Fasting induces the expression of PGC-1α and ERR isoforms in the outer stripe of the outer medulla (OSOM) of the mouse kidney

Peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) family in physiological and pathophysiological process and diseases

Peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) family (PGC-1s), consisting of three members encompassing PGC-1α, PGC-1β, and PGC-1-related coactivator (PRC), was discovered more than a quarter-century ago. PGC-1s are essential coordinators of many vital cellular events, including mitochondrial functions, oxidative stress, endoplasmic reticulum homeostasis, and inflammation. Accumulating evidence has shown that PGC-1s are implicated in many diseases, such as cancers, cardiac diseases and cardiovascular diseases, neurological disorders, kidney diseases, motor system diseases, and metabolic disorders. Examining the upstream modulators and co-activated partners of PGC-1s and identifying critical biological events modulated by downstream effectors of PGC-1s contribute to the presentation of the elaborate network of PGC-1s. Furthermore, discussing the correlation between PGC-1s and diseases as well as summarizing the therapy targeting PGC-1s helps make individualized and precise intervention methods. In this review, we summarize basic knowledge regarding the PGC-1s family as well as the molecular regulatory network, discuss the physio-pathological roles of PGC-1s in human diseases, review the application of PGC-1s, including the diagnostic and prognostic value of PGC-1s and several therapies in pre-clinical studies, and suggest several directions for future investigations. This review presents the immense potential of targeting PGC-1s in the treatment of diseases and hopefully facilitates the promotion of PGC-1s as new therapeutic targets.

Arginine Methylation of the PGC-1α C-Terminus Is Temperature-Dependent

We set out to determine whether the C-terminus (amino acids 481-798) of peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α, UniProt Q9UBK2), a regulatory metabolic protein involved in mitochondrial biogenesis, and respiration, is an arginine methyltransferase substrate. Arginine methylation by protein arginine methyltransferases (PRMTs) alters protein function and thus contributes to various cellular processes. In addition to confirming methylation of the C-terminus by PRMT1 as described in the literature, we have identified methylation by another member of the PRMT family, PRMT7. We performed in vitro methylation reactions using recombinant mammalian PRMT7 and PRMT1 at 37, 30, 21, 18, and 4 °C. Various fragments of PGC-1α corresponding to the C-terminus were used as substrates, and the methylation reactions were analyzed by fluorography and mass spectrometry to determine the extent of methylation throughout the substrates, the location of the methylated PGC-1α arginine residues, and finally, whether temperature affects the deposition of methyl groups. We also employed two prediction programs, PRmePRed and MePred-RF, to search for putative methyltransferase sites. Methylation reactions show that arginine residues R548 and R753 in PGC-1α are methylated at or below 30 °C by PRMT7, while methylation by PRMT1 was detected at these same residues at 30 °C. Computational approaches yielded additional putative methylarginine sites, indicating that since PGC-1α is an intrinsically disordered protein, additional methylated arginine residues have yet to be experimentally verified. We conclude that temperature affects the extent of arginine methylation, with more methylation by PRMT7 occurring below physiological temperature, uncovering an additional control point for PGC-1α.

Study on the experimental verification and regulatory mechanism of Rougui-Ganjiang herb-pair for the actions of thermogenesis in brown adipose tissue based on network pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Cinnamomum cassia Presl (Rougui) has character of xin、gan、wen, belongs to Jing of heart、lung、bladder, and has the effect of dispersing cold and relieving pain. It is widely used to resolve the exterior and dissipate cold in Treatise on Febrile Diseases (Shang Han Lun), such as Chaihu Guizhi Ganjiang Tang and Guizhi Renshen Tang. Both these two prescriptions contain Cinnamomum cassia Presl and Zingiber officinale Rosc (Ganjiang). Rougui-Ganjiang herb-pair (RGHP) can warm viscera and remove cold, which is widely used in Shang Han Lun. And in modern times, recent studies have showed that cinnamon and ginger also have the effect of thermogenesis and regulating the body temperature, respectively.

AIM OF THE STUDY

To maintain the body thermal homeostasis and prevent cold invasion of main organs, in this study, we assessed the underlying physiological changes induced by RGHP in mice exposed to -20 °C and explored the mechanisms for the thermogenic actions of RGHP in brown adipose tissue (BAT) by network pharmacology and molecular docking.

