Functional roles of TRPC channels in the developing brain

TRPC3 suppression ameliorates synaptic dysfunctions and memory deficits in Alzheimer's disease

Transient receptor potential canonical (TRPC) channels are widely expressed in the brain; however, their precise roles in neurodegeneration, such as Alzheimer's disease (AD) remain elusive. Bioinformatic analysis of the published single-cell RNA-seq data collected from AD patient cohorts indicates that the Trpc3 gene is uniquely upregulated in excitatory neurons. TRPC3 expression is also upregulated in post-mortem AD brains, and in both acute and chronic mouse models of AD. Functional screening of TRPC3 antagonists resulted in a lead inhibitor JW-65, which completely rescued Aβ-induced neurotoxicity, impaired synaptic plasticity (e.g., LTP), and learning memory in acute and chronic experimental AD models. In cultured rat hippocampal neurons, we found that treatment with soluble β-amyloid oligomers (AβOs) induces rapid and sustained upregulation of the TRPC3 expression selectively in excitatory neurons. This aberrantly upregulated TRPC3 contributes to AβOs-induced Ca 2+ overload through the calcium entry and store-release mechanisms. The neuroprotective action of JW-65 is primarily mediated via restoring AβOs-impaired Ca 2+ /calmodulin-mediated signaling pathways, including calmodulin kinases CaMKII/IV and calcineurin (CaN). The synaptic protective mechanism via TRPC3 inhibition was further supported by hippocampal RNA-seq data from the symptomatic 5xFAD mice after chronic treatment with JW-65. Overall, these findings not only validate TRPC3 as a novel therapeutic target for treating synaptic dysfunction of AD but most importantly, disclose a distinct role of upregulated TRPC3 in AD pathogenesis in mediating Ca 2+ dyshomeostasis.

Functionalized nanoparticles to deliver nucleic acids to the brain for the treatment of Alzheimer's disease

Brain-targeted gene delivery across the blood-brain barrier (BBB) is a significant challenge in the 21st century for the healthcare sector, particularly in developing an effective treatment strategy against Alzheimer's disease (AD). The Internal architecture of the brain capillary endothelium restricts bio-actives entry into the brain. Additionally, therapy with nucleic acids faces challenges like vulnerability to degradation by nucleases and potential immune responses. Functionalized nanocarrier-based gene delivery approaches have resulted in safe and effective platforms. These nanoparticles (NPs) have demonstrated efficacy in protecting nucleic acids from degradation, enhancing transport across the BBB, increasing bioavailability, prolonging circulation time, and regulating gene expression of key proteins involved in AD pathology. We provided a detailed review of several nanocarriers and targeting ligands such as cell-penetrating peptides (CPPs), endogenous proteins, and antibodies. The utilization of functionalized NPs extends beyond a singular system, serving as a versatile platform for customization in related neurodegenerative diseases. Only a few numbers of bioactive regimens can go through the BBB. Thus, exploring functionalized NPs for brain-targeted gene delivery is of utmost necessity. Currently, genes are considered high therapeutic potential molecules for altering any disease-causing gene. Through surface modification, nanoparticulate systems can be tailored to address various diseases by replacing the target-specific molecule on their surface. This review article presents several nanoparticulate delivery systems, such as lipid NPs, polymeric micelles, exosomes, and polymeric NPs, for nucleic acids delivery to the brain and the functionalization strategies explored in AD research.

Calcium and Neural Stem Cell Proliferation

Intracellular calcium plays a pivotal role in central nervous system (CNS) development by regulating various processes such as cell proliferation, migration, differentiation, and maturation. However, understanding the involvement of calcium (Ca2+) in these processes during CNS development is challenging due to the dynamic nature of this cation and the evolving cell populations during development. While Ca2+ transient patterns have been observed in specific cell processes and molecules responsible for Ca2+ homeostasis have been identified in excitable and non-excitable cells, further research into Ca2+ dynamics and the underlying mechanisms in neural stem cells (NSCs) is required. This review focuses on molecules involved in Ca2+ entrance expressed in NSCs in vivo and in vitro, which are crucial for Ca2+ dynamics and signaling. It also discusses how these molecules might play a key role in balancing cell proliferation for self-renewal or promoting differentiation. These processes are finely regulated in a time-dependent manner throughout brain development, influenced by extrinsic and intrinsic factors that directly or indirectly modulate Ca2+ dynamics. Furthermore, this review addresses the potential implications of understanding Ca2+ dynamics in NSCs for treating neurological disorders. Despite significant progress in this field, unraveling the elements contributing to Ca2+ intracellular dynamics in cell proliferation remains a challenging puzzle that requires further investigation.

Pathophysiological Roles of Transient Receptor Potential (Trp) Channels and Zinc Toxicity in Brain Disease

Maintaining the correct ionic gradient from extracellular to intracellular space via several membrane-bound transporters is critical for maintaining overall cellular homeostasis. One of these transporters is the transient receptor potential (TRP) channel family that consists of six putative transmembrane segments systemically expressed in mammalian tissues. Upon the activation of TRP channels by brain disease, several cations are translocated through TRP channels. Brain disease, especially ischemic stroke, epilepsy, and traumatic brain injury, triggers the dysregulation of ionic gradients and promotes the excessive release of neuro-transmitters and zinc. The divalent metal cation zinc is highly distributed in the brain and is specifically located in the pre-synaptic vesicles as free ions, usually existing in cytoplasm bound with metallothionein. Although adequate zinc is essential for regulating diverse physiological functions, the brain-disease-induced excessive release and translocation of zinc causes cell damage, including oxidative stress, apoptotic cascades, and disturbances in energy metabolism. Therefore, the regulation of zinc homeostasis following brain disease is critical for the prevention of brain damage. In this review, we summarize recent experimental research findings regarding how TRP channels (mainly TRPC and TRPM) and zinc are regulated in animal brain-disease models of global cerebral ischemia, epilepsy, and traumatic brain injury. The blockade of zinc translocation via the inhibition of TRPC and TRPM channels using known channel antagonists, was shown to be neuroprotective in brain disease. The regulation of both zinc and TRP channels may serve as targets for treating and preventing neuronal death.

