Role of Peroxisome Proliferator-Activated Receptor-γ in Vascular Inflammation

Relation between resistin, PPAR-γ, obesity and atherosclerosis in male albino rats

Obesity and atherosclerosis are inflammatory states involving variable metabolic signals. The adipokine resistin is implicated in adipose tissue dysfunction and is modulated by PPARγ. In this study, resistin and PPARγ role is investigated in the development of CVS disease. Forty-eight Adult male albino rats were divided into control, obesity and atherosclerotic groups; each group is divided into two subgroups; with and without PPARγ agonist administration for 8 weeks. To assess pathological changes; lipid profile, inflammatory mediator, serum resistin level and resistin expression in adipose tissue were measured. Aorta is histopathologically evaluated. It was found that resistin expression is significantly correlated with lipid profile and inflammatory status in obesity and atherosclerotic groups, and PPARγ agonist administration significantly improves inflammatory status and dyslipidemic profile across studied groups (p < .05). Aortic wall shows histopathological evidence of atherosclerosis in obesity group which is more evident in atherosclerotic group, and milder changes upon receiving PPARγ agonist.

Matrix Metalloproteinase-12 Is Required for Granuloma Progression

Background

Sarcoidosis is a chronic inflammatory disease of unknown cause characterized by granuloma formation. Mechanisms for chronic persistence of granulomas are unknown. Matrix Metalloproteinase-12 (MMP12) degrades extracellular matrix elastin and enables infiltration of immune cells responsible for inflammation and granuloma formation. Previous studies report increased MMP12 in sarcoidosis patients and association between MMP12 expression and disease severity. We also observed elevated MMP12 in our multiwall carbon nanotube (MWCNT) murine model of granulomatous inflammation. Here we hypothesized that MMP12 is important to acute and late phases of granuloma pathogenesis. To test this hypothesis, we analyzed granulomatous and inflammatory responses of Mmp12 knock-out (KO) mice at 10 (acute) and 60 days (late) after MWCNT instillation.

Methods

C57BL/6 (wildtype) and Mmp12 KO mice underwent oropharyngeal instillation of MWCNT. Lungs were harvested at 3, 10, 20, and 60 days post instillation for evaluation of MMP12 expression and granulomatous changes. Bronchoalveolar lavage (BAL) cells were analyzed 60 days after MWCNT instillation for expression of mediators thought to play a role in sarcoid granulomatosis: peroxisome proliferator-activated receptor-gamma (PPARγ), interferon-gamma (IFN-γ), and CCL2 (MCP-1).

Results

Pulmonary granuloma appearance at 10 days after MWCNT instillation showed no differences between wildtype and Mmp12 KO mice. In contrast, by 60 days after MWCNT instillation, Mmp12 KO mice revealed markedly attenuated granuloma formation together with elevated PPARγ and reduced IFNγ expression in BAL cells compared to wildtype. Unexpectedly, Mmp12 KO mice further demonstrated increased alveolar macrophages with increased CCL2 at 60 days.

Conclusions

The striking reduction of granuloma formation at day 60 in Mmp12 KO mice suggests that MMP12 is required to maintain chronic granuloma pathophysiology. The increased PPARγ and decreased IFNγ findings suggest that these mediators also may be involved since previous studies have shown that PPARγ suppresses IFNγ and PPARγ deficiency amplifies granuloma formation. Interestingly, a role of MMP12 in granuloma resolution is also suggested by increases in both macrophage influx and CCL2. Overall, our results strongly implicate MMP12 as a key factor in granuloma persistence and as a possible therapeutic target in chronic pulmonary sarcoidosis.

Ginsenoside Rb1 ameliorates CKD-associated vascular calcification by inhibiting the Wnt/β-catenin pathway

Vascular calcification (VC) is a pathological process underpinning major cardiovascular conditions and has attracted public attention due to its high morbidity and mortality. Chronic kidney disease (CKD) is a common disease related to VC. Ginsenoside Rb1 (Rb1) has been reported to protect the cardiovascular system against vascular diseases, yet its role in VC and the underlying mechanisms remain unclear. In this study, we established a CKD‐associated VC rat model and a β‐glycerophosphate (β‐GP)‐induced vascular smooth muscle cell (VSMC) calcification model to investigate the effects of Rb1 on VC. Our results demonstrated that Rb1 ameliorated calcium deposition and VSMC osteogenic transdifferentiation both in vivo and in vitro. Rb1 treatment inhibited the Wnt/β‐catenin pathway by activating peroxisome proliferator‐activated receptor‐γ (PPAR‐γ), and confocal microscopy was used to show that Rb1 inhibited β‐catenin nuclear translocation in VSMCs. Furthermore, SKL2001, an agonist of the Wnt/β‐catenin pathway, compromised the vascular protective effect of Rb1. GW9662, a PPAR‐γ antagonist, reversed Rb1's inhibitory effect on β‐catenin. These results indicate that Rb1 exerted anticalcific properties through PPAR‐γ/Wnt/β‐catenin axis, which provides new insights into the potential theraputics of VC.

