Increased TRPP2 expression in vascular smooth muscle cells from high-salt intake hypertensive rats: The crucial role in vascular dysfunction

Role of transient receptor potential channels in the regulation of vascular tone

Vascular tone is a major element in the control of hemodynamics. Transient receptor potential (TRP) channels conducting monovalent and/or divalent cations (e.g. Na+ and Ca2+) are expressed in the vasculature. Accumulating evidence suggests that TRP channels participate in regulating vascular tone by regulating intracellular Ca2+ signaling in both vascular smooth muscle cells (VSMCs) and endothelial cells (ECs). Aberrant expression/function of TRP channels in the vasculature is associated with vascular dysfunction in systemic/pulmonary hypertension and metabolic syndromes. This review intends to summarize our current knowledge of TRP-mediated regulation of vascular tone in both physiological and pathophysiological conditions and to discuss potential therapeutic approaches to tackle abnormal vascular tone due to TRP dysfunction.

TRPP2 is located in the primary cilia of human non-pigmented ciliary epithelial cells

PURPOSE

Mechanosensitive channels (MSCs) and primary cilium possess a possible relevance for the sensation of intraocular pressure (IOP). However, there is only limited data on their expression and localization in the ciliary body epithelium (CBE). The purpose of this study was to characterize the expression and localization of TRPP2 in a human non-pigmented ciliary epithelial cell (HNPCE) line.

METHODS

The expression of the TRPP2 was studied by quantitative (q)RT-PCR and in situ hybridization in rat and human tissue. Protein expression and distribution were studied by western blot analysis, immunohistochemistry, and immunoelectron microscopy. Cellular location of TRPP2 was determined in rat and human CBE by immunofluorescence and immunoblot analysis. Electron microscopy studies were conducted to evaluate where and with substructure TRPP2 is localized in the HNPCE cell line.

RESULTS

The expression of TRPP2 in rat and human non-pigmented ciliary epithelium was detected. TRPP2 was mainly located in nuclei, but also showed a punctate distribution pattern in the cytoplasm of HNPCE of the tissue and the cell line. In HNPCE cell culture, primary cilia did exhibit different length following serum starvation and hydrostatic pressure. TRPP2 was found to be colocalized with these cilia in HNPCE cells.

CONCLUSION

The expression of TRPP2 and the primary cilium in the CB may indicate a possible role, such as the sensing of hydrostatic pressure, for the regulation of IOP. Functional studies via patch clamp or pharmacological intervention have yet to clarify the relevance for the physiological situation or aqueous humor regulation.

Recent Advances in Understanding the Mechanistic Role of Transient Receptor Potential Ion Channels in Patients With Hypertension

The transient receptor potential (TRP) channel superfamily is a group of nonselective cation channels that function as cellular sensors for a wide range of physical, chemical, and environmental stimuli. According to sequence homology, TRP channels are categorized into 6 subfamilies: TRP canonical, TRP vanilloid, TRP melastatin, TRP ankyrin, TRP mucolipin, and TRP polycystin. They are widely expressed in different cell types and tissues and have essential roles in various physiological and pathological processes by regulating the concentration of ions (Ca2+, Mg2+, Na+, and K+) and influencing intracellular signalling pathways. Human data and experimental models indicate the importance of TRP channels in vascular homeostasis and hypertension. Furthermore, TRP channels have emerged as key players in oxidative stress and inflammation, important in the pathophysiology of cardiovascular diseases, including hypertension. In this review, we present an overview of the TRP channels with a focus on their role in hypertension. In particular, we highlight mechanisms activated by TRP channels in vascular smooth muscle and endothelial cells and discuss their contribution to processes underlying vascular dysfunction in hypertension.

