Uncoupling serotonin (2C) and dopamine (D2) receptor heterodimers ameliorate PTSD-like behaviors

BACKGROUND

G-protein-coupled receptors (GPCRs), crucial for various physiological functions, can form complexes with themselves or other GPCRs, influencing their signaling and drug interactions. GPCR oligomerization remains an active area of research in neurological diseases, including Post-Traumatic Stress Disorder (PTSD). Here, we illuminated a novel serotonin and dopamine receptor heterodimerization that played an etiological role in fear conditioning behaviors associated with memory defects in the single prolonger stress (SPS) mice and reverting effects of receptors interaction interfering with peptide.

METHODS

To assess our projected goal, we prepared a single prolonged stress (SPS) mice model followed by peptide treatment, behavior assays, and biochemical analysis.

RESULTS

Our study revealed a direct interaction between dopamine D2 receptors (D2R) and serotonin 5-HT2C receptors (5-HT2CR) via the K226-L240 region in the brains of SPS mice. This D2R/5-HT2CR interaction modulated downstream PI3K-AKT signaling and contributed to cognitive deficits in a mouse model of SPS. An interfering peptide (TAT-D2R-KL) designed to disrupt D2R/5-HT2CR heterodimerization reduced the excitatory/inhibitory neuron firing frequency ratio, attenuated PI3K/AKT signaling impairment, and alleviated cognitive deficits in SPS mice. Furthermore, treatment with the PI3K inhibitor, Bisperoxovanadium Compound bpV (pic), reversed the effects of the peptide, confirming the critical role of PI3K/AKT signaling in D2R/5-HT2CR dimerization and the associated pathophysiology of SPS.

CONCLUSION

These findings revealed a causative role of D2R/5-HT2CR hetero-dimer in PTSD and could be reversed by TAT-D2R-KL treatment.

Decoding Proteomic cross-talk between hypobaric and normobaric hypoxia: Integrative analysis of oxidative stress, cytoskeleton remodeling, and inflammatory pathways

AIMS

To investigate the differential regulation of proteomic landscapes elicited by hypobaric hypoxia (HH) and normobaric hypoxia (NH) and to shed light on the molecular cross-talk underlying pre-acclimatization strategies.

MATERIALS AND METHODS

Label-free LCMS-MS quantitative proteomics was employed to evaluate the lung tissues of SD rats (n = 6) subjected to 6 h of acute HH at 25,000 ft associated with reduced barometric pressure, 282 mmHg, and NH at 8 % FiO2.

KEY FINDINGS

Our findings indicate that NH facilitated the minimal downregulation of proteins involved in maintaining pulmonary cytoskeleton integrity, including calpain 2, vitronectin, and beta-arrestin 1, whereas HH leads to severe downregulation of these proteins, causing a greater cytoskeleton disruption. Proteins contributing to redox homeostasis such as iNOS and SOD, were upregulated in both hypoxic conditions. However, SIRT1-mediated ROS-triggered proteins, including FOXO1 and FOXO4, exhibited upregulation in HH and downregulation in NH. Other proteins, HIF-1α and IDH, were upregulated in HH compared to NH. Additionally, Hemopexin was severely downregulated in HH relative to NH.

SIGNIFICANCE

For the first time, this study uncovers the comparative proteomic analysis of two distinct pre-acclimatization interventions by employing varied hypoxia modeling strategies highlighting the key molecular mechanism involved in HH acclimatization induced by differential hypoxia simulating technique.

Oxytocin receptors within the caudal lateral septum regulate social approach-avoidance, long-term social discrimination, and anxiety-like behaviors in adult male and female rats

OTR signaling promotes social approach or facilitates social avoidance, depending on the brain region involved. The lateral septum plays a critical role in regulating social interactions and memory. We investigated the role of OTR signaling in the caudodorsal lateral septum (LSc.d) in modulating social approach-avoidance behavior, long-term social discrimination memory, and anxiety-like behaviors in adult rats. Local infusion of the selective OTR antagonist L-368,899 (1 μg/0.5 μl) into the LSc.d decreased social approach, increased social vigilance, and reduced long-term social discrimination memory in both sexes. Administration of the biased OTR/Gq agonist carbetocin (0.5 μg/0.5 μl) reduced social approach and long-term social discrimination memory in both sexes, and had anxiogenic effects (increased latency to consume palatable food in test arena) only in males. In contrast, the full OTR agonist TGOT (50 ng/0.5 μl) had no effect on social approach or long-term social discrimination memory, and decreased latency to consume palatable food (anxiolytic effect). The results indicate that the oxytocin system can both promote and inhibit social behaviors depending on the differential activation of G-protein subunits and β-arrestins, as well as the pivotal role of the LS in modulating social and anxiety-like behavior in rats.

Growth inhibitory peptides: a potential novel therapeutic approach to cancer treatment

Cancer remains a major global public health concern, with considerable interest in exploring biological molecules for cancer treatment and prevention. Growth inhibitory peptide (GIP), a promising new class of biological therapeutics, has drawn attention for its distinct anti-tumor properties. Derived from human alpha-fetoprotein (HAFP), this synthetic 34-amino-acid peptide has demonstrated substantial anti-tumor effects across various cancer cell lines, effectively inhibiting tumor cell proliferation, migration, and metastasis. Studies reveal that GIP mediates its effects through a range of mechanisms, including interactions with G protein-coupled receptors (GPCRs), anti-cell adhesion activities, inhibition of cell spreading and metastatic processes, morphological alterations, platelet aggregation inhibition, immune enhancement, cell membrane disruption, ion channel blockade, and cell cycle arrest. While GIP has exhibited promising anti-tumor activity in both in vitro and in vivo models, further investigation is essential to advance its development as a therapeutic drug, particularly regarding pharmacokinetics, safety profiles, storage stability, and clinical efficacy.

The potential capacities of FTY720: Novel therapeutic functions, targets, and mechanisms against diseases

Fingolimod (FTY720), an antagonist of sphingosine-1-phosphate (S1P), functions by binding to S1P receptors (S1PRs), excluding S1PR2. It received approval from the Food and Drug Administration (FDA) for the treatment of multiple sclerosis (MS) in 2010. As the first non-selective oral agonist for S1PRs, FTY720's diverse and systemic receptor expression often leads to alterations in various signaling pathways and multiple systems, making it a subject of intense research. Recent studies have identified a wide range of novel or potential functions for FTY720 beyond its application in MS. These include effects on the blood-brain barrier (BBB), vascular system, organelles, and cell death, as well as potential applications in organ transplantation, immune disorders, oncological conditions, neurological and psychiatric disorders, viral infections, and hypersensitivity diseases. This paper reviews the novel roles, targets, and mechanisms of FTY720 that hold promise for clinical utility. Additionally, it summarizes FTY720's derivation and development process, the characterization and mechanism of the structure of FTY720-P bound to S1PRs, the clinical safety profile, future challenges, and potential strategies to address them. These insights aim to guide future research and applications of FTY720, maximizing its therapeutic potential.

G-protein coupled receptors in metabolic reprogramming and cancer

G-protein coupled receptors (GPCR) are one of the frequently investigated drug targets. GPCRs are involved in many human pathophysiologies that lead to various disease conditions, such as cancer, diabetes, and obesity. GPCR receptor activates multiple signaling pathways depending on the ligand and tissue type. However, this review will be limited to the GPCR-mediated metabolic modulations and the activation of relevant signaling pathways in cancer therapy. Cancer cells often have reprogrammed cell metabolism to support tumor growth and metastatic plasticity. Many aggressive cancer cells maintain a hybrid metabolic status, using both glycolysis and mitochondrial metabolism for better metabolic plasticity. In addition to glucose and glutamine pathways, fatty acid is a key mitochondrial energy source in some cancer subtypes. Recently, targeting alternative energy pathways like fatty acid beta-oxidation (FAO) has attracted great interest in cancer therapy. Several in vitro and in vivo experiments in different cancer models reported encouraging responses to FAO inhibitors. However, due to the potential liver toxicity of FAO inhibitors in clinical trials, new approaches to indirectly target metabolic reprogramming are necessary for in vivo targeting of cancer cells. This review specifically focused on free fatty acid receptors (FFAR) and β-adrenergic receptors (β-AR) because of their reported significance in mitochondrial metabolism and cancer. Further understanding the pharmacology of GPCRs and their role in cancer metabolism will help repurpose GPCR-targeting drugs for cancer therapy and develop novel drug discovery strategies to combine them with standard cancer therapy to increase anticancer potential and overcome drug resistance.

