Voltage-sensing phosphatase (VSP) contains a voltage sensor domain (VSD) similar to that in voltage-gated ion channels, and a phosphoinositide phosphatase region similar to phosphatase and tensin ...homolog deleted on chromosome 10 (PTEN). The VSP gene is conserved from unicellular organisms to higher vertebrates. Membrane depolarization induces electrical driven conformational rearrangement in the VSD, which is translated into catalytic enzyme activity. Biophysical and structural characterization has revealed details of the mechanisms underlying the molecular functions of VSP. Coupling between the VSD and the enzyme is tight, such that enzyme activity is tuned in a graded fashion to the membrane voltage. Upon VSP activation, multiple species of phosphoinositides are simultaneously altered, and the profile of enzyme activity depends on the history of the membrane potential. VSPs have been the obvious candidate link between membrane potential and phosphoinositide regulation. However, patterns of voltage change regulating VSP in native cells remain largely unknown. This review addresses the current understanding of the biophysical biochemical properties of VSP and provides new insight into the proposed functions of VSP.
The previous studies revealed that many types of ion channels have sensitivity to PtdIns(4,5)P
, which has been mainly shown using heterologous expression system. On the other hand, there remains few ...evidence showing that PtdIns(4,5)P
natively regulate the ion channel activities in physiological context. Our group recently discovered that a sperm specific K
channel, Slo3, is natively regulated by PtdIns(4,5)P
in sperm flagellum. Very interestingly, a principal piece, to which Slo3 specifically localized, had extremely low density of PtdIns(4,5)P
compared to the regular cell plasma membrane. Furthermore, our studies and the previous ones also revealed that Slo3 had much stronger PtdIns(4,5)P
affinity than KCNQ2/3 channels, which are widely regulated by endogenous PtdIns(4,5)P
in neurons. Thus, the high-PtdIns(4,5)P
affinity of Slo3 is well-adapted to the specialized PtdIns(4,5)P
environment in the principal piece. This study sheds light on the relationship between PtdIns(4,5)P
-affinity of ion channels and their PtdIns(4,5)P
environment in native cells. We discuss the current understanding about PtdIns(4,5)P
affinity of diverse ion channels and their possible regulatory mechanism in native cellular environment.
Voltage-sensing phosphatase (VSP) consists of the voltage sensor domain (VSD) similar to that of voltage-gated ion channels and the cytoplasmic phosphatase region with remarkable similarity to the ...phosphatase and tensin homolog deleted on chromosome 10 (PTEN). Membrane depolarization activates VSD, leading to dephosphorylation of three species of phosphoinositides (phosphatidylinositol phosphates (PIPs)), PI(3,4,5)P3, PI(4,5)P2, and PI(3,4)P2. VSP dephosphorylates 3- and 5-phosphate of PIPs, unlike PTEN, which shows rigid 3-phosphate specificity. In this study, a bioinformatics search showed that some mammals have VSP orthologs with amino acid diversity in the active center motif, Cx5R, which is highly conserved among protein tyrosine phosphatases and PTEN-related phosphatases; lysine next to the active site cysteine in the Cx5R motif was substituted for methionine in VSP orthologs of Tasmanian devil, koala, and prairie deer mouse, and leucine in opossum. Since lysine at the corresponding site in PTEN is known to be critical for enzyme activities, we attempted to address the significance of amino acid diversity among VSP orthologs at this site. K364 was changed to different amino acids in sea squirt VSP (Ci-VSP), and voltage-dependent phosphatase activity in Xenopus oocyte was studied using fluorescent probes for PI(4,5)P2 and PI(3,4)P2. All mutants retained both 5-phosphatase and 3-phosphatase activity, indicating that lysine at this site is dispensable for 3-phosphatase activity, unlike PTEN. Notably, K364M mutant showed increased activity both of 5-phosphatase and 3-phosphatase compared with the wild type (WT). It also showed slower kinetics of voltage sensor motion. Malachite green assay of K364M mutant did not show significant difference of phosphatase activity from WT, suggesting tighter interaction between substrate binding and voltage sensing. Mutation corresponding to K364M in the zebrafish VSP led to enhanced voltage-dependent dephosphorylation of PI(4,5)P2. Further studies will provide clues to understanding of substrate preference in PIPs phosphatases as well as to customization of a molecular tool.
Voltage-gated proton channel (Hv1) has been studied in various immune cells, including neutrophils. However, most studies have taken an in vitro approach using isolated cells or primary cultured ...cells of mammals; therefore, limited evidence is available on the function of Hv1 in a physiological context. In this study, we have developed the in vivo system that enables real-time functional analysis of Hv1 using zebrafish embryos (
).
