Exogenous Thyroxine Increases Cardiac GLUT4 Translocation in Insulin Resistant OLETF Rats

During insulin resistance, the heart undergoes a metabolic shift in which fatty acids (FA) account for roughly about 99% of the ATP production. This metabolic shift is indicative of impaired glucose metabolism. A shift in FA metabolism with impaired glucose tolerance can increase reactive oxygen species (ROS), lipotoxicity, and mitochondrial dysfunction, ultimately leading to cardiomyopathy. Thyroid hormones (TH) may improve the glucose intolerance by increasing glucose reabsorption and metabolism in peripheral tissues, but little is known on its effects on cardiac tissue during insulin resistance. In the present study, insulin resistant Otsuka Long Evans Tokushima Fatty (OLETF) rats were used to assess the effects of exogenous thyroxine (T4) on glucose metabolism in cardiac tissue. Rats were assigned to four groups: (1) lean, Long Evans Tokushima Otsuka (LETO; n=6), (2) LETO + T4 (8 μg/100g BM/d × 5 wks; n=7), (3) untreated OLETF (n=6), and (4) OLETF + T4 (8 μg/100g BM/d × 5 wks; n=7). T4 increased GLUT4 gene expression by 85% in OLETF and increased GLUT4 protein translocation to the membrane by 294%. Additionally, T4 increased p-AS160 by 285%, phosphofructokinase-1 (PFK-1) mRNA, the rate limiting step in glycolysis, by 98% and hexokinase II by 64% in OLETF. T4 decreased both CPT2 mRNA and protein expression in OLETF. The results suggest that exogenous T4 has the potential to increase glucose uptake and metabolism while simultaneously reducing fatty acid transport in the heart of insulin resistant rats. Thus, L-thyroxine may have therapeutic value to help correct the impaired substrate metabolism associated with diabetic cardiomyopathy.

The pyruvate kinase of the whiteleg shrimp Litopenaeus vannamei: Gene structure and responses to short term hypoxia

The shrimp Litopenaeus vannamei is the main farmed crustaceans worldwide. This crustacean suffers environmental changes in oxygen availability that affect its energy metabolism. Pyruvate kinase (PK) catalyzes the last reaction of glycolysis and is key for the regulation of glycolysis and gluconeogenesis. There is ample knowledge about mammalian PK, but in crustaceans, the information is very scarce. In this study, we analyzed in silico the structures of the PK gene and protein. Also, the effects of hypoxia on gene expression, enzymatic activity, glucose, and lactate in hepatopancreas and muscle were analyzed. The PK gene is 15,103 bp and contains 11 exons and 10 introns, producing four mRNA variants by alternative splicing and named PK1, PK2, PK3 and PK4, and two proteins with longer C-terminus and two with a 12 bp insertion. The promoter contains putative binding sites for transcription factors (TF) that are typically involved in stress responses. The deduced amino acid sequences contain the classic domains, binding sites for allosteric effectors and potential reversible phosphorylation residues. Protein modeling indicates a homotetramer with highly conserved structure. The effect of hypoxia for 6 and 12 h showed tissue-specific patterns, with higher expression, enzyme activity and lactate in muscle, but higher glucose in hepatopancreas. Changes in response to hypoxia were detected at 12 h in expression with induction in muscle and reduction in hepatopancreas, while enzyme activity was maintained, and glucose and lactate decreased. These results show rapid changes in expression and metabolites, while enzyme activity was maintained to cope with short-term hypoxia.

Improved lipogenesis gene expression in liver is associated with elevated plasma angiotensin 1-7 after AT1 receptor blockade in insulin-resistant OLETF rats

Increased angiotensin II (Ang II) signaling contributes to insulin resistance and liver steatosis. In addition to ameliorating hypertension, angiotensin receptor blockers (ARBs) improve lipid metabolism and hepatic steatosis, which are impaired with metabolic syndrome (MetS). Chronic blockade of the Ang II receptor type 1 (AT1) increases plasma angiotensin 1-7 (Ang 1-7), which mediates mechanisms counterregulatory to AT1 signaling. Elevated plasma Ang 1-7 is associated with decreased plasma triacylglycerol (TAG), cholesterol, glucose, and insulin; however, the benefits of RAS modulation to prevent non-alcoholic fatty liver disease (NAFLD) are not fully investigated. To better address the relationships among chronic ARB treatment, plasma Ang 1-7, and hepatic steatosis, three groups of 10-week-old-rats were studied: (1) untreated lean Long Evans Tokushima Otsuka (LETO), (2) untreated Otsuka Long Evans Tokushima Fatty (OLETF), and (3) OLETF + ARB (ARB; 10 mg olmesartan/kg/d × 6 weeks). Following overnight fasting, rats underwent an acute glucose load to better understand the dynamic metabolic responses during hepatic steatosis and early MetS. Tissues were collected at baseline (pre-load; T0) and 1 and 2 h post-glucose load. AT1 blockade increased plasma Ang 1-7 and decreased liver lipids, which was associated with decreased fatty acid transporter 5 (FATP5) and fatty acid synthase (FASN) expression. AT1 blockade decreased liver glucose and increased glucokinase (GCK) expression. These results demonstrate that during MetS, overactivation of AT1 promotes hepatic lipid deposition that is stimulated by an acute glucose load and lipogenesis genes, suggesting that the chronic hyperglycemia associated with MetS contributes to fatty liver pathologies via an AT1-mediated mechanism.