The structural basis of the G protein-coupled receptor and ion channel axis

Sensory neurons play an essential role in recognizing and responding to detrimental, irritating, and inflammatory stimuli from our surroundings, such as pain, itch, cough, and neurogenic inflammation. The transduction of these physiological signals is chiefly mediated by G protein-coupled receptors (GPCRs) and ion channels. The binding of ligands to GPCRs triggers a signaling cascade, recruiting G proteins or β-arrestins, which subsequently interact with ion channels (e.g., GIRK and TRP channels). This interaction leads to the sensitization and activation of these channels, initiating the neuron's protective mechanisms. This review delves into the complex interplay between GPCRs and ion channels that underpin these physiological processes, with a particular focus on the role of structural biology in enhancing our comprehension. Through unraveling the intricacies of the GPCR-ion channel axis, we aim to shed light on the sophisticated intermolecular dynamics within these pivotal membrane protein families, ultimately guiding the development of precise therapeutic interventions.

Investigation into biased signaling, glycosylation, and drug vulnerability of acute myeloid leukemia

Understanding and harnessing biased signaling offers significant potential for developing novel therapeutic strategies or enhancing existing treatments. By managing biased signaling, it is possible to minimize adverse effects, including toxicity, and to optimize therapeutic outcomes by selectively targeting beneficial pathways. In the context of acute myeloid leukemia (AML), a highly aggressive blood cancer characterized by the rapid proliferation of abnormal myeloid cells in the bone marrow and blood, the dysregulation of these signaling pathways, particularly those involving G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs), significantly contributes to disease progression and therapeutic resistance. Traditional therapies for AML often struggle with resistance and toxicity, leading to poor patient outcomes. However, by exploiting the concept of biased signaling, researchers may be able to design drugs that selectively activate pathways that inhibit cancer cell growth while avoiding those that contribute to resistance or toxicity. Glycosylation, a key post-translational modification (PTM), plays a crucial role in biased signaling by altering receptor conformation and ligand-binding affinity, thereby affecting the outcome of biased signaling. Chemokine receptors like CXCR4, which are often overexpressed and heavily glycosylated in AML, serve as targets for therapeutic intervention. By externally inducing or inhibiting specific PTMs, it may be possible to further refine therapeutic strategies, unlocking new possibilities for developing more effective and less toxic treatments. This review highlights the importance of understanding the dynamic relationship between glycosylation and biased signaling in AML, which is essential for the development of more effective treatments and overcoming drug resistance, ultimately leading to better patient outcomes.

Opioid Analgesics: Rise and Fall of Ligand Biased Signaling and Future Perspectives in the Quest for the Holy Grail

Opioid analgesics have been used for more than 5000 years and remain the main pain medications prescribed today. Although morphine is considered the gold standard of pain relief, this selective µ-opioid receptor (MOP) agonist provides only moderate relief for many chronic pain conditions and produces a number of unwanted effects that can affect the patient's quality of life, prevent adherence to treatment or lead to addiction. In addition to the lack of progress in developing better analgesics, there have been no significant breakthroughs to date in combating the above-mentioned side effects. Fortunately, a better understanding of opioid pharmacology has given renewed hope for the development of better and safer pain medications. In this review, we describe how clinically approved opioids were initially characterized as biased ligands and what impact this approach might have on clinical practice. We also look at the preclinical and clinical development of biased MOP agonists, focusing on the history of oliceridine, the first specifically designed biased analgesic. In addition, we explore the discrepancies between ligands with low intrinsic efficacy and those with biased properties. Finally, we examine the rationale behind the development of biased ligands during the opioid crisis.

Genetically encoded sensors illuminate in vivo detection for neurotransmission: Development, application, and optimization strategies

Limitations in existing tools have hindered neuroscientists from achieving a deeper understanding of complex behaviors and diseases. The recent development and optimization of genetically encoded sensors offer a powerful solution for investigating intricate dynamics such as calcium influx, membrane potential, and the release of neurotransmitters and neuromodulators. In contrast, traditional methods are constrained by insufficient spatial and/or temporal resolution, low sensitivity, and stringent application conditions. Genetically encoded sensors have gained widespread popularity due to their advantageous features, which stem from their genetic encoding and optical imaging capabilities. These include broad applicability, tissue specificity, and non-invasive operation. When combined with advanced microscopic techniques, optogenetics, and machine learning approaches, these sensors have become versatile tools for studying neuronal circuits in intact living systems, providing millisecond-scale temporal resolution and spatial resolution ranging from nanometers to micrometers. In this review, we highlight the advantages of genetically encoded sensors over traditional methods in the study of neurotransmission. We also discuss their recent advancements, diverse applications, and optimization strategies.

A nanoluciferase complementation-based assay for monitoring β-arrestin2 recruitment to the dopamine D3 receptor

Luciferase complementation assays have emerged as a simple means of monitoring receptor-effector interactions in living cells in a time-resolved manner. Here, we describe a nanoluciferase complementation assay capable of reporting on β-arrestin2 recruitment to the human dopamine D3 receptor (D3R) upon its activation in intact HEK293T cells. Using this assay in time-resolved experiments, we detect differences in arrestin response termination rates between the endogenous agonist dopamine and the synthetic D3R agonist FAUC-73. We also investigate the influence of exogenous GRK2 on β-arrestin2 recruitment to the D3R. We find that, in contrast to the D2R and D4R, the potency of dopamine to induce arrestin recruitment to D3R is not significantly influenced by GRK2 overexpression. In further agreement with a lack of GRK2 regulation of D3R signalling and again contrary to the D2R and D4R, we do not observe dopamine-induced recruitment of GRK2 to D3R. Conversely, dopamine concentration-dependently decreases the interaction between GRK2 and D3R. Additionally, we examine both the Ser-9 and Gly-9 variants of the human D3R, which, according to some earlier reports, differ in terms of dopamine affinity and functional potency. However, we find no difference in the concentration-response relationships between these two variants, neither when arrestin recruitment nor GRK2 interactions are studied. In summary, the present report demonstrates the utility of nanoluciferase complementation for studying D3R pharmacology in living cells.

Development of a long-acting unbiased GIP receptor agonist for studies of GIP's role in bone metabolism

The incretin hormone glucose-dependent insulinotropic polypeptide (GIP) stimulates bone remodeling postprandially. Species variations complicate the development of long-acting agonists with similar effects on rodent and human GIP receptors (GIPR). We created a series of long-acting molecules suitable for rat studies based on human GIP, stabilized with Aib insertion in position 2, lipidations in the middle region (compounds 1-4: positions 14/16/17/20) or the C-terminus (compound 5: position 40), and elongation with an exendin-4 tail in the C-terminus (Cex). The compounds were tested in vitro on the human and rat GIPR for cAMP accumulation, beta-arrestin recruitment and internalization. Pharmacokinetic profiling in rats was completed for two compounds, and one was selected for bone remodeling studies in rats (measurements of C-terminal telopeptide (CTX) and procollagen type 1 N-propeptide). All five compounds retained the potency and efficacy of native (human and rat) GIP in cAMP accumulation and arrestin recruitment on human and rat GIPR with no differences in relative activities from native GIP. Only compound 3 induced internalization like species-matched GIP on respective receptors and was chosen for in vivo assessments in rats. Mean T1/2 was 9.1 h, and it decreased plasma levels of CTX compared to vehicle treatment following 1000 µg·kg-1 injections. In conclusion, the long-acting, unbiased compound 3 (hGIP(1-30-Cex)/Aib2/C16-diacid moiety in position 17), with retained activity for the human and rat GIPR, is suitable for bone remodeling studies in rats; hence, a useful tool compound for future research of GIP's therapeutic potential in bone-related diseases.

