Physiology, phylogeny, and functions of the TRP superfamily of cation channels

Mutation of TRPML1 Channel and Pathogenesis of Neurodegeneration in Haimeria

Neurodegenerative diseases, a group of debilitating disorders, have garnered increasing attention due to their escalating prevalence, particularly among aging populations. Alzheimer's disease (AD) reigns as a prominent exemplar within this category, distinguished by its relentless progression of cognitive impairment and the accumulation of aberrant protein aggregates within the intricate landscape of the brain. While the intricate pathogenesis of neurodegenerative diseases has been the subject of extensive investigation, recent scientific inquiry has unveiled a novel player in this complex scenario-transient receptor potential mucolipin 1 (TRPML1) channels. This comprehensive review embarks on an exploration of the intricate interplay between TRPML1 channels and neurodegenerative diseases, with an explicit spotlight on Alzheimer's disease. It immerses itself in the intricate molecular mechanisms governing TRPML1 channel functionality and elucidates their profound implications for the well-being of neurons. Furthermore, the review ventures into the realm of therapeutic potential, pondering the possibilities and challenges associated with targeting TRPML1 channels as a promising avenue for the amelioration of neurodegenerative disorders. As we traverse this multifaceted terrain of neurodegeneration and the enigmatic role of TRPML1 channels, we embark on a journey that not only broadens our understanding of the intricate machinery governing neuronal health but also holds promise for the development of innovative therapeutic interventions in the relentless battle against neurodegenerative diseases.

Therapeutic Potential of Palmitoylethanolamide in Gastrointestinal Disorders

Palmitoylethanolamide (PEA) is an endocannabinoid-like bioactive lipid mediator belonging to the family of N-acylethanolamines, most abundantly found in peanuts and egg yolk. When the gastrointestinal (GI) effects of PEA are discussed, it must be pointed out that it affects intestinal motility but also modulates gut microbiota. This is due to anti-inflammatory, antioxidant, analgesic, antimicrobial, and immunomodulatory features. Additionally, PEA has shown beneficial effects in several GI diseases, particularly irritable bowel syndrome and inflammatory bowel diseases, as various studies have shown, and it is important to emphasize its relative lack of toxicity, even at high dosages. Unfortunately, there is not enough endogenous PEA to treat disturbed gut homeostasis, even though it is produced in the GI tract in response to inflammatory stimuli, so exogenous intake is mandatory to achieve homeostasis. Intake of PEA could be through animal and/or vegetable food, but bearing in mind that a high dosage is needed to achieve a therapeutic effect, it must be compensated through dietary supplements. There are still open questions pending to be answered, so further studies investigating PEA's effects and mechanisms of action, especially in humans, are crucial to implementing PEA in everyday clinical practice.

Cardiovascular perspectives of the TRP channel polycystin 2

Calcium release from the endoplasmic reticulum (ER) is predominantly driven by two key ion channel receptors, inositol 1, 4, 5-triphosphate receptor (InsP3R) in non-excitable cells and ryanodine receptor (RyR) in excitable and muscle-based cells. These calcium transients can be modified by other less-studied ion channels, including polycystin 2 (PC2), a member of the transient receptor potential (TRP) family. PC2 is found in various cell types and is evolutionarily conserved with paralogues ranging from single-cell organisms to yeasts and mammals. Interest in the mammalian form of PC2 stems from its disease relevance, as mutations in the PKD2 gene, which encodes PC2, result in autosomal dominant polycystic kidney disease (ADPKD). This disease is characterized by renal and liver cysts, and cardiovascular extrarenal manifestations. However, in contrast to the well-defined roles of many TRP channels, the role of PC2 remains unknown, as it has different subcellular locations, and the functional understanding of the channel in each location is still unclear. Recent structural and functional studies have shed light on this channel. Moreover, studies on cardiovascular tissues have demonstrated a diverse role of PC2 in these tissues compared to that in the kidney. We highlight recent advances in understanding the role of this channel in the cardiovascular system and discuss the functional relevance of PC2 in non-renal cells.

The role of TRPV ion channels in adipocyte differentiation: What is the evidence?

Obesity is a complex disorder, and the incidence of obesity continues to rise at an alarming rate worldwide. In particular, the growing incidence of overweight and obesity in children is a major health concern. However, the underlying mechanisms of obesity remain unclear and the efficacy of several approaches for weight loss is limited. As an important calcium-permeable temperature-sensitive cation channel, transient receptor potential vanilloid (TRPV) ion channels directly participate in thermo-, mechano-, and chemosensory responses. Modulation of TRPV ion channel activity can alter the physiological function of the ion channel, leading to neurodegenerative diseases, chronic pain, cancer, and skin disorders. In recent years, increasing studies have demonstrated that TRPV ion channels are abundantly expressed in metabolic organs, including the liver, adipose tissue, skeletal muscle, pancreas, and central nervous system, which has been implicated in various metabolic diseases, including obesity and diabetes mellitus. In addition, as an important process for the pathophysiology of adipocyte metabolism, adipocyte differentiation plays a critical role in obesity. In this review, we focus on the role of TRPV ion channels in adipocyte differentiation to broaden the ideas for prevention and control strategies for obesity.

The versatility of the putative transient receptor potential ion channels in regulating the calcium signaling in Aspergillus nidulans

IMPORTANCE

Transient receptor potential (TRP) ion channels are evolutionarily conserved integral membrane proteins with non-selective ion permeability, and they are widely distributed in mammals and single-cell yeast and serve as crucial mediators of sensory signals. However, the relevant information concerning TRP channels in Aspergillus nidulans remains inadequately understood. In this study, by gene deletion, green fluorescent protein tagging, and cytosolic Ca2+ transient monitoring techniques, the biological functions of three potential TRP channels (TrpA, TrpB, and TrpC) have been explored for which they play distinct and multiple roles in hyphal growth, conidiation, responsiveness to external stress, and regulation of intracellular Ca2+ homeostasis. The findings of this study on the functions of potential TRP channels in A. nidulans may serve as a valuable reference for understanding the roles of TRP homologs in industrial or medical strains of Aspergillus, as well as in other filamentous fungi.

Regulatory mechanisms controlling store-operated calcium entry

Calcium influx through plasma membrane ion channels is crucial for many events in cellular physiology. Cell surface stimuli lead to the production of inositol 1,4,5-trisphosphate (IP3), which binds to IP3 receptors (IP3R) in the endoplasmic reticulum (ER) to release calcium pools from the ER lumen. This leads to the depletion of ER calcium pools, which has been termed store depletion. Store depletion leads to the dissociation of calcium ions from the EF-hand motif of the ER calcium sensor Stromal Interaction Molecule 1 (STIM1). This leads to a conformational change in STIM1, which helps it to interact with the plasma membrane (PM) at ER:PM junctions. At these ER:PM junctions, STIM1 binds to and activates a calcium channel known as Orai1 to form calcium release-activated calcium (CRAC) channels. Activation of Orai1 leads to calcium influx, known as store-operated calcium entry (SOCE). In addition to Orai1 and STIM1, the homologs of Orai1 and STIM1, such as Orai2/3 and STIM2, also play a crucial role in calcium homeostasis. The influx of calcium through the Orai channel activates a calcium current that has been termed the CRAC current. CRAC channels form multimers and cluster together in large macromolecular assemblies termed "puncta". How CRAC channels form puncta has been contentious since their discovery. In this review, we will outline the history of SOCE, the molecular players involved in this process, as well as the models that have been proposed to explain this critical mechanism in cellular physiology.

