Evidence of macrophage modulation in the mouse pubic symphysis remodeling during the end of first pregnancy and postpartum.

In mouse pregnancy, pubic symphysis (PS) remodels into an elastic interpubic ligament (IpL) in a temporally regulated process to provide safe delivery. It restores at postpartum to assure reproductive tract homeostasis. Recently, macrophage localization in the IpL and dynamic changes in the expression of inflammatory mediators observed from the end of pregnancy (D18, D19) to early days postpartum (1dpp, 3dpp) highlighted the necessity of the identification of the key molecules involved in innate immune processes in PS remodeling. Therefore, this study uses morphological and high-sensitivity molecular techniques to identify both macrophage association with extracellular matrix (ECM) remodeling and the immunological processes involved in PS changes from D18 to 3dpp. Results showed macrophage association with active gelatinases and ECM components and 25 differentially expressed genes (DEGs) related to macrophage activities in interpubic tissues from D18 to 3dpp. Additionally, microarray and proteomic analysis showed a significant association of interpubic tissue DEGs with complement system activation and differentially expressed proteins (DEPs) with phagocytosis, highlighting the involvement of macrophage-related activities in mouse PS remodeling. Therefore, the findings suggest that PS ECM remodeling is associated with evidence of macrophage modulation that ensures both IpL relaxation and fast PS recovery postpartum for first labor.

Elastic fiber assembly in the adult mouse pubic symphysis during pregnancy and postpartum.

Impairment of pelvic organ support has been described in mice with genetic modifications of the proteins involved in elastogenesis, such as lysyl oxidase-like 1 (LOXL1) and fibulin 5. During pregnancy, elastic fiber-enriched pelvic tissues are modified to allow safe delivery. In addition, the mouse pubic symphysis is remodeled in a hormone-controlled process that entails the modification of the fibrocartilage into an interpubic ligament (IpL) and the relaxation of this ligament. After first parturition, recovery occurs to ensure pelvic tissue homeostasis. Because ligaments are the main supports of the pelvic organs, this study aimed to evaluate elastogenesis in the IpL during mouse pregnancy and postpartum. Accordingly, virgin, pregnant, and postpartum C57BL/6 mice were studied using light, confocal, and transmission electron microscopy as well as Western blots and real-time PCR. Female mice exhibited the separation of the pubic bones and the formation, relaxation, and postpartum recovery of the IpL. By the time the IpL was formed, the elastic fibers had increased in profile length and diameter, and they consisted of small conglomerates of amorphous material distributed among the bundles of microfibrils. Our analyses also indicated that elastin/tropoelastin, fibrillin 1, LOXL1/Loxl1, and fibulin 5 were spatially and temporally regulated, suggesting that these molecules may contribute to the synthesis of new elastic fibers during IpL development. Overall, this work revealed that adult elastogenesis may be important to assure the elasticity of the pelvic girdle during preparation for parturition and postpartum recovery. This finding may contribute to our understanding of pathological processes involving elastogenesis in the reproductive tract.

Relaxation of the mouse pubic symphysis during late pregnancy is not accompanied by the influx of granulocytes.

In some animals, such as mice and guinea pigs, a hormonally controlled mechanism increases the flexibility of the pubic symphysis and enhances the cervical remodeling necessary for safe delivery. Cervical ripening during pregnancy is associated with a paradoxical influx of leukocytes. However, the changes in cell metabolism during relaxation of the mouse pubic symphysis for delivery have not been extensively studied. In this work, we used light microscopy and transmission and scanning electron microcopy, as well as immunohistochemistry and Western blotting for MMP-8, to investigate the involvement of granulocytes or resident stromal cells in the relaxation of the virgin pubic symphysis during late pregnancy (days 18 and 19, before delivery) in vivo and in explanted joints. MMP-8 was studied because this collagenase is a hallmark for cervical ripening associated with the influx of granulocytes during late pregnancy. Extensive dissolution and disorganization of the extracellular matrix was seen around fibroblastic-like cells in late pregnancy. In contrast to the cervix (positive control), morphological and immunohistochemical analyses revealed that there was no characteristic cellular inflammatory response in the interpubic tissue. Staining for MMP-8 was observed in chondroid and fibroblastic-like cells of virgin and relaxed interpubic ligament, respectively. However, no granulocytes were seen during the extensive remodeling of the pubic joint in late pregnancy. These results indicate that constitutive stromal cells may have an important role in tissue relaxation during remodeling of the pubic symphysis in pregnancy.

The mouse pubic symphysis as a remodeling system: morphometrical analysis of proliferation and cell death during pregnancy, partus and postpartum.

Marked changes in mice pubic symphysis occur by the end of pregnancy. Tissue remodeling involves a dynamic balance between cell proliferation and programmed cell death as well as changes in the extracellular matrix components. Therefore, it is important to consider both of these cellular behaviors when investigating the mechanism that regulates interpubic tissue remodeling, growth during late pregnancy and partus ensuring involution during the postpartum period. Proliferating and programmed death cells were identified by immunohistochemistry (proliferating cell nuclear antigen and TUNEL detection, respectively) and the rates at which these processes occurred were determined by morphometric analysis. The results demonstrated that cellular proliferation was intense during the period of ligament formation, from D15 to D18, thereafter abruptly declining on D19. From parturition (D19) onwards, an ever-increasing decline in the cellular proliferation levels could be observed. The quantitative analyses of cellular death showed opposite results when compared to cellular proliferation. During early pregnancy the cycle of cellular renovation was clearly proliferative and during late mouse pregnancy the cycle was directed by programmed cellular death. Although the high levels of cellular death during postpartum involution could be shown by the TUNEL-positive cells, we were unable to observed picnotic nucleus at the light microscopy.

