Browsing Theses by Subjects
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Heat shock proteins: Interactions with bone and immune cellsHeat shock proteins (Hsps) are increasingly being seen as having roles other than those of intracellular molecular chaperones, particularly with regard to their potential to act as cytokines, and to stimulate the innate immune system. Hsps have also been found to promote bone resorption and osteoclast formation in vitro, although the mechanism has not been previously identified. The overall aims of this thesis were to determine whether Hsps could stimulate bone resorption by affecting the RANKL/OPG pathway, and to address the hypothesis that Hsps can act as a danger signal to the innate immune system. In order for Hsps to affect either the RANKL/OPG system of bone resorption or act as danger signals they would need to be actively released from cells, ideally in a controlled manner following exposure to the source of stress. Hsp60 and Hsp70 were found to be released from a range of immune cells including the cell lines Jurkat and U937, and also PBMCs, T-cells and B-cells. This release was not due to cell damage. The release of Hsp60 and Hsp70 were downregulated by inhibitors of protein secretion, in particular Hsp70 release was reduced by compounds that inhibited lysosomal pathways and Hsp60 release by classical secretion inhibitors. Hsp60, Hsp70, GroEL and LPS all affected the RANKL/OPG system of bone regulation; OPG production and release was down-regulated in the MG63 and GCT osteoblast-like cell lines following treatment with Hsp60, Hsp70 and LPS, and RANKL expression was upregulated following treatment with Hsp60, Hsp70, GroEL and LPS. This effect on the RANKL/OPG system was found to translate into an effect on osteoclast formation when conditioned media from treated osteoblasts was added to osteoclast precursors in the presence of M-CSF. A range of different factors that affected Hsp release were identified; PHA activation of PBMCs was found to upregulate Hsp60 release from PBMCs. GroEL and LPS caused an upregulation in Hsp70 release from PBMCs and GCT osteoblast like cells, and Hsp70 was found to stimulate Hsp60 release from PBMCs and GCT cells. These responses of Hsp release were used to form a theory of a cascade-like danger signal that may occur when cells are exposed to bacterial infection and which would result in activation of antigen presenting cells via previously identified receptors for Hsps such as CD14/TLR4 or by unidentified pathways. The elevated release of Hsps in response to GroEL and LPS was also identified as a mechanism that could stimulate bone loss during infection or autoimmuniry by affecting the RANKL/OPG system. hi conclusion, Hsp60 and Hsp70 can be released from immune cells under normal conditions, and from both immune and osteoblast-like cells following stimulation with LPS and other Hsps. The observed release responses provide a mechanism through which Hsps can act as danger signals to the innate immune system, and also as promoters of bone resorption via the RANKL/OPG system.
Interactions between extracellular Hsp72 and blood cellsIn recent years, compelling evidence has accumulated suggesting heat shock proteins (HSPs) which are generally believed to be localised and functioning mainly within eukaryotic cells as cyto-protective molecular chaperones, are also localised in the extracellular milieu. Depending on their localisation, on the cell surface (membrance-bound or embedded), or in the peripheral circulation, extracellular HSPs may induce apoptotic cell death, or in contrast protect cells from cell damage and/or cell death when exposed to cellular stress, or may even elicit a stimulatory effect on the innate immune response including cell activiation and cytokine secretion. Hence, the localisation of intracellular and extracellular HSPs appears to be critical in determining their roles in terms of stimulating cell death, cyto-protection, or immune activiation under normal physiological conditions and following exposure to stress stimuli. This thesis describes the intracellular expression, up-regulation, and cell surface localisation of endogenous HSPs: HSP27, Hsp60, Hsp72 and Hsp90 by flow cytometry, florescence microscopy and Western blotting, under control conditions and in response to environmental stress using in vitro and ex vivo models with the intention of determining their physiological roles. The ability of extracellularly administered HSPs (Hsp70 and Hsp72) to protect cultured U937 cells in vitro or peripheral primary human leukogytes or erythrocytes ex vivo from various stress stimuli was demonstrated and was found to be dependent on surface binding and/or internalisation via scavenger receptors (SRs) or phosphatidylserine (PS), which could be blocked by receptor specific ligands. Extracellular HSPs were also shown to be able to stimulate an immune response through the induction of U937 monocyte differentiation into macrophages as evidenced through the up-regulation of the surface receptors: CD36, SR-A1 and CD91 analysed by flow cytometry. These proteins were able to stimulate TNF-x and IL-10 production and secretion by U937 macrophages, shown by ELISA, and chemotatic properties were demonstrated using Boyden chambers. The cyto-protective and immune regulatory effects of extracellular HSPs have potential therapeutic value as treatments in a wide variety of clinical situations.
Novel anti-oxidant properties of cobalaminOxidative stress has been associated with a wide range of diseases, including cardiovascular diseases, Alzheimer's disease, atherosclerosis, Parkinson's disease and cancer. It also plays a role in the ageing process. Hyperhomocysteimia is commonly found to be associated with these diseases. The hyperhomocysteimia is a result of a deficiency in both folate and cobalamin Folate is known to reduce Hey and protect cells from apoptosis, but there are no studies investigating the impact of cobalamin on apoptosis induced by oxidative stress or the mechanism(s) of the protection. The aims of the research are to investigate the protective role of cobalamin and the possible mechanism(s) for this protection. It also examines the protective role of novel cobalamin and investigates their superior protection. The methods used in this research for apoptosis detection we used caspase-3 and the annexin-V, while for necrosis we used PI staining, where cell viability were detected using MTS assay. We also measured the generation of superoxide by Lucigenin-enhanced chemiluminescence and reactive oxygene species by using the redox active prob DCFH-DA. Moreover, the intracellular proteins were measured via staining with specific fluorescent-conjugated antibodies were detected using flowcytometry. Our result demonstrated that 25|iM of cobalamin protects cells from apoptosis. The protection by cobalamin was associated with induction of iHsp72 and iHO-1, and these are shown to be essential for the protection. Furthermore, our research demonstrated a novel mechanism of cobalamin-apoptosis protection involving induction of NfkB, ERK1/2 and AKT signal transduction pathways. In order to protect cells from apoptosis induced by oxidative stress, cobalamin induces the pNfkB which in turn regulate the iNOS and HO-1 induction. Cobalamin also induces thepERK1/2 which regulates the induction of Hps72 and Nrf2. And finally, pAKT induced by cobalamin which regulate the Nrf2 and HO-1 induction. The inhibition of any of theses pathways leads to loss the protection. The GSCbl and NACCbl provide a superior protection against oxidative stress, this protection involved induction of the signal transduction pathways and Hsps. To conclude; cobalamin provides protection against cells death induced by oxidative stress. Cobalamin achieves this by multiple pathways which include direct antioxidant stimulation and induction of signal transduction pathways. Different cobalamin derivatives have superior protections. These finding are a useful pharmaceutical tool in the treatment of the oxidative stress related diseases.