Laminin isoforms and lung development: All isoforms are not equal

Future prospects for tissue engineered lung transplantation: decellularization and recellularization-based whole lung regeneration

The shortage of donor lungs for transplantation causes a significant number of patient deaths. The availability of laboratory engineered, functional organs would be a major advance in meeting the demand for organs for transplantation. The accumulation of information on biological scaffolds and an increased understanding of stem/progenitor cell behavior has led to the idea of generating transplantable organs by decellularizing an organ and recellularizing using appropriate cells. Recellularized solid organs can perform organ-specific functions for short periods of time, which indicates the potential for the clinical use of engineered solid organs in the future.   The present review provides an overview of progress and recent knowledge about decellularization and recellularization-based approaches for generating tissue engineered lungs. Methods to improve decellularization, maturation of recellularized lung, candidate species for transplantation and future prospects of lung bioengineering are also discussed.

Enhanced reseeding of decellularized rodent lungs with mouse embryonic stem cells

Repopulation of decellularized lung scaffolds (DLS) is limited due to alterations in the repertoire and ratios of the residual extracellular matrix (ECM) proteins, characterized by e.g., the retention of type I collagen and loss of glycoproteins. We hypothesized that pre-treatment of decellularized matrices with defined ECM proteins, which match the repertoire of integrin receptors expressed by the cells to be seeded (e.g., embryonic stem cells) can increase the efficacy of the reseeding process. To test this hypothesis, we first determined the integrin receptors profile of mouse embryonic stem cells (mESCs). Mouse ESCs express α3, α5, α6, α9 and β1, but not α1, α2 and α4 integrin subunits, as established by Western blotting and adhesion to laminin and fibronectin, but not to collagens type I and IV. Reseeding of DLS with mESCs was inefficient (6.9 ± 0.5%), but was significantly enhanced (2.3 ± 0.1 fold) by pre-treating the scaffolds with media conditioned by A549 human lung adenocarcinoma cells, which we found to contain ∼5 μg/ml laminin. Furthermore, pre-treatment with A549-conditioned media resulted in a significantly more uniform distribution of the seeded mESCs throughout the engineered organ as compared to untreated DLS. Our study may advance whole lung engineering by stressing the importance of matching the integrin receptor repertoire of the seeded cells and the cell binding motifs of DLS.

Transmission electron microscopy analysis of epithelial basement membrane repair in rabbit corneas with haze

PURPOSE

To assess the ultrastructure of the epithelial basement membrane using transmission electron microscopy (TEM) in rabbit corneas with and without subepithelial stroma opacity (haze).

METHODS

Two groups of eight rabbits each were included in this study. Photorefractive keratectomy (PRK) was performed using an excimer laser. The first group had -4.5-diopter (-4.5D) PRK and the second group had -9.0D PRK. Contralateral eyes were unwounded controls. Rabbits were sacrificed at 4 weeks after surgery. Immunohistochemical analysis was performed to detect the myofibroblast marker α-smooth muscle actin (SMA). TEM was performed to analyze the ultrastructure of the epithelial basement membrane and stroma.

RESULTS

At 4 weeks after PRK, α-SMA+ myofibroblasts were present at high density in the subepithelial stroma of rabbit eyes that had -9.0D PRK, along with prominent disorganized extracellular matrix, whereas few myofibroblasts and little disorganized extracellular matrix were noted in eyes that had -4.5D PRK. The epithelial basement membrane was irregular and discontinuous and lacking typical morphology in all corneas at 1 month after -9D PRK compared to corneas at 1 month in the -4.5D PRK group.

CONCLUSIONS

The epithelial basement membrane acts as a critical modulator of corneal wound healing. Structural and functional defects in the epithelial basement membrane correlate to both stromal myofibroblast development from precursor cells and continued myofibroblast viability, likely through the modulation of epithelial-stromal interactions mediated by cytokines. Prolonged stromal haze in the cornea is associated with abnormal regeneration of the epithelial basement membrane.

Engineering a blood-retinal barrier with human embryonic stem cell-derived retinal pigment epithelium: transcriptome and functional analysis

Retinal degenerations are a major cause of impaired vision in the elderly. Degenerations originate in either photoreceptors or the retinal pigment epithelium (RPE). RPE forms the outer blood-retinal barrier and functions intimately with photoreceptors. Animal models and cultures of RPE are commonly used to screen potential pharmaceuticals or explore RPE replacement therapy, but human RPE differs from that of other species. Human RPE forms a barrier using tight junctions composed of a unique set of claudins, proteins that determine the permeability and selectivity of tight junctions. Human adult RPE fails to replicate these properties in vitro. To develop a culture model for drug development and tissue-engineering human retina, RPE were derived from human embryonic stem cells (hESCs). Barrier properties of RPE derived from the H1 and H9 hESC lines were compared with a well-regarded model of RPE function, human fetal RPE isolated from 16-week-gestation fetuses (hfRPE). A serum-free medium (SFM-1) that enhanced the redifferentiation of hfRPE in culture also furthered the maturation of hESC-derived RPE. In SFM-1, the composition, selectivity, and permeability of tight junctions were similar to those of hfRPE. Comparison of the transcriptomes by RNA sequencing and quantitative reverse transcription-polymerase chain reaction revealed a high correlation between the hESCs and hfRPE, but there were notable differences in the expression of adhesion junction and membrane transport genes. These data indicated that hESC-derived RPE is highly differentiated but may be less mature than RPE isolated from 16-week fetuses. The study identified a panel of genes to monitor the maturation of RPE.

