Date of Award
Master of Science
Leptin is a pleiotropic hormone secreted by white adipose tissue. Obesity leads to overexpression of leptin as a result of leptin receptor desensitization. Obese leptin serum levels (160ng/ml) have been found to enhance immune functions in macrophages, natural killer cells, B cells, T cells, and dendritic cells. Previous data from our lab suggests that obese concentrations of leptin cause morphological changes in DCs, although further studies are required to verify these results. We hypothesized that leptin promotes DC cytoskeletal changes though activation of PI3K signaling. Morphological and functional changes were evaluated in JAWS II immortalized DCs though microscopy, transwell migration, assessment of cytokine production, and T cell activation. The results obtained, however, did not correlate with those observed in previous studies using primary DCs. The lack of changes in JAWS cells upon leptin treatment was accompanied by a lack of change in PI3K signaling.
Further studies were conducted to evaluate PI3K signaling and morphological changes in primary DCs upon leptin treatment. Primary DCs from Balb/c mice were observed by light and confocal microscopy. Analysis of cell morphology by light microscopy did not show any significant changes in cell morphology upon leptin treatment. There were, however, morphological changes observed by confocal microscopy in expression and localization of F-actin. Treating cells with Leptin and LPS leads to an increase in F-actin staining compared to media and LPS or leptin alone. Furthermore this increase was lost when cells were treated with a PI3K inhibitor and F-actin levels reverted to those observed in LPS treated cells. F-actin was also found to localize to the borders of cells treated with LPS, leptin, or Leptin and LPS with a high amount of actin visible in dendrites of L+L treated cells.
We proposed that the changes observed in DC morphology were being induced by increased signaling in the PI3K pathway. Leptin has been found to activate PI3K, a pathway important for cell viability and growth. PI3K is able to signal through Rac1, leading to F-actin polymerization. PI3K signaling was assessed by ELISA and flow cytometry for the phosphorylation of Akt, but there was not a significant change in either total Akt expressed or phosphorylation of Akt.
Received from ProQuest
Marisol Ann O'Neill
O'neill, Marisol Ann, "Identification of Kinase Signaling Pathways Inducing Morphological Changes in Dendritic Cells upon Leptin Treatment" (2013). Open Access Theses & Dissertations. 1693.