Troglitazone and pioglitazone interactions via PPAR-γ-independent and -dependent pathways in regulating physiological responses in renal tubule-derived cell lines

Eltroxin and Hesperidin mitigate testicular and renal damage in hypothyroid rats: amelioration of oxidative stress through PPARγ and Nrf2/HO-1 signaling pathway

BACKGROUND

Thyroid hormones (THs) regulate growth, development and function of different tissues. Hypothyroidism is a common clinical disorder characterized by deficiency in THs and adversely affects the development and functions of several organs. This work aimed to investigate the ameliorative effect of eltroxin (ELT), a hypothyroidism medication, and hesperidin (HSP), a flavonoid, against testicular and renal toxicity in hypothyroid rats. Twenty-four rats were divided into four groups and treated orally for 12 weeks. Group I (control), group II (hypothyroidism) received 20 mg/kg carbimazole (CBZ), group III received CBZ and 0.045 mg/kg ELT, and group IV received CBZ and 200 mg/kg HSP.

RESULTS

CBZ administration induced biochemical and histopathological changes in testis and kidney. Co-administration of ELT or HSP significantly (P < 0.05) ameliorated THs, reduced urea and creatinine while raised follicle stimulating hormone (FSH), Luteinizing hormone (LH), and testosterone in serum. Testicular and renal malondialdehyde level as a lipid peroxidation indicator, tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) were significantly (P < 0.05) decreased while glutathione content, glutathione peroxidase, and glutathione-s-transferase activities were significantly (P < 0.05) increased. The histopathological changes were also diminished. Decreased mRNA and protein expressions of nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), and peroxisome proliferator-activated receptor gamma(PPARγ) in hypothyroid rats were up-regulated after ELT or HSP treatment.

CONCLUSIONS

ELT and HSP showed antioxidant and anti-inflammatory effects against CBZ-induced testicular and renal toxicity, and these effects may be promoted via activating Nrf2/HO-1 and PPARγ signaling pathways.

Evaluation of Protein Kinase Cβ and PPARγ Activity in Diabetic Rats Supplemented with Momordica charantia

INTRODUCTION

The present study was taken up to compare and evaluate the effect of Momordica charantia supplementation with pioglitazone on PKC-β and PPAR-γ activity in kidneys of diabetic rats. The hypoglycaemic and lipid lowering effect of Momordica charantia were screened in laboratory animal model and its potency was compared with a Thiazolidinedione (TZD) group antidiabetic drug like pioglitazone.

MATERIALS AND METHODS

Adult healthy albino rats of Wistar strain aged 3-4months, weighing between 170-250gm of either sex were divided into 4 groups; Group 1 (normal controls), Group 2 (diabetic controls), Group 3 (diabetic rats treated with pioglitazone) and Group 4 (diabetic rats treated with bitter melon juice). Type 1 Diabetes was induced in rats by intraperitoneal injection of streptozotocin at a dose of 55 mg/kg body weight, following which glucose levels were estimated by Accu chek- active glucometer on day 0, 7, 14, 21 and 28 days to assess the efficacy of Bitter Melon Juice (BMJ) and pioglitazone. After 28 days of treatment, the rats were sacrificed and blood collected from abdominal vena cava was used for estimation of triglycerides by Glycerol 3 phosphate oxidase phenol aminophenazone method and cholesterol by Cholestrol oxidase phenol aminophenazone method. PKC-β and PPAR-γ were estimated in the dissected kidneys by using double sandwich ELISA based kits on an automated plate reader.

RESULTS

BMJ significantly reduced blood glucose levels in group 4 as compared to diabetic controls (p<0.001). Total cholesterol and triglycerides were significantly reduced in both group 3 and 4. In Group 4, there was reduction in PKC-β levels, when compared to Group 3(p=0.004). PPAR-γ levels were increased in both Group 3 and 4, when compared to Group 2.

CONCLUSION

The results suggest that BMJ has hypoglycaemic and lipid lowering effect in diabetic animal models. BMJ increases PPAR-γ activity and decreases PKC-β activity in kidneys of diabetic rats, thereby preventing the complications of diabetes mellitus. Fresh BMJ mimics action of pioglitazone belonging to TZD group thus showing a potential for further research in identifying the active molecules responsible for glucose and lipid lowering action.

Cancer drug troglitazone stimulates the growth and response of renal cells to hypoxia inducible factors

Troglitazone has been used to suppress the growth of a number of tumors through apoptosis and autophagy. However, previous in vitro studies have employed very high concentrations of troglitazone (≥10(-5) M) in order to elicit growth inhibitory effects. In this report, when employing lower concentrations of troglitazone in defined medium, troglitazone was observed to stimulate the growth of primary renal proximal tubule (RPT) cells. Rosiglitazone, like troglitazone, is a thiazolidinedione (TZD) that is known to activate Peroxisome Proliferator Activated Receptor Υ (PPARΥ). Notably, rosiglitazone also stimulates RPT cell growth, as does Υ-linolenic acids, another PPARΥ agonist. The PPARΥ antagonist GW9662 inhibited the growth stimulatory effect of troglitazone. In addition, troglitazone stimulated transcription by a PPAR Response Element/Luciferase construct. These results are consistent with the involvement of PPARΥ as a mediator of the growth stimulatory effect of troglitazone. In a number of tumor cells, the expression of hypoxia inducible factor (HIF) is increased, promoting the expression of HIF inducible genes, and vascularization. Troglitazone was observed to stimulate transcription by a HIF/luciferase construct. These observations indicate that troglitazone not only promotes growth, also the survival of RPT cells under conditions of hypoxia.