A nonhuman primate model of lung regeneration: detergent-mediated decellularization and initial in vitro recellularization with mesenchymal stem cells

Currently, patients with end-stage lung disease are limited to lung transplantation as their only treatment option. Unfortunately, the lungs available for transplantation are few. Moreover, transplant recipients require life-long immune suppression to tolerate the transplanted lung. A promising alternative therapeutic strategy is decellularization of whole lungs, which permits the isolation of an intact scaffold comprised of innate extracellular matrix (ECM) that can theoretically be recellularized with autologous stem or progenitor cells to yield a functional lung. Nonhuman primates (NHP) provide a highly relevant preclinical model with which to assess the feasibility of recellularized lung scaffolds for human lung transplantation. Our laboratory has successfully accomplished lung decellularization and initial stem cell inoculation of the resulting ECM scaffold in an NHP model. Decellularization of normal adult rhesus macaque lungs as well as the biology of the resulting acellular matrix have been extensively characterized. Acellular NHP matrices retained the anatomical and ultrastructural properties of native lungs with minimal effect on the content, organization, and appearance of ECM components, including collagen types I and IV, laminin, fibronectin, and sulfated glycosaminoglycans (GAG), due to decellularization. Proteomics analysis showed enrichment of ECM proteins in total tissue extracts due to the removal of cells and cellular proteins by decellularization. Cellular DNA was effectively removed after decellularization (∼92% reduction), and the remaining nuclear material was found to be highly disorganized, very-low-molecular-weight fragments. Both bone marrow- and adipose-derived mesenchymal stem cells (MSC) attach to the decellularized lung matrix and can be maintained within this environment in vitro, suggesting that these cells may be promising candidates and useful tools for lung regeneration. Analysis of decellularized lung slice cultures to which MSC were seeded showed that the cells attached to the decellularized matrix, elongated, and proliferated in culture. Future investigations will focus on optimizing the recellularization of NHP lung scaffolds toward the goal of regenerating pulmonary tissue. Bringing this technology to eventual human clinical application will provide patients with an alternative therapeutic strategy as well as significantly reduce the demand for transplantable organs and patient wait-list time.

A rapid lung de-cellularization protocol supports embryonic stem cell differentiation in vitro and following implantation

Pulmonary diseases represent a large portion of neonatal and adult morbidity and mortality. Many of these have no cure, and new therapeutic approaches are desperately needed. De-cellularization of whole organs, which removes cellular elements but leaves intact important extracellular matrix (ECM) proteins and three-dimensional architecture, has recently been investigated for ex vivo generation of lung tissues. As specific cell culture surfaces, including ECM composition, profoundly affect cell differentiation, this approach offers a potential means of using de-cellularized lungs to direct differentiation of embryonic and other types of stem/progenitor cells into lung phenotypes. Several different methods of whole-lung de-cellularization have been reported, but the optimal method that will best support re-cellularization and generation of lung tissues from embryonic stem cells (ESCs) has not been determined. We present a 24-h approach for de-cellularizing mouse lungs utilizing a detergent-based (Triton-X100 and sodium deoxycholate) approach with maintenance of three-dimensional lung architecture and ECM protein composition. Predifferentiated murine ESCs (mESCs), with phenotypic characteristics of type II alveolar epithelial cells, were seeded into the de-cellularized lung scaffolds. Additionally, we evaluated the effect of coating the de-cellularized scaffold with either collagen or Matrigel to determine if this would enhance cell adhesion and affect mechanics of the scaffold. Finally, we subcutaneously implanted scaffolds in vivo after seeding them with mESCs that are predifferentiated to express pro-surfactant protein C (pro-SPC). The in vivo environment supported maintenance of the pro-SPC-expressing phenotype and further resulted in vascularization of the implant. We conclude that a rapid detergent-based de-cellularization approach results in a scaffold that can maintain phenotypic evidence of alveolar epithelial differentiation of ESCs and support neovascularization after in vivo implantation.

Lung-specific loss of the laminin α3 subunit confers resistance to mechanical injury

Laminins are heterotrimeric glycoproteins of the extracellular matrix that are secreted by epithelial cells and which are crucial for the normal structure and function of the basement membrane. We have generated a mouse harboring a conditional knockout of α3 laminin (Lama3(fl/fl)), one of the main laminin subunits in the lung basement membrane. At 60 days after intratracheal treatment of adult Lama3(fl/fl) mice with an adenovirus encoding Cre recombinase (Ad-Cre), the protein abundance of α3 laminin in whole lung homogenates was more than 50% lower than that in control-treated mice, suggesting a relatively long half-life for the protein in the lung. Upon exposure to an injurious ventilation strategy (tidal volume of 35 ml per kg of body weight for 2 hours), the mice with a knockdown of the α3 laminin subunit had less severe injury, as shown by lung mechanics, histology, alveolar capillary permeability and survival when compared with Ad-Null-treated mice. Knockdown of the α3 laminin subunit resulted in evidence of lung inflammation. However, this did not account for their resistance to mechanical ventilation. Rather, the loss of α3 laminin was associated with a significant increase in the collagen content of the lungs. We conclude that the loss of α3 laminin in the alveolar epithelium results in an increase in lung collagen, which confers resistance to mechanical injury.

