Receptors, Volume 5, Issue 1 (March 2026) – 9 articles

Sphingolipids, first discovered in 1874 by Johann Thudicum, are among the eight recognized classes of lipids and are present in essentially all plants, animals, and fungi, as well as some viruses and prokaryotes. In mammals, sphingolipids are enriched in the central nervous system (CNS), where they play vital roles in tissue development; membrane structure; cell adhesion and recognition; and, importantly, signaling. A subset of sphingolipids including ceramide, glucosylceramide, and sphingosine has been shown to have bioactive properties, but two sphingolipids in particular (ceramide-1-phosphate and sphingosine-1-phosphate) have been shown to exert their effects at least in part due to the activation of cell surface-expressed G protein-coupled receptors. In the CNS, sphingosine-1-phosphate signaling has specifically emerged as a productive therapeutic target for the treatment of neurodegenerative disease, with the first small molecule targeting sphingosine-1-phosphate receptors approved roughly 15 years ago for the treatment of multiple sclerosis. As more specific activators and inhibitors of these receptors have been developed and entered the clinical trial pipeline, now is an appropriate time to examine the current state of our knowledge of the role that these receptors play in the CNS and highlight the current landscape of available modulators targeting these pathways. Full article

Progesterone (P₄) regulates diverse reproductive processes across vertebrates through nuclear receptors; however, its mechanisms in squamate reptiles—particularly in viviparous species—remain poorly understood. In Squamata, P₄ primarily acts through progesterone receptor (PR) isoforms A and B, although relatively few reptilian PR sequences have been characterized to date. Squamate PR exhibits ~50% overall sequence divergence from mammalian homologs yet retains striking conservation in both the ligand and DNA-binding domain across vertebrates. Despite the broadly conserved physiological roles of P₄ (folliculogenesis, ovulation, courtship behavior, pregnancy maintenance, and parturition/oviposition), P₄ dynamics in viviparous squamates remain unresolved due to heterogeneous circulating hormone concentrations and limited PR phylogeny and structure studies. While mammalian models dominate P₄ research due to their biomedical relevance, squamates offer unique evolutionary insights: as the only reptile order exhibiting both oviparity and viviparity within the same clade, squamates represent an ideal model for investigating transitions in parity mode. Elucidating P₄ mechanisms in squamates will help bridge this critical evolutionary gap, with important implications for reproductive biology and conservation. Full article

Background: Three-finger toxins (3FTxs) are a major axis of functional diversification in advanced snake venoms, with canonical paralytic activity mediated through muscle-type nicotinic acetylcholine receptors (nAChRs) and a broader set of non-nicotinic targets. This review integrates evidence bearing on coevolution between 3FTxs and target receptors, spanning toxin origin, diversification, receptor evolution, and ecological context. Methods: The synthesis draws on comparative genomic and transcriptomic studies of 3FTx gene-family evolution, codon-model analyses of selection, structural characterisation of toxin–receptor interfaces, and functional assays (including receptor-mimicking peptide binding) that link sequence variation to binding and toxicity. Results: Across lineages, 3FTx diversification is repeatedly structured by strong constraint on the disulphide-rich scaffold with accelerated change concentrated in solvent-exposed loops, alongside birth–death dynamics and exon/segment-level innovation that expand binding specificity. On the receptor side, resistance-associated variation is most intensively characterised for the nAChR α₁ orthosteric site and includes convergent, mechanistically distinct solutions such as electrostatic repulsion and glycosylation-mediated steric interference. Within the predominantly elapid systems currently examined, integrative datasets indicate that prey-selective binding and geographically variable susceptibility can arise from modest substitutions at toxin–receptor interfaces, but they also reveal substantial taxonomic and target-specific biases. Conclusions: Current evidence supports adaptive diversification in both toxins and receptors, while broader evolutionary interpretations are limited by uneven sampling and the frequent lack of matched toxin and receptor variants analysed within a common evolutionary framework. Development of predictive models will require joint pipelines linking genomics, structure-informed evolutionary inference, scalable functional assays, and explicit ecological network context. Full article

