This study addressed the hypothesis that duration and magnitude of applied intermittent hydrostatic pressure (IHP) are critical parameters in regulation of normal human articular chondrocyte aggrecan and type I1 collagen expression. Articular chondrocytes were isolated from knee cartilage and maintained as primary, high-density monolayer cultures. IHP was applied at magnitudes of 1, 5 and 10 MPa at I Hz for durations of either 4 h per day for one day (4 x 1) or 4 h per day for four days (4 x 4). Total cellular RNA was isolated and analyzed for aggrecan and type I1 collagen mRNA signal levels using specific primers and reverse transcription polymerase chain reaction (RT-PCR) nested with beta-actin primers as internal controls. With a 4 x 1 loading regimen, aggrecan mRNA signal levels increased 1.3-and 1.5-fold at 5 and 10 MPa, respectively, relative to beta-actin mRNA when compared to unloaded cultures. Changing the duration of loading to a 4 x 4 regimen increased aggrecan mRNA signal levels by 1.4-, 1.8-and 1.9-fold at loads of 1, 5 and 10 MPa, respectively. In contrast to the effects of IHP on aggrecan, type I1 collagen mRNA signal levels were only upregulated at loads of 5 and 10 MPa with the 4 x 4 loading regimen. Analysis of cell-associated protein by western blotting confirmed that IHP increased aggrecan and type I1 collagen in chondrocyte extracts. These data demonstrate that duration and magnitude of applied IHP differentially alter chondrocyte matrix protein expression. The results show that IHP provides an important stimulus for increasing cartilage matrix anabolism and may contribute to repair and regeneration of damaged or diseased cartilage.
Whether non-steroidal anti-inflammatory drug (NSA1D)-induced suppression of bone ingrowth is due to cyclooxygenase-1 (COX-I ) inhibition, cyclooxygenase-2 (COX-?) inhibition, or through a yet unidentified pathway is unknown. In this study, the effects of a non-specific COX-1 and COX-2 inhibitor, versus a specific COX-2 inhibitor on bone ingrowth and tissue differentiation are examined in vivo. Harvest chambers were implanted unilaterally in the tibiae of eight mature, New Zealand white rabbits. After a 6-week period for osseointegration of the chamber, the following oral treatments were given for 4 weeks each, followed by a harvest in each case: drinking water with no NSAID (control l), Naproxen sodium-a COX-1 and COX-2 non-specific inhibitor at a dose of 110 mglkglday in the drinking water, drinking water with no NSAID (control 2), and Rofecoxib-a COX-2 inhibitor at a dose of 12.5 mglday inserted directly into the rabbit's mouth. Harvested specimens were snap frozen, cut into serial 6 prn sections and stained with hematoxylin and eosin for general morphological characterization, and alkaline phosphatase (osteoblast marker). Sections were also processed for immunoperoxidase staining using monoclonal antibodies to identify cells expressing the vitronectin receptor (osteoclast-like cells). With drinking water alone, the percentage of bone ingrowth averaged 24.8 f 2.9% and 29.9 f 4.5% respectively. Naproxen sodium in the drinking water and oral Rofecoxib decreased bone ingrowth significantly (1 5.9 f 3.3%, p = 0.031 and 18.5 i 2.4%, p = 0.035 compared to drinking water respectively). Both Naproxen sodium ( p = 0.016) and Rofecoxib ( p = 0.02) decreased the number of CD51 positive osteoclast-like cells per section compared with drinking water alone. Rofecoxib decreased the area of osteoblasts per section area ( p = 0.014) compared to controls, although the value for Naproxen sodium did not reach statistical significance. The results of the present study suggest that bone formation is suppressed by oral administration of an NSAID which contains a COX-' inhibitor. COX-2 inhibitors currently taken for arthritis and other conditions may potentially delay fracture healing and bone ingrowth.
Outer mitochondrial membrane cytochrome b 5 (OMb), which is an isoform of cytochrome b 5 (cyt b 5 ) in the endoplasmic reticulum, is a typical tail-anchored protein of the outer mitochondrial membrane. We cloned cDNA containing the complete amino acid sequence of OMb and found that the protein has no typical structural feature common to the mitochondrial targeting signal at the amino terminus. To identify the region responsible for the mitochondrial targeting of OMb, various mutated proteins were expressed in cultured mammalian cells, and the subcellular localization of the expressed proteins was analyzed. The deletion of more than 11 amino acid residues from the carboxyl-terminal end of OMb abolished the targeting of the protein to the mitochondria. When the carboxyl-terminal 10 amino acids of OMb were fused to the cyt b 5 that was previously deleted in the corresponding 10 residues, the fused protein localized in the mitochondria, thereby indicating that the carboxyl-terminal 10 amino acid residues of OMb have sufficient information to transport OMb to the mitochondria. The replacement of either of the two positively charged residues within the carboxyl-terminal 10 amino acids by alanine resulted in the transport of the mutant proteins to the endoplasmic reticulum. The mutant cyt b 5 , in which the acidic amino acid in its carboxyl-terminal end was replaced by basic amino acid, could be transported to the mitochondria. It would thus seem that charged amino acids in the carboxylterminal portion of these proteins determine their locations in the cell.
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