Haemophilus influenzae protein E binds to the extracellular matrix by concurrently interacting with laminin and vitronectin

Nontypeable Haemophilus influenzae (NTHi) causes otitis media and is commonly found in patients with chronic obstructive pulmonary disease (COPD). Adhesins are important for bacterial attachment and colonization. Protein E (PE) is a recently characterized ubiquitous 16 kDa adhesin with vitronectin-binding capacity that results in increased survival in serum. In addition to PE, NTHi utilizes Haemophilus adhesion protein (Hap) that binds to the basement-membrane glycoprotein laminin. We show that most clinical isolates bind laminin and that both Hap and PE are crucial for the NTHi-dependent interaction with laminin as revealed with different mutants. The laminin-binding region is located at the N-terminus of PE, and PE binds to the heparin-binding C-terminal globular domain of laminin. PE simultaneously attracts vitronectin and laminin at separate binding sites, proving the multifunctional nature of the adhesin. This previously unknown PE-dependent interaction with laminin may contribute to NTHi colonization, particularly in smokers with COPD.

Dystroglycan is involved in skin morphogenesis downstream of the Notch signaling pathway

Dystroglycan (Dg) is a transmembrane protein involved both in the assembly and maintenance of basement membrane structures essential for tissue morphogenesis, and the transmission of signals across the plasma membrane. We used a morpholino knockdown approach to investigate the function of Dg during Xenopus laevis skin morphogenesis. The loss of Dg disrupts epidermal differentiation by affecting the intercalation of multiciliated cells, deposition of laminin, and organization of fibronectin in the extracellular matrix (ECM). Depletion of Dg also affects cell-cell adhesion, as shown by the reduction of E-cadherin expression at the intercellular contacts, without affecting the distribution of β(1) integrins. This was associated with a decrease of cell proliferation, a disruption of multiciliated-cell intercalation, and the down-regulation of the transcription factor P63, a marker of differentiated epidermis. In addition, we demonstrated that inhibition or activation of the Notch pathway prevents and promotes transcription of X-dg. Our study showed for the first time in vivo that Dg, in addition to organizing laminin in the ECM, also acts as a key signaling component in the Notch pathway.

Glucocorticoid activity during lung maturation is essential in mesenchymal and less in alveolar epithelial cells

Corticosteroid treatment is an established therapy for preterm infants, and germline inactivation of the glucocorticoid receptor (GR) gene in the mouse leads to respiratory failure and postnatal lethality. Although glucocorticoids have been thought to critically act in epithelial cells inducing the functional maturation of the lung, inactivation of the GR gene exclusively in the epithelium of the developing murine lung did not impair survival. In contrast, mice lacking GR specifically in mesenchyme-derived cells displayed a phenotype strongly reminiscent of GR knockout animals and died immediately after birth. Detailed analysis of gene expression allows the conclusion that GR acts in cells of the fibroblast lineage controlling their proliferation rate and the composition of the extracellular matrix.

Integrin α6β4 identifies an adult distal lung epithelial population with regenerative potential in mice

Laminins and their integrin receptors are implicated in epithelial cell differentiation and progenitor cell maintenance. We report here that a previously unrecognized subpopulation of mouse alveolar epithelial cells (AECs) expressing the laminin receptor α6β4, but little or no pro-surfactant C (pro-SPC), is endowed with regenerative potential. Ex vivo, this subpopulation expanded clonally as progenitors but also differentiated toward mature cell types. Integrin β4 itself was not required for AEC proliferation or differentiation. An in vivo embryonic lung organoid assay, which we believe to be novel, was used to show that purified β4+ adult AECs admixed with E14.5 lung single-cell suspensions and implanted under kidney capsules self-organized into distinct Clara cell 10-kDa secretory protein (CC10+) airway-like and SPC+ saccular structures within 6 days. Using a bleomycin model of lung injury and an SPC-driven inducible cre to fate-map AECs, we found the majority of type II AECs in fibrotic areas were not derived from preexisting type II AECs, demonstrating that SPC- progenitor cells replenished type II AECs during repair. Our findings support the idea that there is a stable AEC progenitor population in the adult lung, provide in vivo evidence of AEC progenitor cell differentiation after parenchymal injury, and identify a strong candidate progenitor cell for maintenance of type II AECs during lung repair.

Nucleus pulposus cell-matrix interactions with laminins

The cells of the nucleus pulposus (NP) region of the intervertebral disc play a critical role in this tissue's generation and maintenance, and alterations in NP cell viability, metabolism, and phenotype with aging may be key contributors to progressive disc degeneration. Relatively little is understood about the phenotype of NP cells, including their cell-matrix interactions which may modulate phenotype and survival. Our previous work has identified strong and region-specific expression of laminins and laminin cell-surface receptors in immature NP tissues, suggesting laminin cell-matrix interactions are uniquely important to the biology of NP cells. Whether these observed tissue-level laminin expression patterns reflect functional adhesion behaviors for these cells is not known. In this study, we examined NP cell-matrix interactions with specific matrix ligands, including various laminin isoforms, using quantitative assays of cell attachment, spreading, and adhesion strength. NP cells were found to attach in higher numbers and exhibited rapid cell spreading and higher resistance to detachment force on two laminin isoforms (LM-511,LM-332) identified to be uniquely expressed in the NP region, as compared to another laminin isoform (LM-111) and several other matrix ligands (collagen, fibronectin). Additionally, NP cells were found to attach in higher numbers to laminins as compared to cells isolated from the disc's annulus fibrosus region. These findings confirm that laminin and laminin receptor expression documented in NP tissues translates into unique functional NP cell adhesion behaviors that may be useful tools for in vitro cell culture and biomaterials that support NP cells.

