Citations

Summary Physical forces shape cell behavior, yet how they integrate with signaling to control fate and disease remains unclear. The alveolar epithelium is patterned by FGF signaling and mechanical stretch, but how these cues specify AT1 and AT2 cells is poorly understood. Here we show that cell membrane tension (CMT) is a conserved regulator of epithelial fate in mouse and human lungs. CMT drops before differentiation and is spatially patterned, defining where bipotent progenitors acquire AT1 or AT2 identity. Lower CMT enhances FGFR2 endocytosis and ERK signaling to drive AT2 differentiation and permits architectural remodeling that enables stretch-mediated YAP/TAZ nuclear entry for AT1 maturation. β-catenin elevates CMT cell-intrinsically independent of its role in canonical WNT transcription, while embedding, osmotic compression, or fibroblast wrapping elevate CMT extrinsically. Combined intrinsic and extrinsic tension traps alveolar epithelial cells in a KRT8⁺ transitional state seen in fibrotic lungs. Membrane tension thus integrates physical and molecular cues linking morphogenesis to fibrosis. Graphical Abstract In Brief We identify a conserved drop in cell membrane tension (CMT) that gates epithelial fate transitions across mouse and human lungs. In bipotent progenitors, reduced CMT promotes Alveolar Type 2 (AT2) fate via FGFR2 endocytosis and ERK signaling, as well as Alveolar Type 1 (AT1) fate by enabling architectural remodeling required for YAP/TAZ nuclear entry. We further show that intrinsic β-catenin and extrinsic confinement cues, including mesenchymal contact, converge to elevate CMT, restricting differentiation and—in adult AT2s—inducing a KRT8⁺ transitional state associated with fibrosis. Highlights Cell membrane tension drops before differentiation and is required for AT1 and AT2 fate acquisition. Reduced tension enhances FGFR2 endocytosis and ERK signaling to drive AT2 specification. Reduced tension permits architectural remodeling and YAP/TAZ nuclear entry required for AT1 maturation. Intrinsic β-catenin and extrinsic confinement elevate CMT to restrict differentiation and together strongly induce a KRT8⁺ transitional state associated with fibrosis.

The hierarchical organization of the connective tissue, more specifically, the musculoskeletal soft tissue, has been extensively studied. With advancements in experimental methodology, investigation of the structure–function relationship has provided more insight into how the mechanical integrity of the tissue is created. Such information is essential in the linking the macroscopic loading environment of the tissue to the microscopic level of the tissue to be experienced by the cell. The flexibility and elastic modulus of gross connective tissue, the fascicle, the fiber and then the collagen molecule are compared based on the data available in the literature.

AbstractBackgroundThe growing adoption of magnetic resonance imaging (MRI)‐guided radiation therapy (RT) platforms and a focus on MRI‐only RT workflows have brought the technical challenge of synthetic computed tomography (sCT) reconstruction to the forefront. Unpaired‐data deep learning‐based approaches to the problem offer the attractive characteristic of not requiring paired training data, but the gap between paired‐ and unpaired‐data results can be limiting.PurposeWe present two distinct approaches aimed at improving unpaired‐data sCT reconstruction results: a cascade ensemble that combines multiple models and a personalized training strategy originally designed for the paired‐data setting.MethodsComparisons are made between the following models: (1) the paired‐data fully convolutional DenseNet (FCDN), (2) the FCDN with the Intentional Deep Overfit Learning (IDOL) personalized training strategy, (3) the unpaired‐data CycleGAN, (4) the CycleGAN with the IDOL training strategy, and (5) the CycleGAN as an intermediate model in a cascade ensemble approach. Evaluation of the various models over 25 total patients is carried out using a five‐fold cross‐validation scheme, with the patient‐specific IDOL models being trained for the five patients of fold 3, chosen at random.ResultsIn both the paired‐ and unpaired‐data settings, adopting the IDOL training strategy led to improvements in the mean absolute error (MAE) between true CT images and sCT outputs within the body contour (mean improvement, paired‐ and unpaired‐data approaches, respectively: 38%, 9%) and in regions of bone (52%, 5%), the peak signal‐to‐noise ratio (PSNR; 15%, 7%), and the structural similarity index (SSIM; 6%, <1%). The ensemble approach offered additional benefits over the IDOL approach in all three metrics (mean improvement over unpaired‐data approach in fold 3; MAE: 20%; bone MAE: 16%; PSNR: 10%; SSIM: 2%), and differences in body MAE between the ensemble approach and the paired‐data approach are statistically insignificant.ConclusionsWe have demonstrated that both a cascade ensemble approach and a personalized training strategy designed initially for the paired‐data setting offer significant improvements in image quality metrics for the unpaired‐data sCT reconstruction task. Closing the gap between paired‐ and unpaired‐data approaches is a step toward fully enabling these powerful and attractive unpaired‐data frameworks.

