Angiotensin II receptor blocker ameliorates stress-induced adipose tissue inflammation and insulin resistance

Molecular mechanisms linking stress and insulin resistance

To date, there is ample evidence to support the strong relationship between stress and insulin resistance. While diabetes mellitus acts as a potent stress inducer, stress may be an upstream event for insulin resistance as well. It is widely recognized that diabetes mellitus is more prevalent among people who have a stressful lifestyle; however, the underlying mechanisms are not well understood. In the current study, we surveyed the scientific literature for possible interactions between stress and insulin resistance and found that stress can impair glucose homeostasis, working through at least six molecular pathways.

Statins Mitigate Stress-Related Vascular Aging and Atherosclerosis in apoE-Deficient Mice Fed High Fat-Diet: The Role of Glucagon-Like Peptide-1/Adiponectin Axis

Objectives

Exposure to chronic psychosocial stress is a risk factor for atherosclerotic cardiovascular diseases. Given that the 3-hydroxy-3-methylglutaryl-coenzyme reductase inhibitor statins prevent atherogenesis, we evaluated whether pitavastatin prevents chronic stress- and high fat diet-induced vascular senescence and atherogenesis in apolipoprotein E-deficient (ApoE^–/–) mice, with a special focus on glucagon-like peptide-1 (GLP-1)/adiponectin (APN) axis.

Methods and Results

6-week-old ApoE^–/– mice loaded a high-fat diet were randomly assigned into non-stress (n = 12) and stress (n = 13) groups for 12 weeks. Non-stress control mice were left undisturbed. Chronic stress accelerated high fat diet-induce arterial senescence and atherosclerotic plaque growth. The chronic stress lowered the levels of circulating GLP-1 as well as adipose and plasma APN. As compared with the stress alone mice, the pitavastatin-treated mice had reduced macrophage infiltration, elastin fragments, and increased plaque collagen volume, and lowered levels of osteopontin, toll-like receptor-2/-4, macrophage chemoattractant protein-1, C-X-C chemokine receptor-4, p47^phox, p47^phox, gp91^phox, cathepsins S, p16, and p21, mRNAs and/or proteins. Pitavastatin increased plasma GLP-1 and APN levels and suppressed matrix metalloproteinase-2/-9 gene expressions and activities in the aortas. Finally, the protective effect of pitavastatin was abrogated by APN blocking.

Conclusion

These findings suggested that the pitavastatin-mediated pleiotropic vasculoprotective effects are likely attributable, at least in part, to the elevation of GLP-1 and APN levels and the inhibition of diet-induced plaque inflammation, oxidative stress, and proteolysis in ApoE^–/– mice received chronic stress conditions.

The Influence of Psychological Stress on the Initiation and Progression of Diabetes and Cancer

CONTEXT

Psychological stress can be considered a risk factor for the initiation and progression of many pathological conditions, including type 1 and 2 diabetes mellitus and cancer.

OBJECTIVES

The aim of this review article was to evaluate the molecular and cellular mechanisms linking psychological stress to the onset and progression of diabetes and cancer.

EVIDENCE ACQUISITION

The current review was conducted to survey and analyze studies related to the effects of psychological stress on diabetes and cancer.

RESULTS

Psychological stress may make individuals prone to the development of diabetes through the impairment of the hypothalamic-pituitary-adrenal (HPA) axis function, sympathetic nerves system (SNS), lipid profile, cytokines balance, renin-angiotensin system (RAS), and insulin signaling pathway. Additionally, psychological stress can contribute to the development of cancer through the perturbation in the HPA axis, SNS function, and cytokines balance. Psychological stress is also capable of decreasing the levels of oxytocin and dopamine, leading to an increased risk of cancer in susceptible individuals.

CONCLUSIONS

It seems that psychological stress plays a significant role in the onset and progression of diabetes and cancer. The identification of the pathways triggered by psychological stress would open up a new avenue for the understanding of molecular mechanisms by which diabetes and cancer could be managed or even prevented.