MATERIALS AND METHODS

Male Kunming (KM) mice were fed normal diet with orally administration of distilled water or ethanol RGHP extract (three doses: 375,750 and 1500 mg/kg) for 21 days, once per day and then exposed to -20 °C for 2 h. The core temperature, activity ability and the degree of frostbite in mice, morphological and ATP content of adipocytes were measured. In addition, the network pharmacology was employed to predict the targets of RGHP' s thermogenesis effect on BAT. Pathway analysis and biological process with key genes was carried out through KEGG and GO analysis, respectively. Furthermore, the core ingredients and targets obtained by network pharmacology were verified by molecular docking and Western blot assays.

RESULTS

RGHP can significantly increase the core body temperature, reduce the degree of frostbite and enhance the activity ability of mice after cold exposure. Meanwhile, it can also improve the lipid morphology and decrease ATP production in BAT. A network pharmacology-based analysis identified 246 ingredients from RGHP (two herbs), which related to 222 target genes. There were 8 common genes between 222 compounds target genes and 62 thermogenesis associated target genes, which linked to 49 potential compounds. There are 24 ingredients which degree are greater than the average. Among them, we found that oleic acid, EIC, 6-gingerol, eugenol, isohomogenol and sitogluside could be detected in mice plasma. The cAMP-PPAR signaling pathway was enriched for thermogenesis after KEGG analysis with 8 genes. Molecular docking analysis and Western blot assay further confirmed that oleic acid, 6-gingerol, eugenol and isohomogenol were potential active ingredients for RGHP's heat production effect. And UCP1, PGC-1α, PPARα and PPARγ are key thermogenesis proteins.

CONCLUSIONS

RGHP treatment can significantly maintain the rectal temperature of mice by enhancing the BAT heat production. RGHP exhibited the heat production effect, which might be mainly attributed to increasing thermogenesis through the cAMP-PPAR signaling pathway in cold exposure mice. Oleic acid, 6-gingerol, eugenol and isohomogenol might be considered the potential therapeutic ingredients which affect the key targets of thermogenesis effect.

PPARγ/PGC1α signaling as a potential therapeutic target for mitochondrial biogenesis in neurodegenerative disorders

Neurodegenerative diseases represent some of the most devastating neurological disorders, characterized by progressive loss of the structure and function of neurons. Current therapy for neurodegenerative disorders is limited to symptomatic treatment rather than disease modifying interventions, emphasizing the desperate need for improved approaches. Abundant evidence indicates that impaired mitochondrial function plays a crucial role in pathogenesis of many neurodegenerative diseases and so biochemical factors in mitochondria are considered promising targets for pharmacological-based therapies. Peroxisome proliferator-activated receptors-γ (PPARγ) are ligand-inducible transcription factors involved in regulating various genes including peroxisome proliferator-activated receptor gamma co-activator-1 alpha (PGC1α). This review summarizes the evidence supporting the ability of PPARγ-PGC1α to coordinately up-regulate the expression of genes required for mitochondrial biogenesis in neurons and provide directions for future work to explore the potential benefit of targeting mitochondrial biogenesis in neurodegenerative disorders. We have highlighted key roles of NRF2, uncoupling protein-2 (UCP2), and paraoxonase-2 (PON2) signaling in mediating PGC1α-induced mitochondrial biogenesis. In addition, the status of PPARγ modulators being used in clinical trials for Parkinson's disease (PD), Alzheimer's disease (AD) and Huntington's disease (HD) has been compiled. The overall purpose of this review is to update and critique our understanding of the role of PPARγ-PGC1α-NRF2 in the induction of mitochondrial biogenesis together with suggestions for strategies to target PPARγ-PGC1α-NRF2 signaling in order to combat mitochondrial dysfunction in neurodegenerative disorders.

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.

Lifestyle and Food Habits Impact on Chronic Diseases: Roles of PPARs

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors that exert important functions in mediating the pleiotropic effects of diverse exogenous factors such as physical exercise and food components. Particularly, PPARs act as transcription factors that control the expression of genes implicated in lipid and glucose metabolism, and cellular proliferation and differentiation. In this review, we aim to summarize the recent advancements reported on the effects of lifestyle and food habits on PPAR transcriptional activity in chronic disease.

