Insights into pulmonary phosphate homeostasis and osteoclastogenesis emerge from the study of pulmonary alveolar microlithiasis.

Pulmonary alveolar microlithiasis is an autosomal recessive lung disease caused by a deficiency in the pulmonary epithelial Npt2b sodium-phosphate co-transporter that results in accumulation of phosphate and formation of hydroxyapatite microliths in the alveolar space. The single cell transcriptomic analysis of a pulmonary alveolar microlithiasis lung explant showing a robust osteoclast gene signature in alveolar monocytes and the finding that calcium phosphate microliths contain a rich protein and lipid matrix that includes bone resorbing osteoclast enzymes and other proteins suggested a role for osteoclast-like cells in the host response to microliths. While investigating the mechanisms of microlith clearance, we found that Npt2b modulates pulmonary phosphate homeostasis through effects on alternative phosphate transporter activity and alveolar osteoprotegerin, and that microliths induce osteoclast formation and activation in a receptor activator of nuclear factor-κB ligand and dietary phosphate dependent manner. This work reveals that Npt2b and pulmonary osteoclast-like cells play key roles in pulmonary homeostasis and suggest potential new therapeutic targets for the treatment of lung disease.

Fetal lung development via quantitative biomarkers from diffusion MRI and histological validation in rhesus macaques.

OBJECTIVE: To demonstrate sensitivity of diffusion-weighted MRI (DW-MRI) to pulmonary cellular-space changes during normal in utero development using fetal rhesus macaques, compared to histological biomarkers. STUDY DESIGN: In vivo/ex vivo DW-MRI was acquired in 26 fetal rhesus lungs (early-canalicular through saccular stages). Apparent diffusion coefficients (ADC) from MRI and tissue area density (H&E), alveolar type-II cells (ABCA3), and epithelial cells (TTF1) from histology were compared between gestational stages. RESULTS: In vivo/ex vivo ADC correlated with each other (Spearman ρ = 0.47, P = 0.038; Bland-Altman bias = 0.0835) and with area-density (in vivo ρ = -0.56, P = 0.011; ex vivo ρ = -0.83, P < 0.0001). In vivo/ex vivo ADC increased exponentially toward saturation with gestational stage (R2 = 0.49/0.49), while area-density decreased exponentially (R2 = 0.53). ABCA3 and TTF1 stains demonstrated expected fetal cellular development. CONCLUSIONS: Fetal DW-MRI provides a non-invasive biomarker for pulmonary structural maturation, with a strong correlation to histological markers during tissue development in rhesus macaques. This method has strong potential for assessing human fetal development, particularly in patients with pulmonary hypoplasia.

Validating in vivo hyperpolarized 129 Xe diffusion MRI and diffusion morphometry in the mouse lung.

PURPOSE: Diffusion and lung morphometry imaging using hyperpolarized gases are promising tools to quantify pulmonary microstructure noninvasively in humans and in animal models. These techniques assume the motion encoded is exclusively diffusive gas displacement, but the impact of cardiac motion on measurements has never been explored. Furthermore, although diffusion morphometry has been validated against histology in humans and mice using 3 He, it has never been validated in mice for 129 Xe. Here, we examine the effect of cardiac motion on diffusion imaging and validate 129 Xe diffusion morphometry in mice. THEORY AND METHODS: Mice were imaged using gradient-echo-based diffusion imaging, and apparent diffusion-coefficient (ADC) maps were generated with and without cardiac gating. Diffusion-weighted images were fit to a previously developed theoretical model using Bayesian probability theory, producing morphometric parameters that were compared with conventional histology. RESULTS: Cardiac gating had no significant impact on ADC measurements (dual-gating: ADC = 0.020 cm2 /s, single-gating: ADC = 0.020 cm2 /s; P = .38). Diffusion-morphometry-generated maps of ADC (mean, 0.0165 ± 0.0001 cm2 /s) and acinar dimensions (alveolar sleeve depth [h] = 44 µm, acinar duct radii [R] = 99 µm, mean linear intercept [Lm ] = 74 µm) that agreed well with conventional histology (h = 45 µm, R = 108 µm, Lm = 63 µm). CONCLUSION: Cardiac motion has negligible impact on 129 Xe ADC measurements in mice, arguing its impact will be similarly minimal in humans, where relative cardiac motion is reduced. Hyperpolarized 129 Xe diffusion morphometry accurately and noninvasively maps the dimensions of lung microstructure, suggesting it can quantify the pulmonary microstructure in mouse models of lung disease.

Longitudinal free-breathing MRI measurement of murine lung physiology in a progressive model of lung fibrosis.