Blocking of Type 1 Angiotensin II Receptor Inhibits T-lymphocyte Activation and IL-2 Production

BACKGROUND/AIM

Novel information on the role of endogenous compounds in regulating physiological and pathological process are of interest, as it may lead to the development of better strategies for disease management. The role of angiotensin II and the signaling of type 1 angiotensin II receptor (AGT1R) in T-lymphocyte activation and interleukin-2 (IL-2) production are largely unknown.

MATERIALS AND METHODS

Jurkat T-cells were treated with AGT1R inhibitor candesartan and stimulated with phorbol myristate acetate (PMA) and ionomycin. T-Cell activation, associated cytokine production and levels of signaling proteins were evaluated by flow cytometry and western blot analysis.

RESULTS

Candesartan significantly suppressed PMA and ionomycin-induced CD25 expression and IL-2 production. Regarding the molecular mechanism involved, we showed that such suppressive effects of blocking of AGT1R by candesartan resulted in the significant inhibition of ERK activation in PMA-stimulated Jurkat T-cells. The effect of ERK inhibition on T-cell activation was further confirmed. Treatment with FR180204, a specific ERK inhibitor, reduced T-cell activation and IL-2 secretion.

CONCLUSION

AGT1R signaling is essential for T-cell activation and IL-2 production, and the inhibition of this pathway suppressed T-cell activation via an ERK-dependent mechanism.

Synergistic action of ursolic acid and metformin in experimental model of insulin resistance and related behavioral alterations

Chronic restraint stress (CRS) is known to cause metabolic and neurological complications in a number of ways. Prolonged exposure to stress evident by increased corticosterone level led to impaired altered insulin signaling and oxidative stress in mice, in the present study. Impaired insulin signaling or insulin resistance was characterized by hyperglycemia, hyperinsulinemia, hyperlipidemia, hypoadiponectinemia, increased glycosylated haemoglobin and HOMA-IR. It was also associated with increased proinflammatory cytokine TNF-α levels. CRS also caused significant increase in acetylcholinesterase activity and oxidative stress in brain along with cognitive impairment in behavioral test. Ursolic acid, metformin, gliclazide and their combinations when administered daily for 30 days significantly improved insulin sensitivity apart from behavioral and biochemical alterations in stressed mice. Treatment with drugs also decreased serum corticosterone and TNF-α levels. The findings of our study revealed that improvement in insulin sensitivity, learning and cognitive performance in stressed mice was attributed to attenuation of proinflammatory cytokines and oxidative stress. Moreover, combination of [Metformin (150 mg/kg) + Ursolic acid (10 mg/kg)] produced enhanced improvement in insulin sensitivity and cognitive impairment as compared to their individual effects, suggesting possibly the common mode of anti-inflammatory and antioxidant mechanisms.

Modulation of the renin-angiotensin system in white adipose tissue and skeletal muscle: focus on exercise training

Overactivation of the renin-angiotensin (Ang) system (RAS) increases the classical arm (Ang-converting enzyme (ACE)/Ang II/Ang type 1 receptor (AT1R)) to the detriment of the protective arm (ACE2/Ang 1-7/Mas receptor (MasR)). The components of the RAS are present locally in white adipose tissue (WAT) and skeletal muscle, which act co-operatively, through specific mediators, in response to pathophysiological changes. In WAT, up-regulation of the classical arm promotes lipogenesis and reduces lipolysis and adipogenesis, leading to adipocyte hypertrophy and lipid storage, which are related to insulin resistance and increased inflammation. In skeletal muscle, the classical arm promotes protein degradation and increases the inflammatory status and oxidative stress, leading to muscle wasting. Conversely, the protective arm plays a counter-regulatory role by opposing the effect of Ang II. The accumulation of adipose tissue and muscle mass loss is associated with a higher risk of morbidity and mortality, which could be related, in part, to overactivation of the RAS. On the other hand, exercise training (ExT) shifts the balance of the RAS towards the protective arm, promoting the inhibition of the classical arm in parallel with the stimulation of the protective arm. Thus, fat mobilization and maintenance of muscle mass and function are facilitated. However, the mechanisms underlying exercise-induced changes in the RAS remain unclear. In this review, we present the RAS as a key mechanism of WAT and skeletal muscle metabolic dysfunction. Furthermore, we discuss the interaction between the RAS and exercise and the possible underlying mechanisms of the health-related aspects of ExT.

