An Update on Addison's Disease.

Addison's disease - the traditional term for primary adrenal insufficiency (PAI) - is defined as the clinical manifestation of chronic glucocorticoid- and/or mineralocorticoid deficiency due to failure of the adrenal cortex which may result in an adrenal crisis with potentially life-threatening consequences. Even though efficient and safe pharmaceutical preparations for the substitution of endogenous gluco- and mineralocorticoids are established in therapy, the mortality in patients with PAI is still increased and the health-related quality of life (HRQoL) is often reduced.PAI is a rare disease but recent data report an increasing prevalence. In addition to the common "classical" causes of PAI like autoimmune, infectious, neoplastic and genetic disorders, other iatrogenic conditions - mostly pharmacological side effects (e. g., adrenal haemorrhage associated with anticoagulants, drugs affecting glucocorticoid synthesis, action or metabolism and some of the novel anti-cancer checkpoint inhibitors) are contributing factors to this phenomenon.Due to the rarity of the disease and often non-specific symptoms at least in the early stages, PAI is frequently not considered resulting in a delayed diagnosis. Successful therapy is mainly based on adequate patient education as a cornerstone in the prevention and management of adrenal crisis. A focus of current research is in the development of pharmacokinetically optimized glucocorticoid preparations as well as regenerative therapies.

Noninvasive management of the diabetic foot with critical limb ischemia: current options and future perspectives.

Foot ulcers are a major complication in patients with diabetes mellitus and involve dramatic restrictions to quality of life and also lead to enormous socio-economical loss due to the high amputation rate. The poor and slow wound healing is often aggravated by the frequent comorbidity of foot ulcers with peripheral arterial disease, making the treatment of this condition even more complicated. While the local treatment of foot ulcers is mainly based on mechanical relief and prevention or treatment of infection, improving perfusion of the impaired tissue remains the major challenge in peripheral arterial disease. While focal arterial stenosis is the domain of interventional angioplasty or vascular surgery, patients with critical limb ischemia and lacking options for revascularization have a much worse prognosis, because current treatment options avoiding amputation are scarce. However, based on recent research efforts, there is rising hope for promising and more-effective therapeutic approaches for these patients. Here, we discuss the current improvements of established therapies aimed at an improvement of limb perfusion, as well as the development of novel cutting-edge therapies based on stem-cell technology. The experiences of a 'high-volume center' for treatment of diabetic foot syndrome with a current major amputation rate of 4% are discussed.

Stimulation of selenoprotein P promoter activity in hepatoma cells by FoxO1a transcription factor.

Selenoprotein P (SeP) is the major selenoprotein in human plasma, acting as an antioxidant and serving the transport of selenium from the liver to extrahepatic tissues. We here demonstrate that the human SeP promoter responds to overexpression of FoxO1a as well as of a constitutively active form of FoxO1a. Two FoxO-responsive elements were identified and characterized by generation of point mutation and deletion constructs. Similarly, SeP mRNA was upregulated in response to activation of FoxO1a in rat hepatoma cells stably transfected with a hydroxytamoxifen-regulatable form of FoxO1a. Insulin, stimulating the phosphorylation and inactivation of FoxO1a via phosphoinositide 3-kinase (PI3K) and Akt, suppressed SeP promoter activity and mRNA synthesis. This suppressive effect of insulin on SeP expression was attenuated by inhibitors of PI3K. In conclusion, the selenoprotein P promoter is a target of the Akt/FoxO signal transduction cascade and SeP expression is regulated at the level of transcription by the forkhead box protein FoxO1a in human and rat hepatoma cells.

Stimulation of phosphoinositide 3-kinase/Akt signaling by copper and zinc ions: mechanisms and consequences.

The phosphoinositide 3'-kinase (PI3K)/Akt signaling cascade controls cellular processes such as apoptosis and proliferation. Moreover, it is a mediator of insulin effects on target cells and as such is a major regulator of fuel metabolism. The PI3K/Akt cascade was demonstrated to be activated by stressful stimuli, including heat shock and reactive oxygen species (ROS). This minireview focuses on activation of the pathway by exposure of cells to heavy metal ions, Cu2+ and Zn2+. It is hypothesized that stimulation of PI3K/Akt is the molecular mechanism underlying the known insulin-mimetic effects of copper and zinc ions. Following a brief summary of PI3K/Akt signaling and of activation of the cascade by Cu2+ and Zn2+, mechanisms of metal-induced PI3K/Akt activation are discussed with a focus on the role of ROS and of cellular thiols (glutathione, thioredoxin) and protein tyrosine phosphatases in Cu2+ and Zn2+ signaling. Finally, consequences of metal-induced PI3K/Akt activation are discussed, focusing on the modulation of FoxO-family transcription factors by Cu2+ and Zn2+.

