The basement membrane microenvironment directs the normalization and survival of bioengineered human skin equivalents

Type IV collagen reduces MUC5AC secretion in the lungs of ovalbumin-sensitized mice

Mucin 5AC (MUC5AC) is excessively secreted in the respiratory tract of patients with asthma. Suppressing this secretion is important for improving the air passages, which facilitates easy breathing. We have previously reported that the addition of type IV collagen, a typical extracellular matrix (ECM) protein, to the culture medium for human cell lines and primary cells reduced MUC5AC secretion. In this report, we further investigated the effect of type IV collagen on MUC5AC secretion in vivo. We employed ovalbumin (OVA)-sensitized mice to model of asthma and exposed them to type IV collagen to verify the reducing effect of MUC5AC in vivo. The amount of MUC5AC in bronchoalveolar lavage fluid was examined after nebulization of type IV collagen. Hypersecretion of MUC5AC of the OVA-sensitized mice was suppressed by type IV collagen exposure in a time- and dose-dependent manner. Furthermore, type IV collagen exposure to OVA-sensitized mice decreased integrin α2 and β1 expression in the lungs and increased the levels of Akt and extracellular signal-regulated kinase (ERK) phosphorylation in the trachea. These results suggest that type IV collagen suppresses MUC5AC hypersecretion via modulating integrin expression and Akt/ERK phosphorylation in the respiratory tract of the OVA-sensitized mice.

Integrin β1 subunit regulates cellular and secreted MUC5AC and MUC5B production in NCI-H292 human lung epithelial cells

The surface of the human respiratory tract is covered with a mucus layer containing mucin 5AC (MUC5AC) and mucin 5B (MUC5B) as the main components. This layer contributes to biological defense by eliminating irritants, but excessive MUC5AC secretion by the airway epithelial cells exacerbates asthma. Therefore, regulating mucin production is important for asthma treatment. In this study, the effects of integrin β1 subunit on MUC5AC and MUC5B production were examined in NCI–H292 human lung cancer epithelial cells. When integrin β1 was overexpressed, cellular and secreted MUC5AC levels were decreased, whereas cellular MUC5B production was increased. Conversely, integrin β1 depletion using siRNA increased cellular and secreted MUC5AC production, but decreased cellular MUC5B production. Further, the activity of extracellular signal-regulated kinase (ERK), which promotes MUC5AC production, was decreased by integrin β1 overexpression and increased by its depletion. These results suggest that integrin β1 suppresses MUC5AC production and promotes MUC5B production by downregulating ERK.

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We studied the regulation of MUC5AC and MUC5B production by integrin β1 subunit.

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Integrin β1 overexpression reduced MUC5AC, but increased MUC5B levels.

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Integrin β1 depletion increased MUC5AC production and ROS level, but decreased MUC5B production.

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Integrin β1 overexpression decreased ERK activity in NCI–H292 airway cells.

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Integrin β1 downregulates ERK to suppress MUC5AC & promote MUC5B production.

De novo production of human extracellular matrix supports increased throughput and cellular complexity in 3D skin equivalent model

Three-dimensional (3D) tissue models of human skin are being developed to better understand disease phenotypes and to screen new drugs for potential therapies. Several factors will increase the value of these in vitro 3D skin tissues for these purposes. These include the need for human-derived extracellular matrix (ECM), higher throughput tissue formats, and greater cellular complexity. Here, we present an approach for the fabrication of 3D skin-like tissues as a platform that addresses these three considerations. We demonstrate that human adult and neonatal fibroblasts deposit an endogenous ECM de novo that serves as an effective stroma for full epithelial tissue development and differentiation. We have miniaturized these tissues to a 24-well format to adapt them for eventual higher throughput drug screening. We have shown that monocytes from the peripheral blood can be incorporated into this model as macrophages to increase tissue complexity. This humanized skin-like tissue decreases dependency on animal-derived ECM while increasing cellular complexity that can enable screening inflammatory responses in tissue models of human skin.

Type IV collagen reduces mucin 5AC secretion in three-dimensional cultured human primary airway epithelial cells

Mucin 5AC (MUC5AC) hypersecretion induces airway narrowing in patients with asthma, which leads to breathing problems. We investigated the regulation of MUC5AC secretion by extracellular matrix (ECM) proteins in human primary airway epithelial cells from patients with asthma. The addition of type IV collagen to three-dimensional cultured human primary airway epithelial cells, which mimics the airway surface, reduced MUC5AC secretion in the medium, while the addition of laminin increased MUC5AC secretion. Furthermore, the addition of fibronectin did not affect MUC5AC secretion. In particular, the repeated addition of a low concentration of type IV collagen demonstrated a cumulative effect on the reduction in MUC5AC secretion. Human primary cells incubated with type IV collagen showed downregulated extracellular signal-regulated kinase (ERK) activity, which induced MUC5AC hypersecretion but did not affect Akt activity. These results suggest that the addition of type IV collagen to the apical surface of primary cells downregulates MUC5AC secretion and has a cumulative effect on MUC5AC secretion which might be effected via the ERK signaling pathway.

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We studied the regulation of MUC5AC secretion by extracellular matrix proteins.

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The addition of type IV collagen reduced MUC5AC secretion in primary airway cells.

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The repeated addition of a low concentration of collagen reduced MUC5AC secretion.

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Type IV collagen induced the downregulation of ERK which induces MUC5AC secretion.

