*4.2. MiRNA Sponging by LncRNAs in Endometriosis*

A growing body of evidence indicates that lncRNAs can act as miRNA sponges in endometriosis (summarized in Table 2). In these cases, a binding site for the miRNA is present in both the lncRNA and the targeted protein-coding gene, and there is a correlation between expression of the lncRNA and the protein-coding gene. In the first reported example of sponging in endometriosis, decreased levels of the H19 lncRNA was shown to be associated with an increase in *let-7* miRNA activity, which inhibits *IGF1R* expression resulting in the reduced proliferation of endometrial stroma cells [53]. These results suggested that the *H19*/*let7*/IGF1R pathway may contribute to impaired endometrial receptivity in women suffering from the disease. *H19* was also shown to regulate cell proliferation and invasion of ectopic endometrial cells by increasing ITGB3 expression via sponging of *miR-124-3p* [54]. *H19* has also been implicated in the impaired immune responses of women with the disease, by acting as a sponge for *miR-342-3p*, which regulates the IER3 pathway. This pathway has been implicated in Th-17 cell differentiation and endometrial stroma cell proliferation in ectopic sites in women with the disease [55]. Another lncRNA that has been shown to act as a sponge in endometriosis is *CDKN2B-AS1*, which acts as a regulator of AKT3 expression by sponging *miR-424-5p* in an in vitro model of ovarian endometriosis [56]. In another example, *LINC01116* promoted the proliferation and migration of endometrial stroma cells by targeting FOXP1 via sponging of *miR-9- 5p*, thereby promoting endometriosis lesion formation and growth [57]. *MALAT1* was identified as a sponge of *miR-200c* involved in the regulation of endometriosis stoma cell proliferation and migration by promoting ZEB1 and ZEB2 expression in women with the disease [58]. This regulation is not restricted to *miR-200c* and may include the entire *miR-200* family, consisting of *miR-200a*, *miR-200b*, *miR-200c*, *miR-141*, and *miR-429* [59]. In addition to these examples, other lncRNAs have also been implicated in endometriosis via their role as sponges for miRNAs, as summarized in Table 2.
