Glycerol kinase stimulates uncoupling protein 1 expression by regulating fatty acid metabolism in beige adipocytes

Abstract

Browning of adipose tissue is induced by specific stimuli such as cold exposure and consists of up-regulation of thermogenesis in white adipose tissue. Recently, it has emerged as an attractive target for managing obesity in humans. Here, we performed a comprehensive analysis to identify genes associated with browning in murine adipose tissue. We focused on glycerol kinase (GYK) because its mRNA expression pattern is highly correlated with that of uncoupling protein 1 (UCP1), which regulates the thermogenic capacity of adipocytes. Cold exposure-induced Ucp1 up-regulation in inguinal white adipose tissue (iWAT) was partially abolished by Gyk knockdown (KD) in vivo. Consistently, the Gyk KD inhibited Ucp1 expression induced by treatment with the β-adrenergic receptors (βAR) agonist isoproterenol (Iso) in vitro and resulted in impaired uncoupled respiration. Gyk KD also suppressed Iso- and adenylate cyclase activator-induced transcriptional activation and phosphorylation of the cAMP response element-binding protein (CREB). However, we did not observe these effects with a cAMP analog. Therefore Gyk KD related to Iso-induced cAMP products. In Iso-treated Gyk KD adipocytes, stearoyl-CoA desaturase 1 (SCD1) was up-regulated, and monounsaturated fatty acids such as palmitoleic acid (POA) accumulated. Moreover, a SCD1 inhibitor treatment recovered the Gyk KD-induced Ucp1 down-regulation and POA treatment down-regulated Iso-activated Ucp1. Our findings suggest that Gyk stimulates Ucp1 expression via a mechanism that partially depends on the βAR-cAMP-CREB pathway and Gyk-mediated regulation of fatty acid metabolism.

Comparative Transcriptome Profiling of Cold Exposure and β3-AR Agonist CL316,243-Induced Browning of White Fat

“…Kyoto Encyclopedia of Genes and Genomes analysis revealed a significant enrichment of glycerolipid metabolism, as well as glycine, serine, and threonine metabolism as a feature of cold-induced gene patterns ( Figure 7A ). qPCR analysis confirmed the increase in mRNA levels of aminolaevulinic acid synthase 2 (ALAS2), the rating-limiting enzyme in heme synthesis which can maintain the mitochondrial function in brown adipocytes ( Galmozzi et al, 2019 ), as well as glycerol kinase (Gyk), which catalyzes the phosphorylation of glycerol to glycerol 3-phosphate and is reported to be involved in UCP1 level induction ( Iwase et al, 2020 ), in cold-treated iWAT versus CL treatment ( Figure 7C ). Meanwhile, we noted that pyruvate metabolism, carbon metabolism, and glycolysis were uniquely enriched in CL treatment, suggesting that in addition to oxidative phosphorylation, fatty acid metabolism, and TCA cycle that were commonly regulated by cold and CL, CL treatment features active glucose mobilization for energy demands ( Figure 7B ).…”

“…In the face of energy demand, for example, during cold or CL stimulation, TG breaks into glycerol and fatty acid ( Beale et al, 2002 ) to provide energy substrates. Via transcriptome data and qPCR confirmation, we confirmed that Gyk, an enzyme critical for glycerol/fatty acid metabolism and UCP1 induction partially through the β3AR-cAMP-CREB pathway ( Iwase et al, 2020 ), was upregulated upon cold exposure, indicating a critical role of lipid metabolism in cold-stimulated browning. Besides, we found that compared to CL treatment, cold exposure specifically promoted glycerolipid metabolism that is an integral part of the glycerolipid/FFA cycle essential for maintaining body temperature by releasing heat at the expense of ATP ( Prentki and Madiraju, 2008 ).…”

Methylglyoxal attenuates isoproterenol-induced increase in uncoupling protein 1 expression through activation of JNK signaling pathway in beige adipocytes

“…Isoproterenol stimulation not only increases the expression of Ucp1 , but also genes related to beige adipocyte function ( Fgf21 , Pgc1α , Cidea , and Dio2 ) by activating PKA signaling [ [28] , [29] , [30] , [31] ]. As shown in Fig.…”

The Effects of Maternal Intake of EPA and DHA Enriched Diet During Pregnancy and Lactation on Offspring’s Muscle Development and Energy Homeostasis

“…ECL immunoblotting clarity system (Bio-Rad) was used to visualize the bands, detected under ChemiDoc TM Touch imaging system (Bio-Rad, California, United States). Band density was analyzed using Image Lab software (Bio-Rad, California, United States) and normalized according to the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) content ( Iwase et al, 2020 ).…”