High calcium transport by Polycystin-2 (TRPP2) induces channel clustering and oscillatory currents

The regulation by Ca²⁺ of Ca²⁺-permeable ion channels represents an important mechanism in the control of cell function. Polycystin-2 (PC2, TRPP2), a member of the TRP channel family (Transient Potential Receptor), is a Ca²⁺ permeable non-selective cation channel. Previous studies from our laboratory demonstrated that physiological concentrations of Ca²⁺ do not regulate in vitro translated PC2 (PC2_iv) channel activity. However, the issue as to PC2's Ca²⁺ permeability and regulation remain ill-defined, in particular because Ca²⁺ transport is usually observed in the presence of other ionic gradients. In this study, we assessed Ca²⁺ transport by PC2_iv in a lipid bilayer reconstitution system in a high Ca²⁺ gradient (CaCl₂ 100 mM cis, CaCl₂ 10 mM trans) in the presence of either 3:7 or 7:3 1-palmitoyl-2-oleoyl-choline and ethanolamine lipid mixtures. Reconstituted PC2_iv showed spontaneous Ca²⁺ currents in both lipid mixtures, with a maximum conductance of 63 ± 13 pS (n = 19) and 105 pS ± 9.8 (n = 9), respectively. In both cases, we best fitted the experimental data with the Goldman-Hodgkin-Katz equation, observing a reversal potential (V_rev ∼ -27 mV) consistent with strict Ca²⁺ selectivity. The R742X mutated PC2 (PC2_R742X), lacking the carboxy terminal domain of the channel showed no differences with wild type PC2. Interestingly, we also observed the onset of spontaneous Ca²⁺ current oscillations whenever PC2-containing samples were reconstituted in the 3:7, but not 7:3 POPC:POPE lipid mixture. The amplitude and frequency of the ionic oscillations were highly dependent on the applied voltage, the imposed Ca²⁺ gradient, and the presence of high Ca²⁺, which induced PC2 channel clustering as observed by atomic force microscopy (AFM). We also used the QuB suite to kinetically model the PC2 channel Ca²⁺ oscillations based on the presence of subconductance states in the channel. The encompassed evidence supports a high Ca²⁺ permeability by PC2, and a novel oscillatory mechanism dependent on the presence of Ca²⁺ and phospholipids that provides the first evidence for the relation between stochasticity and deterministic processes mediated by ion channels.

Polycystin-2 (TRPP2) regulates primary cilium length in LLC-PK1 renal epithelial cells

Polycystin-2 (PC2, TRPP2) is a Ca²⁺ permeable nonselective cation channel whose dysfunction generates autosomal dominant polycystic kidney disease (ADPKD). PC2 is present in different cell locations, including the primary cilium of renal epithelial cells. However, little is known as to whether PC2 contributes to the primary cilium structure. Here, we explored the effect(s) of external Ca²⁺, PC2 channel blockers, and PKD2 gene silencing on the length of primary cilia in wild-type LLC-PK1 renal epithelial cells. Confluent cell monolayers were fixed and immuno-labeled with an anti-acetylated α-tubulin antibody to identify primary cilia and measure their length. Although primary cilia length measurements did not follow a Normal distribution, the data were normalized by Box-Cox transformation rendering statistical differences under all experimental conditions. Cells exposed to high external Ca²⁺ (6.2 mM) decreased a 13.5% (p < 0.001) primary cilia length as compared to controls (1.2 mM Ca²⁺). In contrast, the PC2 inhibitors amiloride (200 μM) and LiCl (10 mM), both increased primary ciliary length by 33.2% (p < 0.001), and 17.4% (p < 0.001), respectively. PKD2 gene silencing by siRNA elicited a statistically significant, 10.3% (p < 0.001) increase in primary cilia length compared to their respective scrambled RNA transfected cells. The data indicate that conditions that regulate PC2 function or gene expression modify the length of primary cilia in renal epithelial cells. Blocking of PC2 mitigates the effects of elevated external Ca²⁺ concentration on primary cilia length. Proper regulation of PC2 function in the primary cilium may be essential in the onset of mechanisms that trigger cyst formation in ADPKD.