Transient receptor potential cation channel 6 (TRPC6) deficiency leads to increased body weight and metabolic dysfunction

TRPC6, a member of the TRPC family, is expressed in the hypothalamus and modulates cell Ca²⁺ influx. However, the role of TRPC6 in controlling metabolic and cardiovascular functions under normal conditions has not been previously determined. Thus, the impacts of TRPC6 deletion on energy balance, metabolic and cardiovascular regulation as well as the anorexic responses to leptin and melanocortin 3/4 receptor (MC3/4R) activation were investigated in this study. Extensive cardiometabolic phenotyping was conducted in male and female TRPC6 knock out (KO) and control mice from 6 to 24 weeks of age to assess mechanisms by which TRPC6 influences regulation of energy balance and blood pressure (BP). We found that TRPC6 KO mice are heavier with greater adiposity, hyperphagic, and have reduced energy expenditure, impaired glucose tolerance, hyperinsulinemia, and increased liver fat compared to controls. TRPC6 KO mice also have smaller brains, reduced POMC mRNA levels in the hypothalamus, and impaired anorexic response to leptin but not to MC3/4R activation. BP and heart rate, assessed by telemetry, were similar in TRPC6 KO and control mice, and BP responses to air-jet stress were attenuated in TRPC6 KO mice despite increased body weight and metabolic disorders that normally raise BP and increase BP responses to stress. Our results provide evidence for a novel and important role of TRPC6 in controlling energy balance, adiposity, and glucose homeostasis, which suggests that normal TRPC6 function may be necessary to link weight gain and hyperleptinemia with BP responses to acute stress.

Novel localizations of TRPC5 channels suggest novel and unexplored roles: A study in the chick embryo brain

Mammalian TRPC5 channels are predominantly expressed in the brain, where they increase intracellular Ca²⁺ and induce depolarization. Because they augment presynaptic vesicle release, cause persistent neural activity, and show constitutive activity, TRPC5s could play a functional role in late developmental brain events. We used immunohistochemistry to examine TRPC5 in the chick embryo brain between 8 and 20 days of incubation, and provide the first detailed description of their distribution in birds and in the whole brain of any animal species. Stained areas substantially increased between E8 and E16, and staining intensity in many areas peaked at E16, a time when chick brains first show organized patterns of whole-brain metabolic activation like what is seen consistently after hatching. Areas showing cell soma staining match areas showing Trpc5 mRNA or protein in adult rodents (cerebral cortex, hippocampus, amygdala, cerebellar Purkinje cells). Chick embryos show protein staining in the optic tectum, cerebellar nuclei, and several brainstem nuclei; equivalent areas in the Allen Institute mouse maps express Trpc5 mRNA. The strongest cell soma staining was found in a dorsal hypothalamic area (matching a group of parvicellular arginine vasotocin neurons and a pallial amygdalohypothalamic cell corridor) and the vagal motor complex. Purkinje cells showed strong dendritic staining at E20. Unexpectedly, we also describe neurite staining in the septum, several hypothalamic nuclei, and a paramedian raphe area; the strongest neurite staining was in the median eminence. These novel localizations suggest new unexplored TRPC5 functions, and possible roles in late embryonic brain development.

AAV Delivery of shRNA Against TRPC6 in Mouse Hippocampus Impairs Cognitive Function

Transient Receptor Potential Canonical 6 (TRPC6) has been suggested to be involved in synapse function and contribute to hippocampal-dependent cognitive processes. Gene silencing of TRPC6 was performed by injecting adeno-associated virus (AAV) expressing TRPC6-specific shRNA (shRNA-TRPC6) into the hippocampal dentate gyrus (DG). Spatial learning, working memory and social recognition memory were impaired in the shRNA-TRPC6 treated mice compared to control mice after 4 weeks. In addition, gene ontology (GO) analysis of RNA-sequencing revealed that viral intervention of TRPC6 expression in DG resulted in the enrichment of the process of synaptic transmission and cellular compartment of synaptic structure. KEGG analysis showed PI3K-Akt signaling pathway were significantly down-regulated. Furthermore, the shRNA-TRPC6 treatment reduced dendritic spines of DG granule neurons, in terms of spine loss, the thin and mushroom types predominated. Accompanying the spine loss, the levels of PSD95, pAkt and CREB in the hippocampus were decreased in the shRNA-TRPC6 treated animals. Taken together, our results suggest that knocking down TRPC6 in the DG have a disadvantageous effect on cognitive processes.

Novel Mechanistic Insights and Potential Therapeutic Impact of TRPC6 in Neurovascular Coupling and Ischemic Stroke

Ischemic stroke is one of the most disabling diseases and a leading cause of death globally. Despite advances in medical care, the global burden of stroke continues to grow, as no effective treatments to limit or reverse ischemic injury to the brain are available. However, recent preclinical findings have revealed the potential role of transient receptor potential cation 6 (TRPC6) channels as endogenous protectors of neuronal tissue. Activating TRPC6 in various cerebral ischemia models has been found to prevent neuronal death, whereas blocking TRPC6 enhances sensitivity to ischemia. Evidence has shown that Ca2+ influx through TRPC6 activates the cAMP (adenosine 3',5'-cyclic monophosphate) response element-binding protein (CREB), an important transcription factor linked to neuronal survival. Additionally, TRPC6 activation may counter excitotoxic damage resulting from glutamate release by attenuating the activity of N-methyl-d-aspartate (NMDA) receptors of neurons by posttranslational means. Unresolved though, are the roles of TRPC6 channels in non-neuronal cells, such as astrocytes and endothelial cells. Moreover, TRPC6 channels may have detrimental effects on the blood-brain barrier, although their exact role in neurovascular coupling requires further investigation. This review discusses evidence-based cell-specific aspects of TRPC6 in the brain to assess the potential targets for ischemic stroke management.

Probing the therapeutic potential of TRPC6 for Alzheimer's disease in live neurons from patient-specific iPSCs

The induced pluripotent stem cells (iPSCs) offer an unprecedented opportunity to model and study Alzheimer's disease (AD) under patient-specific genetic background. The lower expression of transient receptor potential canonical 6 (TRPC6) was associated with AD patients, which might be involved in AD pathogenesis. However, the role of TRPC6 that played in AD process still needs more investigation in patient-relevant neurons. In this study, the iPSCs were generated from peripheral blood cells of sporadic AD patients and efficiently differentiated into mature cortical neurons. These sporadic AD-bearing neurons displayed higher levels of AD pathological markers Aβ and phospho-tau, but lower levels of TRPC6, than those of control neurons. Treatment of AD neurons with TRPC6 protein fragment or agonist inhibited the elevation of Aβ and phospho-tau. Our results in live AD neurons manifest that the compromised expression of TRPC6 substantially contributed to Aβ pathology of sporadic AD, suggesting that targeting TRPC6 could help to develop novel therapeutic strategies for the treatments of AD.

