PhD Scientific Days 2023

Neurosciences II.

Astrocyte: Cell for all season or simple glutamine factory? – Tricarboxylic acid cycle in astrocytes

Text of the abstract

Introduction: In the structure of central nervous system both neurons and glial cells have very important role. In the brain glial cells are mostly astrocytes, which supply the neurons with various substrates (e.g.: glutamine, lactate, glutathione precursors). The literature of the astrocyte’s metabolism is quite inconsistence. The astrocytes have active glycolysis. They can donate the glucose to the neurons via two different routes: deliver directly the glucose molecule or transform throw the glycolysis to pyruvate then convert to lactate what feeds the tricarboxylic acid (TCA) cycle in the neurons. However, pyruvate’s role in the anaplerosis of TCA cycle is still unclear. The various anaplerotic and cataplerotic pathways of the TCA cycle are the key mechanisms of the cell’s metabolism.
Aim: Examination of the astrocyte’s metabolism, including the characteristics of the TCA cycle. Take a stand on the controversial issues of the metabolic pathways of the astrocytes.
Methods: Astrocytes were isolated from new-born (P0-2) mouse brain and cultured in medium (MEM supplemented with FBS, glutamine, amphotericin B, gentamycin). TCA cycle enzyme activities were measured with spectrophotometry on lysed cells. Oxygen consumption was detected on intact and permeabilized cells with Clark-electrode. Metabolite concentration was measured with mass spectrometry.
Results: Astrocytes have active glycolysis but also able to oxidate fatty acids and ketone bodies. The second part of the TCA cycle (molecules with 4 carbon atoms) has higher enzyme activity and substrate concentration compared to the first part of the cycle (molecules with 6 or 5 carbon atoms). The NADP+-dependent isocitrate dehydrogenase (NADP+-IDH) and aconitase have significant extramitochondrial enzyme activity.
Conclusion: Our results suggest that pyruvate is not the main acetyl-CoA donor for the TCA cycle. Ketone body constant oxidation is not favoured in physiological condition. These outcomes may suggest that fatty acid oxidation is quite important in the astrocyte metabolism. α-ketoglutarate gets across throw mitochondrial inner membrane. In the cytosol, it assists the glutamate-glutamine cycle.
Funding: ÚNKP-22