Neuroprotective effects of pioglitazone against transient cerebral ischemic reperfusion injury in diabetic rats: Modulation of antioxidant, anti-inflammatory, and anti-apoptotic biomarkers

BACKGROUND

Recent growing consensus introduced thiazolidinediones, agonists of the nuclear receptor peroxisome proliferator-activated receptor gamma as promising candidates in the management of ischemia in various organs. Thereby, interest was raised to investigate the neuroprotective effects of pioglitazone against transient ischemia/reperfusion (I/R) injury in diabetic rats targeting mainly the oxidative-inflammatory-apoptotic cascades which are involved in this insult.

METHODS

Forebrain ischemia was induced in streptozotocin-diabetic rats by occlusion of the bilateral common carotid arteries for 15min followed by 1h reperfusion. Pioglitazone (10mg/kg; po) was administered daily for 2 weeks prior to I/R.

RESULTS

The drug alleviated hippocampal injury inflicted by diabetes and/or I/R injury where it suppressed nuclear factor kappa (NFκB), and consequently the downstream inflammatory cytokines tumor necrosis factor-α and interleukin-6. In parallel, the anti-inflammatory cytokine interleukin-10 was elevated. Antioxidant potential of pioglitazone was depicted, where it reduced neutrophil infiltration, lipid peroxides, nitric oxide associated with replenished reduced glutathione. Decline of excitatory amino acid glutamate content is a main finding which is probably mediated by the NFκB signaling pathway as well as improved oxidant status. Pioglitazone exerted an anti-apoptotic effect as reflected by the reduction of the cytosolic cytochrome c and the key downstream executioner caspase-3.

CONCLUSIONS

Pioglitazone is endowed with neuroprotective properties which are probably mediated by its antioxidant, anti-inflammatory, and anti-apoptotic mechanisms hence may provide a successful agent for the management of ischemic stroke.

pH-responsive, gluconeogenic renal epithelial LLC-PK1-FBPase+cells: a versatile in vitro model to study renal proximal tubule metabolism and function

Ammoniagenesis and gluconeogenesis are prominent metabolic features of the renal proximal convoluted tubule that contribute to maintenance of systemic acid-base homeostasis. Molecular analysis of the mechanisms that mediate the coordinate regulation of the two pathways required development of a cell line that recapitulates these features in vitro. By adapting porcine renal epithelial LLC-PK1 cells to essentially glucose-free medium, a gluconeogenic subline, termed LLC-PK1-FBPase(+) cells, was isolated. LLC-PK1-FBPase(+) cells grow in the absence of hexoses and pentoses and exhibit enhanced oxidative metabolism and increased levels of phosphate-dependent glutaminase. The cells also express significant levels of the key gluconeogenic enzymes, fructose-1,6-bisphosphatase (FBPase) and phosphoenolpyruvate carboxykinase (PEPCK). Thus the altered phenotype of LLC-PK1-FBPase(+) cells is pleiotropic. Most importantly, when transferred to medium that mimics a pronounced metabolic acidosis (9 mM HCO3 (-), pH 6.9), the LLC-PK1-FBPase(+) cells exhibit a gradual increase in NH4 (+) ion production, accompanied by increases in glutaminase and cytosolic PEPCK mRNA levels and proteins. Therefore, the LLC-PK1-FBPase(+) cells retained in culture many of the metabolic pathways and pH-responsive adaptations characteristic of renal proximal tubules. The molecular mechanisms that mediate enhanced expression of the glutaminase and PEPCK in LLC-PK1-FBPase(+) cells have been extensively reviewed. The present review describes novel properties of this unique cell line and summarizes the molecular mechanisms that have been defined more recently using LLC-PK1-FBPase(+) cells to model the renal proximal tubule. It also identifies future studies that could be performed using these cells.

