The Role of TRPM4 in Cardiac Electrophysiology and Arrhythmogenesis

The transient receptor potential melastatin 4 (TRPM4) channel is a non-selective cation channel that activates in response to increased intracellular Ca²⁺ levels but does not allow Ca²⁺ to pass through directly. It plays a crucial role in regulating diverse cellular functions associated with intracellular Ca²⁺ homeostasis/dynamics. TRPM4 is widely expressed in the heart and is involved in various physiological and pathological processes therein. Specifically, it has a significant impact on the electrical activity of cardiomyocytes by depolarizing the membrane, presumably via Na⁺ loading. The TRPM4 channel likely contributes to the development of cardiac arrhythmias associated with specific genetic backgrounds and cardiac remodeling. This short review aims to overview what is known so far about the TRPM4 channel in cardiac electrophysiology and arrhythmogenesis, highlighting its potential as a novel therapeutic target to effectively prevent and treat cardiac arrhythmias.

Effects of liquefied sake lees on growth performance and faecal and blood characteristics in Japanese Black calves

Liquefied sake lees, a by-product of Japanese sake, is rich in Saccharomyces cerevisiae, proteins, and prebiotics derived from rice and yeast. Previous studies have reported that Saccharomyces cerevisiae fermentation products improved the health, growth, and faecal characteristics of preweaning calves. This study investigated the effects of adding liquefied sake lees to milk replacer on the growth performance, faecal characteristics, and blood metabolites of preweaning Japanese Black calves from 6 to 90 days of age. Twenty-four Japanese Black calves at 6 days of age were randomly assigned to one of three treatments: No liquefied sake lees (C, n = 8), 100 g/d (on a fresh matter basis) liquefied sake lees mixed with milk replacer (LS, n = 8), and 200 g/d (on a fresh matter basis) liquefied sake lees mixed with milk replacer (HS, n = 8). The intake of milk replacer and calf starter, as well as, the average daily gain did not differ between the treatments. The number of days counted with faecal score 1 in LS was higher than in HS (P < 0.05), while the number of days with diarrhoea medication in LS and C was lower than HS (P < 0.05). The faecal n-butyric acid concentration tended to be higher in LS compared to C (P = 0.060). The alpha diversity index (Chao1) was higher in HS than in C and LS at 90 days of age (P < 0.05). The principal coordinate analysis (PCoA) using weighted UniFrac distance showed that the bacterial community structures in faeces among the treatments at 90 days of age were significantly different (P < 0.05). The plasma β-hydroxybutyric acid concentration, an indicator of rumen development, was higher for LS than in C throughout the experiment (P < 0.05). These results suggested that adding liquefied sake lees up to 100 g/d (on a fresh matter basis) might promote rumen development in preweaning Japanese Black calves.

Potential of the TRPM7 channel as a novel therapeutic target for pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an intractable vascular disease characterized by a progressive increase in pulmonary vascular resistance caused by pulmonary vascular remodeling, which ultimately leads to right-sided heart failure. PAH remains incurable, despite the development of PAH-targeted therapeutics centered on pulmonary artery relaxants. It is necessary to identify the target molecules that contribute to pulmonary artery remodeling. Transient receptor potential (TRP) channels have been suggested to modulate pulmonary artery remodeling. Our study focused on the transient receptor potential ion channel subfamily M, member 7, or the TRPM7 channel, which modulates endothelial-to-mesenchymal transition and smooth muscle proliferation in the pulmonary artery. In this review, we summarize the role and expression profile of TRPM7 channels in PAH progression and discuss TRPM7 channels as possible therapeutic targets. In addition, we discuss the therapeutic effect of a Chinese herbal medicine, Ophiocordyceps sinensis (OCS), on PAH progression, which partly involves TRPM7 inhibition.

POS0614 THE RELATIONSHIP BETWEEN DISEASE ACTIVITY AND FINANCIAL TOXICITY IN PATIENTS WITH RHEUMATOID ARTHRITIS ON BIOLOGICS: A CROSS-SECTIONAL STUDY USING THE JAPANESE RHEUMATOID ARTHRITIS REGISTRY

Background

As the number of rheumatoid arthritis (RA) patients using biologics increases, the health financial issues posed by biologics become more important. The health financial issues posed by biologics have been discussed using health economic indicators such as incremental cost-effectiveness ratios (ICERs), but have not been evaluated using the financial burden of medical expenses (financial toxicity). In the field of malignancies, evaluations using financial burden have been conducted and have shown that the stage of malignancy is associated with financial toxicity. It is not known whether disease activity and financial toxicity are similarly associated in RA patients.

Objectives

This study aims to evaluate the relationship between RA activity and financial toxicity in RA patients using biologics, who are especially likely to feel the financial burdens.

Methods

We conducted a cross-sectional study of biologic users enrolled in NinJa2020, a database of rheumatoid arthritis patients in Japan collected from April 1, 2020 to March 31, 2021. We defined the users of TNF inhibitor, IL-6 receptor antagonists, T-cell costimulation blocker, Janus kinase inhibitor and biosimilar as biologic users. The main exposure was the disease activity of RA and was measured using DAS28-CRP. Outcome measure was a financial toxicity and was measured using COmprehensive Score for financial Toxicity (COST). This scale is a patient-reported outcome measure (PROM) consisting of 11 items. The responses are recorded on 5-point Likert Scales (ranging from 0 = strongly disagree to 4 = strongly agree). The score by domains ranges from 0 to 44. Higher scores indicated better results and lower financial toxicity. Multiple linear regression models adjusted for age, sex, disease duration, co-payments for anti-rheumatic drugs, work status, financial support systems were conducted to assess the relationship between the disease activity of RA and financial toxicity. As a secondary analysis, we excluded patients with zero copayments and performed the same analysis as in the main analysis. We used multiple imputation to deal with missing values.

Results

Among 15553 cases in the NinJa database, 649 cases for which RA disease activity and COST were available were included. The median age of the patients was 70 (interquartile range [IQR],56 -77), 83.7% were female. The median copayment amount was ¥12978 per month (IQR 637.2 to 24204.1). The median DAS28-CRP was 1.99 (IQR, 1. - 2.72). The median financial toxicity (COST score) was 21 (IQR 0-27) (Figure 1). In the main analysis using multiple linear regression, COST significantly decreased with disease activity of RA (per 1-pt DAS28-CRP, -1.16 [95% CI -2.04 - -0.28]). In the secondary analysis, COST significantly decreased with disease activity of RA (per 1-pt DAS28-CRP, -1.69 [95% CI -2.29 - -1.10]). Statistical significance was defined as a two-sided p-value < 0.05. All statistical analyses were conducted using STATA 17.0 (Stata Corp LP, College Station, TX). The National Hospital Organization’s research ethics committees evaluated and authorized the NinJa study.

Conclusion

High disease activity of RA was associated with high financial toxicity in biologic users. We reaffirmed the importance of financial considerations and empathy for RA patients using biologics, and suggested a potential demand for more financial support for RA patients who are refractory to treatment.

Disclosure of Interests

None declared

Substantial involvement of TRPM7 inhibition in the therapeutic effect of Ophiocordyceps sinensis on pulmonary hypertension

Ophiocordyceps sinensis (OCS), an entomopathogenic fungus, is known to exert antiproliferative and antitissue remodeling effects. Vascular remodeling and vasoconstriction play critical roles in the development of pulmonary hypertension (PH). The therapeutic potential of OCS for PH was investigated using rodent PH models, and cultured pulmonary artery endothelial and smooth muscle cells (PAECs and PASMCs), with a focus on the involvement of TRPM7. OCS ameliorated the development of PH, right ventricular hypertrophy and dysfunction in the monocrotaline-induced PH rats. The genetic knockout of TRPM7 attenuated the development of PH in mice with monocrotaline pyrrole-induced PH. TRPM7 was associated with medial hypertrophy and the plexiform lesions in rats and humans with PH. OCS suppressed proliferation of PASMCs derived from the PH patients. Ethanol extracts of OCS inhibited TRPM7-like current, TGF-β2-induced endothelial-mesenchymal transition, IL-6-induced STAT3 phosphorylation, and PDGF-induced Akt phosphorylation in PAECs or PASMCs. These inhibitory effects were recapitulated by either siRNA-mediated TRPM7 knockdown or treatment with TRPM7 antagonist FTY-720. OCS and FTY-720 induced vasorelaxation in the isolated normal human pulmonary artery. As a result, the present study proposes the therapeutic potential of OCS for the treatment of PH. The inhibition of TRPM7 is suggested to underlie the therapeutic effect of OCS.