Cellular Stresses and Stress Responses in the Pathogenesis of Insulin Resistance

Insulin resistance (IR), a key component of the metabolic syndrome, precedes the development of diabetes, cardiovascular disease, and Alzheimer's disease. Its etiological pathways are not well defined, although many contributory mechanisms have been established. This article summarizes such mechanisms into the hypothesis that factors like nutrient overload, physical inactivity, hypoxia, psychological stress, and environmental pollutants induce a network of cellular stresses, stress responses, and stress response dysregulations that jointly inhibit insulin signaling in insulin target cells including endothelial cells, hepatocytes, myocytes, hypothalamic neurons, and adipocytes. The insulin resistance-inducing cellular stresses include oxidative, nitrosative, carbonyl/electrophilic, genotoxic, and endoplasmic reticulum stresses; the stress responses include the ubiquitin-proteasome pathway, the DNA damage response, the unfolded protein response, apoptosis, inflammasome activation, and pyroptosis, while the dysregulated responses include the heat shock response, autophagy, and nuclear factor erythroid-2-related factor 2 signaling. Insulin target cells also produce metabolites that exacerbate cellular stress generation both locally and systemically, partly through recruitment and activation of myeloid cells which sustain a state of chronic inflammation. Thus, insulin resistance may be prevented or attenuated by multiple approaches targeting the different cellular stresses and stress responses.

Angiotensin receptor blocker irbesartan reduces stress-induced intestinal inflammation via AT1a signaling and ACE2-dependent mechanism in mice

Stress is associated with pathophysiology of both irritable bowel syndrome (IBS) and hypertension. Angiotensin receptor blockers (ARB) have anti-inflammatory properties via inhibition of angiotensin II (Ang II)/Ang II type I receptor axis (AT1). Inhibition of the classical RAS pathway is also involved in upregulation of angiotensin converting enzyme-2 (ACE2), which activates the Ang-(1-7)/Mas pathway to counteract inflammatory signaling and acts as a partner of the amino acid transporter, B⁰AT-1, to absorb tryptophan for regulation of microbiota-gut-brain axis. In this study, we determined the effects of ARB irbesartan on stress-induced intestinal inflammation. C57BL/6J mice were subjected to 2-week intermittent restraint stress. They were orally treated during the stress with either vehicle, 3 or 10 mg/kg/day irbesartan. Restraint stress resulted in colon inflammation with higher histological damage scores, increased expression of Nox4, TLR-4 and IL1-β, accumulation of reactive oxygen species (ROS), and activation of the ACE-angiotensin II-AT1 receptor axis. Stress also downregulated intestinal amino acid transporter, ACE2/B⁰AT-1, and activity of intestinal mammalian target of rapamycin (mTOR) and p70 S6 kinase (p70S6K), resulting in decrease in α-defensins, changes in intestinal microbial contents, and perturbation of tryptophan metabolism with activation of the kynurenine pathway. Administration of irbesartan inhibited activation of stress-induced AT1 pathway to reduce intestinal ROS accumulation and inflammation, restored expression of ACE2/B⁰AT-1, activity of mTOR and p70S6K, dysbiosis and tryptophan metabolism. Our results suggest that AT1 is a potentially suitable therapeutic target in stress-induced intestinal inflammation, and that irbesartan could be beneficially suitable for the treatment of stressed patients with IBS.

