Reversing the curse on PPARγ

PPARγ Agonist Rosiglitazone and Antagonist GW9662: Antihypertensive Effects on Chronic Intermittent Hypoxia-Induced Hypertension in Rats

The increased incidence of hypertension associated with obstructive sleep apnea (OSA) presents significant physical, psychological, and economic challenges. Peroxisome proliferator-activated receptor gamma (PPARγ) plays a role in both OSA and hypertension, yet the therapeutic potential of PPARγ agonists and antagonists for OSA-related hypertension remains unexplored. Therefore, we constructed a chronic intermittent hypoxia (CIH)-induced hypertension rat model that mimics the pathogenesis of OSA-related hypertension in humans. The model involved administering PPARγ agonist rosiglitazone (RSG), PPARγ antagonist GW9662, or normal saline, followed by regular monitoring of blood pressure and thoracic aorta analysis using staining and electron microscopy. Intriguingly, our results indicated that both RSG and GW9662 appeared to potently counteract CIH-induced hypertension. In silico study suggested that GW9662's antihypertensive effect might mediated through angiotensin II receptor type 1 (AGTR1). Our findings provide insights into the mechanisms of OSA-related hypertension and propose novel therapeutic targets.

BMP8B Activates Both SMAD2/3 and NF-κB Signals to Inhibit the Differentiation of 3T3-L1 Preadipocytes into Mature Adipocytes

Bone morphogenetic protein 8B (BMP8B) has been found to regulate the thermogenesis of brown adipose tissue (BAT) and the browning process of white adipose tissue (WAT). However, there is no available information regarding the role of BMP8B in the process of adipocyte differentiation. Here, we showed that BMP8B down-regulates transcriptional regulators PPARγ and C/EBPα, thereby impeding the differentiation of 3T3-L1 preadipocytes into fully mature adipocytes. BMP8B increased the phosphorylation levels of SMAD2/3, and TP0427736 HCl (SMAD2/3 inhibitor) significantly reduced the ability of BMP8B to inhibit adipocyte differentiation, suggesting that BMP8B repressed adipocyte differentiation through the SMAD2/3 pathway. Moreover, the knockdown of BMP I receptor ALK4 significantly reduced the inhibitory effect of BMP8B on adipogenesis, indicating that BMP8B triggers SMAD2/3 signaling to suppress adipogenesis via ALK4. In addition, BMP8B activated the NF-κB signal, which has been demonstrated to impede PPARγ expression. Collectively, our data demonstrated that BMP8B activates both SMAD2/3 and NF-κB signals to inhibit adipocyte differentiation. We provide previously unidentified insight into BMP8B-mediated adipogenesis.

PPARγ Acetylation in Adipocytes Exacerbates BAT Whitening and Worsens Age-Associated Metabolic Dysfunction

Aging and obesity are the two prominent driving forces of metabolic dysfunction, yet the common underlying mechanisms remain elusive. PPARγ, a central metabolic regulator and primary drug target combatting insulin resistance, is hyperacetylated in both aging and obesity. By employing a unique adipocyte-specific PPARγ acetylation-mimetic mutant knock-in mouse model, namely aKQ, we demonstrate that these mice develop worsened obesity, insulin resistance, dyslipidemia, and glucose intolerance as they age, and these metabolic deregulations are resistant to intervention by intermittent fasting. Interestingly, aKQ mice show a whitening phenotype of brown adipose tissue (BAT) manifested in lipid filling and suppressed BAT markers. Diet-induced obese aKQ mice retain an expected response to thiazolidinedione (TZD) treatment, while BAT function remains impaired. This BAT whitening phenotype persists even with the activation of SirT1 through resveratrol treatment. Moreover, the adverse effect of TZDs on bone loss is exacerbated in aKQ mice and is potentially mediated by their increased Adipsin levels. Our results collectively suggest pathogenic implications of adipocyte PPARγ acetylation, contributing to metabolic dysfunction in aging and thus posing as a potential therapeutic target.