-deficiency (
) in zebrafish completely abolished voltage-gated proton current, which is typically observed in wild-type neutrophils. Importantly,
-deficiency significantly reduced reactive oxygen species production and calcium response of zebrafish neutrophils, comparable to the results observed in mammalian models. These findings verify zebrafish Hv1 (DrHv1) as the primary contributor for native Hv1-derived proton current in neutrophils and suggest the conserved function of Hv1 in the immune cells across vertebrate animals. Taking advantage of Hv1 zebrafish model, we compared real-time behaviors of neutrophils between wild-type and
zebrafish in response to tissue injury and acute bacterial infection. Notably, we observed a significant increase in the number of phagosomes in
neutrophils, raising a possible link between Hv1 and phagosomal maturation. Furthermore, survival analysis of zebrafish larvae potentially supports a protective role of Hv1 in the innate immune response against systemic bacterial infection. This study represents the influence of Hv1 on neutrophil behaviors and highlights the benefits of in vivo approach toward the understanding of Hv1 in a physiological context.
Voltage-sensing phosphatase (VSP) exhibits voltage-dependent phosphatase activity toward phosphoinositides. VSP generates a specialized phosphoinositide environment in mammalian sperm flagellum. ...However, the voltage-sensing mechanism of VSP in spermatozoa is not yet characterized. Here, we found that VSP is activated during sperm maturation, indicating that electric signals in immature spermatozoa are essential. Using a heterologous expression system, we show the voltage-sensing property of mouse VSP (mVSP). The voltage-sensing threshold of mVSP is approximately −30 mV, which is sensitive enough to activate mVSP in immature spermatozoa. We also report several knock-in mice in which we manipulate the voltage-sensitivity or electrochemical coupling of mVSP. Notably, the V312R mutant, with a minor voltage-sensitivity change, exhibits abnormal sperm motility after, but not before, capacitation. Additionally, the V312R mutant shows a significant change in the acyl-chain profile of phosphoinositide. Our findings suggest that electrical signals during sperm maturation are crucial for establishing the optimal phosphoinositide environment in spermatozoa.Membrane potentials in living cells can function as electrical signals. Here, the authors report that spermatozoa utilize their electrical signals during the maturing stage to create appropriate membrane lipids environment that is important for sperm motility.
Voltage-sensing phosphatases (VSP) consist of a membrane-spanning voltage sensor domain and a cytoplasmic region that has enzymatic activity toward phosphoinositides (PIs). VSP enzyme activity is ...regulated by membrane potential, and its activation leads to rapid and reversible alteration of cellular PIP levels. These properties enable VSPs to be used as a tool for studying the effects of phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) binding to ion channels and transporters. For example, by applying simple changes in the membrane potential, Danio rerio VSP (Dr-VSP) has been used effectively to manipulate PI(4,5)P2 in mammalian cells with few, if any, side effects. In the present study, we report an enhanced version of Dr-VSP as an improved molecular tool for depleting PI(4,5)P2 from cultured mammalian cells. We modified Dr-VSP in two ways. Its voltage-dependent phosphatase activity was enhanced by introducing an aromatic residue at the position of Leu-223 within a membrane-interacting region of the phosphatase domain called the hydrophobic spine. In addition, selective plasma membrane targeting of Dr-VSP was facilitated by fusion with the N-terminal region of Ciona intestinalis VSP. This modified Dr-VSP (CiDr-VSPmChe L223F, or what we call eVSP) induced more drastic voltage-evoked changes in PI(4,5)P2 levels, using the activities of Kir2.1, KCNQ2/3, and TRPC6 channels as functional readouts. eVSP is thus an improved molecular tool for evaluating the PI(4,5)P2 sensitivity of ion channels in living cells.
It has been established that voltage‐gated proton channels (VSOP/Hv1), encoded by Hvcn1, support reactive oxygen species (ROS) production in phagocytic activities of neutrophils (El Chemaly et al. ) ...and antibody production in B lymphocytes (Capasso et al. ). VSOP/Hv1 is a potential therapeutic target for brain ischemia, since Hvcn1 deficiency reduces microglial ROS production and protects brain from neuronal damage (Wu et al. ). In the present study, we report that VSOP/Hv1 has paradoxical suppressive role in ROS production in microglia. Extracellular ROS production was lower in neutrophils of Hvcn1−/− mice than WT mice as reported. In contrast, it was drastically enhanced in isolated Hvcn1−/− microglia as compared with cells from WT mice. Actin dynamics was altered in Hvcn1−/− microglia and intracellular distribution of cytosolic NADPH oxidase subunit, p67, was changed. When expression levels of oxidative stress responsive antioxidant genes were compared between WT and Hvcn1−/− in cerebral cortex at different ages of animals, they were slightly decreased in Hvcn1−/− mice at younger stage (1 day, 5 days, 3 weeks old), but drastically increased at aged stage (6 months old), suggesting that the regulation of microglial ROS production by VSOP/Hv1 is age‐dependent. We also performed brain ischemic stroke experiments and found that the neuroprotective effect of VSOP/Hv1deficiency on infarct volume depended on the age of animals. Taken together, regulation of ROS production by VSOP/Hv1 is more complex than previously thought and significance of VSOP/Hv1 in microglial ROS production depends on age.
