From mice to women and back again: Causalities and clues for Chlamydia-induced tubal ectopic pregnancy Ruijin Shao, M.D., Ph.D.,a,d Xiaoqin Wang, M.Sc.,a,b Wei Wang, M.D.,c Elisabet Stener-Victorin, R.P.T., Ph.D.,a €nnstro € m, M.D., Ph.D.,d and H Carina Mallard, Ph.D.,c Mats Bra akan Billig, M.D., Ph.D.a a
Department of Physiology/Endocrinology, Institute of Neuroscience and Physiology; b BIOMATCELL VINN Excellence Center of Biomaterials and Cell Therapy, Department of Biomaterials, Institute of Clinical Sciences; c Department of Physiology/Circulatory Physiology, Institute of Neuroscience and Physiology; and d Department of Obstetrics and Gynecology, Institute of Clinical Sciences, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden
Objective: To provide an overview of knockout mouse models that have pathological tubal phenotypes after Chlamydia muridarum infection, discuss factors and pathological processes that contribute to inflammation, summarize data on tubal transport and progression of tubal implantation from studies in humans and animal models, and highlight research questions in the field. Design: A search of the relevant literature using PubMed and other online tools. Setting: University-based preclinical and clinical research laboratories. Patient(s): Women with tubal ectopic pregnancy after Chlamydia trachomatis infection. Intervention(s): None. Main Outcome Measure(s): Critical review of the literature. Result(s): Chlamydia trachomatis infection poses a major threat to human reproduction. Biological and epidemiological evidence suggests that progression of Chlamydia infection causes intense and persistent inflammation, injury, and scarring in the fallopian tube, leading to a substantially increased risk of ectopic pregnancy and infertility. The main targets of Chlamydia infection are epithelial cells lining the mucosal surface, which play a central role in host immune responses and pathophysiology. Tubal phenotypes at the cellular level in mutant mice appear to reflect alterations in the balance between inflammatory mediator and factor deficiency. While studies in mice infected with Chlamydia muridarum have provided insight into potential inflammatory mediators linked to fallopian tube pathology, it is unclear how inflammation induced by Chlamydia infection prevents or retards normal tubal transport and causes embryo implantation in the fallopian tube. Conclusion(s): Given the similarities in the tubal physiology of humans and rodents, knockout mouse models can be used to study certain aspects of tubal functions, such as gamete transport and early embryo implantation. Elucidation of the exact molecular mechanisms of immune and inflammatory responses caused by Chlamydia infection in human fallopian tubal cells in vitro and understanding how Chlamydia infection affects tubal transport and implantation in animal studies in vivo may explain how Chlamydia trachomatis infection drives inflammation and develops the tubal Use your smartphone pathology in women with tubal ectopic pregnancy. (Fertil SterilÒ 2012;98:1175–85. Ó2012 by to scan this QR code American Society for Reproductive Medicine.) and connect to the Key Words: Mouse models of Chlamydia infection, tubal ectopic pregnancy, human, infertility Discuss: You can discuss this article with its authors and with other ASRM members at http:// fertstertforum.com/shaor-mice-women-chlamydia-tubal-ectopic-pregnancy/
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Received May 1, 2012; revised and accepted July 12, 2012; published online August 9, 2012. R.S. has nothing to disclose. X.W. has nothing to disclose. W.W. has nothing to disclose. E.S.-V. has nothing to disclose. C.M. has nothing to disclose. M.B. has nothing to disclose. H.B. has nothing to disclose. The work was supported by the Swedish Medical Research Council (grant nos. 5859 and 10380), the Swedish federal government under the LUA/ALF agree€ teborgs La €karesa €llskap, Hjalmar Svensson Foundation, Fred G. and Emma E. ment (ALFGBG-147791), the Sahlgrenska Academy Research Council, the Go Kanolds Foundation, Fredrik och Ingrid Thurings Foundation, Emil and Maria Palms Foundation, Mary von Sydow Foundation, Anna Cederbergs Foundation, Tore Nilsons Foundation, Ake Wibergs Foundation, Wilhelm-Martina Lundgrens Foundation, Wennergren Foundation, and the Royal Society of Arts and Sciences in Gothenburg. Reprint requests: Ruijin Shao, M.D., Ph.D., Department of Physiology/Endocrinology, Institute of Neuroscience and Physiology, Sahlgrenska Academy of Gothenburg University, P.O. Box 434, 40530 Gothenburg, Sweden (E-mail:
