Roles of TRPM4 in immune responses in keratinocytes and identification of a novel TRPM4-activating agent.

The skin is a protective interface between the internal organs and environment and functions not only as a physical barrier but also as an immune organ. However, the immune system in the skin is not fully understood. A member of the thermo-sensitive transient receptor potential (TRP) channel family, TRPM4, which acts as a regulatory receptor in immune cells, was recently reported to be expressed in human skin and keratinocytes. However, the function of TRPM4 in immune responses in keratinocytes has not been investigated. In this study, we found that treatment with BTP2, a known TRPM4 agonist, reduced cytokine production induced by tumor necrosis factor (TNF) α in normal human epidermal keratinocytes and in immortalized human epidermal keratinocytes (HaCaT cells). This cytokine-reducing effect was not observed in TRPM4-deficient HaCaT cells, indicating that TRPM4 contributed to the control of cytokine production in keratinocytes. Furthermore, we identified aluminum potassium sulfate, as a new TRPM4 activating agent. Aluminum potassium sulfate reduced Ca2+ influx by store-operated Ca2+ entry in human TRPM4-expressing HEK293T cells. We further confirmed that aluminum potassium sulfate evoked TRPM4-mediated currents, showing direct evidence for TRPM4 activation. Moreover, treatment with aluminum potassium sulfate reduced cytokine expression induced by TNFα in HaCaT cells. Taken together, our data suggested that TRPM4 may serve as a new target for the treatment of skin inflammatory reactions by suppressing the cytokine production in keratinocytes, and aluminum potassium sulfate is a useful ingredient to prevent undesirable skin inflammation through TRPM4 activation.

Polycystic kidney disease 2-like 1 channel contributes to the bitter aftertaste perception of quinine.

Bitterness is an important physiological function in the defense responses to avoid toxic foods. The taste receptor 2 family is well known to mediate bitter taste perception in Type II taste cells. Here, we report that the polycystic kidney disease 2-like 1 (PKD2L1) channel is a novel sensor for the bitter aftertaste in Type III taste cells. The PKD2L1 channel showed rebound activation after the washout of quinine, a bitter tastant, in electrophysiological whole-cell recordings of the PKD2L1-expressing HEK293T cells and Ca2+-imaging analysis of Type III taste cells isolated from wild-type PKD2L1 mice. In the short-term two-bottle preference and lick tests in vivo, the wild-type mice avoided normal water while the PKD2L1-knockout mice preferred normal water after they ingested the quinine-containing water. These results may explain the new mechanism of the quinine-triggered bitter aftertaste perception in Type III taste cells.

White-coat effect on orthostatic hypotension: a nationwide survey of Japanese general practitioners.

OBJECTIVE: The relationship between the white-coat effect (WCE), defined as white-coat hypertension under treatment, and the frequency of orthostatic hypotension (OH) is not known. We conducted an orthostatic test in patients with WCE to determine the frequency of OH. METHODS: This was a cross-sectional study of 5631 patients with hypertension visiting general practitioners nationwide, in which 4305 patients with hypertension recorded their home blood pressure (BP) and consented to the orthostatic test. Patients with hypertension were divided into four groups: controlled hypertension (CHT), masked hypertension (MHT), sustained hypertension (SHT), and WCE. The orthostatic test was performed, and BP and pulse rate were measured immediately and 1 min after orthostasis. RESULTS: The OH frequencies immediately after standing in CHT, WCE, SHT, and MHT patients were 7, 11.7, 12.1, and 6.6%, respectively, and those at 1 min after standing were 7.1, 13.1, 11.6 and 6.9%, respectively (Chi-square test, P < 0.01, respectively). Logistic regression analysis was performed to examine the relationship between WCE and the frequency of OH. The frequency of OH immediately after standing was significantly increased [adjusted odds ratio (AOR), 1.702; 95% confidence interval (CI), 1.246-2.326; P < 0.01]. The frequency of OH at 1 min after standing was also significantly higher (AOR, 1.897; 95% CI, 1.396-2.578; P < 0.01). CONCLUSION: When the standing test was performed for patients with WCE, the frequency of OH increased. Thus, it is important to recognize the possibility of OH in patients with WCE to avoid adverse events associated with excessive hypotension.

Fine-Tuning of Piezo1 Expression and Activity Ensures Efficient Myoblast Fusion during Skeletal Myogenesis.

Mechanical stimuli, such as stretch and resistance training, are essential in regulating the growth and functioning of skeletal muscles. However, the molecular mechanisms involved in sensing mechanical stress during muscle formation remain unclear. Here, we investigated the role of the mechanosensitive ion channel Piezo1 during myogenic progression of both fast and slow muscle satellite cells. We found that Piezo1 level increases during myogenic differentiation and direct manipulation of Piezo1 in muscle stem cells alters the myogenic progression. Indeed, Piezo1 knockdown suppresses myoblast fusion, leading to smaller myotubes. Such an event is accompanied by significant downregulation of the fusogenic protein Myomaker. In parallel, while Piezo1 knockdown also lowers Ca2+ influx in response to stretch, Piezo1 activation increases Ca2+ influx in response to stretch and enhances myoblasts fusion. These findings may help understand molecular defects present in some muscle diseases. Our study shows that Piezo1 is essential for terminal muscle differentiation acting on myoblast fusion, suggesting that Piezo1 deregulation may have implications in muscle aging and degenerative diseases, including muscular dystrophies and neuromuscular disorders.

