Translocation of PKG1α acts on TRPV4-C1 heteromeric channels to inhibit endothelial Ca(2+) entry

Recent advances on the structure and the function relationships of the TRPV4 ion channel

The members of the superfamily of Transient Receptor Potential (TRP) ion channels are physiologically important molecules that have been studied for many years and are still being intensively researched. Among the vanilloid TRP subfamily, the TRPV4 ion channel is an interesting protein due to its involvement in several essential physiological processes and in the development of various diseases. As in other proteins, changes in its function that lead to the development of pathological states, have been closely associated with modification of its regulation by different molecules, but also by the appearance of mutations which affect the structure and gating of the channel. In the last few years, some structures for the TRPV4 channel have been solved. Due to the importance of this protein in physiology, here we discuss the recent progress in determining the structure of the TRPV4 channel, which has been achieved in three species of animals (Xenopus tropicalis, Mus musculus, and Homo sapiens), highlighting conserved features as well as key differences among them and emphasizing the binding sites for some ligands that play crucial roles in its regulation.

Transient receptor potential vanilloid type 4 (TRPV4) promotes tumorigenesis via NFAT4 activation in nasopharyngeal carcinoma

Transient receptor potential vanilloid type 4 (TRPV4) can function as an oncogene or tumor suppressor depending on the tumor types. However, little is known regarding the effect of TRPV4 in nasopharyngeal carcinoma (NPC), a highly prevalent malignancy in Southern China and Southeast Asia. We found that TRPV4 mRNA and protein levels were significantly upregulated in NPC tissues. In addition, activation of TRPV4 in NPC cell lines using GSK1016790A (100 nM) induced a Ca²⁺ influx, whereas pharmacological inhibition or gene knockdown of TRPV4 reduced the proliferation rates of NPC cells. TRPV4 knockdown also decreased the growth of tumor xenografts in vivo. Mechanistically, TRPV4-mediated tumorigenesis is dependent on the activation of Ca²⁺/calcineurin/calcineurin-nuclear factor of activated T cell 4 (NFAT4) signaling. Furthermore, NFAT4 protein level was overexpressed in NPC tissues and correlated positively with TRPV4. Taken together, TRPV4 promotes the malignant potential of NPC cells by activating NFAT4 signaling. Our findings highlight TRPV4-NFAT4 axis as a potential therapeutic target in NPC.

Role of TRPV4 channel in vasodilation and neovascularization

The transient receptor potential vanilloid type 4 (TRPV4) channel, a Ca²⁺ -permeable nonselective cation channel, is widely distributed in the circulatory system, particularly in vascular endothelial cells (ECs) and smooth muscle cells (SMCs). The TRPV4 channel is activated by various endogenous and exogenous stimuli, including shear stress, low intravascular pressure, and arachidonic acid. TRPV4 has a role in mediating vascular tone and arterial blood pressure. The activation of the TRPV4 channel induces Ca²⁺ influx, thereby resulting in endothelium-dependent hyperpolarization and SMC relaxation through SK_Ca and IK_Ca activation on ECs or through BK_Ca activation on SMCs. Ca²⁺ binds to calmodulin, which leads to the production of nitric oxide, causing vasodilation. Furthermore, the TRPV4 channel plays an important role in angiogenesis and arteriogenesis and is critical for tumor angiogenesis and growth, since it promotes or inhibits the development of various types of cancer. The TRPV4 channel is involved in the active growth of collateral arteries induced by flow shear stress, which makes it a promising therapeutic target in the occlusion or stenosis of the main arteries. In this review, we explore the role and the potential mechanism of action of the TRPV4 channel in the regulation of vascular tone and in the induction of neovascularization to provide a reference for future research.

