Benutzerspezifische Werkzeuge

Progress Report 2013


Progress Report 2013: Project 7 - Role of innate immunity pattern recognition receptors in adrenocortical cell dysregulation during inflammation

Summary of achievements:

Within the framework of aim 1, we comprehensively characterized 2 different models of systemic inflammation in mice namely LPS-induced SIRS and CLP induced- sepsis. In particular, we characterized the HPA axis activity, systemic and local inflammation, leukocyte recruitment and apoptosis in the adrenal gland in both models. Both treatments induced a strong inflammatory response with rapid upregulation of proinflammatory cytokine gene expression, including IL-1β, TNF adhesion molecules (ICAM-1 and VCAM-1), complement receptor (C5aR), inducible nitric oxide synthase (iNOS) and several neutrophil-specific (CXCL2) and monocyte-specific (MIP-1β) chemokines, while simultaneously reducing the expression of endothelial nitric oxide synthase. Furthermore, an increased inflammation and strong expression of many chemokine genes resulted in rapid changes in immune cell population including infiltration of neutrophils at 3h and monocytes at 24h time points after LPS administration Figure 2. Finally, an increased inflammation and immune cell infiltration was associated with pronounced increase in apoptosis, hemorrhage, necrosis, and structural changes in the mitochondria of the adrenocortical cells after both LPS and CLP-induced systemic inflammation. Cellular death occurs in both adrenocortical and medullar cells and was correlated with severity of sepsis. Since, apoptosis of adrenocortical cells is also present in adrenal glands of patients with sepsis; the cellular death process may be one of the mechanisms underlying sepsis mediated adrenal gland deregulation. 

Within the framework of aim 2, we tested whether LPS-mediated activation of the HPA axis, inflammation and immune cell recruitment require an intact expression of TLR-signaling major adapter molecule MyD88 in adrenocortical or in hematopoietic cells. For this purpose we have generated mice with MyD88 deletion specifically in adrenocortical cells (Akr1b7-Cre MyD88 fl/fl) and mice lacking MyD88 expression in myeloid cells and in liver (Mx1-Cre MyD88 fl/fl). Our results revealed that an intact myeloid but not adrenocortical TLR-signaling is required for LPS-mediated adrenal IL-1β gene expression and recruitment of neutrophils into adrenal gland. Furthermore, we found that myeloid but not adrenocortical TLR signaling is important for the proper activation of the HPA axis during LPS-mediated endotoxemia in mice. However, this deletion did not abrogate completely the activation of the HPA axis and expression of IL-6, which suggest that adrenocortical TLR-signaling may contribute to local inflammation during more severe conditions, such as CLP-induced long term sepsis.

In our pursuit of aim 3, we characterized expression and function of NOD-like receptors (NLRs, e.g. NOD1, NOD2, NALP3) and their signaling components (ASC, caspase 1) in the adrenal glands during LPS- and CLP-mediated systemic inflammation in vivo. We found that both LPS and CLP induced alterations in the expression of those genes in the adrenal gland and a profound IL-1β secretion but a reduced IL-18 release in both plasma and adrenal lysates, indicating activation of the NALP3 inflammasome complex in the course of sepsis [data unpublished]. However, studies involving primary cultures of human adrenocortical cells and murine (Y1) and human (NCI-H295R) adrenocortical cell lines demonstrated that these cells do not secrete IL-1β upon LPS stimulation, which suggest that inflammasome activation may occur in the immune compartment of the adrenal gland.