Transcriptomic Profiling of Ca2+ Transport Systems During the Formation of the Cerebral Cortex in Mice

Cytosolic calcium (Ca²⁺) transients control key neural processes, including neurogenesis, migration, the polarization and growth of neurons, and the establishment and maintenance of synaptic connections. They are thus involved in the development and formation of the neural system. In this study, a publicly available whole transcriptome sequencing (RNA-Seq) dataset was used to examine the expression of genes coding for putative plasma membrane and organellar Ca²⁺-transporting proteins (channels, pumps, exchangers, and transporters) during the formation of the cerebral cortex in mice. Four ages were considered: embryonic days 11 (E11), 13 (E13), and 17 (E17), and post-natal day 1 (PN1). This transcriptomic profiling was also combined with live-cell Ca²⁺ imaging recordings to assess the presence of functional Ca²⁺ transport systems in E13 neurons. The most important Ca²⁺ routes of the cortical wall at the onset of corticogenesis (E11–E13) were TACAN, GluK5, nAChR β2, Cav3.1, Orai3, transient receptor potential cation channel subfamily M member 7 (TRPM7) non-mitochondrial Na⁺/Ca²⁺ exchanger 2 (NCX2), and the connexins CX43/CX45/CX37. Hence, transient receptor potential cation channel mucolipin subfamily member 1 (TRPML1), transmembrane protein 165 (TMEM165), and Ca²⁺ “leak” channels are prominent intracellular Ca²⁺ pathways. The Ca²⁺ pumps sarco/endoplasmic reticulum Ca²⁺ ATPase 2 (SERCA2) and plasma membrane Ca²⁺ ATPase 1 (PMCA1) control the resting basal Ca²⁺ levels. At the end of neurogenesis (E17 and onward), a more numerous and diverse population of Ca²⁺ uptake systems was observed. In addition to the actors listed above, prominent Ca²⁺-conducting systems of the cortical wall emerged, including acid-sensing ion channel 1 (ASIC1), Orai2, P2X2, and GluN1. Altogether, this study provides a detailed view of the pattern of expression of the main actors participating in the import, export, and release of Ca²⁺. This work can serve as a framework for further functional and mechanistic studies on Ca²⁺ signaling during cerebral cortex formation.

How TRPC Channels Modulate Hippocampal Function

Transient receptor potential canonical (TRPC) proteins constitute a group of receptor-operated calcium-permeable nonselective cationic membrane channels of the TRP superfamily. They are largely expressed in the hippocampus and are able to modulate neuronal functions. Accordingly, they have been involved in different hippocampal functions such as learning processes and different types of memories, as well as hippocampal dysfunctions such as seizures. This review covers the mechanisms of activation of these channels, how these channels can modulate neuronal excitability, in particular the after-burst hyperpolarization, and in the persistent activity, how they control synaptic plasticity including pre- and postsynaptic processes and how they can interfere with cell survival and neurogenesis.

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.

TRPC1 Regulates the Activity of a Voltage-Dependent Nonselective Cation Current in Hippocampal CA1 Neurons

The cation channel subunit TRPC1 is strongly expressed in central neurons including neurons in the CA1 region of the hippocampus where it forms complexes with TRPC4 and TRPC5. To investigate the functional role of TRPC1 in these neurons and in channel function, we compared current responses to group I metabotropic glutamate receptor (mGluR I) activation and looked for major differences in dendritic morphology in neurons from TRPC1^+/+ and TRPC1^-/- mice. mGluR I stimulation resulted in the activation of a voltage-dependent nonselective cation current in both genotypes. Deletion of TRPC1 resulted in a modification of the shape of the current-voltage relationship, leading to an inward current increase. In current clamp recordings, the percentage of neurons that responded to depolarization in the presence of an mGluR I agonist with a plateau potential was increased in TRPC1^-/- mice. There was also a small increase in the minor population of CA1 neurons that have more than one apical dendrite in TRPC1^-/- mice. We conclude that TRPC1 has an inhibitory effect on receptor-operated nonselective cation channels in hippocampal CA1 neurons probably as a result of heterotetramer formation with other TRPC isoforms, and that TRPC1 deletion has only minor effects on dendritic morphology.

Activation of TRPC1 Channel by Metabotropic Glutamate Receptor mGluR5 Modulates Synaptic Plasticity and Spatial Working Memory

Group I metabotropic glutamate receptors, in particular mGluR5, have been implicated in various forms of synaptic plasticity that are believed to underlie declarative memory. We observed that mGluR5 specifically activated a channel containing TRPC1, an isoform of the canonical family of transient receptor potential (TRPC) channels highly expressed in CA1-3 regions of the hippocampus. TRPC1 is able to form tetrameric complexes with TRPC4 and/or TRPC5 isoforms. TRPC1/4/5 complexes have recently been involved in the efficiency of synaptic transmission in the hippocampus. We therefore used a mouse model devoid of TRPC1 expression to investigate the involvement of mGluR5-TRPC1 pathway in synaptic plasticity and memory formation. Trpc1^-/- mice showed alterations in spatial working memory and fear conditioning. Activation of mGluR increased synaptic excitability in neurons from WT but not from Trpc1^-/- mice. LTP triggered by a theta burst could not maintain over time in brain slices from Trpc1^-/- mice. mGluR-induced LTD was also impaired in these mice. Finally, acute inhibition of TRPC1 by Pico145 on isolated neurons or on brain slices mimicked the genetic depletion of Trpc1 and inhibited mGluR-induced entry of cations and subsequent effects on synaptic plasticity, excluding developmental or compensatory mechanisms in Trpc1^-/- mice. In summary, our results indicate that TRPC1 plays a role in synaptic plasticity and spatial working memory processes.

TRPC1 is required for survival and proliferation of cochlear spiral ganglion stem/progenitor cells

OBJECTIVE

The present studies were designed to test the hypothesis that canonical transient receptor potential channel 1 (TRPC1) is required for the proliferation of cochlear spiral ganglion stem/progenitor cells (SPCs).

METHODS AND MATERIALS

TRPC1 were detected and evaluated in postnatal day 1 CBA/CaJ mice pups derived-cochlear spiral ganglion SPCs by reverse transcription-polymerase chain reaction, Western blot, immunocytochemistry, and calcium imaging. The cell viability and proliferation of the spiral ganglion SPCs following si-RNA mediated knockdown of TRPC1 or addition of TRPC channel blocker SKF9635 were compared to controls.

RESULTS

In spiral ganglion SPCs, TRPC1 was found to be the most abundantly expressed TRPC subunit and shown to contribute to store-operated calcium entry. Silencing of TRPC1 or addition of TRPC channel blockers significantly decreased the rate of cell proliferation.

CONCLUSION

The results suggest that TRPC1 might serve as an essential molecule in regulating the proliferation of spiral ganglion SPCs.