Integration of tight junctions and claudins with the barrier functions of the retinal pigment epithelium

The retinal pigment epithelium (RPE) forms the outer blood-retinal barrier by regulating the movement of solutes between the fenestrated capillaries of the choroid and the photoreceptor layer of the retina. Blood-tissue barriers use various mechanisms to accomplish their tasks including membrane pumps, transporters, and channels, transcytosis, metabolic alteration of solutes in transit, and passive but selective diffusion. The last category includes tight junctions, which regulate transepithelial diffusion through the spaces between neighboring cells of the monolayer. Tight junctions are extraordinarily complex structures that are dynamically regulated. Claudins are a family of tight junctional proteins that lend tissue specificity and selectivity to tight junctions. This review discusses how the claudins and tight junctions of the RPE differ from other epithelia and how its functions are modulated by the neural retina. Studies of RPE-retinal interactions during development lend insight into this modulation. Notably, the characteristics of RPE junctions, such as claudin composition, vary among species, which suggests the physiology of the outer retina may also vary. Comparative studies of barrier functions among species should deepen our understanding of how homeostasis is maintained in the outer retina. Stem cells provide a way to extend these studies of RPE-retinal interactions to human RPE.

The laminin β1-competing peptide YIGSR induces a hypercontractile, hypoproliferative airway smooth muscle phenotype in an animal model of allergic asthma

Background

Fibroproliferative airway remodelling, including increased airway smooth muscle (ASM) mass and contractility, contributes to airway hyperresponsiveness in asthma. In vitro studies have shown that maturation of ASM cells to a (hyper)contractile phenotype is dependent on laminin, which can be inhibited by the laminin-competing peptide Tyr-Ile-Gly-Ser-Arg (YIGSR). The role of laminins in ASM remodelling in chronic asthma in vivo, however, has not yet been established.

Methods

Using an established guinea pig model of allergic asthma, we investigated the effects of topical treatment of the airways with YIGSR on features of airway remodelling induced by repeated allergen challenge, including ASM hyperplasia and hypercontractility, inflammation and fibrosis. Human ASM cells were used to investigate the direct effects of YIGSR on ASM proliferation in vitro.

Results

Topical administration of YIGSR attenuated allergen-induced ASM hyperplasia and pulmonary expression of the proliferative marker proliferating cell nuclear antigen (PCNA). Treatment with YIGSR also increased both the expression of sm-MHC and ASM contractility in saline- and allergen-challenged animals; this suggests that treatment with the laminin-competing peptide YIGSR mimics rather than inhibits laminin function in vivo. In addition, treatment with YIGSR increased allergen-induced fibrosis and submucosal eosinophilia. Immobilized YIGSR concentration-dependently reduced PDGF-induced proliferation of cultured ASM to a similar extent as laminin-coated culture plates. Notably, the effects of both immobilized YIGSR and laminin were antagonized by soluble YIGSR.

Conclusion

These results indicate that the laminin-competing peptide YIGSR promotes a contractile, hypoproliferative ASM phenotype in vivo, an effect that appears to be linked to the microenvironment in which the cells are exposed to the peptide.

Serum free cultured bone marrow mesenchymal stem cells as a platform to characterize the effects of specific molecules

Human mesenchymal stem cells (hMSC) are easily isolated from the bone marrow by adherence to plastic surfaces. These cells show self-renewal capacity and multipotency. A unique feature of hMSC is their capacity to survive without serum. Under this condition hMSC neither proliferate nor differentiate but maintain their biological properties unaffected. Therefore, this should be a perfect platform to study the biological effects of defined molecules on these human stem cells. We show that hMSC treated for five days with retinoic acid (RA) in the absence of serum undergo several transcriptional changes causing an inhibition of ERK related pathways. We found that RA induces the loss of hMSC properties such as differentiation potential to either osteoblasts or adipocytes. We also found that RA inhibits cell cycle progression in the presence of proliferating signals such as epidermal growth factor (EGF) combined with basic fibroblast growth factor (bFGF). In the same manner, RA showed to cause a reduction in cell adhesion and cell migration. In contrast to these results, the addition of EGF+bFGF to serum free cultures was enough to upregulate ERK activity and induce hMSC proliferation and cell migration. Furthermore, the addition of these factors to differentiation specific media instead of serum was enough to induce either osteogenesis or adipogenesis. Altogether, our results show that hMSC's ability to survive without serum enables the identification of signaling factors and pathways that are involved in their stem cell biological characteristics without possible serum interferences.

