Transient receptor potential vanilloid 1-6 (Trpv1-6) gene expression in the mouse brain during estrous cycle

Transient Receptor Potential Vanilloid 6 Modulates Aberrant Axonal Sprouting in a Mouse Model of Pilocarpine-Induced Epilepsy

Transient receptor potential vanilloid 6 (TRPV6) is a highly selective calcium-ion channel that belongs to the TRPV family. TRPV6 is widely distributed in the brain, but its role in neurological diseases such as epilepsy remains unknown. Here, we report for the first time that TRPV6 expression is upregulated in the hippocampus of a pilocarpine-induced status epilepticus model, mainly in the suprapyramidal bundle of the mossy fiber (MF) projection of the hippocampal CA3 regions. We found that TRPV6 overexpression via viral vector transduction attenuated abnormal MF sprouting (MFS), whereas TRPV6 knockdown aggravated the development of MFS and the incidence of recurrent seizures during epileptogenic progression. In the in vitro experiments, our results showed that modulation of TRPV6 expression resulted in a change in axonal formation in cultured hippocampal neurons. In addition, we found that TRPV6 was implicated in the regulation of Akt-glycogen synthase kinase-3-β activity, which is closely related to the cellular mechanism of axonal outgrowth. Therefore, these findings suggest that TRPV6 may regulate the formation of aberrant synaptic circuits during epileptogenesis.

Progesterone interacts with the mutational hot-spot of TRPV4 and acts as a ligand relevant for fast Ca2+-signalling

Steroids are also known to induce immediate physiological and cellular response which occurs within minutes to seconds, or even faster. Such non-genomic actions of steroids are rapid and are proposed to be mediated by different ion channels. Transient receptor potential vanilloid sub-type 4 (TRPV4), is a non-specific polymodal ion channel which is involved in several physiological and cellular processes. In this work, we explored the possibilities of Progesterone (P4) as an endogenous ligand for TRPV4. We demonstrate that P4 docks as well as physically interacts with the TM4-loop-TM5 region of TRPV4, a region which is a mutational hotspot for different diseases. Live cell imaging experiments with a genetically encoded Ca2+-sensor suggests that P4 causes quick influx of Ca2+ specifically in the TRPV4 expressing cells, which can be partially blocked by TRPV4-specific inhibitor, suggesting that P4 can act as a ligand for TRPV4. Such P4-mediated Ca2+-influx is altered in cells expressing disease causing TRPV4 mutants, namely in L596P, R616Q, and also in embryonic lethal mutant L618P. P4 dampens, both in terms of "extent" as well as the "pattern" of the Ca2+-influx by other stimulus too in cells expressing TRPV4-Wt, suggesting that P4 crosstalk with the TRPV4-mediated Ca2+-signalling, both in quick and long-term manner. We propose that P4 crosstalk with TRPV4 might be relevant for both acute and chronic pain as well as for other health-related functions.

TRPV3 Ion Channel: From Gene to Pharmacology

Transient receptor potential vanilloid subtype 3 (TRPV3) is an ion channel with a sensory function that is most abundantly expressed in keratinocytes and peripheral neurons. TRPV3 plays a role in Ca²⁺ homeostasis due to non-selective ionic conductivity and participates in signaling pathways associated with itch, dermatitis, hair growth, and skin regeneration. TRPV3 is a marker of pathological dysfunctions, and its expression is increased in conditions of injury and inflammation. There are also pathogenic mutant forms of the channel associated with genetic diseases. TRPV3 is considered as a potential therapeutic target of pain and itch, but there is a rather limited range of natural and synthetic ligands for this channel, most of which do not have high affinity and selectivity. In this review, we discuss the progress in the understanding of the evolution, structure, and pharmacology of TRPV3 in the context of the channel's function in normal and pathological states.

Multiple Chemical Sensitivity: It's time to catch up to the science

Multiple chemical sensitivity (MCS) is a complex medical condition associated with low dose chemical exposures. MCS is characterized by diverse features and common comorbidities, including fibromyalgia, cough hypersensitivity, asthma, and migraine, and stress/anxiety, with which the syndrome shares numerous neurobiological processes and altered functioning within diverse brain regions. Predictive factors linked to MCS comprise genetic influences, gene-environment interactions, oxidative stress, systemic inflammation, cell dysfunction, and psychosocial influences. The development of MCS may be attributed to the sensitization of transient receptor potential (TRP) receptors, notably TRPV1 and TRPA1. Capsaicin inhalation challenge studies demonstrated that TRPV1 sensitization is manifested in MCS, and functional brain imaging studies revealed that TRPV1 and TRPA1 agonists promote brain-region specific neuronal variations. Unfortunately, MCS has often been inappropriately viewed as stemming exclusively from psychological disturbances, which has fostered patients being stigmatized and ostracized, and often being denied accommodation for their disability. Evidence-based education is essential to provide appropriate support and advocacy. Greater recognition of receptor-mediated biological mechanisms should be incorporated in laws, and regulation of environmental exposures.

