Effects of some 5-hydroxytryptamine and related ligands in anxiety models

Drugs acting at 5-HT receptors were evaluated on three animal models of anxiety. On the elevated X-maze test the majority of 5-HT1 agonists were found to be anxiogenic. However, ipsapirone was anxiolytic and buspirone and gepirone were inactive. The 5-HT2 agonist DOI and the 5-HT2 antagonist ritanserin were anxiolytic while ICI 169,369, a 5-HT2 antagonist was inactive. All 5-HT3 antagonists tested were inactive in this test, while the indirect serotomimetics zimeldine and fenfluramine were anxiogenic. Neither beta-adrenoceptor agonists nor antagonists had reproducible effects on anxiety in this model. Combined beta-1/beta-2 adrenoceptor antagonists reversed the anxiogenic effects of 8-OH-DPAT while selective beta-1 or beta-2 antagonists did not. On the social interaction model the 5-HT1 agonists 8-OH-DPAT, RU 24969 and 5-MeODMT were anxiogenic and ipsapirone was anxiolytic. The 5-HT2 agonist DOI and the beta-adrenoceptor- and 5-HT- antagonist pindolol were anxiolytic, while the 5-HT2 and 5-HT3 antagonists were inactive. In the marble burying test, the 5-HT upake inhibitors zimeldine, fluvoxamine, indalpine and citalopram, the 5-HT1B/5-HT1C agonists mCPP and TFMPP and the 5-HT2/5-HT1C agonist DOI reduced marble burying without affecting locomotor activity. 5-HT1A agonists and the 5-HT2 and 5-HT3 antagonists were without effect. Lesions of the dorsal raphe nucleus reversed the anxiogenic effects of 8-OH-DPAT in the X-maze model. The implication of these results for the understanding of the pharmacology of 5-HT in anxiety is discussed.

Mutations of beta-arrestin 2 that limit self-association also interfere with interactions with the beta2-adrenoceptor and the ERK1/2 MAPKs:implications for beta2-adrenoceptor signalling via the ERK1/2 MAPKs

FRET (fluorescence resonance energy transfer) and co-immunoprecipitation studies confirmed the capacity of beta-arrestin 2 to self-associate. Amino acids potentially involved in direct protein-protein interaction were identified via combinations of spot-immobilized peptide arrays and mapping of surface exposure. Among potential key amino acids, Lys(285), Arg(286) and Lys(295) are part of a continuous surface epitope located in the polar core between the N- and C-terminal domains. Introduction of K285A/R286A mutations into beta-arrestin 2-eCFP (where eCFP is enhanced cyan fluorescent protein) and beta-arrestin 2-eYFP (where eYFP is enhanced yellow fluorescent protein) constructs substantially reduced FRET, whereas introduction of a K295A mutation had a more limited effect. Neither of these mutants was able to promote beta2-adrenoceptor-mediated phosphorylation of the ERK1/2 (extracellular-signal-regulated kinase 1/2) MAPKs (mitogen-activated protein kinases). Both beta-arrestin 2 mutants displayed limited capacity to co-immunoprecipitate ERK1/2 and further spot-immobilized peptide arrays indicated each of Lys(285), Arg(286) and particularly Lys(295) to be important for this interaction. Direct interactions between beta-arrestin 2 and the beta2-adrenoceptor were also compromised by both K285A/R286A and K295A mutations of beta-arrestin 2. These were not non-specific effects linked to improper folding of beta-arrestin 2 as limited proteolysis was unable to distinguish the K285A/R286A or K295A mutants from wild-type beta-arrestin 2, and the interaction of beta-arrestin 2 with JNK3 (c-Jun N-terminal kinase 3) was unaffected by the K285A/R286A or L295A mutations. These results suggest that amino acids important for self-association of beta-arrestin 2 also play an important role in the interaction with both the beta2-adrenoceptor and the ERK1/2 MAPKs. Regulation of beta-arrestin 2 self-association may therefore control beta-arrestin 2-mediated beta2-adrenoceptor-ERK1/2 MAPK signalling.

The role of adipokines in beta-cell failure of type 2 diabetes

Beta-cell failure coupled with insulin resistance is a key factor in the development of type 2 diabetes. Changes in circulating levels of adipokines, factors released from adipose tissue, form a significant link between excessive adiposity in obesity and both aforementioned factors. In this review we consider the published evidence for the role of individual adipokines on the function, proliferation, death and failure of beta-cells, focusing on those reported to have the most significant effects (leptin, adiponectin, TNFa, resistin, visfatin, DPP-IV and apelin). It is apparent that some adipokines have beneficial effects whereas others have detrimental properties; the overall contribution to beta-cell failure of changed concentrations of adipokines in the blood of obese pre-diabetic subjects will be highly dependent on the balance between these effects and the interactions between the adipokines which act on the beta-cell via a number of intersecting intracellular signalling pathways. We emphasise the importance, and comparative dearth, of studies into the combined effects of adipokines on beta-cells.

Leptin decreases apoptosis and alters BCL-2:bax ratio in clonal rodent pancreatic beta-cells

The adipocyte derived peptide hormone leptin is known to regulate apoptosis and cell viability in several cells and tissues, as well as having several pancreatic islet beta-cell specific effects such as inhibition of glucose-stimulated insulin secretion. This study investigated the effects of leptin upon apoptosis induced by serum depletion and on expression of the apoptotic regulators B-cell leukaemia 2 gene product (BCL-2) and BCL2-associated X protein (Bax) in the glucose-responsive BRIN-BD11 beta-cell line.