High Serum-Induced AhRL Is Associated with Prevalent Metabolic Syndrome and Future Impairment of Glucose Tolerance in the Elderly

Background@#High circulating levels of dioxins and dioxin-like chemicals, acting via the aryl hydrocarbon receptor (AhR), have previously been linked to diabetes. We now investigated whether the serum AhR ligands (AhRL) were higher in subjects with metabolic syndrome (MetS) and in subjects who had developed a worsened glucose tolerance over time. @*Methods@#Serum AhRL at baseline was measured by a cell-based AhRL activity assay in 70-year-old subjects (n=911) in the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study. The main outcome measures were prevalent MetS and worsening of glucose tolerance over 5 years of follow-up. @*Results@#AhRL was significantly elevated in subjects with prevalent MetS as compared to those without MetS, following adjustment for sex, smoking, exercise habits, alcohol intake and educational level (P=0.009). AhRL at baseline was higher in subjects who developed impaired fasting glucose or diabetes at age 75 years than in those who remained normoglycemic (P=0.0081). The odds ratio (OR) of AhRL for worsening glucose tolerance over 5 years was 1.43 (95% confidence interval [CI], 1.13 to 1.81; P=0.003, continuous variables) and 2.81 (95% CI, 1.31 to 6.02; P=0.008, in the highest quartile) adjusted for sex, life style factors, body mass index, and glucose. @*Conclusion@#These findings support a large body of epidemiologic evidence that exposure to AhR transactivating substances, such as dioxins and dioxin-like chemicals, might be involved in the pathogenesis of MetS and diabetes development. Measurement of serum AhRL in humans can be a useful tool in predicting the onset of metabolic disorders.

High Serum-Induced AhRL Is Associated with Prevalent Metabolic Syndrome and Future Impairment of Glucose Tolerance in the Elderly

Background@#High circulating levels of dioxins and dioxin-like chemicals, acting via the aryl hydrocarbon receptor (AhR), have previously been linked to diabetes. We now investigated whether the serum AhR ligands (AhRL) were higher in subjects with metabolic syndrome (MetS) and in subjects who had developed a worsened glucose tolerance over time. @*Methods@#Serum AhRL at baseline was measured by a cell-based AhRL activity assay in 70-year-old subjects (n=911) in the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study. The main outcome measures were prevalent MetS and worsening of glucose tolerance over 5 years of follow-up. @*Results@#AhRL was significantly elevated in subjects with prevalent MetS as compared to those without MetS, following adjustment for sex, smoking, exercise habits, alcohol intake and educational level (P=0.009). AhRL at baseline was higher in subjects who developed impaired fasting glucose or diabetes at age 75 years than in those who remained normoglycemic (P=0.0081). The odds ratio (OR) of AhRL for worsening glucose tolerance over 5 years was 1.43 (95% confidence interval [CI], 1.13 to 1.81; P=0.003, continuous variables) and 2.81 (95% CI, 1.31 to 6.02; P=0.008, in the highest quartile) adjusted for sex, life style factors, body mass index, and glucose. @*Conclusion@#These findings support a large body of epidemiologic evidence that exposure to AhR transactivating substances, such as dioxins and dioxin-like chemicals, might be involved in the pathogenesis of MetS and diabetes development. Measurement of serum AhRL in humans can be a useful tool in predicting the onset of metabolic disorders.

Clinical Value of Serum Mitochondria-Inhibiting Substances in Assessing Renal Hazards: A Community-Based Prospective Study in Korea

Background@#Mitochondrial dysfunction is strongly associated with several kidney diseases. However, no studies have evaluated the potential renal hazards of serum mitochondria-inhibiting substance (MIS) and aryl hydrocarbon receptor ligand (AhRL) levels. @*Methods@#We used serum level of MIS and AhRL and clinical renal outcomes from 1,511 participants of a prospective community-based cohort in Ansung. MIS was evaluated based on intracellular adenosine triphosphate (MIS-ATP) or reactive oxygen species (MIS-ROS) generation measured using cell-based assays. @*Results@#During a mean 6.9-year follow-up, 84 participants (5.6%) developed a rapid decline in kidney function. In the lowest quartile group of MIS-ATP, patients were older and had metabolically deleterious parameters. In multivariate logistic regression analysis, higher MIS-ATP was associated with decreased odds for rapid decline: the odds ratio (OR) of 1% increase was 0.977 (95% confidence interval [CI], 0.957 to 0.998; P=0.031), while higher MIS-ROS was marginally associated with increased odds for rapid decline (OR, 1.014; 95% CI, 0.999 to 1.028; P=0.055). However, serum AhRL was not associated with the rapid decline in kidney function. In subgroup analysis, the renal hazard of MIS was particularly evident in people with hypertension and low baseline kidney function. @*Conclusion@#Serum MIS was independently associated with a rapid decline in kidney function, while serum AhRL was not. The clinical implication of renal hazard on serum MIS requires further evaluation in future studies.

