Genetic deletion of β2 adrenergic receptors exacerbates hepatocellular lipid accumulation in high-fat diet mice

β₂ Adrenergic receptors (β₂ARs) are G protein-coupled receptors (GPCRs) that are expressed in major insulin target tissues. β₂ARs play an important role in the regulation of lipid metabolism during aging; however, little is known about the significance of β₂ARs in the pathogenesis of hepatic fat accumulation in high-fat diet (HFD) mice. This study aims to examine the role of β₂AR in the development of nonalcoholic fatty liver disease (NAFLD) induced by HFD and the underlying mechanisms. Surprisingly, we found that genetic deletion of β₂AR significantly increased the liver weight of mice fed a HFD for 20 weeks compared to that of wild-type (WT) mice. Moreover, genetic deletion of β₂AR could aggravate HFD-induced liver lipid accumulation and liver injury in mice. Mechanistically, we demonstrated that β₂AR deletion significantly activated PPARγ/CD36 signaling via inactivation of the cAMP response element-binding (CREB) protein to facilitate hepatocellular lipid deposition in HFD mice. Together, our results identify β₂AR as a plausible therapeutic target for preventing or treating NAFLD.

Investigation on temperature-induce conformational change of immobilized β2 adrenergic receptor

The β₂ adrenergic receptor (β₂-AR) is a prototypical family A G protein-coupled receptor (GPCR) and an excellent model system for studying the mechanism of GPCR activation. Purified β₂-AR was immobilized on macroporous silica gel to obtain liquid chromatographic stationary phase. The resulting phase was packed into a stainless steel column (4.6 × 50 mm, 7 μm) and used for on-line chromatographic system. When column oven temperature increased from 20.0 °C to 40.0 °C, uncomplete separate chromatographic peaks of ephedrine and pseudoephedrine as receptor conformational probe were gradually merged into one peak, meanwhile retention time and resolution of the probes were reduced correspondingly, which suggested that temperature could regulate protein conformation. Temperature-induced conformational change of immobilized β₂-AR, especially changes at higher temperatures, indicated that constructed receptor chromatography could simulate fever disease state of human body and clarify receptor conformation change at pathological condition. At the same time this study could also provide new ideas for screening active components in pathological conditions.

Homology modeling of a Class A GPCR in the inactive conformation: A quantitative analysis of the correlation between model/template sequence identity and model accuracy

With the present work we quantitatively studied the modellability of the inactive state of Class A G protein-coupled receptors (GPCRs). Specifically, we constructed models of one of the Class A GPCRs for which structures solved in the inactive state are available, namely the β₂ AR, using as templates each of the other class members for which structures solved in the inactive state are also available. Our results showed a detectable linear correlation between model accuracy and model/template sequence identity. This suggests that the likely accuracy of the homology models that can be built for a given receptor can be generally forecasted on the basis of the available templates. We also probed whether sequence alignments that allow for the presence of gaps within the transmembrane domains to account for structural irregularities afford better models than the classical alignment procedures that do not allow for the presence of gaps within such domains. As our results indicated, although the overall differences are very subtle, the inclusion of internal gaps within the transmembrane domains has a noticeable a beneficial effect on the local structural accuracy of the domain in question.

Structure-guided development of dual β2 adrenergic/dopamine D2 receptor agonists

Aiming to discover dual-acting β2 adrenergic/dopamine D2 receptor ligands, a structure-guided approach for the evolution of GPCR agonists that address multiple targets was elaborated. Starting from GPCR crystal structures, we describe the design, synthesis and biological investigation of a defined set of compounds leading to the identification of the benzoxazinone (R)-3, which shows agonist properties at the adrenergic β2 receptor and substantial G protein-promoted activation at the D2 receptor. This directed approach yielded molecular probes with tuned dual activity. The congener desOH-3 devoid of the benzylic hydroxyl function was shown to be a β2 adrenergic antagonist/D2 receptor agonist with Ki values in the low nanomolar range. The compounds may serve as a promising starting point for the investigation and treatment of neurological disorders.

Activation of Gαq subunits up-regulates the expression of the tumor suppressor Fhit

The tumor suppressor Fhit protein is defective or absent in many tumor cells due to methylation, mutation or deletion of the FHIT gene. Despite numerous attempts to unravel the functions of Fhit, the mechanisms by which the function and expression of Fhit are regulated remain poorly understood. We have recently shown that activated Gαq subunits interact directly with Fhit and enhance its inhibitory effect on cell growth. Here we investigated the regulation of Fhit expression by Gq. Our results showed that Fhit was up-regulated specifically by activating Gα subunits of the Gq subfamily but not by those of the other G protein subfamilies. This up-regulation effect was mediated by a PKC/MEK pathway independent of Src-mediated Fhit Tyr(114) phosphorylation. We further demonstrated that elevated Fhit expression was due to the specific regulation of Fhit protein synthesis in the ribosome by activated Gαq, where the regulations of cap-dependent protein synthesis were apparently not required. Moreover, we showed that activated Gαq could increase cell-cell adhesion through Fhit. These findings provide a possible handle to modulate the level of the Fhit tumor suppressor by manipulating the activity of Gq-coupled receptors.