TRPC6 specifically interacts with APP to inhibit its cleavage by γ-secretase and reduce Aβ production

Generation of β-amyloid (Aβ) peptide in Alzheimer's disease involves cleavage of amyloid precursor protein (APP) by γ-secretase, a protease known to cleave several substrates, including Notch. Finding specific modulators for γ-secretase could be a potential avenue to treat the disease. Here, we report that transient receptor potential canonical (TRPC) 6 specifically interacts with APP leading to inhibition of its cleavage by γ-secretase and reduction in Aβ production. TRPC6 interacts with APP (C99), but not with Notch, and prevents C99 interaction with presenilin 1 (PS1). A fusion peptide derived from TRPC6 also reduces Aβ levels without effect on Notch cleavage. Crossing APP/PS1 mice with TRPC6 transgenic mice leads to a marked reduction in both plaque load and Aβ levels, and improvement in structural and behavioural impairment. Thus, TRPC6 specifically modulates γ-secretase cleavage of APP and preventing APP (C99) interaction with PS1 via TRPC6 could be a novel strategy to reduce Aβ formation.

Attempts to treat Alzheimer's disease by targeting γ-secretase cleavage of APP into Aß have been unsuccessful, partially due to off-target effects. Here, the authors identify TRPC6 as a novel γ-secretase modulator, showing that it interacts with APP to regulate Aß levels while sparing Notch cleavage.

Modeling non-syndromic autism and the impact of TRPC6 disruption in human neurons

An increasing number of genetic variants have been implicated in autism spectrum disorders (ASDs), and the functional study of such variants will be critical for the elucidation of autism pathophysiology. Here, we report a de novo balanced translocation disruption of TRPC6, a cation channel, in a non-syndromic autistic individual. Using multiple models, such as dental pulp cells, induced pluripotent stem cell (iPSC)-derived neuronal cells and mouse models, we demonstrate that TRPC6 reduction or haploinsufficiency leads to altered neuronal development, morphology and function. The observed neuronal phenotypes could then be rescued by TRPC6 complementation and by treatment with insulin-like growth factor-1 or hyperforin, a TRPC6-specific agonist, suggesting that ASD individuals with alterations in this pathway may benefit from these drugs. We also demonstrate that methyl CpG binding protein-2 (MeCP2) levels affect TRPC6 expression. Mutations in MeCP2 cause Rett syndrome, revealing common pathways among ASDs. Genetic sequencing of TRPC6 in 1041 ASD individuals and 2872 controls revealed significantly more nonsynonymous mutations in the ASD population, and identified loss-of-function mutations with incomplete penetrance in two patients. Taken together, these findings suggest that TRPC6 is a novel predisposing gene for ASD that may act in a multiple-hit model. This is the first study to use iPSC-derived human neurons to model non-syndromic ASD and illustrate the potential of modeling genetically complex sporadic diseases using such cells.

The involvement of medial septum 5-HT1 and 5-HT2 receptors on ACPA-induced memory consolidation deficit: possible role of TRPC3, TRPC6 and TRPV2

The present study evaluates the roles of serotonergic receptors of the medial septum on amnesia induced by arachidonylcyclopropylamide (ACPA; as selective cannabinoid CB1 receptor agonist) in adult male Wistar rats. Cannulae were implanted in the medial septum of the brain of the rats. The animals were trained in a passive avoidance learning apparatus, and were tested 24 hours after training for step-through latency. Results indicated that post-training medial septum administration of CP94253 (5-HT1B/1D receptor agonist) and cinancerine (as 5-HT2 receptor antagonist) reduced the step-through latency showing an amnesic response, while GR127935 (5-HT1B/1D receptor antagonist) and αm5htm (as 5-HT2A/2B/2D receptor agonist) did not alter memory consolidation by themselves. On continuing the test, the results showed that CP94253 increased and GR127935 did not alter ACPA (0.02 µg/rat)-induced memory impairment, respectively. Other data indicated that αm5htm induced a modulatory effect, while cinancerine restored ACPA-induced amnesia. Using SKF-96365 (inhibitor of transient receptor potential TRPC3/6 and TRPV2 channels) demonstrated that TRPC3, TRPC3 and TRPV2 channels have a significant role, according to our results.

The Na+/K+-ATPase and the amyloid-beta peptide aβ1-40 control the cellular distribution, abundance and activity of TRPC6 channels

The Na(+)/K(+)-ATPase interacts with the non-selective cation channels TRPC6 but the functional consequences of this association are unknown. Experiments performed with HEK cells over-expressing TRPC6 channels showed that inhibiting the activity of the Na(+)/K(+)-ATPase with ouabain reduced the amount of TRPC6 proteins and depressed Ca(2+) entry through TRPC6. This effect, not mimicked by membrane depolarization with KCl, was abolished by sucrose and bafilomycin-A, and was partially sensitive to the intracellular Ca(2+) chelator BAPTA/AM. Biotinylation and subcellular fractionation experiments showed that ouabain caused a multifaceted redistribution of TRPC6 to the plasma membrane and to an endo/lysosomal compartment where they were degraded. The amyloid beta peptide Aβ(1-40), another inhibitor of the Na(+)/K(+)-ATPase, but not the shorter peptide Aβ1-16, reduced TRPC6 protein levels and depressed TRPC6-mediated responses. In cortical neurons from embryonic mice, ouabain, veratridine (an opener of voltage-gated Na(+) channel), and Aβ(1-40) reduced TRPC6-mediated Ca(2+) responses whereas Aβ(1-16) was ineffective. Furthermore, when Aβ(1-40) was co-added together with zinc acetate it could no longer control TRPC6 activity. Altogether, this work shows the existence of a functional coupling between the Na(+)/K(+)-ATPase and TRPC6. It also suggests that the abundance, distribution and activity of TRPC6 can be regulated by cardiotonic steroids like ouabain and the naturally occurring peptide Aβ(1-40) which underlines the pathophysiological significance of these processes.

Ca(2+) signaling initiated by canonical transient receptor potential channels in dendritic development

The spatial patterns of dendritic structures diverge in different types of neurons as adaptations to their unique functions. Although different intracellular mechanisms underlying dendritic morphogenesis have been suggested, it is evident that the elevation in intracellular Ca(2+) levels plays a major role in the process. Canonical transient receptor potential (TRPC) channels, known to be non-selective Ca(2+)-permeable cation channels, act as environmental detectors to sense and transduce extracellular signals into different intracellular responses, including the regulation of dendritic growth, via Ca(2+) influx. Here, we review recent advances in the understanding of Ca(2+) signaling, especially signals mediated by Ca(2+) influx via TRPC channels, and the underlying molecular events in dendritic development.

