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.water homeostasis | bile acid receptor T he farnesoid X receptor (FXR) is a member of the nuclear receptor superfamily, with the typical functional domains including the DNA binding domain and the ligand binding domain. Upon binding to its ligands, FXR forms a heterodimer with another nuclear receptor, retinoid X receptor, whereupon the receptor dimer binds to the FXR response element (FXRE) located in the promoter regions of FXR target genes, thereby regulating the transcription of these genes (1-3). The single FXR gene gives rise to two isoforms, designated as FXRα and FXRβ, as a result of alternative use of the promoters (4). In addition, each FXR isoform has two variants (FXRα1/FXRβ1 and FXRα2/ β2), depending on the presence or absence of an insert of four amino acids (MYTG) immediately adjacent to the DNA binding domain in the hinge domain (5). Because FXRβ constitutes a pseudogene in humans and primates, all recent studies focus on FXRα (6).FXR is highly expressed in the liver and intestine, where it functions as an intracellular sensor of bile acids and is required for the negative feedback regulation of bile acid biosynthesis and its enterohepatic cycle (7,8). Most recently FXR has been found to be involved in the regulation of adrenal and vascular function, as well as hepatic glucose and lipid metabolism, which suggests an important role for FXR in many tissues beyond the hepatointestinal system (9-12). Among most tissues tested, the kidney exhibits the highest expression levels (13). However, the role of FXR in the kidney remains largely unknown. It has been previously reported that FXR may negatively regulate sterol regulatory element-binding protei...

Prostaglandin E2 (PGE2) plays an important role in vascular homeostasis. Its receptor, E-prostanoid receptor 4 (EP4) is essential for physiological remodeling of the ductus arteriosus (DA). However, the role of EP4 in pathological vascular remodeling remains largely unknown. We found that chronic angiotensin II (AngII) infusion of mice with vascular smooth muscle cell (VSMC)-specific EP4 gene knockout (VSMC-EP4−/−) frequently developed aortic dissection (AD) with severe elastic fiber degradation and VSMC dedifferentiation. AngII-infused VSMC-EP4−/−mice also displayed more profound vascular inflammation with increased monocyte chemoattractant protein-1 (MCP-1) expression, macrophage infiltration, matrix metalloproteinase-2 and -9 (MMP2/9) levels, NADPH oxidase 1 (NOX1) activity, and reactive oxygen species production. In addition, VSMC-EP4−/−mice exhibited higher blood pressure under basal and AngII-infused conditions. Ex vivo and in vitro studies further revealed that VSMC-specific EP4 gene deficiency significantly increased AngII-elicited vasoconstriction of the mesenteric artery, likely by stimulating intracellular calcium release in VSMCs. Furthermore, EP4 gene ablation and EP4 blockade in cultured VSMCs were associated with a significant increase in MCP-1 and NOX1 expression and a marked reduction in α-SM actin (α-SMA), SM22α, and SM differentiation marker genes myosin heavy chain (SMMHC) levels and serum response factor (SRF) transcriptional activity. To summarize, the present study demonstrates that VSMC EP4 is critical for vascular homeostasis, and its dysfunction exacerbates AngII-induced pathological vascular remodeling. EP4 may therefore represent a potential therapeutic target for the treatment of AD.

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 adenovirusmediated 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.arachidonic acid | cyclooxygenase | antidiuretic hormone | gene targeting | water homeostasis U rinary concentration is a key process for maintaining body water homeostasis, which is primarily regulated by the antidiuretic hormone arginine vasopressin (AVP). AVP is produced in the hypothalamus and stored in and released from the posterior pituitary, either in response to increased plasma osmolality or decreased blood volume. It binds to its type 2 receptor (V2R) on the basolateral membrane of the principal cells of renal collecting ducts (CDs), triggering the redistribution of aquaporin 2 (AQP2) from intracellular vesicles into the apical membrane. The prolonged activation of V2R can also increase AQP2 expression in CDs, which is essential for urinary concentration (1). AVP thus increases water permeability of the CDs, resulting in enhanced water reabsorption from the tubule lumens and concentrated urine output (1, 2). In some cases, however, urinary concentration is altered independent of AVP, a phenomenon called vasopressin escape, suggesting additional mechanisms may participate in the process of water reabsorption in renal collecting ducts (3-5).Among many identified factors affecting urine output, prostaglandin E2 (PGE2...

Objective-Restenosis after angioplasty remains a major clinical problem. Prostaglandin E 2 (PGE 2 ) plays an important role in vascular homeostasis. The PGE 2 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 (EP2ϩ/ϩ) and EP2 gene-deficient (EP2Ϫ/Ϫ) mice. In EP2ϩ/ϩ mice, EP2 mRNA expression was increased in injured vessels for at least 4 weeks after vascular injury. Neointimal hyperplasia was markedly accelerated in EP2Ϫ/Ϫ 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 EP2Ϫ/Ϫ mice than in those of EP2ϩ/ϩ mice. Activation and overexpression of EP2 attenuated PDGF-BB-elicited cell proliferation and migration, induced G 1 3 S-phase arrest and reduced PDGF-BB-stimulated extracellular signal-regulated kinase phosphorylation in EP2ϩ/ϩ 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. (Arterioscler Thromb Vasc Biol. 2011;31:1739-1747.)Key Words: angioplasty Ⅲ eicosanoids Ⅲ prostaglandins Ⅲ receptors Ⅲ restenosis P ercutaneous transluminal coronary angioplasty (PTCA) has been widely used for treating coronary atherosclerosis. However, many patients undergoing PTCA experience postangioplasty restenosis. 1 Although new devices for dilatation of stenosed arteries have lowered the incidence of acute complications, restenosis remains a major obstacle in the long-term outcome of PTCA interventions. 2 Restenosis is defined as the healing response of the arterial wall to mechanical injury and consists of 2 main processes: neointimal hyperplasia (smooth muscle migration/proliferation and extracellular matrix deposition) and vessel remodeling. 3 Platelet-derived growth factor-BB (PDGF-BB), an important growth factor released from platelets and leukocytes, plays a critical role in intimal hyperplasia after vascular injury. 4,5 An enormous amount of research has elucidated the molecular pathways involved in neointimal formation and vascular remodeling after vascular injury and has greatly advanced our understanding of the mechanisms contributing to the pathogenesis of restenosis. 6 -8 These efforts have led to many new strategies for effective prevention and treatment options for restenosis.Prostaglandin E 2 (PGE 2 ), a major arachidonic acid metabolite, is produced in the vasculature via a mechanism dependent on cyclooxygenase (COX) and prostaglandin E synthase. PGE 2 has important roles in the regulation of blood pressure, inflammatory response, immune response, an...

Metformin treatment is associated with increased RMIC apoptosis in both normally hydrated and dehydrated T2D mice. The results confirm AMPK as a critical factor involved in the maintenance of RMIC viability in T2D and raise safety concerns for metformin and other AMPK-activating antidiabetic drugs in dehydrated diabetic patients.