New kids on the block: the emerging role of apolipoproteins in the pathogenesis and treatment of asthma.

New treatments are needed for patients with severe asthma. We hypothesized that a clinically relevant experimental model of house dust mite (HDM)-induced murine asthma could be used to discover new pathways that regulate disease severity. In HDM-challenged mice, genome-wide expression profiling of the asthmatic lung transcriptome identified apolipoprotein E (apoE) as a steroid-unresponsive gene with persistently upregulated expression despite dexamethasone treatment. ApoE and low-density lipoprotein receptor (LDLR) knockout mice were used to demonstrate that apoE, which is produced by lung macrophages, functions in a paracrine fashion by binding to LDLRs expressed on ciliated airway epithelial cells, to negatively modulate airway hyperreactivity, mucin gene expression, and goblet cell hyperplasia. Furthermore, administration of an apoE mimetic peptide, which corresponded to the LDLR-binding domain of apoE, prevented the induction of airway inflammation, airway hyperreactivity, and goblet cell hyperplasia in HDM-challenged apoE knockout mice. This suggests that therapeutic strategies that activate the apoE-LDLR pathway, such as apoE mimetic peptides, may represent a novel treatment approach for patients with asthma. Similarly, we showed that administration of a 5A apolipoprotein A-I mimetic peptide attenuated the induction of HDM-mediated asthma in mice. These preclinical data suggest that apoE and apoA-I mimetic peptides might be developed into alternative treatments for patients with severe asthma. Future clinical trials will be required to determine whether inhaled apolipoprotein E or apolipoprotein A-I mimetic peptides are effective for the treatment of severe asthma, including patients with phenotypes that lack effective therapeutic options.