Side population in human uterine myometrium displays phenotypic and functional characteristics of myometrial stem cells

Hypoxia in uterine fibroids: role in pathobiology and therapeutic opportunities

Uterine fibroids are the most common tumors in females affecting up to 70% of women world-wide, yet targeted therapeutic options are limited. Oxidative stress has recently surfaced as a key driver of fibroid pathogenesis and provides insights into hypoxia-induced cell transformation, extracellular matrix pathophysiology, hypoxic cell signaling cascades, and uterine biology. Hypoxia drives fibroid tumorigenesis through (1) promoting myometrial stem cell proliferation, (2) causing DNA damage propelling transformation of stem cells to tumor initiating cells, and (3) driving excess extracellular matrix (ECM) production. Common fibroid-associated DNA mutations include MED12 mutations, HMGA2 overexpression, and Fumarate hydratase loss of function. Evidence suggests an interaction between hypoxia signaling and these mutations. Fibroid development and growth are promoted by hypoxia-triggered cell signaling via various pathways including HIF-1, TGFβ, and Wnt/β-catenin. Fibroid-associated hypoxia persists due to antioxidant imbalance, ECM accumulation, and growth beyond adequate vascular supply. Current clinically available fibroid treatments do not take advantage of hypoxia-targeting therapies. Growing pre-clinical and clinical studies identify ROS inhibitors, anti-HIF-1 agents, Wnt/β-catenin inhibition, and TGFβ cascade inhibitors as agents that may reduce fibroid development and growth through targeting hypoxia.

Equilibrium Tension and Compression Mechanical Properties of the Human Uterus

A successful pregnancy relies on the proper cellular, biochemical, and mechanical functions of the uterus. A comprehensive understanding of uterine mechanical properties during pregnancy is key to understanding different gynecological and obstetric disorders such as preterm birth, placenta accreta, leiomyoma, and endometriosis. This study sought to characterize the macro-scale equilibrium material behaviors of the human uterus in non-pregnancy and late pregnancy under both compressive and tensile loading. Fifty human uterine specimens from 16 patients (8 nonpregnant [NP] and 8 pregnant [PG]) were tested using spherical indentation and uniaxial tension coupled with digital image correlation (DIC). A three-level incremental load-hold protocol was applied to both tests. A microstructurally-inspired material model considering fiber architecture was applied to this dataset. Inverse finite element analysis (IFEA) was then performed to generate a single set of mechanical parameters to describe compressive and tensile behaviors. The freeze-thaw effect on uterine macro mechanical properties was also evaluated. PG tissue exhibits decreased overall stiffness and increased fiber network extensibility compared to NP uterine tissue. Under indentation, ground substance compressibility was similar between NP and PG uterine tissue. In tension, the fiber network of the PG uterus was found to be more extensible and dispersed than in nonpregnancy. Lastly, a single freeze-thaw cycle did not systematically alter the macro-scale material behavior of the human uterus.

Material properties of nonpregnant and pregnant human uterine layers

The uterus has critical biomechanical functions in pregnancy and undergoes dramatic material growth and remodeling from implantation to parturition. The intrinsic material properties of the human uterus and how they evolve in pregnancy are poorly understood. To address this knowledge gap and assess the heterogeneity of these tissues, the time-dependent material properties of all human uterine layers were measured with nanoindentation. The endometrium-decidua layer was found to be the least stiff, most viscous, and least permeable layer of the human uterus in nonpregnant and third-trimester pregnant tissues. In pregnancy, the endometrium-decidua becomes stiffer and less viscous with no material property changes observed in the myometrium or perimetrium. Additionally, uterine material properties did not significantly differ between third-trimester pregnant tissues with and without placenta accreta. The foundational data generated by this study will facilitate the development of physiologically accurate models of the human uterus to investigate gynecologic and obstetric disorders.

Causal relationship between female reproductive factors, sex hormones and uterine leiomyoma: a Mendelian randomization study

RESEARCH QUESTION

Are the observed associations between female reproductive factors and sex hormones with the risk of uterine leiomyoma truly causal associations?

DESIGN

The putative causal relationships between female reproductive factors and sex hormones with uterine leiomyoma were investigated using two-sample Mendelian randomization. Statistics on exposure-associated genetic variants were obtained from genome-wide association studies (GWAS). The uterine leiomyoma GWAS from the FinnGen and FibroGENE consortia were used as outcome data for discovery and replication analyses, respectively. Results were pooled by meta-analysis. Sensitivity analyses ensured robustness of the Mendelian randomization analysis.

RESULTS

When FinnGen GWAS were used as outcome data, a causal relationship was found between age at menarche (OR 0.84, P < 0.0001), age at menopause (OR 1.08, P < 0.0001), number of live births (OR 0.25, P < 0.001) and total testosterone levels (OR 0.90, P < 0.001) with the risk of uterine leiomyoma. When FibroGENE GWAS were used as outcome data, Mendelian randomization results for age at menopause, the number of live births and total testosterone levels were replicated. In the meta-analysis, a later age at menopause (OR 1.08, P < 0.0001) was associated with an increased risk of uterine leiomyoma. A higher number of live births (OR 0.25, P < 0.0001) and higher total testosterone levels (OR 0.90, P < 0.0001) were associated with a decreased risk of uterine leiomyoma.

CONCLUSIONS

A causal relationship between later age at menopause, lower number of live births and lower total testosterone levels with increased risk of uterine leiomyoma was found.

Material Properties of Nonpregnant and Pregnant Human Uterine Layers

The uterus has critical biomechanical functions in pregnancy and undergoes dramatic material growth and remodeling from implantation to parturition. The intrinsic material properties of the human uterus and how they evolve in pregnancy are poorly understood. To address this knowledge gap and assess the heterogeneity of these tissues, the time-dependent material properties of all human uterine layers were measured with nanoindentation. The endometrium-decidua layer was found to be the least stiff, most viscous, and least permeable layer of the human uterus in nonpregnant and third-trimester pregnant tissues. In pregnancy, endometrium-decidua becomes stiffer and less viscous with no material property changes observed in the myometrium or perimetrium. Additionally, uterine material properties did not significantly differ between third-trimester pregnant tissues with and without placenta accreta. The foundational data generated by this study will facilitate the development of physiologically accurate models of the human uterus to investigate gynecologic and obstetric disorders.

Current and Emerging Treatment Options for Uterine Fibroids

Uterine fibroids are the most common benign neoplasm of the female reproductive tract in reproductive age women. Their prevalence is age dependent and can be detected in up to 80% of women by the age of 50 years. Patients affected by uterine fibroids may experience a significant physical, emotional, social, and financial toll as well as losses in their quality of life. Unfortunately, curative hysterectomy abolishes future pregnancy potential, while uterine-sparing surgical and radiologic alternatives are variously associated with reduced long-term reproductive function and/or high tumor recurrence rates. Recently, pharmacological treatment against uterine fibroids have been widely considered by patients to limit uterine fibroid-associated symptoms such as heavy menstrual bleeding. This hormonal therapy seemed effective through blocking the stimulatory effects of gonadal steroid hormones on uterine fibroid growth. However, they are contraindicated in women actively pursuing pregnancy and otherwise effective only during use, which is limited because of long-term safety and other concerns. Accordingly, there is an urgent unmet need for safe, durable, and fertility-compatible non-surgical treatment options for uterine fibroids. In this review article, we cover the current pharmacological treatments for uterine fibroids including their comparable efficacy and side effects as well as emerging safe natural compounds with promising anti-uterine fibroid effects.

TGFβ signaling links early life endocrine-disrupting chemicals exposure to suppression of nucleotide excision repair in rat myometrial stem cells

Environmental exposure to endocrine-disrupting chemicals (EDCs) is linked to the development of uterine fibroids (UFs) in women. UFs, non-cancerous tumors, are thought to originate from abnormal myometrial stem cells (MMSCs). Defective DNA repair capacity may contribute to the emergence of mutations that promote tumor growth. The multifunctional cytokine TGFβ1 is associated with UF progression and DNA damage repair pathways. To investigate the impact of EDC exposure on TGFβ1 and nucleotide excision repair (NER) pathways, we isolated MMSCs from 5-month-old Eker rats exposed neonatally to diethylstilbestrol (DES), an EDC, or to vehicle (VEH). EDC-MMSCs exhibited overactivated TGFβ1 signaling and reduced mRNA and protein levels of NER pathway components compared to VEH-MMSCs. EDC-MMSCs also demonstrated impaired NER capacity. Exposing VEH-MMSCs to TGFβ1 decreased NER capacity while inhibiting TGFβ signaling in EDC-MMSCs restored it. RNA-seq analysis and further validation revealed decreased expression of Uvrag, a tumor suppressor gene involved in DNA damage recognition, in VEH-MMSCs treated with TGFβ1, but increased expression in EDC-MMSCs after TGFβ signaling inhibition. Overall, we demonstrated that the overactivation of the TGFβ pathway links early life exposure to EDCs with impaired NER capacity, which would lead to increased genetic instability, arise of mutations, and fibroid tumorigenesis. We demonstrated that the overactivation of the TGFβ pathway links early life exposure to EDCs with impaired NER capacity, which would lead to increased fibroid incidence.