Mechanical properties of the brain: Focus on the essential role of Piezo1-mediated mechanotransduction in the CNS

BACKGROUND

The brain is a highly mechanosensitive organ, and changes in the mechanical properties of brain tissue influence many physiological and pathological processes. Piezo type mechanosensitive ion channel component 1 (Piezo1), a protein found in metazoans, is highly expressed in the brain and involved in sensing changes of the mechanical microenvironment. Numerous studies have shown that Piezo1-mediated mechanotransduction is closely related to glial cell activation and neuronal function. However, the precise role of Piezo1 in the brain requires further elucidation.

OBJECTIVE

This review first discusses the roles of Piezo1-mediated mechanotransduction in regulating the functions of a variety of brain cells, and then briefly assesses the impact of Piezo1-mediated mechanotransduction on the progression of brain dysfunctional disorders.

CONCLUSIONS

Mechanical signaling contributes significantly to brain function. Piezo1-mediated mechanotransduction regulates processes such as neuronal differentiation, cell migration, axon guidance, neural regeneration, and oligodendrocyte axon myelination. Additionally, Piezo1-mediated mechanotransduction plays significant roles in normal aging and brain injury, as well as the development of various brain diseases, including demyelinating diseases, Alzheimer's disease, and brain tumors. Investigating the pathophysiological mechanisms through which Piezo1-mediated mechanotransduction affects brain function will give us a novel entry point for the diagnosis and treatment of numerous brain diseases.

The role of TRPV2 as a regulator on the osteoclast differentiation during orthodontic tooth movement in rats

When orthodontic forces are applied to teeth, bone remodeling, which consists of bone resorption and bone formation, occurs around the teeth. Transient receptor potential vanilloid 2 (TRPV2) is a cation channel expressed in various cell types that responds to various stimuli, including mechanical stress, and involved in calcium oscillations during the early stages of osteoclast differentiation. However, in vivo expression of TRPV2 in osteoclasts has not yet been reported, and temporo-spatial expression of TRPV2 during osteoclast differentiation is unclear. In this study, we examined the TRPV2 expression during experimental tooth movement and assessed the effect of TRPV2 on osteoclast differentiation. TRPV2 was detected on day 1 after experimental tooth movement on the compression side, and the number of TRPV2-expressing cells significantly increased on day 7. These TRPV2-expressing cells had a single, or multiple nuclei and were positive for TRAP activity. Consistent with these in vivo findings, in vitro experiments using RAW264.7 osteoclast progenitor cells showed that TRPV2 mRNA was increased at the early stage of osteoclast differentiation and maintained until the late stage. Furthermore, a TRPV2 channel selective antagonist significantly inhibited osteoclast differentiation. These findings suggest that TRPV2 may have a regulatory role in osteoclast differentiation during orthodontic tooth movement.

Ion channels in cancer-induced bone pain: from molecular mechanisms to clinical applications

Cancer-induced bone pain (CIBP) caused by bone metastasis is one of the most prevalent diseases, and current treatments rely primarily on opioids, which have significant side effects. However, recent developments in pharmaceutical science have identified several new mechanisms for CIBP, including the targeted modification of certain ion channels and receptors. Ion channels are transmembrane proteins, which are situated on biological cell membranes, which facilitate passive transport of inorganic ions across membranes. They are involved in various physiological processes, including transmission of pain signals in the nervous system. In recent years, there has been an increasing interest in the role of ion channels in chronic pain, including CIBP. Therefore, in this review, we summarize the current literature on ion channels, related receptors, and drugs and explore the mechanism of CIBP. Targeting ion channels and regulating their activity might be key to treating pain associated with bone cancer and offer new treatment avenues.

Targeting Nociceptive Neurons and Transient Receptor Potential Channels for the Treatment of Migraine

Migraine is a neurovascular disorder that affects approximately 12% of the global population. While its exact causes are still being studied, researchers believe that nociceptive neurons in the trigeminal ganglia play a key role in the pain signals of migraine. These nociceptive neurons innervate the intracranial meninges and convey pain signals from the meninges to the thalamus. Targeting nociceptive neurons is considered promising due to their accessibility and distinct molecular profile, which includes the expression of several transient receptor potential (TRP) channels. These channels have been linked to various pain conditions, including migraine. This review discusses the role and mechanisms of nociceptive neurons in migraine, the challenges of current anti-migraine drugs, and the evidence for well-studied and emerging TRP channels, particularly TRPC4, as novel targets for migraine prevention and treatment.

TRPV3: Structure, Diseases and Modulators

Transient receptor potential vanillin 3 (TRPV3) is a member of the transient receptor potential (TRP) superfamily. As a Ca²⁺-permeable nonselective cation channel, TRPV3 can recognize thermal stimulation (31-39 °C), and it plays an important regulatory role in temperature perception, pain transduction, skin physiology, inflammation, cancer and other diseases. TRPV3 is not only activated by the changes in the temperature, but it also can be activated by a variety of chemical and physical stimuli. Selective TRPV3 agonists and antagonists with regulatory effects and the physiological functions for clinical application are highly demanded. In recent years, significant progress has been made in the study of TRPV3, but there is still a lack of modulators with a strong affinity and excellent selectivity. This paper reviews the functional characteristics of TRPV3 in terms of the structure, diseases and the research on TRPV3 modulators.

New Frontiers on ER Stress Modulation: Are TRP Channels the Leading Actors?

The endoplasmic reticulum (ER) is a dynamic structure, playing multiple roles including calcium storage, protein synthesis and lipid metabolism. During cellular stress, variations in ER homeostasis and its functioning occur. This condition is referred as ER stress and generates a cascade of signaling events termed unfolded protein response (UPR), activated as adaptative response to mitigate the ER stress condition. In this regard, calcium levels play a pivotal role in ER homeostasis and therefore in cell fate regulation since calcium signaling is implicated in a plethora of physiological processes, but also in disease conditions such as neurodegeneration, cancer and metabolic disorders. A large body of emerging evidence highlighted the functional role of TRP channels and their ability to promote cell survival or death depending on endoplasmic reticulum stress resolution, making them an attractive target. Thus, in this review we focused on the TRP channels' correlation to UPR-mediated ER stress in disease pathogenesis, providing an overview of their implication in the activation of this cellular response.

Effects of phytase and coccidial vaccine on growth performance, nutrient digestibility, bone mineralization, and intestinal gene expression of broilers

A study was conducted to evaluate effects of phytase and coccidial vaccine on growth performance, bone mineralization, nutrient digestibility, and intestinal gene expression of broiler chickens. The experiment was conducted in a 2 × 4 completely randomized factorial arrangement with 6 replicates per treatment and 10 birds each. Applications of coccidiosis vaccine and different dietary treatments were the 2 main factors in the current study. The dietary treatments included 1) a positive control (PC; 0.90% Ca and 0.45% available P: avP); 2) a negative control (NC; 0.75% Ca and 0.30% AvP); 3) NC + 500 FTU/kg of phytase (NC + 500PHY); and 4) NC + 1500 FTU/kg of phytase (NC + 1500PHY). Data were analyzed using SAS by 2-way ANOVA via GLM procedure. The statistical significance was set at P ≤ 0.05, and means were further separated using Tukey's Test. The results indicated that vaccination had no effect on growth performance except for feed intake from 0 to 14 d but negatively (P < 0.05) regulated bone ash and Ca digestibility. Birds fed with the Ca and P-reduced diet (NC) showed a lower BWG and bone ash compared to birds fed with the normal diet (PC), but supplementing phytase mitigated the negative effects on those birds. Broilers fed the NC diet had higher (P < 0.05) total Ca and P digestibility, and phytate degradation; supplementing phytase further increased P digestibility and phytate degradation of the broilers. A significant interaction (P < 0.05) between phytase and vaccination was observed, suggesting the vaccinated birds fed the PC diet and the unvaccinated birds fed the NC + 1500PHY increased calcium-sensing receptor gene expression compared with the unvaccinated birds fed the PC diet. In conclusion, in spite of coccidiosis vaccine, supplementing phytase at 1,500 FTU/kg alleviated the negative effects on growth performance, bone mineralization, and apparent ileal digestibility of P and phytate.