[email protected]). Fertility and Sterility® Vol. 98, No. 5, November 2012 0015-0282/$36.00 Copyright ©2012 American Society for Reproductive Medicine, Published by Elsevier Inc. http://dx.doi.org/10.1016/j.fertnstert.2012.07.1113 VOL. 98 NO. 5 / NOVEMBER 2012
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hlamydia trachomatis infection is one of the most common sexually transmitted bacterial diseases, particularly in women (1). In the United States, the prevalence of Chlamydia infection in females is estimated to be approximately 2.5%, and 912,718 infected women were reported in 2009 (2). In Sweden, the incidence of Chlamydia infection increased from 171.7 to 406.2 cases per 100,000 between 1998 and 2009, despite public health measures taken to control the infection (3, 4). A high prevalence and incidence of Chlamydia infection have been reported in women in developing countries, including China and India (5). Chlamydia infection is a socioeconomic and public health problem (6). The incidence of genital tract Chlamydia infection is highest in women at the peak of their reproductive life and has a negative impact on reproduction (7). There is no vaccine available (8), and the diagnosis and treatment of Chlamydia infection and its complications incur substantial health care costs (7). We note that in case-control studies, the risk ratio of infection-induced reproductive diseases can be underestimated because up to 70%–80% of acute Chlamydia infections in women are asymptomatic or subclinical and are not diagnosed or treated (9). According to the World Health Organization, 10%–40% women with untreated or repeated infections develop symptomatic pelvic inflammatory disease (10), which results in scarring and fibrosis of the fallopian tubes (11) and can lead to ectopic pregnancy (EP) (12). Moreover, 30%–40% of cases of female infertility are caused by postinfection tubal damage resulting in hydrosalpinx (6, 10). Treatment of Chlamydia infection does not always prevent progressive tubal damage (6). Therefore, the role of a Chlamydia screening program is to reduce the incidence of reproductive tract infection and prevent its complications (9).
PATHOPHYSIOLOGY OF CHLAMYDIA INFECTION Chlamydia is an obligate intracellular bacterium (6) that has a unique, two-phase replication cycle that is required for its survival in host cells (13). Infection is initiated when the elementary body (EB), the transmissible form of the organism capable of extracellular survival, attaches to epithelial cells at the fallopian mucosal surfaces, enters the host cell, and induces endocytosis into a host-derived, membrane-bound endosome called a chlamydial inclusion. Inside the inclusion, the EB differentiates into a noninfective, intracellular reticulate body (RB) within 8–12 hours after invasion (6). C. trachomatis can alternate between metabolically inert EBs and metabolically active RBs. RBs reorganize into EBs 18–30 hours after invasion of host cells, and infected cells undergo lysis and release infectious EBs 48–72 hours after infection. RBs divide exponentially by binary fission and then condense back into EBs, which are released after lysis of infected cells, allowing further propagation of the infection in neighboring cells (14). Chlamydiae primarily infect epithelial cells within 1–2 days after infection of the female reproductive tract, and the inflammatory response of these cells to the infection directs innate and adaptive immune responses (15, 16). The infection is characterized by inflammation, and high levels of cytokine 1176
secretion persist throughout the bacterial infectious cycle (up to 4 days) (14). The extent of tubal cell damage depends on the quality and duration of the preceding infection (17). The host reaction to acute Chlamydia infection is characterized histopathologically by neutrophilic and lymphocytic infiltrates; the cellular features of chronic/repeated Chlamydia infection include mononuclear cell infiltration and fibrosis (16). Infected epithelial cells consequently undergo necrosis (16). The ulcerous epithelium is covered by fibers, and connective tissue structures shrivel. Fibrosis in the fallopian tube is responsible for the severe consequences of persistent Chlamydia infection. Chronic scarring, tubal occlusion, and hydrosalpinx are frequent sequelae of aggressive inflammation from C. trachomatis infection (Fig. 1A) (18). Inadequate clearance of Chlamydia infection may result in a persistent infection (9).
