Effects of glucocorticoids and exercise on pancreatic β-cell function and diabetes development

Blockage of progesterone receptor effectively protects pancreatic islet beta cell viability

The progesterone receptor (PR), a member of nuclear receptor superfamily, is closely associated with gestational, type 1 and type 2 diabetes. However, the underlying mechanisms remain obscure. Here we found that PR activation increased the pro-inflammatory cytokines (PIC)-induced injury in Min6 cells, and PR blockage with siRNA interference protected the cells from damage. Moreover, the new discovered PR antagonist SC51089 effectively improved cell survival by reducing the PIC-stimulated cell apoptosis in Min6 cells. Immunoblotting assays indicated that either PR agonist progesterone (P4) or PR-B over-expression promoted the PIC-induced reinforces of extracellular-signal-regulated kinase 1/2 phosphorylation (p-Erk) and protein 53 (p53), and the attenuations of protein kinase B phosphorylation (p-AKT) and tumor necrosis factor receptor-associated factor 2 (TRAF2). SC51089 could reverse all the P4- or PR-B over-expression induced effects. In addition, PR siRNA inference based assay further supported that SC51089 protected pancreatic islet beta cells from the PR activation or PIC-induced injury by targeting PR and this protective action was mediated by AKT signaling pathway. To our knowledge, this current work might be the first report on the regulation of PR in pancreatic islet beta cell survival. It is expected that SC51089, as a non-steroid PR antagonist, might also find its potential in anti-diabetic research.

Activation and regulation of the pattern recognition receptors in obesity-induced adipose tissue inflammation and insulin resistance

Obesity-associated chronic tissue inflammation is a key contributing factor to type 2 diabetes mellitus, and a number of studies have clearly demonstrated that the immune system and metabolism are highly integrated. Recent advances in deciphering the various immune cells and signaling networks that link the immune and metabolic systems have contributed to our understanding of the pathogenesis of obesity-associated inflammation. Other recent studies have suggested that pattern recognition receptors in the innate immune system recognize various kinds of endogenous and exogenous ligands, and have a crucial role in initiating or promoting obesity-associated chronic inflammation. Importantly, these mediators act on insulin target cells or on insulin-producing cells impairing insulin sensitivity and its secretion. Here, we discuss how various pattern recognition receptors in the immune system underlie the etiology of obesity-associated inflammation and insulin resistance, with a particular focus on the TLR (Toll-like receptor) family protein Radioprotective 105 (RP105)/myeloid differentiation protein-1 (MD-1).

Exogenous glucocorticoids and a high-fat diet cause severe hyperglycemia and hyperinsulinemia and limit islet glucose responsiveness in young male Sprague-Dawley rats

Corticosterone (CORT) and other glucocorticoids cause peripheral insulin resistance and compensatory increases in β-cell mass. A prolonged high-fat diet (HFD) induces insulin resistance and impairs β-cell insulin secretion. This study examined islet adaptive capacity in rats treated with CORT and a HFD. Male Sprague-Dawley rats (age ∼6 weeks) were given exogenous CORT (400 mg/rat) or wax (placebo) implants and placed on a HFD (60% calories from fat) or standard diet (SD) for 2 weeks (N = 10 per group). CORT-HFD rats developed fasting hyperglycemia (>11 mM) and hyperinsulinemia (∼5-fold higher than controls) and were 15-fold more insulin resistant than placebo-SD rats by the end of ∼2 weeks (Homeostatic Model Assessment for Insulin Resistance [HOMA-IR] levels, 15.08 ± 1.64 vs 1.0 ± 0.12, P < .05). Pancreatic β-cell function, as measured by HOMA-β, was lower in the CORT-HFD group as compared to the CORT-SD group (1.64 ± 0.22 vs 3.72 ± 0.64, P < .001) as well as acute insulin response (0.25 ± 0.22 vs 1.68 ± 0.41, P < .05). Moreover, β- and α-cell mass were 2.6- and 1.6-fold higher, respectively, in CORT-HFD animals compared to controls (both P < .05). CORT treatment increased p-protein kinase C-α content in SD but not HFD-fed rats, suggesting that a HFD may lower insulin secretory capacity via impaired glucose sensing. Isolated islets from CORT-HFD animals secreted more insulin in both low and high glucose conditions; however, total insulin content was relatively depleted after glucose challenge. Thus, CORT and HFD, synergistically not independently, act to promote severe insulin resistance, which overwhelms islet adaptive capacity, thereby resulting in overt hyperglycemia.

Regulation of forkhead box O1 (FOXO1) by protein kinase B and glucocorticoids: different mechanisms of induction of beta cell death in vitro

AIMS/HYPOTHESIS

In steroid diabetes insulin secretion does not adequately compensate for enhanced hepatic gluconeogenesis and peripheral insulin resistance. Previous studies suggest that activation of the transcription factor forkhead box O1 (FOXO1) contributes to glucocorticoid-induced beta cell death. This study examines the role and regulation of FOXO1 in insulin-secreting cells.