Developmental reprogramming of myometrial stem cells by endocrine disruptor linking to risk of uterine fibroids

BACKGROUND

The stage, when tissues and organs are growing, is very vulnerable to environmental influences, but it's not clear how exposure during this time causes changes to the epigenome and increases the risk of hormone-related illnesses like uterine fibroids (UFs).

METHODS

Developmental reprogramming of myometrial stem cells (MMSCs), the putative origin from which UFs originate, was investigated in vitro and in the Eker rat model by RNA-seq, ChIP-seq, RRBS, gain/loss of function analysis, and luciferase activity assays.

RESULTS

When exposed to the endocrine-disrupting chemical (EDC) diethylstilbestrol during Eker rat development, MMSCs undergo a reprogramming of their estrogen-responsive transcriptome. The reprogrammed genes in MMSCs are known as estrogen-responsive genes (ERGs) and are activated by mixed lineage leukemia protein-1 (MLL1) and DNA hypo-methylation mechanisms. Additionally, we observed a notable elevation in the expression of ERGs in MMSCs from Eker rats exposed to natural steroids after developmental exposure to EDC, thereby augmenting estrogen activity.

CONCLUSION

Our studies identify epigenetic mechanisms of MLL1/DNA hypo-methylation-mediated MMSC reprogramming. EDC exposure epigenetically targets MMSCs and leads to persistent changes in the expression of a subset of ERGs, imparting a hormonal imprint on the ERGs, resulting in a "hyper-estrogenic" phenotype, and increasing the hormone-dependent risk of UFs.

Epigenetic Modulation of Inflammatory Pathways in Myometrial Stem Cells and Risk of Uterine Fibroids

The period during which tissue and organ development occurs is particularly vulnerable to the influence of environmental exposures. However, the specific mechanisms through which biological pathways are disrupted in response to developmental insults, consequently elevating the risk of hormone-dependent diseases, such as uterine fibroids (UFs), remain poorly understood. Here, we show that developmental exposure to the endocrine-disrupting chemical (EDC), diethylstilbestrol (DES), activates the inflammatory pathways in myometrial stem cells (MMSCs), which are the origin of UFs. Significantly, the secretome of reprogrammed MMSCs enhances the expression of critical inflammation-related genes in differentiated myometrial cells through the paracrine mechanism, which amplifies pro-inflammatory and immune suppression signaling in the myometrium. The expression of reprogrammed inflammatory responsive genes (IRGs) is driven by activated mixed-lineage leukemia protein-1 (MLL1) in MMSCs. The deactivation of MLL reverses the reprogramming of IRG expression. In addition, the inhibition of histone deacetylases (HDACs) also reversed the reprogrammed IRG expression induced by EDC exposure. This work identifies the epigenetic mechanisms of MLL1/HDAC-mediated MMSC reprogramming, and EDC exposure epigenetically targets MMSCs and imparts an IRG expression pattern, which may result in a "hyper-inflammatory phenotype" and an increased hormone-dependent risk of UFs later in life.

Cysteine-rich intestinal protein 1 is a novel surface marker for human myometrial stem/progenitor cells

Myometrial stem/progenitor cells (MyoSPCs) have been proposed as the cells of origin for uterine fibroids, but the identity of the MyoSPC has not been well established. We previously identified SUSD2 as a possible MyoSPC marker, but the relatively poor enrichment in stem cell characteristics of SUSD2+ over SUSD2- cells compelled us to find better markers. We combined bulk RNA-seq of SUSD2+/- cells with single cell RNA-seq to identify markers for MyoSPCs. We observed seven distinct cell clusters within the myometrium, with the vascular myocyte cluster most highly enriched for MyoSPC characteristics and markers. CRIP1 expression was found highly upregulated by both techniques and was used as a marker to sort CRIP1+/PECAM1- cells that were both enriched for colony forming potential and able to differentiate into mesenchymal lineages, suggesting that CRIP1+/PECAM1- cells could be used to better study the etiology of uterine fibroids.

TGFβ signaling links early-life endocrine-disrupting chemicals exposure to suppression of nucleotide excision repair in rat myometrial stem cells

Environmental exposure to endocrine-disrupting chemicals (EDCs) is linked to the development of uterine fibroids (UFs) in women. UFs, non-cancerous tumors, are thought to originate from abnormal myometrial stem cells (MMSCs). Defective DNA repair capacity may contribute to the emergence of mutations that promote tumor growth. The multifunctional cytokine TGFβ1 is associated with UF progression and DNA damage repair pathways. To investigate the impact of EDC exposure on TGFβ1 and nucleotide excision repair (NER) pathways, we isolated MMSCs from 5-months old Eker rats exposed neonatally to Diethylstilbestrol (DES), an EDC, or to vehicle (VEH). EDC-MMSCs exhibited overactivated TGFβ1 signaling and reduced mRNA and protein levels of NER pathway components compared to VEH-MMSCs. EDC-MMSCs also demonstrated impaired NER capacity. Exposing VEH-MMSCs to TGFβ1 decreased NER capacity while inhibiting TGFβ signaling in EDC-MMSCs restored it. RNA-seq analysis and further validation revealed decreased expression of Uvrag, a tumor suppressor gene involved in DNA damage recognition, in VEH-MMSCs treated with TGFβ1, but increased expression in EDC-MMSCs after TGFβ signaling inhibition. Overall, we demonstrated that the overactivation of the TGFβ pathway links early-life exposure to EDCs with impaired NER capacity, which would lead to increased genetic instability, arise of mutations, and fibroid tumorigenesis. We demonstrated that the overactivation of the TGFβ pathway links early-life exposure to EDCs with impaired NER capacity, which would lead to increased fibroid incidence.

Progesterone Signaling and Uterine Fibroid Pathogenesis; Molecular Mechanisms and Potential Therapeutics

Uterine fibroids (UFs) are the most important benign neoplastic threat to women's health worldwide, with a prevalence of up to 80% in premenopausal women, and can cause heavy menstrual bleeding, pain, and infertility. Progesterone signaling plays a crucial role in the development and growth of UFs. Progesterone promotes the proliferation of UF cells by activating several signaling pathways genetically and epigenetically. In this review article, we reviewed the literature covering progesterone signaling in UF pathogenesis and further discussed the therapeutic potential of compounds that modulate progesterone signaling against UFs, including selective progesterone receptor modulator (SPRM) drugs and natural compounds. Further studies are needed to confirm the safety of SPRMs as well as their exact molecular mechanisms. The consumption of natural compounds as a potential anti-UFs treatment seems promising, since these compounds can be used on a long-term basis-especially for women pursuing concurrent pregnancy, unlike SPRMs. However, further clinical trials are needed to confirm their effectiveness.

Cysteine-Rich Intestinal Protein 1 is a Novel Surface Marker for Myometrial Stem/Progenitor Cells

Myometrial stem/progenitor cells (MyoSPCs) have been proposed as the cells of origin for uterine fibroids, which are benign tumors that develop in the myometrium of most reproductive age women, but the identity of the MyoSPC has not been well established. We previously identified SUSD2 as a possible MyoSPC marker, but the relatively poor enrichment in stem cell characteristics of SUSD2+ over SUSD2- cells compelled us to find better discerning markers for more rigorous downstream analyses. We combined bulk RNA-seq of SUSD2+/- cells with single cell RNA-seq to identify markers capable of further enriching for MyoSPCs. We observed seven distinct cell clusters within the myometrium, with the vascular myocyte cluster most highly enriched for MyoSPC characteristics and markers, including SUSD2. CRIP1 expression was found highly upregulated in both techniques and was used as a marker to sort CRIP1+/PECAM1- cells that were both enriched for colony forming potential and able to differentiate into mesenchymal lineages, suggesting that CRIP1+/PECAM1- cells could be used to better study the etiology of uterine fibroids.

A View on Uterine Leiomyoma Genesis through the Prism of Genetic, Epigenetic and Cellular Heterogeneity

Uterine leiomyomas (ULs), frequent benign tumours of the female reproductive tract, are associated with a range of symptoms and significant morbidity. Despite extensive research, there is no consensus on essential points of UL initiation and development. The main reason for this is a pronounced inter- and intratumoral heterogeneity resulting from diverse and complicated mechanisms underlying UL pathobiology. In this review, we comprehensively analyse risk and protective factors for UL development, UL cellular composition, hormonal and paracrine signalling, epigenetic regulation and genetic abnormalities. We conclude the need to carefully update the concept of UL genesis in light of the current data. Staying within the framework of the existing hypotheses, we introduce a possible timeline for UL development and the associated key events—from potential prerequisites to the beginning of UL formation and the onset of driver and passenger changes.

