Intermittent Hypoxia Disrupts Glucose Homeostasis in Liver Cells in an Insulin-Dependent and Independent Manner.

BACKGROUND/AIMS: Obstructive sleep apnea is associated with diabetes and insulin resistance, but the underlying mechanisms remain unclear. The purpose of the current study was to determine the molecular effects of intermittent hypoxia (IH) on hepatic insulin signaling and glucose homeostasis, and whether c-Jun NH2-terminal-kinase (JNK) contributed to metabolic responses to IH in liver cells. METHODS: The human HepG2 cells and rat FAO cells were exposed to 10, 30, 120, 240 or 360 cycles of IH (1% O2 for 60 s followed by 21% O2 for 60s, 7.5 cycles per hour) or normoxia as a control. In a subgroup, we exposed cells to 360 cycles of IH with the JNK inhibitor SP600125. After IH exposure, cell glycogen content and glucose output were measured using colorimetric assay kits. Canonical insulin signaling and gluconeogenic genes were measured by western blot and quantitative polymerase chain reaction. RESULTS: IH decreased insulin-stimulated protein kinase B (AKT)/glycogen synthase kinase-3ß (GSK-3ß) phosphorylation in a time-dependent manner, while inhibiting forkhead box protein O1 (FOXO1) expression and phosphoenolpyruvate carboxykinase (PEPCK) transcription independent of insulin signaling. JNK inhibitor SP600125 partially restored AKT/ GSK-3ß phosphorylation and glycogen synthesis, but did not affect other IH-induced glucose metabolic changes. CONCLUSION: IH in vitro impaired insulin signal transduction in liver cells as assessed by inhibited AKT/GSK-3ß phosphorylation via JNK activation. IH inhibited FOXO1 and gluconeogenesis in an insulin-independent manner.

Angiotensin-(1-7) decreases the expression of collagen I via TGF-ß1/Smad2/3 and subsequently inhibits fibroblast-myofibroblast transition.

Previous studies have shown that the RAS (renin-angiotensin system) might participate in airway remodelling in asthma. As a main component of the RAS, Ang-(1-7) [angiotensin-(1-7)] has been reported in few studies regarding its protective effect on asthma. However, the functional roles and relevant signalling pathways of Ang-(1-7) have not been well illustrated. In the present study, we analysed the effect of Ang-(1-7) on AngII (angiotensin II)-induced HLF (human lung fibroblast)-MF (myofibroblast) transition by detecting Col-I (collagen type I), TGF-ß1 (transforming growth factor-ß1) and α-SMA (α-smooth muscle actin) expression. We explored further the possible signalling pathways involved in HLF-MF transition. Our results showed that Ang-(1-7) could down-regulate the expression of Col-I, α-SMA and TGF-ß1/Smad2/3 (all P<0.05). A significant decrease was found in phosphorylation of PI3K (phosphoinositide 3-kinase), Akt, p38-MAPK (mitogen-activated protein kinase) and JNK (c-Jun N-terminal kinase) signalling pathways during HLF-MF transition (all P<0.05). Our data suggests that Ang-(1-7) decreases the expression of Col-I via TGF-ß1/Smad2/3 and subsequently inhibits HLF-MF transition.

[Characteristics and Sources of Nitrated Phenols in Atmospheric Fine Particles of Northern Suburban Nanjing].

