Horizontally acquired fungal killer protein genes affect cell development in mosses.

The moss Physcomitrium patens is crucial for studying plant development and evolution. Although the P. patens genome includes genes acquired from bacteria, fungi and viruses, the functions and evolutionary significance of these acquired genes remain largely unclear. Killer protein 4 (KP4) is a toxin secreted by the phytopathogenic fungus Ustilago maydis that inhibits the growth of sensitive target strains by blocking their calcium uptake. Here, we show that KP4 genes in mosses were acquired from fungi through at least three independent events of horizontal gene transfer. Two paralogous copies of KP4 (PpKP4-1 and PpKP4-2) exist in P. patens. Knockout mutants ppkp4-1 and ppkp4-2 showed cell death at the protonemal stage, and ppkp4-2 also exhibited defects in tip growth. We provide experimental evidence indicating that PpKP4-1/2 affects P. patens protonemal cell development by mediating cytoplasmic calcium and that KP4 genes are functionally conserved between P. patens and fungi. The present study provides additional insights into the role of horizontal gene transfer in land plant development and evolution.

The phosphorylation of Smad3 by CaMKIIγ leads to the hepatocyte pyroptosis under perfluorooctane sulfonate exposure.

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant and accumulated in the liver of mammals. PFOS exposure is closely associated with the development of pyroptosis. Nevertheless, the underlying mechanism is unclear. We found here that PFOS induced pyroptosis in the mice liver and L-02 cells as demonstrated by activation of the NOD-like receptor protein 3 inflammasome, gasdermin D cleavage and increased release of interleukin-1ß and interleukin-18. The level of cytoplasmic calcium was accelerated in hepatocytes upon exposure to PFOS. The phosphorylated/activated form of calcium/calmodulin-dependent protein kinase II (CaMKII) was augmented by PFOS in vivo and in vitro. PFOS-induced pyroptosis was relieved by CaMKII inhibitor. Among various CaMKII subtypes, we identified that CaMKIIγ was activated specifically by PFOS. CaMKIIγ interacted with Smad family member 3 (Smad3) under PFOS exposure. PFOS increased the phosphorylation of Smad3, and CaMKII inhibitor or CaMKIIγ siRNA alleviated PFOS-caused phosphorylation of Smad3. Inhibiting Smad3 activity was found to alleviate PFOS-induced hepatocyte pyroptosis. This study puts forward that CaMKIIγ-Smad3 is the linkage between calcium homeostasis disturbance and pyroptosis, providing a mechanistic explanation for PFOS-induced pyroptosis.

Distinct Molecular Pattern-Induced Calcium Signatures Lead to Different Downstream Transcriptional Regulations via AtSR1/CAMTA3.

Plants encrypt the perception of different pathogenic stimuli into specific intracellular calcium (Ca2+) signatures and subsequently decrypt the signatures into appropriate downstream responses through various Ca2+ sensors. Two microbe-associated molecular patterns (MAMPs), bacterial flg22 and fungal chitin, and one damage-associated molecular pattern (DAMP), AtPep1, were used to study the differential Ca2+ signatures in Arabidopsis leaves. The results revealed that flg22, chitin, and AtPep1 induced distinct changes in Ca2+ dynamics in both the cytosol and nucleus. In addition, Flg22 and chitin upregulated the expression of salicylic acid-related genes, ICS1 and EDS1, whereas AtPep1 upregulated the expression of jasmonic acid-related genes, JAZ1 and PDF1.2, in addition to ICS1 and EDS1. These data demonstrated that distinct Ca2+ signatures caused by different molecular patterns in leaf cells lead to specific downstream events. Furthermore, these changes in the expression of defense-related genes were disrupted in a knockout mutant of the AtSR1/CAMTA3 gene, encoding a calmodulin-binding transcription factor, in which a calmodulin-binding domain on AtSR1 was required for deciphering the Ca2+ signatures into downstream transcription events. These observations extend our knowledge regarding unique and intrinsic roles for Ca2+ signaling in launching and fine-tuning plant immune response, which are mediated by the AtSR1/CAMTA3 transcription factor.

Blue-light-induced rapid chloroplast de-anchoring in Vallisneria epidermal cells.