Dose rectification of an imbalance between DPP4 and GLP-1 ameliorates chronic stress-related vascular aging and atherosclerosis?

Exposure to psychosocial stress is a risk factor for cardiovascular disease, including vascular aging and regeneration. Dipeptidyl peptidase-4 (DPP-4) exerts many physiological and pharmacological functions by regulating its extremely abundant substrates [eg., glucagon-like peptide-1 (GLP-1), stromal cell-derived factor-1α/C-X-C chemokine receptor type-4, etc.]. Over the past decade, emerging data has revealed unexpected roles for DPP-4 and GLP-1 in intracellular signaling, oxidative stress production, lipid metabolism, cell apoptosis, immune activation, insulin resistance, and inflammation. This mini review focuses on recent findings in this field, highlighting an imbalance between DPP4 and GLP-1 as a potential therapeutic target in the management of vascular aging and atherosclerosis in animals under experimental stress conditions.

Regulation and Functions of the Renin-Angiotensin System in White and Brown Adipose Tissue

The renin angiotensin system (RAS) is a major regulator of blood pressure, fluid, and electrolyte homeostasis. RAS precursor angiotensinogen (Agt) is cleaved into angiotensin I (Ang I) and II (Ang II) by renin and angiotensin converting enzyme (ACE), respectively. Major effects of Ang II, the main bioactive peptide of this system, is mediated by G protein coupled receptors, Angiotensin Type 1 (AGTR1, AT1R) and Type 2 (AGTR2, AT2R) receptors. Further, the discovery of additional RAS peptides such as Ang 1-7 generated by the action of another enzyme ACE2 identified novel functions of this complex system. In addition to the systemic RAS, several local RAS exist in organs such as the brain, kidney, pancreas, and adipose tissue. The expression and regulation of various components of RAS in adipose tissue prompted extensive research into the role of adipose RAS in metabolic diseases. Indeed, animal studies have shown that adipose-derived Agt contributes to circulating RAS, kidney, and blood pressure regulation. Further, mice overexpressing Agt have high blood pressure and increased adiposity characterized by inflammation, adipocyte hypertrophy, and insulin resistance, which can be reversed at least in part by RAS inhibition. These findings highlight the importance of this system in energy homeostasis, especially in the context of obesity. This overview article discusses the depot-specific functions of adipose RAS, genetic and pharmacological manipulations of RAS, and its applications to adipogenesis, thermogenesis, and overall energy homeostasis. © 2017 American Physiological Society. Compr Physiol 7:1137-1150, 2017.

Dipeptidyl Peptidase-4 Regulates Hematopoietic Stem Cell Activation in Response to Chronic Stress

Background

DPP4 (Dipeptidyl peptidase‐4)‐GLP‐1 (glucagon‐like peptide‐1) and its receptor (GLP‐1R) axis has been involved in several intracellular signaling pathways. The Adrβ3 (β3‐adrenergic receptor)/CXCL12 (C‐X‐C motif chemokine 12) signal was required for the hematopoiesis. We investigated the novel molecular requirements between DPP4‐GLP‐1/GLP‐1 and Adrβ3/CXCL12 signals in bone marrow (BM) hematopoietic stem cell (HSC) activation in response to chronic stress.

Methods and Results

Male 8‐week‐old mice were subjected to 4‐week intermittent restrain stress and orally treated with vehicle or the DPP4 inhibitor anagliptin (30 mg/kg per day). Control mice were left undisturbed. The stress increased the blood and brain DPP4 levels, the plasma epinephrine and norepinephrine levels, and the BM niche cell Adrβ3 expression, and it decreased the plasma GLP‐1 levels and the brain GLP‐1R and BM CXCL12 expressions. These changes were reversed by DPP4 inhibition. The stress activated BM sca‐1^highc‐Kit^highCD48^lowCD150^highHSC proliferation, giving rise to high levels of blood leukocytes and monocytes. The stress‐activated HSC proliferation was reversed by DPP4 depletion and by GLP‐1R activation. Finally, the selective pharmacological blocking of Adrβ3 mitigated HSC activation, accompanied by an improvement of CXCL12 gene expression in BM niche cells in response to chronic stress.