Activation of PPARγ by restores mast cell numbers and reactivity in alloxan-diabetic rats by reducing the systemic glucocorticoid levels

Mast cell function and survival have been shown to be down-regulated under diabetic conditions. This study investigates the role of the peroxisome proliferator-activated receptor (PPAR)-γ in reducing mast cell number and reactivity in diabetic rats. The effect of rosiglitazone on mast cell apoptosis was also evaluated. Diabetes was induced by intravenous injection of alloxan into fasted rats and PPARγ agonist rosiglitazone and/or specific antagonist 2-chloro-5-nitrobenzanilide (GW9662) were administered 3 day after diabetes induction, once daily for 18 consecutive days. Mast cell apoptosis and plasma corticosterone levels were evaluated by TUNEL and radioimmunoassay, respectively. Treatment with rosiglitazone restored mast cell numbers in the pleural cavity and mesenteric tissue of diabetic rats. Rosiglitazone also significantly reversed the diabetes-induced reduction of histamine release by mast cells, as measured by fluorescence, following activation with the antigen in vitro. Increased apoptosis in mast cells from diabetic rats were inhibited by rosiglitazone. Moreover, we noted that the increase in plasma corticosterone levels in diabetic rats was inhibited by rosiglitazone. In addition, GW9662 blocked the ability of rosiglitazone to restore baseline numbers of mast cells and plasma corticosterone in diabetic rats. In conclusion, our findings showed that rosiglitazone restored the number and reactivity of mast cells in diabetic rats, accompanied with a suppression of apoptosis, in parallel with impairment of diabetes hypercorticolism, indicating that PPARγ has an important role in these phenomena.

Troglitazone induces extracellular matrix and cytoskeleton remodeling in mouse collecting duct cells

Peroxisome proliferator-activated receptor (PPARγ) has been shown to have a protective role in the nephron through its ability to inhibit a transforming growth factor- (TGF-β) mediated fibrotic response. In contrast, PPARγ was also shown to induce a mesenchymal transformation in epithelial intestinal cells. A fibrotic response in the collecting duct has only recently been established; however, the entire collecting duct has not been fully examined. Inner medullary collecting duct cells (IMCD-K2) and mouse cortical collecting duct cells (M1), representing the cortical and medullary collecting duct, were exposed to 5–10 μM troglitazone for 24 hours. Troglitazone resulted in an elongated morphology, 60% decreases in E-cadherin and β-catenin, a 35% decrease in α-catenin, and a 1.5-fold increase in fibronectin. These effects were not reversed with PPARγ antagonists or affected with PPARγ overexpression. Our results indicate that troglitazone induced a mesenchymal-like transformation in M1 and IMCD-K2 epithelial cells independently of PPARγ.

Stimulatory Effects of Peroxisome Proliferator-Activated Receptor-gamma on Fcgamma Receptor-Mediated Phagocytosis by Alveolar Macrophages

Alveolar macrophages abundantly express PPAR-γ, with both natural and synthetic agonists maintaining the cell in a quiescent state hyporesponsive to antigen stimulation. Conversely, agonists upregulate expression and function of the cell-surface receptor CD36, which mediates phagocytosis of lipids, apoptotic neutrophils, and other unopsonized materials. These effects led us to investigate the actions of PPAR-γ agonists on the Fcγ receptor, which mediates phagocytosis of particles opsonized by binding of immunoglobulin G antibodies. We found that troglitazone, rosiglitazone, and 15-deoxy-Δ12,14-prostaglandin J2 increase the ability of alveolar, but not peritoneal, macrophages to carry out phagocytosis mediated by the Fcγ receptor. Receptor expression was not altered but activation of the downstream signaling proteins Syk, ERK-1, and ERK-2 was observed. Although it was previously known that PPAR-γ ligands stimulate phagocytosis of unopsonized materials, this is the first demonstration that they stimulate phagocytosis of opsonized materials as well.

Pioglitazone limits myocardial infarct size, activates Akt, and upregulates cPLA2 and COX-2 in a PPAR-γ-independent manner

Pioglitazone (PIO), a PPAR-γ agonist, limits myocardial infarct size by activating Akt and upregulating cytosolic phospholipase A(2) (cPLA(2)) and cyclooxygenase (COX)-2. However, PIO has several PPAR-γ-independent effects. We assessed whether PIO limits myocardial infarct size in PPAR-γ-knockout mice, attenuates hypoxia-reoxygenation injury and upregulates P-Akt, cPLA(2), and COX-2 expression in PPAR-γ-knockout cardiomyocytes. Cardiac-specific inducible PPAR-γ knockout mice were generated by crossing αMHC-Cre mice to PPAR-γ(loxp/loxp) mice. PPAR-γ deletion was achieved after 7 days of intraperitoneal tamoxifen (20 mg/kg/day) administration. Mice received PIO (10 mg/kg/day), or vehicle, for 3 days and underwent coronary occlusion (30 min) followed by reperfusion (4 h). We assessed the area at risk by blue dye and infarct size by TTC. Cultured adult cardiomyocytes of PPAR-γ(loxp/loxp/cre) mice without or with pretreatment with tamoxifen were incubated with or without PIO and subjected to 2 h hypoxia/2 h reoxygenation. Cardiac-specific PPAR-γ knockout significantly increased infarct size. PIO reduced infarct size by 51% in PPAR-γ knockout mice and by 55% in mice with intact PPAR-γ. Deleting the PPAR-γ gene increased cell death in vitro. PIO reduced cell death in cells with and without intact PPAR-γ. PIO similarly increased myocardial Ser-473 P-Akt, cPLA(2), and COX-2 levels after hypoxia/reoxygenation in cells with and without intact PPAR-γ. PIO limited infarct size in mice in a PPAR-γ-independent manner. PIO activated Akt, increased the expression of cPLA(2) and COX-2, and protected adult cardiomyocytes against the effects of hypoxia/reoxygenation independent of PPAR-γ activation.

