Elastin distribution in the myometrial and vascular smooth muscle of the human uterus

Current status and challenges in uterine myometrial tissue engineering

The uterus undergoes significant modifications throughout pregnancy to support embryo development and fetal growth. However, conditions like fibroids, adenomyosis, cysts, and C-section scarring can cause myometrial damage. The importance of the uterus and the challenges associated with myometrial damage, and the need for alternative approaches are discussed in this review. The review also explores the recent studies in tissue engineering, which involve principles of combining cells, scaffolds, and signaling molecules to create functional uterine tissues. It focuses on two key approaches in uterine tissue engineering: scaffold technique using decellularized, natural, and synthetic polymer and 3D bioprinting. These techniques create supportive structures for cell growth and tissue formation. Current treatment options for myometrial damage have limitations, leading to the exploration of regenerative medicine and integrative therapies. The review emphasizes the potential benefits of tissue engineering, including more effective and less invasive treatment options for myometrial damage. The challenges of developing biocompatible materials and optimizing cell growth and differentiation are discussed. In conclusion, uterine tissue engineering holds promise for myometrial regeneration and the treatment of related conditions. This review highlights the scientific advancements in the field and underscores the potential of tissue engineering as a viable approach. By addressing the limitations of current treatments, tissue engineering offers new possibilities for improving reproductive health and restoring uterine functionality. Future research shall focus on overcoming challenges and refining tissue engineering strategies to advance the field and provide effective solutions for myometrial damage and associated disorders.

Uterine junctional zone and adenomyosis: comparison of MRI, transvaginal ultrasound and histology

The uterine junctional zone is the subendometrial area in the myometrium that contributes to peristalsis and aids in spermatozoa and blastocyst transport. Alterations in the appearance of the junctional zone on transvaginal sonography (TVS) or magnetic resonance imaging (MRI) are associated with adenomyosis. The lack of standardization of description of its appearance and ill-defined boundaries on both histology and imaging hamper understanding of the junctional zone and limit its role in the diagnosis of adenomyosis. The objectives of this review were to investigate the accordance in definition of the junctional zone across different diagnostic approaches and to examine how imaging findings can be linked to histological findings in the context of diagnosis of adenomyosis. A comprehensive literature review was conducted of articles describing the appearance on imaging and the histological structure of the uterine junctional zone. Our review suggests that the junctional zone is distinguished from the middle and outer myometrium by gradual changes in smooth-muscle cell density, extracellular space, connective tissue, water content and vascular properties. However, while the signal intensity from the junctional zone to the middle myometrium changes abruptly on MRI, the histopathological changes are gradual and its border may be difficult or impossible to distinguish on two-dimensional TVS. Moreover, the thickness of the junctional zone measured on MRI is larger than that measured on TVS. Thus, these two imaging modalities reflect this zone differently. Although a thickened junctional zone is often used to diagnose adenomyosis on MRI, the presence of adenomyosis can be described more accurately as interruptions of the junctional zone by endometrial tissue, which leads to direct signs on imaging such as subendometrial lines and buds on two- and three-dimensional TVS or bright foci on MRI. The histopathological criteria for diagnosis are based on enlargement of the uterus with severe adenomyosis, and might not reflect its early stages. Clinicians should be aware that findings on MRI cannot be extrapolated readily to ultrasound. An understanding of this is necessary when investigating the uterine junctional zone as a functional unit and the association between visualization of direct features of adenomyosis in the junctional zone and clinical symptoms. © 2022 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Collagen and elastic fiber remodeling in the pregnant mouse myometrium†

The myometrium undergoes progressive tissue remodeling from early to late pregnancy to support fetal growth and transitions to the contractile phase to deliver a baby at term. Much of our effort has been focused on understanding the functional role of myometrial smooth muscle cells, but the role of extracellular matrix is not clear. This study was aimed to demonstrate the expression profile of sub-sets of genes involved in the synthesis, processing, and assembly of collagen and elastic fibers, their structural remodeling during pregnancy, and hormonal regulation. Myometrial tissues were isolated from non-pregnant and pregnant mice to analyze gene expression and protein levels of components of collagen and elastic fibers. Second harmonic generation imaging was used to examine the morphology of collagen and elastic fibers. Gene and protein expressions of collagen and elastin were induced very early in pregnancy. Further, the gene expressions of some of the factors involved in the synthesis, processing, and assembly of collagen and elastic fibers were differentially expressed in the pregnant mouse myometrium. Our imaging analysis demonstrated that the collagen and elastic fibers undergo structural reorganization from early to late pregnancy. Collagen and elastin were differentially induced in response to estrogen and progesterone in the myometrium of ovariectomized mice. Collagen was induced by both estrogen and progesterone. By contrast, estrogen induced elastin, but progesterone suppressed its expression. The current study suggests progressive extracellular matrix remodeling and its potential role in the myometrial tissue mechanical function during pregnancy and parturition.