Conclusions

These findings suggest that DPP4 can regulate chronic stress‐induced BM HSC activation and inflammatory cell production via an Adrβ3/CXCL12‐dependent mechanism that is mediated by the GLP‐1/GLP‐1R axis, suggesting that the DPP4 inhibition or the GLP‐1R stimulation may have applications for treating inflammatory diseases.

Exenatide mitigated diet-induced vascular aging and atherosclerotic plaque growth in ApoE-deficient mice under chronic stress

BACKGROUND AND AIMS

Exposure to psychosocial stress is a risk factor for cardiovascular disorders. Because the glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) agonist prevents cardiovascular injury, we investigated the beneficial effects and mechanism of the GLP-1 analogue exenatide on stress-related vascular senescence and atherosclerosis in apolipoprotein E-deficient (ApoE^-/-) mice fed a high-fat (HF) diet.

METHODS

ApoE^-/- mice fed the HF diet were assigned to non-stressed and immobilized-stress groups for 12 weeks. Mice fed the HF diet were divided into 2 groups and administered vehicle or exenatide for 12 weeks under stress conditions.

RESULTS

Chronic stress enhanced vascular endothelial senescence and atherosclerotic plaque growth. The stress increased the levels of plasma depeptidyl peptidase-4 activity and decreased the levels of plasma GLP-1 and both plasma and adipose adiponectin (APN). As compared with the mice subjected to stress alone, the exenatide-treated mice had decreased plaque microvessel density, macrophage accumulation, broken elastin, and enhanced plaque collagen volume, and lowered levels of peroxisome proliferator-activated receptor-α, gp91phox osteopontin, C-X-C chemokine receptor-4, toll-like receptor-2 (TLR2), TLR4, and cathepsins K, L, and S mRNAs and/or proteins. Exenatide reduced aortic matrix metalloproteinase-9 (MMP-9) and MMP-2 gene expression and activities. Exenatide also stimulated APN expression of preadipocytes and inhibited ox-low density lipoprotein-induced foam cell formation of monocytes in stressed mice.

CONCLUSIONS

These results indicate that the exenatide-mediated beneficial vascular actions are likely attributable, at least in part, to the enhancement of APN production and the attenuation of plaque oxidative stress, inflammation, and proteolysis in ApoE^-/- mice under chronic stress.

Renin inhibition improves metabolic syndrome, and reduces angiotensin II levels and oxidative stress in visceral fat tissues in fructose-fed rats

Renin–angiotensin system in visceral fat plays a crucial role in the pathogenesis of metabolic syndrome in fructose-fed rats. However, the effects of renin inhibition on visceral adiposity in metabolic syndrome are not fully investigated. We investigated the effects of renin inhibition on visceral adiposity in fructose-fed rats. Male Wistar–Kyoto rats were divided into 4 groups for 8-week experiments: Group Con (standard chow diet), Group Fru (high-fructose diet; 60% fructose), Group FruA (high-fructose diet and concurrent aliskiren treatment; 100 mg/kg body weight [BW] per day), and Group FruB (high-fructose diet and subsequent, i.e. 4 weeks after initiating high-fructose feeding, aliskiren treatment; 100 mg/kg BW per day). The high-fructose diet induced metabolic syndrome, increased visceral fat weights and adipocyte sizes, and augmented angiotensin II (Ang II), NADPH oxidase (NOX) isoforms expressions, oxidative stress, and dysregulated production of adipocytokines from visceral adipose tissues. Concurrent and subsequent aliskiren administration ameliorated metabolic syndrome, dysregulated adipocytokines, and visceral adiposity in high fructose-fed hypertensive rats, and was associated with reducing Ang II levels, NOX isoforms expressions and oxidative stress in visceral fat tissues. Therefore, this study demonstrates renin inhibition could improve metabolic syndrome, and reduce Ang II levels and oxidative stress in visceral fat tissue in fructose-fed rats, and suggests that visceral adipose Ang II plays a crucial role in the pathogenesis of metabolic syndrome in fructose-fed rats.