Beyond TGFβ1 - novel treatment strategies targeting lung fibrosis

Fibrosis is a key feature of chronic lung diseases and occurs as a consequence of aberrant wound healing. TGFβ1 plays a major role in promoting fibrosis and is the primary target of current treatments that slow, but do not halt or reverse the progression of disease. Accumulating evidence suggests that additional mechanisms, including excessive airway contraction, inflammation and infections including COVID-19, can contribute to fibrosis. This review summarises experimental and clinical studies assessing the potential beneficial effects of novel drugs that possess a unique suite of complementary actions to oppose contraction, inflammation and remodelling, along with evidence that they also limit fibrosis. Translation of these promising findings is critical for the repurposing and development of improved therapeutics for fibrotic lung diseases.

A novel peroxisome proliferator-activated receptor gamma ligand improves insulin sensitivity and promotes browning of white adipose tissue in obese mice

OBJECTIVE

Nuclear receptor Peroxisome Proliferator-Activated Receptor γ (PPARγ) is a promising target for the treatment of type 2 diabetes. The antidiabetic drug thiazolidinediones (TZDs) are potent insulin sensitizers as full agonists of PPARγ, but cause unwanted side effects. Recent discoveries have shown that TZDs improve insulin sensitivity by blocking PPARγ phosphorylation at S273, which decouples the full agonism-associated side effects. PPARγ ligands that act through the blockage of PPARγ phosphorylation but lack the full agonist activity would be expected to improve insulin sensitivity without TZD-associated side effects, however, chemicals that carry such traits and bind to PPARγ with high-affinity are lacking. Moreover, TZDs are known to promote white-to-brown adipocyte conversion and energy expenditure and appear to require their full agonism on PPARγ for this activity. It is unknown whether a partial or non-TZD agonist of PPARγ is capable of promoting browning effect. In this study, we developed a novel non-TZD partial agonist of PPARγ and investigated its function on insulin sensitivity and white-to-brown conversion and energy expenditure in diet-induced obese mice.

METHODS

A novel indole-based chemical WO95E was designed via medicinal chemistry and tested for PPARγ binding and activity and for the effect on PPARγ phosphorylation. Diet-induced obese mice were administered with WO95E for 4 weeks. Insulin sensitivity, glucose tolerance, body weight, fat tissue weight, adipocyte size, morphology, energy expenditure, and expression levels of genes involved in PPARγ activity, thermogenesis/browning, and TZD-related side effects were evaluated.

RESULTS

WO95E binds to PPARγ with high affinity and acts as a PPARγ partial agonist. WO95E inhibits PPARγ phosphorylation and regulates PPARγ phosphorylation-dependent genes. WO95E ameliorates insulin resistance and glucose tolerance in mice of diet-induced obesity, with minimal TZD use-associated side effects. We found that WO95E promotes white-to-brown adipocyte conversion and energy expenditure and hence protects against diet-induced obesity. WO95E decreases the size of adipocytes and suppresses adipose tissue inflammation. WO95E also suppresses obesity-associated liver steatosis.

CONCLUSIONS

WO95E improves insulin sensitivity and glucose homeostasis and promotes browning and energy expenditure by acting as a novel PPARγ phosphorylation inhibitor/partial agonist. Our findings suggest the potential of this compound or its derivative for the therapeutic treatment of insulin resistance and obesity.

PPARγ and TGFβ-Major Regulators of Metabolism, Inflammation, and Fibrosis in the Lungs and Kidneys

Peroxisome proliferator-activated receptor gamma (PPARγ) is a type II nuclear receptor, initially recognized in adipose tissue for its role in fatty acid storage and glucose metabolism. It promotes lipid uptake and adipogenesis by increasing insulin sensitivity and adiponectin release. Later, PPARγ was implicated in cardiac development and in critical conditions such as pulmonary arterial hypertension (PAH) and kidney failure. Recently, a cluster of different papers linked PPARγ signaling with another superfamily, the transforming growth factor beta (TGFβ), and its receptors, all of which play a major role in PAH and kidney failure. TGFβ is a multifunctional cytokine that drives inflammation, fibrosis, and cell differentiation while PPARγ activation reverses these adverse events in many models. Such opposite biological effects emphasize the delicate balance and complex crosstalk between PPARγ and TGFβ. Based on solid experimental and clinical evidence, the present review summarizes connections and their implications for PAH and kidney failure, highlighting the similarities and differences between lung and kidney mechanisms as well as discussing the therapeutic potential of PPARγ agonist pioglitazone.

