Transcriptional regulation of ACSL1 by CHREBP and NF-kappa B in macrophages during hyperglycemia and inflammation
Acyl-CoA synthetase 1 (ACSL1) is an enzyme that converts fatty acids to acyl-CoA-derivatives for use in both lipid catabolism and lipid synthesis, including of arachidonic acid mediators that promote inflammation. ACSL1 has also been linked to the pro-atherosclerotic effects of diabetes in mice. ACSL1 expression has been reported to be upregulated in monocytes and macrophages by hyperglycemia, as well as enhanced by inflammatory stimuli, yet surprisingly little is known about the mechanisms underlying its transcriptional regulation. Here we show that increased Acsl1 mRNA expression in mouse macrophages by hyperglycemia is via transcription initiation such that nascent ACSL1 RNA and Acsl1 promoter activity are increased. We further demonstrate that the hyperglycemic-dependent induction of Acsl1 mRNA is governed by the glucose-sensing transcription factor, Carbohydrate Response Element Binding Protein (CHREBP), since the hyperglycemic upregulation of Acsl1 mRNA is lost in mouse bone marrow derived macrophages (BMDMs) from Chrebp knock out mice. In addition, we show that LPS treatment of mouse BMDMs increased Acsl1 mRNA, and this is attenuated by an NF-kappa B inhibitor that blocks p65 subunit binding to DNA. We further show that LPS treatment increased ACSL1 protein abundance and stimulated ACSL1 protein localization to membranes where it likely exerts its activity. Using an ACSL1 reporter gene containing the promoter and 1.6 Kb of upstream regulatory region, which contain multiple predicted CHREBP and NF-kappa B (RELA) binding sites conserved between the human and mouse ACSL1 gene, we found a synergistic increase of ACSL1 promoter activity when CHREBP and RELA were co-expressed. Thus, we have identified pathways controlling the expression of ACSL1 by hyperglycemia and inflammation through CHREBP and NF-kappa B.