Although enhanced activation of the EGF receptor (EGFR) associates with the development and progression of renal fibrosis, the mechanisms linking these observations are not completely understood. ...Here, after unilateral ureteral obstruction (UUO), wild-type mice exhibited sustained EGFR phosphorylation in the kidney and developed renal fibrosis that was more severe than the renal fibrosis observed in waved-2 mice, which have reduced EGFR tyrosine kinase activity. Waved-2 mice also showed fewer renal tubular cells arrested at G2/M, reduced expression of α-smooth muscle actin (α-SMA), downregulation of multiple genes encoding profibrogenic cytokines, including TGF-β1, and dephosphorylation of Smad3, STAT3, and ERK1/2. Administration of the specific EGFR inhibitor gefitinib recapitulated this phenotype in wild-type mice after UUO. Furthermore, inactivation of either EGFR or STAT3 reduced UUO-induced expression of lipocalin-2, a molecule associated with the pathogenesis of CKD. In cultured renal interstitial fibroblasts, inhibition of EGFR also abrogated TGF-β1- or serum-induced phosphorylation of EGFR, STAT3, ERK1/2, and Smad3 as well as expression of α-SMA and extracelluar matrix proteins. Taken together, these data suggest that EGFR may mediate renal fibrogenesis by promoting transition of renal epithelial cells to a profibrotic phenotype, increased production of inflammatory factors, and activation of renal interstitial fibroblasts. Inhibition of EGFR may have therapeutic potential for fibrotic kidney disease.
Accumulation of both interstitial myofibroblasts and excessive production of extracellular matrix proteins is a common pathway contributing to chronic kidney disease. In a number of tissues, ...activation of STAT3 (signal transducer and activator of transcription 3) increases expression of multiple profibrotic genes. Here, we examined the effect of a STAT3 inhibitor, S3I-201, on activation of renal interstitial fibroblasts and progression of renal fibrosis. Treatment of cultured rat renal interstitial fibroblasts with S3I-201 inhibited their activation, as evidenced by dose- and time-dependent blockade of α-smooth muscle actin and fibronectin expression. In a mouse model of renal interstitial fibrosis induced by unilateral ureteral obstruction, STAT3 was activated, and administration of S3I-201 attenuated both this activation and extracellular matrix protein deposition following injury. S3I-201 reduced infiltration of the injured kidney by inflammatory cells and suppressed the injury-induced expression of fibronectin, α-smooth muscle actin, and collagen type-1 proteins, as well as the expression of multiple cytokines. Furthermore, S3I-201 inhibited proliferation and induced apoptosis preferentially in renal interstitial fibroblasts of the obstructed kidney. Thus, our results suggest that increased STAT3 activity mediates activation of renal interstitial fibroblasts and the progression of renal fibrosis. Inhibition of STAT3 signaling with S3I-201 may hold therapeutic potential for fibrotic kidney diseases.
Activation of renal interstitial fibroblasts is critically involved in the development of tubulointerstitial fibrosis in chronic kidney diseases. In this study, we investigated the effect of ...trichostatin A (TSA), a specific histone deacetylase (HDAC) inhibitor, on the activation of renal interstitial fibroblasts in a rat renal interstitial fibroblast line (NRK-49F) and the development of renal fibrosis in a murine model of unilateral ureteral obstruction (UUO). alpha-Smooth muscle actin (alpha-SMA) and fibronectin, two hallmarks of fibroblast activation, were highly expressed in cultured NRK-49F cells, and their expression was inhibited in the presence of TSA. Similarly, administration of TSA suppressed the expression of alpha-SMA and fibronectin and attenuated the accumulation of renal interstitial fibroblasts in the kidney after the obstructive injury. Activation of renal interstitial fibroblasts was accompanied by phosphorylation of signal transducer and activator of transcription 3 (STAT3), and TSA treatment also abolished these responses. Furthermore, inhibition of the STAT3 pathway with AG490 inhibited expression of alpha-SMA and fibronectin in NRK-49F cells. Finally, TSA treatment inhibited tubular cell apoptosis and caspase-3 activation in the obstructive kidney. Collectively, we suggest that pharmacological HDAC inhibition may induce antifibrotic activity by inactivation of renal interstitial fibroblasts and inhibition of renal tubular cell death. STAT3 may mediate those actions of HDACs.
The activation of cytokine and growth factor receptors associates with the development and progression of renal fibrosis. Suramin is a compound that inhibits the interaction of several cytokines and ...growth factors with their receptors, but whether suramin inhibits the progression of renal fibrosis is unknown. Here, treatment of cultured renal interstitial fibroblasts with suramin inhibited their activation induced by TGF-β1 and serum. In a mouse model of obstructive nephropathy, administration of a single dose of suramin immediately after ureteral obstruction abolished the expression of fibronectin, largely suppressed expression of α-SMA and type I collagen, and reduced the deposition of extracellular matrix proteins. Suramin also decreased the expression of multiple cytokines including TGF-β1 and reduced the interstitial infiltration of leukocytes. Moreover, suramin decreased expression of the type II TGF-β receptor, blocked phosphorylation of the EGF and PDGF receptors, and inactivated several signaling pathways associated with the progression of renal fibrosis. In a rat model of CKD, suramin abrogated proteinuria, limited the decline of renal function, and prevented glomerular and tubulointerstitial damage. Collectively, these findings indicate that suramin is a potent antifibrotic agent that may have therapeutic potential for patients with fibrotic kidney diseases.