Importance of Fibrosis in the Pathogenesis of Uterine Leiomyoma and the Promising Anti-fibrotic Effects of Dipeptidyl Peptidase-4 and Fibroblast Activation Protein Inhibitors in the Treatment of Uterine Leiomyoma

Uterine fibroid or leiomyoma is the most common benign uterus tumor. The tumor is primarily composed of smooth muscle (fibroid) cells, myofibroblast, and a significant amount of extracellular matrix components. It mainly affects women of reproductive age. They are uncommon before menarche and usually disappear after menopause. The fibroids have excessive extracellular matrix components secreted by activated fibroblast cells (myofibroblast). Myofibroblast has the characteristics of fibroblast and smooth muscle cells. These cells possess contractile capability due to the expression of contractile proteins which are normally found only in muscle tissues. The rigid nature of the tumor is responsible for many side effects associated with uterine fibroids. The current drug treatment strategies are primarily hormone-driven and not anti-fibrotic. This paper emphasizes the fibrotic background of uterine fibroids and the mechanisms behind the deposition of excessive extracellular matrix components. The transforming growth factor-β, hippo, and focal adhesion kinase-mediated signaling pathways activate the fibroblast cells and deposit excessive extracellular matrix materials. We also exemplify how dipeptidyl peptidase-4 and fibroblast activation protein inhibitors could be beneficial in reducing the fibrotic process in leiomyoma. Dipeptidyl peptidase-4 and fibroblast activation protein inhibitors prevent the fibrotic process in organs such as the kidneys, lungs, liver, and heart. These inhibitors are proven to inhibit the signaling pathways mentioned above at various stages of their activation. Based on literature evidence, we constructed a narrative review on the mechanisms that support the beneficial effects of dipeptidyl peptidase-4 and fibroblast activation protein inhibitors for treating uterine fibroids.

Uterine Tissue Engineering: Where We Stand and the Challenges Ahead

Tissue engineering is an innovative approach to develop allogeneic tissues and organs. The uterus is a very sensitive and complex organ, which requires refined techniques to properly regenerate and even, to rebuild itself. Many therapies were developed in 20th century to solve reproductive issues related to uterus failure and, more recently, tissue engineering techniques provided a significant evolution in this issue. Herein we aim to provide a broad overview and highlights of the general concepts involved in bioengineering to reconstruct the uterus and its tissues, focusing on strategies for tissue repair, production of uterine scaffolds, biomaterials and reproductive animal models, highlighting the most recent and effective tissue engineering protocols in literature and their application in regenerative medicine. In addition, we provide a discussion about what was achieved in uterine tissue engineering, the main limitations, the challenges to overcome and future perspectives in this research field.

The role of extracellular matrix in normal and pathological pregnancy: Future applications of microphysiological systems in reproductive medicine

IMPACT STATEMENT

Extracellular matrix in the womb regulates the initiation, progression, and completion of a healthy pregnancy. The composition and physical properties of extracellular matrix in the uterus and at the maternal-fetal interface are remodeled at each gestational stage, while maladaptive matrix remodeling results in obstetric disease. As in vitro models of uterine and placental tissues, including micro-and milli-scale versions of these organs on chips, are developed to overcome the inherent limitations of studying human development in vivo, we can isolate the influence of cellular and extracellular components in healthy and pathological pregnancies. By understanding and recreating key aspects of the extracellular microenvironment at the maternal-fetal interface, we can engineer microphysiological systems to improve assisted reproduction, obstetric disease treatment, and prenatal drug safety.