PPARs as Nuclear Receptors for Nutrient and Energy Metabolism

It has been more than 36 years since peroxisome proliferator-activated receptors (PPARs) were first recognized as enhancers of peroxisome proliferation. Consequently, many studies in different fields have illustrated that PPARs are nuclear receptors that participate in nutrient and energy metabolism and regulate cellular and whole-body energy homeostasis during lipid and carbohydrate metabolism, cell growth, cancer development, and so on. With increasing challenges to human health, PPARs have attracted much attention for their ability to ameliorate metabolic syndromes. In our previous studies, we found that the complex functions of PPARs may be used as future targets in obesity and atherosclerosis treatments. Here, we review three types of PPARs that play overlapping but distinct roles in nutrient and energy metabolism during different metabolic states and in different organs. Furthermore, research has emerged showing that PPARs also play many other roles in inflammation, central nervous system-related diseases, and cancer. Increasingly, drug development has been based on the use of several selective PPARs as modulators to diminish the adverse effects of the PPAR agonists previously used in clinical practice. In conclusion, the complex roles of PPARs in metabolic networks keep these factors in the forefront of research because it is hoped that they will have potential therapeutic effects in future applications.

Disruption of peroxisome proliferator-activated receptor γ coactivator (PGC)-1α reverts key features of the neoplastic phenotype of glioma cells

The peroxisome proliferator-activated receptor γ coactivator (PGC)-1α is a master regulator of mitochondrial biogenesis and controls metabolism by coordinating transcriptional events. Here, we interrogated whether PGC-1α is involved in tumor growth and the metabolic flexibility of glioblastoma cells. PGC-1α was expressed in a subset of established glioma cell lines and primary glioblastoma cell cultures. Furthermore, a higher PGC-1α expression was associated with an adverse outcome in the TCGA glioblastoma dataset. Suppression of PGC-1α expression by shRNA in the PGC-1α-positive U343MG glioblastoma line suppressed mitochondrial gene expression, reduced mitochondrial membrane potential, and diminished oxygen as well as glucose consumption, and lactate production. Compatible with the known PGC-1α functions in reactive oxygen species (ROS) metabolism, glioblastoma cells deficient in PGC-1α displayed ROS accumulation, had reduced RNA levels of proteins involved in ROS detoxification, and were more susceptible to death induction by H₂O₂ compared with control cells. PGC-1αsh cells also had impaired proliferation and migration rates in vitro and displayed less stem cell characteristics. Complementary effects were observed in PGC-1α-low LNT-229 cells engineered to overexpress PGC-1α. In an in vivo xenograft experiment, tumors formed by U343MG PGC-1αsh glioblastoma cells grew much slower than control tumors and were less invasive. Interestingly, the PGC-1α knockdown conferred protection against hypoxia-induced cell death, probably as a result of less active anabolic pathways, and this effect was associated with reduced epidermal growth factor expression and mammalian target of rapamycin signaling. In summary, PGC-1α modifies the neoplastic phenotype of glioblastoma cells toward more aggressive behavior and therefore makes PGC-1α a potential target for anti-glioblastoma therapies.

Pivotal Roles of Peroxisome Proliferator-Activated Receptors (PPARs) and Their Signal Cascade for Cellular and Whole-Body Energy Homeostasis

Peroxisome proliferator-activated receptors (PPARs), members of the nuclear receptor superfamily, are important in whole-body energy metabolism. PPARs are classified into three isoforms, namely, PPARα, β/δ, and γ. They are collectively involved in fatty acid oxidation, as well as glucose and lipid metabolism throughout the body. Importantly, the three isoforms of PPARs have complementary and distinct metabolic activities for energy balance at a cellular and whole-body level. PPARs also act with other co-regulators to maintain energy homeostasis. When endogenous ligands bind with these receptors, they regulate the transcription of genes involved in energy homeostasis. However, the exact molecular mechanism of PPARs in energy metabolism remains unclear. In this review, we summarize the importance of PPAR signals in multiple organs and focus on the pivotal roles of PPAR signals in cellular and whole-body energy homeostasis.

Estrogen-related receptor (ERR) γ protects against puromycin aminonucleoside-induced podocyte apoptosis by targeting PI3K/Akt signaling

