Inhaled ultrafine particulate matter affects CNS inflammatory processes and may act via MAP kinase signaling pathways

Abstract

In addition to evidence that inhalation of ambient particulate matter (PM) can increase cardiopulmonary morbidity and mortality, the brain may also constitute a site adversely effected by the environmental presence of airborne particulate matter. We have examined the association between exposure to PM and adverse CNS effects in apolipoprotein E knockout (ApoE-/-) mice exposed to two levels of concentrated ultrafine particulate matter in central Los Angeles. Mice were euthanized 24h after the last exposure and brain, liver, heart, lung and spleen tissues were collected and frozen for subsequent bioassays. There was clear evidence of aberrant immune activation in the brains of exposed animals as judged by a dose-related increase in nuclear translocation of two key transcription factors, NF-kappaB and AP-1. These factors are involved in the promotion of inflammation. Increased levels of glial fibrillary acidic protein (GFAP) were also found consequent to particulate inhalation suggesting that glial activation was taking place. In order to determine the mechanism by which these events occurred, levels of several MAP kinases involved in activation of these transcription factors were assayed by Western blotting. There were no significant changes in the proportion of active (phosphorylated) forms of ERK-1, IkB and p38. However, the fraction of JNK in the active form was significantly increased in animals receiving the lower concentration of concentrated ambient particles (CAPs). This suggests that the signaling pathway by which these transcription factors are activated involves the activation of JNK.

Figure 1. Cortical levels of a) AP-1 and b) NF-κB following inhalation of CAPs

Integrated density of the shifted AP-1 bands in cortex relative to control value. CAP4 = 4-fold concentrated particulates, CAP15 = 15-fold concentrated particulates. * Value differs (P≤0.05) from control group receiving purified air, + Value differs (P≤0.05) from both other groups. Bars represent mean of 6-7 samples ± S.E. Photographs of each gel shift analyzed are also shown.

Figure 2. Levels of GFAP in cortex of animals exposed to CAPs

Integrated density of the GFAP bands derived from Western blotting. Bars represent mean of 6 samples ± S.E. relative to control value. CAP4 = 4-fold concentrated particulates, CAP15 = 15-fold concentrated particulates. * Value differs (P≤0.05) from group receiving purified air.

Figure 3. Proportion of cortical JNK in activated form following exposure to CAPs

Integrated density of the bands derived from Western blotting. CAP4 = 4-fold concentrated particulates, CAP15 = 15-fold concentrated particulates. Value expressed as ratio of phosphorylated pJNK to that for JNK. *: value is significantly different (P≤0.05) from the group receiving purified air. Bars represent mean of 6 samples ± S.E. Since the sensitivity of antibodies for pJNK and JNK are likely to differ, this ratio is not absolute but changes represent a relative shift in the proportions of the two forms of JNK.