In the outer periclinal cytoplasm of leaf epidermal cells of an aquatic angiosperm Vallisneria, blue light induces "chloroplast de-anchoring", a rapid decline in the resistance of chloroplasts against centrifugal force. Chloroplast de-anchoring is known induced within 1 min of irradiation with high-fluence-rate blue light specifically, preceding the commencement of chloroplasts migration toward the anticlinal cytoplasm. However, its regulatory mechanism has remained elusive, although pharmacological analysis suggested that a calcium release from intracellular calcium stores is necessary for the response. In search of the responsible photoreceptors, immunoblotting analysis using antibodies against phototropins demonstrated that cross-reactive polypeptides of 120-kDa exist in the plasma-membrane fraction prepared from the leaves. In vitro phosphorylation analysis revealed that 120-kDa polypeptides were phosphorylated by exposure to blue light in a fluence-dependent manner. The blue-light-induced phosphorylation activity was sensitive to a Ser/Thr kinase inhibitor, staurosporine, and unusually was retained at a high level for a long time in darkness. Furthermore, phototropin gene homologs (Vallisneria PHOTOTROPIN1 and PHOTOTROPIN2) expressed in leaves were isolated. We propose that calcium-regulated chloroplast de-anchoring, possibly mediated by phototropins, is an initial process of the blue-light-induced avoidance response of chloroplasts in Vallisneria.

Arginine promotes myogenic differentiation and myotube formation through the elevation of cytoplasmic calcium concentration.

This study aimed to explore the mechanism underlying arginine-promoted myogenesis of myoblasts. C2C12 cells were cultured with a medium containing 0.1, 0.4, 0.8, or 1.2 mmol/L arginine, respectively. Cell proliferation, viability, differentiation indexes, cytoplasmic Ca2+ concentration, and relative mRNA expression levels of myogenic regulatory factors (MRF) and key Ca2+ channels were measured in the absence or presence of 2 chemical inhibitors, dantrolene (DAN, 10 µmol/L) and nisoldipine (NIS, 10 µmol/L), respectively. Results demonstrated that arginine promoted myogenic differentiation and myotube formation. Compared with the control (0.4 mmol/L arginine), 1.2 mmol/L arginine upregulated the relative mRNA expression levels of myogenin (MyoG) and Myomaker at d 2 during myogenic induction (P < 0.05). Cytoplasmic Ca2+ concentrations were significantly elevated by arginine supplementation at d 2 and 4 (P < 0.05). Relative mRNA expression levels of Ca2+ channels including the type 1 ryanodine receptor (RyR1) and voltage-gated Ca2+ channel (Cav1.1) were upregulated by 1.2 mmol/L arginine during 2-d myogenic induction (P < 0.01). However, arginine-promoted myogenic potential of myoblasts was remarkably compromised by DAN and NIS, respectively (P < 0.05). These findings evidenced that the supplementation of arginine promoted myogenic differentiation and myotube formation through increasing cytoplasmic Ca2+ concentration from both extracellular and sarcoplasmic reticulum Ca2+.

Harpagide exerts a neuroprotective effect by inhibiting endoplasmic reticulum stress via SERCA following oxygen-glucose deprivation/reoxygenation injury.

Cerebrovascular diseases endanger human health, and the physiological and pathological processes of cerebral ischemia/reperfusion injury (CIRI) are critical for the occurrence of these diseases and as targets for their treatment. Here, we evaluated the effects of harpagide-mediated pharmacological and genetic inhibition of sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) in vitro in PC12 cells. The molecular mechanism by which harpagide protects PC12 cells against oxygen-glucose deprivation/reoxygenation (OGD/R) injury was investigated by evaluating the cell survival rate with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, assessing apoptosis by flow cytometry, determining the intracellular Ca2+ concentration ([Ca2+]i) by laser scanning confocal microscopy (LSCM), and measuring the expression of proteins related to SERCA and endoplasmic reticulum stress (ERS) by Western blotting. The results revealed that harpagide significantly decreased thapsigargin (TG)-induced apoptosis of PC12 cells, downregulated the expression of ERS-related markers, considerably improved the TG-induced expression of SERCA-related proteins and reduced the [Ca2+]i, suggesting that harpagide effectively inhibited ERS directly. Moreover, harpagide did not significantly reduce OGD/R-induced apoptosis but increased the expression of ERS markers in PC12/SERCA- cells, indicating that harpagide targets SERCA to protect against CIRI by suppressing ERS-mediated apoptosis.

