TRPC5 controls the adrenaline-mediated counter regulation of hypoglycemia

Hypoglycemia triggers autonomic and endocrine counter-regulatory responses to restore glucose homeostasis, a response that is impaired in patients with diabetes and its long-term complication hypoglycemia-associated autonomic failure (HAAF). We show that insulin-evoked hypoglycemia is severely aggravated in mice lacking the cation channel proteins TRPC1, TRPC4, TRPC5, and TRPC6, which cannot be explained by alterations in glucagon or glucocorticoid action. By using various TRPC compound knockout mouse lines, we pinpointed the failure in sympathetic counter-regulation to the lack of the TRPC5 channel subtype in adrenal chromaffin cells, which prevents proper adrenaline rise in blood plasma. Using electrophysiological analyses, we delineate a previously unknown signaling pathway in which stimulation of PAC1 or muscarinic receptors activates TRPC5 channels in a phospholipase-C-dependent manner to induce sustained adrenaline secretion as a crucial step in the sympathetic counter response to insulin-induced hypoglycemia. By comparing metabolites in the plasma, we identified reduced taurine levels after hypoglycemia induction as a commonality in TRPC5-deficient mice and HAAF patients.

BTDAzo: A Photoswitchable TRPC5 Channel Activator

Photoswitchable reagents can be powerful tools for high-precision biological control. TRPC5 is a Ca2+ -permeable cation channel with distinct tissue-specific roles, from synaptic function to hormone regulation. Reagents giving spatiotemporally-resolved control over TRPC5 activity may be key to understanding and harnessing its biology. Here we develop the first photoswitchable TRPC5-modulator, BTDAzo, to address this goal. BTDAzo can photocontrol TRPC5 currents in cell culture, as well as controlling endogenous TRPC5-based neuronal Ca2+ responses in mouse brain slices. BTDAzos are also the first reported azo-benzothiadiazines, an accessible and conveniently derivatised azoheteroarene with strong two-colour photoswitching. BTDAzo's ability to control TRPC5 across relevant channel biology settings makes it suitable for a range of dynamically reversible photoswitching studies in TRP channel biology, with the aim to decipher the various biological roles of this centrally important ion channel.

Schwarzinicine A inhibits transient receptor potential canonical channels and exhibits overt vasorelaxation effects

This study investigated the vasorelaxant effects of schwarzinicine A, an alkaloid recently reported from Ficus schwarzii Koord. Regulation of calcium homeostasis in vascular smooth muscle cells (VSMC) is viewed as one of the main mechanisms for controlling blood pressure. L‐type voltage‐gated calcium channel (VGCC) blockers are commonly used for controlling hypertension. Recently, the transient receptor potential canonical (TRPC) channels were found in blood vessels of different animal species with evidence of their roles in the regulation of vascular contractility. In this study, we studied the mechanism of actions of schwarzinicine A focusing on its regulation of L‐type VGCC and TRPC channels. Schwarzinicine A exhibited the highest vasorelaxant effect (123.1%) compared to other calcium channel blockers. It also overtly attenuated calcium‐induced contractions of the rat isolated aortae in a calcium‐free environment showing its mechanism to inhibit calcium influx. Fluorometric intracellular calcium recordings confirmed its inhibition of hTRPC3‐, hTRPC4‐, hTRPC5‐ and hTRPC6‐mediated calcium influx into HEK cells with IC₅₀ values of 3, 17, 19 and 7 μM, respectively. The evidence gathered in this study suggests that schwarzinicine A blocks multiple TRPC channels and L‐type VGCC to exert a significant vascular relaxation response.

Nonselective TRPC channel inhibition and suppression of aminoglycoside-induced premature termination codon readthrough by the small molecule AC1903

Nonsense mutations, which occur in ∼11% of patients with genetic disorders, introduce premature termination codons (PTCs) that lead to truncated proteins and promote nonsense-mediated mRNA decay. Aminoglycosides such as G418 permit PTC readthrough and so may be used to address this problem. However, their effects are variable between patients, making clinical use of aminoglycosides challenging. In this study, we tested whether TRPC nonselective cation channels contribute to the variable PTC readthrough effect of aminoglycosides by controlling their cellular uptake. Indeed, a recently reported selective TRPC5 inhibitor, AC1903, consistently suppressed G418 uptake and G418-induced PTC readthrough in the DMS-114 cancer cell line and junctional epidermolysis bullosa (JEB) patient-derived keratinocytes. Interestingly, the effect of AC1903 in DMS-114 cells was mimicked by nonselective TRPC inhibitors, but not by well-characterized inhibitors of TRPC1/4/5 (Pico145, GFB-8438) or TRPC3/6/7 (SAR7334), suggesting that AC1903 may work through additional or undefined targets. Indeed, in our experiments, AC1903 inhibited multiple TRPC channels including TRPC3, TRPC4, TRPC5, TRPC6, TRPC4-C1, and TRPC5-C1, as well as endogenous TRPC1:C4 channels in A498 renal cancer cells, all with low micromolar IC50 values (1.8-18 μM). We also show that AC1903 inhibited TRPV4 channels, but had weak or no effects on TRPV1 and no effect on the nonselective cation channel PIEZO1. Our study reveals that AC1903 has previously unrecognized targets, which need to be considered when interpreting results from experiments with this compound. In addition, our data strengthen the hypothesis that nonselective calcium channels are involved in aminoglycoside uptake.

