Analysis of TRPC3-interacting proteins by tandem mass spectrometry

Enhanced TRPC3 transcription through AT1R/PKA/CREB signaling contributes to mitochondrial dysfunction in renal tubular epithelial cells in D-galactose-induced accelerated aging mice

Aging-associated renal dysfunction promotes the pathogenesis of chronic kidney disease. Mitochondrial dysfunction in renal tubular epithelial cells is a hallmark of senescence and leads to accelerated progression of renal disorders. Dysregulated calcium profiles in mitochondria contribute to aging-associated disorders, but the detailed mechanism of this process is not clear. In this study, modulation of the sirtuin 1/angiotensin II type 1 receptor (Sirt1/AT1R) pathway partially attenuated renal glomerular sclerosis, tubular atrophy, and interstitial fibrosis in D-galactose (D-gal)-induced accelerated aging mice. Moreover, modulation of the Sirt1/AT1R pathway improved mitochondrial dysfunction induced by D-gal treatment. Transient receptor potential channel, subtype C, member 3 (TRPC3) upregulation mediated dysregulated cellular and mitochondrial calcium homeostasis during aging. Furthermore, knockdown or knockout (KO) of Trpc3 in mice ameliorated D-gal-induced mitochondrial reactive oxygen species production, membrane potential deterioration, and energy metabolism disorder. Mechanistically, activation of the AT1R/PKA pathway promoted CREB phosphorylation and nucleation of CRE2 binding to the Trpc3 promoter (-1659 to -1648 bp) to enhance transcription. Trpc3 KO significantly improved the renal disorder and cell senescence in D-gal-induced mice. Taken together, these results indicate that TRPC3 upregulation mediates age-related renal disorder and is associated with mitochondrial calcium overload and dysfunction. TRPC3 is a promising therapeutic target for aging-associated renal disorders.

The rapid activation of cPKCβII by progesterone results in the negative regulation of Ca 2+ influx in human resting T cells

BACKGROUND

Progesterone-stimulated rapid suppression of phytohemagglutinin (PHA)-activated sustained membrane Ca 2+ influx is revealed by Mn 2+ quenching fura-2 fluorescence. Ca 2+ influx suppression results in immunosuppression of T-cell proliferation. Downregulation of protein kinase C (PKC) activity by phorbol 12-myristate 13-acetate (PMA) enhances the PHA-activated increase in sustained intracellular Ca 2+ concentration ([Ca 2+ ] i ) via Ca 2+ influx in T cells. Conventional PKC (cPKC) inhibitors also enhance the [Ca 2+ ] i increase in resting T cells caused by progesterone. This study explores whether cPKC activation by progesterone results in suppression of Ca 2+ influx in resting T cells.

METHODS

Progesterone, its analogs (R5020/Org OD 02-0), and plasma membrane-impermeable progesterone-bovine serum albumin conjugate were used to stimulate human resting T cells. Inhibitors and PKC downregulation by PMA were used to investigate whether cPKC affects Ca 2+ influx.

RESULTS

Progesterone and analogs dose-dependently suppressed Ca 2+ influx in T cells. One cPKC inhibitor, Ro318220, attenuated Ca 2+ influx suppression, and enhanced the increase in [Ca 2+ ] i caused by progesterone and analogs. U73122 did not affect Ca 2+ influx suppression but did decrease the [Ca 2+ ] i increase. Ca 2+ influx suppression was not attenuated by the cPKCα/βI isoform-selective inhibitor, Go6976, nevertheless, a cPKCβI/βII isoform-selective inhibitor, LY333531 did. Ca 2+ influx suppression was attenuated by the cPKCβII-specific inhibitor CGP53353. After PKC downregulated by PMA, Ca 2+ influx suppression by progesterone and analogs was almost abolished in parallel with a massive reduction in cPKCβII expression. This suggests cPKCβII activation by progesterone and analogs mediate Ca 2+ influx suppression in resting T cells.