Glutaminolysis and glycolysis regulation by troglitazone in breast cancer cells: Relationship to mitochondrial membrane potential

We studied the roles of glycolysis and glutaminolysis following an acute reduction in mitochondrial membrane potential (Ψ(m)) induced by the thiazolidinedione troglitazone (TRO) and compared the responses with CCCP-induced depolarization in breast cancer derived MCF-7 and MDA-MB-231 cells as well as in the MCF-10A normal breast cell line. TRO and CCCP both acutely reduced Ψ(m) but after 24 h TRO-treated cells had restored Ψ(m) associated with both increased glycolysis and glutaminolysis. In contrast, CCCP-treated cells exhibited only a partial restoration of Ψ(m) associated with increased glycolysis but decreased glutaminolysis. TRO-induced glutaminolysis was coupled to increased ammonium (GDH flux) and decreased alanine production (ALT flux) in all three cell lines. Both cancer cell lines exhibited a higher spontaneous GDH/ALT flux than the normal breast cell line associated with a reduced keto-acid pool. TRO's effect on GDH/ALT fluxes and mitochondrial keto-acid pool homeostasis was additive with glucose withdrawal suggesting limited intramitochondrial pyruvate availability. The TRO-induced acceleration in GDH flux supplies substrate for Complex I contributing to the restoration of Ψ(m) as well as Krebs cycle intermediates for biosynthesis. Inhibiting mitochondrial proton ATPase with oligomycin or nullifying the proton gradient with CCCP prevented both the TRO-induced recovery of Ψ(m) and accelerated GDH flux but restored ALT flux consonant with important roles for proton pumping in regulating GDH flux and Ψ(m) recovery. Blocking enhanced GDH flux reduced DNA synthesis consistent with glutaminolysis via GDH playing an important biosynthetic role in tumorigenesis.

Role of the energy sensor AMP-activated protein kinase in renal physiology and disease

The ultrasensitive energy sensor AMP-activated protein kinase (AMPK) orchestrates the regulation of energy-generating and energy-consuming pathways. AMPK is highly expressed in the kidney where it is reported to be involved in a variety of physiological and pathological processes including ion transport, podocyte function, and diabetic renal hypertrophy. Sodium transport is the major energy-consuming process in the kidney, and AMPK has been proposed to contribute to the coupling of ion transport with cellular energy metabolism. Specifically, AMPK has been identified as a regulator of several ion transporters of significance in renal physiology, including the cystic fibrosis transmembrane conductance regulator (CFTR), the epithelial sodium channel (ENaC), the Na(+)-K(+)-2Cl(-) cotransporter (NKCC), and the vacuolar H(+)-ATPase (V-ATPase). Identified regulators of AMPK in the kidney include dietary salt, diabetes, adiponectin, and ischemia. Activation of AMPK in response to adiponectin is described in podocytes, where it reduces albuminuria, and in tubular cells, where it reduces glycogen accumulation. Reduced AMPK activity in the diabetic kidney is associated with renal accumulation of triglyceride and glycogen and the pathogenesis of diabetic renal hypertrophy. Acute renal ischemia causes a rapid and powerful activation of AMPK, but the functional significance of this observation remains unclear. Despite the recent advances, there remain significant gaps in the present understanding of both the upstream regulating pathways and the downstream substrates for AMPK in the kidney. A more complete understanding of the AMPK pathway in the kidney offers potential for improved therapies for several renal diseases including diabetic nephropathy, polycystic kidney disease, and ischemia-reperfusion injury.

Peroxisome proliferator-activated receptors and angiogenesis

The peroxisome proliferator-activated receptors (PPARs) are a group of three nuclear receptor isoforms, PPARalpha, PPARgamma and PPARdelta, encoded by different genes, and they form a subfamily of the nuclear receptor superfamily. The clinical interest in PPARs originates with fibrates and thiazolidinediones, which, respectively, act on PPARalpha and PPARgamma and are used to ameliorate hyperlipidaemia and hyperglycaemia in subjects with type 2 diabetes mellitus (T2DM). PPARs play a central role in these patients due to their ability to regulate the expression of numerous genes involved in glycaemic control, lipid metabolism, vascular tone and inflammation. Abnormal angiogenesis is implicated in several of the long-term complications of diabetes mellitus, characterized by vasculopathy associated with aberrant growth of new blood vessels. This pathological process plays a crucial role in diabetic retinopathy, nephropathy and neuropathy, impaired wound healing and impaired coronary collateral vessel development. In recent years, there has been increasing appreciation of the fact that PPARs might be involved in the molecular mechanisms that regulate angiogenesis through the action of growth factors and cytokines that stimulate migration, proliferation and survival of endothelial cells. During the last few years direct comparative analyses have been performed, using selective PPARs agonists, to clarify the angiogenic properties of the different members of the PPAR family. Lately, the findings provide new information to order to understand the biological, clinical and therapeutic effects of PPARs, and the role of these nuclear receptors in angiogenesis, with potentially important implications for the management of subjects affected by T2DM.

