Abstract
Surfactant protein A (SP-A) plays a role in lung innate immunity and surfactant-related functions. Two functional genes, SP-A1 (SFTPA1) and SP-A2 (SFTPA2), are present in humans and primates (rodents have one gene). Single gene SP-A1 or SP-A2 proteins expressed in vitro are functional. To study their role in vivo, we generated humanized transgenic (hTG) C57BL/6 mice, SP-A1(6A(4)) and SP-A2(1A(3)). The SP-A cDNA in experimental constructs was driven by the 3.7-kb SP-C promoter. Positive hTG mice were bred with SP-A knock-out mice to generate F8 offspring for study. Epithelial alveolar type II cells were SP-A-positive, and Clara cells were negative by immunohistochemistry in hTG mice. The levels of SP-A in lungs of two hTG lines used were comparable with those in human lungs. Southern blot analysis indicated that two cDNA copies of either SP-A1(6A(4)) or SP-A2(1A(3)) were integrated as a concatemer into the genome of each of the two hTG lines. Electron microscopy analysis revealed that hTG mice with a single SP-A1(6A(4)) or SP-A2(1A(3)) gene product lacked tubular myelin (TM), but hTG mice carrying both had TM. Furthermore, TM was observed in human bronchoalveolar lavage fluid only if both SP-A1 and SP-A2 gene products were present and not in those containing primarily (>99.7%) either SP-A1 or SP-A2 gene products. In vivo rescue study confirmed that TM can only be restored after administering exogenous SP-A containing both SP-A1 and SP-A2 into the lungs of SP-A knock-out mice. These observations indicate that SP-A1 and SP-A2 diverged functionally at least in terms of TM formation.
Highlights
Surfactant protein A (SP-A),2 a member of the C-type lectin protein family, plays an important role in the innate host defense and surfactant-related functions [1, 2]
Generation of humanized transgenic (hTG) SP-A1 and SP-A2 Mice and Transmission of SP-A1 and SP-A2 in hTG Mice—Before beginning the DNA microinjection into mouse fertilized oocytes, we examined whether the constructs could express human SP-A (hSP-A) protein in H441 cells by transient transfection as described previously [54]
Human SP-A is encoded by two functional genes, SP-A1 and SP-A2 [13]
Summary
Surfactant protein A (SP-A), a member of the C-type lectin protein family, plays an important role in the innate host defense and surfactant-related functions [1, 2]. SP-A knock-out (KO) mice, either in the NIH Swiss black strain [3, 4] or in the C57BL/6 background [5, 6], have shown altered surfactant structure and function These mice exhibited a phenotype deficient in the formation of the extracellular structural form of surfactant, the tubular myelin (TM) [3, 4], as well as increased susceptibility to infection by a variety of pathogens (6 –10) and to environmental pollutant factors, such as ozone [11, 12]. Studies with SP-A1 and SP-A2 variants from in vitro expressed cell systems have demonstrated functional differences between SP-A1 and SP-A2, with SP-A2 variants exhibiting higher activity than SP-A1 variants in numerous assays These include differences in their ability to stimulate THP-1 cells to produce TNF-␣ (26 –28), inhibit surfactant secretion [29], enhance bacterial phagocytosis by rat and human alveolar macrophages (30 –32), and bind carbohydrates [33]. Until the present study, it was unknown whether either SP-A1 or SP-A2 or both are necessary for TM formation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