CONCLUSION

Nongenomic membrane activation of cPKCβII by progesterone causes immunosuppression via negative regulation of Ca 2+ influx into human resting T cells. This prevents resting T-cell activation and proliferation, which protects the fetus from maternal immune attack while decreasing maternal autoimmune disease flare-ups during pregnancy. Thus, cPKCβII modulators might provide a new therapeutic approach to balancing T-cell tolerance and immunity.

Mitochondrial Calcium: Effects of Its Imbalance in Disease

Calcium is used in many cellular processes and is maintained within the cell as free calcium at low concentrations (approximately 100 nM), compared with extracellular (millimolar) concentrations, to avoid adverse effects such as phosphate precipitation. For this reason, cells have adapted buffering strategies by compartmentalizing calcium into mitochondria and the endoplasmic reticulum (ER). In mitochondria, the calcium concentration is in the millimolar range, as it is in the ER. Mitochondria actively contribute to buffering cellular calcium, but if matrix calcium increases beyond physiological demands, it can promote the opening of the mitochondrial permeability transition pore (mPTP) and, consequently, trigger apoptotic or necrotic cell death. The pathophysiological implications of mPTP opening in ischemia-reperfusion, liver, muscle, and lysosomal storage diseases, as well as those affecting the central nervous system, for example, Parkinson’s disease (PD), Alzheimer’s disease (AD), Huntington’s disease (HD), and amyotrophic lateral sclerosis (ALS) have been reported. In this review, we present an updated overview of the main cellular mechanisms of mitochondrial calcium regulation. We specially focus on neurodegenerative diseases related to imbalances in calcium homeostasis and summarize some proposed therapies studied to attenuate these diseases.

Photopharmacology and opto-chemogenetics of TRPC channels-some therapeutic visions

Non-selective cation conductances formed by transient receptor potential canonical (TRPC) proteins govern the function and fate of a wide range of human cell types. In the past decade, evidence has accumulated for a pivotal role of these channels in human diseases, raising substantial interest in their therapeutic targeting. As yet, an appreciable number of small molecules for block and modulation of recombinant TRPC conductances have been identified. However, groundbreaking progress in TRPC pharmacology towards therapeutic applications is lagging behind due to incomplete understanding of their molecular pharmacology and their exact role in disease. A major breakthrough that is expected to overcome these hurdles is the recent success in obtaining high-resolution structure information on TRPC channel complexes and the advent of TRP photopharmacology and optogenetics. Here, we summarize current concepts of enhancing the precision of therapeutic interference with TRPC signaling and TRPC-mediated pathological processes.

Assembly of ER-PM Junctions: A Critical Determinant in the Regulation of SOCE and TRPC1

Store-operated calcium entry (SOCE), a unique plasma membrane Ca²⁺ entry mechanism, is activated when ER-[Ca²⁺] is decreased. SOCE is mediated via the primary channel, Orai1, as well as others such as TRPC1. STIM1 and STIM2 are ER-Ca²⁺ sensor proteins that regulate Orai1 and TRPC1. SOCE requires assembly of STIM proteins with the plasma membrane channels which occurs within distinct regions in the cell that have been termed as endoplasmic reticulum (ER)-plasma membrane (PM) junctions. The PM and ER are in close proximity to each other within this region, which allows STIM1 in the ER to interact with and activate either Orai1 or TRPC1 in the plasma membrane. Activation and regulation of SOCE involves dynamic assembly of various components that are involved in mediating Ca²⁺ entry as well as those that determine the formation and stabilization of the junctions. These components include proteins in the cytosol, ER and PM, as well as lipids in the PM. Recent studies have also suggested that SOCE and its components are compartmentalized within ER-PM junctions and that this process might require remodeling of the plasma membrane lipids and reorganization of structural and scaffolding proteins. Such compartmentalization leads to the generation of spatially- and temporally-controlled Ca²⁺signals that are critical for regulating many downstream cellular functions.

