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David A Young

Publications and source records attributed to David A Young.

At least 19 recordsLinked to original sources
PubMed2026

Molecular dynamics simulations of positively selected codons in FcγRI reveal novel biochemical binding properties.

FcγRI is a high-affinity receptor for IgG, associated with autoimmune disease pathology and determines clinical responses to antibody-based immunotherapies. FcγRI has a complex evolutionary history that is not fully understood, and to address this we explored signatures of positive selection in the receptor's functional gene, FCGR1A, using codon-based selection tests on aligned 1-1 orthologous sequences from placental mammals (n = 32). Signatures of positive selection have occurred at several locations within the gene, with two sites (H148 (M2a ω 0.997 & M8 ω = 0.993)) and (W149 (M2a ω = 0.999 & M8 ω = 1.000)) exhibiting highest posterior probabilities, suggesting strong evidence of positive selection; these positions are known to form one of the FcγRI-IgG binding interfaces. We employed ancestral reconstruction to statistically infer prior codon sequences at these sites and identified ancestral H148P and W149R codons at different nodes in the phylogeny. Employing molecular dynamics simulations, we determined how evolutionary changes at these sites may have influenced the binding of FcγRI-IgG of modern-day Homo sapiens. Measuring RMSD, free energy, radius of gyration, hydrogen bond formation, and analyzing free energy landscapes, we demonstrate that structural instability between mutant structures vs the WT counterpart; however, overall binding potential increases at position 148, yet decreases at 149 in potential. H148P protonation at physiological pH remains similar, yet during acidotic calculations, protonation is likely reduced, with predicted reduction in affinity for IgG. While ancestral W149R substitutions demonstrate an implication for electron conjugation. Examining key sites at this binding FcγRI-IgG interface, our data demonstrate that these two codons have evolved in humans to be relatively insensitive to shifts in pH promoting a more stable interaction with the Fc portion of IgG during diseases that promote acidosis.

Receptors, IgG↗
PubMed2007

Acetylation in the regulation of metalloproteinase and tissue inhibitor of metalloproteinases gene expression.

Together, the matrix metalloproteinases (MMPs) are capable of degrading every component of the extracellular matrix (ECM). Besides degradation of the ECM, MMPs release bioactive molecules from the matrix or cell surface and play important role in tissue repair after injury, development and in a number of pathologies including arthritis and cancer metastasis. Small molecules that inhibit a broad spectrum of metalloproteinases have not proved useful in the treatment of various diseases, probably due to the diverse roles of this large family of enzymes. An alternative therapeutic approach for a number of pathologies is to modulate the expression of specific metalloproteinase genes. Acetylation represents a recently identified covalent protein modification that is strongly implicated in transcriptional regulation. Histones were the first proteins demonstrated to show variable acetylation leading to gene activation. Subsequently, a large number of molecules including structural proteins, intracellular signaling molecules, nuclear membrane receptors and transcription factors were shown to be acetylated. Acetylation, like phosphorylation, is a reversible modification. Acetyl groups are added by a family of histone acetyl transferase enzymes (HATs) and are removed by histone deacetylases (HDACs). Inhibitors of HDACs (HDACi) have potent anti-proliferative and pro-apoptotic activities in cancer cells and may be used as cancer therapeutics. In this review, we examine the impact of changes in acetylation on the expression of the MMPs and their inhibitors (tissue inhibitors of metalloproteinases, TIMPs). We discuss the suggestion that HDACi may act in a dual fashion: selectively decreasing cancer cell viability and reducing metastatic potential by decreasing stromal cell expression of specific metalloproteinases. Furthermore, we consider the possibility that selective HDACi have a potential as anti-inflammatory agents and in a range of degradative diseases such as arthritis.

Acetylation↗
PubMed2007

Collagenase gene regulation by pro-inflammatory cytokines in cartilage.

The essentially irreversible degradation of articular cartilage collagen represents a key, rate-limiting process in arthritic diseases. This process is typically initiated as a consequence of an inflammatory response, and if left unchecked ultimately leads to loss of joint function, pain, disability and a need for joint replacement surgery. Although we have identified the enzymes capable of effecting such destructive proteolysis, and considerable evidence indicates that tumour necrosis factor alpha and interleukin-1 are major pro-inflammatory mediators in joint destruction, we still know relatively little about how these mediators regulate collagenase gene expression in chondrocytes. Inflammatory arthritis has long been considered to be synovium-driven but compelling data now also implicate the chondrocyte, the sole cell type present in cartilage, as an active player in the destructive process. An understanding of how different cytokines interact, and how the pathways they activate cross-talk will not only provide important new insight into the mechanisms of joint destruction but also identify new targets for therapeutic intervention.

