Overexpression of TGF-β1 induces renal fibrosis and accelerates the decline in kidney function in polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the presence of numerous fluid-filled cysts, extensive fibrosis, and the progressive decline in kidney function. Transforming growth factor-β1 (TGF-β1), an important mediator for renal fibrosis and chronic kidney disease, is overexpressed by cystic cells compared with normal kidney cells; however, its role in PKD pathogenesis remains undefined. To investigate the effect of TGF-β1 on cyst growth, fibrosis, and disease progression, we overexpressed active TGF-β1 specifically in collecting ducts (CDs) of phenotypic normal (Pkd1^RC/+) and Pkd1^RC/RC mice. In normal mice, CD-specific TGF-β1 overexpression caused tubule dilations by 5 wk of age that were accompanied by increased levels of phosphorylated SMAD3, α-smooth muscle actin, vimentin, and periostin; however, it did not induce overt cyst formation by 20 wk. In Pkd1^RC/RC mice, CD overexpression of TGF-β1 increased cyst epithelial cell proliferation. However, extensive fibrosis limited cyst enlargement and caused contraction of the kidneys, leading to a loss of renal function and a shortened lifespan of the mice. These data demonstrate that TGF-β1-induced fibrosis constrains cyst growth and kidney enlargement and accelerates the decline of renal function, supporting the hypothesis that a combined therapy that inhibits renal cyst growth and fibrosis will be required to effectively treat ADPKD.

Transforming Growth Factor Beta Signaling in Dendritic Cells Is Required for Immunotolerance to Sperm in the Epididymis

The epididymis exhibits a less restrictive physical blood–tissue barrier than the testis and, while numerous immunosuppressive factors have been identified in the latter, no mechanisms for epididymal immunotolerance have been identified to date. Therefore, data are currently insufficient to explain how the immune system tolerates the extremely large load of novel antigens expressed on sperm, which become present in the male body after puberty, i.e., long after central tolerance was established. This study tested the hypothesis that transforming growth factor beta (TGFβ) signaling in dendritic cells (DCs) is required for immunotolerance to sperm located in the epididymis, and that male mice lacking TGFβ signaling in DCs would develop severe epididymal inflammation. To test this, we employed adult Tgfbr2^ΔDC males, which exhibit a significant reduction of Tgfbr2 expression and TGFβ signaling in DCs, as reported previously. Results show that Tgfbr2^ΔDC males exhibit sperm-specific immune response and severe epididymal leukocytosis. This phenotype is consistent with epididymal loss of immunotolerance to sperm and suggests that TGFβ signaling in DCs is a factor required for a non-inflammatory steady state in the epididymis, and therefore for male tract homeostasis and function.

Bicarbonate exchangers SLC26A3 and SLC26A6 are localized at the apical membrane of porcine vas deferens epithelium

The goal of this study was to test for expression of HCO3 (-) exchangers SLC26A3 and SLC26A6 in primary cultures of porcine vas deferens epithelial cells (1°PVD) and native porcine vas deferens. Quantitative RT-PCR revealed that mRNA coding for SLC26A6 was six times more abundant than mRNA coding for SLC26A3 in 1°PVD cells. Western blot analyses combined with surface biotinylation of 1°PVD demonstrated SLC26A3 and SLC26A6 immunoreactivities in whole-cell lysates and apical surfaces of monolayers. Laser scanning confocal microscopy (LSCM) of the 1°PVD cell monolayers demonstrated that SLC26A3 immunoreactivity was primarily in the apical region but present throughout the basal-apical cellular axis, whereas SLC26A6 immunoreactivity was present in the apical region and sometimes accumulated in the nuclear region. LSCM also demonstrated SLC26A3 and SLC26A6 immunoreactivities present along the entire apical lining of the native porcine vas deferens epithelium and in basal cells. The patterns and apparent abundance of SLC26A3 and SLC26A6 immunoreactivities in the proximal vas deferens were not different from the corresponding immunoreactivities in the distal region. There is no evidence of preferential expression of SLC26A3 or SLC26A6 in any portion of the vas deferens, as has been proposed for epithelia that secrete HCO3 (-) in other duct systems. Thus, vas deferens epithelia express transporters throughout the duct that can contribute to rapid alkalinization of the luminal contents as it has been demonstrated in vivo.

