Segment-specific changes with age in the expression of junctional proteins and the permeability of the blood-epididymis barrier in rats

Changes in gene expression during aging in the Brown Norway rat epididymis

Aging of the Brown Norway rat is associated with a decline in reproductive function. With advancing age, serum testosterone and sperm production decrease and sperm morphology is altered. In the epididymis, the site of sperm maturation and storage, dramatic histological and biochemical changes occur with age; these changes occur in a region-specific manner. In order to provide insight into the process of aging in the epididymis, we employed cDNA microarrays to analyze changes in gene expression with age in the initial segment, caput, corpus and cauda epididymidis. The overwhelming effect was a decrease in the relative intensity of gene expression during aging. In the initial segment, corpus and cauda epididymidis, more genes had decreased relative intensity with age than did not change. Interestingly, the magnitude of the decreases in relative intensity was considerably larger in the corpus and cauda epididymidis, where expression of 83% (211 of 254) and 62% (157 of 254), respectively, of the genes decreased by greater than 50% with age. This is in contrast to the initial segment, in which only 31% of genes (78 of 254) had relative intensities that decreased by at least 50%, and the caput epididymidis, the only segment where the largest proportion of genes did not change with age (less than 33% change between young and old). No genes had increased relative intensity with age throughout the tissue, however the expression of four transcripts was increased in a segment-specific manner. The expression of oxidative stress related genes, heat shock proteins and components of intracellular degradation pathways were examined in particular detail. We found that the relative intensity of some gene families decreased with age in a segment-specific manner; these decreases correlated well with the histological changes that occur in the aging epididymis.

Claudin-1 is not restricted to tight junctions in the rat epididymis

The blood-epididymal barrier creates a unique microenvironment critical for sperm maturation. There is little information on proteins comprising epididymal tight and adhering junctions or on factors regulating their expression. Claudins are a family of transmembrane proteins reported to be exclusively localized to tight junctions. In the present study the expression of claudin-l (Cl-1) was examined with respect to the different cell types of the epididymis and its various regions as well as its expression during postnatal development and regulation by testicular factors, using both immunocytochemistry and Northern blot analysis. RT-PCR of adult epididymal and testicular RNA (positive control) indicated that Cl-1 messenger RNA (mRNA) transcripts were present in all regions of the epididymis. In the adult, Cl-1 was localized immunocytochemically along the entire length of the lateral plasma membranes between adjacent principal cells, including apical areas containing tight junctions, as well as at the interface between principal and basal cells and along the basal plasma membrane of the epithelium in relation to the basement membrane. Northern blot analysis of adult epididymis with a rat Cl-1 complementary DNA indicated the presence of two hybridizing bands of 4.0 and 1.5 kb. Postnatally, in the caput-corpus and cauda epididymidis, mRNA levels for both transcripts were lowest on day 7. In the caput-corpus epididymidis, mRNA levels for the 1.5-kb transcript increased significantly between 7 and 14 days, whereas the levels of the 4.0-kb transcript were significantly higher by day 21. Postnatal studies revealed that in the initial segment and caput epididymidis, Cl-1 immunostaining was present along the entire length of the lateral plasma membranes of undifferentiated epididymal epithelial cells as early as day 7, including apical areas containing tight junctions. By day 21, staining was identical to that of adult animals, but as this is an age when androgen levels are not at their peak, the data would suggest that they are not a prominent factor regulating Cl-1 expression. Orchidectomy and orchidectomy plus testosterone replacement experiments revealed differences in Cl-1 immunostaining in the initial segment, suggesting that localization of Cl-1 in epididymal tight junctions is androgen dependant. Thus, Cl-1 expression in the initial segment appears to be only partially under the control of androgens. However, in all other epididymal regions, orchidectomy with or without testosterone replacement, revealed no changes to the normal staining pattern, suggesting that androgens do not regulate Cl-1 expression in these regions. Taken together, these studies demonstrate that Cl-1 expression in the epididymis is not localized exclusively to tight junctions, but appears along the entire interfaces of adjacent epithelial cells as well as along the basal plasma membrane, suggesting a role for Cl-1 as an adhesion molecule. The data also suggest that the regulation of Cl-1 in the epididymis is complex and multifactorial.