Chronic angiotensin receptor activation promotes hepatic triacylglycerol accumulation during an acute glucose challenge in obese-insulin-resistant OLETF rats

PURPOSE

Angiotensin receptor blockers (ARBs) can ameliorate metabolic syndrome (MetS)-associated dyslipidemia, hepatic steatosis, and glucose intolerance, suggesting that angiotensin receptor (AT1) over-activation contributes to impaired lipid and glucose metabolism, which is characteristic of MetS. The aim of this study was to evaluate changes in the lipid profile and proteins of fatty acid uptake, triacylglycerol (TAG) synthesis, and β-oxidation to better understand the links between AT1 overactivation and non-alcoholic fatty liver disease (NAFLD) during MetS.

METHODS

Four groups of 25-week-old-rats were used: (1) untreated LETO, (2) untreated OLETF, (3) OLETF + angiotensin receptor blocker (ARB; 10 mg olmesartan/kg/d × 8 weeks) and (4) OLETF ± ARB (MINUS; 10 mg olmesartan/kg/d × 4 weeks, then removed until dissection). To investigate the dynamic shifts in metabolism, animals were dissected after an oral glucose challenge (fasting, 3 and 6 h post-glucose).

RESULTS

Compared to OLETF, plasma total cholesterol and TAG remained unchanged in ARB. However, liver TAG was 55% lesser in ARB than OLETF, and remained lower throughout the challenge. Basal CD36 and ApoB were 28% and 29% lesser, respectively, in ARB than OLETF. PRDX6 abundance in ARB was 45% lesser than OLETF, and it negatively correlated with liver TAG in ARB.

CONCLUSIONS

Chronic blockade of AT1 protects the liver from TAG accumulation during glucose overload. This may be achieved by modulating NEFA uptake and increasing TAG export via ApoB. Our study highlights the contributions of AT1 signaling to impaired hepatic substrate metabolism and the detriments of a high-glucose load and its potential contribution to steatosis during MetS.

A potential inflammatory role of IL-31 in psoriatic arthritis: A correlation with Th17 cytokine profile

The goals of our study were to determine the possible association of interleukin (IL)-31 with Th17 cytokine profile in serum and to quantify retinoic acid-related orphan receptor C (RORC) mRNA expression in psoriatic arthritis (PsA) patients. This cross-sectional study was conducted in 50 patients with PsA and 30 control subjects (CS) matched by age and gender. The cytokine serum levels were quantified by magnetic bead–based assay using the Bio-Plex MAGPIX system, and RORC mRNA expression was determined by quantitative polymerase chain reaction (qPCR). As a result, significant differences in IL-31 were observed between study groups (77.23 pg/mL in PsA vs 64.4 pg/mL in CS, P < 0.001) and Th17 cytokine profile serum levels (IL-17A: 6.36 pg/mL in PsA vs 2.97 pg/mL in CS, P = 0.02; IL-17F: 44.15 pg/mL in PsA vs 23.36 pg/mL in PsA, P = 0.01; IL-17E: 3.03 pg/mL in PsA vs 0.82 pg/mL in CS, P < 0.001; IL-21: 36.45 pg/mL in PsA vs 12.44 pg/mL in CS, P = 0.02); however, significant differences were not observed for IL-23 (31.2 pg/mL in PsA vs 53.26 pg/mL in CS, P = 0.58). Furthermore, positive correlations between IL-31 and Th17 cytokine profile serum levels were found (IL-17A: r_s = 0.64, P < 0.001; IL-17F: r_s = 0.73, P < 0.001; IL-17E: r_s = 0.70, P < 0.001; IL-21: r_s = 0.54, P = 0.002; IL-23: r_s = 0.5, P < 0.01). Regarding RORC gene expression, the PsA group showed an increase of 6.85-fold compared to the CS group. We did not find any association between the serum levels of cytokines and RORC gene expression. In conclusion, in PsA, there are increased serum levels of IL-31, IL-17A, IL-17F, IL-17E, and IL-21, but not IL-23. Moreover, there was a positive correlation of IL-31 with the Th17 cytokine profile and a high RORC gene expression. Altogether, these findings suggest a proinflammatory contribution of IL-31 in close association with the Th17 cytokine profile in PsA.

Regulation of lactate dehydrogenase in response to WSSV infection in the shrimp Litopenaeus vannamei

Lactate dehydrogenase (LDH) is key for anaerobic glycolysis. LDH is induced by the hypoxia inducible factor -1 (HIF-1). HIF-1 induces genes involved in glucose metabolism and regulates cellular oxygen homeostasis. HIF-1 is formed by a regulatory α-subunit (HIF-1α) and a constitutive β-subunit (HIF-1β). The white spot syndrome virus (WSSV) induces anaerobic glycolysis in shrimp hemocytes, associated with lactate accumulation. Although infection and lactate production are associated, the LDH role in WSSV-infected shrimp has not been examined. In this work, the effects of HIF-1 silencing on the expression of two LDH subunits (LDHvan-1 and LDHvan-2) in shrimp infected with the WSSV were studied. HIF-1α transcripts increased in gills, hepatopancreas, and muscle after WSSV infection, while HIF-1β remained constitutively expressed. The expression for both LDH subunits increased in each tissue evaluated during the WSSV infection, translating into increased enzyme activity. Glucose concentration increased in each tissue evaluated, while lactate increased in gills and hepatopancreas, but not in muscle. Silencing of HIF-1α blocked the increase of LDH expression and enzyme activity, along with glucose (all tissues) and lactate (gills and hepatopancreas) concentrations produced by WSSV infection. These results demonstrate that HIF-1 up regulates the expression of LDH subunits during WSSV infection, and that this induction contributes to substrate metabolism in energetically active tissues of infected shrimp.