A Review and Reconsideration of Nonneoplastic Myometrial Pathology

From 1861 to 1962, clinicopathologic research tried to explain the association of abnormal uterine bleeding with uterine enlargement. The etiology was theorized as metropathy, suggesting that myometrial dysfunction may predispose to abnormal uterine bleeding. Research reached a nadir in 1962, when a major review dismissed myometrial hypertrophy as a plausible explanation after prior rejections of the theories of chronic myometritis, fibrosis uteri, and subinvolution as causes of bleeding. Subsequent to this arose a crusade against unnecessary hysterectomies in the 1970s. Although myometrial hyperplasia was proposed in 1868, it is only in the past 25 years that tangible evidence has supported that idea. It now appears that clinically enlarged uteri are due to globoid outward bulging of the uterus, caused by increased intramural pressure—often unrelated to either uterine weight or myometrial thickness. Abnormal (dysfunctional) uterine bleeding may often be due to spontaneous rupture of thrombosed dilated endometrial vessels, due to the combined effects of obstructed venous drainage by increased intramural pressure, and Virchow’s triad. Despite a century-old known association of parity with naturally occurring outer wall myometrial scars (fibrosis uteri with elastosis), it was not previously suggested that these may reflect healing reactions to muscle tears during labor and delivery. We now suggest that smaller, similar inner wall elastotic scars in the nerve-rich inner myometrium may explain many cases of pelvic pain. This review suggests that diverse pressure-related lesions may be present in clinically abnormal uteri that have been called “normal” since the crusade against unnecessary hysterectomy.

Postablation neuroma of the myometrium-a report of 5 cases

When hysterectomy is performed for chronic pelvic pain, routine pathology examination often provides no explanation. However, analysis of small uterine nerves using immunostains may help to address this deficiency. Small uterine nerves tend to be sparse or absent in wide areas of normal myometrium. Some studies of uterine nerves have suggested that endometriosis, adenomyosis, and fibroids are not inherently painful, with increased small nerves in the inner uterine wall associated with the history of pelvic pain. Although such areas may appear normal on hematoxylin and eosin (H&E), we have found a subtle inner wall lesion termed inner myometrial elastosis, best detected with trichrome or elastic stains, which may be a reaction to microscopic tears of inner myometrium. Such tears may induce increased inner wall innervation via the generation of nerve growth factor in granulation tissue. In the course of studying uterine nerves with immunostains, we found 5 cases with florid nerve proliferation, after deep endometrial ablation for abnormal uterine bleeding led to increased pelvic pain. We suggest that immunostains for postablation neuromas should be done in hysterectomies when pelvic pain increases after endometrial ablation. This may offer gynecologists and their patients an objective finding with a rational, scientific explanation for the pelvic pain.

The pathophysiology of uterine adenomyosis: an update

The diagnosis of adenomyosis using noninvasive techniques such as vaginal ultrasounds and magnetic resonance has clear clinical applications and has renewed the interest in the pathogenesis of uterine adenomyosis. However, the research remains hampered by the lack of consensus on the classification of lesions. Magnetic resonance imaging and transvaginal ultrasound have comparable diagnostic accuracy. Minimal interventional biopsy techniques have recently been introduced. This article reviews human and animal studies and provides an update on the pathophysiology of adenomyosis. Recent views on the pathogenesis and links with endometriosis are discussed.

Assessing the risk of ovarian hyperstimulation syndrome in egg donation: implications for human embryonic stem cell research

Stem cell research has important implications for medicine. The source of stem cells influences their therapeutic potential, with stem cells derived from early-stage embryos remaining the most versatile. Somatic cell nuclear transfer (SCNT), a source of embryonic stem cells, allows for understandings about disease development and, more importantly, the ability to yield embryonic stem cell lines that are genetically matched to the somatic cell donor. However, SCNT requires women to donate eggs, which involves injection of ovulation-inducing hormones and egg retrieval through laparoscopy or transvaginal needle aspiration. Risks from this procedure are fiercely debated, most notably risk of ovarian hyperstimulation syndrome (OHSS). This review examines risk of OHSS resulting from oocyte donation. We conclude that risk posed by OHSS in egg donation is not significant enough to warrant undue concern, and much of this can be eliminated when proper precautions are taken. This bears relevance to the future of stem cell research policymaking.

