Uncovering molecular mechanisms involved in activation of G protein-coupled receptors

Photobiomodulation and Stem Cell Therapy for Temporomandibular Joint Disc Disorders

Background: Temporomandibular disorder (TMD) refers to a group of disorders affecting the temporomandibular joint (TMJ) and its related muscles. The two commonly used treatment modalities for TMD are occlusal splint therapy and relaxation therapy. Neither comprises definitive treatment. Objective: The objective of this review was to report updated information on photobiomodulation and stem cells, as an alternative treatment for the degenerative TMJ disc as a part of TMJ disorders. Materials and methods: With only a few research studies reported till date, this review also proposes the mechanism of laser irradiation on inflammatory mediators to treat TMD. Results: Photobiomodulation of stem cells with and without scaffolds could be used indirectly or directly as modulation of degenerative changes of the TMJ disc. Conclusions: The need for a distinct shift of the research margin in this field of dentistry is evident, specifically regarding the application of photobiomodulation and stem cells for tissue engineering of the TMJ disc.

Selectivity in agonist and antagonist binding to Serotonin1A receptors via G-protein coupling

G protein-coupled receptors (GPCRs) constitute the largest superfamily of membrane proteins in higher eukaryotes, and facilitate information transfer from the extracellular environment to the cellular interior upon activation by ligands. Their role in diverse signaling processes makes them an attractive choice as drug targets. GPCRs are coupled to heterotrimeric G-proteins which represent an important interface through which signal transduction occurs across the plasma membrane upon activation by ligands. To obtain further insight into the molecular details of interaction of G-proteins with GPCRs, in this work, we explored the selectivity of binding of specific agonists and antagonists to the serotonin_1A receptor under conditions of progressive G-protein inactivation. The serotonin_1A receptor is an important neurotransmitter receptor belonging to the GPCR family and is a popular drug target. By use of a number of agents to inactivate G-proteins, we show here that the serotonin_1A receptor displays differential discrimination between agonist and antagonist binding. Our results show a reduction in binding sites of the receptor upon treatment with G-protein inactivating agents. In addition, G-protein coupling efficiency was enhanced when G-proteins were inactivated using urea and alkaline pH. We envision that our results could be useful in achieving multiple signaling states of the receptor by fine tuning the conditions of G-protein inactivation and in structural biology of GPCRs bound to specific ligands.

Estrogen Promotes cAMP Production in Mesenchymal Stem Cells by Regulating ADCY2

Background and Objectives

The maternal-fetal interface is an important source of mesenchymal stem cells (MSCs), and it is influenced by high levels of estradiol (E2) during pregnancy. It is highly important to study the role of E2 in MSCs for both clinical application and understanding of the mechanisms underlying pregnancy related diseases.

Methods and Results

In this study, differently expressed genes (DEGs) were found in the MSCs after exposure to E2. Then, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of DEGs was performed and the integrated regulatory network of DEGs-miRNA was constructed. A total of 390 DEGs were found in the MSCs exposed to E2, including 164 upregulated DEGs (e.g. ADCY2, VEGFA and PPY) and 226 downregulated DEGs (e.g. KNG1, AGT and NPY). Additionally, 10 miRNAs (such as miR-148A/B, miR-152, miR-182) identified the integrated regulatory network of DEGs-miRNAs. Among them, the expression of ADCY2 was significantly upregulated, and this was associated with multiple changed genes. We confirmed that the expression of ADCY2 is significantly promoted by E2 and subsequently promoted the production of cAMP in MSCs. We also found that E2 promoted ADCY2 expression by inhibiting miR-152 and miR-148a.

Conclusions

E2 promotes the expression of cAMP through miR-148a/152-ADCY2 in MSCs. It is suggested that E2 plays a key role in the growth and function of MSCs.

Characterization of gonadotropin receptors Fshr and Lhr in Japanese medaka, Oryzias latipes

Reproduction in vertebrates is controlled by the brain-pituitary-gonad axis, where the two gonadotropins follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh) play vital parts by activating their cognate receptors in the gonads. The main purpose of this work was to study intra- and interspecies ligand promiscuity of teleost gonadotropin receptors, since teleost receptor specificity is unclear, in contrast to mammalian receptors. Receptor activation was investigated by transfecting COS-7 cells with either Fsh receptor (mdFshr, tiFshr) or Lh receptor (mdLhr, tiLhr), and tested for activation by recombinant homologous and heterologous ligands (mdFshβα, mdLhβα, tiFshβα, tiLhβα) from two representative fish orders, Japanese medaka (Oryzias latipes, Beloniformes) and Nile tilapia (Oreochromis niloticus, Cichliformes). Results showed that each gonadotropin preferentially activates its own cognate receptor. Cross-reactivity was detected to some extent as mdFshβα was able to activate the mdLhr, and mdLhβα the mdFshr. Medaka pituitary extract (MPE) stimulated CRE-LUC activity in COS-7 cells expressing mdlhr, but could not stimulate cells expressing mdfshr. Recombinant tiLhβα, tiFshβα and tilapia pituitary extract (TPE) could activate the mdLhr, suggesting cross-species reactivity for mdLhr. Cross-species reactivity was also detected for mdFshr due to activation by tiFshβα, tiLhβα, and TPE, as well as for tiFshr and tiLhr due to stimulation by mdFshβα, mdLhβα, and MPE. Tissue distribution analysis of gene expression revealed that medaka receptors, fshr and lhr, are highly expressed in both ovary and testis. High expression levels were found for lhr also in brain, while fshr was expressed at low levels. Both fshr and lhr mRNA levels increased significantly during testis development. Amino acid sequence alignment and three-dimensional modelling of ligands and receptors highlighted conserved beta sheet domains of both Fsh and Lh between Japanese medaka and Nile tilapia. It also showed a higher structural homology and similarity of transmembrane regions of Lhr between both species, in contrast to Fshr, possibly related to the substitution of the conserved cysteine residue in the transmembrane domain 6 in medaka Fshr with glycine. Taken together, this is the first characterization of medaka Fshr and Lhr using homologous ligands, enabling to better understand teleost hormone-receptor interactions and specificities. The data suggest partial ligand promiscuity and cross-species reactivity between gonadotropins and their receptors in medaka and tilapia.

Phote-HrTH (Phormia terraenovae Hypertrehalosaemic Hormone), the Metabolic Hormone of the Fruit Fly: Solution Structure and Receptor Binding Model

Fruit flies are a widely distributed pest insect that pose a significant threat to food security. Flight is essential for the dispersal of the adult flies to find new food sources and ideal breeding spots. The supply of metabolic fuel to power the flight muscles of insects is regulated by adipokinetic hormones (AKHs). The fruit fly, Drosophila melanogaster, has the same AKH that is present in the blowfly, Phormia terraenovae; this AKH has the code-name Phote-HrTH. Binding of the AKH to the extra-cellular binding site of a G protein-coupled receptor causes its activation. In this paper, the structure of Phote-HrTH in sodium dodecyl sulfate (SDS) micelle solution was determined using NMR restrained molecular dynamics. The peptide was found to bind to the micelle and be fairly rigid, with an S2 order parameter of 0.96. The translated protein sequence of the AKH receptor from the fruit fly, D. melanogaster, Drome-AKHR, was used to construct two models of the receptor. It is proposed that these two models represent the active and inactive state of the receptor. The model based on the crystal structure of the β-2 adrenergic receptor was found to bind Phote-HrTH with a binding constant of −102kJmol−1, while the other model, based on the crystal structure of rhodopsin, did not bind the peptide. Under molecular dynamic simulation, in a palmitoyloleoylphosphatidylcholine (POPC) membrane, the receptor complex changed from an inactive to an active state. The identification and characterisation of the ligand binding site of Drome-AKHR provide novel information of ligand–receptor interaction, which could lead to the development of species-specific control substances to use discriminately against the fruit fly.