Effect of Dialysis on Aryl Hydrocarbon Receptor Transactivating Activity in Patients with Chronic Kidney Disease

miR-24-mediated knockdown of H2AX damages mitochondria and the insulin signaling pathway

Mitochondrial deficits or altered expressions of microRNAs are associated with the pathogenesis of various diseases, and microRNA-operated control of mitochondrial activity has been reported. Using a retrovirus-mediated short-hairpin RNA (shRNA) system, we observed that miR-24-mediated H2AX knockdown (H2AX-KD) impaired both mitochondria and the insulin signaling pathway. The overexpression of miR-24 decreased mitochondrial H2AX and disrupted mitochondrial function, as indicated by the ATP content, membrane potential and oxygen consumption. Similar mitochondrial damage was observed in shH2AX-mediated specific H2AX-KD cells. The H2AX-KD reduced the expression levels of mitochondrial transcription factor A (TFAM) and mitochondrial DNA-dependent transcripts. H2AX-KD mitochondria were swollen, and their cristae were destroyed. H2AX-KD also blocked the import of precursor proteins into mitochondria and the insulin-stimulated phosphorylation of IRS-1 (Y632) and Akt (S473 and T308). The rescue of H2AX, but not the nuclear form of ΔC24-H2AX, restored all features of miR-24- or shH2AX-mediated impairment of mitochondria. Hepatic miR-24 levels were significantly increased in db/db and ob/ob mice. A strong feedback loop may be present among miR-24, H2AX, mitochondria and the insulin signaling pathway. Our findings suggest that H2AX-targeting miR-24 may be a novel negative regulator of mitochondrial function and is implicated in the pathogenesis of insulin resistance.

Circadian regulation of low density lipoprotein receptor promoter activity by CLOCK/BMAL1, Hes1 and Hes6

Low density lipoprotein receptor (LDLR) plays an important role in the cholesterol homeostasis. We examined the possible circadian regulation of LDLR and mechanism(s) underlying it. In mice, blood glucose and plasma triglyceride, total and high density lipoprotein cholesterol varied distinctively throughout a day. In addition, LDLR mRNA oscillated in the liver in a functional clock-dependent manner. Accordingly, analysis of human LDLR promoter sequence revealed three putative E-boxes, raising the possible regulation of LDLR expression by E-box-binding transcription factors. To test this possibility, human LDLR promoter reporter constructs were transfected into HepG2 cells and the effects of CLOCK/BMAL1, Hes1, and Hes6 expression were analyzed. It was found that positive circadian transcription factor complex CLOCK/BMAL1 upregulated human LDLR promoter activity in a serum-independent manner, while Hes family members Hes1 and Hes6 downregulated it only under serum-depleted conditions. Both effects were mapped to proximal promoter region of human LDLR, where mutation or deletion of well-known sterol regulatory element (SRE) abolished only the repressive effect of Hes1. Interestingly, hes6 and hes1 mRNA oscillated in an anti-phasic manner in the wild-type but not in the per1-/-per2-/- mouse. Comparative analysis of mouse, rat and human hes6 genes revealed that three E-boxes are conserved among three species. Transfection and site-directed mutagenesis studies with hes6 reporter constructs confirmed that the third E-box in the exon IV is functionally induced by CLOCK/BMAL1. Taken together, these results suggest that LDLR expression is under circadian control involving CLOCK/BMAL1 and Hes family members Hes1 and Hes6.

