|Ph.D Student||Bardoogo-Leichtmann Yael|
|Subject||Mechanisms and Controls of Iron Transport through the Blood|
|Department||Department of Biotechnology and Food Engineering||Supervisor||Dr. Esther Meyron Holtz|
|Full Thesis text|
The universal importance of iron, its high toxicity and complex chemistry present a challenge to biological systems in general and to protected compartments in particular. The high mitotic rate and avid mitochondriogenesis of developing male germ-cells imply high iron requirements. Yet, access to germ cells is tightly regulated by the blood-testis-barrier that protects the meiotic and post-meiotic germ cells. To elucidate how iron is supplied to developing male germ cells and how supply is regulated, we analyzed iron deposition by Perls stain and iron transport proteins in testes of mice with iron overload and with genetic ablation of the iron regulators Hfe and Iron Regulatory Protein 2 by immunohistochemistry and immunoblots. In addition, ferritin secretion was analyzed. In the testes, iron accumulated mainly around seminiferous tubules and only small amounts localized within the seminiferous tubules. The localization and regulation of proteins involved in iron import, storage and export such as transferrin, transferrin receptor, the divalent metal transporter-1, cytosolic ferritin and ferroportin strongly support a model of a largely autonomous iron-cycle within seminiferous tubules. Within the seminiferous tubules, highest transferrin receptor expression is found on early to mid primary spermatocytes. The colocalization of transferrin receptor with transferrin and divalent metal transporter-1 suggested an active role for transferrin receptor in transferrin dependent iron import to primary spermatocytes, within the seminiferous tubules. Divalent metal transporter-1 localization in the luminal compartment of the seminiferous tubules supported our hypothesis that its main role may be in iron transport during the final steps of germ cell maturation. Our data show that most peripheral iron remains stored in ferritin in the interstitial space, that ferritin within the seminiferous tubules was mainly synthesized in Sertoli cells and that ferritin-secretion from Sertoli cells may play an important role in iron acquisition of primary spermatocytes. Ferroportin is located at the periphery of the seminiferous tubules and on interstitial blood vessels and demonstrated a testis specific regulation. We suggest that during spermatogenesis, iron moves from primary spermatocytes to spermatids, which deliver during elongation most iron to the apical compartment of Sertoli cells. From there iron is routed back to a new generation of spermatocytes. Losses are replenished by the peripheral circulation. Such an internal iron cycle detaches iron homeostasis within the seminiferous tubules from the periphery and protects developing germ cells from peripheral nutrient fluctuations. This newly developed model explains how compartmentalization can optimize cellular and systemic nutrient homeostasis.