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Title: The involvement of hyaluronan matrix in regulating peritoneal infection, inflammation & fibrosis
Author: Williams, Aled
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2019
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The prevalence of Chronic Kidney Disease (CKD) is rising owing to increased diabetes and obesity in our ageing populations. Hence, end-stage renal disease (ESRD) has become a major global health burden. For many ESRD patients, kidney transplantation is not possible. Hence these patients require dialysis to regulate their salt/fluid levels, and to remove toxins from the body. Peritoneal Dialysis (PD) is a well-established and effective form of treatment for ESRD. However, the longevity of PD is limited because of the constant exposure of the peritoneum to bioincompatible PD solutions. This, alongside unavoidable repeated episodes of PD peritonitis, alters the structural and functional integrity of the peritoneal membrane and plays a pivotal role in the development of peritoneal fibrosis leading to failure of the peritoneal tissue to act as a semi-permeable membrane. This results in failure of PD as a therapy for ESRD, limiting a patient's options for renal-replacement therapy. A key process that drives peritoneal fibrosis during PD is mesothelial-to-mesenchymal transition (MMT). MMT is a process whereby mesothelial cells (known to comprise the majority of cells in the peritoneal membrane) undergo myofibroblast differentiation and lay down increased fibrous matrix. Numerous studies have demonstrated that TGF-β1 plays an established role in driving MMT and in the subsequent development of peritoneal fibrosis. Therefore, delineating the regulators of TGF-β1-driven MMT are important in identifying novel mechanisms to prevent peritoneal fibrosis and PD failure. In solid organ fibrosis (lungs, kidneys, skin) TGF-β1-driven myofibroblast differentiation is mediated through increased expression and alterations in the matrix polysaccharide, hyaluronan (HA). Previous studies demonstrate that PD therapy is associated with increased HA generation by mesothelial cells. However, the role of this in mediating TGF-β1-driven in the peritoneum has not been established and the role of increased HA generation during PD is not understood. The aim of this study was to determine the role of the increased HA generated during PD in regulating peritoneal infection, inflammation and fibrosis. This work uses primary human peritoneal mesothelial cells to study the involvement of HA in mediating TGF-β1-driven MMT in an in vitro experimental model. The role of HA in prevention and/or reversal of TGF-β1-driven MMT is also investigated in vitro. The role of HA in modulating peritoneal immunity and inflammation following acute bacterial infection is also examined using an in vivo mouse-model of PD peritonitis. Patients with PD peritonitis had significantly increased HA concentrations in their PD effluent after developing acute bacterial peritonitis compared to non-infected patients. Cell studies established that TGF-β1-driven MMT in primary human mesothelial cells significantly increased HA generation, and this was predominantly driven by Hyaluronan Synthase-1 (HAS1) isoenzyme expression. However, the increased HA was not causally related to TGF-β1- driven MMT; but was simply a consequence of this process. The increased HA also did not mediate prevention and/or reversal of TGF-β1-driven MMT in primary human mesothelial cells. Blocking HA in the peritoneum with PEP1 blocking antibody during bacterial infection lead to a delayed resolution of inflammation, characterized by increased and persistent neutrophil infiltration, dysregulated monocyte recruitment and decreased cytokine and chemokine release. In conclusion, following peritoneal injury, HA generated by mesothelial cells is predominantly HAS1 driven and promotes enhanced peritoneal inflammation and alters leukocyte recruitment following acute bacterial infection.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available