Transforming growth factor-β1 impairs CFTR-mediated anion secretion across cultured porcine vas deferens epithelial monolayer via the p38 MAPK pathway

The goal of this study was to determine whether transforming growth factor-β1 (TGF-β1) affects epithelial cells lining the vas deferens, an organ that is universally affected in cystic fibrosis male patients. In PVD9902 cells, which are derived from porcine vas deferens epithelium, TGF-β1 exposure significantly reduced short-circuit current (Isc) stimulated by forskolin or a cell membrane-permeant cAMP analog, 8-pCPT-cAMP, suggesting that TGF-β1 affects targets of the cAMP signaling pathway. Electrophysiological results indicated that TGF-β1 reduces the magnitude of current inhibited by cystic fibrosis transmembrane conductance regulator (CFTR) channel blockers. Real-time RT-PCR revealed that TGF-β1 downregulates the abundance of mRNA coding for CFTR, while biotinylation and Western blot showed that TGF-β1 reduces both total CFTR and apical cell surface CFTR abundance. These results suggest that TGF-β1 causes a reduction in CFTR expression, which limits CFTR-mediated anion secretion. TGF-β1-associated attenuation of anion secretion was abrogated by SB431542, a TGF-β1 receptor I inhibitor. Signaling pathway studies showed that the effect of TGF-β1 on Isc was reduced by SB203580, an inhibitor of p38 mitogen-activated protein kinase (MAPK). TGF-β1 exposure also increased the amount of phospho-p38 MAPK substantially. In addition, anisomycin, a p38 MAPK activator, mimicked the effect of TGF-β1, which further suggests that TGF-β1 affects PVD9902 cells through a p38 MAPK pathway. These observations suggest that TGF-β1, via TGF-β1 receptor I and p38 MAPK signaling, reduces CFTR expression to impair CFTR-mediated anion secretion, which would likely compound the effects associated with mild CFTR mutations and ultimately would compromise male fertility.

Transforming growth factor beta 1 induces tight junction disruptions and loss of transepithelial resistance across porcine vas deferens epithelial cells

Epithelial cells lining the male excurrent duct contribute to male fertility by employing a number of physiological mechanisms that generate a luminal microenvironment conducive to spermatozoa maturation and storage. Among these mechanisms, male duct epithelia establish intercellular tight junctions that constitute a barrier to paracellular diffusion of water, solutes, large molecules, and cells. Mechanisms regulating the male duct epithelial barrier remain unidentified. Transforming growth factor beta (TGFB) is a regulatory cytokine present in high concentrations in human semen. This study examined whether TGFB has any effects on epithelial function exhibited by primary cultures of porcine vas deferens epithelia. TGFB1 exposure caused a 70%-99% decrease in basal transepithelial electrical resistance (R(TE), a sensitive indicator of barrier integrity), while a significant decrease in anion secretory response to forskolin was detected at the highest levels of TGFB1 exposure employed. SB431542, a selective TGFB receptor I (TGFBR1) inhibitor, prevented decreases in barrier function. Results also demonstrated that TGFB1 exposure modifies the distribution pattern of tight junction proteins occludin and claudin 7. TGFBR1 is localized at the apical border of the native porcine vas deferens epithelium. Pharmacological inhibition of mitogen-activated protein kinase (MAPK) 11 (also known as p38-MAPK) did not alter the effect of TGFB1 on R(TE) significantly. These data suggest that epithelia lining the vas deferens are subject to disruptions in the physical barrier if active TGFB becomes bioavailable in the luminal fluid, which might be expected to compromise fertility.

