PPARs and the kidney in metabolic syndrome

Morroniside attenuates podocytes lipid deposition in diabetic nephropathy: A network pharmacology, molecular docking and experimental validation study

BACKGROUND

Dysregulation of lipid metabolism is a key factor influencing the progression of diabetic nephropathy (DN). Morroniside (MOR) is a major active compound isolated from the traditional Chinese herb Cornus officinalis, our previous research found that it can improve the lipid deposition of renal tubular epithelial cells. The purpose of this study is to explore whether MOR can improve podocyte lipid deposition and its mechanism of reducing DN.

METHODS

Initially, we used network pharmacology and bioinformatics techniques to predict the relationship between renal lipid metabolism of MOR and DN. Subsequently, the binding activity of MOR with lipid-related proteins was studied by molecular docking to determine how MOR acts through these proteins. After determining the target of MOR, animal experiments and cell tests were carried out to verify it.

RESULTS

Using network pharmacology, bioinformatics, and molecular docking, target proteins for MOR treatment of DN were predicted and screened, including PGC-1α, LXRs, ABCA1, PPARY, CD36, and nephrin. It is particularly noted that MOR effectively binds to PGC-1α, while LXRs, ABCA1, PPARY and CD36 are downstream molecules of PGC-1α. Silencing the PGC-1α gene significantly reduced the therapeutic effects of MOR. Conversely, in groups without PGC-1α knockdown, MOR was able to increase the expression levels of PGC-1α and influence the expression of downstream proteins. Furthermore, through in vivo and in vitro experiments, utilizing techniques such as lipid droplet staining, PAS, MASSON staining, immunofluorescence, and Western blot, we found that MOR effectively elevated the expression levels of the podocyte protein nephrin and lipid metabolism-regulating proteins PGC-1α, PPARY, and ABCA1, while significantly inhibiting the expression of the lipid accumulation promoter CD36.

CONCLUSION

MOR can regulate the cholesterol efflux in podocytes via the PGC-1α/LXRs/ABCA1 signaling pathway, and control cholesterol intake via the PGC-1α/PPARY/CD36 signaling pathway, thereby ameliorating lipid deposition in DN.

Why is chronic kidney disease progressive? Evolutionary adaptations and maladaptations

Despite significant advances in renal physiology, the global prevalence of chronic kidney disease (CKD) continues to increase. The emergence of multicellular organisms gave rise to increasing complexity of life resulting in trade-offs reflecting ancestral adaptations to changing environments. Three evolutionary traits shape CKD over the lifespan: 1) variation in nephron number at birth, 2) progressive nephron loss with aging, and 3) adaptive kidney growth in response to decreased nephron number. Although providing plasticity in adaptation to changing environments, the cell cycle must function within constraints dictated by available energy. Prioritized allocation of energy available through the placenta can restrict fetal nephrogenesis, a risk factor for CKD. Moreover, nephron loss with aging is a consequence of cell senescence, a pathway accelerated by adaptive nephron hypertrophy that maintains metabolic homeostasis at the expense of increased vulnerability to stressors. Driven by reproductive fitness, natural selection operates in early life but diminishes thereafter, leading to an exponential increase in CKD with aging, a product of antagonistic pleiotropy. A deeper understanding of the evolutionary constraints on the cell cycle may lead to manipulation of the balance between progenitor cell renewal and differentiation, regulation of cell senescence, and modulation of the balance between cell proliferation and hypertrophy. Application of an evolutionary perspective may enhance understanding of adaptation and maladaptation by nephrons in the progression of CKD, leading to new therapeutic advances.

Smad3 Mediates Diabetic Dyslipidemia and Fatty Liver in db/db Mice by Targeting PPARδ

Transforming growth factor-β (TGF-β)/Smad3 signaling has been shown to play important roles in fibrotic and inflammatory diseases. However, the role of Smad3 in dyslipidemia and non-alcoholic fatty liver disease (NAFLD) in type 2 diabetes remains unclear, and whether targeting Smad3 has a therapeutic effect on these metabolic abnormalities remains unexplored. These topics were investigated in this study in Smad3 knockout (KO)-db/db mice and by treating db/db mice with a Smad3-specific inhibitor SIS3. Compared to Smad3 wild-type (WT)-db/db mice, Smad3 KO-db/db mice were protected against dyslipidemia and NAFLD. Similarly, treatment of db/db mice with SIS3 at week 4 before the onset of type 2 diabetes until week 12 was capable of lowering blood glucose levels and improving diabetic dyslipidemia and NAFLD. In addition, using RNA-sequencing, the potential Smad3-target genes related to lipid metabolism was identified in the liver tissues of Smad3 KO/WT mice, and the regulatory mechanisms were investigated. Mechanistically, we uncovered that Smad3 targeted peroxisome proliferator-activated receptor delta (PPARδ) to induce dyslipidemia and NAFLD in db/db mice, which was improved by genetically deleting and pharmacologically inhibiting Smad3.

Maternal High-Fat Diet Controls Offspring Kidney Health and Disease

A balanced diet during gestation is critical for fetal development, and excessive intake of saturated fats during gestation and lactation is related to an increased risk of offspring kidney disease. Emerging evidence indicates that a maternal high-fat diet influences kidney health and disease of the offspring via so-called renal programming. This review summarizes preclinical research documenting the connection between a maternal high-fat diet during gestation and lactation and offspring kidney disease, as well as the molecular mechanisms behind renal programming, and early-life interventions to offset adverse programming processes. Animal models indicate that offspring kidney health can be improved via perinatal polyunsaturated fatty acid supplementation, gut microbiota changes, and modulation of nutrient-sensing signals. These findings reinforce the significance of a balanced maternal diet for the kidney health of offspring.

Reno- and hepato-protective effect of allopurinol after renal ischemia/reperfusion injury: Crosstalk between xanthine oxidase and peroxisome proliferator-activated receptor gamma signaling

Renal ischemia/reperfusion (I/R) is a common cause of acute kidney injury and remote liver damage is an ultimate negative outcome. Current treatments for I/R typically involve the use of antioxidants and anti-inflammatory to protect against oxidative stress and inflammation. Xanthine oxidase (XO) and PPAR-γ contribute to renal I/R-induced oxidative stress; however, the crosstalk between the two pathways remains unexplored. In the present study, we report that XO inhibitor, allopurinol (ALP), protects kidney and liver after renal I/R by PPAR-γ activation. Rats with renal I/R showed reduced kidney and liver functions, increased XO, and decreased PPAR-γ. ALP increased PPAR-γ expression and improved liver and kidney functions. ALP also reduced inflammation and nitrosative stress indicated by reduction in TNF-α, iNOS, nitric oxide (NO), and peroxynitrite formation. Interestingly, rats co-treated with PPAR-γ inhibitor, BADGE, and ALP showed diminished beneficial effect on renal and kidney functions, inflammation, and nitrosative stress. This data suggests that downregulation of PPAR-γ contributes to nitrosative stress and inflammation in renal I/R and the use of ALP reverses this effect by increasing PPAR-γ expression. In conclusion, this study highlights the potential therapeutic value of ALP and suggests targeting XO-PPAR-γ pathway as a promising strategy for preventing I/R injury.

Dietary regulation of peroxisome proliferator-activated receptors in metabolic syndrome

BACKGROUND

Peroxisome proliferator-activated receptors (PPARs) are a class of ligand-activated nuclear transcription factors, members of the type nuclear receptor superfamily, with three subtypes, namely PPARα, PPARβ/δ, and PPARγ, which play a key role in the metabolic syndrome. In the past decades, a large number of studies have shown that natural products can act by regulating metabolic pathways mediated by PPARs.

PURPOSE

This work summarizes the physiological importance and clinical significance of PPARs and reviews the experimental evidence that natural products mediate metabolic syndrome via PPARs.