Increased dipeptidyl peptidase-4 accelerates diet-related vascular aging and atherosclerosis in ApoE-deficient mice under chronic stress

OBJECTIVES

Exposure to psychosocial stress is a risk factor for cardiovascular disease. Given that dipeptidyl peptidase-4 (DPP4) regulates several intracellular signaling pathways associated with glucagon-like peptide-1 (GLP-1) metabolism, we investigated the role of DPP4 in stress-related vascular senescence and atherosclerosis in apolipoprotein E-deficient (ApoE^-/-) mice.

METHODS AND RESULTS

ApoE^-/- mice fed a high-fat (HF) diet were randomly assigned to one of non-stress and immobilized stress groups for 12weeks. Chronic stress accelerated vascular senescence and atherosclerotic plaque growth at the aortic roots. Stressed mice had increased levels of plasma DPP4 and decreased levels of plasma GLP-1 and adiponectin (APN) and adipose APN expression. Stress increased plaque macrophage infiltration, neovessel density, and elastin fragmentation, lessened the plaque collagen content, and increased the levels of toll-like receptor-2 (TLR2), TLR4, C-X-C chemokine receptor-4, cathepsins S and K, osteopontin, peroxisome proliferator-activated receptor-α, p16^INK4A, p21, and gp91phox mRNAs and/or proteins. Stressed aortas had also increased matrix metalloproteinase-2 (MMP-2) and MMP-9 activities. DPP4 inhibition with anagliptin reversed stress-related atherosclerotic lesion formation, and this benefit was abrogated by APN blocking. In vitro, the GLP-1 receptor agonist exenatide stimulated APN expression in 3T3-L1 cells.

CONCLUSIONS

These results indicate that the DPP4 inhibition-mediated benefits are likely attributable, at least in part, to attenuation of plaque inflammation, oxidative stress and proteolysis associated with GLP-1-mediated APN production in ApoE^-/- mice under stress. Thus, DPP4 will be a novel therapeutic target for the treatment of stress-related cardiovascular disease.

Xanthine oxidase inhibition by febuxostat attenuates stress-induced hyperuricemia, glucose dysmetabolism, and prothrombotic state in mice

Chronic stress is closely linked to the metabolic syndrome, diabetes, hyperuricemia and thromboembolism, but the mechanisms remain elusive. We reported recently that stress targets visceral adipose tissue (VAT), inducing lipolysis, low-grade inflammation with production of inflammatory adipokines, metabolic derangements such as insulin resistance, and prothrombotic state. In the present study, we hypothesized the involvement of VAT xanthine oxidoreductase (XOR), a source of reactive oxygen species (ROS) and uric acid (UA) in the above processes. Restraint stress in mice resulted in upregulation of XOR and xanthine oxidase activity, accumulation of ROS in VAT as well as liver and intestine, increase in serum UA levels, upregulation of NADPH oxidase subunits and downregulation of antioxidant enzymes. Immunohistochemistry and RT-PCR analysis also showed that restraint stress induced VAT monocyte accumulation and proinflammatory adipokine production, resulting in reduced insulin sensitivity and induction of plasminogen activator inhibitor-1 and tissue factor in VAT. Treatment with febuxostat, a potent XO inhibitor, suppressed stress-induced ROS production and VAT inflammation, resulting in improvement of serum UA levels, insulin sensitivity, and prothrombotic tendency. Our results suggest that stress perturbs glucose and UA metabolism, and promotes prothrombotic status, and that XO inhibition by febuxostat might be a potential therapy for stress-related disorders.

