Peroxisome Proliferator-Activated Receptors and the Heart: Lessons from the Past and Future Directions

Myocardial Expression of PPARγ and Exercise Capacity in Patients after Coronary Artery Bypass Surgery

Activation of PPARs may be involved in the development of heart failure (HF). We evaluated the relationship between expression of PPARγ in the myocardium during coronary artery bypass grafting (CABG) and exercise tolerance initially and during follow-up. 6-minute walking test was performed before CABG, after 1, 12, 24 months. Patients were divided into two groups (HF and non-HF) based on left ventricular ejection fraction and plasma proBNP level. After CABG, 67% of patients developed HF. The mean distance 1 month after CABG in HF was 397 ± 85 m versus 420 ± 93 m in non-HF. PPARγ mRNA expression was similar in both HF and non-HF groups. 6MWT distance 1 month after CABG was inversely correlated with PPARγ level only in HF group. Higher PPARγ expression was related to smaller LVEF change between 1 month and 1 year (R = 0.18, p < 0.05), especially in patients with HF. Higher initial levels of IL-6 in HF patients were correlated with longer distance in 6MWT one month after surgery and lower PPARγ expression. PPARγ expression is not related to LVEF before CABG and higher PPARγ expression in the myocardium of patients who are developing HF following CABG may have some protecting effect.

Chronic Psychological Stress Accelerates Vascular Senescence and Impairs Ischemia-Induced Neovascularization: The Role of Dipeptidyl Peptidase-4/Glucagon-Like Peptide-1-Adiponectin Axis

BACKGROUND

Exposure to psychosocial stress is a risk factor for cardiovascular disease, including vascular aging and regeneration. Given that dipeptidyl peptidase-4 (DPP4) regulates several intracellular signaling pathways associated with the glucagon-like peptide-1 (GLP-1) metabolism, we investigated the role of DPP4/GLP-1 axis in vascular senescence and ischemia-induced neovascularization in mice under chronic stress, with a special focus on adiponectin -mediated peroxisome proliferator activated receptor-γ/its co-activator 1α (PGC-1α) activation.

METHODS AND RESULTS

Seven-week-old mice subjected to restraint stress for 4 weeks underwent ischemic surgery and were kept under immobilization stress conditions. Mice that underwent ischemic surgery alone served as controls. We demonstrated that stress impaired the recovery of the ischemic/normal blood-flow ratio throughout the follow-up period and capillary formation. On postoperative day 4, stressed mice showed the following: increased levels of plasma and ischemic muscle DPP4 and decreased levels of GLP-1 and adiponectin in plasma and phospho-AMP-activated protein kinase α (p-AMPKα), vascular endothelial growth factor, peroxisome proliferator activated receptor-γ, PGC-1α, and Sirt1 proteins and insulin receptor 1 and glucose transporter 4 genes in the ischemic tissues, vessels, and/or adipose tissues and numbers of circulating endothelial CD31⁺/c-Kit⁺ progenitor cells. Chronic stress accelerated aortic senescence and impaired aortic endothelial sprouting. DPP4 inhibition and GLP-1 receptor activation improved these changes; these benefits were abrogated by adiponectin blocking and genetic depletion.

CONCLUSIONS

These results indicate that the DPP4/GLP-1-adiponectin axis is a novel therapeutic target for the treatment of vascular aging and cardiovascular disease under chronic stress conditions.

Peroxisome proliferator-activated receptors as therapeutic targets for heart failure

Heart failure (HF) is a common clinical syndrome that affects more than 23 million individuals worldwide. Despite the marked advances in its management, the mortality rates in HF patients have remained unacceptably high. Peroxisome proliferator-activated receptors (PPARs) are nuclear transcription regulators, involved in the regulation of fatty acid and glucose metabolism. PPAR agonists are currently used for the treatment of type II diabetes mellitus and hyperlipidemia; however, their role as therapeutic agents for HF remains under investigation. Preclinical studies have shown that pharmacological modulation of PPARs can upregulate the expression of fatty acid oxidation genes in cardiomyocytes. Moreover, PPAR agonists were proven able to improve ventricular contractility and reduce cardiac remodelling in animal models through their anti-inflammatory, anti-oxidant, anti-fibrotic, and anti-apoptotic activities. Whether these effects can be replicated in humans is yet to be proven. This article reviews the interactions of PPARs with the pathophysiological mechanisms of HF and how the pharmacological modulation of these receptors can be of benefit for HF patients.

Live cell screening platform identifies PPARδ as a regulator of cardiomyocyte proliferation and cardiac repair

Zebrafish can efficiently regenerate their heart through cardiomyocyte proliferation. In contrast, mammalian cardiomyocytes stop proliferating shortly after birth, limiting the regenerative capacity of the postnatal mammalian heart. Therefore, if the endogenous potential of postnatal cardiomyocyte proliferation could be enhanced, it could offer a promising future therapy for heart failure patients. Here, we set out to systematically identify small molecules triggering postnatal cardiomyocyte proliferation. By screening chemical compound libraries utilizing a Fucci-based system for assessing cell cycle stages, we identified carbacyclin as an inducer of postnatal cardiomyocyte proliferation. In vitro, carbacyclin induced proliferation of neonatal and adult mononuclear rat cardiomyocytes via a peroxisome proliferator-activated receptor δ (PPARδ)/PDK1/p308Akt/GSK3β/β-catenin pathway. Inhibition of PPARδ reduced cardiomyocyte proliferation during zebrafish heart regeneration. Notably, inducible cardiomyocyte-specific overexpression of constitutively active PPARδ as well as treatment with PPARδ agonist after myocardial infarction in mice induced cell cycle progression in cardiomyocytes, reduced scarring, and improved cardiac function. Collectively, we established a cardiomyocyte proliferation screening system and present a new drugable target with promise for the treatment of cardiac pathologies caused by cardiomyocyte loss.

