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Preserved glucose tolerance in high-fat-fed C57BL/6 mice transplanted with PPARgamma-/-, PPARdelta-/-, PPARgammadelta-/-, or LXRalphabeta-/- bone marrow.

Marathe C, Bradley MN, Hong C, Chao L, Wilpitz D, Salazar J, Tontonoz P - J. Lipid Res. (2008)

Bottom Line: Despite their inhibitory effects on inflammatory gene expression, loss of PPARs or LXRs in macrophages did not exert major effects on obesity or glucose tolerance induced by a high-fat diet.Treatment with rosiglitazone effectively improved glucose tolerance in mice lacking macrophage PPARgamma, suggesting that cell types other than macrophages are the primary mediators of the anti-diabetic effects of PPARgamma agonists in our model system.Our results do not exclude a contribution of macrophage PPAR and LXR expression to systemic metabolism in certain contexts, but these factors do not appear to be dominant contributors to glucose tolerance in a high-fat-fed Th1-biased bone marrow transplant model.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Molecular Biology Institute and Department of Pathology and Laboratory Medicine, University of California, Los Angeles, CA 90095, USA.

ABSTRACT
Macrophage lipid metabolism and inflammatory responses are both regulated by the nuclear receptors PPAR and LXR. Emerging links between inflammation and metabolic disease progression suggest that PPAR and LXR signaling may alter macrophage function and thereby impact systemic metabolism. In this study, the function of macrophage PPAR and LXR in Th1-biased C57BL/6 mice was tested using a bone marrow transplantation approach with PPARgamma(-/-), PPARdelta(-/-), PPARgammadelta(-/-), and LXRalphabeta(-/-) cells. Despite their inhibitory effects on inflammatory gene expression, loss of PPARs or LXRs in macrophages did not exert major effects on obesity or glucose tolerance induced by a high-fat diet. Treatment with rosiglitazone effectively improved glucose tolerance in mice lacking macrophage PPARgamma, suggesting that cell types other than macrophages are the primary mediators of the anti-diabetic effects of PPARgamma agonists in our model system. C57BL/6 macrophages lacking PPARs or LXRs exhibited normal expression of most alternative activation gene markers, indicating that macrophage alternative activation is not absolutely dependent on these receptors in the C57BL/6 background under the conditions used here. These studies suggest that genetic background may be an important modifier of nuclear receptor effects in macrophages. Our results do not exclude a contribution of macrophage PPAR and LXR expression to systemic metabolism in certain contexts, but these factors do not appear to be dominant contributors to glucose tolerance in a high-fat-fed Th1-biased bone marrow transplant model.

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Induction of the Mx promoter effectively disrupts PPARĪ³, whereas LysM Cre cannot efficiently delete PPARĪ³ exon 2. Cells were harvested and pooled from three to five mice per group. The presented data are representative of at least three independent experiments. A: Thioglycollate-elicited wild-type and Mx Cre PPARĪ³āˆ’/āˆ’ peritoneal macrophages were treated with PPARĪ³ or PPARĪ“ ligands (GW7845 or GD742, respectively; 100 nM each) overnight. PPARĪ³ exon 2 could not be detected in PPARĪ³āˆ’/āˆ’ cells (P < 0.005), whereas PPARĪ³ exon 6 expression was unaffected. Known PPARĪ³ target genes (aP2, ADRP, and PGAR) were tested to confirm loss of ligand response in PPARĪ³āˆ’/āˆ’ macrophages. B: Thioglycollate-elicited wild-type and LysM Cre PPARĪ³āˆ’/āˆ’ peritoneal macrophages were treated with PPARĪ³ ligand (GW7845; 100 nM) overnight. PPARĪ³ exon 2 could still be detected in PPARĪ³āˆ’/āˆ’ macrophages, and PGAR, a known PPARĪ³ target gene, could still be induced by PPARĪ³ ligand in these cells (P < 0.02). Error bars represent SEM.
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fig1: Induction of the Mx promoter effectively disrupts PPARĪ³, whereas LysM Cre cannot efficiently delete PPARĪ³ exon 2. Cells were harvested and pooled from three to five mice per group. The presented data are representative of at least three independent experiments. A: Thioglycollate-elicited wild-type and Mx Cre PPARĪ³āˆ’/āˆ’ peritoneal macrophages were treated with PPARĪ³ or PPARĪ“ ligands (GW7845 or GD742, respectively; 100 nM each) overnight. PPARĪ³ exon 2 could not be detected in PPARĪ³āˆ’/āˆ’ cells (P < 0.005), whereas PPARĪ³ exon 6 expression was unaffected. Known PPARĪ³ target genes (aP2, ADRP, and PGAR) were tested to confirm loss of ligand response in PPARĪ³āˆ’/āˆ’ macrophages. B: Thioglycollate-elicited wild-type and LysM Cre PPARĪ³āˆ’/āˆ’ peritoneal macrophages were treated with PPARĪ³ ligand (GW7845; 100 nM) overnight. PPARĪ³ exon 2 could still be detected in PPARĪ³āˆ’/āˆ’ macrophages, and PGAR, a known PPARĪ³ target gene, could still be induced by PPARĪ³ ligand in these cells (P < 0.02). Error bars represent SEM.