Supplemental Leuconostoc mesenteroides strain NTM048 attenuates imiquimod-induced psoriasis in mice

AIMS

Psoriasis, a chronic inflammatory skin disease, is associated with altered intestinal microbiota. Here, we investigated the ameliorative effect of Leuconostoc mesenteroides NTM048 strain in imiquimod (IMQ)-induced psoriasis in mice.

METHODS AND RESULTS

Mice were administered NTM048 for 21 days alongside the topical application of IMQ on the dorsal skin for 6 consecutive days. IMQ induced psoriatic symptoms such as erythema and scaling and also upregulated interleukin (IL)-17, a key effector cytokine of psoriasis, in the skin. Supplemental NTM048 suppressed these abnormalities, increased the levels of plasma deoxycholic acid (DCA), a secondary bile acid and altered the faecal microbiota composition, as indicated by the increased abundance of Akkermansia and decreased abundance of Staphylococcus and Streptococcus. Notably, DCA treatment of murine splenocytes reduced IL-17 production.

CONCLUSIONS

The NTM048-mediated reduction of psoriasis was shown to involve the downregulation of IL-17 in mouse skin, which was possibly associated with the plasma DCA derived from intestinal microbiota.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our findings propose not only a novel approach for psoriasis reduction but also a crosstalk between the skin and intestine in psoriasis.

Volume-regulated chloride channel regulates cell proliferation and is involved in the possible interaction between TMEM16A and LRRC8A in human metastatic oral squamous cell carcinoma cells

OBJECTIVES

Volume-regulated anion channels (VRACs), expressed in various cells, play an important role in cell volume regulation. Despite being physiologically defined almost half a century ago, only the molecular candidates of VRAC, TMEM16A, LRRC8A, and bestrophin-1 (BEST1), are known. Here, we aimed to explore the functional significance of VRAC in, HST-1, an oral squamous cell carcinoma (OSCC) cell line.

METHODS

Cell proliferation assays, RT-PCR, Western blot, and flow cytometry were used to estimate changes in gene expression and cell proliferation. Ion channel activity was recorded using the patch-clamp technique. Specific genes were knocked-down by siRNA assays.

RESULTS

VRAC, identified as a hypotonicity-induced current, was highly functional and associated with the proliferation of HST-1 cells but not of HaCaT (a normal keratinocyte) cells. The pharmacological profile of VRAC in HST-1 was similar to that reported previously. DCPIB, a specific VRAC inhibitor, completely inhibited VRAC and proliferation of HST-1 cells, eventually leading to apoptosis. VRAC in HST-1 was attenuated by the knockdown of TMEM16A and LRRC8A, while knockdown of BEST1 affected cell proliferation. In situ proximity ligation assay showed that TMEM16A and LRRC8A co-localized under isotonic conditions (300 mOsM) but were separated under hypotonic conditions (250 mOsM) on the plasma membrane.

CONCLUSIONS

We have found that VRAC acts to regulate the proliferation of human metastatic OSCC cells and the composition of VRAC may involve in the interactions between TMEM16A and LRRC8A in HST-1 cells.

Pathological activation of CaMKII induces arrhythmogenicity through TRPM4 overactivation

TRPM4 is a Ca²⁺-activated nonselective cation channel involved in cardiovascular physiology and pathophysiology. Based on cellular experiments and numerical simulations, the present study aimed to explore the potential arrhythmogenicity of CaMKII-mediated TRPM4 channel overactivation linked to Ca²⁺ dysregulation in the heart. The confocal immunofluorescence microscopy, western blot, and proximity ligation assay (PLA) in HL-1 atrial cardiomyocytes and/or TRPM4-expressing TSA201 cells suggested that TRPM4 and CaMKII proteins are closely localized. Co-expression of TRPM4 and CaMKIIδ or a FRET-based sensor Camui in HEK293 cells showed that the extent of TRPM4 channel activation was correlated with that of CaMKII activity, suggesting their functional interaction. Both expressions and interaction of the two proteins were greatly enhanced by angiotensin II treatment, which induced early afterdepolarizations (EADs) at the repolarization phase of action potentials (APs) recorded from HL-1 cells by the current clamp mode of patch clamp technique. This arrhythmic change disappeared after treatment with the TRPM4 channel blocker 9-phenanthrol or CaMKII inhibitor KN-62. In order to quantitatively assess how CaMKII modulates the gating behavior of TRPM4 channel, the ionomycin-permeabilized cell-attached recording was employed to obtain the voltage-dependent parameters such as steady-state open probability and time constants for activation/deactivation at different [Ca²⁺]_i. Numerical simulations incorporating these kinetic data into a modified HL-1 model indicated that > 3-fold increase in TRPM4 current density induces EADs at the late repolarization phase and CaMKII inhibition (by KN-62) completely eliminates them. These results collectively suggest a novel arrhythmogenic mechanism involving excessive CaMKII activity that causes TRPM4 overactivation in the stressed heart.

Electronic phenotyping of heart failure from a national clinical information database

Introduction

A database of clinical information collected from several medical institutions, including national university hospitals and private hospital groups, and the medical information database network, MID-NET, have been available to the public in Japan since 2018. To analyse clinical events, i.e., to perform electronic phenotyping, it is important to extract data from clinical information correctly, combine multiple pieces of information, and define the target disease. Herein, we investigated a study to find patients with heart failure and validated our findings using MID-NET data.

Methods

A criterion to describe heart failure cases was determined according to clinical guidelines released by the Japanese Circulation Society. The data studied were based on records from April 1–December 31, 2013. The initial rule was based on disease names, examinations, and medications pertaining to heart failure. We extracted and analysed clinical data from MID-NET and found patients with heart failure. Two doctors, including a cardiologist, reviewed the medical records and verified the legitimacy of the cases, following which we calculated precision and recall rates. Next, we examined a method to identify factors to extract true cases correctly using machine learning with XGBoost in R.

Results

A total of 5,282 cases extracted via disease names were related to heart failure. Of these, 2,799 cases corresponding to the initial rule were retrieved, and 200 cases were randomly sampled and assessed. A total of 70 cases were found to be true. Thus, a precision rate of 0.350 and a recall rate of 0.912 were determined. A machine learning method revealed the correlation of heart failure with several factors, including the serum b-type natriuretic peptide (BNP) value, link between commencement date of the disease and actual hospitalization date, and medications for the treatment of heart failure. Using this data, we could determine the conditions contributing to improving the validity of the cases with heart failure. In this manner, patient cases were extracted using the disease name as it is related to heart failure and hospitalisation within two weeks after the commencement date of the disease. Furthermore, the candidates were categorised into three groups according to serum BNP values (high, middle, and low ranges). The high group was labelled “heart failure”, and the low group was excluded. In the middle group, candidates were additionally categorised according to their prescribed medication for heart failure. Our analysis indicated that the precision rate increased to 0.878 while the recall rate decreased to 0.697. The F-measure also increased from 0.506 to 0.777.