Mechanosensitive Ion Channels, Axonal Growth, and Regeneration

Cells sense and respond to mechanical stimuli by converting those stimuli into biological signals, a process known as mechanotransduction. Mechanotransduction is essential in diverse cellular functions, including tissue development, touch sensitivity, pain, and neuronal pathfinding. In the search for key players of mechanotransduction, several families of ion channels were identified as being mechanosensitive and were demonstrated to be activated directly by mechanical forces in both the membrane bilayer and the cytoskeleton. More recently, Piezo ion channels were discovered as a bona fide mechanosensitive ion channel, and its characterization led to a cascade of research that revealed the diverse functions of Piezo proteins and, in particular, their involvement in neuronal repair.

Hyperthermia and Serotonin: The Quest for a “Better Cyproheptadine”

Fine temperature control is essential in homeothermic animals. Both hyper- and hypothermia can have deleterious effects. Multiple, efficient and partly redundant mechanisms of adjusting the body temperature to the value set by the internal thermostat exist. The neural circuitry of temperature control and the neurotransmitters involved are reviewed. The GABAergic inhibitory output from the brain thermostat in the preoptic area POA to subaltern neural circuitry of temperature control (Nucleus Raphe Dorsalis and Nucleus Raphe Pallidus) is a function of the balance between the (opposite) effects mediated by the transient receptor potential receptor TRPM2 and EP3 prostaglandin receptors. Activation of TRPM2-expressing neurons in POA favors hypothermia, while inhibition has the opposite effect. Conversely, EP3 receptors induce elevation in body temperature. Activation of EP3-expressing neurons in POA results in hyperthermia, while inhibition has the opposite effect. Agonists at TRPM2 and/or antagonists at EP3 could be beneficial in hyperthermia control. Activity of the neural circuitry of temperature control is modulated by a variety of 5-HT receptors. Based on the theoretical model presented the “ideal” antidote against serotonin syndrome hyperthermia appears to be an antagonist at the 5-HT receptor subtypes 2, 4 and 6 and an agonist at the receptor subtypes 1, 3 and 7. Very broadly speaking, such a profile translates in a sympatholytic effect. While a compound with such an ideal profile is presently not available, better matches than the conventional antidote cyproheptadine (used off-label in severe serotonin syndrome cases) appear to be possible and need to be identified.

Ion channels in stem cells and their roles in stem cell biology and vascular diseases

Stem cell therapy may be a promising option for the treatment of vascular diseases. In recent years, significant progress has been made in stem cell research, especially in the mechanism of stem cell activation, homing and differentiation in vascular repair and reconstruction. Current research on stem cells focuses on protein expression and transcriptional networks. Ion channels are considered to be the basis for the generation of bioelectrical signals, which control the proliferation, differentiation and migration of various cell types. Although heterogeneity of multiple ion channels has been found in different types of stem cells, it is unclear whether the heterogeneous expression of ion channels is related to different cell subpopulations and/or different stages of the cell cycle. There is still a long way to go in clinical treatment by using the regulation of stem cell ion channels. In this review, we reviewed the main ion channels found on stem cells, their expression and function in stem cell proliferation, differentiation and migration, and the research status of stem cells' involvement in vascular diseases.

Roles of Intramolecular Interactions in the Regulation of TRP Channels

The transient receptor potential (TRP) channels, classified into six (-A, -V, -P, -C, -M, -ML, -N and -Y) subfamilies, are important membrane sensors and mediators of diverse stimuli including pH, light, mechano-force, temperature, pain, taste, and smell. The mammalian TRP superfamily of 28 members share similar membrane topology with six membrane-spanning helices (S1-S6) and cytosolic N-/C-terminus. Abnormal function or expression of TRP channels is associated with cancer, skeletal dysplasia, immunodeficiency, and cardiac, renal, and neuronal diseases. The majority of TRP members share common functional regulators such as phospholipid PIP2, 2-aminoethoxydiphenyl borate (2-APB), and cannabinoid, while other ligands are more specific, such as allyl isothiocyanate (TRPA1), vanilloids (TRPV1), menthol (TRPM8), ADP-ribose (TRPM2), and ML-SA1 (TRPML1). The mechanisms underlying the gating and regulation of TRP channels remain largely unclear. Recent advances in cryogenic electron microscopy provided structural insights into 19 different TRP channels which all revealed close proximity of the C-terminus with the N-terminus and intracellular S4-S5 linker. Further studies found that some highly conserved residues in these regions of TRPV, -P, -C and -M members mediate functionally critical intramolecular interactions (i.e., within one subunit) between these regions. This review provides an overview on (1) intramolecular interactions in TRP channels and their effect on channel function; (2) functional roles of interplays between PIP2 (and other ligands) and TRP intramolecular interactions; and (3) relevance of the ligand-induced modulation of intramolecular interaction to diseases.

Identification and Characterization Analysis of Transient Receptor Potential Mucolipin Protein of Laodelphax striatellus Fallén

Transient receptor potential mucolipin (TRPML) protein in flies plays a pivotal role in Ca²⁺ ions release, resulting in membrane trafficking, autophagy and ion homeostasis. However, to date, the characterization of TRPML in agricultural pests remains unknown. Here, we firstly reported the TRPML of a destructive pest of gramineous crops, Laodelphax striatellus. The L. striatellus TRPML (Ls-TRPML) has a 1818 bp open reading frame, encoding 605 amino acid. TRPML in agricultural pests is evolutionarily conserved, and the expression of Ls-TRPML is predominately higher in the ovary than in other organs of L. striatellus at the transcript and protein level. The Bac-Bac system showed that Ls-TRPML localized in the plasma membrane, nuclear membrane and nucleus and co-localized with lysosome in Spodoptera frugiperda cells. The immunofluorescence microscopy analysis showed that Ls-TRPML localized in the cytoplasm and around the nuclei of the intestine cells or ovary follicular cells of L. striatellus. The results from the lipid-binding assay revealed that Ls-TRPML strongly bound to phosphatidylinositol-3,5-bisphosphate, as compared with other phosphoinositides. Overall, our results helped is identify and characterize the TRPML protein of L. striatellus, shedding light on the function of TRPML in multiple cellular processes in agricultural pests.

A Transient Receptor Potential-like Calcium Ion Channel in the Filamentous Fungus Aspergillus nidulans

Transient Receptor Potential (TRP) proteins constitute a superfamily that encodes transmembrane ion channels with highly diverse permeation and gating properties. Filamentous fungi possess putative TRP channel-encoded genes, but their functions remain elusive. Here, we report that a putative TRP-like calcium channel, trpR, in the filamentous fungus Aspergillus nidulans, performs important roles in conidiation and in adapting to cell wall disruption reagents in a high temperature-induced defect-dependent manner, especially under a calcium-limited culture condition. The genetic and functional relationship between TrpR and the previously identified high-affinity calcium channels CchA/MidA indicates that TrpR has an opposite response to CchA/MidA when reacting to cell wall disruption reagents and in regulating calcium transients. However, a considerable addition of calcium can rescue all the defects that occur in TrpR and CchA/MidA, meaning that calcium is able to bypass the necessary requirement. Nevertheless, the colocalization at the membrane of the Golgi for TrpR and the P-type Golgi Ca²⁺ ATPase PmrA suggests two channels that may work as ion transporters, transferring Ca²⁺ from the cytosol into the Golgi apparatus and maintaining cellular calcium homeostasis. Therefore, combined with data for the trpR deletion mutant revealing abnormal cell wall structures, TrpR works as a Golgi membrane calcium ion channel that involves cell wall integration.

