Distinct functions of the dual leucine zipper kinase depending on its subcellular localization.

The dual leucine zipper kinase DLK induces ß-cell apoptosis by inhibiting the transcriptional activity conferred by the ß-cell protective transcription factor cAMP response element binding protein CREB. This action might contribute to ß-cell loss and ultimately diabetes. Within its kinase domain DLK shares high homology with the mixed lineage kinase (MLK) 3, which is activated by tumor necrosis factor (TNF) α and interleukin (IL)-1ß, known prediabetic signals. In the present study, the regulation of DLK in ß-cells by these cytokines was investigated. Both, TNFα and IL-1ß induced the nuclear translocation of DLK. Mutations within a putative nuclear localization signal (NLS) prevented basal and cytokine-induced nuclear localization of DLK and binding to the importin receptor importin α, thereby demonstrating a functional NLS within DLK. DLK NLS mutants were catalytically active as they phosphorylated their down-stream kinase c-Jun N-terminal kinase to the same extent as DLK wild-type but did neither inhibit CREB-dependent gene transcription nor transcription conferred by the promoter of the anti-apoptotic protein BCL-xL. In addition, the ß-cell apoptosis-inducing effect of DLK was severely diminished by mutation of its NLS. In a murine model of prediabetes, enhanced nuclear DLK was found. These data demonstrate that DLK exerts distinct functions, depending on its subcellular localization and thus provide a novel level of regulating DLK action. Furthermore, the prevention of the nuclear localization of DLK as induced by prediabetic signals with consecutive suppression of ß-cell apoptosis might constitute a novel target in the therapy of diabetes mellitus.

Transcriptional Pathways in cPGI2-Induced Adipocyte Progenitor Activation for Browning.

De novo formation of beige/brite adipocytes from progenitor cells contributes to the thermogenic adaptation of adipose tissue and holds great potential for the therapeutic remodeling of fat as a treatment for obesity. Despite the recent identification of several factors regulating browning of white fat, there is a lack of physiological cell models for the mechanistic investigation of progenitor-mediated beige/brite differentiation. We have previously revealed prostacyclin (PGI2) as one of the few known endogenous extracellular mediators promoting de novo beige/brite formation by relaying ß-adrenergic stimulation to the progenitor level. Here, we present a cell model based on murine primary progenitor cells defined by markers previously shown to be relevant for in vivo browning, including a simplified isolation procedure. We demonstrate the specific and broad induction of thermogenic gene expression by PGI2 signaling in the absence of lineage conversion, and reveal the previously unidentified nuclear relocalization of the Ucp1 gene locus in association with transcriptional activation. By profiling the time course of the progenitor response, we show that PGI2 signaling promoted progenitor cell activation through cell cycle and adhesion pathways prior to metabolic maturation toward an oxidative cell phenotype. Our results highlight the importance of core progenitor activation pathways for the recruitment of thermogenic cells and provide a resource for further mechanistic investigation.

The modulatory effect of lithium on doxorubicin-induced cardiotoxicity in rat.

Doxorubicin is an effective anti-neoplastic agent application of which has been limited due to its cardiotoxic side effects. Lithium is widely used for treatment of neuropsychiatric symptoms in bipolar disorders. Lines of evidence point to the cardioprotective effects of lithium against heart injuries. The current study aims to investigate the protective effects of lithium against doxorubicin-induced cardiotoxicity in rat model. Male Wistar rats were treated with 300 mg/kg p.o. lithium in their water supply and/or doxorubicin (1.25 mg/kg, i.p.), four times per week for four weeks. General conditions, mortality rate and body weight were measured during the experiment. At the end of the experiment, ECG parameters and papillary muscle contractility force were assessed. Serum samples were collected to measure the lithium concentrations as well as cardiac troponin T level (cTNT, a biomarker of cardiac injury). In addition, heart weight was measured and the cardiac tissues were evaluated both macroscopically and microscopically. The results of the present study indicate that lithium might diminish mortality rate, general toxicity (edema, alopecia and cachexia), improve S(alpha)-T segment and QT interval prolongations as well as heart contractility force. Application of lithium could inhibit the increase of cardiac troponin T and formation of myocardial lesions. These outcomes show the protective effects of lithium against doxorubicin-induced cardiotoxicity in rat. On the whole, the results of the present study suggest that lithium might be considered as a new indication for the prevention of doxorubicin-induced cardiotoxicity.