HIF-1 expression is associated with CCL2 chemokine expression in airway inflammatory cells: implications in allergic airway inflammation

Background: The pathogenesis of allergic airway inflammation in asthmatic patients is complex and characterized by cellular infiltrates and activity of many cytokines and chemokines. Both the transcription factor hypoxia inducible factor-1 (HIF-1) and chemokine CCL2 have been shown to play pivotal roles in allergic airway inflammation. The interrelationship between these two factors is not known. We hypothesized that the expression of HIF-1 and CCL2 may be correlated and that the expression of CCL2 may be under the regulation of HIF-1. Several lines of evidence are presented to support this hypothesis. Methods: The effects of treating wild-type OVA (ovalbumin)-sensitized/challenged mice with ethyl-3, 4-dihydroxybenzoate (EDHB), which upregulate HIF, on CCL2 expression, were determined. Mice conditionally knocked out for HIF-1 beta was examined for their ability to mount an allergic inflammatory response and CCL2 expression in the lung after intratracheal exposure to ovalbumin. The association of HIF-1 alpha and CCL2 levels was also measured in endobronchial biopsies and bronchial fluid of asthma patients after challenge. Results: We show that both HIF-1 alpha and CCL2 were upregulated during an OVA (ovalbumin)-induced allergic response in mice. The levels of HIF-1 alpha and CCL2 were significantly increased following treatment with a pharmacological agent which upregulates HIF-1 alpha, ethyl-3,4-dihydroxybenzoate (EDHB). In contrast, the expression levels of HIF-1 alpha and CCL2 were decreased in the lungs of mice that have been conditionally knocked out for ARNT (HIF-1 beta) following sensitization with OVA when compared to levels in wild type mice. In asthma patients, the levels of HIF-1 alpha and CCL2 increased after challenge with the allergen. Conclusions: These data suggest that CCL2 expression is regulated, in part, by HIF-1 in the lung. These findings also demonstrate that both CCL2 and HIF-1 are implicated in the pathogenesis of allergic airway inflammation.