Intracellular Helix-Loop-Helix Domain Modulates Inactivation Kinetics of Mammalian TRPV5 and TRPV6 Channels

TRPV5 and TRPV6 are calcium-selective ion channels expressed at the apical membrane of epithelial cells. Important for systemic calcium (Ca²⁺) homeostasis, these channels are considered gatekeepers of this cation transcellular transport. Intracellular Ca²⁺ exerts a negative control over the activity of these channels by promoting inactivation. TRPV5 and TRPV6 inactivation has been divided into fast and slow phases based on their kinetics. While slow inactivation is common to both channels, fast inactivation is characteristic of TRPV6. It has been proposed that the fast phase depends on Ca²⁺ binding and that the slow phase depends on the binding of the Ca²⁺/Calmodulin complex to the internal gate of the channels. Here, by means of structural analyses, site-directed mutagenesis, electrophysiology, and molecular dynamic simulations, we identified a specific set of amino acids and interactions that determine the inactivation kinetics of mammalian TRPV5 and TRPV6 channels. We propose that the association between the intracellular helix-loop-helix (HLH) domain and the TRP domain helix (TDh) favors the faster inactivation kinetics observed in mammalian TRPV6 channels.

Evaluating the Antinociceptive Efficacy of Cannabidiol Alone or in Combination with Morphine Using the Formalin Test in Male and Female Mice

Introduction: Phytocannabinoids have emerged as a potential alternative treatment option for individuals experiencing persistent pain. However, evidence-based research regarding their clinical utility in both males and females remains incomplete. In addition, it is unknown whether combining readily available cannabinoids with opioids has a synergistic or subadditive effect on pain modulation. To begin to fill this knowledge gap, we investigated the antinociceptive effects of the phytocannabinoid, CBD, either alone or in combination with opioids in male and female C57BL/6J mice. Results: Using the formalin test, our results show that CBD (10 mg/kg, i.p.) treatment evoked antinociception in phase I, but not in phase II, of the formalin test in male mice. However, in female mice, CBD showed no significant antinociceptive effect. In addition, a direct sex comparison showed that CBD evoked a significant increase in nociceptive behaviors in female versus male mice during phase I of the formalin test. Furthermore, we show that CBD (10 mg/kg, i.p.) in combination with low-dose morphine (1 mg/kg, i.p.) was ineffective at eliciting a synergistic antinociceptive response in both male and female mice. Lastly, consistent with previous literature, we showed that females treated with a relatively higher dose of morphine (10 mg/kg, i.p.) displayed a significant increase in the variability of nociceptive behaviors compared to morphine-treated male mice. Conclusion: Overall, our results suggest that CBD treatment may have beneficial antinociceptive effects during the acute phase of persistent pain, but these effects are more beneficial to males than females. We provide further pre-clinical support that treatments geared toward reducing nociceptive behaviors differentially affect males and females.

Unrevealing functional candidate genes for bovine fertility through RNA sequencing meta-analysis and regulatory elements networks of co-expressed genes and lncRNAs

The high genetic heterogeneity and environmental effects of subfertility in livestock species make the elucidation of the genetic mechanisms associated with reproductive efficiency a difficult task. Network and co-expression network meta-analyses were applied alongside genetic variant calling and long non-coding RNA (lncRNA) characterization to identify functionally relevant target genes and regulatory subnetworks associated with fertility in dairy cattle. In total, 505 lncRNAs (441 previously annotated in the bovine reference genome ARS-UCD 1.2 and 64 novel lncRNAs) were identified. Seven differentially expressed genes between high-fertile (HF) and sub-fertile (SF) Holstein cows were identified in the network meta-analysis (CA5A, ENSBTAG00000051149, ENSBTAG00000003272, DEFB7, DIO2, TRPV3, and COL4A4). Additionally, seven functional candidate differentially co-expressed (DcoExp) modules with a differential regulatory pattern (|z-score|>2) were identified between HF and SF cows. The functional candidate genes and DcoExp modules identified were associated with fertility relevant processes such as the regulation of embryonic implantation and proliferation, interaction and molecule transfer between the fetus and the cow, and the immune system. These results help to better understand the genetic mechanisms associated with reproductive efficiency in dairy cattle through the identification of potential biomarkers and genetic variants associated with differentially expressed regulatory gene and lncRNAs regulatory element networks.