Modulation of FoxO signaling in human hepatoma cells by exposure to copper or zinc ions.

Cells respond to heavy metal stress by activating signaling cascades regulating cellular proliferation and survival. We here demonstrate that the anti-apoptotic kinase Akt is activated in HepG2 human hepatoma cells exposed to copper or zinc ions. Cu2+- and Zn2+-induced phosphorylation of Akt was blocked by phosphoinositide 3-kinase (PI3K) inhibitors, wortmannin and LY294002. Moreover, several endogenous Akt substrates were phosphorylated, including glycogen synthase kinase-3 and transcription factors of the FoxO family, FoxO1a and FoxO4. Exposure to Cu2+ or Zn2+ elicited the subcellular redistribution of an overexpressed FoxO1a-EGFP fusion protein from nucleus to cytoplasm, which was not seen with a mutant FoxO1a form devoid of Akt phosphorylation sites. Both FoxO phosphorylation and nuclear exclusion were blocked by wortmannin. Likewise, the subcellular translocation from nucleus to cytoplasm of the Caenorhabditis elegans FoxO ortholog, DAF-16, was caused in starved worms exposed to copper ions. Activity of the promoter of the human glucose 6-phosphatase gene, known to be regulated by insulin and FoxO1a, was demonstrated in reporter gene assays to be attenuated in hepatoma cells exposed to Cu2+. However, this suppression of glucose 6-phosphatase promoter activity was independent of modulation of the PI3K/Akt pathway. In summary, the PI3K/Akt pathway is activated in human hepatoma cells exposed to Cu2+ or Zn2+, resulting in the phosphorylation and subcellular relocalisation of transcription factor FoxO1a. Furthermore, copper is demonstrated to exert an insulin-mimetic effect also independently of the PI3K/Akt/FoxO pathway.

Evidence for an indirect transcriptional regulation of glucose-6-phosphatase gene expression by liver X receptors.

Liver X receptor (LXR) paralogues alpha and beta (LXRalpha and LXRbeta) are members of the nuclear hormone receptor family and have oxysterols as endogenous ligands. LXR activation reduces hepatic glucose production in vivo through the inhibition of transcription of the key gluconeogenic enzymes phosphoenolpyruvate carboxykinase and glucose-6-phosphatase (G6Pase). In the present study, we investigated the molecular mechanisms involved in the regulation of G6Pase gene expression by LXR. Both T0901317, a synthetic LXR agonist, and the adenoviral overexpression of either LXRalpha or LXRbeta suppressed G6Pase gene expression in H4IIE hepatoma cells. However, compared to the suppression of G6Pase expression seen by insulin, the decrease of G6Pase mRNA by LXR activation was delayed and was blocked by cycloheximide, an inhibitor of protein synthesis. These observations, together with the absence of a conserved LXR-binding element within the G6Pase promoter, suggest an indirect inhibition of G6Pase gene expression by liver X receptors.

Phosphoinositide 3-kinase signaling in the cellular response to oxidative stress.

Oxidative stress is linked to the pathogenesis and pathobiochemistry of various diseases, including cancer, diabetes and cardiovascular disorders. The non-specific damaging effect of reactive oxygen species (ROS) generated during oxidative stress is involved in the development of diseases, as well as the activation of specific signaling cascades in cells exposed to the higher oxidant load. A cellular signaling cascade that is activated by several types of reactive oxygen species is the phosphoinositide 3'-kinase (PI 3-kinase)/protein kinase B (PKB) pathway, which regulates cellular survival and fuel metabolism, thus establishing a link between oxidative stress and signaling in neoplastic, metabolic or degenerative diseases. Several links of PI 3-kinase/PKB signaling to ROS are discussed in this review, with particular focus on the molecular mechanisms involved in the regulation of PI 3-kinase signaling by oxidative stress and important players such as (i) the glutathione and glutaredoxin system, (ii) the thioredoxin system and (iii) Ser/Thr- and Tyr phosphatases.

FoxO proteins in insulin action and metabolism.

