We next explored possible mechanisms that could explain how dietary zinc supplementation preserved lung bacterial clearance in alcohol-fed rats. We had previous work determined that chronic alcohol ingestion down-regulates GM-CSF receptor expression signaling via its master transcription factor, PU.1. Therefore, we next cultured alveolar macrophages from control-fed and alcohol-fed rats overnight with or without zinc acetate (20 μM) in vitro, and then performed electromobility shift assays on nuclear preparations to determine if zinc could improve nuclear binding of PU.1 (which is required to mediate GM-CSF signaling and induce alveolar macrophage immune functions including bacterial phagocytosis). As shown in Figure 2, panel A and consistent with our previously published findings, nuclear binding of PU.1 was decreased in macrophages isolated from alcohol-fed rats compared to macrophages from control-fed rats (Lane 3 vs. Lane 1). In contrast, zinc treatment in vitro completely restored PU.1 nuclear binding in macrophages from alcohol-fed rats (Lane 4 vs. Lane 3) but had no effect on macrophages from control-fed rats (Lane 2 vs. Lane 1).
