Calpain7 Negatively Regulates Human Endometrial Stromal Cell Decidualization in EMS by Promoting Foxo1 Nuclear Exclusion by Increasing the Phosphorylation of AKT1

Background: Endometrial receptivity damage caused by impaired decidualization may be one of the mechanisms of infertility in endometriosis (EMs). Our previous study demonstrated that CAPN7 is abnormally overexpressed in EMs. Whether CAPN7 affects the regulation of decidualization remains to be determined. Methods: The expression of CAPN7 during decidualization in endometria was examined by IHC and western blotting. The transduction of a CAPN7 recombinant adenovirus into human endometrial stromal cells was performed to investigate relevant decidualization marker genes. An artificial decidualization experiment was performed to study the role of CAPN7 in decidualization in vivo. The potential molecular mechanisms were further confirmed through immunofluorescence and coimmunoprecipitation analyses. IHC analysis was performed to evaluate differentially expressed proteins, including CAPN7, p-AKT1 and p-FoxO1, between the fertile control and EMs groups. Findings: CAPN7 expression decreased during human endometrial stromal cell (HESC) decidualization in vitro. CAPN7 negatively regulated decidualization in vitro and in vivo. In addition, CAPN7 notably promoted the phosphorylation of FoxO1 at Ser319, Ser256 and Thr24, leading to increased FoxO1 exclusion from nuclei in decidualized HESCs. Furthermore, the overexpression of CAPN7 obviously promoted the phosphorylation of AKT1, which is upstream of FoxO1, at Ser473. We also identified one conserved potential PEST sequence in the AKT1 protein and found that CAPN7 was able to hydrolyse AKT1. Interpretation: CAPN7 might serve as a promising therapeutic target for improving endometrial receptivity in women with EMs. Funding: This work was supported by the National Key Research and Development Program of China (2018YFC1004400), the National Natural Science Foundation of China (No. 81070492, No. 81871165 and No. 31872846), a grant from Jiangsu Provincial Key Research and Development (BE2018602), and a special grant for principal investigators from the Health Department of Jiangsu Province (ZDRCA2016070). Declaration of Interest: We declare no potential conflicts of interest concerning the research, authorship, and/or publication of this article. Ethical Approval: All samples were collected with the informed consent of the patients, and approval from the ethics committee was obtained for this study.