Animals↗
PubMed2006

Rac upregulates tissue inhibitor of metalloproteinase-1 expression by redox-dependent activation of extracellular signal-regulated kinase signaling.

The Rho-like GTPase Rac regulates distinct actin cytoskeleton changes required for adhesion, migration and invasion of cells. Tiam1 specifically activates Rac, and Rac has been shown to affect several signaling pathways in a partly cell-type-specific manner. Recently, we demonstrated that Rac activation inhibits Matrigel invasion of human carcinoma cells by transcriptional upregulation of tissue inhibitor of metalloproteinase-1. The purpose of the present study was to identify key mediators of Tiam1/Rac-induced tissue inhibitor of metalloproteinase-1 expression. Mutational analysis of the human tissue inhibitor of metalloproteinase-1 promoter revealed a major role for a distinct activating protein-1 site at -92/-86 and a minor role for an adjacent polyoma enhancer A3 site. Moreover, Rac activation induced the generation of reactive oxygen species and subsequent reactive oxygen species-dependent activation of extracellular signal-regulated kinase 1,2. In contrast, c-Jun N-terminal kinase and p38 mitogen-activated protein kinase activities were not affected. In line with this, Tiam1/Rac-induced tissue inhibitor of metalloproteinase-1 expression as well as Tiam1/Rac-induced binding of nuclear extracts to the activating protein-1 site at -92/-86 were inhibited by catalase and by specific inhibitors of the extracellular signal-related kinase-1,2 activators, mitogen-activated protein kinase kinase-1 and mitogen-activated protein kinase kinase-2 (PD098059, U0126). In conclusion, Rac-induced transcriptional upregulation of tissue inhibitor of metalloproteinase-1 is mediated by reactive oxygen species-dependent activation of extracellular signal-related kinase-1,2 and by transcription factors of the activating protein-1 family.

Antineoplastic Agents↗
PubMed2006

Fibroblast activation protein alpha is expressed by chondrocytes following a pro-inflammatory stimulus and is elevated in osteoarthritis.

Arthritis is characterised by the proteolytic degradation of articular cartilage leading to a loss of joint function. Articular cartilage is composed of an extracellular matrix of proteoglycans and collagens. We have previously shown that serine proteinases are involved in the activation cascades leading to cartilage collagen degradation. The aim of this study was to use an active-site probe, biotinylated fluorophosphonate, to identify active serine proteinases present on the chondrocyte membrane after stimulation with the pro-inflammatory cytokines IL-1 and oncostatin M (OSM), agents that promote cartilage resorption. Fibroblast activation protein alpha (FAPalpha), a type II integral membrane serine proteinase, was identified on chondrocyte membranes stimulated with IL-1 and OSM. Real-time PCR analysis shows that FAPalpha gene expression is up-regulated by this cytokine combination in both isolated chondrocytes and cartilage explant cultures and is significantly higher in cartilage from OA patients compared to phenotypically normal articular cartilage. Immunohistochemistry analysis shows FAPalpha expression on chondrocytes in the superficial zone of OA cartilage tissues. This is the first report demonstrating the expression of active FAPalpha on the chondrocyte membrane and elevated levels in cartilage from OA patients. Its cell surface location and expression profile suggest that it may have an important pathological role in the cartilage turnover prevalent in arthritic diseases.

Animals↗
PubMed2006

Ocular abnormalities in Apert syndrome: genotype/phenotype correlations with fibroblast growth factor receptor type 2 mutations.

