Systemic activation of activin A signaling causes chronic kidney disease-mineral bone disorder

The high cardiovascular mortality associated with chronic kidney disease (CKD) is caused in part by the CKD-mineral bone disorder (CKD-MBD) syndrome. The CKD-MBD consists of skeletal, vascular and cardiac pathology caused by metabolic derangements produced by kidney disease. The prevalence of osteopenia/osteoporosis resulting from the skeletal component of the CKD-MBD, renal osteodystrophy (ROD), in patients with CKD exceeds that of the general population and is a major public health concern. That CKD is associated with compromised bone health is widely accepted, yet the mechanisms underlying impaired bone metabolism in CKD are not fully understood. Therefore, clarification of the molecular mechanisms by which CKD produces ROD is of crucial significance. We have shown that activin A, a member of the transforming growth factor (TGF)-β super family, is an important positive regulator of receptor activator of nuclear factor kappa-B ligand (RANKL)-induced osteoclastogenesis with Smad-mediated signaling being crucial for inducing osteoclast development and function. Recently, we have demonstrated systemic activation of activin receptors and activin A levels in CKD mouse models, such as diabetic CKD and Alport (AL) syndrome. In these CKD mouse models, bone remodeling caused by increased osteoclast numbers and activated osteoclastic bone resorption was observed and treatment with an activin receptor ligand trap repaired CKD-induced-osteoclastic bone resorption and stimulated individual osteoblastic bone formation, irrespective of parathyroid hormone (PTH) elevation. These findings have opened a new field for exploring mechanisms of activin A-enhanced osteoclast formation and function in CKD. Activin A appears to be a strong candidate for CKD-induced high-turnover ROD. Therefore, the treatment with the decoy receptor for activin A might be a good candidate for treatment for CKD-induced osteopenia or osteoporosis, indicating that the new findings from in these studies will lead to the identification of novel therapeutic targets for CKD-related and osteopenia and osteoporosis in general. In this review, we describe the impact of CKD-induced Smad signaling in osteoclasts, osteoblasts and vascular cells in CKD

Increase in claudin-2 expression by an EGFR/MEK/ERK/c-Fos pathway in lung adenocarcinoma A549 cells

AbstractIn human adenocarcinoma, claudin-2 expression is higher than that in normal lung tissue, but the regulatory mechanism of its expression has not been clarified. In human adenocarcinoma A549 cells, claudin-2 level time-dependently increased under the control conditions. In contrast, claudin-1 expression remained constant for 24h. The concentration of epidermal growth factor (EGF) in medium time-dependently increased, which was inhibited by matrix metalloproteinase (MMP) inhibitor II, an inhibitor of MMP-1, 3, 7, and 9. MMP inhibitor II decreased claudin-2 and phosphorylated ERK1/2 (p-ERK1/2) levels, which were recovered by EGF. Both claudin-2 and p-ERK1/2 levels were decreased by EGF neutralizing antibody, EGF receptor (EGFR) siRNA, AG1478, an inhibitor of EGFR, U0126, an inhibitor of MEK, and the exogenous expression of dominant negative-MEK. These results suggest that EGF is secreted from A549 cells by MMP and increases claudin-2 expression mediated via the activation of an EGFR/MEK/ERK pathway. The inhibition of the signaling pathway decreased phosphorylated c-Fos and nuclear c-Fos levels. The introduction of c-Fos siRNA decreased claudin-2 level without affecting claudin-1. The promoter activity of human claudin-2 was decreased by AG1478 and U0126. Furthermore, the activity was decreased by the deletion or mutation of the AP-1 binding site of claudin-2 promoter. Chromatin immunoprecipitation and avidin–biotin conjugated DNA assays showed that c-Fos binds to the AP-1 binding site. We suggest that a secreted EGF up-regulates the transcriptional activity of claudin-2 mediated by the activation of an EGFR/MEK/ERK/c-Fos pathway in A549 cells

Effects of dietary inulin, statin, and their co-treatment on hyperlipidemia, hepatic steatosis and changes in drug-metabolizing enzymes in rats fed a high-fat and high-sucrose diet

<p>Abstract</p> <p>Background</p> <p>Rats fed a high-fat and high-sucrose (HF) diet develop hepatic steatosis and hyperlipidemia. There are several reports that a change in nutritional status affects hepatic levels of drug-metabolizing enzymes. Synthetic inulin is a dietary component that completely evades glucide digestion. Supplementing a HF diet with inulin ameliorates hypertriglycemia and hepatic steatosis, but not hypercholesterolemia. This study aimed at distinguishing the effects of synthetic inulin and 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor (statin), which inhibit cholesterol biosynthesis.</p> <p>Methods</p> <p>We examined effects of co-treatment with synthetic inulin (5%) and fluvastatin (0, 4, and 8 mg/kg, <it>per os</it>) on body weight, epidydimal white adipose tissue weight, serum and hepatic lipid profiles, and hepatic cytochrome P450 (CYP) mRNA and protein profiles in rats fed a standard diet or a HF diet for 3 weeks.</p> <p>Results</p> <p>Treatment with the synthetic inulin (5%) or fluvastatin at 4 mg/kg (lethal dose in rats fed the HF diet, 8 mg/kg) ameliorated the elevation in hepatic triacylglycerol and total cholesterol levels in rats fed the HF diet. Whereas co-treatment with the inulin (5%) and fluvastatin (4 mg/kg) had a tendency to more strongly suppress the elevation in serum levels of very low density lipoprotein triacylglycerol than either treatment alone, no additive or synergistic effect was found in decrease in hepatic lipid levels. Hepatic levels of CYP1A1/2 and CYP2E1 mRNA and protein and methoxyresorufin <it>O</it>-demethylase and ethoxyresorufin <it>O</it>-deethylase activities were reduced in rats fed the HF diet. The synthetic inulin alleviated the reduction in hepatic levels of CYP1A1/2 and CYP2E1 mRNA and protein more strongly than fluvastatin, and no synergistic effects were observed on co-treatment. Furthermore, hepatic levels of aryl hydrocarbon receptor mRNA were decreased in rats fed the HF diet and recovered to near normal values with the intake of dietary inulin, which correlated with change in CYP1A1/2.</p> <p>Conclusions</p> <p>Dietary inulin alone was effective to prevent the development of hepatic steatosis, ameliorate nutritional effects, and alleviate the hepatic change in the expression of CYP1A1/2 and CYP2E1, while co-treatment with statin did not have additive or synergistic effects and statin may cause adverse effects in rats fed the HF diet.</p