The extracellular matrix in development and morphogenesis: a dynamic view

The extracellular matrix (ECM) is synthesized and secreted by embryonic cells beginning at the earliest stages of development. Our understanding of ECM composition, structure and function has grown considerably in the last several decades and this knowledge has revealed that the extracellular microenvironment is critically important for cell growth, survival, differentiation and morphogenesis. ECM and the cellular receptors that interact with it mediate both physical linkages with the cytoskeleton and the bidirectional flow of information between the extracellular and intracellular compartments. This review considers the range of cell and tissue functions attributed to ECM molecules and summarizes recent findings specific to key developmental processes. The importance of ECM as a dynamic repository for growth factors is highlighted along with more recent studies implicating the 3-dimensional organization and physical properties of the ECM as it relates to cell signaling and the regulation of morphogenetic cell behaviors. Embryonic cell and tissue generated forces and mechanical signals arising from ECM adhesion represent emerging areas of interest in this field.

Extracellular remodelling during oncogenic Ras-induced epithelial-mesenchymal transition facilitates MDCK cell migration

Epithelial-mesenchymal transition (EMT) describes a process whereby immotile epithelial cells escape structural constraints imposed by cellular architecture and acquire a phenotype characteristic of migratory mesenchymal cells. Implicated in carcinoma progression and metastasis, EMT has been the focus of several recent proteomics-based studies aimed at identifying new molecular players. To gain insights into extracellular mediators associated with EMT, we conducted an extensive proteomic analysis of the secretome from MDCK cells following oncogenic Ras-induced EMT (21D1 cells). Using Orbitrap technology and a label-free quantitative approach, differential expression of several secreted modulators were revealed. Proteomic findings were further substantiated by mRNA transcript expression analysis with 71% concordance. MDCK cells undergoing Ras-induced EMT remodel the extracellular matrix (ECM) via diminished expression of basement membrane constituents (collagen type IV and laminin 5), up-regulation of extracellular proteases (MMP-1, kallikreins -6 and -7), and increased production and secretion of ECM constituents (SPARC, collagen type I, fibulins -1 and -3, biglycan, and decorin). Collectively, these findings suggest that hierarchical regulation of a subset of extracellular effectors may coordinate a biological response during EMT that enhances cell motility. Transient silencing of MMP-1 in 21D1 cells via siRNA-mediated knockdown attenuated cell migration. Many of the secretome proteins identified broaden our understanding of the EMT process.

Role of dermal-epidermal basement membrane zone in skin, cancer, and developmental disorders

The dermal-epidermal basement membrane zone is an important epithelial and stromal interface, consisting of an intricately organized collection of intracellular, transmembrane, and extracellular matrix proteins. The basement membrane zone has several main functions including acting as a permeability barrier, forming an adhesive interface between epithelial cells and the underlying matrix, and controlling cellular organization and differentiation. This article identifies key molecular players of the dermal-epidermal membrane zone, and highlights recent research studies that have identified structural and functional roles of these components in the context of various blistering, neoplastic, and developmental syndromes.

Integrin signaling and lung cancer

The poor prognosis of most non small cell lung carcinomas is due to their ability to efficiently invade surrounding tissues and blood vessels, finally metastasizing to distant organs. Integrin mediated adhesive interaction with the surrounding extracellular matrix is a key limiting step in the regulation of the invasive properties of several cancer cell types. Here, we examine the rising evidences about the role that integrins can play in the physiopathology of non small cell lung carcinomas by regulating cell adhesion as well as the activation of growth factors and the traffic of their cognate receptors. Modulation of the signaling pathways controlled by integrins in lung cancer cells might offer the opportunity to design and develop new drugs that might be successfully combined with conventional chemotherapy and radiotherapy.

The developmental roles of the extracellular matrix: beyond structure to regulation

Cells in multicellular organisms are surrounded by a complex three-dimensional macromolecular extracellular matrix (ECM). This matrix, traditionally thought to serve a structural function providing support and strength to cells within tissues, is increasingly being recognized as having pleiotropic effects in development and growth. Elucidation of the role that the ECM plays in developmental processes has been significantly advanced by studying the phenotypic and developmental consequences of specific genetic alterations of ECM components in the mouse. These studies have revealed the enormous contribution of the ECM to the regulation of key processes in morphogenesis and organogenesis, such as cell adhesion, proliferation, specification, migration, survival, and differentiation. The ECM interacts with signaling molecules and morphogens thereby modulating their activities. This review considers these advances in our understanding of the function of ECM proteins during development, extending beyond their structural capacity, to embrace their new roles in intercellular signaling.

Development, repair and fibrosis: what is common and why it matters

The complex structure of the lung is developed sequentially, initially by epithelial tube branching and later by septation of terminal air sacs with accompanying coordinated growth of a variety of lung epithelial and mesenchymal cells. Groups of transcriptional factors, peptide growth factors and their intracellular signaling regulators, as well as extracellular matrix proteins are programmed to be expressed at appropriate levels in the right place at the right time to control normal lung formation. Studies of lung development and lung repair/fibrosis to date have discovered that many of the same factors that control normal development are also key players in lung injury repair and fibrosis. Transforming growth factor-beta (TGF-beta) family peptide signaling is a prime example. Lack of TGF-beta signaling results in abnormal lung branching morphogenesis and alveolarization during development, whereas excessive amounts of TGF-beta signaling cause severe hypoplasia in the immature lung and fibrosis in mature lung. This leads us to propose the 'Goldilocks' hypothesis of regulatory signaling in lung development and injury repair that everything must be done just right!