Conclusions

To find target cases from a large clinical database, precise electronic phenotyping is required. A machine learning method can enable accurate identification of patients with heart failure. Leveraging large amounts of clinical data may be beneficial for medical research progress.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): Japan Agency for Medical Research and Development

Eicosapentaenoic acid ameliorates pulmonary hypertension via inhibition of tyrosine kinase Fyn

Pulmonary arterial hypertension (PAH) is a multifactorial disease characterized by pulmonary arterial vasoconstriction and remodeling. Src family tyrosine kinases, including Fyn, play critical roles in vascular remodeling via the inhibition of STAT3 signaling. EPA is known to inhibit Fyn kinase activity. This study investigated the therapeutic potential and underlying mechanisms of EPA and its metabolite, resolvin E1 (RvE1), to treat PAH using monocrotaline-induced PAH model rats (MCT-PAH), human pulmonary artery endothelial cells (HPAECs), and human pulmonary artery smooth muscle cells (HPASMCs). Administration of EPA 1 and 2 weeks after MCT injection both ameliorated right ventricular hypertrophy, remodeling and dysfunction, and medial wall thickening of the pulmonary arteries and prolonged survival in MCT-PAH rats. EPA attenuated the enhanced contractile response to 5-hydroxytryptamine in isolated pulmonary arteries of MCT-PAH rats. Mechanistically, the treatment with EPA and RvE1 or the introduction of dominant-negative Fyn prevented TGF-β2-induced endothelial-to-mesenchymal transition and IL-6-induced phosphorylation of STAT3 in cultured HPAECs. EPA and RvE1 suppressed Src family kinases' activity as evaluated by their phosphorylation status in cultured HPAECs and HPASMCs. EPA and RvE1 suppressed vasocontraction of rat and human PA. Furthermore, EPA and RvE1 inhibited the enhanced proliferation and activity of Src family kinases in HPASMCs derived from patients with idiopathic PAH. EPA ameliorated PAH's pathophysiology by mitigating vascular remodeling and vasoconstriction, probably inhibiting Src family kinases, especially Fyn. Thus, EPA is considered a potent therapeutic agent for the treatment of PAH.

Implications of immune-inflammatory responses in smooth muscle dysfunction and disease

In the past few decades, solid evidence has been accumulated for the pivotal significance of immunoinflammatory processes in the initiation, progression, and exacerbation of many diseases and disorders. This groundbreaking view came from original works by Ross who first described that excessive inflammatory-fibroproliferative response to various forms of insult to the endothelium and smooth muscle of the artery wall is essential for the pathogenesis of atherosclerosis (Ross, Nature 1993; 362(6423): 801–9). It is now widely recognized that both innate and adaptive immune reactions are avidly involved in the inflammation-related remodeling of many tissues and organs. When this state persists, irreversible fibrogenic changes would occur often culminating in fatal insufficiencies of many vital parenchymal organs such as liver, lung, heart, kidney and intestines. Thus, inflammatory diseases are becoming the common life-threatening risk for and urgent concern about the public health in developed countries (Wynn et al., Nature Medicine 2012; 18(7): 1028–40). Considering this timeliness, we organized a special symposium entitled “Implications of immune/inflammatory responses in smooth muscle dysfunction and disease” in the 58th annual meeting of the Japan Society of Smooth Muscle Research. This symposium report will provide detailed synopses of topics presented in this symposium; (1) the role of inflammasome in atherosclerosis and abdominal aortic aneurysms by Fumitake Usui-Kawanishi and Masafumi Takahashi; (2) Mechanisms underlying the pathogenesis of hyper-contractility of bronchial smooth muscle in allergic asthma by Hiroyasu Sakai, Wataru Suto, Yuki Kai and Yoshihiko Chiba; (3) Vascular remodeling in pulmonary arterial hypertension by Keizo Hiraishi, Lin Hai Kurahara and Ryuji Inoue.

SGLT2 inhibitor ipragliflozin attenuates breast cancer cell proliferation

Cancer is currently one of the major causes of death in patients with type 2 diabetes mellitus. We previously reported the beneficial effects of the glucagon-like peptide-1 receptor agonist exendin-4 against prostate and breast cancer. In the present study, we examined the anti-cancer effect of the sodium-glucose cotransporter 2 (SGLT2) inhibitor ipragliflozin using a breast cancer model. In human breast cancer MCF-7 cells, SGLT2 expression was detected using both RT-PCR and immunohistochemistry. Ipragliflozin at 1-50 μM significantly and dose-dependently suppressed the growth of MCF-7 cells. BrdU assay also revealed that ipragliflozin attenuated the proliferation of MCF-7 cells in a dose-dependent manner. Because the effect of ipragliflozin against breast cancer cells was completely canceled by knocking down SGLT2, ipragliflozin could act via inhibiting SGLT2. We next measured membrane potential and whole-cell current using the patch clamp technique. When we treated MCF-7 cells with ipragliflozin or glucose-free medium, membrane hyperpolarization was observed. In addition, glucose-free medium and knockdown of SGLT2 by siRNA suppressed the glucose-induced whole-cell current of MCF-7 cells, suggesting that ipragliflozin inhibits sodium and glucose cotransport through SGLT2. Furthermore, JC-1 green fluorescence was significantly increased by ipragliflozin, suggesting the change of mitochondrial membrane potential. These findings suggest that the SGLT2 inhibitor ipragliflozin attenuates breast cancer cell proliferation via membrane hyperpolarization and mitochondrial membrane instability.

Endoscopic Biliary Intervention Using Traction Devices for Periampullary Diverticulum

We describe the case a 92-year-old woman who was admitted to our hospital with choledocholithiasis and periampullary diverticulum (PAD). Due to PAD, clear visualization of the ampulla of Vater could not be obtained. Although selective bile duct cannulation was difficult, a 7-Fr plastic stent was placed during the first session. Fifteen days later, endoscopic retrograde cholangiopancreatography was retried using traction devices, and the papilla became visible. Endoscopic sphincterotomy and stone extraction were performed without any complications. The application of traction devices in endoscopic submucosal dissection may be a promising technique in cases in which endoscopic biliary intervention is difficult due to PAD.

Construction of a Fluorescent Screening System of Allosteric Modulators for the GABAA Receptor Using a Turn-On Probe

γ-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the central nervous system. The fast inhibitory actions of GABA are mainly mediated by GABA_A receptors (GABA_ARs), which are widely recognized as clinically relevant drug targets. However, it remains difficult to create screening systems for drug candidates that act on GABA_ARs because of the existence of multiple ligand-binding sites and the delicate pentameric structures of GABA_ARs. We here developed the first turn-on fluorescent imaging probe for GABA_ARs, which can be used to quantitatively evaluate ligand-receptor interactions under live cell conditions. Using noncovalent labeling of GABA_ARs with this turn-on probe, a new imaging-based ligand assay system, which allows discovery of positive allosteric modulators (PAMs) for the GABA_AR, was successfully constructed. Our system is applicable to high-throughput ligand screening, and we discovered new small molecules that function as PAMs for GABA_ARs. These results highlight the power of the use of a turn-on fluorescent probe to screen drugs for complicated membrane proteins that cannot be addressed by conventional methods.

Contribution of Coiled-Coil Assembly to Ca2+/Calmodulin-Dependent Inactivation of TRPC6 Channel and its Impacts on FSGS-Associated Phenotypes

BACKGROUND

TRPC6 is a nonselective cation channel, and mutations of this gene are associated with FSGS. These mutations are associated with TRPC6 current amplitude amplification and/or delay of the channel inactivation (gain-of-function phenotype). However, the mechanism of the gain-of-function in TRPC6 activity has not yet been clearly solved.

METHODS

We performed electrophysiologic, biochemical, and biophysical experiments to elucidate the molecular mechanism underlying calmodulin (CaM)-mediated Ca²⁺-dependent inactivation (CDI) of TRPC6. To address the pathophysiologic contribution of CDI, we assessed the actin filament organization in cultured mouse podocytes.