Transient receptor potential channels and their role in modulating radial glial-neuronal interaction: a signaling pathway involving mGluR5

The guidance of developing neurons to the right position in the central nervous system is of central importance in brain development. Canonical transient receptor potential (TRPC) channels are thought to mediate turning responses of growth cones to guidance cues through fine control of calcium transients. Proliferating and 1- to 5-day-differentiated neural progenitor cells (NPCs) showed expression of Trpc1 and Trpc3 mRNA, while Trpc4-7 was not clearly detected. Time-lapse imaging showed that the motility pattern of neuronal cells was phasic with bursts of rapid movement (>60 μm/h), changes in direction, and intermittent slow phases or stallings (<40 μm/h), which frequently occurred in close contact with radial glial processes. Genetic interference with the TRPC3 and TRPC1 channel enhanced the motility of NPCs (burst frequency/stalling frequency). TRPC3-deficient cells or cells treated with the TRPC3 blocker pyr3 infrequently changed direction and seldom contacted radial glial processes. TRPC channels are also activated by group I metabotropic glutamate receptors (mGluR1 and mGluR5). As shown here, pyr3 blocked the calcium response mediated through mGluR5 in radial glial processes. Furthermore, 2-methyl-6-(phenylethynyl)pyridine, a blocker of mGluR5, affected the motility pattern in a similar way as TRPC3/6 double knockout or pyr3. The results suggest that radial glial cells exert attractant signals to migrating neuronal cells, which alter their motility pattern. Our results suggest that mGluR5 acting through TRPC3 is of central importance in radial glial-mediated neuronal guidance.

Transient receptor potential channels as drug targets: from the science of basic research to the art of medicine

The large Trp gene family encodes transient receptor potential (TRP) proteins that form novel cation-selective ion channels. In mammals, 28 Trp channel genes have been identified. TRP proteins exhibit diverse permeation and gating properties and are involved in a plethora of physiologic functions with a strong impact on cellular sensing and signaling pathways. Indeed, mutations in human genes encoding TRP channels, the so-called "TRP channelopathies," are responsible for a number of hereditary diseases that affect the musculoskeletal, cardiovascular, genitourinary, and nervous systems. This review gives an overview of the functional properties of mammalian TRP channels, describes their roles in acquired and hereditary diseases, and discusses their potential as drug targets for therapeutic intervention.

TRPC6: physiological function and pathophysiological relevance

TRPC6 is a non-selective cation channel 6 times more permeable to Ca(2+) than to Na(+). Channel homotetramers heterologously expressed have a characteristic doubly rectifying current-voltage relationship and are directly activated by the second messenger diacylglycerol (DAG). TRPC6 proteins are also regulated by specific tyrosine or serine phosphorylation and phosphoinositides. Given its specific expression pattern, TRPC6 is likely to play a number of physiological roles which are confirmed by the analysis of a Trpc6 (-/-) mouse model. In smooth muscle Na(+) influx through TRPC6 channels and activation of voltage-gated Ca(2+) channels by membrane depolarisation is the driving force for contraction. Permeability of pulmonary endothelial cells depends on TRPC6 and induces ischaemia-reperfusion oedema formation in the lungs. TRPC6 was also identified as an essential component of the slit diaphragm architecture of kidney podocytes and plays an important role in the protection of neurons after cerebral ischaemia. Other functions especially in immune and blood cells remain elusive. Recently identified TRPC6 blockers may be helpful for therapeutic approaches in diseases with highly activated TRPC6 channel activity.

Phylogeny and expression of canonical transient receptor potential (TRPC) genes in developing zebrafish

BACKGROUND

Canonical transient receptor potential (TRPC) channels are nonselective, calcium-permeable cation channels that are expressed in a great variety of organisms, tissues, and cell types. TRPC channels are known to be involved in the transduction of polymodal sensory input. Additionally, they are implicated in a variety of developmental processes. Distinct gating mechanisms have been elucidated so far, but their exact functional role in vertebrate organisms still needs to be resolved.

RESULTS

We now used the teleost Danio rerio to perform a comprehensive expression analysis of the trpc gene subfamily. Based on the sequence homology to the seven described mammalian TRPC channels, we identified 12 trpc genes in the zebrafish genome. All but trpc1 and trpc3 are represented by two paralogs. We further describe the specific expression patterns of trpc transcripts in whole-mounts during the first 5 days of development.

CONCLUSIONS

Consistent with their proposed role in sensory transduction zebrafish trpcs are predominantly expressed in neural structures such as the olfactory, visual, mechanosensitive, and motor systems. Intriguingly, zebrafish paralogs show mainly nonoverlapping expression patterns, suggesting that duplicated genes have either split their functions or have adapted new ones.

Effect of glutamate receptor antagonists on migrating neural progenitor cells

Neurotransmitters such as glutamate are potential regulators of neurogenesis. Interference with defined glutamate receptor subtypes affects proliferation, migration and differentiation of neural progenitor cells. The cellular targets for the actions of different glutamate receptor ligands are less well known. In this study we have combined calcium imaging, measurement of membrane potential, time-lapse imaging and immunocytochemistry to obtain a spatial overview of migrating mouse embryonic neural progenitor cell-derived cells responding to glutamate receptor agonists and antagonists. Responses via metabotropic glutamate receptor 5 correlated with radial glial cells and dominated in the inner migration zones close to the neurosphere. Block of metabotropic glutamate receptor 5 resulted in shorter radial glial processes, a transient increase in neuron-like cells emerging from the neurosphere and increased motility of neuron-like cells. α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptors are present on the majority of migrating neuronal cells, which with time accumulate at the outer edge of the migration zone. Blocking these receptors leads to an enhanced extension of radial glial processes and a reduced motility of neuron-like cells. Our results indicate that functional glutamate receptors have profound effects on the motility of neural progenitor cells. The main target for metabotropic glutamate receptor 5 appears to be radial glial cells while AMPA/kainate receptors are mainly expressed in newborn neuronal cells and regulate the migratory progress of these cells. The results suggest that both metabotropic glutamate receptor 5 and AMPA/kainate receptors are of importance for the guidance of migrating embryonic progenitor cells.

Effects of a non-selective TRPC channel blocker, SKF-96365, on melittin-induced spontaneous persistent nociception and inflammatory pain hypersensitivity

OBJECTIVE

Melittin is the main peptide in bee venom and causes both persistent spontaneous nociception and pain hypersensitivity. Our recent studies indicated that both transient receptor potential (TRP) vanilloid receptor 1 (TRPV1) and canonical TRPs (TRPCs) are involved in mediating the melittin-induced activation of different subpopulations of primary nociceptive cells. Here, we further determined whether TRPC channels are involved in melittin-induced inflammatory nociceptive responses in behavioral assays.

METHODS

The anti-nociceptive and anti-hyperalgesic effects of localized peripheral administration of three doses of the non-selective TRPC antagonist, SKF-96365 (1-{β-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenyl}-1H-imidazole hydrochloride), were evaluated in melittin tests. Pain-related behaviors were rated by counting the number of paw flinches, and measuring paw withdrawal thermal latency (s) and paw withdrawl mechanical threshold (g), over a 1-h time-course.

