Interdistsiplinaarne kardioloogia. Seitsmeks lõiguks tükeldatud südameõpetus

Eesti Arst 2013; 92(4):238–24

Hüperkolesteroleemia kombineeritud ravi statiinide ja esetimiibiga

Paljude epidemioloogiliste uuringutega on tõestatud, et suur vere kolesteroolisisaldus on üheks koronaartõve riskiteguriks. Vaatamata sellele ei ole piisavalt igapäeva praktikasse juurdunud vere kolesteroolitaseme mõõtmine ja selle ravimitega mõjustamine ei südamehaiguste riskirühma kuuluvatel ega koronaartõvega patsientidel. Eesti Arst 2005; 84 (1): 47-4

Oomega-3 rasvhapped vähendavad märkimisväärselt seerumi triglütseriidisisaldust düslipideemiaga patsientidel

Hüpertriglütserideemiat peetakse südame-veresoonkonnahaiguste iseseisvaks riskiteguriks, kusjuures triglütseriidisisalduse suurenemine veres 1 mmol/l suurendab kardiovaskulaarse haigestumise riski meestel 30% ning naistel isegi kuni 76%. Uuringud kalast ja kalaõlist toodetud oomega-3 rasvhapete mõjust tõestavad nende kaitsvat toimet aterosklerootilise südamehaiguse ning koronaarse äkksurma vastu. Uurimuse eesmärgiks oli hinnata 1,2 grammi oomega-3 rasvhapete toimet seerumi triglütseriidisisaldusele hüpertriglütserideemiaga patsientidel, kellel dieedisoovitustele vaatamata ei olnud seerumi triglütseriidisisaldus normaliseerunud ning kes ei saanud statiinravi. Eesti Arst 2005; 84 (11): 771–77