Mentions: To investigate the function of macrophage PPARĪ³, we used a Cre recombinase system to disrupt the PPARĪ³ gene. Specifically, we crossed C57BL/6 mice with loxP sites flanking the second exon of PPARĪ³ (PPARĪ³fl/fl) with C57BL/6 mice expressing Cre recombinase downstream of the Ī±/Ī² interferon-inducible (Mx) promoter. Cre recombinase activity was initiated by intraperitoneal injection of the Mx activator poly IC 3 to 4 weeks after birth. Interestingly, injection of poly IC at weaning age caused a permanent disruption of PPARĪ³ in myeloid precursor cells; new myeloid cells generated postinjection remain PPARĪ³- for the life of the mouse. Typically, we analyzed macrophages from these mice at least 4 weeks after inducing recombination to reduce any potential effects of the poly IC. Quantitative real-time PCR confirmed that the Mx Cre system was extremely efficient, yielding nearly complete (>95%) deletion of PPARĪ³ exon 2 in vivo (Fig. 1A). As expected, induction of PPAR target genes (aP2, ADRP, PGAR) by PPARĪ³ but not PPARĪ“ agonists was lost in Mx Cre PPARĪ³āˆ’/āˆ’ macrophages (Fig. 1A).


Preserved glucose tolerance in high-fat-fed C57BL/6 mice transplanted with PPARgamma-/-, PPARdelta-/-, PPARgammadelta-/-, or LXRalphabeta-/- bone marrow.

Marathe C, Bradley MN, Hong C, Chao L, Wilpitz D, Salazar J, Tontonoz P - J. Lipid Res. (2008)

Induction of the Mx promoter effectively disrupts PPARĪ³, whereas LysM Cre cannot efficiently delete PPARĪ³ exon 2. Cells were harvested and pooled from three to five mice per group. The presented data are representative of at least three independent experiments. A: Thioglycollate-elicited wild-type and Mx Cre PPARĪ³āˆ’/āˆ’ peritoneal macrophages were treated with PPARĪ³ or PPARĪ“ ligands (GW7845 or GD742, respectively; 100 nM each) overnight. PPARĪ³ exon 2 could not be detected in PPARĪ³āˆ’/āˆ’ cells (P < 0.005), whereas PPARĪ³ exon 6 expression was unaffected. Known PPARĪ³ target genes (aP2, ADRP, and PGAR) were tested to confirm loss of ligand response in PPARĪ³āˆ’/āˆ’ macrophages. B: Thioglycollate-elicited wild-type and LysM Cre PPARĪ³āˆ’/āˆ’ peritoneal macrophages were treated with PPARĪ³ ligand (GW7845; 100 nM) overnight. PPARĪ³ exon 2 could still be detected in PPARĪ³āˆ’/āˆ’ macrophages, and PGAR, a known PPARĪ³ target gene, could still be induced by PPARĪ³ ligand in these cells (P < 0.02). Error bars represent SEM.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC2636915&req=5