RESULTS

Localized peripheral SKF-96365 given before melittin prevented, and given after melittin significantly suppressed, the melittin-evoked persistent spontaneous nociception. Pre-blockade and post-suppression of activation of primary nociceptive activity resulted in decreased hypersensitivity to both thermal and mechanical stimuli applied to the primary injury site of the ipsilateral hindpaw, despite dose-effect differences between thermal and mechanical hyperalgesia. However, local administration of SKF-96365 into the contralateral hindpaw had no significant effect on any pain-associated behaviors. In addition, SKF-96365 had no effect on baseline threshold for either thermal or mechanical sensitivity under normal conditions.

CONCLUSION

Besides TRPV1, SKF-96365-sensitive TRPC channels might also be involved in the pathophysiological processing of melittin-induced inflammatory pain and hypersensitivity. Therapeutically, SKF-96365 is equally effective in preventing primary thermal and mechanical hyperalgesia as well as persistent spontaneous nociception. However, this drug is likely to be more effective in the relief of thermal hyperalgesia than mechanical hyperalgesia when applied 5 min after establishment of primary afferent activation.

TRPC6: an underlying target for human glaucoma

Glaucoma is one of the leading causes of visual impairment and blindness worldwide. Of known risk factors for glaucoma, an increased in intraocular pressure is most highly correlated with glaucomatous damage. Irrespective of the cause, apoptosis of the retinal ganglion cells is the eventual outcome. It is widely accepted that glaucoma is a neurodegenerative disease that is strongly correlated with central nervous system disorders, such as Alzheimer's disease. These two disorders also share some similarities in pathogenic mechanisms. Recent studies suggest that the transient receptor potential canonical 6 channel could work together with brain-derived neurotrophic factor to promote neuron survival in brain and retina. In this study, we propose that transient receptor potential canonical 6 may contribute to the pathogenesis of human glaucoma and become a potential therapeutic target.

Mechanoregulation of cytoskeletal dynamics by TRP channels

The ability of cells to respond to mechanical stimulation is crucial to a variety of biological processes, including cell migration, axonal outgrowth, perception of pain, cardiovascular responses and kidney physiology. The translation of mechanical cues into cellular responses, a process known as mechanotransduction, typically takes place in specialized multiprotein structures such as cilia, cell-cell or cell-matrix adhesions. Within these structures, mechanical forces such as shear stress and membrane stretch activate mechanosensitive proteins, which set off a series of events that lead to altered cell behavior. Members of the transient receptor potential (TRP) family of cation channels are emerging as important players in mechanotransductory pathways. Localized within mechanosensory structures, they are activated by mechanical stimuli and trigger fast as well as sustained cytoskeletal responses. In this review, we will provide an overview of how TRP channels affect cytoskeletal dynamics in various mechano-regulated processes.

Mechanisms controlling neurite outgrowth in a pheochromocytoma cell line: the role of TRPC channels

Transient Receptor Potential Canonical (TRPC) channels are implicated in modulating neurite outgrowth. The expression pattern of TRPCs changes significantly during brain development, suggesting that fine-tuning TRPC expression may be important for orchestrating neuritogenesis. To study how alterations in the TRPC expression pattern affect neurite outgrowth, we used nerve growth factor (NGF)-differentiated rat pheochromocytoma 12 (PC12) cells, a model system for neuritogenesis. In PC12 cells, NGF markedly up-regulated TRPC1 and TRPC6 expression, but down-regulated TRPC5 expression while promoting neurite outgrowth. Overexpression of TRPC1 augmented, whereas TRPC5 overexpression decelerated NGF-induced neurite outgrowth. Conversely, shRNA-mediated knockdown of TRPC1 decreased, whereas shRNA-mediated knockdown of TRPC5 increased NGF-induced neurite extension. Endogenous TRPC1 attenuated the anti-neuritogenic effect of overexpressed TRPC5 in part by forming the heteromeric TRPC1-TRPC5 channels. Previous reports suggested that TRPC6 may facilitate neurite outgrowth. However, we found that TRPC6 overexpression slowed down neuritogenesis, whereas dominant negative TRPC6 (DN-TRPC6) facilitated neurite outgrowth in NGF-differentiated PC12 cells. Consistent with these findings, hyperforin, a neurite outgrowth promoting factor, decreased TRPC6 expression in NGF-differentiated PC12 cells. Using pharmacological and molecular biological approaches, we determined that NGF up-regulated TRPC1 and TRPC6 expression via a p75(NTR)-IKK(2)-dependent pathway that did not involve TrkA receptor signaling in PC12 cells. Similarly, NGF up-regulated TRPC1 and TRPC6 via an IKK(2) dependent pathway in primary cultured hippocampal neurons. Thus, our data suggest that a balance of TRPC1, TRPC5, and TRPC6 expression determines neurite extension rate in neural cells, with TRPC6 emerging as an NGF-dependent "molecular damper" maintaining a submaximal velocity of neurite extension.

TRPs in the Brain

The Transient receptor potential (TRP) family of cation channels is a large protein family, which is mainly structurally uniform. Proteins consist typically of six transmembrane domains and mostly four subunits are necessary to form a functional channel. Apart from this, TRP channels display a wide variety of activation mechanisms (ligand binding, G-protein coupled receptor dependent, physical stimuli such as temperature, pressure, etc.) and ion selectivity profiles (from highly Ca(2+) selective to non-selective for cations). They have been described now in almost every tissue of the body, including peripheral and central neurons. Especially in the sensory nervous system the role of several TRP channels is already described on a detailed level. This review summarizes data that is currently available on their role in the central nervous system. TRP channels are involved in neurogenesis and brain development, synaptic transmission and they play a key role in the development of several neurological diseases.

Lack of kinase regulation of canonical transient receptor potential 3 (TRPC3) channel-dependent currents in cerebellar Purkinje cells

Canonical transient receptor potential (TRPC) channels are widely expressed in the brain and play several roles in development and normal neuronal function. In the cerebellum, Purkinje cell TRPC3 channels underlie the slow excitatory postsynaptic potential observed after parallel fiber stimulation. In these cells TRPC3 channel opening requires stimulation of metabotropic glutamate receptor 1, activation of which can also lead to the induction of long term depression (LTD), which underlies cerebellar motor learning. LTD induction requires protein kinase C (PKC) and protein kinase G (PKG) activation, and although PKC phosphorylation targets are well established, virtually nothing is known about PKG targets in LTD. Because TRPC3 channels are inhibited after phosphorylation by PKC and PKG in expression systems, we examined whether native TRPC3 channels in Purkinje cells are a target for PKG or PKC, thereby contributing to cerebellar LTD. We find that in Purkinje cells, activation of TRPC3-dependent currents is not inhibited by conventional PKC or PKG to any significant extent and that inhibition of these kinases does not significantly impact on TRPC3-mediated currents either. Based on these and previous findings, we propose that TRPC3-dependent currents may differ significantly in their regulation from those overexpressed in expression systems.