Plant guard cell anion channel SLAC1 regulates stomatal closure

Plants are rooted to their growth place; therefore it is important that they react adequately to changes in environmental conditions. Stomatal pores, which are formed of a pair of guard cells in leaf epidermis, regulate plant gas-exchange. Importantly, guard cells protect the plant from desiccation in drought conditions by reducing the aperture of the stomatal pore. They serve also as the first barrier against the major air pollutant ozone, but the behaviour of guard cells during ozone exposure has not been sufficiently addressed. Aperture of the stomatal pore is regulated by the influx and efflux of osmotically active ions via ion channels and transporters across the guard cell membrane, however the molecular identity of guard cell plasma membrane anion channel has remained unknown. In the frame of this study, guard cell behaviour during ozone exposure was studied using the newly constructed Arabidopsis whole-rosette gas-exchange system. Ozone induced a Rapid Transient Decrease (RTD) in stomatal conductance within 10 min from the start of exposure, which was followed by a recovery in the conductance within the next 40 min. The decrease in stomatal conductance was dependent on the applied ozone concentration. Three minutes of ozone exposure was sufficient to induce RTD and further ozone application during the closure-recovery process had no effect on RTD, demonstrating that the whole process is programmed within the first three minutes. To address the molecular components responsible for RTD, the ozone response was measured in 59 different Arabidopsis mutants involved in guard cell signalling. Four of the tested mutants slac1 (originally rcd3), ost1, abi1-1 and abi2-1 lacked RTD completely. As the ozone sensitive mutant slac1 lacked RTD, the next aim of this study was to identify and characterize SLAC1. SLAC1 was shown to be a central regulator in response to all major factors regulating guard cell aperture: CO2, light/darkness transitions, ozone, relative air humidity, ABA, NO, H2O2, and extracellular Ca2+. It encodes the first guard cell plasma membrane slow type anion channel to be identified at the molecular level. Interestingly, the rapid type anion conductance was intact in slac1 mutant plants. For activation, SLAC1 needs to be phosphorylated. Protein kinase OST1 was shown to phosphorylate several amino acids in the N-terminal tail of SLAC1, Ser120 was one of its main targets, which led to SLAC1 activation. The lack of RTD in type 2C protein phosphatase mutants abi1-1 and abi2-1, suggests that these proteins have a regulatory role in ozoneinduced activation of the slow type anion channel.Kasvit ovat juurtuneet kasvualustaansa; tämän vuoksi on tärkeää, että ne reagoivat riittävästi ympäristön muuttuviin olosuhteisiin. Ilmaraot, jotka ovat muodostuneet huulisoluparista lehtien päällysketossa, säätelevät kasvien kaasunvaihtoa. Mikä tärkeintä, huulisolut suojelevat kasvia kuivumiselta sateettomissa olosuhteissa rajoittamalla ilmaraon avautumisastetta. Ne toimivat myös ensimmäisenä esteenä merkittävää ilmansaastetta, otsonia vastaan, mutta huulisolujen toimintaa otsonialtistuksen aikana ei ole tutkittu riittävästi. Ilmaraon avautumisastetta säätelevät osmoottisesti aktiivisten ionien sisään- ja ulosvirtaus ionikanavien kautta sekä niitä ympäröivät kuljettajaproteiinit huulisolujen kalvolla; huulisolun solukalvon anionikanavan molekyylibiologinen tausta on kuitenkin jäänyt tunnistamatta. Tämän tutkimuksen puitteissa huulisolujen toimintaa tarkasteltiin äskettäin rakennetun laitteiston avulla, jossa lituruohon (Arabidopsis) ilmarakojen kaasujenvaihtoa voidaan seurata kokonaisesta lehtiruusukkeesta. Otsoni aikaansai nopean ja hetkellisen vähentymisen ilmarakojen johtavuudessa kymmenen minuutin aikana altistuksen alkamisesta, minkä jälkeen ilmarakojen johtavuus palautui neljässäkymmenessä minuutissa. Ilmarakojen johtavuuden vähentyminen oli riippuvainen lisätyn otsonin pitoisuudesta. Kolmen minuutin otsonialtistus oli riittävä aikaansaamaan nopean ja hetkellisen vähentymisen ilmarakojen johtavuudessa, eikä tämän jälkeen lisätty otsoni enää vaikuttanut siihen; tämä osoittaa että koko tapahtumasarja on ohjelmoitu kolmen ensimmäisen minuutin aikana. Jotta ilmarakojen johtavuuden nopean ja hetkellisen vähenemisen molekyylibiologisia osatekijöitä voisi saada selville, 59 erilaisesta lituruohomutantista, jotka liittyvät huulisolujen signalointiin, mitattiin otsonivaste. Neljältä testatuista mutanteista, nimiltään slac1 (alun perin rcd3), ost1, abi1-1 ja abi2-1, puuttui nopea ja hetkellinen ilmarakojen johtavuus täysin. Koska otsoniherkästä slac1-mutantista puuttui nopea ja hetkellinen ilmarakojen johtavuuden vähentyminen, oli tämän tutkimuksen seuraava tavoite tunnistaa ja karakterisoida SLAC1. SLAC1 osoitettiin olevan keskeinen säätelytekijä kaikissa merkittävissä vasteissa, jotka ohjaavat huulisolujen avautumisastetta: CO2, valo-pimeä siirtymä, otsoni, ilman suhteellinen kosteus, ABA, NO, H2O2 ja solunulkoinen Ca2+. Se koodaa huulisolujen solukalvojen hidas-tyyppistä (engl. slow type ) anionikanavaproteiinia, joka on ensimmäinen osoitettu proteiini tällä molekyylibiologisella tasolla. SLAC1 tarvitsee aktivoituakseen fosforylaation. Proteiinikinaasi OST1:n osoitettiin fosforyloivan useita aminohappoja SLAC1:n N-terminaalisesta aminopäästä. Ser120 oli sen pääkohteista, mikä johti SLAC1:n aktivoitumiseen. Nopean ja hetkellisen ilmarakojen johtavuuden vähentymisen puuttuminen 2C-tyyppisten abi1-1 ja abi2-1 fosfataasimutanteissa viittaa siihen, että näillä proteiineilla on säätelytehtävä otsonin aikaansaamassa anionikanavien hidas-tyyppisessä aktivoinnissa

