Nonylphenol Alters Connexin 43 Levels and Connexin 43 Phosphorylation Via an Inhibition of the p38-Mitogen-Activated Protein Kinase Pathway1

Abstract

Endocrine-disrupting chemicals are exogenous compounds that mimic or inhibit the action of estrogens or other hormones. Nonylphenol, an environmental contaminant distributed along the St. Lawrence River, has been reported to act as a weak estrogen. Previous studies from our laboratory have shown that rats that were fed fish taken from nonylphenol contaminated sites have altered spermatogenesis and decreased sperm count. The mechanism responsible for this effect is unknown. Gap junctional intercellular communication (GJIC) in the testis is critical for coordinating spermatogenesis. The objectives of the study were to determine the effects of nonylphenol on GJIC and connexin 43 (Cx43) in a murine Sertoli cell line, TM4. Cells were exposed for 24 h to different concentrations (1 to 50 microM) of either nonylphenol or 17beta-estradiol. GJIC was determined using a microinjection approach in which Lucifer yellow was injected directly into a single cell, and GJIC was assessed 3 min postinjection. Nonylphenol exposure decreased GJIC between adjacent cells by almost 80% relative to controls. A significant concentration-dependent reduction in GJIC was observed at nonylphenol concentrations between 1 and 50 microM. Cx43 immunofluorescent staining was reduced at both 10 and 50 microM doses of nonylphenol. Cx43 phosphorylation, as determined by Western blot analysis, was reduced at both 10 and 50 microM concentrations, which may explain, at least in part, the inhibition of GJIC. In contrast, no effect on GJIC or Cx43 protein was observed in cells exposed to 17beta-estradiol at these concentrations. Cx43 has been reported to be phosphorylated via the p38-mitogen-activated protein kinase (MAPK) pathway. P38-MAPK activity was assessed in both control and nonylphenol-exposed cells. A dose-dependent decrease in p38-MAPK activity was observed in nonylphenol-exposed Sertoli cells. Protein kinase C activity was also measured and was not influenced by nonylphenol. These results suggest that nonylphenol inhibits GJIC between Sertoli cells and that this is modulated via nonestrogenic pathways.

In utero exposure to tributyltin chloride differentially alters male and female fetal gonad morphology and gene expression profiles in the Sprague–Dawley rat

“…This effect was observed for both exposure periods in interstitial Leydig cells while the effects on adjacent Sertoli cells appeared to occur only during the 8-19 days exposure period. The presence of Cx43 gap junctions has been demonstrated by Aravindakshan and Cyr [49] to be essential for cellular communication between Sertoli cells. Cellular coordination, which is mediated by gap junctions, is crucial for the development and function of reproductive tissues [50].…”

Nonylphenol‐induced cytosolic Ca2+ elevation and death in renal tubular cells

“…Nonylphenol is toxic to several cell lines [Gong and Han, 2006a,b;Yao et al, 2006Yao et al, , 2007Kim et al, 2006;Aravindakshan and Cyr, 2005]. We show that nonylphenol was cytotoxic to MDCK cells in a concentration-dependent manner.…”

“…Furthermore, several lines of evidence show that nonylphenol can activate the constitutive androstane receptor [Hernandez et al, 2007], evoke apoptosis in human embryonic stem cells via Fas-Fas ligand pathways [Kim et al, 2006], affect steroidogenesis of rat Leydig cells [Gong and Han, 2006a,b], inhibit neurotrophin-dependent neurite outgrowth [Bevan et al, 2006], and alter connexin-43 levels and connexi0 43 phosphorylation via inhibition of the p38-mitogen-activated protein kinase pathway [Aravindakshan and Cyr, 2005].…”

Effects of a major municipal effluent on the St. Lawrence River: A case study

“…Furthermore, there was a decrease in Cx43 in Sertoli cells suggesting decreased intercellular communication (Aravindakshan et al 2004b). This effect on Cx43 appeared to result from exposure to alkylphenols, as opposed to an estrogenic effect of the effluent mixture (Aravindakshan and Cyr 2005). Immune function was also altered, as indicated by a significant decrease in the number of splenocytes in adult rats exposed to EDCs via maternal milk.…”