C-type natriuretic peptide-induced relaxation through cGMP-dependent protein kinase and SERCA activation is impaired in two kidney-one clip rat aorta

AIMS

Hypertension underlies endothelial dysfunction, and activation of vasorelaxation signaling with low dependence on nitric oxide (NO) represents a good alternative for vascular modulation. C-type natriuretic peptide (CNP) causes relaxation by increasing cyclic guanosine 3',5'-monophosphate (cGMP) or Gi-protein activation through its natriuretic peptide receptor-B or -C, respectively. We have hypothesized that CNP could exerts its effects and could overcome endothelial dysfunction in two kidney-one clip (2K-1C) hypertensive rat aorta. Here, we investigate the intracellular signaling involved in CNP effects in hypertension.

MATERIALS AND METHODS

The 2K-1C hypertension was induced in male Wistar rats (200 g). CNP-induced vascular relaxation and cGMP production were investigated in rat thoracic aortas. The natriuretic peptide receptor-B and -C localization was evaluated by immunofluorescence. Calcium mobilization was assessed in endothelial cells from rat aortas.

KEY FINDINGS

CNP induced similar relaxation in normotensive and 2K-1C hypertensive rat aortas, which increased after endothelium removal. CNP-induced relaxation involved natriuretic peptide receptor-B and -C activation in 2K-1C rats. Nitric oxide synthase (NOS) and soluble guanylyl cyclase (sGC) counter-regulated CNP-particulate GC (pGC) activation in aortas. CNP reduced endothelial calcium and increased cGMP production, which was lower in 2K-1C. CNP-induced cGMP-dependent protein kinase (PKG) and sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase (SERCA) activation was impaired in 2K-1C rat aorta.

SIGNIFICANCE

Our results indicated CNP triggered relaxation through its natriuretic peptide receptor-B and -C in 2K-1C rat aortas, and that CNP-induced relaxation overcomes endothelial dysfunction in hypertension. In addition, NOS and sGC activities counter-regulate CNP-pGC activation to induce vascular relaxation.

Post-Translational Modification and Natural Mutation of TRPC Channels

Transient Receptor Potential Canonical (TRPC) channels are homologues of Drosophila TRP channel first cloned in mammalian cells. TRPC family consists of seven members which are nonselective cation channels with a high Ca²⁺ permeability and are activated by a wide spectrum of stimuli. These channels are ubiquitously expressed in different tissues and organs in mammals and exert a variety of physiological functions. Post-translational modifications (PTMs) including phosphorylation, N-glycosylation, disulfide bond formation, ubiquitination, S-nitrosylation, S-glutathionylation, and acetylation play important roles in the modulation of channel gating, subcellular trafficking, protein-protein interaction, recycling, and protein architecture. PTMs also contribute to the polymodal activation of TRPCs and their subtle regulation in diverse physiological contexts and in pathological situations. Owing to their roles in the motor coordination and regulation of kidney podocyte structure, mutations of TRPCs have been implicated in diseases like cerebellar ataxia (moonwalker mice) and focal and segmental glomerulosclerosis (FSGS). The aim of this review is to comprehensively integrate all reported PTMs of TRPCs, to discuss their physiological/pathophysiological roles if available, and to summarize diseases linked to the natural mutations of TRPCs.

Heteromeric TRPV4/TRPC1 channels mediate calcium-sensing receptor-induced relaxations and nitric oxide production in mesenteric arteries: comparative study using wild-type and TRPC1-/- mice