A potential dermal substitute using decellularized dermis extracellular matrix derived bio-ink

Upon bioprinting, cells are mixed with a biomaterial to fabricate a living tissue, thus emphasizing the importance of biomaterials. The biomaterial used in this study was a bio-ink prepared using skin decellularized extracellular matrix (dECM). Skin dECM was extracted by treating the dermis with chemicals and enzymes; the basic structural and functional proteins of the ECM, including collagen, glycosaminoglycans (GAGs), bioreactive materials and growth factors, were preserved, whereas the resident cells that might cause immune rejection or inflammatory responses were removed. The bio-ink based on dECM powder, together with human dermal fibroblasts (HDFs), was loaded into the nozzle of the 3D bioprinter to create the 3D construct. This construct underwent gelation with changing temperature while its shape was maintained for 7 days. The cells showed over 90% viability and proliferation. By analysing the gene expression pattern in the cells of the construct, the skin regenerative mechanism of the bio-ink was verified. Microarray results confirmed that the gene expression related to skin morphology and development had been enhanced because the bioreactive molecules and growth factors, in addition to residual ECM in dECM, provided an optimal condition for the HDFs.

A proof of concept study demonstrating that environmental levels of carbamazepine impair early stages of chick embryonic development

Carbamazepine (CBZ) is an anticonvulsant drug used for epilepsy and other disorders. Prescription of CBZ during pregnancy increases the risk for congenital malformations. CBZ is ubiquitous in effluents and persistent during wastewater treatment. Thus, it is re-introduced into agricultural ecosystems upon irrigation with reclaimed wastewater. People consuming produce irrigated with reclaimed wastewater were found to be exposed to CBZ. However, environmental concentrations of CBZ (μgL^-1) are magnitudes lower than its therapeutic levels (μgml^-1), raising the question of whether and how environmental levels of CBZ affect embryonic development. The chick embryo is a powerful and highly sensitive amniotic model system that enables to assess environmental contaminants in the living organism. Since the chick embryonic development is highly similar to mammalians, yet, it develops in an egg, toxic effects can be directly analyzed in a well-controlled system without maternal influences. This research utilized the chick embryo to test whether CBZ is embryo-toxic by using morphological, cellular, molecular and imaging strategies. Three key embryonic stages were monitored: after blastulation (st.1HH), gastrulation/neurulation (st.8HH) and organogenesis (st.15HH). Here we demonstrate that environmental relevant concentrations of CBZ impair morphogenesis in a dose- and stage- dependent manner. Effects on gastrulation, neural tube closure, differentiation and proliferation were exhibited in early stages by exposing embryos to CBZ dose as low as 0.1μgL^-1. Quantification of developmental progression revealed a significant difference in the total score obtained by CBZ-treated embryos compared to controls (up to 5-fold difference, p<0.05). Yet, defects were unnoticed as embryos passed gastrulation/neurulation. This study provides the first evidence for teratogenic effect of environmental-relevant concentrations of CBZ in amniotic embryos that impair early but not late stages of development. These findings call for in-depth risk analysis to ensure that the environmental presence of CBZ and other drugs is not causing irreversible ecological and public-health damages.

Lysyl oxidase enzymes mediate TGF-β1-induced fibrotic phenotypes in human skin-like tissues

Cutaneous fibrosis is a common complication seen in mixed connective tissue diseases. It often occurs as a result of TGF-β-induced deposition of excessive amounts of collagen in the skin. Lysyl oxidases (LOXs), a family of extracellular matrix (ECM)-modifying enzymes responsible for collagen cross-linking, are known to be increased in dermal fibroblasts from patients with fibrotic diseases, denoting a possible role of LOXs in fibrosis. To directly study this, we have developed two bioengineered, in vitro skin-like models: human skin equivalents (hSEs), and self-assembled stromal tissues (SASs) that contain either normal or systemic sclerosis (SSc; scleroderma) patient-derived fibroblasts. These tissues provide an organ-level structure that could be combined with non-invasive, label-free, multiphoton microscopy (SHG/TPEF) to reveal alterations in the organization and cross-linking levels of collagen fibers during the development of cutaneous fibrosis, which demonstrated increased stromal rigidity and activation of dermal fibroblasts in response to TGF-β1. Specifically, inhibition of specific LOXs isoforms, LOX and LOXL4, in foreskin fibroblasts (HFFs) resulted in antagonistic effects on TGF-β1-induced fibrogenic hallmarks in both hSEs and SASs. In addition, a translational relevance of these models was seen as similar antifibrogenic phenotypes were achieved upon knocking down LOXL4 in tissues containing SSc patient-derived-dermal fibroblasts (SScDFs). These findings point to a pivotal role of LOXs in TGF-β1-induced cutaneous fibrosis through impaired ECM homeostasis in skin-like tissues, and show the value of these tissue platforms in accelerating the discovery of antifibrosis therapeutics.

Differentiation of diabetic foot ulcer-derived induced pluripotent stem cells reveals distinct cellular and tissue phenotypes

Diabetic foot ulcers (DFUs) are a major complication of diabetes, and there is a critical need to develop novel cell- and tissue-based therapies to treat these chronic wounds. Induced pluripotent stem cells (iPSCs) offer a replenishing source of allogeneic and autologous cell types that may be beneficial to improve DFU wound-healing outcomes. However, the biologic potential of iPSC-derived cells to treat DFUs has not, to our knowledge, been investigated. Toward that goal, we have performed detailed characterization of iPSC-derived fibroblasts from both diabetic and nondiabetic patients. Significantly, gene array and functional analyses reveal that iPSC-derived fibroblasts from both patients with and those without diabetes are more similar to each other than were the primary cells from which they were derived. iPSC-derived fibroblasts showed improved migratory properties in 2-dimensional culture. iPSC-derived fibroblasts from DFUs displayed a unique biochemical composition and morphology when grown as 3-dimensional (3D), self-assembled extracellular matrix tissues, which were distinct from tissues fabricated using the parental DFU fibroblasts from which they were reprogrammed. In vivo transplantation of 3D tissues with iPSC-derived fibroblasts showed they persisted in the wound and facilitated diabetic wound closure compared with primary DFU fibroblasts. Taken together, our findings support the potential application of these iPSC-derived fibroblasts and 3D tissues to improve wound healing.-Kashpur, O., Smith, A., Gerami-Naini, B., Maione, A. G., Calabrese, R., Tellechea, A., Theocharidis, G., Liang, L., Pastar, I., Tomic-Canic, M., Mooney, D., Veves, A., Garlick, J. A. Differentiation of diabetic foot ulcer-derived induced pluripotent stem cells reveals distinct cellular and tissue phenotypes.

