Endogenous Energy Stores Maintain a High ATP Concentration for Hours in Glucose-Depleted Cultured Primary Rat Astrocytes

Abstract

Adenosine triphosphate (ATP) is the central energy currency of all cells. Cultured primary rat astrocytes contain a specific cellular ATP content of 27.9 ± 4.7 nmol/mg. During incubation in a glucose- and amino acid-free incubation buffer, this high cellular ATP content was maintained for at least 6 h, while within 24 h the levels of ATP declined to around 30% of the initial value without compromising cell viability. In contrast, cells exposed to 1 mM and 5 mM glucose maintained the initial high cellular ATP content for 24 and 72 h, respectively. The loss in cellular ATP content observed during a 24 h glucose-deprivation was fully prevented by the presence of glucose, fructose or mannose as well as by the mitochondrial substrates lactate, pyruvate, β-hydroxybutyrate or acetate. The high initial specific ATP content in glucose-starved astrocytes, was almost completely abolished within 30 min after application of the respiratory chain inhibitor antimycin A or the mitochondrial uncoupler BAM-15, while these inhibitors lowered in glucose-fed cells the ATP content only to 60% (BAM-15) and 40% (antimycin A) within 5 h. Inhibition of the mitochondrial pyruvate carrier by UK5099 alone or of mitochondrial fatty acid uptake by etomoxir alone hardly affected the high ATP content of glucose-deprived astrocytes during an incubation for 8 h, while the co-application of both inhibitors depleted cellular ATP levels almost completely within 5 h. These data underline the importance of mitochondrial metabolism for the ATP regeneration of astrocytes and demonstrate that the mitochondrial oxidation of pyruvate and fatty acids strongly contributes to the maintenance of a high ATP concentration in glucose-deprived astrocytes.

Copper induces neuron‐sparing, ferredoxin 1‐independent astrocyte toxicity mediated by oxidative stress

“…One possible explanation for the divergence between Tsvetkov et al's (2022) findings and the results presented here is that cells that are heavily reliant on mitochondrial respiration for energy production are most vulnerable to cuproptosis (Tsvetkov et al, 2022). Astrocytes, however, are more metabolically flexible, utilizing oxidative phosphorylation, glycolysis, and β‐oxidation of fatty acids, amongst other pathways, for energy production (Arend et al, 2019; Harders et al, 2023; Hertz et al, 2007; Juaristi et al, 2019). Of note, a recent study found proliferating astrocytes in culture are not dependent on oxidative phosphorylation for growth or survival (Silva et al, 2023).…”

“…Astrocytes, however, are more metabolically flexible, utilizing oxidative phosphorylation, glycolysis, and β-oxidation of fatty acids, amongst other pathways, for energy production (Arend et al, 2019;Harders et al, 2023;Hertz et al, 2007;Juaristi et al, 2019). Of note, a recent study found proliferating astrocytes in culture are not dependent on oxidative phosphorylation for growth or survival (Silva et al, 2023).…”

Astrocyte mitochondria: Potential therapeutic targets for epilepsy

“…Inhibition of mitochondrial pyruvate carrier with UK5099 alone or mitochondrial fatty acid uptake with etomoxil alone had little effect on glucose deprivation of high ATP content in astrocytes during 8-h incubation. The combined application of these two inhibitors almost completely depleted the cell's ATP levels within 5 h [ 47 ]. This suggests that mitochondrial oxidation of pyruvate and fatty acids strongly contributes to maintaining high ATP concentrations in glucose-deprived astrocytes.…”

Exogenous Substrates Prevent the Decline in the Cellular ATP Content of Primary Rat Astrocytes During Glucose Deprivation

“…Extensive knowledge has been accumulated during the last decades on the astrocytic metabolism of carbohydrates [ 2 – 4 ], the astrocytic mitochondrial metabolism [ 5 ], the metabolism of amino acids such as glutamate and glutamine [ 6 ], the fatty acid metabolism [ 7 , 8 ] as well as their nucleotide metabolism [ 9 , 10 ]. Although brain astrocytes are considered to be rather glycolytic cells [ 5 , 11 , 12 ], astrocytes at least in culture regenerate most of their ATP by oxidative phosphorylation [ 13 ]. During glucose-deprivation, cultured astrocytes maintain a high cellular ATP concentration of around 7 mM for at least 8 h by using endogenous energy stores such as fatty acids as substrates to fuel ATP regeneration [ 13 ].…”

“…Although brain astrocytes are considered to be rather glycolytic cells [ 5 , 11 , 12 ], astrocytes at least in culture regenerate most of their ATP by oxidative phosphorylation [ 13 ]. During glucose-deprivation, cultured astrocytes maintain a high cellular ATP concentration of around 7 mM for at least 8 h by using endogenous energy stores such as fatty acids as substrates to fuel ATP regeneration [ 13 ]. However, also several external substrates have been reported to be metabolized in glucose-deprived cultured astrocytes to prevent ATP depletion including monocarboxylates [ 13 ], hexoses such as mannose and fructose [ 13 ] and purine nucleosides [ 14 ].…”