We have previously provided pharmacological evidence that stimulation of calcium-sensing receptors (CaSR) induces endothelium-dependent relaxations of rabbit mesenteric arteries through activation of heteromeric TRPV4/TRPC1 channels and nitric oxide (NO) production. The present study further investigates the role of heteromeric TRPV4/TRPC1 channels in these CaSR-induced vascular responses by comparing responses in mesenteric arteries from wild-type (WT) and TRPC1^-/- mice. In WT mice, stimulation of CaSR induced endothelium-dependent relaxations of pre-contracted tone and NO generation in endothelial cells (ECs), which were inhibited by the TRPV4 channel blocker RN1734 and the TRPC1 blocking antibody T1E3. In addition, TRPV4 and TRPC1 proteins were colocalised at, or close to, the plasma membrane of endothelial cells (ECs) from WT mice. In contrast, in TRPC1^-/- mice, CaSR-mediated vasorelaxations and NO generation were greatly reduced, unaffected by T1E3, but blocked by RN1734. In addition, the TRPV4 agonist GSK1016790A (GSK) induced endothelium-dependent vasorelaxations which were blocked by RN1734 and T1E3 in WT mice, but only by RN1734 in TRPC1^-/- mice. Moreover, GSK activated cation channel activity with a 6pS conductance in WT ECs but with a 52 pS conductance in TRPC1^-/- ECs. These results indicate that stimulation of CaSR activates heteromeric TRPV4/TRPC1 channels and NO production in ECs, which are responsible for endothelium-dependent vasorelaxations. This study also suggests that heteromeric TRPV4-TRPC1 channels may form the predominant TRPV4-containing channels in mouse mesenteric artery ECs. Together, our data further implicates CaSR-induced pathways and heteromeric TRPV4/TRPC1 channels in the regulation of vascular tone.

Morin induces endothelium-dependent relaxation by activating TRPV4 channels in rat mesenteric arteries

Morin, a natural flavonol, has been reported to have beneficial pharmacological effects. Although its vascular protective effects have been studied, little is known about its effects on the mesenteric artery and the underlying mechanisms. Transient receptor potential vanilloid type 4 (TRPV4) channels are one of the most important Ca²⁺-permeable cation channels in vascular endothelial cells and play an important role in regulating rat mesenteric vascular tone. In the present study, the myogenic effects of morin were investigated using wire and pressure myography in the isolated mesenteric artery. Morin induced endothelium-dependent relaxation of isolated rat mesenteric arteries in a concentration-dependent manner. In addition, morin stimulated relaxation by activating TRPV4-mediated Ca²⁺ influx without affecting the nitric oxide (NO), hydrogen peroxide (H₂O₂), cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) pathways. In primary cultured rat mesenteric artery endothelial cells and over-expressing TRPV4 HEK 293 cells, the TRPV4 inhibitor HC067047 significantly reduced the morin-induced increase in intracellular Ca²⁺ concentration. Furthermore, in rats with hypertension induced by N^Ꞷ-nitro-L-arginine methyl ester (L-NAME), oral administration of morin (50 mg/kg/day) decreased systolic blood pressure. In L-NAME-induced hypertensive rats, morin significantly improved the relaxation response of the arteries to acetylcholine. Thus, we demonstrated that morin induces endothelium-dependent relaxation in the rat mesenteric artery by acting on TRPV4 channels to mediate Ca²⁺ influx and attenuate blood pressure in L-NAME-induced hypertension, thereby highlighting the potential of morin in the treatment of hypertension.

Functional Interaction among KCa and TRP Channels for Cardiovascular Physiology: Modern Perspectives on Aging and Chronic Disease

Effective delivery of oxygen and essential nutrients to vital organs and tissues throughout the body requires adequate blood flow supplied through resistance vessels. The intimate relationship between intracellular calcium ([Ca²⁺]_i) and regulation of membrane potential (V_m) is indispensable for maintaining blood flow regulation. In particular, Ca²⁺-activated K⁺ (K_Ca) channels were ascertained as transducers of elevated [Ca²⁺]_i signals into hyperpolarization of V_m as a pathway for decreasing vascular resistance, thereby enhancing blood flow. Recent evidence also supports the reverse role for K_Ca channels, in which they facilitate Ca²⁺ influx into the cell interior through open non-selective cation (e.g., transient receptor potential; TRP) channels in accord with robust electrical (hyperpolarization) and concentration (~20,000-fold) transmembrane gradients for Ca²⁺. Such an arrangement supports a feed-forward activation of V_m hyperpolarization while potentially boosting production of nitric oxide. Furthermore, in vascular types expressing TRP channels but deficient in functional K_Ca channels (e.g., collecting lymphatic endothelium), there are profound alterations such as downstream depolarizing ionic fluxes and the absence of dynamic hyperpolarizing events. Altogether, this review is a refined set of evidence-based perspectives focused on the role of the endothelial K_Ca and TRP channels throughout multiple experimental animal models and vascular types. We discuss the diverse interactions among K_Ca and TRP channels to integrate Ca²⁺, oxidative, and electrical signaling in the context of cardiovascular physiology and pathology. Building from a foundation of cellular biophysical data throughout a wide and diverse compilation of significant discoveries, a translational narrative is provided for readers toward the treatment and prevention of chronic, age-related cardiovascular disease.