Topical Application of Culture-Expanded CD34+ Umbilical Cord Blood Cells from Frozen Units Accelerates Healing of Diabetic Skin Wounds in Mice

Chronic and nonhealing wounds are constant health issues facing patients with type 2 diabetes. As the incidence of type 2 diabetes mellitus (T2DM) increases, the incidence of chronic wounds and amputations will rise. T2DM is associated with peripheral arterial occlusive disease, which leads to the development of nonhealing skin ulcers after minor trauma. Patients develop severe pain limiting their mobility and ability to work and take care of themselves, thus putting a significant burden on the family and society. CD34+ cells from umbilical cord blood (UCB) grown in fibroblast growth factor-4 (FGF-4), stem cell factor, and Flt3-ligand produced a population of cells that have the ability to proliferate and develop properties enabling them to enhance tissue regeneration. The goal of this study was to assess in vitro cultured CD34+ cells in a setting where they would eventually be rejected so we could isolate paracrine signaling mediated therapeutic effect from the therapeutic effect due to engraftment and differentiation. To achieve this, we used db/db mice as a model for diabetic skin ulcers. Here, we report that in vitro cultured UCB CD34+ cells from frozen units can accelerate wound healing and resulted in the regeneration of full thickness skin. This study demonstrates a new indication for banked UCB units in the area of tissue regeneration. Stem Cells Translational Medicine 2018;7:591-601.

Type IV collagen aggregates promote keratinocyte proliferation and formation of epidermal layer in human skin equivalents

Type IV collagen isolated from lens capsule without enzymatic treatment is known to form a gel under physiological condition and influences cellular activities. In case of human keratinocytes, the suppression of proliferation on reconstituted type IV collagen gels was reported in monolayer culture. In this study, we examined effects of type IV collagen isolated from porcine lens capsule on epidermal formation in human skin equivalents (HSEs). Type IV collagen aggregates were prepared under the culture condition and the aggregates suppressed keratinocyte proliferation in monolayer culture as well as the culture on the gels. In HSEs, type IV collagen aggregates were reconstituted on the surface of contracted collagen gels containing human dermal fibroblasts and the keratinocytes were then cultured on the aggregates for 14 days. Interestingly, in HSEs with type IV collagen aggregates, the BrdU-positive keratinocytes were increased and the thickness of the epidermal layer was around twice than that of control culture. Epidermal differentiation markers were expressed in the upper layer of the epidermis and the defined deposition of human basement membrane components were increased at the dermal-epidermal junction. These results indicate that the type IV collagen aggregates stimulate the proliferation of basal keratinocytes and improve the stratification of epidermal layers in HSEs.

Heparanase Inhibitors Facilitate the Assembly of the Basement Membrane in Artificial Skin

Recent research suggests that the basement membrane at the dermal-epidermal junction of the skin plays an important role in maintaining a healthy epidermis and dermis, and repeated damage to the skin can destabilize the skin and accelerate the aging process. Skin-equivalent models are suitable for studying the reconstruction of the basement membrane and its contribution to epidermal homeostasis because they lack the basement membrane and show abnormal expression of epidermal differentiation markers. By using these models, it has been shown that reconstruction of the basement membrane is enhanced not only by supplying basement membrane components, but also by inhibiting proteinases such as urokinase and matrix metalloproteinase. Although matrix metalloproteinase inhibitors assist in the reconstruction of the basement membrane structure, their action is not sufficient to promote its functional recovery. However, heparanase inhibitors stabilize the heparan sulfate chains of perlecan (a heparan sulfate proteoglycan) and promote the regulation of heparan sulfate binding growth factors in the basement membrane. Heparan sulfate promotes effective protein-protein interactions, thereby facilitating the assembly of type VII collagen anchoring fibrils and elastin-associated microfibrils. Using both matrix metalloproteinase inhibitors and heparanase inhibitors, the basement membrane in a skin-equivalent model comes close to recapitulating the structure and function of an in vivo basement membrane. Therefore, by using an appropriate dermis model and suitable protease inhibitors, it may be possible to produce skin-equivalent models that are more similar to natural skin

Effects of C-xylopyranoside derivative on epithelial regeneration in an in vitro 3D oral mucosa model

Identifying substandard tissue-engineered oral mucosa grafts with a poor epithelium before clinical use is critical to ensure quality assurance/control in regenerative medicine, leading to success of grafting. This study investigated the effects of one of the C-xylopyranoside derivatives, β-D-xylopyranoside-n-propane-2-one (XPP), on oral epithelial regeneration. Using a three-dimensional oral mucosa model, we analyzed changes of the epithelial structure, glycosaminoglycan (GAG) synthesis, the expression levels of basement membrane zone markers, and substrates of Akt/mTOR signaling. Compared with the control, 2 mM XPP treatment increased the mean and minimal epithelial thickness, and reduced the variation of epithelial thickness. It also stimulated expressions of decorin and syndecan-1 with change of GAG amount and/or composition, and enhanced the expressions of integrin α6, CD44, and Akt/mTOR signaling substrates. These findings suggest that XPP supplementation contributes to consistent epithelial regeneration. Moreover, upregulation of those markers may play a role in increasing the quality of the oral mucosal epithelium.

