Prevention of Chlamydia-Induced Infertility by Inhibition of Local Caspase Activity

Abstract

Tubal factor infertility (TFI) represents 36% of female infertility and genital infection by Chlamydia trachomatis (C. trachomatis) is a major cause. Although TFI is associated with host inflammatory responses to bacterial components, the molecular pathogenesis of Chlamydia-induced infertility remains poorly understood. We investigated the hypothesis that activation of specific cysteine proteases, the caspases, during C. trachomatis genital infection causes the disruption of key fertility-promoting molecules required for embryo development and implantation. We analyzed the effect of caspase inhibition on infertility and the integrity of Dicer, a caspase-sensitive, fertility-promoting ribonuclease III enzyme, and key micro-RNAs in the reproductive system. Genital infection with the inflammation- and caspase-inducing, wild-type C. trachomatis serovar L2 led to infertility, but the noninflammation-inducing, plasmid-free strain did not. We confirmed that caspase-mediated apoptotic tissue destruction may contribute to chlamydial pathogenesis. Caspase-1 or -3 deficiency, or local administration of the pan caspase inhibitor, Z-VAD-FMK into normal mice protected against Chlamydia-induced infertility. Finally, the oviducts of infected infertile mice showed evidence of caspase-mediated cleavage inactivation of Dicer and alteration in critical miRNAs that regulate growth, differentiation, and development, including mir-21. These results provide new insight into the molecular pathogenesis of TFI with significant implications for new strategies for treatment and prevention of chlamydial complications.

Profile of Anti-Chlamydia Immune Responses in Complicated (Infertile) and Non-complicated (Fertile) Genital Infections

“…Thus, when infected Z-VAD-FMK treated and non-treated mice were monitored for chlamydial shedding, Figure 1 shows that all animals were infected to the same degree and shed chlamydiae from their genital tracts to the same intensity during the initial 2 weeks covering the peak period of shedding after infection. However, as shown in Figure 2, treatment with the pan-caspase inhibitor, Z-VAD-FMK protected infected mice from infertility, as previously reported [19]. To identify the specific initiator caspase that mediate infertility, groups of mice were treated with specific inhibitors of the key initiator capases (caspase-1, -3 and -8), namely Z-WEHD-FMK, Z-DEVD-FMK, and Z-IETD-FMK, respectively, and fertility was assessed after infection.…”

“…To better characterize the contributions of the host and pathogen to chlamydial disease, we recently reported that although both the wild-type and the plasmid-free strain of C. trachomatis could colonize the genital tracts of female mice, the latter failed to induce infertility as compared to the former [19]. In addition, the local genital tract application of the pan-caspase inhibitor, Z-VAD-FMK conferred protection against infertility without affecting infectivity, as assessed by shedding of chlamydiae into the cervic-vaginal vault [19].…”

“…In addition, the local genital tract application of the pan-caspase inhibitor, Z-VAD-FMK conferred protection against infertility without affecting infectivity, as assessed by shedding of chlamydiae into the cervic-vaginal vault [19]. Thus, when infected Z-VAD-FMK treated and non-treated mice were monitored for chlamydial shedding, Figure 1 shows that all animals were infected to the same degree and shed chlamydiae from their genital tracts to the same intensity during the initial 2 weeks covering the peak period of shedding after infection.…”

“…In addition, the profile of cytokines and immune effectors of an anti-chlamydial immune response in infections with and without pathologic complications may also provide a useful molecular and immunological biomarker for predicting chlamydial pathologies. In Chlamydia-susceptible hosts, the presence of the cryptic plasmid and the profile of cytokines produced by anti-chlamydial T cell lines and clones were important factors that determined the development of infection complications [10,11,19,20]. Besides, successful chlamydial infection in humans was attributed to the skewing to immune response to a predominantly Th2 type and low Th1 response [21].…”

“…The apparent biological and pathologic relationship between the profile of immune effectors and the outcome of chlamydial infection, led us to hypothesize that the profile of anti-chlamydial immune responses in hosts who resolved the infection without complications may be different from when the host suffers complications. To test this hypothesis, we analyzed the serum antibody and cytokine responses in an establish mouse model of Chlamydia-induced infertility in which anti-caspase treatment prevented the onset of infertility without affecting infectivity [19]. The results from immune profile analysis in animals suggested that chlamydial infection with tubal pathologies elicited a predominantly Th2 immune response, and infections without pathologies are likely to be predominantly Th1 type, providing a useful prognostic biomarker to also guide the design and evaluation of safe efficacious vaccines.…”