PPAR gamma agonist, pioglitazone, rescues liver damage induced by renal ischemia/reperfusion injury

Remote organ damage is the major cause of death in patients with acute kidney injury (AKI) due to renal ischemia reperfusion (IR). Liver is one of the vital organs which are profoundly affected by AKI. The present study aims to investigate the role of peroxisome proliferator activator receptor gamma (PPARγ) in liver damage induced by IR injury in rats. Renal IR was induced by right nephrectomy, occlusion of left renal pedicle for 45 min to induce ischemia, and then reperfusion for 6 or 24 h. The PPARγ agonist, pioglitazone, was given orally for 7 days before renal IR procedure. Animals receiving pioglitazone showed improvement in renal and hepatic functions when compared to IR groups. Renal IR increased renal, hepatic and serum levels of tumor necrosis factor-α (TNF-α) and induced apoptotic cell death in liver. These effects were diminished with pioglitazone. In addition, pioglitazone reduced renal IR-induced oxidative stress in liver. Pioglitazone reduced malondialdehyde (MDA) content and NADPH oxidase mRNA expression and induced further increase in nuclear factor erythroid 2-related factor 2 (Nrf2) expression when compared to IR groups. Furthermore, pioglitazone increased the expression of PPARγ target genes such as renal and hepatic PPARγ1 (Pparg1), hepatic hemoxygenase-1 (Hmox1), and hepatic thioredoxin (TRx). Histological profiles for kidney and liver were also ameliorated with pioglitazone. Hence, PPARγ is a potential target to protect liver in patients with renal IR injury.

Adiponectin and Orexin-A as a Potential Immunity Link Between Adipose Tissue and Central Nervous System

Adipose tissue (AT) is strongly associated with development and progression of immune disorders through adipokines secretion, such as adiponectin. This protein has beneficial energetic properties and is involved in inflammation and immunity processes. Three oligomers of circulating adiponectin with different molecular weight are described: High (HMW), Medium (MMW), and Low (LMW). The HMW is the most biologically active oligomers. On binding to its receptors AdipoR1, AdipoR2, and T-cadherin, adiponectin acts on both innate and acquired immunity. The suppression of NF-κB activation and pro-inflammatory cytokine expression in macrophages is mediated by AdipoR1. AdipoR2 mediates polarization of anti-inflammatory M2 macrophages T-cadherin is essential for the M2 macrophage proliferation. Furthermore, adiponectin reduces T cells responsiveness and B cells lymphopoiesis. The immune system is very sensitive to environmental changes and it is not only interconnected with AT but also with the central nervous system (CNS). Cytokines, which are mediators of the immune system, exercise control over mediators of the CNS. Microglia, which are immunity cells belonging to the macrophage family, are present within the CNS. The nervous system is also involved in immunity through the production of neuropeptides such as orexin-A/hypocretin-1. This neuropeptide is involved in metabolic disorders, inflammation and in the immune response. The relationship between adipokines, immunity, and the nervous system is validated by both the role of orexin-A on fat, food intake, and energy expenditure, as well as by role of adiponectin on the CNS. In this review, we focused on the functions of adiponectin and orexin-A as a potential immunity link between AT and CNS.

The effects of oleanolic acid on atherosclerosis in different animal models

In the present study, three animal models, including C57BL/6J mice, low-density lipoprotein receptor knockout (LDLR-/-) mice, and rabbit that mimicked atherosclerosis, were established to investigate the inhibitory effect of oleanolic acid (OA) on atherosclerosis. In rabbit model, serum total cholesterol (TC), triglyceride, low density lipoprotein cholesterol (LDL-C), and high density lipoprotein cholesterol (HDL-C) were measured. Carotid artery lesions were isolated for histological analysis. The red oil O and hematoxylin-eosin staining in liver were examined. The messenger ribonucleicacid (mRNA) levels of PPARγ, AdipoR1, and AdipoR2 related to lipid metabolism were determined. Compared with model group, OA and atorvastatin significantly lowered the levels of TC and LDL-C. The result of red oil O staining showed that OA and atorvastatin had similar effect on reducing the accumulation of lipid. Histological result demonstrated that OA reduced the thickness of intima. AdipoR1 was markedly increased, while AdipoR2 was remarkably decreased in OA group compared with that in the control group of the rabbit model. In LDLR-/- mouse model, lipid parameters in blood and mRNA levels of PPARγ, AdipoR1, and AdipoR2 were measured. It was found that OA exhibited similar effects as atorvastatin including reduced TG, LDL-C, and enhanced HDL-C. Notably, OA elevated the levels of AdipoR1 and PPARγ. At the same time, OA decreased TC and LDL-C in C57BL/6J mice model. Our results in three different animal models all revealed that OA retarded the development of atherosclerosis by influencing serum lipid levels, lipid accumulation in liver and intimal thickening of artery. And the underlying mechanism of OA on atherosclerosis may involve in lipid metabolism genes: PPARγ, AdipoR1, and AdipoR2.