Airway hyperresponsiveness development and the toxicity of PM2.5.

Airway hyperresponsiveness (AHR) is characterized by excessive bronchoconstriction in response to nonspecific stimuli, thereby leading to airway stenosis and increased airway resistance. AHR is recognized as a key characteristic of asthma and is associated with significant morbidity. At present, many studies on the molecular mechanisms of AHR have mainly focused on the imbalance in Th1/Th2 cell function and the abnormal contraction of airway smooth muscle cells. However, the specific mechanisms of AHR remain unclear and need to be systematically elaborated. In addition, the effect of air pollution on the respiratory system has become a worldwide concern. To date, numerous studies have indicated that certain concentrations of fine particulate matter (PM2.5) can increase airway responsiveness and induce acute exacerbation of asthma. Of note, the concentration of PM2.5 does correlate with the degree of AHR. Numerous studies exploring the toxicity of PM2.5 have mainly focused on the inflammatory response, oxidative stress, genotoxicity, apoptosis, autophagy, and so on. However, there have been few reviews systematically elaborating the molecular mechanisms by which PM2.5 induces AHR. The present review separately sheds light on the underlying molecular mechanisms of AHR and PM2.5-induced AHR.

Ginkgolide B Maintains Calcium Homeostasis in Hypoxic Hippocampal Neurons by Inhibiting Calcium Influx and Intracellular Calcium Release.

Ginkgolide B (GB), a terpene lactone and active ingredient of Ginkgo biloba, shows protective effects in neuronal cells subjected to hypoxia. We investigated whether GB might protect neurons from hypoxic injury through regulation of neuronal Ca2+ homeostasis. Primary hippocampal neurons subjected to chemical hypoxia (0.7 mM CoCl2) in vitro exhibited an increase in cytoplasmic Ca2+ (measured from the fluorescence of fluo-4), but this effect was significantly diminished by pre-treatment with 0.4 mM GB. Electrophysiological recordings from the brain slices of rats exposed to hypoxia in vivo revealed increases in spontaneous discharge frequency, action potential frequency and calcium current magnitude, and all these effects of hypoxia were suppressed by pre-treatment with 12 mg/kg GB. Western blot analysis demonstrated that hypoxia was associated with enhanced mRNA and protein expressions of Cav1.2 (a voltage-gated Ca2+ channel), STIM1 (a regulator of store-operated Ca2+ entry) and RyR2 (isoforms of Ryanodine Receptor which mediates sarcoplasmic reticulum Ca2+ release), and these actions of hypoxia were suppressed by GB. Taken together, our in vitro and in vivo data suggest that GB might protect neurons from hypoxia, in part, by regulating Ca2+ influx and intracellular Ca2+ release to maintain Ca2+ homeostasis.

Function and solution structure of the Arabidopsis thaliana RALF8 peptide.

We report the recombinant preparation from Escherichia coli cells of samples of two closely related, small, secreted cysteine-rich plant peptides: rapid alkalinization factor 1 (RALF1) and rapid alkalinization factor 8 (RALF8). Purified samples of the native sequence of RALF8 exhibited well-resolved nuclear magnetic resonance (NMR) spectra and also biological activity through interaction with a plant receptor kinase, cytoplasmic calcium mobilization, and in vivo root growth suppression. By contrast, RALF1 could only be isolated from inclusion bodies as a construct containing an N-terminal His-tag; its poorly resolved NMR spectrum was indicative of aggregation. We prepared samples of the RALF8 peptide labeled with 15 N and 13 C for NMR analysis and obtained near complete 1 H, 13 C, and 15 N NMR assignments; determined the disulfide pairing of its four cysteine residues; and examined its solution structure. RALF8 is mostly disordered except for the two loops spanned by each of its two disulfide bridges.

Pre-treatment with nimodipine and 7.5% hypertonic saline protects aged rats against postoperative cognitive dysfunction via inhibiting hippocampal neuronal apoptosis.