Mechanical Stretch on Human Skin Equivalents Increases the Epidermal Thickness and Develops the Basement Membrane

All previous reports concerning the effect of stretch on cultured skin cells dealt with experiments on epidermal keratinocytes or dermal fibroblasts alone. The aim of the present study was to develop a system that allows application of stretch stimuli to human skin equivalents (HSEs), prepared by coculturing of these two types of cells. In addition, this study aimed to analyze the effect of a stretch on keratinization of the epidermis and on the basement membrane. HSEs were prepared in a gutter-like structure created with a porous silicone sheet in a silicone chamber. After 5-day stimulation with stretching, HSEs were analyzed histologically and immunohistologically. Stretch-stimulated HSEs had a thicker epidermal layer and expressed significantly greater levels of laminin 5 and collagen IV/VII in the basal layer compared with HSEs not subjected to stretch stimulation. Transmission electron microscopy revealed that the structure of the basement membrane was more developed in HSEs subjected to stretching. Our model may be relevant for extrapolating the effect of a stretch on the skin in a state similar to an in vivo system. This experimental system may be useful for analysis of the effects of stretch stimuli on skin properties and wound healing and is also expected to be applicable to an in vitro model of a hypertrophic scar in the future.

Dermal expression of laminin-332 and type IV collagen in humans with severe sepsis

BACKGROUND

An intact basement membrane at the dermal-epidermal junction is essential to the viability of the skin. The effect of sepsis on the basement membrane is unknown.

METHODS

Skin biopsies were used to study basement membrane structure in severe sepsis (Day 1). Subsequent biopsies were taken on Day 8 and at 3 months in the survivors. Immunohistochemical staining was undertaken using laminin-223 and type IV collagen. Twenty patients with severe sepsis and four control subjects were included in the analysis.

RESULTS

Intensive care unit mortality was 4/20, and total 30-day mortality was 5/20. Exactly, 7/17 of patients with severe sepsis exhibited weak or absent laminin-332 expression and 11/15 exhibited weak or absent type IV collagen expression compared with 0/4 of control subjects on Day 1 in intact skin. The proportion of sepsis patients with weak or absent laminin-332 expression was 5/11 on Day 8 and fell to 1/7 at 3 months. The proportion of sepsis patients with weak or absent type IV collagen expression was 10/11 on Day 8 and 4/7 at 3 months.

CONCLUSION

These findings suggest that basement membrane formation may be compromised in patients with severe sepsis.

Bioengineering a human plasma-based epidermal substitute with efficient grafting capacity and high content in clonogenic cells

Cultured epithelial autografts (CEAs) produced from a small, healthy skin biopsy represent a lifesaving surgical technique in cases of full-thickness skin burn covering >50% of total body surface area. CEAs also present numerous drawbacks, among them the use of animal proteins and cells, the high fragility of keratinocyte sheets, and the immaturity of the dermal-epidermal junction, leading to heavy cosmetic and functional sequelae. To overcome these weaknesses, we developed a human plasma-based epidermal substitute (hPBES) for epidermal coverage in cases of massive burn, as an alternative to traditional CEA, and set up critical quality controls for preclinical and clinical studies. In this study, phenotypical analyses in conjunction with functional assays (clonal analysis, long-term culture, or in vivo graft) showed that our new substitute fulfills the biological requirements for epidermal regeneration. hPBES keratinocytes showed high potential for cell proliferation and subsequent differentiation similar to healthy skin compared with a well-known reference material, as ascertained by a combination of quality controls. This work highlights the importance of integrating relevant multiparameter quality controls into the bioengineering of new skin substitutes before they reach clinical development.

SIGNIFICANCE

This work involves the development of a new bioengineered epidermal substitute with pertinent functional quality controls. The novelty of this work is based on this quality approach.

Three-dimensional human tissue models that incorporate diabetic foot ulcer-derived fibroblasts mimic in vivo features of chronic wounds

Diabetic foot ulcers (DFU) are a major, debilitating complication of diabetes mellitus. Unfortunately, many DFUs are refractory to existing treatments and frequently lead to amputation. The development of more effective therapies has been hampered by the lack of predictive in vitro methods to investigate the mechanisms underlying impaired healing. To address this need for realistic wound-healing models, we established patient-derived fibroblasts from DFUs and site-matched controls and used them to construct three-dimensional (3D) models of chronic wound healing. Incorporation of DFU-derived fibroblasts into these models accurately recapitulated the following key aspects of chronic ulcers: reduced stimulation of angiogenesis, increased keratinocyte proliferation, decreased re-epithelialization, and impaired extracellular matrix deposition. In addition to reflecting clinical attributes of DFUs, the wound-healing potential of DFU fibroblasts demonstrated in this suite of models correlated with in vivo wound closure in mice. Thus, the reported panel of 3D DFU models provides a more biologically relevant platform for elucidating the cell-cell and cell-matrix-related mechanisms responsible for chronic wound pathogenesis and may improve translation of in vitro findings into efficacious clinical applications.

