Inflammatory modulation of PPARγ expression and activity
Introduction
The MRL/MpJ-Faslpr (MRL/lpr) mouse model of systemic lupus erythematosus (SLE) is characterized by SLE-like renal histopathology, auto-antibody production, arthritis, and vasculitis [1], [2], [3]. It has been demonstrated by our laboratory and others that enhanced NO production occurs in MRL/lpr mice [4], [5], [6], [7], [8]. Spontaneous NO production in these mice is reflective of renal pathology and increases with age. Additionally, stimulated NO production by MRL/lpr macrophages is significantly elevated compared to normal BALB/c mice [6].
The excess production of NO in MRL/lpr mice is likely multifactorial. We hypothesize that a potential cause of chronically enhanced NO production is a defect in the modulators of the inducible nitric oxide synthase (iNOS) inflammatory pathway. One protein involved in down-regulation of inflammatory mediators, including NO, is the nuclear hormone receptor peroxisome proliferation activated receptor gamma (PPARγ) [9], [10], [11].
Evidence for a role for PPARγ agonists in suppressing inflammation in mouse macrophage cell lines was recently demonstrated [9], [10], [11]. Activation of PPARγ with either synthetic thiazoledinediones (TZDs) or prostaglandin J2 (PGJ2) metabolites inhibited the production of inflammatory mediators such as NO, IL-6, and TNFα [4], [10]. Previous studies by our laboratory indicated that 15-deoxy-Δ12, 14PGJ2 (15ΔPGJ2) and TZDs reduced NO production and iNOS expression in mesangial cells from MRL/lpr mice [4], [5]. Though PPARγ agonists inhibit the production of some inflammatory mediators, Ponstler et al. demonstrated that PPARγ actually stimulates COX-2 through a PPARγ response element (PPRE) present in the COX-2 promoter [12]. A recently identified endogenous PPARγ agonist, lysophosphatidic acid (LPA), has not been studied for anti-inflammatory function through PPARγ [13]. However, it has recently been shown that 15ΔPGJ2 can inhibit NF-κB translocation independent of PPARγ activation [14]. Thus, the role of PPARγ as an intrinsic regulator of inflammation remains unclear.
PPARγ is a member of the nuclear hormone receptor family and is primarily expressed in adipocytes, monocytes, and macrophages and is less expressed in the heart and kidney [15], [16]. PPARγ has three isoforms. Isoforms 1 and 3 are identical and when fully translated only differ in their splice variants [17]. PPARγ2 is predominantly found in adipocytes and differs from the other isoforms at its extended N-terminus [17], [18]. PPARγ has the structural features of most nuclear hormone receptors [19], [20]. The N-terminus contains the ligand-independent transcriptional activation domain (AF1). This site contains a serine that can be phosphorylated by MAP kinases. Such alterations decrease ligand-binding affinity and PPARγ activation [21], [22], [23], [24].
Based on the enhanced NO production in MRL/lpr mice and that PPARγ functions as a repressor of iNOS, we analyzed the expression of PPARγ protein and mRNA, and PPARγ function in MRL/lpr kidneys and mesangial cells. The results indicate that PPARγ expression/function is diminished in the chronic inflammatory state present in the kidney of MRL/lpr mice and likely contribute to the enhanced inflammatory state characteristic of lupus nephritis.
Section snippets
Reagents
Lipopolysaccharide (LPS) was purchased from Sigma (St. Louis, MO), IFNγ from PharMingen (San Diego, CA), and 15ΔPGJ2 from Cayman Chemical (Ann Arbor, MI). Media and fetal calf sera (FCS) were purchased from Invitrogen (Carlsbad, CA). All other reagents were from Sigma (St. Louis, MO). NG-monomethyl-l-arginine (l-NMMA) was purchased from Paragon Biochemicals (Salt Lake City, UT). Ciglitazone was purchased from Biomol (Plymouth, PA). GW347845X (GW) was a gift from Kathleen Brown of
iNOS expression is upregulated in aging MRL/lpr mice
Kidneys were harvested from aging MRL/lpr and BALB/c mice at 9, 15, and 21 weeks, and the kidney cortices were used in protein and RNA analysis. As shown in Fig. 1, iNOS protein and mRNA expression increased with aging and disease progression in MRL/lpr kidney cortices from 3 different mice at each time point in each group. A representative blot is shown. Elevated levels of iNOS mRNA and protein were evident beginning at 15 weeks. In contrast, neither iNOS protein nor mRNA was detected in
Discussion
Our in vitro and in vivo findings provide evidence for a dysfunctional intrinsic PPARγ pathway of inflammatory suppression in MRL/lpr mice. Our data suggest that PPARγ expression is decreased in chronic inflammatory states, like lupus nephritis, while PPARγ activity is reduced in the induced acute inflammatory setting. In primary and immortalized mesangial cells from MRL/lpr mice, there is a baseline reduction in PPARγ expression as compared with BALB/c control mesangial cells. In the B6
Acknowledgments
This research was supported by the Medical Research Service, Ralph H. Johnson VAMC, and by NIH grants AR45476 and AR47451. Ms. Crosby was supported by a Dissertation Fellowship from the American Association of University Women and NIH Medical Scientist Training Program grant NGMS-GM08716.
