Effect of female sex hormones on the developmental cycle of Chlamydia abortus compared to a penicillin-induced model of persistent infection

Abstract

Background: Chlamydia abortus, an obligate intracellular pathogen with an affinity for placenta, causes reproductive failure. In non-pregnant animals, an initial latent infection is established until the next gestation, when the microorganism is reactivated, causing abortion. The precise mechanisms that trigger the awakening of C. abortus are still unknown. Sexual hormones such as estradiol and progesterone have been shown to affect the outcome of infection in other species of the family Chlamydiaceae, while estrogens increase chlamydial infection, progesterone has the opposite effect. To try to establish whether there is a relationship between these events and the latency/ reactivation of C. abortus in the reproductive tract of small ruminants, ovine endometrial (LE) and trophoblastic (AH-1) cells were treated with estradiol or progesterone prior to their infection with C. abortus. The results are compared with those obtained for treatment with penicillin prior to infection, which is a well-established model for studying persistent infection in other chlamydial species. Cells were examined by transmission electron microscopy, and an mRNA expression analysis of 16 genes related to the chlamydial developmental cycle was made.

Results: The changes observed in this study by the action of sex hormones seem to depend on the type of cell where the infection develops. In addition, while the changes are morphologically similar to those induced by treatment with penicillin, the patterns of gene expression are different. Gene expression patterns therefore, seem to depend on the persistence induced models of C. abortus used. Hormone treatments induced aberrant forms in infected endometrial cells but did not affect the chlamydial morphology in trophoblast cells. At the genetic level, hormones did not induce significant changes in the expression of the studied genes.

Conclusions: The results suggest that penicillin induces a state of persistence in in vitro cultured C. abortus with characteristic morphological features and gene transcriptional patterns. However, the influence of hormones on the C. abortus developmental cycle is mediated by changes in the host cell environment. Furthermore, a persistent state in C. abortus cannot be characterised by a single profile of gene expression pattern, but may change depending on the model used to induce persistence.

Keywords: Chlamydia abortus; Female sex hormones; Ovine enzootic abortion; Penicillin; Persistence.

Fig. 1

Transmission electron micrographs of C. abortus inclusions in LE (pictures in left column) and AH-1 cells (right column) at 72 h pi without treatment (a, b) or under estradiol (c, d), progesterone (e, f) or penicillin (g, h) treatment. a Untreated LE cell, normal inclusion containing numerous RBs and few IBs. b Untreated AH-1 cell showing a conventional large inclusion with RBs, IBs and EBs. c Pre-incubation with estradiol induced the presence of several pleomorphic enlarged RBs of different sizes and empty vesicle membranes within the inclusion in LE cells. d AH-1 cell treated with estradiol showing a typical mature inclusion with predominance of EBs and IBs over RBs. e Progesterone treated LE cell containing an inclusion with 2–4 abnormally enlarged atypical AB forms. f Progesterone supplemented AH-1 cell, large inclusion containing many RBs, IBs and EBs with normal shape and morphology. g, h Penicillin treated cultures showing characteristics consistent with a persistent chlamydial infection, both cell lines presented small inclusions with 2–4 giant ABs exclusively

Fig. 2

Transmission electron micrograph of a C. abortus inclusion in an infected AH-1 cell treated with 200 U/ml penicillin. Small inclusion containing a single large amorphous aberrant body. Multifocal deposition of electron-dense material can be observed on its outer membrane. Empty vesicle membranes from smaller reticular bodies are also present in the limited space of the vacuole left by the aberrant form

Fig. 3

Experimental design. The diagram illustrates on a timeline the hormone or beta-lactam antibiotic exposure of AH1 and LE cells, infection and samples collection at different times. Cells were pre-exposed to progesterone (P4), estradiol (E2) or penicillin G (Pen G) added in incubation medium for 24 h. At this time, the cells were infected by the AB7 strain of C. abortus and, two hours later, they were again exposed to P4, E2 or Pen G in incubation medium, and incubated until 48 and 72 hpi, when samples were collected for genomic studies. In addition, samples were collected at 72 hpi for morphological studies using transmission electron microscopy (TEM)