Biology and Biomedical Sciences: Molecular Cell Biology
Date of Award
Doctor of Philosophy (PhD)
Chair and Committee
Andrey S Shaw
I. Podocytes are specialized epithelial cells in the kidney glomerulus that play important structural and functional roles in maintaining the filtration barrier. In nephrotic syndrome, a major breakdown of the kidney filtration barrier associated with proteinuria, hyperlipidemia, and edema, podocytes undergo changes in morphology and appear to internalize serum proteins. We postulated that fluid-phase uptake by podocytes might play a role in maintaining the integrity of the filtration barrier. Using fluid-phase tracers, we show that podocytes in vivo actively internalize fluid from the serum and that the rate of internalization is enhanced when the filtration barrier is disrupted. In vitro experiments demonstrated that lipids associated with serum albumin stimulate macropinocytosis in podocytes. This process was specific to podocytes as known stimuli that induce macropinocytosis in other cells had no effect on podocytes, while serum lipids did not stimulate macropinocytosis in other cells. A candidate lipid approach showed that certain unsaturated free fatty acids stimulate macropinocytosis through G protein coupled receptors, FFAR1, FFAR2 and FFAR3 and the Gβ/Gγ complex. Meanwhile, long-chain fatty acids were found to induce apoptosis in podocytes. These results suggest that podocytes sense the disruption of the filtration barrier via free fatty acids carried by albumin and respond to the increased protein by enhancing fluid-phase uptake. However, alterations in free fatty acids to albumin ratio during nephrotic syndrome may lead to dysregulation of macropinocytosis and podocyte toxicity and play an important role in the development of podocyte diseases.
II. The early events that initiate inflammation in the adipose tissue during obesity are not well defined. It is unclear whether the recruitment of CD8 T cells to the adipose tissue during onset of obesity occurs through antigen-dependent or -independent processes. We have previously shown that interaction between NKG2D (natural-killer group 2, member D) and its ligand Rae-1ɛ is sufficient to recruit cytotoxic T lymphocytes to the pancreas and induce insulitis. Here, we tested to see whether NKG2D-NKG2D ligand interaction is also involved in obesity-induced adipose tissue inflammation and insulin resistance. We observed a significant induction of NKG2D ligand expression in the adipose tissue of obese mice, especially during the early stages of obesity. However, mice lacking NKG2D developed similar levels of insulin resistance and adipose tissue inflammation compared to control mice when placed on a high fat diet. Moreover, overexpression of Rae-1ɛ in the adipose tissue did not increase immune cell infiltration to the adipose tissue neither in the setting of a normal or high fat diet. These results indicate that, unlike in the pancreas, NKG2D-NKG2D ligand interaction does not play a critical role in obesity-induced inflammation in the adipose tissue.
Chung, Jun-Jae, "Regulation of Fluid-phase Uptake in Podocytes by Albumin-associated Lipids" (2014). All Theses and Dissertations (ETDs). 1293.