Mechanobiology of annulus fibrosus and nucleus pulposus cells in intervertebral discs

Low back pain (LBP) is a chronic condition that can affect up to 80% of the global population. It is the number one cause of disability worldwide and has enormous socioeconomic consequences. One of the main causes of this condition is intervertebral disc (IVD) degeneration. IVD degenerative processes and inflammation associated with it has been the subject of many studies in both tissue and cell level. It is believed that the phenotype of the resident cells within the IVD directly affects homeostasis of the tissue. At the same time, IVDs located between vertebral bodies of spine are under various mechanical loading conditions in vivo. Therefore, investigating how mechanical loading can affect the behaviour of IVD cells has been a subject of many research articles. In this review paper, following a brief explanation of the anatomy of the IVD and its resident cells, we compiled mechanobiological studies of IVD cells (specifically, annulus fibrosus and nucleus pulposus cells) and synthesized and discussed the key findings of the field.

Integrated structural modeling and super-resolution imaging resolve GPCR oligomers

Formation of G protein-coupled receptors (GPCRs) dimers and higher order oligomers represents a key mechanism in pleiotropic signaling, yet how individual protomers function within oligomers remains poorly understood. For the Class A/rhodopsin subfamily of glycoprotein hormone receptors (GpHRs), di/oligomerization has been demonstrated to play a significant role in regulating its signaling activity at a cellular and physiological level and even pathophysiologically. Here we will describe and discuss the developments in our understanding of GPCR oligomerization, in both health and disease, from the study of this unique and complex subfamily of GPCRs with light on the luteinizing hormone receptor (LHR). Focus will be put on the results of an approach relying on the combination of atomistic modeling by protein-protein docking with super-resolution imaging. The latter could resolve single LHR molecules to ~8nm resolution in functional asymmetric dimers and oligomers, using dual-color photoactivatable dyes and localization microscopy (PD-PALM). Structural modeling of functionally asymmetric LHR trimers and tetramers strongly aligned with PD-PALM-imaged spatial arrangements, identifying multiple possible helix interfaces mediating inter-protomer associations. Diverse spatial and structural assemblies mediating GPCR oligomerization may acutely fine-tune the cellular signaling profile.

The repertoire of family A-peptide GPCRs in archaic hominins

Given the importance of G-protein coupled receptors in the regulation of many physiological functions, deciphering the relationships between genotype and phenotype in past and present hominin GPCRs is of main interest to understand the evolutionary process that contributed to the present-day variability in human traits and health. Here, we carefully examined the publicly available genomic and protein sequence databases of the archaic hominins (Neanderthal and Denisova) to draw up the catalog of coding variations in GPCRs for peptide ligands, in comparison with living humans. We then searched in the literature the functional changes, phenotypes and risk of disease possibly associated with the detected variants. Our survey suggests that Neanderthal and Denisovan hominins were likely prone to lower risk of obesity, to enhanced platelet aggregation in response to thrombin, to better response to infection, to less anxiety and aggressiveness and to favorable sociability. While some archaic variants were likely advantageous in the past, they might be responsible for maladaptive disorders today in the context of modern life and/or specific regional distribution. For example, an archaic haplotype in the neuromedin receptor 2 is susceptible to confer risk of diabetic nephropathy in type 1 diabetes in present-day Europeans. Paying attention to the pharmacological properties of some of the archaic variants described in this study may be helpful to understand the variability of therapeutic efficacy between individuals or ethnic groups.

Ligand-Induced Conformational Dynamics of A Tyramine Receptor from Sitophilus oryzae

Tyramine receptor (TyrR) is a biogenic amine G protein-coupled receptor (GPCR) associated with many important physiological functions in insect locomotion, reproduction, and pheromone response. Binding of specific ligands to the TyrR triggers conformational changes, relays the signal to G proteins, and initiates an appropriate cellular response. Here, we monitor the binding effect of agonist compounds, tyramine and amitraz, to a Sitophilus oryzae tyramine receptor (SoTyrR) homology model and their elicited conformational changes. All-atom molecular dynamics (MD) simulations of SoTyrR-ligand complexes have shown varying dynamic behavior, especially at the intracellular loop 3 (IL3) region. Moreover, in contrast to SoTyrR-tyramine, SoTyrR-amitraz and non-liganded SoTyrR shows greater flexibility at IL3 residues and were found to be coupled to the most dominant motion in the receptor. Our results suggest that the conformational changes induced by amitraz are different from the natural ligand tyramine, albeit being both agonists of SoTyrR. This is the first attempt to understand the biophysical implication of amitraz and tyramine binding to the intracellular domains of TyrR. Our data may provide insights into the early effects of ligand binding to the activation process of SoTyrR.

The coupling of the M2 muscarinic receptor to its G protein is voltage dependent

G protein coupled receptors (GPCRs) participate in the majority of signal transduction processes in the body. Specifically, the binding of an external agonist promotes coupling of the GPCR to its G protein and this, in turn, induces downstream signaling. Recently, it was shown that agonist binding to the M2 muscarinic receptor (M2R) and to other GPCRs is voltage dependent. Here we examine, whether the coupling of the M2R to its G protein is also voltage-dependent. We first show, in Xenopus oocytes, that the activity of the M2R in the absence of agonist (constitutive activity) can be used to report the coupling. We then show that the coupling is, by itself, voltage dependent. This novel finding is of physiological importance, as it shows that the actual signal transduction, whose first step is the coupling of the GPCR to its cognate G protein, is voltage dependent.

Molecular Mechanism of S1P Binding and Activation of the S1P1 Receptor

Sphingosine-1-phosphate (S1P) is a lipidic mediator in mammals that functions either as a second messenger or as a ligand. In the latter case, it is transported by its HDL-associated apoM carrier and circulated in blood where it binds to specific S1P receptors on cell membranes and induces downstream reactions. Although S1P signaling pathways are essential for many biological processes, they are poorly understood at the molecular level. Here, the solved crystal structures of the S1P₁ receptor were used to evaluate molecular dynamics (MD) simulations to generate greater detailed molecular insights into the mechanism of S1P signaling. The MD simulations provided observations at the coarse-grained and atomic levels indicating that S1P may access the receptor binding pocket directly from solvents. Lifting of the bulky N-terminal cap region of the receptor precedes initial S1P binding. Glu121^3.29 guides S1P penetration, and together with Arg292^7.34 is responsible for the stabilization of S1P in the binding pocket, which is consistent with experimental predictions. The complete binding of S1P is followed by receptor activation, wherein Trp269^6.48 moves toward the transmembrane helix (TM) 7, resulting in the formation of an enhanced hydrogen bond network in the lower region of TM7. The distance between TM3 and TM6 is subsequently increased, resulting in the opening of the intracellular binding pocket that enables G protein binding. Further analysis of the force distribution network in the receptor yielded a detailed molecular understanding of the signal transmission network that is activated upon agonist binding.