Effect of TRPM2-Mediated Calcium Signaling on Cell Proliferation and Apoptosis in Esophageal Squamous Cell Carcinoma

Esophageal squamous cell carcinoma (ESCC) is the sixth leading cause of death due to cancer, indicating that finding new therapeutic targets or approaches for ESCC treatment is imperative. Transient Receptor Potential cation channel subfamily M, member 2 (TRPM2) is a calcium-permeable, nonselective cation channel that responds to reactive oxygen species (ROS), which are found in the tumor microenvironment and are important regulators of tumorigenesis, cell proliferation, apoptosis, and the therapeutic response. Here, we used immunohistochemical analysis of tumor tissue derived from patients with ESCC to find that the TRPM2 channel protein expression level was increased in tumor tissue compared with adjacent normal tissue. Intracellular calcium concentration measurements, western blotting, and ROS and cell viability assays were used with a human ESCC cell line (TE-1 cells) to find that TRPM2 participated in the ROS hydrogen peroxide-induced increase in intracellular calcium. This increased calcium inhibited cell proliferation and enhanced apoptosis. Pretreatment of cells with the anticancer agent 5-fluorouracil (5-FU) significantly increased ROS production, which potentiated TRPM2-mediated calcium signaling, decreased cell proliferation, and increased apoptosis in TE-1 cells, suggesting that the therapeutic effect of 5-FU in ESCC cells may be mediated by the TRPM2 channel-mediated calcium influx. These findings offer a potential treatment target and provide mechanistic insight into the therapeutic effects of 5-FU in patients with ESCC.

Physical interaction of tropomyosin 3 and STIM1 regulates vascular smooth muscle contractility and contributes to hypertension

SCOPE

Tropomyosin (TPM), an actin-binding protein widely expressed across different cell types, is primarily involved in cellular contractile processes. We investigated whether TPM3 physically and functionally interacts with stromal interaction molecule 1 (STIM1) to contribute to vascular smooth muscle cell (VSMC) contraction, store-operated calcium entry (SOCE), and high-salt intake-induced hypertension in rats.

METHODS AND RESULTS

Analysis of a rat RNA-seq data set of 80 samples showed that the STIM1 and Tpm3 transcriptome expression pattern is highly correlated, and co-immunoprecipitation results indicated that TPM3 and STIM1 proteins physically interacted in rat VSMCs. Immunohistochemical data displayed obvious co-localization of TPM3 and STIM1 in rat VSMCs. Knockdown of TPM3 or STIM1 in VSMCs with specific small interfering RNA significantly suppressed contractions in tension measurement assays and decreased SOCE in calcium assays. Rats fed a high-salt diet for 4 weeks had significantly higher systolic blood pressure than controls, with significantly increased contractility and markedly increased TPM3 and STIM1 expression levels in the mesenteric resistance artery (shown by tension measurements and immunoblotting, respectively). Additionally, high salt environment in vitro induced significant enhancement of TPM3 and STIM1 expression levels in VSMCs.

CONCLUSIONS

We showed for the first time that TPM3 and STIM1 physically and functionally interact to contribute to VSMC contraction, SOCE, and high-salt intake-induced hypertension. Our findings provide mechanistic insights and offer a potential therapeutic target for high-salt intake-induced hypertension.

Differentially expressed transcripts and associated protein pathways in basilar artery smooth muscle cells of the high-salt intake-induced hypertensive rat

The pathology of cerebrovascular disorders, such as hypertension, is associated with genetic changes and dysfunction of basilar artery smooth muscle cells (BASMCs). Long-term high-salt diets have been associated with the development of hypertension. However, the molecular mechanisms underlying salt-sensitive hypertension-induced BASMC modifications have not been well defined, especially at the level of variations in gene transcription. Here, we utilized high-throughput sequencing and subsequent signaling pathway analyses to find a two–fold change or greater upregulated expression of 203 transcripts and downregulated expression of 165 transcripts in BASMCs derived from rats fed a high-salt diet compared with those from control rats. These differentially expressed transcripts were enriched in pathways involved in cellular, morphological, and structural plasticity, autophagy, and endocrine regulation. These transcripts changes in the BASMCs derived from high-salt intake–induced hypertensive rats may provide critical information about multiple cellular processes and biological functions that occur during the development of cerebrovascular disorders and provide potential new targets to help control or block the development of hypertension.

