Jones, Steven R.
Regulation and characterization of the ATP-binding cassette transporter-B1 in the epididymis and epididymal spermatozoa of the rat
Québec, Université du Québec, Institut National de la Recherche Scientifique, Maîtrise en sciences expérimentales de la santé, 118 p.
The epididymis and maturing spermatozoa are susceptible to the effects of xenobiotics. A functional blood-epididymis barrier (BEB)attenuates the entry and facilitates the elimination of potentially harmful substances from the epididymal epithelium. ln addition to providing a sophisticated immunological barrier, the BEB barrier provides a specialized, protected environment where sperm transit, are concentrated and acquire both motility and the ability to fertilize. The BEB is composed of both tight junctions and specialized transporters capable of regulating the types and quantities of compounds entering the epididymal lumen.
Recent evidence suggests that oral administration of alkylphenols (AP), wh ile being able to reach the testis and epididymis, fait to accumulate in these tissues. This suggested that these tissues could either rapidly metabolize AP or expulse them from the cells. Severa specialized efflux transporters that function to exclude xenobiotics from target cells have been identified. ABCBl is a broad specificity ATP-binding cassette (ABC) transporter capable of excluding xenobiotics out of cancerous and normal tissues serving barrier or secretory function.
Little is known about the role of ABC xenobiotic efflux transporters in the epididmyis. The objectives of this study were to characterize the expression profile and functional rote of ABCBla and ABCB1 b along the different regions (initial segment, caput, corpus, cauda) of the rat epididymis.
ABCB1a and ABCB b transcripts were detected in ali regions of the epididymis. Immunohistochemistry conducted with an antibody that recognizes both forms of rodent ABCB l revealed a unique expression gradient in both the epididymal epithelium and epididymal spermatozoa along the length of the tissue. Little to no staining was present on the sperm present in the lumen or epithelium in proximal regions of the epididymis, whereas a strong immunoreaction was observed in distal caput, corpus and cauda. Expression gradients in the tissue and epididymal spermatozoa were confirmed by western blot. These results suggested an important role for ABCBl in epididymal tissue defense and spennatozoal protection, as weil as a unique process where spem1 acquire ABCB1 protein during epididymal transit.
ABCBl functionality in epididymal principal cells and epididymal spennatozoa was confinned using a multi drug resistance (MOR) assay. A rat principal cell line (RCE) and epididymal spennatozoa exctracted from proximal and distal regions of the epididymis demonstrated an inhibitable MDR phenotype when incubated with calcein, an ABCBl substrate, in the presence of specifie ABCBl inhibitors.
Lastly, to assess whether or not the system was inducible by xenobiotics, RCE cells were exposed to various concentrations of nonylphenol (NP), an AP,and doxorubicin (DOX),an an ti-cancer agent and known inducer of ABCB1. RCE cells exposed to NP and DOX revealed a significant induction of ABCB la and ABCB lb mRNA, as weil ABCB l protein, suggesting the existence of a dynamic defense mechanism that can respond to chemical insult.
The unique expression profile and induction of ABCBl in epididymis suggests a role in regulating epididymal barrier function and protection of spennatozoa. ABCB l may be an important toxicokinetic regulator of AP and other xenobiotics in the adult rat epididymis.
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