To longitudinally monitor progressive fibrosis in the transforming growth factor-α (TGF-α) transgenic mouse model of lung fibrosis, we used retrospective self-gating ultrashort echo time (UTE) magnetic resonance imaging (MRI) to image mouse lung at baseline and after 4 and 8 wk of fibrosis initiation via doxycycline administration. Only bitransgenic mice were used in this study and divided into two cohorts: six mice were fed doxycycline food to induce lung fibrosis (referred to as Dox cohort), and five other mice were fed normal food (referred to as control cohort). Lung mechanics, histology, and hydroxyproline were assessed after the final MRI. A linear mixed-effects model was used to analyze MRI-derived longitudinal lung-function parameters. Tidal volume decreased at a rate of -0.016 ± 0.002 ml/week [χ2(1) = 16.48, P < 0.001] for Dox cohort and increased at a rate of 0.010 ± 0.003 ml/week [χ2(1) = 6.37, P = 0.01] for control cohort. Minute ventilation decreased at a rate of -1.71 ± 0.26 ml·min-1·wk-1 [χ2(1) = 14.04, P < 0.001] for Dox cohort but did not change significantly over time for control cohort. High-density lung volume percentage increased at a rate of 3.9 ± 0.7%/wk for Dox cohort [χ2(1) = 11.47, P < 0.001] but did not change significantly over time for control cohort. MRI-derived lung structure and function parameters were strongly correlated with pleural thickness, hydroxyproline content, lung compliance, airway resistance, and airway elastance. We conclude that self-gating UTE MRI could be used to longitudinally monitor lung fibrosis in the TGF-α transgenic mouse model. NEW & NOTEWORTHY Self-gating UTE MRI was used to monitor morphology and physiology in lung fibrosis in a transforming growth factor-α transgenic mouse model. Tidal volume was shown for the first time to correlate strongly with conventional metrics of fibrosis such as hydroxyproline and pleural thickness.

Localized surface plasmon resonance modulation of totally encapsulated VO2/Au/VO2 composite structure.

We design and fabricate a totally encapsulated VO2/Au/VO2 composite structure which is aimed to improve the tunability of the localized surface plasmon resonance (LSPR) peak. In this work, the structure will ensure all the Au NPs' resonant electric field area is filled with VO2. The modulation range of the totally encapsulated structure is larger than that of the semi-coated structure. To further improve the modulation range, we also explore the VO2 thickness dependence of the structure's LSPR modulation. With the increase of the top layer VO2 thin film thickness, the modulation range becomes larger. When the thickness is about 80 nm, the absorption peak achieves a largest shift of 112 nm. FDTD solution and equivalent model of series capacitor are used to explain the phenomenon. These results will contribute to the area of metamaterial electromagnetic wave absorber and other fields.

Murine pulmonary imaging at 7T: T2* and T1 with anisotropic UTE.

PURPOSE: To measure the T2* and T1 of mouse lung at 7T via anisotropic-resolution radial ultrashort echo-time imaging with ellipsoidal k-space coverage. METHODS: Ellipsoidal field-of-view was created by expanding uniform spherical k-space coverage. The effects of T2* and ellipsoidal sampling on image resolution were investigated by using point-spread-function analysis and resolution phantoms. Finally, this ellipsoidal sampling approach was used to measure the lung T2* and T1 of healthy C57BL/6 mice at the increasingly common preclinical field strength of 7T. RESULTS: Lung parenchyma T2* of 17- to 23-week-old mice at 7T was 0.395 ± 0.033 ms. T1 of lung and left- and right-heart ventricles was 1452.5 ± 87.0 ms, 1810.5 ± 54.6 ms, and 1602.6 ± 120.9 ms, respectively. Ellipsoidal k-space sampling provides enhanced resolution for a fixed scanning time or provides equivalent (although anisotropic) spatial resolution with reduced scanning times, while simultaneously avoiding fold-in artifacts. CONCLUSION: Using these techniques, the first T2* and T1 measures of mouse lung at 7T are reported. Ultrashort echo-time imaging with ellipsoidal k-space coverage significantly increases in-plane resolution without increasing scanning time, or equivalently, decreases scanning time while maintaining equivalent in-plane resolution. Magn Reson Med 79:2254-2264, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Magnetic resonance imaging of disease progression and resolution in a transgenic mouse model of pulmonary fibrosis.

Pulmonary fibrosis contributes to morbidity and mortality in a range of diseases, and there are no approved therapies for reversing its progression. To understand the mechanisms underlying pulmonary fibrosis and assess potential therapies, mouse models are central to basic and translational research. Unfortunately, metrics commonly used to assess murine pulmonary fibrosis require animals to be grouped and euthanized, increasing experimental difficulty and cost. We examined the ability of magnetic resonance imaging (MRI) to noninvasively assess lung fibrosis progression and resolution in a doxycycline (Dox) regulatable, transgenic mouse model that overexpresses transforming growth factor-α (TGF-α) under control of a lung-epithelial-specific promoter. During 7 wk of Dox treatment, fibrotic lesions were readily observed as high-signal tissue. Mean weighted signal and percent signal volume were found to be the most robust MRI-derived measures of fibrosis, and these metrics correlated significantly with pleural thickness, histology scores, and hydroxyproline content (R = 0.75-0.89). When applied longitudinally, percent high signal volume increased by 1.5% wk-1 (P < 0.001) and mean weighted signal increased at a rate of 0.0065 wk-1 (P = 0.0062). Following Dox treatment, lesions partially resolved, with percent high signal volume decreasing by -3.2% wk-1 (P = 0.0034) and weighted mean signal decreasing at -0.015 wk-1 (P = 0.0028). Additionally, longitudinal MRI revealed dynamic remodeling in a subset of lesions, a previously unobserved behavior in this model. These results demonstrate MRI can noninvasively assess experimental lung fibrosis progression and resolution and provide unique insights into its pathobiology.

