Targets, models and challenges in osteoarthritis research

Osteoarthritis is a chronic degenerative disorder of the joint and represents one of the most common diseases worldwide. Its prevalence and severity are increasing owing to aging of the population, but treatment options remain largely limited to painkillers and anti-inflammatory drugs, which only provide symptomatic relief. In the late stages of the disease, surgical interventions are often necessary to partially restore joint function. Although the focus of osteoarthritis research has been originally on the articular cartilage, novel findings are now pointing to osteoarthritis as a disease of the whole joint, in which failure of different joint components can occur. In this Review, we summarize recent progress in the field, including data from novel ‘omics’ technologies and from a number of preclinical and clinical trials. We describe different in vitro and in vivo systems that can be used to study molecules, pathways and cells that are involved in osteoarthritis. We illustrate that a comprehensive and multisystem approach is necessary to understand the complexity and heterogeneity of the disease and to better guide the development of novel therapeutic strategies for osteoarthritis

Aberrant Calreticulin Expression in Articular Cartilage of Dio2 Deficient Mice.

OBJECTIVE:To identify intrinsic differences in cartilage gene expression profiles between wild-type- and Dio2-/--mice, as a mechanism to investigate factors that contribute to prolonged healthy tissue homeostasis. METHODS:Previously generated microarray-data (Illumina MouseWG-6 v2) of knee cartilage of wild-type and Dio2 -/- -mice were re-analyzed to identify differential expressed genes independent of mechanical loading conditions by forced treadmill-running. RT-qPCR and western blot analyses of overexpression and knockdown of Calr in mouse chondro-progenitor cells (ATDC5) were applied to assess the direct effect of differential Calr expression on cartilage deposition. RESULTS:Differential expression analyses of articular cartilage of Dio2-/- (N = 9) and wild-type-mice (N = 11) while applying a cutoff threshold (P < 0.05 (FDR) and FC > |1,5|) resulted in 1 probe located in Calreticulin (Calr) that was found significantly downregulated in Dio2-/- mice (FC = -1.731; P = 0.044). Furthermore, overexpression of Calr during early chondrogenesis in ATDC5 cells leads to decreased proteoglycan deposition and corresponding lower Aggrecan expression, whereas knocking down Calr expression does not lead to histological differences of matrix composition. CONCLUSION:We here demonstrate that the beneficial homeostatic state of articular cartilage in Dio2-/- mice is accompanied with significant lower expression of Calr. Functional analyses further showed that upregulation of Calr expression could act as an initiator of cartilage destruction. The consistent association between Calr and Dio2 expression suggests that enhanced expression of these genes facilitate detrimental effects on cartilage integrity

The pathogenesis of pulmonary fibrosis: a moving target

Pulmonary fibrosis is the end stage of many diffuse parenchymal lung diseases. It is characterised by excessive matrix formation leading to destruction of the normal lung architecture and finally death. Despite an exponential increase in our understanding of potentially important mediators and mechanisms, the delineation of primary pathways has proven to be elusive. In this review susceptibility and injurious agents, such as viruses and gastro-oesophageal reflux, and their probable role in initiating disease will be discussed. Further topics that are elaborated are candidate ancillary pathways, including immune mechanisms, oxidative and endoplasmic reticulum stress, activation of the coagulation cascade and the potential role of stem cells. This review will try to provide the reader with an integrated view on the current knowledge and attempts to provide a road map for future research. It is important to explore robust models of overall pathogenesis, reconciling a large number of clinical and scientific observations. We believe that the integration of current data into a "big picture" overview of fibrogenesis is essential for the development of effective antifibrotic strategies. The latter will probably consist of a combination of agents targeting a number of key pathways

Calreticulin expression stratified for treadmill-running and knockout.

<p>Representation of the <i>Calr</i> expression values of all individual samples plotted by genotype-group (Wild-type and <i>Dio2</i>^<i>-/-</i>) and treadmill-running-group (No Run and Run). Showing the significant reduction of <i>Calr</i> expression upon forced treadmill-running in wild-type-mice (<i>P</i> = 0,005) and the absence of change in the knockout-mice. P-values depicted are derived from Student T-Test.</p

Overexpressing <i>Calr</i> resulted in significantly lower Alcian Blue (AB) staining intensities.

<p>Staining intensities of Alcian Blue staining measured with a photospectrometer (620 nm). Values are displayed as the average±SEM, relative to the control sample. Differences were analyzed with Student T-Test ((*) P < 0.05).</p

Expression analyses in <i>Calr</i> overexpressing ATDC5 cells.

<p>RT-qPCR expression of <i>Calr</i>, <i>Dio2 and Acan</i> in ATDC5 cells transfected with either a <i>Calr</i>-containing vector for overexpression (<i>Calr</i>+) or 3 unique 27mer siRNA duplexes, specific for Calr, for knockdown (<i>Calr</i>-). Values of the RT-qPCR are displayed as the average±SEM, normalized for <i>GAPDH</i> expression and relative to the control samples (dashed line). Differences were analyzed with Student T-Test ((*) P < 0.05).</p