Author/Editor		Muhič, Marko; Vardjan, Nina; Chowdhury Haque, Helena; Zorec, Robert; Kreft, Marko
Title		Insulin and IGF-1 modulate cytoplasmic glucose and glycogen levels but not glucose transport across the membrane in astrocytes
Type		članek
Publication year		2015
ISSN		0021-9258 - The Journal of biological chemistry
Language		eng
Abstract		Astrocytes contain glycogen, an energy buffer, which can bridge local short-term energy requirements in the brain. Glycogen levels reflect a dynamic equilibrium between glycogen synthesis and glycogenolysis. Many factors that include hormones and neuropeptides, such as insulin and insulin-like growth factor 1 (IGF-1) likely modulate glycogen stores in astrocytes, but detailed mechanisms at the cellular level are sparse. We used a glucose nanosensor based on Förster resonance energy transfer to monitor cytosolic glucose concentration with high temporal resolution and a cytochemical approach to determine glycogen stores in single cells. The results show that after glucose depletion, glycogen stores are replenished. Insulin and IGF-1 boost the process of glycogen formation. Although astrocytes appear to express glucose transporter GLUT4, glucose entry across the astrocyte plasma membrane is not affected by insulin. Stimulation of cells with insulin and IGF-1 decreased cytosolic glucose concentration, likely due to elevated glucose utilization for glycogen synthesis.
Keywords		astrocyte glucose metabolism insulin insulin-like growth factor (IGF) glycogen fluorescence resonance energy transfer (FRET)