Histone deacetylases (HDACs) are enzymes that balance the acetylation activities of histone acetyltransferases on chromatin remodeling and play essential roles in regulating gene transcription. In ...the past several years, the role of HDACs in cancer initiation and progression, as well as the therapeutic effects of HDAC inhibitors in various types of cancer, has been well studied. Recent studies indicated that HDAC activity is also associated with the development and progression of some chronic diseases characterized by fibrosis, including chronic kidney disease, cardiac hypertrophy, and idiopathic pulmonary fibrosis. Here, we review what is known about HDACs in the progression of tissue fibrosis and the potential applications of HDAC inhibitors in the treatment of disorders associated with fibroblast activation and proliferation.
Aspartyl‐(Asparagyl)‐β‐hydroxylase (AAH) is overexpressed in various malignant neoplasms, including hepatocellular carcinomas (HCCs). The upstream regulation of AAH and its functional role in ...Notch‐mediated signaling and motility in HCC cells was accessed. The mRNA transcript levels of AAH, insulin receptor substrate (IRS), insulin and insulin‐like growth factor (IGF) receptors and polypeptides, Notch, Jagged, and HES were measured in 15 paired samples of HCC and adjacent HCC‐free human liver biopsy specimens using real‐time quantitative RT‐PCR and Western blot analysis. Overexpression of AAH was detected in 87% of the HCC relative to the paired HCC‐free liver tissue. IRS‐1, IRS‐2, and IRS‐4 were each overexpressed in 80% of the HCC samples, and IGF‐I and IGF‐2 receptors were overexpressed in 40% and 100% of the HCCs, respectively. All HCC samples had relatively increased levels of Notch‐1 and HES‐1 gene expression. Overexpression of AAH led to increased levels of Notch, and co‐immunoprecipitation experiments demonstrated a direct interaction between AAH and Notch as well as its ligand Jagged. In conclusion, contributions to the malignant phenotype of HCC is due to activation of IGF‐I and IGF‐II signaling that results in over‐expression of both AAH and Notch. The functional role of AAH in relation to cell motility has been linked to increased activation of the Notch signaling pathway. (HEPATOLOGY 2006;44:446–457.)
Background/Aims Chronic ethanol exposure impairs liver regeneration due to inhibition of insulin signaling and oxidative injury. PPAR agonists function as insulin sensitizers and anti-inflammatory ...agents. We investigated whether treatment with a PPARδ agonist could restore hepatic insulin sensitivity, survival signaling, and regenerative responses vis-a-vis chronic ethanol feeding. Methods Adult rats were fed isocaloric liquid diets containing 0% or 37% ethanol, and administered a PPARδ agonist by i.p. injection. We used liver tissue to examine histopathology, gene expression, oxidative stress, insulin signaling, and regenerative responses to 2/3 hepatectomy. Results Chronic ethanol feeding caused insulin resistance, increased oxidative stress, lipid peroxidation, DNA damage, and hepatocellular injury in liver. These effects were associated with reduced insulin receptor binding and affinity, impaired survival signaling through PI3K/Akt/GSK3β, and reduced expression of insulin responsive genes mediating energy metabolism and tissue remodeling. PPARδ agonist treatment reduced ethanol-mediated hepatic injury, oxidative stress, lipid peroxidation, and insulin resistance, increased signaling through PI3K/Akt/GSK3β, and enhanced the regenerative response to partial hepatectomy. Conclusions PPARδ agonist administration may attenuate the severity of chronic ethanol-induced liver injury and ethanol’s adverse effects on the hepatic repair by restoring insulin responsiveness, even in the context of continued high-level ethanol consumption.
Aim: Chronic ethanol exposure impairs insulin signaling in the liver. Peroxisome‐proliferator activated receptor (PPAR) agonists function as insulin sensitizers and are used to treat type 2 diabetes ...mellitus. We examined the therapeutic effectiveness of PPAR agonists in reducing alcoholic hepatitis and hepatic insulin resistance in a model of chronic ethanol feeding.
Methods: Adult male Long Evans rats were pair fed with isocaloric liquid diets containing 0% (control) or 37% ethanol (caloric content; 9.2% v/v) for 8 weeks. After 3 weeks on the diets, the rats were treated with vehicle, or a PPAR‐α, PPAR‐δ or PPAR‐γ agonist twice weekly by i.p. injection. Livers were harvested for histopathological, gene expression (reverse transcription polymerase chain reaction), protein (western and ELISA) and receptor binding studies.
Results: Ethanol‐fed rats developed steatohepatitis with disordered hepatic chord architecture, increased hepatocellular apoptosis, reduced binding to the insulin, insulin‐like growth factor (IGF)‐1 and IGF‐2 receptors, and decreased expression of glyceraldehyde‐3‐phosphate dehydrogenase and aspartyl‐(asparaginyl)‐β‐hydroxylase (mediating remodeling), which are regulated by insulin/IGF signaling. PPAR‐α, PPAR‐δ or PPAR‐γ agonist treatments reduced the severity of ethanol‐mediated liver injury, including hepatic architectural disarray and steatosis. In addition, PPAR‐δ and PPAR‐γ agonists reduced insulin/IGF resistance and increased insulin/IGF‐responsive gene expression.
Conclusion: PPAR agonists may help reduce the severity of chronic ethanol‐induced liver injury and insulin/IGF resistance, even in the context of continued high‐level ethanol consumption.
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