Histochemical and ultrastructural study of collagen fibers in mouse pubic symphysis during late pregnancy.

Reference is usually made to the parallel orientation towards the main line of exerted tension at the pubic joint in mice, for supporting forces applied to the joint. Despite the wealth of morphological information about the extracellular matrix in this joint, little is known regarding the involvement of the crimp of collagen fibers in the dramatic transformations occurring in this region during the last 3 days of pregnancy. Examination of the collagenous architecture suggests that the biomechanical properties are directly related to fibril diameters, composition of ground substance and changes in the bundle morphology, particularly in the crimp structure. The purpose of this study was to further describe the transformation of the collagen fibers of the pubic symphysis during late mouse pregnancy. We examined the architecture of collagen fibers in the symphysis and pubic ligament through the Picrosirius-polarization method and also through scanning electron microscopy to directly visualize and measure the crimping from pregnant and virgin mice. The crimp angle and the length of five consecutive crimps were measured according to Patterson-Kane et al. [Connect. Tissue Res. 36 (1997) 253]. It could be demonstrated that the angles progressively decreased and the crimp length increased, denoting that the fibers have untwisted during the relaxation process. Our findings suggest that a disruption of the helical arrangement of the collagen containing fibers may contribute to explaining the rapid remodeling that occurs at the end of pregnancy and that is responsible for an increase in pliancy and length of the pubic ligament in mice.

Phenotypic modulation of fibroblastic cells in mice pubic symphysis during pregnancy, partum and postpartum.

In many species, the cartilaginous pubic symphysis of the pregnant female is gradually replaced by a fibrous connective tissue, forming a flexible and elastic interpubic ligament. This newly formed ligament is responsible for the separation of the pubic bones, enabling safe delivery of the young. Following labor, the ligament undergoes rapid involution. To our knowledge, no previous work has focused on the phenotypic modulation that is responsible for the changes present at the interpubic ligament throughout the relaxation and closing of the symphysis. The purpose of this study was to investigate the ultrastructural features and immunophenotype of the peculiar cell type found in the pubic symphysis of cycling, pregnant and postpartum mice. In particular, immunohistochemistry studies were conducted on the expressions of the cytoskeletal proteins desmin, vimentin and alpha-smooth muscle actin (alpha-SMA). During pregnancy, the pubic symphysis cells always expressed alpha-SMA, whereas the expression of vimentin and desmin was transient from early pregnancy to postpartum. Furthermore, the expression patterns of these three cytoskeletal proteins were distinct. Cells present in the medial region of the mouse symphysis in cycling and at D12 displayed ultrastructural features characteristic of a typical fibroblast. In contrast, during the last week of pregnancy and in postpartum these cells acquired ultrastructural features representative of a myofibroblast; for example, a fibronexus and a contractile apparatus were found to be present lying in close contact with the extracellular collagenous and elastic system fibrils. Taken together, these results strongly suggest a contractile function for these cells which might contribute to support of the varying mechanical stresses present during pubic bone movement.

Morphological characteristics of the interpubic joint (Symphysis pubica) of rats, guinea pigs and mice in different physiological situations. A comparative study.

The pubic joint of male and female rats, guinea pigs and mice was studied using the Picrosirius polarization method which selectively discloses the fibers of the collagenous system. Besides that, considerations were made regarding joint classification. In adult rats (both males and females, including intrapartum specimens), our results confirm those of earlier studies showing that the interpubic joint contains a central core of hyaline cartilage surrounded by fibrocartilaginous areas. Thus, in rats, the pubic joint should more properly be classified as a true synchondrosis. In virgin female guinea pigs and mice, the interpubic joint is formed of fibrocartilage (a true symphysis); whereas at term the bones are joined by a connective ligament, constituting a syndesmosis. Male mice have a similar (fibrocartilaginous) joint structure to virgin female mice, whereas male guinea pigs (like rats) have a hyaline cartilage joint. The foregoing observations indicate that the classification of the pubic joint depends upon the species, age, sex, and physiological reproductive stage studied. Species that are very similar in most other aspects (such as rats and mice) displayed different morphological features of the pubic joint to support the same reproductive processes. Together, the data reported here suggest that interspecies differences are likely to be found in other parameters and should be considered when choosing an appropriate animal model for research or teaching purposes.

[Multiplication of the different varieties of cells of the mouse pubic symphysis during growth and early gestation: radioautographic study with the use of tritiated thymidine]. / Multiplication des différentes variétés cellulaires de la symphyse pubienne de souris au cours de la croissance et de la première gestation : étude radioautographique à l'aide de la thymidine tritiée

1) A radioautographic study was undertaken after injection of tritiated thymidine during post-natal growth. The mitotic activity was localized in the three constituents of the mouse pubic symphysis: - in the osteogenic cartilage, labelled nuclei are numerous throughout animal growth; - in the articular cartilage, labelled nuclei are seldom encountered; - in the medial region, the chondroblasts, elongated dorso-ventrally, and the fibroblasts of the dorsal ligament show numerous labelled nuclei. 2. During the first pregnancy, the mitotic activity of the three constituents were examined separately: - in the osteogenic cartilage, the number of labelled cells increases at the beginning of the first pregnancy : the tibia epiphyseal cartilage apparently simultaneously shows revival of mitotic activity. After the 15th day of pregnancy, the osteogenic cartilage disappears by endochondral ossification; - in the articular cartilage and fibrocartilage, no mitotic activity is detectable as long as their typical characteristics are conserved. However, mititic activity becomes evident again when these cartilaginous cells cease to be surrounded by the typical chondroid matrix and become incorporated into the ligament. Cell multiplication therefore participated in symphyseal ligament dilatation.