The expression of the RLF/INSL3 gene is reduced in Leydig cells of the aging rat testis

The relaxin-like factor (RLF), which is the product of the INSL3 gene, is highly expressed in the fetal and adult-type Leydig cells of all species so far examined. In adult testes it is upregulated at puberty but appears subsequently to be expressed in a constitutive manner, independently of acute changes in the hypothalamic-pituitary-gonadal (HPG) axis. Functional hypogonadism with decreased testosterone is prevalent in the aging male. In order to test whether this is a property of the HPG axis, or of the Leydig cells themselves. RLF/INSL3 was used as an independent marker to assess rat Leydig cell differentiation status. Hybridization analysis showed that in the testes of old (2 years) rats, RLF/INSL3 mRNA expression was dramatically reduced, compared to young (3 months) animals. This was also evident at the protein level using immunohistochemistry. The results suggest that increasing functional hypogonadism in older male mammals is likely caused by a dedifferentiation of the Leydig cells themselves. (C) 2002 Elsevier Science Inc. All rights reserved.