Cyclic mechanical pressure-loading alters epithelial homeostasis in a three-dimensional in vitro oral mucosa model: clinical implications for denture-wearers

Denture-wearing affects the quality and quantity of epithelial cells in the underlying healthy oral mucosa. The physiologic mechanisms, however, are poorly understood. This study aimed to compare histologic changes and cellular responses of an epithelial cell layer to cyclic mechanical pressure-loading mimicking denture-wearing using an organotypic culture system to develop a three-dimensional in vitro oral mucosa model (3DOMM). Primary human oral keratinocytes and fibroblasts were serially grown in a monolayer culture, and cell viability was measured under continuous cyclic mechanical pressure (50 kPa) for 7 days (cycles of 60 min on, 20 s off to degas and inject air). Upon initiation of an air-liquid interface culture for epithelial stratification, the cyclic pressure, set to the mode above mentioned, was applied to the 3DOMMs for 7 days. Paraffin-embedded 3DOMMs were examined histologically and immunohistochemically. In the monolayer culture, the pressure did not affect the viability of oral keratinocytes or fibroblasts. Few histologic changes were observed in the epithelial layer of the control and pressure-loaded 3DOMMs. Immunohistochemical examination, however, revealed a significant decrease in Ki-67 labelling and an increase in filaggrin and involucrin expression in the suprabasal layer of the pressure-loaded 3DOMMs. Pressure-loading attenuated integrin β1 expression and increased matrix metalloproteinase-9 activity. Incomplete deposition of laminin and type IV collagen beneath the basal cells was observed only in the pressure-loaded 3DOMM. Cyclic pressure-loading appeared to disrupt multiple functions of the basal cells in the 3DOMM, resulting in a predisposition towards terminal differentiation. Thus, denture-wearing could compromise oral epithelial homeostasis.

Sequential keratinocytic differentiation and maturation in a three-dimensional model of human artificial oral mucosa

BACKGROUND AND OBJECTIVE

Oral mucosa shortage may limit or condition some clinical approaches in maxillofacial, periodontal and implant treatment. The availability of a human oral mucosa model generated by tissue engineering could help clinicians to address the lack of oral mucosa. In this work, we carried out a sequential maturation and differentiation study of the epithelial cell layer of an artificial human oral mucosa substitute based on fibrin-agarose biomaterials with fibroblasts and keratinocytes.

MATERIAL AND METHODS

Histological, immunohistochemical and gene expression analyses were carried out in artificial human oral mucosa models developed and cultured for 1, 2 and 3 wk.

RESULTS

Artificial oral mucosa models showed expression of tight junction proteins and cytokeratins from the first week of in vitro development. Mature samples of 3 wk of development subjected to air-liquid conditions showed signs of epithelial differentiation and expressed specific RNAs and proteins corresponding to adherent and gap junctions and basement lamina. Moreover, these mature samples overexpressed some desmosomal and tight junction transcripts, with gap junction components being downregulated.

CONCLUSION

These results suggest that bioengineered human oral mucosa substitutes form a well-developed epithelial layer that was very similar to human native tissues. In consequence, the epithelial layer could be fully functional in these oral mucosa substitutes, thus implying that these tissues may have clinical usefulness.

Effects of Shiga toxin type 2 on a bioengineered three-dimensional model of human renal tissue

Shiga toxins (Stx) are a family of cytotoxic proteins that can cause hemolytic-uremic syndrome (HUS), a thrombotic microangiopathy, following infections by Shiga toxin-producing Escherichia coli (STEC). Renal failure is a key feature of HUS and a major cause of childhood renal failure worldwide. There are currently no specific therapies for STEC-associated HUS, and the mechanism of Stx-induced renal injury is not well understood primarily due to a lack of fully representative animal models and an inability to monitor disease progression on a molecular or cellular level in humans at early stages. Three-dimensional (3D) tissue models have been shown to be more in vivo-like in their phenotype and physiology than 2D cultures for numerous disease models, including cancer and polycystic kidney disease. It is unknown whether exposure of a 3D renal tissue model to Stx will yield a more in vivo-like response than 2D cell culture. In this study, we characterized Stx2-mediated cytotoxicity in a bioengineered 3D human renal tissue model previously shown to be a predictor of drug-induced nephrotoxicity and compared its response to Stx2 exposure in 2D cell culture. Our results demonstrate that although many mechanistic aspects of cytotoxicity were similar between 3D and 2D, treatment of the 3D tissues with Stx resulted in an elevated secretion of the kidney injury marker 1 (Kim-1) and the cytokine interleukin-8 compared to the 2D cell cultures. This study represents the first application of 3D tissues for the study of Stx-mediated kidney injury.

Skin extracellular matrix components accelerate the regenerative potential of Lin− cells

Due to their unique properties, bone marrow-derived Lin− cells can be used to regenerate damaged tissues, including skin. The objective of our study was to determine the influence of the skin tissue-specific microenvironment on mouse Lin− cell proliferation and migration in vitro. Cells were analyzed for the expression of stem/progenitor surface markers by flow cytometry. Proliferation of MACS-purified cells in 3D cultures was investigated by WST-8 assay. Lin− cell migration was evaluated by in vitro scratch assay. The results obtained show that basement membrane matrix is more effective for Lin− cell proliferation in vitro. However, type I collagen matrix better enhances the re-epithelization process, that depends on the cell migratory properties. These studies are important for preparing cells to be used in transplantation.

Tissue-engineered kidney disease models

Renal disease represents a major health problem that often results in end-stage renal failure necessitating dialysis and eventually transplantation. Historically these diseases have been studied with patient observation and screening, animal models, and two-dimensional cell culture. In this review, we focus on recent advances in tissue engineered kidney disease models that have the capacity to compensate for the limitations of traditional modalities. The cells and materials utilized to develop these models are discussed and tissue engineered models of polycystic kidney disease, drug-induced nephrotoxicity, and the glomerulus are examined in detail. The application of these models has the potential to direct future disease treatments and preclinical drug development.