Swine models of cystic fibrosis reveal male reproductive tract phenotype at birth

Nearly all male cystic fibrosis (CF) patients exhibit tissue abnormalities in the reproductive tract, a condition that renders them azoospermic and infertile. Two swine CF models have been reported recently that include respiratory and digestive manifestations that are comparable to human CF. The goal of this study was to determine the phenotypic changes that may be present in the vas deferens of these swine CF models. Tracts from CFTR(-/-) and CFTR(ΔF508/ΔF508) neonates revealed partial or total vas deferens and/or epididymis atresia at birth, while wild-type littermates were normal. Histopathological analysis revealed a range of tissue abnormalities and disruptions in tubular organization. Vas deferens epithelial cells were isolated and electrophysiological results support that CFTR(-/-) monolayers can exhibit Na(+) reabsorption but reveal no anion secretion following exposure to cAMP-generating compounds, suggesting that CFTR-dependent Cl(-) and/or HCO(3)(-) transport is completely impaired. SLC26A3 and SLC26A6 immunoreactivities were detected in all experimental groups, indicating that these two chloride-bicarbonate exchangers were present, but were either unable to function or their activity is electroneutral. In addition, no signs of increased mucus synthesis and/or secretion were present in the male excurrent ducts of these CF models. Results demonstrate a causal link between CFTR mutations and duct abnormalities that are manifested at birth.

Xenogeneic transplantation of equine testicular cells into seminiferous tubules of immunocompetent rats

The objectives were to develop a transplantation assay for equine testicular cells using busulfan-treated prepubertal immunocompetent rats as recipients, and to determine if putative equine spermatogonial stem cells (SSCs) could be enriched by flow cytometric cell sorting (based on light scattering properties), thereby improving engraftment efficiency. Four weeks after transplantation of frozen/thawed PKH26-labeled equine testicular cells, 0.029 ± 0.045% (mean ± SD) of viable donor cells transplanted had engrafted. Donor cells were present in seminiferous tubules of all recipient rats forming chains, pairs, mesh structures, or clusters (with two to >30 cells/structure). Cells were localized to the basal compartment by the basement membrane. Although equine cells proliferated within rat seminiferous tubules, no donor-derived spermatogenesis was evident. Furthermore, there was no histologic evidence of acute cellular rejection. No fluorescent cells were present in control testes. When equine testicular cells were sorted based on light scattering properties, the percentage of transplanted donor cells that engrafted was higher after injection of cells from the small, low complexity fraction (II; 0.169 ± 0.099%) than from either the large, high complexity fraction (I; 0.046 ± 0.051%) or unsorted cells (0.009 ± 0.007%; P < 0.05). Seminiferous tubules of busulfan-treated prepubertal immunocompetent rats provided a suitable niche for engraftment and proliferation, but not differentiation, of equine testicular cells. Sorting equine testicular cells based on light scattering properties resulted in a 19-fold improvement in colonization efficiency by cells with high forward scatter and low side scatter, which may represent putative equine SSCs.

Porcine vas deferens luminal pH is acutely increased by systemic xylazine administration

Data are accumulating to demonstrate that pH regulation in the male reproductive tract has a vital role in modulating sperm cell fertilizing capacity, and therefore male fertility. Bicarbonate uptake by sperm cells is required for the achievement of motility levels required for fertilization. Vas deferens epithelial cells can carry out measurable bicarbonate secretion, but the available literature to date reports that the vas deferens luminal content is typically acidic. This study aimed to determine pH in the boar vas deferens lumen and whether modulatory mechanisms exist for regulation of pH in this compartment of the male reproductive tract. A fiberoptic pH probe was used to assess pH in the vas deferens of anesthetized adult boars. The mean pH, derived from multiple measurements at variable positions along the vas deferens lumen, was 7.39 +/- 0.09. Furthermore, administration of xylazine, an alpha-2 adrenergic receptor agonist rapidly (<10 min) alkalinized the vas deferens lumen in most cases. Because the duct was transected proximal to the site of measurements, the observations rule out the possibility that alkalinization resulted from secretion in more proximal portions of the duct. These results indicate that the boar vas deferens lumen can be alkaline, and they suggest that porcine vas deferens epithelia increase net bicarbonate secretion in vivo after systemic alpha-2 adrenergic stimulation. This secretory response greatly changes the luminal environment to which sperm cells are exposed, which will initiate or enhance motility, and is expected to modulate male fertility.

