Gene expression profiles of U937 human macrophages exposed to Chlamydophila pneumoniae and/or low density lipoprotein in five study models using differential display and real-time RT-PCR

Many studies on atherosclerosis have indicated an association with Chlamydophila pneumoniae, a respiratory intracellular pathogen that can infect bronchoalveolar macrophages, and be transported to sites of vascular injury. Furthermore, the connection between low density lipoprotein (LDL), macrophages, foam cell formation, and atherosclerosis is well established. Five study models were designed to mimic the early events in plaque formation, i.e. untreated U937 human macrophages as control; macrophages treated with LDL only; macrophages infected with the AR-39 strain of C. pneumoniae only; and the last two models in which macrophages were exposed to both C. pneumoniae and LDL but in different order. Differential display RT-PCR was employed to analyze mRNAs from the five models to elucidate the transcriptional responses arising from macrophage interactions with C. pneumoniae and/or LDL. Out of 235 expressed sequence tags, the altered expression patterns of 29 selected genes at various time-points were authenticated by semi-quantitative and real-time RT-PCR. In relation to atherosclerosis, some interesting modified transcripts are involved in cell proliferation (CDC2, CDC27, CDC42EP3, GBDR1, GPR6, RPL27A, Similar to COX2), apoptosis (BCL2A1), ubiquitination (CTSH, HSPC150, NUC2), and structural integrity (ACTG1, FLOT1). Other genes exhibiting altered expression include those that modulate inflammatory and immune responses or signal transduction linking infection to host immunity (ARPP-19, BLAME, HCA58, IK cytokine, IRS2, STAT1P1). The transcriptional alterations of critical human genes in response to C. pneumoniae infection and foam cell development provide insights into certain key molecular pathophysiological mechanisms of atherosclerosis.