RESULTS

Both lobes of CaM helped induce CDI. Moreover, CaM binding to the TRPC6 CaM-binding domain (CBD) was Ca²⁺-dependent and exhibited a 1:2 (CaM/CBD) stoichiometry. The TRPC6 coiled-coil assembly, which brought two CBDs into adequate proximity, was essential for CDI. Deletion of the coiled-coil slowed CDI of TRPC6, indicating that the coiled-coil assembly configures both lobes of CaM binding on two CBDs to induce normal CDI. The FSGS-associated TRPC6 mutations within the coiled-coil severely delayed CDI and often increased TRPC6 current amplitudes. In cultured mouse podocytes, FSGS-associated channels and CaM mutations led to sustained Ca²⁺ elevations and a disorganized cytoskeleton.

CONCLUSIONS

The gain-of-function mechanism found in FSGS-causing mutations in TRPC6 can be explained by impairments of the CDI, caused by disruptions of TRPC's coiled-coil assembly which is essential for CaM binding. The resulting excess Ca²⁺ may contribute to structural damage in the podocytes.

Integrative and theoretical research on the architecture of a biological system and its disorder

An organism stems from assemblies of a variety of cells and proteins. This complex system serves as a unit, and it exhibits highly sophisticated functions in response to exogenous stimuli that change over time. The complete sequencing of the entire human genome has allowed researchers to address the enigmas of life and disease at the gene- or molecular-based level. The consequence of such studies is the rapid accumulation of a multitude of data at multiple levels, ranging from molecules to the whole body, that has necessitated the development of entirely new concepts, tools, and methodologies to analyze and integrate these data. This necessity has given birth to systems biology, an advanced theoretical and practical research framework that has totally changed the directions of not only basic life science but also medicine. During the symposium of the 95th Annual Meeting of The Physiological Society of Japan 2018, five researchers reported on their respective studies on systems biology. The topics included reactions of drugs, ion-transport architecture in an epithelial system, multi-omics in renal disease, cardiac electrophysiological systems, and a software platform for computer simulation. In this review article these authors have summarized recent achievements in the field and discuss next-generation studies on health and disease.

TRP channels in cardiac and intestinal fibrosis

It is now widely accepted that advanced fibrosis underlies many chronic inflammatory disorders and is the main cause of morbidity and mortality of the modern world. The pathogenic mechanism of advanced fibrosis involves diverse and intricate interplays between numerous extracellular and intracellular signaling molecules, among which the non-trivial roles of a stress-responsive Ca²⁺/Na⁺-permeable cation channel superfamily, the transient receptor potential (TRP) protein, are receiving growing attention. Available evidence suggests that several TRP channels such as TRPC3, TRPC6, TRPV1, TRPV3, TRPV4, TRPA1, TRPM6 and TRPM7 may play central roles in the progression and/or prevention of fibroproliferative disorders in vital visceral organs such as lung, heart, liver, kidney, and bowel as well as brain, blood vessels and skin, and may contribute to both acute and chronic inflammatory processes involved therein. This short paper overviews the current knowledge accumulated in this rapidly growing field, with particular focus on cardiac and intestinal fibrosis, which are tightly associated with the pathogenesis of atrial fibrillation and inflammatory bowel diseases such as Crohn's disease.

Daikenchuto (Da-Jian-Zhong-Tang) ameliorates intestinal fibrosis by activating myofibroblast transient receptor potential ankyrin 1 channel

AIM

To investigate the anti-fibrotic effects of the traditional oriental herbal medicine Daikenchuto (DKT) associated with transient receptor potential ankyrin 1 (TRPA1) channels in intestinal myofibroblasts.

METHODS

Inflammatory and fibrotic changes were detected in a 2,4,6-trinitrobenzenesulfonic acid (TNBS) chronic colitis model of wild-type and TRPA1-knockout (TRPA1-KO) mice via pathological staining and immunoblotting analysis. Ca²⁺ imaging experiments examined the effects of DKT and its components/ingredients on intestinal myofibroblast (InMyoFib) cell TRPA1 channel function. Pro-fibrotic factors and transforming growth factor (TGF)-β1-associated signaling were tested in an InMyoFib cell line by qPCR and immunoblotting experiments. Samples from non-stenotic and stenotic regions of the intestines of patients with Crohn’s disease (CD) were used for pathological analysis.

RESULTS

Chronic treatment with TNBS caused more severe inflammation and fibrotic changes in TRPA1-KO than in wild-type mice. A one-week enema administration of DKT reduced fibrotic lesions in wild-type but not in TRPA1-KO mice. The active ingredients of DKT, i.e., hydroxy α-sanshool and 6-shogaol, induced Ca²⁺ influxes in InMyoFib, and this was antagonized by co-treatment with a selective TRPA1 channel blocker, HC-030031. DKT counteracted TGF-β1-induced expression of Type I collagen and α-smooth muscle actin (α-SMA), which were accompanied by a reduction in the phosphorylation of Smad-2 and p38-mitogen-activated protein kinase (p38-MAPK) and the expression of myocardin. Importantly, 24-h incubation with a DKT active component Japanese Pepper increased the mRNA and protein expression levels of TRPA1 in InMyoFibs, which in turn negatively regulated collagen synthesis. In the stenotic regions of the intestines of CD patients, TRPA1 expression was significantly enhanced.

CONCLUSION

The effects of DKT on the expression and activation of the TRPA1 channel could be advantageous for suppressing intestinal fibrosis, and benefit inflammatory bowel disease treatment.

TRPM7-mediated spontaneous Ca2+ entry regulates the proliferation and differentiation of human leukemia cell line K562

Continuous Ca2+ influx is essential to maintain intracellular Ca2+ homeostasis and its dysregulation leads to a variety of cellular dysfunctions. In this study, we explored the functional roles of spontaneous Ca2+ influx for the proliferation and differentiation of a human erythromyeloid leukemia cell line K562. mRNA/protein expressions were assessed by the real-time RT-PCR, western blotting, and immunocytochemical staining. Intracellular Ca2+ concentration ([Ca2+ ]i ) and ionic currents were measured by fluorescent imaging and patch clamping techniques, respectively. Cell counting/viability and colorimetric assays were applied to assess proliferation rate and hemoglobin synthesis, respectively. Elimination of extracellular Ca2+ decreased basal [Ca2+ ]i in proliferating K562 cells. Cation channel blockers such as SK&F96365, 2-APB, Gd3+ , and FTY720 dose dependently decreased basal [Ca2+ ]i . A spontaneously active inward current (Ispont ) contributive to basal [Ca2+ ]i was identified by the nystatin-perforated whole-cell recording. Ispont permeated Ca2+ comparably to Na+ , and was greatly eliminated by siRNA targeting TRPM7, a melastatin member of the transient receptor potential (TRP) superfamily. Consistent with these findings, TRPM7 immune reactivity was detected by western blotting, and immunofluorescence representing TRPM7 was found localized to the K562 cell membrane. Strikingly, all these procedures, that is, Ca2+ removal, TRPM7 blockers and siRNA-mediated TRPM7 knockdown significantly retarded the growth and suppressed hemin-induced γ-globin and hemoglobin syntheses in K562 cells, respectively, both of which appeared associated with the inhibition of ERK activation. These results collectively suggest that spontaneous Ca2+ influx through constitutively active TRPM7 channels may critically regulate both proliferative and erythroid differentiation potentials of K562 cells.

Uncovering the arrhythmogenic potential of TRPM4 activation in atrial-derived HL-1 cells using novel recording and numerical approaches

Aims

Transient receptor potential cation channel subfamily melastatin member 4 (TRPM4), a Ca2+-activated nonselective cation channel abundantly expressed in the heart, has been implicated in conduction block and other arrhythmic propensities associated with cardiac remodelling and injury. The present study aimed to quantitatively evaluate the arrhythmogenic potential of TRPM4.