Testosterone upregulates anion secretion across porcine vas deferens epithelia in vitro

Testosterone induces and maintains prostaglandin endoperoxide synthase 2 (PTGS2, also known as cyclooxygenase 2) expression in vas deferens epithelial cells, but it remains unknown whether this has a physiological role in the context of male reproductive biology. Prostaglandins induce concentration-dependent increases in anion secretion in porcine vas deferens epithelial cell (1 degrees PVD) monolayers, where bicarbonate contributes to cAMP-stimulated anion secretion. Moreover, bradykinin induces anion secretion across 1 degrees PVD monolayers that is indomethacin sensitive, and both PTGS2 and PTGS1 are expressed in this model system. Therefore, it was hypothesized that testosterone modulates anion secretion across vas deferens epithelia via PTGS-dependent pathways and prostaglandin synthesis. Porcine vas deferens epithelial cells were isolated and cultured as monolayers on permeable supports until assayed in modified Ussing chambers. RNA and protein were isolated concurrently for semiquantitative expression analysis. Testosterone upregulated basal and bradykinin-induced short-circuit current across 1 degrees PVD monolayers, indicative of anion secretion. Testosterone also induced greater transepithelial electrical resistance. Increases in anion secretion were associated with preferential upregulation of PTGS2 at the mRNA and protein levels. In addition, testosterone induced greater basal and bradykinin-induced anion secretion across vas deferens epithelial cells isolated from the distal segment of the duct. Taken together, these results suggest that testosterone upregulates epithelial responsiveness to acute modulations of anion secretion (likely bicarbonate secretion), which ultimately modifies the environment to which sperm are exposed.

Bradykinin-stimulated cyclooxygenase activity stimulates vas deferens epithelial anion secretion in vitro in swine and humans

Epithelia lining the male reproductive duct modulate fertility by altering the luminal environment to which sperm are exposed. Although vas deferens epithelial cells reportedly express high levels of cyclooxygenases (Ptgs), and activation of bradykinin (BK) receptors can lead to upregulation of PTGS activity in epididymal epithelia, it remains unknown whether BKs and/or PTGSs have any role in modulating epithelial ion transport across vas deferens epithelia. Porcine and human vas deferens epithelial cell primary cultures and the PVD9902 cell line responded to lysylbradykinin with an increase in short circuit current (I SC; indicating net anion secretion), an effect that was 60%-93% reduced by indomethacin. The BK effect was inhibited by the B2 receptor subtype (BDKRB2) antagonist HOE140, whereas the B1 receptor subtype agonist des-Arg9-BK had no effect. BDKRB2 immunoreactivity was documented in most epithelial cells composing the native epithelium and on Western blots derived from cultured cells. Gene expression analysis revealed that the PTGS2 transcript is 20 times more abundant than its PTGS1 counterpart in cultured porcine vas deferens epithelia and that BDKRB2 mRNA is likewise highly expressed. Subsequent experiments revealed that prostaglandin E2, 1-OH prostaglandin E1 (prostaglandin E receptor 4 [PTGER4] agonist) and butaprost (PTGER2 agonist) increase I SC in a concentration-dependent manner, whereas sulprostone (mixed PTGER1 and PTGER3 agonist) produced no change in I SC. These results demonstrate that autacoids can affect epithelial cells to acutely modulate the luminal environment to which sperm are exposed in the vas deferens by enhancing PTGS activity, leading to the production of prostaglandins that act at PTGER4 and/or PTGER2 to induce or enhance anion secretion.

PVD9902, a porcine vas deferens epithelial cell line that exhibits neurotransmitter-stimulated anion secretion and expresses numerous HCO3(-) transporters