ABSTRACTBackgroundCurrently available structural variant (SV) detection methods do not span the complete spectrum of disease‐causing SVs. Optical genome mapping (OGM), an emerging technology with the potential to resolve diagnostic dilemmas, was performed to investigate clinically‐relevant SVs in a 4‐year‐old male with an epileptic encephalopathy of undiagnosed molecular origin.MethodsOGM was utilized to image long, megabase‐size DNA molecules, fluorescently labeled at specific sequence motifs throughout the genome with high sensitivity for detection of SVs greater than 500 bp in size. OGM results were confirmed in a CLIA‐certified laboratory via mate‐pair sequencing.ResultsOGM identified a mosaic, de novo 90 kb deletion and inversion on the X chromosome disrupting the CDKL5 gene. Detection of the mosaic deletion, which had been previously undetected by chromosomal microarray, an infantile epilepsy panel including exon‐level microarray for CDKL5, exome sequencing as well as genome sequencing, resulted in a diagnosis of X‐linked dominant early infantile epileptic encephalopathy‐2.ConclusionOGM affords an effective technology for the detection of SVs, especially those that are mosaic, since these remain difficult to detect with current NGS technologies and with conventional chromosomal microarrays. Further research in undiagnosed populations with OGM is warranted.

ABSTRACTAchilles tendon is one of the most commonly injured tendons. Mechanical force is regarded as a major causative factor. However, the biomechanics of Achilles tendon and mechanical mechanism of the injuries are unclear. Lubricin expresses at regions exposed to sliding motion and shear force in a number of tissues. This study investigated the distribution and concentration of lubricin in human Achilles tendons for better understanding the biomechanics of Achilles tendon. Achilles tendons were harvested from nine cadavers. Lubricin was extracted from various locations proximal to the calcaneal insertion and quantified with ELISA. The distribution of lubricin was investigated with immunohistochemistry. Lubricin was mainly identified at the interfaces of tendon fascicles, especially in the mid‐portion of the tendon. The concentration of lubricin in Achilles tendons varied by individual and the distance from its calcaneal insertion. The distal portion of the tendon had a higher concentration of lubricin than the proximal regions of the tendon. This study suggests the presence of intratendinous sliding motion of fascicles and shear force at interfaces of fascicles in human Achilles tendon. Shear force could be an important mechanical factor for the development of Achilles tendinopathy and rupture. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:932–937, 2015.

Tendon disuse, or stress deprivation, frequently accompanies clinical disorders and treatments, yet the metabolism of tendons subject to stress deprivation has rarely been investigated systematically. The effects of stress deprivation on canine flexor tendon were investigated in this study. One adult canine forepaw was suspended for 21 or 42 days. Control forepaws were collected from dogs that had no intervention on their limbs and paws. The expression of collagen I and III was not significantly altered in the tendons disused for 21 days but was significantly decreased at 42 days ( P < 0.03). The expression of collagen II, aggrecan, decorin, and fibronectin was significantly decreased in the tendons in the suspended limbs at 21 days ( P < 0.002) and further reduced at 42 days. With stress deprivation, the expression of matrix metalloproteinase 2 (MMP2) was significantly increased ( P < 0.004) at 21 and 42 days. The expression of MMP3 was significantly decreased at 21 and 42 days ( P < 0.03). The expression of MMP13 was not altered with stress deprivation at 21 and 42 days. The expression of MMP14 was significantly increased at 21 days ( P = 0.0015) and returned to the control level at 42 days. Tissue inhibitor of metalloproteinase 1 (TIMP1) expression was decreased after the limbs were suspended for 42 days ( P = 0.0043), but not 21 days. However, TIMP2 expression was not significantly different from control at 21 or 42 days. Furthermore, the cross-sectional area of the stress-deprived tendons at 42 days was decreased compared with the control group ( P < 0.01). The intervention method in this study did not result in any alteration of stiffness of the tendon. Our study demonstrated that stress deprivation decreases the anabolic process and increases the catabolic process of extracellular matrix in flexor tendon.