A Role for PPARbeta/delta in Ocular Angiogenesis

[Effects of Fibrates on Risk of Development of Diabetic Retinopathy in Japanese Working Age Patients with Type 2 Diabetes and Dyslipidemia: a Retrospective Cohort Study]

The aims of the present study were to investigate the effects of fenofibrate and bezafibrate on the risk of development of diabetic retinopathy (DR) in patients with type 2 diabetes and dyslipidemia. Japanese working age patients with type 2 diabetes and dyslipidemia were extracted from the Nihon University School of Medicine Clinical Data Warehouse. These patients were divided into three groups: control group (n=2549), fenofibrate group (n=40), and bezafibrate group (n=135). Multivariate logistic regression analysis was performed to assess the association between fibrates and the development of DR. After adjustment for covariates, fenofibrate showed no association with the risk of DR [adjusted odds ratio (OR), 0.160; 95% CI, 0.021-1.209; p=0.0758]. Bezafibrate also showed no association with the risk of DR (adjusted OR, 0.731; 95% CI, 0.411-1.299; p=0.2855). However, poor control of hemoglobin A1c (HbA1c ≥8.0%; adjusted OR, 3.623; 95% CI, 2.649-4.956; p<0.0001) and high low-density lipoprotein cholesterol (LDL-C ≥140 mg/dL; adjusted OR, 1.399; 95% CI, 1.013-1.932; p=0.0415) within the follow-up period of type 2 diabetes and dyslipidemia increased the risk of DR. Our results suggested that to prevent development of DR in patients with type 2 diabetes and dyslipidemia, controlling LDL-C levels as well as HbA1c levels under coexistence type 2 diabetes and dyslipidemia is more important than the selection of fibrate.

Progress in developing rodent models of age-related macular degeneration (AMD)

Age-related macular degeneration (AMD) is the leading cause of irreversible central vision loss, typically affecting individuals from mid-life onwards. Its multifactorial aetiology and the lack of any effective treatments has spurred the development of animal models as research and drug discovery tools. Several rodent models have been developed which recapitulate key features of AMD and provide insights into its underlying pathology. These have contributed to making significant progress in understanding the disease and the identification of novel therapeutic targets. However, a major caveat with existing models is that they do not demonstrate the full disease spectrum. In this review, we outline advances in rodent AMD models from the last decade. These models feature various hallmarks associated with AMD, including oxidative stress, hypoxia, immune dysregulation, genetic mutations and environmental risk factors. The review summarises the methods by which each model was created, its pathological characteristics as well as its relation to the disease in humans.

The Emerging Role of PPAR Beta/Delta in Tumor Angiogenesis

PPARs are ligand-activated transcriptional factors that belong to the nuclear receptor superfamily. Among them, PPAR alpha and PPAR gamma are prone to exert an antiangiogenic effect, whereas PPAR beta/delta has an opposite effect in physiological and pathological conditions. Angiogenesis has been known as a hallmark of cancer, and our recent works also demonstrate that vascular-specific PPAR beta/delta overexpression promotes tumor angiogenesis and progression in vivo. In this review, we will mainly focus on the role of PPAR beta/delta in tumor angiogenesis linked to the tumor microenvironment to further facilitate tumor progression and metastasis. Moreover, the crosstalk between PPAR beta/delta and its downstream key signal molecules involved in tumor angiogenesis will also be discussed, and the network of interplay between them will further be established in the review.

Rethinking Nuclear Receptors as Potential Therapeutic Targets for Retinal Diseases

Collectively, retinal diseases, including age-related macular degeneration, retinitis pigmentosa, and diabetic retinopathy, result in severe vision impairment worldwide. The absence and/or limited availability of successful drug therapies for these blinding disorders necessitates further understanding their pathobiology and identifying new targetable signaling pathways. Nuclear receptors are transcription regulators of many key aspects of human physiology, as well as pathophysiology, with reported roles in development, aging, and disease. Some of the pathways regulated by nuclear receptors include, but are not limited to, angiogenesis, inflammation, and lipid metabolic dysregulation, mechanisms also important in the initiation and development of several retinal diseases. Herein, we present an overview of the biology of three diseases affecting the posterior eye, summarize a growing body of evidence that suggests direct or indirect involvement of nuclear receptors in disease progression, and discuss the therapeutic potential of targeting nuclear receptors for treatment.