Background: Transmissible gastroenteritis virus (TGEV), a coronavirus (CoV) infecting pigs, uses its spike (S) glycoprotein to bind porcine aminopeptidase N (pAPN) for cell entry. Although structural studies have identified receptor-binding motifs (RBMs) within the receptor-binding domain (RBD) of the S protein, the functional relevance of individual residues for TGEV receptor recognition, cell entry, and infection remain unclear. Methods: In this study, we performed structure-guided mutagenesis of the TGEV RBD to evaluate the contribution of specific residues to receptor binding and viral infectivity. Results: Using soluble RBD proteins, we found that most of the RBD residues within the pAPN-binding interface contribute to the binding interaction. Nonetheless, TGEV reverse genetics experiments revealed that just three RBD residues (Gly527, Tyr528, and Trp571) were indispensable for viral cell entry. Mutations at these positions, which are conserved among group 1 alpha-CoVs abolished infectivity, highlighting their central role in the virus–receptor interface. Conclusions: Our findings provide a detailed functional map of the TGEV RBD and offer insights into the evolution of receptor recognition across CoV. Full article

Multipotent mesenchymal stromal stem cells have captivated the scientific community in recent years due to their ability to differentiate into multiple adult cell types. Central to this potential are many members of the nuclear hormone receptor superfamily, comprising 48 ligand-modulated transcription factors involved in key biological processes such as metabolism, physiology, embryonic development, and reproduction. These transcription factors influence cellular fate by regulating gene expression networks critical for MSC specification, commitment, and differentiation. This review explores the role of nuclear receptors in MSC development, focusing on interactions with chromatin structure, co-regulatory complexes, and responsiveness to extracellular stimuli such as hormones, metabolic cues, and endocrine-disrupting chemicals. We conclude with a discussion of the dangers posed by exogenous and aberrant signaling through nuclear receptors. Full article

The Hedgehog (Hh) signaling pathway regulates key cellular processes, such as proliferation, differentiation, and morphogenesis. Although its canonical activation involves ligand binding to PTCH1, which activates Smoothened (SMO), noncanonical features of the pathway significantly contribute to cancer progression, particularly in prostate cancer (PCa). GLI3, a central transcription factor in the Hh pathway, can act as a repressor or activator depending on posttranslational modifications. In androgen-deprived PCa, GLI3 plays a critical role in driving castration-resistant phenotypes by interacting with the androgen receptor (AR), particularly the AR-V7 variant. This interaction enhances tumor survival and growth even under androgen deprivation therapy (ADT). Aberrant GLI3 activity is further driven by mutations in upstream regulators such as SPOP and MED12, which contribute to the progression of both prostate and other malignancies. Preclinical studies have shown promise in reducing tumor cell proliferation and migration, and in inducing apoptosis, by pharmacologically inhibiting the GLI3 pathway with SMO antagonists or GSK3β inhibitors. Recent evidence also highlights reciprocal interactions between Sonic Hedgehog (Shh) signaling and the AR that sustain tumor growth under ADT. GLI3 engagement with AR reinforces AR-dependent transcription, supporting tumor progression through noncanonical pathways. These findings suggest that targeting GLI3, particularly in combination with AR inhibition, could effectively overcome castration resistance and improve outcomes in patients with castration-resistant prostate cancer (CRPC). This review explores the role of GLI3 in both canonical and noncanonical Hh signaling, its potential as a therapeutic target, and future directions for overcoming resistance in Hh-driven cancers. Full article