The atypical chemokine receptor 4 in red sea bream (Pagrus major): Molecular characterization and gene expression analysis

Atypical chemokine receptor 4 (ACKR4) is regulated by cytokines, binds chemokines and regulates the chemokine gradient. We verified the cDNA sequence by confirming ACKR4 from red sea bream (PmACKR4) by next generation sequencing (NGS) and analysed the molecular characteristics and gene expression profile. In the analysis using the predicted amino acid sequence of PmACKR4, a highly conserved G protein-coupled receptor 1 region and two cysteine residues were identified and included in the ACKR4 teleost cluster in the phylogenetic analysis. In healthy red sea bream, PmACKR4 mRNA was expressed at the highest levels in head kidney and was upregulated in all immune -related tissues used in the experiment after challenges with Streptococcus iniae (S. iniae) and red sea bream iridovirus (RSIV). These results suggest that ACKR4 is highly conserved in red sea bream and may play an important role in the immune system as previously reported. It is thought that ACKR4 acts as a regulator of immune -related cells via immune reactions after pathogenic infection.

Effects of Post-translational Modifications on Membrane Localization and Signaling of Prostanoid GPCR-G Protein Complexes and the Role of Hypoxia

G protein-coupled receptors (GPCRs) play a pivotal role in the adaptive responses to cellular stresses such as hypoxia. In addition to influencing cellular gene expression profiles, hypoxic microenvironments can perturb membrane protein localization, altering GPCR effector scaffolding and altering downstream signaling. Studies using proteomics approaches have revealed significant regulation of GPCR and G proteins by their state of post-translational modification. The aim of this review is to examine the effects of post-translational modifications on membrane localization and signaling of GPCR-G protein complexes, with an emphasis on vascular prostanoid receptors, and to highlight what is known about the effect of cellular hypoxia on these mechanisms. Understanding post-translational modifications of protein targets will help to define GPCR targets in treatment of disease, and to inform research into mechanisms of hypoxic cellular responses.

The role of GPCRs in bone diseases and dysfunctions

The superfamily of G protein-coupled receptors (GPCRs) contains immense structural and functional diversity and mediates a myriad of biological processes upon activation by various extracellular signals. Critical roles of GPCRs have been established in bone development, remodeling, and disease. Multiple human GPCR mutations impair bone development or metabolism, resulting in osteopathologies. Here we summarize the disease phenotypes and dysfunctions caused by GPCR gene mutations in humans as well as by deletion in animals. To date, 92 receptors (5 glutamate family, 67 rhodopsin family, 5 adhesion, 4 frizzled/taste2 family, 5 secretin family, and 6 other 7TM receptors) have been associated with bone diseases and dysfunctions (36 in humans and 72 in animals). By analyzing data from these 92 GPCRs, we found that mutation or deletion of different individual GPCRs could induce similar bone diseases or dysfunctions, and the same individual GPCR mutation or deletion could induce different bone diseases or dysfunctions in different populations or animal models. Data from human diseases or dysfunctions identified 19 genes whose mutation was associated with human BMD: 9 genes each for human height and osteoporosis; 4 genes each for human osteoarthritis (OA) and fracture risk; and 2 genes each for adolescent idiopathic scoliosis (AIS), periodontitis, osteosarcoma growth, and tooth development. Reports from gene knockout animals found 40 GPCRs whose deficiency reduced bone mass, while deficiency of 22 GPCRs increased bone mass and BMD; deficiency of 8 GPCRs reduced body length, while 5 mice had reduced femur size upon GPCR deletion. Furthermore, deficiency in 6 GPCRs induced osteoporosis; 4 induced osteoarthritis; 3 delayed fracture healing; 3 reduced arthritis severity; and reduced bone strength, increased bone strength, and increased cortical thickness were each observed in 2 GPCR-deficiency models. The ever-expanding number of GPCR mutation-associated diseases warrants accelerated molecular analysis, population studies, and investigation of phenotype correlation with SNPs to elucidate GPCR function in human diseases.

Regulation of Membrane Turnover by Phosphatidic Acid: Cellular Functions and Disease Implications

Phosphatidic acid (PA) is a simple glycerophospholipid with a well-established role as an intermediate in phospholipid biosynthesis. In addition to its role in lipid biosynthesis, PA has been proposed to act as a signaling molecule that modulates several aspects of cell biology including membrane transport. PA can be generated in eukaryotic cells by several enzymes whose activity is regulated in the context of signal transduction and enzymes that can metabolize PA thus terminating its signaling activity have also been described. Further, several studies have identified PA binding proteins and changes in their activity are proposed to be mediators of the signaling activity of this lipid. Together these enzymes and proteins constitute a PA signaling toolkit that mediates the signaling functions of PA in cells. Recently, a number of novel genetic models for the analysis of PA function in vivo and analytical methods to quantify PA levels in cells have been developed and promise to enhance our understanding of PA functions. Studies of several elements of the PA signaling toolkit in a single cell type have been performed and are presented to provide a perspective on our understanding of the biochemical and functional organization of pools of PA in a eukaryotic cell. Finally, we also provide a perspective on the potential role of PA in human disease, synthesizing studies from model organisms, human disease genetics and analysis using recently developed PLD inhibitors.

Molecular basis for high-affinity agonist binding in GPCRs

G protein-coupled receptors (GPCRs) in the G protein-coupled active state have higher affinity for agonists as compared with when they are in the inactive state, but the molecular basis for this is unclear. We have determined four active-state structures of the β1-adrenoceptor (β1AR) bound to conformation-specific nanobodies in the presence of agonists of varying efficacy. Comparison with inactive-state structures of β1AR bound to the identical ligands showed a 24 to 42% reduction in the volume of the orthosteric binding site. Potential hydrogen bonds were also shorter, and there was up to a 30% increase in the number of atomic contacts between the receptor and ligand. This explains the increase in agonist affinity of GPCRs in the active state for a wide range of structurally distinct agonists.

