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 sever al lipoproteins, has been detected in many peripheral tissues and is p ostulated to function in facilitating the transfer of cholesterol/lipi ds between cells. We examined the expression of apo E mRNA in the test es and epididymides of juvenile rats (21 days old), prepubescent rats (34-36 days old), and sexually mature rats (75-80 days old). In situ h ybridization using S-35-labeled rat apo E riboprobes was used to ident ify cells containing apo E mRNA. Such cells were located in the inters titial area of testes obtained from rats of all ages. This cell popula tion consisted of primarily Leydig cells with occasional macrophages, according to immunoreactivity to SB-hydroxysteroid dehydrogenase and a ntimacrophage antibodies, respectively. Caput epididymides obtained fr om sexually mature and prepubescent rats contained apo E mRNA-positive cells located in the basal region of the epididymal tubules and withi n the interstitial stroma. Our data are consistent with the concept th at locally produced apo E plays a role in the physiologic function of the rat testis and epididymis.