UPLC-MS-Based Serum Metabolomics Reveals Potential Biomarkers of Ang II-Induced Hypertension in Mice

Hypertension is caused by polygenic inheritance and the interaction of various environmental factors. Abnormal function of the renin-angiotensin-aldosterone system (RAAS) is closely associated with changes in blood pressure. As an essential factor in the RAAS, angiotensin II (Ang II) contributes to vasoconstriction and inflammatory responses. However, the effects of overproduction of Ang II on the whole body-metabolism have been unclear. In this study, we established a hypertensive mouse model by micro-osmotic pump perfusion of Ang II, and the maximum systolic blood pressure reached 140 mmHg after 2 weeks. By ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry, the metabolites in the serum of hypertensive model and control mice were analyzed. Partial least squares discriminant analysis (PLS-DA) in both positive and negative ionization modes showed clear separation of the two groups. Perfusion of Ang II induced perturbations of multiple metabolic pathways in mice, such as steroid hormone biosynthesis and galactose metabolism. Tandem mass spectrometry revealed 40 metabolite markers with potential diagnostic value for hypertension. Our data indicate that non-targeted metabolomics can reveal biochemical pathways associated with Ang II-induced hypertension. Although researches about the clinical use of these metabolites as potential biomarkers in hypertension is still needed, the current study improves the understanding of systemic metabolic response to sustained release of Ang II in hypertensive mice, providing a new panel of biomarkers that may be used to predict blood pressure fluctuations in the early stages of hypertension.

Peroxisome proliferator-activated receptor agonists and reversal of vascular degeneration through DNA repair, a step toward drug-induced regenerative medicine

Endothelial dysfunction with subsequent degeneration and vasoocclusive remodeling is the hallmark of many cardiovascular disorders including pulmonary vascular disease (PVD). To date, the available treatments slows disease progression but does not prevent deterioration. Reversing such pathologies would spare many patients risky surgeries and long waiting lists for a possible organ donor. Peroxisome proliferator-activated receptor agonists were first introduced as sole insulin sensitizers, however, there is increasing body of evidence that they have different actions on DNA which might help reverse vascular degeneration. This effect appears to be mainly achieved through enhancement of DNA damage responses (DDR). The aforementioned effect could offer new insights about repurposing drugs for achieving organ or tissue regeneration, an understudied field named drug-induced regenerative medicine.

PPARγ Deacetylation Confers the Antiatherogenic Effect and Improves Endothelial Function in Diabetes Treatment

Cardiovascular disease (CVD) is the leading cause of death in patients with diabetes, and tight glycemic control fails to reduce the risk of developing CVD. Thiazolidinediones (TZDs), a class of peroxisome proliferator-activated receptor γ (PPARγ) agonists, are potent insulin sensitizers with antiatherogenic properties, but their clinical use is limited by side effects. PPARγ deacetylation on two lysine residues (K268 and K293) induces brown remodeling of white adipose tissue and uncouples the adverse effects of TZDs from insulin sensitization. Here we show that PPARγ deacetylation confers antiatherogenic properties and retains the insulin-sensitizing effects of TZD while circumventing its detriments. We generated mice homozygous with mice with deacetylation-mimetic PPARγ mutations K268R/K293R (2KR) on an LDL-receptor knockout (Ldlr ^-/- ) background. 2KR:Ldlr ^-/- mice showed smaller atherosclerotic lesion areas than Ldlr ^-/- mice, particularly in aortic arches. With rosiglitazone treatment, 2KR:Ldlr ^-/- mice demonstrated a residual antiatherogenic response and substantial protection against bone loss and fluid retention. The antiatherosclerotic effect of 2KR was attributed to the protection of endothelium, indicated by improved endothelium-dependent vasorelaxation and repressed expression of proatherogenic factors including inducible nitric oxide synthase, interleukin-6, and NADPH oxidase 2. Therefore, manipulating PPARγ acetylation is a promising therapeutic strategy to control risk of CVD in diabetes treatment.

