Aims/hypothesisAnimal studies have indicated that disturbed diurnal rhythms of clock gene expression in adipose tissue can induce obesity and type 2 diabetes. The importance of the circadian timing... Show moreAims/hypothesisAnimal studies have indicated that disturbed diurnal rhythms of clock gene expression in adipose tissue can induce obesity and type 2 diabetes. The importance of the circadian timing system for energy metabolism is well established, but little is known about the diurnal regulation of (clock) gene expression in obese individuals with type 2 diabetes. In this study we aimed to identify key disturbances in the diurnal rhythms of the white adipose tissue transcriptome in obese individuals with type 2 diabetes.MethodsIn a case-control design, we included six obese individuals with type 2 diabetes and six healthy, lean control individuals. All participants were provided with three identical meals per day for 3days at zeitgeber time (ZT, with ZT 0:00 representing the time of lights on) 0:30, 6:00 and 11:30. Four sequential subcutaneous abdominal adipose tissue samples were obtained, on day 2 at ZT 15:30, and on day 3 at ZT 0:15, ZT 5:45 and ZT 11:15. Gene expression was measured using RNA sequencing.ResultsThe core clock genes showed reduced amplitude oscillations in the individuals with type 2 diabetes compared with the healthy control individuals. Moreover, in individuals with type 2 diabetes, only 1.8% (303 genes) of 16,818 expressed genes showed significant diurnal rhythmicity, compared with 8.4% (1421 genes) in healthy control individuals. Enrichment analysis revealed a loss of rhythm in individuals with type 2 diabetes of canonical metabolic pathways involved in the regulation of lipolysis. Enrichment analysis of genes with an altered mesor in individuals with type 2 diabetes showed decreased activity of the translation initiating pathway EIF2 signaling'. Individuals with type 2 diabetes showed a reduced diurnal rhythm in postprandial glucose concentrations.Conclusions/interpretationDiurnal clock and metabolic gene expression rhythms are decreased in subcutaneous adipose tissue of obese individuals with type 2 diabetes compared with lean control participants. Future investigation is needed to explore potential treatment targets as identified by our study, including clock enhancement and induction of EIF2 signalling.Data availabilityThe raw sequencing data and supplementary files for rhythmic expression analysis and Ingenuity Pathway Analysis have been deposited in NCBI Gene Expression Omnibus (GEO series accession number GSE104674). Show less
Nahon, J.E.; Hoekstra, M.; Harmelen, V. van; Rensen, P.C.N.; Dijk, K.W. van; Kooijman, S.; Eck, M. van 2019
ObjectiveProteoglycan 4 (Prg4) has emerged from human association studies as a possible factor contributing to weight gain, dyslipidemia and insulin resistance. In the current study, we... Show moreObjectiveProteoglycan 4 (Prg4) has emerged from human association studies as a possible factor contributing to weight gain, dyslipidemia and insulin resistance. In the current study, we investigated the causal role of Prg4 in controlling lipid and glucose metabolism in mice.MethodsPrg4 knockout (KO) mice and wild-type (WT) littermates were challenged with an obesogenic high-fat diet (45% of total calories as fat) for 16 weeks. To further stimulate the development of metabolic alterations, 10% fructose water was provided starting from week 13.ResultsPrg4 deficiency only tended to reduce diet-induced body weight gain, but significantly improved glucose handling (AUC: −29%; p < 0.05), which was also reflected by a tendency towards a reduced HOMA-IR score (−49%; p = 0.06 as compared to WT mice). This coincided with lower hepatic expression of glycolysis (Gck: −30%; p < 0.05) and lipogenesis (Acc: −21%; p < 0.05 and Scd1: −38%; p < 0.001) genes, which translated in significantly lower hepatic triglyceride levels (−56%; p < 0.001) in Prg4 KO mice as compared to WT mice. Prg4 KO mice likely had lower glucose utilization by skeletal muscle as compared to WT mice, judged by a significant reduction in the genes Glut4 (−29%; p < 0.01), Pfkm (−21%; p < 0.05) and Hk2 (−39%; p < 0.001). Moreover, Prg4 KO mice showed a favorable white adipose tissue phenotype with lower uptake of triglyceride-derived fatty acids (−46%; p < 0.05) and lower gene expression of inflammatory markers Cd68, Mcp1 and Tnfα (−65%, −81% and −63%, respectively; p < 0.01) than WT mice.ConclusionPrg4 KO mice are protected from high-fat diet-induced glucose intolerance and fatty liver disease. Show less
