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Papers by Hans Harn

Cold Spring Harbor Perspectives in Biology, Dec 12, 2022

Journal of Investigative Dermatology, May 1, 2018

Cysteinyl leukotrienes (CysLTs; LTC 4 , LTD 4 , and LTE 4) are inflammatory mediators known for t... more Cysteinyl leukotrienes (CysLTs; LTC 4 , LTD 4 , and LTE 4) are inflammatory mediators known for their involvement in bronchoconstriction, asthma and allergy, and primarily signal through the receptors CysLT1 and CysLT2. Interestingly, recent studies have found that CysLT receptors are expressed in normal skin, and that CysLT signaling may interfere with wound healing. Furthermore, our preliminary data show that enzymes associated with CysLT synthesis are highly upregulated in burned murine skin compared to healthy skin, while a previous study showed that blister fluids from burn patients contain high LTC 4 levels. Collectively, these observations suggest that CysLTs may propagate inflammation at the burn injury site. Conversely, previous in vitro studies demonstrate that CysLT signaling promotes contraction and collagen production by fibroblasts, and induces proliferation of endothelial cells, suggesting that CysLTs may promote healing after injury. To elucidate the effects of CysLTs in an inflammatory wound such as burn, we induced scald burn injury to C57BL/6 mice treated with montelukast, a FDA-approved CysLT1 antagonist, or vehicle. Intriguingly, we found that montelukast-treated mice exhibited significantly delayed re-epithelialization, which was associated with fewer proliferating keratinocytes and endothelial cells, when compared to the vehicle-treated control mice. We also demonstrate that montelukast-treated wounds expressed lower levels of pro-healing genes, and higher levels of the inflammatory gene, inos. Collectively, our data identify a new mechanism activated at the burn wound site, and strongly suggest that CysLT signaling promotes burn wound healing. This study reveals a novel therapeutic potential of exploiting the CysLT1 signaling pathway to accelerate healing in burn patients.

Pharmaceutics, Sep 12, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Frontiers in Cell and Developmental Biology, Feb 19, 2021

During aging, the skin undergoes changes in architecture and composition. Skin aging phenotypes o... more During aging, the skin undergoes changes in architecture and composition. Skin aging phenotypes occur due to accumulated changes in the genome/epigenome, cytokine/cell adhesion, cell distribution/extracellular matrix (ECM), etc. Here we review data suggesting that tissue mechanics also plays a role in skin aging. While mouse and human skin share some similarities, their skin architectures differ in some respects. However, we use recent research in haired murine skin because of the available experimental data. Skin suffers from changes in both its appendages and interappendage regions. The elderly exhibit wrinkles and loose dermis and are more likely to suffer from wounds and superficial abrasions with poor healing. They also have a reduction in the number of skin appendages. While telogen is prolonged in aging murine skin, hair follicle stem cells can be rejuvenated to enter anagen if transplanted to a young skin environment. We highlight recent single-cell analyses performed on epidermis and aging human skin which identified new basal cell subpopulations that shift in response to wounding. This may be due to alterations of basement membrane stiffness which would change tissue mechanics in aging skin, leading to altered homeostatic dynamics. We propose that the extracellular matrix (ECM) may play a key role as a chemo-mechanical integrator of the multi-layered senescence-associated signaling pathways, dictating the tissue mechanical landscape of niche microenvironments in aging phenotypes. We show examples where failed chemo-mechanical signaling leads to deteriorating homeostasis during skin aging and suggest potential therapeutic strategies to guide future research to delay the aging processes.

Biochimica Et Biophysica Acta - General Subjects, Mar 1, 2017

Background: Focal adhesions (FAs) are large, dynamic protein complexes located close to the plasm... more Background: Focal adhesions (FAs) are large, dynamic protein complexes located close to the plasma membrane, which serve as the mechanical linkages and a biochemical signaling hub of cells. The coordinated and dynamic regulation of focal adhesion is required for cell migration. Degradation, or turnover, of FAs is a major event at the trailing edge of a migratory cell, and is mediated by Ca 2+ /calpain-dependent proteolysis and disassembly. Here, we investigated how Ca 2+ influx induces cascades of FA turnover in living cells. Methods: Images obtained with a total internal reflection fluorescence microscope (TIRFM) showed that Ca 2+ ions induce different processes in the FA molecules focal adhesion kinase (FAK), paxillin, vinculin, and talin. Three mutated calpain-resistant FA molecules, FAK-V744G, paxillin-S95G, and talin-L432G, were used to clarify the role of each FA molecule in FA turnover. Results: Vinculin was resistant to degradation and was not significantly affected by the presence of mutated calpain-resistant FA molecules. In contrast, talin was more sensitive to calpain-mediated turnover than the other molecules. Three-dimensional (3D) fluorescence imaging and immunoblotting demonstrated that outer FA molecules were more sensitive to calpain-mediated proteolysis than internal FA molecules. Furthermore, cell contraction is not involved in degradation of FA. Conclusions: These results suggest that Ca 2+-mediated degradation of FAs was mediated by both proteolysis and disassembly. The 3D architecture of FAs is related to the different dynamics of FA molecule degradation during Ca 2+-mediated FA turnover. General significance: This study will help us to clearly understand the underlying mechanism of focal adhesion turnover by Ca 2+. Highlights  Degradation of focal adhesions by Ca 2+ /calpain-dependent proteolysis is demonstrated.  Outer FA molecules are more sensitive to calpain-mediated proteolysis.  The 3D architecture of FAs is related to the dynamics of FA molecule degradation.