METHODS

This study reviews relevant literature on clinical trials, epidemiology, animals, and cell cultures published in NCBI PubMed, Scopus, Web of Science, Google Scholar, and other databases from 2001 to October 2022. Search keywords were "natural product" OR "botanical" OR "phytochemical" AND "PPAR" as well as free text words.

RESULTS

The modulatory involvement of PPARs in the metabolic syndrome has been supported by prior research. It has been observed that many natural products can treat metabolic syndrome by altering PPARs. The majority of currently described natural compounds are mild PPAR-selective agonists with therapeutic effects that are equivalent to synthetic medicines but less harmful adverse effects.

CONCLUSION

PPAR agonists can be combined with natural products to treat and prevent metabolic syndrome. Further human investigations are required because it is unknown how natural products cause harm and how they might have negative impacts.

Pathological pathway analysis in an experimental rheumatoid arthritis model and the tissue repair effect of acupuncture at ST36

Rheumatoid arthritis (RA) is an autoimmune disease that generally affects the joints. In the face of inflammation-induced cartilage and bone damage, RA treatment remains insufficient. While research evidence indicates that acupuncture can exert anti-inflammatory and analgesic effects, improve the joint function of RA patients, and delay the disease, data on whether it can promote RA repair are lacking. Findings from the present work demonstrated that both the antigen-induced arthritis (AIA) and collagen-induced arthritis (CIA) models can simulate joint swelling of RA. The AIA model was more stable than the CIA model, with a higher incidence of successful arthritis modeling. Moreover, the AIA mice model could simulate the signal molecules and related pathological processes of the autoimmune response in RA, as well as major pathways related to RA and antigen immune response mechanisms. Manual acupuncture (MA) at Zusanli (ST36) significantly improved paw redness and swelling, pain, and inflammatory cell infiltration in the joints in AIA mice. The therapeutic effect of MA on AIA is achieved primarily through the regulation of steroid hormone biosynthesis, cell metabolism, and tissue repair processes. MA at ST36 can increase the gene contents of tissue repair growth factors, including PEG3, GADD45A, GDF5, FGF5, SOX2, and ATP6V1C2 in the inflammatory side joints of AIA mice, as well as the gene expression of the anti-inflammatory cytokine IL-10. In conclusion, acupuncture may alleviate RA in the joints via modulating the tissue healing process.

Klotho, Oxidative Stress, and Mitochondrial Damage in Kidney Disease

Reducing oxidative stress stands at the center of a prevention and control strategy for mitigating cellular senescence and aging. Kidney disease is characterized by a premature aging syndrome, and to find a modulator targeting against oxidative stress, mitochondrial dysfunction, and cellular senescence in kidney cells could be of great significance to prevent and control the progression of this disease. This review focuses on the pathogenic mechanisms related to the appearance of oxidative stress damage and mitochondrial dysfunction in kidney disease. In this scenario, the anti-aging Klotho protein plays a crucial role by modulating signaling pathways involving the manganese-containing superoxide dismutase (Mn-SOD) and the transcription factors FoxO and Nrf2, known antioxidant systems, and other known mitochondrial function regulators, such as mitochondrial uncoupling protein 1 (UCP1), B-cell lymphoma-2 (BCL-2), Wnt/β-catenin, peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1 alpha), transcription factor EB, (TFEB), and peroxisome proliferator-activated receptor gamma (PPAR-gamma). Therefore, Klotho is postulated as a very promising new target for future therapeutic strategies against oxidative stress, mitochondria abnormalities, and cellular senescence in kidney disease patients.

PPARG agonist pioglitazone influences diurnal kidney medulla mRNA expression of core clock, inflammation-, and metabolism-related genes disrupted by reverse feeding in mice

This study examined the influence of PPARG activation by pioglitazone (PG) on the mRNA of core clock, inflammation- and metabolism-related genes in the mouse kidney medulla as well as urinary sodium/potassium excretion rhythms disrupted by reverse feeding. Mice were assigned to daytime feeding and nighttime feeding groups. PG 20 mg/kg was administered at 7 am or 7 pm. On day 8 of the feeding intervention, mice were killed at noon and midnight. Kidney medulla expression of Arntl, Clock, Nr1d1, Cry1, Cry2, Per1, Per2, Nfe2l2, Pparg, and Scnn1g was determined by qRT PCR. We measured urinary K⁺ , Na⁺ , urine volume, food, and H₂ O intake. The reverse feeding uncoupled the peripheral clock gene rhythm in mouse kidney tissues. It was accompanied by a decreased expression of Nfe2l2 and Pparg as well as an increased expression of Rela and Scnn1g. These changes in gene expressions concurred with an increase in urinary Na⁺ , K⁺ , water excretion, microcirculation disorders, and cell loss, especially in distal tubules. PG induced the restoration of diurnal core clock gene expression as well as Nfe2l2, Pparg, Scnn1g mRNA, and decreased Rela expressions, stimulating Na⁺ reabsorption and inhibiting K⁺ excretion. PG intake at 7 pm was more effective than at 7 am.

The Potential Role of PPARs in the Fetal Origins of Adult Disease

The fetal origins of adult disease (FOAD) hypothesis holds that events during early development have a profound impact on one’s risk for the development of future adult disease. Studies from humans and animals have demonstrated that many diseases can begin in childhood and are caused by a variety of early life traumas, including maternal malnutrition, maternal disease conditions, lifestyle changes, exposure to toxins/chemicals, improper medication during pregnancy, and so on. Recently, the roles of Peroxisome proliferator-activated receptors (PPARs) in FOAD have been increasingly appreciated due to their wide variety of biological actions. PPARs are members of the nuclear hormone receptor subfamily, consisting of three distinct subtypes: PPARα, β/δ, and γ, highly expressed in the reproductive tissues. By controlling the maturation of the oocyte, ovulation, implantation of the embryo, development of the placenta, and male fertility, the PPARs play a crucial role in the transition from embryo to fetus in developing mammals. Exposure to adverse events in early life exerts a profound influence on the methylation pattern of PPARs in offspring organs, which can affect development and health throughout the life course, and even across generations. In this review, we summarize the latest research on PPARs in the area of FOAD, highlight the important role of PPARs in FOAD, and provide a potential strategy for early prevention of FOAD.

Hypertension and renal disease programming: focus on the early postnatal period

The developmental origin of hypertension and renal disease is a concept highly supported by strong evidence coming from both human and animal studies. During development there are periods in which the organs are more vulnerable to stressors. Such periods of susceptibility are also called 'sensitive windows of exposure'. It was shown that as earlier an adverse event occurs; the greater are the consequences for health impairment. However, evidence show that the postnatal period is also quite important for hypertension and renal disease programming, especially in rodents because they complete nephrogenesis postnatally, and it is also important during preterm human birth. Considering that the developing kidney is vulnerable to early-life stressors, renal programming is a key element in the developmental programming of hypertension and renal disease. The purpose of this review is to highlight the great number of studies, most of them performed in animal models, showing the broad range of stressors involved in hypertension and renal disease programming, with a particular focus on the stressors that occur during the early postnatal period. These stressors mainly include undernutrition or specific nutritional deficits, chronic behavioral stress, exposure to environmental chemicals, and pharmacological treatments that affect some important factors involved in renal physiology. We also discuss the common molecular mechanisms that are activated by the mentioned stressors and that promote the appearance of these adult diseases, with a brief description on some reprogramming strategies, which is a relatively new and promising field to treat or to prevent these diseases.

Revisiting the Principles of Preservation in an Era of Pandemic Obesity

The current obesity epidemic has caused a significant decline in the health of our donor population. Organs from obese deceased donors are more prone to ischemia reperfusion injury resulting from organ preservation. As a consequence, these donors are more likely to be discarded under the assumption that nothing can be done to make them viable for transplant. Our current methods of organ preservation-which remain relatively unchanged over the last ~40 years-were originally adopted in the context of a much healthier donor population. But methods that are suitable for healthier deceased donors are likely not optimal for organs from obese donors. Naturally occurring models of acute obesity and fasting in hibernating mammals demonstrate that obesity and resilience to cold preservation-like conditions are not mutually exclusive. Moreover, recent advances in our understanding of the metabolic dysfunction that underlies obesity suggest that it may be possible to improve the resilience of organs from obese deceased donors. In this mini-review, we explore how we might adapt our current practice of organ preservation to better suit the current reality of our deceased donor population.