Neuroactive steroids activate membrane progesterone receptors to induce sex specific effects on protein kinase activity

Neuroactive steroids (NAS), which are synthesized in the brain from progesterone, exert potent effects on behavior and are used to treat postpartum depression, yet how these compounds induce sustained modifications in neuronal activity are ill-defined. Here, we examined the efficacy of NAS for membrane progesterone receptors (mPRs) δ and ε, members of a family of GPCRs for progestins that are expressed in the CNS. NAS increase PKC activity via the Gq activation of mPRδ with EC50s between 3 and 11nM. In contrast, they activate Gs via mPRε to potentiate PKA activity with similar potencies. NAS also induced the rapid internalization of only mPRδ. In the forebrain of female mice, mPRδ expression levels were 8-fold higher than in males. Consistent with this, the activation of PKC by NAS was evident in acute brain slices from female mice. Collectively, our results suggest that NAS may exert sex-specific effects on intracellular signaling in the brain via the activation of mPRs.

Regulation of autophagy: Insights into O-GlcNAc modification mechanisms

Autophagy is a "self-eating" biological process that degrades cytoplasmic contents to ensure cellular homeostasis. Its response to stimuli occurs in two stages: Within a few to several hours of exposure to a stress condition, autophagic flow rapidly increases, which is mediated by post-translational modification (PTM). Subsequently, the transcriptional program is activated and mediates the persistent autophagic response. O-linked β-N-acetylglucosamine (O-GlcNAc) modification is an inducible and dynamically cycling PTM; mounting evidence suggests that O-GlcNAc modification participates in the total autophagic process, including autophagy initiation, autophagosome formation, autophagosome-lysosome fusion, and transcriptional process. In this review, we summarize the current knowledge on the emerging role of O-GlcNAc modification in regulating autophagy-associated proteins and explain the different regulatory effects on autophagy exerted by O-GlcNAc modification.

Deficiency of β-arrestin2 ameliorates MASLD in mice by promoting the activation of TAK1/AMPK signaling

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a liver manifestation of metabolic syndrome characterized by excessive hepatic lipid accumulation and lipid metabolism disorders. It has become the most common chronic liver disease worldwide. β-arrestin2 is a multifunctional scaffold protein that is among the most important regulatory molecules, and it exerts key roles in regulating various cellular processes, such as immune response, cellular collagen production, and inflammation. In the current study, we aimed to explore the function of β-arrestin2 in the development and progression of MASLD. Firstly, we observed that the expression of β-arrestin2 was upregulated in liver samples from patients with MASLD. Then, the western diet (WD) combined with CCl4 injection-induced MASLD was established in wild-type mice, and showed that liver β-arrestin2 expression was also gradually increased, and positively correlated with the degree of lipid metabolism disorder during MASLD progression. Ulteriorly, β-arrestin2 knockout (Arrb2 KO) mice were utilized to induce the MASLD model and found that β-arrestin2 deficiency significantly ameliorated lipid accumulation and inflammatory response in the liver of MASLD mice. Furthermore, the in vitro depletion and overexpression experiments showed that increased β-arrestin2 aggravated lipid accumulation via inhibiting the activation of the TAK1/AMPK pathway, which may be mediated by competitively binding to TAB1 with TAK1. These findings suggest that β-arrestin2 is essential to regulate intrahepatic lipid metabolism. Here, we provide a novel insight in understanding of the expression and function of β-arrestin2 in MASLD, demonstrating that it may be a potential therapeutic target for MASLD treatment.

Abundance of dopamine and its receptors in the brain and adipose tissue following diet-induced obesity or caloric restriction

While obesity and type 2 diabetes (T2D) are associated with altered dopaminergic activity in the central nervous system and in adipose tissue (AT), the direction and underlying mechanisms remain inconclusive. Therefore, we characterized changes in the abundance of dopamine, its metabolites, and receptors DRD1 and DRD2 in the brain and AT upon dietary intervention or obesity. Male Wistar rats were fed either a standard pellet diet, a cafeteria diet inducing obesity and insulin resistance, or a calorie-restricted diet for 12 weeks. Abundance of dopamine and its receptors DRD1 and DRD2 were examined in brain regions relevant for feeding behavior and energy homeostasis. Furthermore, DRD1 and DRD2 protein levels were analyzed in rat inguinal and epidydimal AT and in human subcutaneous and omental AT from individuals with or without obesity. Rats with diet-induced obesity displayed higher dopamine levels, as well as DRD1 or DRD2 receptor levels in the caudate putamen and the nucleus accumbens core. Surprisingly, caloric restriction induced similar changes in DRD1 and DRD2, but not dopamine levels, in the brain. Both diets reduced DRD1 abundance in inguinal and epidydimal AT, but upregulated DRD2 levels in inguinal AT. Furthermore, in human obesity, DRD1 protein levels were elevated only in omental AT, while DRD2 was upregulated in both omental and subcutaneous AT. These findings highlight dopaminergic responses to changes in energy balance, occurring both in the brain and AT. We propose that dopaminergic pathways are involved in tissue crosstalk during the development of obesity and T2D.

Bioprinting of transparent and adhesive corneal patches: Integrating photo-crosslinkable dopamine-conjugated silk fibroin and decellularized cornea matrix for sutureless tissue integration and regeneration

Corneal injuries, a leading cause of visual impairment, are traditionally addressed through tissue transplantation. However, challenges such as donor shortages, graft rejection, and complications from suturing often limit their effectiveness. Current corneal adhesives frequently fall short in both adhesion strength and biocompatibility. We present an innovative solution: a photocurable hydrogel that integrates dopamine-conjugated methacrylated silk fibroin (d-MSF) with a decellularized corneal matrix (DCM). This hydrogel combines advanced materials to create a bioadhesive system that offers superior adhesion inspired by mussel adhesion and mimics the native tissue environment. FTIR and NMR analyses confirm that our conjugation process prevents unwanted beta-sheet aggregation, ensuring both stability and transparency. The hydrogel demonstrates excellent rheological properties, including enhanced shear-thinning and impressive shear and creep recovery, making it highly suitable for extrusion-based bioprinting. We successfully bioprinted a bilayer corneal patch, featuring a concentric ring of d-MSF as the first layer, overlaid with a second layer of DCM. The implants exhibit strong tissue adhesion, with an adhesion strength of 85 ± 5.6 KPa, and Young's modulus of 0.48 ± 0.064 MPa, ensuring excellent structural integrity. This results in a highly transparent (>80 %) and functional adhesive corneal patch. This advancement offers a promising, biocompatible alternative to traditional keratoprostheses, advancing corneal repair technology.

Assembling the jigsaw puzzle of life

The cell is a dynamic system where millions of molecules of thousands different kinds act within a complex network with numerous feedback loops. Because we cannot pursue many targets simultaneously, 'big data' rarely yield useful leads. Comprehensive models can place the snippets obtained in simplified experimental conditions into a coherent picture.

The path of GPR87: from a P2Y-like receptor to its role in cancer progression

GPR87 is a G protein-coupled seven-transmembrane receptor first described as an orphan receptor in 2001. Despite its high structural homology to several extracellular nucleotide-activated P2Y receptors and sharing conserved sequence motifs in transmembrane regions, identification of endogenous ligands from the class of nucleotides and their analogues has failed for GPR87. Although lysophosphatidic acid was proposed to be a natural ligand for this cell surface receptor, these data are preliminary and inconsistent, and IUPHAR is currently considering GPR87 as an orphan receptor. Thus, the endogenous ligands and physiological functions of GPR87 are still required to be determined and/or confirmed. The remarkably higher expression of GPR87 in human malignant tissues compared to the normal healthy ones clearly suggests that this receptor may be involved in the development and progression of cancerous neoplasms. Therefore, in this review article, the main focus is placed on the oncogenic role of GPR87 in various human malignancies, presenting it as a potential novel target site for therapeutic interventions using both humanized monoclonal antibodies and gene therapy but also selective antagonists which are still waiting for their identification. Furthermore, the importance of the expression of GPR87 as a predictive biomarker for evaluating the prognosis and overall survival of cancer patients is also highlighted.

cFos-mediated β-Arrestin1 in the RVLM alleviates sympathetic hyperactivity induced by ovariectomy

