Deleted in Breast Cancer 1 (DBC1) Protein Regulates Hepatic Gluconeogenesis

Liver gluconeogenesis is essential to provide energy to glycolytic tissues during fasting periods. However, aberrant up-regulation of this metabolic pathway contributes to the progression of glucose intolerance in individuals with diabetes. Phosphoenolpyruvate carboxykinase (PEPCK) expression plays a critical role in the modulation of gluconeogenesis. Several pathways contribute to the regulation of PEPCK, including the nuclear receptor Rev-erbα and the histone deacetylase SIRT1. Deleted in breast cancer 1 (DBC1) is a nuclear protein that binds to and regulates both Rev-erbα and SIRT1 and, therefore, is a candidate to participate in the regulation of PEPCK. In this work, we provide evidence that DBC1 regulates glucose metabolism and the expression of PEPCK. We show that DBC1 levels decrease early in the fasting state. Also, DBC1 KO mice display higher gluconeogenesis in a normal and a high-fat diet. DBC1 absence leads to an increase in PEPCK mRNA and protein expression. Conversely, overexpression of DBC1 results in a decrease in PEPCK mRNA and protein levels. DBC1 regulates the levels of Rev-erbα, and manipulation of Rev-erbα activity or levels prevents the effect of DBC1 on PEPCK. In addition, Rev-erbα levels decrease in the first hours of fasting. Finally, knockdown of the deacetylase SIRT1 eliminates the effect of DBC1 knockdown on Rev-erbα levels and PEPCK expression, suggesting that the mechanism of PEPCK regulation is, at least in part, dependent on the activity of this enzyme. Our results point to DBC1 as a novel regulator of gluconeogenesis.     

High-Fat Diet: Bacteria Interactions Promote Intestinal Inflammation Which Precedes and Correlates with Obesity and Insulin Resistance in Mouse

Background

Obesity induced by high fat (HF) diet is associated with inflammation which contributes to development of insulin resistance. Most prior studies have focused on adipose tissue as the source of obesity-associated inflammation. Increasing evidence links intestinal bacteria to development of diet-induced obesity (DIO). This study tested the hypothesis that HF western diet and gut bacteria interact to promote intestinal inflammation, which contributes to the progression of obesity and insulin resistance.

Methodology/Principal Findings

Conventionally raised specific-pathogen free (CONV) and germ-free (GF) mice were given HF or low fat (LF) diet for 2–16 weeks. Body weight and adiposity were measured. Intestinal inflammation was assessed by evaluation of TNF-α mRNA and activation of a NF-κB^EGFP reporter gene. In CONV but not GF mice, HF diet induced increases in body weight and adiposity. HF diet induced ileal TNF-α mRNA in CONV but not GF mice and this increase preceded obesity and strongly and significantly correlated with diet induced weight gain, adiposity, plasma insulin and glucose. In CONV mice HF diet also resulted in activation of NF-κB^EGFP in epithelial cells, immune cells and endothelial cells of small intestine. Further experiments demonstrated that fecal slurries from CONV mice fed HF diet are sufficient to activate NF-κB^EGFP in GF NF-κB^EGFP mice.

Conclusions/Significance

Bacteria and HF diet interact to promote proinflammatory changes in the small intestine, which precede weight gain and obesity and show strong and significant associations with progression of obesity and development of insulin resistance. To our knowledge, this is the first evidence that intestinal inflammation is an early consequence of HF diet which may contribute to obesity and associated insulin resistance. Interventions which limit intestinal inflammation induced by HF diet and bacteria may protect against obesity and insulin resistance.     

Differential Responses of Hepatic Endoplasmic Reticulum Stress and Inflammation in Diet-Induced Obese Rats with High-Fat Diet Rich in Lard Oil or Soybean Oil

Scopes

To investigate the effects of high-fat diet enriched with lard oil or soybean oil on liver endoplasmic reticulum (ER) stress and inflammation markers in diet-induced obese (DIO) rats and estimate the influence of following low-fat diet feeding.