Absence of tissue inhibitor of metalloproteinases 3 disrupts alveologenesis in the mouse

Tissue inhibitors of metalloproteinases (TIMPs) regulate extracellular matrix (ECM) degradation by matrix metalloproteinases (MMPs) throughout lung development. We examined lungs from TIMP3 null mice and found significant air space enlargement compared with wild type (WT) animals during a time course spanning early alveologenesis (post-partum days 1, 5, 9 and 14). Trichrome staining revealed a similar pattern of collagen distribution in the walls of nascent alveoli; however, the alveolar walls of TIMP3 mutant mice appeared to be thinner than controls. Assessment of MMP2 and MMP9 activities by gelatin zymography demonstrated a significant elevation in the active form of MMP2 at post-partum days 1 and 5. Treatment of null pregnant dams with a broad spectrum synthetic metalloproteinase inhibitor, GM6001, on embryonic day 16.5 enhanced the formation of primitive alveoli during the saccular stage of lung development as evidenced by a partial, but significant, rescue of alveolar size in post-partum day 1 animals. We propose that increased MMP activity in the absence of TIMP3 enhances ECM proteolysis, upsetting proper formation of primitive alveolar septa during the saccular stage of alveologenesis. Therefore, TIMP3 indirectly regulates alveolar formation in the mouse. To our knowledge, ours is the first study to demonstrate that in utero manipulation of the TIMP/MMP proteolytic axis, to specifically inhibit proteolysis, significantly affects lung development.

Insulin-induced laminin expression promotes a hypercontractile airway smooth muscle phenotype

Airway smooth muscle (ASM) plays a key role in the development of airway hyperresponsiveness and remodeling in asthma, which may involve maturation of ASM cells to a hypercontractile phenotype. In vitro studies have indicated that long-term exposure of bovine tracheal smooth muscle (BTSM) to insulin induces a functional hypercontractile, hypoproliferative phenotype. Similarly, the extracellular matrix protein laminin has been found to be involved in both the induction and maintenance of a contractile ASM phenotype. Using BTSM, we now investigated the role of laminins in the insulin-induced hypercontractile, hypoproliferative ASM phenotype. The results demonstrate that insulin-induced hypercontractility after 8 days of tissue culture was fully prevented by combined treatment of BTSM-strips with the laminin competing peptides Tyr-Ile-Gly-Ser-Arg (YIGSR) and Arg-Gly-Asp-Ser (RGDS). YIGSR also prevented insulin-induced increases in sm-myosin expression and abrogated the suppressive effects of prolonged insulin treatment on platelet-derived growth factor-induced DNA synthesis in cultured cells. In addition, insulin time-dependently increased laminin alpha2, beta1, and gamma1 chain protein, but not mRNA abundance in BTSM strips. Moreover, as previously found for contractile protein accumulation, signaling through PI3-kinase- and Rho kinase-dependent pathways was required for the insulin-induced increase in laminin abundance and contractility. Collectively, our results indicate a critical role for beta1-containing laminins, likely laminin-211, in the induction of a hypercontractile, hypoproliferative ASM phenotype by prolonged insulin exposure. Increased laminin production by ASM could be involved in the increased ASM contractility and contractile protein expression in asthma. Moreover, the results may be of interest for the use of inhaled insulin administrations by diabetics.

Role for ephrinB2 in postnatal lung alveolar development and elastic matrix integrity

Alveoli are formed in the lung by the insertion of secondary tissue folds, termed septa, which are subsequently remodeled to form the mature alveolar wall. Secondary septation requires interplay between three cell types: endothelial cells forming capillaries, contractile interstitial myofibroblasts, and epithelial cells. Here, we report that postnatal lung alveolization critically requires ephrinB2, a ligand for Eph receptor tyrosine kinases expressed by the microvasculature. Mice homozygous for the hypomorphic knockin allele ephrinB2DeltaV/DeltaV, encoding mutant ephrinB2 with a disrupted C-terminal PDZ interaction motif, show severe postnatal lung defects including an almost complete absence of lung alveoli and abnormal and disorganized elastic matrix. Lung alveolar formation is not sensitive to loss of ephrinB2 cytoplasmic tyrosine phosphorylation sites. Postnatal day 1 mutant lungs show extracellular matrix alterations without differences in proportions of major distal cell populations. We conclude that lung alveolar formation relies on endothelial ephrinB2 function.

Dissection of the osteogenic effects of laminin-332 utilizing specific LG domains: LG3 induces osteogenic differentiation, but not mineralization

The overall mechanisms governing the role of laminins during osteogenic differentiation of human mesenchymal stem cells (hMSC) are poorly understood. We previously reported that laminin-332 induces an osteogenic phenotype in hMSC and does so through a focal adhesion kinase (FAK) and extracellular signal-related kinase (ERK) dependent pathway. We hypothesized that this is a result of integrin-ECM binding, and that it occurs via the known alpha3 LG3 integrin binding domain of laminin-332. To test this hypothesis we cultured hMSC on several different globular domains of laminin-332. hMSC adhered best to the LG3 domain, and this adhesion maximally activated FAK and ERK within 120 min. Prolonged culturing (8 or 16 days) of hMSC on LG3 led to activation of the osteogenic transcription factor Runx2 and expression of key osteogenic markers (osterix, bone sialoprotein 2, osteocalcin, alkaline phosphatase, extracellular calcium) in hMSC. LG3 domain binding did not increase matrix mineralization, demonstrating that the LG3 domain alone is not sufficient to induce complete osteogenic differentiation in vitro. We conclude that the LG3 domain mediates attachment of hMSC to laminin-332 and that this adhesion recapitulates most, but not all, of the osteogenic differentiation associated with laminin-5 binding to hMSC.