Journal of Investigative Dermatology, May 1, 2019

Proceedings of the National Academy of Sciences of the United States of America, May 9, 2019

Networked structures integrate numerous elements into one functional unit, while providing a bala... more Networked structures integrate numerous elements into one functional unit, while providing a balance between efficiency, robustness, and flexibility. Understanding how biological networks self-assemble will provide insights into how these features arise. Here, we demonstrate how nature forms exquisite muscle networks that can repair, regenerate, and adapt to external perturbations using the feather muscle network in chicken embryos as a paradigm. The selfassembled muscle networks arise through the implementation of a few simple rules. Muscle fibers extend outward from feather buds in every direction, but only those muscle fibers able to connect to neighboring buds are eventually stabilized. After forming such a nearest-neighbor configuration, the network can be reconfigured, adapting to perturbed bud arrangement or mechanical cues. Our computational model provides a bioinspired algorithm for network self-assembly, with intrinsic or extrinsic cues necessary and sufficient to guide the formation of these regenerative networks. These robust principles may serve as a useful guide for assembling adaptive networks in other contexts.

Journal of Biomedical Science, Aug 19, 2017

Background: Vibrio vulnificus is a marine bacterial species that causes opportunistic infections ... more Background: Vibrio vulnificus is a marine bacterial species that causes opportunistic infections manifested by serious skin lesions and fulminant septicemia in humans. We have previously shown that the multifunctional autoprocessing repeats in toxin (MARTX Vv1) of a biotype 1 V. vulnificus strain promotes survival of this organism in the host by preventing it from engulfment by the phagocytes. The purpose of this study was to further explore how MARTX Vv1 inhibits phagocytosis of this microorganism by the macrophage. Methods: We compared between a wild-type V. vulnificus strain and its MARTX Vv1-deficient mutant for a variety of phagocytosis-related responses, including morphological change and activation of signaling molecules, they induced in the macrophage. We also characterized a set of MARTX Vv1 domain-deletion mutants to define the regions associated with antiphagocytosis activity. Results: The RAW 264.7 cells and mouse peritoneal exudate macrophages underwent cell rounding accompanied by F-actin disorganization in the presence of MARTX Vv1. In addition, phosphorylation of some F-actin rearrangementassociated signaling molecules, including Lyn, Fgr and Hck of the Src family kinases (SFKs), focal adhesion kinase (FAK), proline-rich tyrosine kinase 2 (Pyk2), phosphoinositide 3-kinase (PI3K) and Akt, but not p38, was decreased. By using specific inhibitors, we found that these kinases were all involved in the phagocytosis of MARTX Vv1-deficient mutant in an order of SFKs-FAK/Pyk2-PI3K-Akt. Deletion of the effector domains in the central region of MARTX Vv1 could lead to reduced cytotoxicity, depending on the region and size of deletion, but did not affect the antiphagocytosis activity and ability to cause rounding of macrophage. Reduced phosphorylation of Akt was closely associated with inhibition of phagocytosis by the wild-type strain and MARTX Vv1 domain-deletion mutants, and expression of the constitutively active Akt, myr-Akt, enhanced the engulfment of these strains by macrophage. Conclusions: MARTX Vv1 could inactivate the SFKs-FAK/Pyk2-PI3K-Akt signaling pathway in the macrophages. This might lead to impaired phagocytosis of the V. vulnificus-infected macrophage. The majority of the central region of MARTX Vv1 is not associated with the antiphagocytosis activity.

