![Mechanisms of activation of latent transforming growth factor-beta during wound healing için kapak resmi Mechanisms of activation of latent transforming growth factor-beta during wound healing için kapak resmi](/client/assets/d79c3e4af2b6d196/ctx/images/no_image.png)
Mechanisms of activation of latent transforming growth factor-beta during wound healing
Başlık:
Mechanisms of activation of latent transforming growth factor-beta during wound healing
Yazar:
Ludlow, Anna, author.
ISBN:
9780438043312
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (267 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-08C.
Özet:
Transforming growth factor-beta (TGF-beta) plays a pivotal role in the co-ordination of wound repair. However, its pro-fibrotic effects also promote scar formation. TGF-beta is produced by cells in a latent form that cannot elicit a biological response until it becomes activated. Therefore, activation of the latent form is a key event in the regulation of TGF-beta activity. Several mechanisms of latent TGF-beta activation have been identified in vitro. However, in vivo this process is poorly understood. Successful manipulation of TGF-beta isoform activation at the wound site using therapeutic agents suggests that this might represent a strategy to reduce scar formation and improve the quality of wound repair. We have reported recently that significant amounts of latent TGF-beta are activated within the first hour of wound repair. The molecular mechanism/s of activation, however, are not yet understood. The first response of the tissue to injury is to limit haemorrhage through the formation of a fibrin clot. As platelets are a major source of TGF-beta1 and release their contents during coagulation, the aims of my thesis were to evaluate the release and activation of platelet TGF-beta1 during clot formation and identify potential mechanisms of activation. The plasminogen activator inhibitor-1/luciferase (PAI/L) bioassay for TGF-beta was used to determine the kinetics of latent TGF-beta1 release and activation in platelet releasates. Platelet activation was characterised by an initial burst of latent TGF-beta release which correlated with platelet degranulation as determined by the measurement of the alpha-granule-specific protein, platelet factor 4, in the releasates. Active TGF-beta1 was also released, but on a slower time course, possibly as a result of activation of a small percentage of the latent TGF-beta by the platelets. In addition, analysis of cryosections of fibrin clots for active and latent TGF-beta, using a modified version of the PAI/L assay, indicated that during blood coagulation a significant amount of TGF-beta is trapped within the clot, the majority of which is in an active form (up to 82%). Latent TGF-beta activation is a highly complex process that has been shown in vitro to involve a variety of enzymes, receptors and extracellular matrix molecules. Using in vitro methods to explore the mechanism/s of latent TGF-beta activation by isolated, thrombin-stimulated platelets, I found that activation (or possibly release of active TGF-beta) could be significantly reduced by inhibiting serine or acid proteases, or thrombospondin-1 (TSP-1)-TGF-beta interactions. Inhibition was incomplete in all cases suggesting that platelets may activate latent TGF-beta by more than one mechanism. As a first attempt to analyse the mechanism of TGF-beta activation by platelets in vivo, the presence of TGF-p detectable by the antibody AF-101-NA (which may selectively detect active TGF-beta) in platelets from transgenic mice with gene deletions in components involved in known TGF-beta activation pathways, was compared to that of wild type control animals. Liver tissue sections from mice deficient in either plasminogen, TSP-1 or both the mannose-6-phosphate receptor and insulin-like growth factor II showed co-localisation of the AF-101-NA antibody, which may specifically recognise active TGF-beta1, with the platelet marker, CD41. These data tentatively suggest that platelets of these mice were capable of activating latent TGF-beta1 and that above proteins are not essential in this process. Confocal microscopy revealed that part of the active TGF-beta1 detected in platelets was located intracellularly, suggesting intracellular activation prior to release, or, uptake following release and activation. Analysis of the levels of active and latent TGF-beta in platelet releasates using the PAI/L assay did not indicate significant differences between transgenic and wild type mice. In conclusion, I found that thrombin-stimulated platelets release and may activate latent TGF-beta1 extra- and possibly intracellularly in a time-dependent, autocrine fashion, involving several mechanisms including TGF-beta interaction with TSP-1 as well as limited proteolysis by serine or acid proteases. I have provided evidence that blood clotting might trigger latent TGF-beta activation with much higher efficiency than isolated platelets possibly involving distinct mechanisms of activation. These results might provide the basis for further studies towards the design of novel therapeutic strategies to improve the quality of wound repair and scarring.
Notlar:
School code: 1543
Tüzel Kişi Ek Girişi:
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(684268.1) | 684268-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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