The Effect of PPARγ rs1801282 Variant on Mortality Risk Among Asians With Chronic Kidney Disease: A Cohort Study and Meta-Analysis

Background: Chronic kidney disease (CKD) is a public health issue, and an independent risk factor for cardiovascular disease. The peroxisome proliferator-activated receptor gamma (PPARG) plays an important role in the cardiovascular system. Previous studies have examined one important exon polymorphism, Pro12Ala, in PPARG with respect to mortality of CKD patients, but the results were inconsistent and current evidence is insufficient to support a strong conclusion. This study aimed to examine the correlation between Pro12Ala gene polymorphism and mortality among Asians with CKD by trial sequential analysis (TSA).

Methods: The research was divided into observational research and meta-analysis. For the cohort study, 767 subjects from dialysis centers in Taipei were selected as samples, and tracked from December 2015 to February 2017. For the meta-analysis, relevant literature from “PubMed” and “Embase” databases (until December 2016), was searched and TSA was used to verify the results. In order to achieve the best evidence hierarchies, our retrospective cohort study was added to the meta-analysis and the TSA.

Results: The combined sample size for Asian was 1,685 after adding our cohort study, and there was no significant correlation between PPARG Pro12Ala and mortality by the allele model (RR: 0.85, 95% CI: 0.39–1.83, I² = 79.3%). Under the parameter setting with the RR value of 1.5, TSA estimation presented that the cumulative sample size entered into the futility area, and it confirmed the conclusion in this study.

Conclusion: We found that PPARG Pro12Ala gene polymorphism was not related to mortality in CKD Asians patients, and validated our conclusion using TSA after adding our sample.

The Role of Peroxisome Proliferator-Activated Receptors in Kidney Diseases

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily of ligand-activated transcription factors. Accumulating evidence suggests that PPARs may play an important role in the pathogenesis of kidney disease. All three members of the PPAR subfamily, PPARα, PPARβ/δ, and PPARγ, have been implicated in many renal pathophysiological conditions, including acute kidney injury, diabetic nephropathy, and chronic kidney disease, among others. Emerging data suggest that PPARs may be potential therapeutic targets for renal disease. This article reviews the physiological roles of PPARs in the kidney and discusses the therapeutic utility of PPAR agonists in the treatment of kidney disease.

Altered lipidomic profiles in lung and serum of rat after sub-chronic exposure to ozone

Ozone (O) exposure not only causes lung injury and lung inflammation but also changes blood composition. Previous studies have mainly focused on inflammatory processes and metabolic diseases caused by acute or chronic ozone exposure. However, the effect of ozone on lipid expression profiles remains unclear. This study aimed to investigate the lipidomic changes in lung tissue and serum of rats after ozone exposure for three months and explore the lipid metabolic pathway involved in an ozone-induced injury. Based on the non-targeted lipidomic analysis platform of the UPLC Orbitrap mass spectrometry system, we found that sub-chronic exposure to ozone significantly changed the characteristics of lipid metabolism in lungs and serum of rats. First, the variation in sphingomyelin (SM) and triglyceride (TG) levels in the lung and serum after O₃ exposure are shown. SM decreased in both tissues, while TG decreased in the lungs and increased in the serum. Further, the effect of ozone on glycerophospholipids in the lung and serum was completely different. Phosphatidylethanolamine (PE), phosphatidylserine (PS), and phosphatidylinositol (PI) were the major glycerophospholipids whose levels were altered in the lung, while phosphatidylglycerol (PG), phosphatidic acid (PA), and phosphatidylcholine (PC) levels changed dramatically in the serum. Third, after O₃ exposure, the level of monogalactosyldiacylglycerol (MGDG), mainly MGDG (43, 11), a saccharolipid, declined significantly and uniquely in the serum. These results suggested that sub-chronic O₃ exposure may play a role in the development of several diseases through perturbation of lipidomic profiles in the lungs and blood. In addition, changes in the lipids of the lung and blood may induce or exacerbate respiratory diseases.

Nuclear receptors in renal health and disease

As a major social and economic burden for the healthcare system, kidney diseases contribute to the constant increase of worldwide deaths. A deeper understanding of the underlying mechanisms governing the etiology, development and progression of kidney diseases may help to identify potential therapeutic targets. As a superfamily of ligand-dependent transcription factors, nuclear receptors (NRs) are critical for the maintenance of normal renal function and their dysfunction is associated with a variety of kidney diseases. Increasing evidence suggests that ligands for NRs protect patients from renal ischemia/reperfusion (I/R) injury, drug-induced acute kidney injury (AKI), diabetic nephropathy (DN), renal fibrosis and kidney cancers. In the past decade, some breakthroughs have been made for the translation of NR ligands into clinical use. This review summarizes the current understanding of several important NRs in renal physiology and pathophysiology and discusses recent findings and applications of NR ligands in the management of kidney diseases.

Use of Lipid-Modifying Agents for the Treatment of Glomerular Diseases

Although dyslipidemia is associated with chronic kidney disease (CKD), it is more common in nephrotic syndrome (NS), and guidelines for the management of hyperlipidemia in NS are largely opinion-based. In addition to the role of circulating lipids, an increasing number of studies suggest that intrarenal lipids contribute to the progression of glomerular diseases, indicating that proteinuric kidney diseases may be a form of "fatty kidney disease" and that reducing intracellular lipids could represent a new therapeutic approach to slow the progression of CKD. In this review, we summarize recent progress made in the utilization of lipid-modifying agents to lower renal parenchymal lipid accumulation and to prevent or reduce kidney injury. The agents mentioned in this review are categorized according to their specific targets, but they may also regulate other lipid-relevant pathways.

Design, synthesis, and biological evaluation of a novel dual peroxisome proliferator-activated receptor alpha/delta agonist for the treatment of diabetic kidney disease through anti-inflammatory mechanisms

Diabetic kidney disease (DKD) is a major feature of the final stage of nearly all cause types of diabetes mellitus (DM). To date, few safe and effective drugs are available to treat. Peroxisome proliferator-activated receptors (PPARs), comprised of three members: PPAR-α, PPAR-δ and PPAR-γ, play a protective role in the DKD through glycemic control and lipid metabolism, whereas systemic activation of PPAR-γ causes serious side-effects in clinical trials. GFT505 is a dual PPAR-α/δ agonist, and the selectivity against PPAR-γ is still to be improved. Sulfuretin has been shown to suppress the expression of PPAR-γ and improve the pathogenesis of diabetic complications. In this study, by hybridizing the carboxylic acid of GFT505 and the parent nucleus of sulfuretin, we pioneeringly designed and synthetized a series of novel dual PPAR-α/δ agonists, expecting to provide a better benefit/risk ratio for PPARs. Of all the synthesized compounds, compound 12 was identified with highly activity on PPAR-α/δ and higher selectivity against PPAR-γ than that of GFT505 (EC₅₀: hPPAR-α: 0.26 μM vs.0.76 μM; hPPAR-δ: 0.50 μM vs.0.73 μM; hPPAR-γ: 4.22 μM vs.2.79 μM). The molecular docking studies also depicted good binding affinity of compound 12 for PPAR-α and PPAR-δ compared to GFT505. Furthermore, compound 12 exhibited an evidently renoprotective effect on the DKD through inhibiting inflammatory process, which might at least partly via JNK/NF-κB pathways in vivo and in vitro. Overall, compound 12 hold therapeutic promise for DKD.