Localization and stretch-dependence of lung elastase activity in development and compensatory growth.

Synthesis and remodeling of the lung matrix is necessary for primary and compensatory lung growth. Because cyclic negative force is applied to developing lung tissue during the respiratory cycle, we hypothesized that stretch is a critical regulator of lung matrix remodeling. By using quantitative image analysis of whole-lung and whole-lobe elastin in situ zymography images, we demonstrated that elastase activity increased twofold during the alveolar stage of postnatal lung morphogenesis in the mouse. Remodeling was restricted to alveolar walls and ducts and was nearly absent in dense elastin band structures. In the mouse pneumonectomy model of compensatory lung growth, elastase activity increased threefold, peaking at 14 days postpneumonectomy and was higher in the accessory lobe compared with other lobes. Remodeling during normal development and during compensatory lung growth was different with increased major airway and pulmonary arterial remodeling during development but not regeneration, and with homogenous remodeling throughout the parenchyma during development, but increased remodeling only in subpleural regions during compensatory lung growth. Left lung wax plombage prevented increased lung elastin during compensatory lung growth. To test whether the adult lung retains an innate capacity to remodel elastin, we developed a confocal microscope-compatible stretching device. In ex vivo adult mouse lung sections, lung elastase activity increased exponentially with strain and in peripheral regions of lung more than in central regions. Our study demonstrates that lung elastase activity is stretch-dependent and supports a model in which externally applied forces influence the composition, structure, and function of the matrix during periods of alveolar septation.

Imaging mouse lung allograft rejection with (1)H MRI.

PURPOSE: To demonstrate that longitudinal, noninvasive monitoring via MRI can characterize acute cellular rejection in mouse orthotopic lung allografts. METHODS: Nineteen Balb/c donor to C57BL/6 recipient orthotopic left lung transplants were performed, further divided into control-Ig versus anti-CD4/anti-CD8 treated groups. A two-dimensional multislice gradient-echo pulse sequence synchronized with ventilation was used on a small-animal MR scanner to acquire proton images of lung at postoperative days 3, 7, and 14, just before sacrifice. Lung volume and parenchymal signal were measured, and lung compliance was calculated as volume change per pressure difference between high and low pressures. RESULTS: Normalized parenchymal signal in the control-Ig allograft increased over time, with statistical significance between day 14 and day 3 posttransplantation (0.046→0.789; P < 0.05), despite large intermouse variations; this was consistent with histopathologic evidence of rejection. Compliance of the control-Ig allograft decreased significantly over time (0.013→0.003; P < 0.05), but remained constant in mice treated with anti-CD4/anti-CD8 antibodies. CONCLUSION: Lung allograft rejection in individual mice can be monitored by lung parenchymal signal changes and by lung compliance through MRI. Longitudinal imaging can help us better understand the time course of individual lung allograft rejection and response to treatment.

Longitudinal, noninvasive monitoring of compensatory lung growth in mice after pneumonectomy via (3)He and (1)H magnetic resonance imaging.

In rodents and some other mammals, partial pneumonectomy (PNX) of adult lungs results in rapid compensatory lung growth. In the past, quantification of compensatory lung growth and realveolarization could only be accomplished after killing the animal, removal of lungs, and histologic analysis of lungs at single time points. Hyperpolarized (3)He diffusion magnetic resonance imaging (MRI) allows in vivo morphometry of human lungs; our group has adapted this technique for application to mouse lungs. Through imaging, we can obtain maps of lung microstructural parameters that allow quantification of morphometric and physiologic measurements. In this study, we employed our (3)He MRI technique to image in vivo morphometry at baseline and to serially assess compensatory growth after left PNX of mice. (1)H and hyperpolarized (3)He diffusion MRI were performed at baseline (pre-PNX), 3-days, and 30-days after PNX. Compared with the individual mouse's own baseline, MRI was able to detect and serially quantify changes in lung volume, alveolar surface area, alveolar number, and regional changes in alveolar size that occurred during the course of post-PNX lung growth. These results are consistent with morphometry measurements reported in the literature for mouse post-PNX compensatory lung growth. In addition, we were also able to serially assess and quantify changes in the physiologic parameter of lung compliance during the course of compensatory lung growth; this was consistent with flexiVent data. With these techniques, we now have a noninvasive, in vivo method to serially assess the effectiveness of therapeutic interventions on post-PNX lung growth in the same mouse.