3D bio-printed endometrial construct restores the full-thickness morphology and fertility of injured uterine endometrium

Severe damage to the uterine endometrium, which results in scar formation and endometrial dysfunction, eventually leads to infertility or pregnancy-related complications. No effective therapeutic treatment is currently available for such injuries owing to the structural complexity, internal environment, and function of the uterus. Three-dimensional (3D) bio-printing to engineer biomimetic structural constructs provides a unique opportunity for tissue regeneration. Herein, using 3D extrusion-based bioprinting (EBB), we constructed a bilayer endometrial construct (EC) based on a sodium alginate-hyaluronic acid (Alg-HA) hydrogel for functional regeneration of the endometrium. The upper layer of the 3D bio-printed EC is a monolayer of endometrial epithelial cells (EECs), while the lower layer has a grid-like microstructure loaded with endometrial stromal cells (ESCs). In a partial full-thickness uterine excision rat model, our bilayer EC not only restored the morphology and structure of the endometrial wall (including organized luminal/ glandular epithelium, stroma, vasculature and the smooth muscle layer), but also significantly improved the reproductive outcome in the surgical area after implantation (75%, 12/16, p < 0.01). Therefore, repair of the uterine endometrium using the developed 3D bio-printed bilayer EC may represent an effective regenerative treatment for severe endometrial injury. STATEMENT OF SIGNIFICANCE: Achieving structural and functional recovery of the endometrium following severe injury is still a challenge. Here, we designed a 3D bio-printed endometrial construct (EC) to mimic the native bilayer structure and cellular components of the endometrium. The bio-printed EC consists of a dense upper layer with endometrial epithelial cells and a lower layer with endometrial stromal cells. In particular, the 3D bio-printed EC significantly improved the reproductive outcome in the surgical area (75%, 12/16) compared to that of the cell-loaded non-printed group (12.5%, 2/16). This study demonstrates that a biomimetic bilayer construct can facilitate endometrial repair and regeneration. Therefore, an endometrial cells-loaded 3D-bioprinted EC is a promising therapeutic option for patients suffering from severe endometrial damage.

Gene Expression Profile of Uterine Leiomyoma from Women Exposed to Different Air Pollution Levels in Metropolitan Cities of Sao Paulo, Brazil

Leiomyomas (LMs) are the most frequent uterine benign tumors, representing the leading cause of hysterectomy indications worldwide. They are highly associated with women's reproductive complications, and endocrine disruptors may influence their etiology. In this sense, air pollution represents a relevant hormonal disruptor that acts on key signaling pathways, resulting in tumor development and infertility. Our goal was to evaluate submucosal LM samples from patients living in the metropolitan and Sao Paulo city regions, focusing on genes involved in tumor development and infertility features. Twenty-four patients were selected based on their region of residence and clinical information availability. Several genes were differentially expressed between women living in metropolitan areas and Sao Paulo city. Significant associations were observed between BCL-2, DVL1, FGFR3, and WNT5b downregulation and contraceptive use in the samples from women living in Sao Paulo city. ESR1 and HHAT downregulation was associated with ethnicity. WNT5b and GREM were associated with LM treatment and related pathologies, respectively. In the samples from women living in other cities of the metropolitan region, abortion occurrence was associated with BMP4 upregulation. Although further studies may be necessary, our results showed that air pollution exposure influences the expression of genes related to LM development and female reproductive features.

Pivotal Role of Ubiquitin Carboxyl-Terminal Hydrolase L1 (UCHL1) in Uterine Leiomyoma

Uterine leiomyomas are smooth-muscle tumors originating in the myometrium and are the most common pelvic tumors in women of reproductive age. Symptomatic tumors may result in abnormal uterine bleeding, bladder dysfunction, pelvic discomfort, and reproductive issues, such as infertility and miscarriage. There are currently few non-invasive treatments for leiomyoma, but there are no practical early intervention or preventive methods. In this study, human uterine leiomyoma and myometrial tissues were used to detect the protein and mRNA expression levels of UCHL1. To explore the effects of UCHL1 knockdown and inhibition in leiomyoma and myometrial cells, we determined the mRNA expressions of COL1A1 and COL3A1. Collagen gel contraction and wound-healing assays were performed on myometrial and leiomyoma cells. We found that UCHL1 expression was considerably higher in uterine leiomyomas than in the myometrium. COL1A1 and COL3A1 expression levels were downregulated after inhibition of UCHL1 in human leiomyoma cells. Furthermore, the elimination of UCHL1 significantly decreased the migration and contractility of leiomyoma cells. In conclusion, these results indicate that UCHL1 is involved in the growth of leiomyoma in humans. For the treatment of uterine leiomyoma, targeting UCHL1 activity may be a unique and possible therapeutic strategy.

Reproductive Functions of the Mitochondrial Progesterone Receptor (PR-M)

Classic transcriptional regulation by progesterone via the nuclear progesterone receptors A and B (PR-A, PR-B) has been recognized for decades. Less attention has been given to a mitochondrial progesterone receptor (PR-M) responsible for non-nuclear activities. PR-M is derived from the progesterone receptor (PR) gene from an alternate promoter with the cDNA encoding a unique 5' membrane binding domain followed by the same hinge and hormone-binding domain of the nPR. The protein binds to the mitochondrial outer membrane and functions to increase cellular respiration via increased beta-oxidation and oxidative phosphorylation with resulting adenosine triphosphate (ATP) production. Physiologic activities of PR-M have been studied in cardiac function, spermatozoa activation, and myometrial growth, all known to respond to progesterone. Progesterone via PR-M increases cardiomyocyte cellular respiration to meet the metabolic demands of pregnancy with increased contractility. Consequential gene changes associated with PR-M activation include production of proteins for sarcomere development and for fatty acid oxidation. Regarding spermatozoa function, progesterone via PR-M increases cellular energy production necessary for progesterone-dependent hyperactivation. A role of progesterone in myometrial and leiomyomata growth may also be explained by the increase in necessary cellular energy for proliferation. Lastly, the multi-organ increase in cellular respiration may contribute to the progesterone-dependent increase in metabolic rate reflected by an increase in body temperature through compensatory non-shivering thermogenesis. An evolutionary comparison shows PR-M expressed in humans, apes, and Old World monkeys, but the necessary gene sequence is absent in New World monkeys and lower species. The evolutionary advantage to PR-M remains to be defined, but its presence may enhance catabolism to support the extended gestation and brain development found in these primates.

SFRP4+ stromal cell subpopulation with IGF1 signaling in human endometrial regeneration

Our understanding of full-thickness endometrial regeneration after injury is limited by an incomplete molecular characterization of the cell populations responsible for the organ functions. To help fill this knowledge gap, we characterized 10,551 cells of full-thickness normal human uterine from two menstrual phases (proliferative and secretory phase) using unbiased single cell RNA-sequencing. We dissected cell heterogeneity of main cell types (epithelial, stromal, endothelial, and immune cells) of the full thickness uterine tissues, cell population architectures of human uterus cells across the menstrual cycle. We identified an SFRP4⁺ stromal cell subpopulation that was highly enriched in the regenerative stage of the human endometria during the menstrual cycle, and the SFRP4⁺ stromal cells could significantly enhance the proliferation of human endometrial epithelial organoid in vitro, and promote the regeneration of endometrial epithelial glands and full-thickness endometrial injury through IGF1 signaling pathway in vivo. Our cell atlas of full-thickness uterine tissues revealed the cellular heterogeneities, cell population architectures, and their cell-cell communications during the monthly regeneration of the human endometria, which provide insight into the biology of human endometrial regeneration and the development of regenerative medicine treatments against endometrial damage and intrauterine adhesion.

A mediator complex subunit 12 gain-of-function mutation induces partial leiomyoma cell properties in human uterine smooth muscle cells

OBJECTIVE

To clarify whether a mediator complex subunit 12 (MED12) gain-of-function mutation induces leiomyoma cell properties in human uterine smooth muscle cells (USMCs).

DESIGN

Experimental study.

SETTING

Academic research laboratory.

PATIENT(S)

Women undergoing hysterectomy for leiomyoma.

INTERVENTION(S)

CRISPR/Cas9-mediated genome editing to introduce an MED12 gain-of-function mutation (G44D) into human USMCs.

MAIN OUTCOME MEASURE(S)

Cell proliferation, collagen production, and in vivo tumorigenicity of USMCs with vs. without the MED12 mutation.

RESULT(S)

Uterine smooth muscle cells isolated from the uterine myometrium of a 44-year-old patient were subjected to lentiviral vector-mediated gene transduction of the fluorescent protein Venus, followed by long-term passage. Uterine smooth muscle cells with a normal female karyotype, high cell proliferative activity, and Venus expression, but without stem/progenitor cell populations, were obtained and designated as USMC44. Using CRISPR/Cas9-mediated genome editing, mtUSMC44 (MED12, 131G>A, p.G44D) and mock USMC44 without MED12 mutation (wtUSMC44) were established from USMC44. wtUSMC44 and mtUSMC44 showed similar cell proliferation activity, even in the presence of estradiol and progesterone (EP) together with transforming growth factor-beta 3 (TGFB3). In addition, wtUSMC44 and mtUSMC44 generated similar tiny smooth muscle-like tissue constructs when xenotransplanted beneath the kidney capsule in immunodeficient mice treated with EP alone or TGFB3. In contrast, mtUSMC44 produced more collagen type I than wtUSMC in vitro, and this production was likely enhanced by EP and TGFB3.