A Systematical Survey on the TRP Channels Provides New Insight into Its Functional Diversity in Zhikong Scallop (Chlamys farreri)

Transient receptor potential (TRP) channel plays a significant role in mediating various sensory physiological functions. It is widely present in the vertebrate and invertebrate genomes and can be activated by multiple compounds, messenger molecules, temperature, and mechanical stimulation. Mollusks are the second largest phylum of the animal kingdom and are sensitive to environmental factors. However, the molecular underpinnings through which mollusks sense and respond to environmental stimulus are unknown. In this study, we systematically identified and characterized 17 TRP channels (C.FA TRPs, seven subfamilies) in the genome of the Zhikong scallop (Chlamys farreri). All C.FA TRPs had six transmembrane structures (TM1–TM6). The sequences and structural features of C.FA TRPs are highly conserved with TRP channels of other species. Spatiotemporal expression profiling suggested that some C.FA TRPs participated in the early embryonic development of scallops and the sensory process of adult tissues. Notably, the expression of C.FA TRPM3 continuously increased during developmental stages and was highest among all C.FA TRPs. C.FA TRPC-α was specifically expressed in eyes, which may be involved in light transmission of scallop eyes. Under high temperature stress, C.FA TRPA1 and C.FA TRPA1-homolog upregulated significantly, which indicated that the TRPA subfamily is the thermoTRPs channel of scallops. Our results provided the first systematic study of TRP channels in scallops, and the findings will provide a valuable resource for a better understanding of TRP evolution and function in mollusks.

Complement C3 Aggravates Post-epileptic Neuronal Injury Via Activation of TRPV1

Epilepsy is a brain condition characterized by the recurrence of unprovoked seizures. Recent studies have shown that complement component 3 (C3) aggravate the neuronal injury in epilepsy. And our previous studies revealed that TRPV1 (transient receptor potential vanilloid type 1) is involved in epilepsy. Whether complement C3 regulation of neuronal injury is related to the activation of TRPV1 during epilepsy is not fully understood. We found that in a mouse model of status epilepticus (SE), complement C3 derived from astrocytes was increased and aggravated neuronal injury, and that TRPV1-knockout rescued neurons from the injury induced by complement C3. Circular RNAs are abundant in the brain, and the reduction of circRad52 caused by complement C3 promoted the expression of TRPV1 and exacerbated neuronal injury. Mechanistically, disorders of neuron-glia interaction mediated by the C3-TRPV1 signaling pathway may be important for the induction of neuronal injury. This study provides support for the hypothesis that the C3-TRPV1 pathway is involved in the prevention and treatment of neuronal injury and cognitive disorders.

Conserved Modules Required for Drosophila TRP Function in Vivo

Transient receptor potential (TRP) channels are broadly required in animals for sensory physiology. To provide insights into regulatory mechanisms, the structures of many TRPs have been solved. This has led to new models, some of which have been tested in vitro Here, using the classical TRP required for Drosophila visual transduction, we uncovered structural requirements for channel function in photoreceptor cells. Using a combination of molecular genetics, field recordings, protein expression analysis, and molecular modeling, we interrogated roles for the S4-S5 linker and the TRP domain, and revealed mutations in the S4-S5 linker that impair channel opening or closing. We also uncovered differential requirements for the two highly conserved motifs in the TRP domain for activation and protein stability. By performing genetic complementation, we found an intrasubunit interaction between the S4-S5 linker and the S5 segment that contributes to activation. This analysis highlights key structural requirements for TRP channel opening, closing, folding, and for intrasubunit interactions in a native context-Drosophila photoreceptor cells.SIGNIFICANCE STATEMENT The importance of TRP channels for sensory biology and human health has motivated tremendous effort in trying to understand the roles of the structural motifs essential for their activation, inactivation, and protein folding. In the current work, we have exploited the unique advantages of the Drosophila visual system to reveal mechanistic insights into TRP channel function in a native system-photoreceptor cells. Using a combination of electrophysiology (field recordings), cell biology, and molecular modeling, we have revealed roles of key motifs for activation, inactivation and protein folding of TRP in vivo.

Intestinal Calcium Absorption

In this article, we focus on mammalian calcium absorption across the intestinal epithelium in normal physiology. Intestinal calcium transport is essential for supplying calcium for metabolism and bone mineralization. Dietary calcium is transported across the mucosal epithelia via saturable transcellular and nonsaturable paracellular pathways, both of which are under the regulation of 1,25-dihydroxyvitamin D₃ and several other endocrine and paracrine factors, such as parathyroid hormone, prolactin, 17β-estradiol, calcitonin, and fibroblast growth factor-23. Calcium absorption occurs in several segments of the small and large intestine with varying rates and capacities. Segmental heterogeneity also includes differential expression of calcium transporters/carriers (e.g., transient receptor potential cation channel and calbindin-D_9k ) and the presence of favorable factors (e.g., pH, luminal contents, and gut motility). Other proteins and transporters (e.g., plasma membrane vitamin D receptor and voltage-dependent calcium channels), as well as vesicular calcium transport that probably contributes to intestinal calcium absorption, are also discussed. © 2021 American Physiological Society. Compr Physiol 11:1-27, 2021.

Functional Expression of TRPV1 Ion Channel in the Canine Peripheral Blood Mononuclear Cells

TRPV1, known as a capsaicin receptor, is the best-described transient receptor potential (TRP) ion channel. Recently, it was shown to be expressed by non-excitable cells such as lymphocytes. However, the data regarding the functional expression of the TRPV1 channel in the immune cells are often contradictory. In the present study, we performed a phylogenetical analysis of the canine TRP ion channels, we assessed the expression of TRPV1 in the canine peripheral blood mononuclear cells (PBMC) by qPCR and Western blot, and we determined the functionality of TRPV1 by whole-cell patch-clamp recordings and calcium assay. We found high expression of TRPV2, -M2, and -M7 in the canine PBMCs, while expression of TRPV1, -V4 and, -M5 was relatively low. We confirmed that TRPV1 is expressed on the protein level in the PBMC and it localizes in the plasma membrane. The whole-cell patch-clamp recording revealed that capsaicin application caused a significant increase in the current density. Similarly, the results from the calcium assay show a dose-dependent increase in intracellular calcium level in the presence of capsaicin that was partially abolished by capsazepine. Our study confirms the expression of TRPV1 ion channel on both mRNA and protein levels in the canine PBMC and indicates that the ion channel is functional.

Contact repellency by l-menthol is mediated by TRPM channels in the red flour beetle Tribolium castaneum

BACKGROUND

Among insects, beetles are one of the most destructive pests of agricultural and stored products. Researchers have been investigating alternatives to pesticides for more sustainable pest management. Here, we focused on insect transient receptor potential (TRP) channel-targeted repellency. Among transient receptor potential melastatin (TRPM) channels, mammalian TRPM8 is activated by menthol and its derivatives, but few previous studies have reported on whether the insect TRPM channel is activated by chemical compounds. Here, we investigated whether the TRPM channel (TcTRPM) of the red flour beetle Tribolium castaneum (Herbst), a major stored-products pest, mediated the repellent behavior of l-menthol and its derivatives.