Accelerated Expansion of Epidermal Keratinocyte and Improved Dermal Reconstruction Achieved by Engineered Amniotic Membrane

In this study, we used human amniotic membrane (AM) to prepare a dermal scaffold with intact basement membrane (BM) and good biostability for quick expansion and transplantation of epidermal keratinocytes (EKs). Fresh AM was treated by repeated freeze–thaw cycles and DNase digestion. This new method was able to cleanse the cell components effectively and retain the BM structure with continuous distributions of laminin, collagen IV, VI, and VII. Subsequently, the acellular amniotic membrane (AAM) was cross-linked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) for 5 min, 30 min, and 6 h. With the time of cross-linking prolonging, the mechanical strength and biostability of AAM increased gradually, while its cytotoxicity to EKs also increased. The 5-min cross-linked AAM (5min-AAM) had no significant cytotoxicity with good histocompatibility. The relative cell viability of EKs seeded on the 5min-AAM surface was 367 ± 33% and 631 ± 43% at 7 and 14 days of culture, respectively, both higher than 294 ± 30% and 503 ± 41% of the conventional cell culture dish (CCD) group, and the proportion of P63-positive cells was significantly higher than that of the CCD group on day 7 (54.32 ± 4.27% vs. 33.32 ± 3.18%, p < 0.05). When the 5min-AAM loaded with EKs (EK-AAM) was grafted onto full-thickness skin defects in nude mice, the cells survived well and formed an epidermis similar to normal skin. The new epidermis was thicker, and reconstruction of the dermal structure was good with an intact BM. Four weeks after transplantation, the wound contraction rate in the EK-AAM group was 43.09 ± 7.05%, significantly lower than that in the EK sheet group (57.49 ± 5.93%) and control group (69.94 ± 9.47%) ( p < 0.05). In conclusion, repeated freeze–thaw treatment with appropriate EDC cross-linking offers AAM an intact BM structure with good operability and biostability. It may prove to be an ideal dermal scaffold to promote expansion of EKs in vitro and be transplanted for reconstruction of the dermal structure.

Microenvironment-dependent homeostasis and differentiation of epidermal basal undifferentiated keratinocytes and their clinical applications in skin repair

Skin homeostasis is maintained by controlling the balance between proliferation and differentiation of epidermal stem cells. The microenvironment, including extrinsic stresses, growth factors, soluble molecules, cell-ECM and cell-cell communications, plays an important role in cell fate determination in vivo and in vitro. In response to external signals, keratinocytes cooperate with other cell types to modulate and facilitate the wound microenvironment during wound healing; however, the aberrant signals or conjunctions in the environment will lead to pathologic abnormalities. In addition, despite some drawbacks, the epidermal stem-cellbased bioengineered skin substitutes have greatly improved the quality of cutaneous repair. Thus, exploring the characteristics and regulation mechanisms of microenvironment-dependent homeostasis and differentiation of epidermal basal undifferentiated keratinocytes is necessary to understand skin development and wound repair and to design novel therapeutic strategies for skin wound healing.

Development of microfabricated dermal epidermal regenerative matrices to evaluate the role of cellular microenvironments on epidermal morphogenesis

Topographic features at the dermal-epidermal junction (DEJ) provide instructive cues critical for modulating keratinocyte functions and enhancing the overall architecture and organization of skin. This interdigitated interface conforms to a series of rete ridges and papillary projections on the dermis that provides three-dimensional (3D) cellular microenvironments as well as structural stability between the dermal and epidermal layers during mechanical loading. The dimensions of these cellular microenvironments exhibit regional differences on the surface of the body, and quantitative histological analyses have shown that localization of highly proliferative keratinocytes also varies, according to the regional geometries of these microenvironments. In this study, we combined photolithography, collagen processing, and biochemical conjugation techniques to create microfabricated dermal epidermal regeneration matrices (μDERMs) with features that mimic the native 3D cellular microenvironment at the DEJ. We used this model system to study the effect of the 3D cellular microenvironment on epithelialization and basal keratinocyte interaction with the microenvironment on the surface of the μDERMs. We found that features closely mimicking those in high-friction areas of the body (deep, narrow channels) epithelialized faster than features mimicking low-friction areas. Additionally, when evaluating β1 expression, an integrin involved in epidermal morphogenesis, it was found that integrin-bright expression was localized in the depths of the features, suggesting that the μDERMs may play a role in defining cellular microenvironments as well as a protective environment for the regenerative population of keratinocytes. The outcomes of this study suggest that μDERMs can serve as a robust biomimetic model system to evaluate the roles of the 3D microenvironment on enhancing the regenerative capacity and structural stability of bioengineered skin substitutes.

Stem cell niches for skin regeneration

Stem cell-based therapies offer tremendous potential for skin regeneration following injury and disease. Functional stem cell units have been described throughout all layers of human skin and the collective physical and chemical microenvironmental cues that enable this regenerative potential are known as the stem cell niche. Stem cells in the hair follicle bulge, interfollicular epidermis, dermal papillae, and perivascular space have been closely investigated as model systems for niche-driven regeneration. These studies suggest that stem cell strategies for skin engineering must consider the intricate molecular and biologic features of these niches. Innovative biomaterial systems that successfully recapitulate these microenvironments will facilitate progenitor cell-mediated skin repair and regeneration.

Stem cells of the human epidermis and their niche: composition and function in epidermal regeneration and carcinogenesis

Skin, as the largest organ, has long been subject of excellent and pioneering studies on stem cells and their role in tissue regulation and tumor formation. In particular, intensive research on mouse skin, and here especially the hair follicle, has largely extended our knowledge. Surprisingly, human skin, although the most easily accessible tissue in man, is far less conceived with regard to its stem cells and their specific environment (the niche). In consequence, these features are as yet only insufficiently defined and it still has to be elucidated how insights in cutaneous stem cell biology gained in mice can be extrapolated to humans. In the last few years, human model systems such as humanized mice or in vitro organotypic cultures that support maintenance or reconstruction of human skin and long-term epidermal regeneration have been developed. These models allow lineage tracing experiments and can be modified by adopting genetically manipulated cell types. Accordingly, they represent proper tools for human stem cell research and will clearly help to improve our still incomplete understanding. Like normal skin, the non-melanoma skin cancers and their respective tumors have gained considerable interest in basic as well as in clinical research. Being the most frequent human tumors globally, basal cell carcinomas and cutaneous squamous cell carcinomas (SCCs) continue to increase in incidence and specifically SCCs predominate in immunosuppressed transplant recipients. This review intends to compile the present knowledge on keratinocyte stem cells and their niches in normal skin and skin carcinomas with a special focus on the human situation. In particular, the role of the microenvironment, the niche, is emphasized, promoting our view of the decisive importance of the niche as a key regulatory element for controlling position, fate and regenerative potential of the stem cell population both in healthy skin and in carcinomas.