CONCLUSION(S)

The results suggest that the MED12 gain-of-function mutation is involved in collagen production. Although approximately 70% of leiomyomas have MED12 mutations, additional factors and/or events other than MED12 and/or myometrial stem/progenitor cells may be required for fully inducing leiomyoma cell properties, including transformation, in USMCs.

Comprehensive Review of Uterine Fibroids: Developmental Origin, Pathogenesis, and Treatment

Uterine fibroids are benign monoclonal neoplasms of the myometrium, representing the most common tumors in women worldwide. To date, no long-term or noninvasive treatment option exists for hormone-dependent uterine fibroids, due to the limited knowledge about the molecular mechanisms underlying the initiation and development of uterine fibroids. This paper comprehensively summarizes the recent research advances on uterine fibroids, focusing on risk factors, development origin, pathogenetic mechanisms, and treatment options. Additionally, we describe the current treatment interventions for uterine fibroids. Finally, future perspectives on uterine fibroids studies are summarized. Deeper mechanistic insights into tumor etiology and the complexity of uterine fibroids can contribute to the progress of newer targeted therapies.

Stem Cell Growth and Differentiation in Organ Culture: New Insights for Uterine Fibroid Treatment

Organ culture allows for the understanding of normal and tumor cell biology, and tissues generally remain viable for 5–7 days. Strikingly, we determined that myometrial and MED12 mutant leiomyoma cells repopulated cell-depleted tissue slices after 20 days of culture. Using immunofluorescence and quantitative PCR of stem cell and undifferentiated cell markers, we observed clusters of CD49b⁺ cells in tumor slices. CD49b⁺ cells, however, were sparsely detected in the myometrial slices. Almost all LM cells strongly expressed Ki67, while only a few myometrial cells were stained for this proliferation marker. The CD73 marker was expressed only in tumor cells, whereas the mesenchymal stem cell receptor KIT was detected only in normal cells. HMGA2 and CD24 showed broader expression patterns and higher signal intensity in leiomyoma than in myometrial cells. In this study, we propose that activating CD49b⁺ stem cells in myometrium leads to asymmetrical division, giving rise to transit-amplifying KIT⁺ cells that differentiate to smooth muscle cells. On the contrary, activated leiomyoma CD49b⁺ cells symmetrically divide to form clusters of stem cells that divide and differentiate to smooth muscle cells without losing proliferation ability. In conclusion, normal and mutant stem cells can proliferate and differentiate in long-term organ culture, constituting a helpful platform for novel therapeutic discovery.

Human Myometrial and Uterine Fibroid Stem Cell-Derived Organoids for Intervening the Pathophysiology of Uterine Fibroid

Uterine fibroids (UFs) (leiomyomas or myomas) are the most common clonal neoplasms of the uterus in women of reproductive age worldwide. UFs originate from myometrium consist of smooth muscle and fibroblast components, in addition to a substantial amount of fibrous extracellular matrix which all contribute to the pathogenetic process. Current treatments are primarily limited to surgical and interventional. Here, we have established a novel and promising organoid model from both normal and patient myometrial stem cells (MMSCs). MMSCs embedded in Matrigel in stem cell media swiftly formed organoids which successfully proliferate and self-organized into complex structures developing a sustainable organoid culture that maintain their capacity to differentiate into the different cell types recapitulating their tissue of origin and shows responsiveness to the reproductive hormones (estrogen and progesterone). Gene expression analysis and structural features indicated the early onset of uterine fibrosis led to the accumulation of extracellular matrix suggesting the potential use of this model in better understanding of the pathophysiology associated with UFs and inventing novel therapeutics for the treatment of UFs.

Aberrant R-loop-induced replication stress in MED12-mutant uterine fibroids

Uterine fibroid (UF) driver mutations in Mediator complex subunit 12 (MED12) trigger genomic instability and tumor development through unknown mechanisms. Herein, we show that MED12 mutations trigger aberrant R-loop-induced replication stress, suggesting a possible route to genomic instability and a novel therapeutic vulnerability in this dominant UF subclass. Immunohistochemical analyses of patient-matched tissue samples revealed that MED12 mutation-positive UFs, compared to MED12 mutation-negative UFs and myometrium, exhibited significantly higher levels of R-loops and activated markers of Ataxia Telangiectasia and Rad3-related (ATR) kinase-dependent replication stress signaling in situ. Single molecule DNA fiber analysis revealed that primary cells from MED12 mutation-positive UFs, compared to those from patient-matched MED12 mutation-negative UFs and myometrium, exhibited defects in replication fork dynamics, including reduced fork speeds, increased and decreased numbers of stalled and restarted forks, respectively, and increased asymmetrical bidirectional forks. Notably, these phenotypes were recapitulated and functionally linked in cultured uterine smooth muscle cells following chemical inhibition of Mediator-associated CDK8/19 kinase activity that is known to be disrupted by UF driver mutations in MED12. Thus, Mediator kinase inhibition triggered enhanced R-loop formation and replication stress leading to an S-phase cell cycle delay, phenotypes that were rescued by overexpression of the R-loop resolving enzyme RNaseH. Altogether, these findings reveal MED12-mutant UFs to be uniquely characterized by aberrant R-loop induced replication stress, suggesting a possible basis for genomic instability and new avenues for therapeutic intervention that involve the replication stress phenotype in this dominant UF subtype.

Epigenomic and enhancer dysregulation in uterine leiomyomas

BACKGROUND

Uterine leiomyomas, also known as uterine fibroids or myomas, are the most common benign gynecological tumors and are found in women of reproductive and postmenopausal age. There is an exceptionally high prevalence of this tumor in women by the age of 50 years. Black women are particularly affected, with an increased incidence, earlier age of onset, larger and faster growing fibroids and greater severity of symptoms as compared to White women. Although advances in identifying genetic and environmental factors to delineate these fibroids have already been made, only recently has the role of epigenomics in the pathogenesis of this disease been considered.

OBJECTIVE AND RATIONALE

Over recent years, studies have identified multiple epigenomic aberrations that may contribute to leiomyoma development and growth. This review will focus on the most recent discoveries in three categories of epigenomic changes found in uterine fibroids, namely aberrant DNA methylation, histone tail modifications and histone variant exchange, and their translation into altered target gene architecture and transcriptional outcome. The findings demonstrating how the altered 3D shape of the enhancer can regulate gene expression from millions of base pairs away will be discussed. Additionally, translational implications of these discoveries and potential roadblocks in leiomyoma treatment will be addressed.

SEARCH METHODS

A comprehensive PubMed search was performed to identify published articles containing keywords relevant to the focus of the review, such as: uterine leiomyoma, uterine fibroids, epigenetic alterations, epigenomics, stem cells, chromatin modifications, extracellular matrix [ECM] organization, DNA methylation, enhancer, histone post-translational modifications and dysregulated gene expression. Articles until September 2021 were explored and evaluated to identify relevant updates in the field. Most of the articles focused on in the discussion were published between 2015 and 2021, although some key discoveries made before 2015 were included for background information and foundational purposes. We apologize to the authors whose work was not included because of space restrictions or inadvertent omission.

OUTCOMES

Chemical alterations to the DNA structure and of nucleosomal histones, without changing the underlying DNA sequence, have now been implicated in the phenotypic manifestation of uterine leiomyomas. Genome-wide DNA methylation analysis has revealed subsets of either suppressed or overexpressed genes accompanied by aberrant promoter methylation. Furthermore, differential promoter access resulting from altered 3D chromatin structure and histone modifications plays a role in regulating transcription of key genes thought to be involved in leiomyoma etiology. The dysregulated genes function in tumor suppression, apoptosis, angiogenesis, ECM formation, a variety of cancer-related signaling pathways and stem cell differentiation. Aberrant DNA methylation or histone modification is also observed in altering enhancer architecture, which leads to changes in enhancer-promoter contact strength, producing novel explanations for the overexpression of high mobility group AT-hook 2 and gene dysregulation found in mediator complex subunit 12 mutant fibroids. While many molecular mechanisms and epigenomic features have been investigated, the basis for the racial disparity observed among those in the Black population remains unclear.

WIDER IMPLICATIONS

A comprehensive understanding of the exact pathogenesis of uterine leiomyoma is lacking and requires attention as it can provide clues for prevention and viable non-surgical treatment. These findings will widen our knowledge of the role epigenomics plays in the mechanisms related to uterine leiomyoma development and highlight novel approaches for the prevention and identification of epigenome targets for long-term non-invasive treatment options of this significantly common disease.