Fallopian Tubal EP: Wrong Time and Place EP is the leading cause of pregnancy-related death in the first trimester of pregnancy (19). EP is defined as an extrauterine pregnancy due to embryo implantation outside the uterus (20, 21). EP accounts for 1.5%–2% of all pregnancies in the Western world (21), and approximately 98% of EPs are in the fallopian tube (20). In addition, tubal EP is a growing problem in developing countries (19, 22). In early pregnancy, abdominal or pelvic pain and vaginal bleeding may indicate EP (23). Many facets of tubal EP remain unclear, so it is difficult to predict the initiation and development of tubal EP. Unruptured EP can be diagnosed rapidly and accurately by transvaginal ultrasound and measurement of serum hCG (19). Despite improvements in the clinical diagnosis and management of early-stage tubal EP, the treatment and prevention options are limited (20, 23). Current treatment strategies are surgical intervention or medical therapy with methotrexate (19, 20). Women with tubal EP are at increased risk of infertility and tubal EP in future pregnancies (19, 24). A critical function of the human fallopian tube is to provide the optimal microenvironment for the transport and maturation of gametes and the establishment of pregnancy (25). Although our understanding of tubal physiology is impressive (26), there is still no diagnostic test of tubal function. The human fallopian tube consists of an inner mucosal layer (the endosalpinx) supported by a lamina propria, a muscular layer (the myosalpinx), and a serosal coat (the mesosalpinx) (27) and is composed of ciliated and secretory epithelial cells and smooth muscle cells (28). Normal pregnancy is preceded by the transport of gametes and early embryo through the fallopian tube in an orderly process that involves ciliary beating, muscle contraction, and the tubal fluid microenvironment (25). The tubal epithelium is normally not receptive to implantation and acts as a mechanical barrier to prevent the early embryo from interacting with the epithelium during the tubal transport (26); however, during transport, there is a dialog between tubal epithelial cells and gametes/early embryos (29, 30). Alterations in the molecular dialog between the implanting blastocyst and tubal cells at the implantation site may contribute to EP (31). Tubal epithelial cells also function as a protective barrier to VOL. 98 NO. 5 / NOVEMBER 2012
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FIGURE 1
(A) Schematic representation of how Chlamydia infection causes fallopian tube pathology in humans. Studies in animals have suggested that Chlamydia induces intense and persistent local inflammation that leads to tubal cell damage, hydrosalpinx formation, and scarring. However, the mechanism for ectopic embryo implantation and development of tubal EP in humans after Chlamydia infection is unknown. (B) Chlamydia etiology and known mechanisms of immune responses and cellular components in mice after C. muridarum infection. In mice infected with C. muridarum, multiple inflammatory mediators contribute to fallopian tube pathology mediated by the host response to infection. Different mechanisms may interact to cause progressive tubal damage due to Chlamydia infection. IC ¼ immune cells; THp ¼ T helper cells (CD4þ); TCyto ¼ T cytotoxic cells (CD8þ); Mac ¼ macrophages; Neu ¼ neutrophils; CEC ¼ ciliated epithelial cells; SEC ¼ secretory epithelial cells; SM ¼ smooth muscle cells; MMP-9 (gelatinase B) ¼ matrix metalloproteinase-9; ATP ¼ adenosine 5'-triphosphate. Shao. Chlamydia-induced tubal ectopic pregnancy. Fertil Steril 2012.
foreign pathogens (28, 32). Tubal structure and function can be impaired by infection, surgery, adhesion, and other pathological processes (20, 33). Excessive or chronic inflammation of the fallopian tube is the primary cause of VOL. 98 NO. 5 / NOVEMBER 2012
tubal disease (15). Suggested risk factors for EP include C. trachomatis infection, smoking, and IVF (20, 22, 31). Although the exact events leading to tubal EP are still poorly defined, several hypotheses about tubal implantation 1177
ORIGINAL ARTICLE: EARLY PREGNANCY have been proposed, including inhibition of ciliary beating and muscle contraction, stimulation of tubal secretion, and early embryo–tubal cell interaction (31). It has been speculated that an antibody response to the Chlamydia 60-kDa heat shocks the protein (hsp-60) and causes a tubal inflammatory response, leading to tubal blockage or a predisposition to tubal implantation (34, 35). Development of effective tools to prevent and treat tubal EP induced by C. trachomatis infection has been exceedingly difficult (6). This difficulty reflects our incomplete understanding of the molecular and cellular mechanisms that lead to tubal dysfunction and result in tubal implantation and EP in women with C. trachomatis infection (Fig. 1A).