Nuclear receptors in the kidney during health and disease

Over the last 30 years, nuclear receptors (NRs) have been increasingly recognized as key modulators of systemic homeostasis and as contributing factors in many diseases. In the kidney, NRs play numerous important roles in maintaining homeostasis-many of which continue to be unraveled. As "master regulators", these important transcription factors integrate and coordinate many renal processes such as circadian responses, lipid metabolism, fatty acid oxidation, glucose handling, and inflammatory responses. The use of recently-developed genetic tools and small molecule modulators have allowed for detailed studies of how renal NRs contribute to kidney homeostasis. Importantly, while NRs are intimately involved in proper kidney function, they are also implicated in a variety of renal diseases such as diabetes, acute kidney injury, and other conditions such as aging. In the last 10 years, our understanding of renal disease etiology and progression has been greatly shaped by knowledge regarding how NRs are dysregulated in these conditions. Importantly, NRs have also become attractive therapeutic targets for attenuation of renal diseases, and their modulation for this purpose has been the subject of intense investigation. Here, we review the role in health and disease of six key renal NRs including the peroxisome proliferator-activated receptors (PPAR), estrogen-related receptors (ERR), the farnesoid X receptors (FXR), estrogen receptors (ER), liver X receptors (LXR), and vitamin D receptors (VDR) with an emphasis on recent findings over the last decade. These NRs have generated a wealth of data over the last 10 years that demonstrate their crucial role in maintaining normal renal homeostasis as well as their capacity to modulate disease progression.

Serum metabonomics coupled with HPLC-LTQ/orbitrap MS and multivariate data analysis on the ameliorative effects of Bidens bipinnata L. in hyperlipidemic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Hyperlipidemia (HLP) is a prevalence chronic cardiovascular disease, which is treated by traditional Chinese medicine (TCM) in China. More and more attention has been paid to the application of metabolomics in the study of TCM. Bidens bipinnata L. (BBL), a folk medicine in contemporary China, has the efficacy in the treatment of hyperlipidemia (HLP) in China. However, little is known of the underlying mechanism of BBL. This research aimed to investigate ameliorative effects of BBL on hyperlipidemic rats and explore the mechanism by metabolomics method.

MATERIALS AND METHODS

Hyperlipidemic rats were established by high fat diet (HFD). Biochemical assay was used to evaluate the efficacy of BBL. A metabolomics approach based on high performance liquid chromatography-linear ion trap/orbitrap high-resolution mass spectrometry (HPLC-LTQ/orbitrap MS) was performed to analyze the serum biomarkers from model group, control group and BBL group. Principle component analysis (PCA) and partial least-squares discriminate analysis (PLS-DA) were utilized to identify differences of metabolic profiles in rats among the three groups. In order to identify possible pathways that were affected by HLP, the identified endogenous metabolites were analyzed by using MetaboAnalyst. In the network pharmacology study, our research group found that PPAR signaling pathway was the most important pathway of BBL in the treatment of HLP. Then, it was found that changes in the major metabolic pathways would affect the PPAR signaling pathway through comprehensive analysis based on KEGG database. Therefore, the expression of key genes in the PPAR signaling pathway was detected by real-time quantitative fluorescence PCR (RT-qPCR).

RESULTS

Six metabolites, which showed a significantly restoring trend from HLP to normal condition, were regarded as potential biomarkers of BBL treatment. The levels of phosphorylcholine, mevalonic acid and leukotriene B₄ (LTB₄) increased significantly (P < 0.01) in hyperlipidemic rats, while the levels of linoleic acid, arachidonic acid (AA) and lysophosphatidylcholine (18:0) (Lyso PC (18:0)) decreased significantly (P < 0.01) in comparison with control rats. Those endogenous metabolites were chiefly involved in linoleic acid metabolism, AA metabolism and terpenoid backbone biosynthesis. According to the results of RT-qPCR analysis, the mRNA expressions of PPAR α, PPAR β and PPARγ in model group were difference compared with control group. And the expression difference could be regulated closer to normal level after BBL intervention.

CONCLUSIONS

The results of biochemical assay, serum metabolic pattern and RT-qPCR analysis showed that BBL could exert a significant improvement on lipid levels, liver function, renal function, as well as the mRNA expression level of PPAR signaling pathway.

Soluble (pro)renin receptor treats metabolic syndrome in mice with diet-induced obesity via interaction with PPARγ

The therapies available for management of obesity and associated conditions are limited, because they are often directed toward an individual component of metabolic syndrome and are associated with adverse effects. Here, we report the multifaceted therapeutic potential of histidine-tagged recombinant soluble (pro)renin receptor (sPRR), termed sPRR-His, in a mouse model of diet-induced obesity (DIO). In the DIO model, 2-week administration of sPRR-His lowered body weight and remarkably improved multiple metabolic parameters in the absence of fluid retention. Conversely, inhibition of endogenous sPRR production by PF429242 induced diabetes and insulin resistance, both of which were reversed by the sPRR-His supplement. At the cellular level, sPRR-His enhanced insulin-induced increases in glucose uptake via upregulation of phosphorylated AKT and protein abundance of glucose transporter 4. Promoter and gene expression analysis revealed PRR as a direct target gene of PPARγ. Adipocyte-specific PPARγ deletion induced severe diabetes and insulin resistance associated with reduced adipose PRR expression and circulating sPRR. The sPRR-His supplement in the null mice nearly normalized blood glucose and insulin levels. Additionally, sPRR-His treatment suppressed DIO-induced renal sodium-glucose cotransporter-2 (SGLT2) expression. Overall, sPRR-His exhibits a therapeutic potential in management of metabolic syndrome via interaction with PPARγ.

Importance of thorough tissue and cellular level characterization of targeted drugs in the evaluation of pharmacodynamic effects

Targeted nanoparticle delivery is a promising strategy for increasing efficacy and limiting side effects of therapeutics. When designing a targeted liposomal formulation, the in vivo biodistribution of the particles must be characterized to determine the value of the targeting approach. Peroxisome proliferator-activated receptor (PPAR) agonists effectively treat metabolic syndrome by decreasing dyslipidemia and insulin resistance but side effects have limited their use, making them a class of compounds that could benefit from targeted liposomal delivery. The adipose targeting sequence peptide (ATS) could fit this role, as it has been shown to bind to adipose tissue endothelium and induce weight loss when delivered conjugated to a pro-apoptotic peptide. To date, however, a full assessment of ATS in vivo biodistribution has not been reported, leaving important unanswered questions regarding the exact mechanisms whereby ATS targeting enhances therapeutic efficacy. We designed this study to evaluate the biodistribution of ATS-conjugated liposomes loaded with the PPARα/γ dual agonist tesaglitazar in leptin-deficient ob/ob mice. The ATS-liposome biodistribution in adipose tissue and other organs was examined at the cellular and tissue level using microscopy, flow cytometry, and fluorescent molecular tomography. Changes in metabolic parameters and gene expression were measured by target and off-target tissue responses to the treatment. Unexpectedly, ATS targeting did not increase liposomal uptake in adipose relative to other tissues, but did increase uptake in the kidneys. Targeting also did not significantly alter metabolic parameters. Analysis of the liposome cellular distribution in the stromal vascular fraction with flow cytometry revealed high uptake by multiple cell types. Our findings highlight the need for thorough study of in vivo biodistribution when evaluating a targeted therapy.

Mitochondrial Damage and Activation of the STING Pathway Lead to Renal Inflammation and Fibrosis

Fibrosis is the final common pathway leading to end-stage renal failure. By analyzing the kidneys of patients and animal models with fibrosis, we observed a significant mitochondrial defect, including the loss of the mitochondrial transcription factor A (TFAM) in kidney tubule cells. Here, we generated mice with tubule-specific deletion of TFAM (Ksp-Cre/Tfamflox/flox). While these mice developed severe mitochondrial loss and energetic deficit by 6 weeks of age, kidney fibrosis, immune cell infiltration, and progressive azotemia causing death were only observed around 12 weeks of age. In renal cells of TFAM KO (knockout) mice, aberrant packaging of the mitochondrial DNA (mtDNA) resulted in its cytosolic translocation, activation of the cytosolic cGAS-stimulator of interferon genes (STING) DNA sensing pathway, and thus cytokine expression and immune cell recruitment. Ablation of STING ameliorated kidney fibrosis in mouse models of chronic kidney disease, demonstrating how TFAM sequesters mtDNA to limit the inflammation leading to fibrosis.

