Glycolytic control of keratinocyte differentiation

Ligand-activation of the aryl hydrocarbon receptor (AHR) promotes the differentiation of normal human epidermal keratinocytes (NHEKs) in vitro and the formation of the epidermal barrier in vivo. Activation of the AHR in NHEKs decreased glycolysis as measured by a reduction in the uptake of glucose and a reduction in the production of pyruvate and lactate. Increases in ligand-activated AHR binding to chromatin near the transcriptional start sites of a glucose transporter, SLC2A1, and a glycolytic enzyme, ENO1, were measured by ChIP-Seq and ChIP-PCR. This increased chromatin binding corresponded to decreased levels of SLC2A1 and ENO1 mRNA, protein and activities. Measurements of the activity of the ENO1 promoter using a reporter assay demonstrated that activation of the AHR decreased the rate of transcription of ENO1. Inhibition of glycolysis, by activation of the AHR, by chemical inhibitors of glycolysis, or by an inhibitor of facilitated glucose transport, resulted in increases in the levels of SIRT1 protein and subsequently, in increases in the levels of differentiation markers. Keratinocyte differentiation in response to decreased glucose metabolism was dependent on SIRT1 and increases in SIRT1 were abrogated by the addition of pyruvate. These results indicate that keratinocyte differentiation is regulated by glycolysis and that the ligand-activated AHR, by decreasing the expression of SLC2A1 and ENO1, metabolically reprograms keratinocytes to promote their differentiation.