Nitrated phenols are a group of nitrogen-containing organics ubiquitously present in ambient air, which are also important components of atmospheric light-absorbing organic matter (brown carbon) that have significant impacts on climate change, air quality, and human health. In this study, we collected a total of 265 daily filter samples of fine particles (PM2.5) in northern suburban Nanjing from March 2019 to January 2020. We used ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS) to detect and quantify eight nitrated phenolic species. The results showed that the average annual concentration of total nitrated phenols in the sampling site was 18.77 ng·m-3, and the average concentrations in spring, summer, autumn, and winter were 16.82, 8.59, 17.28, and 44.79 ng·m-3, respectively. Such concentrations were obviously higher than those determined in other countries but were similar to those in domestic cities, such as Jinan. 4-Nitrophenol was the most abundant nitrated phenol, followed by 4-nitrocatechol and 2-methoxy-5-nitrophenol. Correlation analysis showed that 3-nitrosalicylic acid was from a specific source different from that of other species. Finally, we used a positive matrix factorization model to quantify the source contributions of nitrated phenols. The major sources were vehicle emissions (32%), mixed coal and biomass burning emissions (44%), and industrial emissions (24%). The mixed coal and biomass burning emissions were dominant in autumn and winter. The mass fraction of 3-nitrosalicylic acid in the factor of industrial emissions was>90%, consistent with the results of the correlation analysis. Overall, this study provides valuable insights into the understanding of concentrations, characteristics, and sources of atmospheric nitrated phenols in ambient air.

AMPK/FOXO1 signaling pathway is indispensable in visfatin-regulated myosin heavy chain expression in C2C12 myotubes.

OBJECTIVE: Few studies have addressed the effects of visfatin on skeletal muscle remodeling. The aim of the study was to investigate the effects of visfatin on the expressions of myosin heavy chain (MHC) and its isoforms, the major indicator of fiber types and contractile properties of skeletal muscle. MATERIALS AND METHODS: Levels of MHC, MHC I, MHC IIa, MHC IIb, adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK), p-AMPK and forkhead box protein O1 (FOXO1) were tested in visfatin-treated C2C12 myotubes. C2C12 myotubes were treated with visfatin combined with AMPK inhibitor or AMPK activator to investigate the role of AMPK in visfatin-mediated MHC expression. FOXO1 was overexpressed or knocked down in C2C12 myotubes to explore the role of FOXO1 in visfatin-mediated MHC expression. RESULTS: Compared with the vehicle group, treatment with 5 µg/ml visfatin increased the levels of total MHC and its isoforms, MHC I, MHC IIa and MHC IIb, by 1.93, 1.84, 1.80, and 1.92 folds, respectively (all p = 0,001). Visfatin suppressed AMPK phosphorylation and decreased FOXO1 expression in C2C12 myotubes. The effects of visfatin on MHC I and MHC IIa expression were canceled by AMPK activator AICAR. FOXO1 overexpression minimized the visfatin-induced upregulation of MHC I, MHC IIa and MHC IIb. The effect of AMPK activator AICAR on MHC and its isoforms expression was minimized by knockdown of FOXO1. CONCLUSIONS: The findings revealed that visfatin promoted expressions of MHC and its isoforms in C2C12 myotubes via suppressing AMPK/FOXO1 signaling pathway.

Sex Differences in the Effects of Obesity on Lung Volume.

BACKGROUND: Obesity is linked to variation of lung volume; however, it is still unclear whether a sex difference exists. The study aimed to find out the effect of obesity on lung volume and sex difference among the Chinese population. METHOD: Pulmonary function test results were collected from 300 patients (aged 18 to ~80 years) with normal airway function and a wide range of body mass indexes (BMI). Measures of total lung capacity, vital capacity (VC), inspiratory capacity (IC), reserve volume, expiratory reserve volume (ERV) and functional reserve capacity (FRC) were analyzed by sex and different BMI groups. RESULTS: BMI was correlated with VC inversely and IC positively in liner relationships (VC: r = -0.115, P < 0.05; IC: r = 0.168, P < 0.05, respectively), whereas ERV and FRC decreased exponentially with increasing BMI (FRC: r = -0.298, P < 0.01; ERV: r=-0.348, P < 0.01, respectively). Significant correlations were identified for the effect of BMI on ERV and IC and FRC in females (r = -0.354, P < 0.01; r = 0.206, P < 0.05; r = -0.335, P < 0.01), whereas only on ERV in males (r = -0.230, P < 0.05). CONCLUSIONS: BMI affected the lung volume, and females were more susceptible to the effects than males.

