Altered growth response to prostaglandin E2 and its receptor signaling in mesangial cells from stroke-prone spontaneously hypertensive rats

Alteration of the Fatty Acid Metabolism in the Rat Kidney Caused by the Injection of Serum from Patients with Collapsing Glomerulopathy

Patients with collapsing glomerulopathy (CG) have marked proteinuria that rapidly progresses to chronic renal failure. In this study, we investigated if the nephropathy produced in a rat model by the injection of serum from CG patients induced alterations in fatty acid (FA) metabolism. Twenty-four female Sprague-Dawley rats were divided into four groups of six rats each: Group I, control rats (C); Group II, rats that received injections of 1 mL of 0.9% NaCl saline solution (SS); Group III, rats injected with 25 mg/mL of serum from healthy subjects (HS); and Group IV, rats injected with 25 mg/mL of serum from CG patients. In all groups, the systolic blood pressure (SBP), proteinuria, creatinine clearance (CC), cholesterol and total FA composition in the kidney and serum were evaluated. The administration of serum from CG patients to rats induced glomerular collapse, proteinuria, reduced CC and elevated SBP (p ≤ 0.01) in comparison with the C, SS and HS rats. The FA composition of the serum of rats that received the CG serum showed an increase in palmitic acid (PA) and a decrease in arachidonic acid (AA) when compared to serum from HS (p ≤ 0.02). In rats receiving the CG serum, there was also a decrease in the AA in the kidney but there was an increase in the PA in the serum and kidney (p ≤ 0.01). These results suggest that the administration of serum from CG patients to rats induces alterations in FA metabolism including changes in PA and in AA, which are precursors for the biosynthesis of the prostaglandins that are involved in the elevation of SBP and in renal injury. These changes may contribute to collapsing glomerulopathy disease.

Prostaglandin E2 enhances neurotrophin-4 production via EP3 receptor in human keratinocytes

Atopic dermatitis is characterized by increased skin innervation. The expression of neurotrophin-4 is enhanced in the epidermal keratinocytes of lesions with atopic dermatitis and may be related to hyperinnervation in these lesions. Prostaglandin E(2) (PGE(2)) levels are increased in lesions with atopic dermatitis; thus, PGE(2) may be involved in the development of this disease. We examined the in vitro effects of PGE(2) on neurotrophin-4 production in human keratinocytes. PGE(2) and EP1/EP3 agonist sulprostone increased neurotrophin-4 secretion and mRNA levels without altering its mRNA stability. Antisense Sp1 oligodeoxynucleotide and Sp1 inhibitor mithramycin A suppressed PGE(2) and sulprostone-induced neurotrophin-4 expression, indicating the requirement for Sp1 for expression. PGE(2) or sulprostone markedly enhanced the phosphorylation, DNA binding, and transcriptional activity of Sp1 and modestly increased Sp1 mRNA and protein levels. PGE(2) or sulprostone induced the membrane translocation of protein kinase Calpha and the phosphorylation of extracellular signal-regulated kinase (ERK). PGE(2)-induced increases in neurotrophin-4 expression, Sp1 transcriptional and DNA-binding activity, Sp1 mRNA and protein levels, and ERK phosphorylation were suppressed by antisense EP3 oligodeoxynucleotide, inhibitors of phosphatidylinositol-specific phospholipase C, conventional protein kinase C, and mitogen-activated protein kinase/ERK kinase 1 (MEK1). These results suggest that PGE(2) enhances neurotrophin-4 production by activating Sp1 via the EP3/phosphatidylinositol-specific phospholipase C/protein kinase Calpha/MEK1/ERK pathway. PGE(2) may promote innervation in skin lesions with atopic dermatitis via the induction of neurotrophin-4.