Transient Receptor Potential Vanilloid 1 Function at Central Synapses in Health and Disease

The transient receptor potential vanilloid 1 (TRPV1), a ligand-gated nonselective cation channel, is well known for mediating heat and pain sensation in the periphery. Increasing evidence suggests that TRPV1 is also expressed at various central synapses, where it plays a role in different types of activity-dependent synaptic changes. Although its precise localizations remain a matter of debate, TRPV1 has been shown to modulate both neurotransmitter release at presynaptic terminals and synaptic efficacy in postsynaptic compartments. In addition to being required in these forms of synaptic plasticity, TRPV1 can also modify the inducibility of other types of plasticity. Here, we highlight current evidence of the potential roles for TRPV1 in regulating synaptic function in various brain regions, with an emphasis on principal mechanisms underlying TRPV1-mediated synaptic plasticity and metaplasticity. Finally, we discuss the putative contributions of TRPV1 in diverse brain disorders in order to expedite the development of next-generation therapeutic treatments.

Pharmacological effects of cannabidiol by transient receptor potential channels

Cannabidiol (CBD), as a major phytocannabinoid of Cannabis sativa, has emerged as a promising natural compound in the treatment of diseases. Its diverse pharmacological effects with limited side effects have promoted researchers to pursue new therapeutic applications. It has little affinity for classical cannabinoid receptors (CB1 and CB2). Considering this and its diverse pharmacological effects, it is logical to set up studies for finding its putative potential targets other than CB1 and CB2. A class of ion channels, namely transient potential channels (TRP), has been identified during two recent decades. More than 30 members of this family have been studied, so far. They mediate diverse physiological functions and are associated with various pathological conditions. Some have been recognized as key targets for natural compounds such as capsaicin, menthol, and CBD. Studies show that CBD has agonistic effects for TRPV1-4 and TRPA1 channels with antagonistic effects on the TRPM8 channel. In this article, we reviewed the recent findings considering the interaction of CBD with these channels. The review indicated that TRP channels mediate, at least in part, the effects of CBD on seizure, inflammation, cancer, pain, acne, and vasorelaxation. This highlights the role of TRP channels in CBD-mediated effects, and binding to these channels may justify part of its paradoxical effects in comparison to classical phytocannabinoids.

Calcium selective channel TRPV6: Structure, function, and implications in health and disease

Calcium-selective channel TRPV6 (Transient Receptor Potential channel family, Vanilloid subfamily member 6) belongs to the TRP family of cation channels and plays critical roles in transcellular calcium (Ca2+) transport, reuptake of Ca2+ into cells, and maintaining a local low Ca2+ environment for certain biological processes. Recent crystal and cryo-electron microscopy-based structures of TRPV6 have revealed mechanistic insights on how the protein achieves Ca2+ selectivity, permeation, and inactivation by calmodulin. The TRPV6 protein is expressed in a range of epithelial tissues such as the intestine, kidney, placenta, epididymis, and exocrine glands such as the pancreas, prostate and salivary, sweat, and mammary glands. The TRPV6 gene is a direct transcriptional target of the active form of vitamin D and is efficiently regulated to meet the body's need for Ca2+ demand. In addition, TRPV6 is also regulated by the level of dietary Ca2+ and under physiological conditions such as pregnancy and lactation. Genetic models of loss of function in TRPV6 display hypercalciuria, decreased bone marrow density, deficient weight gain, reduced fertility, and in some cases alopecia. The models also reveal that the channel plays an indispensable role in maintaining maternal-fetal Ca2+ transport and low Ca2+ environment in the epididymal lumen that is critical for male fertility. Most recently, loss of function mutations in TRPV6 gene is linked to transient neonatal hyperparathyroidism and early onset chronic pancreatitis. TRPV6 is overexpressed in a wide range of human malignancies and its upregulation is strongly correlated to tumor aggressiveness, metastasis, and poor survival in selected cancers. This review summarizes the current state of knowledge on the expression, structure, biophysical properties, function, polymorphisms, and regulation of TRPV6. The aberrant expression, polymorphisms, and dysfunction of this protein linked to human diseases are also discussed.

