IMMUNOLOCALIZATION OF APOLIPOPROTEIN-E IN THE TESTIS AND EPIDIDYMIS OF THE RAT

Apolipoprotein (ape) 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 in the testes an d epididymides of juvenile rats (21 days old), prepubescent rats (34-3 6 days old) and sexually mature rats (75-80 days old). Apo E was local ized by means of a polyclonal rabbit anti-rat apo E antibody and stand ard immunocytochemical techniques. Strong positive staining for apo E was observed in the interstitial space of the testes from all rats. Ap o E-containing cells were identified as Leydig cells through use of a 3 beta-hydroxysteroid dehydrogenase antibody on serial sections. In co ntrast to sexually mature rats, the two younger groups of rats also sh owed positive staining for apo E within the seminiferous tubule associ ated with Sertoli and germ cells. In addition, strong positive stainin g for apo E was observed in the stroma of the caput, corpus, and cauda epididymides from rats of all ages. This study demonstrates that apo E is differentially localized during development of the testes, sugges ting a regulatory and/or cholesterol transport role.