Methods and Results

Male SD rats were fed with standard low-fat diet (LF, n = 10) and two isoenergentic high-fat diets enriched with lard (HL, n = 45) or soybean oil (HS, n = 45) respectively for 10 weeks. Then DIO rats from HL and HS were fed either high-fat diet continuously (HL/HL, HS/HS) or switched to low-fat diet (HL/LF, HS/LF) for another 8 weeks. Rats in control group were maintained with low-fat diet. Body fat, serum insulin level, HOMA-IR and ectopic lipid deposition in liver were increased in HL/HL and HS/HS compared to control, but increased to a greater extent in HL/HL compared to HS/HS. Markers of ER stress including PERK and CHOP protein expression and phosphorylation of eIF2α were significantly elevated in HL/HL group while phosphorylation of IRE1α and GRP78 protein expression were suppressed in both HL/HL and HS/HS. Besides, inflammatory signals (OPN, TLR2, TLR4 and TNF-α) expressions significantly increased in HL/HL compared to others. Switching to low-fat diet reduced liver fat deposition, HOMA-IR, mRNA expression of TLR4, TNF-α, PERK in both HL/LF and HS/LF, but only decreased protein expression of OPN, PERK and CHOP in HL/LF group. In addition, HL/LF and HS/LF exhibited decreased phosphorylation of eIF2α and increased phosphorylation of IRE1α and GRP78 protein expression when compared with HL/HL and HS/HS respectively.

Conclusions

Lard oil was more deleterious in insulin resistance and hepatic steatosis via promoting ER stress and inflammation responses in DIO rats, which may be attributed to the enrichment of saturated fatty acid. Low-fat diet was confirmed to be useful in recovering from impaired insulin sensitivity and liver fat deposition in this study.     

Effects of Pioglitazone Mediated Activation of PPAR-γ on CIDEC and Obesity Related Changes in Mice

Objective

Obesity is a metabolic disorder that can lead to high blood pressure, increased blood cholesterol and triglycerides, insulin resistance, and diabetes mellitus. The aim was to study the effects of pioglitazone mediated sensitization of peroxisome proliferator-activated receptor gamma (PPAR-γ) on the relationship of Cell death-inducing DFFA-like effector C (CIDEC) with obesity related changes in mice.

Methods

Sixty C57B/L6 mice weighing 10–12g at 3 weeks of age were randomly divided into 3 groups. Mice in Group 1 were fed on normal diet (ND) while Group 2 mice were given high fat diet (HFD), and Group 3 mice were given high fat diet and treated with Pioglitazone (HFD+P). Body weight, length and level of blood sugar were measured weekly. Quantitative real-time PCR, fluorescence microscopy, and ELISA were performed to analyze the expression of CIDEC and PPAR-γ in visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT).

Results

Body weight and length of mice increased gradually with time in all groups. Blood sugar in HFD mice started to increase significantly from the mid of late phase of obesity while pioglitazone attenuated blood sugar level in HFD+P mice. The mRNA expressions and protein levels of PPAR-γ and CIDEC genes started to increase in HFD mice as compared to ND mice and decreased gradually during the late phase of obesity in VAT. Pioglitazone enhanced the expression of PPAR-γ and CIDEC genes in HFD+P mice even during the late phase of obesity.

Conclusion

It is insinuated that VAT is associated with late phase obesity CIDEC decrease and insulin resistance, while pioglitazone enhances CIDEC through activation of PPAR-γ, increases its expression, and decreases lipolysis, hence preventing an increase of blood sugar in mice exposed to HFD.     