Connexin43 in mesenchymal lineage cells regulates body adiposity and energy metabolism in mice

Connexin43 (Cx43) is the most abundant gap junction protein present in the mesenchymal lineage. In mature adipocytes, Cx43 mediates white adipose tissue (WAT) beiging in response to cold exposure and maintains the mitochondrial integrity of brown adipose tissue (BAT). We found that genetic deletion of Gja1 (Cx43 gene) in cells that give rise to chondro-osteogenic and adipogenic precursors driven by the Dermo1/Twist2 promoter led to lower body adiposity and partial protection against the weight gain and metabolic syndrome induced by a high-fat diet (HFD) in both sexes. These protective effects were related to increased locomotion, fuel utilization, energy expenditure, nonshivering thermogenesis, and better glucose tolerance in conditionally Gja1-ablated mice. Accordingly, Gja1-mutant mice exhibited reduced adipocyte hypertrophy, partially preserved insulin sensitivity, increased BAT lipolysis, and decreased whitening under HFD. This metabolic phenotype was not reproduced with more restricted Gja1 ablation in differentiated adipocytes, suggesting that Cx43 in adipocyte progenitors or other targeted cells restrains energy expenditures and promotes fat accumulation. These results reveal what we believe is a hitherto unknown action of Cx43 in adiposity, and offer a promising new pharmacologic target for improving metabolic balance in diabetes and obesity

Combined effect of regulatory polymorphisms on transcription of UGT1A1 as a cause of Gilbert syndrome

<p>Abstract</p> <p>Background</p> <p>Gilbert syndrome is caused by defects in bilirubin UDP-glucuronosyltransferase (UGT1A1). The most common variation believed to be involved is A(TA)7TAA. Although several polymorphisms have been found to link with A(TA)7TAA, the combined effect of regulatory polymorphisms in the development of Gilbert syndrome remains unclear.</p> <p>Methods</p> <p>In an analysis of 15 patients and 60 normal subjects, we detected 14 polymorphisms and nine haplotypes in the regulatory region. We classified the 4-kbp regulatory region of the patients into: the TATA box including A(TA)7TAA; a phenobarbital responsive enhancer module including c.-3275T>G; and a region including other ten linked polymorphisms. The effect on transcription of these polymorphisms was studied.</p> <p>Results</p> <p>All haplotypes with A(TA)7TAA had c.-3275T>G and additional polymorphisms. In an <it>in-vitro </it>expression study of the 4-kbp regulatory region, A(TA)7TAA alone did not significantly reduce transcription. In contrast, c.-3275T>G reduced transcription to 69% of that of wild type, and the linked polymorphisms reduced transcription to 88% of wild type. Transcription of the typical regulatory region of the patients was 56% of wild type. Co-expression of constitutive androstane receptor (CAR) increased the transcription of wild type by a factor of 4.3. Each polymorphism by itself did not reduce transcription to the level of the patients, however, even in the presence of CAR.</p> <p>Conclusions</p> <p>These results imply that co-operation of A(TA)7TAA, c.-3275T>G and the linked polymorphisms is necessary in causing Gilbert syndrome.</p

Ligand Trap of the Activin Receptor Type IIA Inhibits Osteoclast Stimulation of Bone Remodeling in Diabetic Mice with Chronic Kidney Disease

Dysregulation of skeletal remodeling is a component of renal osteodystrophy. Previously, we showed that activin receptor signaling is differentially affected in various tissues in chronic kidney disease (CKD). We tested whether a ligand trap for the activin receptor type 2A (RAP-011) is an effective treatment of the osteodystrophy of the CKD-mineral bone disorder. With a 70% reduction in the glomerular filtration rate, CKD was induced at 14 weeks of age in the ldlr−/− high fat-fed mouse model of atherosclerotic vascular calcification and diabetes. Twenty mice with CKD, hyperphosphatemia, hyperparathyroidism, and elevated activin A were treated with RAP-011, wherease 19 mice were given vehicle twice weekly from week 22 until the mice were killed at 28 weeks of age. The animals were then evaluated by skeletal histomorphometry, micro-computed tomography, mechanical strength testing, and ex vivo bone cell culture. Results in the CKD groups were compared with those of the 16 sham-operated ldlr−/− high fat-fed mice. Sham-operated mice had low-turnover osteodystrophy and skeletal frailty. CKD stimulated bone remodeling with significant increases in osteoclast and osteoblast numbers and bone resorption. Compared with mice with CKD and sham-operated mice, RAP-011 treatment eliminated the CKD-induced increase in these histomorphometric parameters and increased trabecular bone fraction. RAP-011 significantly increased cortical bone area and thickness. Activin A-enhanced osteoclastogenesis was mediated through p-Smad2 association with c-fos and activation of nuclear factor of activated T cells c1 (NFATc1). Thus, an ActRIIA ligand trap reversed CKD-stimulated bone remodeling, likely through inhibition of activin-A induced osteoclastogenesis