Methods and results

Patch clamp and biochemical analyses were performed using expression system and an immortalized atrial cardiomyocyte cell line (HL-1), and numerical model simulation was employed. After rapid desensitization, robust reactivation of TRPM4 channels required high micromolar concentrations of Ca2+. However, upon evaluation with a newly devised, ionomycin-permeabilized cell-attached (Iono-C/A) recording technique, submicromolar concentrations of Ca2+ (apparent Kd = ∼500 nM) were enough to activate this channel. Similar submicromolar Ca2+ dependency was also observed with sharp electrode whole-cell recording and in experiments coexpressing TRPM4 and L-type voltage-dependent Ca2+ channels. Numerical simulations using a number of action potential (AP) models (HL-1, Nygren, Luo-Rudy) incorporating the Ca2+- and voltage-dependent gating parameters of TRPM4, as assessed by Iono-C/A recording, indicated that a few-fold increase in TRPM4 activity is sufficient to delay late AP repolarization and further increases (≥ six-fold) evoke early afterdepolarization. These model predictions are consistent with electrophysiological data from angiotensin II-treated HL-1 cells in which TRPM4 expression and activity were enhanced.

Conclusions

These results collectively indicate that the TRPM4 channel is activated by a physiological range of Ca2+ concentrations and its excessive activity can cause arrhythmic changes. Moreover, these results demonstrate potential utility of the first AP models incorporating TRPM4 gating for in silico assessment of arrhythmogenicity in remodelling cardiac tissue.

Cellular mechanism for herbal medicine Junchoto to facilitate intestinal Cl-/water secretion that involves cAMP-dependent activation of CFTR

Constipation is a common symptom frequently compromising the quality of daily life. Several mechanistically different drugs have been used to mitigate constipation, including Japanese herbal (Kampo) medicines. However, the mechanisms of their actions are often not well understood. Here we aimed to investigate the molecular mechanisms underlying the effects of Junchoto (JCT), a Kampo medicine empirically prescribed for chronic constipation. Cl⁻ channel activity was measured by the patch-clamp method in human cystic fibrosis transmembrane conductance regulator (CFTR)-expressing HEK293T cells and human intestinal Caco-2 cells. cAMP was measured by a luciferase-based assay. Cell volume change was measured by a particle-sizing and particle-counting analyzer and video-microscopic measurement. In both CFTR-expressing HEK293T and Caco-2 cells, JCT dose-dependently induced whole-cell currents showing typical biophysical and pharmacological features of CFTR. Robust expression of CFTR was confirmed by RT-PCR and Western blotting in Caco-2 cells. Luciferase-based measurement revealed that JCT increases intracellular cAMP levels. Administration of the adenylate cyclase inhibitor SQ22536 or CFTR inhibitor-172, or treatment with small interfering RNAs (siRNA) targeting CFTR, abolished JCT-induced whole-cell currents, suggesting that elevated intracellular cAMP by JCT causes activation of CFTR in Caco-2 cells. Finally, blockade of CFTR activity by CFTR inhibitor-172 or siRNA-knockdown of CFTR or application of SQ22536 markedly reduced the degree of cell volume decrease induced by JCT. JCT can induce a Cl⁻ efflux through the CFTR channel to promote water secretion, and this effect is likely mediated by increased cAMP production.

Activation of Myofibroblast TRPA1 by Steroids and Pirfenidone Ameliorates Fibrosis in Experimental Crohn's Disease

BACKGROUND & AIMS

The transient receptor potential ankyrin 1 (TRPA1) channel is highly expressed in the intestinal lamina propria, but its contribution to gut physiology/pathophysiology is unclear. Here, we evaluated the function of myofibroblast TRPA1 channels in intestinal remodeling.

METHODS

An intestinal myofibroblast cell line (InMyoFibs) was stimulated by transforming growth factor-β1 to induce in vitro fibrosis. Trpa1 knockout mice were generated using the Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated 9 (Cas9) system. A murine chronic colitis model was established by weekly intrarectal trinitrobenzene sulfonic acid (TNBS) administration. Samples from the intestines of Crohn's disease (CD) patients were used for pathologic staining and quantitative analyses.

RESULTS

In InMyoFibs, TRPA1 showed the highest expression among TRP family members. In TNBS chronic colitis model mice, the extents of inflammation and fibrotic changes were more prominent in TRPA1^-/- knockout than in wild-type mice. One-week enema administration of prednisolone suppressed fibrotic lesions in wild-type mice, but not in TRPA1 knockout mice. Steroids and pirfenidone induced Ca²⁺ influx in InMyoFibs, which was antagonized by the selective TRPA1 channel blocker HC-030031. Steroids and pirfenidone counteracted transforming growth factor-β1-induced expression of heat shock protein 47, type 1 collagen, and α-smooth muscle actin, and reduced Smad-2 phosphorylation and myocardin expression in InMyoFibs. In stenotic intestinal regions of CD patients, TRPA1 expression was increased significantly. TRPA1/heat shock protein 47 double-positive cells accumulated in the stenotic intestinal regions of both CD patients and TNBS-treated mice.

CONCLUSIONS

TRPA1, in addition to its anti-inflammatory actions, may protect against intestinal fibrosis, thus being a novel therapeutic target for highly incurable inflammatory/fibrotic disorders.

Significant contribution of TRPC6 channel-mediated Ca2+ influx to the pathogenesis of Crohn's disease fibrotic stenosis

Intestinal fibrosis is an intractable complication of Crohn's disease (CD), and, when occurring excessively, causes severe intestinal obstruction that often necessitates surgical resection. The fibrosis is characterized by an imbalance in the turnover of extracellular matrix (ECM) components, where intestinal fibroblasts/myofibroblasts play active roles in ECM production, fibrogenesis and tissue remodeling, which eventually leads to the formation of stenotic lesions. There is however a great paucity of knowledge about how intestinal fibrosis initiates and progresses, which hampers the development of effective pharmacotherapies against CD. Recently, we explored the potential implications of transient receptor potential (TRP) channels in the pathogenesis of intestinal fibrosis, since they are known to act as cellular stress sensors/transducers affecting intracellular Ca²⁺ homeostasis/dynamics, and are involved in a broad spectrum of cell pathophysiology including inflammation and tissue remodeling. In this review, we will place a particular emphasis on the intestinal fibroblast/myofibroblast TRPC6 channel to discuss its modulatory effects on fibrotic responses and therapeutic potential for anti-fibrotic treatment against CD-related stenosis.

Cardiac myofibroblast engulfment of dead cells facilitates recovery after myocardial infarction

Myocardial infarction (MI) results in the generation of dead cells in the infarcted area. These cells are swiftly removed by phagocytes to minimize inflammation and limit expansion of the damaged area. However, the types of cells and molecules responsible for the engulfment of dead cells in the infarcted area remain largely unknown. In this study, we demonstrated that cardiac myofibroblasts, which execute tissue fibrosis by producing extracellular matrix proteins, efficiently engulf dead cells. Furthermore, we identified a population of cardiac myofibroblasts that appears in the heart after MI in humans and mice. We found that these cardiac myofibroblasts secrete milk fat globule-epidermal growth factor 8 (MFG-E8), which promotes apoptotic engulfment, and determined that serum response factor is important for MFG-E8 production in myofibroblasts. Following MFG-E8-mediated engulfment of apoptotic cells, myofibroblasts acquired antiinflammatory properties. MFG-E8 deficiency in mice led to the accumulation of unengulfed dead cells after MI, resulting in exacerbated inflammatory responses and a substantial decrease in survival. Moreover, MFG-E8 administration into infarcted hearts restored cardiac function and morphology. MFG-E8-producing myofibroblasts mainly originated from resident cardiac fibroblasts and cells that underwent endothelial-mesenchymal transition in the heart. Together, our results reveal previously unrecognized roles of myofibroblasts in regulating apoptotic engulfment and a fundamental importance of these cells in recovery from MI.

