Human SP-A genetic variants and bleomycin-induced cytokine production by THP-1 cells: effect of ozone-induced SP-A oxidation

Abstract

Surfactant protein A (SP-A) plays a role in innate host defense. Human SP-A is encoded by two functional genes (SP-A1 and SP-A2), and several alleles have been characterized for each gene. We assessed the effect of in vitro expressed human SP-A genetic variants, on TNF-α and IL-8 production by THP-1 cells in the presence of bleomycin, either before or after ozone-induced oxidation of the variants. The oligomerization of SP-A variants was also examined. We found 1) cytokine levels induced by SP-A2 (1A, 1A0) were significantly higher than those by SP-A1 (6A2, 6A4) in the presence of bleomycin. 2) In the presence of bleomycin, ozone-induced oxidation significantly decreased the ability of 1A and 1A/6A4, but not of 6A4, to stimulate TNF-α production. 3) The synergistic effect of bleomycin/SP-A, either before or after oxidation, can be inhibited to the level of bleomycin alone by surfactant lipids. 4) Differences in oligomerization were also observed between SP-A1 and SP-A2. The results indicate that differences among SP-A variants may partly explain the individual variability of pulmonary complications observed during bleomycin chemotherapy and/or in an environment that may promote protein oxidation.

Characterization of a human surfactant protein A1 (SP-A1) gene-specific antibody; SP-A1 content variation among individuals of varying age and pulmonary health

“…Moreover, qualitative and quantitative differences have been observed in vitro between the SP-A1 and SP-A2 genes (22,36,57,60,(77)(78)(79)(80)(81), pointing to the possibility that the overall functional activity of SP-A may depend on the relative SP-A1-to-SP-A2 levels rather than on the total SP-A content. To address this possibility, it .…”

“…Data from in vitro-expressed SP-A1 and SP-A2 variants showed that not only can homooligomers be formed, but these are also functional. In fact, functional (36,57,77) and regulatory (24,39,46,56) differences between SP-A1 and SP-A2 and/or among SP-A variants (78,79) have been observed. Therefore, we deemed it important to assess the SP-A gene-specific protein content in lung health and disease.…”

“…Indeed, it has been observed that regulatory differences between human SP-A1 and SP-A2 exist in the transcriptional/pretranslational levels (38,39) as well as at the translational level (78,79). SP-A1 has been shown in vitro to be less active in host defense activities (36,57,80,81) compared with SP-A2. Whether and how the decreased SP-A1-to-SP-A ratio in aged individuals contributes to altered host defense observed with aging (2,12,30) remains to be determined.…”

“…Structurally, circular dichroic spectroscopy studies have shown SP-A2 to be more stable than SP-A1 (22). Biochemical differences in response to ozone exposure (36,77,81), oligomerization patterns (36,77), aggregation (71), and the ability to bind carbohydrates (60) were also observed for SP-A1 and SP-A2 variants. Quantitative differences between SP-A1 and SP-A2 genes were observed in H441 cells, a lung adenocarcinoma cell line (46,70), and in fetal lung explant cultures under basal conditions and/or in response to dexamethasone (24,38,46,51,56).…”

“…More than 30 alleles have been characterized for these two genes, with four SP-A1 alleles (6A, 6A 2 , 6A 3 , and 6A 4 ) and six SP-A2 alleles (1A, 1A 0 , 1A 1 , 1A 2 , 1A 3 , and 1A 5 ) most frequently observed in the general population (10,14,16,40,67). Although a high level of sequence similarity is shared among the SP-A genes and their corresponding alleles, in vitro studies have identified both qualitative (22,36,57,60,77,80,81) and quantitative (24,35,38,46,56,69,70,78,79) differences between the two genes.…”