Mechanistic evaluation of the insulin response in H4IIE hepatoma cells: new endpoints for toxicity testing?

Trans-omics analysis of insulin action reveals a cell growth subnetwork which co-regulates anabolic processes

Insulin signaling promotes anabolic metabolism to regulate cell growth through multi-omic interactions. To obtain a comprehensive view of the cellular responses to insulin, we constructed a trans-omic network of insulin action in Drosophila cells that involves the integration of multi-omic data sets. In this network, 14 transcription factors, including Myc, coordinately upregulate the gene expression of anabolic processes such as nucleotide synthesis, transcription, and translation, consistent with decreases in metabolites such as nucleotide triphosphates and proteinogenic amino acids required for transcription and translation. Next, as cell growth is required for cell proliferation and insulin can stimulate proliferation in a context-dependent manner, we integrated the trans-omic network with results from a CRISPR functional screen for cell proliferation. This analysis validates the role of a Myc-mediated subnetwork that coordinates the activation of genes involved in anabolic processes required for cell growth.

•

A trans-omic network of insulin action in Drosophila cells was constructed

•

Insulin co-regulates various anabolic processes in a time-dependent manner

•

The trans-omic network and a CRISPR screen for cell proliferation were integrated

•

A Myc-mediated subnetwork promoting anabolic processes is required for cell growth

Integration of TGF-β-induced Smad signaling in the insulin-induced transcriptional response in endothelial cells

Insulin signaling governs many processes including glucose homeostasis and metabolism, and is therapeutically used to treat hyperglycemia in diabetes. We demonstrated that insulin-induced Akt activation enhances the sensitivity to TGF-β by directing an increase in cell surface TGF-β receptors from a pool of intracellular TGF-β receptors. Consequently, increased autocrine TGF-β signaling in response to insulin participates in insulin-induced angiogenic responses of endothelial cells. With TGF-β signaling controlling many cell responses, including differentiation and extracellular matrix deposition, and pathologically promoting fibrosis and cancer cell dissemination, we addressed to which extent autocrine TGF-β signaling participates in insulin-induced gene responses of human endothelial cells. Transcriptome analyses of the insulin response, in the absence or presence of a TGF-β receptor kinase inhibitor, revealed substantial positive and negative contributions of autocrine TGF-β signaling in insulin-responsive gene responses. Furthermore, insulin-induced responses of many genes depended on or resulted from autocrine TGF-β signaling. Our analyses also highlight extensive contributions of autocrine TGF-β signaling to basal gene expression in the absence of insulin, and identified many novel TGF-β-responsive genes. This data resource may aid in the appreciation of the roles of autocrine TGF-β signaling in normal physiological responses to insulin, and implications of therapeutic insulin usage.

Role of microRNA-122 in hepatic lipid metabolism of the weanling female rat offspring exposed to prenatal and postnatal caloric restriction

We examined the role of hepatocyte micro-RNA-122 and hypothalamic neuropeptides, in weanling (21d) female rats exposed to calorie restriction induced growth restriction either prenatally (IUGR), postnatally (PNGR) or both (IPGR) vs. ad lib fed controls (CON). IUGR were hyperinsulinemic, hyperleptinemic and dyslipidemic with high circulating miR-122. In contrast, PNGR and IPGR displayed insufficient glucose, insulin and leptin amidst high ketones with a dichotomy in circulating miR-122 of PNGR Collapse

Key Words

• Circadian rhythm
• Energy balance
• Fatty acid oxidation
• Hepatic fatty acid synthesis
• Hypothalamic genes
• Intra-uterine growth restriction
• microRNA-122

Collapse

MESH Headings

• Animals
• Body Weight
• Caloric Restriction/adverse effects
• Circadian Rhythm
• Energy Metabolism
• Fatty Acids/genetics
• Fatty Acids/metabolism
• Female
• Fetal Growth Retardation/etiology
• Gene Expression
• Growth Disorders/etiology
• Hypothalamus/chemistry
• Lipid Metabolism/genetics
• Lipid Metabolism/physiology
• Liver/chemistry
• Liver/metabolism
• MicroRNAs/genetics
• MicroRNAs/physiology
• Organ Size
• Pregnancy
• RNA, Messenger/analysis
• Rats
• Rats, Sprague-Dawley
• Weaning

