Involvement of nicotinic acetylcholine receptors in controlling Chlamydia pneumoniae growth in epithelial HEp-2 cells

Abstract

Nicotinic acetylcholine receptors (nAChRs) play an essential role in neurotransmission. Recent studies have indicated that nAChRs may be involved in the regulation of some bacterial infections through immunological mechanisms in macrophages. However, the regulation of infection with Chlamydia pneumoniae, which is a ubiquitous pneumonia-causing bacterium, by an nAChR-mediated mechanism is still unclear. In the present study, it was found that stimulation of nAChRs with ligands such as nicotine and acetylcholine altered the growth of C. pneumoniae in epithelial HEp-2 cells. Thus, the results revealed a possible pathophysiological role of nAChRs in the regulation of intracellular bacterial infection.

FIG. 1.

Effect of nicotine on C. pneumoniae growth in HEp-2 cells. Cells infected with bacteria were treated with or without the indicated concentrations of nicotine in the presence or absence of d-TC (10 μM) and then incubated for 72 h. The number of IFU in cells was assessed and expressed as bacterial growth relative to that of the control group. The data shown are the mean plus the standard deviation for triplicate cultures and are representative of three experiments. The number of IFU per culture of the control group 72 h after infection was 2.8 × 10⁴ ± 0.9 × 10⁴. ∗, P < 0.05 (significantly different from the control group).

FIG. 2.

Effects of the nAChR agonists ACh (A) and DMPP (B) on C. pneumoniae growth in HEp-2 cells. Cells were infected with bacteria and then treated with or without ACh (1 μM) or DMPP (1 μM) in the presence or absence of d-TC (10 μM). The number of IFU was assessed at 72 h after infection and expressed as bacterial growth relative to that of the control. The data shown are the mean plus the standard deviation for triplicate cultures and are representative of three experiments. The numbers of IFU per culture of the control group at 72 h after infection in the ACh and DMPP experiments were 2.2 × 10⁴ ± 0.4 × 10⁴ and 2.7 × 10⁴ ± 0.6 × 10⁴, respectively. ∗, P < 0.05 (significantly different from the control group).

FIG. 3.

Transcripts of nAChR subunit genes determined by RT-PCR. Expression of nAChR mRNAs (α4, α7, β2, and β4 subunits) in HEp-2 cells was analyzed by RT-PCR.