Distinct contributions of LRRC8A and its paralogs to the VSOR anion channel from those of the ASOR anion channel

Volume- and acid-sensitive outwardly rectifying anion channels (VSOR and ASOR) activated by swelling and acidification exhibit voltage-dependent inactivation and activation time courses, respectively. Recently, LRRC8A and some paralogs were shown to be essentially involved in the activity and inactivation kinetics of VSOR currents in human colonic HCT116 cells. In human cervix HeLa cells, here, inactivation of VSOR currents was found to become accelerated by RNA silencing only of LRRC8A but never decelerated by that of any LRRC8 isoform. These data suggest that LRRC8A is associated with the deceleration mechanism of VSOR inactivation, while none of LRRC8 members is related to the acceleration mechanism. Activation kinetics of ASOR currents was unaffected by knockdown of any LRRC8 family member. Double, triple and quadruple gene-silencing studies indicated that combinatory expression of LRRC8A with LRRC8D and LRRC8C is essential for VSOR activity, whereas none of LRRC8 family members is involved in ASOR activity.

Optical control of neuronal firing via photoinduced electron transfer in donor-acceptor conjugates

A rationally designed donor–acceptor conjugate efficiently generates a photoinduced charge-separated state in a cellular environment, achieving photoinduction of neuronal firing.

A series of porphyrin–fullerene linked molecules has been synthesized to evaluate the effects of substituents and molecular structures on their charge-separation yield and the lifetime of a final charge-separated state in various hydrophilic environments. The selected high-performance molecule effectively achieved depolarization in a plasma cell membrane by visible light as well as two-photon excitation using a near-infrared light laser. Moreover, it was revealed that the depolarization can trigger neuronal firing in rat hippocampal neurons, demonstrating the potential and versatility for controlling cell functions using light.

Screening of Transient Receptor Potential Canonical Channel Activators Identifies Novel Neurotrophic Piperazine Compounds

Transient receptor potential canonical (TRPC) proteins form Ca(2+)-permeable cation channels activated upon stimulation of metabotropic receptors coupled to phospholipase C. Among the TRPC subfamily, TRPC3 and TRPC6 channels activated directly by diacylglycerol (DAG) play important roles in brain-derived neurotrophic factor (BDNF) signaling, promoting neuronal development and survival. In various disease models, BDNF restores neurologic deficits, but its therapeutic potential is limited by its poor pharmacokinetic profile. Elucidation of a framework for designing small molecules, which elicit BDNF-like activity via TRPC3 and TRPC6, establishes a solid basis to overcome this limitation. We discovered, through library screening, a group of piperazine-derived compounds that activate DAG-activated TRPC3/TRPC6/TRPC7 channels. The compounds [4-(5-chloro-2-methylphenyl)piperazin-1-yl](3-fluorophenyl)methanone (PPZ1) and 2-[4-(2,3-dimethylphenyl)piperazin-1-yl]-N-(2-ethoxyphenyl)acetamide (PPZ2) activated, in a dose-dependent manner, recombinant TRPC3/TRPC6/TRPC7 channels, but not other TRPCs, in human embryonic kidney cells. PPZ2 activated native TRPC6-like channels in smooth muscle cells isolated from rabbit portal vein. Also, PPZ2 evoked cation currents and Ca(2+) influx in rat cultured central neurons. Strikingly, both compounds induced BDNF-like neurite growth and neuroprotection, which were abolished by a knockdown or inhibition of TRPC3/TRPC6/TRPC7 in cultured neurons. Inhibitors of Ca(2+) signaling pathways, except calcineurin, impaired neurite outgrowth promotion induced by PPZ compounds. PPZ2 increased activation of the Ca(2+)-dependent transcription factor, cAMP response element-binding protein. These findings suggest that Ca(2+) signaling mediated by activation of DAG-activated TRPC channels underlies neurotrophic effects of PPZ compounds. Thus, piperazine-derived activators of DAG-activated TRPC channels provide important insights for future development of a new class of synthetic neurotrophic drugs.

TRPC6 regulates cell cycle progression by modulating membrane potential in bone marrow stromal cells

BACKGROUND AND PURPOSE

Ca(2+) influx is important for cell cycle progression, but the mechanisms involved seem to vary. We investigated the potential roles of transient receptor potential (TRP) channels and store-operated Ca(2+) entry (SOCE)-related molecules STIM (stromal interaction molecule)/Orai in the cell cycle progression of rat bone marrow stromal cells (BMSCs), a reliable therapeutic resource for regenerative medicine.

EXPERIMENTAL APPROACH

PCR and immunoblot analyses were used to examine mRNA and protein levels, fluorescence imaging and patch clamping for Ca(2+) influx and membrane potential measurements, and flow cytometry for cell cycle analysis.

KEY RESULTS

Cell cycle synchronization of BMSCs revealed S phase-specific enhancement of TRPC1, STIM and Orai mRNA and protein expression. In contrast, TRPC6 expression decreased in the S phase and increased in the G1 phase. Resting membrane potential (RMP) of BMSCs was most negative and positive in the S and G1 phases, respectively, and was accompanied by an enhancement and attenuation of SOCE respectively. Chemically depolarizing/hyperpolarizing the membrane erased these differences in SOCE magnitude during the cell cycle. siRNA knockdown of TRPC6 produced a negative shift in RMP, increased SOCE and caused redistribution of BMSCs with increased populations in the S and G2 /M phases and accumulation of cyclins A2 and B1. A low concentration of Gd(3+) (1 μM) suppressed BMSC proliferation at its concentration to inhibit SOC channels relatively specifically.

CONCLUSIONS AND IMPLICATIONS

TRPC6, by changing the membrane potential, plays a pivotal role in controlling the SOCE magnitude, which is critical for cell cycle progression of BMSCs. This finding provides a new therapeutic strategy for regulating BMSC proliferation.

Living situations associated with poor dietary intake among healthy Japanese elderly: the Ohasama Study

BACKGROUND

Rapid increases in life expectancy have led to concurrent increases in the number of elderly people living alone or those forced to change living situations. Previous studies have found that poor dietary intake was common in elderly people living alone. However, there have been few studies about the dietary intake in elderly people living in other situations, particularly those living with family other than a spouse (nonspouse family), which is common in Japan.

OBJECTIVE

To examine the differences in dietary intake by different living situations in elderly Japanese people. We analyzed the data of 1542 healthy residents in the town of Ohasama aged 60 years and over who had completed self-administered questionnaires.

METHODS

The dietary intake was measured using a validated 141-item food frequency questionnaire. Multiple regression models with robust (White-corrected) standard errors were individually fitted for nutrients and foods by living situation.

RESULTS

In men, although the presence of other family was correlated with significantly lower intake of protein-related foods, e.g., legumes, fish and shellfish, and dairy products, these declines were more serious in men living with nonspouse family. Conversely, in men living alone the intake of fruits and vegetables was significantly lower. In women, lower intakes of fruit and protein-related foods were significantly more common in participants living with nonspouse family than those living with only a spouse.

CONCLUSION

These findings revealed that elderly people living alone as well as those living with family other than a spouse had poor dietary intake, suggesting that strategies to improve food choices and skills for food preparation could promote of healthy eating in elderly Japanese people.

Dynamics of receptor-operated Ca(2+) currents through TRPC channels controlled via the PI(4,5)P2-PLC signaling pathway

Transient receptor potential canonical (TRPC) channels are Ca²⁺-permeable, nonselective cation channels that carry receptor-operated Ca²⁺ currents (ROCs) triggered by receptor-induced, phospholipase C (PLC)-catalyzed hydrolysis of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P₂]. Within the vasculature, TRPC channel ROCs contribute to smooth muscle cell depolarization, vasoconstriction, and vascular remodeling. However, TRPC channel ROCs exhibit a variable response to receptor-stimulation, and the regulatory mechanisms governing TRPC channel activity remain obscure. The variability of ROCs may be explained by their complex regulation by PI(4,5)P₂ and its metabolites, which differentially affect TRPC channel activity. To resolve the complex regulation of ROCs, the use of voltage-sensing phosphoinositide phosphatases and model simulation have helped to reveal the time-dependent contribution of PI(4,5)P₂ and the possible role of PI(4,5)P₂ in the regulation of ROCs. These approaches may provide unprecedented insight into the dynamics of PI(4,5)P₂ regulation of TRPC channels and the fundamental mechanisms underlying transmembrane ion flow. Within that context, we summarize the regulation of TRPC channels and their coupling to receptor-mediated signaling, as well as the application of voltage-sensing phosphoinositide phosphatases to this research. We also discuss the controversial bidirectional effects of PI(4,5)P₂ using a model simulation that could explain the complicated effects of PI(4,5)P₂ on different ROCs.

