Yuling Chi

Background/Objectives: Clear cell renal cell carcinoma (ccRCC) is the most common form of kidney cancer. Human ccRCCs have increased glycolytic metabolism and decreased mitochondrial oxidative metabolism relative to normal kidneys. Our research using human RCC4 ccRCC cells and a murine model of ccRCC, TRACK (TRAnsgenic model/Cancer/Kidney), in which a triple-mutant (P402A, P564A, N803A) human HIF1α is selectively expressed in proximal tubule cells (PTCs), revealed highly induced ATF4, a stress-responsive transcription factor. We then investigated the role of ATF4 in the metabolic changes in ccRCC. Methods: We performed comprehensive analysis of the ccRCC Cancer Genomics Atlas (TCGA) data. We deleted ATF4 in PTCs of TRACK mice and human RCC4 cells. We conducted genome-wide transcriptomic and untargeted metabolomic studies of cortices of WT and CGERA∆T (TRACK mice with PTC-specific ATF4-knockout (KO)) mice and performed glucose isotopologue tracing in parental and ATF4 KO RCC4 cells. Results: Analysis of TCGA data showed increased mRNAs of enzymes in glycolysis and reduced mRNAs of enzymes in the TCA cycle. Transcriptomic and metabolomic studies demonstrated that ATF4 deletion suppressed glycolysis and enhanced TCA cycle metabolism in CGERA∆T versus WT cortices. Glucose isotopologue tracing showed that ATF4 deletion altered glycolysis pathway metabolite levels and shifted glucose metabolism towards the TCA cycle, evidenced by increased intracellular [¹³C₂]citrate in RCC4-ATF4 KO cells. Using the Seahorse XFe96 analyzer we also showed reduced glycolytic capacity and reserve in RCC4-ATF4 KO cells. Conclusions: Collectively, our results demonstrate that ATF4 regulates glycolysis in ccRCC, supporting ATF4 as a therapeutic target.

Differentially altered expression of transcripts of retinoic acid receptors α, β, γ (Rarα, β, γ), which mediate the actions of all-trans retinoic acid (RA), is observed in glomeruli of nephrotic syndrome (NS) patients vs normal individuals, with Rarβ reduced and both RARα and RARγ increased. Thus, we generated a mouse model (PCRB) with Rarβ specifically deleted in podocytes to define the glomerular actions of Rarβ. Rarβ deletion in PCRB mice results in podocyte loss, podocyte foot process effacement, glomerular basement membrane (GBM) thickening, reduced podocyte adhesion to the GBM, lipid accumulation in glomeruli, and hyperfiltration leading to albuminuria. Genome-wide transcriptomics and proteomics studies of glomeruli revealed that Rarβ deletion increased Mogat, Dgat, and Hmgcs mRNAs, which catalyze triglyceride and cholesterol synthesis, and Slc27a2 and Cd36, which mediate fatty acid uptake, recapitulating NS symptoms. Surprisingly, podocyte-specific Rarβ deletion also increased key mRNAs and proteins involved in fatty acid uptake and lipid biosynthesis in the liver, promoting steatohepatitis and systemic hyperlipidemia. These data indicate that Rarβ signaling in the kidney has a profound impact on both kidney and liver functions and suggest that Rarβ plays an important role in regulating kidney-liver crosstalk. PCRB mice may be a useful model of NS.

Excessive long-term consumption of dietary carbohydrates, including glucose, sucrose, or fructose, has been shown to have significant impact on genome-wide gene expression, which likely results from changes in metabolic substrate flux. However, there has been no comprehensive study on the acute effects of individual sugars on the genome-wide gene expression that may reveal the genetic changes altering signaling pathways, subsequent metabolic processes, and ultimately physiological/pathological responses. Considering that gene expressions in response to acute carbohydrate ingestion might be different in nutrient sensitive and insensitive mammals, we conducted comparative studies of genome-wide gene expression by deep mRNA sequencing of the liver in nutrient sensitive C57BL/6J and nutrient insensitive BALB/cJ mice. Furthermore, to determine the temporal responses, we compared livers from mice in the fasted state and following ingestion of standard laboratory mouse chow supplemented with plain drinking water or water containing 20% glucose, sucrose, or fructose. Supplementation with these carbohydrates induced unique extents and temporal changes in gene expressions in a strain specific manner. Fructose and sucrose stimulated gene changes peaked at 3 h postprandial, whereas glucose effects peaked at 12 h and 6 h postprandial in C57BL/6J and BABL/cJ mice, respectively. Network analyses revealed that fructose changed genes were primarily involved in lipid metabolism and were more complex in C57BL/6J than in BALB/cJ mice. These data demonstrate that there are qualitative and antitative differences in the normal physiological responses of the liver between these two strains of mice and C57BL/6J is more sensitive to sugar intake than BALB/cJ.

