RXR antagonism induces G0 /G1 cell cycle arrest and ameliorates obesity by up-regulating the p53-p21(Cip1) pathway in adipocytes.
ABSTRACT The peroxisome proliferator activated receptor-γ (PPARγ) agonist, pioglitazone (PIO), exerts anti-diabetic properties associated with increased fat mass, whereas the retinoid X receptor (RXR) antagonist HX531 demonstrates anti-obesity and anti-diabetic effects with reduced body weight and fat pad mass. The cell cycle abnormality in adipocytes has not been well-investigated in obesity or during treatment with modulators of nuclear receptors. We therefore investigated cell size and cell cycle distributions of adipocytes in vivo and examined the expression of cell cycle regulators in cultured human visceral preadipocytes. The cell size distribution and cell cycle analyses of in vivo adipocytes derived from OLETF rats demonstrated that HX531 brought about G0/G1 cell cycle arrest associated with the inhibition of cellular hypertrophy, which resulted in the reduction of fat pad mass. In contrast, PIO promoted proliferation activities associated with the increase in M + late M:G0 + G1 ratio and the appearance of both small and hypertrophied adipocytes. In cultured human visceral preadipocytes HX531 up-regulated cell cycle regulators, p53, p21(Cip1), cyclin D1, Fbxw7 and Skp2, which are known contributors towards G0 /G1 cell cycle arrest. The knockdown of p53 with a shRNA lentivirus reversed the HX531-induced up-regulation of p21(Cip1), which is one of the major p53-effector molecules. We conclude that HX531 exerts anti-obesity and anti-diabetes properties by up-regulating the p53-p21(Cip1) pathway, resulting in G0/G1 cell cycle arrest and the inhibition of cellular hypertrophy of adipocytes.
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ABSTRACT: Obesity has become a major public health problem of global significance. Today, aspirin remains the most commonly used medication for the treatment of pyrexia, pain, inflammation and antiplatelet. The present study aims at evaluating the possible existence of a putative p53-dependent pathway underlying the aspirin-induced inhibition of adipogenesis. Cell migration assay was identified by the ability to migrate through Transwell insert. Oil Red O staining was employed to quantify adipose accumulation. The concentration of glucose and triglyceride were measured by using assay kits. The expression levels of several master regulatory molecules controlling various signal pathways were monitored using the immunoblotting techniques. Aspirin significantly inhibited preadipocyte migration and adipose accumulation. The p53-p21 signaling and the expression of differentiation marker glycerol-3-phosphate dehydrogenase were increased in a dose-dependent manner. It indicated that aspirin induced adipocyte differentiation through p53-p21 pathway. The oncogenic ERK 1/2 MAPK signaling was induced, whereas, the expression of adipogenic markers peroxisome proliferator-activated receptor γ (PPARγ), adipocyte fatty acid-binding protein (A-FABP) and inflammatory factors cyclooxygenase-2 (Cox-2), tumor necrosis factor α (TNFα) and inducible nitric oxide synthase (iNOS) were inhibited. Aspirin negatively regulated the pentose phosphate pathway (PPP) by inhibiting the expression of rate-limiting enzyme glucose-6-phosphate dehydrogenase. Knockdown the expression of oncogenic ERK 1/2 MAPK by using 10μM PD98059 significantly increased triglyceride synthesis, adipose accumulation and activated PPP, however, decreased glucose uptake. Diverted the glucose flux to PPP, rather than increased glucose uptake, was associated with adipogenesis. Down-regulated the expression of tumor suppressor p53 by 10μM pifithrin-α (PFTα) alone had no effect on adipose accumulation. However, administration of aspirin accompanied with PFTα abolished aspirin-induced inhibition of adipogenesis. We demonstrated that aspirin-induced inhibition of adipogenesis was p53-dependent and associated with inactivation of PPP. Blockade PPP may be a novel strategy for obesity prevention and therapy. Moreover, when use aspirin in therapeutic strategy, the p53 status should be considered.European journal of pharmacology 04/2014; · 2.59 Impact Factor
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ABSTRACT: Lemon (Citrus limon) contains various bioactive flavonoids, and prevents obesity and obesity-associated metabolic diseases. We focused on eriocitrin (eriodictyol 7-rutinoside), a powerful antioxidative flavonoid in lemon with lipid-lowering effects in a rat model of high-fat diet. To investigate the mechanism of action of eriocitrin, we conducted feeding experiments on zebrafish with diet-induced obesity. Oral administration of eriocitrin (32 mg/kg/day for 28 days) improved dyslipidaemia and decreased lipid droplets in the liver. DNA microarray analysis revealed that eriocitrin increased mRNA of mitochondrial biogenesis genes, such as mitochondria transcription factor, nuclear respiratory factor 1, cytochrome c oxidase subunit 4, and ATP synthase. In HepG2 cells, eriocitrin also induced the corresponding orthologues, and reduced lipid accumulation under conditions of lipid loading. Eriocitrin increased mitochondrial size and mtDNA content, which resulted in ATP production in HepG2 cells and zebrafish. In summary, dietary eriocitrin ameliorates diet-induced hepatic steatosis with activation of mitochondrial biogenesis.Scientific Reports 01/2014; 4:3708. · 5.08 Impact Factor
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ABSTRACT: Introduction: Retinoid X receptors (RXRs) are nuclear receptors that act as ligand-dependent transcription factors. RXRs function as homodimers or as heterodimers with other nuclear receptors, such as retinoic acid receptors, PPARs, liver X receptors, farnesoid X receptor, vitamin D receptor or thyroid hormone receptors. RXR ligands (agonists or antagonists) show various physiological effects, depending on their partner receptors. RXR agonist bexarotene (Targretin®) is used for the treatment of cutaneous T-cell lymphoma in clinical practice. RXR agonists were also reported to be useful for treatment of type 2 diabetes, autoimmune disease and Alzheimer's disease. RXR antagonists were also reported to be effective in type 2 diabetes treatment. Areas covered: Here patent applications (2007-2013) concerning RXR ligands are summarized, and the usefulness of RXR ligands as pharmaceutical agents is discussed. Expert opinion: RXR agonists show a wide variety of biological effects. However, they cause serious side effects, such as blood triglyceride elevation, hypothyroidism and others. Thus, for clinical application of RXR agonists, abrogation of these side effects is required. RXR heterodimer-selective agonists and RXR partial agonists exhibiting desired effects without side effects are expected to find clinical application.Expert Opinion on Therapeutic Patents 01/2014; · 3.53 Impact Factor