In this study, LAMC2 mRNA was found to be differentially expressed in the ectopic endometrium of women with endometriosis compared with their eutopic endometrium (Figure 1B). The role of the laminin gamma 2 chain in the pathogenesis of endometriosis has not been previously evaluated, although some studies have implicated this protein in cancer invasion and metastasis. Therefore, we hypothesised that laminin gamma 2 chain could also play a role in the adhesion, migration and invasion of endometrial cells, which are required for the development of endometriosis . Laminin was previously found to be expressed in the glands and stroma of eutopic and ectopic endometrium however, the type of laminin investigated was unclear [14, 15]. Recently, altered expression of the LAMC1 gene was described in the endometrium of patients with endometriosis (compared with healthy endometrium) . The specific expression of the laminin gamma 2 chain has not been evaluated in human endometriosis; however, the laminin gamma 2 chain was recently described as being strongly associated with the initiation of endometriosis in a mouse model .
Endometriosis is a benign disease, although cells from endometriotic tissue and cancer cells share the ability to spread into and invade adjacent tissue. The molecular mechanisms that drive endometriosis cells to target other tissues are largely unknown. Our present data suggest that the laminin gamma 2 chain could be involved in the invasive activity of endometriotic cells as it has been found in the majority of ectopic endometrial glands.
The comparison of laminin gamma 2 chain expression in eutopic endometrium from patients without or with endometriosis also revealed significant differences (Figure 4C). The global expression score was significantly lower in eutopic endometrium from patients without endometriosis due to the number of positive glands and their intensity. Indeed, the eutopic endometrium of women without endometriosis more often displayed weaker glandular expression of the laminin gamma 2 chain. However, when analysing LAMC2 mRNA levels, we did not observe differences between eutopic endometrium from women with and without endometriosis (Figure 1C). One possible explanation for this result could be that the mRNA analysis was performed only on a limited number of RNA samples from the eutopic endometrium of women suffering from endometriosis (n = 9), whereas for protein analysis, a greater number of patients were analysed (n = 25). The differences between gene and protein expression could also be explained by post-transcriptional modification of mRNA and mature protein as well as protein degradation [18, 19]. Alternatively, small non-coding RNAs such as miRNAs, which are essentially translational repressors, could be involved in this process [20, 21]. Their absence in some physiological or pathogenic conditions can contribute to increases in the amount of protein translated from a given target mRNA without altering the amount of RNA.
The facts that the laminin gamma 2 chain was expressed unevenly and that its expression was interrupted at some points could facilitate epithelial cell motility. Our results are in agreement with a previous study showing that the laminin gamma 2 chain and the alpha 3 beta 1 integrin receptor could be involved in the mechanism of endometriosis .
Numerous studies using immunohistochemistry and in situ hybridisation have shown that the laminin gamma 2 chain is localised at the leading edge of invading carcinomas and that its expression is positively correlated with invasiveness and patient survival . However, other studies have shown that the expression of LN-332 is reduced during the progression of human carcinomas, and its expression is associated with lower invasive and metastatic activity [24, 25]. This discordance can be explained by the overexpression of the laminin gamma 2 chain monomer in tumour cells, as the laminin alpha 3 and/or beta 3 chains are often decreased or impaired in these cells [26–28]. We have previously shown that the acquisition of a migratory phenotype in epithelial cells in vitro is associated with the overexpression of MT1-MMP, which can participate in the pericellular degradation of the laminin gamma 2 chain monomer deposited by the migratory cells themselves, thereby providing a modified substrate that promotes cell migration . Differential laminin gamma 2 chain localisation and expression levels have been shown to be of prognostic value in colorectal , pancreatic  and lung adenocarcinomas  as well as gastric cancer . The serum concentrations of laminin gamma 2 fragments are also useful for assessing the treatment results and clinical courses of patients with head and neck squamous cell carcinoma . A weakness of our study is that sera from patients with and without endometriosis were not collected with the tissue samples.