Collapse

Grants

• R01 HD041230 NICHD NIH HHS
• R01 HD081206 NICHD NIH HHS

Collapse

Affiliation(s)

Yun Dai Department of Pediatrics and the Children's Discovery and Innovation Institute, David Geffen School of Medicine UCLA, Los Angeles, CA
Shubhamoy Ghosh Department of Pediatrics and the Children's Discovery and Innovation Institute, David Geffen School of Medicine UCLA, Los Angeles, CA
Bo-Chul Shin Department of Pediatrics and the Children's Discovery and Innovation Institute, David Geffen School of Medicine UCLA, Los Angeles, CA
Sherin U Devaskar Department of Pediatrics and the Children's Discovery and Innovation Institute, David Geffen School of Medicine UCLA, Los Angeles, CA.

Collapse

Trans-omic Analysis Reveals Selective Responses to Induced and Basal Insulin across Signaling, Transcriptional, and Metabolic Networks

The concentrations of insulin selectively regulate multiple cellular functions. To understand how insulin concentrations are interpreted by cells, we constructed a trans-omic network of insulin action in FAO hepatoma cells using transcriptomic data, western blotting analysis of signaling proteins, and metabolomic data. By integrating sensitivity into the trans-omic network, we identified the selective trans-omic networks stimulated by high and low doses of insulin, denoted as induced and basal insulin signals, respectively. The induced insulin signal was selectively transmitted through the pathway involving Erk to an increase in the expression of immediate-early and upregulated genes, whereas the basal insulin signal was selectively transmitted through a pathway involving Akt and an increase of Foxo phosphorylation and a reduction of downregulated gene expression. We validated the selective trans-omic network in vivo by analysis of the insulin-clamped rat liver. This integrated analysis enabled molecular insight into how liver cells interpret physiological insulin signals to regulate cellular functions.

Self-assembling asymmetric peptide-dendrimer micelles - a platform for effective and versatile in vitro nucleic acid delivery

Despite advancements in the development of high generation cationic-dendrimer systems for delivery of nucleic acid-based therapeutics, commercially available chemical agents suffer from major drawbacks such as cytotoxicity while being laborious and costly to synthesize. To overcome the aforementioned limitations, low-generation cationic peptide asymmetric dendrimers with side arm lipid (cholic and decanoic acid) conjugation were designed, synthesized and systematically screened for their ability to self-assemble into micelles using dynamic light scattering. Cytotoxicity profiling revealed that our entire asymmetric peptide dendrimer library when trialled alone, or as asymmetric dendrimer micelle-nucleic acid complexes, were non-cytotoxic across a broad concentration range. Further, the delivery efficiency of asymmetric peptide dendrimers in H-4-II-E (rat hepatoma), H2K (mdx mouse myoblast), and DAOY (human medulloblastoma) cells demonstrated that cholic acid-conjugated asymmetric dendrimers possess far superior delivery efficiency when compared to the commercial standards, Lipofectamine 2000 or Lipofectin^®.

Pioglitazone inhibits mitochondrial pyruvate metabolism and glucose production in hepatocytes

Pioglitazone is used globally for the treatment of type 2 diabetes mellitus (T2DM) and is one of the most effective therapies for improving glucose homeostasis and insulin resistance in T2DM patients. However, its mechanism of action in the tissues and pathways that regulate glucose metabolism are incompletely defined. Here we investigated the direct effects of pioglitazone on hepatocellular pyruvate metabolism and the dependency of these observations on the purported regulators of mitochondrial pyruvate transport, MPC1 and MPC2. In cultured H4IIE hepatocytes, pioglitazone inhibited [2-¹⁴ C]-pyruvate oxidation and pyruvate-driven oxygen consumption and, in mitochondria isolated from both hepatocytes and human skeletal muscle, pioglitazone selectively and dose-dependently inhibited pyruvate-driven ATP synthesis. Pioglitazone also suppressed hepatocellular glucose production (HGP), without influencing the mRNA expression of key HGP regulatory genes. Targeted siRNA silencing of MPC1 and 2 caused a modest inhibition of pyruvate oxidation and pyruvate-driven ATP synthesis, but did not alter pyruvate-driven HGP and, importantly, it did not influence the actions of pioglitazone on either pathway. In summary, these findings outline a novel mode of action of pioglitazone relevant to the pathogenesis of T2DM and suggest that targeting pyruvate metabolism may lead to the development of effective new T2DM therapies.

