Effect of a two-week treatment with a low dose of 2,2'4,4',5,5'-hexachlorobiphenyl (PCB153) on tight junction protein expression in ovine choroid plexus during long and short photoperiods.

Ortho-substituted polychlorinated biphenyls (PCBs) preferentially accumulate in the brain and cerebrospinal fluid (CSF) compared to other PCBs. We previously reported that the same dose of 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153) induced higher concentrations in the CSF of treated animals compared to controls during short days (SD), while no differences were observed during long days (LD). Similarly, the plasma concentration of PCB153 in treated ewes was higher during SD than LD. To understand the structural and molecular events explaining the photoperiodically different concentration of PCBs in the CSF in sheep, we studied the effect of photoperiod on PCB153 action on tight junction (TJ) protein expression in the choroid plexus (CP) of ewes. For that purpose, we collected CP from ovariectomised, estradiol-treated ewes maintained under artificial LD or SD and orally administered with a low dose (0.33 mg/kg/day, 3 times per week for 3 weeks) of PCB153 or vehicle. Exposure to PCB153 affected TJ proteins only during SD, and the levels of claudin-1, zonula occludens-2 (ZO-2), and afadin (AF-6) were significantly lower when compared to vehicle-treated animals. No differences were observed for occludin, junctional adhesion molecule-1 (JAM-1), claudin-5, ZO-1 and ZO-3. There was no effect of PCB153 treatment on TJ-mRNA levels. These results indicate that PCB153 selectively alters TJ proteins in the ovine CP. These alterations appear to be associated with the level of PCB153 in the blood plasma, which is modulated by the photoperiod. This study emphasises the importance of photoperiod in the susceptibility of adult sheep to PCBs.