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

TRPC channels: Structure, function, regulation and recent advances in small molecular probes

Transient receptor potential canonical (TRPC) channels constitute a group of receptor-operated calcium-permeable nonselective cation channels of the TRP superfamily. The seven mammalian TRPC members, which can be further divided into four subgroups (TRPC1, TRPC2, TRPC4/5, and TRPC3/6/7) based on their amino acid sequences and functional similarities, contribute to a broad spectrum of cellular functions and physiological roles. Studies have revealed complexity of their regulation involving several components of the phospholipase C pathway, G_i and G_o proteins, and internal Ca²⁺ stores. Recent advances in cryogenic electron microscopy have provided several high-resolution structures of TRPC channels. Growing evidence demonstrates the involvement of TRPC channels in diseases, particularly the link between genetic mutations of TRPC6 and familial focal segmental glomerulosclerosis. Because TRPCs were discovered by the molecular identity first, their pharmacology had lagged behind. This is rapidly changing in recent years owning to great efforts from both academia and industry. A number of potent tool compounds from both synthetic and natural products that selective target different subtypes of TRPC channels have been discovered, including some preclinical drug candidates. This review will cover recent advancements in the understanding of TRPC channel regulation, structure, and discovery of novel TRPC small molecular probes over the past few years, with the goal of facilitating drug discovery for the study of TRPCs and therapeutic development.

RNA-Sequencing Analyses Demonstrate the Involvement of Canonical Transient Receptor Potential Channels in Rat Tooth Germ Development

Tooth development depends on multiple molecular interactions between the dental epithelium and mesenchyme, which are derived from ectodermal and ectomesenchymal cells, respectively. We report on a systematic RNA sequencing analysis of transcriptional expression levels from the bud to hard tissue formation stages of rat tooth germ development. We found that GNAO1, ENO1, EFNB1, CALM1, SIAH2, ATP6V0A1, KDELR2, GTPBP1, POLR2C, SORT1, and members of the canonical transient receptor potential (TRPC) channel family are involved in tooth germ development. Furthermore, Cell Counting Kit 8 (CCK8) and Transwell migration assays were performed to explore the effects of these differentially expressed genes (DEGs) on the proliferation and migration of dental pulp stem cells. Immunostaining revealed that TRPC channels are expressed at varying levels during odontogenesis. The identified genes represent novel candidates that are likely to be vital for rat tooth germ development. Together, the results provide a valuable resource to elucidate the gene regulatory mechanisms underlying mammalian tooth germ development.

Characterization of Rebound Depolarization in Neurons of the Rat Medial Geniculate Body In Vitro

Rebound depolarization (RD) is a response to the offset from hyperpolarization of the neuronal membrane potential and is an important mechanism for the synaptic processing of inhibitory signals. In the present study, we characterized RD in neurons of the rat medial geniculate body (MGB), a nucleus of the auditory thalamus, using whole-cell patch-clamp and brain slices. RD was proportional in strength to the duration and magnitude of the hyperpolarization; was effectively blocked by Ni(2+) or Mibefradil; and was depressed when the resting membrane potential was hyperpolarized by blocking hyperpolarization-activated cyclic nucleotide-gated (HCN) channels with ZD7288 or by activating G-protein-gated inwardly-rectifying K(+) (GIRK) channels with baclofen. Our results demonstrated that RD in MGB neurons, which is carried by T-type Ca(2+) channels, is critically regulated by HCN channels and likely by GIRK channels.

Screening of Transient Receptor Potential Canonical Channel Activators Identifies Novel Neurotrophic Piperazine Compounds

Transient receptor potential canonical (TRPC) proteins form Ca(2+)-permeable cation channels activated upon stimulation of metabotropic receptors coupled to phospholipase C. Among the TRPC subfamily, TRPC3 and TRPC6 channels activated directly by diacylglycerol (DAG) play important roles in brain-derived neurotrophic factor (BDNF) signaling, promoting neuronal development and survival. In various disease models, BDNF restores neurologic deficits, but its therapeutic potential is limited by its poor pharmacokinetic profile. Elucidation of a framework for designing small molecules, which elicit BDNF-like activity via TRPC3 and TRPC6, establishes a solid basis to overcome this limitation. We discovered, through library screening, a group of piperazine-derived compounds that activate DAG-activated TRPC3/TRPC6/TRPC7 channels. The compounds [4-(5-chloro-2-methylphenyl)piperazin-1-yl](3-fluorophenyl)methanone (PPZ1) and 2-[4-(2,3-dimethylphenyl)piperazin-1-yl]-N-(2-ethoxyphenyl)acetamide (PPZ2) activated, in a dose-dependent manner, recombinant TRPC3/TRPC6/TRPC7 channels, but not other TRPCs, in human embryonic kidney cells. PPZ2 activated native TRPC6-like channels in smooth muscle cells isolated from rabbit portal vein. Also, PPZ2 evoked cation currents and Ca(2+) influx in rat cultured central neurons. Strikingly, both compounds induced BDNF-like neurite growth and neuroprotection, which were abolished by a knockdown or inhibition of TRPC3/TRPC6/TRPC7 in cultured neurons. Inhibitors of Ca(2+) signaling pathways, except calcineurin, impaired neurite outgrowth promotion induced by PPZ compounds. PPZ2 increased activation of the Ca(2+)-dependent transcription factor, cAMP response element-binding protein. These findings suggest that Ca(2+) signaling mediated by activation of DAG-activated TRPC channels underlies neurotrophic effects of PPZ compounds. Thus, piperazine-derived activators of DAG-activated TRPC channels provide important insights for future development of a new class of synthetic neurotrophic drugs.