Hematopoietic Cell–Restricted Deletion of CD36 Reduces High-Fat Diet–Induced Macrophage Infiltration and Improves Insulin Signaling in Adipose Tissue

OBJECTIVE: The fatty acid translocase and scavenger receptor CD36 is important in the recognition and uptake of lipids. Accordingly, we hypothesized that it plays a role in saturated fatty acid-induced macrophage lipid accumulation and proinflammatory activation. RESEARCH DESIGN AND METHODS: In vitro, the effect of CD36 inhibition and deletion in lipid-induced macrophage inflammation was assessed using the putative CD36 inhibitor, sulfosuccinimidyl oleate (SSO), and bone marrow-derived macrophages from mice with (CD36KO) or without (wild-type) global deletion of CD36. To investigate whether deletion of macrophage CD36 would improve insulin sensitivity in vivo, wild-type mice were transplanted with bone marrow from CD36KO or wild-type mice and then fed a standard or high-fat diet (HFD) for 20 weeks. RESULTS: SSO treatment markedly reduced saturated fatty acid-induced lipid accumulation and inflammation in RAW264.7 macrophages. Mice harboring CD36-specific deletion in hematopoietic-derived cells (HSC CD36KO) fed an HFD displayed improved insulin signaling and reduced macrophage infiltration in adipose tissue compared with wild-type mice, but this did not translate into protection against HFD-induced whole-body insulin resistance. Contrary to our hypothesis and our results using SSO in RAW264.7 macrophages, neither saturated fatty acid-induced lipid accumulation nor inflammation was reduced when comparing CD36KO with wild-type bone marrow-derived macrophages. CONCLUSIONS: Although CD36 does not appear important in saturated fatty acid-induced macrophage lipid accumulation, our study uncovers a novel role for CD36 in the migration of proinflammatory phagocytes to adipose tissue in obesity, with a concomitant improvement in insulin action

Plasma lysophosphatidylcholine levels are reduced in obesity and type 2 diabetes

BACKGROUND: Obesity and type 2 diabetes (T2DM) are associated with increased circulating free fatty acids and triacylglycerols. However, very little is known about specific molecular lipid species associated with these diseases. In order to gain further insight into this, we performed plasma lipidomic analysis in a rodent model of obesity and insulin resistance as well as in lean, obese and obese individuals with T2DM. METHODOLOGY/PRINCIPAL FINDINGS: Lipidomic analysis using liquid chromatography coupled to mass spectrometry revealed marked changes in the plasma of 12 week high fat fed mice. Although a number of triacylglycerol and diacylglycerol species were elevated along with of a number of sphingolipids, a particularly interesting finding was the high fat diet (HFD)-induced reduction in lysophosphatidylcholine (LPC) levels. As liver, skeletal muscle and adipose tissue play an important role in metabolism, we next determined whether the HFD altered LPCs in these tissues. In contrast to our findings in plasma, only very modest changes in tissue LPCs were noted. To determine when the change in plasma LPCs occurred in response to the HFD, mice were studied after 1, 3 and 6 weeks of HFD. The HFD caused rapid alterations in plasma LPCs with most changes occurring within the first week. Consistent with our rodent model, data from our small human cohort showed a reduction in a number of LPC species in obese and obese individuals with T2DM. Interestingly, no differences were found between the obese otherwise healthy individuals and the obese T2DM patients. CONCLUSION: Irrespective of species, our lipidomic profiling revealed a generalized decrease in circulating LPC species in states of obesity. Moreover, our data indicate that diet and adiposity, rather than insulin resistance or diabetes per se, play an important role in altering the plasma LPC profile

AMP-activated protein kinase controls exercise training- and AICAR-induced increases in SIRT3 and MnSOD

