Chlamydia Infection Across Host Species Boundaries Promotes Distinct Sets of Transcribed Anti-Apoptotic Factors

Abstract

Chlamydiae, obligate intracellular bacteria, cause significant human and veterinary associated diseases. Having emerged an estimated 700-million years ago, these bacteria have twice adapted to humans as a host species, causing sexually transmitted infection (C. trachomatis) and respiratory associated disease (C. pneumoniae). The principle mechanism of host cell defense against these intracellular bacteria is the induction of cell death via apoptosis. However, in the "arms race" of co-evolution, Chlamydiae have developed mechanisms to promote cell viability and inhibit cell death. Herein we examine the impact of Chlamydiae infection across multiple host species on transcription of anti-apoptotic genes. We found mostly distinct patterns of gene expression (Mcl1 and cIAPs) elicited by each pathogen-host pair indicating Chlamydiae infection across host species boundaries does not induce a universally shared host response. Understanding species specific host-pathogen interactions is paramount to deciphering how potential pathogens become emerging diseases.

Keywords: Chlamydia; apoptosis; emerging disease; evolution; transcription.

Figure 1

Enhanced growth in the presence of host cell translation—Cells were infected in 24 well plates (10⁵ cells/well) for 30 h with or without CHX (1.5 μg/mL). Supernatants of hypotonically lysed cells were clarified by centrifugation and titered. Chlamydiae were stained with α-HSP60 to quantitate infectious units/ml (A). Presented is the ratio of (-CHX/CHX). Growth curves of Cm and Ct (MOI = 1 at 1 × 10⁵ IFU) were determined in mouse and guinea pig cells (Gray line-Cm, solid line-Ct, dashed line-Cc open marker—guinea pig, solid marker—mouse) (B). Ct-C. trachomatis, Cc-C.caviae Cm-C.muridarum. ^*p < 0.05 (data are representative of two independent trials).

Figure 2

Chlamydiae inhibit Caspase three activation in diverse hosts—Cell lines were infected with the indicated pathogens and allowed to incubate for 26 h. Staurosporine was added for 4 h before cell lysates were collected for colorimetric analysis of caspase three activity in mouse cells (A), human cells (B), and guinea pig cells (C). Ct-C. trachomatis, Cc-C.caviae Cm-C.muridarum. ^**p < 0.01, ^*p < 0.05 (representative of greater than three independent trials).

Figure 3

Chlamydiae inhibit nuclear fragmentation induced by staurosporine—Cell lines were plated on coverslips (A,B) or infected with pathogens for 26 h (C,D). Staurosporine was added for 4 h (B–D) before cells were fixed and stained to visualize Chlamydiae (αHSP-60) and DNA (Hoechst). White arrows indicate apoptotic cells. Percent apoptotic in each of the treatment conditions is quantified (E). Ct-C. trachomatis, Cc-C.caviae Cm-C.muridarum. ^**p < 0.01, ^*p < 0.05 (representative of four independent trials).

Figure 4

Infection induced transcription of anti-apoptotic factors in the presence or absence of host translation. Cell lines were plated in six well plates and infected for 30 h prior to lysis and RNA extraction. Relative expression was normalized to host GAPDH and then the ratio of infected vs. uninfected gene expression was determined in human cells (A–C), mouse cells (D–F) and guinea pig cells (G–I). ^**p < 0.01, ^*p < 0.05 (representative of three independent trials).