen is preferentially localised in the chondron where it may be involved in cell attachment. In actively remodelling developing cartilage, the distribution is less certain. We have used confocal immunohistochemistry and in situ hybridisation to investigate type VI collagen distribution in third trimester bovine proximal femoral epiphyses. In general, type VI collagen immunofluorescence was concentrated in the chondrocyte pericellular matrix, with staining intensity strongest in regions which persist to maturity and weakest in regions that remodel during development. Type VI collagen was also present in cartilage canals. In the growth plate and around the secondary centre of ossification, the intensity of type VI collagen stain rapidly decreased with chondrocyte maturation and was absent at hypertrophy, except where canal branches penetrated the growth plate and stain was retained around the adjacent chondrocytes. In situ hybridisation confirmed the presence of type VI collagen mRNA in cartilage canal mesenchymal cells but the signal was low in chondrocytes, suggesting minimal levels of synthesis and turnover. The results are consistent with a role for type VI collagen in stabilising the extracellular matrix during development.

Effect of ovarian steroid deficiency on oestrogen receptor alpha expression in bone

The mechanism by which oestrogen and hormone replacement therapy (HRT) maintain bone mass in women is still unclear. It has previously been shown that cells of osteoblast lineage in vivo, particularly osteocytes, express oestrogen receptor alpha (ERalpha). Nevertheless, it is still debatable whether oestrogen and the ovarian steroids have a direct affect on osteocytes. If they could regulate osteocyte ERalpha expression, this would be strong evidence for the involvement of these cells in the hormonal regulation of bone mass. This study therefore aimed to compare bone biopsies from women who were replete with ovarian steroids (pre-ovariectomy or post-HRT) with those from the same women when hormone-deficient (post-ovariectomy or pre-HRT) for cellular localization of ERalpha protein or mRNA expression by indirect immunofluorescence, or by in situ hybridization combined with reverse transcriptase-polymerase chain reaction (IS-RT-PCR) respectively. Image analysis showed that proportions of osteocytes positive for immunodetectable ERalpha were higher in hormone-replete than in hormone-deficient women (25+/-SEM 3 per cent, 12+/-SEM 4 per cent, respectively; n=5), with similar but non-statistically significant changes in osteoblasts. This was observed even when HRT was commenced 18 years after menopause. In contrast, grain volume/unit cell area of osteoblast mRNA signal was markedly higher when hormone-deficient (0.055+/-0.01) than when hormone-replete (0.016+/-0.004), with similar but non-significant differences in osteocytes. This preliminary study indicates up-regulation of osteocyte ERalpha protein by ovarian steroids in these patients, which is accompanied by decreased osteoblast ERalpha mRNA expression, providing further evidence for the involvement of osteocytes in the regulation of skeletal structure by ovarian steroids.

Sites of mRNA expression of the cystic fibrosis (CF) and multidrug resistance (MDR1) genes in the human placenta of early pregnancy: No evidence for complementary expression

The aims of this study were to establish the sites of mRNA expression of both the cystic fibrosis (CF) and multidrug resistance (MDR1) genes in human placental sections from early pregnancy (first, early and mid-second trimesters). Riboprobes specific for each of these two genes were generated and used for in situ hybridization experiments. The results show parallel mRNA expression for the CF and MDR1 genes, with the signal detected in the syncytiotrophoblast and cytotrophoblast cells of the placental villi. Other cell types within the villous core were negative. Similar results were obtained at all stages of pregnancy studied.

In situ zymographic localisation of type II collagen degrading activity in osteoarthritic human articular cartilage

OBJECTIVES

Chondrocytic matrix metalloproteinases (MMPs) are believed to be important in osteoarthritic cartilage degradation. The cartilage lesion of osteoarthritis (OA) is focal and often progressive. During its development chondrocytes differentially up and down regulate production of mRNA for individual MMPs. This observation has potential implications for understanding the disease processes that lead to progressive cartilage loss in OA and designing appropriate targeted treatment. The complex regulation of MMP mediated effects means there is a pressing need to establish whether visualisation of MMP mRNA or protein equates to enzyme activity. The technique of in situ zymography (ISZ) offers a way of examining diseased human tissue for in vivo production of an excess of degrading enzyme over inhibitor. The primary objective of this study was to assess, and if positive follow, collagen II degrading activity in cartilage during development of the OA lesion. A secondary objective was to assess whether there was any correlation between sites of collagen II degrading activity and expression of the collagenase (MMP-13), recently implicated in type II collagen degredation in this lesion.

