The Role of Endoplasmic Reticulum in the Differential Endurance against Redox Stress in Cortical and Spinal Astrocytes from the Newborn SOD1G93A Mouse Model of Amyotrophic Lateral Sclerosis

Recent studies reported that the uptake of [18F]-fluorodeoxyglucose (FDG) is increased in the spinal cord (SC) and decreased in the motor cortex (MC) of patients with ALS, suggesting that the disease might differently affect the two nervous districts with different time sequence or with different mechanisms. Here we show that MC and SC astrocytes harvested from newborn B6SJL-Tg (SOD1G93A) 1Gur mice could play different roles in the pathogenesis of the disease. Spectrophotometric and cytofluorimetric analyses showed an increase in redox stress, a decrease in antioxidant capacity and a relative mitochondria respiratory uncoupling in MC SOD1G93A astrocytes. By contrast, SC mutated cells showed a higher endurance against oxidative damage, through the increase in antioxidant defense, and a preserved respiratory function. FDG uptake reproduced the metabolic response observed in ALS patients: SOD1G93A mutation caused a selective enhancement in tracer retention only in mutated SC astrocytes, matching the activity of the reticular pentose phosphate pathway and, thus, of hexose-6P dehydrogenase. Finally, both MC and SC mutated astrocytes were characterized by an impressive ultrastructural enlargement of the endoplasmic reticulum (ER) and impairment in ER–mitochondria networking, more evident in mutated MC than in SC cells. Thus, SOD1G93A mutation differently impaired MC and SC astrocyte biology in a very early stage of life.

Energy Metabolism Response to Low-Temperature and Frozen Conditions in Psychrobacter cryohalolentis

ABSTRACT Studies of cold-active enzymes have provided basic information on the molecular and biochemical properties of psychrophiles; however, the physiological strategies that compensate for low-temperature metabolism remain poorly understood. We investigated the cellular pools of ATP and ADP in Psychrobacter cryohalolentis K5 incubated at eight temperatures between 22�C and −80�C. Cellular ATP and ADP concentrations increased with decreasing temperature, and the most significant increases were observed in cells that were incubated as frozen suspensions (<−5�C). Respiratory uncoupling significantly decreased this temperature-dependent response, indicating that the proton motive force was required for energy adaptation to frozen conditions. Since ATP and ADP are key substrates in metabolic and energy conservation reactions, increasing their concentrations may provide a strategy for offsetting the kinetic temperature effect, thereby maintaining reaction rates at low temperature. The adenylate levels increased significantly <1 h after freezing and also when the cells were osmotically shocked to simulate the elevated solute concentrations encountered in the liquid fraction of the ice. Together, these data demonstrate that a substantial change in cellular energy metabolism is required for the cell to adapt to the low temperature and water activity conditions encountered during freezing. This physiological response may represent a critical biochemical compensation mechanism at low temperature, have relevance to cellular survival during freezing, and be important for the persistence of microorganisms in icy environments.