Mouse Models of Chlamydia Infection Female mice with C. muridarum infection of the genital tract are frequently used as a model of human C. trachomatis reproductive tract infection (16). C. muridarum, a mouse biovariant of C. trachomatis (16), results in upper genital tract pathologies that closely resemble those in human genital tracts infected with C. trachomatis (6). These pathologies— including flattened epithelia and increased tubal dilatation, epithelial fibrosis and tubal occlusion in the isthmus, and hydrosalpinx formation in the ampulla (18, 36–38)—are likely induced by reinfection with C. muridarum rather than by a single acute infection (6). Multiple immune cells are present in the female genital tract, including T lymphocytes (CD4-positive helper T cells and CD8-positive cytotoxic T cells) and tissue-associated phagocytes (macrophages and neutrophils) (15, 16). These cells accumulate at the site of Chlamydia infection and participate in the cell-mediated immune response (6). T-cell responses are negatively regulated by T-cell immunoglobulin and mucin domain 3 (Tim-3) and programmed death-1 (PD1). In mice infected with C. muridarum, blocking T-cell activation by Tim-3 and PD-1 enhances inflammation and tubal pathology (39), whereas the absence of CD8-positive cytotoxic T cells reduces hydrosalpinx formation (40). However, the tubal epithelium seems to play a dominant role in Chlamydia-induced tubal pathologies (41), as Chlamydia infection and replication in tubal epithelial cells can ascend and persist for long periods (17). Besides triggering the inflammatory process that directs both the innate and adaptive immune responses (14), infected tubal epithelium recruits effector immune cells and amplifies their responses, leading to secretion of an array of proinflammatory cytokines (14, 42) and tissue remodeling (43, 44) (Fig. 1B). Moreover, the release of ‘‘danger signals’’ such as ATP and uric acid from infected and damaged epithelial cells may promote inflammatory responses (45) and regulate necrosis (16) and apoptosis (46). Perturbation of inflammatory cytokine and chemokine production and signaling pathways has been implicated in fallopian tube pathology in mice after C. muridarum infection (14, 42, 47) (Fig. 1B). Signaling mediated by Toll-like receptors (TLRs) is a key pathway in the induction of innate immune and inflammatory responses (6, 15). So far, 10–12 transmembrane TLRs have been identified in humans and 1178
mice, and different TLRs have been detected in immune and nonimmune cells, including tubal epithelial cells in humans (48, 49) and mice (41). TLR signaling is activated by microbial products and bacterial cell wall components (50). For example, host-derived, endogenous hsp-60 is a ligand for both TLR2 and TLR4; peptidoglycan, lipopeptide, and lipoprotein are ligands for TLR2, and lipopolysaccharide (LPS) is a ligand for TLR4 (51). However, in vivo infection studies show that TLR2 knockout mice have less tubal dilatation than TLR4 knockout mice or wild-type mice (52) and do not develop hydrosalpinx; in contrast, TLR4 and TLP9 deficiency does not affect tubal structure and function after C. muridarum infection (53, 54). In line with these observations, when LPS is applied to both fallopian tube and uterus in mice, only uterus with increased dilatation and hydrosalpinx-like formation is observed (our unpublished data). These results suggest that TLR2-dependent signaling is responsible for chronic tubal pathology after Chlamydia infection. Among TLRs, TLR3 is a receptor for double-stranded RNA produced by many viruses during replication (51). The effects of TLR3 deficiency on tubal pathology related to C. muridarum infection in vivo have not been reported; however, C. muridarum replication in mouse tubal epithelial cells in vitro is more robust in the absence of TLR3 (55, 56). These results reflect the contributions of different TLRs to tubal function, but their precise roles are complex. Further work using selective TLR agonist may help define the different roles of TLRs in the fallopian tube during Chlamydia infection. TLRs signal through common intracellular pathways that lead to translocation and activation of transcription factors, such as nuclear factor-kB (NF-kB) and interferon regulatory transcription factors, and to the generation of various inflammatory cytokines such as tumor necrosis factor (TNF) -a, interleukin (IL) -1b, and IL-6, (50, 51), which can directly damage fallopian tube epithelium. Knockout of inflammatory cytokines and their signaling components, such as TNF-a (40), IL-1b (57), IL-1R (58), or caspase-1 (59) (a regulator of IL-1b activation), prevents tubal pathology in mice infected with C. muridarum. However, in mice lacking interferon regulatory factor 3 (60), a regulator of TNF-a and IL-1b, C. muridarum causes pathological effects in the fallopian tubes. Thus, manifestations of C. muridarum infection may be determined by a fine balance between regulators of inflammatory cytokines. Furthermore, CD4-positive helper T cells that produce gamma interferon (IFN-g), and possibly CD8positive cytotoxic T cells, are required to clear Chlamydia and prevent reinfection (6, 16). Studies in knockout mice have shown that, unlike IFN-ab (61), IFN-g protects against tubal inflammation and destruction after C. muridarum infection (62).