Downregulation of endothelial transient receptor potential vanilloid type 4 channel underlines impaired endothelial nitric oxide-mediated relaxation in the mesenteric arteries of hypertensive rats

The endothelium contributes to the maintenance of vasodilator tone by releasing endothelium-derived relaxing factors, including nitric oxide (NO). In hypertension, endothelial nitric oxide synthase (eNOS) produces less NO and could be one of the contributing factors to the increased peripheral vascular resistance. Agonist-induced Ca(2+) entry is essential for the activation of eNOS. The transient receptor potential vanilloid type 4 (TRPV4) channel, a Ca(2+)-permeant cation channel, is expressed in the endothelial cells and involved in the regulation of vascular tone. The present study aimed to investigate the role of TRPV4 channel in endothelium-dependent NO-mediated relaxation of the resistance artery in hypertensive rats. Using a wire myograph, relaxation response to the TRPV4 activator, 4alpha-phorbol-12,13-didecanoate (4alphaPDD) was assessed in mesenteric arteries obtained from Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHRs). Compared to WKY, SHR demonstrated a significantly attenuated 4alphaPDD-induced endothelium-dependent NO-mediated relaxation. Immunohistochemical analysis revealed positive staining for TRPV4 in the endothelium of mesenteric artery sections in both WKY and SHR. Furthermore, TRPV4 mRNA and protein expressions in SHR were significantly lower than their expression levels in WKY rats. We conclude that 4alphaPDD-induced endothelium-dependent NO-mediated vasorelaxation is reduced in SHR and downregulation of TRPV4 could be one of the contributing mechanisms.

TRPV4 activates cytosolic phospholipase A2 via Ca2+ -dependent PKC/ERK1/2 signalling in controlling hypertensive contraction

Activation of TRPV4 (transient receptor potential vanilloid 4) has been reported to result in endothelium-dependent contraction in the aortae of hypertensive mice. This contraction involved increased cPLA2 (cytosolic phospholipase A2 ) activity. The mechanism by which TRPV4 regulates cPLA2 activity to induce contraction in hypertension, however, is unknown. Through measurements of arterial tension and protein level, we showed that high-salt diet induced hypertension increases activity of PKC (protein kinase C) and ERK1/2 (extracellular signal-regulated kinase 1/2). GSK1016790A, a TRPV4 agonist and ACh (acetylcholine) induced contractions were suppressed by Go6983, a PKC inhibitor and PD98059, an ERK1/2 inhibitor. TRPV4 activation increased activity of PKC and ERK1/2 in endothelial cells from hypertensive mice and this response was suppressed by HC067047, a TRPV4 inhibitor and BAPTA/AM, a Ca2+ chelator. PLA2 assay and western blotting showed that blocking of PKC or ERK1/2 inhibited TRPV4 or ACh-induced cPLA2 activity. Enzyme immunoassay showed that GSK1016790A or ACh triggered the release of PGF2α (prostaglandin F2α ) was reduced by inhibition of PKC or ERK1/2. These data further suggest Ca2+ /PKC/ERK1/2 axis as a novel mechanism for TRPV4 in the activation of cPLA2 in hypertension.