Insulin-dependent suppression of cholesterol 7alpha-hydroxlase is a possible link between glucose and cholesterol metabolisms

Cholesterol 7alpha-hydroxylase (CYP7A1) regulates the balance between cholesterol supply and metabolism by catalyzing the rate-limiting step of bile acid biosynthesis. The transcriptional activity of CYP7A1 is tightly controlled by various nuclear receptors. A forkhead transcription factor O1 (FOXO1) plays a critical role in metabolism, and insulin inactivates FOXO1 through Akt-dependent phosphorylation and nuclear exclusion. We investigated the role of insulin-Akt-FOXO1 signaling pathway in CYP7A1 transcriptional regulation since we found putative insulin-response elements, FOXO1 binding sequences, in both rat and human CYP7A1 promoters. However, ectopic expression of FOXO1 increased the rat CYP7A1-, but mildly reduced human CYP7A1-promoter activities in a dose-dependent manner. Similarly to bile acids, insulin treatment increased small heterodimer partner (SHP) mRNA rapidly and transiently, leading to the suppression of CYP7A1 transcription in both human and rodents. Chromatin immunoprecipitation showed that FOXO1 directly bound to rat CYP1A1 promoter in the absence of insulin. FOXO1 binding to the rat promoter was diminished by insulin treatment as well as by expression of SHP. Our results suggest that the stimulation of insulin- signaling pathway of Akt-FOXO1 and SHP expression may regulate cholesterol/bile acid metabolisms in liver, linking carbohydrate and cholesterol metabolic pathways. A prolonged exposure of insulin in hyperinsulinemic insulin resistance or diabetic status represses CYP7A1 transcription and bile acid biosynthesis through SHP induction and FOXO1 inactivation, leading to impairment of the hepatic cholesterol/bile acid metabolisms.

Insulin-dependent suppression of cholesterol 7alpha-hydroxlase is a possible link between glucose and cholesterol metabolisms

Cholesterol 7alpha-hydroxylase (CYP7A1) regulates the balance between cholesterol supply and metabolism by catalyzing the rate-limiting step of bile acid biosynthesis. The transcriptional activity of CYP7A1 is tightly controlled by various nuclear receptors. A forkhead transcription factor O1 (FOXO1) plays a critical role in metabolism, and insulin inactivates FOXO1 through Akt-dependent phosphorylation and nuclear exclusion. We investigated the role of insulin-Akt-FOXO1 signaling pathway in CYP7A1 transcriptional regulation since we found putative insulin-response elements, FOXO1 binding sequences, in both rat and human CYP7A1 promoters. However, ectopic expression of FOXO1 increased the rat CYP7A1-, but mildly reduced human CYP7A1-promoter activities in a dose-dependent manner. Similarly to bile acids, insulin treatment increased small heterodimer partner (SHP) mRNA rapidly and transiently, leading to the suppression of CYP7A1 transcription in both human and rodents. Chromatin immunoprecipitation showed that FOXO1 directly bound to rat CYP1A1 promoter in the absence of insulin. FOXO1 binding to the rat promoter was diminished by insulin treatment as well as by expression of SHP. Our results suggest that the stimulation of insulin- signaling pathway of Akt-FOXO1 and SHP expression may regulate cholesterol/bile acid metabolisms in liver, linking carbohydrate and cholesterol metabolic pathways. A prolonged exposure of insulin in hyperinsulinemic insulin resistance or diabetic status represses CYP7A1 transcription and bile acid biosynthesis through SHP induction and FOXO1 inactivation, leading to impairment of the hepatic cholesterol/bile acid metabolisms.

Sterol-independent repression of low density lipoprotein receptor promoter by peroxisome proliferator activated receptor gamma coactivator-1alpha (PGC-1alpha)

Peroxisome proliferator activated receptor (PPAR) gamma coactivator-1alpha (PGC-1alpha) may be implicated in cholesterol metabolism since PGC-1alpha co-activates estrogen receptor alpha (ERalpha) transactivity and estrogen/ERalpha induces the transcription of LDL receptor (LDLR). Here, we show that overexpression of PGC-1alpha in HepG2 cells represses the gene expression of LDLR and does not affect the ERalpha-induced LDLR expression. PGC-1alpha suppressed the LDLR promoter-luciferase (pLR1563-luc) activity regardless of cholesterol or functional sterol-regulatory element-1. Serial deletions of the LDLR promoter revealed that the inhibition by PGC-1alpha required the LDLR promoter regions between -650 bp and -974 bp. Phosphorylation of PGC-1alpha may not affect the suppression of LDLR expression because treatment of SB202190, a p38 MAP kinase inhibitor, did not reverse the LDLR down-regulation by PGC-1alpha. This may be the first report showing the repressive function of PGC-1alpha on gene expression. PGC-1alpha might be a novel modulator of LDLR gene expression in a sterol-independent manner, and implicated in atherogenesis.