Human Studies Cause-and-effect relationships between Chlamydia infection and fallopian tube pathology are difficult to establish in humans, owing to ethical considerations. However, clinical studies have described the expression and regulation of TLR2 (48, 63, 64), TNF-a (65–68), IL-1b (35, 68–70), IL-1R (69, 70), caspase-1 (24), IFN-g (68, 71), CD8 (72), and VOL. 98 NO. 5 / NOVEMBER 2012
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TABLE 1 Genes/proteins implicated in fallopian tube pathology: results from mutant mice after C. muridarum infection and women with/without tubal EP or infertility. Gene
Tubal phenotype in mice
Tlr2
No hydrosalpinx and dilatation
Tnfa
Reduced hydrosalpinx and dilatation
Il1b
1. No acute, chronic, or plasma cell infiltration 2. Reduced dilatation
Il1r1
Reduced hydrosalpinx and dilatation
Casp1
1. Decreased inflammatory damage 2. Reduced dilatation 1. Increased inflammation and fat necrosis 2. Increased destruction of epithelial cells 3. Increased loss of luminal plicae Reduced hydrosalpinx 1. Increased acute and chronic inflammation 2. Induced dilatation Induced hydrosalpinx
Ifng
Ifnar1 Irf3 Icam1 CD8 Mmp9 Cftr
Reduced hydrosalpinx and dilatation 1. Decreased acute inflammation 2. Reduced hydrosalpinx No hydrosalpinx
Human studies
Reference
1. TLR2 mRNA and protein are highly expressed in the fallopian tube. 2. TLR2 genotype is not associated with C. trachomatis infection and tubal factor infertility. 1. TNF-a is detected in the fallopian tube fluid 2. TNF-a levels in serum and peritoneal fluid are higher in women with EP than in those with intrauterine pregnancy. 3. TNF-a-308 A allele increases the risk of severe tubal damage in women with infertility associated with C. trachomatis. 1. Tubal IL-1b mRNA and protein are higher in the secretory phase than in the proliferative phase. 2. Tubal IL-1b mRNA and protein are lower in EP sites than in non-EP sites. 3. IL-1b levels in serum are higher in women with EP than in those with intrauterine pregnancy. 4. IL-1b levels in serum are lower in women with EP who are anti-CT antibody-positive than in those who are anti-CT antibody-negative. 5. High levels of IL-1b in fallopian tube fluid. 1. Regulation of IL-1R protein expression is cell-type dependent during the reproductive cycle. 2. Tubal IL-1R mRNA and protein is higher in EP sites than in non-EP sites. Caspase-1 protein is expressed in the fallopian tube.
54, 58, 69–70
1. IFN-g is detected in the fallopian tube fluid. 2. Circulating IFN-g levels are higher in infertile women than in fertile women.
ND ND
46, 71–74
41, 63, 74–76
64, 75, 76
24, 65 68, 74, 77
67 66
ICAM1 mRNA and protein are only expressed in ciliated and secretory epithelial cells. There is no difference in the number of CD8 T cells between women with EP and during the menstrual cycle. MMP9 immunoreactivity is absent in tubal cells of women with EP. CFTR mRNA and protein are higher in fallopian tubes with hydrosalpinx than in normal fallopian tubes.