Calcium and electrical signaling in arterial endothelial tubes: New insights into cellular physiology and cardiovascular function

The integral role of the endothelium during the coordination of blood flow throughout vascular resistance networks has been recognized for several decades now. Early examination of the distinct anatomy and physiology of the endothelium as a signaling conduit along the vascular wall has prompted development and application of an intact endothelial "tube" study model isolated from rodent skeletal muscle resistance arteries. Vasodilatory signals such as increased endothelial cell (EC) Ca²⁺ ([Ca²⁺ ]_i ) and hyperpolarization take place in single ECs while shared between electrically coupled ECs through gap junctions up to distances of millimeters (≥2 mm). The small- and intermediate-conductance Ca²⁺ activated K⁺ (SK_Ca /IK_Ca or K_Ca 2.3/K_Ca 3.1) channels function at the interface of Ca²⁺ signaling and hyperpolarization; a bidirectional relationship whereby increases in [Ca²⁺ ]_i activate SK_Ca /IK_Ca channels to produce hyperpolarization and vice versa. Further, the spatial domain of hyperpolarization among electrically coupled ECs can be finely tuned via incremental modulation of SK_Ca /IK_Ca channels to balance the strength of local and conducted electrical signals underlying vasomotor activity. Multifunctional properties of the voltage-insensitive SK_Ca /IK_Ca channels of resistance artery endothelium may be employed for therapy during the aging process and development of vascular disease.

TRPV4 (Transient Receptor Potential Vanilloid 4) Mediates Endothelium-Dependent Contractions in the Aortas of Hypertensive Mice

The role of TRPV4 (transient receptor potential vanilloid 4) in regulating vascular contraction in hypertensive mice is poorly established. We tested the hypothesis that TRPV4 regulates endothelium-dependent contractions in aortas from hypertensive mice through the activation of cytosolic cPLA₂ (phospholipase A₂) and COX2 (cyclooxygenase 2) and identified the possible endothelium-derived contracting factor generated by COX2. Using myography, we demonstrated that GSK1016790A (a TRPV4 agonist) and acetylcholine (ACh) trigger endothelium-dependent contractions in aortas from hypertensive mice, and the contractions were abolished with TRPV4 deletion. PLA₂ assay and Western blotting showed that cPLA₂ activity was higher in salt-induced hypertension and HC067047 or a Ca²⁺ chelator inhibited cPLA₂ activity. Contractions induced by TRPV4 and ACh were inhibited by the cPLA₂ inhibitor or removal of extracellular Ca²⁺ COX2 expression was enhanced in the endothelium from hypertensive mice and contractions induced by TRPV4 or ACh were inhibited by the COX2 inhibitor. Enzyme immunoassay showed that the release of prostaglandin F_2α (PGF_2α) was increased in hypertensive mice. GSK1016790A or ACh triggered the release of PGF_2α and this was inhibited by HC067047, the cPLA₂ inhibitor, and COX2 inhibitor. GSK1016790A, ACh, and PGF_2α induced contractions were significantly reduced by S18886 in salt-induced hypertensive mice. The present study demonstrates that PGF_2α generated by COX2 in the endothelium is the most likely endothelium-derived contracting factor underlying endothelium-dependent, TRPV4-mediated contraction in hypertensive mice. This contraction involved increased intracellular Ca²⁺ concentrations and cPLA₂ activity. These results suggested an important role of TRPV4 in endothelium-dependent contraction in mice during hypertension.

Heteromeric TRPV4/TRPC1 channels mediate calcium-sensing receptor-induced nitric oxide production and vasorelaxation in rabbit mesenteric arteries