Metabolite-Sensing G Protein-Coupled Receptors Connect the Diet-Microbiota-Metabolites Axis to Inflammatory Bowel Disease

Increasing evidence has indicated that diet and metabolites, including bacteria- and host-derived metabolites, orchestrate host pathophysiology by regulating metabolism, immune system and inflammation. Indeed, autoimmune diseases such as inflammatory bowel disease (IBD) are associated with the modulation of host response to diets. One crucial mechanism by which the microbiota affects the host is signaling through G protein-coupled receptors (GPCRs) termed metabolite-sensing GPCRs. In the gut, both immune and nonimmune cells express GPCRs and their activation generally provide anti-inflammatory signals through regulation of both the immune system functions and the epithelial integrity. Members of GPCR family serve as a link between microbiota, immune system and intestinal epithelium by which all these components crucially participate to maintain the gut homeostasis. Conversely, impaired GPCR signaling is associated with IBD and other diseases, including hepatic steatosis, diabetes, cardiovascular disease, and asthma. In this review, we first outline the signaling, function, expression and the physiological role of several groups of metabolite-sensing GPCRs. We then discuss recent findings on their role in the regulation of the inflammation, their existing endogenous and synthetic ligands and innovative approaches to therapeutically target inflammatory bowel disease.

Flip-Flopping Retinal in Microbial Rhodopsins as a Template for a Farnesyl/Prenyl Flip-Flop Model in Eukaryote GPCRs

Thirty years after the first description and modeling of G protein coupled receptors (GPCRs), information about their mode of action is still limited. One of the questions that is hard to answer is: how do the allosteric changes in the GPCR induced by, e.g., ligand binding in the end activate a G protein-dependent intracellular pathway (e.g., via the cAMP or the phosphatidylinositol signal pathways). Another question relates to the role of prenylation of G proteins. Today's "consensus model" states that protein prenylation is required for the assembly of GPCR-G protein complexes. Although it is well-known that protein prenylation is the covalent addition of a farnesyl- or geranylgeranyl moiety to the C terminus of specific proteins, e.g., α or γ G protein, the reason for this strong covalent binding remains enigmatic. The arguments for a fundamental role for prenylation of G proteins other than just being a hydrophobic linker, are gradually accumulating. We uncovered a dilemma that at first glance may be considered physiologically irrelevant, however, it may cause a true change in paradigm. The consensus model suggests that the only functional role of prenylation is to link the G protein to the receptor. Does the isoprenoid nature of the prenyl group and its exact site of attachment somehow matter? Or, are there valid arguments favoring the alternative possibility that a key role of the G protein is to guide the covalently attached prenyl group to - and it hold it in - a very specific location in between specific helices of the receptor? Our model says that the farnesyl/prenyl group - aided by its covalent attachment to a G protein -might function in GPCRs as a horseshoe-shaped flexible (and perhaps flip-flopping) hydrophobic valve for restricting (though not fully inhibiting) the untimely passage of Ca2+, like retinal does for the passage of H+ in microbial rhodopsins that are ancestral to many GPCRs.

Molecular determinants of the response to medical treatment of growth hormone secreting pituitary neuroendocrine tumors

Acromegaly is a chronic systemic disease mainly caused by a growth hormone (GH)-secreting pituitary neuroendocrine tumor (PitNETs), which is associated with many health complications and increased mortality when not adequately treated. Transsphenoidal surgery is considered the treatment of choice in GH-secreting PitNETs, but patients in whom surgery cannot be considered or with persistent disease after surgery require medical therapy. Treatment with available synthetic somatostatin analogues (SSAs) is considered the mainstay in the medical management of acromegaly which exert their beneficial effects through the binding to a family of G-protein coupled receptors encoded by 5 genes (SSTR1-5). However, although it has been demonstrated that the SST1-5 receptors are physically present in tumor cells, SSAs are in many cases ineffective (i.e. approximately 10-30% of patients with GH-secreting PitNET are unresponsive to SSAs), suggesting that other cellular/molecular determinants could be essential for the response to the pharmacological treatment in patients with GH-secreting PitNETs. Therefore, the scrutiny of these determinants might be used for the identification of subgroups of patients in whom an appropriate pharmacological treatment can be successfully employed (responders vs. non-responders). In this review, we will describe some of the existing, classical and novel, genetic and molecular determinants involved in the response of patients with GH-secreting PitNETs to the available therapeutic treatments, as well as new molecular/therapeutic approaches that could be potentially useful for the treatment of GH-secreting PitNETs.

Cinacalcet corrects biased allosteric modulation of CaSR by AHH autoantibody

Biased agonism is a paradigm that may explain the selective activation of a signaling pathway via a GPCR that activates multiple signals. The autoantibody-induced inactivation of the calcium-sensing receptor (CaSR) causes acquired hypocalciuric hypercalcemia (AHH). Here, we describe an instructive case of AHH in which severe hypercalcemia was accompanied by an increased CaSR antibody titer. These autoantibodies operated as biased allosteric modulators of CaSR by targeting its Venus flytrap domain near the Ca2+-binding site. A positive allosteric modulator of CaSR, cinacalcet, which targets its transmembrane domain, overcame this autoantibody effect and successfully corrected the hypercalcemia in this patient. Hence, this is the first study to our knowledge that identifies the interaction site of a disease-causing GPCR autoantibody working as its biased allosteric modulator and demonstrates that cinacalcet can correct the AHH autoantibody effects both in vitro and in our AHH patient. Our observations provide potentially new insights into how biased agonism works and how to design a biased allosteric modulator of a GPCR. Our observations also indicate that the diagnosis of AHH is important because the severity of hypercalcemia may become fatal if the autoantibody titer increases. Calcimimetics may serve as good treatment options for some patients with severe AHH.

Neuropeptide PEN and Its Receptor GPR83: Distribution, Signaling, and Regulation

Neuropeptides are chemical messengers that act to regulate a number of physiological processes, including feeding, reward, pain, and memory, among others. PEN is one of the most abundant hypothalamic neuropeptides; however, until recently, its target receptor remained unknown. In this Review, we summarize recent developments in research focusing on PEN and its receptor GPR83. We describe the studies leading to the deorphanization of GPR83 as the receptor for PEN. We also describe the signaling mediated by the PEN-GPR83 system, as well as the physiological roles in which PEN-GPR83 has been implicated. As studies have suggested a role for the PEN-GPR83 system in food intake and body weight regulation, as well as in drug addiction and reward disorders, a thorough understanding of this novel neuropeptide-receptor system will help identify novel therapeutic targets to treat pathophysiological conditions involving PEN-GPR83.

Advances in Models of Fibrous Dysplasia/McCune-Albright Syndrome

The G_s G-protein coupled receptor pathway is a critical regulator of normal bone formation and function. The G_s pathway increases intracellular cAMP levels by ultimately acting on adenylate cyclase. McCune-Albright Syndrome (MAS) and fibrous dysplasia (FD) of the bone are two proto-typical conditions that result from increased cellular G_s signaling activity. Both are caused by somatic activating mutations in the GNAS gene that encodes for the G_sα subunit. FD bone lesions are particularly difficult to treat because of their variability and because of the lack of effective medical therapies. In this review, we briefly discuss the key clinical presentations of FD/MAS. We also review the current status of mouse models that target the G_s GPCR signaling pathway and human cellular models for FD/MAS. These powerful tools and our improving clinical knowledge will allow further elucidation of the roles of GPCR signaling in FD/MS pathogenesis, and facilitate the development of novel therapies for these medically significant conditions.

