In the brain, to each one neurone, there are 9 astrocytes (1). They are surrounded by capillaries and are close to the both blood-brain and blood-cerebrospinal “the first cellular barrier encountered by glucose entering the brain tissue, which makes them a prevalent site of glucose uptake”(2)

Astrocytes interacts with neurons and synapses; they express neurotransmitter receptors and transporters. The delivery of lactate from astrocytes to neurons is enhanced during increased synaptic activity. But astrocytes (according to 2) are also able to process fatty acids for the ketogenesis depending on neuronal energy demands. The ketone bodies and acetoacetate can replace glucose as the major source of brain energy during starvation and in the immature brain. Ketone bodies produced by astrocytes seem to be used together with lactate as substrates for neuronal oxidative metabolism in situations such as enhanced synaptic activity and hypoxia .

Astrocytes are able to metabolize fatty acid

Not only the liver but also astrocytes can produce ketone bodies from fatty acids and the ketogenic system in astrocytes is pretty much similar to the ketogenic system in the liver.

a) both hepatocytes and astrocytes prefer to deal with fatty acids rather than glucose as their primary energy fuel
b) both produce large amounts of ketone bodies
c) regulatory mechanisms of ketogenesis have similar major steps in hepatocytes and astrocytes
d) properties of acetyl-CoA carboxylase are similar in hepatocytes and astrocytes
e) in hepatocytes and in astrocytes ketogenesis is flexible and is modulated by stimuli coupled to activation of, for example, AMP-activated protein kinase

(2)Sources:

1. Pope, A. (1978) Neuroglia: quantitative aspects. In “Dynamic Properties of Glial Cells”, pp. 13–20, Pergamon Press.

2. Manuel Guzman and Cristina Blazquez. Is there an astrocyte–neuron ketone body shuttle? TRENDS in Endocrinology & Metabolism Vol.12 No.4 May/June 2001