Nuclear receptors (NRs) are ligand-activated transcription factors that mediate diverse cellular processes, including signalling, survival, proliferation, immune response and metabolism, through both genomic and non-genomic mechanisms in response to hormones and metabolic ligands. Given their central role in inter-organ, tissue, and cellular communication, NRs are critical for maintaining homeostasis and have become a major focus in biomedical research and drug discovery due to their association with numerous diseases. Among NRs, the NR4A subfamily (NR4A1/Nur77, NR4A2/Nurr1, and NR4A3/Nor1) responds to various stimuli—such as insulin, growth factors, inflammatory cytokines, and β-adrenergic signals—though their endogenous ligands remain unidentified. Their expression is tissue-dependent, particularly in energy-demanding tissues, where they modulate leukocyte function and promote an anti-inflammatory profile. Like other NRs, NR4As regulate acute and chronic inflammation by suppressing pro-inflammatory transcription factors (e.g., NF-κB) or enhancing their inhibitors, thereby polarising macrophages toward an anti-inflammatory phenotype. This review summarises current knowledge on the role of NR4A receptors in immune responses. Given their well-documented involvement in autoimmune diseases, inflammatory conditions, and cancer, elucidating their contributions to neuro–immune–endocrine crosstalk may uncover their therapeutic potential for immunopathological disorders. Full article

Astrocytes are increasingly recognized as active participants of synaptic communication, yet their role in the basal ganglia circuitry remains poorly defined. Emerging evidence indicates that astrocytes in this region express a diverse array of neurotransmitter receptors thought to regulate intracellular calcium signaling, gliotransmitter release, synaptic plasticity, and neuroimmune responses. However, the literature is limited by methodological variability and a pronounced focus on the striatum, with comparatively little data on other basal ganglia nuclei. This review aims to organize the current literature on astrocytic receptor systems within the basal ganglia, including dopaminergic (D1–D5), glutamatergic (AMPA, NMDA, mGluRs), GABAergic (GABA-A, GABA-B), purinergic (P1, P2), and adrenergic (α, β) receptors. By organizing receptor-specific findings across basal ganglia structures, this review provides a foundation for future investigations into astrocytic function in this complex neural network. Full article

Background: The insulin-like growth factor 2 receptor (IGF-2R), also known as the cation-independent mannose 6-phosphate receptor (CI-M6PR), is emerging as a critical receptor for brain function and disease. IGF-2R, in fact, plays a key role in long-term memory, and its activation by several ligands shows beneficial effects in multiple neurodevelopmental and neurodegenerative disease models. Thus, its targeting is very promising for neuropsychiatric therapeutic interventions. IGF-2R’s main known functions are transport of lysosomal enzymes and regulation of developmental tissue growth, but in the brain, it also controls learning-dependent protein synthesis underlying long-term memory. However, little is known about this receptor in brain cells, including its cell-type-specific and subcellular expression. Methods: We conducted a comprehensive investigation to comparatively assess IGF-2R protein levels in different brain cell types across various brain regions in adult male C57BL/6J mice using dual and multiplex immunofluorescent staining with cell-type-specific markers. The IGF-2R protein distribution was also compared with Igf2r mRNA expression in publicly available single-cell RNA sequencing databases. Results: A ranking of IGF-2R levels in the soma of various cell types in the hippocampus and cortical regions revealed that the highest enrichment is, by far, in excitatory and inhibitory neurons, followed by vascular mural cells and subpopulations of oligodendrocyte lineage cells, with low to undetectable levels in astrocytes, microglia, vascular endothelial cells, and perivascular fibroblasts. High levels of IGF-2R were also found in ependymal cells, choroid plexus epithelial cells, and a subpopulation of meningeal fibroblast-like cells. IGF-2R was found in dendritic and putative axonal compartments throughout the brain, with particularly high levels in the stratum lucidum. The receptor’s protein distribution aligned with that of the mRNA in mouse brain databases. Conclusions: These results suggest that IGF-2R-mediated functions in the brain vary across different cell types and subcellular compartments, with the most active roles in specific subpopulations of neurons, mural cells, ependymal cells, meningeal cells, and cells of the oligodendrocyte lineage. This study advances our understanding of IGF-2R’s distribution in the brain, which is essential for formulating new hypotheses about its functions and therapeutic targeting. Full article