fig1: Induction of the Mx promoter effectively disrupts PPARĪ³, whereas LysM Cre cannot efficiently delete PPARĪ³ exon 2. Cells were harvested and pooled from three to five mice per group. The presented data are representative of at least three independent experiments. A: Thioglycollate-elicited wild-type and Mx Cre PPARĪ³āˆ’/āˆ’ peritoneal macrophages were treated with PPARĪ³ or PPARĪ“ ligands (GW7845 or GD742, respectively; 100 nM each) overnight. PPARĪ³ exon 2 could not be detected in PPARĪ³āˆ’/āˆ’ cells (P < 0.005), whereas PPARĪ³ exon 6 expression was unaffected. Known PPARĪ³ target genes (aP2, ADRP, and PGAR) were tested to confirm loss of ligand response in PPARĪ³āˆ’/āˆ’ macrophages. B: Thioglycollate-elicited wild-type and LysM Cre PPARĪ³āˆ’/āˆ’ peritoneal macrophages were treated with PPARĪ³ ligand (GW7845; 100 nM) overnight. PPARĪ³ exon 2 could still be detected in PPARĪ³āˆ’/āˆ’ macrophages, and PGAR, a known PPARĪ³ target gene, could still be induced by PPARĪ³ ligand in these cells (P < 0.02). Error bars represent SEM.
Mentions: To investigate the function of macrophage PPARĪ³, we used a Cre recombinase system to disrupt the PPARĪ³ gene. Specifically, we crossed C57BL/6 mice with loxP sites flanking the second exon of PPARĪ³ (PPARĪ³fl/fl) with C57BL/6 mice expressing Cre recombinase downstream of the Ī±/Ī² interferon-inducible (Mx) promoter. Cre recombinase activity was initiated by intraperitoneal injection of the Mx activator poly IC 3 to 4 weeks after birth. Interestingly, injection of poly IC at weaning age caused a permanent disruption of PPARĪ³ in myeloid precursor cells; new myeloid cells generated postinjection remain PPARĪ³- for the life of the mouse. Typically, we analyzed macrophages from these mice at least 4 weeks after inducing recombination to reduce any potential effects of the poly IC. Quantitative real-time PCR confirmed that the Mx Cre system was extremely efficient, yielding nearly complete (>95%) deletion of PPARĪ³ exon 2 in vivo (Fig. 1A). As expected, induction of PPAR target genes (aP2, ADRP, PGAR) by PPARĪ³ but not PPARĪ“ agonists was lost in Mx Cre PPARĪ³āˆ’/āˆ’ macrophages (Fig. 1A).

Bottom Line: Despite their inhibitory effects on inflammatory gene expression, loss of PPARs or LXRs in macrophages did not exert major effects on obesity or glucose tolerance induced by a high-fat diet.Treatment with rosiglitazone effectively improved glucose tolerance in mice lacking macrophage PPARgamma, suggesting that cell types other than macrophages are the primary mediators of the anti-diabetic effects of PPARgamma agonists in our model system.Our results do not exclude a contribution of macrophage PPAR and LXR expression to systemic metabolism in certain contexts, but these factors do not appear to be dominant contributors to glucose tolerance in a high-fat-fed Th1-biased bone marrow transplant model.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Molecular Biology Institute and Department of Pathology and Laboratory Medicine, University of California, Los Angeles, CA 90095, USA.

ABSTRACT
Macrophage lipid metabolism and inflammatory responses are both regulated by the nuclear receptors PPAR and LXR. Emerging links between inflammation and metabolic disease progression suggest that PPAR and LXR signaling may alter macrophage function and thereby impact systemic metabolism. In this study, the function of macrophage PPAR and LXR in Th1-biased C57BL/6 mice was tested using a bone marrow transplantation approach with PPARgamma(-/-), PPARdelta(-/-), PPARgammadelta(-/-), and LXRalphabeta(-/-) cells. Despite their inhibitory effects on inflammatory gene expression, loss of PPARs or LXRs in macrophages did not exert major effects on obesity or glucose tolerance induced by a high-fat diet. Treatment with rosiglitazone effectively improved glucose tolerance in mice lacking macrophage PPARgamma, suggesting that cell types other than macrophages are the primary mediators of the anti-diabetic effects of PPARgamma agonists in our model system. C57BL/6 macrophages lacking PPARs or LXRs exhibited normal expression of most alternative activation gene markers, indicating that macrophage alternative activation is not absolutely dependent on these receptors in the C57BL/6 background under the conditions used here. These studies suggest that genetic background may be an important modifier of nuclear receptor effects in macrophages. Our results do not exclude a contribution of macrophage PPAR and LXR expression to systemic metabolism in certain contexts, but these factors do not appear to be dominant contributors to glucose tolerance in a high-fat-fed Th1-biased bone marrow transplant model.

Show MeSH
Related in: MedlinePlus