BACKGROUND/PURPOSE: Apert syndrome, a disorder of craniosynostosis, syndactyly, and other craniofacial malformations, is caused by point mutations (Ser252Trp or Pro253Arg) in the fibroblast growth factor receptor 2 gene. This study's goal was to determine ophthalmic phenotype/genotype correlations in patients with either mutation. METHODS: A retrospective chart review of demographic and ophthalmologic data was performed for 18 children carrying either the S252W (11) or the P253R (7) mutation. Fisher exact tests were performed to determine significance of variable phenotypes between the two mutation groups. RESULTS: In the P253R group, 85% had strabismus (14% required surgery), 71% had ptosis, 43% had amblyopia, 14% had nasolacrimal duct obstruction, 14% had myopia, 14% had hyperopia, and 14% had astigmatism. In the S252W group, 91% had strabismus (64% required surgery), 73% had ptosis, 73% had amblyopia, 100% had nasolacrimal duct obstruction, 36% had myopia, 9% had hyperopia, and 82% had astigmatism. Overall, S252W and P253R groups showed significantly different numbers of patients with strabismus requiring surgery (p = 0.039), superior rectus muscle underaction (p = 0.024), nasolacrimal duct obstruction (p = 0.0002), and astigmatism (p = 0.005). CONCLUSIONS: Compared with patients with the P253R mutation, Apert syndrome patients with the S252W mutation may have more severe ocular phenotypes with a higher likelihood of developing strabismus, especially vertical deviation. They also are more likely to develop astigmatic refractive errors and tearing secondary to nasolacrimal system anomalies.

Acrocephalosyndactylia↗
PubMed2006

Chronic hypoxia augments uterine artery distensibility and alters the circumferential wall stress-strain relationship during pregnancy.

Pregnancy-associated increases in uterine artery (UA) blood flow are due, in part, to vasoactive and growth-related changes that enlarge UA diameter. Although active and passive mechanical factors can contribute to this enlargement, their role is less well understood. We hypothesized that pregnancy increased UA distensibility and/or decreased myogenic tone. Given the fetal growth restriction and lower UA flow seen under chronic hypoxia, we further hypothesized that chronic hypoxia opposed these normal active and passive mechanical changes. UA were isolated from 12 nonpregnant and 12 pregnant (0.7 gestation) guinea pigs housed under normoxia or chronic hypoxia (3,960 m) and studied by pressure myography. Pregnancy increased UA diameter similarly under normoxia and hypoxia. Although chronic hypoxia raised resting tone in UA from nonpregnant guinea pigs to approximately 20% and tone was greater in preconstricted pregnant chronically hypoxic vs. normoxic UA (both P<0.01), there was an absence of myogenic response (i.e., an increase in tone with rising pressure) in all groups. Pregnancy increased UA distensibility 1.5-fold but did not change stiffness or the stress-strain relationship. Compared with vessels from normoxic pregnant animals, hypoxic pregnancy raised UA distensibility fourfold, decreased stiffness (rate constant b=3.80+/-1.06 vs. 8.92+/-1.25, respectively, P<0.01), lowered elastin by 50%, and shifted the stress-strain relationship upward such that four times as much strain was present at a given stress. We concluded that increased distensibility and low myogenic tone contribute to enlarging UA diameter and raising UA blood flow during pregnancy. Chronic hypoxia exaggerates the rise in distensibility and alters the stress-strain relationship in ways that may provoke vascular injury.

Animals↗
PubMed2006

Metalloproteinase and inhibitor expression profiling of resorbing cartilage reveals pro-collagenase activation as a critical step for collagenolysis.