A Revised Stem Cell Theory for the Pathogenesis of Endometriosis

During the past decade, a stem cell-based hypothesis has emerged (among many others) to explain the pathogenesis of endometriosis. The initial hypothesis proposed that endometriosis arose from a single or a few specific cells with stem cell properties, including self-renewal and multi-lineage cell differentiation. The origins of the endometriosis-initiating stem cells were thought to be the bone marrow, uterine endometrium, and other tissues. Based on the implantation or metastatic theory in combination with the initial stem cell theory, one or a few multipotent stem/progenitor cells present in the eutopic endometrium or bone marrow translocate to ectopic sites via fallopian tubes during menstruation, vasculolymphatic routes, or through direct migration and invasion. Subsequently, they give rise to endometriotic lesions followed by differentiation into various cell components of endometriosis, including glandular and stromal cells. Recent somatic mutation analyses of deep infiltrating endometriosis, endometrioma, and eutopic normal endometrium using next-generation sequencing techniques have redefined the stem cell theory. It is now proposed that stem/progenitor cells of at least two different origins—epithelium and stroma—sequentially, differentially, but coordinately contribute to the genesis of endometriosis. The dual stem cell theory on how two (or more) stem/progenitor cells differentially and coordinately participate in the establishment of endometriotic lesions remains to be elucidated. Furthermore, the stem/progenitor cells involved in this theory also remain to be identified. Given that the origin of endometriosis is eutopic endometrium, the candidate cells for endometriotic epithelium-initiating cells are likely to be endometrial epithelial cells positive for either N-cadherin or SSEA-1 or both. The candidate cells for endometriotic stroma-initiating cells may be endometrial mesenchymal stem cells positive for SUSD2. Endometrial side population cells are also a possible candidate because they contain unipotent or multipotent cells capable of behaving as endometrial epithelial and stromal stem/progenitor cells.

Differential response to hypoxia in leiomyoma and myometrial cells

AIMS

Recent evidence suggests that repetitive hypoxia occurs during menstrual cycles due to vasoconstriction and myometrial contraction. It is unknown if hypoxia contributes to the development of uterine leiomyoma, the most common tumor of the female reproductive system. This study aims to characterize the response to hypoxia in leiomyoma and myometrial cells; and determine if an aberrant leiomyoma response to hypoxia may contribute to leiomyomatogenesis.

MAIN METHODS

Primary and immortalized leiomyoma and myometrial cells were cultured under normoxic and hypoxic conditions. Expression levels of vascular endothelial growth factor-A (VEGF-A), adrenomedullin (ADM), endothelin-1 (ET-1), and hypoxia-inducible factor-1 alpha (HIF-1α) were measured by qRT-PCR, western blotting and ELISA. Cell proliferation was assessed using MTT assay and proliferating-cell-nuclear-antigen (PCNA) expression. KC7F2 (HIF-1α inhibitor) was used to examine the regulating mechanisms.

KEY FINDINGS

As expected, hypoxia induced HIF-1α expression in both leiomyoma and myometrial cells. However, hypoxia induced VEGF-A, ET-1 and ADM expression and VEGF-A secretion into the culture media in leiomyoma but not myometrial cells. MTT assay and PCNA expression showed that hypoxia induces proliferation in leiomyoma, but not myometrial cells. HIF-1α inhibitor abrogated the hypoxia-induced VEGF-A, ET-1, ADM, and PCNA expression in leiomyoma cells.

SIGNIFICANCE

This study suggests an aberrant leiomyoma cellular response to hypoxia compared to myometrium. This differential response to menstruation-related repetitive hypoxia episodes may lead to selective proliferation of hypoxia-adaptive leiomyoma cells and contribute to leiomyoma growth. Thus, in addition to adding to our understanding of leiomyoma pathobiology, the study proposes angiogenic factors as a potential leiomyoma therapeutic target.

Mesenchymal stem cells establish a pro-regenerative immune milieu after decellularized rat uterus tissue transplantation

Decellularized tissue is generally considered immune privileged after transplantation and is an attractive scaffold type for tissue regeneration, including applications for infertility treatment. However, the immune response following transplantation of decellularized tissue is insufficiently studied, in particular after they have been recellularized with mesenchymal stem cells (MSCs). Therefore, we replaced a large uterus segment with a bioengineered graft developed from decellularized uterus tissue and analyzed the immune response during the first 4 months in acellular or MSCs-recellularized scaffolds in the rat. Immunohistochemistry-stained infiltrating immune cells and plasma levels for 16 cytokines and chemokines were quantified. Results revealed that MSCs created an advantageous microenvironment by increasing anti-inflammatory interleukin 10 levels, and increasing the population of FOXP3⁺ T_Regs and CD163⁺ M2 macrophages, and by reducing the CD8⁺ cytotoxic T cell population. Hence, MSCs should be considered an immunotherapeutic cell source with the ability to dictate regeneration success after decellularized tissue transplantation.

Endocrine-Disrupting Chemicals and Vitamin D Deficiency in the Pathogenesis of Uterine Fibroids

Uterine fibroids (UFs) are the most prevalent gynecologic neoplasm, affecting 70-80% of women over their lifespan. Although UFs are benign they can become life-threatening and require invasive surgeries such as myomectomy and hysterectomy. Notwithstanding the significant negative influence UFs have on female reproductive health, very little is known about early events that initiate tumor development. Several risk factors for UFs have been identified including vitamin D deficiency, inflammation, DNA repair deficiency, and environmental exposures to endocrine-disrupting chemicals (EDCs). EDCs have come under scrutiny recently due to their role in UF development. Epidemiologic studies have found an association between increased risk for early UF diagnosis and in utero EDC exposure. Environmental exposure to EDCs during uterine development increases UF incidence in a UF animal model. Notably, several studies demonstrated that abnormal myometrial stem cells (MMSCs) are the cell origin for UFs development. Our recent studies demonstrated that early-life EDC exposure reprogrammed the MMSCs toward a pro-fibroid landscape and altered the DNA repair and inflammation pathways. Notably, Vitamin D3 (VITD3) as a natural compound shrank the UF growth concomitantly with the reversion of several abnormal biological pathways and ameliorated the developmental exposure-induced DNA damage and pro-inflammation pathway in primed MMSCs. This review highlights and emphasizes the importance of multiple pathway interactions in the context of hypovitaminosis D at the MMSCs level and provides proof-of-concept information that can help develop a safe, long-term, durable, and non-surgical therapeutic option for UFs.

Identification and characterization of the mediator kinase-dependent myometrial stem cell phosphoproteome

OBJECTIVE

To identify, in myometrial stem/progenitor cells, the presumptive cell of origin for uterine fibroids, substrates of Mediator-associated cyclin dependent kinase 8/19 (CDK8/19), which is known to be disrupted by uterine fibroid driver mutations in Mediator complex subunit 12 (MED12).

DESIGN

Experimental study.

SETTING

Academic research laboratory.

PATIENT(S)

Women undergoing hysterectomy for uterine fibroids.

INTERVENTION(S)

Stable isotopic labeling of amino acids in cell culture (SILAC) coupled with chemical inhibition of CDK8/19 and downstream quantitative phosphoproteomics and transcriptomic analyses in myometrial stem/progenitor cells.

MAIN OUTCOME MEASURE(S)

High-confidence Mediator kinase substrates identified by SILAC-based quantitative phosphoproteomics were determined using an empirical Bayes analysis and validated orthogonally by in vitro kinase assay featuring reconstituted Mediator kinase modules comprising wild-type or G44D mutant MED12 corresponding to the most frequent uterine fibroid driver mutation in MED12. Mediator kinase-regulated transcripts identified by RNA sequencing were linked to Mediator kinase substrates by computational analyses.

RESULT(S)

A total of 296 unique phosphosites in 166 proteins were significantly decreased (≥ twofold) upon CDK8/19 inhibition, including 118 phosphosites in 71 nuclear proteins representing high-confidence Mediator kinase substrates linked to RNA polymerase II transcription, RNA processing and transport, chromatin modification, cytoskeletal architecture, and DNA replication and repair. Orthogonal validation confirmed a subset of these proteins, including Cut Like Homeobox 1 (CUX1) and Forkhead Box K1 (FOXK1), to be direct targets of MED12-dependent CDK8 phosphorylation in a manner abrogated by the most common uterine fibroid driver mutation (G44D) in MED12, implicating these substrates in disease pathogenesis. Transcriptome-wide profiling of Mediator kinase-inhibited myometrial stem/progenitor cells revealed alterations in cell cycle and myogenic gene expression programs to which Mediator kinase substrates could be linked directly. Among these, CUX1 is an established transcriptional regulator of the cell cycle whose corresponding gene on chromosome 7q is the locus for a recurrent breakpoint in uterine fibroids, linking MED12 and Mediator kinase with CUX1 for the first time in uterine fibroid pathogenesis. FOXK1, a transcriptional regulator of myogenic stem cell fate, was found to be coordinately enriched along with kinase, but not core, Mediator subunits in myometrial stem/progenitor cells compared with differentiated uterine smooth muscle cells.

CONCLUSION(S)

These studies identify a new catalog of pathologically and biologically relevant Mediator kinase substrates implicated in the pathogenesis of MED12 mutation-positive uterine fibroids, and further uncover a biochemical basis to link Mediator kinase activity with CUX1 and FOXK1 in the regulation of myometrial stem/progenitor cell fate.

Pathogenesis, diagnosis and treatment of uterine lipoleiomyoma: A review

Uterine lipoleiomyomas are variants of uterine leiomyomas and are characterized by progressive enlargement that can occur even after menopause. These tumors can produce serious clinical symptoms and are difficult to diagnosis preoperatively. The growth rate of uterine lipoleiomyomas after menopause is comparatively higher than that of conventional uterine leiomyomas, and lipoleiomyosarcomas as well as tumor-to-tumor metastasis associated with lipoleiomyomas have been reported. However, detailed histogenic mechanisms of the tumor remain unclear. Surgical treatments are the current choice for the management of lipoleiomyomas. The purpose of this review is to promote greater awareness of lipoleiomyoma characteristics with a focus on histogenesis, diagnosis, and treatment. We performed an exhaustive literature review and have summarized the available data. We assessed the interpretation of auxiliary examinations to help physicians in making an early accurate diagnosis of the disease and to help with treatment decision-making, particularly regarding whether surgery should be performed or avoided.

