Qifei Han

Comparative proteomic study reveals 17β-HSD13 as a pathogenic protein in nonalcoholic fatty liver disease

Significance Nonalcoholic fatty liver disease (NAFLD) is a common chronic hepatic disease affecting up to 25% of subjects in the developed world, and represents a progressive illness eventually leading to liver fibrosis and cirrhosis. This study reports an extensive set of human liver lipid droplet (LD)-associated proteins and an array of proteins differentially expressed in human NAFLD. We also uncover 17β-hydroxysteroid dehydrogenase-13, a newly identified LD-associated protein, as a pathogenic molecule in the development of NAFLD. The present study provides a potential link between LD proteins and the pathogenesis of hepatic steatosis. Nonalcoholic fatty liver disease (NAFLD) is characterized by a massive accumulation of lipid droplets (LDs). The aim of this study was to determine the function of 17β-hydroxysteroid dehydrogenase-13 (17β-HSD13), one of our newly identified LD-associated proteins in human subjects with normal liver histology and simple steatosis, in NAFLD development. LDs were isolated from 21 human liver biopsies, including 9 cases with normal liver histology (group 1) and 12 cases with simple steatosis (group 2). A complete set of LD-associated proteins from three liver samples of group 1 or group 2 were determined by 2D LC-MS/MS. By comparing the LD-associated protein profiles between subjects with or without NAFLD, 54 up-regulated and 35 down-regulated LD-associated proteins were found in NAFLD patients. Among them, 17β-HSD13 represents a previously unidentified LD-associated protein with a significant up-regulation in NAFLD. Because the 17β-HSD family plays an important role in lipid metabolism, 17β-HSD13 was selected for validating the proteomic findings and exploring its role in the pathogenesis of NAFLD. Increased hepatic 17β-HSD13 and its LD surface location were confirmed in db/db (diabetic) and high-fat diet-fed mice. Adenovirus-mediated hepatic overexpression of human 17β-HSD13 induced a fatty liver phenotype in C57BL/6 mice, with a significant increase in mature sterol regulatory element-binding protein 1 and fatty acid synthase levels. The present study reports an extensive set of human liver LD proteins and an array of proteins differentially expressed in human NAFLD. We also identified 17β-HSD13 as a pathogenic protein in the development of NAFLD.

Disruption of prostaglandin E2 receptor EP4 impairs urinary concentration via decreasing aquaporin 2 in renal collecting ducts

Significance Prostaglandin E2 (PGE2) plays an important role in maintaining water and sodium homeostasis via its four membrane-associated receptors including EP1, EP2, EP3, and EP4. This study uncovers a unique role for the EP4 receptor in controlling urine volume independent of antidiuretic hormone (arginine vasopressin). EP4 activation increases collecting duct aquaporin 2 (AQP2) expression in a cAMP/cAMP-response element binding protein (CREB)-dependent manner and promotes its membrane sorting via the cAMP/protein kinase A and extracellular signal-regulated kinase pathways. The ability of EP4 to increase AQP2 membrane targeting and cellular abundance makes it a potential therapeutic target for the treatment of clinical disorders including acquired and congenital diabetes insipidus. The antidiuretic hormone arginine vasopressin is a systemic effector in urinary concentration. However, increasing evidence suggests that other locally produced factors may also play an important role in the regulation of water reabsorption in renal collecting ducts. Recently, prostaglandin E2 (PGE2) receptor EP4 has emerged as a potential therapeutic target for the treatment of nephrogenic diabetes insipidus, but the underlying mechanism is unknown. To evaluate the role of EP4 in regulating water homeostasis, mice with renal tubule-specific knockout of EP4 (Ksp-EP4−/−) and collecting duct-specific knockout of EP4 (AQP2-EP4−/−) were generated using the Cre-loxP recombination system. Urine concentrating defect was observed in both Ksp-EP4−/− and AQP2-EP4−/− mice. Decreased aquaporin 2 (AQP2) abundance and apical membrane targeting in renal collecting ducts were evident in Ksp-EP4−/− mice. In vitro studies demonstrated that AQP2 mRNA and protein levels were significantly up-regulated in mouse primary inner medullary collecting duct (IMCD) cells after pharmacological activation or adenovirus-mediated overexpression of EP4 in a cAMP/cAMP-response element binding protein-dependent manner. In addition, EP4 activation or overexpression also increased AQP2 membrane accumulation in a mouse IMCD cell line (IMCD3) stably transfected with the AQP2 gene, mainly through the cAMP/protein kinase A and extracellular signal-regulated kinase pathways. In summary, the EP4 receptor in renal collecting ducts plays an important role in regulating urinary concentration under physiological conditions. The ability of EP4 to promote AQP2 membrane targeting and increase AQP2 abundance makes it a potential therapeutic target for the treatment of clinical disorders including acquired and congenital diabetes insipidus.

Farnesoid X receptor (FXR) gene deficiency impairs urine concentration in mice.

