Aims/hypothesis: Activin receptor-like kinase 7 (ALK7), a member of the type I receptor serine/threonine kinases of the TGF-β superfamily, was recently reported to regulate cell proliferation and apoptosis. We hypothesised that ALK7 may play a role in modulating pancreatic beta cell proliferation and/or apoptosis. Methods: We detected ALK7 expression in beta cells using RT-PCR, immunostaining and western blotting. Constitutively active, dominant negative or wild-type ALK7 was introduced into beta cells using adenoviral delivery. Proliferation was assessed using 3 H-thymidine incorporation and apoptosis was quantified using terminal deoxynucleotidyl transferase biotin-dUTP nick end labelling detection, DNA degradation analysis and caspase-3 assays. Results: Induction of constitutively active ALK7 in beta cells resulted in growth inhibition and enhanced apoptosis; no effect was seen with INS-1 cells expressing wild-type or dominant negative ALK7. Elevated glucose concentrations and fatty acid (palmitate) markedly increased expression levels of ALK7 transcripts and proteins in INS-1 and rat islets and increased beta cell apoptosis. Activation of ALK7 increased Smad2 phosphorylation, reduced protein kinase B (Akt) kinase activity and was associated with increased levels of the bioactive forms of caspase-3, whereas co-expression of constitutively active ALK7 with dominant negative Smad2 or constitutively active Akt significantly diminished ALK7-induced growth inhibition and apoptosis in INS-1 cells. Although overexpression of constitutively active Akt significantly reduced ALK7-induced growth inhibition and ALK7-enhanced beta cell apoptosis, ALK7-stimulated Smad2 phosphorylation was not affected. Conclusions/ interpretation: These results suggest that the pancreatic beta cell apoptosis induced by ALK7 activation occurs via the activation of two distinct downstream pathways: the suppression of Akt activation and the activation of the Smad2-caspase-3 cascade.

Background and purpose: Some non-steroidal anti-inflammatory drugs (NSAIDs) incidentally induce hypoglycemia, which is often seen in diabetic patients receiving sulphonylureas. NSAIDs influence various ion channel activities, thus they may cause hypoglycemia by affecting ion channel functions in insulin secreting beta cells. This study investigated the effects of the NSAID meclofenamic acid (MFA) on the electrical excitability and the secretion of insulin from pancreatic beta cells. Experimental approach: Using patch clamp techniques and insulin secretion assays, the effects of MFA on the membrane potential and transmembrane current of INS-1 cells, and insulin secretion were studied. Key results: Under perforated patch recordings, MFA induced a rapid depolarization in INS-1 cells bathed in low (2.8mM), but not high (28mM) glucose solutions. MFA, as well as acetylsalicylic acid (ASA) and flufenamic acid (FFA), excited the cells by inhibiting ATP-sensitive potassium channels (K ATP ). In whole cell recordings, K ATP conductance consistently appeared when intracellular ATP was diluted. Intracellular glibenclamide prevented the development of K ATP activity, whereas intracellular MFA had no effect. At low glibenclamide concentrations, MFA induced additional inhibition of the K ATP current. Live cell Ca 2 þ imaging displayed that MFA elevated intracellular Ca 2 þ at low glucose concentrations. Furthermore, MFA dose-dependently increased insulin release under low, but not high, glucose conditions. Conclusions and Implications: MFA blocked K ATP through an extracellular mechanism and thus increased insulin secretion. As some NSAIDs synergistically inhibit K ATP activity together with sulphonylureas, the risk of NSAID-induced hypoglycemia should be considered when glucose-lowering compounds are administered.