A unique mode of keratinocyte death requires intracellular acidification.

The stratum corneum (SC), the outermost epidermal layer, consists of nonviable anuclear keratinocytes, called corneocytes, which function as a protective barrier. The exact modes of cell death executed by keratinocytes of the upper stratum granulosum (SG1 cells) remain largely unknown. Here, using intravital imaging combined with intracellular Ca2+- and pH-responsive fluorescent probes, we aimed to dissect the SG1 death process in vivo. We found that SG1 cell death was preceded by prolonged (∼60 min) Ca2+ elevation and rapid induction of intracellular acidification. Once such intracellular ionic changes were initiated, they became sustained, irreversibly committing the SG1 cells to corneocyte conversion. Time-lapse imaging of isolated murine SG1 cells revealed that intracellular acidification was essential for the degradation of keratohyalin granules and nuclear DNA, phenomena specific to SC corneocyte formation. Furthermore, intravital imaging showed that the number of SG1 cells exhibiting Ca2+ elevation and the timing of intracellular acidification were both tightly regulated by the transient receptor potential cation channel V3. The functional activity of this protein was confirmed in isolated SG1 cells using whole-cell patch-clamp analysis. These findings provide a theoretical framework for improved understanding of the unique molecular mechanisms underlying keratinocyte-specific death mode, namely corneoptosis.

Retrospective Analysis of the Renoprotective Effects of Long-Term Use of Six Types of Sodium-Glucose Cotransporter 2 Inhibitors in Japanese Patients with Type 2 Diabetes Mellitus and Chronic Kidney Disease.

Aim: Sodium-glucose cotransporter 2 inhibitors (SGLT2is) provide renal protection in patients with type 2 diabetes mellitus (T2DM). The aim of this study was to elucidate the renal effects of long-term use of six types of SGLT2is in Japanese patients with T2DM and chronic kidney disease (CKD). Materials and Methods: The Kanagawa Physicians Association maintains a registry of patients who visit their 31 clinics. We retrieved clinical data of patients with T2DM and CKD who were prescribed with SGLT2is for >1 year. Results: A total of 763 patients with a median treatment duration of 33 months were included. The logarithmic value of urine albumin-creatinine ratio (LNACR) decreased significantly from 1.60 ± 0.65 to 1.51 ± 0.67. The multiple linear regression analysis revealed that the LNACR at the initiation of treatment, change in (Δ) diastolic blood pressure, and Δ hemoglobin A1c were independently correlated with ΔLNACR (P < 0.001). The decrease in the LNACR was significantly smaller in the patients with estimated glomerular filtration rate (eGFR) [mL/(min ·1.73 m2)] of <60 (P < 0.05). The eGFR decreased from 77.4 ± 22.3 to 72.7 ± 22.5 mL/(min ·1.73 m2) (P < 0.001). The multiple linear regression analysis showed that the LNACR at the initiation of treatment, Δbody weight at the previous survey, ΔeGFR at the previous survey, and the eGFR at the initiation of treatment correlated independently with ΔeGFR during the maintenance period (P < 0.001). Greater changes in the eGFR during the maintenance period were observed in the patients with macroalbuminuria or eGFR of <60 (P < 0.01). Conclusions: The study confirmed that the long-term use of six types of SGLT2i improved the albumin-creatinine ratio (ACR), although the eGFR gradually decreased during the treatment. The change in the ACR was significantly smaller in the patients with eGFR of <60 mL/(min ·1.73 m2) than in those with eGFR of >60 mL/(min ·1.73 m2). However, this was a retrospective observational study; further studies are needed to formulate final conclusions.

Blood pressure after treatment with sodium-glucose cotransporter 2 inhibitors influences renal composite outcome: Analysis using propensity score-matched models.