Excess proteolysis of the extracellular matrix (ECM) of articular cartilage is a key characteristic of arthritis. The main enzymes involved belong to the metalloproteinase family, specifically the matrix metalloproteinases (MMPs) and a group of proteinases with a disintegrin and metalloproteinase domain with thrombospondin motifs (ADAMTS). Chondrocytes are the only cell type embedded in the cartilage ECM, and cell-matrix interactions can influence gene expression and cell behaviour. Thus, although the use of monolayer cultures can be informative, it is essential to study chondrocytes encapsulated within their native environment, cartilage, to fully assess cellular responses. The aim of this study was to profile the temporal gene expression of metalloproteinases and their endogenous inhibitors, the tissue inhibitors of metalloproteinases (TIMPs), reversion-inducing cysteine-rich protein with Kazal motifs (RECK), and alpha2-macroglobulin (alpha2M), in actively resorbing cartilage. The addition of the pro-inflammatory cytokine combination of interleukin-1 (IL-1) + oncostatin M (OSM) to bovine nasal cartilage induces the synthesis and subsequent activation of pro-metalloproteinases, leading to cartilage resorption. We show that IL-1+OSM upregulated the expression of MMP-1, -2, -3, -9, 12, -13, -14, TIMP-1, and ADAMTS-4, -5, and -9. Differences in basal expression and the magnitude of induction were observed, whilst there was no significant modulation of TIMP-2, -3, RECK, or ADAMTS-15 gene expression. IL-1+OSM downregulated MMP-16,TIMP-4, and alpha2M expression. All IL-1+OSM-induced metalloproteinases showed marked upregulation early in the culture period, whilst inhibitor expression was reduced throughout the stimulation period such that metalloproteinase production would be in excess of inhibitors. Moreover, although pro-collagenases were upregulated and synthesized early (by day 5), collagenolysis became apparent later with the presence of active collagenases (day 10) when inhibitor levels were low. These findings indicate that the activation cascades for pro-collagenases are delayed relative to collagenase expression, further confirm the coordinated regulation of metalloproteinases in actively resorbing cartilage, and support the use of bovine nasal cartilage as a model system to study the mechanisms that promote cartilage degradation.

ADAM Proteins↗
PubMed2005

MRI-negative bucket-handle tears of the lateral meniscus in athletes: a case series.

Magnetic resonance imaging (MRI) is the most widely used non-invasive test for assessing intra-articular injuries of the knee. It has been suggested that a negative MRI can be useful in avoiding the need for diagnostic arthroscopy in cases where clinical examination is equivocal. However, the sensitivity and specificity of MRI is not 100%, particularly for tears of the lateral meniscus. Furthermore, a false negative MRI scan may result in premature return to play in athletes, resulting in increased risk of further damage to a torn meniscus. To illustrate this issue, we present a case series of eight elite athletes who all presented with mechanical knee symptoms and where MRI scans revealed no significant intra-articular pathology. Five of the athletes were allowed to return to sport on the basis of a negative MRI. All patients were subsequently found to have a bucket-handle tear of their lateral meniscus at arthroscopy. Two independent, experienced musculoskeletal radiologists were asked to review the MRI films without being given any clinical history of the cases. Although injuries to the popliteus tendon were noted in two of the athletes who had sustained a recent acute injury to their knee, no meniscal tears were identified. Thus arthroscopy remains the gold standard for the assessment and management of high-demand patients with a clinical suspicion of meniscal pathology.

Adolescent↗
PubMed2005

Histone deacetylase inhibitors modulate metalloproteinase gene expression in chondrocytes and block cartilage resorption.

Cartilage destruction in the arthritides is thought to be mediated by two main enzyme families: the matrix metalloproteinases (MMPs) are responsible for cartilage collagen breakdown, and enzymes from the ADAMTS (a disintegrin and metalloproteinase domain with thrombospondin motifs) family mediate cartilage aggrecan loss. Many genes subject to transcriptional control are regulated, at least in part, by modifications to chromatin, including acetylation of histones. The aim of this study was to examine the impact of histone deacetylase (HDAC) inhibitors on the expression of metalloproteinase genes in chondrocytes and to explore the potential of these inhibitors as chondroprotective agents. The effects of HDAC inhibitors on cartilage degradation were assessed using a bovine nasal cartilage explant assay. The expression and activity of metalloproteinases was measured using real-time RT-PCR, western blot, gelatin zymography, and collagenase activity assays using both SW1353 chondrosarcoma cells and primary human chondrocytes. The HDAC inhibitors trichostatin A and sodium butyrate potently inhibit cartilage degradation in an explant assay. These compounds decrease the level of collagenolytic enzymes in explant-conditioned culture medium and also the activation of these enzymes. In cell culture, these effects are explained by the ability of HDAC inhibitors to block the induction of key MMPs (e.g. MMP-1 and MMP-13) by proinflammatory cytokines at both the mRNA and protein levels. The induction of aggrecan-degrading enzymes (e.g. ADAMTS4, ADAMTS5, and ADAMTS9) is also inhibited at the mRNA level. HDAC inhibitors may therefore be novel chondroprotective therapeutic agents in arthritis by virtue of their ability to inhibit the expression of destructive metalloproteinases by chondrocytes.

Animals↗
PubMed2005

A randomized-controlled trial of prophylactic hydrocortisone supplementation for the prevention of hypotension in extremely low birth weight infants.