Activation of endothelial transient receptor potential C3 channel is required for small conductance calcium-activated potassium channel activation and sustained endothelial hyperpolarization and vasodilation of cerebral artery

Background

Transient receptor potential C3 (TRPC3) has been demonstrated to be involved in the regulation of vascular tone through endothelial cell (EC) hyperpolarization and endothelium‐dependent hyperpolarization–mediated vasodilation. However, the mechanism by which TRPC3 regulates these processes remains unresolved. We tested the hypothesis that endothelial receptor stimulation triggers rapid TRPC3 trafficking to the plasma membrane, where it provides the source of Ca²⁺ influx for small conductance calcium‐activated K⁺ (SK_Ca) channel activation and sustained EC hyperpolarization.

Methods and Results

Pressurized artery studies were performed with isolated mouse posterior cerebral artery. Treatment with a selective TRPC3 blocker (Pyr3) produced significant attenuation of endothelium‐dependent hyperpolarization–mediated vasodilation and endothelial Ca²⁺ response (EC‐specific Ca²⁺ biosensor) to intraluminal ATP. Pyr3 treatment also resulted in a reduced ATP‐stimulated global Ca²⁺ and Ca²⁺ influx in primary cultures of cerebral endothelial cells. Patch‐clamp studies with freshly isolated cerebral ECs demonstrated 2 components of EC hyperpolarization and K⁺ current activation in response to ATP. The early phase was dependent on intermediate conductance calcium‐activated K⁺ channel activation, whereas the later sustained phase relied on SK_Ca channel activation. The SK_Ca channel–dependent phase was completely blocked with TRPC3 channel inhibition or in ECs of TRPC3 knockout mice and correlated with increased trafficking of TRPC3 (but not SK_Ca channel) to the plasma membrane.

Conclusions

We propose that TRPC3 dynamically regulates SK_Ca channel activation through receptor‐dependent trafficking to the plasma membrane, where it provides the source of Ca²⁺ influx for sustained SK_Ca channel activation, EC hyperpolarization, and endothelium‐dependent hyperpolarization–mediated vasodilation.

Trafficking mechanisms and regulation of TRPC channels

TRPC channels are Ca(2+)-permeable cation channels which are regulated downstream from receptor-coupled PIP2 hydrolysis. These channels contribute to a wide variety of cellular functions. Loss or gain of channel function has been associated with dysfunction and aberrant physiology. TRPC channel functions are influenced by their physical and functional interactions with numerous proteins that determine their regulation, scaffolding, trafficking, as well as their effects on the downstream cellular processes. Such interactions also compartmentalize the Ca(2+) signals arising from TRPC channels. A large number of studies demonstrate that trafficking is a critical mode by which plasma membrane localization and surface expression of TRPC channels are regulated. This review will provide an overview of intracellular trafficking pathways as well as discuss the current state of knowledge regarding the mechanisms and components involved in trafficking of the seven members of the TRPC family (TRPC1-TRPC7).

Physiological functions and regulation of TRPC channels

The TRP-canonical (TRPC) subfamily, which consists of seven members (TRPC1-TRPC7), are Ca(2+)-permeable cation channels that are activated in response to receptor-mediated PIP2 hydrolysis via store-dependent and store-independent mechanisms. These channels are involved in a variety of physiological functions in different cell types and tissues. Of these, TRPC6 has been linked to a channelopathy resulting in human disease. Two key players of the store-dependent regulatory pathway, STIM1 and Orai1, interact with some TRPC channels to gate and regulate channel activity. The Ca(2+) influx mediated by TRPC channels generates distinct intracellular Ca(2+) signals that regulate downstream signaling events and consequent cell functions. This requires localization of TRPC channels in specific plasma membrane microdomains and precise regulation of channel function which is coordinated by various scaffolding, trafficking, and regulatory proteins.

Canonical transient receptor potential 3 channels regulate mitochondrial calcium uptake

Mitochondrial Ca(2+) homeostasis is fundamental to regulation of mitochondrial membrane potential, ATP production, and cellular Ca(2+) homeostasis. It has been known for decades that isolated mitochondria can take up Ca(2+) from the extramitochondrial solution, but the molecular identity of the Ca(2+) channels involved in this action is largely unknown. Here, we show that a fraction of canonical transient receptor potential 3 (TRPC3) channels is localized to mitochondria, a significant fraction of mitochondrial Ca(2+) uptake that relies on extramitochondrial Ca(2+) concentration is TRPC3-dependent, and the up- and down-regulation of TRPC3 expression in the cell influences the mitochondrial membrane potential. Our findings suggest that TRPC3 channels contribute to mitochondrial Ca(2+) uptake. We anticipate our observations may provide insights into the mechanisms of mitochondrial Ca(2+) uptake and advance understanding of the physiological role of TRPC3.

