Immunohistochemical Studies on the Localization of Cellular Retinol-Binding Protein in Rat Testis and Epididymis

Abstract

The immunohistochemical localization of cellular retinol-binding protein (CRBP) was studied in rat testis and epididymis. Parallel studies were also carried out on the localization of plasma retinol-binding protein (RBP) and transthyretin (TTR) in testis. The studies employed antibodies purified by immunosorbent affinity chromatography, permitting the specific staining and localization of each antigen by the unlabeled peroxidase-antiperoxidase method. For RBP and TTR, specific immune staining was found in the interstitial spaces between the seminiferous tubules, and not in the tubules themselves. In contrast, strong specific immune staining for CRBP was found in the seminiferous tubules, with a striking localization within Sertoli cells. Moreover, a distinct cyclic variation of specific staining for CRBP within Sertoli cells was observed during the spermatogenic cycle. This cyclic variation was seen with regard to both the intensity of staining and to the anatomic distribution of CRBP within the Sertoli cells. Within the epididymis CRBP was selectively localized to the proximal portion of the caput epididymidis, with variations in intensity of the staining of the epithelium of the ducts in different histological zones. Specific immune staining for CRBP was very weak or absent in the other portions of the epididymis. These results were confirmed by radioimmunoassay. Vitamin A-deficient rats showed markedly reduced specific immune staining for CRBP in both testes and epididymides, and greatly reduced levels of CRBP in these tissues on radioimmunoassay. These studies on the localization of CRBP provide information concerning the specific cells and anatomic loci within the testis and epididymis where retinol may be playing an important role in sperm formation and maturation.

Importance of ALDH1A enzymes in determining human testicular retinoic acid concentrations

“…Previously, rat ALDH1A1 has been shown to recognize holo-CRBP1 as a substrate ( 9 ), but the effect of CRBP1 on at RA formation by human ALDH1A enzymes has never been reported. Similarly CBRP1 expression in the Sertoli cells of rats ( 42 ) has been shown suggesting that CRBPs play an important role in modulating intratesticular RA metabolism. While ALDH1A1 was predicted to be the major contributor to at RA formation in the absence of CRBPs, when the inhibition of ALDH1A1 and activation of ALDH1A2 by CRBP1 was accounted for, ALDH1A2 was predicted to be the predominant enzyme forming at RA in the testis.…”

Plasma and cellular retinoid-binding proteins and transthyretin (prealbumin) are all localized in the islets of Langerhans in the rat.

“…Each' of these proteins was found to be localized in specific cells within each organ. Highly specific localization of CRBP has also been observed in the testis and epididymis (8,9). These studies provide information concerning the specific cells and anatomic loci, within different organs, where retinol and/or its binding proteins may be playing important biological roles.…”

“…*The islet values given in this column are considered less accurate than the values given in units of ug/mg of protein, because of the lower accuracy inherent in the estimate of the wet weight of the islets studied. These values are, however, useful for comparison with values available for other tissues in these units (9,10,20,31).…”

Localization of cellular retinol-binding protein and retinol-binding protein in cells comprising the blood-brain barrier of rat and human.

“…The Sertoli cells of the testes and the retinal pigment epithelium (RPE) of the eye contain tight junctions between adjacent cells, forming the blood-testes and part of the blood-retina barriers, respectively. Sertoli cells and RPE cells contain high levels of CRBP (3)(4)(5). The presence of CRBP within four different cell types comprising separate blood-organ barriers strongly suggests a common functional link for CRBP in these cells.…”

“…A cytoplasmic protein termed cellular retinol-binding protein (CRBP) may then transport the internalized retinol through the aqueous milieu of the cytoplasm to intracellular sites of action or metabolism (2). Studies of the retina (3) and testes (4,5) have demonstrated high levels of CRBP in some of the cells that form the blood-retina and blood-testis barriers, suggesting a role for CRBP in the transcellular movement of retinol across these blood-organ barriers. CRBP is present in human (6) and rat (7,8) brain and further fixed for 1 hr in cacodylate-buffered 1% osmium tetroxide, dehydrated, and embedded in Araldite 502 (CIBA Pharmaceutical).…”