Tissue Engineering Part A, Sep 1, 2013

Current hemodialysis has functional limitations and is insufficient for renal transplantation. Th... more Current hemodialysis has functional limitations and is insufficient for renal transplantation. The bioartificial tubule device has been developed to contribute to metabolic functions by implanting renal epithelial cells into hollow tubes and showed a higher survival rate in acute kidney injury patients. In healthy kidney, epithelial cells are surrounded by various types of cells that interact with extracellular matrices, which are primarily composed of laminin and collagen. The current study developed a microfluidic coculture platform to enhance epithelial cell function in bioartificial microenvironments with multiple microfluidic channels that are microfabricated by polydimethylsiloxane. Collagen gel (CG) encapsulated with adipose-derived stem cells (CG-ASC) was injected into a central microfluidic channel for three-dimensional (3D) culture. The resuspended Madin-Darby canine kidney (MDCK) cells were injected into nascent channels and formed an epithelial monolayer. In comparison to coculture different cells using the commercial transwell system, the current coculture device allowed living cell monitoring of both the MDCK epithelial monolayer and CG-ASC in a 3D microenvironment. By coculture with CG-ASC, the cell height was increased with columnar shapes in MDCK. Promotion of cilia formation and functional expression of the ion transport protein in MDCK were also observed in the cocultured microfluidic device. When applying fluid flow, the intracellular protein dynamics can be monitored in the current platform by using the time-lapse confocal microscopy and transfection of GFP-tubulin plasmid in MDCK. Thus, this microfluidic coculture device provides the renal epithelial cells with both morphological and functional improvements that may avail to develop bioartificial renal chips.

Biomaterials Science, 2014

Materials and methods Mechanical testing of patch The mechanical properties of aligned or randoml... more Materials and methods Mechanical testing of patch The mechanical properties of aligned or randomly oriented EPs were performed using uniaxial load testing equipment (H1KH-0048; Tinius Olsen) with a crosshead speed of 5 mm/min. EP was cut into strips of 3 cm long and 1 cm wide. Samples were stretched under

Oncotarget, May 19, 2015

This is an open-access article distributed under the terms of the Creative Commons Attribution Li... more This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

International Journal of Rehabilitation Research, Dec 1, 2012

plus approprié s que les deux autres, mais uniquement pour la stimulation des extenseurs dorsaux ... more plus approprié s que les deux autres, mais uniquement pour la stimulation des extenseurs dorsaux unilaté raux. Né anmoins, dans une optique d'amé lioration de la force musculaire, les mouvements à plat ventre modifié pourrait é galement ê tre envisagé s.

Journal of Investigative Dermatology, May 1, 2021

PLOS Biology, Mar 25, 2019

Periodic patterning represents a fundamental process in tissue morphogenesis. In chicken dorsal s... more Periodic patterning represents a fundamental process in tissue morphogenesis. In chicken dorsal skin, feather formation starts from the midline; then the morphogenetic wave propagates bilaterally, leaving a regular hexagonal array of feather germs. Yet, in vitro reconstitution showed feather germs appear simultaneously, leading to the hypothesis that the feather-forming wave results from the coupling of local Turing patterning processes with an unidentified global event. In this issue, Ho and colleagues showed such a global event in chicken feathers involves a spreading Ectodysplasin A (EDA) wave and Fibroblast Growth Factor 20 (FGF20)-cell aggregate-based mechanochemical coupling. In flightless birds, feather germs form periodically but without precise hexagonal patterning due to the lack of global wave.

Nature Communications, May 10, 2021

Tissue regeneration is a process that recapitulates and restores organ structure and function. Al... more Tissue regeneration is a process that recapitulates and restores organ structure and function. Although previous studies have demonstrated wound-induced hair neogenesis (WIHN) in laboratory mice (Mus), the regeneration is limited to the center of the wound unlike those observed in African spiny (Acomys) mice. Tissue mechanics have been implicated as an integral part of tissue morphogenesis. Here, we use the WIHN model to investigate the mechanical and molecular responses of laboratory and African spiny mice, and report these models demonstrate opposing trends in spatiotemporal morphogenetic field formation with association to wound stiffness landscapes. Transcriptome analysis and K14-Cre-Twist1 transgenic mice show the Twist1 pathway acts as a mediator for both epidermal-dermal interactions and a competence factor for periodic patterning, differing from those used in development. We propose a Turing model based on tissue stiffness that supports a two-scale tissue mechanics process: (1) establishing a morphogenetic field within the wound bed (mm scale) and (2) symmetry breaking of the epidermis and forming periodically arranged hair primordia within the morphogenetic field (μm scale). Thus, we delineate distinct chemomechanical events in building a Turing morphogenesis-competent field during WIHN of laboratory and African spiny mice and identify its evo-devo advantages with perspectives for regenerative medicine.

