The primary cause of hypoglycaemia in Type 2 diabetes is diabetes medication-in particular, those which raise insulin levels independently of blood glucose, such as sulphonylureas (SUs) and exogenous insulin. The risk of hypoglycaemia is increased in older patients, those with longer diabetes duration, lesser insulin reserve and perhaps in the drive for strict glycaemic control. Differing definitions, data collection methods, drug type/regimen and patient populations make comparing rates of hypoglycaemia difficult. It is clear that patients taking insulin have the highest rates of self-reported severe hypoglycaemia (25% in patients who have been taking insulin for > 5 years). SUs are associated with significantly lower rates of severe hypoglycaemia. However, large numbers of patients take SUs in the UK, and it is estimated that each year > 5000 patients will experience a severe event caused by their SU therapy which will require emergency intervention. Hypoglycaemia has substantial clinical impact, in terms of mortality, morbidity and quality of life. The cost implications of severe episodes-both direct hospital costs and indirect costs-are considerable: it is estimated that each hospital admission for severe hypoglycaemia costs around £1000. Hypoglycaemia and fear of hypoglycaemia limit the ability of current diabetes medications to achieve and maintain optimal levels of glycaemic control. Newer therapies, which focus on the incretin axis, may carry a lower risk of hypoglycaemia. Their use, and more prudent use of older therapies with low risk of hypoglycaemia, may help patients achieve improved glucose control for longer, and reduce the risk of diabetic complications. Diabet. Med. 25, 245-254 (2008)

Both ␤ 2 -and ␤ 3 -adrenergic receptors (ARs) are able to activate the extracellular signal-regulated kinase (ERK) pathway. We previously showed that c-Src is required for ERK activation by ␤ 2 AR and that it is recruited to activated ␤ 2 AR through binding of the Src homology 3 (SH3) domain to proline-rich regions of the adapter protein ␤-arrestin1. Despite the absence of sites for phosphorylation and ␤-arrestin binding, ERK activation by ␤ 3 AR still requires c-Src. Agonist activation of ␤ 2 AR, but not ␤ 3 AR, led to redistribution of green fluorescent protein-tagged ␤-arrestin to the plasma membrane. In ␤-arrestin-deficient COS-7 cells, ␤-agonist-dependent coprecipitation of c-Src with the ␤ 2 AR required exogenous ␤-arrestin, but activated ␤ 3 AR co-precipitated c-Src in the absence or presence of ␤-arrestin. ERK activation and Src co-precipitation with ␤ 3 AR also occurred in adipocytes in an agonist-dependent and pertussis toxinsensitive manner. Protein interaction studies show that the ␤ 3 AR interacts directly with the SH3 domain of Src through proline-rich motifs (PXXP) in the third intracellular loop and the carboxyl terminus. ERK activation and Src co-precipitation were abolished in cells expressing point mutations in these PXXP motifs. Together, these data describe a novel mechanism of ERK activation by a G protein-coupled receptor in which the intracellular domains directly recruit c-Src.During the past several years, transmembrane signaling traffic through G protein-coupled receptors (GPCRs) 1 has grown from the classic G protein effectors such as adenylyl cyclase and phospholipases to include novel mechanisms for activation of mitogen-activated protein (MAP) kinase cascades. These signaling systems typically involve receptor and nonreceptor tyrosine kinases as scaffolds and intermediaries (1-6). An example of this flexibility in GPCR signaling includes the ␤ 2 -adrenergic receptor (␤ 2 AR). Although this receptor is classically known to couple to Gs and stimulate adenylyl cyclase, it can also activate the ERK1/2 MAP kinase pathway (7,8). In some cell types, the ␤ 2 AR activates ERK through its coupling to a PTX-sensitive G i protein and subsequent Ras-dependent MAP kinase activation (7, 9), whereas in other systems this occurs in a PTX-independent and a G s -and cAMP-dependent process (10, 11) through the activation of Rap1 (11).In exploring the mechanisms of ␤ 2 AR-stimulated MAP kinase activation, we have found that some of the same signaling molecules required for receptor desensitization can also be intimately involved in the activation of the MAP kinase cascade. Following agonist activation, most GPCRs are phosphorylated by GPCR kinases (GRKs), with subsequent binding of ␤-arrestin to the phosphorylated receptor serving to interdict G protein coupling and signal transduction (5, 12, 13). However, in addition to its role in desensitization, ␤-arrestin can also participate in the events leading to MAP kinase activation. Binding of ␤-arrestin1 to the agonist-activated ␤ 2 AR rapidly recruits ...

The ␤ 3 -adrenergic receptor (␤ 3 AR) is expressed predominantly in adipocytes, and it plays a major role in regulating lipolysis and adaptive thermogenesis. Its expression in a variety of adipocyte cell models is preceded by the appearance of CCAAT/enhancer-binding protein ␣ (C/EBP␣), which has been shown to regulate a number of other adipocyte-specific genes. Importantly, it has been demonstrated that several adipocyte cell lines that fail to express C/EBP␣ exhibit reduced insulin sensitivity, despite an apparent adipogenic phenotype. Here we show that transcription and function of the ␤ 3 AR correlates with C/EBP␣ expression in these adipocyte models. A 5.13-kilobase pair fragment of the mouse ␤ 3 AR promoter was isolated and sequenced. This fragment conferred a 50-fold increase in luciferase reporter gene expression in adipocytes. Two putative C/EBP binding sites exist at ؊3306 to ؊3298 and at ؊1462 to ؊1454, but only the more distal site is functional. Oligonucleotides corresponding to both the wild-type and mutated ؊3306 element were inserted upstream of a thymidine kinase luciferase construct. When cotransfected in fibroblasts with a C/EBP␣ expression vector, reporter gene expression increased 3-fold only in the wild-type constructs. The same mutation, when placed into the intact 5.13-kilobase pair promoter, reduced promoter activity in adipocytes from 50-fold to <10-fold. Electrophoretic mobility shift analysis demonstrated that the site at ؊3306 generated a specific protein-oligonucleotide complex that was supershifted by C/EBP␣ antibody, while a probe corresponding to a putative site at ؊1462 did not. These results define C/EBP␣ as a key transcriptional regulator of the mouse ␤ 3 AR gene during adipogenesis.The ␤ 3 -adrenergic receptor (␤ 3 AR) 1 is a unique member of the ␤AR family because, unlike the ␤ 1 AR and ␤ 2 AR, it is expressed predominantly in adipocytes and regulates both lipolysis and nonshivering thermogenesis (reviewed in Ref. 1). In genetic and dietary models of obesity, progressive accumulation of adipose tissue is associated with defects in the ability of catecholamines to mobilize lipid stores (2-4). We have previously shown that the expression and function of the adipocyte ␤ARs are blunted in most models of obesity (5, 6). Nevertheless, a curious aspect of ␤ 3 AR biology is that, despite defects in ␤ 3 AR expression and function, selective agonists for this receptor have been shown to prevent or reverse obesity (4, 7-10). The efficacy of these drugs is related to increased brown adipose tissue thermogenesis and a restoration of expression of the ␤ 3 AR and ␤ 1 AR in white adipose tissue depots (4). For these reasons it is important to understand the tissue-specific and hormonal factors that regulate the expression of this receptor. Two groups of transcription factors are known to be responsible for initiating and maintaining adipocyte differentiation: the CCAAT/enhancer-binding proteins (C/EBP) (11-17) and . From a large body of work in model adipocyte cell lines, such as 3T3-L1, it ...