A Critical Analysis of Molecular Mechanisms Underlying Membrane Cholesterol Sensitivity of GPCRs

G protein-coupled receptors (GPCRs) are the largest and a diverse family of proteins involved in signal transduction across biological membranes. GPCRs mediate a wide range of physiological processes and have emerged as major targets for the development of novel drug candidates in all clinical areas. Since GPCRs are integral membrane proteins, regulation of their organization, dynamics, and function by membrane lipids, in particular membrane cholesterol, has emerged as an exciting area of research. Cholesterol sensitivity of GPCRs could be due to direct interaction of cholesterol with the receptor (specific effect). Alternately, GPCR function could be influenced by the effect of cholesterol on membrane physical properties (general effect). In this review, we critically analyze the specific and general mechanisms of the modulation of GPCR function by membrane cholesterol, taking examples from representative GPCRs. While evidence for both the proposed mechanisms exists, there appears to be no clear-cut distinction between these two mechanisms, and a combination of these mechanisms cannot be ruled out in many cases. We conclude that classifying the mechanism underlying cholesterol sensitivity of GPCR function merely into these two mutually exclusive classes could be somewhat arbitrary. A more holistic approach could be suitable for analyzing GPCR-cholesterol interaction.

Cloning, expression and functional characterization of a novel luteinizing hormone receptor in the orange-spotted grouper, Epinephelus coioides

Luteinizing hormone receptor (LHR) plays a critical role in reproduction by mediating LH signaling in the gonad. In this study, we cloned a novel lhr gene from the orange-spotted grouper, named glhr2. The cloned complete open reading frame sequence of glhr2 was 2082 bp in length, encoding a protein of 693 amino acids, sharing approximately 50% amino acid identity with glhr1. glhr1 and glhr2 were primarily expressed in gonad, brain and hypothalamus with low expression in other tissues such as gill, spleen, etc. The expressions of both glhr1 and glhr2 increased during vitellogenesis, while decreased during natural female to male sex change. The two gLHRs both could be activated by equine LH or human chorionic gonadotropin, but not by human follicle stimulating hormone. Both gLHR1 and gLHR2 activation stimulated the expression of cAMP response element driven reporter gene in a dose-dependent manner, while gLHR2 but not gLHR1 also activated serum response element driven reporter gene expression. This was the first study to demonstrate that two active LHRs exist in fish with possible different functional roles.

Behavior and histopathology as biomarkers for evaluation of the effects of paracetamol and propranolol in the neotropical fish species Phalloceros harpagos

Pharmaceutical drugs in the aquatic environment can induce adverse effects on nontarget organisms. This study aimed to assess the short-term effects of sublethal concentrations of both paracetamol and propranolol on the fish Phalloceros harpagos, specifically light/dark preference, swimming patterns, skin pigmentation, histopathology, and liver glycogen levels. Fish were acutely exposed to sublethal concentrations of both paracetamol (0.008, 0.08, 0.8, 8, 80 mg L^-1) and propranolol (0.0001, 0.001, 0.01, 0.1, 1 mg L^-1) under controlled conditions. For scototaxis, a significant preference for the dark compartment was observed for the group exposed to the highest concentration of paracetamol (80 mg L^-1). Propranolol exposure significantly altered the swimming pattern, especially in fish exposed to the 0.001 mg L^-1 concentration. Pigmentation was reduced in propranolol-exposed fish (0.1, 1 mg L^-1). The lowest concentration of propranolol (0.0001 mg L^-1) induced a decrease of histochemical reaction for hepatic glycogen. These data demonstrate that pharmaceuticals can induce sublethal effects in nontarget organisms, even at low concentrations, compromising specific functions of the individual with ecological relevance, such as energy balance and behavior.

Link between a high k on for drug binding and a fast clinical action: to be or not to be?

Review articles on binding kinetics essentially focus on drugs that dissociate slowly from their target since this is required for the successful treatment of many pathophysiological conditions. Recently, the therapeutic benefit of a high k on (i.e. the second order association rate constant) has also been linked to fast association and to a fast clinical action. Other studies, however, called this assertion into question since additional factors, like the dosing paradigm and the binding mechanism, are important as well. The still ongoing reticence about integrating binding kinetics in lead optimization programs motivated us to critically review the link between the drug's kinetic rate constants and their in vitro and in vivo target occupancy profile, with special focus on k on. The presented simulations tally with a positive link between a drug's effective/observed association rate (which is quite easy to determine in vitro) and the swiftness of its clinical action. On the other hand, the simulations show that the k on-concept should not be confounded with the effective association process since increasing this parameter only enhances the drug's in vitro and in vivo association under certain conditions: the binding mechanism should be suitable, rebinding (and thus the factors within the target's micro-environment that favour this mechanism) should not be too prominent and the dosage should not be kept in par with the drug's affinity. Otherwise, increasing k on could be ineffective or even be counter-productive.

Molecular cloning and functional expression of the 5-HT7 receptor in Chinese mitten crab (Eriocheir sinensis)

Serotonin (5-HT) regulates numerous physiological functions and processes, such as light adaptation, food intake and ovarian maturation, and plays the role through 5-HT receptors. To our knowledge, this is the first study to isolate and characterize the serotonin receptor 7 (5-HT₇ receptor) cDNA encoded in Eriocheir sinensis, an economically important aquaculture species in China, by performing rapid-amplification of cDNA ends. The full-length of 5-HT₇ receptor gene cDNA is 2328 bp and encodes a polypeptide with 590 amino acids that are highly homologous with other crustaceans 5-HT₇ receptor genes. Analysis of the deduced amino acid sequence of the 5-HT₇, including 7 transmembrane domains and some common features of G protein-coupled receptors (GPCRs), indicated that 5-HT₇ receptor was a member of GPCRs family. A gene expression analysis of the 5-HT₇ receptor by RT-PCR revealed that the 5-HT₇ receptor transcripts were widely distributed in various tissues, in which high expression levels were observed in the cranial ganglia, thoracic ganglia and intestines. Further study about the effects of photoperiods on the 5-HT₇ expression in the tissues showed that a significantly increasing expression of the 5-HT₇ receptor was observed in the thoracic ganglia induced by constant light. In addition, in the eyestalks, the expression levels of 5-HT₇ mRNA in constant darkness and constant light were lower than control treatment. Then, the expression levels of the 5-HT₇ receptor in three feeding statuses displayed that there were significantly increasing expressions in the hepatopancreas and intestines after feeding, compared with before feeding and during the feeding period. Finally, the 5-HT₇ mRNA expression levels in stage III and stage IV were higher than the levels in stage I of ovarian development. Our experimental results showed that the 5-HT₇ receptor structurally belongs to GPCRs, and the thoracic ganglia and eyestalks are the important tissues of the 5-HT₇ receptor for light adaptation. The 5-HT₇ receptor may also be involved in the physiological regulation of the hepatopancreas and intestines after ingestion in E. sinensis. In addition, the 5-HT₇ receptor is involved in the process of ovarian maturation. The study provided a foundation for further research of light adaptation, digestive functions and ovarian maturation of the 5-HT₇ receptor in Decapoda.