Effect of menstrual cycle and female hormones on TRP and TREK channels in modifying thermosensitivity and physiological functions in women

Thermoregulation is crucial for human survival at various ambient temperatures. Transient receptor potential (TRP) and TWIK-related K⁺ (TREK) channels expressed in sensory neurons play a role in peripheral thermosensitivity for temperature detection. In addition, these channels have various physiological roles in the skeletal, nervous, immune, vascular, digestive, and urinary systems. In women, the female hormones estradiol (E2) and progesterone (P4), which fluctuate during the menstrual cycle, affect various physiological functions, such as thermoregulation in hot and cold environments. The present review describes the effect of female hormones on TRP and TREK channels and related physiological functions. The P4 decreased thermosensitivity via TRPV1. E2 facilitates temporomandibular joint disease (TRPV1), breast cancer (TRPM8), and calcium absorption in the digestive system (TRPV5 and TRPV6), inhibits the facilitation of vasoconstriction (TRPM3), nerve inflammation (TRPM4), sweetness sensitivity (TRPM5), and menstrual disorders (TRPC1), and prevents insulin resistance (TRPC5) via each channel. P4 inhibits vasoconstriction (TRPM3), sweetness sensitivity (TRPM5), ciliary motility in the lungs (TRPV4), menstrual disorder (TRPC1), and immunity (TRPC3), and facilitates breast cancer (TRPV6) via each channel as indicated. The effects of female hormones on TREK channels and physiological functions are still under investigation. In summary, female hormones influence physiological functions via some TRP channels; however, the literature is not comprehensive and future studies are needed, especially those related to thermoregulation in women.

TRPV4 integrates matrix mechanosensing with Ca2+ signaling to regulate extracellular matrix remodeling

In healthy connective tissues, mechanosensors trigger the generation of Ca²⁺ signals, which enable cells to maintain the structure of the fibrillar collagen matrix through actomyosin contractile forces. Transient receptor potential vanilloid type 4 (TRPV4) is a mechanosensitive Ca²⁺ -permeable channel that, when expressed in cell-matrix adhesions of the plasma membrane, regulates extracellular matrix (ECM) remodeling. In high prevalence disorders such as fibrosis and tumor metastasis, dysregulated matrix remodeling is associated with disruptions of Ca²⁺ homeostasis and TRPV4 function. Here, we consider that ECM polymers transmit cell-activating mechanical signals to TRPV4 in cell adhesions. When activated, TRPV4 regulates fibrillar collagen remodeling, thereby altering the mechanical properties of the ECM. In this review, we integrate functionally connected processes of matrix remodeling to highlight how TRPV4 in cell adhesions and matrix mechanics are reciprocally regulated through Ca²⁺ signaling.

Cannabidiol activation of vagal afferent neurons requires TRPA1

Vagal afferent neurons abundantly express excitatory transient receptor potential (TRP) channels, which strongly influence afferent signaling. Cannabinoids have been identified as direct agonists of TRP channels, including TRPA1 and TRPV1, suggesting that exogenous cannabinoids may influence vagal signaling via TRP channel activation. The diverse therapeutic effects of electrical vagus nerve stimulation also result from administration of the nonpsychotropic cannabinoid, cannabidiol (CBD); however, the direct effects of CBD on vagal afferent signaling remain unknown. We investigated actions of CBD on vagal afferent neurons, using calcium imaging and electrophysiology. CBD produced strong excitatory effects in neurons expressing TRPA1. CBD responses were prevented by removal of bath calcium, ruthenium red, and the TRPA1 antagonist A967079, but not the TRPV1 antagonist SB366791, suggesting an essential role for TRPA1. These pharmacological experiments were confirmed using genetic knockouts where TRPA1 KO mice lacked CBD responses, whereas TRPV1 knockout (KO) mice exhibited CBD-induced activation. We also characterized CBD-provoked inward currents at resting potentials in vagal afferents expressing TRPA1 that were absent in TRPA1 KO mice, but persisted in TRPV1 KO mice. CBD also inhibited voltage-activated sodium conductances in A-fiber, but not in C-fiber afferents. To simulate adaptation, resulting from chronic cannabis use, we administered cannabis extract vapor daily for 3 wk. Cannabis exposure reduced the magnitude of CBD responses, likely due to a loss of TRPA1 signaling. Together, these findings detail a novel excitatory action of CBD at vagal afferent neurons, which requires TRPA1 and may contribute to the vagal mimetic effects of CBD and adaptation following chronic cannabis use.NEW & NOTEWORTHY CBD usage has increased with its legalization. The clinical efficacy of CBD has been demonstrated for conditions including some forms of epilepsy, depression, and anxiety that are also treatable by vagus nerve stimulation. We found CBD exhibited direct excitatory effects on vagal afferent neurons that required TRPA1, were augmented by TRPV1, and attenuated following chronic cannabis vapor exposure. These effects may contribute to vagal mimetic effects of CBD and adaptation after chronic cannabis use.