AIMS/INTRODUCTION: Sodium-glucose cotransporter 2 inhibitors (SGLT2i) improve renal outcome in patients with type 2 diabetes mellitus, but the mechanism is not fully understood. The aim of this retrospective study was to assess the association of achieved blood pressure with renal outcomes in Japanese type 2 diabetes mellitus patients with chronic kidney disease. MATERIALS AND METHODS: We assessed 624 Japanese type 2 diabetes mellitus patients with chronic kidney disease taking SGLT2i for >1 year. The patients were classified as those with post-treatment mean arterial pressure (MAP) of ≥92 mmHg (n = 344) and those with MAP of <92 mmHg (n = 280) for propensity score matching (1:1 nearest neighbor match with 0.04 of caliper value and no replacement). The end-point was a composite of progression of albuminuria or a decrease in the estimated glomerular filtration rate by ≥15% per year. RESULTS: By propensity score matching, a matched cohort model was constructed, including 201 patients in each group. The incidence of renal composite outcome was significantly lower among patients with MAP of <92 mmHg than among patients with MAP of ≥92 mmHg (n = 11 [6%] vs n = 26 [13%], respectively, P = 0.001). The change in estimated glomerular filtration rate was similar in the two groups; however, the change in the albumin-to-creatinine ratio was significantly larger in patients with MAP of <92 mmHg. CONCLUSIONS: In Japanese type 2 diabetes mellitus patients with chronic kidney disease, blood pressure after SGLT2i administration influences the renal composite outcome. Blood pressure management is important, even during treatment with SGLT2i.

Novel TRPV6 mutations in the spectrum of transient neonatal hyperparathyroidism.

Maternal-fetal calcium (Ca2+) transport in the placenta plays a critical role in maintaining fetal bone mineralization. Mutations in the gene encoding the transient receptor potential cation channel, subfamily V, member 6 (TRPV6) have been identified as causative mutations of transient neonatal hyperparathyroidism due to insufficient maternal-fetal Ca2+ transport in the placenta. In this study, we found two novel mutations in subjects that have transient neonatal hyperparathyroidism. TRPV6 carrying the mutation p.Arg390His that localizes to the outer edge of the first transmembrane domain (S1) showed impaired trafficking to the plasma membrane, whereas TRPV6 having the mutation p.Gly291Ser in the sixth ankyrin repeat (AR) domain had channel properties that were comparable those of WT channels, although the increases in steady-state intracellular Ca2+ concentration could have led to Ca2+ overload and subsequent death of cells expressing this mutant channel. These results indicate that the AR6 domain contributes to TRPV6-mediated maintenance of intracellular Ca2+ concentrations, and that this region could play a novel role in regulating the activity of TRPV6 Ca2+-selective channels.

TRPM8 channel is involved in the ventilatory response to CO2 mediating hypercapnic Ca2+ responses.

The role of TRP channels in the ventilatory response to CO2 was investigated in vivo. To this end, the respiration of unrestrained adult TRPM8-, TRPV1- and TRPV4-channel knockout mice was measured using whole-body plethysmography. Under control conditions and hyperoxic hypercapnia, no difference in respiratory parameters was observed between adult wild-type mice and TRPV1- and TRPV4-channel knockout mice. However, TRPM8-channel knockout mice showed decreased tidal volume under both hypercapnia and resting conditions. In addition, the expression of TRPM8, TRPV1 and TRPV4 mRNAs was detected in EGFP-positive glial cells in the medulla of GFAP promoter-EGFP transgenic mice by real-time PCR. Furthermore, we measured intracellular Ca2+ responses of TRPM8-overexpressing HEK-293 cells to hypercapnic acidosis. Subpopulations of cells that exhibited hypercapnic acidosis-induced Ca2+ response also responded to the application of menthol. These results suggest that TRPM8 partially mediates the ventilatory response to CO2 via changes in intracellular Ca2+ and is a chemosensing protein that may be involved in detecting endogenous CO2 production.

TRPV6 Gene Mutation in a Dizygous Twin With Transient Neonatal Hyperparathyroidism.

Maternal-fetal transport of calcium (Ca2+) is important for bone mineralization in fetal development. Insufficient Ca2+ transport causes transient neonatal hyperparathyroidism (TNHP). Transient receptor potential cation channel, subfamily V, member 6 (TRPV6), has been found to play an important role in the active transport of Ca2+ through the placenta. Recently, TRPV6 gene was found to be the gene responsible for TNHP with severe skeletal undermineralization. To date, only seven cases of TNHP caused by TRPV6 recessive mutations have been reported. We present a case of TNHP caused by TRPV6 gene mutations. A female newborn was hospitalized because of respiratory distress. Marked undermineralization of the skeleton was observed in X-ray imaging. Laboratory examination revealed markedly high PTH and absence of hypercalcemia along with vitamin D deficiency. Her twin brother presented with almost no symptoms. Maternal laboratory findings indicated normocalcemia, but vitamin D deficiency with a high PTH level for the lactation period was observed. We initially diagnosed the patient as having secondary hyperparathyroidism because of maternal vitamin D deficiency. Nevertheless, the reasons underlying the discordant clinical manifestations between the twin siblings remained unclear. Our analysis of TRPV6 gene clarified that the patient had compound heterozygote mutations, which were reported previously (p.Ile223Thr and p.Gly428Arg). Pathologic mutations in TRPV6 gene were not detected in the other sibling. The clinical symptoms in the patient were transient: they resolved during infancy. TNHP caused by TRPV6 gene mutations is a unique disease in terms of its transient pathology in utero and relief after birth.