Transcriptomic evidence of remodeling in postpartum levator ani muscle associated with maternal age and recovery time after first vaginal delivery

BACKGROUND: Older maternal age at first vaginal delivery, defined in some studies as ≥30 years old, confers a substantial increased risk of pelvic organ prolapse. Age-related impairment of postpartum recovery of levator ani muscles may help explain this association; yet, little is known about the biomolecular changes that occur in the levator ani after vaginal delivery, or with aging. OBJECTIVE: To evaluate the transcriptional signature of the levator ani immediately after vaginal delivery and 6 to 8 weeks postpartum among young primiparas (18-25 years) and older primiparas (≥35 years). STUDY DESIGN: This study is a prospective study in which nulliparous women were recruited in the third trimester of pregnancy. Levator ani muscle biopsies were obtained immediately after vaginal delivery and at 6 to 8 weeks postpartum. Clinical measures of pelvic floor support and levator ani muscle function were obtained at the 6 to 8-week postpartum visit. Biopsies were analyzed using RNA sequencing methods and differentially expressed genes were compared with those reported in prior studies of pelvic organ prolapse patients. We used a moderated t test (false discovery rate <5%) to identify differentially expressed genes associated with postpartum delivery, maternal age, and the interaction between the 2. Principal component analysis confirmed segregation of clinical phenotype variables based on gene expression. RESULTS: Eight women (3 young and 5 older) underwent levator ani biopsies at both time points and had sufficient tissue for analyses. A total of 58 differentially expressed genes were identified when evaluating the interaction of age and recovery interval, including TP53BP1 (upregulated), PRR12 (upregulated), ZNF316 (upregulated), and PLK3 (downregulated). Between age groups, 309 differentially expressed genes were identified, while 159 were identified between time points. Both age groups were enriched for core tissue repair and homeostatic programs. Twenty of the differentially expressed genes identified in the separate analyses of age and time were previously identified in 4 case-control studies of pelvic organ prolapse. The correlation between the transcriptomic signature (principal component 3) and the overall clinical phenotype profile (principal component 1) was significant (ρ=0.88, false discovery rate <0.05), while the correlation observed with maternal age alone was not (ρ=-0.72). CONCLUSION: In agreement with clinical evidence, the effects of maternal age on levator ani muscle recovery can be seen at the transcriptional level. Age and recovery time share similar biological processes that, when disrupted, may predispose the levator ani to altered recovery and long-term susceptibility to pelvic organ prolapse. Specifically, elevated TP53BP1 combined with reduced PLK3 suggests a pattern of disrupted p53-regulated checkpoint and elevated cellular senescence(definition) which would impair healing. Results from the principal component analysis indicate that the transcriptomic signature captures clinical features beyond chronological age alone. Together, this study suggests a mechanistic pathway whereby aged levator ani may be at an increased risk of further dysfunction and disease and opens the possibility of targeted therapies to prevent pelvic organ prolapse.