Lnc-HZ01 with m6A RNA methylation inhibits human trophoblast cell proliferation and induces miscarriage by up-regulating BPDE-activated lnc-HZ01/MXD1 positive feedback loop

Environmental BaP (benzo(a)pyrene) and its metabolite BPDE (benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide) inhibit proliferation of human villous trophoblast cells, which might further induce recurrent miscarriage (RM). However, the underlying mechanisms remain largely unknown. In this work, we identified a novel lncRNA HZ01 (lnc-HZ01) that is up-regulated in both RM tissues and BPDE-exposed trophoblast cells. Lnc-HZ01 inhibits trophoblast cell proliferation and induces miscarriage. Mechanistically, lnc-HZ01 promotes MXD1 mRNA transcription by up-regulating its transcription factor c-JUN and also enhances MXD1 protein stability by up-regulating its deubiquitin enzyme USP36. Reversely, MXD1 up-regulates lnc-HZ01 level by enhancing its RNA stability due to the increased level of m6A RNA methylation on lnc-HZ01, the first example that m6A modification regulates trophoblast cell functions. Thus, lnc-HZ01 and MXD1 comprise a positive self-feedback loop, which is up-regulated in both RM tissues and BPDE-exposed trophoblast cells. Once this loop is activated by BaP or BPDE exposure, both pathways in this loop would be up-regulated, promote EIF4E transcription, inhibit trophoblast cell proliferation, and further induce miscarriage. This work provides new clinical and scientific understanding in unexplained miscarriage.