New experimental trends for phosphoinositides research on ion transporter/channel regulation

Phosphoinositides(4,5)-bisphosphates [PI(4,5)P2] critically controls membrane excitability, the disruption of which leads to pathophysiological states. PI(4,5)P2 plays a primary role in regulating the conduction and gating properties of ion channels/transporters, through electrostatic and hydrophobic interactions that allow direct associations. In recent years, the development of many molecular tools have brought deep insights into the mechanisms underlying PI(4,5)P2-mediated regulation. This review summarizes the methods currently available to manipulate the cell membrane PI(4,5)P2 level including pharmacological interventions as well as newly designed molecular tools. We concisely introduce materials and experimental designs suitable for the study of PI(4,5)P2-mediated regulation of ion-conducting molecules, in order to assist researchers who are interested in this area. It is our further hope that the knowledge introduced in this review will help to promote our understanding about the pathology of diseases such as cardiac arrhythmias, bipolar disorders, and Alzheimer's disease which are somehow associated with a disruption of PI(4,5)P2 metabolism.

PLC-mediated PI(4,5)P2 hydrolysis regulates activation and inactivation of TRPC6/7 channels

Transient receptor potential classical (or canonical) (TRPC)3, TRPC6, and TRPC7 are a subfamily of TRPC channels activated by diacylglycerol (DAG) produced through the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) by phospholipase C (PLC). PI(4,5)P2 depletion by a heterologously expressed phosphatase inhibits TRPC3, TRPC6, and TRPC7 activity independently of DAG; however, the physiological role of PI(4,5)P2 reduction on channel activity remains unclear. We used Förster resonance energy transfer (FRET) to measure PI(4,5)P2 or DAG dynamics concurrently with TRPC6 or TRPC7 currents after agonist stimulation of receptors that couple to Gq and thereby activate PLC. Measurements made at different levels of receptor activation revealed a correlation between the kinetics of PI(4,5)P2 reduction and those of receptor-operated TRPC6 and TRPC7 current activation and inactivation. In contrast, DAG production correlated with channel activation but not inactivation; moreover, the time course of channel inactivation was unchanged in protein kinase C-insensitive mutants. These results suggest that inactivation of receptor-operated TRPC currents is primarily mediated by the dissociation of PI(4,5)P2. We determined the functional dissociation constant of PI(4,5)P2 to TRPC channels using FRET of the PLCδ Pleckstrin homology domain (PHd), which binds PI(4,5)P2, and used this constant to fit our experimental data to a model in which channel gating is controlled by PI(4,5)P2 and DAG. This model predicted similar FRET dynamics of the PHd to measured FRET in either human embryonic kidney cells or smooth muscle cells, whereas a model lacking PI(4,5)P2 regulation failed to reproduce the experimental data, confirming the inhibitory role of PI(4,5)P2 depletion on TRPC currents. Our model also explains various PLC-dependent characteristics of channel activity, including limitation of maximum open probability, shortening of the peak time, and the bell-shaped response of total current. In conclusion, our studies demonstrate a fundamental role for PI(4,5)P2 in regulating TRPC6 and TRPC7 activity triggered by PLC-coupled receptor stimulation.

Hepatic arterial infusion chemotherapy with cisplatin before radical local treatment of early hepatocellular carcinoma (JIS score 0/1) improves survival

BACKGROUND

It has not yet been determined whether hepatic arterial infusion (HAI) chemotherapy improves survival in patients with early hepatocellular carcinoma (HCC). We evaluated the effectiveness of HAI with high-concentration cisplatin (DDP-H) for the treatment of HCC by comparing outcomes between patients who received HAI with DDP-H before radical local treatment of early-stage HCC [Japan Integrated Staging (JIS) score 0/1] and patients who did not receive HAI chemotherapy.

PATIENTS AND METHODS

Survival was analyzed in 114 patients with early-stage HCC who underwent radical local treatment. The patients were divided into two groups: a HAI group (n = 79) who received DDP-H infusion into the whole liver via the proper hepatic artery, and a non-HAI group (n = 35) who did not receive HAI chemotherapy.

RESULTS

The cumulative survival rates at 1, 3, and 5 years were 77.4%, 69.2%, and 55.3% in the non-HAI group and 97.4%, 87.0%, and 84.4% in the HAI group, respectively. Survival time prolonged significantly in the HAI group compared with the non-HAI group (log-rank test: P = 0.023; generalized Wilcoxon test: P = 0.012) Multivariate analysis using the Cox proportional hazards model identified HAI with DDP-H as the most important factor affecting survival.

CONCLUSIONS

Whole-liver HAI with DDP-H before radical local treatment can improve the prognosis of patients with early-stage HCC.

Brain-derived neurotrophic factor (BDNF) induces sustained intracellular Ca2+ elevation through the up-regulation of surface transient receptor potential 3 (TRPC3) channels in rodent microglia

Microglia are immune cells that release factors, including proinflammatory cytokines, nitric oxide (NO), and neurotrophins, following activation after disturbance in the brain. Elevation of intracellular Ca(2+) concentration ([Ca(2+)]i) is important for microglial functions such as the release of cytokines and NO from activated microglia. There is increasing evidence suggesting that pathophysiology of neuropsychiatric disorders is related to the inflammatory responses mediated by microglia. Brain-derived neurotrophic factor (BDNF) is a neurotrophin well known for its roles in the activation of microglia as well as in pathophysiology and/or treatment of neuropsychiatric disorders. In this study, we sought to examine the underlying mechanism of BDNF-induced sustained increase in [Ca(2+)]i in rodent microglial cells. We observed that canonical transient receptor potential 3 (TRPC3) channels contribute to the maintenance of BDNF-induced sustained intracellular Ca(2+) elevation. Immunocytochemical technique and flow cytometry also revealed that BDNF rapidly up-regulated the surface expression of TRPC3 channels in rodent microglial cells. In addition, pretreatment with BDNF suppressed the production of NO induced by tumor necrosis factor α (TNFα), which was prevented by co-adiministration of a selective TRPC3 inhibitor. These suggest that BDNF induces sustained intracellular Ca(2+) elevation through the up-regulation of surface TRPC3 channels and TRPC3 channels could be important for the BDNF-induced suppression of the NO production in activated microglia. We show that TRPC3 channels could also play important roles in microglial functions, which might be important for the regulation of inflammatory responses and may also be involved in the pathophysiology and/or the treatment of neuropsychiatric disorders.

Novel HCN2 mutation contributes to febrile seizures by shifting the channel's kinetics in a temperature-dependent manner

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channel-mediated currents, known as I h, are involved in the control of rhythmic activity in neuronal circuits and in determining neuronal properties including the resting membrane potential. Recent studies have shown that HCN channels play a role in seizure susceptibility and in absence and limbic epilepsy including temporal lobe epilepsy following long febrile seizures (FS). This study focused on the potential contributions of abnormalities in the HCN2 isoform and their role in FS. A novel heterozygous missense mutation in HCN2 exon 1 leading to p.S126L was identified in two unrelated patients with FS. The mutation was inherited from the mother who had suffered from FS in a pedigree. To determine the effect of this substitution we conducted whole-cell patch clamp electrophysiology. We found that mutant channels had elevated sensitivity to temperature. More specifically, they displayed faster kinetics at higher temperature. Kinetic shift by change of temperature sensitivity rather than the shift of voltage dependence led to increased availability of I h in conditions promoting FS. Responses to cyclic AMP did not differ between wildtype and mutant channels. Thus, mutant HCN2 channels cause significant cAMP-independent enhanced availability of I h during high temperatures, which may contribute to hyperthermia-induced neuronal hyperexcitability in some individuals with FS.