Peroxisome proliferator-activated receptor δ agonist, HPP593, prevents renal necrosis under chronic ischemia

The Goldblatt’s 2 kidney 1 clip (2K1C) rat animal model of renovascular hypertension is characterized by ischemic nephropathy of the clipped kidney. 2K1C rats were treated with a specific peroxisome proliferator-activated receptor δ (PPARδ) agonist, HPP593. Clipped kidneys from untreated rats developed tubular and glomerular necrosis and massive interstitial, periglomerular and perivascular fibrosis. HPP593 kidneys did not exhibit any histochemical features of necrosis; fibrotic lesions were present only in perivascular areas. Necrosis in the untreated clipped kidneys was associated with an increased oxidative stress, up regulation and mitochondrial translocation of the pro-death protein BNIP3 specifically in tubules. In the kidneys of HPP593-treated rats oxidative stress was attenuated and BNIP3 protein decreased notably in the mitochondrial fraction when compared to untreated animals. In untreated clipped kidneys, mitochondria were dysfunctional as revealed by perturbations in the levels of MCAD, COXIV, TFAM, and Parkin proteins and AMPK activation, while in HPP593-treated rats these proteins remained at the physiological levels. Nuclear amounts of oxidative stress-responsive proteins, NRF1 and NRF2 were below physiological levels in treated kidneys. Mitochondrial biogenesis and autophagy were inhibited similarly in both treated and untreated 2K1C kidneys as indicated by a decrease in PGC1-α and deficiency of the autophagy-essential proteins LC3-II and ATG5. However, HPP593 treatment resulted in increased accumulation of p62 protein, an autophagic substrate and an enhancer of NRF2 activity. Therefore, inhibition of BNIP3 activation by the preservation of mitochondrial function and control of oxidative stress by PPARδ is the most likely mechanism to account for the prevention of necrotic death in the kidney under conditions of persistent ischemia.

The platelet as a model system for the acute actions of nuclear receptors

Platelets are circulating cell fragments which play a critical role in thrombosis, and whose activity is associated with the progress of cardiovascular diseases, diabetes, inflammation, and cancer cell metastasis. Recently, a number of nuclear receptors have been found present in human platelets, including the receptors for sex steroids, and glucocorticoids, along with peroxisome proliferator-activated receptors (PPAR)s and retinoid X receptors (RXR)s. Although the platelet contains no nucleus, selective ligands for these receptors activate their respective platelet nuclear receptors and regulate platelet aggregation and activation. The human platelet, because of its abundance and accessibility therefore represents an excellent model system to study the rapid non-genomic mechanism of nuclear receptors. Moreover, since targeting platelets is a major clinical therapeutic area, analysis of platelet nuclear receptors may provide clues for new drug targets as well as provide important information regarding the physiological roles of nuclear receptors in the circulation.

Emerging roles of peroxisome proliferator-activated receptor-beta/delta in inflammation

Peroxisome proliferator-activated receptor (PPAR)-beta/delta is a member of the PPAR nuclear hormone receptor family. The PPARs are a family of 3 ligand-activated transcription factors: PPARalpha (NR1C1), PPARbeta/delta (NR1C2), and PPARgamma (NR1C3). All the PPARs play important roles in the regulation of metabolic pathways, including those of lipid of biosynthesis and glucose metabolism, as well as in a variety of cell differentiation, proliferation, and apoptosis pathways. Recently, there has been a great deal of interest in the involvement of PPARs in the inflammatory processes. In particular, PPARalpha and PPARgamma inhibit the activation of inflammatory gene expression and can negatively interfere with pro-inflammatory transcription factor signalling pathways in vascular and inflammatory cells. In contrast, the roles of PPARbeta/delta regulating inflammation and immunity are only just emerging. This review will focus on these emerging roles of PPARbeta/delta in regulating inflammatory processes.