RESULTS

We initially investigated the repellent activity of l-menthol and menthoxypropanediol (MPD) against T. castaneum. The laboratory bioassay revealed that the repellent activities of l-menthol and MPD were dose dependent. RNA interference was used for transcriptional knockdown of TcTRPM and revealed that a reduced transcript level resulted in a significant decrease in l-menthol and MPD repellent activities. However, no significant decrease was observed for N,N-diethyl-3-methylbenzamide (DEET) repellency. The most abundant TcTRPM transcripts were observed in the antennae. However, antennae-plucked beetles maintained their repellent behavior with l-menthol.

CONCLUSION

The repellent activities of l-menthol and MPD for T. castaneum are mediated by TcTRPM, and it was suggested that the olfactory response is not adequate for avoidance, but that contact repellency might be a more important repellant method. © 2020 Society of Chemical Industry.

Transient receptor potential channel-dependent myogenic responsiveness in small-sized resistance arteries

It is well documented that the inherent ability of small arteries and arterioles to regulate intraluminal diameter in response to alterations in intravascular pressure determines peripheral vascular resistance and blood flow (termed myogenic response or pressure-induced vasoconstriction/dilation). This autoregulatory property of resistance arteries is primarily originated from mechanosensitive vascular smooth muscle cells (VSMCs). There are diverse biological apparatuses in the plasma membrane of VSMCs that sense mechanical stimuli and generate intracellular signals for the contractility of VSMCs. Although the roles of transient receptor potential (TRP) channels in pressure-induced vasoconstriction are not fully understood to date, TRP channels that are directly activated by mechanical stimuli (e.g., stretch of VSMCs) or indirectly evoked by intracellular molecules (e.g., inositol trisphosphate) provide the major sources of Ca²⁺ (e.g., Ca²⁺ influx or release from the sarcoplasmic reticulum) and in turn, evoke vascular reactivity. This review sought to summarize mounting evidence over several decades that the activation of TRP canonical, TRP melastatin, TRP vanilloid, and TRP polycystin channels contributes to myogenic vasoconstriction.

TRPC6 Attenuates Cortical Astrocytic Apoptosis and Inflammation in Cerebral Ischemic/Reperfusion Injury

Transient receptor potential canonical 6 (TRPC6) channel is an important non-selective cation channel with a variety of physiological roles in the central nervous system. Evidence has shown that TRPC6 is involved in the process of experimental stroke; however, the underlying mechanisms remain unclear. In the present study, the role of astrocytic TRPC6 was investigated in an oxygen-glucose deprivation cell model and middle cerebral artery occlusion (MCAO) mouse model of stroke. HYP9 (a selective TRPC6 agonist) and SKF96365 (SKF; a TRPC antagonist) were used to clarify the exact functions of TRPC6 in astrocytes after ischemic stroke. TRPC6 was significantly downregulated during ischemia/reperfusion (IR) injury in cultured astrocytes and in cortices of MCAO mice. Application of HYP9 in vivo alleviated the brain infarct lesion, astrocytes population, apoptosis, and interleukin-6 (IL-6) and IL-1β release in mouse cortices after ischemia. HYP9 dose-dependently inhibited the downregulation of TRPC6 and reduced astrocytic apoptosis, cytotoxicity and inflammatory responses in IR insult, whereas SKF aggravated the damage in vitro. In addition, modulation of TRPC6 channel diminished IR-induced Ca²⁺ entry in astrocytes. Furthermore, decreased Ca²⁺ entry due to TRPC6 contributed to reducing nuclear factor kappa light chain enhancer of activated B cells (NF-κB) nuclear translocation and phosphorylation. Overexpression of astrocytic TRPC6 also attenuated apoptosis, cytotoxicity, inflammatory responses, and NF-κB phosphorylation in modeled ischemia in astrocytes. The results of the present study indicate that the TRPC6 channel can act as a potential target to reduce both inflammatory responses and apoptosis in astrocytes during IR injury, subsequently attenuating ischemic brain damage. In addition, we provide a novel view of stroke therapy by targeting the astrocytic TRPC6 channel.

Drosophila model of anti-retroviral therapy induced peripheral neuropathy and nociceptive hypersensitivity

The success of antiretroviral therapy (ART) has improved the survival of HIV-infected patients significantly. However, significant numbers of patients on ART whose HIV disease is well controlled show peripheral sensory neuropathy (PSN), suggesting that ART may cause PSN. Although the nucleoside reverse transcriptase inhibitors (NRTIs), one of the vital components of ART, are thought to contribute to PSN, the mechanisms underlying the PSN induced by NRTIs are unclear. In this study, we developed a Drosophila model of NRTI-induced PSN that recapitulates the salient features observed in patients undergoing ART: PSN and nociceptive hypersensitivity. Furthermore, our data demonstrate that pathways known to suppress PSN induced by chemotherapeutic drugs are ineffective in suppressing the PSN or nociception induced by NRTIs. Instead, we found that increased dynamics of a peripheral sensory neuron may possibly underlie NRTI-induced PSN and nociception. Our model provides a solid platform in which to investigate further mechanisms of ART-induced PSN and nociceptive hypersensitivity.

This article has an associated First Person interview with the first author of the paper.

Summary: Nucleoside reverse transcriptase inhibitors (NRTIs) that are important components of anti-retroviral therapies also cause peripheral sensory neuropathies (PSN). This article investigates ways in which NRTIs may cause PSN and outlines ways to better understand the mechanisms underlying it.

Molecular and Functional Study of Transient Receptor Potential Vanilloid 1-4 at the Rat and Human Blood-Brain Barrier Reveals Interspecies Differences

Transient receptor potential vanilloid 1-4 (TRPV1-4) expression and functionality were investigated in brain microvessel endothelial cells (BMEC) forming the blood-brain barrier (BBB) from rat and human origins. In rat, Trpv1-4 were detected by qRT-PCR in the brain cortex, brain microvessels, and in primary cultures of brain microvessel endothelial cells [rat brain microvessel endothelial cells (rPBMEC)]. A similar Trpv1-4 expression profile in isolated brain microvessels and rPBMEC was found with the following order: Trpv4 > Trpv2 > Trpv3 > Trpv1. In human, TRPV1-4 were detected in the BBB cell line human cerebral microvessel endothelial cells D3 cells (hCMEC/D3) and in primary cultures of BMEC isolated from human adult and children brain resections [human brain microvascular endothelial cells (hPBMEC)], showing a similar TRPV1-4 expression profile in both hCMEC/D3 cells and hPBMECs as follow: TRPV2 > > TRPV4 > TRPV1 > TRPV3. Western blotting and immunofluorescence experiments confirmed that TRPV2 and TRPV4 are the most expressed TRPV isoforms in hCMEC/D3 cells with a clear staining at the plasma membrane. A fluorescent dye Fluo-4 AM ester was applied to record intracellular Ca2+ levels. TRPV4 functional activity was demonstrated in mediating Ca2+ influx under stimulation with the specific agonist GSK1016790A (ranging from 3 to 1000 nM, EC50 of 16.2 ± 4.5 nM), which was inhibited by the specific TRPV4 antagonist, RN1734 (30 μM). In contrast, TRPV1 was slightly activated in hCMEC/D3 cells as shown by the weak Ca2+ influx induced by capsaicin at a high concentration (3 μM), a highly potent and specific TRPV1 agonist. Heat-induced Ca2+ influx was not altered by co-treatment with a selective potent TRPV1 antagonist capsazepine (20 μM), in agreement with the low expression of TRPV1 as assessed by qRT-PCR. Our present study reveals an interspecies difference between Rat and Human. Functional contributions of TRPV1-4 subtype expression were not identical in rat and human tissues reflective of BBB integrity. TRPV2 was predominant in the human whereas TRPV4 had a larger role in the rat. This interspecies difference from a gene expression point of view should be taken into consideration when modulators of TRPV2 or TRPV4 are investigated in rat models of brain disorders.

