Transient receptor potential canonical (TRPC) 4 and TRPC5 channels are modulated by the Gαq-PLC pathway. Since phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) maintains TRPC4 and TRPC5 channel function, the Gαq-PLC pathway inhibits channel activity by depleting PI(4,5)P2. Here we investigated the difference in PI(4,5)P2 sensitivity between homomeric and heteromeric TRPC channels. First, by using a Danio rerio voltage-sensing phosphatase (DrVSP), we show that PI(4,5)P2 dephosphorylation robustly inhibits TRPC4α, TRPC4β, and TRPC5 homotetramer currents and also TRPC1/4α, TRPC1/4β, and TRPC1/5 heterotetramer currents. Secondly, sensitivity of channels to PI(4,5)P2 dephosphorylation was suggested through the usage of FRET in combination with patch clamping. The sensitivity increased in the sequence TRPC4β < TRPC4α < TRPC5 in homotetramers, whereas when forming heterotetramers with TRPC1, the sensitivity was approximately equal between the channels. Thirdly, we determined putative PI(4,5)P2 binding sites based on a TRPC4 prediction model. By neutralization of basic residues, we identified putative PI(4,5)P2 binding sites because the mutations reduced FRET to a PI(4,5)P2 sensor and reduced the current amplitude. Therefore, one functional TRPC4 has 8 pockets with the two main binding regions; K419, K664/R511, K518, H630. We conclude that TRPC1 channel function as a regulator in setting PI(4,5)P2 affinity for TRPC4 and TRPC5 that changes PI(4,5)P2 sensitivity.

The development of treatment for neurodegenerative diseases (NDs) such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis is facing medical challenges due to the increasingly aging population. However, some pharmaceutical companies have ceased the development of therapeutics for NDs, and no new treatments for NDs have been established during the last decade. The relationship between ND pathogenesis and risk factors has not been completely elucidated. Herein, we review the potential involvement of transient receptor potential (TRP) channels in NDs, where oxidative stress and disrupted Ca 2+ homeostasis consequently lead to neuronal apoptosis. Reactive oxygen species (ROS) -sensitive TRP channels can be key risk factors as polymodal sensors, since progressive late onset with secondary pathological damage after initial toxic insult is one of the typical characteristics of NDs. Recent evidence indicates that the dysregulation of TRP channels is a missing link between disruption of Ca 2+ homeostasis and neuronal loss in NDs. In this review, we discuss the latest findings regarding TRP channels to provide insights into the research and quests for alternative therapeutic candidates for NDs. As the structures of TRP channels have recently been revealed by cryo-electron microscopy, it is necessary to develop new TRP channel antagonists and reevaluate existing drugs.

Transient receptor potential (TRP) channels are a superfamily of Ca2+-permeable cation channels that translate cellular stimuli into electrochemical signals. Aberrant activity of TRP channels has been implicated in a variety of human diseases, such as neurological disorders, cardiovascular disease and cancer. To facilitate the understanding of the molecular network by which TRP channels are associated with biological and disease processes, we have developed the TRIP (TRansient receptor potential channel-Interacting Protein) Database (http://www.trpchannel.org), a manually curated database that aims to offer comprehensive information on protein–protein interactions (PPIs) of mammalian TRP channels. The TRIP Database was created by systematically curating 277 peer-reviewed literature; the current version documents 490 PPI pairs, 28 TRP channels and 297 cellular proteins. The TRIP Database provides a detailed summary of PPI data that fit into four categories: screening, validation, characterization and functional consequence. Users can find in-depth information specified in the literature on relevant analytical methods and experimental resources, such as gene constructs and cell/tissue types. The TRIP Database has user-friendly web interfaces with helpful features, including a search engine, an interaction map and a function for cross-referencing useful external databases. Our TRIP Database will provide a valuable tool to assist in understanding the molecular regulatory network of TRP channels.

Transient receptor potential canonical (TRPC) 4 channels are calcium-permeable, nonselective cation channels and are widely expressed in mammalian tissue, especially in the GI tract and brain. TRPC4 channels are known to be involved in neurogenic contraction of ileal smooth muscle cells via generating cationic current after muscarinic stimulation (muscarinic cationic current (mIcat)). Polyamines exist in numerous tissues and are believed to be involved in cell proliferation, differentiation, scar formation, wound healing, and carcinogenesis. Besides, physiological polyamines are essential to maintain inward rectification of cardiac potassium channels (Kir2.1). At membrane potentials more positive than equilibrium potential, intracellular polyamines plug the cytosolic surface of the Kir2.1 so that potassium ions cannot pass through the pore. Recently, it was reported that polyamines inhibit not only cardiac potassium channels but also nonselective cation channels that mediate the generation of mIcat. Here, we report that TRPC4, a definite mIcat mediator, is inhibited by intracellular spermine with great extent. The inhibition was specific to TRPC4 and TRPC5 channels but was not effective to TRPC1/4, TRPC1/5, and TRPC3 channels. For this inhibition to occur, we found that glutamates at 728th and 729th position of TRPC4 channels are essential whereby we conclude that spermine blocks the TRPC4 channel with electrostatic interaction between negative amino acids at the C-terminus of the channel.