Decreased levels of nucleotide pyrophosphatase phosphodiesterase 1 are associated with cartilage calcification in osteoarthritis and trigger osteoarthritic changes in mice.

OBJECTIVE: To analyse the function of nucleotide pyrophosphatase phosphodiesterase (NPP1), a member of the pyrophosphate pathway, in osteoarthritis (OA). METHODS: mRNA expression of NPP1, ANK ankylosing protein and tissue non-specific alkaline phosphatase was assessed by quantitative PCR. NPP1 protein levels were analysed in mouse and human cartilage samples. Bone metabolism was analysed by F18-positron emission tomography-scanning and µCT in ttw/ttw mice. Ttw/ttw mice are mice carrying a loss-of-function mutation in NPP1. Calcification of articular cartilage was assessed using von Kossa staining and OA severity using the Mankin score. Cartilage remodelling was investigated by type X collagen immunohistochemistry. RESULTS: Expression of NPP1, but not the other members of this pathway, inversely correlated with cartilage calcification and OA severity in mouse and humans. Proinflammatory cytokines downregulated the expression of NPP1, demonstrating an influence of inflammation on matrix calcification. Ttw/ttw mutant mice, carrying a loss-of-function mutation in NPP1, exhibit increased bone formation process in joints compared with wild types. Ttw/ttw mice also developed spontaneous OA-like changes, evaluated by histological analysis and in vivo imaging. Ectopic calcifications were associated with increased expression of collagen X in the cartilage. CONCLUSION: The authors conclude that OA is characterised by the reactivation of molecular signalling cascades involving proinflammatory cytokines, thereby regulating the pyrophosphate pathway which consequently leads to cartilage ossification, at least in part resembling endochondral ossification.

High density micromass cultures of a human chondrocyte cell line: a reliable assay system to reveal the modulatory functions of pharmacological agents.

Osteoarthritis is a highly prevalent and disabling disease for which we do not have a cure. The identification of suitable molecular targets is hindered by the lack of standardized, reproducible and convenient screening assays. Following extensive comparisons of a number of chondrocytic cell lines, culture conditions, and readouts, we have optimized an assay utilizing C-28/I2, a chondrocytic cell line cultured in high-density micromasses. Utilizing molecules with known effects on cartilage (e.g. IL-1ß, TGFß1, BMP-2), we have exploited this improved protocol to (i) evoke responses characteristic of primary chondrocytes; (ii) assess the pharmacodynamics of gene over-expression using non-viral expression vectors; (iii) establish the response profiles of known pharmacological treatments; and (iv) investigate their mechanisms of action. These data indicate that we have established a medium-throughput methodology for studying chondrocyte-specific cellular and molecular responses (from gene expression to rapid quantitative measurement of sulfated glycosaminoglycans by Alcian blue staining) that may enable the discovery of novel therapeutics for pharmacological modulation of chondrocyte activation in osteoarthritis.

Synthesis of picosecond pulses by spectral compression and shaping of femtosecond pulses in engineered quadratic nonlinear media.

Narrow-bandwidth picosecond pulses of predetermined spectral and temporal shapes are generated with high efficiency by frequency conversion of femtosecond pulses in lithium tantalate crystals with engineered quasi-phase-matching structures. We give examples of the synthesis of Gaussian and super-Gaussian picosecond pulses and also of a pair of synchronized phase-coherent picosecond pulses with a predetermined carrier-frequency difference.

Higher-order effects in bandwidth-limited soliton propagation in optical fibers.

By means of numerical studies and soliton perturbation theory we examine the effects of higher-order linear and nonlinear terms in bandwidth-limited amplified soliton propagation. We show that these effects are responsible for strong reductions of soliton-soliton interaction in such systems.