Trophoblast- and vascular smooth muscle cell-derived MMP-12 mediates elastolysis during uterine spiral artery remodeling

During the first trimester of pregnancy, the uterine spiral arteries are remodeled, creating heavily dilated conduits that lack maternal vasomotor control but allow the placenta to meet an increasing requirement for nutrients and oxygen. To effect permanent vasodilatation, the internal elastic lamina and medial elastin fibers must be degraded. In this study, we sought to identify the elastolytic proteases involved in this process. Primary first-trimester cytotrophoblasts (CTBs) derived from the placenta exhibited intracellular and membrane-associated elastase activity; membrane-associated activity was primarily attributable to matrix metalloproteinases (MMP). Indeed, Affymetrix microarray analysis and immunocytochemistry implicated MMP-12 (macrophage metalloelastase) as a key mediator of elastolysis. Cultured human aortic smooth muscle cells (HASMCs) exhibited constitutive membrane-associated elastase activity and inducible intracellular elastase activity; these cells also expressed MMP-12 protein. Moreover, a specific inhibitor of MMP-12 significantly reduced CTB- and HASMC-mediated elastolysis in vitro, to 31.7 ± 10.9% and 23.3 ± 8.7% of control levels, respectively. MMP-12 is expressed by both interstitial and endovascular trophoblasts in the first-trimester placental bed and by vascular SMCs (VSMCs) in remodeling spiral arteries. Perfusion of isolated spiral artery segments with CTB-conditioned medium stimulated MMP-12 expression in medial VSMCs. Our data support a model in which trophoblasts and VSMCs use MMP-12 cooperatively to degrade elastin during vascular remodeling in pregnancy, with the localized release of elastin peptides and CTB-derived factors amplifying elastin catabolism.

Uterus models for use in virtual reality hysteroscopy simulators

OBJECTIVES

Virtual reality models of human organs are needed in surgery simulators which are developed for educational and training purposes. A simulation can only be useful, however, if the mechanical performance of the system in terms of force-feedback for the user as well as the visual representation is realistic. We therefore aim at developing a mechanical computer model of the organ in question which yields realistic force-deformation behavior under virtual instrument-tissue interactions and which, in particular, runs in real time.

STUDY DESIGN

The modeling of the human uterus is described as it is to be implemented in a simulator for minimally invasive gynecological procedures. To this end, anatomical information which was obtained from specially designed computed tomography and magnetic resonance imaging procedures as well as constitutive tissue properties recorded from mechanical testing were used. In order to achieve real-time performance, the combination of mechanically realistic numerical uterus models of various levels of complexity with a statistical deformation approach is suggested. In view of mechanical accuracy of such models, anatomical characteristics including the fiber architecture along with the mechanical deformation properties are outlined. In addition, an approach to make this numerical representation potentially usable in an interactive simulation is discussed.

RESULTS AND CONCLUSIONS

The numerical simulation of hydrometra is shown in this communication. The results were validated experimentally. In order to meet the real-time requirements and to accommodate the large biological variability associated with the uterus, a statistical modeling approach is demonstrated to be useful.

Comparison of c-DNA microarray analysis of gene expression between eutopic endometrium and ectopic endometrium (endometriosis)

PROBLEM

As recent studies have suggested abnormalities in the regulation of specific genes in the development of endometriosis, we investigated differentially expressed genes in endometriosis compared to endometrium.

METHOD OF STUDY

Gene expression profiles using the Atlas microarray were performed in endometriotic tissue and endometrium. Nine of the 13 genes of endometriotic tissue showed an up-regulation in relation to endometrium and four of the 13 genes a down-regulation.

RESULTS

Of the 1176 genes on the Atlas Human 1,2 array, only 13 differentially expressed identical genes were detected after repeating the gene analysis three times.

CONCLUSION

According to our c-DNA analysis some differentially expressed genes may be involved in the pathogenesis of endometriosis. An imbalance in the genes responsible for the reproductive process may lead to a decrease in embryo implantation in patients with endometriosis.

