Both Human SP-A1 and SP-A2 Genes are Expressed in Small and Large Intestine

The alveolar macrophage toponome of female SP-A knockout mice differs from that of males before and after SP-A1 rescue

Using the Toponome Imaging System (TIS), a serial immunostainer, we studied the patterns of expression of multiple markers in alveolar macrophages (AM) from female mice lacking surfactant protein A (SP-A knockouts; KO) after "rescue" with exogenous SP-A1. We also used a 7-marker subset to compare with AM from males. AM were harvested 18 h after intrapharyngeal SP-A1 or vehicle, attached to slides, and subjected to serial immunostaining for 12 markers. Expression of the markers in each pixel of the image was analyzed both in the whole image and in individual selected cells. The marker combination in each pixel is referred to as a combinatorial molecular phenotype (CMP). A subset of antibodies was used to compare AM from male mice to the females. We found: (a) extensive AM heterogeneity in females by CMP analysis and by clustering analysis of CMPs in single cells; (b) AM from female KO mice respond to exogenous SP-A1 by increasing CMP phenotypic diversity and perhaps enhancing their potential innate immune capabilities; and (c) comparison of male and female AM responses to SP-A1 revealed that males respond more vigorously than females and clustering analysis was more effective in distinguishing males from females rather than treated from control.

Differential Impact of Co-expressed SP-A1/SP-A2 Protein on AM miRNome; Sex Differences

In humans there are two surfactant protein A (SP-A) functional genes SFTPA1 and SFTPA2 encoding innate immune molecules, SP-A1 and SP-A2, respectively, with numerous genetic variants each. SP-A interacts and regulates many of the functions of alveolar macrophages (AM). It is shown that SP-A variants differ in their ability to regulate the AM miRNome in response to oxidative stress (OxS). Because humans have both SP-A gene products, we were interested to determine the combined effect of co-expressed SP-A1/SP-A2 (co-ex) in response to ozone (O₃) induced OxS on AM miRNome. Human transgenic (hTG) mice, carrying both SP-A1/SP-A2 (6A²/1A⁰, co-ex) and SP-A- KO were utilized. The hTG and KO mice were exposed to filtered air (FA) or O₃ and miRNA levels were measured after AM isolation with or without normalization to KO. We found: (i) The AM miRNome of co-ex males and females in response to OxS to be largely downregulated after normalization to KO, but after Bonferroni multiple comparison analysis only in females the AM miRNome remained significantly different compared to control (FA); (ii) The targets of the significantly changed miRNAs were downregulated in females and upregulated in males; (iii) Several of the validated mRNA targets were involved in pro-inflammatory response, anti-apoptosis, cell cycle, cellular growth and proliferation; (iv) The AM of SP-A2 male, shown, previously to have major effect on the male AM miRNome in response to OxS, shared similarities with the co-ex, namely in pathways involved in the pro-inflammatory response and anti-apoptosis but also exhibited differences with the cell-cycle, growth, and proliferation pathway being involved in co-ex and ROS homeostasis in SP-A2 male. We speculate that the presence of both gene products vs. single gene products differentially impact the AM responses in males and females in response to OxS.

Retinal degeneration mutation in Sftpa1tm1Kor/J and Sftpd -/- targeted mice

Surfactant proteins are important collectin immune molecules with a wide distribution throughout the body, including the ocular system. Mice with gene deletions for the surfactant protein genes Sftpa1 and Sftpd were observed to have visual impairment and thinning of the outer nuclear layers of the retina. We hypothesized that gene deletion of Sftpa1 and Sftpd (Sftpa1tm1Kor/J and Sftpd-/-) results in early retinal degeneration in these mice. Sftpa1tm1Kor/J and Sftpd-/- retinas were evaluated by histopathology and optical coherence tomography (OCT). Retinas from Sftpa1tm1Kor/J and Sftpd -/- mice showed early retinal degeneration with loss of the outer nuclear layer. After screening of mice for known retinal degeneration mutations, the mice were found to carry a previously unrecognized Pde6brd1 genotype which resulted from earlier breeding of the strain with Black Swiss mice during their generation. The mutation was outbred and the genotype of Sftpa1tm1Kor/J and Sftpd-/- was confirmed. Outbreeding of the Pde6brd1 mutation resulted in restoration of normal retinal architecture confirmed by in vivo and in vitro examination. We can therefore conclude that loss of Sftpa1 and Sftpd do not result in retinal degeneration. We have now generated retinal Sftpa1 and Sftpd targeted mice that exhibit normal retinal histology.

