Cell-specific localization of apolipoprotein E messenger ribonucleic acid in the testis and epididymis of the rat.

Apolipoprotein (apo) E, a 35-kDa protein found on the surface of several lipoproteins, has been detected in many peripheral tissues and is postulated to function in facilitating the transfer of cholesterol/lipids between cells. We examined the expression of apo E mRNA in the testes and epididymides of juvenile rats (21 days old), prepubescent rats (34-36 days old), and sexually mature rats (75-80 days old). In situ hybridization using 35S-labeled rat apo E riboprobes was used to identify cells containing apo E mRNA. Such cells were located in the interstitial area of testes obtained from rats of all ages. This cell population consisted of primarily Leydig cells with occasional macrophages, according to immunoreactivity to 3 beta-hydroxysteroid dehydrogenase and antimacrophage antibodies, respectively. Caput epididymides obtained from sexually mature and prepubescent rats contained apo E mRNA-positive cells located in the basal region of the epididymal tubules and within the interstitial stroma. Our data are consistent with the concept that locally produced apo E plays a role in the physiologic function of the rat testis and epididymis.