CREB-Regulated Transcription During Glycogen Synthesis in Astrocytes
Glycogen storage, conversion and utilization in astrocytes play important roles in brain energy metabolism. The conversion of glycogen to lactate through glycolysis occurs through the coordinated activities of various enzymes, and inhibition of this process can impair different brain processes including formation of long-lasting memories. To replenish depleted glycogen stores, astrocytes undergo glycogen synthesis, a cellular process that has been shown to require transcription and translation during specific stimulation paradigms. However, the detailed nuclear signaling mechanisms and transcriptional regulation during glycogen synthesis in astrocytes remain to be explored. In this report, we study the molecular details of vasoactive intestinal peptide (VIP)-induced glycogen synthesis in astrocytes. VIP is a potent neuropeptide that triggers glycogenolysis followed by glycogen synthesis in astrocytes. We show evidence that VIP-induced glycogen synthesis requires CREB-mediated transcription that is Protein Kinase C and calcium-dependent but is independent of Protein Kinase A. In parallel to CREB activation, we demonstrate that VIP also triggers nuclear accumulation of the CREB coactivator CRTC2 only in astrocytic nuclei that also requires Protein Kinase C activity. Transcriptome profiles of VIP-induced astrocytes identified robust CREB-dependent transcription of glycogenic genes including the upregulation of Ppp1r3c along with robust repression of Phkg1, the catalytic subunit of phosphorylase kinase. Overall, our data demonstrates the importance of CREB-mediated transcription in astrocytes during stimulus-driven glycogenesis. Overall design: To examine the extent of CREB-mediated transcription upon VIP induction, we transduced cortical astrocytes with either control or dominant negative ACREB expression vectors and treated cells with either PBS or VIP before harvesting RNA for RNAseq.