Accumulating evidence has shown that podocyte apoptosis is of vital importance for the development of glomerulosclerosis and progressive loss of renal function. However, the molecular mechanisms leading to podocyte apoptosis are still elusive. In this study, we investigated the role of estrogen-related receptor (ERR) γ in podocyte apoptosis, as well as the underlying mechanisms. Treatment of PAN caused a dose- and time-dependent podocyte apoptosis in line with a significant downregulation of ERRγ. Interestingly, the occurrence of ERRγ downregulation appeared earlier than the onset of cell apoptosis, suggesting a potential that ERRγ reduction triggered apoptotic response in podocyte. To test this hypothesis, ERRγ siRNA was administered to the podocytes. Strikingly, ERRγ silencing resulted in a significant cell apoptosis accompanied with increased injury markers of B7-1 and cathepsin L and decreased podocyte protein nephrin. In contrast, overexpression of ERRγ remarkably attenuated PAN-induced cell apoptosis. Moreover, ERRγ overexpression stimulated PI3K/Akt signaling pathway evidenced by increased expression of PI3K subunits p85α and p110α and phosphorylated Akt. Importantly, a specific PI3K inhibitor LY294002 entirely reversed the anti-apoptotic effect of ERRγ following PAN treatment. Finally, we observed a striking downregulation of ERRγ in PAN-treated rat kidneys, suggesting that our cell model replicated the in vivo condition. Taken together, these data highly suggested that ERRγ played a novel role in modulating podocyte apoptosis by targeting PI3K/Akt signaling pathway.

Estrogen-Related Receptor α (ERRα) is required for adaptive increases in PGC-1 isoform expression during electrically stimulated contraction of adult cardiomyocytes in sustained hypoxic conditions

BACKGROUND AND OBJECTIVES

In adult myocardium, Estrogen-Related Receptor α (ERRα) programs energetic capacity of cardiomyocytes by regulating expression of target genes required for mitochondrial biogenesis, fatty acid metabolism and oxidative phosphorylation. Transcriptional activation by ERRα is dependent on the α or β isoform of Peroxisome Proliferator-Activated Receptor γ Coactivator-1 (PGC-1). This study utilized a model of continuously contracting adult cardiomyocytes to determine the effects of sustained oxygen reduction (hypoxia) on ERRα target gene expression.

METHODS AND RESULTS

Adult feline cardiomyocytes in primary culture were electrically stimulated to contract at 1 Hz in either normoxia (21% O2) or hypoxia (0.5% O2). Compared to normoxia, hypoxia increased PGC-1α mRNA and PGC-1β mRNA levels by 16-fold and 14-fold after 24h. ERRα mRNA levels were increased 3-fold by hypoxia over the same time period. Treatment of cardiomyocytes with XCT-790, an ERRα inverse agonist, caused knockdown of ERRα protein expression. The increases in PGC-1 mRNA levels in response to hypoxia were blocked by XCT-790 treatment, which indicates that expression of PGC-1 isoforms is dependent on ERRα activity. The products of two ERRα target genes required for energy metabolism, Cox6c mRNA and Fabp3 mRNA, increased by 4.5-fold and 3.5 fold after 24h of hypoxia as compared to normoxic controls. These increases were blocked by XCT-790 treatment of hypoxic cardiomyocytes with a concomitant decrease in ERRα expression.

CONCLUSIONS

ERRα activity is required to increase expression of PGC-1 isoforms and downstream target genes as part of the adaptive response of contracting adult cardiomyocytes to sustained hypoxia.

Nuclear hormone receptor expression in mouse kidney and renal cell lines

Nuclear hormone receptors (NHRs) are transcription factors that regulate carbohydrate and lipid metabolism, immune responses, and inflammation. Although several NHRs, including peroxisome proliferator-activated receptor-γ (PPARγ) and PPARα, demonstrate a renoprotective effect in the context of diabetic nephropathy (DN), the expression and role of other NHRs in the kidney are still unrecognized. To investigate potential roles of NHRs in the biology of the kidney, we used quantitative real-time polymerase chain reaction to profile the expression of all 49 members of the mouse NHR superfamily in mouse kidney tissue (C57BL/6 and db/m), and cell lines of mesangial (MES13), podocyte (MPC), proximal tubular epithelial (mProx24) and collecting duct (mIMCD3) origins in both normal and high-glucose conditions. In C57BL/6 mouse kidney cells, hepatocyte nuclear factor 4α, chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) and COUP-TFIII were highly expressed. During hyperglycemia, the expression of the NHR 4A subgroup including neuron-derived clone 77 (Nur77), nuclear receptor-related factor 1, and neuron-derived orphan receptor 1 significantly increased in diabetic C57BL/6 and db/db mice. In renal cell lines, PPARδ was highly expressed in mesangial and proximal tubular epithelial cells, while COUP-TFs were highly expressed in podocytes, proximal tubular epithelial cells, and collecting duct cells. High-glucose conditions increased the expression of Nur77 in mesangial and collecting duct cells, and liver x receptor α in podocytes. These data demonstrate NHR expression in mouse kidney cells and cultured renal cell lines and suggest potential therapeutic targets in the kidney for the treatment of DN.