Renoprotective effect of Zhenwu decoction against renal fibrosis by regulation of oxidative damage and energy metabolism disorder

Zhenwu decoction (ZWD) is a promising traditional Chinese prescription against renal fibrosis, while its underlying mechanism remains unclear. Rat model of renal fibrosis were established and divided into control group, model group, ZWD treatment group and enalapril maleate treatment group. Metabolic profiles on serum samples from each group were acquired by using ultra performance liquid chromatography coupled with quadrupole time-of-flight high-resolution mass spectrometry. Metabolomics combined with molecular biology were comparatively conducted on samples of various groups. Fifteen potential biomarkers were identified and these biomarkers are mainly phospholipids and fatty acids. The results showed renal fibrosis was associated with oxidative damage and energy metabolism disorder. The results of histopathology, biochemistry and metabolomics demonstrated that ZWD exhibited an efficient renoprotective effect by alleviating oxidative stress, increasing energy metabolism and regulating fibrotic cytokines. This study provided scientific support for the research and development of new drugs from traditional Chinese medicine.

Novel Targets for Treating Ischemia-Reperfusion Injury in the Liver

Liver ischemia-reperfusion injury (IRI) is a major complication of hemorrhagic shock, liver transplantation, and other liver surgeries. It is one of the leading causes for post-surgery hepatic dysfunction, always leading to morbidity and mortality. Several strategies, such as low-temperature reperfusion and ischemic preconditioning, are useful for ameliorating liver IRI in animal models. However, these methods are difficult to perform in clinical surgeries. It has been reported that the activation of peroxisome proliferator activated receptor gamma (PPARγ) protects the liver against IRI, but with unidentified direct target gene(s) and unclear mechanism(s). Recently, FAM3A, a direct target gene of PPARγ, had been shown to mediate PPARγ’s protective effects in liver IRI. Moreover, noncoding RNAs, including LncRNAs and miRNAs, had also been reported to play important roles in the process of hepatic IRI. This review briefly discussed the roles and mechanisms of several classes of important molecules, including PPARγ, FAM3A, miRNAs, and LncRNAs, in liver IRI. In particular, oral administration of PPARγ agonists before liver surgery or liver transplantation to activate hepatic FAM3A pathways holds great promise for attenuating human liver IRI.

Zhen-wu-tang protects against podocyte injury in rats with IgA nephropathy via PPARγ/NF-κB pathway

Zhen-wu-tang (ZWT) has been widely applied in chronic kidney diseases. However, the mechanism of ZWT remains unclear. Peroxisome proliferator-activated receptors-γ (PPARγ) is known as a protective factor for podocyte and kidney function. This study is aimed to investigate the protective effects of ZWT on IgA nephropathy (IgAN) in rats against podocyte injury and the underlying mechanism related to PPARγ. IgAN model rats were induced by administering bovine serum albumin, lipopolysaccharide, and carbon tetrachloride. ZWT at two doses and GW9662 (PPARγ antagonist) was administered once daily for 4 weeks respectively. Cultured podocyte induced by LPS were used to evaluate the podocyte-protective effect and related mechanism of ZWT in vitro. Results showed that ZWT observably reduced proteinuria and hematuria excretion, as well as the levels of blood urea nitrogen, serum creatinine, serum uric acid, low-density lipoprotein cholesterol, total cholesterol and triglycerides, but increased the contents of high-density lipoprotein cholesterol, ameliorating renal function and hyperlipidemia state in IgAN rats. Besides, both ZWT administration groups alleviated kidney pathological lesion, macrophage infiltration, IgA and C3 deposition in glomeruli. To further demonstrate the protective effects of ZWT, we found that podocyte damage was markedly ameliorated with ZWT treatments in IgAN rats and LPS-induced podocyte injury model by suppressing the expressions of desmin, reducing podocyte apoptosis and augmenting nephrin and podocin levels. Moreover, ZWT inhibited the phosphorylation of NF-κB and IκBα, simultaneously upregulated PPARγ. However, GW9662 made no difference in all the above effects compared to the model group, and was reversed by ZWT in vitro study. In conclusion, these results demonstrated that ZWT ameliorated IgAN-induced podocyte injury via upregulation PPARγ and the underlying mechanism might involve the inhibition of NF-κB pathway.

PGC-1α ameliorates kidney fibrosis in mice with diabetic kidney disease through an antioxidative mechanism

The production of reactive oxygen species (ROS) is a common phenomenon in podocyte impairment, which leads to the irreversible progression of chronic kidney diseases, such as diabetic kidney disease (DKD). Previous research has indicated that peroxisome proliferator-activated receptor γ (PPARγ) coactivator-1α (PGC-1α) participates in mitochondrial biogenesis and energy metabolism in certain mitochondria-enriched cells, including myocardial and skeletal muscle cells. Therefore, we hypothesized that PGC-1α may be a protective nuclear factor against energy and oxidative stress in DKD. To investigate this hypothesis, db/db diabetic mice were used to establish a DKD model and the PPARγ agonist rosiglitazone was employed to induce PGC-1α expression in vivo. Additionally, immortalized mouse podocytes and SV40 MES 13 renal mesangial cells were utilized for in vitro experiments. The expression levels of PGC-1α and genes associated with kidney and cell injury were determined by western blotting or reverse transcription-quantitative polymerase chain reaction and intracellular ROS levels were assessed by 2′,7′-dichlorodihydrofluorescein diacetate. The results of the present study demonstrated that endogenous PGC-1α expression exhibited protective effects against oxidative stress, glomerulosclerosis and tubulointerstitial fibrosis in experimental DKD. These results indicated a potential role of PGC-1α in the amelioration of key pathophysiological features of DKD and provided evidence for PGC-1α as a potential therapeutic target in DKD.

Biochemical basis for pharmacological intervention as a reprogramming strategy against hypertension and kidney disease of developmental origin

The concept of "developmental origins of health and disease" (DOHaD) stipulates that both hypertension and kidney disease may take origin from early-life insults. The DOHaD concept also offers reprogramming strategies aiming at shifting therapeutic interventions from adulthood to early life, even before clinical symptoms are evident. Based on those two concepts, this review will present the evidence for the existence of, and the programming mechanisms in, kidney developmental programming that may lead to hypertension and kidney disease. This will be followed by potential pharmacological interventions that may serve as a reprogramming strategy to counter the rising epidemic of hypertension and kidney disease. We point out that before patients could benefit from this strategy, the most pressing issue is for the growing body of evidence from animal studies in support of pharmacological intervention as a reprogramming strategy to long-term protect against hypertension and kidney disease of developmental origins to be validated clinically and the critical window, drug dose, dosing regimen, and therapeutic duration identified.

Peroxisome proliferator activating receptor-γ and the podocyte

Over the past two decades it has become clear that the glomerular podocyte is a key cell in preventing albuminuria, kidney failure and cardiovascular morbidity. Understanding the key pathways that protect the podocyte in times of glomerular stress, which can also be therapeutically manipulated, are highly attractive. In the following review we assess the evidence that the peroxisome proliferator activating receptor (PPAR) agonists are beneficial for podocyte and kidney function with a focus on PPAR-γ. We explain our current understanding of the mechanisms of action of these agonists and the evidence they are beneficial in diabetic and non-diabetic kidney disease. We also outline why these drugs have not been widely used for kidney disease in the past but they may be in the future.