Sympathetic hyperactivity is a key feature of cardiovascular dysfunction in postmenopausal women and is closely linked to the onset, progression, and outcomes of cardiovascular events. However, the mechanisms underlying sympathetic nerve hyperactivity due to menopause remain unclear. β-arrestin is a versatile class of intracellular proteins that were initially discovered for their ability to disrupt the G protein-coupled receptors (GPCRs) signaling by binding to activated receptors. A notable reduction in the expression of β-arrestin1 in the rostral ventrolateral medulla (RVLM) associated with increased sympathetic activity and elevated blood pressure (BP) in spontaneously hypertensive rats. It has been reported that the cellular oncogene fos (cFos), as a transcription factor, plays a crucial role in BP regulation. This study aimed to investigate whether β-arrestin1, regulated by cFos in the RVLM, contributes to sympathetic hyperactivity induced by menopause. Bilateral ovariectomy (OVX) was performed to establish a postmenopausal rat model. We found that the expression of β-arrestin1 in the RVLM of OVX rats was reduced, whereas estrogen supplementation increased the expression of β-arrestin1. Furthermore, overexpression of β-arrestin1 in the RVLM of OVX rats attenuated the sympathetic hyperactivity. Conversely, reducing β-arrestin1 expression in the RVLM compromised the cardioprotective effects of estrogen in OVX rats. Additionally, inhibiting the expression of the transcription factor cFos in the RVLM of OVX rats diminished the estrogen-induced increase in the expression of β-arrestin1. These findings suggest that estrogen enhances the expression of β-arrestin1 mediated by cFos in the RVLM of OVX rats, thereby alleviating sympathetic nerve hyperactivity and hypertension.

Next-generation small molecule inhibitors of clathrin function acutely inhibit endocytosis

Clathrin-mediated endocytosis (CME) is the predominant endocytic pathway in eukaryotic cells and a major regulator of cell physiology as it facilitates the internalization of receptors, channels, and transporters and viral entry. The clathrin terminal domain acts as a central protein interaction hub within the endocytic protein network. Previously described inhibitors of CME display off-target activities that result in cytotoxicity, providing limitations to their use. We report the development and characterization of next-generation small molecule inhibitors of clathrin terminal domain function. These compounds termed Pitstop 2c and Pitstop 2d occupy the binding site within the clathrin terminal domain for endocytic protein ligands including epsin, resulting in potent inhibition of receptor-mediated endocytosis and reduced entry of vesicular stomatitis virus (VSV) with minimal cytotoxic side effects. Next-generation Pitstops thus provide an improved toolset to address clathrin function in cell physiology with potential applications as inhibitors of virus and pathogen entry.

Mechanosensitive adhesion G protein-coupled receptors: Insights from health and disease

Ontogeny cannot be separated from mechanical forces. Cells are continuously subjected to different types of mechanical stimuli that convert into intracellular signals through mechanotransduction. As a member of the G protein-coupled receptor superfamily, adhesion G protein-coupled receptors (aGPCRs) have attracted extensive attention due to their unique extracellular domain and adhesion properties. In the past few decades, increasing evidence has indicated that sensing mechanical stimuli may be one of the main physiological activities of aGPCRs. Here, we review the general structure and activation mechanisms of these receptors and highlight the lesion manifestations relevant to each mechanosensitive aGPCR.

Protein Modeling with DEER Spectroscopy

Double electron-electron resonance (DEER) combined with site-directed spin labeling can provide distance distributions between selected protein residues to investigate protein structure and conformational heterogeneity. The utilization of the full quantitative information contained in DEER data requires effective protein and spin label modeling methods. Here, we review the application of DEER data to protein modeling. First, we discuss the significance of spin label modeling for accurate extraction of protein structural information and review the most popular label modeling methods. Next, we review several important aspects of protein modeling with DEER, including site selection, how DEER restraints are applied, common artifacts, and the unique potential of DEER data for modeling structural ensembles and conformational landscapes. Finally, we discuss common applications of protein modeling with DEER data and provide an outlook.

Macromolecular crystallography and biology at the Linac Coherent Light Source

The Linac Coherent Light Source (LCLS) has significantly impacted the field of biology by providing advanced capabilities for probing the structure and dynamics of biological molecules with high precision. The ultrashort coherent X-ray pulses from the LCLS have enabled ultrafast, time-resolved, serial femtosecond crystallography that is inaccessible at conventional synchrotron light sources. Since the facility's founding, scientists have captured detailed insights into biological processes at atomic resolution and fundamental timescales. The ability to observe these processes in real time and under conditions closely resembling their natural state is transforming our approach to studying biochemical mechanisms and developing new medical and energy applications. This work recounts some of the history of the LCLS, advances in biological research enabled by the LCLS, key biological areas that have been impacted and how the LCLS has helped to unravel complex biological phenomena in these fields.

Interaction of opioid and D2-like dopamine receptors in the nucleus accumbens modulate acute pain-related behaviors

As a pivotal component of the reward circuitry in the brain, the nucleus accumbens (NAc) is essential in influencing pain-related reactions. Its involvement suggests a significant interplay with the systems that utilize opioids and dopamine. This research investigated the interplay between opioidergic and D2-like dopamine receptors within the NAc on acute pain-related behaviors. Male Wistar rats underwent unilateral cannula implantation into the NAc. In the initial phase, separate groups of animals were administered varying doses of morphine (5, 10, and 25 mmol/0.5 μL) and quinpirole (2, 4, 8, and 16 mmol/0.5 μL), acting as an opioid and a D2-like receptor agonist in the NAc, respectively. Following this, the animals received different doses of sulpiride (1.5, 3, 6, 12, and 24 mmol/0.5 μl), a D2-like receptor antagonist, prior to receiving an effective dose of morphine (10 mmol/0.5 μL). In the final phase, animals were given varying doses of naloxone (1.5, 5, 15, and 45 mmol/0.5 μl) before administering the efficacious dose of quinpirole (8 mmol/0.5 μl). This study employed the tail-flick test, which was subsequently used to assess the subjects' acute pain threshold. The primary results indicated that the administration of morphine and quinpirole into the NAc independently produced antinociceptive effects. Conversely, injecting sulpiride into the NAc significantly reduced the pain-relieving effects of morphine in the NAc. Additionally, introducing naloxone into the NAc greatly weakened the antinociceptive consequences linked to the quinpirole administration. The findings suggest a possible interaction between the dopamine and opioid systems within the NAc that may lead to pain relief. This understanding could guide the creation of new medications designed to enhance pain management while reducing the risks linked to conventional opioid treatments.

Exploring a novel mechanism for targeting β-arrestin-2 in the management of diabetic nephropathy

Diabetic nephropathy (DN) is a well-known microvascular complication in patients with diabetes mellitus, which is characterized by the accumulation of extracellular matrix in the glomerular and tubulointerstitial compartments, along with the hyalinization of intrarenal vasculature. DN has recently emerged as a leading cause of chronic and end-stage renal disease. While the pathobiology of other diabetic microvascular complications, such as retinopathy, is largely understood and has reasonable therapeutic options, the mechanisms and management strategies for DN remain incompletely elucidated. In this editorial, we comment on the article by Liu et al, focusing on the mechanisms underlying the detrimental impact of β-arrestin-2 on the kidneys in the context of DN. The authors suggest that inhibiting β-arrestin-2 could alleviate renal damage through suppressing apoptosis of glomerular endothelial cells (GENCs), highlighting β-arrestin-2 as a promising therapeutic target for DN. The study proposed that β-arrestin-2 triggers endoplasmic reticulum (ER) stress via the ATF6 signaling pathway, thereby promoting GENC apoptosis and exacerbating DN progression. Given the novel and crucial role of β-arrestin-2 in ER stress-related DN, it is imperative to further explore β-arrestin-2, its roles in ER stress and the potential therapeutic implications in DN.