METHODS

INS-1E cells and mouse islet cells were cultured in the presence of dexamethasone. Signalling pathways were modified pharmacologically or by small interfering (si)RNA-mediated inhibition of protein synthesis. Changes in protein abundance and phosphorylation were analysed by western blotting, and subcellular localisation was assessed using confocal microscopy. Transcript levels were examined by RT-PCR.

RESULTS

Surprisingly, downregulation of FOXO1 by siRNA did not affect dexamethasone-induced apoptosis or Bim expression, but it prevented the effects of the pan protein kinase B (AKT) inhibitor (Akti-1/2). Indeed, dexamethasone and Akti-1/2 synergistically increased beta cell death and Bim expression. Akti-1/2 triggered dephosphorylation and nuclear translocation of FOXO1. Glucocorticoid-receptor activation stimulated Foxo1 transcription, but FOXO1 phosphorylation was unchanged and the cytosolic concentration of FOXO1 remained high in relation to its nuclear concentration. However, subcellular fractionation revealed a significant increase in both cytosolic and nuclear FOXO1 compared with untreated cells. Dexamethasone diminished Pdx1 mRNA level, an effect which was not reversed by siRNA against Foxo1. Downregulation of AKT isoforms and serum/glucocorticoid-regulated kinase 1 (SGK1) suggests that only sustained suppression of all three AKT isoforms caused dephosphorylation and nuclear accumulation of FOXO1.

CONCLUSIONS/INTERPRETATION

This study reveals that FOXO1 is not the main mediator of glucocorticoid-receptor-induced beta cell apoptosis, but rather that it escalates beta cell death when AKT activity is inhibited by distinct pathways.

Therapy of adrenal insufficiency: an update

Adrenal insufficiency may be caused by the destruction or altered function of the adrenal gland with a primary deficit in cortisol secretion (primary adrenal insufficiency) or by hypothalamic-pituitary pathologies determining a deficit of ACTH (secondary adrenal insufficiency). The clinical picture is determined by the glucocorticoid deficit, which may in some conditions be accompanied by a deficit of mineralcorticoids and adrenal androgens. The substitutive treatment is aimed at reducing the signs and symptoms of the disease as well as at preventing the development of an addisonian crisis, a clinical emergency characterized by hypovolemic shock. The oral substitutive treatment should attempt at mimicking the normal circadian profile of cortisol secretion, by using the lower possible doses able to guarantee an adequate quality of life to patients. The currently available hydrocortisone or cortisone acetate preparations do not allow an accurate reproduction of the physiological secretion pattern of cortisol. A novel dual-release formulation of hydrocortisone, recently approved by EMEA, represents an advancement in the optimization of the clinical management of patients with adrenal insufficiency. Future clinical trials of immunomodulation or immunoprevention will test the possibility to delay (or prevent) the autoimmune destruction of the adrenal gland in autoimmune Addison's disease.

MicroRNAs and Glucocorticoid-Induced Apoptosis in Lymphoid Malignancies

The initial response of lymphoid malignancies to glucocorticoids (GCs) is a critical parameter predicting successful treatment. Although being known as a strong inducer of apoptosis in lymphoid cells for almost a century, the signaling pathways regulating the susceptibility of the cells to GCs are only partly revealed. There is still a need to develop clinical tests that can predict the outcome of GC therapy. In this paper, I discuss important parameters modulating the pro-apoptotic effects of GCs, with a specific emphasis on the microRNA world comprised of small players with big impacts. The journey through the multifaceted complexity of GC-induced apoptosis brings forth explanations for the differential treatment response and raises potential strategies for overcoming drug resistance.

The circadian clock in cancer development and therapy

Most aspects of mammalian function display circadian rhythms driven by an endogenous clock. The circadian clock is operated by genes and comprises a central clock in the brain that responds to environmental cues and controls subordinate clocks in peripheral tissues via circadian output pathways. The central and peripheral clocks coordinately generate rhythmic gene expression in a tissue-specific manner in vivo to couple diverse physiological and behavioral processes to periodic changes in the environment. However, with the industrialization of the world, activities that disrupt endogenous homeostasis with external circadian cues have increased. This change in lifestyle has been linked to an increased risk of diseases in all aspects of human health, including cancer. Studies in humans and animal models have revealed that cancer development in vivo is closely associated with the loss of circadian homeostasis in energy balance, immune function, and aging, which are supported by cellular functions important for tumor suppression including cell proliferation, senescence, metabolism, and DNA damage response. The clock controls these cellular functions both locally in cells of peripheral tissues and at the organismal level via extracellular signaling. Thus, the hierarchical mammalian circadian clock provides a unique system to study carcinogenesis as a deregulated physiological process in vivo. The asynchrony between host and malignant tissues in cell proliferation and metabolism also provides new and exciting options for novel anticancer therapies.