Lysosomal integral membrane proteins exhibit region and cell type specific distribution in the epididymis of the adult rat

Postnatal development and regulation of beta-hexosaminidase in epithelial cells of the rat epididymis

beta-Hexosaminidase (Hex) catalyzes the hydrolysis of terminal sugar residues from a number of substrates such as GM2 gangliosides, glycoproteins, glycolipids, and glycosaminoglycans. As an enzyme present in lysosomes of epithelial cells of the adult rat epididymis, it serves to degrade substances endocytosed from the epididymal lumen. In this way, it modifies and creates a luminal environment where sperm can undergo their maturational modifications. In this study, the postnatal developmental pattern of expression of Hex was examined in animals from days 7-56. In addition, the role of testicular factors on Hex expression in the different cell types and regions of the epididymis of adult rats was examined in orchidectomized and efferent duct-ligated rats. Both parameters were examined on Bouin-fixed epididymides in conjunction with light microscope immunocytochemistry. At postnatal day 7, the epithelium of the entire epididymis was unreactive for anti-Hex antibody. By day 21, narrow and clear cells of their respective regions became reactive, whereas basal cells became reactive only by day 29. Principal cells displayed only an occasional reactive lysosome at day 21, several by day 29, and numerous reactive lysosomes by day 39, comparable to the region-specific distribution noted for 90-day-old animals, and at an age when high androgen levels are attained. Thus, postnatal onset of Hex expression varies according to the different cell types of the epididymis, suggesting different regulatory factors. This finding was confirmed from studies employing adult orchidectomized and efferent duct-ligated adult rats. Indeed, in all experimental animals, Hex immunostaining in narrow, clear, and basal cells was intense and comparable to control animals. In contrast, there was a notable absence of lysosomal staining in principal cells at all time points after orchidectomy, which was restored, however, following testosterone replacement. No effect on Hex expression was observed in efferent duct-ligated animals. Taken together, the data suggest that Hex expression in lysosomes of principal cells is regulated by testosterone or one of its metabolites. However, the expression of Hex being independent of testicular factors in narrow, clear, and basal cells of adult animals, but occurring at different time points during postnatal development, suggests that different regulatory factors are responsible for onset of Hex expression in these cell types during development.

Characterization of cell- and region-specific abnormalities in the epididymis of cathepsin a deficient mice

Cathepsin A (PPCA), a lysosomal carboxypeptidase that functions as a protective protein for alpha-neuraminidase and beta-galactosidase in a multi-enzyme complex, has been shown to be expressed in the epithelial cells of the epididymis. In the present study, the epididymis of PPCA-/- mice from 2 to 10 months of age was compared with those of their wild-type counterparts. Major accumulations of pale vacuoles, corresponding to lysosomes, were noted in principal and narrow/apical cells in PPCA-/- mice, and clear cells also appearing highly vacuolated, were grossly enlarged in size. This was especially evident in the caput and corpus regions, where quantitative analyses confirmed that the epithelium of the tubules in these regions was expanding in profile area. In addition, the base of the epithelium in these regions was often greatly vacuolated, corresponding to cells that presented no identifiable features and appeared to be degenerating. Halo cells dispersed at various levels in the epithelium also appeared to be abnormal, accumulating pale lysosomes. Furthermore, numerous macrophages were observed in the intertubular space of the entire duct, presenting a large size and plethora of pale lysosomes. Taken together, the present data indicate major lysosomal abnormalities in the epididymis of PPCA-/- mice in a cell type and region specific manner. In addition, it is suggested that the compromised halo cells, due to PPCA deficiency within their lysosomes, cannot function properly and as a result there is a recruitment of macrophages in the intertubular space.

Regulation of sulfated glycoprotein-1 and cathepsin D expression in adult rat epididymis

Endocytosis, whereby proteins are internalized from the epididymal lumen to be eventually degraded in lysosomes, is one of the major functions of the epididymal epithelial cells in maintaining a proper luminal milieu conducive for sperm maturation. In the present study, using light microscope immunocytochemical methods, we examined the regulation of 2 lysosomal enzymes, sulfated glycoprotein-1 (SGP-1) and cathepsin D, in adult rat epididymides fixed in Bouin fixative and embedded in paraffin. After orchidectomy (O) with or without testosterone (T) supplementation, efferent duct ligation (EDL), or hypophysectomy (H), lysosomes of principal cells were intensely reactive with the anti-SGP-1 antibody, as were narrow, clear, and basal cells, with staining patterns similar to that of control animals. These experimental procedures also had no effect on cathepsin D expression in all cell types, except for clear cells of the corpus and cauda epididymidis, which after orchiedectomy and hypophysectomy, became intensely reactive, unlike their completely unreactive state in control animals. In O+T animals, as well as in EDL animals, clear cells remained unreactive. These data taken together suggest that expression of SGP-1 is not under the control of testicular or pituitary factors, as is also the case for cathepsin D expression by principal, narrow, and basal cells. However, specific inhibition of cathepsin D expression by testosterone or one of its metabolites appears to occur in clear cells of the corpus and cauda epididymidis. Furthermore, in addition to small, typical lysosomes, principal cells also revealed large supranuclear and infranuclear spherical structures that were immunoreactive with both anti-SGP-1 and anti-cathepsin D antibodies, suggesting their lysosomal nature. With electron microscopy, these structures appeared electron-lucent and contained membranous profiles embedded in an electron-dense, granular background. Such images suggest that the various experimental procedures adversely affect the expression of several other lysosomal enzymes in principal cells, leading to a lysosomal phenotype similar to that observed in various lysosomal storage diseases.