Immunolocalization of Surfactant Proteins SP-A, SP-B, SP-C, and SP-D in Infantile Labial Glands and Mucosa

Surfactant proteins in different glandular structures of the oral cavity display antimicrobial activity for protection of invading microorganisms. Moreover, they are involved in lowering liquid tension in fluids and facilitate secretion flows. Numerous investigations for studying the occurrence of surfactant proteins in glandular tissues were performed using different methods. In the oral cavity, minor salivary glands secrete saliva continuously for the maintenance of a healthy oral environment. For the first time, we could show that infantile labial glands show expression of the surfactant proteins (SP) SP-A, SP-B, SP-C, and SP-D in acinar cells and the duct system in different intensities. The stratified squamous epithelium of the oral mucosa revealed positive staining for SPs in various cell layers.

Lipopolysaccharide-induced expression of surfactant proteins A1 and A2 in human renal tubular epithelial cells

Background

Surfactant protein A (SP-A), encoded by two functional genes, SP-A1 and SP-A2, is essential for the inflammatory process and host defence in the lungs. Recent studies have demonstrated the extrapulmonary expression of SP-A. Similar to the lungs, the kidneys are organs exposed to external pathogens. The present study evaluated the expression and location of SP-A in the kidneys. The effect of lipopolysaccharide (LPS) on the expression of SP-A subtypes was also studied in renal tubular epithelial (HK-2) cells.

Methods

Immunohistochemical staining was performed using polyclonal antibody against SP-A. RT-PCR was also performed using mRNA from normal human renal tissues and HK-2 cells. The expressions of the SP-A1 and SP-A2 genes were determined by PCR-based RFLP analysis, gene-specific amplification, and direct sequencing of RT-PCR products. Western blot was conducted to analyse the SP-A protein. HK-2 cells were treated with LPS at various concentrations (0, 0.1, 1, 2, 5, and 10 μg/mL) for 8 h and at 5 μg/mL at various time points (0, 2, 4, 8, 16, and 24 h). The LPS-induced expressions of SP-A1 and SP-A2 mRNA and protein were analysed by RT-PCR and Western blot.

Results

SP-A was localised in the renal tubular epithelial cells in the proximal and distal convoluted tubules. SP-A1 and SP-A2 mRNA and protein were expressed in HK-2 cells and human renal tissues, which were significantly increased in time- and dose-dependent manners after LPS treatment (P < 0.05).

Conclusions

Human renal tubular epithelial cells can express both SP-A1 and SP-A2 genes, which may play important roles in the inflammatory modulation of the kidney.

Surfactant protein A is defective in abrogating inflammation in asthma

Surfactant protein A (SP-A) regulates a variety of immune cell functions. We determined the ability of SP-A derived from normal and asthmatic subjects to modulate the inflammatory response elicited by Mycoplasma pneumoniae, a pathogen known to exacerbate asthma. Fourteen asthmatic and 10 normal control subjects underwent bronchoscopy with airway brushing and bronchoalveolar lavage (BAL). Total SP-A was extracted from BAL. The ratio of SP-A1 to total SP-A (SP-A1/SP-A) and the binding of total SP-A to M. pneumoniae membranes were determined. Airway epithelial cells from subjects were exposed to either normal or asthmatic SP-A before exposure to M. pneumoniae. IL-8 protein and MUC5AC mRNA were measured. Total BAL SP-A concentration did not differ between groups, but the percentage SP-A1 was significantly increased in BAL of asthmatic compared with normal subjects. SP-A1/SP-A significantly correlated with maximum binding of total SP-A to M. pneumoniae, but only in asthma. SP-A derived from asthmatic subjects did not significantly attenuate IL-8 and MUC5AC in the setting of M. pneumoniae infection compared with SP-A derived from normal subjects. We conclude that SP-A derived from asthmatic subjects does not abrogate inflammation effectively, and this dysfunction may be modulated by SP-A1/SP-A.

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.

Surfactant-associated protein A provides critical immunoprotection in neonatal mice

The collectins surfactant-associated protein A (SP-A) and SP-D are components of innate immunity that are present before birth. Both proteins bind pathogens and assist in clearing infection. The significance of SP-A and SP-D as components of the neonatal immune system has not been investigated. To determine the role of SP-A and SP-D in neonatal immunity, wild-type, SP-A null, and SP-D null mice were bred in a bacterium-laden environment (corn dust bedding) or in a semisterile environment (cellulose fiber bedding). When reared in the corn dust bedding, SP-A null pups had significant mortality (P < 0.001) compared to both wild-type and SP-D null pups exposed to the same environment. The mortality of the SP-A null pups was associated with significant gastrointestinal tract pathology but little lung pathology. Moribund SP-A null newborn mice exhibited Bacillus sp. and Enterococcus sp. peritonitis. When the mother or newborn produced SP-A, newborn survival was significantly improved (P < 0.05) compared to the results when there was a complete absence of SP-A in both the mother and the pup. Significant sources of SP-A likely to protect a newborn include the neonatal lung and gastrointestinal tract but not the lactating mammary tissue of the mother. Furthermore, exogenous SP-A delivered by mouth to newborn SP-A null pups with SP-A null mothers improved newborn survival in the corn dust environment. Therefore, a lack of SP-D did not affect newborn survival, while SP-A produced by either the mother or the pup or oral exogenous SP-A significantly reduced newborn mortality associated with environmentally induced infection in SP-A null newborns.