Metabolic features and regulation of the healing cycle-A new model for chronic disease pathogenesis and treatment

Without healing, multicellular life on Earth would not exist. Without healing, one injury predisposes to another, leading to disability, chronic disease, accelerated aging, and death. Over 60% of adults and 30% of children and teens in the United States now live with a chronic illness. Advances in mass spectrometry and metabolomics have given scientists a new lens for studying health and disease. This study defines the healing cycle in metabolic terms and reframes the pathophysiology of chronic illness as the result of metabolic signaling abnormalities that block healing and cause the normal stages of the cell danger response (CDR) to persist abnormally. Once an injury occurs, active progress through the stages of healing is driven by sequential changes in cellular bioenergetics and the disposition of oxygen and carbon skeletons used for fuel, signaling, defense, repair, and recovery. >100 chronic illnesses can be organized into three persistent stages of the CDR. One hundred and two targetable chemosensory G-protein coupled and ionotropic receptors are presented that regulate the CDR and healing. Metabokines are signaling molecules derived from metabolism that regulate these receptors. Reframing the pathogenesis of chronic illness in this way, as a systems problem that maintains disease, rather than focusing on remote trigger(s) that caused the initial injury, permits new research to focus on novel signaling therapies to unblock the healing cycle, and restore health when other approaches have failed.

Dynamic States of the Ligand-Free Class A G Protein-Coupled Receptor Extracellular Side

G protein-coupled receptors (GPCRs) make up the largest family of drug targets. The second extracellular loop (ECL2) and extracellular end of the third transmembrane helix (TM3) are basic structural elements of the GPCR ligand binding site. Currently, the disulfide bond between the two conserved cysteines in the ECL2 and TM3 is considered to be a basic GPCR structural feature. This disulfide bond has a significant effect on receptor dynamics and ligand binding. Here, molecular dynamics simulations and experimental results show that the two cysteines are distant from one another in the highest-population conformational state of ligand-free class A GPCRs and do not form a disulfide bond, indicating that the dynamics of the GPCR extracellular side are different from our conventional understanding. These surprising dynamics should have important effects on the drug binding process. On the basis of the two distinct ligand-free states, we suggest two kinetic processes for binding of ligands to GPCRs. These results challenge our commonly held beliefs regarding both GPCR structural features and ligand binding.

The Role of Metabolite-Sensing G Protein-Coupled Receptors in Inflammation and Metabolic Disease

SIGNIFICANCE

Great attention has been placed on the link between metabolism and immune function giving rise to the term "immunometabolism." It is widely accepted that inflammation and oxidative stress are key processes that underlie metabolic complications during obesity, diabetes, and atherosclerosis. Therefore, identifying the mechanisms and mediators that are involved in the regulation of both inflammation and metabolic homeostasis is of high scientific and therapeutic interest. Recent Advances: G protein-coupled receptors (GPCRs) that signal in response to metabolites have emerged as attractive therapeutic targets in inflammatory disease. Critical Issues and Future Directions: In this review, we discuss recent findings about the physiological role of the main metabolite-sensing GPCRs, their implication in immunometabolic disorders, their principal endogenous and synthetic ligands, and their potential as drug targets in inflammation and metabolic disease. Antioxid. Redox Signal. 29, 237-256.

Activation of the Immune-Metabolic Receptor GPR84 Enhances Inflammation and Phagocytosis in Macrophages

GPR84 is a member of the metabolic G protein-coupled receptor family, and its expression has been described predominantly in immune cells. GPR84 activation is involved in the inflammatory response, but the mechanisms by which it modulates inflammation have been incompletely described. In this study, we investigated GPR84 expression, activation, and function in macrophages to establish the role of the receptor during the inflammatory response. We observed that GPR84 expression in murine tissues is increased by endotoxemia, hyperglycemia, and hypercholesterolemia. Ex vivo studies revealed that GPR84 mRNA expression is increased by LPS and other pro-inflammatory molecules in different murine and human macrophage populations. Likewise, high glucose concentrations and the presence of oxidized LDL increased GPR84 expression in macrophages. Activation of the GPR84 receptor with a selective agonist, 6-(octylamino) pyrimidine-2,4(1H,3H)-dione (6-n-octylaminouracil, 6-OAU), enhanced the expression of phosphorylated Akt, p-ERK, and p65 nuclear translocation under inflammatory conditions and elevated the expression levels of the inflammatory mediators TNFα, IL-6, IL-12B, CCL2, CCL5, and CXCL1. In addition, GPR84 activation triggered increased bacterial adhesion and phagocytosis in macrophages. The enhanced inflammatory response mediated by 6-OAU was not observed in GPR84-/- cells nor in macrophages treated with a selective GPR84 antagonist. Collectively, our results reveal that GPR84 functions as an enhancer of inflammatory signaling in macrophages once inflammation is established. Therefore, molecules that antagonize the GPR84 receptor may be potential therapeutic tools in inflammatory and metabolic diseases.

The Neuropeptides Vasoactive Intestinal Peptide and Pituitary Adenylate Cyclase-Activating Polypeptide Control HIV-1 Infection in Macrophages Through Activation of Protein Kinases A and C

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are highly similar neuropeptides present in several tissues, endowed with immunoregulatory functions and other systemic effects. We previously reported that both neuropeptides reduce viral production in HIV-1-infected primary macrophages, with the participation of β-chemokines and IL-10, and now we describe molecular mechanisms engaged in this activity. Macrophages exposed to VIP or PACAP before HIV-1 infection showed resistance to viral replication, comparable to that observed when the cells were treated after infection. Also, multiple treatments with a suboptimal dose of VIP or PACAP after macrophage infection resulted in a decline of virus production similar to the inhibition promoted by a single exposure to the optimal inhibitory concentration. Cellular signaling pathways involving cAMP production and activation of protein kinases A and C were critical components of the VIP and PACAP anti-HIV-1 effects. Analysis of the transcription factors and the transcriptional/cell cycle regulators showed that VIP and PACAP induced cAMP response element-binding protein activation, inhibited NF-kB, and reduced Cyclin D1 levels in HIV-1-infected cells. Remarkably, VIP and PACAP promoted G-to-A mutations in the HIV-1 provirus, matching those derived from the activity of the APOBEC family of viral restriction factors, and reduced viral infectivity. In conclusion, our findings strengthen the antiretroviral potential of VIP and PACAP and point to new therapeutic approaches to control the progression of HIV-1 infection.

Characterization of a β2 adrenergic receptor protein precursor in the European eel (Anguilla anguilla) and its tissue distribution across silvering

This study provides the characterization and tissue distribution of a β2-AR in the female European eel during silvering, aiming to better understand the adrenergic system involvement in this critical maturation event. A putative β2-AR (ADRB2) mRNA was cloned and sequenced. Amino acid residues and motifs important for ligand binding are generally conserved across fish and between fish and mammals, although the occurrence of some sequence variabilities may explain the noted peculiarities of eel AR interaction with pharmacological ligands. The tissue distribution of the ADRB2 gene product was analyzed in five tissues of the eel at different silvering stages and compared with that of the ADRA1 mRNA encoding an α1-AR subtype. On the whole, data suggested that relative ADRA1/ADRB2 tissue expression across silvering is part of the preparatory (molecular) adjustments required to face changes in habitats and migration efforts.