OBJECTIVE: Extremely low birth weight (ELBW) infants are at risk for hypotension. Abnormal adrenal function may play a role in the pathogenesis of hypotension, and therefore, the administration of hydrocortisone (HC) may be an effective treatment for hypotension in some infants. However, the efficacy of prophylactic HC to prevent the use of vasopressors for a defined hypotensive state has not been studied. We conducted a randomized-controlled trial to determine the potential role on adrenal insufficiency in early neonatal hypotension and to determine the effectiveness of prophylactic HC in reducing treatment of hypotension in ELBW infants. STUDY DESIGN: Infants were assigned to receive either HC or placebo within the first 3 hours of life. Therapy was continued for 5 days. The presence of hypotension was based on an operational definition and treatment with vasopressors (VP) was standardized based on an a priori protocol. RESULTS: A total of 34 patients were enrolled. Baseline characteristics were similar between groups. Of the HC group 25% received VP at 24 hours of age compared to 44% of the placebo group. On day of life 2, only 7% of the HC group received VP compared to 39% of the placebo group (p<0.05). CONCLUSION: Prophylactic treatment with HC reduces the incidence of hypotension, defined by treatment with VP, among ELBW infants during the first 2 days of life. However, the mounting evidence that prophylactic administration of glucocorticoids in the first days of life is harmful to ELBW infants makes HC prophylaxis unwise until the efficacy of treatment relative to safety can be clearly established.

Adrenal Insufficiency↗
PubMed2005

Intra-aortic balloon pumping: does posture matter?

BACKGROUND: The effect of the posture of semirecumbent patients on the hemodynamics and performance of intra-aortic balloon (IAB) were studied in vivo and in vitro. METHODS: An IAB was inserted into a glass tube filled with saline, fully inflated and deflated using an intra-aortic balloon pump (IABP). Three successive cycles were filmed at 125 frames/s with the tube positioned at various angles between 0 degrees (horizontal) and 90 degrees (vertical). Pressure and flow were measured distal to both ends of the balloon. In parallel, coronary left anterior descending (LAD) flow velocity and aortic pressure were recorded in 6 patients using IABP, postcardiac surgery in the intensive care unit. Recordings were made when the patient was lying horizontally (recumbent) and when the patient's torso was inclined at 30 degrees to the horizontal (semirecumbent). RESULTS: With the tube horizontal, the inflation was effectively uniform along the length of the balloon. At all other angles, the higher end of the balloon inflated first, and mean pressure and flow measured distal to the higher end of the balloon were less than those measured at 0 degrees . Mean aortic pressure and LAD flow decreased by 10 +/- 2% (P = 0.001) and 15 +/- 3% (P = 0.001), respectively, when the patient was semirecumbent compared to when the patient was recumbent. CONCLUSION: The decreased mean aortic pressure and LAD flow velocity suggests that unless patients using IABP are required to be semirecumbent, it may be best to position them horizontally to gain the full benefits of balloon counter pulsation to the coronary circulation.

Aged↗
PubMed2005

Differential effects of histone deacetylase inhibitors on phorbol ester- and TGF-beta1 induced murine tissue inhibitor of metalloproteinases-1 gene expression.

Expression of the tissue inhibitor of metalloproteinases-1 (Timp-1) gene can be induced by either phorbol myristate acetate (PMA) or transforming growth factor beta1 (TGF-beta1), although the signalling pathways involved are not clearly defined. Canonically, histone deacetylase inhibitors (HDACi) such as trichostatin A (TSA) or sodium butyrate (NaB) increase total cellular histone acetylation and activate expression of susceptible genes. Remarkably, PMA and TGF-beta1 stimulation of Timp-1 show a differential response to TSA or NaB. TSA or NaB potentiate PMA-induced Timp-1 expression but repress TGF-beta1-induced Timp-1 expression. The repression of TGF-beta1-induced Timp-1 by TSA was maximal at 5 ng.mL(-1), while for the superinduction of PMA-induced Timp-1 expression, the maximal dose is > 500 ng x mL(-1) TSA. A further HDACi, valproic acid, did not block TGF-beta1-induced Timp-1 expression, demonstrating that different HDACs impact on the induction of Timp-1. For either PMA or TGF-beta1 to induce Timp-1 expression, new protein synthesis is required, and the induction of AP-1 factors closely precedes that of Timp-1. The effects of the HDACi can be reiterated in transient transfection using Timp-1 promoter constructs. Mutation or deletion of the AP-1 motif (-59/-53) in the Timp-1 promoter diminishes PMA-induction of reporter constructs, however, the further addition of TSA still superinduces the reporter. In c-Jun-/- cells, PMA still stimulates Timp-1 expression, but TSA superinduction is lost. Transfection of a series of Timp-1 promoter constructs identified three regions through which TSA superinduces PMA-induced Timp-1 and we have demonstrated specific protein binding to two of these regions which contain either an avian erythroblastosis virus E26 (v-ets) oncogene homologue (Ets) or Sp1 binding motif.