Invasive trophoblasts stimulate vascular smooth muscle cell apoptosis by a fas ligand-dependent mechanism

During pregnancy, trophoblasts migrate from the placenta into uterine spiral arteries, transforming them into wide channels that lack vasoconstrictive properties. In pathological pregnancies, this process is incomplete. To define the fundamental events involved in spiral artery remodeling, we have studied the effect of trophoblasts on vascular smooth muscle cells (SMCs). Here we demonstrate for the first time that apoptosis of SMCs can be initiated by invading trophoblasts. When trophoblasts isolated from normal placenta (primary trophoblasts) or conditioned medium was perfused into spiral or umbilical artery segments, apoptosis of SMCs resulted. Culture of human aortic SMCs (HASMCs) with primary trophoblasts, primary trophoblast-conditioned medium, or a trophoblast-derived cell line (SGHPL-4) also significantly increased SMC apoptosis. Fas is expressed by spiral artery SMCs, and a Fas-activating antibody triggered HASMC apoptosis. Furthermore, a Fas ligand (FasL)-blocking antibody significantly inhibited HASMC apoptosis induced by primary trophoblasts, SGHPL-4, or trophoblast-conditioned medium. Depleting primary trophoblast-conditioned medium of FasL also abrogated SMC apoptosis in vessels in situ. These results suggest that apoptosis triggered by the release of soluble FasL from invading trophoblasts contributes to the loss of smooth muscle from the walls of spiral arteries during pregnancy.

The normal human myometrium has a vascular spatial gradient absent in small fibroids

BACKGROUND

The human uterine vasculature is highly structured, exhibiting circumferential and radial branching. Previously published angiograms of the arterial network describe a system of regular coils. Uterine fibroids lack this structured vasculature. In this study, we make a comparison between the vasculature in normal myometrium and in fibroids using robust stereological methods thus far lacking in the literature.

METHODS

Stereological and morphometric analysis of the vascular system was carried out on 15 normal and 27 small fibroid (5-40 mm) uteri taken from women suffering menorrhagia. Projected images of published angiograms were also re-examined, measuring tortuosity.

RESULTS

A decreasing gradient of vascular smooth muscle from outer to inner myometrium was found in normal uteri, with no corresponding gradient in capillary tissue fraction. An association between vascular luminal size, amplitude and frequency of vessel bending was also established. Conversely, fibroids were found to lack structured or muscularized vasculature.

CONCLUSIONS

A quantitative gradient within the myometrial vascular system, which is absent in fibroids, has been demonstrated. These structural differences between diseased and healthy tissues are probably because of differing expression of angiogenic growth factors and may explain the distribution of particles seen after uterine artery embolization.

Three-dimensional fiber architecture of the nonpregnant human uterus determined ex vivo using magnetic resonance diffusion tensor imaging

The global muscle and collagen fiber orientation in the human uterus has been analyzed hitherto by various standard microscopic techniques. However, no widely accepted model of the fiber architecture of the myometrium could be acquired. The purpose of the present study was to investigate the uterus by magnetic resonance (MR) diffusion tensor imaging (DTI) in a 3D macroscopic approach. Ex vivo MR DTI measurements were performed on five uteri from nonpregnant patients. The main diffusion directions reflecting the orientation of directional structures in the examined tissues were determined from diffusion-weighted spin-echo measurements. A fiber tracking algorithm was used to extrapolate the fiber architecture. The method was validated against histological slides and indirectly through the analysis of leiomyomas, which exhibit less anisotropy than normal myometrium. Significant anisotropy was found in most regions of all examined nonpregnant human uteri. But only two systems of fibers were found running circularly along the intramural part of the uterine tubes. They merged caudally and built a close fitting envelope of circular layers around the uterine cavity. On the cervix, circular fibers were observed in the outer part as well as mostly longitudinal fibers in the inner part. These results confirm the existence of directional structures in the complex fiber architecture of the human uterus. They also indicate that MR DTI is a beneficial and complementary tool to standard microscopic techniques to determine the intrinsic fiber architecture in human organs.

Current applications of orcein in histochemistry. A brief review with some new observations concerning influence of dye batch variation and aging of dye solutions on staining

Current uses of orcein to demonstrate elastic fibers and, following permanganate oxidation (Shikata's modification), hepatitis B surface antigen, copper associated protein, and sulfated mucins, are reviewed. Variations in staining performance with batch of dye and age of dye solution is also discussed. Additional experimental findings support the view that the orcein stain for elastic tissue and Shikata's modification produces consistent, high quality results as long as appropriate controls and suitable dye batches, e.g., Biological Stain Commission certified dyes, are used.