Cholesterol Sulfate and Cholesterol Sulfotransferase Inhibit Gluconeogenesis by Targeting Hepatocyte Nuclear Factor 4α

Sulfotransferase (SULT)-mediated sulfation represents a critical mechanism in regulating the chemical and functional homeostasis of endogenous and exogenous molecules. The cholesterol sulfotransferase SULT2B1b catalyzes the sulfoconjugation of cholesterol to synthesize cholesterol sulfate (CS). In this study, we showed that the expression of SULT2B1b in the liver was induced in obese mice and during the transition from the fasted to the fed state, suggesting that the regulation of SULT2B1b is physiologically relevant. CS and SULT2B1b inhibited gluconeogenesis by targeting the gluconeogenic factor hepatocyte nuclear factor 4α (HNF4α) in both cell cultures and transgenic mice. Treatment of mice with CS or transgenic overexpression of the CS-generating enzyme SULT2B1b in the liver inhibited hepatic gluconeogenesis and alleviated metabolic abnormalities both in mice with diet-induced obesity (DIO) and in leptin-deficient (ob/ob) mice. Mechanistically, CS and SULT2B1b inhibited gluconeogenesis by suppressing the expression of acetyl coenzyme A (acetyl-CoA) synthetase (Acss), leading to decreased acetylation and nuclear exclusion of HNF4α. Our results also suggested that leptin is a potential effector of SULT2B1b in improving metabolic function. We conclude that SULT2B1b and its enzymatic by-product CS are important metabolic regulators that control glucose metabolism, suggesting CS as a potential therapeutic agent and SULT2B1b as a potential therapeutic target for metabolic disorders.     

Acute Systemic Infection with Dengue Virus Leads to Vascular Leakage and Death through Tumor Necrosis Factor-α and Tie2/Angiopoietin Signaling in Mice Lacking Type I and II Interferon Receptors

Severe dengue is caused by host responses to viral infection, but the pathogenesis remains unknown. This is, in part, due to the lack of suitable animal models. Here, we report a non-mouse-adapted low-passage DENV-3 clinical isolate, DV3P12/08, derived from recently infected patients. DV3P12/08 caused a lethal systemic infection in type I and II IFN receptor KO mice (IFN-α/β/γR KO mice), which have the C57/BL6 background. Infection with DV3P12/08 induced a cytokine storm, resulting in severe vascular leakage (mainly in the liver, kidney and intestine) and organ damage, leading to extensive hemorrhage and rapid death. DV3P12/08 infection triggered the release of large amounts of TNF-α, IL-6, and MCP-1. Treatment with a neutralizing anti-TNF-α antibody (Ab) extended survival and reduced liver damage without affecting virus production. Anti-IL-6 neutralizing Ab partly prolonged mouse survival. The anti-TNF-α Ab suppressed IL-6, MCP-1, and IFN-γ levels, suggesting that the severe response to infection was triggered by TNF-α. High levels of TNF-α mRNA were expressed in the liver and kidneys, but not in the small intestine, of infected mice. Conversely, high levels of IL-6 mRNA were expressed in the intestine. Importantly, treatment with Angiopoietin-1, which is known to stabilize blood vessels, prolonged the survival of DV3P12/08-infected mice. Taken together, the results suggest that an increased level of TNF-α together with concomitant upregulation of Tie2/Angiopoietin signaling have critical roles in severe dengue infection.     

Mechanical Stretch Induces Apoptosis Regulator TRB3 in Cultured Cardiomyocytes and Volume-Overloaded Heart