References (45)
- et al.
Cytokine gene expression in the MRL/lpr model of lupus nephritis
Kidney Int.
(1996) - et al.
Prostaglandin J(2) inhibition of mesangial cell iNOS expression
Clin. Immunol.
(2001) - et al.
Expression of inducible-NOS in human glomerulonephritis: the possible source is infiltrating monocytes/macrophages
Kidney Int.
(1996) - et al.
Cyclooxygenase-2 is induced in monocytes by peroxisome proliferator activated receptor gamma and oxidized alkyl phospholipids from oxidized low density lipoprotein
J. Biol. Chem.
(2002) - et al.
PPARgamma3 mRNA: a distinct PPARgamma mRNA subtype transcribed from an independent promoter
FEBS Lett.
(1998) - et al.
Transcriptional activation by peroxisome proliferator-activated receptor gamma is inhibited by phosphorylation at a consensus mitogen-activated protein kinase site
J. Biol. Chem.
(1997) - et al.
Transforming growth factor-beta 1 (TGF-beta 1) and TGF-beta 2 decrease expression of CD36, the type B scavenger receptor, through mitogen-activated protein kinase phosphorylation of peroxisome proliferator-activated receptor-gamma
J. Biol. Chem.
(2000) - et al.
Inhibition of adipogenesis by a COOH-terminally truncated mutant of PPARgamma2 in 3T3-L1 cells
Biochem. Biophys. Res. Commun.
(1999) - et al.
Measurement of nitrate and nitrite in biological samples using nitrate reductase and Griess reaction
Methods Enzymol.
(1996) - et al.
Regulation of peroxisome proliferator-activated receptor gamma activity by mitogen-activated protein kinase
J. Biol. Chem.
(1997)
Interferon-gamma-induced regulation of peroxisome proliferator-activated receptor gamma and STATs in adipocytes
J. Biol. Chem.
The identification and characterization of a STAT 1 binding site in the PPARgamma2 promoter
Biochem. Biophys. Res. Commun.
Amelioration of experimental autoimmune encephalomyelitis in C57BL/6 mice by an agonist of peroxisome proliferator-activated receptor-gamma
J. Neuroimmunol.
Impaired expression of peroxisome proliferator-activated receptor gamma in ulcerative colitis
Gastroenterology
An open-label trial of the PPAR-gamma ligand rosiglitazone for active ulcerative colitis
Am. J. Gastroenterol.
Lupus nephritis: a clinical review for practicing nephrologists
Clin. Nephrol.
Nephritogenic autoantibodies in lupus: current concepts and continuing controversies
Arthritis Rheum.
Inhibition of mesangial cell nitric oxide in MRL/lpr mice by prostaglandin J2 and proliferator activation receptor-gamma agonists
J. Immunol.
The role of nitric oxide in the pathogenesis of spontaneous murine autoimmune disease: increased nitric oxide production and nitric oxide synthase expression in MRL-lpr/lpr mice, and reduction of spontaneous glomerulonephritis and arthritis by orally administered NG-monomethyl-l-arginine
J. Exp. Med.
Increased nitric oxide production accompanied by the up-regulation of inducible nitric oxide synthase in vascular endothelium from patients with systemic lupus erythematosus
Arthritis Rheum.
The peroxisome proliferator-activated receptor(PPARgamma) as a regulator of monocyte/macrophage function
J. Leukocyte Biol.
The peroxisome proliferator-activated receptor-gamma is a negative regulator of macrophage activation
Nature
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