METHODS

Biopsied human normal and osteoarthritic cartilage, showing various degrees of damage, was examined by in situ zymography, with and without enzyme inhibitors, to establish sites of type II collagenase activity. Paired samples were probed for MMP-13 mRNA using 35S-labelled oligonucleotide probes. Comparative analyses were performed.

RESULTS

In situ zymography showed collagen II degrading activity over chondrocytes only in osteoarthritic cartilage. Distribution and amount varied with the extent of cartilage damage and position of chondrocytes, being greatest in deep cartilage and in cartilage lesions where fissuring was occurring. The enzyme causing the degradation behaved as a matrix metalloproteinase. MMP-13 mRNA expression codistributed with the type II collagenase activity.

CONCLUSION

In OA, chondrocytes can degrade type II collagen. The type II collagen degrading activity varies in site and amount as the cartilage lesion progresses and throughout codistributes with MMP-13 mRNA expression.

Expression of the gene encoding the matrix gla protein by mature osteoblasts in human fracture non-unions

BACKGROUND

Osteoblast phenotypic abnormality, namely the expression of collagen type III, has been shown previously in fracture non-union woven bone.

AIMS

To investigate osteoblasts from fracture non-unions for evidence of gene expression of non-collagenous bone matrix proteins that have been implicated in mineralisation, namely matrix gla protein (MGP), osteonectin, osteopontin, and osteocalcin. MGP is a consistent component of bone matrix, but there are no reports of osteoblasts in the skeleton expressing the gene for MGP, and the site of synthesis of skeletal MGP (perhaps the liver) has yet to be determined.

METHODS

Biopsies from normally healing human fractures and non-unions were examined by means of in situ hybridisation, using 35S labelled probes and autoradiography to disclose levels of gene expression.

RESULTS

In normally healing fractures, mature osteoblasts on woven bone were negative for MGP mRNA, but positive for osteonectin, osteopontin, and osteocalcin mRNA molecules. In non-unions, osteoblasts displayed a novel phenotype: they were positive for MGP mRNA, in addition to osteonectin, osteopontin, and osteocalcin mRNA molecules.

CONCLUSIONS

Mature osteoblasts in slowly healing fractures have an unusual phenotype: they express the gene encoding MGP, which indicates that control of osteoblast gene expression in non-unions is likely to be abnormal. This might be of importance in the pathogenesis of non-uniting human fractures, and is of current interest given the emerging status of MGP as an inhibitor of mineralisation.

Osteoblastic differentiation and mRNA analysis of STRO-1-positive human bone marrow stromal cells using primary in vitro culture and poly (A) PCR

Investigation of osteoblast dysfunction in osteoporosis has been hampered by a poor understanding of normal early osteoblast differentiation, due to a relative lack of markers for the earliest cells in the lineage. Attempts to identify such markers have used cultures of animal or immortalized human cells, of uncertain relevance to human biology, or heterogeneous cultures in which genetic variability precludes the isolation of stage-specific genotypic markers. Primary in vitro generation of clonal populations of human bone marrow stromal cells was used in order to overcome these problems. Fibroblast-like stromal cells were isolated from human sternal bone marrow. They showed differentiation to an osteoblastic phenotype when stimulated with dexamethasone (10(-7) M) and fluorescence activated cell analysis demonstrated immunopositivity for STRO-1 (an antibody that recognizes osteoprogenitor stem cells of the colony-forming unit-fibroblastic) in from 8 to 40 per cent of the cells, dependent on time post-harvest. Cells positive for STRO-1 were immunoselected using magnetic activated cell sorting and seeded at low density (10 cells/cm2) to produce clones. Each clone was subpassaged, osteoblastic differentiation stimulated with dexamethasone, and mRMA-extracted at time points post-stimulation (0 h and 1-14 days). A novel poly (A) reverse transcriptase-polymerase chain reaction (RT-PCR) was used to amplify cDNA representative of all transcripts expressed at each time point. Differential gene expression within the amplified cDNA was assessed using 3' end cDNA probes to osteocalcin, osteopontin, and collagen type I (positive), demonstrating the acquisition of an osteoblastic phenotype. Time-specific gene products for early osteoblast differentiation have been generated from primary human cultures, utilizing very low density seeding and poly (A) RT-PCR. These products overcome the problems associated with animal, immortalized or heterogeneous culture and can be used to study normal and altered early osteoblast differentiation, indicating the possibility of using the same system to study other disease states.

