(W171) THE EXPRESSION AND LOCALIZATION OF THE SCAVENGER RECEPTOR CLASS B TYPE I (SRBI) AND TYPE II (SRBII) IN THE TWO COMPARTMENTS OF THE TESTIS DURING THE POSTNATAL DEVELOPMENT AND THE SEASONAL ANNUAL REPRODUCTIVE CYCLE IN THE ADULT IN THE MINK.
Akpovi, Casimir1, Vitale, María1, Pelletier, R.-Marc1, 1 Université de Montréal, Montréal, QC, Canada
ABSTRACT- We showed that the total cholesterol concentration in the interstitium equals that in seminiferous tubules. In Leydig cells, cholesterol origins from synthesis or from the blood via HDL and LDL. However, in the tubules, the origin of cholesterol is enigmatic because a blood-tubule barrier prevents entry of the circulating cholesterol and the Sertoli cells likely synthesize insignificant quantities of the compound in vivo. We hypothesize that the selective transporters of cholesterol SRBI and SRBII bypass the blood barrier to contribute in the tubules the cholesterol levels necessary for completion of spermatogenesis. To assess whether SRBI and SRBII played distinct roles in each of the two cellular compartments of the testis, the expression of each isoform was measured in enriched fractions of tubules (STf) and interstitial tissue (ITf) obtained each 30 days- (d) interval throughout postnatal development (from 60d to 270d after birth) and throughout the twelve-month seasonal reproductive cycle in adult mink. Western blot analyses showed that SRBI antibodies detected a band of 82kDa and SRBII antibodies recognized a band of 85kDa in both tissue fractions. In ITf, SRBI levels increased significantly with development. Thelevels were increased during the active spermatogenic phase and peaked by January-February but they decreased significantly during the inactive phase in the adult. SRBI also increased during the first half of development peaked in STf by 150d however, they decreased significantly until 270d. The profiles of SRBI in adult STf were similar to the ones described in ITf. SRBII increased significantly but later than SRBI during development, from 150d to 270d. In addition, SRBII also increased significantly with the spermatogenic activity in adult ITf but later than SRBI during the annual seasonal reproductive cycle. The profiles of SRBII in STf were similar to the ones described above in ITf during postnatal development and during the annual reproductive cycle. SRBI localized to Sertoli cells, germ cells, Leydig cells and endothelial cells and SRBII to spermatids and Sertoli cells during the testicular regression. The results support the notion that SRBI and SRBII play distinct roles in the cholesterol transport within the testis. Supported by NSERC.
KEY WORDS: SRBI, SRBII, cholesterol, testis