PPARγ is a gatekeeper for extracellular matrix and vascular cell homeostasis: beneficial role in pulmonary hypertension and renal/cardiac/pulmonary fibrosis

PURPOSE OF REVIEW

Pulmonary arterial hypertension (PAH) is characterized by pulmonary arterial endothelial cell (PAEC) dysfunction and apoptosis, pulmonary arterial smooth muscle cell (PASMC) proliferation, inflammation, vasoconstriction, and metabolic disturbances that include disrupted bone morphogenetic protein receptor (BMPR2)-peroxisome proliferator-activated receptor gamma (PPARγ) axis and DNA damage. Activation of PPARγ improves many of these mechanisms, although erroneous reports on potential adverse effects of thiazolidinedione (TZD)-class PPARγ agonists reduced their clinical use in the past decade. Here, we review recent findings in heart, lung, and kidney research related to the pathobiology of vascular remodeling and tissue fibrosis, and also potential therapeutic effects of the PPARγ agonist pioglitazone.

RECENT FINDINGS

Independent of its metabolic effects (improved insulin sensitivity and fatty acid handling), PPARγ activation rescues BMPR2 dysfunction, inhibits TGFβ/Smad3/CTGF and TGFβ/pSTAT3/pFoxO1 pathways, and induces the PPARγ/apoE axis, inhibiting vascular remodeling. PPARγ activation dampens mtDNA damage via PPARγ/UBR5/ATM pathway, improves function of endothelial progenitor cells (EPCs), and decrease renal fibrosis by repressing TGFβ/pSTAT3 and TGFβ/EGR1.

SUMMARY

Pharmacological PPARγ activation improves many hallmarks of PAH, including dysfunction of BMPR2-PPARγ axis, PAEC, PASMC, EPC, mitochondria/metabolism, and inflammation. Recent randomized controlled trials, including IRIS (Insulin Resistance Intervention After Stroke Trial), emphasize the beneficial effects of PPARγ agonists in PAH patients, leading to recent revival for clinical use.

Trace Elements, PPARs, and Metabolic Syndrome

Metabolic syndrome (MetS) is a constellation of metabolic derangements, including central obesity, insulin resistance, hypertension, glucose intolerance, and dyslipidemia. The pathogenesis of MetS has been intensively studied, and now many factors are recognized to contribute to the development of MetS. Among these, trace elements influence the structure of proteins, enzymes, and complex carbohydrates, and thus an imbalance in trace elements is an independent risk factor for MetS. The molecular link between trace elements and metabolic homeostasis has been established, and peroxisome proliferator-activated receptors (PPARs) have appeared as key regulators bridging these two elements. This is because on one hand, PPARs are actively involved in various metabolic processes, such as abdominal adiposity and insulin sensitivity, and on the other hand, PPARs sensitively respond to changes in trace elements. For example, an iron overload attenuates hepatic mRNA expression of Ppar-α; zinc supplementation is considered to recover the DNA-binding activity of PPAR-α, which is impaired in steatotic mouse liver; selenium administration downregulates mRNA expression of Ppar-γ, thereby improving lipid metabolism and oxidative status in the liver of high-fat diet (HFD)-fed mice. More importantly, PPARs' expression and activity are under the control of the circadian clock and show a robust 24 h rhythmicity, which might be the reasons for the side effects and the clinical limitations of trace elements targeting PPARs. Taken together, understanding the casual relationships among trace elements, PPARs' actions, and the pathogenesis of MetS is of great importance. Further studies are required to explore the chronopharmacological effects of trace elements on the diurnal oscillation of PPARs and the consequent development of MetS.

Activation of the Metabolic Master Regulator PPARγ: A Potential PIOneering Therapy for Pulmonary Arterial Hypertension

Translational research is essential to the development of reverse-remodeling strategies for the treatment of pulmonary vascular disease, pulmonary hypertension, and heart failure via mechanistic in vivo studies using animal models resembling human pulmonary arterial hypertension (PAH), cardiovascular remodeling, and progressive right heart failure. Since 2007, peroxisome proliferator-activated receptor γ (PPARγ) agonists have emerged as promising novel, antiproliferative, antiinflammatory, insulin-sensitizing, efficient medications for the treatment of PAH. However, early diabetes study results, their subsequent misinterpretations, errors in published review articles, and rumors regarding potential adverse effects in the literature have dampened enthusiasm for considering pharmacological PPARγ activation for the treatment of cardiovascular diseases, including PAH. Most recently, the thiazolidinedione class PPARγ agonist pioglitazone underwent a clinical revival, especially based on the IRIS (Insulin Resistance Intervention After Stroke) study, a randomized controlled trial in 3,876 patients without diabetes status post-transient ischemic attack/ischemic stroke who were clinically followed for 4.8 years. We discuss preclinical basic translational findings and randomized controlled trials related to the beneficial and adverse effects of PPARγ agonists of the thiazolidinedione class, with a particular focus on the last 5 years. The objective is a data-driven approach to set the preclinical and clinical study record straight. The convincing recent clinical trial data on the lack of significant toxicity in high-risk populations justify the timely conduct of clinical studies to achieve "repurposing" or "repositioning" of pioglitazone for the treatment of clinical PAH.