Stimulation of calcium-sensing receptors (CaSR) by increasing the external calcium concentration (Ca^2 +]_o) induces endothelium-dependent vasorelaxation through nitric oxide (NO) production and activation of intermediate Ca^2 +-activated K⁺ currents (IK_Ca) channels in rabbit mesenteric arteries. The present study investigates the potential role of heteromeric TRPV4-TRPC1 channels in mediating these CaSR-induced vascular responses. Immunocytochemical and proximity ligation assays showed that TRPV4 and TRPC1 proteins were expressed and co-localised at the plasma membrane of freshly isolated endothelial cells (ECs). In wire myography studies, increasing [Ca^2 +]_o between 1 and 6 mM induced concentration-dependent relaxations of methoxamine (MO)-induced pre-contracted tone, which were inhibited by the TRPV4 antagonists RN1734 and HC067047, and the externally-acting TRPC1 blocking antibody T1E3. In addition, CaSR-evoked NO production in ECs measured using the fluorescent NO indicator DAF-FM was reduced by RN1734 and T1E3. In contrast, [Ca^2 +]_o-evoked perforated-patch IK_Ca currents in ECs were unaffected by RN1734 and T1E3. The TRPV4 agonist GSK1016790A (GSK) induced endothelium-dependent relaxation of MO-evoked pre-contracted tone and increased NO production, which were inhibited by the NO synthase inhibitor L-NAME, RN1734 and T1E3. GSK activated 6pS cation channel activity in cell-attached patches from ECs which was blocked by RN1734 and T1E3. These findings indicate that heteromeric TRPV4-TRPC1 channels mediate CaSR-induced vasorelaxation through NO production but not IK_Ca channel activation in rabbit mesenteric arteries. This further implicates CaSR-induced pathways and heteromeric TRPV4-TRPC1 channels in regulating vascular tone.

11,12-Epoxyeicosatrienoic acid induces vasodilator response in the rat perfused mesenteric vasculature

Epoxyeicosatrienoic acids (EETs) are endogenous ligands that undergo hydrolysis by soluble epoxide hydrolase (sEH). The responses of 11, 12‐EET in comparison with other vasodilator agonists including carbachol and sodium nitroprusside (SNP) were investigated. The effect of 1‐cyclohexyl‐3‐dodecyl urea (CDU), a sEH, was tested on the vasodilator effect induced by 11, 12‐EET in the perfused mesenteric beds isolated from normo‐glycaemic and type‐1 STZ‐diabetic rats.

In the perfused mesenteric beds of control and diabetic animals, 11, 12‐EET produced vasodilation in a dose‐dependent manner. The vasodilator response induced by 11, 12‐EET was significantly decreased in tissues obtained from diabetic animals, but this was significantly corrected through inhibition of sEH.

The effects of nitric oxide synthase inhibitor, cyclo‐oxygenase inhibitor, specific potassium channel inhibitors, soluble guanylyl cyclase inhibitor and transient receptor potential channel V4 inhibitor, on vasodilator response to 11, 12‐EET were investigated.

In tissues isolated from control animals, vasodilator responses to 11, 12‐EET were not inhibited by acute incubation with l‐NAME, l‐NAME with indomethacin, glibenclamide, iberiotoxin, charybdotoxin, apamin or ODQ.

Incubation with the transient receptor potential channel V4 inhibitor ruthenium red caused significantly reduced vasodilator responses induced by 11, 12‐EET.

In conclusion, results from this study indicate that 11, 12‐EET has a vasodilator effect in the perfused mesenteric bed, partly through activation of vanilloid receptor. A strategy to elevate the levels of EETs may have a significant impact in correcting microvascular abnormality associated with diabetes.

TRPC5-induced autophagy promotes drug resistance in breast carcinoma via CaMKKβ/AMPKα/mTOR pathway

Adriamycin is a first-line chemotherapy agent against cancer, but the development of resistance has become a major problem. Although autophagy is considered to be an adaptive survival response in response to chemotherapy and may be associated with chemoresistance, its inducer and the underlying molecular mechanisms remain unclear. Here, we demonstrate that adriamycin up-regulates the both levels of TRPC5 and autophagy, and the increase in autophagy is mediated by TRPC5 in breast cancer cells. Blockade of TRPC5 or autophagy increased the sensitivity to chemotherapy in vitro and in vivo. Notably, we revealed a positive correlation between TRPC5 and the autophagy-associated protein LC3 in paired patients with or without anthracycline-taxane-based chemotherapy. Furthermore, pharmacological inhibition and gene-silencing showed that the cytoprotective autophagy mediated by TRPC5 during adriamycin treatment is dependent on the CaMKKβ/AMPKα/mTOR pathway. Moreover, adriamycin-resistant MCF-7/ADM cells maintained a high basal level of autophagy, and silencing of TRPC5 and inhibition of autophagy counteracted the resistance to adriamycin. Thus, our results revealed a novel role of TRPC5 as an inducer of autophagy, and this suggests a novel mechanism of drug resistance in chemotherapy for breast cancer.