Smooth muscle cell-specific deletion of Col15a1 unexpectedly leads to impaired development of advanced atherosclerotic lesions

Atherosclerotic plaque rupture with subsequent embolic events is a major cause of sudden death from myocardial infarction or stroke. Although smooth muscle cells (SMCs) produce and respond to collagens in vitro, there is no direct evidence in vivo that SMCs are a crucial source of collagens and that this impacts lesion development or fibrous cap formation. We sought to determine how conditional SMC-specific knockout of collagen type XV (COL15A1) in SMC lineage tracing mice affects advanced lesion formation given that 1) we have previously identified a Col15a1 sequence variant associated with age-related atherosclerosis, 2) COL15A1 is a matrix organizer enhancing tissue structural integrity, and 3) small interfering RNA-mediated Col15a1 knockdown increased migration and decreased proliferation of cultured human SMCs. We hypothesized that SMC-derived COL15A1 is critical in advanced lesions, specifically in fibrous cap formation. Surprisingly, we demonstrated that SMC-specific Col15a1 knockout mice fed a Western diet for 18 wk failed to form advanced lesions. SMC-specific Col15a1 knockout resulted in lesions reduced in size by 78%, with marked reductions in numbers and proliferating SMCs, and lacked a SMC and extracellular matrix-rich lesion or fibrous cap. In vivo RNA-seq analyses on SMC Col15a1 knockout and wild-type lesions suggested that a mechanism for these effects is through global repression of multiple proatherogenic inflammatory pathways involved in lesion development. These results provide the first direct evidence that a SMC-derived collagen, COL15A1, is critical during lesion pathogenesis, but, contrary to expectations, its loss resulted in marked attenuation rather than exacerbation of lesion pathogenesis.NEW & NOTEWORTHY We report the first direct in vivo evidence that a smooth muscle cell (SMC)-produced collagen, collagen type XV (COL15A1), is critical for atherosclerotic lesion development. SMC Col15a1 knockout markedly attenuated advanced lesion formation, likely through reducing SMC proliferation and impairing multiple proatherogenic inflammatory processes.

Minireview: Challenges and opportunities in development of PPAR agonists

The clinical impact of the fibrate and thiazolidinedione drugs on dyslipidemia and diabetes is driven mainly through activation of two transcription factors, peroxisome proliferator-activated receptors (PPAR)-α and PPAR-γ. However, substantial differences exist in the therapeutic and side-effect profiles of specific drugs. This has been attributed primarily to the complexity of drug-target complexes that involve many coregulatory proteins in the context of specific target gene promoters. Recent data have revealed that some PPAR ligands interact with other non-PPAR targets. Here we review concepts used to develop new agents that preferentially modulate transcriptional complex assembly, target more than one PPAR receptor simultaneously, or act as partial agonists. We highlight newly described on-target mechanisms of PPAR regulation including phosphorylation and nongenomic regulation. We briefly describe the recently discovered non-PPAR protein targets of thiazolidinediones, mitoNEET, and mTOT. Finally, we summarize the contributions of on- and off-target actions to select therapeutic and side effects of PPAR ligands including insulin sensitivity, cardiovascular actions, inflammation, and carcinogenicity.

Peroxisome proliferator-activated receptor agonists (PPARs): a promising prospect in the treatment of psoriasis and psoriatic arthritis

Psoriasis is a polygenic, inflammatory and progressive disease, characterized by an abnormal differentiation and hyperproliferation of keratinocytes, associated with impaired immunologic activation and systemic disorders, while psoriatic arthritis is a chronic inflammatory articular disease. Pathophysiology of psoriasis comprises a dysfunction of the immune system cells with an interactive network between cells and cytokines supporting the initiation and perpetuation of disease and leading to inflammation of skin, enthesis and joints. Recent studies have shown an important role of systemic inflammation in the development of atherosclerosis. Corroborating these findings, patients with severe Psoriasis have marked incidence of psoriatic arthritis, cardiovascular diseases, hypertension, dyslipidemia, obesity and diabetes mellitus, showing an increased risk for acute myocardial infarction, which suggests that the condition is not restricted to the skin. Nuclear receptors are ligand-dependent transcription factors, whose activation affects genes that control vital processes. Among them the peroxisome proliferator-activated receptor is responsible for establishing the relationship between lipids, metabolic diseases and innate immunity. In the skin, peroxisome proliferator-activated receptors have an important effect in keratinocyte homeostasis, suggesting a role in diseases such as psoriasis. The peroxisome proliferator-activated receptors agonists represent a relevant source of research in the treatment of skin conditions, however more clinical studies are needed to define the potential response of these drugs in patients with psoriasis and psoriatic arthritis.