Exploring the roles of myeloid cells in kidney injury and repair
2017-02-27T05:51:18Z (GMT) by
Kidney disease is a major health concern, affecting a growing number of people and placing an enormous burden on health care systems worldwide. There is no cure for kidney disease and the current treatments heavily impact patient quality of life. However, the kidneys possess a limited capacity to regenerate, which provides hope for the future development of treatments aimed at promoting endogenous repair. This approach, however, will not be without challenges, due to the broad range of kidney diseases arising from different aetiologies. The macrophage is a myeloid cell type recognised for its roles in both inflammation and tissue repair. Originally identified as a contributor to innate host defence, these cells are now known to also possess immunomodulatory and wound healing capabilities. For these reasons, manipulating macrophage function may help promote endogenous repair in damaged kidneys. Recent attempts to define macrophage activation states as either classical (M1) or alternative (M2) have been useful, although this classification system appears too simplistic, due in part to the complexity of the in vivo environment during injury and disease, where macrophages receive a broad and changing range of stimuli. Therefore, this thesis presents a series of studies that examine the contribution of myeloid cells to the initial inflammatory phase and subsequent resolution/remodelling phase of experimental ischaemia/reperfusion (IR) injury, a model of acute kidney injury (AKI). Chapter Two describes the establishment of a flow cytometry protocol for detecting and analysing myeloid cells in injured and non-injured kidneys. This involved optimising enzymatic digestion methods and identifying important monocyte and macrophage subpopulations, in addition to neutrophils and epithelial cells in the context of IR injury. Chapter Three utilised these methods to comprehensively characterise myeloid populations, inflammatory cytokines and epithelial cell loss throughout the initiation and resolution phases of kidney IR injury. The histopathology corresponding to each of the time-points was also examined. Finally, Chapter Four explored and compared the effects of granulocyte macrophage-colony stimulating factor (GM-CSF) and colony stimulating factor-1 receptor (CSF-1R) blockade, using neutralising antibodies, on IR-mediated damage and repair. GM-CSF and CSF-1 are principal myeloid growth factors linked to pathogenesis and repair in a range of diseases. The effects on different cell types, serum cytokines, collagen content and renal function were assessed. While GM-CSF and CSF-1R blockade were able to reduce a number of inflammatory mediators, the benefits were outweighed by impacts on reparative subpopulations of myeloid cells. In particular, CSF-1R blockade substantially reduced infiltrating inflammatory monocytes shortly following injury but also depleted mannose receptor (MR) expressing M2 macrophages. The prolonged administration of this antibody also resulted in a significant increase in the total collagen content at 14 days post-IR injury. Monocyte-derived macrophages contribute to the pathogenesis of IR injury but are also crucial mediators of kidney remodelling. Therefore, selective/targeted depletion or manipulation of specific myeloid populations may be beneficial in reducing inflammation-mediated damage, whilst still allowing reparative subpopulations to resolve tissue damage, promote tubular regeneration and mediate tissue remodelling.