Dipeptidyl peptidase- IV inhibitor alogliptin improves stress-induced insulin resistance and prothrombotic state in a murine model

BACKGROUND

Stress evokes lipolytic release of free fatty acid (FFA) and low-grade inflammation in visceral adipose tissue, mediated by increased adipokine secretion, and contributes to glucose metabolism disorder and prothrombotic state. We tested the hypothesis that alogliptin, a dipeptidyl peptidase-4 inhibitor, can ameliorate the biological effects of chronic stress in mice.

METHOD AND RESULTS

C57BL/6J mice were subjected to 2-week intermittent restraint stress and orally treated with vehicle or alogliptin (dose: 15 or 45mg/kg/day). Plasma levels of lipids, proinflammatory cytokines (monocyte chemoattractant protein-1, tumor necrosis factor-α, and interleukin-6), and 8-hydroxydeoxyguanosine were measured with enzyme-linked immunosorbent assay. Monocyte/macrophage accumulation in inguinal white adipose tissue (WAT) was examined by CD11b-positive cell count and mRNA expression of CD68 and F4/80 was examined by immunohistochemistry and RT-PCR, respectively. The mRNA levels of the above-mentioned proinflammatory cytokines, NADPH oxidase 4, adiponectin, and coagulation factors (plasminogen activation inhibitor-1 and tissue factor) in WAT were also assessed with RT-PCR. Glucose metabolism was assessed by glucose and insulin tolerance tests, plasma levels of DPP-4 activity, glucagon-like peptide-1, expression of DPP-4, insulin receptor substrate-1 and glucose transporter 4 in WAT and skeletal muscle. Alogliptin administration suppressed stress-induced FFA release, oxidative stress, adipose tissue inflammation, DPP-4 activation, and prothrombotic state in a dose-dependent manner, and improved insulin sensitivity in stressed mice.

CONCLUSIONS

The results indicate that alogliptin improves stress-induced prothrombotic state and insulin resistance; suggesting that alogliptin could have beneficial therapeutic effects against cardiovascular complications in diabetic patients under stress.

Peroxisome proliferator-activated receptor α-dependent renoprotection of murine kidney by irbesartan

Activation of renal peroxisome proliferator-activated receptor α (PPARα) is renoprotective, but there is no safe PPARα activator for patients with chronic kidney disease (CKD). Studies have reported that irbesartan (Irbe), an angiotensin II receptor blocker (ARB) widely prescribed for CKD, activates hepatic PPARα. However, Irbe's renal PPARα-activating effects and the role of PPARα signalling in the renoprotective effects of Irbe are unknown. Herein, these aspects were investigated in healthy kidneys of wild-type (WT) and Ppara-null (KO) mice and in the murine protein-overload nephropathy (PON) model respectively. The results were compared with those of losartan (Los), another ARB that does not activate PPARα. PPARα and its target gene expression were significantly increased only in the kidneys of Irbe-treated WT mice and not in KO or Los-treated mice, suggesting that the renal PPARα-activating effect was Irbe-specific. Irbe-treated-PON-WT mice exhibited decreased urine protein excretion, tubular injury, oxidative stress (OS), and pro-inflammatory and apoptosis-stimulating responses, and they exhibited maintenance of fatty acid metabolism. Furthermore, the expression of PPARα and that of its target mRNAs encoding proteins involved in OS, pro-inflammatory responses, apoptosis and fatty acid metabolism was maintained upon Irbe treatment. These renoprotective effects of Irbe were reversed by the PPARα antagonist MK886 and were not detected in Irbe-treated-PON-KO mice. These results suggest that Irbe activates renal PPARα and that the resultant increased PPARα signalling mediates its renoprotective effects.