BackgroundHuman innate host defense molecules, surfactant protein A1 (SP-A1), and SP-A2 differentially affect the function and proteome of the alveolar macrophage (AM). We hypothesized that SP-A genes differentially regulate the AM miRNome.MethodsHumanized transgenic mice expressing SP-A1 and SP-A2 were subjected to O3-induced oxidative stress (OxS) or filtered air (FA), AMs were isolated, and miRNA levels were measured.ResultsIn SP-A2 males, we found significant changes in miRNome in terms of sex and sex-OxS effects, with 11 miRNAs differentially expressed under OxS. Their mRNA targets included BCL2, CAT, FOXO1, IL6, NF-kB, SOD2, and STAT3. We followed the expression of these transcripts as well as key cytokines, and we found that (a) the STAT3 mRNA significantly increased at 4 h post OxS and returned to baseline at 18 h post OxS. (b) The anti-oxidant protein SOD2 level significantly increased, but the CAT level did not change after 4 h post OxS compared to control. (c) The anti-apoptotic BCL2 mRNA increased significantly (18 h post OxS), but the levels of the other transcripts were decreased. The presence of the SP-A2 gene had a protective role in apoptosis of AMs under OxS compared to mice lacking SP-A (knockout, KO). (d) Pro-inflammatory cytokine IL-6 protein levels were significantly increased in SP-A2 mice compared to KO (4 and 18 h post OxS), which signifies the role of SP-A2 in pro-inflammatory protein expression. (e) SOD2 and CAT mRNAs changed significantly in OxS indicating a plausible role of SP-A2 in the homeostasis of reactive oxygen species. (f) Gonadectomy of transgenic mice showed that sex hormones contribute to significant changes of the miRNome expression.ConclusionsWe conclude that SP-A2 influences the miRNA-mediated sex-specific differences in response to OxS. In males, these differences pertain to inflammatory, anti-apoptotic, and anti-oxidant pathways.Electronic supplementary materialThe online version of this article (10.1186/s13293-017-0158-2) contains supplementary material, which is available to authorized users.

Childhood asthma is an umbrella of multifactorial diseases with similar clinical features such as mast cell and eosinophil infiltration causing airway hyper responsiveness, inflammation, and airway obstruction. There are various factors that are implicated in childhood asthma pathogenesis. A combined contribution of genetic predisposition, environmental insults, and epigenetic changes account for polarisation of the immune system towards T helper (Th) type 2 cell responses that include production of pro-inflammatory cytokines, IgE, and eosinophil infiltrates, shown to associate with asthma. Environmental cues in prenatal, perinatal, and early childhood seem to determine development of asthma incidence or protection against it. Mode of birth delivery, use of antibiotics, oxidative stress, exposure to tobacco smoke and an industrialised lifestyle are significant contributors to childhood asthma exacerbation. Environmental stimuli such as exposure to maternal antibodies through breast milk, and certain early infections favour Th1 cell responses, leading to the production of anti-inflammatory cytokines that protect from asthma. Aside from the Th cell responses the role of innate immunity in the context of alveolar macrophages, dendritic cells, and surfactant protein A (SP-A) and SP-D is discussed. SP-A and SP-D enhance pathogen phagocytosis and cytokine production by alveolar macrophages, bind and clear pathogens, and interact with dendritic cells to mediate adaptive immunity responses. Further study of the interactions between genetic variants of genes of interest (SP-A and SP-D) and the environment may provide valuable knowledge about the underlying mechanisms of various interactions that differentially affect asthma susceptibility, disease severity, and reveal potential points for therapeutic interventions.

Human surfactant protein A, an innate immunity molecule, is encoded by two genes: SFTPA1 (SP-A1) and SFTPA2 (SP-A2). The 5' untranslated (5'UTR) splice variant of SP-A2 (ABD), but not of SP-A1 (AD), contains exon B (eB), which is an enhancer for transcription and translation. We investigated whether eB contains cis-regulatory elements that bind trans-acting factors in a sequence-specific manner as well as the role of the eB mRNA secondary structure. Binding of cytoplasmic NCI-H441 proteins to wild-type eB, eB mutant, AD, and ABD 5'UTR mRNAs were studied by RNA electromobility shift assays (REMSAs). The bound proteins were identified by mass spectroscopy and specific antibodies (Abs). We found that 1) proteins bind eB mRNA in a sequence-specific manner, with two cis-elements identified within eB to be important; 2) eB secondary structure is necessary for binding; 3) mass spectroscopy and specific Abs in REMSAs identified 14-3-3 proteins to bind (directly or indirectly) eB and the natural SP-A2 (ABD) splice variant but not the SP-A1 (AD) splice variant; 4) other ribosomal and cytoskeletal proteins, and translation factors, are also present in the eB mRNA-protein complex; 5) knockdown of 14-3-3 β/α isoform resulted in a downregulation of SP-A2 expression. In conclusion, proteins including the 14-3-3 family bind two cis-elements within eB of hSP-A2 mRNA in a sequence- and secondary structure-specific manner. Differential regulation of SP-A1 and SP-A2 is mediated by the 14-3-3 protein family as well as by a number of other proteins that bind UTRs with or without eB mRNA.