The PPARgamma agonist pioglitazone ameliorates aging-related progressive renal injury

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists not only improve metabolic abnormalities of diabetes and consequent diabetic nephropathy, but they also protect against nondiabetic chronic kidney disease in experimental models. Here, we found that the PPAR-gamma agonist pioglitazone protected against renal injury in aging; it reduced proteinuria, improved GFR, decreased sclerosis, and alleviated cell senescence. Increased local expression of PPAR-gamma paralleled these changes. Underlying mechanisms included increased expression of klotho, decreased systemic and renal oxidative stress, and decreased mitochondrial injury. Pioglitazone also regulated p66(Shc) phosphorylation, which integrates many signaling pathways that affect mitochondrial function and longevity, by reducing protein kinase C-beta. These results suggest that PPAR-gamma agonists may benefit aging-related renal injury by improving mitochondrial function.

Pioglitazone enhances collateral blood flow in ischemic hindlimb of diabetic mice through an Akt-dependent VEGF-mediated mechanism, regardless of PPARgamma stimulation

Background

Type 2 diabetes mellitus (T2DM) is commonly associated with both microvascular and macrovascular complications and a strong correlation exists between glycaemic control and the incidence and progression of vascular complications. Pioglitazone, a Peroxisome proliferator-activated receptor-γ (PPARγ) ligand indicated for therapy of type T2DM, induces vascular effects that seem to occur independently of glucose lowering.

Methods

By using a hindlimb ischemia murine model, in this study we have found that pioglitazone restores the blood flow recovery and capillary density in ischemic muscle of diabetic mice and that this process is associated with increased expression of Vascular Endothelial Growth Factor (VEGF). Importantly, these beneficial effects are abrogated when endogenous Akt is inhibited; furthermore, the direct activation of PPARγ, with its selective agonist GW1929, does not restore blood flow recovery and capillary density. Finally, an important collateral vessel growth is obtained with combined treatment with pioglitazone and selective PPARγ inhibitor GW9662.

Conclusion

These data demonstrate that Akt-VEGF pathway is essential for ischemia-induced angiogenic effect of pioglitazone and that pioglitazone exerts this effect via a PPARγ independent manner.

Rosiglitazone prevents high glucose-induced vascular endothelial growth factor and collagen IV expression in cultured mesangial cells

Peroxisome proliferator-activated receptor (PPARγ), a ligand-dependent transcription factor, negatively modulates high glucose effects. We postulated that rosiglitazone (RSG), an activator of PPARγ prevents the upregulation of vascular endothelial growth factor (VEGF) and collagen IV by mesangial cells exposed to high glucose. Primary cultured rat mesangial cells were growth-arrested in 5.6 mM (NG) or 25 mM D-glucose (HG) for up to 48 hours. In HG, PPARγ mRNA and protein were reduced within 3 h, and enhanced ROS generation, expression of p22^phox, VEGF and collagen IV, and PKC-ζ membrane association were prevented by RSG. In NG, inhibition of PPARγ caused ROS generation and VEGF expression that were unchanged by RSG. Reduced AMP-activated protein kinase (AMPK) phosphorylation in HG was unchanged with RSG, and VEGF expression was unaffected by AMPK inhibition. Hence, PPARγ is a negative modulator of HG-induced signaling that acts through PKC-ζ but not AMPK and regulates VEGF and collagen IV expression by mesangial cells.

Acquisition of brain Na sensitivity contributes to salt-induced sympathoexcitation and cardiac dysfunction in mice with pressure overload

In animal models of salt-sensitive hypertension, high salt augments sympathetic outflow via central mechanisms. It is not known, however, whether pressure overload affects salt sensitivity, thereby modifying central sympathetic outflow and cardiac function. We induced left ventricular hypertrophy with aortic banding in mice. Four weeks after aortic banding (AB-4), the left ventricle wall thickness was increased without changing the percentage fractional shortening. AB-4 mice were then fed either a high-salt (8%) diet or regular-salt diet for additional 4 weeks. Cardiac dysfunction, wall thickness, and 24-hour urinary catecholamine excretion were increased with high-salt diet compared with regular-salt diet. We then examined brain Na sensitivity. Intracerebroventricular infusion of high-Na (0.2 mol/L) artificial cerebrospinal fluid into AB-4 mice and mice Sham-4 increased urinary catecholamine excretion, arterial pressure, and heart rate more in AB-4 mice than in Sham-4 mice. Intracerebroventricular infusion of an epithelial Na channel blocker (benzamil) into mice with high-salt diet significantly decreased urinary catecholamine excretion and improved cardiac function. Infusion of either an angiotensin II type 1 receptor blocker or a Rho-kinase inhibitor also attenuated the salt-induced sympathetic hyperactivation and cardiac dysfunction in mice with high-salt diet. The levels of angiotensin II type 1 receptor and phosphorylated moesin, a substrate of Rho-kinase, were significantly greater in AB-4 mice than in Sham-4 mice. These results suggest that mice with pressure overload acquire brain Na sensitivity because of the activation of epithelial Na channel via Rho-kinase and angiotensin II, and this mechanism contributes to salt-induced sympathetic hyperactivation, further pressure overload, and cardiac dysfunction.