A novel physiological role for cardiac myoglobin in lipid metabolism

Continuous contractile activity of the heart is essential and the required energy is mostly provided by fatty acid (FA) oxidation. Myocardial lipid accumulation can lead to pathological responses, however the underlying mechanisms remain elusive. The role of myoglobin in dioxygen binding in cardiomyocytes and oxidative skeletal muscle has widely been appreciated. Our recent work established myoglobin as a protector of cardiac function in hypoxia and disease states. We here unravel a novel role of cardiac myoglobin in governing FA metabolism to ensure the physiological energy production through β-oxidation, preventing myocardial lipid accumulation and preserving cardiac functions. In vivo¹H magnetic resonance spectroscopy unveils a 3-fold higher deposition of lipids in mouse hearts lacking myoglobin, which was associated with depressed cardiac function compared to wild-type hearts as assessed by echocardiography. Mass spectrometry reveals a marked increase in tissue triglycerides with preferential incorporation of palmitic and oleic acids. Phospholipid levels as well as the metabolome, transcriptome and proteome related to FA metabolism tend to be unaffected by myoglobin ablation. Our results reveal a physiological role of myoglobin in FA metabolism with the lipid accumulation-suppressing effects of myoglobin preventing cardiac lipotoxicity.

Reduced up-regulation of the nitric oxide pathway and impaired endothelial and smooth muscle functions in the female type 2 diabetic goto-kakizaki rat heart

Background

Type 2 diabetes is associated with greater relative risk of cardiovascular diseases in women than in men, which is not well understood. Consequently, we have investigated if male and female displayed differences in cardiac function, energy metabolism, and endothelial function which could contribute to increased cardiovascular complications in type 2 diabetic female.

Methods

Male and female Control and type 2 diabetic Goto-Kakizaki (GK) isolated rat hearts were perfused during 28 min with a physiological buffer before freeze-clamping for biochemical assays. High energy phosphate compounds and intracellular pH were followed using ³¹P magnetic resonance spectroscopy with simultaneous measurement of contractile function. Nitric oxide (NO) pathway and endothelium-dependent and independent vasodilatations were measured as indexes of endothelial function. Results were analyzed via two-way ANOVA, p < 0.05 was considered as statistically significant.

Results

Myocardial function was impaired in male and female diabetic versus Control groups (p < 0.05) without modification of energy metabolism. Coronary flow was decreased in both diabetic versus Control groups but to a higher extent in female GK versus male GK rat hearts (p < 0.05). NO production was up-regulated in diabetic groups but to a less extent in female GK rat hearts (p < 0.05). Endothelium-dependent and independent vasodilatations were impaired in female GK rat compared with male GK (p < 0.05) and female Control (p < 0.05) rat hearts.

Conclusions

We reported here an endothelial damage characterized by a reduced up-regulation of the NO pathway and impaired endothelial and smooth muscle functions, and coronary flow rates in the female GK rat hearts while energy metabolism was normal. Whether these results are related to the higher risk of cardiovascular complications among type 2 diabetic female needs to be further elicited in the future.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0157-z) contains supplementary material, which is available to authorized users.

Pioglitazone Attenuates Drug-Eluting Stent-Induced Proinflammatory State in Patients by Blocking Ubiquitination of PPAR

The inflammatory response after polymer-based drug-eluting stent (DES) placement has recently emerged as a major concern. The biologic roles of peroxisome proliferator-activated receptor-γ (PPAR-γ) activators thiazolidinedione (TZD) remain controversial in cardiovascular disease. Herein, we investigated the antiinflammatory effects of pioglitazone (PIO) on circulating peripheral blood mononuclear cells (MNCs) in patients after coronary DES implantation. Methods and Results. Twenty-eight patients with coronary artery disease and who underwent DES implantations were randomly assigned to pioglitazone (30 mg/d; PIO) or placebo (control; Con) treatment in addition to optimal standard therapy. After 12 weeks of treatment, plasma concentrations of high-sensitivity C-reactive protein (hs-CRP), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and matrix metalloproteinase-9 (MMP-9) were significantly decreased in PIO group compared to the Con group (P = 0.035, 0.011, 0.008, and 0.012, resp.). DES-induced mRNA expressions of IL-6, TNF-α, and MMP-9 in circulating MNC were significantly blocked by PIO (P = 0.031, 0.012, and 0.007, resp.). In addition, PIO markedly inhibited DES-enhanced NF-κB function and DES-blocked PPAR-γ activity. Mechanically, DES induced PPAR-γ ubiquitination and degradation in protein level, which can be totally reversed by PIO. Conclusion. PIO treatment attenuated DES-induced PPAR loss, NF-κB activation, and proinflammation, indicating that PIO may have a novel direct protective role in modulating proinflammation in DES era.

Peroxisome Proliferator-Activated Receptor-γ Is Critical to Cardiac Fibrosis

Peroxisome proliferator-activated receptor-γ (PPARγ) is a ligand-activated transcription factor belonging to the nuclear receptor superfamily, which plays a central role in regulating lipid and glucose metabolism. However, accumulating evidence demonstrates that PPARγ agonists have potential to reduce inflammation, influence the balance of immune cells, suppress oxidative stress, and improve endothelial function, which are all involved in the cellular and molecular mechanisms of cardiac fibrosis. Thus, in this review we discuss the role of PPARγ in various cardiovascular conditions associated with cardiac fibrosis, including diabetes mellitus, hypertension, myocardial infarction, heart failure, ischemia/reperfusion injury, atrial fibrillation, and several other cardiovascular disease (CVD) conditions, and summarize the developmental status of PPARγ agonists for the clinical management of CVD.