A molecular dynamics study of membrane positioning for 7-transmembrane RGS proteins to modulate G-protein-mediated signaling in plants

Protein phosphorylation regulates G protein signaling in plants. AtRGS1 primarily modulates AtGPA1, the canonical Gα subunit in the heterotrimeric G protein complex. AtRGS1 possesses both a seven-transmembrane (7TM) domain connected to a cytoplasmic Regulator of G Protein Signaling domain (RGS box domain) by a flexible linker region. This study presents the novel function of a highly conserved, known phosphorylation site, Ser278, within this linker region utilizing molecular dynamics (MD) simulations with in vivo experimental validation. We show that phosphorylation at Ser278 is crucial for establishing specific AtRGS1 interactions with AtGPA1, primarily by stabilizing the positioning and orientation of the RGS domain within the membrane. Phosphorylation at Ser278 enhances the formation of stable hydrogen bonds between phosphorylated Ser278 and conserved residues within the RGS box domain, influencing the flexibility of RGS domain mobility and thus modulating its interface to AtGPA1. Consistent with the MD simulations, in vivo assays demonstrated that this phosphorylation reduced the binding of AtRGS1 to AtGPA1 and conferred changes in physiology. Specifically, the non-phosphorylation mutation of Ser278 decreased both plant immune responses and AtRGS1 endocytosis evoked by the bacterial effector, flg22. MD simulations and sequence analysis of diverse plant 7TM-RGS proteins suggest conservation of this mechanism across land plants, emphasizing the critical role of this previously overlooked linker region.

Protein Kinases as Mediators for miRNA Modulation of Neuropathic Pain

Neuropathic pain is a chronic condition resulting from injury or dysfunction in the somatosensory nervous system, which leads to persistent pain and a significant impairment of quality of life. Research has highlighted the complex molecular mechanisms that underlie neuropathic pain and has begun to delineate the roles of microRNAs (miRNAs) in modulating pain pathways. miRNAs, which are small non-coding RNAs that regulate gene expression post-transcriptionally, have been shown to influence key cellular processes, including neuroinflammation, neuronal excitability, and synaptic plasticity. These processes contribute to the persistence of neuropathic pain, and miRNAs have emerged as critical regulators of pain behaviors by modulating signaling pathways that control pain sensitivity. miRNAs can influence neuropathic pain by targeting genes that encode protein kinases involved in pain signaling. This review focuses on miRNAs that have been demonstrated to modulate neuropathic pain behavior through their effects on protein kinases or their immediate upstream regulators. The relationship between miRNAs and neuropathic pain behaviors is characterized as either an upregulation or a downregulation of miRNA levels that leads to a reduction in neuropathic pain. In the case of miRNA upregulation resulting in an alleviation of neuropathic pain behaviors, protein kinases exhibit a positive correlation with neuropathic pain, whereas decreased protein kinase levels correlate with diminished neuropathic pain behaviors. The only exception is GRK2, which shows an inverse correlation with neuropathic pain. In the case of miRNA downregulation resulting in a reduction in neuropathic pain behaviors, protein kinases display mixed relationships to neuropathic pain, with some kinases exhibiting positive correlation, while others exhibit negative correlation. By exploring how protein kinases mediate miRNA modulation of neuropathic pain, valuable insight may be gained into the pathophysiology of neuropathic pain, offering potential therapeutic targets for developing more effective strategies for pain management.

Computational drug repurposing in Parkinson's disease: Omaveloxolone and cyproheptadine as promising therapeutic candidates

Background: Parkinson's disease (PD), a prevalent and progressive neurodegenerative disorder, currently lacks effective and satisfactory pharmacological treatments. Computational drug repurposing represents a promising and efficient strategy for drug discovery, aiming to identify new therapeutic indications for existing pharmaceuticals. Methods: We employed a drug-target network approach to computationally repurpose FDA-approved drugs from databases such as DrugBank. A literature review was conducted to select candidates not previously reported as pharmacoprotective against PD. Subsequent in vitro evaluation utilized Cell Counting Kit-8 (CCK8) assays to assess the neuroprotective effects of the selected compounds in the SH-SY5Y cell model of Parkinson's disease induced by 1-methyl-4-phenylpyridinium (MPP+). Furthermore, an in vivo mouse model of Parkinson's disease induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was developed to investigate the mechanisms of action and therapeutic potential of the identified drug candidates. Results: Our approach identified 176 drug candidates, with 28 selected for their potential anti-Parkinsonian effects and lack of prior PD-related reporting. CCK8 assays showed significant neuroprotection in SH-SY5Y cells for Omaveloxolone and Cyproheptadine. In the MPTP-induced mouse model, Cyproheptadine inhibited interleukin-6 (IL-6) expression and prevented Tyrosine Hydroxylase (TH) downregulation via the MAPK/NFκB pathway, while Omaveloxolone alleviated TH downregulation, potentially through the Kelch-like ECH-associated protein 1 (KEAP1)-NF-E2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway. Both drugs preserved dopaminergic neurons and improved neurological deficits in the PD model. Conclusion: This study elucidates potential drug candidates for the treatment of Parkinson's disease through the application of computational repurposing, thereby underscoring its efficacy as a drug discovery strategy.

Molecular Insights into Diapause Mechanisms in Telenomus remus for Improved Biological Control

This study explores the molecular mechanisms underlying diapause in the parasitoid wasp Telenomus remus (Nixon) (Hymenoptera: Platygastridae), a critical egg parasitoid for the biological control of the invasive pest Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae). While effective in pest management, T. remus faces limitations in large-scale applications due to its short lifespan and low viability under storage conditions. Diapause, a state of developmental arrest, was successfully induced in T. remus using photoperiod manipulation (0L:24D), allowing for extended survival and improved storage potential. Transcriptome sequencing identified 2642 differentially expressed genes, with 617 involved in 284 enriched pathways, including calcium signaling and phototransduction. The study found that the expression levels of CBP1 and CBP2, genes encoding calcium-binding proteins, were significantly downregulated during diapause. As key regulators in calcium ion-mediated signal transduction pathways, the downregulation of CBP1 and CBP2 may lead to the suppression of intracellular calcium signaling, thereby affecting light signal transduction and energy metabolism regulation. This suggests that during diapause, insects may reduce calcium signaling activity to suppress physiological functions, maintain a low metabolic state, and decrease sensitivity to environmental stimuli. Additionally, ARR genes still exhibited differential expression, further supporting their potential role in phototransduction and diapause regulation.

Icariin improves erectile function in spontaneously hypertensive rats by downregulating GRK2 in penile cavernous tissue

BACKGROUND

Hypertension is an independent risk factor for erectile dysfunction (ED). Icariin can improve erectile function of spontaneous hypertensive rats (SHRs). GRK2 is closely related to the phosphorylation of eNOS and endothelial function.

AIM

To explore whether icariin can improve erectile function in SHRs by regulating the expression of GRK2 in penile cavernous tissue.

METHODS

Eight-week-old WKY and SHR rats were randomly divided into four groups (n = 6 per group) as follows: WKY, WKY + icariin, SHR and SHR + icariin. The WKY + icariin and SHR + icariin groups were treated with 10 mg/kg/day icariin. After 4 weeks, the ICPmax/mean arterial pressure (MAP), serum testosterone, the levels of GRK2, p-AKT/AKT, p-eNOS/eNOS, and caspase-3; the protein interaction between GRK2 and AKT; the levels of nitric oxide (NO), superoxide dismutase (SOD), and malondialdehyde (MDA); and the level of apoptosis in rat penile cavernous tissue were measured.

OUTCOME

The expression of GRK2 in penile cavernous tissue of SHR was significantly higher than that in WKY rats, resulting in the inhibition of the AKT/eNOS/NO pathway, increased levels of oxidative stress and apoptosis, and the impairment of erectile function.

RESULTS

The ICPmax/MAP ratio in the SHR group was significantly lower than those in WKY and SHR + icariin groups (P < .01). In the SHR + icariin group, the expression levels of GRK2 and caspase-3, the interaction between GRK2 and AKT, the level of MDA and the rate of apoptosis in the penile cavernous tissue were significantly lower, and the levels of p-AKT and p-eNOS, the p-AKT/AKT and p-eNOS/eNOS ratios, and NO and SOD were significantly greater than those in the SHR group (P < .01).

CLINICAL IMPLICATIONS

Icariin may improve the erectile function of hypertension by downregulating GRK2 expression in penile cavernous tissue.

STRENGTHS AND LIMITATIONS

The specific mechanism via which icariin downregulates GRK2 needs to be further elucidated.

