Impact of ozone exposure on the phagocytic activity of human surfactant protein A (SP-A) and SP-A variants

Abstract

Surfactant protein A (SP-A) enhances phagocytosis of Pseudomonas aeruginosa. SP-A1 and SP-A2 encode human (h) SP-A; SP-A2 products enhance phagocytosis more than SP-A1. Oxidation can affect SP-A function. We hypothesized that in vivo and in vitro ozone-induced oxidation of SP-A (as assessed by its carbonylation level) negatively affects its function in phagocytosis (as assessed by bacteria cell association). To test this, we used P. aeruginosa, rat alveolar macrophages (AMs), hSP-As with varying levels of in vivo (natural) oxidation, and ozone-exposed SP-A2 (1A, 1A 0 ) and SP-A1 (6A 2 , 6A 4 ) variants. SP-A oxidation levels (carbonylation) were measured; AMs were incubated with bacteria in the presence of SP-A, and the phagocytic index was calculated. We found: 1) the phagocytic activity of hSP-A is reduced with increasing levels of in vivo SP-A carbonylation; 2) in vitro ozone exposure of hSP-A decreases its function in a dose-dependent manner as well as its ability to enhance phagocytosis of either gram-negative or gram-positive bacteria; 3) the activity of both SP-A1 and SP-A2 decreases in response to in vitro ozone exposure of proteins with SP-A2 being affected more than SP-A1. We conclude that both in vivo and in vitro oxidative modifications of SP-A by carbonylation reduce its ability to enhance phagocytosis of bacteria and that the activity of SP-A2 is affected more by in vitro ozone-induced oxidation. We speculate that functional differences between SP-A1 and SP-A2 exist in vivo and that the redox status of the lung microenvironment differentially affects function of SP-A1 and SP-

Regulation of translation by upstream translation initiation codons of surfactant protein A1 splice variants

“…SP-A1 exhibits lower activity than SP-A2 in several cases. For instance, SP-A2 showed higher biological activity in inducing TNF␣ production by THP-1 cells (92,93), stimulating Pseudomonas aeruginosa association with rat alveolar macrophages (58,59) and inhibiting phosphatidylcholine secretion from alveolar type II cells (87). The relative amounts of SP-A1 and SP-A2 vary and seem to be affected by age and health status (81,94).…”

Human Surfactant Proteins (SP-) A1 and SP-A2: to Include or Not in Surfactant Replacement Therapy, and If Yes, Both or Which One?

“…However, in preliminary studies [23], we observed that SP-A1 produced a higher reduction in surface tension than SP-A2, with no significant differences observed between SP-A1 and SP-A that contained both SP-A1 and SP-A2. Furthermore, in the presence of oxidative stress the activity of SP-A2 to enhance phagocytosis may be reduced more than that of SP-A1 [3], and the SP-A2 resistance to trypsin is lower than that observed in SP-A1 and SP-A1/SP-A2 [15]. Collectively, these observations indicate that SP-A1 and SP-A2 may each be better for different functions in the lung i.e.…”

“…The SP-A1 and SP-A2 gene products have been shown to differ in several functions related to innate immunity [12] and in surfactantrelated functions [13,14]. These differences have been reviewed previously [12] and include differences in their oligomerization status [13,15,16], their ability to form phospholipid monolayers [17], their ability to bind sugars [18], and their ability to enhance the phagocytic activity and cytokine production by the alveolar macrophages and macrophage-like cell lines, respectively [3,[19][20][21][22], as well inhibit surfactant secretion by Type II cells [13]. In most of these cases SP-A2 appeared to exhibit higher functional activity.…”

“…Among the protein groups affected were actin-related/cytoskeletal proteins, which was the major group, proteins regulating inflammatory processes, and proteins related to Nrf2-mediated oxidative stress. Of interest, earlier studies have also indicated a role for SP-A in actin filament dynamics via its ability to enhance cell migration and AM chemotaxis [2], phagocytosis [3], other actin-dependent processes [4][5][6] and F-actin assembly [7]. The actin cytoskeleton is highly regulated and dynamic, with globular (G) and filamentous (F) actin, under the influence of many actin binding proteins, constantly changing by polymerization, depolymerization, branching, and remodeling, modulating inflammatory response and oxidative stress ( Figure 1).…”

“…inflammation, oxidative stress, phagocytosis, and other]. For example, human SP-A variants have been shown to differentially enhance the phagocytic activity of AM [3] and mice that lacked SP-A exhibited a lower phagocytic activity and survival [10].…”