Pregnancy-induced adaptations in intramuscular extracellular matrix of rat pelvic floor muscles

Abstract

BACKGROUND Birth trauma to pelvic floor muscles is a major risk factor for pelvic floor disorders. Intramuscular extracellular matrix determines muscle stiffness, supports contractile component, and shields myofibers from mechanical strain. OBJECTIVE Our goal was to determine whether pregnancy alters extracellular matrix mechanical and biochemical properties in a rat model, which may provide insights into the pathogenesis of pelvic floor muscle birth injury. To examine whether pregnancy effects were unique to pelvic floor muscles, we also studied a hind limb muscle. STUDY DESIGN Passive mechanical properties of coccygeus, iliocaudalis, pubocaudalis, and tibialis anterior were compared among 3-month old Sprague–Dawley virgin, late-pregnant, and postpartum rats. Muscle tangent stiffness was calculated as the slope of the stress–sarcomere length curve between 2.5 and 4.0 μm, obtained from a stress-relaxation protocol at a bundle level. Elastin and collagen isoform concentrations were quantified by the use of enzyme-linked immunosorbent assay. Enzymatic and glycosylated collagen crosslinks were determined by high-performance liquid chromatography. Data were compared by the use of repeated-measures, 2-way analysis of variance with Tukey post-hoc testing. Correlations between mechanical and biochemical parameters were assessed by linear regressions. Significance was set to P < .05. Results are reported as mean ± SEM. RESULTS Pregnancy significantly increased stiffness in coccygeus (P < .05) and pubocaudalis (P < .0001) relative to virgin controls, with no change in iliocaudalis. Postpartum, pelvic floor muscle stiffness did not differ from virgins (P > .3). A substantial increase in collagen V in coccygeus and pubocaudalis was observed in late-pregnant, compared with virgin, animals, (P < .001). Enzymatic crosslinks decreased in coccygeus (P < .0001) and pubocaudalis (P < .02) in pregnancy, whereas glycosylated crosslinks were significantly elevated in late-pregnant rats in all pelvic floor muscles (P < .05). Correlations between muscle stiffness and biochemical parameters were inconsistent. In contrast to the changes observed in pelvic floor muscles, the tibialis anterior was unaltered by pregnancy. CONCLUSIONS In contrast to other pelvic tissues, pelvic floor muscle stiffness increased in pregnancy, returning to prepregnancy state post-partum. This adaptation may shield myofibers from excessive mechanical strain during parturition. Biochemical alterations in pelvic floor muscle extracellular matrix due to pregnancy include increase in collagen V and a differential response in enzymatic vs glycosylated collagen crosslinks. The relationships between pelvic floor muscle biochemical and mechanical parameters remain unclear.

Structure–function relationship of the human external anal sphincter

“…[23]. Briefly, three bundles from the anterior and posterior portions of each specimen were tested using a custom apparatus, equipped with a motor and a force-transducer [24]. L s , measured throughout experiments by laser diffraction, provided objective quantification of muscle strain and myofibrillar array quality control.…”

“…Force - L s data were generated for each bundle subjected to a stress-relaxation protocol, consisting of bundle elongation until failure, or to an L s of 4.0 μm in 10% strain increments followed by 3-min stress-relaxation periods. Force was converted to stress by dividing force by baseline cross-sectional area, assuming isovolumetric cylindrical shape of fiber bundles [24]. The slopes of the stress-L s curves between 2.0 and 4.0 μm were used to calculate tangent stiffness, which quantifies stiffness at a given L s .…”

Effect of Pregnancy and Delivery on Cytokine Expression in a Mouse Model of Pelvic Organ Prolapse

“…During pregnancy, pelvic tissues undergo significant remodeling in preparation for childbirth, a process in which LOXL1 and its absence has a significant impact. 16,32–35 For example, matrix metalloproteinase-2 (MMP2), which has been shown to modulate CCL-7, is upregulated late in pregnancy by high levels of estrogen and progesterone. 36 Therefore the increase in Ccl7 and Cxcl12 expression in KO mice could be due to differences in tissue remodeling between the two genotypes due to Loxl1 deficiency.…”

Multimodal imaging assessment and histologic correlation of the female rat pelvic floor muscles’ anatomy

“…Furthermore, using this model, we have discovered the existence of protective pregnancy‐induced adaptations in these muscles (Alperin et al. , ). The above is the first step in the continuum of research focused on deciphering what segregates women who do and do not sustain PFM birth trauma (Catanzarite et al.…”