TRPC channels are involved in calcium-dependent migration and proliferation in immortalized GnRH neurons

Gonadotropin-releasing hormone (GnRH)-secreting neurons are key regulators of the reproductive behaviour in vertebrates. These neurons show a peculiar migratory pattern during embryonic development, and its perturbations have profound impact on fertility and other related functional aspects. Changes in the intracellular calcium concentration, [Ca(2+)](i), induced by different extracellular signals, play a central role in the control of neuronal migration, but the available knowledge regarding GnRH neurons is still limited. Our goal was to investigate mechanisms that may be involved in the Ca(2+) dependence of the migratory behaviour in these neurons. We focused on the "classical" Transient Receptor Potential (TRPC) subfamily of Ca(2+)-permeable cation channels, recently shown to be involved in other aspects of neuronal development. Using GN11 cells, immortalized early stage GnRH neurons, we set to investigate Ca(2+) signals under basal conditions and in the presence of a well-established motogen, fetal calf serum (FCS), and the effect of pharmacological TRPC agonists and antagonists on Ca(2+) oscillations, cell motility and proliferation. We have found that a subpopulation of GN11 cells shows spontaneous Ca(2+) transients and that this activity is increased in the presence of serum. Quantitative real-time PCR showed that transcripts of some TRPC members are expressed in GN11 cells. Interestingly, pharmacological experiments with inhibitors, SKF-96365, lanthanum, anti-TRPC1 antibody, and activators, 1-oleil 2-acetyl-sn-glycerol, of TRPCs suggested that the activation of these channels can account for both the basal Ca(2+) oscillations and the increased activity in the presence of FCS. Moreover, functional studies using the same pharmacological tools supported their involvement in the control of motility and proliferation. Thus, our data provide evidence for the involvement of Ca(2+)-permeable channels of the TRPC subfamily in the control of functional properties of neurosecretory cells and neuronal motility.

Intrinsic phototransduction persists in melanopsin-expressing ganglion cells lacking diacylglycerol-sensitive TRPC subunits

In mammals, intrinsically photosensitive retinal ganglion cells (ipRGCs) mediate various non-image-forming photic responses, such as circadian photoentrainment, pupillary light reflex and pineal melatonin suppression. ipRGCs directly respond to environmental light by activation of the photopigment melanopsin followed by the opening of an unidentified cation-selective channel. Studies in heterologous expression systems and in the native retina have strongly implicated diacylglycerol-sensitive transient receptor potential channels containing TRPC3, TRPC6 and TRPC7 subunits in melanopsin-evoked depolarization. Here we show that melanopsin-evoked electrical responses largely persist in ipRGCs recorded from early postnatal (P6-P8) and adult (P22-P50) mice lacking expression of functional TRPC3, TRPC6 or TRPC7 subunits. Multielectrode array (MEA) recordings performed at P6-P8 stages under conditions that prevent influences from rod/cone photoreceptors show comparable light sensitivity for the melanopsin-evoked responses in these mutant mouse lines in comparison to wild-type (WT) mice. Patch-clamp recordings from adult mouse ipRGCs lacking TRPC3 or TRPC7 subunits show intrinsic light-evoked responses equivalent to those recorded in WT mice. Persistence of intrinsic light-evoked responses was also noted in ipRGCs lacking TRPC6 subunits, although with significantly smaller magnitudes. These results demonstrate that the melanopsin-evoked depolarization in ipRGCs is not mediated by either TRPC3, TRPC6 or TRPC7 channel subunits alone. They also suggest that the melanopsin signaling pathway includes TRPC6-containing heteromeric channels in mature retinas.

No association between the KCNH1, KCNJ10 and KCNN3 genes and schizophrenia in the Han Chinese population

Schizophrenia is a common severe mental illness affecting 0.3-2.0% of the world's population. The potassium channels are thought to have a role in modulating electrical excitability in neurons, regulating calcium signaling in oligodendrocytes and regulating action potential duration in presynaptic terminals and GABA release. Previous studies have reported that some potassium channel genes might be candidate genes for susceptibility to schizophrenia. In the present study, we chose three potassium channel genes, KCNH1, KCNJ10, KCNN3 to investigate the role of potassium channels in schizophrenia by genotyping 23 SNPs (9 in KCNH1, 5 in KCNJ10 and 9 in KCNN3) in a Han Chinese sample consisting of 893 schizophrenia patients and 611 healthy controls. No significant difference in allelic or genotypic frequency was revealed between schizophrenia patients and healthy individuals. Nor was a significant difference in haplotypic distribution detected. MDR analysis revealed no gene-gene interaction within the three potassium channel genes. Our study suggests that the 23 SNPs within the three potassium genes we examined do not play a major role in schizophrenia in the Han Chinese population.

Evidence for a supportive role of classical transient receptor potential 6 (TRPC6) in the exploration behavior of mice

Non-selective classical transient receptor potential (TRPC) cation channels share important roles in processes of neuronal development and function. To test the influence of TRPC6 activity on behavior, we developed a TRPC6-deficient (TRPC6(-/-)) mouse model in a BALB/c genetic background. Both, TRPC6(-/-) and wild-type (WT) mice were analyzed first for their general health and reflex status (modified SHIRPA protocol) and then in three different behavioral tests (marble-burying test, square open field and elevated star maze). No abnormalities were detected in the SHIRPA protocol. Most interestingly, TRPC6(-/-) mice showed no significant differences in anxiety in a marble-burying test, but demonstrated reduced exploration in the square open field and the elevated star maze. Therefore, TRPC6 channel activity may play a yet unknown role for exploration behavior.

A transient receptor potential channel regulates basal ganglia output

The substantia nigra pars reticulata (SNr) is a key basal ganglia output nucleus critical for movement control. A hallmark of the SNr gamma-aminobutyric acid (GABA)-containing projection neurons is their depolarized membrane potential, accompanied by rapid spontaneous spikes. Parkinsonian movement disorders are often associated with abnormalities in SNr GABA neuron firing intensity and/or pattern. A fundamental question is the molecular identity of the ion channels that drive these neurons to a depolarized membrane potential. Recent data show that SNr GABA projection neurons selectively express type 3 canonical transient receptor potential (TRPC3) channels. Such channels are tonically active and mediate an inward, Na(+)-dependent current, leading to a substantial depolarization and ensuring appropriate firing intensity and pattern in SNr GABA projection neurons. Equally important, TRPC3 channels in SNr GABA neurons are up-regulated by dopamine (DA) released from neighboring nigral DA neuron dendrites. Co-activation of D1 and D5 DA receptors leads to a TRPC3 channel-mediated inward current and increased firing in SNr GABA neurons, whereas D1-like receptor blockade reduces SNr GABA neuron firing frequency and increases their firing irregularity. TRPC3 channels serve as the effector channels mediating an ultra-short SNc-->SNr DA pathway that regulates the firing intensity and pattern of the basal ganglia output neurons.