Quantitative monitoring of lipid accumulation over time in cultured adipocytes as function of culture conditions: toward controlled adipose tissue engineering

Adipose tissue engineering is investigated for native fat substitutes and wound healing model systems. Research and clinical applications of bioartificial fat require a quantitative and objective method to continuously measure adipogenesis in living cultures as opposed to currently used culture-destructive techniques that stain lipid droplet (LD) accumulation. To allow standardization, automatic quantification of LD size is further needed, but currently LD size is measured mostly manually. We developed an image processing-based method that does not require staining to monitor adipose cell maturation in vitro nondestructively using optical micrographs taken consecutively during culturing. We employed our method to monitor LD accumulation in 3T3-L1 and mesenchymal stem cells over 37 days. For each cell type, percentage of lipid area, number of droplets per cell, and droplet diameter were obtained every 2-3 days. In 3T3-L1 cultures, high insulin concentration (10 microg/mL) yielded a significantly different (p < 0.01) time course of all three outcome measures. In mesenchymal stem cell cultures, high fetal bovine serum concentration (12.5%) produced significantly more lipid area (p < 0.01). Our method was able to successfully characterize time courses and extents of adipogenesis and is useful for a wide range of applications testing the effects of biochemical, mechanical, and thermal stimulations in tissue engineering of bioartificial fat constructs.

The role of fibroblast Tiam1 in tumor cell invasion and metastasis

The co-evolution of tumors and their microenvironment involves bidirectional communication between tumor cells and tumor-associated stroma. Various cell types are present in tumor-associated stroma, of which fibroblasts are the most abundant. The Rac exchange factor Tiam1 is implicated in multiple signaling pathways in epithelial tumor cells and lack of Tiam1 in tumor cells retards tumor growth in Tiam1 knock-out mouse models. Conversely, tumors arising in Tiam1 knock-out mice have increased invasiveness. We have investigated the role of Tiam1 in tumor-associated fibroblasts as a modulator of tumor cell invasion and metastasis, using retroviral delivery of short hairpin RNA to suppress Tiam1 levels in three different experimental models. In spheroid co-culture of mammary epithelial cells and fibroblasts, Tiam1 silencing in fibroblasts led to increased epithelial cell outgrowth into matrix. In tissue-engineered human skin, Tiam1 silencing in dermal fibroblasts led to increased invasiveness of epidermal keratinocytes with premalignant features. In a model of human breast cancer in mice, co-implantation of mammary fibroblasts inhibited tumor invasion and metastasis, which was reversed by Tiam1 silencing in co-injected fibroblasts. These results suggest that stromal Tiam1 may play a role in modulating the effects of the tumor microenvironment on malignant cell invasion and metastasis. This suggests a set of pathways for further investigation, with implications for future therapeutic targets.

Integrin-blocking antibodies delay keratinocyte re-epithelialization in a human three-dimensional wound healing model

The alpha6beta4 integrin plays a significant role in tumor growth, angiogenesis and metastasis through modulation of growth factor signaling, and is a potentially important therapeutic target. However, alpha6beta4-mediated cell-matrix adhesion is critical in normal keratinocyte attachment, signaling and anchorage to the basement membrane through its interaction with laminin-5, raising potential risks for targeted therapy. Bioengineered Human Skin Equivalent (HSE), which have been shown to mimic their normal and wounded counterparts, have been used here to investigate the consequences of targeting beta4 to establish toxic effects on normal tissue homeostasis and epithelial wound repair. We tested two antibodies directed to different beta4 epitopes, one adhesion-blocking (ASC-8) and one non-adhesion blocking (ASC-3), and determined that these antibodies were appropriately localized to the basal surface of keratinocytes at the basement membrane interface where beta4 is expressed. While normal tissue architecture was not altered, ASC-8 induced a sub-basal split at the basement membrane in non-wounded tissue. In addition, wound closure was significantly inhibited by ASC-8, but not by ASC-3, as the epithelial tongue only covered 40 percent of the wound area at 120 hours post-wounding. These results demonstrate beta4 adhesion-blocking antibodies may have adverse effects on normal tissue, whereas antibodies directed to other epitopes may provide safer alternatives for therapy. Taken together, we conclude that these three-dimensional tissue models provide a biologically relevant platform to identify toxic effects induced by candidate therapeutics, which will allow generation of findings that are more predictive of in vivo responses early in the drug development process.

Rac1 is essential for basement membrane-dependent epiblast survival

During murine peri-implantation development, the egg cylinder forms from a solid cell mass by the apoptotic removal of inner cells that do not contact the basement membrane (BM) and the selective survival of the epiblast epithelium, which does. The signaling pathways that mediate this fundamental biological process are largely unknown. Here we demonstrate that Rac1 ablation in embryonic stem cell-derived embryoid bodies (EBs) leads to massive apoptosis of epiblast cells in contact with the BM. Expression of wild-type Rac1 in the mutant EBs rescues the BM-contacting epiblast, while expression of a constitutively active Rac1 additionally blocks the apoptosis of inner cells and cavitation, indicating that the spatially regulated activation of Rac1 is required for epithelial cyst formation. We further show that Rac1 is activated through integrin-mediated recruitment of the Crk-DOCK180 complex and mediates BM-dependent epiblast survival through activating the phosphatidylinositol 3-kinase (PI3K)-Akt signaling pathway. Our results reveal a signaling cascade triggered by cell-BM interactions essential for epithelial morphogenesis.