The expression of TRB3 (tribbles 3), an apoptosis regulated gene, increases during endoplasmic reticulum (ER) stress. How mechanical stress affects the regulation of TRB3 in cardiomyocytes during apoptosis is not fully understood. An in vivo model of aorta-caval shunt in adult rats demonstrated the increased TRB3 protein expression in the myocardium. The tumor necrosis factor-alpha (TNF-α) antagonist etanercept reversed the TRB3 protein expression and cardiomyocyte apoptosis induced by AV shunt. An in vitro model of cyclic stretch in neonatal rats was also used to investigate TRB3 expression. We hypothesized that cardiomyocyte apoptosis induced by cyclic stretch is TRB3 dependent. Neonatal rat cardiomyocytes grown on a flexible membrane base were stretched by vacuum to 20% of maximum elongation, at 60 cycles/min. Cyclic stretch significantly increased TRB3 protein and mRNA expression. Addition of c-jun N-terminal kinase (JNK) inhibitor SP600125, TNF-α antibody and etanercept 30 min before stretch reversed the induction of TRB3 protein induced by stretch. Cyclic stretch induced the DNA-binding activity of growth arrest and DNA damaged inducible gene-153 (GADD153) by electrophoretic mobility shift assay. SP600125, JNK siRNA, TNF-α antibody and etanercept abolished the binding activity induced by stretch. TRB3 promoter activity was enhanced by stretch and TRB3-mut plasmid, SP600125, TNF-α antibody and etanercept attenuated TRB3 promoter activity induced by stretch. Exogenous administration of TNF-α recombinant protein to the non-stretched cardiomyocytes increased TRB3 protein expression similar to that seen after stretch. Cyclic stretch induced cardiomyocyte apoptosis is inhibited by TRB3 siRNA and etanercept. The stretch-induced TRB3 is mediated by TNF-α、JNK and GADD153 pathway. These results indicate that TRB3 plays an important role in stretch-induced cardiomyocyte apoptosis.     

Obesity Increases Airway Hyperresponsiveness via the TNF-α Pathway and Treating Obesity Induces Recovery

Obesity is a known risk factor for allergic asthma. It has been recognized as a key player in the pathogenesis of several inflammatory disorders via activation of macrophages, which is also vital to the development of allergic asthma. We investigated the mechanism of obesity-related asthma and whether treating obesity through exercise or diet ameliorates the severity of asthma in the obesity-related asthma model. We generated diet-induced obesity (DIO) in C57BL/6 mice by high-fat-feeding and ovalbumin-induced asthma (lean-OVA or DIO-OVA). The DIO-OVA mice were then treated with tumor necrosis factor (TNF)-α neutralizing antibody as a TNF-α blockade or a Cl₂MDP-containing liposome to induce an alveolar macrophage deficiency. To treat obesity, the DIO-OVA mice were under dietary restrictions or exercised. The pathophysiological and immunological responses were analyzed. Airway hyperresponsiveness (AHR), serum IgE and TNF-α levels in the lung tissue increased in the DIO-OVA mice compared to the lean-OVA mice. Both the TNF-α blockade and depletion of alveolar macrophages in the DIO-OVA mice decreased AHR compared to the DIO-OVA mice. Treating obesity by exercise or through dietary means also reduced pulmonary TNF-α levels and AHR in the DIO-OVA mice. These results suggest that restoring normal body weight is an appropriate strategy for reducing TNF-α levels, and controlling inflammation may help improve asthma severity and control in obesity-related asthma.     

LARP4 Is Regulated by Tumor Necrosis Factor Alpha in a Tristetraprolin-Dependent Manner

LARP4 is a protein with unknown function that independently binds to poly(A) RNA, RACK1, and the poly(A)-binding protein (PABPC1). Here, we report on its regulation. We found a conserved AU-rich element (ARE) in the human LARP4 mRNA 3′ untranslated region (UTR). This ARE, but not its antisense version or a point-mutated version, significantly decreased the stability of β-globin reporter mRNA. We found that overexpression of tristetraprolin (TTP), but not its RNA binding mutant or the other ARE-binding proteins tested, decreased cellular LARP4 levels. RNA coimmunoprecipitation showed that TTP specifically associated with LARP4 mRNA in vivo. Consistent with this, mouse LARP4 accumulated to higher levels in TTP gene knockout (KO) cells than in control cells. Stimulation of WT cells with tumor necrosis factor alpha (TNF-α), which rapidly induces TTP, robustly decreased LARP4 with a coincident time course but had no such effect on LARP4B or La protein or on LARP4 in the TTP KO cells. The TNF-α-induced TTP pulse was followed by a transient decrease in LARP4 mRNA that was quickly followed by a subsequent transient decrease in LARP4 protein. Involvement of LARP4 as a target of TNF-α–TTP regulation provides a clue as to how its functional activity may be used in a physiologic pathway.     