Disease-syndrome combination modeling: metabolomic strategy for the pathogenesis of chronic kidney disease

Conventional disease animal models have limitations on the conformity to the actual clinical situation. Disease-syndrome combination (DS) modeling may provide a more efficient strategy for biomedicine research. Disease model and DS model of renal fibrosis in chronic kidney disease were established by ligating the left ureter and by ligating unilateral ureteral combined with exhaustive swimming, respectively. Serum metabolomics was conducted to evaluate disease model and DS model by using ultra performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry. Potential endogenous biomarkers were identified by multivariate statistical analysis. There are no differences between two models regarding their clinical biochemistry and kidney histopathology, while metabolomics highlights their difference. It is found that abnormal sphingolipid metabolism is a common characteristic of both models, while arachidonic acid metabolism, linolenic acid metabolism and glycerophospholipid metabolism are highlighted in DS model. Metabolomics is a promising approach to evaluate experiment animal models. DS model are comparatively in more coincidence with clinical settings, and is superior to single disease model for the biomedicine research.

Kidney triglyceride accumulation in the fasted mouse is dependent upon serum free fatty acids

Lipid accumulation is a pathological feature of every type of kidney injury. Despite this striking histological feature, physiological accumulation of lipids in the kidney is poorly understood. We studied whether the accumulation of lipids in the fasted kidney are derived from lipoproteins or NEFAs. With overnight fasting, kidneys accumulated triglyceride, but had reduced levels of ceramide and glycosphingolipid species. Fasting led to a nearly 5-fold increase in kidney uptake of plasma [¹⁴C]oleic acid. Increasing circulating NEFAs using a β adrenergic receptor agonist caused a 15-fold greater accumulation of lipid in the kidney, while mice with reduced NEFAs due to adipose tissue deficiency of adipose triglyceride lipase had reduced triglycerides. Cluster of differentiation (Cd)36 mRNA increased 2-fold, and angiopoietin-like 4 (Angptl4), an LPL inhibitor, increased 10-fold. Fasting-induced kidney lipid accumulation was not affected by inhibition of LPL with poloxamer 407 or by use of mice with induced genetic LPL deletion. Despite the increase in CD36 expression with fasting, genetic loss of CD36 did not alter fatty acid uptake or triglyceride accumulation. Our data demonstrate that fasting-induced triglyceride accumulation in the kidney correlates with the plasma concentrations of NEFAs, but is not due to uptake of lipoprotein lipids and does not involve the fatty acid transporter, CD36.

Developmental Origins of Chronic Kidney Disease: Should We Focus on Early Life?

Chronic kidney disease (CKD) is becoming a global burden, despite recent advances in management. CKD can begin in early life by so-called "developmental programming" or "developmental origins of health and disease" (DOHaD). Early-life insults cause structural and functional changes in the developing kidney, which is called renal programming. Epidemiological and experimental evidence supports the proposition that early-life adverse events lead to renal programming and make subjects vulnerable to developing CKD and its comorbidities in later life. In addition to low nephron endowment, several mechanisms have been proposed for renal programming. The DOHaD concept opens a new window to offset the programming process in early life to prevent the development of adult kidney disease, namely reprogramming. Here, we review the key themes on the developmental origins of CKD. We have particularly focused on the following areas: evidence from human studies support fetal programming of kidney disease; insight from animal models of renal programming; hypothetical mechanisms of renal programming; alterations of renal transcriptome in response to early-life insults; and the application of reprogramming interventions to prevent the programming of kidney disease.

Early postnatal treatment with soluble epoxide hydrolase inhibitor or 15-deoxy-Δ(12,14)-prostagandin J2 prevents prenatal dexamethasone and postnatal high saturated fat diet induced programmed hypertension in adult rat offspring

Prenatal dexamethasone (DEX) exposure, postnatal high-fat (HF) intake, and arachidonic acid pathway are closely related to hypertension. We tested whether a soluble epoxide hydrolase (SEH) inhibitor, 12-(3-adamantan-1-yl-ureido)-dodecanoic acid (AUDA) or 15-deoxy-Δ(12,14)-prostagandin J2 (15dPGJ2) therapy can rescue programmed hypertension in the DEX+HF two-hit model. Four groups of Sprague Dawley rats were studied: control, DEX+HF, AUDA, and 15dPGJ2. Dexamethasone (0.1mg/kg body weight) was intraperitoneally administered to pregnant rats from gestational day 16-22. Male offspring received high-fat diet (D12331, Research Diets) from weaning to 4 months of age. In AUDA group, mother rats received 25mg/L in drinking water during lactation. In the 15dPGJ2 group, male offspring received 15dPGJ2 1.5mg/kg BW by subcutaneous injection once daily for 1 week after birth. We found postnatal HF diet aggravated prenatal DEX-induced programmed hypertension, which was similarly prevented by early treatment with AUDA or 15dPGJ2. The beneficial effects of AUDA and 15d-PGJ2 therapy include inhibition of SEH, increases of renal angiotensin converting enzyme-2 (ACE2) and angiotensin II type 2 receptor (AT2R) protein levels, and restoration of nitric oxide bioavailability. Better understanding of the impact of arachidonic acid pathway in the two-hit model will help prevent programmed hypertension in children exposed to corticosteroids and postnatal HF intake.

PPARs Link Early Life Nutritional Insults to Later Programmed Hypertension and Metabolic Syndrome

Hypertension is an important component of metabolic syndrome. Adulthood hypertension and metabolic syndrome can be programmed in response to nutritional insults in early life. Peroxisome proliferator-activated receptors (PPARs) serve as a nutrient-sensing signaling linking nutritional programming to hypertension and metabolic syndrome. All three members of PPARs, PPARα, PPARβ/δ, and PPARγ, are expressed in the kidney and involved in blood pressure control. This review provides an overview of potential clinical applications of targeting on the PPARs in the kidney to prevent programmed hypertension and metabolic syndrome, with an emphasis on the following areas: mechanistic insights to interpret programmed hypertension; the link between the PPARs, nutritional insults, and programmed hypertension and metabolic syndrome; the impact of PPAR signaling pathway in a maternal high-fructose model; and current experimental studies on early intervention by PPAR modulators to prevent programmed hypertension and metabolic syndrome. Animal studies employing a reprogramming strategy via targeting PPARs to prevent hypertension have demonstrated interesting results. It is critical that the observed effects on developmental reprogramming in animal models are replicated in human studies, to halt the globally-growing epidemic of metabolic syndrome-related diseases.

Protective effect of thymol on high fat diet induced diabetic nephropathy in C57BL/6J mice

Obesity is one of several factors implicated in chronic kidney disease (CKD). Thymol, a monoterpene phenolic compound found in the oils of thyme with multiple biological properties especially antidiabetic activity. The present study was undertaken to evaluate the thymol against diabetic nephropathy by high fat diet (HFD)-induced diabetic C57BL/6J mice. After 10 weeks of continuous dietary intervention, HFD (fat- 35.2%) to mice presented characteristic features of progressive nephropathy by significant increased in kidney weight, blood, and urinary parameters, glomerulosclerosis, oxidative stress, hyperlipidemia and subsequent renal injuries. After intragastric administration of thymol (40 mg/kg BW) daily for the subsequent 5 weeks significantly decreased the blood, urinary parameters and kidney weight. Thymol inhibited the activation of transforming growth factor-β1 (TGF-β1) and vascular endothelial growth factor (VEGF). Also, significantly increased the antioxidants and suppresses the lipid peroxidation markers in erythrocytes and kidney tissue compared to the diabetic mice. Thymol downregulated the expression level of sterol regulatory element binding protein-1c (SREBP-1c) and reduced the lipid accumulation in renal. Histopathological study of kidney tissues showed that extracellular mesangial matrix expansion, glomerulosclerosis in diabetic mice were suppressed by thymol. Further, our results indicate that administration of thymol afforded remarkable protection against HFD-induced diabetic nephropathy.