Experimental Dermatology, Apr 1, 2019

Wound-induced hair follicle neogenesis (WIHN) has been demonstrated in laboratory mice (Mus muscu... more Wound-induced hair follicle neogenesis (WIHN) has been demonstrated in laboratory mice (Mus musculus) after large (>1.5 × 1.5 cm 2) full-thickness wounds. WIHN occurs more robustly in African Spiny mice (Acomys cahirinus), which undergo autotomy to escape predation. Yet, the non-WIHN regenerative ability of the spiny mouse skin has not been explored. To understand the regenerative ability of the spiny mouse, we characterized skin features such as hair types, hair cycling, and the response to small and large wounds. We found that spiny mouse skin contains a large portion of adipose tissue. The spiny mouse hair bulge is larger and shows high expression of stem cell markers, K15 and CD34. All hair types cycle synchronously. To our surprise, the hair cycle is longer and less frequent than in laboratory mice. Newborn hair follicles in anagen, are more mature than C57Bl/6 and demonstrate molecular features similar to C57Bl/6 adult hairs. The second hair cycling wave begins at week 4 and lasts for 5 weeks, then telogen lasts for 30 weeks. The third wave has a 6-week anagen, and even longer telogen. After plucking, spiny mouse hairs regenerate in about 5 days, similar to that of C57Bl/6. After large full-thickness excisional wounding, there is more de novo hair formation than C57Bl/6. Also, all hair types are present and *

Journal of Dermatological Science, Jun 1, 2018

Mechanical forces are known to regulate homeostasis of the skin and play a role in the pathogenes... more Mechanical forces are known to regulate homeostasis of the skin and play a role in the pathogenesis of skin diseases. The epidermis consists of keratinocytes that are tightly adhered to each other by cell junctions. Defects in keratins or desmosomal/hemidesmosomal proteins lead to the attenuation of mechanical strength and formation of intraepidermal blisters in the case of epidermolysis bullosa simplex. The dermis is rich in extracellular matrix, especially collagen, and provides the majority of tensile force in the skin. Keloid and hypertrophic scar, which is the result of overproduction of collagen by fibroblasts during the wound healing, are associated with extrinsic tensile forces and changes of intrinsic mechanical properties of the cell. Increasing evidences shows that stiffness of the skin environment determines the regenerative ability during wound healing process. Mechanotransduction pathways are also involved in the morphogenesis and cyclic growth of hair follicles. The development of androgenetic alopecia is correlated to tensile forces generated by the fibrous tissue underlying the scalp. Acral melanoma predominantly occurs in the weightbearing area of the foot suggesting the role of mechanical stress. Increased dermal stiffness from fibrosis might be the cause of recessive dystrophic epidermolysis bullosa associated squamous cell carcinoma. Strategies to change the mechanical forces or modify the mechanotransduction signals may lead to a new way to treat skin diseases and promote skin regeneration.

Cell Adhesion & Migration, May 3, 2016

Any cellular response leading to morphological changes is highly tuned to balance the force gener... more Any cellular response leading to morphological changes is highly tuned to balance the force generated from structural reorganization, provided by actin cytoskeleton. Actin filaments serve as the backbone of intracellular force, and transduce external mechanical signal via focal adhesion complex into the cell. During migration, cells not only undergo molecular changes but also rapid mechanical modulation. Here we focus on determining, the role of spatial distribution of mechanical changes of actin filaments in epithelial, mesenchymal, fibrotic and cancer cells with non-migration, directional migration, and non-directional migration behaviors using the atomic force microscopy. We found 1) non-migratory cells only generated one type of filament elasticity, 2) cells generating spatially distributed two types of filament elasticity showed directional migration, and 3) pathologic cells that autonomously generated two types of filament elasticity without spatial distribution were actively migrating non-directionally. The demonstration of spatial regulation of filament elasticity of different cell types at the nano-scale highlights the coupling of cytoskeletal function with physical characters at the sub-cellular level, and provides new research directions for migration related disease.

Journal of Cellular Physiology, May 26, 2015

Ca(2+) -mediated formation of cell polarity is essential for directional migration, which plays a... more Ca(2+) -mediated formation of cell polarity is essential for directional migration, which plays an important role inphysiological and pathological processes in organisms. To examine the critical role of store-operated Ca(2+) entry, which is the major form of extracellular Ca(2+) influx in non-excitable cells, in the formation of cell polarity, we employed human bone osteosarcoma U2OS cells, which exhibit distinct morphological polarity during directional migration. Our analyses showed that Ca(2+) was concentrated at the rear end of cells and that extracellular Ca(2+) influx was important for cell polarization. Inhibition of store-operated Ca(2+) entry using specific inhibitors disrupted the formation of cell polarity in a dose-dependent manner. Moreover, the channelosomal components caveolin-1, TRPC1and Orai1 were concentrated at the rear end of polarized cells. Knockdown of TRPC1 or a TRPC inhibitor, but not knockdown of Orai1,reduced cell polarization. Furthermore, disruption of lipid rafts or overexpression of caveolin-1 contributed to the downregulation of cell polarity.On the other hand, we also found that cell polarity, store-operated Ca(2+) entry activity and cell stiffness were markedly decreased by low substrate rigidity, which may be caused by the disorganization of actin filaments and microtubules that occurs while regulating the activity of the mechanosensitive TRPC1 channel. This article is protected by copyright. All rights reserved.