Anion channel sensitivity to cytosolic organic acids implicates a central role for oxaloacetate in integrating ion flux with metabolism in stomatal guard cells

Stomatal guard cells play a key role in gas exchange for photosynthesis and in minimizing transpirational water loss from plants by opening and closing the stomatal pore. The bulk of the osmotic content driving stomatal movements depends on ionic fluxes across both the plasma membrane and tonoplast, the metabolism of organic acids, primarily Mal (Imitate), and its accumulation and loss. Anion channels at the plasma membrane are thought to comprise a major pathway for Mal efflux during stomatal closure, implicating their key role in linking solute flux with metabolism. Nonetheless, little is known of the regulation of anion channel current (I(Cl)) by cytosolic Mal or its immediate metabolite OAA (oxaloacetate). In the present study, we have examined the impact of Mal, OAA and of the monocarboxylic acid anion acetate in guard cells of Vicia faba L. and report that all three organic acids affect I(Cl), but with markedly different characteristics and sidedness to their activities. Most prominent was a suppression of I(Cl) by OAA within the physiological range of concentrations found in vivo. These findings indicate a capacity for OAA to co-ordinate organic acid metabolism with I(Cl), through the direct effect of organic acid pool size. The findings of the present study also add perspective to in vivo recordings using acetate-based electrolytes

Exploring emergent properties in cellular homeostasis using OnGuard to model K+ and other ion transport in guard cells

It is widely recognized that the nature and characteristics of transport across eukaryotic membranes are so complex as to defy intuitive understanding. In these circumstances, quantitative mathematical modeling is an essential tool, both to integrate detailed knowledge of individual transporters and to extract the properties emergent from their interactions. As the first, fully integrated and quantitative modeling environment for the study of ion transport dynamics in a plant cell, OnGuard offers a unique tool for exploring homeostatic properties emerging from the interactions of ion transport, both at the plasma membrane and tonoplast in the guard cell. OnGuard has already yielded detail sufficient to guide phenotypic and mutational studies, and it represents a key step toward ‘reverse engineering’ of stomatal guard cell physiology, based on rational design and testing in simulation, to improve water use efficiency and carbon assimilation. Its construction from the HoTSig libraries enables translation of the software to other cell types, including growing root hairs and pollen. The problems inherent to transport are nonetheless challenging, and are compounded for those unfamiliar with conceptual ‘mindset’ of the modeler. Here we set out guidelines for the use of OnGuard and outline a standardized approach that will enable users to advance quickly to its application both in the classroom and laboratory. We also highlight the uncanny and emergent property of OnGuard models to reproduce the ‘communication’ evident between the plasma membrane and tonoplast of the guard cell

Stomatal CO2/bicarbonate sensor consists of two interacting protein kinases, Raf-like HT1 and nonkinase-activity activity requiring MPK12/MPK4

Publisher Copyright: © 2022 The Authors.The continuing rise in the atmospheric carbon dioxide (CO2) concentration causes stomatal closing, thus critically affecting transpirational water loss, photosynthesis, and plant growth. However, the primary CO2 sensor remains unknown. Here, we show that elevated CO2 triggers interaction of the MAP kinases MPK4/MPK12 with the HT1 protein kinase, thus inhibiting HT1 kinase activity. At low CO2, HT1 phosphorylates and activates the downstream negatively regulating CBC1 kinase. Physiologically relevant HT1-mediated phosphorylation sites in CBC1 are identified. In a genetic screen, we identify dominant active HT1 mutants that cause insensitivity to elevated CO2. Dominant HT1 mutants abrogate the CO2/bicarbonate-induced MPK4/12-HT1 interaction and HT1 inhibition, which may be explained by a structural AlphaFold2- and Gaussian-accelerated dynamics-generated model. Unexpectedly, MAP kinase activity is not required for CO2 sensor function and CO2-triggered HT1 inhibition and stomatal closing. The presented findings reveal that MPK4/12 and HT1 together constitute the long-sought primary stomatal CO2/bicarbonate sensor upstream of the CBC1 kinase in plants.Peer reviewe

