Endogenous retrotransposons cause catastrophic deoxyribonucleic acid damage in human trophoblasts

Objective: To determine the mechanistic role of mobile genetic elements in causing widespread DNA damage in primary human trophoblasts.

Design: Experimental ex vivo study.

Setting: Hospital-affiliated University.

Patient(s): Trophoblasts from a patient with unexplained recurrent pregnancy loss and patients with spontaneous and elective abortions (n = 10).

Intervention(s): Biochemical and genetic analysis and modification of primary human trophoblasts.

Main outcome measure(s): To phenotype and systematically evaluate the underlying pathogenic mechanism for elevated DNA damage observed in trophoblasts derived from a patient with unexplained recurrent pregnancy loss, transcervical embryoscopy, G-band karyotyping, RNA sequencing, quantitative polymerase chain reaction, immunoblotting, biochemical and siRNA assays, and whole-genome sequencing were performed.

Result(s): Transcervical embryoscopy revealed a severely dysmorphic embryo that was euploid on G-band karyotyping. RNA sequencing was notable for markedly elevated LINE-1 expression, confirmed with quantitative polymerase chain reaction, and that resulted in elevated expression of LINE-1-encoded proteins, as shown by immunoblotting. Immunofluorescence, biochemical and genetic approaches demonstrated that overexpression of LINE-1 caused reversible widespread genomic damage and apoptosis.

Conclusion(s): Derepression of LINE-1 elements in early trophoblasts results in reversible but widespread DNA damage.