CONCLUSION

Icariin downregulates the expression of GRK2 in the penile cavernous tissue of SHRs, upregulates the AKT/eNOS/NO pathway, decreases oxidative stress and apoptosis, and ultimately improves erectile function.

β-Arrestin Condensates Regulate G Protein-Coupled Receptor Function

G protein-coupled receptors (GPCRs) are the largest class of receptors in the genome and control many signaling cascades essential for survival. GPCR signaling is regulated by β-arrestins, multifunctional adapter proteins that direct receptor desensitization, internalization, and signaling. While at many GPCRs, β-arrestins interact with a wide array of signaling effectors, it is unclear how β-arrestins promote such varied functions. Here we show that β-arrestins undergo liquid-liquid phase separation (LLPS) to form condensates that regulate GPCR function. We demonstrate that β-arrestin oligomerization occurs in proximity to the GPCR and regulates GPCR functions such as internalization and signaling. This model is supported by a cryoEM structure of the adhesion receptor ADGRE1 in a 2:2 complex with β-arrestin 1, with a β-arrestin orientation that can promote oligomerization. Our work provides a paradigm for β-arrestin condensates as regulators of GPCR function, with LLPS serving as an important promoter of signaling compartmentalization at GPCRs.

Sunlight-mediated environmental risks of tinidazole in seawater: A neglected ocular toxicity of photolysis mixtures

Tinidazole (TNZ), a common nitroimidazole antibiotic, is pervasive in aquatic ecosystems, posing potential threats to marine organisms. The environmental fate of TNZ, particularly under solar irradiation, and the associated secondary risks are not well characterized. Herein, the photochemical reactivity of TNZ and four other typical nitroimidazoles (i.e., metronidazole, ornidazole, dimetridazole, and secnidazole) were quantified for multiple photoreactive species. The photolysis products of these nitroimidazoles were identified under solar irradiation, from which the reaction pathways were tentatively proposed. Furthermore, the photo-induced toxicity evolution mechanisms of TNZ were investigated by comparing phenotypic, transcriptomic, and metabolomic changes in marine medaka embryos (Oryzias melastigma) after exposure to TNZ and its photo-irradiated mixtures. Our results indicated that the photo-irradiated TNZ enhanced visual toxicity to marine medaka embryos compared to the parent compound. The photolysis mixtures induced embryonic ocular malformation and significantly affected the expression of the associated genes with the initiation/termination of the phototransduction cascade, leading to metabolite changes related to visual impairment. This work reported the first comprehensive assessment of the photolysis-mediated environmental fate and secondary risks of TNZ in seawater. The findings highlighted the necessity of including complex photolysis mixtures under solar irradiation in future chemical risk assessments of marine environments.

Orphan G Protein-Coupled Receptor GPR88: Mapping Its Significance in Central Nervous System Disorders

G protein-coupled receptors (GPCRs), comprising the largest family of membrane receptors in humans, play a crucial roles in various physiological and pathological processes. Although several drugs that target GPCRs have been discovered, the characterization of orphan GPCRs (oGPCRs) remains a significant challenge. Despite extensive research, knowledge on a significant portion of these receptors, along with their ligands and target sites, remains undefined. GPR88 belongs to the category of oGPCR that is expressed in various tissues and organs, with numerous studies indicating that it plays a regulatory role in cognitive processes, emotional responses, and motor control, thereby influencing various brain behaviors and functions associated with learning. Therefore, the purpose of this review was to thoroughly examine the role of GPR88 in various central nervous system diseases, with the ultimate aim of positioning it as a potential and promising target for drug development, particularly for the treatment of a broad spectrum of neurological disorders.

Monogenic Retinal Diseases Associated With Genes Encoding Phototransduction Proteins: A Review

Phototransduction, the process by which captured photons elicit electrical changes in retinal rod and cone cells, represents the first neuronal step in vision and involves interactions between several highly specialised proteins. Pathogenic variants in genes encoding many of these proteins can give rise to significant vision impairment, accounting for a substantial portion of inherited retinal disease. Such genes include RHO, OPN1LW, OPN1MW, GNAT1, GNAT2, GNB3, PDE6A, PDE6B, PDE6G, PDE6C, PDE6H, CNGA1, CNGB1, CNGA3, CNGB3, GRK1, SAG, ARR3, RGS9, RGS9BP, GUCY2D, GUCA1A and SLC24A1. Many of these conditions have distinct mechanisms and clinical features. They follow several modes of inheritance (including in one case digenic, or tri-allelic, inheritance). Some conditions also entail myopia. Rod and cone phototransduction will be outlined, followed by the discussion of diseases associated with these genes. Some phenotypic features will be highlighted as well as their prevalence in a large genotyped inherited retinal disease cohort.

Functional dynamics of G protein-coupled receptors reveal new routes for drug discovery

G protein-coupled receptors (GPCRs) are the largest human membrane protein family that transduce extracellular signals into cellular responses. They are major pharmacological targets, with approximately 26% of marketed drugs targeting GPCRs, primarily at their orthosteric binding site. Despite their prominence, predicting the pharmacological effects of novel GPCR-targeting drugs remains challenging due to the complex functional dynamics of these receptors. Recent advances in X-ray crystallography, cryo-electron microscopy, spectroscopic techniques and molecular simulations have enhanced our understanding of receptor conformational dynamics and ligand interactions with GPCRs. These developments have revealed novel ligand-binding modes, mechanisms of action and druggable pockets. In this Review, we highlight such aspects for recently discovered small-molecule drugs and drug candidates targeting GPCRs, focusing on three categories: allosteric modulators, biased ligands, and bivalent and bitopic compounds. Although studies so far have largely been retrospective, integrating structural data on ligand-induced receptor functional dynamics into the drug discovery pipeline has the potential to guide the identification of drug candidates with specific abilities to modulate GPCR interactions with intracellular effector proteins such as G proteins and β-arrestins, enabling more tailored selectivity and efficacy profiles.

Arrestin-independent internalization of the GLP-1 receptor is facilitated by a GRK, clathrin, and caveolae-dependent mechanism

The glucagon-like peptide-1 receptor (GLP-1R) plays an important role in regulating insulin secretion and reducing body weight, making it a prominent target in the treatment of type 2 diabetes and obesity. Extensive research on GLP-1R signaling has provided insights into the connection between receptor function and physiological outcomes, such as the correlation between Gs signaling and insulin secretion, yet the exact mechanisms regulating signaling remain unclear. Here, we explore the internalization pathway of GLP-1R, which is crucial for controlling insulin release and maintaining pancreatic beta-cell function. Utilizing a reliable and sensitive time-resolved fluorescence resonance energy transfer (TR-FRET) internalization assay, combined with HEK293-derived knockout cell lines, we were able to directly compare the involvement of different endocytic machinery in GLP-1R internalization. Our findings indicate that the receptor internalizes independently of arrestin and is dependent on Gs and Gi/o activation and G protein-coupled receptor kinase phosphorylation. Mechanistically, we observed that the receptor undergoes distinct clathrin- and caveolae-mediated internalization in HEK293 cells. This study also investigated the role of arrestins in GLP-1R function and regulation. These insights into key endocytic components that are involved in the GLP-1R internalization pathway could enhance the rational design of GLP-1R therapeutics for type 2 diabetes and other GLP-1R-related diseases.

Calmodulin kinase II inhibition suppresses atrioventricular conduction by regulating intracellular Ca2+ homeostasis

BACKGROUND

Ca2+/calmodulin-dependent protein kinase II (CaMKII) inhibition decelerates atrioventricular node (AVN) conduction, providing a potential treatment of tachycardia. However, the effectiveness of CaMKII inhibition on tachycardia and its underlying mechanism remains unclear.

OBJECTIVE

We aimed to assess the effectiveness of CaMKII inhibition in reducing ventricular rates during atrial fibrillation and to elucidate the underlying mechanism in affecting AVN electrophysiology.

METHODS

Cardiac CaMKII inhibition (AC3-I) mice were used. Transesophageal atrial pacing was performed to evaluate AVN conduction function and to induce atrial fibrillation. Patch-clamp techniques were employed to record action potentials and ionic currents in AVN cells. Intracellular Ca2+ transients and sarcomere length measurements were obtained with the IonOptix system. Masson trichrome stain was used to evaluate fibrosis in the AVN region. Western blotting and immunofluorescence techniques were employed to detect connexin expression and localization.