Molecular and Cellular Insights into the Development of Uterine Fibroids

Uterine leiomyomas represent the most common benign gynecologic tumor. These hormone-dependent smooth-muscle formations occur with an estimated prevalence of ~70% among women of reproductive age and cause symptoms including pain, abnormal uterine bleeding, infertility, and recurrent abortion. Despite the prevalence and public health impact of uterine leiomyomas, available treatments remain limited. Among the potential causes of leiomyomas, early hormonal exposure during periods of development may result in developmental reprogramming via epigenetic changes that persist in adulthood, leading to disease onset or progression. Recent developments in unbiased high-throughput sequencing technology enable powerful approaches to detect driver mutations, yielding new insights into the genomic instability of leiomyomas. Current data also suggest that each leiomyoma originates from the clonal expansion of a single transformed somatic stem cell of the myometrium. In this review, we propose an integrated cellular and molecular view of the origins of leiomyomas, as well as paradigm-shifting studies that will lead to better understanding and the future development of non-surgical treatments for these highly frequent tumors.

Integrin Adhesion Complex Organization in Sheep Myometrium Reflects Changing Mechanical Forces during Pregnancy and Postpartum

Simple Summary

IACs assemble within the sheep myometrium during early-to-mid gestation in response to increased stretch of the uterine wall and continue to increase as pregnancy progresses. Fibronectin (FN1) is important in its ability to attach to IACs in myometrial cells to generate force to sustain powerful contractions during labor. After parturition, IACs are disassembled but the integrin subunits ITGA5 and ITGB1 remain expressed at the protein level at least two weeks postpartum.

Abstract

Cells respond to extracellular mechanical forces through the assembly of integrin adhesion complexes (IACs) that provide a scaffold through which cells sense and transduce responses to those forces. IACs are composed of transmembrane integrin receptors that bind to extracellular matrix (ECM) proteins externally and connect with the actomyosin cytoskeleton internally. Myometrial smooth muscle cells respond to forces that arise due to increases in fetal growth/weight, placental fluid volumes, and blood flow. As a result, the uterus transforms into an organ that can forcefully expel the fetus and placental membranes during parturition. While earlier studies focused on IAC expression in the myometrial compartment of rodents and humans to explore pregnancy-associated responses, the present study examines IAC assembly in ovine myometrium where mechanical forces are expected to be amplified in a manner similar to humans. Results indicate that the ITGA5 and ITGB1 heterodimers associate with the ECM protein FN1 externally, and with VCL and TLN1 internally, to form IACs in myometrial cells during the first trimester of pregnancy. These IACs become increasingly ordered until parturition. This ordered structure is lost by one day postpartum; however, the abundance of the integrin proteins remains elevated for at least two weeks postpartum. Implications of the present study are that sheep are similar to humans regarding the assembly of IACs in the pregnant myometrium and suggest that IACs may form much earlier in human gestation than was previously implied by the rat model. Results highlight the continued value of the sheep model as a flagship gynecological model for understanding parturition in humans.

Wnt/β-catenin signaling pathway in uterine leiomyoma: role in tumor biology and targeting opportunities

Uterine leiomyoma is the most common tumor of the female reproductive system and originates from a single transformed myometrial smooth muscle cell. Despite the immense medical, psychosocial, and financial impact, the exact underlying mechanisms of leiomyoma pathobiology are poorly understood. Alterations of signaling pathways are thought to be instrumental in leiomyoma biology. Wnt/β-catenin pathway appears to be involved in several aspects of the genesis of leiomyomas. For example, Wnt5b is overexpressed in leiomyoma, and the Wnt/β-catenin pathway appears to mediate the role of MED12 mutations, the most common mutations in leiomyoma, in tumorigenesis. Moreover, Wnt/β-catenin pathway plays a paracrine role where estrogen/progesterone treatment of mature myometrial or leiomyoma cells leads to increased expression of Wnt11 and Wnt16, which induces proliferation of leiomyoma stem cells and tumor growth. Constitutive activation of β-catenin leads to myometrial hyperplasia and leiomyoma-like lesions in animal models. Wnt/β-catenin signaling is also closely involved in mechanotransduction and extracellular matrix regulation and relevant alterations in leiomyoma, and crosstalk is noted between Wnt/β-catenin signaling and other pathways known to regulate leiomyoma development and growth such as estrogen, progesterone, TGFβ, PI3K/Akt/mTOR, Ras/Raf/MEK/ERK, IGF, Hippo, and Notch signaling. Finally, evidence suggests that inhibition of the canonical Wnt pathway using β-catenin inhibitors inhibits leiomyoma cell proliferation. Understanding the molecular mechanisms of leiomyoma development is essential for effective treatment. The specific Wnt/β-catenin pathway molecules discussed in this review constitute compelling candidates for therapeutic targeting.

Bioengineering of the Uterus

Impairment of uterine structure and function causes infertility, pregnancy loss, and perinatal complications in humans. Some types of uterine impairments such as Asherman’s syndrome, also known as uterine synechiae, can be treated medically and surgically in a standard clinical setting, but absolute defects of uterine function or structure cannot be cured by conventional approaches. To overcome such hurdles, partial or whole regeneration and reconstruction of the uterus have recently emerged as new therapeutic strategies. Transplantation of the whole uterus into patients with uterine agenesis results in the successful birth of children. However, it remains an experimental treatment with numerous difficulties such as the need for continuous and long-term use of immunosuppressive drugs until a live birth is achieved. Thus, the generation of the uterus by tissue engineering technologies has become an alternative but indispensable therapeutic strategy to treat patients without a functional or well-structured uterus. For the past 20 years, the bioengineering of the uterus has been studied intensively in animal models, providing the basis for clinical applications. A variety of templates and scaffolds made from natural biomaterials, synthetic materials, or decellularized matrices have been characterized to efficiently generate the uterus in a manner similar to the bioengineering of other organs and tissues. The goal of this review is to provide a comprehensive overview and perspectives of uterine bioengineering focusing on the type, preparation, and characteristics of the currently available scaffolds.

Reconstruction of functional uterine tissues through recellularizing the decellularized rat uterine scaffolds by MSCs in vivo and in vitro

Infertile people who suffered from loss of uterine structures and/or functions can be treated through gestational surrogacy or uterus transplantation, which remains challenging due to the ethical and social issues, the lack of donor organs as well as technical and safety risks. One promising solution is to regenerate and reconstruct a bioartificial uterus for transplantation through the engineering of uterine architecture and appropriate cellular constituents. Here, we developed a well-defined system to regenerate a functional rat uterine through recellularization of the decellularized uterine matrix (DUM) patches reseeded with human mesenchymal stem cells (hMSCs). Engraftment of the recellularized DUMs on the partially excised uteri yielded a functional rat uterus with a pregnancy rate and number of fetuses per uterine horn comparable to that of the control group with an intact uterus. Particularly, the recellularized DUMs enhanced the regeneration of traumatic uterine in vivo because of MSC regulation. The established system here will shed light on the treatment of uterine infertility with heterogeneous DUMs/cell resources through tissue engineering in the future.

The pathogenesis of abnormal uterine bleeding in myopathic uteri

It has been suggested that impaired venous drainage and endometrial vascular ectasia (EMVE), secondary to increased intramural pressure, explains abnormal bleeding in fibroid uteri. Striking EMVE with extravasated red blood cells (ecchymosis) has also been seen in uteri with grossly obvious myometrial hyperplasia (MMH), suggesting that increased intramural pressure can cause EMVE in the absence of fibroids. EMVE with MMH may explain the century old association of clinically enlarged uteri with abnormal bleeding, and this same mechanism may be operative in myopathic uteri with grossly obvious adenomyosis. EMVE with associated thrombosis, ecchymosis, and/or stromal breakdown is commonly seen in random sections of hysterectomies for bleeding. EMVE may also be associated with endothelial hyperplasia, consistent with a reaction to endothelial injury due to impaired venous drainage. This further supports the theory that EMVE bleeds when thrombosis occurs, due to Virchow's Triad (stasis, endothelial injury, and hypercoagulability). EMVE may be "the lesion for which surgery was performed" in hysterectomies with otherwise unexplained bleeding.

ABCB1, ABCG2, ABCC1, ABCC2, and ABCC3 drug transporter polymorphisms and their impact on drug bioavailability: what is our current understanding?

INTRODUCTION

Interindividual differences in drug response are a frequent clinical challenge partly due to variation in pharmacokinetics. ATP-binding cassette (ABC) transporters are crucial determinants of drug disposition. They are subject of gene regulation and drug-interaction; however, it is still under debate to which extend genetic variants in these transporters contribute to interindividual variability of a wide range of drugs.