The role of the LTB4-BLT1 axis in chemotactic gradient sensing and directed leukocyte migration

Directed leukocyte migration is a hallmark of inflammatory immune responses. Leukotrienes are derived from arachidonic acid and represent a class of potent lipid mediators of leukocyte migration. In this review, we summarize the essential steps leading to the production of LTB₄ in leukocytes. We discuss the recent findings on the exosomal packaging and transport of LTB₄ in the context of chemotactic gradients formation and regulation of leukocyte recruitment. We also discuss the dynamic roles of the LTB₄ receptors, BLT1 and BLT2, in mediating chemotactic signaling in leukocytes and contrast them to other structurally related leukotrienes that bind to distinct GPCRs. Finally, we highlight the specific roles of the LTB₄-BLT1 axis in mediating signal-relay between chemotaxing neutrophils and its potential contribution to a wide variety of inflammatory conditions including tumor progression and metastasis, where LTB₄ is emerging as a key signaling component.

A new insight into identification of in silico analysis of natural compounds targeting GPR120

G-protein coupled receptor (GPR120) is an omega-3 fatty acid receptor that inhibits macrophage-induced tissue inflammation. Recent studies revealed GPR120 promotes colorectal carcinoma through modulation of VEGF, IL-8, PGE2, and NF-kB expression. However, three-dimensional structure of GPR120 is not yet available in Protein Data Bank (PDB). In the present study, we focused on a 3-D structural model of GPR120 has been constructed using homology modeling techniques. The structural quality of the predicted GPR120 model was verified using Procheck, Whatif, ProSA, and Verify 3D. After this chemical database of natural compounds have been constructed and screened for its druggability using molinspiration server. Molecular docking studies of natural compounds on GPR120 model revealed that silibinin (− 6.87 kcal/mol), withanolide (− 6.19 kcal/mol), limonene (− 6.17 kcal/mol), and cervical (− 6.15 kcal/mol) have shown good docking interactions with active site residues of the target. Active site residues of Arg280, Asp275, and Gly122 showed hydrogen-bonding interactions with predicted compounds. Based on these in silico findings, we proposed that virtual screening of natural compounds against of GPR120 is a novel approach to find potential anti-colorectal cancer therapeutics.

Assessing the real-time activation of the cannabinoid CB1 receptor and the associated structural changes using a FRET biosensor

The cannabinoid receptor 1 (CB1) is mainly expressed in the nervous system and regulates learning, memory processes, pain and energy metabolism. However, there is no way to directly measure its activation. In this study, we constructed a CB1 intramolecular fluorescence resonance energy transfer (FRET) sensor, which could measure CB1 activation by monitoring structural changes between the third intracellular loop and the C-terminal tail. CB1 agonists induced a time- and concentration-dependent increase in the FRET signal, corresponding to a reduction in the distance between the third intracellular loop and the C-terminal tail. This, in turn, mobilized intracellular Ca²⁺, inhibited cAMP accumulation, and increased phosphorylation of the ERK1/2 MAP kinases. The activation kinetics detected using this method were consistent with those from previous reports. Moreover, the increased FRET signal was markedly inhibited by the CB1 antagonist rimonabant, which also reduced phosphorylation of the ERK1/2 MAP kinases. We mutated a single cysteine residue in the sensor (at position 257 or 264) to alanine. Both mutation reduced the agonist-induced increase in FRET signal and structural changes in the CB1 receptor, which attenuated phosphorylation of the ERK1/2 MAP kinases. In summary, our sensor directly assesses the kinetics of CB1 activation in real-time and can be used to monitor CB1 structure and function.

Cloning and functional characterization of the DA2 receptor gene in Chinese mitten crab (Eriocheir sinensis)

Dopamine (DA) plays a modulatory role in numerous physiological processes such as light adaptation and food intake, and exerts these functions through DA receptors (DARs). This study presents, for the first time, isolation and characterization of the dopamine receptor 2(DA₂ receptor) cDNA from the intestinal tissue of Eriocheir sinensis, an economically important freshwater aquaculture species in China. The DA₂ receptor cDNA sequence, which was obtained by rapid amplification of cDNA ends, is 2369bp long, encode peptide of 589 amino acid, and is highly homologous to related sequences in crustaceans. Analysis of the deduced amino acid sequence and the structure of the DA₂ indicated that this receptor is a member of the family of G protein-coupled receptors (GPCRs), as it contains seven transmembrane domains and other common signatures of GPCRs. RT-PCR showed that the expression of the DA₂ receptor gene was distributed in various tissues, and high expression levels were observed in the cranial ganglia and the thoracic ganglia. Further study of the effect of photoperiod on DA₂ expression showed that constant darkness induced a significant increase in DA₂ expression in the cranial ganglia. Finally, analysis of DA₂ receptor expression under different feeding statuses showed that there was significantly greater expression in the hepatopancreas and intestines after feeding than before feeding, but there were no differences in expression between the before feeding and during feeding periods in either tissue. Our results indicate that the DA₂ receptor structurally belongs to the family of G protein-coupled receptors, and that the cranial ganglia are the main tissues in which the DA₂ receptor participates in light adaptation during dark hours. In addition, the DA₂ receptor in E. sinensis may be involved in the physiological regulation of the hepatopancreas and digestive tract after the ingestion of food. This study provides a foundation for further exploration of the light adaptation and digestive functions of the DA₂ receptor in decapods.

Single-molecule imaging reveals dimerization/oligomerization of CXCR4 on plasma membrane closely related to its function

Dimerization and oligomerization of G-protein coupled receptors (GPCRs) have emerged as important characters during their trans-membrane signal transduction. However, until now the relationship between GPCR dimerization and their trans-membrane signal transduction function is still uncovered. Here, using pertussis toxin (PTX) to decouple the receptor from G protein complex and with single-molecule imaging, we show that in the presence of agonist, cells treated with PTX showed a decrease in the number of dimers and oligomers on the cell surface compared with untreated ones, which suggests that oligomeric status of CXCR4 could be significantly influenced by the decoupling of G protein complex during its signal transduction process. Moreover, with chlorpromazine (CPZ) to inhibit internalization of CXCR4, it was found that after SDF-1α stimulation, cells treated with CPZ showed more dimers and oligomers on the cell surface than untreated ones, which suggest that dimers and oligomers of CXCR4 tend to internalize more easily than monomers. Taken together, our results demonstrate that dimerization and oligomerization of CXCR4 is closely related with its G protein mediated pathway and β-arrestin mediated internalization process, and would play an important role in regulating its signal transduction functions.