Collectins and cationic antimicrobial peptides of the respiratory epithelia

The respiratory epithelium is a primary site for the deposition of microorganisms that are acquired during inspiration. The innate immune system of the respiratory tract eliminates many of these potentially harmful agents preventing their colonization. Collectins and cationic antimicrobial peptides are antimicrobial components of the pulmonary innate immune system produced by respiratory epithelia, which have integral roles in host defense and inflammation in the lung. Synthesis and secretion of these molecules are regulated by the developmental stage, hormones, as well as many growth and immunoregulatory factors. The purpose of this review is to discuss antimicrobial innate immune elements within the respiratory tract of healthy and pneumonic lung with emphasis on hydrophilic surfactant proteins and beta-defensins.

Differences in the translation efficiency and mRNA stability mediated by 5'-UTR splice variants of human SP-A1 and SP-A2 genes

Surfactant protein A (SP-A) plays an important role in host defense, modulation of inflammatory processes, and surfactant-related functions of the lung. The human SP-A (hSP-A) locus consists of two functional genes, SP-A1 and SP-A2. Several hSP-A 5'-untranslated region (UTR) splice variants for each gene have been characterized and shown to be translated in vitro and in vivo. In this report, we investigated the role of hSP-A 5'-UTR splice variants on SP-A production and molecular mechanisms involved. We used in vitro transient expression of hSP-A 5'-UTR constructs containing luciferase as the reporter gene and quantitative real-time PCR to study hSP-A 5'-UTR-mediated gene expression. We found that 1) the four (A'D', ABD, AB'D', and A'CD') 5'-UTR splice variants under study enhanced gene expression, by increasing luciferase activity from 2.5- to 19.5-fold and luciferase mRNA from 4.3- to 8.8-fold compared with the control vector that lacked hSP-A 5'-UTR; 2) all four 5'-UTR splice variants studied regulated mRNA stability. The ABD variant exhibited the lowest rate of mRNA decay compared with the other three constructs (A'D', AB'D', and A'CD'). These three constructs also exhibited significantly lower rate of mRNA decay compared with the control vector; 3) based on the indexes of translational efficiency (luciferase activity/mRNA), ABD and AB'D' exhibited higher translational efficiency compared with the control vector, whereas the translational efficiency of each A'D' and A'CD' was lower than that of the control vector. These findings indicate that the hSP-A 5'-UTR splice variants play an important role in both SP-A translation and mRNA stability.

Expression and localization of lung surfactant protein A in human tissues

Lung surfactant protein A (SP-A) is a collectin produced by alveolar type II cells and Clara cells. It binds to carbohydrate structures on microorganisms, initiating effector mechanisms of innate immunity and modulating the inflammatory response in the lung. Reverse transcriptase-polymerase chain reaction was performed on a panel of RNAs from human tissues for SP-A mRNA expression. The lung was the main site of synthesis, but transcripts were readily amplified from the trachea, prostate, pancreas, and thymus. Weak expression was observed in the colon and salivary gland. SP-A sequences derived from lung and thymus mRNA revealed the presence of both SP-A1 and SP-A2, whereas only SP-A2 expression was found in the trachea and prostate. Monoclonal antibodies were raised against SP-A and characterized. One of these (HYB 238-4) reacted in Western blotting with both reduced and unreduced SP-A, with N-deglycosylated and collagenase-treated SP-A, and with both recombinant SP-A1 and SP-A2. This antibody was used to demonstrate SP-A in immunohistochemistry of human tissues. Strong SP-A immunoreactivity was seen in alveolar type-II cells, Clara cells, and on and within alveolar macrophages, but no extrapulmonary SP-A immunoreactivity was observed. In contrast to lung surfactant protein D (SP-D), which is generally expressed on mucosal surfaces, SP-A seems to be restricted to the respiratory system.

Heterogeneous allele expression of pulmonary SP-D gene in rat large intestine and other tissues

Random allele expression has recently been observed for several genes including interleukins and genes of the lymphoid system. We studied the hypothesis that the surfactant protein D (SP-D) gene, an innate host defense molecule, exhibits random allele expression in a tissue-specific manner. SP-D gene expression is tissue specific in the 14 tissues studied. Study of SP-D allelic expression in several tissues revealed a balanced biallelic (BB) in lung, and, in several extrapulmonary tissues, a heterogeneous pattern: BB, imbalanced biallelic (IB), and monoallelic (MO). The results from 103 heterozygous rats showed an expression profile in large intestine of BB (22%), IB (58%), and MO (20%). Among eight families, the percent of BB in siblings varied from 0 to 41%, MO from 0 to 33%, and IB from 49 to 83%. The parent-of-origin does not play a role in SP-D allele-specific expression. However, acquired epigenetic factors, family background, or other factors may contribute to the overall pattern of expression.