AREAS COVERED

This review discusses the current literature on the impact of genetic variants in ABCB1, ABCG2 as well as ABCC1, ABCC2, and ABCC3 on pharmacokinetics and drug response. The aim was to evaluate if results from recent studies would increase the evidence for potential clinically relevant pharmacogenetic effects.

EXPERT OPINION

Although enormous efforts have been made to investigate effects of ABC transporter genotypes on drug pharmacokinetics and response, the majority of studies showed only weak if any associations. Despite few unique results, studies mostly failed to confirm earlier findings or still remained inconsistent. The impact of genetic variants on drug bioavailability is only minor and other factors regulating the transporter expression and function seem to be more critical. In our opinion, the findings on the so far investigated genetic variants in ABC efflux transporters are not suitable as predictive biomarkers.

Uterine Stem Cells and Benign Gynecological Disorders: Role in Pathobiology and Therapeutic Implications

Stem cells in the endometrium and myometrium possess an immense regenerative potential which is necessary to maintain the menstrual cycle and support pregnancy. These cells, as well as bone marrow stem cells, have also been implicated in the development of common benign gynecological disorders including leiomyomas, endometriosis and adenomyosis. Current evidence suggests the conversion of uterine stem cells to tumor initiating stem cells in leiomyomas, endometriosis stem cells, and adenomyosis stem cells, acquiring genetic and epigenetic alterations for the progression of each benign condition. In this comprehensive review, we aim to summarize the progress that has been made to characterize the involvement of stem cells in the pathogenesis of benign gynecologic conditions which, despite their enormous burden, are not yet fully understood. We focus on the stem cell characteristics and aberrations that contribute to the development of benign gynecological disorders and the possible clinical implications of what is known so far. Lastly, we discuss the role of uterine stem cells in the setting of regenerative medicine, particularly in the treatment of Asherman syndrome.Graphical abstract.

Role of DNA damage and repair mechanisms in uterine fibroid/leiomyomas: a review

There has been a significant annual increase in the number of cases of uterine leiomyomas or fibroids (UF) among women of all races and ages across the world. A fortune is usually spent by the healthcare sector for fibroid-related treatments and management. Molecular studies have established the higher mutational heterogeneity in UF as compared to normal myometrial cells. The contribution of DNA damage and defects in repair responses further increases the mutational burden on the cells. This in turn leads to genetic instability, associated with cancer risk and other adverse reproductive health outcomes. Such and many more growing bodies of literature have highlighted the genetic/molecular, biochemical and clinical aspects of UF; none the less there appear to be a lacuna bridging the bench to bed gap in addressing and preventing this disease. Presented here is an exhaustive review of not only the molecular mechanisms underlying the predisposition to the disease but also possible strategies to effectively diagnose, prevent, manage, and treat this disease.

Developmental mechanisms regulating the formation of smooth muscle layers in the mouse uterus†

Uterine smooth muscle cells differentiate from mesenchymal cells, and gap junctions connect the muscle cells in the myometrium. At the neonatal stage, a uterine smooth muscle layer is situated away from the epithelium when smooth muscle cells are grafted near the epithelium, suggesting that the epithelium plays an important role in differentiation, proliferation, and/or migration of smooth muscle cells. In this study, developmental mechanisms regulating the formation of the smooth muscle layers in the mouse uterus were analyzed using an in vitro culture model. Differentiation of smooth muscle cells occurs at a neonatal stage because ACTA2 gene expression was increased at the outer layer, and GJA1 was not expressed in cellular membranes of uterine smooth muscle cells by postnatal day 15. To analyze the effects of the epithelium on the differentiation of smooth muscle cells, a bulk uterine mesenchymal cell line was established from p53−/− mice at postnatal day 3 (P3US cells). Co-culture with Müllerian ductal epithelial cells (E1 cells) induced repulsive migration of ACTA2-positive cells among bulk P3US cells from E1 cells, but it had no effects on the migration of any of 100% ACTA2-positive or negative smooth muscle cell lines cloned from P3US cells. Thus, uterine epithelial cells indirectly affected the repulsive migration of smooth muscle cells via mesenchymal cells. Conditioned medium by E1 cells inhibited differentiation into smooth muscle cells of clonal cells established from P3US cells. Therefore, the uterine epithelium inhibits the differentiation of stem-like progenitor mesenchymal cells adjacent to the epithelium into smooth muscle cells.

CXCL12 Attracts Bone Marrow-Derived Cells to Uterine Leiomyomas

Uterine leiomyomas, also known as fibroids or myomas, are a common benign gynecologic tumor found in women of reproductive age. Though advances have been made in understanding leiomyomas, the etiology and pathogenesis of this disease are not fully characterized. Current evidence supports a role of putative human uterine stem/progenitor cells in the onset of uterine disease such as uterine myomas. In this study, we report that increased expression of CXCL12 in leiomyomas recruits bone marrow-derived cells (BMDCs) that may contribute to leiomyoma growth. Tissue was collected from leiomyomas or control myometrium from women with or without leiomyomas. qRT-PCR analysis showed increased expression of CXCL12 and decreased CXCR4 expression in the leiomyoma and myometrium of women with leiomyoma compared with normal myometrium. Increased CXCL12 protein secretion from cultured myoma cells was confirmed by ELISA. Further, we found that BMDCs migration was increased toward leiomyoma conditioned medium compared with conditioned medium from normal myometrium. CXCR4 antagonist AMD3100 completely blocked this migration. Engraftment of BMDCs significantly increased in myoma of mouse uteri treated with CXCL12 compared with placebo. We conclude that CXCL12 may play a role in leiomyomas growth by attracting bone marrow-derived cells to leiomyoma. Therefore, CXCL12 and its receptors are novel targets for leiomyoma therapy.

Putative human myometrial and fibroid stem-like cells have mesenchymal stem cell and endometrial stromal cell properties

STUDY QUESTION

Can endometrial stromal stem/progenitor cell markers, SUSD2 and CD146/CD140b, enrich for human myometrial and fibroid stem/progenitor cells?

SUMMARY ANSWER

SUSD2 enriches for myometrial and fibroid cells that have mesenchymal stem cell (MSC) characteristics and can also be induced to decidualise.

WHAT IS KNOWN ALREADY

Mesenchymal stem-like cells have been separately characterised in the endometrial stroma and myometrium and may contribute to diseases in their respective tissues.

STUDY DESIGN, SIZE, DURATION

Normal myometrium, fibroids and endometrium were collected from hysterectomies with informed consent. Primary cells or tissues were used from at least three patient samples for each experiment.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Flow cytometry, immunohistochemistry and immunofluorescence were used to characterise tissues. In vitro colony formation in normoxic and hypoxic conditions, MSC lineage differentiation (osteogenic and adipogenic) and decidualisation were used to assess stem cell activity. Xenotransplantation into immunocompromised mice was used to determine in vivo stem-like activity. Endpoint measures included quantitative PCR, colony formation, trichrome, Oil Red O and alkaline phosphatase activity staining.

MAIN RESULTS AND THE ROLE OF CHANCE

CD146+CD140b+ and/or SUSD2+ myometrial and fibroid cells were located in the perivascular region and formed more colonies in vitro compared to control cells and differentiated down adipogenic and osteogenic mesenchymal lineages in vitro. SUSD2+ myometrial cells had greater in vitro decidualisation potential, and SUSD2+ fibroid cells formed larger tumours in vivo compared to control cells.

LARGE-SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Markers used in this study enrich for cells with stem/progenitor cell activity; however, they do not distinguish stem from progenitor cells. SUSD2+ myometrial cells express markers of decidualisation when treated in vitro, but in vivo assays are needed to fully demonstration their ability to decidualise.

WIDER IMPLICATIONS OF THE FINDINGS

These results suggest a possible common MSC for the endometrial stroma and myometrium, which could be the tumour-initiating cell for uterine fibroids.

STUDY FUNDING/COMPETING INTEREST(S)

These studies were supported by NIH grants to JMT (R01OD012206) and to ALP (F32HD081856). The authors certify that we have no conflicts of interest to disclose.

Pathogenomics of Uterine Fibroids Development

We review recent studies dealing with the molecular genetics and basic results of omics analysis of uterine leiomyoma (LM)-a common benign muscle tumor of the uterus. Whole genome studies of LM resulted in the discovery of many new gene nets and biological pathways, including its origin, transcriptomic, and epigenetic profiles, as well as the impact of the inter-cell matrix in LM growth and involvement of microRNA in its regulation. New data on somatic cell mutations ultimately involved in the origin, distribution and growth of LM are reviewed. Putative identification of LM progenitor SC (stem cells) giving rise to maternal fibroid nodes and junctional zones provide a new clue for hypotheses on the pathogenomics of LM. The reviewed data are consistent with at least two different but probably intimately interacted molecular mechanisms of LM. One of them (the genetic hypothesis) is focused primarily on the MED12 gene mutations and suggests its onset in the side population of embryonic myoblasts of the female reproductive system, which later gave rise to multiple small and medium fibroids. The single and usually large-size fibroids are induced by predominantly epigenetic disorders in LM SC, provoked by enhanced expression of the HMGA2 gene caused by its hypomethylation and epigenetic deregulation enhanced by hypoxia, muscle tension, or chromosome instability/aberrations. The pathogenomics of both genetic and epigenetic programs of LM with many peculiarities at the beginning later became rather similar and partly overlapped due to the proximity of their gene nets and epigenetic landscape. Pathogenomic studies of LM open ways for elaboration of novel strategies of prevention and treatment of this common disease.