A network perspective on unraveling the role of TRP channels in biology and disease

Transient receptor potential (TRP) channels are a large family of non-selective cation channels that mediate numerous physiological and pathophysiological processes; however, still largely unknown are the underlying molecular mechanisms. With data generated on an unprecedented scale, network-based approaches have been revolutionizing the way in which we understand biology and disease, discover disease genes, and develop therapeutic strategies. These circumstances have created opportunities to encounter TRP channel research to data-intensive science. In this review, we provide an introduction of network-based approaches in biomedical science, describe the current state of TRP channel network biology, and discuss the future direction of TRP channel research. Network perspective will facilitate the discovery of latent roles and underlying mechanisms of TRP channels in biology and disease.

The dynamic complexity of the TRPC1 channelosome

A rise in cytoplasmic [Ca2+] due to store-operated Ca2+ entry (SOCE) triggers a plethora of responses, both acute and long term. This leads to the important question of how this initial signal is decoded to regulate specific cellular functions. It is now clearly established that local [Ca2+] at the site of SOCE can vary significantly from the global [Ca2+] in the cytosol. Such Ca2+ microdomains are generated by the assembly of key Ca2+ signaling proteins within the domains. For example, GPCR, IP 3 receptors, TRPC3 channels, the plasma membrane Ca2+ pump and the endoplasmic reticulum (ER) Ca2+ pump have all been found to be assembled in a complex and all of them contribute to the Ca2+ signal. Recent studies have revealed that two other critical components of SOCE, STIM1 and Orai1, are also recruited to these regions. Thus, the entire machinery for activation and regulation of SOCE is compartmentalized in specific cellular domains which facilitates the specificity and rate of protein-protein interactions that are required for activation of the channels. In the case of TRPC1-SOC channels, it appears that specific lipid domains, lipid raft domains (LRDs), in the plasma membrane, as well as cholesterol-binding scaffolding proteins such as caveolin-1 (Cav-1), are involved in assembly of the TRPC channel complexes. Thus, plasma membrane proteins and lipid domains as well as ER proteins contribute to the SOCE-Ca2+ signaling microdomain and modulation of the Ca2+ signals per se. Of further interest is that modulation of Ca2+ signals, i.e. amplitude and/or frequency, can result in regulation of specific cellular functions. The emerging data reveal a dynamic Ca2+ signaling complex composed of TRPC1/Orai1/STIM1 that is physiologically consistent with the dynamic nature of the Ca2+ signal that is generated. This review will focus on the recent studies which demonstrate critical aspects of the TRPC1 channelosome that are involved in the regulation of TRPC1 function and TRPC1-SOC-generated Ca2+ signals.

mGluR1/TRPC3-mediated Synaptic Transmission and Calcium Signaling in Mammalian Central Neurons

Metabotropic glutamate receptors type 1 (mGluR1s) are required for a normal function of the mammalian brain. They are particularly important for synaptic signaling and plasticity in the cerebellum. Unlike ionotropic glutamate receptors that mediate rapid synaptic transmission, mGluR1s produce in cerebellar Purkinje cells a complex postsynaptic response consisting of two distinct signal components, namely a local dendritic calcium signal and a slow excitatory postsynaptic potential. The basic mechanisms underlying these synaptic responses were clarified in recent years. First, the work of several groups established that the dendritic calcium signal results from IP(3) receptor-mediated calcium release from internal stores. Second, it was recently found that mGluR1-mediated slow excitatory postsynaptic potentials are mediated by the transient receptor potential channel TRPC3. This surprising finding established TRPC3 as a novel postsynaptic channel for glutamatergic synaptic transmission.