LRP1 Deficiency in Vascular SMC Leads to Pulmonary Arterial Hypertension That Is Reversed by PPARγ Activation

RATIONALE

Arterial remodeling-a hallmark of many cardiovascular pathologies including pulmonary arterial hypertension (PAH)-is regulated by TGFβ1 (transforming growth factor-β1)-TGFβ receptors and the antagonistic, vasoprotective BMPR2 (bone morphogenetic protein receptor 2)-PPARγ (peroxisome proliferator-activated receptor-γ) axis. However, it is unclear which factors drive detrimental TGFβ1 pathways in the hypertensive pulmonary vasculature.

OBJECTIVE

We hypothesized that LRP1 (low-density lipoprotein receptor-related protein 1) expression is decreased in PAH, leading to enhancement (disinhibition) of TGFβ1 signals and that the PPARγ agonist pioglitazone can restore vascular homeostasis and prevent PAH resulting from LRP1 deletion in vascular smooth muscle cells (SMCs).

METHODS AND RESULTS

Targeted deletion of LRP1 in vascular SMC (smLRP1^-/-) in mice disinhibited TGFβ1-CTGF (connective tissue growth factor) signaling, leading to spontaneous PAH and distal pulmonary arterial muscularization as assessed by closed-chest cardiac catheterization and anti-αSMA staining. Pioglitazone inhibited the canonical TGFβ1-CTGF axis in human pulmonary artery SMC and smLRP1^-/- main pulmonary artery (CTGF and NOX4) and reversed PAH in smLRP1^-/- mice. TGFβ1 boosted pSmad3 in PASMC from smLRP1^-/- mice versus controls. Pioglitazone-activated PPARγ binds to Smad3 in human pulmonary artery SMC (coimmunoprecipitation), thereby blocking its phosphorylation and overriding LRP1 deficiency. Finally, mRNA and protein expression of LRP1 was decreased in pulmonary plexiform lesions of patients with end-stage idiopathic PAH (laser capture microdissection, qPCR, and immunohistochemistry). Downregulation of LRP1 protein was also demonstrated in explanted PASMC from patients with PAH and accompanied by enhanced TGFβ1-pSmad3-CTGF signaling and increased TGFβ1-induced PASMC proliferation that was prevented by pioglitazone.

CONCLUSIONS

Here, we identify LRP1 as an integrator of TGFβ1-mediated mechanisms that regulate vascular remodeling in mice and clinical PAH and PPARγ as a therapeutic target that controls canonical TGFβ1 pathways. Hence, pharmacologic PPARγ activation represents a promising new therapy for patients with PAH who lack the vasoprotective LRP1 in vascular SMC.

The Suv420h histone methyltransferases regulate PPAR-γ and energy expenditure in response to environmental stimuli

Obesity and its associated metabolic abnormalities have become a global emergency with considerable morbidity and mortality. Epidemiologic and animal model data suggest an epigenetic contribution to obesity. Nevertheless, the cellular and molecular mechanisms through which epigenetics contributes to the development of obesity remain to be elucidated. Suv420h1 and Suv420h2 are histone methyltransferases responsible for chromatin compaction and gene repression. Through in vivo, ex vivo, and in vitro studies, we found that Suv420h1 and Suv420h2 respond to environmental stimuli and regulate metabolism by down-regulating peroxisome proliferator-activated receptor gamma (PPAR-γ), a master transcriptional regulator of lipid storage and glucose metabolism. Accordingly, mice lacking Suv420h proteins activate PPAR-γ target genes in brown adipose tissue to increase mitochondria respiration, improve glucose tolerance, and reduce adipose tissue to fight obesity. We conclude that Suv420h proteins are key epigenetic regulators of PPAR-γ and the pathways controlling metabolism and weight balance in response to environmental stimuli.