Impaired functioning of pancreatic β cells is a key hallmark of type 2 diabetes. β cell function is modulated by the actions of different classes of heterotrimeric G proteins. The functional consequences of activating specific β cell G protein signaling pathways in vivo are not well understood at present, primarily due to the fact that β cell G protein-coupled receptors (GPCRs) are also expressed by many other tissues. To circumvent these difficulties, we developed a chemical-genetic approach that allows for the conditional and selective activation of specific β cell G proteins in intact animals. Specifically, we created two lines of transgenic mice each of which expressed a specific designer GPCR in β cells only. Importantly, the two designer receptors differed in their G protein-coupling properties (G _q/11 versus G _s ). They were unable to bind endogenous ligand(s), but could be efficiently activated by an otherwise pharmacologically inert compound (clozapine-N-oxide), leading to the conditional activation of either β cell G _q/11 or G _s G proteins. Here we report the findings that conditional and selective activation of β cell G _q/11 signaling in vivo leads to striking increases in both first- and second-phase insulin release, greatly improved glucose tolerance in obese, insulin-resistant mice, and elevated β cell mass, associated with pathway-specific alterations in islet gene expression levels. Selective stimulation of β cell G _s triggered qualitatively similar in vivo metabolic effects. Thus, this developed chemical-genetic strategy represents a powerful approach to study G protein regulation of β cell function in vivo.

In this work we discuss how to use photophysical information for improved quantitative measurements using Photo Activated Localization Microscopy (PALM) imaging. We introduce a method that reliably estimates the number of photoblinking molecules present in a biological sample and gives a robust way to quantify proteins at the single-cell level from PALM images. We apply this method to determine the amount of β2 adrenergic receptor, a prototypical G Protein Coupled Receptor, expressed on the plasma membrane of HeLa cells.

Atypical antipsychotics (AAPs) are commonly prescribed medications to treat schizophrenia, bipolar disorders and other psychotic disorders. However, they might cause metabolic syndrome (MetS) in terms of weight gain, dyslipidemia, type 2 diabetes (T2D), and high blood pressure, which are responsible for reduced life expectancy and poor adherence. Importantly, there is clear evidence that early metabolic disturbances can precede weight gain, even if the latter still remains the hallmark of AAPs use. In fact, AAPs interfere profoundly with glucose and lipid homeostasis acting mostly on hypothalamus, liver, pancreatic β-cells, adipose tissue, and skeletal muscle. Their actions on hypothalamic centers via dopamine, serotonin, acetylcholine, and histamine receptors affect neuropeptides and 5′AMP-activated protein kinase (AMPK) activity, thus producing a supraphysiological sympathetic outflow augmenting levels of glucagon and hepatic glucose production. In addition, altered insulin secretion, dyslipidemia, fat deposition in the liver and adipose tissues, and insulin resistance become aggravating factors for MetS. In clinical practice, among AAPs, olanzapine and clozapine are associated with the highest risk of MetS, whereas quetiapine, risperidone, asenapine and amisulpride cause moderate alterations. The new AAPs such as ziprasidone, lurasidone and the partial agonist aripiprazole seem more tolerable on the metabolic profile. However, these aspects must be considered together with the differences among AAPs in terms of their efficacy, where clozapine still remains the most effective. Intriguingly, there seems to be a correlation between AAP’s higher clinical efficacy and increase risk of metabolic alterations. Finally, a multidisciplinary approach combining psychoeducation and therapeutic drug monitoring (TDM) is proposed as a first-line strategy to avoid the MetS. In addition, pharmacological treatments are discussed as well.

Evidence for heterodimerization has recently been provided for dopamine D₁ and adenosine A₁ receptors as well as for dopamine D₂ and somatostatin SSTR₅ receptors. In this paper, we have studied the possibility that D₂ and D₃receptors interact functionally by forming receptor heterodimers. Initially, we split the two receptors at the level of the third cytoplasmic loop into two fragments. The first, containing transmembrane domains (TM) I to V and the N-terminal part of the third cytoplasmic loop, was named D_2trunk or D_3trunk, and the second, containing the C-terminal part of the third cytoplasmic loop, TMVI and TMVII, and the C-terminal tail, was named D_2tail or D_3tail. Then we defined the pharmacological profiles of the homologous (D_2trunk/D_2tail and D_3trunk/D_3tail) as well as of the heterologous (D_2trunk/D_3tail and D_3trunk/D_2tail) cotransfected receptor fragments. The pharmacological profile of the cross-cotransfected fragments was different from that of the native D₂ or D₃ receptors. In most cases, the D_3trunk/D_2tail was the one with the highest affinity for most agonists and antagonists. Moreover, we observed that all of these receptor fragments reduced the expression of the wild type dopamine D₂ and D₃ receptors, suggesting that D₂ and D₃ receptors can form complexes with these fragments and that these complexes bind [³H]nemonapride less efficiently or are not correctly targeted to the membrane. In a second set of experiments, we tested the ability of the split and the wild type receptors to inhibit adenylyl cyclase (AC) types V and VI. All of the native and split receptors inhibited AC-V and AC-VI, with the exception of D₃, which was unable to inhibit AC-VI. We therefore studied the ability of D₂ and D₃ to interact functionally with one another to inhibit AC-VI. We found that with D₂ alone, R-(+)-7-hydroxydypropylaminotetralin hydrobromide inhibited AC-VI with an IC₅₀ of 2.05 ± 0.15 nm, while in the presence of D₂ and D₃ it inhibited AC-VI with an IC₅₀ of 0.083 ± 0.011 nm. Similar results were obtained with a chimeric cyclase made from AC-V and AC-VI. Coimmunoprecipitation experiments indicate that D₂ and D₃ receptors are capable of physical interaction.