Mineral deposition in the extracellular matrices of vertebrate tissues: identification of possible apatite nucleation sites on type I collagen.
*Calcification; Animals; Apatites/*metabolism; Calcium/metabolism; Collagen Type I/chemistry/*metabolism; Extracellular Matrix/*metabolism; Humans; Microfibrils/chemistry; Models; Molecular; Phosphates/metabolism; Physiologic; Vertebrates/*metabolism
The possible means by which type I collagen may mediate mineralization in normal vertebrate bone, tendon, dentin and cementum as well as in pathological mineral formation are not fully understood. One consideration in this regard is that the structure of the protein is somehow important in binding calcium and phosphate ions in a stereochemical configuration conducive to nucleation of apatite crystals. In the present study, type I collagen, packed in a quarter-staggered arrangement in two dimensions and a quasi-hexagonal model of microfibrillar assembly in three dimensions, has been examined in terms of several of its charged amino acid residues. These included glutamic and aspartic acid, lysine, arginine, hydroxylysine and histidine, whose positions along the three alpha-chain axes of the collagen molecule were determined with respect to each other. It was found that the locations of these residues specified sites uniquely suited as potential apatite nucleation centers following binding of calcium and phosphate ions. From this analysis, it would appear that type I collagen provides a template of charged amino acid residues that dictates ion binding critical to subsequent nucleation events for mineral formation in vertebrate tissues.
Landis William J; Silver Frederick H
Cells, tissues, organs
2009
2009
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1159/000151454" target="_blank" rel="noreferrer noopener">10.1159/000151454</a>
The presence of extracellular matrix alters the chondrocyte response to endoplasmic reticulum stress.
*Stress; Animals; Apoptosis/drug effects; Articular/cytology; Blotting; Cartilage; Cattle; Cells; Chondrocytes/cytology/drug effects/*metabolism; Cultured; DNA-Binding Proteins/genetics/metabolism; Dose-Response Relationship; Drug; Endoplasmic Reticulum/*metabolism; Extracellular Matrix/*metabolism; Glucose/pharmacology; Heat-Shock Proteins/genetics/metabolism; Physiological; Proto-Oncogene Proteins c-bcl-2/genetics/metabolism; Reverse Transcriptase Polymerase Chain Reaction; Thapsigargin/pharmacology; Time Factors; Transcription Factors/genetics/metabolism; Tunicamycin/pharmacology; Western
The objective of this study was to test the hypothesis that extracellular matrix (ECM) would alter the endoplasmic reticulum (ER) stress response of chondrocytes. Chondrocytes were isolated from calf knees and maintained in monolayer culture or suspended in collagen I to form spot cultures (SCs). Our laboratory has shown that bovine chondrocytes form cartilage with properties similar to native cartilage after 2-4 weeks in SCs. Monolayer cultures treated with ER stressors glucose withdrawal (-Glu), tunicamycin (TN), or thapsigargin (TG) up-regulated Grp78 and Gadd153, demonstrating a complete ER stress response. SCs were grown at specific times from 1 day to 6 weeks before treatment with ER stressors. Additionally, SCs grown for 1, 2, or 6 weeks were treated with increasing concentrations of TN or TG. Western blotting of SCs for Grp78 indicated that increased ECM accumulation results in delayed expression; however, Grp78 mRNA is up-regulated in response to ER stressors even after 6 weeks in culture. SCs treated with ER stressors did not up-regulate Gadd153, suggesting that the cells experienced ER stress but would not undergo apoptosis. In fact, SCs undergo apoptosis upon ER stress treatment after 0-1 day of growth; however, after 4 days and to 6 weeks, apoptosis in treated samples was not different than controls. Pro-survival molecules Bcl-2 and Bag-1 were up-regulated upon ER stress in SCs. These results suggest that presence of ECM confers protection from ER stressors. Future studies involving chondrocyte physiology should focus on responses in conditions more closely mimicking the in vivo cartilage environment.
Nugent Ashleigh E; McBurney Denise L; Horton Walter E Jr
Journal of cellular biochemistry
2011
2011-04
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1002/jcb.23025" target="_blank" rel="noreferrer noopener">10.1002/jcb.23025</a>