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.

Borderline personality disorder: health service use and social functioning among a national household population

BACKGROUND

It is unclear whether Axis II psychopathology or co-morbid clinical syndromes result in the treatment-seeking behaviour and social impairment of patients with borderline personality disorder (BPD). This study examined the independent associations between social functioning and service use and Axis I and Axis II disorders in persons with BPD in the national household population of Britain.

METHOD

The study was a cross-sectional survey of adults aged 16-74 years in households (n=8397). Data included self-reported consultations with health-care professionals and behavioural problems. Diagnosis was determined by computer-assisted interviews. Analyses included logistic regression adjusting for demography, co-morbid Axis I clinical syndromes and other Axis II disorders.

RESULTS

Consultation in the past year was reported by 57.5% of persons with BPD but only 13.4% reported lifetime psychiatric admission. BPD was not independently associated with impaired functioning but was associated with co-morbid psychotic, depressive and anxiety disorders. Only general practitioners (GPs) were consulted for problems independently due to BPD.

CONCLUSIONS

Functional effects of BPD are mediated through co-morbid clinical syndromes, not Axis II psychopathology. A subgroup do not have co-morbid disorders or seek treatment, and are high functioning.

Severe impaired respiratory ciliary function in Wegener granulomatosis

OBJECTIVE

The pathogenesis of granulomatous inflammation in the respiratory tract and autoimmunity in Wegener granulomatosis (WG) are poorly understood. Since mucociliar clearance represents the first major line of defence in the respiratory tract and its breakdown facilitates chronic inflammation, we investigated ciliary beat frequency (CBF) in WG.

METHODS

Nasal epithelial cells were obtained from 30 patients with WG with involvement of the upper respiratory tract, 12 patients with other inflammatory rheumatic disease and 10 healthy controls. CBF was measured at 5 and 24 h after collection.

RESULTS

were correlated with clinical data. Results: CBF was significantly reduced in WG compared to disease and healthy controls after 5 and 24 h. In WG, CBF almost stagnated after 24 h. Reduction of CBF correlated with the cumulative number of immunosuppressive agents in WG, but not in disease controls. No correlation was found between CBF impairment and cyclophosphamide levels, disease extent, disease activity, disease duration, serological and microbiological findings, or inflammation markers.

CONCLUSION

CBF is severely impaired in WG, potentially influenced by immunosuppressive treatment. To what extent CBF impairment and subsequent barrier dysfunction are caused by other factors still has to be elucidated. Supportive measures to improve mucociliary clearance should be discussed in patients with WG.