Evolutionary Aspects of TRPMLs and TPCs

Transient receptor potential (TRP) or transient receptor potential channels are a highly diverse family of mostly non-selective cation channels. In the mammalian genome, 28 members can be identified, most of them being expressed predominantly in the plasma membrane with the exception of the mucolipins or TRPMLs which are expressed in the endo-lysosomal system. In mammalian organisms, TRPMLs have been associated with a number of critical endo-lysosomal functions such as autophagy, endo-lysosomal fusion/fission and trafficking, lysosomal exocytosis, pH regulation, or lysosomal motility and positioning. The related non-selective two-pore cation channels (TPCs), likewise expressed in endosomes and lysosomes, have also been found to be associated with endo-lysosomal trafficking, autophagy, pH regulation, or lysosomal exocytosis, raising the question why these two channel families have evolved independently. We followed TRP/TRPML channels and TPCs through evolution and describe here in which species TRP/TRPMLs and/or TPCs are found, which functions they have in different species, and how this compares to the functions of mammalian orthologs.

Elevation of Transient Receptor Potential Vanilloid 1 Function in the Lateral Habenula Mediates Aversive Behaviors in Alcohol-withdrawn Rats

WHAT WE ALREADY KNOW ABOUT THIS TOPIC

Chronic alcohol use and withdrawal leads to increased pain perception, anxiety, and depression. These aberrant behaviors are accompanied by increased excitatory glutamatergic transmission to, and activity of, the lateral habenula neurons.Vanilloid type 1, or TRPV1, channels are expressed in the habenula and they facilitate glutamatergic transmission. Whether TRPV1 channel plays a role in habenula hyperactivity is not clear.

WHAT THIS ARTICLE TELLS US THAT IS NEW

Glutamatergic transmission in the lateral habenula was inhibited by TRPV1 channel antagonists. In vivo, local administration of TRPV1 antagonists into the lateral habenula attenuated hyperalgesia, anxiety, and relapse-like drinking in rats who chronically consumed alcohol.The data suggest that enhanced TRPV1 channel function during withdrawal may contribute to aberrant behavior that promotes relapse alcohol consumption.

BACKGROUND

Recent rat studies indicate that alcohol withdrawal can trigger a negative emotional state including anxiety- and depression-like behaviors and hyperalgesia, as well as elevated glutamatergic transmission and activity in lateral habenula neurons. TRPV1, a vanilloid receptor expressed in the habenula, is involved in pain, alcohol dependence, and glutamatergic transmission. The authors therefore hypothesized that TRPV1 contributes to the changes in both the behavioral phenotypes and the habenula activity in alcohol-withdrawn rats.

METHODS

Adult male Long-Evans rats (n = 110 and 280 for electrophysiology and behaviors, respectively), randomly assigned into the alcohol and water (Naïve) groups, were trained to consume either alcohol or water-only using an intermittent-access procedure. Slice electrophysiology was used to measure spontaneous excitatory postsynaptic currents and firing of lateral habenula neurons. The primary outcome was the change in alcohol-related behaviors and lateral habenula activity induced by pharmacologic manipulation of TRPV1 activity.

RESULTS

The basal frequency of spontaneous excitatory postsynaptic currents and firing of lateral habenula neurons in alcohol-withdrawn rats was significantly increased. The TRPV1 antagonist capsazepine (10 µM) induced a stronger inhibition on spontaneous excitatory postsynaptic currents (mean ± SD; by 26.1 ± 27.9% [n = 11] vs. 6.7 ± 18.6% [n = 17], P = 0.027) and firing (by 23.4 ± 17.6% [n = 9] vs. 11.9 ± 16.3% [n = 12], P = 0.025) in Withdrawn rats than Naive rats. By contrast, the TRPV1 agonist capsaicin (3 μM) produced a weaker potentiation in Withdrawn than Naïve rats (spontaneous excitatory postsynaptic currents: by 203.6 ± 124.7% [n = 20] vs. 415.2 ± 424.3% [n = 15], P < 0.001; firing: 38.1 ± 14.7% [n = 11] vs. 73.9 ± 41.9% [n = 11], P < 0.001). Conversely, capsaicin's actions in Naïve but not in Withdrawn rats were significantly attenuated by the pretreatment of TRPV1 endogenous agonist N-Oleoyldopamine. In Withdrawn rats, intra-habenula infusion of TRPV1 antagonists attenuated hyperalgesia and anxiety-like behaviors, decreased alcohol consumption upon resuming drinking, and elicited a conditioned place preference.

CONCLUSIONS

Enhanced TRPV1 function may contribute to increased glutamatergic transmission and activity of lateral habenula neurons, resulting in the aberrant behaviors during ethanol withdrawal.

Novel Targets for Stroke Therapy: Special Focus on TRPC Channels and TRPC6

Stroke remains a leading cause of death, disability, and medical care burden worldwide. However, transformation from laboratory findings toward effective pharmacological interventions for clinical stroke has been unsatisfactory. Novel evidence has been gained on the underlying mechanisms and therapeutic potential related to the transient receptor potential (TRP) channels in several disorders. The TRP superfamily consists of a diverse group of Ca²⁺ permeable non-selective cation channels. In particular, the members of TRP subfamilies, TRP canonical (TRPC) channels and TRPC6, have been found in different cell types in the whole body and have high levels of expression in the central nervous system (CNS). Notably, the TRPCs and TRPC6 channel have been implicated in neurite outgrowth and neuronal survival during normal development and in a range of CNS pathological conditions. Recent studies have shown that suppression of TRPC6 channel degradation prevents ischemic neuronal cell death in experimental stroke. Accumulating evidence supports the important functions of TRPC6 in brain ischemia. We have highlighted some crucial advancement that points toward an important involvement of TRPCs and TRPC6 in ischemic stroke. This review will make an overview of the TRP and TRPC channels due to their roles as targets for clinical trials and CNS disorders. Besides, the primary goal is to discuss and update the critical role of TRPC6 channels in stroke and provide a promising target for stroke prevention and therapy.

Transient Receptor Potential Canonical (TRPC) Channels as Modulators of Migration and Invasion

Calcium (Ca2+) is perhaps the most versatile signaling molecule in cells. Ca2+ regulates a large number of key events in cells, ranging from gene transcription, motility, and contraction, to energy production and channel gating. To accomplish all these different functions, a multitude of channels, pumps, and transporters are necessary. A group of channels participating in these processes is the transient receptor potential (TRP) family of cation channels. These channels are divided into 29 subfamilies, and are differentially expressed in man, rodents, worms, and flies. One of these subfamilies is the transient receptor potential canonical (TRPC) family of channels. This ion channel family comprises of seven isoforms, labeled TRPC1-7. In man, six functional forms are expressed (TRPC1, TRPC3-7), whereas TRPC2 is a pseudogene; thus, not functionally expressed. In this review, we will describe the importance of the TRPC channels and their interacting molecular partners in the etiology of cancer, particularly in regard to regulating migration and invasion.

