Regulation of testicular tight junctions by gonadotrophins in the adult Djungarian hamster in vivo

Abstract

This study aimed to assess the effect of gonadotrophin suppression and FSH replacement on testicular tight junction dynamics and blood-testis barrier (BTB) organisation in vivo, utilising the seasonal breeding Djungarian hamster. Confocal immunohistology was used to assess the cellular organisation of tight junction proteins and real-time PCR to quantify tight junction mRNA. The effect of tight junction protein organisation on the BTB permeability was also investigated using a biotin-linked tracer. Tight junction protein (claudin-3, junctional adhesion molecule (JAM)-A and occludin) localisation was present but disorganised after gonadotrophin suppression, while mRNA levels (claudin-11, claudin-3 and occludin) were significantly (two-to threefold) increased. By contrast, both protein localisation and mRNA levels for the adaptor protein zona occludens-1 decreased after gonadotrophin suppression. FSH replacement induced a rapid reorganisation of tight junction protein localisation. The functionality of the BTB (as inferred by biotin tracer permeation) was found to be strongly associated with the organisation and localisation of claudin-11. Surprisingly, JAM-A was also recognised on spermatogonia, suggesting an additional novel role for this protein in trans-epithelial migration of germ cells across the BTB. It is concluded that gonadotrophin regulation of tight junction proteins forming the BTB occurs primarily at the level of protein organisation and not gene transcription in this species, and that immunolocalisation of the organised tight junction protein claudin-11 correlates with BTB functionality.

Claudin and occludin expression and function in the seminiferous epithelium

“…However, in rats, occludin expression is stage-specific, with immunostain not detectable in Stage VIII tubules but strongly expressed at all other stages (Li et al 2006). Occludin expression is also stage-specific in Djungarian hamsters exposed to long-day photoperiods; the stage distribution was not reported (Tarulli et al 2008). Interestingly, occludin is not expressed in the seminiferous tubules of guinea pigs (Cavia porcellus) and men (Moroi et al 1998).…”

“…Thus in Djungarian hamsters, increased mRNA expressions of claudins 3 and 11 and occludin do not indicate increased BTB functionality. It was noted that in Djungarian hamsters, the responses of testicular claudins 3 and 11 and occludin to FSH stimulation occur during a time period when intratesticular testosterone levels are low (Tarulli et al 2008). This was interpreted as a difference between Djungarian hamsters and other rodent species regarding the importance of testosterone in establishing and maintaining the BTB.…”

“…There is no difference in claudin 11 mRNA and protein expression per Sertoli cell between irradiated testes of rats killed 10 days after local X-ray irradiation and non-irradiated testes of control rats; Table 3. Effects of FSH on expression of claudins 3 and 11 and occludin in Djungarian hamsters (Tarulli et al 2006(Tarulli et al , 2008 Review. Claudins and occludin in spermatogenesis C. M. K. Morrow et al 1689 at this time point spermatogonia are absent but spermatocytes and spermatids are present (Florin et al 2005).…”

AKAP9, a Regulator of Microtubule Dynamics, Contributes to Blood-Testis Barrier Function

“…The consequences of the shift in Factin and BTB proteins on BTB functionality cannot be predicted because it has been reported that the localization and/or expression of TJ proteins can change over the cycle of the seminiferous epithelium but permeability to the small molecule biotin is still restricted as far as the organized TJ immunoreactivity. 43 The shift, at least for F-actin, is likely not an indirect consequence of germ cell loss because the subcellular distribution of F-actin and intermediate filaments (vimentin) at the BTB is not markedly affected in W/W v mice, which also lack spermatogenic cells. 44,45 …”

Molecular mechanisms by which hormones and cytokines regulate cell junction dynamics in the testis

“…Other than rat models, studies on Djungarian hamsters have also demonstrated that exogenous supply of FSH to short-day photoperiod (8 h light:16 h darkness) hamsters whose gonadotropins are suppressed could restore the localization of junction proteins such as actin and espin at the apical ES, and claudin-11 and zonula occludens-1 (ZO-1) at the basal region of the seminiferous epithelium (Tarulli et al 2006). Using the same animal model, Tarulli et al (2008) have recently found that similar to claudin-11, claudin-3, occludin and JAM-A can rapidly be reorganized at the BTB upon FSH replacement. These results strongly suggest that in addition to spermiation, FSH regulates the integrity and functionality of the BTB via reorganization and relocalization of junction proteins.…”