Chronic intermittent hypoxia increases ß cell mass and activates the mammalian target of rapamycin/hypoxia inducible factor 1/vascular endothelial growth factor A pathway in mice pancreatic islet.

BACKGROUND: Growing evidence from population and clinic based studies showed that obstructive sleep apnea (OSA) and its characterizing chronic intermittent hypoxia (IH) were independently associated with the development of type 2 diabetes mellitus. However, the pathogenesis by which OSA induces glucose metabolic disorders is not clear. We determined changes in pancreatic ß cell mass and the mammalian target of rapamycin (mTOR)/hypoxia inducible factor 1 (HIF-1)/vascular endothelial growth factor A (VEGF-A) pathway following IH exposure. METHODS: A controlled gas delivery system regulated the flow of nitrogen and oxygen into a customized cage housing mice during the experiment. Twenty-four male wild C57BL/6J mice were either exposed to IH (n = 12) or intermittent air as a control (n = 12) for 56 days. Mice were anaesthetized and sacrificed after exposure, pancreas samples were dissected for immunofluorescent staining. Insulin and DAPI staining labelled islet ß cells. Insulin positive area and ß cell number per islet were measured. P-S6, HIF-1α and VEGF-A staining were performed to detect the activation of mTOR/HIF-1/VEGF-A pathway. RESULTS: After eight weeks of IH exposure, insulin positive area increased by an average of 18.5% (P < 0.05). The ß cell number per islet increased (92 vs. 55, respectively for IH and the control groups, P < 0.05) with no change in the size of individual ß cells. Islet expression of HIF-1α and VEGF-A were higher in IH group than control group, and percentage of p-S6 positive ß cell also increased after IH exposure (16.8% vs. 4.6% respectively for IH and the control groups, P < 0.05). CONCLUSION: The number of pancreatic ß cells increased as did the activity of the mTOR/HIF-1/VEGF-A pathway after exposure to IH.

Obstructive sleep apnea is associated with impaired glucose metabolism in Han Chinese subjects.

BACKGROUND: Increasingly, evidence from population, clinic-based and laboratory studies supports an independent association between obstructive sleep apnea syndrome (OSAS) and an increased risk of type 2 diabetes; however, this observation has yet to be replicated in China and the potential mechanisms that link these two conditions are not clear. METHODS: A total of 179 Han Chinese subjects were enrolled in this study. All subjects underwent polysomnography, the oral glucose tolerance-insulin releasing test (OGTT-IRT) and serum HbA(1)c measurement. Indexes including homeostasis model assessment-IR (HOMA-IR), Matsuda index, HOMA-ß, early phase insulinogenic index (ΔI(30)/ΔG(30)), AUC-I(180) and oral disposition index (DIo) were calculated for the assessment of insulin resistance and pancreatic ß-cell function. RESULTS: Based on OGTT, 25.4%, 44.6% and 54.5% subjects were diagnosed having glucose metabolic disorders respectively in control, mild to moderate and severe OSAS groups (P < 0.05). Serum HbA(1)c levels were highest in subjects with severe OSAS (P < 0.05). In contrast, compared with normal subjects, HOMA-ß, ΔI(30)/Δ(G30) and DIO were lower in severe OSAS group (P < 0.05). In stepwise multiple linear regressions, 0-min glucose and HbA(1)c were positively correlated with the percentage of total sleep time below an oxyhemoglobin saturation of 90% (T90) (Beta = 0.215 and 0.368, P < 0.05); 30-min and 60-min glucose was negatively correlated with the lowest SpOO(2) (LSpO(2)) (Beta = -0.214 and -0.241, P < 0.05). HOMA-ß and DI(O) were negatively correlated with T90 (Beta = -0.153 and -0.169, P < 0.05) while body mass index (BMI) was the only determinant of HOMA-IR and Matsuda index. CONCLUSIONS: OSAS is associated with impairment in glucose tolerance and pancreatic ß-cell function in Han Chinese subjects while insulin sensitivity is mainly determined by obesity.