104, 105 46, 78 49, 79 104, 105
Note: Tlr2 ¼ toll-like receptor 2; Tnf-a ¼ tumor necrosis factor alpha; Il1b ¼ interleukin-1beta; Il1r1 ¼ interleukin-1 receptor; Casp1 ¼ caspase-1; Ifng ¼ interferon gamma; Ifnar1 ¼ interferon (alpha and beta) receptor-1; Irf3 ¼ interferon regulatory transcription factor 3; Icam1 ¼ intercellular adhesion molecule 1; Cd8 ¼ CD8þ T cells; Mmp9 ¼ matrix metalloproteinase-9; Cftr ¼ cystic fibrosis transmembrane conductance regulator; anti-CT antibody ¼ anti-C. trachomatis outer membrane protein antibody; ND = not determined. Shao. Chlamydia-induced tubal ectopic pregnancy. Fertil Steril 2012.
matrix metalloproteinase 9 (73) in human fallopian tubes (Table 1). Although differences between C. trachomatis and C. muridarum infections might affect the immunobiology of infection (6), these Chlamydia strains are closely related phylogenetically. Thus it is reasonable to assume that they produce fallopian tube pathology through the same molecular mechanisms and can be used interchangeably to investigate the infection process and progressive inflammation. The knockout mouse models (40, 43, 52, 57–62) discussed above provide insights into processes and factors that contribute to Chlamydia-induced tubal inflammation and pathology. The use of in vitro models will continue to VOL. 98 NO. 5 / NOVEMBER 2012
deepen our understanding of the signaling pathways involved in humans. In tubal epithelial cells in vitro, C. trachomatis is reported to modulate epithelial cell adhesion and polarity, regulate the function of epithelial cell-adhesion molecules, facilitate cell-cell communication within epithelia, and activate the Wnt signaling pathway, leading to disruption of epithelial structure and function (74). On the other hand, C. trachomatis in tubal epithelial cells in vitro also enhances proliferation of both infected and noninfected epithelial cells (74). Furthermore, a low oxygen environment such as hypoxia blocks the antichlamydial properties of IFN-g in human tubal epithelial cells in vitro (75). In combination with in vivo data from animal studies, these 1179
ORIGINAL ARTICLE: EARLY PREGNANCY results support the notion that the outcome of Chlamydia infection is determined by the balance between inflammatory responses and protective activities in the fallopian tube. The prokineticins are proangiogenic factors, and their expression profile of proangiogenic factors relate to intrauterine implantation (76). The actions of prokineticins are mediated by prokineticin receptors (PROKR1 and 2), and PROKR2, but not PROKR1, is expressed at a high level in fallopian tubes of women with evidence of past C. trachomatis infection (77). In vitro infection studies show that Chlamydiae alter PROKR2 expression in the fallopian tube and oviductal epithelial OE-E6/E7 cells (77). In addition, while treatment with triacetylated lipoprotein (a TLR2 ligand) increases TLR2 expression, blocking TLR2 or NF-kB signaling prevents Chlamydia-induced expression of PROKR2 in OE-E6/E7 cells in vitro (77). These observations suggest that activation of TLR2 signaling by C. trachomatis leads to activation of NFkB, which is partially responsible for the high levels of PROKR2 in the fallopian tube (77). However, PROKR1/2 expression is lower in women with tubal EP than in those with intrauterine pregnancy (78). Thus, prokineticinPROKR2 signaling may have other proangiogenic functions in tubal EP induced by infection with organisms other than Chlamydia.
Unanswered Questions and Gaps
TNF-a, IL-1b, IL-6, and MCP-1) (Fig. 2). Although these results suggest that E2/P4 and their receptors directly contribute to both immune and tubal functions, we need to know the extent to which and how endogenous E2/P4 affects immune responses and the production of inflammatory mediators in the fallopian tube under physiological and pathophysiological conditions in vivo. The transcription factor NF-kB has a critical role in coordinating the inflammatory response and cell-survival pathways (93). Since NF-kB signaling is activated in the epithelial cells with persistent Chlamydia infection in vitro (94), fallopian tube damage or blockage induced by Chlamydia infection in vivo may be due to persistent inflammatory activation mediated by NF-kB (15). The ER and PR interact with NF-kB and also repress its activities associated with the antiinflammatory properties of steroids in a cell-type-dependent manner (95). Thus, it is unlikely that a single pathway is involved in tubal implantation caused by C. trachomatis infection. Many different cytokines, chemokines, and adhesion molecules contribute to intrauterine receptivity to implantation (34, 96). A reasonable question is what key downstream targets of the cooperative action of ER/PR and NF-kB contribute to an increase in tubal receptivity after Chlamydia infection (Fig. 3). It will be of great interest to identify the molecules responsible for the initial in vivo tubal implantation after activation of ER/PR and NF-kB signaling.