Focused microarray analysis of peripheral mononuclear blood cells from Churg-Strauss syndrome patients

DNA diagnostics are useful but are hampered by difficult ethical issues. Moreover, it cannot provide enough information on the environmental factors that are important for pathogenesis of certain diseases. However, this is not a problem for RNA diagnostics, which evaluate the expression of the gene in question. We here report a novel RNA diagnostics tool that can be employed with peripheral blood mononuclear cells (PBMCs). To establish this tool, we identified 290 genes that are highly expressed in normal PBMCs but not in TIG-1, a normal human fibroblast cell. These genes were entitled PREP after predominantly expressed in PBMC and included 50 uncharacterized genes. We then conducted PREP gene-focused microarray analysis on PBMCs from seven cases of Churg-Strauss syndrome (CSS), which is a small-vessel necrotizing vasculitis. We found that PREP135 (coactosin-like protein), PREP77 (prosaposin), PREP191 (cathepsin D), PREP234 (c-fgr), and PREP136 (lysozyme) were very highly up-regulated in all seven CSS patients. Another 28 genes were also up-regulated, albeit more moderately, and three were down-regulated in all CSS patients. The nature of these up- and down-regulated genes suggest that the immune systems of the patients are activated in response to invading microorganisms. These observations indicate that focused microarray analysis of PBMCs may be a practical, useful, and low-cost bedside diagnostics tool.

Role of basement membrane in EMMPRIN/CD147 induction in rat tracheal epithelial cells

Extracellular matrix metalloproteinase inducer (EMMPRIN) is a glycosylated transmembrane protein known to induce matrix metalloproteinases (MMPs). Although the expression of EMMPRIN is physiologically limited to fetal lung epithelium, the transcriptional regulation of this protein remains to be elucidated. We hypothesized that the interaction of epithelial cells with the basement membrane regulates EMMPRIN expression. The basement membrane has highly integrated architecture composed of specific extracellular matrix, such as laminins and type IV collagen, and exhibits multiple functions. We previously developed a structured basement membrane mimic, a synthesized basement membrane (sBM) substratum, in which laminin-111, a unique component of embryonic lungs, is incorporated. In the present study we quantified expression of EMMPRIN mRNA of rat tracheal epithelial cells cultured on sBM, laminin-111, type IV collagen, or laminin-332. EMMPRIN was upregulated on sBM and laminin-111, although this was not accompanied by MMP-9 induction. In contrast, type IV collagen and laminin-332 did not induce EMMPRIN. These findings suggest potential roles for basement membrane in the transcriptional regulation of tracheal epithelial EMMPRIN.

Laminin-332-integrin interaction: a target for cancer therapy?

For many years, extracellular matrix (ECM) was considered to function as a tissue support and filler. However, we now know that ECM proteins control many cellular events through their interaction with cell-surface receptors and cytoplasmic signaling pathways. For example, they regulate cell proliferation, cell division, cell adhesion, cell migration, and apoptosis. We focus in this review on a laminin isoform, laminin-332 (formerly termed laminin-5), a major component of the basement membrane (BM) of skin and other epithelial tissues. It is composed of 3 subunits (alpha3beta3 and gamma3 and interacts with at least two integrin receptors expressed by epithelial cells (alpha3beta1 and alpha6beta4 integrin. Mutations in either laminin-332 or integrin alpha6beta4 result in junctional epidermolysis bullosa, a blistering skin disease, while targeting of laminin-332 by autoantibodies in cicatricial pemphigoid leads to dysadhesion of epithelial cells from their underlying connective tissue. Abnormal expression of laminin-332 and its integrin receptors is also a hallmark of certain tumor types and is believed to promote invasion of colon, breast and skin cancer cells. Moreover, there is emerging evidence that laminin-332 and its protease degradation products are not only found at the leading front of several tumors but also likely induce and/or promote tumor cell migration. Thus, in this review, we focus specifically on the role of laminin-332 and its integrin receptors in adhesion, proliferation, and migration/invasion of cancer cells. Finally, we discuss strategies for the development of laminin-332-based antagonists for the treatment of malignant tumors.

