Mitochondrial impairment and recovery after heat shock treatment in a human microglial cell line.

The application of a heat shock on the human microglial cell line (CHME 5) has been shown to cause cytoskeleton modifications and alterations in phosphorylated metabolite content (Macouillard-Poulletier de Gannes et al., 1998a Metabolic and cellular characterization of immortalized human microglial cells under heat stress. Neurochem. Int. 33, 61-73). In this study, we focused on the possible involvement of mitochondria in this heat stress response. The cell respiratory properties were followed during the recovering period and the possible relationships between mitochondria and the cytoskeleton were studied. We observed that the heat shock induced changes in mitochondrial activity due to protein denaturation, rather than mitochondrial loss. Furthermore, these alterations were correlated with cytoskeleton disorganization since vimentine, tubuline and mitochondria shift, simultaneously, to a perinuclear location. The perturbations of the mitochondrial distribution persisted until cytoskeleton networks had recovered. Nevertheless, the respiratory properties recovered rapidly suggesting a renaturation of mitochondrial proteins in connection with mitochondrial cytoplasmic redistribution.

Compartmentation of lactate and glucose metabolism in C6 glioma cells. A 13c and 1H NMR study.

13C and 1H NMR spectroscopy was used to investigate the metabolism of L-lactate and D-glucose in C6 glioma cells. The changing of lactate and glucose concentration in the extracellular medium of C6 glioma cells incubated with 5.5 mM glucose and 11 mM lactate indicated a net production of lactate as the consequence of an active aerobic glycolysis. The 13C enrichments of various metabolites were determined after 4-h cell incubation in media containing both substrates, each of them being alternatively labeled in the form of either [3-13C]L-lactate or [1-13C]D-glucose. Using 11 mM [3-13C]L-lactate, the enrichment of glutamate C4, 69%, was found higher than that of alanine C3, 32%, when that of acetyl-CoA C2 was 78%. These results indicated that exogenous lactate was the major substrate for the oxidative metabolism of the cells. Nevertheless, an active glycolysis occurred, leading to a net lactate production. This lactate was, however, metabolically different from the exogenous lactate as both lactate species did not mix into a unique compartment. The results were actually consistent with the concept of the existence of two pools of both lactate and pyruvate, wherein one pool was closely connected with exogenous lactate and was the main fuel for the oxidative metabolism, and the other pool was closely related to aerobic glycolysis.

Metabolic and cellular characterization of immortalized human microglial cells under heat stress.

Microglia are able to shift from a resting to an activated state during which they acquire functions typical of primitive forms of mononuclear phagocytes, as well as highly differentiated forms of these cell types. Activation of the microglia after a trauma involves functional readjustments including both the resurrection of basic cell functions and the development of functions implicated in cell-cell interactions. Here, the behaviour of the human microglial cell line CHME-5 was observed after hyperthermia. The strong expression of the inducible form of the hsp70 proteins and their nuclear location, like the more nucleolar presence of the hsc70 proteins seemed to confer heat resistance to the cells. Following minor morphological changes, the observation of the cytoskeleton network during stress recovery revealed a differential sensitivity of actin and tubuline to heat shock. The energy metabolism of both the microglial cell line and the monocyte cell line U937 were compared, under basal conditions, using phosphorus-31 NMR, to discern those phosphorylated metabolites which could be specific of either the monocytic or the macrophagic phenotype. A very high content of phosphocreatine was observed in the microglial clone whereas this compound was absent in monocytes. The lower CHME-5 phosphomonoester content as compared to monocytes also suggested that the microglial cell line displayed a more macrophagic metabolic pattern. After heat shock, the CHME-5 phosphorylated compounds showed large, transient, perturbations. Cells recovered their basal metabolic content 24 h after heat stress. This behaviour, in addition to the expression of inducible hsp70 proteins and the cytoskeleton rearrangement, are indicative of the particular adaptation of the microglial cell line to stress situations.