Increased Adiposity,Dysregulated Glucose Metabolism and Systemic Inflammation in Galectin-3 KO Mice

Obesity and type 2 diabetes are associated with increased production of Galectin-3 (Gal-3), a protein that modulates inflammation and clearance of glucose adducts. We used Lean and Diet-induced Obese (DIO) WT and Gal-3 KO mice to investigate the role of Gal-3 in modulation of adiposity, glucose metabolism and inflammation. Deficiency of Gal-3 lead to age-dependent development of excess adiposity and systemic inflammation, as indicated by elevated production of acute-phase proteins, number of circulating pro-inflammatory Ly6C^high monocytes and development of neutrophilia, microcytic anemia and thrombocytosis in 20-week-old Lean and DIO male Gal-3 KO mice. This was associated with impaired fasting glucose, heightened response to a glucose tolerance test and reduced adipose tissue expression of adiponectin, Gal-12, ATGL and PPARγ, in the presence of maintained insulin sensitivity and hepatic expression of gluconeogenic enzymes in 20-week-old Gal-3 KO mice compared to their diet-matched WT controls. Expression of PGC-1α and FGF-21 in the liver of Lean Gal-3 KO mice was comparable to that observed in DIO animals. Impaired fasting glucose and altered responsiveness to a glucose load preceded development of excess adiposity and systemic inflammation, as demonstrated in 12-week-old Gal-3 KO mice. Finally, a role for the microflora in mediating the fasting hyperglycemia, but not the excessive response to a glucose load, of 12-week-old Gal-3 KO mice was demonstrated by administration of antibiotics. In conclusion, Gal-3 is an important modulator of glucose metabolism, adiposity and inflammation.     

Tumor Necrosis Factor - Alpha Is Essential for Angiotensin II-Induced Ventricular Remodeling: Role for Oxidative Stress

The functional crosstalk between angiotensin II (Ang II) and tumor necrosis factor (TNF)-α has been shown to cause adverse left ventricular remodeling and hypertrophy in hypertension. Previous studies from our lab showed that mice lacking TNF-α (TNF-α^-/-) have attenuated hypertensive response to Ang II; however, the signaling mechanisms involved are not known. In this study, we investigated the signaling pathways involved in the Ang II and TNF-α interaction. Chronic Ang II infusion (1μg/kg/min, 14 days) significantly increased cardiac collagen I, collagen III, CTGF and TGF-β mRNA and protein expression in wild-type (WT) mice, whereas these changes were decreased in TNF-α^-/- mice. TNF-α^-/- mice with Ang II infusion showed reduced myocardial perivascular and interstitial fibrosis compared to WT mice with Ang II infusion. In WT mice, Ang II infusion increased reactive oxygen species formation and the expression of NADPH oxidase subunits, indicating increased oxidative stress, but not in TNF-α^-/- mice. In addition, treatment with etanercept (8 mg/kg, every 3 days) for two weeks blunted the Ang II-induced hypertension (133±4 vs 154±3 mmHg, p<0.05) and cardiac hypertrophy (heart weight to body weight ratio, 4.8±0.2 vs 5.6±0.3, p<0.05) in WT mice. Furthermore, Ang II-induced activation of NF-κB, p38 MAPK, and JNK were reduced in both TNF-α^-/- mice and mice treated with etanercept. Together, these findings indicate that TNF-α contributes to Ang II-induced hypertension and adverse cardiac remodeling, and that these effects are associated with changes in the oxidative stress dependent MAPK/TGF-β/NF-κB pathway. These results may provide new insight into the mechanisms of Ang II and TNF-α interaction.     