Genome-wide scan identifies opioid overdose risk locus close to MCOLN1

The United States is experiencing the worst opioid overdose (OpOD) crisis in its history. We carried out a genome-wide association study on OpOD severity among 3 477 opioid-exposed individuals, 1 019 of whom experienced OpODs, including 2 032 European Americans (EAs) (653 overdose cases), and 1 445 African Americans (AAs) (366 overdose cases). Participants were scored 1 to 4 based on their reported overdose status and the number of times that medical treatment was required. Genome-wide association study (GWAS) of EAs and AAs separately resulted in two genome-wide significant (GWS) signals in AAs but none in EAs. The first signal was represented by three closely mapped variants (rs115208233, rs116181528, and rs114077267) located near mucolipin 1 (MCOLN1) and patatin-like phospholipase domain containing 6 (PNPLA6), and the other signal was represented by rs369098800 near dead-box helicase 18 (DDX18). There were no additional GWS signals in the trans-population meta-analysis, so that post-GWAS analysis focused on these loci. In network analysis, MCOLN1 was coexpressed with PNPLA6, but only MCOLN1-associated genes were enriched in functional categories relevant to OpOD, including calcium and cation channel activities; no enrichment was observed for PNPLA6-associated genes. Drug repositioning analysis was carried out in the connectivity map (CMap) database for MCOLN1 (PNPLA6 was not available in CMap) and showed that the opioid agonist drug-induced expression profile is similar to that of MCOLN1 overexpression and yielded the highest-ranked expression profile of 83 drug classes. Thus, MCOLN1 may be a risk gene for OpOD, but replication is needed. This knowledge could be helpful in the identification of drug targets for preventing OpOD.

Infrared inhibition and waveform modulation of action potentials in the crayfish motor axon

The infrared (IR) inhibition of axonal activities in the crayfish neuromuscular preparation is studied using 2 µm IR light pulses with varying durations. The intracellular neuronal activities are monitored with two-electrode current clamp, while the IR-induced temperature changes are measured by the open patch technique simultaneously. It is demonstrated that the IR pulses can reversibly shape or block locally initiated action potentials. Suppression of the AP amplitude and duration and decrease in axonal excitability by IR pulses are quantitatively analyzed. While the AP amplitude and duration decrease similarly during IR illumination, it is discovered that the recovery of the AP duration after the IR pulses is slower than that of the AP amplitude. An IR-induced decrease in the input resistance (8.8%) is detected and discussed together with the temperature dependent changes in channel kinetics as contributing factors for the inhibition reported here.

The Pivotal Role of TRP Channels in Homeostasis and Diseases throughout the Gastrointestinal Tract

The transient receptor potential (TRP) channels superfamily are a large group of proteins that play crucial roles in cellular processes. For example, these cation channels act as sensors in the detection and transduction of stimuli of temperature, small molecules, voltage, pH, and mechanical constrains. Over the past decades, different members of the TRP channels have been identified in the human gastrointestinal (GI) tract playing multiple modulatory roles. Noteworthy, TRPs support critical functions related to the taste perception, mechanosensation, and pain. They also participate in the modulation of motility and secretions of the human gut. Last but not least, altered expression or activity and mutations in the TRP genes are often related to a wide range of disorders of the gut epithelium, including inflammatory bowel disease, fibrosis, visceral hyperalgesia, irritable bowel syndrome, and colorectal cancer. TRP channels could therefore be promising drug targets for the treatment of GI malignancies. This review aims at providing a comprehensive picture of the most recent advances highlighting the expression and function of TRP channels in the GI tract, and secondly, the description of the potential roles of TRPs in relevant disorders is discussed reporting our standpoint on GI tract–TRP channels interactions.

Decrypting the Heat Activation Mechanism of TRPV1 Channel by Molecular Dynamics Simulation

As a prototype cellular sensor, the TRPV1 cation channel undergoes a closed-to-open gating transition in response to various physical and chemical stimuli including noxious heat. Despite recent progress, the molecular mechanism of heat activation of TRPV1 gating remains enigmatic. Toward decrypting the structural basis of TRPV1 heat activation, we performed extensive molecular dynamics simulations (with cumulative simulation time of ∼11 μs) for the wild-type channel and a constitutively active double mutant at different temperatures (30, 60, and 72°C), starting from a high-resolution closed-channel structure of TRPV1 solved by cryo-electron microscopy. In the wild-type simulations, we observed heat-activated conformational changes (e.g., expansion or contraction) in various key domains of TRPV1 (e.g., the S2-S3 and S4-S5 linkers) to prime the channel for gating. These conformational changes involve a number of dynamic hydrogen-bond interactions that were validated with previous mutational studies. Next, our mutant simulations observed channel opening after a series of conformational changes that propagate from the channel periphery to the channel pore via key intermediate domains (including the S2-S3 and S4-S5 linkers). The gating transition is accompanied by a large increase in the protein-water electrostatic interaction energy, which supports the contribution of desolvation of polar/charged residues to the temperature-sensitive TRPV1 gating. Taken together, our molecular dynamics simulations and analyses offered, to our knowledge, new structural, dynamic, and energetic information to guide future mutagenesis and functional studies of the TRPV1 channels and development of TRPV1-targeting drugs.

Heat activation mechanism of TRPV1: New insights from molecular dynamics simulation

As a member of the transient receptor potential (TRP) channels superfamily, the TRPV1 channel undergoes a closed-to-open gating transition in response to various physical and chemical stimuli including heat. Thanks to recent progress in cryo-electron microscopy, high-resolution structures are becoming available for various TRP channels including TRPV1. This has enabled us to study the molecular mechanism of TRPV1 channel gating by using molecular simulation. Here we review recent progress in molecular simulations of TRPV1 channel by us and others, with focus on our molecular dynamics (MD) simulations of TRPV1 at different temperatures. While no consensus has been reached on the heat activation mechanism of TRPV1, the simulations have offered specific predictions and models for future experimental studies to test.

TRP Channel Reconstitution in Lipid Bilayers

The family of the transient receptor potential (TRP) proteins presents a diverse group of polymodal ion channels intertwined in the regulation of various physiological processes. Currently, TRP channels are well established in temperature-sensation, thermoregulation, pain sensation, and mineral homeostasis. Furthermore, new evidence suggests that TRP channels are also implicated in hormonal signaling, where the channels are responsible for propagating hormone-induced signals along the neural circuitry and also regulating cellular processes of nonexcitable cells. Due to this wide assortment of actions, TRP channels have been attracting immense scientific interest in various fields.In this chapter, I describe incorporation and characterization of several TRP channels using an electrophysiological approach known as planar lipid bilayers. This technique features measurements of functional activities of ion channels in a well-defined reconstituted system. The priority of this electrophysiological approach is identifying intrinsic properties of ion channels, which is particularly valuable in appreciating intrinsic temperature sensitivity concerning thermo-TRP channels, but also direct mechanisms of channels agonists, antagonists, cofactors, and other modifiers.

Molecular Evolution Bioinformatics Toward Structural Biology of TRPV1-4 Channels

Bioinformatics is a very resourceful tool to understand evolution of membrane proteins, such as transient receptor potential channels. Expert bioinformatics users rely on specialized scripting and programming skills. Several web servers and standalone tools are available for nonadvanced users willing to develop projects to understand their system of choice. In this case, we present a desktop-based protocol to develop evostructural hypotheses based on basic bioinformatics skills and resources, specifically for a small subgroup of TRPV channels, which can be further implemented for larger datasets.