The mitochondrial protein deacetylase sirtuin (SIRT) 3 may mediate exercise training-induced increases in mitochondrial biogenesis and improvements in reactive oxygen species (ROS) handling. We determined the requirement of AMP-activated protein kinase (AMPK) for exercise training-induced increases in skeletal muscle abundance of SIRT3 and other mitochondrial proteins. Exercise training for 6.5 weeks increased SIRT3 (p<0.01) and superoxide dismutase 2 (MnSOD; p<0.05) protein abundance in quadriceps muscle of wild-type (WT; n=13-15), but not AMPK α2 kinase dead (KD; n=12-13) mice. We also observed a strong trend for increased MnSOD abundance in exercise-trained skeletal muscle of healthy humans (p=0.051; n=6). To further elucidate a role for AMPK in mediating these effects, we treated WT (n=7-8) and AMPK α2 KD (n=7-9) mice with 5-amino-1-β-D-ribofuranosyl-imidazole-4-carboxamide (AICAR). Four weeks of daily AICAR injections (500 mg/kg) resulted in AMPK-dependent increases in SIRT3 (p<0.05) and MnSOD (p<0.01) in WT, but not AMPK α2 KD mice. We also tested the effect of repeated AICAR treatment on mitochondrial protein levels in mice lacking the transcriptional coactivator peroxisome proliferator-activated receptor γ-coactivator 1α (PGC-1α KO; n=9-10). Skeletal muscle SIRT3 and MnSOD protein abundance was reduced in sedentary PGC-1α KO mice (p<0.01) and AICAR-induced increases in SIRT3 and MnSOD protein abundance was only observed in WT mice (p<0.05). Finally, the acetylation status of SIRT3 target lysine residues on MnSOD (K122) or oligomycin-sensitivity conferring protein (OSCP; K139) was not altered in either mouse or human skeletal muscle in response to acute exercise. We propose an important role for AMPK in regulating mitochondrial function and ROS handling in skeletal muscle in response to exercise training

The effect of high-fat diet on the plasma lipidome.

<p>Significant mean fold changes (P&lt;0.05) observed in plasma lipids from mice fed a high fat diet for 12 week (N = 6) relative to low fat fed animals (N = 8). Plasma lipids were analysed by LC ESI-MS/MS and absolute lipid levels were expressed relative to the low fat fed control group. Plasma samples were obtained from 5 hour fasted animals. BMP, bismonoacylglycerolphosphate; Cer, ceramide; DG, diacylglycerol; DHC, dihexosylceramide; LPC, lysophosphatidylcholine; MHC, monohexosylceramide; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PG, phosphatidylglycerol; SM, sphingomyelin; Sph, sphingosine; TG, triacylglycerol; THC, trihexosylceramide.</p

Plasma LPC levels in lean, obese non-diabetic and obese type 2 diabetic individuals.

<p>Samples were obtained following an overnight (10–12 hour) fast. Data are mean ± SEM.</p>a<p>P&lt;0.05 vs lean;</p>b<p>P&lt;0.01 vs lean;</p>c<p>P = 0.052 vs lean;</p>d<p>P = 0.06 vs lean.</p

Metabolic parameters of C57Bl/6 mice fed a low or high fat diet for 12 wk.

<p>All measurements were made in 5 hour fasted mice. Data are mean ± SEM.</p>a<p>P&lt;0.05 vs Chow;</p>b<p>P&lt;0.001 vs Chow. LFD, low fat diet; HFD, high fat diet.</p

Time course changes in metabolic parameters measured in mice fed a high fat diet.

<p>Body mass (A), fat mass (B), fasting blood glucose (C), plasma insulin (D), blood glucose during an intraperitoneal glucose tolerance test (E) and blood glucose area under the curve during an intraperitoneal glucose tolerance test (F) were measured in mice (N = 11) following a 5 hour fast at baseline (time 0) and after 1, 3 and 6 weeks of high fat feeding. Data are presented as mean ± SEM. *P&lt;0.05 versus baseline; ^†P&lt;0.05 versus week 1; ^‡P&lt;0.05 versus week 3.</p

Tissue lysophosphatidylcholine levels in low and high fat fed mice.

<p>Liver (A), skeletal muscle (B) and adipose tissue (C) lysophosphatidylcholine (LPC) levels measured by LC ESI-MS/MS in mice fed a low (N = 8) or high fat diet (HFD, N = 6). Tissues were collected from 5 hour fasted animals. Data are presented as mean ± SEM. *P&lt;0.05 versus low fat.</p