RESULTS

CaMKII inhibition decreased the ventricular rate during atrial fibrillation and isoproterenol-induced tachycardia. Esophageal electrocardiogram results from AC3-I mice showed longer AVN conduction than in wild-type mice. AN- and N-type AVN cells from AC3-I mice exhibited slower action potential frequencies and diastolic depolarization rates than those of wild-type mice. The study revealed that CaMKII inhibition reduced AVN cell sarcoplasmic reticulum (SR) Ca2+ content, Ca2+ release rate from the SR during diastole, Ca2+ transient amplitude, and SR Ca2+ uptake rate. In addition, CaMKII inhibition prolonged the sarcomere diastole duration and enhanced the sensitivity of sarcomeres to Ca2+.

CONCLUSION

CaMKII inhibition effectively decreases the ventricular rate during atrial fibrillation and tachycardia by slowing down AVN conduction through suppressing Ca2+ overload in AVN cells.

Biased signaling in drug discovery and precision medicine

Receptors are crucial for converting chemical and environmental signals into cellular responses, making them prime targets in drug discovery, with about 70% of drugs targeting these receptors. Biased signaling, or functional selectivity, has revolutionized drug development by enabling precise modulation of receptor signaling pathways. This concept is more firmly established in G protein-coupled receptor and has now been applied to other receptor types, including ion channels, receptor tyrosine kinases, and nuclear receptors. Advances in structural biology have further refined our understanding of biased signaling. This targeted approach enhances therapeutic efficacy and potentially reduces side effects. Numerous biased drugs have been developed and approved as therapeutics to treat various diseases, demonstrating their significant therapeutic potential. This review provides a comprehensive overview of biased signaling in drug discovery and disease treatment, highlighting recent advancements and exploring the therapeutic potential of these innovative modulators across various diseases.

Adaptive genomic signatures of globally invasive populations of the yellow fever mosquito Aedes aegypti

In the arboviral vector Aedes aegypti, adaptation to anthropogenic environments has led to a major evolutionary shift separating the domestic Aedes aegypti aegypti (Aaa) ecotype from the wild Aedes aegypti formosus (Aaf) ecotype. Aaa mosquitoes are distributed globally and have higher vectorial capacity than Aaf, which remained in Africa. Despite the evolutionary and epidemiological relevance of this separation, inconsistent morphological data and a complex population structure have hindered the identification of genomic signals distinguishing the two ecotypes. Here we assessed the correspondence between the geographic distribution, population structure and genome-wide selection of 511 Aaf and 123 Aaa specimens and report adaptive signals in 186 genes that we call Aaa molecular signatures. Our results indicate that Aaa molecular signatures arose from standing variation associated with extensive ancestral polymorphisms in Aaf populations and have been co-opted for self-domestication through genomic and functional redundancy and local adaptation. Overall, we show that the behavioural shift of Ae. aegypti mosquitoes to live in association with humans relied on the fine regulation of chemosensory, neuronal and metabolic functions, as seen in the domestication processes of rabbits and silkworms. Our results also provide a foundation for the investigation of new genic targets for the control of Ae. aegypti populations.

Ligand-based cheminformatics and free energy-inspired molecular simulations for prioritizing and optimizing G-protein coupled receptor kinase-6 (GRK6) inhibitors in multiple myeloma treatment

Multiple myeloma (MM) is the second most frequently diagnosed hematological malignancy, presenting limited treatment options with no curative potential and significant drug resistance. Recent studies involving genetic knockdown established the crucial role of GRK6 in upholding the viability of MM cells, emphasizing the need to identify potential inhibitors. Computational exploration of GRK6 inhibitors has not been attempted previously. Herein, the present study reports a multilayered lead prioritization and optimization framework using chemometrics and molecular simulations. 2D QSAR studies revealed that hydrogen bonding and polar interactions enhanced GRK6 inhibitory activity, while increased electron accessibility posed a risk of off-target effects. The pharmacophore hypothesis (DDHRRR_1) featured two hydrogen bond donors, one hydrophobic region, and three aromatic rings, laying the foundation for the 3D QSAR models. Hydrophobic groups, such as pyridine and pyrazole, were shown to enhance inhibition, while smaller groups, like ethyl and hydroxyl, reduced activity. 12,557 DrugBank compounds were screened using the developed chemometric models and molecular docking in tandem, which led to the identification of 7 potential parent leads for subsequent QSAR-guided structural optimizations. 350 lead analogs were generated and the top 4 were further analyzed using molecular docking, ADMET, molecular dynamics, and metadynamics analysis based on Principal Component Analysis (PCA), Probability Density Function (PDF), and Free Energy Landscapes (FEL). Upon cumulative retrospection, we propose a novel analog of DB07168 (DB07168-A13) (docking score: -11.2 kcal/mol, MM-GBSA binding energy: -55.2 kcal/mol) as the most promising GRK6 inhibitor, warranting further in vitro validation, for addressing prospective therapeutic intervention in MM.

Progresses in Questing for the Truth of Opioid-Related Constipation in Cancer Patients

Opioids are extensively utilised to manage pain in cancer patients, but may cause constipation which significantly impacts their prognosis and quality of life. Opioid-induced constipation (OIC) lacks effective drugs and management strategies. Opioids act on the enteric nervous system, intestinal barrier, intestinal immunity and intestinal microbiota, implying that OIC is a multifactorial process. This paper aims to examine the effects of opioids on the intestine, specifically the enteric nervous system, intestinal barrier and interstitial cells of Cajal (ICCs), and elucidate the primary mechanisms underlying OIC development and deterioration. This review suggests that enteric neurons, intestinal immunity and intestinal flora could serve as potential therapeutic targets for OIC.

Functionally Selective Dopamine D1 Receptor Endocytosis and Signaling by Catechol and Noncatechol Agonists

The dopamine D1 receptor (D1R) has fundamental roles in voluntary movement and memory and is a validated drug target for neurodegenerative and neuropsychiatric disorders. However, previously developed D1R selective agonists possess a catechol moiety which displays poor pharmacokinetic properties. The first selective noncatechol D1R agonists were recently discovered and unexpectedly many of these ligands showed G protein biased signaling. Here, we investigate both catechol and noncatechol D1R agonists to validate potential biased signaling and examine if this impacts agonist-induced D1R endocytosis. We determined that most, but not all, noncatechol agonists display G protein biased signaling at the D1R and have reduced or absent β-arrestin2 recruitment. A notable exception was compound (Cmpd) 19, a noncatechol agonist with full efficacy at both D1R-G protein and D1R-β-arrestin2 pathways. In addition, the catechol ligand A-77636 was a highly potent, super agonist for D1R-β-arrestin2 activity. When examined for agonist-induced D1R endocytosis, balanced agonists SKF-81297 and Cmpd 19 induced robust D1R endocytosis while the G protein biased agonists did not. The β-arrestin2 super agonist, A-77636, showed statistically significant increases in D1R endocytosis. Moreover, β-arrestin2 recruitment efficacy of tested agonists strongly correlated with total D1R endocytosis. Taken together, these results indicate the degree of D1R signaling functional selectivity profoundly impacts D1R endocytosis regardless of pharmacophore. The range of functional selectivity of these D1R agonists will provide valuable tools to further investigate D1R signaling, trafficking and therapeutic potential.

Biased signaling by human follicle-stimulating hormone variants

Follicle-stimulating hormone (FSH) or follitropin plays a fundamental role in several mammalian species, including humans. This gonadotropin is produced by the anterior pituitary gland and has as its main targets the granulosa cells of the ovary and the Sertoli cells of the testis. Structurally, FSH is composed of two non-convalently linked subunits, the α- and β-subunit, as well as highly heterogenous oligosaccharide structures, which play a key role in determining a number of physiological and biological features of the hormone. Glycosylation in FSH and the other members belonging to the glycoprotein hormone family, is essential for many functions of the gonadotropin, including subunit assembly and stability, secretion, circulatory half-life and biological activity. Carbohydrate heterogeneity in FSH comes in two forms, microheterogeneity, which results from variations in the carbohydrate structural complexity in those oligosaccharides attached to the α- or β-subunit of the hormone and macroheterogeneity, which results from the absence of carbohydrate chain at FSHβ Asn-glycosylation sites. A number of in vitro and in vivo studies have conclusively demonstrated differential, unique and even opposing effects provoked by variations in the carbohydrate structures of FSH, including circulatory survival, binding to and activation of its cognate receptor in the gonads, intracellular signaling, and activation/inhibition of a number of FSH-regulated genes essential for follicle development. Herein, we review the effects of the FSH oligosaccharides on several functions of FSH, and how variations in these structures have been shown to lead to functional selectivity of the hormone.

