Decrease of Bcl-xL and augmentation of thymocyte apoptosis in GILZ overexpressing transgenic mice

Abstract

Glucocorticoids promote thymocyte apoptosis and modulate transcription of numerous genes. GILZ (glucocorticoidinduced leucine zipper), being one of them, is strongly up-regulated in the thymus. To elucidate its function we generated transgenic mice overexpressing it specifically in the T-cell lineage and characterized its influence on thymus function. In young adult transgenic mice CD4 ؉ CD8 ؉ thymocyte number was significantly decreased and ex vivo thymocyte apoptosis was increased. Apoptotic pathway analysis detected reduced antiapoptotic B-cell leukemia XL (Bcl-xL) expression and increased activation of caspase-8 and caspase-3. Time-course experiments showed that in wild-type (WT) thymocytes GILZ up-regulation was followed by sequential Bcl-xL decreased expression and activation of caspase-8 and of caspase-3. Moreover, GILZ delivered inside WT thymocytes by a fusion protein with the transactivator of transcription (TAT) peptide decreased Bcl-xL and promoted their apoptosis. In aged mice perturbation of thymic subset numbers was amplified over time, as demonstrated by a further decrease in CD4 ؉ CD8 ؉ cells and increases in CD4 ؉ CD8 ؊ , CD4 ؊ CD8 ؊ , and CD8 ؉ CD4 ؊ cell counts. These results support the hypothesis that GILZ participates in the regulation of thymocyte apoptosis by glucocorticoids. IntroductionGlucocorticoids (GCs) are hormones and drugs that express their functions by binding and activating their specific intracellular receptor (GR), thus acting through genomic and nongenomic mechanisms. The thymus, one of their target organs, promotes thymocyte maturation to functional CD4 ϩ or CD8 ϩ single positive (SP) T lymphocytes that are ready to migrate to the periphery. T-cell development in the thymus is ordered by sequential steps that involve waves of cell proliferation and apoptosis. Apoptosis is a key process in thymus physiology and is triggered in 3 well-known ways: (1) negative selection, involving 5% of all thymocytes, eliminates autoreactive T-cell clones at the level of CD4 ϩ CD8 ϩ double-positive (DP) cells; (2) death by neglect involves 90% of DP thymocytes that are neither positively nor negatively selected; and (3) stress-induced cell death. 1 GCs promote apoptosis of DP thymocytes 2 but are not involved in apoptosis by negative selection. 3 Their role in apoptosis by neglect is uncertain, but they certainly mediate stress-induced apoptosis. 1 The apoptotic signaling pathway triggered by the synthetic GC dexamethasone (DEX) in thymocytes has recently been clarified to some extent. The GC receptor coordinates activation of gene transcription and caspase-8, -9, and -3 in a sequence that leads to thymocyte apoptosis. [4][5][6][7] Additionally, GC-mediated thymic apoptosis is regulated by many different molecules, and the B-cell leukemia 2 (Bcl-2) family of proteins is a critical regulator of apoptosis. 8 The family is subdivided into antiapoptotic members such as Bcl-2 and Bcl-xL, and proapoptotic members such as Bcl-2-associated X protein (Bax) and BCL-2 homologous antagonist/killer (Ba...

Glucocorticoid-Induced Leucine Zipper (GILZ) Over-Expression in T Lymphocytes Inhibits Inflammation and Tissue Damage in Spinal Cord Injury

“…Therefore, as the case of other inflammatory and autoimmune diseases is important to monitor the efficacy of treatment and to develop new pharmacological approaches for therapy of SCI, our present study indicates a role of GILZ in controlling SCI-induced inflammation. In particular, using transgenic mice, in which GILZ is selectively over-expressed in T lymphocytes at levels comparable to that obtained with dexamethasone treatment [20,24,25], we demonstrate that T lymphocytes play an important role in SCI.…”

“…Using GILZ transgenic (GILZ TG ) mice, in which GILZ is selectively over-expressed in the T-cell lineage at levels comparable to that induced by pharmacological GC treatment [20,25], we show that GILZ inhibits the inflammatory process and the development of SCI. These results indicate that GILZ is an anti-inflammatory molecule representing a potential pharmacological target for modulation of T-cellmediated immune/inflammatory response in SCI.…”

The Role and Effects of Glucocorticoid-Induced Leucine Zipper in the Context of Inflammation Resolution

“…Alternatively, another study showed that GILZ inhibited thymocyte apoptosis induced by TCR activation by inhibiting NF-kB activity and IL-10 production (45). Additionally, GILZ did not induce apoptosis in mature mouse T cell lymphocytes (8,44). These results indicate that GILZ regulates T cell apoptosis and, similar to GC, induces apoptosis in resting T cells while protecting activated T lymphocytes.…”

“…The involvement of GILZ in the process of apoptosis has been suggested by experiments in GILZ transgenic mice, which overexpress GILZ in the T cell lineage. Thymocytes from these mice undergo apoptosis, activate caspase-8 and caspase-3, and downregulate Bcl-x L , suggesting that GILZ has effects similar those of GCs (44). Alternatively, another study showed that GILZ inhibited thymocyte apoptosis induced by TCR activation by inhibiting NF-kB activity and IL-10 production (45).…”

Dual regulation of glucocorticoid-induced leucine zipper (GILZ) by the glucocorticoid receptor and the PI3-kinase/AKT pathways in multiple myeloma

“…Eddleston et al [25] report a similar siRNA induced decrease in GC-induced GILZ results in reduced anti-inflammatory actions of GC in HEK293 cells. The function of GILZ has been studied extensively in T cells where both pro-and anti-apoptotic functions have been reported [19,49]. However, the function of GILZ had yet to be characterized in B cells or myeloma before this study.…”