Obesity Induces Hypothalamic Endoplasmic Reticulum Stress and Impairs Proopiomelanocortin (POMC) Post-translational Processing

It was shown previously that abnormal prohormone processing or inactive proconverting enzymes that are responsible for this processing cause profound obesity. Our laboratory demonstrated earlier that in the diet-induced obesity (DIO) state, the appetite-suppressing neuropeptide α-melanocyte-stimulating hormone (α-MSH) is reduced, yet the mRNA of its precursor protein proopiomelanocortin (POMC) remained unaltered. It was also shown that the DIO condition promotes the development of endoplasmic reticulum (ER) stress and leptin resistance. In the current study, using an in vivo model combined with in vitro experiments, we demonstrate that obesity-induced ER stress obstructs the post-translational processing of POMC by decreasing proconverting enzyme 2, which catalyzes the conversion of adrenocorticotropin to α-MSH, thereby decreasing α-MSH peptide production. This novel mechanism of ER stress affecting POMC processing in DIO highlights the importance of ER stress in regulating central energy balance in obesity.     

Tristetraprolin Mediates Radiation-Induced TNF-α Production in Lung Macrophages

The efficacy of radiation therapy for lung cancer is limited by radiation-induced lung toxicity (RILT). Although tumor necrosis factor-alpha (TNF-α) signaling plays a critical role in RILT, the molecular regulators of radiation-induced TNF-α production remain unknown. We investigated the role of a major TNF-α regulator, Tristetraprolin (TTP), in radiation-induced TNF-α production by macrophages. For in vitro studies we irradiated (4 Gy) either a mouse lung macrophage cell line, MH-S or macrophages isolated from TTP knockout mice, and studied the effects of radiation on TTP and TNF-α levels. To study the in vivo relevance, mouse lungs were irradiated with a single dose (15 Gy) and assessed at varying times for TTP alterations. Irradiation of MH-S cells caused TTP to undergo an inhibitory phosphorylation at Ser-178 and proteasome-mediated degradation, which resulted in increased TNF-α mRNA stabilization and secretion. Similarly, MH-S cells treated with TTP siRNA or macrophages isolated from ttp (−/−) mice had higher basal levels of TNF-α, which was increased minimally after irradiation. Conversely, cells overexpressing TTP mutants defective in undergoing phosphorylation released significantly lower levels of TNF-α. Inhibition of p38, a known kinase for TTP, by either siRNA or a small molecule inhibitor abrogated radiation-induced TNF-α release by MH-S cells. Lung irradiation induced TTP^Ser178 phosphorylation and protein degradation and a simultaneous increase in TNF-α production in C57BL/6 mice starting 24 h post-radiation. In conclusion, irradiation of lung macrophages causes TTP inactivation via p38-mediated phosphorylation and proteasome-mediated degradation, leading to TNF-α production. These findings suggest that agents capable of blocking TTP phosphorylation or stabilizing TTP after irradiation could decrease RILT.     

A Novel Role for Adipose Ephrin-B1 in Inflammatory Response

Aims

Ephrin-B1 (EfnB1) was selected among genes of unknown function in adipocytes or adipose tissue and subjected to thorough analysis to understand its role in the development of obesity.

Methods and Results

EfnB1 mRNA and protein levels were significantly decreased in adipose tissues of obese mice and such reduction was mainly observed in mature adipocytes. Exposure of 3T3-L1 adipocytes to tumor necrosis factor-α (TNF-α) and their culture with RAW264.7 cells reduced EFNB1 levels. Knockdown of adipose EFNB1 increased monocyte chemoattractant protein-1 (Mcp-1) mRNA level and augmented the TNF-α-mediated THP-1 monocyte adhesion to adipocytes. Adenovirus-mediated adipose EFNB1-overexpression significantly reduced the increase in Mcp-1 mRNA level induced by coculture of 3T3-L1 adipocytes with RAW264.7 cells. Monocyte adherent assay showed that adipose EfnB1-overexpression significantly decreased the increase of monocyte adhesion by coculture with RAW264.7 cells. TNF-α-induced activation of extracellular signal-regulated kinase 1/2 (ERK1/2) was reduced by EFNB1-overexpression.