There is increasing evidence that Forkhead box 'Other' (FoxO) proteins, a subgroup of the Forkhead transcription factor family, have an important role in mediating the effects of insulin and growth factors on diverse physiological functions, including cell proliferation, apoptosis and metabolism. Genetic studies in Caenorhabditis (Caenorhabditis elegans) and Drosophila demonstrate that FoxO proteins are ancient targets of insulin-like signaling involved in the regulation of metabolism and longevity. Studies in mammalian cells reveal that FoxO proteins regulate cell cycle progression and promote resistance to oxidative stress; both in vivo and cell culture studies support the concept that FoxO proteins have an important role in mediating the effects of insulin on metabolism, including its effects on hepatic glucose production. Phosphorylation and acetylation modulate FoxO function and control nuclear-cytoplasmic shuttling, DNA binding and protein-protein interactions. FoxO transcription factors exert positive and negative effects on gene expression, through direct binding to DNA target sites and protein-protein interactions with other transcription factors and coactivators. This paper provides an overview of studies leading to the identification of FoxO proteins as targets of insulin action and the mechanisms mediating the effects of insulin-like signaling on FoxO function, emphasizing the role of FoxO proteins in mediating the effects of insulin on metabolism.

Protein kinase B activity is sufficient to mimic the effect of insulin on glucagon gene transcription.

Insulin inhibits glucagon gene transcription, and insulin deficiency is associated with hyperglucagonemia that contributes to hyperglycemia in diabetes mellitus. However, the insulin signaling pathway to the glucagon gene is unknown. Protein kinase B (PKB) is a key regulator of insulin signaling and glucose homeostasis. Impaired PKB function leads to insulin resistance and diabetes mellitus. Therefore, the role of PKB in the regulation of glucagon gene transcription was investigated. After transient transfections of glucagon promoter-reporter genes into a glucagon-producing islet cell line, the use of kinase inhibitors indicated that the inhibition of glucagon gene transcription by insulin depends on phosphatidylinositol (PI) 3-kinase. Furthermore, insulin caused a PI 3-kinase-dependent phosphorylation and activation of PKB in this cell line as revealed by phospho-immunoblotting and kinase assays. Overexpression of constitutively active PKB mimicked the effect of insulin on glucagon gene transcription. Both insulin and PKB responsiveness of the glucagon promoter were abolished when the binding sites for the transcription factor Pax6 within the G1 and G3 promoter elements were mutated. Recruitment of Pax6 or its potential coactivator, the CREB-binding protein (CBP), to G1 and G3 by using the GAL4 system restored both insulin and PKB responsiveness. These data suggest that insulin inhibits glucagon gene transcription by signaling via PI 3-kinase and PKB, with the transcription factor Pax6 and its potential coactivator CBP being critical components of the targeted promoter-specific nucleoprotein complex. The present data emphasize the importance of PKB in insulin signaling and glucose homeostasis by defining the glucagon gene as a novel target gene for PKB.

Impaired adrenal stress response in Toll-like receptor 2-deficient mice.

Septicemia is one of the major health concerns worldwide, and rapid activation of adrenal steroid release is a key event in the organism's first line of defense during this form of severe illness. The family of Toll-like receptors (TLRs) is critical in the early immune response upon bacterial infection, and TLR polymorphisms are frequent in humans. Here, we demonstrate that TLR-2 deficiency in mice is associated with reduced plasma corticosterone levels and marked cellular alterations in adrenocortical tissue. TLR-2-deficient mice have an impaired adrenal corticosterone release after inflammatory stress induced by bacterial cell wall compounds. This defect appears to be mediated by a decrease in systemic and intraadrenal cytokine expression, including IL-1, tumor necrosis factor alpha, and IL-6. Our data demonstrate a link between the innate immune system and the endocrine stress response. The critical role of TLR-2 in adrenal glucocorticoid regulation needs to be considered in patients with inflammatory disease.

Cellular models for the analysis of signaling by protein kinase B and the forkhead transcription factor FKHR (Foxo1a).

