Intestinal lipid absorption is not affected in CD36 deficient mice

Increasing evidence has implicated the membrane protein CD36 (or fatty acid translocase, FAT) to be involved in high affinity fatty acid uptake. CD36 is expressed in tissues active in fatty acid metabolism, like adipose tissue and skeletal and cardiac muscle, but also in intestine. CD36 is localized in the intestine mainly in the jejunal villi, where it is confined to enterocyte apical membrane. The aim was to determine the role of CD36 in intestinal lipid absorption. Lipid absorption was determined by administering 3H-labeled triolein and 14C-labeled palmitic acid as an olive oil bolus by intragastric gavage and determine appearance of 3H and 14C label in plasma, after blocking lipolysis by i.v. injections of Triton WR 1339. Surprisingly, no differences in plasma appearance of 3H-label or 14C-label were observed in CD36(-/-) mice compared to wild type controls. These results suggest that CD36 does not play a role in intestinal lipid absorption after an acute lipid loa

Contribution of fatty acids released from lipolysis of plasma triglycerides to total plasma fatty acid flux and tissue-specific fatty acid uptake

There is controversy over the extent to which fatty acids (FAs) derived from plasma free FAs (FFAs) or from hydrolysis of plasma triglycerides (TGFAs) form communal or separate pools and what the contribution of each FA source is to cellular FA metabolism. Chylomicrons and lipid emulsions were labeled with [(3)H]triolein, injected into mice, and appearance in plasma of [(3)H]oleic acid was estimated, either through a steady-state approach or by compartmental modeling. [(14)C]oleic acid was included to trace plasma FFA. Eighty to 90% of triglyceride (TG) label was recovered in plasma, irrespective of tracer method or TG source. The contribution of TG lipolysis to total plasma FA turnover was 10-20%. After infusion of [(3)H]TG and [(14)C]FA, the retention of these labels varied substantially among liver, adipose tissue, and skeletal and heart muscle. Retention of TG label changed during fasting in the same direction as lipoprotein lipase (LPL) activity is regulated. We propose a model that reconciles the paradoxical 80-90% loss of TG label into plasma with LPL-directed differential uptake of TGFA in tissues. In this model, TGFAs mix locally at the capillaries with plasma FFAs, where they would lead to an increase in the local FA concentration, and hence, FA uptake. Our data indicate that a distinction between TG-derived FA and plasma FFA cannot be mad

CD36 deficiency increases insulin sensitivity in muscle, but induces insulin resistance in the liver in mice

CD36 (fatty acid translocase) is involved in high-affinity peripheral fatty acid uptake. Mice lacking CD36 exhibit increased plasma free fatty acid and triglyceride (TG) levels and decreased glucose levels. Studies in spontaneous hypertensive rats lacking functional CD36 link CD36 to the insulin-resistance syndrome. To clarify the relationship between CD36 and insulin sensitivity in more detail, we determined insulin-mediated whole-body and tissue-specific glucose uptake in CD36-deficient (CD36-/-) mice. Insulin-mediated whole-body and tissue-specific glucose uptake was measured by d-[3H]glucose and 2-deoxy-d-[1-3H]glucose during hyperinsulinemic clamp in CD36-/- and wild-type control littermates (CD36+/+) mice. Whole-body and muscle-specific insulin-mediated glucose uptake was significantly higher in CD36-/- compared with CD36+/+ mice. In contrast, insulin completely failed to suppress endogenous glucose production in CD36-/- mice compared with a 40% reduction in CD36+/+ mice. This insulin-resistant state of the liver was associated with increased hepatic TG content in CD36-/- mice compared with CD36+/+ mice (110.9 +/- 12.0 and 68.9 +/- 13.6 microg TG/mg protein, respectively). Moreover, hepatic activation of protein kinase B by insulin, measured by Western blot, was reduced by 54%. Our results show a dissociation between increased muscle and decreased liver insulin sensitivity in CD36-/- mic

Quantitative analysis of ChIP-seq data uncovers dynamic and sustained H3K4me3 and H3K27me3 modulation in cancer cells under hypoxia

Abstract Background A comprehensive assessment of the epigenetic dynamics in cancer cells is the key to understanding the molecular mechanisms underlying cancer and to improving cancer diagnostics, prognostics and treatment. By combining genome-wide ChIP-seq epigenomics and microarray transcriptomics, we studied the effects of oxygen deprivation and subsequent reoxygenation on histone 3 trimethylation of lysine 4 (H3K4me3) and lysine 27 (H3K27me3) in a breast cancer cell line, serving as a model for abnormal oxygenation in solid tumors. A priori, epigenetic markings and gene expression levels not only are expected to vary greatly between hypoxic and normoxic conditions, but also display a large degree of heterogeneity across the cell population. Where traditionally ChIP-seq data are often treated as dichotomous data, the model and experiment here necessitate a quantitative, data-driven analysis of both datasets. Results We first identified genomic regions with sustained epigenetic markings, which provided a sample-specific reference enabling quantitative ChIP-seq data analysis. Sustained H3K27me3 marking was located around centromeres and intergenic regions, while sustained H3K4me3 marking is associated with genes involved in RNA binding, translation and protein transport and localization. Dynamic marking with both H3K4me3 and H3K27me3 (hypoxia-induced bivalency) was found in CpG-rich regions at loci encoding factors that control developmental processes, congruent with observations in embryonic stem cells. Conclusions In silico-identified epigenetically sustained and dynamic genomic regions were confirmed through ChIP-PCR in vitro, and obtained results are corroborated by published data and current insights regarding epigenetic regulation

Quantitative analysis of ChIP-seq data uncovers dynamic and sustained H3K4me3 and H3K27me3 modulation in cancer cells under hypoxia

BACKGROUND: A comprehensive assessment of the epigenetic dynamics in cancer cells is the key to understanding the molecular mechanisms underlying cancer and to improving cancer diagnostics, prognostics and treatment. By combining genome-wide ChIP-seq epigenomics and microarray transcriptomics, we studied the effects of oxygen deprivation and subsequent reoxygenation on histone 3 trimethylation of lysine 4 (H3K4me3) and lysine 27 (H3K27me3) in a breast cancer cell line, serving as a model for abnormal oxygenation in solid tumors. A priori, epigenetic markings and gene expression levels not only are expected to vary greatly between hypoxic and normoxic conditions, but also display a large degree of heterogeneity across the cell population. Where traditionally ChIP-seq data are often treated as dichotomous data, the model and experiment here necessitate a quantitative, data-driven analysis of both datasets. RESULTS: We first identified genomic regions with sustained epigenetic markings, which provided a sample-specific reference enabling quantitative ChIP-seq data analysis. Sustained H3K27me3 marking was located around centromeres and intergenic regions, while sustained H3K4me3 marking is associated with genes involved in RNA binding, translation and protein transport and localization. Dynamic marking with both H3K4me3 and H3K27me3 (hypoxia-induced bivalency) was found in CpG-rich regions at loci encoding factors that control developmental processes, congruent with observations in embryonic stem cells. CONCLUSIONS: In silico-identified epigenetically sustained and dynamic genomic regions were confirmed through ChIP-PCR in vitro, and obtained results are corroborated by published data and current insights regarding epigenetic regulation. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13072-016-0090-4) contains supplementary material, which is available to authorized users