PPARgamma in Kidney Physiology and Pathophysiology

Involvement of the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) in kidney physiology has been explored recently. Synthetic PPARγ ligands can ameliorate the diabetic kidney disease through different mechanisms, involving inhibition of mesangial cell growth, reduction of mesangial matrix, and cytokine production of glomerular cells as well as promoting endothelial cell survival within the kidney glomeruli. Activation of PPARγ has additional profibrotic consequences, which can contribute to wound healing in diabetic glomerulonephritis. Beside many beneficial effects, PPARγ activation, however, can lead to severe water retention, a common side effect of thiazolidinedione therapy. This unwanted effect is due to the activation of PPARγ in the mesonephric distal collecting system, where PPARγ positively regulates sodium and water resorbtion leading to the expansion of interstitial fluid volume. Recent studies indicate that PPARγ is also involved in the normal kidney development, renal lipid metabolism, and activation of the renin-angiotensin system. In this paper, we give a synopsis of the current knowledge on PPARγ functions in kidney phyisology and pathophysiology.

Tonic glutamatergic input in the rostral ventrolateral medulla is increased in rats with chronic heart failure

Chronic heart failure (CHF) is characterized by increased sympathetic tone. The glutamatergic input in the rostral ventrolateral medulla (RVLM), which is a key region involved in sympathetic outflow, seems not to be involved in the generation of sympathetic tone in the normal state. The aim of this study was to determine the role of the RVLM glutamate receptors in the generation of sympathetic tone in CHF. CHF was produced by coronary artery ligation. Bilateral microinjection of the glutamate receptor antagonist kynurenic acid, the N-methyl-d-aspartate (NMDA) receptor antagonist D-2-amino-5-phosphonopentanoate, or the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione into the RVLM dose-dependently reduced resting blood pressure and renal sympathetic nerve activity in CHF but not in sham rats. Picoinjection of kynurenic acid (100 pmol in 5 nL) significantly decreased the basal discharge by 47% in 25 RVLM presympathetic neurons in CHF rats. In contrast, kynurenic acid had no effect on the discharge in all 22 of the RVLM presympathetic neurons tested in sham rats. These data suggest that upregulated glutamate receptors, including NMDA and non-NMDA, in the RVLM are involved in tonic control of elevated sympathetic tone in CHF.

PPAR-gamma agonist attenuates renal interstitial fibrosis and inflammation through reduction of TGF-beta

Thiazolidinediones (TZDs), synthetic peroxisome proliferator-activated receptor (PPAR)-gamma ligands, have a central role in insulin sensitization and adipogenesis. It has been reported that TZDs exert protective effects in both diabetic and nondiabetic models of renal disease, although the exact mechanism is not well understood. In particular, only a few studies have reported the renoprotective effects of TZDs in nondiabetic models of tubulointerstitial fibrosis and inflammation. Therefore, we investigated the anti-fibrotic and anti-inflammatory effects of the TZD troglitazone in the mouse model of unilateral ureteral obstruction (UUO). C57BL/6J mice underwent UUO and were studied after 3 and 7 days. Animals were divided into three groups and received control vehicle, troglitazone (150 mg/kg per day) or troglitazone (300 mg/kg per day) by gavage. Kidneys were harvested for morphological, mRNA and protein analysis. Reverse-transcriptase-PCR was used to assess the expression of transforming growth factor-beta1 (TGF-beta1) and the TGF-beta1 type I receptor (TGF beta R-I). Protein expression was assessed by western blotting (TGF beta R-I) and immunostaining (TGF beta R-I, alpha-smooth muscle actin (alpha-SMA), type I collagen (collagen I), F4/80, and proliferating cell nuclear antigen (PCNA)). The expression of alpha-SMA, collagen I, and F4/80 was decreased in mice treated with troglitazone compared with the control group. The numbers of PCNA-positive interstitial cells were decreased in mice treated with troglitazone. TGF-beta1 mRNA and TGF beta R-I mRNA and protein expression were decreased in the group treated with troglitazone compared with the control group. The beneficial effects of troglitazone treatment were also dose dependent. PPAR-gamma agonist significantly reduced TGF-beta and attenuated renal interstitial fibrosis and inflammation in the model of UUO.

