Regulation of energy metabolism in macrophages during hypoxia - Roles of fructose 2,6-bisphosphate and ribose 1,5-bisphosphate

Macrophages can adapt to the absence of oxygen by switching to anaerobic gl ycolysis. In this study, we investigated (a) the roles of fructose 2,6-bisp hosphate (Fru-2,6-P-2) and ribose 1,5-bisphosphate (Rib-1,5-P-2), Potent ac tivators of phosphofructokinase, (b) the enzymes responsible for the synthe sis of Rib-1,5-P-2, and (c) the mechanisms of regulation of these enzymes i n H36.12j macrophages during the initial phase of hypoxia. Within I min aft er initiating hypoxia, glycolysis was activated through activation of phosp hofructokinase. Over the same period, Fru-2,6-P-2 decreased 50% and recover ed completely upon reoxygenation. Similar changes in cAMP levels were obser ved. In contrast, the Rib-1,5-P-2 concentration rapidly increased to a maxi mum level of 8.0 +/- 0.9 nmol/g cell 30 s after hypoxia. Thus, Rib-1,5-P-2 was the major factor increasing the rate of glycolysis during the initial p hase of hypoxia. Moreover, we found that Rib-1,5-P-2 was synthesized by two steps: the ribose-phosphate pyrophosphokinase (5-phosphoribosyl-1-pyrophos phate synthetase; PRPP synthetase) reaction (EC 2.7.6.1) catalyzing the rea ction, Rib-5-P + ATP --> PRPP + AMP and a new enzyme, "PRPP pyrophosphatase " catalyzing the reaction, PRPP --> Rib-1,5-P-2 + P-i. Both PRPP synthetase and PRPP pyrophosphatase were significantly activated 30 s after hypoxia. Pretreatment with 1-octadecyl-2-methyl-rac-glycero-3-phosphocholine and cal phostin C prevented the activation of ribose PRPP synthetase and PRPP pyrop hosphatase as well as increase in Rib-1,5-P-2 and activation of phosphofruc tokinase 30 s after hypoxia. These data suggest that the activation of the above enzymes was mediated by protein kinase C acting via activation of pho sphatidylinositol specific phospholipase C in the macrophages during hypoxi a.