Pharmacology of TRPC Channels and Its Potential in Cardiovascular and Metabolic Medicine

Transient receptor potential canonical (TRPC) proteins assemble to form homo- or heterotetrameric, nonselective cation channels permeable to K⁺, Na⁺, and Ca²⁺. TRPC channels are thought to act as complex integrators of physical and chemical environmental stimuli. Although the understanding of essential physiological roles of TRPC channels is incomplete, their implication in various pathological mechanisms and conditions of the nervous system, kidneys, and cardiovascular system in combination with the lack of major adverse effects of TRPC knockout or TRPC channel inhibition is driving the search of TRPC channel modulators as potential therapeutics. Here, we review the most promising small-molecule TRPC channel modulators, the understanding of their mode of action, and their potential in the study and treatment of cardiovascular and metabolic disease.

Role of Store-Operated Ca2+ Entry in the Pulmonary Vascular Remodeling Occurring in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a severe and multifactorial disease. PAH pathogenesis mostly involves pulmonary arterial endothelial and pulmonary arterial smooth muscle cell (PASMC) dysfunction, leading to alterations in pulmonary arterial tone and distal pulmonary vessel obstruction and remodeling. Unfortunately, current PAH therapies are not curative, and therapeutic approaches mostly target endothelial dysfunction, while PASMC dysfunction is under investigation. In PAH, modifications in intracellular Ca2+ homoeostasis could partly explain PASMC dysfunction. One of the most crucial actors regulating Ca2+ homeostasis is store-operated Ca2+ channels, which mediate store-operated Ca2+ entry (SOCE). This review focuses on the main actors of SOCE in human and experimental PASMC, their contribution to PAH pathogenesis, and their therapeutic potential in PAH.

DogCatcher allows loop-friendly protein-protein ligation

There are many efficient ways to connect proteins at termini. However, connecting at a loop is difficult because of lower flexibility and variable environment. Here, we have developed DogCatcher, a protein that forms a spontaneous isopeptide bond with DogTag peptide. DogTag/DogCatcher was generated initially by splitting a Streptococcus pneumoniae adhesin. We optimized DogTag/DogCatcher through rational design and evolution, increasing reaction rate by 250-fold and establishing millimolar solubility of DogCatcher. When fused to a protein terminus, DogTag/DogCatcher reacts slower than SpyTag003/SpyCatcher003. However, inserted in loops of a fluorescent protein or enzyme, DogTag reacts much faster than SpyTag003. Like many membrane proteins, the ion channel TRPC5 has no surface-exposed termini. DogTag in a TRPC5 extracellular loop allowed normal calcium flux and specific covalent labeling on cells in 1 min. DogTag/DogCatcher reacts under diverse conditions, at nanomolar concentrations, and to 98% conversion. Loop-friendly ligation should expand the toolbox for creating protein architectures.

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Spontaneous transamidation at internal sites harnessing a DogTag/DogCatcher pair

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DogCatcher is designed and bred for high solubility and rapid reaction

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Within protein loops DogTag can clamp on its partner faster than SpyTag003

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Fast and faithful fluorescent labeling of an ion channel at the cell surface via DogTag

Human TRPC5 structures reveal interaction of a xanthine-based TRPC1/4/5 inhibitor with a conserved lipid binding site

TRPC1/4/5 channels are non-specific cation channels implicated in a wide variety of diseases, and TRPC1/4/5 inhibitors have recently entered clinical trials. However, fundamental and translational studies require a better understanding of TRPC1/4/5 channel regulation by endogenous and exogenous factors. Although several potent and selective TRPC1/4/5 modulators have been reported, the paucity of mechanistic insights into their modes-of-action remains a barrier to the development of new chemical probes and drug candidates. Xanthine-based modulators include the most potent and selective TRPC1/4/5 inhibitors described to date, as well as TRPC5 activators. Our previous studies suggest that xanthines interact with a, so far, elusive pocket of TRPC1/4/5 channels that is essential to channel gating. Here we report the structure of a small-molecule-bound TRPC1/4/5 channel-human TRPC5 in complex with the xanthine Pico145-to 3.0 Å. We found that Pico145 binds to a conserved lipid binding site of TRPC5, where it displaces a bound phospholipid. Our findings explain the mode-of-action of xanthine-based TRPC1/4/5 modulators, and suggest a structural basis for TRPC1/4/5 modulation by endogenous factors such as (phospho)lipids and Zn2+ ions. These studies lay the foundations for the structure-based design of new generations of TRPC1/4/5 modulators.