UVM Theses and Dissertations
Format:
Print
Author:
Lirussi, Darío
Dept./Program:
Microbiology and Molecular Genetics
Year:
2013
Degree:
PhD
Abstract:
During the course of the adaptive immune response, changes in metabolism have been shown to be crucial for activation of T lymphocytes and for the appropriate development of immunological memory. The main changes affecting the development of T helper cells during antigen-TCR engagement are related to calcium signaling. Although the role of mitochondria during T cell activation has been ignored for many years, nowadays it is clear that Mitochondria are the main subcellular organelle that regulates calcium metabolism in most cell types. During CD4 T cell activation, the role of mitochondria is not restricted to changes in energy generation, but also calcium signaling. Furthermore, it has been shown that cytokines can regulate T cell metabolism during activation, by affecting somehow mitochondrial functions.
Herein, we show that STAT3, the main signal transducer for IL-6 is present in mitochondria during activation, and its phosphorylated form is increased in mitochondria when IL-6 is present. In addition, we show that IL-6 maintains a higher mitochondrial membrane potential (MMP) during activation in CD4 T cells, counteracting activation-induced mitochondrial membrane depolarization. This effect of IL-6 in CD4 T cells is not reproducible in CD8 T cells, and is not reproduced by other cytokines (IL-2 and IL-4). We demonstrate that this IL-6 dependent increased MMP is not related to an expected increase in ATP. We assessed that these cells are equally glycolytic than cells activated in the absence of IL-6. We show here that calcium metabolism in CD4 T cells is affected by IL-6, through enhanced mitochondrial membrane potential (MMP).
We demonstrate that these changes in MMP are not accompanied by an increase in mitochondrial ROS, on the contrary, ROS are decreased in the presence of IL-6. We demonstrate that the lack of STAT3 renders mitochondria irresponsive to the IL-6 stimulus, implying a direct involvement of STAT3 in IL-6 enhanced MMP. Furthermore, we show that the effects of electron transport chain inhibitor .rotenone decrease cytosolic calcium suggesting the involvement of mitochondria in sustaining a high mitochondrial calcium signaling. This IL-6 altered calcium signaling is important for many effector functions and specific cytokine production as revealed by IL-21 and IL-4 calcium dependency. These results show how cytokines and particularly IL-6 can modulate calcium metabolism during activation, involving unexpected action of transcription factor STA13 in mitochondrial metabolism.
Herein, we show that STAT3, the main signal transducer for IL-6 is present in mitochondria during activation, and its phosphorylated form is increased in mitochondria when IL-6 is present. In addition, we show that IL-6 maintains a higher mitochondrial membrane potential (MMP) during activation in CD4 T cells, counteracting activation-induced mitochondrial membrane depolarization. This effect of IL-6 in CD4 T cells is not reproducible in CD8 T cells, and is not reproduced by other cytokines (IL-2 and IL-4). We demonstrate that this IL-6 dependent increased MMP is not related to an expected increase in ATP. We assessed that these cells are equally glycolytic than cells activated in the absence of IL-6. We show here that calcium metabolism in CD4 T cells is affected by IL-6, through enhanced mitochondrial membrane potential (MMP).
We demonstrate that these changes in MMP are not accompanied by an increase in mitochondrial ROS, on the contrary, ROS are decreased in the presence of IL-6. We demonstrate that the lack of STAT3 renders mitochondria irresponsive to the IL-6 stimulus, implying a direct involvement of STAT3 in IL-6 enhanced MMP. Furthermore, we show that the effects of electron transport chain inhibitor .rotenone decrease cytosolic calcium suggesting the involvement of mitochondria in sustaining a high mitochondrial calcium signaling. This IL-6 altered calcium signaling is important for many effector functions and specific cytokine production as revealed by IL-21 and IL-4 calcium dependency. These results show how cytokines and particularly IL-6 can modulate calcium metabolism during activation, involving unexpected action of transcription factor STA13 in mitochondrial metabolism.