C57BL/6J and BALB/cJ mouse strains were analyzed by deep mRNA sequencing of the liver in the fasted state and following ingestion of standard laboratory mouse chow supplemented with plain drinking water or water containing 20% glucose, sucrose or fructose. Supplementation with these carbohydrates induced unique extents and temporal changes in gene expressions in a strain specific manner. Fructose and sucrose stimulated gene changes peaked at 3 h postprandial, whereas glucose effects peaked at 12 h postprandial in C57BL/6J mice and at 6 h postprandial in BABL/cJ mice. Network analyses revealed that fructose changed genes were primarily involved in lipid metabolism and were more complex in C57BL/6J than in BALB/cJ mice. These data demonstrate that there are qualitative and quantitative differences in the normal physiological responses of the liver between these two strains of mice and C57BL/6J is more sensitive to sugar intake than BALB/cJ.

/ SUMMARY: Prostaglandins play fundamental roles in adipose tissue function. While prostaglandin F _2α inhibits adipogenesis, prostaglandin E ₂ promotes adipose beiging. PGF _2α and PGE ₂ are both inactivated through uptake by the plasma membrane transporter (PGT). We hypothesized that inhibiting PGT would increase PGF _2α and PGE ₂ levels, thereby reducing white fat expansion and inducing beiging. Consistent with this hypothesis, inhibiting PGT in mice on high fat diet via genetic knockout or pharmacological blockade reduced body fat stores and induced thermogenesis at thermoneutrality. Inguinal white adipose tissue (iWAT) of these mice exhibited robust UCP1-independent thermogenesis characterized by mitochondrial expansion, coupling of O ₂ consumption to ATP synthesis, and induction of the creatine pathway. Enhanced coupled respiration persisted in PGT-KO iWAT adipocytes in a creatine shuttle-dependent manner. Thus, inhibiting PGT increases mitochondrial biogenesis and coupled respiration—each supported by the creatine pathway in a system lacking UCP1 expression—revealing PGT as a promising drug target against obesity.

One of the main causes of hyperglycemia is inefficient or impaired glucose utilization by skeletal muscle, which can be exacerbated by chronic high caloric intake. Previously, we identified a natural compound, mangiferin (MGF) that improved glucose utilization in high fat diet (HFD)-induced insulin resistant mice. To further identify the molecular mechanisms of MGF action on glucose metabolism, we conducted targeted metabolomics and transcriptomics studies of glycolyic and mitochondrial bioenergetics pathways in skeletal muscle. These data revealed that MGF increased glycolytic metabolites that were further augmented as glycolysis proceeded from the early to the late steps. Consistent with an MGF-stimulation of glycolytic flux there was a concomitant increase in the expression of enzymes catalyzing glycolysis. MGF also increased important metabolites in the tricarboxylic acid (TCA) cycle, such as α-ketoglutarate and fumarate. Interestingly however, there was a reduction in succinate, a metabolite that also feeds into the electron transport chain to produce energy. MGF increased succinate clearance by enhancing the expression and activity of succinate dehydrogenase, leading to increased ATP production. At the transcriptional level, MGF induced mRNAs of mitochondrial genes and their transcriptional factors. Together, these data suggest that MGF upregulates mitochondrial oxidative capacity that likely drives the acceleration of glycolysis flux.

The recent emergence of a worldwide epidemic of metabolic disorders, such as obesity and diabetes, demands effective strategy to develop nutraceuticals or pharmaceuticals to halt this trend. Natural products have long been and continue to be an attractive source of nutritional and pharmacological therapeutics. One such natural product is mangiferin (MGF), the predominant constituent of extracts of the mango plant Mangifera indica L. Reports on biological and pharmacological effects of MGF increased exponentially in recent years. MGF has documented antioxidant and anti‐inflammatory effects. Recent studies indicate that it modulates multiple biological processes involved in metabolism of carbohydrates and lipids. MGF has been shown to improve metabolic abnormalities and disorders in animal models and humans. This review focuses on the recently reported biological and pharmacological effects of MGF on metabolism and metabolic disorders. © 2016 BioFactors, 42(5):492–503, 2016