The transcription factor FKHR (FOXO1a) is regulated by protein kinase B (PKB) and insulin controls the expression of hepatic genes like glucose-6-phosphatase (G6Pase) at least in part via these proteins. However, insulin is known to activate several pathways and it is therefore difficult to establish which effects of the hormone are attributed to PKB and FKHR signaling. The aim of the present study was the generation of cellular models which allow the specific analysis of molecular events controlled by PKB and FKHR, respectively. We generated two H4IIEC3 rat hepatoma cell lines stably expressing either a hydroxytamoxifen-regulatable form of PKB (myristoylated PKB estrogen receptor chimera; MER-PKB) or FKHR (FKHR estrogen receptor chimera; FKHR-ER) by retroviral infection and determined the regulation of the G6Pase transcript by Northern blotting and enzyme assays. Activation of the regulatable PKB fusion protein almost completely reduced the dexamethasone/cAMP-stimulated G6Pase mRNA levels comparable to the effect of insulin. In contrast, stimulation of FKHR-ER with tamoxifen increased the expression of the dexamethasone/cAMP-induced G6Pase mRNA and the G6Pase enzymatic activity about 2.5- to 3-fold. The present data demonstrate that activation of PKB is sufficient to mimic the effect of insulin on the expression of G6Pase and that FKHR acts as an activator of the G6Pase gene indicating that the established cellular models are suitable for the specific analysis of downstream targets of these signaling molecules. Therefore, these cell systems might serve as useful tools for the development of anti-diabetic drugs.

Tumour necrosis factor alpha decreases glucose-6-phosphatase gene expression by activation of nuclear factor kappaB.

The key insulin-regulated gluconeogenic enzyme G6Pase (glucose-6-phosphatase) has an important function in the control of hepatic glucose production. Here we examined the inhibition of G6Pase gene transcription by TNF (tumour necrosis factor) in H4IIE hepatoma cells. TNF decreased dexamethasone/dibtuyryl cAMP-induced G6Pase mRNA levels. TNFalpha, but not insulin, led to rapid activation of NFkappaB (nuclear factor kappaB). The adenoviral overexpression of a dominant negative mutant of IkappaBalpha (inhibitor of NFkappaB alpha) prevented the suppression of G6Pase expression by TNFalpha, but did not affect that by insulin. The regulation of G6Pase by TNF was not mediated by activation of the phosphoinositide 3-kinase/protein kinase B pathway, extracellular-signal-regulated protein kinase or p38 mitogen-activated protein kinase. Reporter gene assays demonstrated a concentration-dependent down-regulation of G6Pase promoter activity by the transient overexpression of NFkappaB. Although two binding sites for NFkappaB were identified within the G6Pase promoter, neither of these sites, nor the insulin response unit or binding sites for Sp proteins, was necessary for the regulation of G6Pase promoter activity by TNFalpha. In conclusion, the data indicate that the activation of NFkappaB is sufficient to suppress G6Pase gene expression, and is required for the regulation by TNFalpha, but not by insulin. We propose that NFkappaB does not act by binding directly to the G6Pase promoter.

Alternative splicing variants of dual specificity tyrosine phosphorylated and regulated kinase 1B exhibit distinct patterns of expression and functional properties.

The dual specificity tyrosine phosphorylated and regulated kinase (DYRK) family of protein kinases is a group of evolutionarily conserved protein kinases that have been characterized as regulators of growth and development in mammals, Drosophila and lower eukaryotes. In the present study, we have characterized three splicing variants of DYRK1B (DYRK1B-p65, DYRK1B-p69 and DYRK1B-p75) with different expression patterns and enzymic activities. DYRK1B-p65 and DYRK1B-p69 exhibited similar, but not identical, patterns of expression in mouse tissues, with the highest protein levels found in the spleen, lung, brain, bladder, stomach and testis. In contrast, DYRK1B-p75 was detected specifically in skeletal muscles, in the neuronal cell line GT1-7 and also in differentiated, adipocyte-like 3T3-L1 cells, but not in undifferentiated 3T3-L1 preadipocytes. A comparison of the mouse and human Dyrk1b genomic and cDNA sequences defined the alternative splicing events that produce the variants of DYRK1B. In DYRK1B-p75, transcription starts with exon 1B instead of exon 1A, generating a new translation start, which extends the open reading frame by 60 codons. This gene structure suggests that alternative promoters direct the expression of DYRK1B-p69 and DYRK1B-p75. Both splicing variants exhibited kinase activity in vitro and contained phosphotyrosine when expressed in COS-7 cells. Owing to differential recognition of the 3'-splice site in exon 9, DYRK1B-p65 differs from DYRK1B-p69 by the absence of 40 amino acids within the catalytic domain. DYRK1B-p65 lacked kinase activity in vitro and did not contain phosphotyrosine. DYRK1B-p69 and DYRK1B-p75 stimulated reporter gene activity driven by the f or kh ead in r habdosarcoma (FKHR)-dependent glucose-6-phosphatase promoter more strongly when compared with DYRK1B-p65, indicating that the DYRK1B splicing variants exhibit functional differences.