Biomedical subjects

Jonathan B Fitzgerald

Publications and source records attributed to Jonathan B Fitzgerald.

4 recordsLinked to original sources

PubMed2006

Shear and compression differentially regulate clusters of functionally related temporal transcription patterns in cartilage tissue.

Chondrocytes are subjected to a variety of biophysical forces and flows during physiological joint loading, including mechanical deformation, fluid flow, hydrostatic pressure, and streaming potentials; however, the role of these physical stimuli in regulating chondrocyte behavior is still being elucidated. To isolate the effects of these forces, we subjected intact cartilage explants to 1-24 h of continuous dynamic compression or dynamic shear loading at 0.1 Hz. We then measured the transcription levels of 25 genes known to be involved in cartilage homeostasis using real-time PCR and compared the gene expression profiles obtained from dynamic compression, dynamic shear, and our recent results on static compression amplitude and duration. Using clustering analysis, we determined that transcripts for proteins with similar function had correlated responses to loading. However, the temporal expression patterns were strongly dependent on the type of loading applied. Most matrix proteins were up-regulated by 24 h of dynamic compression or dynamic shear, but down-regulated by 24 h of 50% static compression, suggesting that cyclic matrix deformation is a key stimulator of matrix protein expression. Most matrix proteases were up-regulated by 24 h under all loading types. Transcription factors c-Fos and c-Jun maximally responded within 1 h to all loading types. Pre-incubating cartilage explants with either a chelator of intracellular calcium or an inhibitor of the cyclic AMP pathway demonstrated the involvement of both pathways in transcription induced by dynamic loading.

Animals↗

PubMed2006

Systems biology and combination therapy in the quest for clinical efficacy.

Combinatorial control of biological processes, in which redundancy and multifunctionality are the norm, fundamentally limits the therapeutic index that can be achieved by even the most potent and highly selective drugs. Thus, it will almost certainly be necessary to use new 'targeted' pharmaceuticals in combinations. Multicomponent drugs are standard in cytotoxic chemotherapy, but their development has required arduous empirical testing. However, experimentally validated numerical models should greatly aid in the formulation of new combination therapies, particularly those tailored to the needs of specific patients. This perspective focuses on opportunities and challenges inherent in the application of mathematical modeling and systems approaches to pharmacology, specifically with respect to the idea of achieving combinatorial selectivity through use of multicomponent drugs.

Drug Therapy, Combination↗

PubMed2005

Mechanical injury of cartilage explants causes specific time-dependent changes in chondrocyte gene expression.

OBJECTIVE: Joint injury in young adults leads to an increased risk of developing osteoarthritis (OA) later in life. This study was undertaken to determine if injurious mechanical compression of cartilage explants results in changes at the level of gene transcription that may lead to subsequent degradation of the cartilage. METHODS: Cartilage was explanted from the femoropatellar groove of newborn calves. Levels of messenger RNA encoding matrix molecules, proteases, their natural inhibitors, transcription factors, and cytokines were assessed in free swelling control cultures as compared with cartilage cultures at 1, 2, 4, 6, 12, and 24 hours after application of a single injurious compression. RESULTS: Gene-expression levels measured in noninjured, free swelling cartilage varied over 5 orders of magnitude. Matrix molecules were the most highly expressed of the genes tested, while cytokines, matrix metalloproteinases (MMPs), aggrecanases (ADAMTS-5), and transcription factors showed lower expression levels. Matrix molecules showed little change in expression after injurious compression, whereas MMP-3 increased approximately 250-fold, ADAMTS-5 increased approximately 40-fold, and tissue inhibitor of metalloproteinases 1 increased approximately 12-fold above the levels in free swelling cultures. Genes typically used as internal controls, GAPDH and beta-actin, increased expression levels approximately 4-fold after injury, making them unsuitable for use as normalization genes in this study. The expression levels of tumor necrosis factor alpha and interleukin-1beta, cytokines known to be involved in the progression of OA, did not change in the chondrocytes after injury. CONCLUSION: Changes in the level of gene expression after mechanical injury are gene specific and time dependent. The quantity of specific proteins may be altered as a result of these changes in gene expression, which may eventually lead to degradation at the tissue level and cause a compromise in cartilage structure and function.

Animals↗

PubMed2004

Mechanical compression of cartilage explants induces multiple time-dependent gene expression patterns and involves intracellular calcium and cyclic AMP.

Chondrocytes are influenced by mechanical forces to remodel cartilage extracellular matrix. Previous studies have demonstrated the effects of mechanical forces on changes in biosynthesis and mRNA levels of particular extracellular matrix molecules, and have identified certain signaling pathways that may be involved. However, the broad extent and kinetics of mechano-regulation of gene transcription has not been studied in depth. We applied static compressive strains to bovine cartilage explants for periods between 1 and 24 h and measured the response of 28 genes using real time PCR. Compression time courses were also performed in the presence of an intracellular calcium chelator or an inhibitor of cyclic AMP-activated protein kinase A. Cluster analysis of the data revealed four main expression patterns: two groups containing either transiently up-regulated or duration-enhanced expression profiles could each be subdivided into genes that did or did not require intracellular calcium release and cyclic AMP-activated protein kinase A for their mechano-regulation. Transcription levels for aggrecan, type II collagen, and link protein were up-regulated approximately 2-3-fold during the first 8 h of 50% compression and subsequently down-regulated to levels below that of free-swelling controls by 24 h. Transcription levels of matrix metalloproteinases-3, -9, and -13, aggrecanase-1, and the matrix protease regulator cyclooxygenase-2 increased with the duration of 50% compression 2-16-fold by 24 h. Thus, transcription of proteins involved in matrix remodeling and catabolism dominated over anabolic matrix proteins as the duration of static compression increased. Immediate early genes c-fos and c-jun were dramatically up-regulated 6-30-fold, respectively, during the first 8 h of 50% compression and remained up-regulated after 24 h.

ADAM Proteins↗