Molecular determinants for cardiovascular TRPC6 channel regulation by Ca2+/calmodulin-dependent kinase II

The molecular mechanism underlying Ca(2+)/calmodulin (CaM)-dependent kinase II (CaMKII)-mediated regulation of the mouse transient receptor potential channel TRPC6 was explored by chimera, deletion and site-directed mutagenesis approaches. Induction of currents (ICCh) in TRPC6-expressing HEK293 cells by a muscarinic agonist carbachol (CCh; 100 μm) was strongly attenuated by a CaMKII-specific peptide, autocamtide-2-related inhibitory peptide (AIP; 10 μm). TRPC6/C7 chimera experiments showed that the TRPC6 C-terminal sequence is indispensable for ICCh to be sensitive to AIP-induced CaMKII inhibition. Further, deletion of a distal region (Gln(855)-Glu(877)) of the C-terminal CaM/inositol-1,4,5-trisphosphate receptor binding domain (CIRB) of TRPC6 was sufficient to abolish ICCh. Systematic alanine scanning for potential CaMKII phosphorylation sites revealed that Thr(487) was solely responsible for the activation of the TRPC6 channel by receptor stimulation. The abrogating effect of the alanine mutation of Thr(487) (T487A) was reproduced with other non-polar amino acids, namely glutamine or asparagine, while being partially rescued by phosphomimetic mutations with glutamate or aspartate. The cellular expression and distribution of TRPC6 channels did not significantly change with these mutations. Electrophysiological and immunocytochemical data with the Myc-tagged TRPC6 channel indicated that Thr(487) is most likely located at the intracellular side of the cell membrane. Overexpression of T487A caused significant reduction of endogenous TRPC6-like current induced by Arg(8)-vasopressin in A7r5 aortic myocytes. Based on these results, we propose that the optimal spatial arrangement of a C-terminal domain (presumably the distal CIRB region) around a single CaMKII phosphorylation site Thr(487) may be essential for CaMKII-mediated regulation of TRPC6 channels. This mechanism may be of physiological significance in a native environment such as in vascular smooth muscle cells.

Protection from non-alcoholic steatohepatitis and liver tumourigenesis in high fat-fed insulin receptor substrate-1-knockout mice despite insulin resistance

AIMS/HYPOTHESIS

Epidemiological studies have revealed that obesity and diabetes mellitus are independent risk factors for the development of non-alcoholic steatohepatitis (NASH) and hepatocellular carcinoma. However, the debate continues on whether insulin resistance as such is directly associated with NASH and liver tumourigenesis. Here, we investigated the incidence of NASH and liver tumourigenesis in Irs1 ( -/- ) mice subjected to a long-term high-fat (HF) diet. Our hypothesis was that hepatic steatosis, rather than insulin resistance may be related to the pathophysiology of these conditions.

METHODS

Mice (8 weeks old, C57Bl/6J) were given free access to standard chow (SC) or an HF diet. The development of NASH and liver tumourigenesis was evaluated after mice had been on the above-mentioned diets for 60 weeks. Similarly, Irs1 ( -/- ) mice were also subjected to an HF diet for 60 weeks.

RESULTS

Long-term HF diet loading, which causes obesity and insulin resistance, was sufficient to induce NASH and liver tumourigenesis in the C57Bl/6J mice. Obesity and insulin resistance were reduced by switching mice from the HF diet to SC, which also protected these mice against the development of NASH and liver tumourigenesis. However, compared with wild-type mice fed the HF diet, Irs1 ( -/- ) mice fed the HF diet were dramatically protected against NASH and liver tumourigenesis despite the presence of severe insulin resistance and marked postprandial hyperglycaemia.

CONCLUSIONS/INTERPRETATION

IRS-1 inhibition might protect against HF diet-induced NASH and liver tumourigenesis, despite the presence of insulin resistance.

Aldosterone-to-renin ratio as a predictor of stroke under conditions of high sodium intake: the Ohasama study

BACKGROUND

Aldosterone is thought to have deleterious effects on the cardiovascular system. The aldosterone-to-renin ratio (ARR) is more reproducible than aldosterone levels alone and could be an index for inappropriate aldosterone secretion or activity. We previously reported the apparent relation between ARR and hypertension in subjects with high sodium intake. This prospective study investigated the risk of ARR for a first stroke in a general population stratified by sodium intake.

METHODS

We obtained plasma renin activity (PRA) and plasma aldosterone concentrations (PAC) for 883 participants aged ≥ 35 years not receiving antihypertensive treatment in the general population of Ohasama (mean age: 59.0 ± 11.3 years; 65.6% women).

RESULTS

Over a mean of 10.9 follow-up years, 45 strokes occurred. The median PRA, PAC, and ARR were 1.2 ng/ml/h, 6.4 ng/dl, and 5.3 ng/dl per ng/ml/h, respectively. Using Cox regression, we computed hazard ratios adjusted for sex, age, body mass index (BMI), and systolic blood pressure. No association between logARR and stroke was observed in subjects overall. However, in subjects with high sodium intake (≥ median of 4,058 mg/day (salt equivalent, 10.5 g/day)), each 1 s.d. increase in logARR was associated with an increased hazard ratio for stroke (hazard ratio: 1.49, P = 0.04). No significant association was observed in subjects with low sodium intake (P = 0.7). When we repeated all the analyses using logPRA or logPAC, no significant associations were found.

CONCLUSION

These results suggest that high ARR, that is, relative aldosterone excess, is a predictor for stroke under conditions of high sodium intake.

Independent association of cognitive dysfunction with cardiac hypertrophy irrespective of 24-h or sleep blood pressure in older hypertensives

BACKGROUND

Our aim was to assess whether cardiac hypertrophy is associated with cognitive function independently of office, 24-h, or sleep blood pressure (BP) levels in older hypertensive patients treated with antihypertensive medications.

METHODS

In this cross-sectional study, we recruited 443 hypertensive patients aged over 60 years (mean age: 73.0 years; 41% men) who were ambulatory, lived independently, and were without clinically overt dementia. They underwent measurements of 24-h BP monitoring, echocardiographic left ventricular mass index (LVMI), and cognitive function (mini-mental state examination, MMSE).

RESULTS

MMSE score was inversely associated with office, 24-h, awake, and sleep systolic BP (SBP) (each, P < 0.05). There was a close association between MMSE score and LVMI (ρ = -0.32; P < 0.001). Using multiple logistic regression analysis including numerous covariates (i.e., age, sex, obesity, current smoking, educational level, duration of antihypertensive medications, renal dysfunction, statin use, and previous history of cardiovascular disease), the odds ratio (OR) for the presence of cognitive dysfunction, defined as the lowest quartile of MMSE score (median MMSE score: 23 points; n = 115), was estimated; the presence of cardiac hypertrophy (LVMI ≥125 kg/m(2) in men and ≥110 kg/m(2) in women) as well as uncontrolled 24-h BP (mean 24-h SBP/diastolic BP (DBP) ≥130/80 mm Hg) or sleep BP (mean sleep SBP/DBP ≥120/70 mm Hg), but not uncontrolled office BP (mean office SBP/DBP ≥140/90 mm Hg), were independently associated with cognitive dysfunction (all P < 0.05).

CONCLUSIONS

Among older hypertensive patients with antihypertensive medications, those who had echocardiographically determined cardiac hypertrophy may be at high risk for cognitive dysfunction, irrespective of their office BP and 24-h BP levels.