Aims/Introduction
Brown adipose tissue (BAT) utilizes large amounts of fuel for thermogenesis, but the mechanism by which fuel substrates are switched in response to changes in energy status is poorly understood. We have now investigated the role of Kruppel‐like factor 15 (KLF15), a transcription factor expressed at a high level in adipose tissue, in the regulation of fuel utilization in BAT.
Materials and Methods
Depletion or overexpression of KLF15 in HB2 differentiated brown adipocytes was achieved by adenoviral infection. Glucose and fatty acid oxidation were measured with radioactive substrates, pyruvate dehydrogenase complex activity was determined with a colorimetric assay, and gene expression was examined by reverse transcription and real‐time polymerase chain reaction analysis.
Results
Knockdown of KLF15 in HB2 cells attenuated fatty acid oxidation in association with downregulation of the expression of genes related to this process including Acox1 and Fatp1, whereas it increased glucose oxidation. Expression of the gene for pyruvate dehydrogenase kinase 4 (PDK4), a negative regulator of pyruvate dehydrogenase complex, was increased or decreased by KLF15 overexpression or knockdown, respectively, in HB2 cells, with these changes being accompanied by a respective decrease or increase in pyruvate dehydrogenase complex activity. Chromatin immunoprecipitation showed that Pdk4 is a direct target of KLF15 in HB2 cells. Finally, fasting increased expression of KLf15, Pdk4 and genes involved in fatty acid utilization in BAT of mice, whereas refeeding suppressed Klf15 and Pdk4 expression.
Conclusions
Our results implicate KLF15 in the regulation of fuel switching between glucose and fatty acids in response to changes in energy status in BAT.
Background:
Insulin regulates various biological processes in adipocytes, and adipose tissue dysfunction due to insulin resistance in this tissue plays a central role in the development of metabolic diseases, including NAFLD and NASH. However, the combined impact of adipose tissue insulin resistance and dietary factors on the pathogenesis of NAFLD-NASH has remained unknown.
Methods and Results:
3′-phosphoinositide–dependent kinase 1 (PDK1) is a serine-threonine protein kinase that mediates the metabolic actions of insulin. We recently showed that adipocyte-specific PDK1 knockout (A-PDK1KO) mice maintained on normal chow exhibit metabolic disorders, including progressive liver disease leading to NASH, in addition to reduced adipose tissue mass. We here show that maintenance of A-PDK1KO mice on the Gubra amylin NASH (GAN) diet rich in saturated fat, cholesterol, and fructose exacerbates inflammation and fibrosis in the liver. Consistent with these histological findings, RNA-sequencing analysis of the liver showed that the expression of genes related to inflammation and fibrosis was additively upregulated by adipocyte-specific PDK1 ablation and the GAN diet. Of note, the reduced adipose tissue mass of A-PDK1KO mice was not affected by the GAN diet. Our results thus indicate that adipose tissue insulin resistance and the GAN diet additively promote inflammation and fibrosis in the liver of mice.
Conclusions:
A-PDK1KO mice fed with the GAN diet, constitute a new mouse model for studies of the pathogenesis of NAFLD-NASH, especially that in lean individuals, as well as for the development of potential therapeutic strategies for this disease.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.