Molecular mechanisms of steroid hormone action and infection. Ovarian steroid hormones have relatively complementary roles, reflected in their temporal and cyclical fluctuations in females (79). There is evidence that the steroid hormones 17b-estradiol (E2) and progesterone (P4) increase susceptibility to Chlamydia infection and modulate inflammation in epithelial cells (80, 81). However, one question is whether Chlamydia infection influences the metabolism and distribution of steroid hormones in females. We have a good understanding of the physiological actions of E2 and P4 acting through estrogen receptors (ERs) and progesterone receptors (PRs) in reproductive function. However, the role of E2-ER and P4-PR signaling in the fallopian tubal disorder is poorly defined. Several studies have shown that human and rodent fallopian tubal cells express ERs and PRs (82– 88). Notably, we showed that in vivo treatment with ICI 182,780 (an ER antagonist) and clomiphene citrate (an ER modulator) blocks oocyte transport in rodent fallopian tubes (85, 89), whereas treatment with the PR antagonists Org 31710 and CDB 2194 does not (our unpublished data). Timely establishment of endometrial receptivity is crucial for successful embryo implantation (90). E2 and P4 regulate the cellular changes in the endometrial tissue for establishment of endometrial receptivity through ERs and PRs (90) and modulate the paracrine and autocrine effects of adhesive molecules, growth factors, cytokines, and chemokines (34, 91). Both E2 and P4 have anti-inflammatory and immunomodulatory properties (34, 92). Comparative expression analysis of in vitro mouse tubal tissues revealed that treatment with E2 and/or ICI 182,780 and treatment with P4 and/or RU486 (a PR antagonist) and Org 31710 result in the secretion of different cytokines and chemokines (e.g.,
Chlamydia-induced hydrosalpinx. Although tubal secretory function is incompletely characterized, epithelial cell secretions are known to affect gamete fertilization and early human embryo development (97). The composition and volume of fallopian tube fluid depend on physiological and pathophysiological conditions (97). During the infection process, it is important for Chlamydia to efficiently adapt to the changing environment within the tube. One consequence of tubal infection in mice is hydrosalpinx, as defined by tubal dilatation and abnormal fluid accumulation (18). Cystic fibrosis transmembrane conductance regulator (CFTR) is thought to regulate epithelial electrolytes, secretion, and fluid volume, which has been implicated in successful uterine implantation (98). CFTR is expressed in human and mouse fallopian tubes (99, 100), and high CFTR levels have been observed in human tubal epithelia and hydrosalpinx (99). Furthermore, in mice, knockout of CFTR prevents hydrosalpinx after C. muridarum infection (101). Thus, an abnormal increase in CFTR may be responsible for hydrosalpinx formation during Chlamydia infection. On the other hand, intercellular adhesion molecule-1 (ICAM1) is expressed in human fallopian tubes (102), and mice lacking ICAM1 have an increased incidence of hydrosalpinx after C. muridarum infection (103). These results suggest that Chlamydia infection can target different host proteins involved in hydrosalpinx formation. Hydrosalpinx has adverse effects on ongoing pregnancy and female fertility, perhaps by reducing endometrial receptivity (104). Since successful intrauterine implantation requires a sustainable microenvironment (79), an important question is how Chlamydia-induced hydrosalpinx formation changes the local microenvironment and consequently triggers tubal implantation in women.
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Shao. Chlamydia-induced tubal ectopic pregnancy. Fertil Steril 2012.
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FIGURE 2 Continued Effects of ovarian-derived steroid hormones and their receptor antagonists on the concentration of cytokines and chemokines in mouse fallopian tubes in vitro. Intact prepubertal female C57BL/6 mice (age 21 days; Taconic, Copenhagen, Denmark) were used. Fallopian tube explants were treated with 10 nM E2, 0.1 mM P4, and ER antagonist (0.1 mM ICI 182,780) or PR antagonists (0.1 mM RU 486 and 0.1 mM Org 31710) for 24 hours. Samples of culture medium were collected, and the secretion of cytokines TNF-a, IL-1b, IL-6, IFN-g, MCP-1, and RANTES was quantified by sandwich immunoassays. Values are mean SEM (n ¼ 6/treatment). Significance was tested by two-way analysis of variance with Bonferroni correction for multiple comparisons when appropriate. *P