TRPP2 associates with STIM1 to regulate cerebral vasoconstriction and enhance high salt intake-induced hypertensive cerebrovascular spasm

Cerebrovascular spasm is a life-threatening event in salt-sensitive hypertension. The relationship between store-operated calcium entry (SOCE) and vasoconstriction in hypertension has not been fully clarified. This study investigated the changes in cerebrovascular contractile responses in high salt intake-induced hypertension and the functional roles of the main components of SOCE, namely, polycystin-2 (TRPP2), stromal interaction molecule 1 (STIM1), and Orai3. Polycystic kidney disease 2 (which encodes TRPP2) knockout mice displayed decreased cerebrovascular SOCE-induced contraction. The blood pressure of age-matched rats fed a normal or high-salt diet for 4 weeks was monitored weekly using noninvasive tail-cuff plethysmography. The systolic blood pressure of the rats fed a high-salt diet was significantly higher than that of controls. Western blotting and immunohistochemical results showed that these hypertensive rats expressed higher levels of cerebrovascular TRPP2, STIM1, and Orai3 than controls. Cerebrovascular tension measurements of the basilar artery indicated that SOCE-mediated contraction was significantly increased in hypertensive rats compared with control rats. In addition, SOCE-mediated contraction was decreased in the basilar arteries of rats pretreated with the SOCE inhibitor BTP-2 (10 μM) or transfected with TRPP2-specific or STIM1-specific small interfering RNA. Staining with 2,3,5-triphenyltetrazolium chloride (TTC) was used to quantify the infarcted brain area 24 h after middle cerebral artery occlusion, a model of ischemic stroke, in rodents. The infarcted brain area was significantly greater in hypertensive rats and significantly lower in BTP-2-treated rats than in controls. Taken together, these findings indicate that SOCE-induced contraction may be overactive in the basilar arteries of salt-sensitive hypertensive rats, suggesting the dysregulation of TRPP2 and SOCE and its other components.

A high-salt diet aggravates retinal ischaemia/reperfusion injury

Ischaemia/reperfusion contributes to the pathophysiological process of many retinal diseases. Previous studies have shown that retinal ischaemia/reperfusion mainly results in neuronal degeneration, including thinning of the retina, retinal ganglion cell death and reductions in electroretinography. A high-salt diet contributes to the inflammatory response and tissue hypoperfusion and may be associated with ischaemia/reperfusion injury. In the present study, we investigated the influence of a high-salt diet on retinal ischaemia/reperfusion injury and explored the potential mechanism in a rat model. The results revealed that the high-salt diet aggravated ischaemia/reperfusion-induced thinning of the retina. A TUNEL assay and Brn-3a staining revealed substantially more severe cell death and loss of retinal ganglion cells, and electroretinography confirmed worse retinal function in the ischaemia/reperfusion eyes of rats fed the high-salt diet. These effects may be associated with upregulation of Caspase-3, Bax, Interleukin-1β and Interleukin-6 and decreased expression of nitric oxide. In summary, a high-salt diet aggravates ischaemia/reperfusion-induced retinal neuronal impairment by activating pro-apoptotic and pro-inflammatory signalling pathways and inhibiting vasodilation.

Role of TRPP2 in mouse airway smooth muscle tension and respiration

The transient receptor potential polycystin-2 (TRPP2) is encoded by the Pkd2 gene, and mutation of this gene can cause autosomal dominant polycystic kidney disease (ADPKD). Some patients with ADPKD experience extrarenal manifestations, including radiologic and clinical bronchiectasis. We hypothesized that TRPP2 may regulate airway smooth muscle (ASM) tension. Thus, we used smooth muscle-Pkd2 conditional knockout (Pkd2^SM-CKO) mice to investigate whether TRPP2 regulated ASM tension and whether TRPP2 deficiency contributed to bronchiectasis associated with ADPKD. Compared with wild-type mice, Pkd2^SM-CKO mice breathed more shallowly and faster, and their cross-sectional area ratio of bronchi to accompanying pulmonary arteries was higher, suggesting that TRPP2 may regulate ASM tension and contribute to the occurrence of bronchiectasis in ADPKD. In a bioassay examining isolated tracheal ring tension, no significant difference was found for high-potassium-induced depolarization of the ASM between the two groups, indicating that TRPP2 does not regulate depolarization-induced ASM contraction. By contrast, carbachol-induced contraction of the ASM derived from Pkd2^SM-CKO mice was significantly reduced compared with that in wild-type mice. In addition, relaxation of the carbachol-precontracted ASM by isoprenaline, a β-adrenergic receptor agonist that acts through the cAMP/adenylyl cyclase pathway, was also significantly attenuated in Pkd2^SM-CKO mice compared with that in wild-type mice. Thus, TRPP2 deficiency suppressed both contraction and relaxation of the ASM. These results provide a potential target for regulating ASM tension and for developing therapeutic alternatives for some ADPKD complications of the respiratory system or for independent respiratory disease, especially bronchiectasis.