The endocannabinoid system of the skin. A potential approach for the treatment of skin disorders

The skin is the largest organ of the body and has a complex and very active structure that contributes to homeostasis and provides the first line defense against injury and infection. In the past few years it has become evident that the endocannabinoid system (ECS) plays a relevant role in healthy and diseased skin. Specifically, we review how the dysregulation of ECS has been associated to dermatological disorders such as atopic dermatitis, psoriasis, scleroderma and skin cancer. Therefore, the druggability of the ECS could open new research avenues for the treatment of the pathologies mentioned. Numerous studies have reported that phytocannabinoids and their biological analogues modulate a complex network pharmacology involved in the modulation of ECS, focusing on classical cannabinoid receptors, transient receptor potential channels (TRPs), and peroxisome proliferator-activated receptors (PPARs). The combined targeting of several end-points seems critical to provide better chances of therapeutically success, in sharp contrast to the one-disease-one-target dogma that permeates current drug discovery campaigns.

The role of transient receptor potential polycystin channels in bone diseases

Transient receptor potential (TRP) channels are cation channels which act as molecular sensors that enable cells to detect and respond to a plethora of mechanical and environmental cues. TRPs are involved in various physiological processes, such as mechanosensation, non-inception and thermosensation, while mutations in genes encoding them can lead to pathological conditions, called "channelopathies". The subfamily of transient receptor potential polycystins (TRPPs), Polycystin 1 (PC1, TRPP1) and Polycystin 2 (PC2, TRPP2), act as mechanoreceptors, sensing external mechanical forces, including strain, stretch and fluid shear stress, triggering a cascade of signaling pathways involved in osteoblastogenesis and ultimately bone formation. Both in vitro studies and research on animal models have already identified their implications in bone homeostasis. However, uncertainty veiling the role of polycystins (PCs) in bone disease urges studies to elucidate further their role in this field. Mutations in TRPPs have been related to autosomal polycystic kidney disease (ADKPD) and research groups try to identify their role beyond their well-established contribution in kidney disease. Such an elucidation would be beneficial for identifying signaling pathways where polycystins are involved in bone diseases related to exertion of mechanical forces such as osteoporosis, osteopenia and craniosynostosis. A better understanding of the implications of TRPPs in bone diseases would possibly lay the cornerstone for effective therapeutic schemes.

Expression of TRPC5 is decreased in the sperm of patients with varicocele-associated asthenozoospermia

The present study aimed to determine whether the expression of transient receptor potential channel 5 (TRPC5) protein is altered in spermatozoa of patients with varicocele-associated asthenozoospermia. TRPC5 expression in spermatozoa was determined by polymerase chain reaction and western blotting analyses, and indirect immunofluorescence was used for identification and immunolocalization of the TRPC5 channel in human sperm. Sperm motility and superoxide dismutase (SOD) activity were also determined with a computer-assisted semen analysis system and assay kit, respectively. Compared with levels in control subjects, it was identified that TRPC5 protein expression, SOD activity and cellular motility in the sperm of patients with varicocele-associated asthenozoospermia were reduced (P<0.001). Furthermore, the expression of TRPC5 was positively correlated with sperm motility (r=0.781, P<0.001) and SOD activity (r=0.933, P<0.001), indicated by partial correlation analysis. The present study may provide a novel target for the study and treatment of varicocele-associated asthenozoospermia.

TRPC Channel Structure and Properties

TRPC channels are the first identified members in the TRP family. They function as either homo- or heterotetramers regulating intracellular Ca²⁺ concentration in response to numerous physiological or pathological stimuli. TRPC channels are nonselective cation channels permeable to Ca²⁺. The properties and the functional domains of TRPC channels have been identified by electrophysiological and biochemical methods. However, due to the large size, instability, and flexibility of their complexes, the structures of the members in TRPC family remain unrevealed. More efforts should be made on structure analysis and generating good tools, including specific antibodies, agonist, and antagonist.

Bilaterian Giant Ankyrins Have a Common Evolutionary Origin and Play a Conserved Role in Patterning the Axon Initial Segment

In vertebrate neurons, the axon initial segment (AIS) is specialized for action potential initiation. It is organized by a giant 480 Kd variant of ankyrin G (AnkG) that serves as an anchor for ion channels and is required for a plasma membrane diffusion barrier that excludes somatodendritic proteins from the axon. An unusually long exon required to encode this 480Kd variant is thought to have been inserted only recently during vertebrate evolution, so the giant ankyrin-based AIS scaffold has been viewed as a vertebrate adaptation for fast, precise signaling. We re-examined AIS evolution through phylogenomic analysis of ankyrins and by testing the role of ankyrins in proximal axon organization in a model multipolar Drosophila neuron (ddaE). We find giant isoforms of ankyrin in all major bilaterian phyla, and present evidence in favor of a single common origin for giant ankyrins and the corresponding long exon in a bilaterian ancestor. This finding raises the question of whether giant ankyrin isoforms play a conserved role in AIS organization throughout the Bilateria. We examined this possibility by looking for conserved ankyrin-dependent AIS features in Drosophila ddaE neurons via live imaging. We found that ddaE neurons have an axonal diffusion barrier proximal to the cell body that requires a giant isoform of the neuronal ankyrin Ank2. Furthermore, the potassium channel shal concentrates in the proximal axon in an Ank2-dependent manner. Our results indicate that the giant ankyrin-based cytoskeleton of the AIS may have evolved prior to the radiation of extant bilaterian lineages, much earlier than previously thought.

The axon initial segment (AIS) is currently thought to be a distinguishing feature of vertebrate neurons that adapts them for rapid, precise signaling. It serves as a hub for the regulation of neuronal excitability as the site of action potential initiation and also acts as the boundary between the highly-specialized axon and the rest of the cell. Here we show that the giant ankyrins that structurally organize the AIS, and were thought to be vertebrate-specific, instead have an ancient origin in a bilaterian ancestor. We further show the presence of a giant ankyrin-dependent AIS-like plasma membrane boundary between the axon and soma in a Drosophila sensory neuron. These results suggest that the cytoskeletal backbone for the AIS is not unique to vertebrates, but instead may be an evolutionarily conserved feature of bilaterian neurons.

Nociceptive TRP Channels: Sensory Detectors and Transducers in Multiple Pain Pathologies

Specialized receptors belonging to the transient receptor potential (TRP) family of ligand-gated ion channels constitute the critical detectors and transducers of pain-causing stimuli. Nociceptive TRP channels are predominantly expressed by distinct subsets of sensory neurons of the peripheral nervous system. Several of these TRP channels are also expressed in neurons of the central nervous system, and in non-neuronal cells that communicate with sensory nerves. Nociceptive TRPs are activated by specific physico-chemical stimuli to provide the excitatory trigger in neurons. In addition, decades of research has identified a large number of immune and neuromodulators as mediators of nociceptive TRP channel activation during injury, inflammatory and other pathological conditions. These findings have led to aggressive targeting of TRP channels for the development of new-generation analgesics. This review summarizes the complex activation and/or modulation of nociceptive TRP channels under pathophysiological conditions, and how these changes underlie acute and chronic pain conditions. Furthermore, development of small-molecule antagonists for several TRP channels as analgesics, and the positive and negative outcomes of these drugs in clinical trials are discussed. Understanding the diverse functional and modulatory properties of nociceptive TRP channels is critical to function-based drug targeting for the development of evidence-based and efficacious new generation analgesics.