OBJECTIVE: This study aimed to investigate the effects of pre-treatment with nimodipine and 7.5% hypertonic saline (HS) on postoperative cognitive dysfunction (POCD) in aged rats. METHODS: Healthy Sprague-Dawley aged rats were randomly assigned into 4 groups: POCD group, nimodipine group, HS group, and nimodipine+HS group. Rats in POCD group received normal saline injection and then splenectomy 30min later under 1.8% isoflurane inhalation for 2h. In remaining groups, rats received injection of 1mg/kg nimodipine (i.p) and/or 4ml/kg 7.5% HS (i.v) and then splenectomy. Morris water maze test was performed before and after surgery. The hippocampus was harvested for the detection of neuronal apoptosis rate (AR), cytoplasmic calcium ([Ca2+]i), Bcl-2 and Bax mRNA expression and hippocampal neuronal ultrastructure. RESULTS: When compared with POCD group, the latency to escape, neuronal AR, [Ca2+]i, Bax mRNA expression and Bax/Bcl-2 ratio reduced dramatically, but the times of crossing the platform and Bcl-2 mRNA expression increased significantly (P<0.05) in nimodipine group, NS group and nimodipine+HS group. In addition, the latency to escape, neuronal AR, [Ca2+]i, Bax mRNA expression and Bax/Bcl-2 ratio reduced markedly, but the times of crossing the platform and Bcl-2 mRNA expression increased significantly in nimodipine+HS group as compared to nimodipine group and NS group (P<0.05). Hippocampal neuronal ultrastructure damage was observed in all 4 groups, but it was the mildest in nimodipine+HS group. CONCLUSION: Pre-treatment with both nimodipine and 7.5% HS exerts better protective effects, which is related to the inhibition of hippocampal neuronal apoptosis.

At the cross-point of connexins, calcium, and ATP: blocking hemichannels inhibits vasoconstriction of rat small mesenteric arteries.

AIMS: Connexins form gap-junctions (GJs) that directly connect cells, thereby coordinating vascular cell function and controlling vessel diameter and blood flow. GJs are composed of two hemichannels contributed by each of the connecting cells. Hemichannels also exist as non-junctional channels that, when open, lead to the entry/loss of ions and the escape of ATP. Here we investigated cross-talk between hemichannels and Ca2+/purinergic signalling in controlling blood vessel contraction. We hypothesized that hemichannel Ca2+ entry and ATP release contributes to smooth muscle cell (SMC) Ca2+ dynamics, thereby influencing vessel contractility. We applied several peptide modulators of hemichannel function and inhibitors of Ca2+ and ATP signalling to investigate their influence on SMC Ca2+ dynamics and vessel contractility. METHODS AND RESULTS: Confocal Ca2+ imaging studies on small mesenteric arteries (SMAs) from rat demonstrated that norepinephrine-induced SMC Ca2+ oscillations were inhibited by blocking IP3 receptors with xestospongin-C and by interfering with hemichannel function, most notably by the specific Cx43 hemichannel blocking peptide TAT-L2 and by TAT-CT9 that promotes Cx43 hemichannel opening. Evidence for hemichannel involvement in SMC function was supported by the fact that TAT-CT9 significantly increased SMC resting cytoplasmic Ca2+ concentration, indicating it facilitated Ca2+ entry, and by the observation that norepinephrine-triggered vessel ATP release was blocked by TAT-L2. Myograph tension measurements on isolated SMAs showed significant inhibition of norepinephrine-triggered contractility by the ATP receptor antagonist suramin, but the strongest effect was observed with TAT-L2 that gave ∼80% inhibition at 37 °C. TAT-L2 inhibition of vessel contraction was significantly reduced in conditional Cx43 knockout animals, indicating the effect was Cx43 hemichannel-dependent. Computational modelling suggested these results could be explained by the opening of a single hemichannel per SMC. CONCLUSIONS: These results indicate that Cx43 hemichannels contribute to SMC Ca2+ dynamics and contractility, by facilitating Ca2+ entry, ATP release, and purinergic signalling.

Decichine enhances hemostasis of activated platelets via AMPA receptors.