Expression and regulation of H+K+ATPase in lysosomes of epithelial cells of the adult rat epididymis

Endocytosis is an important event in the epididymis as it contributes to a luminal environment conducive for sperm maturation. Principal and clear cells contain numerous lysosomes which degrade many substances internalized by endocytosis from the epididymal lumen. The interior of the lysosomes depends on low pH to activate the release of their enzymes and to activate their acid hydrolases. In the present study, H+K+ATPase was localized by light microscopy in the adult rat epididymis of intact and of orchidectomized animals supplemented with testosterone or not. In normal animals, numerous lysosomes of nonciliated cells of the efferent ducts were intensely reactive for anti-H+K+ATPase antibody. In the initial segment, only a few lysosomes of principal cells were reactive. In the intermediate zone of the epididymis, numerous lysosomes of principal cells were intensely reactive, while the number of intensely reactive lysosomes decreased progressively from the proximal caput to the distal caput with none being seen in the proximal corpus region. In the distal corpus and cauda regions, only a few lysosomes of some principal cells were reactive. In contrast, clear cells of all regions showed intense reactivity. Orchidectomy resulted in the abolishion of H+K+ATPase in lysosomes of principal cells of all regions except the initial segment. However, while clear cells of the caput and corpus regions also became unreactive, those of the cauda region remained as reactive as in controls. Orchidectomized animals supplemented with testosterone maintained a staining pattern similar to controls for both cell types. These observations demonstrate the presence in principal and clear cells of H+K+ ATPase which may have an important role in acidifying the interior of their lysosomes. However, there is a region-specific expression of H+K+ATPase in lysosomes of principal cells, unlike that for clear cells. In addition, H+K+ATPase expression in lysosomes of principal cells depends on testosterone in all regions except the initial segment. However, in the case of clear cells, only those of the caput and the corpus regions are dependent on testosterone, while those of the cauda region appear to be regulated by some other factor.

Cathepsin A is expressed in a cell- and region-specific manner in the testis and epididymis and is not regulated by testicular or pituitary factors

The epithelial cells of the testis are involved in the production, differentiation, and sustenance of sperm, and those of the epididymis play a major role in sperm maturation, protection, and storage. These tissues express various proteins that respond differently to androgens. Cathepsin A is a multifunctional lysosomal carboxypeptidase that also functions as a protective and an activator protein for neuraminidase and beta-galactosidase. In this study, cathepsin A was immunolocalized by light and electron microscopy using a polyclonal affinity-purified antibody on the testis and epididymis of normal, orchidectomized with or without testosterone supplementation, efferent duct-ligated, and hypophysectomized adult rats. In normal rats, cathepsin A expression was noted in lysosomes of Sertoli and Leydig cells but not in germ cells of the testis, as well as nonciliated cells of the efferent ducts. In the epididymis, a cell- and region-specific distribution of cathepsin A was noted. In experimentally treated animals, no changes were noted in the expression of cathepsin A. Immunolabeling of tissues examined at the electron microscopic level revealed that lysosomes were reactive. These data indicate cell- and region-specific expression of cathepsin A in cells of the testis and epididymis and also indicate that cathepsin A expression is not regulated by testicular or pituitary factors.

Two Golgi integral membrane proteins (GIMPS) exhibit region- and cell type-specific distribution in the epididymis of the adult rat

The epididymis participates in the post-testicular maturation and storage of spermatozoa by secreting proteins into the tubule lumen in a region-specific fashion. The underlying molecular mechanisms leading to biogenesis of these region-specific differences, however, are not known, although components of the Golgi complex membrane container must undoubtedly be intimately involved. Two monoclonal antibodies raised against Golgi integral membrane proteins, recognizing either the cis (GIMPc) or trans Golgi (GIMPt) cisternae, were used as molecular probes of these regions to begin the characterization of the Golgi complex of in vivo and in vitro epididymal cells. Immunolocalization of GIMPs was performed on frozen sections and in cultured cells using biotin-streptavidin-peroxidase immunocytochemistry. In tissue sections, immunostaining of GIMPt was extremely robust in the supranuclear cytoplasm throughout the epididymis. In contrast, no GIMPc immunostaining was detected in the initial segment or in clear cells of the distal caput, corpus, and cauda. Immunodetection of GIMPc and GIMPt in epididymal cells in vitro revealed a reticular, perinuclear pattern, and NH4Cl treatment preferentially disrupted the GIMPt immunolocalization. These results characterizing the molecular components of the Golgi complex will form the basis of additional studies to gain further insight into mechanisms leading to generation of regional differences in epididymal function.