Adrenal Gland Tumorigenesis after Gonadectomy in Mice Is a Complex Genetic Trait Driven by Epistatic Loci

Postgonadectomy adrenocortical tumorigenesis is a strain-specific phenomenon in inbred mice, assumed to be caused by elevated LH secretion and subsequent ectopic LH receptor (LHR) overexpression in adrenal gland. However, the molecular mechanisms of this cascade of events remain unknown. In this study, we took advantage of the mouse strain dependency of the phenotype to unravel its genetic basis. Our results present the first genome-wide screening related to this pathology in two independent F2 and backcross populations generated between the neoplastic DBA/2J and the nonsusceptible C57BL/6J strains. Surprisingly, the postgonadectomy elevation of serum LH was followed by similar up-regulation of adrenal LHR expression in both parental strains and their crosses, irrespective of their tumor status, indicating that it is not the immediate cause of the tumorigenesis. Linkage analysis revealed one major significant locus for the tumorigenesis on chromosome 8, modulated by epistasis with another quantitative trait locus on chromosome 18. Weight gain, a secondary phenotype after gonadectomy, showed a significant but separate quantitative trait locus on chromosome 7. Altogether, postgonadectomy adrenocortical tumorigenesis in DBA/2J mice is a dominant trait that is not a direct consequence of adrenal LHR expression but is driven by a complex genetic architecture. Analysis of candidate genes in the tumorigenesis linkage region showed that Sfrp1 (secreted frizzled-related protein 1), a tumor suppressor gene, is differentially expressed in the neoplastic areas. These findings may have relevance to the human pathogenesis of macronodular adrenal hyperplasia and adrenocortical tumors in postmenopausal women and why some of them develop obesity.