Significance Farnesoid X (FXR) receptor is a ligand-activated transcription factor that regulates bile acid, lipid and glucose metabolism. It can be activated by endogenous bile acids, including chenodeoxycholic acid. This study uncovers a unique role for FXR to regulate urine volume independently of antidiuretic hormone and identifies aquaporin 2 as a direct target gene of FXR in renal collecting ducts. These findings provide a unique mechanism involved in the regulation of urinary concentrating process. The present study may also help understand the pathogenesis of hepatorenal syndrome, a state with increased circulating bile acid levels and impaired renal function. The farnesoid X receptor (FXR) is a ligand-activated transcription factor belonging to the nuclear receptor superfamily. FXR is mainly expressed in liver and small intestine, where it plays an important role in bile acid, lipid, and glucose metabolism. The kidney also has a high FXR expression level, with its physiological function unknown. Here we demonstrate that FXR is ubiquitously distributed in renal tubules. FXR agonist treatment significantly lowered urine volume and increased urine osmolality, whereas FXR knockout mice exhibited an impaired urine concentrating ability, which led to a polyuria phenotype. We further found that treatment of C57BL/6 mice with chenodeoxycholic acid, an FXR endogenous ligand, significantly up-regulated renal aquaporin 2 (AQP2) expression, whereas FXR gene deficiency markedly reduced AQP2 expression levels in the kidney. In vitro studies showed that the AQP2 gene promoter contained a putative FXR response element site, which can be bound and activated by FXR, resulting in a significant increase of AQP2 transcription in cultured primary inner medullary collecting duct cells. In conclusion, the present study demonstrates that FXR plays a critical role in the regulation of urine volume, and its activation increases urinary concentrating capacity mainly via up-regulating its target gene AQP2 expression in the collecting ducts.

Targeted Disruption of the Prostaglandin E2 E-Prostanoid 2 Receptor Exacerbates Vascular Neointimal Formation in Mice

Objective—Restenosis after angioplasty remains a major clinical problem. Prostaglandin E2 (PGE2) plays an important role in vascular homeostasis. The PGE2 receptor E-prostanoid 2 (EP2) is involved in the proliferation and migration of various cell types. We aimed to determine the role of EP2 in the pathogenesis of neointimal formation after vascular injury. Methods and Results—Wire-mediated vascular injury was induced in the femoral arteries of male wild-type (EP2+/+) and EP2 gene-deficient (EP2−/−) mice. In EP2+/+ mice, EP2 mRNA expression was increased in injured vessels for at least 4 weeks after vascular injury. Neointimal hyperplasia was markedly accelerated in EP2−/− mice, which was associated with increased proliferation and migration of vascular smooth muscle cells (VSMCs) and increased cyclin D1 expression in the neointima layer. Platelet-derived growth factor-BB (PDGF-BB) treatment resulted in more significant cell proliferation and migration in VSMCs of EP2−/− mice than in those of EP2+/+ mice. Activation and overexpression of EP2 attenuated PDGF-BB–elicited cell proliferation and migration, induced G1→S-phase arrest and reduced PDGF-BB–stimulated extracellular signal–regulated kinase phosphorylation in EP2+/+ VSMCs. Conclusion—These findings reveal a novel role of the EP2 receptor in neointimal hyperplasia after arterial injury. The EP2 receptor may represent a potential therapeutic target for restenosis after angioplasty.

Metformin induces renal medullary interstitial cell apoptosis in type 2 diabetic mice.

Metformin is a first‐line antidiabetic drug for type 2 diabetes (T2D) with a relatively good safety profile. Metformin activates AMP‐activated protein kinase (AMPK), which is crucial in maintaining renal medullary function, with inappropriate AMPK activation facilitating renal medullary interstitial cells (RMICs) apoptosis under hypertonic challenge. The present study was to determine the effects of metformin on RMIC survival in both normal and T2D mice.

Metformin induces renal medullary interstitial cell apoptosis in type 2 diabetic mice (二甲双胍诱导2型糖尿病小鼠模型肾髓间质细胞凋亡)

Metformin is a first‐line antidiabetic drug for type 2 diabetes (T2D) with a relatively good safety profile. Metformin activates AMP‐activated protein kinase (AMPK), which is crucial in maintaining renal medullary function, with inappropriate AMPK activation facilitating renal medullary interstitial cells (RMICs) apoptosis under hypertonic challenge. The present study was to determine the effects of metformin on RMIC survival in both normal and T2D mice.

Metformin induces renal medullary interstitial cell apoptosis in type 2 diabetic mice (二甲双胍诱导2型糖尿病小鼠模型肾髓间质细胞凋亡): Metformin induces renal medullary cell death

Metformin is a first‐line antidiabetic drug for type 2 diabetes (T2D) with a relatively good safety profile. Metformin activates AMP‐activated protein kinase (AMPK), which is crucial in maintaining renal medullary function, with inappropriate AMPK activation facilitating renal medullary interstitial cells (RMICs) apoptosis under hypertonic challenge. The present study was to determine the effects of metformin on RMIC survival in both normal and T2D mice.