Exosome-delivered TRPP2 siRNA inhibits the epithelial-mesenchymal transition of FaDu cells

The prognosis for patients with head and neck cancer (HNC) remains poor, owing to uncontrolled tumor invasion and metastasis. Epithelial-mesenchymal transition (EMT) serves an important role in this invasion and metastasis, and transient receptor potential polycystic 2 (TRPP2) enhances metastasis and invasion by regulating EMT in human laryngeal squamous cell carcinoma. The present study examined whether exosomes/TRPP2 small interfering RNA (siRNA) complexes were able to reduce EMT by suppressing TRPP2 expression in FaDu cells, a cell line of human pharyngeal squamous cell carcinoma. Using agarose gel electrophoresis, it was determined that exosome/TRPP2 siRNA complexes were stable in the presence of nucleases and serum. A fluorescence assay and western blotting analysis was performed, and it was reported that the FaDu cells took up exosomes, the exosomes effectively delivered TRPP2 siRNA into FaDu cells and that exosome/TRPP2 siRNA complexes significantly suppressed TRPP2 protein expression levels in FaDu cells. Furthermore, expression levels of E-cadherin were significantly increased, whereas expression levels of N-cadherin and vimentin were significantly decreased in FaDu cells transfected with TRPP2 siRNA. Thus, exosome/TRPP2 siRNA complexes markedly suppressed TRPP2 expression and EMT in FaDu cells. These results suggested that further development of exosome/TRPP2 siRNA complexes for use as an RNA-based gene therapy in the treatment of HNC is warranted.

Contribution of Apelin-17 to Collateral Circulation Following Cerebral Ischemic Stroke

Apelin, an essential mediator of homeostasis, is crucially involved in cardiovascular diseases, including ischemic stroke. However, the functional roles of apelin-17 in cerebral collateral circulation and ischemic stroke protection are unknown. Here, we investigated the association between plasma apelin-17 levels and collateral circulation in patients with ischemic stroke and examined the mechanism undergirding the effects of apelin-17 on cerebral artery contraction and ischemic stroke protection in an animal model. Plasma nitric oxide (NO), apelin-17, and apelin-36 levels were assessed by enzyme-linked immunosorbent assays in ischemic stroke patients with good or poor collateral circulation and in healthy participants. Additionally, the effects of apelin-17 on rat basilar artery contractions (in vitro) and cerebral ischemia (in vivo) were determined using vessel tension measurements and nuclear magnetic resonance, respectively. Patients with good collateral circulation had significantly higher plasma apelin-17 and apelin-36 levels than both patients with poor collateral circulation and healthy participants and plasma NO levels significantly higher than those in healthy participants. In vitro, apelin-17 pretreatment markedly attenuated U46619-induced rat basilar artery contractions in an endothelium-dependent manner. Additionally, NO production or guanylyl cyclase inhibitors abolished the apelin-17 effect on U46619-induced vascular contraction. Intravenous pretreatment of rats with apelin-17 markedly reduced cerebral infarct volume at 24 h after middle cerebral artery occlusion. Plasma apelin-17 levels in ischemic stroke patients were positively associated with enhanced collateral circulation, which our animal study data suggested may have resulted from an apelin-17-induced cerebral artery dilation mediated through the NO-cGMP pathway.