Classification of G-protein coupled receptors based on a rich generation of convolutional neural network, N-gram transformation and multiple sequence alignments

Sequence classification is crucial in predicting the function of newly discovered sequences. In recent years, the prediction of the incremental large-scale and diversity of sequences has heavily relied on the involvement of machine-learning algorithms. To improve prediction accuracy, these algorithms must confront the key challenge of extracting valuable features. In this work, we propose a feature-enhanced protein classification approach, considering the rich generation of multiple sequence alignment algorithms, N-gram probabilistic language model and the deep learning technique. The essence behind the proposed method is that if each group of sequences can be represented by one feature sequence, composed of homologous sites, there should be less loss when the sequence is rebuilt, when a more relevant sequence is added to the group. On the basis of this consideration, the prediction becomes whether a query sequence belonging to a group of sequences can be transferred to calculate the probability that the new feature sequence evolves from the original one. The proposed work focuses on the hierarchical classification of G-protein Coupled Receptors (GPCRs), which begins by extracting the feature sequences from the multiple sequence alignment results of the GPCRs sub-subfamilies. The N-gram model is then applied to construct the input vectors. Finally, these vectors are imported into a convolutional neural network to make a prediction. The experimental results elucidate that the proposed method provides significant performance improvements. The classification error rate of the proposed method is reduced by at least 4.67% (family level I) and 5.75% (family Level II), in comparison with the current state-of-the-art methods. The implementation program of the proposed work is freely available at: https://github.com/alanFchina/CNN .

Anti-inflammatory effects of low-level laser therapy on human periodontal ligament cells: in vitro study

Periodontal disease is a chronic inflammatory disease that is commonly treated with surgical and nonsurgical techniques. However, both approaches have limitations. Low-level laser therapy (LLLT) has been widely applied in reducing inflammatory reactions, and research indicates that LLLT induces an anti-inflammatory effect that may enhance periodontal disease therapy. The purpose of this study was to investigate the anti-inflammatory effect of LLLT on human periodontal ligament cells (hPDLCs) in an inflammatory environment and aimed to determine the possible mechanism of action. Cells were cultured and treated with or without lipopolysaccharide (LPS) from Porphryromonas gingivalis or Escherichia coli, followed by irradiation with a gallium-aluminum-arsenide (GaAlAs) laser (660 nm) at an energy density of 8 J/cm². Quantitative real-time polymerase chain reactions were used to assess the expression of pro-inflammatory genes, including tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, and IL-8. The dual-luciferase reporter assay was used to examine nuclear factor-κB (NF-κB) transcriptional activity. An enzyme-linked immunosorbent assay was used to monitor the concentration of intracellular cyclic adenosine monophosphate (cAMP). Both LPS treatments significantly induced the mRNA expression of pro-inflammatory cytokines. However, LLLT inhibited the LPS-induced pro-inflammatory cytokine expression and elevated intracellular levels of cAMP. The LLLT inhibitory effect may function by downregulating NF-κB transcriptional activity and by increasing the intracellular levels of cAMP. LLLT might inhibit LPS-induced inflammation in hPDLCs through cAMP/NF-κB regulation. These results should be further studied to improve periodontal therapy.

Functional autoantibodies targeting G protein-coupled receptors in rheumatic diseases

G protein-coupled receptors (GPCRs) comprise the largest and most diverse family of integral membrane proteins that participate in different physiological processes such as the regulation of the nervous and immune systems. Besides the endogenous ligands of GPCRs, functional autoantibodies are also able to bind GPCRs to trigger or block intracellular signalling pathways, resulting in agonistic or antagonistic effects, respectively. In this Review, the effects of functional GPCR-targeting autoantibodies on the pathogenesis of autoimmune diseases, including rheumatic diseases, are discussed. Autoantibodies targeting β1 and β2 adrenergic receptors, which are expressed by cardiac and airway smooth muscle cells, respectively, have an important role in the development of asthma and cardiovascular diseases. In addition, high levels of autoantibodies against the muscarinic acetylcholine receptor M3 as well as those targeting endothelin receptor type A and type 1 angiotensin II receptor have several implications in the pathogenesis of rheumatic diseases such as Sjögren syndrome and systemic sclerosis. Expanding the knowledge of the pathophysiological roles of autoantibodies against GPCRs will shed light on the biology of these receptors and open avenues for new therapeutic approaches.

Omega-3 polyunsaturated fatty acids ameliorate ethanol-induced adipose hyperlipolysis: A mechanism for hepatoprotective effect against alcoholic liver disease

Alcohol exposure induces adipose hyperlipolysis and causes excess fatty acid influx into the liver, leading to alcoholic steatosis. The impacts of omega-3 polyunsaturated fatty acids (n-3 PUFA) on ethanol-induced fatty liver are well documented. However, the role of n-3 PUFA in ethanol-induced adipose lipolysis has not been sufficiently addressed. In this study, the fat-1 transgenic mice that synthesizes endogenous n-3 from n-6 PUFA and their wild type littermates with an exogenous n-3 PUFA enriched diet were subjected to a chronic ethanol feeding plus a single binge as model to induce liver injury with adipose lipolysis. Additionally, the differentiated adipocytes from 3T3-L1 cells were treated with docosahexaenoic acid or eicosapentaenoic acid for mechanism studies. Our results demonstrated that endogenous and exogenous n-3 PUFA enrichment ameliorates ethanol-stimulated adipose lipolysis by increasing PDE3B activity and reducing cAMP accumulation in adipocyte, which was associated with activation of GPR120 and regulation of Ca²⁺/CaMKKβ/AMPK signaling, resultantly blocking fatty acid trafficking from adipose tissue to the liver, which contributing to ameliorating ethanol-induced adipose dysfunction and liver injury. Our findings identify that endogenous and exogenous n-3 PUFA enrichment ameliorated alcoholic liver injury by activation of GPR120 to suppress ethanol-stimulated adipose lipolysis, which provides the new insight to the hepatoprotective effect of n-3 PUFA against alcoholic liver disease.

Characterization of three serotonin receptors from the small white butterfly, Pieris rapae

Serotonin (5-hydroxytryptamine, 5-HT) plays a key role in modulating diverse physiological processes and behaviors in both protostomes and deuterostomes. These functions are mediated through the binding of serotonin to its receptors, which are recognized as potential insecticide targets. We investigated the sequence, pharmacology and tissue distribution of three 5-HT receptors (Piera5-HT_1A, Piera5-HT_1B, Piera5-HT₇) from the small white butterfly Pieris rapae, an important pest of cultivated cabbages and other mustard family crops. Activation of Piera5-HT_1A or Piera5-HT_1B by 5-HT inhibited the production of cAMP in a dose-dependent manner. Stimulation of Piera5-HT₇ with 5-HT increased cAMP level significantly. Surprisingly, with the exception of 5-methoxytryptamine, agonists including α-methylserotonin, 8-Hydroxy-DPAT and 5-carboxamidotryptamine activated these receptors poorly. The results are consistent with previous findings in Manduca sexta. All three receptors were blocked by methiothepin, but ketanserin and yohimbine were not effective. The selective mammalian 5-HT receptor antagonists SB 216641 and SB 269970 displayed potent inhibition effects on Piera5-HT_1B and Piera5-HT₇ respectively. The results we achieved here indicate that the pharmacological properties of Lepidoptera 5-HT receptors are quite different from those in other insects and vertebrates and may contribute to development of new selective pesticides. This study offers important information on three 5-HT receptors from P. rapae that will facilitate further analysis of the functions of 5-HT receptors in insects.