Uterine stem cells: from basic research to advanced cell therapies

BACKGROUND

Stem cell research in the endometrium and myometrium from animal models and humans has led to the identification of endometrial/myometrial stem cells and their niches. This basic knowledge is beginning to be translated to clinical use for incurable uterine pathologies. Additionally, the implication of bone marrow-derived stem cells (BMDSCs) in uterine physiology has opened the field for the exploration of an exogenous and autologous source of stem cells.

OBJECTIVE AND RATIONALE

In this review, we outline the progress of endometrial and myometrial stem/progenitor cells in both human and mouse models from their characterization to their clinical application, indicating roles in Asherman syndrome, atrophic endometrium and tissue engineering, among others.

SEARCH METHODS

A comprehensive search of PubMed and Google Scholar up to December 2017 was conducted to identify peer-reviewed literature related to the contribution of bone marrow, endometrial and myometrial stem cells to potential physiological regeneration as well as their implications in pathologies of the human uterus.

OUTCOMES

The discovery and main characteristics of stem cells in the murine and human endometrium and myometrium are presented together with the relevance of their niches and cross-regulation. The current state of advanced stem cell therapy using BMDSCs in the treatment of Asherman syndrome and atrophic endometrium is analyzed. In the myometrium, the understanding of genetic and epigenetic defects that result in the development of tumor-initiating cells in the myometrial stem niche and thus contribute to the growth of uterine leiomyoma is also presented. Finally, recent advances in tissue engineering based on the creation of novel three-dimensional scaffolds or decellularisation open up new perspectives for the field of uterine transplantation.

WIDER IMPLICATIONS

More than a decade after their discovery, the knowledge of uterine stem cells and their niches is crystalising into novel therapeutic approaches aiming to treat with cells those conditions that cannot be cured with drugs, particularly the currently incurable uterine pathologies. Additional work and improvements are needed, but the basis has been formed for this therapeutic application of uterine cells.

The ontogeny of myometrial stem cells in OCT4-GFP transgenic mouse model

BACKGROUND

Myometrium, the muscular wall of the uterus, is an active organ markedly remodeled during a woman's reproductive life, especially during pregnancy. Different studies using the 5-bromo-2'-deoxyuridine and side population methods in murine and human myometrium have suggested the presence of somatic stem cells in this tissue because of its remarkable regenerative capacity. Recently, our group has developed a surface-marker (Stro1/CD44)-specific approach to isolate and characterize myometrial somatic stem cells (SSCs) from humans and rats.

OBJECTIVE

In this study, we aimed to identify and localize the putative myometrial stem cell population in the murine uterus by using the specific surface markers, Nanog/CD44.

METHODS

Uteri from OCT4-GFP transgenic mice at different early-life time points were analyzed via single and double immunohistochemistry to co-localize myometrial stem cell marker CD44 with other general stemmness markers, e.g., Nanog and Oct-4. Finally, we correlated the frequency of myometrial stem cells in vivo with the expression of sex steroid hormone receptors, estrogen receptor α (ERα), and progesterone receptors A and B (PR A&B).

RESULTS

Nanog⁺/CD44⁺ stem cells were present in murine myometrium. Both stem cell markers were shown to co-localize with Oct-4 expression. Time-course experiments demonstrated that their percentages were significantly lower at the pre-sexual age of 1 week than at the sexually mature ages of 3 to 24 weeks. Importantly, both ERα and PR A&B were abundantly expressed in the myometrium at ages 1, 3 and 4 weeks.

CONCLUSIONS

We demonstrated that murine CD44⁺ myometrial cells have features of somatic stem cells with the expression of typical undifferentiated markers. Furthermore, our results suggest that myometrial stem cells are sex steroid hormone dependent, likely via paracrine pathway, and increase in numbers with reproductive maturity and rise in serum estrogen and progesterone levels around 3 weeks of age in mice. The abundance and early onset expression of ER/PR emphasize the vulnerability of neonatal myometrium to environmental endocrine disruptors which can potentially lead to permanent reprograming and adult onset of myometrial disorders such as uterine fibroids.

Label-Retaining, Putative Mesenchymal Stem Cells Contribute to Murine Myometrial Repair During Uterine Involution

Uterine remodeling during pregnancy is a fundamental, dynamic process required for successful propagation of eutherian species. The uterus can increase in size up to 40-fold during pregnancy, which is largely attributed to expansion of the myometrium by hyperplasia and hypertrophy. After pregnancy, the uterus repairs the remodeled or "damaged" tissue during uterine involution (INV). Little is known about this repair process, particularly the role of mesenchymal stem/progenitor cells. The objective of this study was to identify and characterize putative mesenchymal stem/progenitor cells in the murine myometrium using a combination of label retention and mesenchymal stem cell (MSC) marker expression and a pregnancy and uterine INV model. Tet-off transgenic mice with the Cre-lox system were used to specifically label mesenchymal cells (ie, myometrial and endometrial stromal cells) within the uterus while avoiding other cell types (eg, epithelial, immune, and endothelial cells) to identify slowly dividing cells and assess their stem cell qualities. We identified myometrial label-retaining cells (LRCs) that persisted for at least 3 months, expressed CD146 and CD140b (MSC markers), and proliferated at a higher rate during uterine INV compared with nonlabeled cells. The LRCs did not appear to express either estrogen receptor alpha or progesterone receptor, nor did the number of LRCs change at different estrous stages or in response to exogenous estradiol or progesterone administration, suggesting that LRCs were not involved in normal estrous cycling. The results from this study provide important insight into putative stem/progenitor cells in the myometrium and their possible role in uterine physiology.

Expanding upon the Human Myometrial Stem Cell Hypothesis and the Role of Race, Hormones, Age, and Parity in a Profibroid Environment

Uterine fibroids (UFs) are clonal, hormonally regulated, benign smooth-muscle myometrial tumors that severely affect female reproductive health, although their unknown etiology limits effective care. UFs occur fourfold more commonly in African American women than in Caucasian women, and African American women generally have earlier disease onset and greater UF tumor burden, although the mechanism of this ethnic disparity has not been identified. Recent findings have linked cancer (ie, tumor) risk to increased tissue-specific stem cell division and self-renewal and suggest that somatic mutations in myometrial stem cells (MyoSCs) convert them into tumor-initiating cells, leading to UF. Specifically, preliminary results in paraffin-embedded myometrial tissues have shown increased STRO-1⁺/CD44⁺ MyoSCs in African American versus Caucasian women. Using specific methods of flow cytometry and automated quantitative pathology imaging, a large cohort of myometrial samples were investigated to determine how the STRO-1⁺/CD44⁺ MyoSCs change with regard to a patient's race, age, parity, fibroid and hormone statuses, and the location of UFs within the uterus. We confirmed that the STRO-1⁺/CD44⁺ MyoSC population is expanded in African American women, is correlated with parity and fibroid number, and fluctuates with cyclic menstrual cycle hormone changes and age. Our data suggest that an expanded MyoSC population increases the formation of tumor-initiating cells, ultimately contributing to increased UF prevalence and burden in African American women.

Molecular targets of dietary phytochemicals for possible prevention and therapy of uterine fibroids: Focus on fibrosis

Uterine fibroids (myomas or leiomyomas) are common benign tumors of reproductive aged women. Fibroids are clinically apparent in 20-50% of women, and cause abnormal uterine bleeding, abdominal pain and discomfort, pregnancy complications and infertility. Unfortunately, limited numbers of medical treatment are available but no effective preventive strategies exist. Moreover, the benefits of medical treatments are tempered by lack of efficacy or serious adverse side effects. Fibrosis has recently been recognized as a key pathological event in leiomyoma development and growth. It is defined by the excessive deposition of extracellular matrix (ECM). ECM plays important role in making bulk structure of leiomyoma, and ECM-rich rigid structure is believed to be a cause of abnormal bleeding and pelvic pain/pressure. Dietary phytochemicals are known to regulate fibrotic process in different biological systems, and being considered as potential tool to manage human health. At present, very few dietary phytochemicals have been studied in uterine leiomyoma, and they are mostly known for their antiproliferative effects. Therefore, in this review, our aim was to introduce some dietary phytochemicals that could target fibrotic processes in leiomyoma. Thus, this review could serve as useful resource to develop antifibrotic drugs for possible prevention and treatment of uterine fibroids.

Uterine fibroids - what's new?

Uterine fibroids are the commonest benign tumours of women and affect all races with a cumulative lifetime risk of around 70%. Despite their high prevalence and the heavy economic burden of treatment, fibroids have received remarkably little attention compared to common female malignant tumours. This article reviews recent progress in understanding the biological nature of fibroids, their life cycle and their molecular genetic origins. Recent progress in surgical and interventional management is briefly reviewed, and medical management options, including treatment with selective progesterone receptor modulators, are also discussed.