Reduced Mitochondrial Properties in Putative Progenitor/Stem Cells of Human Keratinocytes

BACKGROUND: The characterization of progenitor/keratinocyte stem cells (KSC) remains an unachieved goal. A previous study showed that rapid adhering cells to collagen IV had the characteristics of putative progenitor/KSCs. OBJECTIVE: The purpose of this study was to investigate the genetic expression of rapid adhering cells compared to non adhering cells to determine the characteristic of KSCs. METHODS: We isolated rapid adhering cells representative of KSCs from non adhering cells representative of transient amplifying cells. In addition, we differentiated cells from human tonsilar keratinocytes utilizing the adhering capability of the KSCs to collagen IV. Annealing control primer based differentially displayed polymerase chain reaction (PCR) was performed as well as Western blot analysis. RESULTS: The levels of mitochondria-related gene expression were low in the rapid adhering cells compared to the non adhering cells. Mitochondrial complex I, COX IV, peroxiredoxins (I, II and IV) and mitochondrial membrane potential were all low in the rapid adhering cells compared to the non adhering cells. CONCLUSION: Using an adhesion method on human collagen IV-coated plates, our results suggest that reduced mitochondrial function may be an important characteristic of KSCs.

Growth impairment of primary chondrocyte cells by serum of rats with chronic renal failure

Insulin-like growth factor (IGF)/IGF binding protein (IGFBP) abnormalities may be important in the pathogenesis of growth failure in chronic renal failure (CRF). We induced experimental CRF by 5/6 nephrectomy in Sprague Dawley rats (100 g) and observed for 2 weeks comparing with sham-operated pair-fed control rats (Sham- C). CRF rats gained 30% less height than Sham- C rats (P10 kDa, containing IGFBPs) and low (<10 kDa, containing free IGF) molecular weight fractions using a gel filtration column. Both fractions obtained from CRF sera decreased the growth of control chondrocytes up to 40% compared with those from control sera. We suggest that the pathogenesis of growth failure in CRF may be involved in the increase of circulating IGFBP4 as well as the unidentified small molecular weight uremic serum factors which block the growth of chondrocytes in growth plate.

Gene expression in uremic left ventricular hypertrophy: effects of hypertension andanemia

Hypertension and anemia may be causes of left ventricular hypertrophy (LVH) in uremia but the molecular mechanism is not known. Uremia was induced in male Spraugue Dawley rats by 5/6 nephrectomy. The following groups of rats were studied for 6 weeks; uremic rats (U) fed ad. lib., control rats (C) pair-fed with U, U rats given hydralazine (100 mg/kg/day) (UH), U rats given erythropoietin (48U/kg/week, i.p.) (UE). Both diastolic and mean arterial pressures are higher (P<0.01) in U and UE compared with C whereas both pressures in UH were normalized. Hemoglobin in U was lower than in C, and was normalized in UE. U, UH and UE had higher heart weight/body weight ratios (HW/BW) as well as left ventricular weight/body weight ratios (LV/BW) compared with C (P<0.01). Compared with U, UH has lower HW/BW and LV/BW (P <0.05) and UE has normal HW/BW but lower LV/BW than U (P<0.05). To see if the gene expression in uremic LVH is similar to that described in pressure overload LVH in which mRNA levels of angiotensin converting enzyme (ACE), transforming growth factor-beta1 (TGF-beta1), atrial natriuretic factors (ANF) and skeletal alpha-actin were increased, we measured these mRNA levels by Northern analysis. TGF-beta, ACE and alpha-actin mRNA levels were not changed in all 4 groups. ANF mRNA in U and UE was increased 3 fold over C, and normalized in UH. Treatment of anemia with erythropoietin improved uremic LVH but did not change ANF mRNA; whereas treatment of hypertension with hydralazine normalized ANF mRNA but did not completely correct uremic LVH. Thus, gene expression in uremic LVH is distinct from that in pressure- overload LVH, suggesting that other unidentified factor(s) might be involved in uremic LVH.