Kruppel‐like factor 15 regulates fuel switching between glucose and fatty acids in brown adipocytes

Abstract

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.

KLF15 controls brown adipose tissue transcriptional flexibility and metabolism in response to various energetic demands

“…Notably, thermogenesis pathways were among the topmost enriched pathways as well, supporting observations that body temperature decreases with fasting ( Figure 1 C) ( Chatamra et al., 1984 ). The RNA-seq data are concordant with past studies that have shown decreased BAT Pdk4 transcription, PDK4 activity, and glucose oxidation in fasting with a concurrent increase in lipid metabolism gene expression ( Nabatame et al., 2021 ). These findings also suggest that fasting induces a nutrient switch in BAT like that seen in liver and muscle, where nutrient consumption is downregulated to preserve circulating glucose for glucose obligate organs, such as the brain.…”

“…Yet, it can also robustly partake in FA synthesis, storage, and release much like WAT ( Festuccia et al., 2011 ; Yu et al., 2002 ). Here, we found that concordant with past studies, BAT Klf15 expression is upregulated in fasting conditions like that in liver and muscle ( Marmol et al., 2020 ; Nabatame et al., 2021 ). Furthermore, KLF15 exhibits a similar circadian rhythmicity across BAT, liver, and muscle, which corresponds with times of relative nutrient abundance and deficit, suggesting a similar function in energy mobilization and utilization.…”

“…Concordant with the pattern observed during the light phase ( i.e. , when food intake and activity are decreased in mice), Klf15 expression acutely increases in BAT in response to fasting ( Marmol et al., 2020 ; Nabatame et al., 2021 ). Additionally, mice that are chronically cold challenged at 4°C show significant upregulation of BAT Klf15 expression as well ( Figure 1 E).…”

“…This upregulation of lipid metabolism pathways is reminiscent of BAT adaptations in states of fasting where survival again is dependent on appropriate and selective nutrient mobilization and utilization ( Nabatame et al., 2021 ). We performed RNA-seq on BAT harvested from control mice (RT, fed ad libitum ) and on BAT harvested after an overnight fast (12 h, no food) and identified 4351 DEGs.…”

Diurnal variations of brown fat thermogenesis and fat oxidation in humans

“…The present study demonstrated a diurnal variation in fat oxidation, but not in carbohydrate oxidation, in the High-BAT group, suggesting that BAT utilizes fatty acids more preferentially in the morning than in the evening. Recently, we [ 42 ] reported a role of Kruppel-like factor 15 (KLF15), a transcription factor highly expressed in adipose tissue, in the regulation of fuel switching between glucose and fatty acids in response to changes in energy status in BAT. It is also known that KLF15 expression exhibits a clear circadian rhythm in several peripheral organs and coordinates diurnal variations of plasma levels and catabolism of amino acids including branched-chain amino acids (BCAA) [ 43 ].…”