INTRODUCTION: Dencichine, one of the non-protein amino acids present in the roots of Panax notoginseng, has been found to shorten bleeding time of mice and increase the number of platelets. However, the exact underlying mechanisms have not been elucidated yet. This study was aimed to identify the hemostatic effect of dencichine and uncover its mechanisms. MATERIALS AND METHODS: Hemostatic effect was assessed by measuring tail bleeding time and coagulation indices of rats. PT, APTT, TT and FIB concentration were measured using a Sysmex CA-1500 plasma coagulation analyzer. Platelet aggregation rate was determined by using a platelet aggregometer. Concentration of cyotosolic calcium was evaluated by Fluo-3 and levels of cyclic adenosine monophosphate (cAMP) and thromboxane A2 (TXA2) were measured by ELISA method. RESULTS AND CONCLUSION: Dencichine administered orally shortened tail bleeding time, reduced APTT and TT but increased the concentration of FIB in plasma in a dose-dependent manner. When induced with trap, dencichine could elevate the cytoplasmic concentration of calcium, and secretion of TXA2 as well as the ratio of TXA2 to PGI2 from platelets. Meanwhile, it decreased the level of intracellular cAMP. However, CNQX could block the enhanced hemostatic effect of dencichine. These results suggested that dencichine exerted hemostatic function via AMPA receptors on platelets, therefore, facilitated coagulation cascade in a paracrine fashion by control of platelet cytosolic calcium influx, cAMP production and TXA2 release. Current study may contribute to its clinical use in therapy of hemorrhage.

Activation of PAC1 Receptors in Rat Cerebellar Granule Cells Stimulates Both Calcium Mobilization from Intracellular Stores and Calcium Influx through N-Type Calcium Channels.

High concentrations of pituitary adenylate cyclase-activating polypeptide (PACAP) and a high density of PACAP binding sites have been detected in the developing rat cerebellum. In particular, PACAP receptors are actively expressed in immature granule cells, where they activate both adenylyl cyclase and phospholipase C. The aim of the present study was to investigate the ability of PACAP to induce calcium mobilization in cerebellar granule neurons. Administration of PACAP-induced a transient, rapid, and monophasic rise of the cytosolic calcium concentration ([Ca(2+)]i), while vasoactive intestinal peptide was devoid of effect, indicating the involvement of the PAC1 receptor in the Ca(2+) response. Preincubation of granule cells with the Ca(2+) ATPase inhibitor, thapsigargin, or the d-myo-inositol 1,4,5-trisphosphate (IP3) receptor antagonist, 2-aminoethoxydiphenyl borate, markedly reduced the stimulatory effect of PACAP on [Ca(2+)]i. Furthermore, addition of the calcium chelator, EGTA, or exposure of cells to the non-selective Ca(2+) channel blocker, NiCl2, significantly attenuated the PACAP-evoked [Ca(2+)]i increase. Preincubation of granule neurons with the N-type Ca(2+) channel blocker, ω-conotoxin GVIA, decreased the PACAP-induced [Ca(2+)]i response, whereas the L-type Ca(2+) channel blocker, nifedipine, and the P- and Q-type Ca(2+) channel blocker, ω-conotoxin MVIIC, had no effect. Altogether, these findings indicate that PACAP, acting through PAC1 receptors, provokes an increase in [Ca(2+)]i in granule neurons, which is mediated by both mobilization of calcium from IP3-sensitive intracellular stores and activation of N-type Ca(2+) channel. Some of the activities of PACAP on proliferation, survival, migration, and differentiation of cerebellar granule cells could thus be mediated, at least in part, through these intracellular and/or extracellular calcium fluxes.

An electrical model for the cytoplasmic calcium wave in fertilized eggs.

The calcium wave subsequent to fertilization of the egg is analyzed interms of an electrical equivalent circuit. The circuit consists of aswitch, capacitor, an inductor, and a resistor. The switch symbolizes aseries of chemical reactions initiated by the sperm the lead to thedevelopment of the calcium wave. Its closure signifies the onset of thecalcium wave. The capacitor and inductor represent the endoplasmicreticulum. The capacitive component of the endoplasmic reticulum controlsthe release of calcium ions while the inductive component regulates thesequestration of clacium ions. The resistor represents the inductor andcytoplasm and has very low resistance. The analysis of the circuit showsthat the period of the calcium oscillations is proportional to the size ofthe egg. It agrees with the measurements on various types of eggs.