Genetic dissection of the Nrf2-dependent redox signaling-regulated transcriptional programs of cell proliferation and cytoprotection

The beta zipper (bZip) transcription factor, nuclear factor erythroid 2, like 2 (Nrf2), acting via an antioxidant/electrophile response element, regulates the expression of several antioxidant enzymes and maintains cellular redox homeostasis. Nrf2 deficiency diminishes pulmonary expression of several antioxidant enzymes, rendering them highly susceptible to various mouse models of prooxidant-induced lung injury. We recently demonstrated that Nrf2 deficiency impairs primary cultured pulmonary epithelial cell proliferation and greatly enhances sensitivity to prooxidant-induced cell death. Glutathione (GSH) supplementation rescued cells from these defects associated with Nrf2 deficiency. To further delineate the mechanisms by which Nrf2, via redox signaling, regulates cellular protection and proliferation, we compared the global expression profiling of Nrf2-deficient cells with and without GSH supplementation. We found that GSH regulates the expression of various networks of transcriptional programs including 1) several antioxidant enzymes involved in cellular detoxification of reactive oxygen species and recycling of thiol status and 2) several growth factors, growth factor receptors, and integrins that are critical for cell growth and proliferation. We also found that Nrf2 deficiency enhances the expression levels of several genes encoding proinflammatory cytokines; however, GSH supplementation markedly suppressed their expression. Collectively, these findings uncover an important insight into the nature of genes regulated by Nrf2-dependent redox signaling through GSH that are involved in cellular detoxification and proliferation.

Compositional differences between infant and adult human corneal basement membranes

PURPOSE

Adult human corneal epithelial basement membrane (EBM) and Descemet's membrane (DM) components exhibit heterogeneous distribution. The purpose of the study was to identify changes of these components during postnatal corneal development.

METHODS

Thirty healthy adult corneas and 10 corneas from 12-day- to 3-year-old children were studied by immunofluorescence with antibodies against BM components.

RESULTS

Type IV collagen composition of infant corneal central EBM over Bowman's layer changed from alpha1-alpha2 to alpha3-alpha4 chains after 3 years of life; in the adult, alpha1-alpha2 chains were retained only in the limbal BM. Laminin alpha2 and beta2 chains were present in the adult limbal BM where epithelial stem cells are located. By 3 years of age, beta2 chain appeared in the limbal BM. In all corneas, limbal BM contained laminin gamma3 chain. In the infant DM, type IV collagen alpha1-alpha6 chains, perlecan, nidogen-1, nidogen-2, and netrin-4 were found on both faces, but they remained only on the endothelial face of the adult DM. The stromal face of the infant but not the adult DM was positive for tenascin-C, fibrillin-1, SPARC, and laminin-332. Type VIII collagen shifted from the endothelial face of infant DM to its stromal face in the adult. Matrilin-4 largely disappeared after the age of 3 years.

CONCLUSIONS

The distribution of laminin gamma3 chain, nidogen-2, netrin-4, matrilin-2, and matrilin-4 is described in the cornea for the first time. The observed differences between adult and infant corneal BMs may relate to changes in their mechanical strength, corneal cell adhesion and differentiation in the process of postnatal corneal maturation.

Laminins in the developing and adult human small intestine: relation with the functional absorptive unit

The expression of the five laminin alpha-chains was analyzed in the developing and mature human small intestine at the protein and transcript levels in order to further delineate specific involvement of individual laminins in relation to the epithelial cell state as defined along the functional crypt-villus axis. The results show that all of the alpha-laminin transcripts are expressed in significant amounts in the small intestine relative to a panel of other tissues and organs. Further analysis of their expression by indirect immunofluorescence and semi-quantitative and quantitative RT-PCR demonstrates a close correlation between transcript and protein expression, distinct epithelial and mesenchymal origins, as well as differential occurrence in intestinal basement membranes according to developmental stage, along the crypt-villus axis and in compartment-related experimental intestinal cell models. Taken together, the data point out the prime importance of alpha2-, alpha3-, and alpha5-containing laminins for the development and maintenance of the functional human intestinal epithelium.

Laminin-332 alters connexin profile, dye coupling and intercellular Ca2+ waves in ciliated tracheal epithelial cells

BACKGROUND

Tracheal epithelial cells are anchored to a dynamic basement membrane that contains a variety of extracellular matrix proteins including collagens and laminins. During development, wound repair and disease of the airway epithelium, significant changes in extracellular matrix proteins may directly affect cell migration, differentiation and events mediated by intercellular communication. We hypothesized that alterations in cell matrix, specifically type I collagen and laminin alpha3beta3gamma2 (LM-332) proteins within the matrix, directly affect intercellular communication in ciliated rabbit tracheal epithelial cells (RTEC).

METHODS

Functional coupling of RTEC was monitored by microinjection of the negatively charged fluorescent dyes, Lucifer Yellow and Alexa 350, into ciliated RTEC grown on either a LM-332/collagen or collagen matrix. Coupling of physiologically significant molecules was evaluated by the mechanism and extent of propagated intercellular Ca2+ waves. Expression of connexin (Cx) mRNA and proteins were assayed by reverse transcriptase - polymerase chain reaction and immunocytochemistry, respectively.

RESULTS

When compared to RTEC grown on collagen alone, RTEC grown on LM-332/collagen displayed a significant increase in dye transfer. Although mechanical stimulation of RTEC grown on either LM-332/collagen or collagen alone resulted in intercellular Ca2+ waves, the mechanism of transfer was dependent on matrix: RTEC grown on LM-332/collagen propagated Ca2+waves via extracellular purinergic signaling whereas RTEC grown on collagen used gap junctions. Comparison of RTEC grown on collagen or LM-332/collagen matrices revealed a reorganization of Cx26, Cx43 and Cx46 proteins.

CONCLUSION

Alterations in airway basement membrane proteins such as LM-332 can induce connexin reorganizations and result in altered cellular communication mechanisms that could contribute to airway tissue function.