Nitric oxide switches on glycolysis through the AMP protein kinase and 6-phosphofructo-2-kinase pathway

Abstract

After inhibition of cytochrome c oxidase by nitric oxide, astrocytes maintain energy production by upregulating glycolysis--a response which does not seem to be available to neurons. Here, we show that in astrocytes, after inhibition of respiration by nitric oxide, there is a rapid, cyclic GMP-independent increase in the activity of 6-phosphofructo-1-kinase (PFK1), a master regulator of glycolysis, and an increase in the concentration of its most powerful positive allosteric activator, fructose-2,6-bisphosphate (F2,6P(2)). In neurons, nitric oxide failed to alter F2,6P(2) concentration or PFK1 activity. This failure could be accounted for by the much lower amount of 6-phosphofructo-2-kinase (PFK2, the enzyme responsible for F2,6P(2) biosynthesis) in neurons. Indeed, full activation of neuronal PFK1 was achieved by adding cytosol from nitric oxide-treated astrocytes. Furthermore, using the small interfering RNA (siRNA) strategy, we demonstrated that the rapid activation of glycolysis by nitric oxide is dependent on phosphorylation of the energy charge-sensitive AMP-activated protein kinase, resulting in activation of PFK2 and protection of cells from apoptosis. Thus the virtual absence of PFK2 in neurons may explain their extreme sensitivity to energy depletion and degeneration.

Troglitazone causes acute mitochondrial membrane depolarisation and an AMPK-mediated increase in glucose phosphorylation in muscle cells

“…4c), suggesting that troglitazone increased hexokinase flux. This result is in agreement with previous studies suggesting that TZDs acutely accelerate glycolytic flux in muscle and astrocytes, resulting in heightened glucose consumption and lactate production [6,64,65]. With our current finding of mitochondria membrane depolarisation by troglitazone, these metabolic adaptations are consistent with the Pasteur effect, in which glycolytic energy production is enhanced to compensate for a deficiency in ATP derived from mitochondrial respiration.…”

“…Co Control, Tro troglitazone product inhibition by glucose-6-phosphate. AMPK accelerates glycolytic flux by directly phosphorylating and activating phosphofructokinase 2 in cardiomyocytes, monocytes and astrocytes [62][63][64]. The ensuing increase in fructose-2,6-bisphosphate and the resulting allosteric stimulation of phosphofructokinase 1 increases the utilisation of glucose-6-phosphate, thus relieving an inhibitory allosteric input on hexokinase.…”

Underestimation of the Pentose–Phosphate Pathway in Intact Primary Neurons as Revealed by Metabolic Flux Analysis

“…Unfortunately, it was not taken into account that a fraction of [1,[3][4][5][6][7][8][9][10][11][12][13] C]F6P formed from PPP, by conversion into [1,[3][4][5][6][7][8][9][10][11][12][13] C]G6P through PGI, returns [2,[3][4][5][6][7][8][9][10][11][12][13] C]F6P in the second PPP round. Thus, as from the second PPP round and thereafter -up to the 4 hours of incubation-such [2,[3][4][5][6][7][8][9][10][11][12][13] C]F6P will label [1-13 C]acetylCoA hence largely over-estimating glycolysis. 2 We therefore conclude that an important proportion of glucose entering neurons is oxidized through the PPP …”

Poly(ADP-ribose) polymerase-1 protects neurons against apoptosis induced by oxidative stress

“…Cerebral cortex neurons in primary culture were prepared from foetal Wistar rats at 16 days of gestation. 35 Dissociated cell suspensions were plated at a density of 2.5 Â 10 5 cells/cm 2 in six-or 12-well plates previously coated with poly-D-lysine (15 mg/ml) in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% foetal calf serum (FCS). Cells were incubated at 371C in a humidified atmosphere containing 5% CO 2 /95% air.…”