Animals↗
PubMed2004

Expression of metalloproteinases and inhibitors in the differentiation of P19CL6 cells into cardiac myocytes.

P19CL6 are a clonal derivative of P19 embryonal carcinoma cells, a euploid, multipotent mouse cell line, that differentiate efficiently into cardiac myocytes, with spontaneous beating evident within 10 days, following DMSO treatment. Using real-time quantitative RT-PCR we have profiled the expression of the complete matrix metalloproteinase and tissue inhibitor of metalloproteinase gene families during P19CL6 differentiation to cardiac myocytes. The genes subdivide into eight groups based upon their expression profile. Their expression was both qualitatively and quantitatively highly homologous to that seen during mouse heart development.

Animals↗
PubMed2004

Expression profiling of metalloproteinases and their inhibitors in cartilage.

OBJECTIVE: To profile the expression of all known members of the matrix metalloproteinase (MMP), ADAMTS, and tissue inhibitor of metalloproteinases (TIMP) gene families in normal cartilage and cartilage from patients with osteoarthritis (OA). METHODS: Human cartilage was obtained from femoral heads at joint replacement for OA or following fracture to the femoral neck. Total RNA was purified, and gene expression was assayed using quantitative real-time polymerase chain reaction. RESULTS: Several members of the above gene families were regulated in OA. Genes that showed increased expression in OA were MMP13, MMP28, and ADAMTS16 (all at P < 0.001), MMP9, MMP16, ADAMTS2, and ADAMTS14 (all at P < 0.01), and MMP2, TIMP3, and ADAMTS12 (all at P < 0.05). Genes with decreased expression in OA were MMP1, MMP3, and ADAMTS1 (all at P < 0.001), MMP10, TIMP1, and ADAMTS9 (all at P < 0.01), and TIMP4, ADAMTS5, and ADAMTS15 (all at P < 0.05). Correlation analysis revealed that groups of genes across the gene families were coexpressed in cartilage. CONCLUSION: This is the first comprehensive expression profile of all known MMP, ADAMTS, and TIMP genes in cartilage. Elucidation of patterns of expression provides a foundation with which to understand mechanisms of gene regulation in OA and potentially to refine the specificity of antiproteolytic therapies.

ADAM Proteins↗
PubMed2004

Sulindac improves memory and increases NMDA receptor subunits in aged Fischer 344 rats.

Inflammatory processes in the central nervous system are thought to contribute to Alzheimer's disease (AD). Chronic administration of nonsteroidal anti-inflammatory drugs (NSAIDs) decreases the incidence of Alzheimer's disease. There are very few studies, however, on the cognitive impact of chronic NSAID administration. The N-methyl-d-aspartate (NMDA) receptor is implicated in learning and memory, and age-related decreases in the NMDA NR2B subunit correlate with memory deficits. Sulindac, an NSAID that is a nonselective cyclooxygenase (COX) inhibitor was chronically administered to aged Fischer 344 rats for 2 months. Sulindac, but not its non-COX active metabolite, attenuated age-related deficits in learning and memory as assessed in the radial arm water maze and contextual fear conditioning tasks. Sulindac treatment also attenuated an age-related decrease in the NR1 and NR2B NMDA receptor subunits and prevented an age-related increase in the pro-inflammatory cytokine, interleukin 1beta (IL-1beta), in the hippocampus. These findings support the inflammation hypothesis of aging and have important implications for potential cognitive enhancing effects of NSAIDs in the elderly.

Aging↗