Chondrocyte function is regulated partly by mechanical stimulation. Optimal mechanical stimulation maintains articular cartilage integrity, whereas abnormal mechanical stimulation results in development and progression of osteoarthritis (OA). The responses of signal transduction pathways in human articular chondrocytes (HAC) to mechanical stimuli remain unclear. Previous work has shown the involvement of integrins and integrin-associated signaling pathways in activation of plasma membrane apamin-sensitive Ca2+-activated K+ channels that results in membrane hyperpolarization of HAC after 0.33 Hz cyclical mechanical stimulation. To further investigate mechanotransduction pathways in HAC and show that the hyperpolarization response to mechanical stimulation is a result of an integrin-dependent release of a transferable secreted factor, we used this response. Neutralizing antibodies to interleukin 4 (IL-4) and IL-4 receptor α inhibit mechanically induced membrane hyperpolarization and anti–IL-4 antibodies neutralize the hyperpolarizing activity of medium from mechanically stimulated cells. Antibodies to interleukin 1β (IL-1β) and cytokine receptors, interleukin 1 receptor type I and the common γ chain/CD132 (γ) have no effect on me- chanically induced membrane hyperpolarization. Chondrocytes from IL-4 knockout mice fail to show a membrane hyperpolarization response to cyclical mechanical stimulation. Mechanically induced release of the chondroprotective cytokine IL-4 from HAC with subsequent autocrine/paracrine activity is likely to be an important regulatory pathway in the maintenance of articular cartilage structure and function. Finally, dysfunction of this pathway may be implicated in OA.

In previous work we demonstrated that the matrix-forming phenotype of cultured human cells from whole meniscus was enhanced by hypoxia (5% oxygen). Because the meniscus contains an inner region that is devoid of vasculature and an outer vascular region, here we investigate, by gene expression analysis, the separate responses of cells isolated from the inner and outer meniscus to lowered oxygen, and compared it with the response of articular chondrocytes. In aggregate culture of outer meniscus cells, hypoxia (5% oxygen) increased the expression of type II collagen and SOX9 (Sry-related HMG box-9), and decreased the expression of type I collagen. In contrast, with inner meniscus cells, there was no increase in SOX9, but type II collagen and type I collagen increased. The articular chondrocytes exhibited little response to 5% oxygen in aggregate culture, with no significant differences in the expression of these matrix genes and SOX9. In both aggregate cultures of outer and inner meniscus cells, but not in chondrocytes, there was increased expression of collagen prolyl 4-hydroxylase (P4H)α(I) in response to 5% oxygen, and this hypoxia-induced expression of P4Hα(I) was blocked in monolayer cultures of meniscus cells by the hypoxia-inducible factor (HIF)-1α inhibitor (YC-1). In fresh tissue from the outer and inner meniscus, the levels of expression of the HIF-1α gene and downstream target genes (namely, those encoding P4Hα(I) and HIF prolyl 4-hydroxylase) were significantly higher in the inner meniscus than in the outer meniscus. Thus, this study revealed that inner meniscus cells were less responsive to 5% oxygen tension than were outer meniscus cells, and they were both more sensitive than articular chondrocytes from a similar joint. These results suggest that the vasculature and greater oxygen tension in the outer meniscus may help to suppress cartilage-like matrix formation.

The use of stem cells to support tissue repair is facilitated by loading of the therapeutic cells with magnetic nanoparticles (MNPs) enabling magnetic tracking and targeting. Current methods for magnetizing cells use artificial MNPs and have disadvantages of variable uptake, cellular cytotoxicity and loss of nanoparticles on cell division. Here we demonstrate a transgenic approach to magnetize human mesenchymal stem cells (MSCs). MSCs are genetically modified by transfection with the mms6 gene derived from Magnetospirillum magneticum AMB-1, a magnetotactic bacterium that synthesises single-magnetic domain crystals which are incorporated into magnetosomes. Following transfection of MSCs with the mms6 gene there is bio-assimilated synthesis of intracytoplasmic magnetic nanoparticles which can be imaged by MR and which have no deleterious effects on cell proliferation, migration or differentiation. The assimilation of magnetic nanoparticle synthesis into mammalian cells creates a real and compelling, cytocompatible, alternative to exogenous administration of MNPs.

This study investigated whether long-term treatment with antiepileptic drugs (AEDs) had negative effects on statural growth and serum calcium levels in children with epilepsy in Taiwan.

Background: Recent studies provide evidence of roles for integrins in mechanical signalling in bone and cartilage. Integrin signalling is modulated by various mechanisms, including interaction with other transmembrane proteins. We aimed to identify whether one such protein, integrin-associated protein (CD47/IAP), is expressed by chondrocytes and whether it may regulate integrin-dependent mechanotransduction. Methods: Chondrocytes, isolated from macroscopically normal and osteoarthritic articular cartilage of human knee joints, were studied in a resting state or following mechanical stimulation at 0.33 Hz. CD47/IAP expression and associations were confirmed by immunohistology, reverse transcription-polymerase chain reaction, Western blotting, and immunoprecipitation. Roles in mechanotransduction were studied by assessing effects of function-blocking antibodies on a range of electrophysiological, cellular, and molecular responses of primary chondrocytes and responses of CD47/IAP-null cell lines transfected with CD47/IAP. Results: Human articular chondrocytes were shown to express CD47/IAP, predominantly the type 2 isoform. Immunoprecipitation showed association of CD47/IAP with α5 integrin and thrombospondin but not SIRPα (signal-regulatory protein-alpha). The function-blocking anti-CD47/IAP antibody Bric 126 inhibited changes in membrane potential, tyrosine phosphorylation, and elevation of relative levels of aggrecan mRNA induced by mechanical stimulation, whereas in the presence of B6H12, an antibody that has partial agonist activity, a membrane depolarisation rather than a membrane hyperpolarisation response was induced by mechanical stimulation. CD47-null cell lines did not show changes in cell membrane potential following mechanical stimulation. Changes in cell membrane potential following mechanical stimulation were seen when CD47-null cells were transfected with CD47/IAP expression vectors but were not seen following mechanical stimulation of cells transfected with vectors for the extracellular immunoglobulin variable (IgV) domain of CD47/IAP in the absence of the transmembrane and intracellular domains. Conclusion: CD47/IAP is necessary for chondrocyte mechanotransduction. Through interactions with α5β1 integrin and thrombospondin, CD47/IAP may modulate chondrocyte responses to mechanical signals.