Prevention and reversal of renal injury by leptin in a new mouse model of diabetic nephropathy

Diabetic nephropathy is the leading cause of end-stage renal disease, for which effective therapy to prevent the progression at advanced stages remains to be established. There is also a long debate whether diabetic glomerular injury is reversible or not. Lipoatrophic diabetes, a syndrome caused by paucity of adipose tissue, is characterized by severe insulin resistance, dyslipidemia, and fatty liver. Here, we show that a genetic model of lipoatrophic diabetes (A-ZIP/F-1 mice) manifests a typical renal injury observed in human diabetic nephropathy that is associated with glomerular hypertrophy, diffuse and pronounced mesangial widening, accumulation of extracellular matrix proteins, podocyte damage, and overt proteinuria. By crossing A-ZIP/F-1 mice with transgenic mice overexpressing an adipocyte-derived hormone leptin, we also reveal that leptin completely prevents the development of hyperglycemia and nephropathy in A-ZIP/F-1 mice. Furthermore, continuous leptin administration to A-ZIP/F-1 mice by minipump beginning at 40 weeks of age significantly alleviates the glomerular injury and proteinuria. These findings demonstrate the therapeutic usefulness of leptin at least for a certain type of diabetic nephropathy. The model presented here will serve as a novel tool to analyze the molecular mechanism underlying not only the progression but also the regression of diabetic nephropathy.

Role of prostaglandin E receptor EP1 subtype in the development of renal injury in genetically hypertensive rats

One of the major causes of end-stage renal diseases is hypertensive renal disease, in which enhanced renal prostaglandin (PG) E2 production has been shown. PGE2, a major arachidonic acid metabolite produced in the kidney, acts on 4 receptor subtypes, EP1 through EP4, but the pathophysiological importance of the PGE2/EP subtypes in the development of hypertensive renal injury remains to be elucidated. In this study, we investigated whether an orally active EP1-selective antagonist (EP1A) prevents the progression of renal damage in stroke-prone spontaneously hypertensive rats (SHRSP), a model of human malignant hypertension. Ten-week-old SHRSP, with established hypertension but with minimal renal damage, were given EP1A or vehicle for 5 weeks. After the treatment period, vehicle-treated SHRSP showed prominent proliferative lesions in arterioles, characterized by decreased alpha-smooth muscle actin expression in multilayered vascular smooth muscle cells. Upregulation of transforming growth factor-beta expression and tubulointerstitial fibrosis were also observed in vehicle-treated SHRSP. All these changes were dramatically attenuated in EP1A-treated SHRSP. Moreover, EP1A treatment significantly inhibited both increase in urinary protein excretion and decrease in creatinine clearance but had little effect on systemic blood pressure. These findings indicate that the PGE2/EP1 signaling pathway plays a crucial role in the development of renal injury in SHRSP. This study opens a novel therapeutic potential of selective blockade of EP1 for the treatment of hypertensive renal disease.

Bcl-(xL) antagonism of BCR-coupled mitochondrial phospholipase A(2) signaling correlates with protection from apoptosis in WEHI-231 B cells

Crosslinking of the antigen receptors on the immature B-cell lymphoma, WEHI-231, leads to growth arrest and apoptosis. Commitment to such B-cell receptor (BCR)-mediated apoptosis correlates with mitochondrial phospholipase A2 activation, disruption of mitochondrial function, and cathepsin B activation. CD40 signaling has been reported to rescue WEHI-231 B cells from BCR-driven apoptosis primarily via up-regulation of the antiapoptotic protein Bcl-xL. Coupling of the BCR to the mitochondrial phospholipase A2-dependent apoptotic pathway can be prevented by rescue signals via CD40. We now show that overexpression of Bcl-xL can prevent mitochondrial phospholipase A2 activation, disruption of mitochondrial potential, and postmitochondrial execution of BCR-mediated apoptosis via cathepsin B activation. Moreover, overexpression of Bcl-xL protects WEHI-231 B cells from mitochondrial disruption and apoptosis resulting from culture with exogenous arachidonic acid, the product of phospholipase A2 action, suggesting that Bcl-xL may act to antagonize arachidonic acid-mediated disruption of mitochondrial integrity. However, although Bcl-xL expression can mimic CD40-mediated rescue of BCR-driven apoptosis, it cannot substitute for CD40 signaling in the reversal of BCR-mediated growth arrest of WEHI-231 B cells. Rather, CD40 signaling additionally induces conversion of arachidonic acid to prostaglandin E2 (PGE2), which promotes WEHI-231 B-cell proliferation by restoring the sustained, cycling extracellular signal-regulated/mitogen-activated protein kinase (ErkMAPkinase) signaling required for cell cycle progression.

