Atrial fibrillation (AF) is prevalent in diabetes mellitus (DM); however, the basis for this is unknown. This study investigated AF susceptibility and atrial electrophysiology in type 1 diabetic Akita mice using in vivo intracardiac electrophysiology, high-resolution optical mapping in atrial preparations, and patch clamping in isolated atrial myocytes. qPCR and western blotting were used to assess ion channel expression. Akita mice were highly susceptible to AF in association with increased P-wave duration and slowed atrial conduction velocity. In a second model of type 1 DM, mice treated with streptozotocin (STZ) showed a similar increase in susceptibility to AF. Chronic insulin treatment reduced susceptibility and duration of AF and shortened P-wave duration in Akita mice. Atrial action potential (AP) morphology was altered in Akita mice due to a reduction in upstroke velocity and increases in AP duration. In Akita mice, atrial Na+current (INa) and repolarizing K+current (IK) carried by voltage gated K+(Kv1.5) channels were reduced. The reduction in INaoccurred in association with reduced expression ofSCN5aand voltage gated Na+(NaV1.5) channels as well as a shift in INaactivation kinetics. Insulin potently and selectively increased INain Akita mice without affecting IK. Chronic insulin treatment increased INain association with increased expression of NaV1.5. Acute insulin also increased INa, although to a smaller extent, due to enhanced insulin signaling via phosphatidylinositol 3,4,5-triphosphate (PIP3). Our study reveals a critical, selective role for insulin in regulating atrial INa, which impacts susceptibility to AF in type 1 DM.

Oxidative stress is implicated in the pathogenesis of many inflammatory pulmonary diseases, including cystic fibrosis (CF). Delineating how oxidative stress stimulates CF transmembrane conductance regulator (CFTR) in airway epithelial cells is useful, both to increase the understanding of airways host defense and suggest therapeutic approaches to reduce the oxidant stress burden in the CF lung. Using the airway epithelial cell line Calu-3, we investigated the hypothesis that hydrogen peroxide (H 2 O 2 ), which stimulates anion efflux through CFTR, does so via the production of prostaglandin E 2 (PGE 2 ). Using iodide efflux as a biochemical marker of CFTR activity and short circuit current (I sc ) recordings, we found that the H 2 O 2 -stimulated efflux was abolished by cyclooxygenase-1 inhibition and potentially also involves microsomal prostaglandin E synthase-1 activity, implicating a role for PGE 2 production. Furthermore, H 2 O 2 application resulted in a rapid release of PGE 2 from Calu-3 cells. We additionally hypothesized that the PGE 2 subtype 4 (EP 4 ) receptor was involved in mediating this response. In the presence of (4Z)-7-[(rel-1S,2S,5R)-5-((1,1Ј-biphenyl-4-yl)methoxy)-2-(4-morpholinyl)-3-oxocyclopentyl]-4-heptenoic acid (AH23848) (which blocks the EP 4 receptor), the H 2 O 2 -stimulated response was abolished. To investigate this finding in a polarized system, we measured the increase in I sc induced by H 2 O 2 addition in the presence and absence of AH23848. H 2 O 2 induced a robust increase in I sc , which was significantly attenuated in the presence of AH23848, suggesting some role for the EP 4 receptor. In conclusion, with H 2 O 2 as a model oxidant stress, stimulation of CFTR seems to involve PGE 2 production and likely EP 4 receptor activation in Calu-3 airway epithelial cells. This mechanism would be compromised in the CF airways.

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Interleukin (IL)‐22 is a pleiotropic cytokine which predominately targets epithelial cells. IL‐22 has been implicated in increasing epithelial host defence via a number of different mechanisms and we hypothesized its IL‐22 application would stimulate several protective mechanisms in airway epithelial cells. Using the model human airway bronchial epithelial cell line 16HBEo− we investigated the ability of IL‐22 to increase CFTR expression, and determined that treatment for 24 hours increased CFTR gene and protein expression, resulting in increased CFTR activity measured via iodide efflux assays. Furthermore, IL‐22 increased mRNA expression for the anti‐microbial peptides human beta‐defensin‐2 (hDB‐2) and neutrophil gelatinase‐associated lipocalin (NGAL), but had no effect on expression of the cathelicidin LL‐37. Additionally, we investigated the ability of IL‐22 to enhance epithelial repair using a mechanical wounding model, and determined that its presence significantly enhanced would healing in this model. IL‐22 application was associated with increased STAT‐3 phosphorylation. This is the first report of IL‐22 acting to increase CFTR expression and functionality, which together with its ability to increase anti‐microbial peptide expression and would healing ability, confirm its role as a potentially important factor in the airway epithelial host defence and repair. CFCanada and NSERC.

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Psoriasin is a low molecular weight, Ca2+binding protein with antimicrobial activity. Using RT‐PCR and immunoblotting, we determined that psoriasin is expressed in a number of human airway epithelial cells lines. We next investigated physiological and pathophysiological mediators we hypothesised might influence psoriasin expression, specifically comparing the normal human bronchial epithelial cell line 16HBE14o‐ to the CF bronchial epithelial cell line CFBE41o‐. Psoriasin was expressed at much lower levels in the CFBE41o‐ cells compared to non‐CF cells. Treatment with the cytokine IL‐22 significantly upregulated psoriasin expression in the 16HBE14o‐ cells, while there was no effect on the CFBE41o‐ cells. Treatment with the pro‐inflammatory cytokines IFNγ, TNF‐α and IL‐1β also effected psoriasin expression: IFNγ and TNF‐α increased expression in both cell lines, while IL‐1β increased expression in the CFBE41o‐ cells only. Exposure to the oxidant stresser t‐butylhydroperoxide decreased psoriasin expression in normals with no effect on the CF cell line. Finally, inhibition of the CFTR Cl‐ channel also affected psoriasin expression. This is the first evidence of psoriasin expression in human airway epithelia, and suggests that differential responses exist between normal and CF airway cells, potentially contributing to their innate antimicrobial defence. Supported by the Canadian CF Foundation.

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