Human bone marrow megakaryocytes and platelets express PPARγ, and PPARγ agonists blunt platelet release of CD40 ligand and thromboxanes

Abstract

Peroxisome proliferator-activated receptor ␥ (PPAR␥) is a ligand-activated transcription factor important in lipid metabolism, diabetes, and inflammation. We evaluated whether human platelets and megakaryocytes express PPAR␥ and whether PPAR␥ agonists influence platelet release of bioactive mediators. Although PPAR␥ is mainly considered a nuclear receptor, we show that enucleate platelets highly express PPAR␥ protein as shown by Western blotting, flow cytometry, and immunocytochemistry. Meg-01 megakaryocyte cells and human bone marrow megakaryocytes also express PPAR␥. Platelet and Meg-01 PPAR␥ bound the PPAR␥ DNA consensus sequence, and this was enhanced by PPAR␥ agonists. Platelets are essential not only for clotting, but have an emerging role in inflammation in part due to their release or production of the proinflammatory and proatherogenic mediators CD40 ligand (CD40L) and thromboxanes (TXs). Platelet incubation with a natural PPAR␥ agonist, 15d-PGJ 2 , or with a potent synthetic PPAR␥ ligand, rosiglitazone, prevented thrombin-induced CD40L surface expression and release of CD40L and thromboxane B 2 (TXB 2 ). 15d-PGJ 2 also inhibited platelet aggregation and adenosine triphosphate ( IntroductionPeroxisome proliferator-activated receptors (PPARs) are members of a nuclear hormone receptor superfamily of ligandactivated transcription factors. There are 3 PPAR subtypes: PPAR␣, PPAR␤/␦, and PPAR␥. The genes encoding the PPAR subtypes each reside on different chromosomes and have distinct tissue expression patterns. 1 While many reports focus on PPAR expression in the nucleus, PPAR␥, in particular, is also found in the cytoplasm. 2,3 PPAR␥ is highly expressed in white adipose tissue and was initially described as important for regulating gene expression in metabolism, insulin responsiveness, and adipocyte differentiation. 4,5 While PPAR␥ was originally thought to be found mainly in fat tissue, it is in fact widely expressed by many types of cells including macrophages, B and T lymphocytes, epithelial, endothelial, smooth muscle, and fibroblastic cells. 2,[6][7][8][9][10][11] PPAR␥ has also come to prominence as PPAR␥ agonists play an important role in immune function by dampening inflammation, attenuating macrophage/monocyte synthesis of proinflammatory cytokines, and inducing apoptosis in B lymphocytes. 2,6,12,13 PPAR␥ has also emerged as a key target for malignant cells as PPAR␥ agonists have shown therapeutic potential for B lymphoma and various epithelialderived cancers. 2,14,15 Megakaryocytes are the biggest cell of the bone marrow and the parent cell of platelets. Platelets are derived from the cytoplasm of megakaryocytes and are released to the bloodstream under the effects of cytokines such as interleukin-6 (IL-6) and 17 Platelets are enuclear cells that have a plasma membrane, surface-connected canalicular and tubular system, mitochondria, granules, lysosomes, and peroxisomes. 18 Recent studies demonstrate that platelets and many of their products are important not only in hemostasis, but have now emerg...

The effect of sensitisation to insulin with pioglitazone on fasting and postprandial lipid metabolism, lipoprotein modification by lipases, and lipid transfer activities in type 2 diabetic patients

“…In our study, pioglitazone reduced fasting triglyceride levels; however, this does not seem to be the case with rosiglitazone, which has been shown to enhance postprandial triglyceride disposal, with this effect being attributed to an improvement in the lipolysis of intact chylomicrons [46]. The reason for the differences in action of these two TZDs is not known, but may lie in the fact that pioglitazone reportedly has a greater potential than rosiglitazone to react with the PPAR-α receptor, but other differences in their pleiotropic effects or actions not involving nuclear genes cannot be ruled out [47][48][49][50]. After treatment with pioglitazone, we have also shown a significant improvement in the disposal of chylomicrons, and also in chylomicron remnant metabolism, which, coupled with the reduction in fasting VLDL and triglyceride, is responsible for a 35% improvement in postprandial triglyceride clearance.…”

Functional Synergy between CD40 Ligand and HIV-1 Tat Contributes to Inflammation: Implications in HIV Type 1 Dementia

“…Platelet-rich plasma was obtained by centrifugation of blood (from anonymous donors obtained via the American Red Cross) at 1800 ϫ g for 8 min, followed by removal into a transfer bag (Charter Medical) at room temperature as described (32). A Pall Biomedical Purecell LRF high-efficiency leukoreduction filter was used to remove leukocytes, microaggregates, and anaphylatoxin.…”

“…sCD40L was measured in plasma and CeSF samples derived from HIV-1-infected individuals using a human CD40L ELISA kit (R&D Systems) and methods outlined previously (32,34). This assay has a minimum sensitivity of 2-10 pg/ml.…”

Novel uses for anti‐platelet agents as anti‐inflammatory drugs

“…Selective agonists for all three receptors (fenofibrate: PPARa; GW0742 and L165041: PPARb; and rosiglitazone: PPARg) are capable of inhibiting platelet aggregation (Ali et al, 2005). Recently, PPARg agonists acting on platelets have been shown to have anti-inflammatory properties, inhibiting platelet release of CD40L and TXA 2 production (Akbiyik et al, 2004;Ray et al, 2006). The efficacy of PPAR agonists in inflammatory diseases needs to be thoroughly investigated.…”