TRPV1-Estradiol Stereospecific Relationship Underlies Cell Survival in Oxidative Cell Death

17β-estradiol is a neuronal survival factor against oxidative stress that triggers its protective effect even in the absence of classical estrogen receptors. The polymodal transient receptor potential vanilloid subtype 1 (TRPV1) channel has been proposed as a steroid receptor implied in tissue protection against oxidative damage. We show here that TRPV1 is sufficient condition for 17β-estradiol to enhance metabolic performance in injured cells. Specifically, in TRPV1 expressing cells, the application of 17β-estradiol within the first 3 h avoided H₂O₂-dependent mitochondrial depolarization and the activation of caspase 3/7 protecting against the irreversible damage triggered by H₂O₂. Furthermore, 17β-estradiol potentiates TRPV1 single channel activity associated with an increased open probability. This effect was not observed after the application of 17α-estradiol. We explored the TRPV1-Estrogen relationship also in primary culture of hippocampal-derived neurons and observed that 17β-estradiol cell protection against H₂O₂-induced damage was independent of estrogen receptors pathway activation, membrane started and stereospecific. These results support the role of TRPV1 as a 17β-estradiol-activated ionotropic membrane receptor coupling with mitochondrial function and cell survival.

Steroids and TRP Channels: A Close Relationship

Transient receptor potential (TRP) channels are remarkable transmembrane protein complexes that are essential for the physiology of the tissues in which they are expressed. They function as non-selective cation channels allowing for the signal transduction of several chemical, physical and thermal stimuli and modifying cell function. These channels play pivotal roles in the nervous and reproductive systems, kidney, pancreas, lung, bone, intestine, among others. TRP channels are finely modulated by different mechanisms: regulation of their function and/or by control of their expression or cellular/subcellular localization. These mechanisms are subject to being affected by several endogenously-produced compounds, some of which are of a lipidic nature such as steroids. Fascinatingly, steroids and TRP channels closely interplay to modulate several physiological events. Certain TRP channels are affected by the typical genomic long-term effects of steroids but others are also targets for non-genomic actions of some steroids that act as direct ligands of these receptors, as will be reviewed here.

Strategies for Neuroprotection in Multiple Sclerosis and the Role of Calcium

Calcium ions are vital for maintaining the physiological and biochemical processes inside cells. The central nervous system (CNS) is particularly dependent on calcium homeostasis and its dysregulation has been associated with several neurodegenerative disorders including Parkinson’s disease (PD), Alzheimer’s disease (AD) and Huntington’s disease (HD), as well as with multiple sclerosis (MS). Hence, the modulation of calcium influx into the cells and the targeting of calcium-mediated signaling pathways may present a promising therapeutic approach for these diseases. This review provides an overview on calcium channels in neurons and glial cells. Special emphasis is put on MS, a chronic autoimmune disease of the CNS. While the initial relapsing-remitting stage of MS can be treated effectively with immune modulatory and immunosuppressive drugs, the subsequent progressive stage has remained largely untreatable. Here we summarize several approaches that have been and are currently being tested for their neuroprotective capacities in MS and we discuss which role calcium could play in this regard.

TRPV1 Inhibits the Ventilatory Response to Hypoxia in Adult Rats, but Not the CO₂-Drive to Breathe

Receptors of the transient receptor potential (TRP) channels superfamily are expressed in many tissues and have different physiological functions. However, there are few studies investigating the role of these channels in cardiorespiratory control in mammals. We assessed the role of central and peripheral TRPV1 receptors in the cardiorespiratory responses to hypoxia (10% O₂) and hypercapnia (7% CO₂) by measuring pulmonary ventilation (V˙E), heart rate (HR), mean arterial pressure (MAP) and body temperature (Tb) of male Wistar rats before and after intraperitoneal (AMG9810 [2.85 µg/kg, 1 mL/kg]) or intracebroventricular (AMG9810 [2.85 µg/kg, 1 µL] or AMG7905 [28.5 μg/kg, 1 µL]) injections of TRPV1 antagonists. Central or peripheral injection of TRPV1 antagonists did not change cardiorespiratory parameters or Tb during room air and hypercapnic conditions. However, the hypoxic ventilatory response was exaggerated by both central and peripheral injection of AMG9810. In addition, the peripheral antagonist blunted the drop in Tb induced by hypoxia. Therefore, the current data provide evidence that TRPV1 channels exert an inhibitory modulation on the hypoxic drive to breathe and stimulate the Tb reduction during hypoxia.