Interaction between cardiac sympathetic afferent reflex and chemoreflex is mediated by the NTS AT1 receptors in heart failure

Several sympathoexcitatory reflexes, such as the cardiac sympathetic afferent reflex (CSAR) and arterial chemoreflex, are significantly augmented and contribute to elevated sympathetic outflow in chronic heart failure (CHF). This study was undertaken to investigate the interaction between the CSAR and the chemoreflex in CHF and to further identify the involvement of angiotensin II type 1 receptors (AT1Rs) in the nucleus of the tractus solitarius (NTS) in this interaction. CHF was induced in rats by coronary ligation. Acute experiments were performed in anesthetized rats. The chemoreflex-induced increase in cardiovascular responses was significantly greater in CHF than in sham-operated rats after either chemical or electrical activation of the CSAR. The inhibition of the CSAR by epicardial lidocaine reduced the chemoreflex-induced effects in CHF rats but not in sham-operated rats. Bilateral NTS injection of the AT1R antagonist losartan (10 and 100 pmol) dose-dependently decreased basal sympathetic nerve activity in CHF but not in sham-operated rats. This procedure also abolished the CSAR-induced enhancement of the chemoreflex. The discharge and chemosensitivity of NTS chemosensitive neurons were significantly increased following the stimulation of the CSAR in sham-operated and CHF rats, whereas CSAR inhibition by epicardial lidocaine significantly attenuated chemosensitivity of NTS neurons in CHF but not in sham-operated rats. Finally, the protein expression of AT1R in the NTS was significantly higher in CHF than in sham-operated rats. These results demonstrate that the enhanced cardiac sympathetic afferent input contributes to an excitatory effect of chemoreflex function in CHF, which is mediated by an NTS-AT1R-dependent mechanism.

Selective activation of peroxisome proliferator-activated receptor (PPAR)alpha and PPAR gamma induces neoangiogenesis through a vascular endothelial growth factor-dependent mechanism

OBJECTIVE

Peroxisome proliferator-activated receptors (PPARs) are therapeutic targets for fibrates and thiazolidinediones, which are commonly used to ameliorate hyperlipidemia and hyperglycemia in type 2 diabetes. In this study, we evaluated whether activation of PPAR alpha and PPAR gamma stimulates neoangiogenesis.

RESEARCH DESIGN AND METHODS

We used selective synthetic PPAR alpha and PPAR gamma agonists and investigated their angiogenic potentials in vitro and in vivo.

RESULTS

Activation of PPAR alpha and PPAR gamma leads to endothelial tube formation in an endothelial/interstitial cell co-culture assay. This effect is associated with increased production of the angiogenic cytokine vascular endothelial growth factor (VEGF). Neovascularization also occurs in vivo, when PPAR alpha and PPAR gamma agonists are used in the murine corneal angiogenic model. No vascular growth is detectable when PPAR alpha and PPAR gamma agonists are respectively used in PPAR alpha knockout mice and mice treated with a specific PPAR gamma inhibitor, demonstrating that this angiogenic response is PPAR mediated. PPAR alpha- and PPAR gamma-induced angiogenesis is associated with local VEGF production and does not differ in extent and morphology from that induced by VEGF. In addition, PPAR alpha- and PPAR gamma-induced in vitro and in vivo angiogenesis may be significantly decreased by inhibiting VEGF activity. Finally, in corneas treated with PPAR alpha and PPAR gamma agonists, there is increased phosphorylation of endothelial nitric oxide synthase and Akt.

CONCLUSIONS

These findings demonstrate that PPAR alpha and PPAR gamma activation stimulates neoangiogenesis through a VEGF-dependent mechanism. Neoangiogenesis is a crucial pathological event in type 2 diabetes. The ability of PPAR alpha and PPAR gamma agonists to induce neoangiogenesis might have important implications for the clinical and therapeutic management of type 2 diabetes.

Peroxisome proliferator-activated receptor gamma activates fas ligand gene promoter inducing apoptosis in human breast cancer cells

In just over a decade, apart from established metabolic actions, peroxisome proliferator-activated receptor gamma (PPARgamma) has evolved as key therapeutic target in cancer disease. Fas ligand (FasL), a trans-membrane protein, induces apoptosis by crosslinking with the Fas receptor. Despite the FasL relevance, little is available on the regulation of its expression. In the current study, we explored for the first time the potential role of PPARgamma in triggering apoptotic events through the Fas/FasL pathway in breast cancer cells. In MCF7 cells, by reverse transcription-polymerase chain reaction and Western blotting, we showed that the synthetic PPARgamma ligand rosiglitazone (BRL) enhanced FasL expression, that was abrogated by a specific PPARgamma antagonist GW9662. Transient transfection assays demonstrated that BRL transactivated human FasL promoter gene in a PPARgamma-dependent manner. Progressive 5' deletion analysis has identified a minimal promoter fragment spanning nucleotides from -318 to -237 bp, which is still sensitive to BRL treatment. FasL promoter activity was abrogated by mithramycin, suggesting an involvement of Sp1 transcription factor in PPARgamma action. Electrophoretic mobility shift and chromatin immuno-precipitation assays demonstrated that BRL increased the binding of PPARgamma and Sp1 to the Sp1 sequence located within the FasL gene promoter. The role of PPARgamma and Fas/FasL pathways in BRL-induced apoptotic events was assessed by caspase 8 cleavage in the presence of GW as well as PPARgamma and FasL RNA interferences. Our results indicate that PPARgamma positively regulates the FasL gene expression also in MDA-MB231 and in BT20, revealing a new molecular mechanism by which BRL induces apoptosis in breast cancer cells.