Differential patterns of altered bone formation in different bone compartments in established osteoporosis

AIM

To investigate the level of bone formation in the different bone compartments in cases of established osteoporosis, as previous work has concentrated on trabecular bone alone.

METHODS

Bone formation rates were measured histomorphometrically, in the periosteal (P), cortical (C), subcortical (SC), and trabecular (T) compartments in iliac crest biopsies from 159 patients with established osteoporosis. The values were standardised using age and sex matched control data and patterns of differential change determined by analysis of parametric status (increased, normal, reduced).

RESULTS

Mean bone formation was reduced in all four compartments. This was more marked (4.4/4.1 standard deviations below the mean in C/T, v 2.3/0.9 in P/SC) and more frequent (reduced in 81.5%/78.3% in T/C, v 43.3%/44% in P/SC) in the trabecular and cortical compartments than in the periosteal or subcortical bone. Parametric status was equal in trabecular and cortical bone in 85.4% of cases, and in periosteal and subcortical bone in 65.7%, but in all four compartments in only 35.1%, indicating differential alteration of bone formation in the two sets of compartments (T/C v P/SC).

CONCLUSIONS

Altered trabecular bone formation is important in osteoporosis, but there are differential patterns of alteration in the other three compartments, emphasising the presence of different microenvironments in bone; thus the effect on the cortical compartment was similar to that on the trabecular, while the subcortical and periosteal compartments also showed linkage. The linkage between the two pairs was divergent, indicating different control of bone formation, with resultant different patterns of perturbation in osteoporosis.

Immunofluorescent localization of estrogen receptor-alpha in growth plates of rabbits, but not in rats, at sexual maturity

Estrogens are considered essential to the mechanism for closure of epiphyses in both males and females. The mechanism for this, however, is still unclear. It is likely that estrogen acts directly on growth plate chondrocytes, but the localization of the cells expressing the estrogen receptor (ER) has yet to be ascertained. Moreover, in rodents, growth plates remain open well into adult life. Whether the distribution of estrogen target cells in rodent epiphyses differs from that in other species, is also unclear. We therefore compared localization of estrogen target cells (denoted by ER-alpha protein expression) in species in which growth plates fuse, with that in rodents. Thus, we have investigated ER-alpha protein expression in femoral growth plates from male and female rabbits, just at sexual maturity (6 months), when growth plate fusion was just commencing, and in rats of equivalent developmental stage (9 weeks). ER-alpha was detected in undecalcified cryosections by immunofluorescence with 1D5 monoclonal antibody, raised to human ER-alpha; uterine sections were positive controls. ER-alpha-positive cells were localized to the proliferative/early hypertrophic zone of male and female rabbits. By contrast, cells in the similar region of the mature rat growth plate were ER-alpha-negative in both genders, although receptor could be readily detected in uteri of mature female rats. In growth plates of immature male and female rats (6 weeks), however, ER-alpha was clearly expressed by cells of the proliferative/early hypertrophic zone, but was barely detectable in uteri from immature females. Our findings support the view that estrogen may act directly on the growth plate and, in species in which there is epiphyseal fusion, may thus have a role in this process. If ER-alpha expression is lost at sexual maturity, as in rodents, growth plates may remain open into adulthood. Our results also show the changes in ER-alpha expression in growth plates of maturing rats may be opposite to that in the uterus and raise the possibility that receptor expression may be controlled differently in reproductive and skeletal tissues.

The bcl-2 knockout mouse exhibits marked changes in osteoblast phenotype and collagen deposition in bone as well as a mild growth plate phenotype

Histological examination of long bones from 1-day-old bcl-2 knockout and age-matched control mice revealed no obvious differences in length of bone, growth plate architecture or stage of endochondral ossification. In 35-day-old bcl-2 knockout mice that are growth retarded or 'dwarfed'. the proliferative zone of the growth plate appeared slightly thinner and the secondary centres of ossification less well developed than their age-matched wild-type controls. The most marked histological effects of bcl-2 ablation were on osteoblasts and bone. 35-day-old knockout mouse bones exhibited far greater numbers of osteoblasts than controls and the osteoblasts had a cuboidal phenotype in comparison with the normal flattened cell appearance. In addition, the collagen deposited by the osteoblasts in the bcl-2 knockout mouse bone was disorganized in comparison with control tissue and had a pseudo-woven appearance. The results suggest an important role for Bcl-2 in controlling osteoblast phenotype and bone deposition in vivo.