Peroxisome proliferator-activated receptor agonists in a battle against the aging kidney

As aging is a complex phenomenon characterized by intraindividual and interindividual diversities in the maintenance of the homeostatic condition of cells and tissues, changes in renal function are not uniform and depend on associated diseases and environmental factors. Multiple studies have investigated the possible underlying mechanisms of age-related decline in kidney function. Evolutionary, molecular, cellular and systemic theories have been postulated to explain the primary disease independent age-related changes and adaptive responses. As peroxisome proliferator-activated receptors (PPARs) are involved in a broad spectrum of biological processes, PPAR activation might have an effect on the prevention of cell senescence. In this review, we will focus on the experimental and clinical evidence of PPAR agonists in a battle against the aging kidney.

Pathophysiology of the diabetic kidney

Diabetes mellitus contributes greatly to morbidity, mortality, and overall health care costs. In major part, these outcomes derive from the high incidence of progressive kidney dysfunction in patients with diabetes making diabetic nephropathy a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved and of the early dysfunctions observed in the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. Here we review the pathophysiological changes that occur in the kidney in response to hyperglycemia, including the cellular responses to high glucose and the responses in vascular, glomerular, podocyte, and tubular function. The molecular basis, characteristics, and consequences of the unique growth phenotypes observed in the diabetic kidney, including glomerular structures and tubular segments, are outlined. We delineate mechanisms of early diabetic glomerular hyperfiltration including primary vascular events as well as the primary role of tubular growth, hyperreabsorption, and tubuloglomerular communication as part of a "tubulocentric" concept of early diabetic kidney function. The latter also explains the "salt paradox" of the early diabetic kidney, that is, a unique and inverse relationship between glomerular filtration rate and dietary salt intake. The mechanisms and consequences of the intrarenal activation of the renin-angiotensin system and of diabetes-induced tubular glycogen accumulation are discussed. Moreover, we aim to link the changes that occur early in the diabetic kidney including the growth phenotype, oxidative stress, hypoxia, and formation of advanced glycation end products to mechanisms involved in progressive kidney disease.

Polymorphisms in PPAR Genes (PPARD, PPARG, and PPARGC1A) and the Risk of Chronic Kidney Disease in Japanese: Cross-Sectional Data from the J-MICC Study

Chronic kidney disease (CKD) is well known as a strong risk factor for both end stage renal disease and cardiovascular disease. To clarify the association of polymorphisms in the PPAR genes (PPARD, PPARG, and PPARGC1A) with the risk of CKD in Japanese, we examined this association among the Japanese subjects using the cross-sectional data of J-MICC (Japan Multi-Institutional Collaborative Cohort) Study. The subjects for this analysis were 3,285 men and women, aged 35–69 years, selected from J-MICC Study participants; genotyping was conducted by multiplex polymerase chain reaction-based Invader assay. The prevalence of CKD was determined for CKD stages 3–5 (defined as eGFR < 60 ml/min/1.73 m²). Participants with CKD accounted for 17.3% of the study population. When those with PPARD T-842C T/T were defined as reference, those with PPARD T-842C T/C and C/C demonstrated the OR for CKD of 1.26 (95%CI 1.04–1.53) and 1.31 (95%CI 0.83–2.06), respectively. There were no significant associations between the polymorphisms in other PPAR genes and the risk of CKD. The present study found a significantly increased risk of CKD in those with the C allele of PPARD T-842C, which may suggest the possibility of personalized risk estimation of this life-limiting disease in the near future.

Peroxisome proliferator-activated receptor delta protects against obesity-related glomerulopathy through the P38 MAPK pathway

OBJECTIVE

Obesity is a prominent component of metabolic syndrome and a major risk factor for renal disease. The aim of this study was to explore the effect of cross-talk between peroxisome proliferator-activated receptor (PPAR)δ and p38 mitogen-activated protein kinase (p38 MAPK) on obesity-related glomerulopathy.

DESIGN AND METHODS

Male Wistar rats were randomly assigned to standard laboratory chow or a high-fat diet for 32 weeks. Glomerular mesangial cells HBZY-1 and mature differentiation 3T3-L1 cells were cocultured and were transfected with PPARδ-expressing vectors or treated with agonist or inhibitor of PPARδ or p38 MAPK.

RESULTS

Rats on a high-fat diet showed typical characteristics of metabolic syndrome including obesity, dyslipidemia, insulin resistance, and hypertension. Rats on a high-fat diet also had significant glomerular hypertrophy and extracellular matrix accumulation, which were accompanied by increased p38 MAPK phosphorylation and decreased PPARδ expression in the kidney tissue. The roles of p38 MAPK and PPARδ in a coculture system of mesangial cells and mature differentiation 3T3-L1 cells were further explored. PPARδ suppression promoted laminin and type IV collagen secretion through p38 MAPK phosphorylation in mesangial cells, whereas PPARδ overexpression or PPARδ agonist attenuated phosphorylation of p38 MAPK and laminin and type IV collagen secretion.

CONCLUSIONS

The characteristics of obesity-related glomerulopathy, which might be partly caused by PPARδ suppression-induced p38 MAPK activation and laminin and type IV collagen secretion was demonstrated.

Protective effects of peroxisome proliferator-activated receptor agonists on human podocytes: proposed mechanisms of action

BACKGROUND AND PURPOSE

Peroxisome proliferator-activated receptor (PPAR) agonists exert anti-albuminuric effects. However, the nephroprotective effects of these drugs remain to be fully understood. We have investigated whether gemfibrozil, GW0742 and pioglitazone protect human podocytes against nutrient deprivation (ND)-induced cell death and the role of mitochondrial biogenesis as a cytoprotective process.

EXPERIMENTAL APPROACH

Immortalized human podocytes were pre-treated with the PPAR agonists and exposed to ND (5 h) under normoxia, hypoxia or in the presence of pyruvate. Cell death was measured at the end of the ND and of the recovery phase (24 h). Mitochondrial mass, cytochrome c oxidase (COX) subunits 1 and 4 were measured as markers of mitochondrial cell content, while membrane potential as an index of mitochondrial function. PGC-1α, NRF1 and Tfam expression was studied, as crucial regulators of mitochondrial biogenesis.

KEY RESULTS

Cell pre-treatment with gemfibrozil, GW0742, or pioglitazone significantly decreased the ND-induced cell loss, necrosis and apoptosis. These effects were attenuated by hypoxia and potentiated by pyruvate. Pre-treatment with these drugs significantly increased mitochondrial cell content, while it did not affect mitochondrial function. In all these experiments pioglitazone exerted significantly larger effects than gemfibrozil or GW0742.

CONCLUSIONS AND IMPLICATIONS

Gemfibrozil, GW0742 and pioglitazone may exert direct protective effects on human podocytes. Mitochondrial biogenesis is a cell response to the PPAR agonists related to their cytoprotective activity. These results provide a mechanistic support to the clinical evidence indicating PPAR agonists as disease-modifying agents for glomerular diseases.

Nuclear hormone receptors in podocytes

Nuclear receptors are a family of ligand-activated, DNA sequence-specific transcription factors that regulate various aspects of animal development, cell proliferation, differentiation, and homeostasis. The physiological roles of nuclear receptors and their ligands have been intensively studied in cancer and metabolic syndrome. However, their role in kidney diseases is still evolving, despite their ligands being used clinically to treat renal diseases for decades. This review will discuss the progress of our understanding of the role of nuclear receptors and their ligands in kidney physiology with emphasis on their roles in treating glomerular disorders and podocyte injury repair responses.