Three-dimensional human tissue models of wounded skin

Human skin equivalents (HSEs) are in vitro tissues in which a fully differentiated, stratified squamous epithelium is grown at an air-liquid interface on a Type I collagen gel harboring human dermal fibroblasts. HSEs now provide experimental human tissue models to study factors that direct re-epithelialization and epithelial-mesenchymal cross-talk following wounding. This chapter describes the fabrication of HSEs from human keratinocytes and fibroblasts and how HSEs can be modified to characterize the response of the human epithelium during wound repair. The protocols outlined first describe techniques for the generation of human tissues that closely approximate the architectural features, differentiation, and growth of human skin. This will be followed by a description of a protocol that enables HSEs to be adapted to monitor their response following wounding. These engineered human tissues provide powerful tools to study biological process in tissues that mimic the healing of human skin and of the epithelial tissue.

Cancer progression is associated with increased expression of basement membrane proteins in three-dimensional in vitro models of human oral cancer

BACKGROUND

Although basement membrane was traditionally considered an inert barrier that tumour cells had to cross before invasion into the surrounding stroma, recent studies suggest that basement membrane components are not only degraded during tumour progression, but also newly synthesised at the invasive front.

OBJECTIVE

This study aimed at evaluating (1) the expression of basement membrane proteins in human oral carcinogenesis and (2) the role that epithelial-mesenchymal interactions play on it, by using an in vitro oral cancer progression model.

MATERIAL AND METHODS

In vitro three-dimensional (3D) organotypic cultures of normal, early neoplastic and neoplastic human oral mucosa were developed by growing primary normal human oral keratinocytes, dysplastic human oral keratinocytes (DOK cell line), and neoplastic human oral keratinocytes (PE/CA-PJ15 cell line) on type I collagen biomatrices, with or without primary fibroblasts isolated from normal human oral mucosa. The cultured tissues were immunohistochemically assessed for the expression of the major basement membrane proteins laminin-332, type IV collagen, and fibronectin.

RESULTS

Expression of laminin-332, type IV collagen, and fibronectin was gradually more pronounced in neoplastic models when compared to normal mucosa models, and, with the exception of laminin-332, it was further enhanced by presence of fibroblasts. Deposition of type IV collagen at the epithelium-biomatrix interface occurred only in presence of fibroblasts, as well as the extracellular matrix deposition of fibronectin.

CONCLUSIONS

These findings, obtained in a 3D in vitro model that closely mirrors the in vivo human oral cancer progression, show an enhanced basement membrane protein expression during human oral cancer progression that is dependent on the epithelial-mesenchymal environment, respectively the existence of fibroblasts.

Co-culture of intestinal epithelial and stromal cells in 3D collagen-based environments

AIM

To investigate the co-culture of established intestinal epithelial cell lines and stromal cells in a series of collagen-based environments for production of tissue-engineered intestinal epithelium for in vitro investigations.

MATERIALS & METHODS

Intestinal epithelial cells were co-cultured with fibroblasts on a range of supporting collagen matrices including commercially available Promogran and on collagen-based gels.

RESULTS

Epithelial growth was achieved with one combination of vimentin-expressing stromal and cytokeratin-expressing intestinal epithelial cells grown on collagen gels supplemented with Matrigel, and held at an air-liquid interface.

CONCLUSIONS

Collagen-based gels can support the co-culture of intestinal epithelial and stromal cells resulting in the growth of an epithelium that has some morphological similarity to normal intestinal tissue.

Three-dimensional tissue models of normal and diseased skin

Over the last decade, the development of in vitro, human, three-dimensional (3D) tissue models, known as human skin equivalents (HSEs), has furthered understanding of epidermal cell biology and provided novel experimental systems. Signaling pathways that mediate the linkage between growth and differentiation function optimally when cells are spatially organized to display the architectural features seen in vivo, but are uncoupled and lost in two-dimensional culture systems. HSEs consist of a stratified squamous epithelium grown at an air-liquid interface on a collagen matrix populated with dermal fibroblasts. These 3D tissues demonstrate in vivo-like epithelial differentiation and morphology, and rates of cell division, similar to those found in human skin. This unit describes fabrication of HSEs, allowing the generation of human tissues that mimic the morphology, differentiation, and growth of human skin, as well as disease processes of cancer and wound re-epithelialization, providing powerful new tools for the study of diseases in humans.

The distributions of type IV collagen alpha chains in basement membranes of human epidermis and skin appendages

Distributions of type IV collagen alpha chains in the basement membrane (BM) of human skin and its appendages were analyzed by immunofluorescent microscopy using chain-specific monoclonal antibodies. The basement membrane beneath the epidermis contained [alpha1(IV)](2)alpha2(IV) and [alpha5(IV)](2)alpha6(IV) but no alpha3(IV)alpha4(IV)alpha5(IV); this held true for at the eccrine sweat glands and glandular ducts, sebaceous glands, hair follicles, and arrector muscles of hair. The secretary portion of the eccrine sweat glands was rich in [alpha1(IV)](2) alpha2(IV) and had less [alpha5(IV)](2)alpha6(IV), while [alpha5(IV)](2) alpha6(IV) was abundant in the ductal portion. In the subepidermal zone, alpha5(IV)/alpha6(IV) chain negative spots (1.9-15.0 microm) were frequently observed. Triple staining samples (Mel.2, alpha2(IV) and alpha5(IV) chains) showed that about 50% of epidermal melanocytes colocalized with such spots. Results suggest that these alpha5(IV)/alpha6(IV) chain negative spots of the subepidermal basement membrane have a particular relationship with melanocytes and are sites for certain interactions between the two.