Humanized SFTPA1 and SFTPA2 transgenic mice reveal functional divergence of SP-A1 and SP-A2: formation of tubular myelin in vivo requires both gene products.
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.
Wang
Guirong
G
Penn State Center for Host Defense, Inflammation, and Lung Disease Research, Department of Pediatrics, Penn State HersheyCollege ofMedicine, Pennsylvania State University, Hershey, Pennsylvania 17033, USA.
Guo
Xiaoxuan
X
Diangelo
Susan
S
Thomas
Neal J
NJ
Floros
Joanna
J
D000818:Animals; D001483:Base Sequence; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry / Q000166:cytology; D017931:DNA Primers / Q000235:genetics*; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D008168:Lung / Q000378:metabolism / Q000648:ultrastructure; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D046529:Microscopy, Electron, Transmission; D009186:Myelin Sheath / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism; D037662:Pulmonary Surfactant-Associated Protein A / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*; D037701:Pulmonary Surfactant-Associated Protein B / Q000378:metabolism; D037721:Pulmonary Surfactant-Associated Protein C; D037663:Pulmonary Surfactant-Associated Protein D / Q000378:metabolism
D017931:DNA Primers; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D037662:Pulmonary Surfactant-Associated Protein A; D037701:Pulmonary Surfactant-Associated Protein B; D037721:Pulmonary Surfactant-Associated Protein C; D037663:Pulmonary Surfactant-Associated Protein D; C445842:SFTPA1 protein, human; C445843:SFTPA2 protein, human; C489680:Sftpc protein, mouse; C018167:tubular myelin