Interleukin (IL)-13, Prostaglandin E2 (PGE2), and Prostacyclin 2 (PGI2) Activate Hepatic Stellate Cells via Protein kinase C (PKC) Pathway in Hepatic Fibrosis

BACKGROUND Protein kinase C (PKC), interleukin (IL)-13, prostaglandin E2 (PGE2), and prostacyclin 2 (PGI2) can all play crucial roles in pulmonary fibrosis. However, their functions remain unclear in hepatic fibrosis mediated by hepatic stellate cells (HSCs), which has been demonstrated to be related to transforming growth factor-β (TGF-β) and platelet-derived growth factor (PDGF). MATERIAL AND METHODS All the experiments were based on LX-2 Hepatic stellate cells. The expression of TGF-β1 and PDGF were assessed by ELISA, RT-PCR, and Western blotting in human HSCs treated by IL-13, PGE2, and PGI2, respectively. At the same time, bridge assay and CCK8 assay were used to detect the cell proliferation and activity, PKC activity assay was used to test the activity of PKC, and PKC agonist and antagonist were used to verify the results obtained previously. RESULTS We found that IL-13, PGE2, and PGI2 significantly enhanced the expression of TGF-β1 and PDGF in human HSCs, which also clearly improved the proliferation and cell activity of HSCs. Moreover, PKC activity was significantly increased following IL-13, PGE2, and PGI2 treatments. We also found that the expression of TGF-β1 and PDGF, as well as the proliferation and cell activity of HSCs, were significantly enhanced by the PKC agonist phorbol 12-myristate 13-acetate (PMA), but suppressed by the PKC antagonist calphostin C. CONCLUSIONS We found that IL-13, PGE2, and PGI2 stimulated HSCs proliferation and secretion of TGF-β1 and PDGF by activating PKC, which predicted their potential roles in hepatic fibrosis.

Muscling in on TRP channels in vascular smooth muscle cells and cardiomyocytes

The human TRP protein family comprises a family of 27 cation channels with diverse permeation and gating properties. The common theme is that they are very important regulators of intracellular Ca²⁺ signaling in diverse cell types, either by providing a Ca²⁺ influx pathway, or by depolarising the membrane potential, which on one hand triggers the activation of voltage-gated Ca²⁺ channels, and on the other limits the driving force for Ca²⁺ entry. Here we focus on the role of these TRP channels in vascular smooth muscle and cardiac striated muscle. We give an overview of highlights from the recent literature, and highlight the important and diverse roles of TRP channels in the pathophysiology of the cardiovascular system. The discovery of the superfamily of Transient Receptor Potential (TRP) channels has significantly enhanced our knowledge of multiple signal transduction mechanisms in cardiac muscle and vascular smooth muscle cells (VSMC). In recent years, multiple studies have provided evidence for the involvement of these channels, not only in the regulation of contraction, but also in cell proliferation and remodeling in pathological conditions. The mammalian family of TRP cation channels is composed by 28 genes which can be divided into 6 subfamilies groups based on sequence similarity: TRPC (Canonical), TRPM (Melastatin), TRPML (Mucolipins), TRPV (Vanilloid), TRPP (Policystin) and TRPA (Ankyrin-rich protein). Functional TRP channels are believed to form four-unit complexes in the plasma, each of them expressed with six transmembrane domain and intracellular N and C termini. Here we review the current knowledge on the expression of TRP channels in both muscle types, and discuss their functional properties and role in physiological and pathophysiological processes.

High salt intake as a multifaceted cardiovascular disease: new support from cellular and molecular evidence

Scientists worldwide have disseminated the idea that increased dietary salt increases blood pressure. Currently, salt intake in the general population is ten times higher than that consumed in the past and at least two times higher than the current recommendation. Indeed, a salt-rich diet increases cardiovascular morbidity and mortality. For a long time, however, the deleterious effects associated with high salt consumption were only related to the effect of salt on blood pressure. Currently, several other effects have been reported. In some cases, the deleterious effects of high salt consumption are independently associated with other common risk factors. In this article, we gather data on the effects of increased salt intake on the cardiovascular system, from infancy to adulthood, to describe the route by which increased salt intake leads to cardiovascular diseases. We have reviewed the cellular and molecular mechanisms through which a high intake of salt acts on the cardiovascular system to lead to the progressive failure of a healthy heart.