Absolute Number of Thalamic Parafascicular and Striatal Cholinergic Neurons, and the Three-Dimensional Spatial Array of Striatal Cholinergic Neurons, in the Sprague-Dawley Rat

The absolute number of neurons and their spatial distribution yields important information about brain function and species comparisons. We studied thalamic parafascicular neurons and striatal cholinergic interneurons (CINs) because the parafascicular neurons are the main excitatory input to the striatal CINs. This circuit is of increasing interest due to research showing its involvement in specific types of learning and behavioral flexibility. In the Sprague-Dawley rat, the absolute number of thalamic parafascicular neurons and striatal CINs is unknown. They were estimated in this study using modern stereological counting methods. From each of six young adult rats, complete sets of serial 40 µm glycol methacrylate sections were used to quantify neuronal numbers in the right parafascicular nucleus (PFN). From each of five young adult rats, complete sets of serial 20 µm frozen sections were immunostained and used to quantify cholinergic neuronal numbers in the right striatum. The spatial distribution, in three dimensions, of striatal CINs was also determined from exhaustive measurement of the x, y, z coordinates of each large interneuron in 40 µm glycol methacrylate sections in sampled sets of five consecutive serial sections from each of two rats. Statistical analysis of spatial distribution was conducted by comparing observed three-dimensional data with computer models of 10,000 pseudorandom distributions, using measures of nearest neighbor distance and Ripley's K-function for inhomogeneous samples. We found that the right PFN consisted, on average, of 30,073 neurons (with a coefficient of variation of 0.11). The right striatum consisted, on average, of 10,778 CINs (0.14). The statistical analysis of spatial distribution showed no evidence of clustering of striatal CINs in three dimensions in the rat striatum, consistent with previous findings in the mouse striatum. The results provide important data for the transfer of information through the PFN and striatum, species comparisons, and computer modeling.

IgStrand: A universal residue numbering scheme for the immunoglobulin-fold (Ig-fold) to study Ig-proteomes and Ig-interactomes

The Immunoglobulin fold (Ig-fold) is found in proteins from all domains of life and represents the most populous fold in the human genome, with current estimates ranging from 2 to 3% of protein coding regions. That proportion is much higher in the surfaceome where Ig and Ig-like domains orchestrate cell-cell recognition, adhesion and signaling. The ability of Ig-domains to reliably fold and self-assemble through highly specific interfaces represents a remarkable property of these domains, making them key elements of molecular interaction systems: the immune system, the nervous system, the vascular system and the muscular system. We define a universal residue numbering scheme, common to all domains sharing the Ig-fold in order to study the wide spectrum of Ig-domain variants constituting the Ig-proteome and Ig-Ig interactomes at the heart of these systems. The "IgStrand numbering scheme" enables the identification of Ig structural proteomes and interactomes in and between any species, and comparative structural, functional, and evolutionary analyses. We review how Ig-domains are classified today as topological and structural variants and highlight the "Ig-fold irreducible structural signature" shared by all of them. The IgStrand numbering scheme lays the foundation for the systematic annotation of structural proteomes by detecting and accurately labeling Ig-, Ig-like and Ig-extended domains in proteins, which are poorly annotated in current databases and opens the door to accurate machine learning. Importantly, it sheds light on the robust Ig protein folding algorithm used by nature to form beta sandwich supersecondary structures. The numbering scheme powers an algorithm implemented in the interactive structural analysis software iCn3D to systematically recognize Ig-domains, annotate them and perform detailed analyses comparing any domain sharing the Ig-fold in sequence, topology and structure, regardless of their diverse topologies or origin. The scheme provides a robust fold detection and labeling mechanism that reveals unsuspected structural homologies among protein structures beyond currently identified Ig- and Ig-like domain variants. Indeed, multiple folds classified independently contain a common structural signature, in particular jelly-rolls. Examples of folds that harbor an "Ig-extended" architecture are given. Applications in protein engineering around the Ig-architecture are straightforward based on the universal numbering.

Molecular mechanism of the arrestin-biased agonism of neurotensin receptor 1 by an intracellular allosteric modulator

Biased allosteric modulators (BAMs) of G protein-coupled receptors (GPCRs) have been at the forefront of drug discovery owing to their potential to selectively stimulate therapeutically relevant signaling and avoid on-target side effects. Although structures of GPCRs in complex with G protein or GRK in a BAM-bound state have recently been resolved, revealing that BAM can induce biased signaling by directly modulating interactions between GPCRs and these two transducers, no BAM-bound GPCR-arrestin complex structure has yet been determined, limiting our understanding of the full pharmacological profile of BAMs. Herein, we developed a chemical protein synthesis strategy to generate neurotensin receptor 1 (NTSR1) with defined hexa-phosphorylation at its C-terminus and resolved high-resolution cryo-EM structures (2.65-2.88 Å) of NTSR1 in complex with both β-arrestin1 and the BAM SBI-553. These structures revealed a unique "loop engagement" configuration of β-arrestin1 coupling to NTSR1 in the presence of SBI-553, markedly different from the typical "core engagement" configuration observed in the absence of BAMs. This configuration is characterized by the engagement of the intracellular loop 3 of NTSR1 with a cavity in the central crest of β-arrestin1, representing a previously unobserved, arrestin-selective conformation of GPCR. Our findings fill the critical knowledge gap regarding the regulation of GPCR-arrestin interactions and biased signaling by BAMs, which would advance the development of safer and more efficacious GPCR-targeted therapeutics.

Traffic control: Mechanisms of ligand-specific internalization and intracellular distribution of CCR5

CC chemokine receptor (CCR) 5 promotes inflammatory responses by driving cell migration and scavenging chemokine. A CCR5 inhibitor Maraviroc has been approved for blocking HIV entry; however, inhibitors for the treatment of other diseases have had limited success, likely because of the complexity of CCR5 pharmacology and biology. CCR5 is activated by natural and engineered chemokines that elicit distinct signaling and trafficking responses, including receptor sequestration inside the cell. Intracellular sequestration may be therapeutically exploitable as a strategy for receptor inhibition, but the mechanisms by which different ligands promote receptor intracellular retention versus presence on the cell membrane are poorly understood. In this study, we systematically compared the time-dependent trafficking behavior of CCR5 following stimulation with its endogenous agonist, CCL5, and 2 CCL5 variants that promote CCR5 intracellular retention. Using a broad panel of pharmacologic assays, fluorescence microscopy, and live cell ascorbic acid peroxidase proximity labeling proteomics, we identified distinct ligand-dependent CCR5 trafficking patterns with temporal and spatial resolution. All 3 chemokines internalize CCR5 via β-arrestin-dependent, clathrin-mediated endocytosis but to different extents, with different kinetics and varying dependencies on G protein-coupled receptor kinase subtypes. The agonists differ in their ability to target the receptor to lysosomes for degradation, as well as to the Golgi compartment and the trans-Golgi network, and these trafficking patterns translate into distinct levels of ligand scavenging. The results provide insight into the cellular mechanisms behind CCR5 intracellular sequestration and suggest how trafficking can be exploited for the development of functional antagonists of CCR5. SIGNIFICANCE STATEMENT: CC chemokine receptor (CCR) 5 plays a crucial role in the immune system and is important in numerous physiological and pathological processes such as inflammation, cancer, and transmission of HIV. It responds to different ligands with distinct signaling and trafficking behaviors; notably, some ligands induce retention of the receptor inside the cell. This study reveals the cellular basis for receptor sequestration that can be exploited as a therapeutic strategy for inhibiting CCR5 function.