PPARγ and stress: implications for aging

Complex interactions link psychological stress and aging - stress generally promotes aging processes, and conversely, aging can contribute to stress dysregulation. Stress and aging have remarkably similar effects on brain. Both induce neuroinflammation and alter neuronal metabolism and activity, which to varying extents are causally-linked to the development of stress and aging pathology. As such, induction of one or more of these brain disturbances by either stress or aging could predispose for the development of dysfunction in the other. Notably, peroxisome proliferator-activated receptor γ (PPARγ) is expressed in brain regions that regulate both stress and aging (e.g., hippocampus) and can act to prevent the consequences of aging and stress on the brain. In addition, PPARγ agonists reduce the physiological stress response itself. Thus, PPARγ may represent a critical mechanistic link between brain aging and stress that could hold therapeutic potential for the prevention and treatment of age-related cognitive and mood disorders.

Insulin sensitization with a peroxisome proliferator-activated receptor γ agonist prevents adrenocortical lipid infiltration and secretory changes induced by a high-sucrose diet

It has been hypothesized that deviations in glucocorticoid secretion and/or action may contribute to somatic and biochemical changes observed in patients with and animal models of insulin resistance (IR). In this study, we analyzed changes in rat adrenocortical function and morphology associated with the development of IR, generated in male adult rats by the addition of 30% sucrose to the drinking water. Caloric intake, body and adipose tissue weights, and biochemical parameters associated with IR were determined. Expression levels of Star, Cyp11A1, Mc2r, Pparγ (Pparg), and Cd36 were evaluated by real-time PCR, histochemical analysis of the adrenal cortex was performed using Masson's trichrome and Sudan III staining, and corticosterone levels were measured by RIA. After 7 weeks of sucrose administration, higher serum glucose, insulin, and triglyceride levels and an altered glycemic response to an i.p. insulin test were detected. Adrenal glands showed a neutral lipid infiltration. An increase in Star, Cyp11A1, Mc2r, Pparg and Cd36 and a decrease in Mc2r levels were also found. Furthermore, sucrose-treated animals exhibited higher basal corticosterone levels and a blunted response to ACTH injection. Noteworthy, the adrenocortical (functional and histological) abnormalities were prevented in sucrose-treated rats by the simultaneous administration of an insulin-sensitizing PPARγ agonist. In conclusion, sucrose-induced IR affects adrenocortical morphology and function possibly via the generation of adipokines or lipid metabolites within the adrenal gland. These abnormalities are prevented by the administration of a PPARγ agonist by mechanisms involving both extra- and intra-adrenal effects.

Accelerated renal disease is associated with the development of metabolic syndrome in a glucolipotoxic mouse model

Individuals with metabolic syndrome are at high risk of developing chronic kidney disease (CKD) through unclear pathogenic mechanisms. Obesity and diabetes are known to induce glucolipotoxic effects in metabolically relevant organs. However, the pathogenic role of glucolipotoxicity in the aetiology of diabetic nephropathy is debated. We generated a murine model, the POKO mouse, obtained by crossing the peroxisome proliferator-activated receptor gamma 2 (PPARγ2) knockout (KO) mouse into a genetically obese ob/ob background. We have previously shown that the POKO mice showed: hyperphagia, insulin resistance, hyperglycaemia and dyslipidaemia as early as 4 weeks of age, and developed a complete loss of normal β-cell function by 16 weeks of age. Metabolic phenotyping of the POKO model has led to investigation of the structural and functional changes in the kidney and changes in blood pressure in these mice. Here we demonstrate that the POKO mouse is a model of renal disease that is accelerated by high levels of glucose and lipid accumulation. Similar to ob/ob mice, at 4 weeks of age these animals exhibited an increased urinary albumin:creatinine ratio and significantly increased blood pressure, but in contrast showed a significant increase in the renal hypertrophy index and an associated increase in p27(Kip1) expression compared with their obese littermates. Moreover, at 4 weeks of age POKO mice showed insulin resistance, an alteration of lipid metabolism and glomeruli damage associated with increased transforming growth factor beta (TGFβ) and parathyroid hormone-related protein (PTHrP) expression. At this age, levels of proinflammatory molecules, such as monocyte chemoattractant protein-1 (MCP-1), and fibrotic factors were also increased at the glomerular level compared with levels in ob/ob mice. At 12 weeks of age, renal damage was fully established. These data suggest an accelerated lesion through glucolipotoxic effects in the renal pathogenesis in POKO mice.

The role of nuclear receptors in the kidney in obesity and metabolic syndrome

Nuclear receptors are ligand-activated transcriptional regulators of several key aspects of renal physiology and pathophysiology. As such, nuclear receptors control a large variety of metabolic processes, including kidney lipid metabolism, drug clearance, inflammation, fibrosis, cell differentiation, and oxidative stress. Derangement of nuclear receptor regulation, that is, mainly due to obesity may induce metabolic syndrome, may contribute to the pathogenesis and progression of chronic renal disease and may result in end-stage renal disease. This places nuclear receptors at the forefront of novel therapeutic approaches for a broad range of kidney disorders and diseases, including glomerulosclerosis, tubulointerstitial disease, renal lipotoxicity, kidney fibrosis, and hypertension. This review focuses on the importance of the transcription factors peroxisome proliferator-activated receptor alpha, peroxisome proliferator-activated receptor beta, peroxisome proliferator-activated receptor gamma, liver X receptors, farnesoid X receptor, and the pregnane X receptor/steroid and xenobiotic receptor (PXR) on the physiology and pathophysiology of renal diseases associated with obesity and metabolic syndrome.

PPARγ as a therapeutic target in diabetic nephropathy and other renal diseases

PURPOSE OF REVIEW

Peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-activated nuclear transcription factor that regulates many important physiological processes including glucose and lipid metabolism, energy homeostasis, cell proliferation, inflammation, immunity and reproduction. The current review aims to summarize and discuss recent findings evaluating the protective effects of PPARγ against kidney diseases with a focus on diabetic nephropathy. We will also delineate the potential underlying mechanisms.

RECENT FINDINGS

PPARγ plays important roles in renal physiology and pathophysiology. Agonists of PPARγ exert protective effects against various kidney diseases including diabetic nephropathy, ischemic renal injury, IgA nephropathy, chemotherapy-associated kidney damage, polycystic kidney diseases and age-related kidney diseases via both systemic and renal actions.

SUMMARY

PPARγ agonists are effective in delaying and even preventing the progression of many renal diseases, especially diabetic nephropathy. PPARγ may represent a promising target for the treatment of renal diseases.

Reno-protective mechanisms of epoxyeicosatrienoic acids in cardiovascular disease

Cardiovascular disease (CVD) is the leading cause of mortality worldwide, and it is well known that end-stage renal disease (ESRD) is a profound consequence of the progression of CVD. Present treatments only slow CVD progression to ESRD, and it is imperative that new therapeutic strategies are developed to prevent the incidence of ESRD. Because epoxyeicosatrienoic acids (EETs) have been shown to elicit reno-protective effects in hypertensive animal models, the current review will focus on addressing the reno-protective mechanisms of EETs in CVD. The cytochrome P-450 epoxygenase catalyzes the oxidation of arachidonic acid to EETs. EETs have been identified as endothelium-derived hyperpolarizing factors (EDHFs) with vasodilatory, anti-inflammatory, antihypertensive, and antiplatelet aggregation properties. EETs also have profound effects on vascular migration and proliferation and promote angiogenesis. The progression of CVD has been linked to decreased EETs levels, leading to the concept that EETs should be therapeutically targeted to prevent end-organ damage associated with CVD. However, EETs are quickly degraded by the enzyme soluble epoxide hydrolase (sEH) to their less active diols, dihydroxyeicosatrienoic acids (DHETs). As such, one way to increase EETs level is to inhibit their degradation to DHETs by using sEH inhibitors. Inhibition of sEH has been shown to effectively reduce blood pressure and organ damage in experimental models of CVD. Another approach to target EETs is to develop EET analogs with improved solubility and resistance to auto-oxidation and metabolism by sEH. For example, stable ether EET analogs dilate afferent arterioles and lower blood pressure in hypertensive rodent animal models. EET agonists also improve insulin signaling and vascular function in animal models of metabolic syndrome.