Abstract
Pelvic floor muscle (PFM) injury during childbirth is a key risk factor for subsequent pelvic floor disorders that affect millions of women worldwide. Muscle stem cells (MuSCs) play a central role in the regeneration of injured skeletal muscles, where they activate, proliferate, and differentiate to assure myogenesis needed for muscle recovery. For robust regenerative function, MuSCs require the support of fibro-adipogenic progenitors (FAPs) and immune cells. To elucidate the role of MuSCs, FAPs, and immune infiltrate in female PFM regeneration, we used radiation to perturb the system and followed PFM recovery in a simulated birth injury (SBI) rat model. Non-irradiated and irradiated rats were euthanized at 3,7, 10, and 28 days after SBI; PFMs were harvested and prepared for immunohistochemistry. Cross sectional area (CSA) of all PFM myofibers 28 days after injury in irradiated animals was significantly lower relative to non-irradiated injured controls, indicating impairment of PFM recovery. Following SBI in non-irradiated animals, the number of MuSCs and FAPs expanded significantly at 7 and 3 days after injury, respectively; this expansion did not occur in irradiated animals at the same time points. CSA of embryonic myosin heavy chain (eMyHC, marker of newly regenerated myofibers) positive fibers was also significantly smaller following SBI in irradiated muscles compared to PFMs from non-irradiated injured controls at 7 days. Our results demonstrate that loss of function and decreased expansion of MuSCs and FAPs associated with irradiation results in impaired PFM recovery, signifying essential roles for MuSCs and FAPs in the regenerative process of female PFMs after birth injury. These findings can inform the identification of novel preventative and therapeutic targets and the development of new treatments for PFM dysfunction and associated pelvic floor disorders.
Competing Interest Statement
KLC is co-founder, consultant, board member, and holds equity interest in Ventrix, Inc. MA serves on the Medical Advisory Board of Renovia, Inc. and receives editorial stipend from American Journal of Obstetrics and Gynecology. KLC, MA, and PD are inventors on a patent application (US20200197567A1).
Footnotes
Declaration of interest: KLC is co-founder, consultant, board member, and holds equity interest in Ventrix, Inc. MA serves on the Medical Advisory Board of Renovia, Inc. and receives editorial stipend from American Journal of Obstetrics and Gynecology. KLC, MA, and PD are inventors on a patent application (US20200197567A1) related to this work.
Funding: The authors gratefully acknowledge funding for this project provide by the National Institute of Health/ Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) grants R01HD092515 and R01HD102184, and the Academic Senate Grant, University of California San Diego.