Epithelial ion transport disorders, including cystic fibrosis, adversely affect male reproductive function by nonobstructive mechanisms and by obstruction of the distal duct. Continuous cell lines that could be used to define ion transport mechanisms in this tissue are not readily available. In the present study, porcine vas deferens epithelial cells were isolated by standard techniques, and the cells spontaneously immortalized to form a porcine vas deferens epithelial cell line that we have titled PVD9902. Cells were maintained in continuous culture for >4 yr and 200 passages in a typical growth medium. Frozen stocks were generated, and thawed cells exhibited growth characteristics indistinguishable from their nonfrozen counterparts. Molecular and immunocytochemical studies confirmed the origin and epithelial nature of these cells. When seeded on permeable supports, PVD9902 cells grew as electrically tight (>6,000 ohms x cm2), confluent monolayers that responded to forskolin with an increase in short-circuit current (I(sc); 8 +/- 1 microA/cm2) that required Cl-, HCO3(-), and Na+, and was partially sensitive to bumetanide. mRNA was expressed for a number of anion transporters, including CFTR, electrogenic Na+-HCO3(-) cotransporter 1b (NBCe1b), downregulated in adenoma, pendrin, and Cl-/formate exchanger. Both forskolin and isoproterenol caused an increase in cellular cAMP levels. In addition, PVD9902 cell monolayers responded to physiological (i.e., adenosine, norepinephrine) and pharmacological [i.e., 5'-(N-ethylcarboxamido)adenosine, isoproterenol] agonists with increases in I(sc). Unlike their freshly isolated counterparts, however, PVD9902 cells did not respond to glucocorticoid exposure with an increase in amiloride-sensitive I(sc). RT-PCR analysis revealed the presence of both glucocorticoid and mineralocorticoid receptor mRNA as well as mRNA for the alpha- and gamma-subunits of the epithelia Na+ channels (alpha- and gamma-ENaC), but not beta-ENaC. Nonetheless, PVD9902 cells recapitulated most observations in freshly isolated cells and thus represent a powerful new tool to characterize mechanisms that contribute to male reproductive function.

Colocalization of WT1 and cell proliferation reveals conserved mechanisms in temperature-dependent sex determination

During vertebrate development the gonad has two possible fates, the testis or the ovary. The choice between these fates is made by a variety of sex-determining mechanisms, from the sex-determining gene on the Y chromosome (Sry) in mammals, to nongenetic temperature-dependent systems in many reptiles. Despite the differences in the mechanisms at the top of the sex-determining cascade, the resulting morphology and many genes involved in early testis and ovarian development are common to most vertebrates, leading to the hypothesis that the underlying processes of sex determination are conserved. In this study, we examined the early steps of gonad development in the red-eared slider turtle (Trachemys scripta), a species that uses the temperature of egg incubation to determine sex. A dramatic increase in cell proliferation was observed in the male gonad during the earliest stages of sex determination. Using the localization of Wilms' Tumor suppressor 1 (WT1), we determined that this proliferation increase occurred in a population that contained pre-Sertoli cells. The proliferation of pre-Sertoli cells has been documented during sex determination in both mice and alligators, suggesting that proliferation of this cell type has an important role in vertebrate testis organogenesis and the determination of male fate.

A developmental study of the Desert hedgehog-null mouse testis

Desert hedgehog (Dhh) is a cell-signaling molecule that was first discovered in Drosophila. A unique testicular phenotype has been described in neonatal and adult Dhh-null animals that includes anastomotic seminiferous tubules, pertitubular cell abnormalities, and absence of adult-type Leydig cells. In the present study, we addressed the developmental basis for the abnormalities previously described for the adult Dhh-null phenotype. The source of Dhh is the Sertoli cell, and receptors are localized on peritubular cells and possibly Leydig cells. The development of testes from Dhh-null mouse embryos was studied using light and electron microscopy at 11.5, 12.5, 13.5, and 16.5 days postcoitum (dpc) and was compared with that in control Dhh heterozygous and wild-type embryos. Dhh-null and control testes were generally similar during the period of early cord formation (11.5-12.5 dpc). By 13.5 dpc, the basal lamina delimiting the cords was lacking in some regions and disorganized in Dhh-null testes, and occasional germ cells were seen outside cords. At 16.5 dpc, these defects were more prominent and cord organization was less well defined than in controls. In addition, there were numerous extracordal germ cells, some of which were partially enclosed by a somatic cell of unknown identity. Numerous fibroblast-like cells, apparently secreting collagen and basal lamina, characterized the interstitium of the Dhh-null testis. These defects likely stem from abnormal peritubular stimulation due to the lack of Dhh, leading to the abnormalities seen in the developmental stages studied here and in the adult testis.