Estradiol suppresses mesangial cell type I collagen synthesis via activation of the MAP kinase cascade.

We have previously shown that estradiol suppresses the synthesis of type I collagen by murine mesangial cells grown in the presence of serum via activation of the transcription factor activator protein-1 (AP-1). We hypothesized that estradiol upregulates AP-1 via activation of the mitogen-activated protein (MAP) kinase cascade, a signal transduction pathway that regulates AP-1 activity. Estradiol (10(-10) to 10(-7) M) upregulated the MAP kinase pathway in murine mesangial cells grown in the presence of serum in a dose-dependent manner. Activation was evident by 1 min, peaked at 10 min, and was completely dissipated by 2 h. In contrast, estradiol had no significant effect on total (phosphorylated + unphosphorylated) p44 extracellular signal-related protein kinase (ERK) or p42 ERK. Nuclear extracts isolated from mesangial cells treated with estradiol showed increased binding to a consensus sequence AP-1 binding oligonucleotide in gel shift assays. In contrast, nuclear extracts from cells exposed to PD-98059, a highly selective inhibitor of MAP kinase-ERK kinase 1 (MEK1) and MEK2, showed reduced binding. In addition, PD-98059 antagonizes the enhanced binding induced by estradiol. Estradiol (10(-9) M) suppressed mesangial cell type I collagen synthesis (37.8 +/- 2.4%, expressed as a percentage of control values, P < 0.001 vs. control). In contrast, PD-98059 increased type I collagen synthesis (344.6 +/- 98.8, P < 0.01) and reversed the suppression of type I collagen synthesis induced by estradiol. The effects of estradiol, PD-98059, and PD-98059 plus estradiol on type I collagen protein synthesis were closely paralleled by their effects on steady-state levels of mRNA for the alpha(1) chain of type I collagen. These data suggest that estradiol suppresses type I collagen synthesis via upregulation of the MAP kinase cascade, leading to stimulation of AP-1 activity.

Effects of sex hormones on fluid and solute transport in Madin-Darby canine kidney cells.

Polycystic kidney disease progresses more rapidly in men than in women. To investigate the basis for this sexual dimorphism, we exposed Madin-Darby canine kidney (MDCK) cells grown on collagen-coated cell culture inserts to control media, or to estradiol or testosterone (1 nM-1 microM). Compared to control and estradiol-treated cells, testosterone stimulated fluid secretion in a dose-dependent manner, enhancing fluid secretion 4.8-fold at 1 nM and 19.7-fold at 1 microM (0.59 +/- 0.18 vs. 0.03 +/- 0.01 microliter/cm2/hr, P < 0.001). Chloride transport paralleled fluid secretion. Testosterone increased cellular cyclic AMP levels 3.2-fold at 1 nM and 12.3-fold at 1 microM (81.3 +/- 30.7 vs. 6.6 +/- 3.3 pmol/mg protein, P < 0.001). GDP beta S (500 microM), an inhibitor of Gs, and 2',3'-dideoxyadenosine (10 microM), an inhibitor of the catalytic subunit of adenylate cyclase, suppressed testosterone-induced fluid and solute secretion. Neither testosterone nor estradiol had any effect on microsomal Na,K-ATPase activity, cellular proliferation or cellular total protein content. Our studies show that testosterone stimulates fluid secretion and solute transport by MDCK cells by increasing cAMP generation. In vivo, testosterone may contribute to cyst expansion by enhancing fluid secretion. This observation may help explain the worse prognosis of polycystic kidney disease observed in men.

Effects of sex hormones on mesangial cells.

Male gender is associated with a more rapid progression of chronic renal disease. In various experimental models of renal injury, manipulation of the hormonal milieu can replicate the effects of gender on the course of renal disease. These observations suggest that sex hormones per se may be important determinants of the greater susceptibility of the male kidney to progressive renal injury. Sex hormones may influence many of the processes implicated in the pathogenesis of renal disease progression, including cell proliferation and the synthesis and degradation of collagen and proteoglycans. In addition, sex hormones may indirectly influence these processes by modulating the synthesis and release of vasoactive agents, cytokines, and other growth factors, which in turn are capable of altering mesangial cell function. Finally, estrogens also exert potent antioxidant effects that may contribute to the protective effect of female gender on the course of renal disease.

The impact of gender on the progression of chronic renal disease.

Observations in experimental animals and in humans have shown that the rate of progression of renal disease is influenced by gender. Deterioration of renal function in patients with chronic renal disease is more rapid in men than in women, independent of differences in blood pressure or serum cholesterol levels. In addition to genetically determined differences between the sexes in renal structure and function, sex hormones may directly influence many of the processes implicated in the pathogenesis of renal disease progression. Potential mechanisms include receptor-mediated effects of sex hormones on glomerular hemodynamics and mesangial cell proliferation and matrix accumulation as well as effects on the synthesis and release of cytokines, vasoactive agents, and growth factors. In addition, estrogens may exert potent antioxidant actions in the mesangial microenvironment, which may contribute to the protective effect of female gender.

Defective glomerular beta-adrenergic signal transmission in spontaneously diabetic rats.

Previous studies in experimental diabetes have demonstrated cardiovascular abnormalities of the beta-adrenergic system and reduced adrenergically stimulated renal renin secretion. To examine the defect in the beta-adrenergic signal, glomerular cyclic adenosine monophosphate (cAMP) levels were measured in response to isoproterenol and other humoral agonists (coincubated with the phosphodiesterase inhibitor isomethylxanthine) in nondiabetic and diabetic BB/Wor rats. Basal (unstimulated) levels of glomerular cAMP did not differ between control and diabetic BB/Wor rats, nor did cAMP accumulation differ on incubation with the humoral agonists PGE2 and histamine. However, on incubation with varied concentrations of the nonselective beta-adrenergic agonist isoproterenol, control glomeruli demonstrated a twofold increase in cAMP while a negligible response was observed in diabetic glomeruli. Peak levels of cAMP were higher in control (192 +/- 24 pmol/mg protein) than in diabetic (141 +/- 8 pmol/mg protein) glomeruli (p < 0.01). No differences were observed on incubation with the adenylate cyclase stimulator forskolin. Measurement of glomerular beta-adrenoreceptors by coincubation with iodine 125-labeled cyanopindolol demonstrated no differences in either receptor number (Bmax) or affinity (KD). These data indicate that a specific defect in beta-adrenergic signalling exists in glomerular tissue from spontaneously diabetic rats. Because no decrease in forskolin-stimulated adenylate cyclase was observed, defective coupling of the receptor to its effector, perhaps through the guanine nucleotide stimulatory protein, may account for these observations.