Voltage gated proton channel (VSOP/Hv1) has been believed to support reactive oxygen species (ROS) production in microglia. We found that VSOP/Hv1 has also paradoxical suppressive role in microglial ROS production possibly by changing actin dynamics. We also suggested that neuroprotective effect of VSOP/Hv1 deficiency on infarct volume in brain ischemia depends on the age of animals.
Despite the prognostic importance of hypoalbuminemia, the prognostic implication of a change in albumin levels has not been fully investigated during hospitalization in patients with acute ...decompensated heart failure (ADHF).
Using the data from the Kyoto Congestive Heart Failure registry on 3160 patients who were discharged alive for acute heart failure hospitalization and in whom the change in albumin levels was calculated at discharge, we evaluated the association with an increase in serum albumin levels from admission to discharge and clinical outcomes by a multivariable Cox hazard model. The primary outcome measure was a composite of all-cause death or hospitalization for heart failure.
Patients with increased albumin levels (N = 1083, 34.3%) were younger and less often had smaller body mass index and renal dysfunction than those with no increase in albumin levels (N = 2077, 65.7%). Median follow-up was 475 days with a 96% 1-year follow-up rate. Relative to the group with no increase in albumin levels, the lower risk of the increased albumin group remained significant for the primary outcome measure (hazard ratio: 0.78, 95% confidence interval: 0.69-0.90: P = 0.0004) after adjusting for confounders including baseline albumin levels. When stratified by the quartiles of baseline albumin levels, the favorable effect of increased albumin was more pronounced in the lower quartiles of albumin levels, but without a significant interaction effect (interaction P = 0.49).
Independent of baseline albumin levels, an increase in albumin during index hospitalization was associated with a lower 1-year risk for a composite of all-cause death and hospitalization in patients with acute heart failure.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Gonadotropin-releasing hormone (GnRH) is well known as a hypophysiotropic hormone that is produced in the hypothalamus and facilitates the release of gonadotropins from the pituitary gonadotropes. On ...the other hand, the functions of extrahypothalamic GnRH systems still remain elusive. Here we examined whether the activity of the olfactory bulbar neural circuits is modulated by GnRH that originates mainly from the terminal nerve (TN) GnRH system in goldfish (Carassius auratus). As the morphological basis, we first observed that goldfish TNs mainly express salmon GnRH (sGnRH) mRNA and that sGnRH-immunoreactive fibers are distributed in both the mitral and the granule cell layers. We then examined by extracellular recordings the effect of GnRH on the electrically evoked in vitro field potentials that arise from synaptic activities from mitral to granule cells. We found that GnRH enhances the amplitude of the field potentials. Furthermore, these effects were observed in both cases when the field potentials were evoked by stimulating either the lateral or the medial olfactory tract, conveying functionally different sensory information, separately, and suggesting that GnRH may modulate the responsiveness to wide categories of odorants in the olfactory bulb. Because GnRH also changed the paired-pulse ratio, it is suggested that the increased amplitude of the field potential results from changes in the presynaptic glutamate release of mitral cells rather than the increase in the glutamate receptor sensitivity of granule cells. These results suggest that TN regulates the olfactory responsiveness of animals appropriately by releasing sGnRH peptides in the olfactory bulbar neural circuits.
The complex link between nutritional status, protein and lipid synthesis, and immunity plays an important prognostic role in patients with heart failure. However, the association between appetite ...loss at discharge and long-term outcome remains unclear.
The Kyoto Congestive Heart Failure registry is a prospective cohort study that enrolled consecutive patients hospitalized for acute decompensated heart failure (ADHF) in Japan. We assessed 3528 patients alive at discharge, and for whom appetite and follow-up data were available. We compared one-year clinical outcomes in patients with and without appetite loss at discharge.
In the multivariable logistic regression analysis using 19 clinical and laboratory factors with P value < 0.1 by univariate analysis, BMI < 22 kg/m2 (odds ratio (OR): 1.57, 95% confidence interval (CI): 1.11-2.24, P = 0.01), CRP >1.0mg/dL (OR: 1.49, 95%CI: 1.04-2.14, P = 0.03), and presence of edema at discharge (OR: 4.30, 95%CI: 2.99-6.22, P<0.001) were associated with an increased risk of appetite loss at discharge, whereas ambulatory status (OR: 0.57, 95%CI: 0.39-0.83, P = 0.004) and the use of ACE-I/ARB (OR: 0.70, 95% CI: 0.50-0.98, P = 0.04) were related to a decreased risk in the presence of appetite loss. The cumulative 1-year incidence of all-cause death (primary outcome measure) was significantly higher in patients with appetite loss than in those without appetite loss (31.0% vs. 15.0%, P<0.001). The excess adjusted risk of appetite loss relative to no appetite loss remained significant for all-cause death (hazard ratio (HR): 1.63, 95%CI: 1.29-2.07, P<0.001).
Loss of appetite at discharge was associated with worse 1-year mortality in patients with ADHF. Appetite is a simple, reliable, and useful subjective marker for risk stratification of patients with ADHF.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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