141. DEVELOPMENT OF A MODEL SYSTEM TO ASSESS THE REGULATION OF LEYDIG STEM CELL DIFFERENTIATION

Abstract

The Leydig cells of the testis are responsible for the production of ca. 95% of all circulating androgens in the adult male. There is substantial evidence now that loss of Leydig cell (LC) functionality may account in part for declining androgen levels in the ageing male. Some of this loss of functionality appears to be due to disruption of early LC differentiation processes caused by exposure to environmental endocrine disrupting substances. We have made use of the ability of the alkylating agent ethane dimethane sulfonate (EDS) to destroy specifically all immature and adult LC to develop a model system which allows us to quantitatively assess the differentiation of a new population of LC from resident stem cells in the testis. Following a single bolus injection of EDS into adult Sprague Dawley rats, unless additional testosterone is present to suppress the HPG axis, new LC redifferentiate from the resident stem cells in the testis. These are small spindle-shaped mesenchymal cells which are located in the peritubular region adjacent to the seminiferous tubules. In the absence of mature LC these mesenchymal cells differentiate first into LC progenitor cells, then immature LC, and finally into adult LC, following a precisely defined kinetic which can be mapped using quantitative RT-PCR for LC specific genes in whole testis samples. We are using this model to examine the effect of in vivo application of known environmental endocrine disrupting agents on LC differentiation, and hence their potential to cause long-term loss of LC functionality.