Prevention of diabetic nephropathy in rats by prostaglandin E receptor EP1-selective antagonist

Local production of prostaglandins (PGs) in the kidney is increased in clinical and experimental diabetic nephropathy, but the role of PGs in the pathogenesis and progression of diabetic nephropathy has remained unclear. It is here shown that an orally active antagonist selective for the PGE receptor EP1 subtype potently prevents the progression of nephropathy in streptozotocin-induced diabetic rats. The effects are shown by ameliorated renal and glomerular hypertrophy, decreased mesangial expansion, inhibited transcriptional activation of transforming growth factor-beta (TGF-beta) and fibronectin, and complete suppression of proteinuria. In vitro, this agent completely inhibits TGF-beta and fibronectin upregulation in mesangial cells cultured under high-glucose conditions. These data indicate that the PGE2-EP1 system plays a crucial role in the development of diabetic renal injury in rats. It is further shown that both the EP1 antagonist and aspirin, a nonselective PG synthase inhibitor, markedly attenuate mesangial expansion, whereas only the EP1 antagonist inhibits glomerular hypertrophy and proteinuria, which suggests that these changes are caused by different mechanisms. This study reveals a potential usefulness of selective EP1 blockade as a novel therapeutic strategy for diabetic nephropathy and also brings a new insight into our understanding of this disease.

Role of connective tissue growth factor in fibronectin expression and tubulointerstitial fibrosis

Connective tissue growth factor (CTGF) is one of the candidate factors mediating downstream events of transforming growth factor-beta (TGF-beta), but its role in fibrogenic properties of TGF-beta and in tubulointerstitial fibrosis has not yet been clarified. Using unilateral ureteral obstruction (UUO) in rats, we analyzed gene expression of TGF-beta1, CTGF, and fibronectin. We further investigated the effect of blockade of endogenous CTGF on TGF-beta-induced fibronectin expression in cultured rat renal fibroblasts by antisense oligodeoxynucleotide (ODN) treatment. After UUO, CTGF mRNA expression in the obstructed kidney was significantly upregulated subsequent to TGF-beta1, followed by marked induction of fibronectin mRNA. By in situ hybridization, CTGF mRNA was detected mainly in the interstitial fibrotic areas and tubular epithelial cells as well as in parietal glomerular epithelial cells in the obstructed kidney. The interstitial cells expressing CTGF mRNA were also positive for alpha-smooth muscle actin. CTGF antisense ODN transfected into cultured renal fibroblasts significantly attenuated TGF-beta-stimulated upregulation of fibronectin mRNA and protein compared with control ODN transfection, together with inhibited synthesis of type I collagen. With the use of a reporter assay, rat fibronectin promoter activity was increased by 2.5-fold with stimulation by TGF-beta1, and this increase was abolished with antisense CTGF treatment. Thus CTGF plays a crucial role in fibronectin synthesis induced by TGF-beta, suggesting that CTGF blockade could be a possible therapeutic target against tubulointerstitial fibrosis.

Role of adrenomedullin and its receptor system in renal pathophysiology

Adrenomedullin (AM), a potent vasorelaxing, natriuretic and cell growth-modulating peptide, is thought to act as an autocrine/paracrine regulator in renal glomeruli and tubules. AM receptors comprise the calcitonin receptor-like receptor (CRLR) and a family of receptor-activity-modifying proteins (RAMPs 1-3); however, the pathophysiological role of AM and its receptor system in the kidney remains to be clarified. We examined the regulation of their expression in a rat model of renal injury and found that RAMP1, RAMP2 and CRLR expressions were markedly upregulated upon induction of fibrosis during obstructive nephropathy. Since AM exerts potent antiproliferative effects in various cell types, upregulation of the AM receptor system may play important roles in modulating the progression of renal diseases.