Molecular Mechanisms of Treatment Resistance in Endometriosis: The Role of Progesterone-Hox Gene Interactions

HOX genes, encoding homeodomain transcription factors, are dynamically expressed in endometrium, where they are necessary for endometrial growth, differentiation, and implantation. In human endometrium, the expression of HOXA10 and HOXA11 is driven by sex steroids, with peak expression occurring at time of implantation in response to rising progesterone levels. However, the maximal HOXA10 and HOXA11 expression fails to occur in women with endometriosis. In endometriosis, altered progesterone receptor expression or diminished activity may lead to attenuated or dysregulated progesterone response and decreased expression of progesterone-responsive genes including HOX genes in the eutopic endometrium. In turn, other mediators of endometrial receptivity that are regulated by HOX genes, such as pinopodes, alpha v beta 3 integrin, and IGFBP-1, are downregulated in endometriosis. HOXA10 hypermethylation has recently been demonstrated to silence HOXA10 gene expression and account for decreased HOXA10 in the endometrium of women with endometriosis. Silencing of progesterone target genes by methylation is an epigenetic mechanism that mediates progesterone resistance. The relatively permanent nature of methylation may explain the widespread failure of treatments for endometriosis-related infertility.