The functions of TRPP2 in the vascular system

TRPP2 (polycystin-2, PC2 or PKD2), encoded by the PKD2 gene, is a non-selective cation channel with a large single channel conductance and high Ca(2+) permeability. In cell membrane, TRPP2, along with polycystin-1, TRPV4 and TRPC1, functions as a mechanotransduction channel. In the endoplasmic reticulum, TRPP2 modulates intracellular Ca(2+) release associated with IP3 receptors and the ryanodine receptors. Noteworthily, TRPP2 is widely expressed in vascular endothelial and smooth muscle cells of all major vascular beds, and contributes to the regulation of vessel function. The mutation of the PKD2 gene is a major cause of autosomal dominant polycystic kidney disease (ADPKD), which is not only a common genetic disease of the kidney but also a systemic disorder associated with abnormalities in the vasculature; cardiovascular complications are the leading cause of mortality and morbidity in ADPKD patients. This review provides an overview of the current knowledge regarding the TRPP2 protein and its possible role in cardiovascular function and related diseases.

The cAMP Signaling Pathway and Direct Protein Kinase A Phosphorylation Regulate Polycystin-2 (TRPP2) Channel Function

Polycystin-2 (PC2) is a TRP-type, Ca(2+)-permeable non-selective cation channel that plays an important role in Ca(2+) signaling in renal and non-renal cells. The effect(s) of the cAMP pathway and kinase mediated phosphorylation of PC2 seem to be relevant to PC2 trafficking and its interaction with polycystin-1. However, the role of PC2 phosphorylation in channel function is still poorly defined. Here we reconstituted apical membranes of term human syncytiotrophoblast (hST), containing endogenous PC2 (PC2hst), and in vitro translated channel protein (PC2iv). Addition of the catalytic subunit of PKA increased by 566% the spontaneous PC2hst channel activity in the presence of ATP. Interestingly, 8-Br-cAMP also stimulated spontaneous PC2hst channel activity in the absence of the exogenous kinase. Either stimulation was inhibited by addition of alkaline phosphatase, which in turn, was reversed by the phosphatase inhibitor vanadate. Neither maneuver modified the single channel conductance but instead increased channel mean open time. PKA directly phosphorylated PC2, which increased the mean open time but not the single channel conductance of the channel. PKA phosphorylation did not modify either R742X truncated or S829A-mutant PC2iv channel function. The data indicate that the cAMP pathway regulates PC2-mediated cation transport in the hST. The relevant PKA site for PC2 channel regulation centers on a single residue serine 829, in the carboxyl terminus.

Maternal high-salt diets affected pressor responses and microvasoconstriction via PKC/BK channel signaling pathways in rat offspring

SCOPE

High-salt (HS) intake is linked to hypertension, and prenatal exposure to maternal HS diets may have long-term impact on cardiovascular systems. The relationship between HS diets and cardiovascular disease has received extensive attention. This study determined pressor responses and microvessel functions in the adult offspring rats exposed to prenatal HS.

METHODS AND RESULTS

The offspring of 5-month old as young adults in rats were used. Blood pressure, vascular tone, intracellular Ca(2+), and BK channels in mesenteric arteries were measured in the offspring. Phenylephrine (Phe)-induced pressor responses were significantly higher in the prenatal HS offspring. Vessel tension and intracellular Ca(2+) concentrations associated with Phe-induced pressor responses were increased in the mesenteric arteries of the HS offspring. PKC α- and δ-isoforms were upregulated in mesenteric arteries of the HS offspring. The enhanced Phe-mediated vascular activity was linked to the altered PKC-modulated BK channel functions.

CONCLUSION

The results suggested that prenatal exposure to HS altered microvascular activity probably via changes in PKC/BK signaling pathways, which may lead to increased risks of hypertension in the offspring.