Essential role of TRPC6 channels in G2/M phase transition and development of human glioma

BACKGROUND

Patients with glioblastoma multiforme, the most aggressive form of glioma, have a median survival of approximately 12 months. Calcium (Ca(2+)) signaling plays an important role in cell proliferation, and some members of the Ca(2+)-permeable transient receptor potential canonical (TRPC) family of channel proteins have demonstrated a role in the proliferation of many types of cancer cells. In this study, we investigated the role of TRPC6 in cell cycle progression and in the development of human glioma.

METHODS

TRPC6 protein and mRNA expression were assessed in glioma (n = 33) and normal (n = 17) brain tissues from patients and in human glioma cell lines U251, U87, and T98G. Activation of TRPC6 channels was tested by platelet-derived growth factor-induced Ca(2+) imaging. The effect of inhibiting TRPC6 activity or expression using the dominant-negative mutant TRPC6 (DNC6) or RNA interference, respectively, was tested on cell growth, cell cycle progression, radiosensitization of glioma cells, and development of xenografted human gliomas in a mouse model. The green fluorescent protein (GFP) and wild-type TRPC6 (WTC6) were used as controls. Survival of mice bearing xenografted tumors in the GFP, DNC6, and WTC6 groups (n = 13, 15, and 13, respectively) was compared using Kaplan-Meier analysis. All statistical tests were two-sided.

RESULTS

Functional TRPC6 was overexpressed in human glioma cells. Inhibition of TRPC6 activity or expression attenuated the increase in intracellular Ca(2+) by platelet-derived growth factor, suppressed cell growth and clonogenic ability, induced cell cycle arrest at the G2/M phase, and enhanced the antiproliferative effect of ionizing radiation. Cyclin-dependent kinase 1 activation and cell division cycle 25 homolog C expression regulated the cell cycle arrest. Inhibition of TRPC6 activity also reduced tumor volume in a subcutaneous mouse model of xenografted human tumors (P = .014 vs GFP; P < .001 vs WTC6) and increased mean survival in mice in an intracranial model (P < .001 vs GFP or WTC6).

CONCLUSIONS

In this preclinical model, TRPC6 channels were essential for glioma development via regulation of G2/M phase transition. This study suggests that TRPC6 might be a new target for therapeutic intervention of human glioma.

Diversity of lysophosphatidic acid receptor-mediated intracellular calcium signaling in early cortical neurogenesis

Lysophosphatidic acid (LPA) is a membrane-derived lysophospholipid that can induce pleomorphic effects in neural progenitor cells (NPCs) from the cerebral cortex, including alterations in ionic conductance. LPA-induced, calcium-mediated conductance changes have been reported; however, the underlying molecular mechanisms have not been determined. We show here that activation of specific cognate receptors accounts for nearly all intracellular calcium responses evoked by LPA in acutely cultured nestin-positive NPCs from the developing mouse cerebral cortex. Fast-onset changes in intracellular calcium levels required release from thapsigargin-sensitive stores by a pertussis toxin-insensitive mechanism. The influx of extracellular calcium through Cd(2+)/Ni(2+)-insensitive influx pathways, approximately one-half of which were Gd(3+) sensitive, contributed to the temporal diversity of responses. Quantitative reverse transcription-PCR revealed the presence of all five known LPA receptors in primary NPCs, with prominent expression of LPA(1), LPA(2), and LPA(4). Combined genetic and pharmacological studies indicated that NPC responses were mediated by LPA(1) (approximately 30% of the cells), LPA(2) (approximately 30%), a combination of receptors on single cells (approximately 30%), and non-LPA(1,2,3) pathways (approximately 10%). LPA responsivity was significantly reduced in more differentiated TuJ1(+) cells within cultures. Calcium transients in a large proportion of LPA-responsive NPCs were also initiated by the closely related signaling lipid S1P (sphingosine-1-phosphate). These data demonstrate for the first time the involvement of LPA receptors in mediating surprisingly diverse NPC calcium responses involving multiple receptor subtypes that function within a single cell. Compared with other known factors, lysophospholipids represent the major activator of calcium signaling identified within NPCs at this early stage in corticogenesis.

TRPC channels and their implication in neurological diseases

Calcium is an essential intracellular messenger and serves critical cellular functions in both excitable and non-excitable cells. Most of the physiological functions in these cells are uniquely regulated by changes in cytosolic Ca2+ levels ([Ca2+](i)), which are achieved via various mechanisms. One of these mechanism(s) is activated by the release of Ca2+ from the endoplasmic reticulum (ER), followed by Ca2+ influx across the plasma membrane (PM). Activation of PM Ca2+ channel is essential for not only refilling of the ER Ca2+ stores, but is also critical for maintaining [Ca2+](i) that regulates biological functions, such as neurosecretion, sensation, long term potentiation, synaptic plasticity, gene regulation, as well as cellular growth and differentiation. Alterations in Ca2+ homeostasis have been suggested in the onset/progression of neurological diseases, such as Parkinson's, Alzheimer's, bipolar disorder, and Huntington's. Available data on transient receptor potential conical (TRPC) protein indicate that these proteins initiate Ca2+ entry pathways and are essential in maintaining cytosolic, ER, and mitochondrial Ca2+ levels. A number of biological functions have been assigned to these TRPC proteins. Silencing of TRPC1 and TRPC3 has been shown to inhibit neuronal proliferation and loss of TRPC1 is implicated in neurodegeneration. Thus, TRPC channels not only contribute towards normal physiological processes, but are also implicated in several human pathological conditions. Overall, it is suggested that these channels could be used as potential therapeutic targets for many of these neurological diseases. Thus, in this review we have focused on the functional implication of TRPC channels in neuronal cells along with the elucidation of their role in neurodegeneration.

The puzzling role of TRPC3 channels in motor coordination

Transient receptor potential canonical 3 (TRPC3) proteins are nonselective cation channels activated downstream of phospholipase-C-coupled receptors. TRPC3 channels have emerged as major players in the function of the central nervous system. They have been described as important contributors to brain-derived neurotrophic factor mediated survival and growth-cone guidance of cerebellar granule neurons. TRPC3 were also identified as postsynaptic cation channels essential for metabotropic glutamate receptor1-dependent synaptic transmission in cerebellar Purkinje neurons. A recent report described motor coordination defects in TRPC3 knockout mice while a subsequent study reported a similar phenotype in so-called moonwalker mice, harboring a TRPC3 gain-of-function mutation. How can opposing aspects of TRPC3 channel activation lead to the same phenotype? Here we discuss the salient features of TRPC3 knockout mice and moonwalker mice and attempt to reconcile the apparently conflicting findings from these two animal models.