Conclusions

EFNB1 contributes to the suppression of adipose inflammatory response. In obesity, reduction of adipose EFNB1 may accelerate the vicious cycle involved in adipose tissue inflammation.     

Regulation of MRP2/ABCC2 and BSEP/ABCB11 Expression in Sandwich Cultured Human and Rat Hepatocytes Exposed to Inflammatory Cytokines TNF-α, IL-6, and IL-1β

In the present study MRP2/ABCC2 and BSEP/ABCB11 expression were investigated in sandwich cultured (SC) human and rat hepatocytes exposed to the proinflammatory cytokines. The investigation was also done in lipopolysaccharide (LPS)-treated rats. In SC human hepatocytes, both absolute protein and mRNA levels of MRP2/ABCC2 were significantly down-regulated by TNF-α, IL-6, or IL-1β. In contrast to mRNA decrease, which was observed for BSEP/ABCB11, the protein amount was significantly increased by IL-6 or IL-1β. A discrepancy between the change in BSEP/ABCB11 mRNA and protein levels was encountered in SC human hepatocytes treated with proinflammatory cytokines. In SC rat hepatocytes, Mrp2/Abcc2 mRNA was down-regulated by TNF-α and IL-6, whereas the protein level was decreased by all three cytokines. Down-regulations of both Bsep/Abcb11 mRNA and protein levels were found in SC rat hepatocytes exposed to TNF-α or IL-1β. Administration of LPS triggered the release of the proinflammatory cytokines and caused the decrease of Mrp2/Abcc2 and Bsep/Abcb11 protein in liver at 24 h post-treatment; however, the Mrp2 and Bsep protein levels rebounded at 48 h post-LPS treatment. In total, our results indicate that proinflammatory cytokines regulate the expression of MRP2/Mrp2 and BSEP/Bsep and for the first time demonstrate the differential effects on BSEP/Bsep expression between SC human and rat hepatocytes. Furthermore, the agreement between transporter regulation in vitro in SC rat hepatocytes and in vivo in LPS-treated rats during the acute response phase demonstrates the utility of in vitro SC hepatocyte models for predicting in vivo effects.     

Diet-Induced Obesity Exacerbates Auditory Degeneration via Hypoxia,Inflammation, and Apoptosis Signaling Pathways in CD/1 Mice

The aim of this study was to investigate the mechanisms of diet-induced obesity on hearing degeneration in CD/1 mice. Sixty 4-week-old male CD/1 mice were randomly and equally divided into 2 groups. For 16 weeks, the diet-induced obesity (DIO) group was fed a high fat diet and the control group was fed a standard diet of 13.43 % kcal fat. The morphometry, biochemistry, auditory brainstem response thresholds, omental fat, and histopathology of the cochlea were compared between the beginning and end of the study (4 vs. 20 weeks old). The results show that the body weight, fasting plasma triglyceride concentrations, and omental fat weight were higher in the DIO group than in the control group at the end of experiment. The auditory brainstem response thresholds at high frequencies were significantly elevated in the DIO group compared to those of the control group. Histology studies showed that, compared to the control group, the DIO group had blood vessels with smaller diameters and thicker walls in the stria vascularis at the middle and basal turns of the cochlea. The cell densities in the spiral ganglion and spiral ligament at the basal turn of the cochlea were significantly lower in the DIO group. Immunohistochemical staining showed that hypoxia-induced factor 1 (HIF-1), tumor necrosis factor alpha (TNF-α), nuclear factor kappa B (NF-κB), caspase 3, poly(ADP-ribose) polymerase-1, and apoptosis inducing factor were all significantly more dense in the spiral ganglion and spiral ligament at the basal turn of cochlea in the DIO group. Our results suggest that diet-induced obesity exacerbates hearing degeneration via increased hypoxia, inflammatory responses, and cell loss in the spiral ganglion and spiral ligament and is associated with the activation of both caspase-dependent and -independent apoptosis signaling pathways in CD/1 mice.