STIM-TRP Pathways and Microdomain Organization: Contribution of TRPC1 in Store-Operated Ca2+ Entry: Impact on Ca2+ Signaling and Cell Function

Store-operated calcium entry (SOCE) is a ubiquitous Ca²⁺ entry pathway that is activated in response to depletion of ER-Ca²⁺ stores and critically controls the regulation of physiological functions in a wide variety of cell types. The transient receptor potential canonical (TRPC) channels (TRPCs 1-7), which are activated by stimuli leading to PIP₂ hydrolysis, were first identified as molecular components of SOCE channels. While TRPC1 was associated with SOCE and regulation of function in several cell types, none of the TRPC members displayed I _CRAC, the store-operated current identified in lymphocytes and mast cells. Intensive search finally led to the identification of Orai1 and STIM1 as the primary components of the CRAC channel. Orai1 was established as the pore-forming channel protein and STIM1 as the ER-Ca²⁺ sensor protein involved in activation of Orai1. STIM1 also activates TRPC1 via a distinct domain in its C-terminus. However, TRPC1 function depends on Orai1-mediated Ca²⁺ entry, which triggers recruitment of TRPC1 into the plasma membrane where it is activated by STIM1. TRPC1 and Orai1 form distinct store-operated Ca²⁺ channels that regulate specific cellular functions. It is now clearly established that regulation of TRPC1 trafficking can change plasma membrane levels of the channel, the phenotype of the store-operated Ca²⁺ current, as well as pattern of SOCE-mediated [Ca²⁺]_i signals. Thus, TRPC1 is activated downstream of Orai1 and modifies the initial [Ca²⁺]_i signal generated by Orai1. This review will highlight current concepts of the activation and regulation of TRPC1 channels and its impact on cell function.

Calcium homeostasis alterations in a mouse model of the Dynamin 2-related centronuclear myopathy

Autosomal dominant centronuclear myopathy (CNM) is a rare congenital myopathy characterized by centrally located nuclei in muscle fibers. CNM results from mutations in the gene encoding dynamin 2 (DNM2), a large GTPase involved in endocytosis, intracellular membrane trafficking, and cytoskeleton regulation. We developed a knock-in mouse model expressing the most frequent DNM2-CNM mutation; i.e. the KI-Dnm2^R465W model. Heterozygous (HTZ) KI-Dnm2 mice progressively develop muscle atrophy, impairment of contractile properties, histopathological abnormalities, and elevated cytosolic calcium concentration. Here, we aim at better characterizing the calcium homeostasis impairment in extensor digitorum longus (EDL) and soleus muscles from adult HTZ KI-Dnm2 mice. We demonstrate abnormal contractile properties and cytosolic Ca²⁺ concentration in EDL but not soleus muscles showing that calcium impairment is correlated with muscle weakness and might be a determinant factor of the spatial muscle involvement. In addition, the elevated cytosolic Ca²⁺ concentration in EDL muscles is associated with an increased sarcolemmal permeability to Ca²⁺ and releasable Ca²⁺ content from the sarcoplasmic reticulum. However, amplitude and kinetics characteristics of the calcium transient appear unchanged. This suggests that calcium defect is probably not a primary cause of decreased force generation by compromised sarcomere shortening but may be involved in long-term deleterious consequences on muscle physiology. Our results highlight the first pathomechanism which may explain the spatial muscle involvement occurring in DNM2-related CNM and open the way toward development of a therapeutic approach to normalize calcium content.

Summary: Dynamin 2 mutations cause centronuclear myopathy via unclear mechanisms. We show in a mouse model that changes in cytosolic calcium via incorrect membrane permeability correlate with muscle weakness.