PHO1 expression in guard cells mediates the stomatal response to abscisic acid in Arabidopsis.

Stomatal opening and closing are driven by ion fluxes that cause changes in guard cell turgor and volume. This process is, in turn, regulated by environmental and hormonal signals, including light and the phytohormone abscisic acid (ABA). Here, we present genetic evidence that expression of PHO1 in guard cells of Arabidopsis thaliana is required for full stomatal responses to ABA. PHO1 is involved in the export of phosphate into the root xylem vessels and, as a result, the pho1 mutant is characterized by low shoot phosphate levels. In leaves, PHO1 was found expressed in guard cells and up-regulated following treatment with ABA. The pho1 mutant was unaffected in production of reactive oxygen species following ABA treatment, and in stomatal movements in response to light cues, high extracellular calcium, auxin, and fusicoccin. However, stomatal movements in response to ABA treatment were severely impaired, both in terms of induction of closure and inhibition of opening. Micro-grafting a pho1 shoot scion onto wild-type rootstock resulted in plants with normal shoot growth and phosphate content, but failed to restore normal stomatal response to ABA treatment. PHO1 knockdown using RNA interference specifically in guard cells of wild-type plants caused a reduced stomatal response to ABA. In agreement, specific expression of PHO1 in guard cells of pho1 plants complemented the mutant guard cell phenotype and re-established ABA sensitivity, although full functional complementation was dependent on shoot phosphate sufficiency. Together, these data reveal an important role for phosphate and the action of PHO1 in the stomatal response to ABA

Anion channel SLAH3 is a regulatory target of chitin receptor-associated kinase PBL27 in microbial stomatal closure

In plants, antimicrobial immune responses involve the cellular release of anions and are responsible for the closure of stomatal pores. Detection of microbe-associated molecular patterns (MAMPs) by pattern recognition receptors (PRRs) induces currents mediated via slow-type (S-type) anion channels by a yet not understood mechanism. Here, we show that stomatal closure to fungal chitin is conferred by the major PRRs for chitin recognition, LYK5 and CERK1, the receptor-like cytoplasmic kinase PBL27, and the SLAH3 anion channel. PBL27 has the capacity to phosphorylate SLAH3, of which S127 and S189 are required to activate SLAH3. Full activation of the channel entails CERK1, depending on PBL27. Importantly, both S127 and S189 residues of SLAH3 are required for chitin-induced stomatal closure and anti-fungal immunity at the whole leaf level. Our results demonstrate a short signal transduction module from MAMP recognition to anion channel activation, and independent of ABA-induced SLAH3 activation

FIA functions as an early signal component of abscisic acid signal cascade in Vicia faba guard cells

An abscisic acid (ABA)-insensitive Vicia faba mutant, fia (fava bean impaired in ABA-induced stomatal closure) had previously been isolated. In this study, it was investigated how FIA functions in ABA signalling in guard cells of Vicia faba. Unlike ABA, methyl jasmonate (MeJA), H2O2, and nitric oxide (NO) induced stomatal closure in the fia mutant. ABA did not induce production of either reactive oxygen species or NO in the mutant. Moreover, ABA did not suppress inward-rectifying K+ (Kin) currents or activate ABA-activated protein kinase (AAPK) in mutant guard cells. These results suggest that FIA functions as an early signal component upstream of AAPK activation in ABA signalling but does not function in MeJA signalling in guard cells of Vicia faba