Selective control of up-regulated and down-regulated genes by temporal patterns and doses of insulin

Secretion of insulin transiently increases after eating, resulting in a high circulating concentration. Fasting limits insulin secretion, resulting in a low concentration of insulin in the circulation. We analyzed transcriptional responses to different temporal patterns and doses of insulin in the hepatoma FAO cells and identified 13 up-regulated and 16 down-regulated insulin-responsive genes (IRGs). The up-regulated IRGs responded more rapidly than did the down-regulated IRGs to transient stepwise or pulsatile increases in insulin concentration, whereas the down-regulated IRGs were repressed at lower concentrations of insulin than those required to stimulate the up-regulated IRGs. Mathematical modeling of the insulin response as two stages-(i) insulin signaling to transcription and (ii)transcription and mRNA stability-indicated that the first stage was the more rapid stage for the down-regulated IRGs, whereas the second stage of transcription was the more rapid stage for the up-regulated IRGs. A subset of the IRGs that were up-regulated or down-regulated in the FAO cells was similarly regulated in the livers of rats injected with a single dose of insulin. Thus, not only can cells respond to insulin but they can also interpret the intensity and pattern of signal to produce distinct transcriptional responses. These results provide insight that may be useful in treating obesity and type 2 diabetes associated with aberrant insulin production or tissue responsiveness.

Identification of Putative Receptors for the Novel Adipokine CTRP3 Using Ligand-Receptor Capture Technology

C1q TNF Related Protein 3 (CTRP3) is a member of a family of secreted proteins that exert a multitude of biological effects. Our initial work identified CTRP3’s promise as an effective treatment for Nonalcoholic fatty liver disease (NAFLD). Specifically, we demonstrated that mice fed a high fat diet failed to develop NAFLD when treated with CTRP3. The purpose of this current project is to identify putative receptors which mediate the hepatic actions of CTRP3.

Gastroretentive systems - a proposed strategy to modulate anthocyanin release and absorption for the management of diabetes

Several reports have indicated a positive correlation between the consumption of anthocyanins (ACN) and biomarkers relating to the improvement of type 2 diabetes (T2D). However, the results from in vitro studies often do not translate into clinical evidence. Potential causes of these discrepancies are experimental conditions that lack physiological relevancy; extensive degradation of these compounds in vivo due to changes in pH and metabolism; and a short residence time in the absorption window in relation to the absorption rate. Here, gastroretentive systems (GRS) are proposed as a strategy to overcome the limitations in ACN delivery and to reduce the existing bench-to-subject gap. This review summarizes recent literature on the use of ACN for the management and control of T2D, followed by GRS platforms to promote a sustained release of ACN for increased health benefits.

The mechanisms of genome-wide target gene regulation by TCF7L2 in liver cells

In the liver Wnt-signaling contributes to the metabolic fate of hepatocytes, but the precise role of the TCF7L2 in this process is unknown. We employed a temporal RNA-Seq approach to examine gene expression 3–96 h following Tcf7l2 silencing in rat hepatoma cells, and combined this with ChIP-Seq to investigate mechanisms of target gene regulation by TCF7L2. Silencing Tcf7l2 led to a time-dependent appearance of 406 differentially expressed genes (DEGs), including key regulators of cellular growth and differentiation, and amino acid, lipid and glucose metabolism. Direct regulation of 149 DEGs was suggested by strong proximal TCF7L2 binding (peak proximity score > 10) and early mRNA expression changes (≤18 h). Indirect gene regulation by TCF7L2 likely occurred via alternate transcription factors, including Hnf4a, Foxo1, Cited2, Myc and Lef1, which were differentially expressed following Tcf7l2 knock-down. Tcf7l2-silencing enhanced the expression and chromatin occupancy of HNF4α, and co-siRNA experiments revealed that HNF4α was required for the regulation of a subset of metabolic genes by TCF7L2, particularly those involved in lipid and amino-acid metabolism. Our findings suggest TCF7L2 is an important regulator of the hepatic phenotype, and highlight novel mechanisms of gene regulation by TCF7L2 that involve interplay between multiple hepatic transcriptional pathways.