Glucose to lactate metabolism from extracelullar and intracelullar sources in rat astrocytes

Astrociti so številčne celice centralnega živčnega sistema, med katerimi komunikacija poteka s citoplazemsko vzdražnostjo preko sekundarnih sporočevalcev ali presnovkov, ki se vežejo na številne z G-proteini sklopljene receptorje na astrocitni membrani. Astrociti imajo primerno lego, da lahko iz endotelija možganskih kapilar prevzemajo glukozo. Zadnja leta ima vedno več podpore hipoteza, da astrociti nevronom posredujejo laktat, presnovek, ki v astrocitih nastaja z aerobno glikolizo. Nevroni laktat domnevno uporabljajo kot vir energije, ki je pomembnejši od glukoze. Namen naše naloge je bilo ugotoviti, ali raven znotrajceličnega laktata poraste ob stimulaciji adrenergičnih receptorjev z noradrenalinom, če 1.) zavremo glikolizo z 2-deoksi glukozo, 2.) zavremo razgradnjo glikogena z 1,4-dideoksi-1,4-imino-d-arabinitol, 3.) zavremo Krebsov cikel s 3-nitropropionsko kislino in 4.) inhibiramo delovanje encima laktat dehidrogenaze z oksamatom in s tem pretvorbo piruvata v laktat. V naših poskusih smo spodbudili presnovo z noradrenalinom in merili raven koncentracije laktata v realnem času s tehniko rprenos energije z resonanco fluorescence in nanosenzorjem Laconic. Z blokadami različnih delov presnove smo pokazali na ravni posamezne celice, da je za nastanek laktata po adrenergčni aktivaciji nujen vstop glukoze iz zunajceličnine v astrocit, da praktično ves laktat nastane iz glikogena in da v astrocitih laktat ob prisotnosti glukoze in blokadi Krebsovega cikla nastaja kot energijska molekula. Z zaviranjem encima laktat dehidrogenaze, laktat ne nastane, kar potrjuje domnevo, da ves laktat po adrenergični aktivaciji v astrocitu nastane iz piruvata.Astrocytes are numerous neuroglial cells of the central nervous system, which communicate with neighbouring cells when excited via various GPCRs at the astrocytic membrane and the ensuing changes in second messengers. Astrocytes are positioned between neurons and blood vessels, hence are ideally positioned to uptake glucose from the endothelium of brain capillaries. Recently, new data has added support for the hypothesis that astrocytes are passing lactate to neurons. Lactate is a metabolite produced in astrocytes by aerobic glycolysis. Neurons likely use lactate as a preferential source of energy. The aim of our research was to determine whether the level of intracellular lactate increases following the stimulation of adrenergic receptors by noradrenaline, while we: 1) inhibited glycolysis by 2-DG, 2) inhibited degradation of glycogen by DAB, 3) blocked the citric acid cycle with 3-NPA and 4) blocked LDH by Oxamate, which inhibits the conversion of pyruvate to lactate. We measured changes in cytosolic lactate in single living astrocytes in real time. For this we used the FRET nanosensor Laconic. By pharmacological modulation of distinct segments of metabolism, the results revealed that glucose uptake is essential for the production of lactate in astrocytes upon adrenergic activation. We have also shown that practically all lactate increase upon adrenergic activation originates from glycogen. Glycolysis appears an essential energy source for astrocytes when the citric acid cycle was blocked. When the enzyme LDH was inhibited, no lactate was formed, confirming the view that lactate produced upon adrenergic activation in astrocytes is formed via pyruvate