Baroreceptor reflex modulation by circulating angiotensin II is mediated by AT1 receptors in the nucleus tractus solitarius

Circulating ANG II modulates the baroreceptor reflex control of heart rate (HR), at least partly via activation of ANG II type 1 (AT1) receptors on neurons in the area postrema. In this study, we tested the hypothesis that the effects of circulating ANG II on the baroreflex also depend on AT1 receptors within the nucleus tractus solitarius (NTS). In confirmation of previous studies in other species, increases in arterial pressure induced by intravenous infusion of ANG II had little effect on HR in urethane-anesthetized rats, in contrast to the marked bradycardia evoked by equipressor infusion of phenylephrine. In the presence of a continuous background infusion of ANG II, the baroreflex control of HR was shifted to higher levels of HR but had little effect on the baroreflex control of renal sympathetic activity. The modulatory effects of circulating ANG II on the cardiac baroreflex were significantly reduced by microinjection of candesartan, an AT1 receptor antagonist, into the area postrema and virtually abolished by microinjections of candesartan into the medial NTS. After acute ablation of the area postrema, a background infusion of ANG II still caused an upward shift of the cardiac baroreflex curve, which was reversed by subsequent microinjection of candesartan into the medial NTS. The results indicate that AT1 receptors in the medial NTS play a critical role in modulation of the cardiac baroreflex by circulating ANG II via mechanisms that are at least partly independent of AT1 receptors in the area postrema.

Rosiglitazone attenuates transplant arteriosclerosis after allogeneic aorta transplantation in rats

BACKGROUND

Transplant arteriosclerosis is a leading cause of chronic transplant dysfunction and is characterized by occlusive neointima formation in intragraft arteries. Development of transplant arteriosclerosis is refractory to conventional immunosuppressive drugs and adequate therapy is not available. In this study, we determined the efficacy of the synthetic peroxisome proliferator-activated receptor (PPAR)-gamma agonist rosiglitazone to attenuate the development of transplant arteriosclerosis in rat aortic allografts.

METHODS

Lewis aortic allografts were transplanted into Brown Norway recipient rats. Recipient rats received either approximately 5 mg rosiglitazone/day (starting 1 week before transplantation until the end of the experiment) or were left untreated. Transplant arteriosclerosis was quantified using morphometric analysis. Alloreactivity was measured in vitro using mixed lymphocyte reactions. Regulatory T cell frequency and function were analyzed using flow cytometry and in vitro suppression assays, respectively. Intragraft gene expression was analyzed using real-time polymerase chain reaction. Finally, medial and neointimal vascular smooth muscle cell proliferation was analyzed in vitro.

RESULTS

Rosiglitazone significantly reduced transplant arteriosclerosis development 8 weeks after transplantation (P<0.01 vs. nontreated). Rosiglitazone reduced T cell alloreactivity which was not mediated through modulation of CD4+CD25+FoxP3+ regulatory T cells. Reduced development of transplant arteriosclerosis coincided with reduced intragraft expression of stromal-derived factor-1alpha and platelet-derived growth factor receptor-beta. Finally, rosiglitazone reduced growth-factor-driven proliferation of both medial and neointimal vascular smooth muscle cells in vitro, which was not mediated through PPARgamma.

CONCLUSION

PPARgamma agonists may offer a new therapeutic strategy in clinical transplantation to attenuate the development of transplant arteriosclerosis and thereby chronic transplant dysfunction.

Contribution of AMPA/kainate receptors in the rostral ventrolateral medulla to the hypotensive and sympathoinhibitory effects of clonidine

The depressor and sympathoinhibitory effect of the imidazoline drug clonidine is reported to be associated with functional states of the central glutamate receptors. The rostral ventrolateral medulla (RVLM) has been recognized as a specific target area for mediating the central depressor mechanism of clonidine. The objective of this study was to determine the role of the glutamate receptor subtype α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptor within the RVLM in clonidine-induced depressor and sympathoinhibitory action in anesthetized normotensive rats. Unilateral microinjection of 200 pmol of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a potent AMPA/kainate receptor antagonist, into the RVLM completely abolished the pressor action evoked by AMPA (5 pmol) without affecting the pressor action of N-methyl-d-aspartate (20 pmol). Pretreatment with intra-RVLM injection of CNQX (20 and 200 pmol) dose dependently attenuated the reduction in blood pressure (BP), heart rate (HR), and renal sympathetic nerve activity (RSNA) elicited by intra-RVLM clonidine (5 nmol) or intravenous clonidine (10 μg/kg), while 2 pmol of CNQX did not alter clonidine-induced cardiovascular action. Furthermore, the decreases in BP, HR, and RSNA evoked by intravenous clonidine (10 μg/kg) or intra-RVLM clonidine (5 nmol) were reversed when CNQX (20 and 200 pmol) was subsequently injected into the RVLM. In conclusion, these data show that blockade of AMPA/kainate receptors in the RVLM significantly antagonizes decreases in BP, HR, and sympathetic activity induced by clonidine, suggesting that the AMPA/kainate receptors within the RVLM contribute to the depressor and sympathoinhibitory effect of clonidine.