Preparation and composition of alveolar extracellular matrix and incorporated basement membrane

Decellularized human-sized pulmonary scaffolds for lung tissue engineering: a comprehensive review

The ultimate goal of lung bioengineering is to produce transplantable lungs for human beings. Therefore, large-scale studies are of high importance. In this paper, we review the investigations on decellularization and recellularization of human-sized lung scaffolds. First, studies that introduce new ways to enhance the decellularization of large-scale lungs are reviewed, followed by the investigations on the xenogeneic sources of lung scaffolds. Then, decellularization and recellularization of diseased lung scaffolds are discussed to assess their usefulness for tissue engineering applications. Next, the use of stem cells in recellularizing acellular lung scaffolds is reviewed, followed by the case studies on the transplantation of bioengineered lungs. Finally, the remaining challenges are discussed, and future directions are highlighted.

How to build a lung: latest advances and emerging themes in lung bioengineering

Chronic respiratory diseases remain a major cause of morbidity and mortality worldwide. The only option at end-stage disease is lung transplantation, but there are not enough donor lungs to meet clinical demand. Alternative options to increase tissue availability for lung transplantation are urgently required to close the gap on this unmet clinical need. A growing number of tissue engineering approaches are exploring the potential to generate lung tissue ex vivo for transplantation. Both biologically derived and manufactured scaffolds seeded with cells and grown ex vivo have been explored in pre-clinical studies, with the eventual goal of generating functional pulmonary tissue for transplantation. Recently, there have been significant efforts to scale-up cell culture methods to generate adequate cell numbers for human-scale bioengineering approaches. Concomitantly, there have been exciting efforts in designing bioreactors that allow for appropriate cell seeding and development of functional lung tissue over time. This review aims to present the current state-of-the-art progress for each of these areas and to discuss promising new ideas within the field of lung bioengineering.

Small cell and non small cell lung cancer form metastasis on cellular 4D lung model

BACKGROUND

Metastasis is the main cause of death for lung cancer patients. The ex vivo 4D acellular lung model has been shown to mimic this metastatic process. However, the main concern is the model's lack of cellular components of the tumor's microenvironment. In this study, we aim to determine if the intact lung microenvironment will still allow lung cancer metastasis to form.

METHODS

We harvested a heart-lung block from a rat and placed it in a bioreactor after cannulating the pulmonary artery, trachea and tying the right main bronchus for 10-15 days without any tumor cells as a control group or with NSCLC (A549, H1299 or H460), SCLC (H69, H446 or SHP77) or breast cancer cell lines (MCF7 or MDAMB231) through the trachea. We performed lobectomy, H&E staining and IHC for human mitochondria to determine the primary tumor's growth and formation of metastatic lesions. In addition, we isolated circulating tumor cells (CTC) from the model seeded with GFP tagged cells.

RESULTS

In the control group, no gross tumor nodules were found, H&E staining showed hyperplastic cells and IHC showed no staining for human mitochondria. All of the models seeded with cancer cell lines formed gross primary tumor nodules that had microscopic characteristics of human cancer cells on H&E staining with IHC showing staining for human mitochondria. CTC were isolated for those cells labeled with GFP and they were viable in culture. Finally, all cell lines formed metastatic lesions with cells stained for human mitochondria.

CONCLUSION

The cellular ex vivo 4D model shows that human cancer cells can form a primary tumor, CTC and metastatic lesions in an intact cellular environment. This study suggests that the natural matrix scaffold is the only necessary component to drive metastatic progression and that cellular components play a role in modulating tumor progression.

The clinical use of regenerative therapy in COPD

Regenerative or stem cell therapy is an emerging field of treatment based on stimulation of endogenous resident stem cells or administration of exogenous stem cells to treat diseases or injury and to replace malfunctioning or damaged tissues. Current evidence suggests that in the lung, these cells may participate in tissue homeostasis and regeneration after injury. Animal and human studies have demonstrated that tissue-specific stem cells and bone marrow-derived cells contribute to lung tissue regeneration and protection, and thus administration of exogenous stem/progenitor cells or humoral factors responsible for the activation of endogenous stem/progenitor cells may be a potent next-generation therapy for chronic obstructive pulmonary disease. The use of bone marrow-derived stem cells could allow repairing and regenerate the damaged tissue present in chronic obstructive pulmonary disease by means of their engraftment into the lung. Another approach could be the stimulation of resident stem cells by means of humoral factors or photobiostimulation.

Can stem cells be used to generate new lungs? Ex vivo lung bioengineering with decellularized whole lung scaffolds

For patients with end-stage lung diseases, lung transplantation is the only available therapeutic option. However, the number of suitable donor lungs is insufficient and lung transplants are complicated by significant graft failure and complications of immunosuppressive regimens. An alternative to classic organ replacement is desperately needed. Engineering of bioartificial organs using either natural or synthetic scaffolds is an exciting new potential option for generation of functional pulmonary tissue for human clinical application. Natural organ scaffolds can be generated by decellularization of native tissues; these acellular scaffolds retain the native organ ultrastructure and can be seeded with autologous cells towards the goal of regenerating functional tissues. Several decellularization strategies have been employed for lungs; however, there is no consensus on the optimal approach. A variety of cell types have been investigated as potential candidates for effective recellularization of acellular lung scaffolds. Candidate cells that might be best utilized are those which can be easily and reproducibly isolated, expanded in vitro, seeded onto decellularized matrices, induced to differentiate into pulmonary lineage cells, and which survive to functional maturity. Whole lung cell suspensions, endogenous progenitor cells, embryonic and adult stem cells and induced pluripotent stem (iPS) cells have been investigated for their applicability to repopulate acellular lung matrices. Ideally, patient-derived autologous cells would be used for lung recellularization as they have the potential to reduce the need for post-transplant immunosuppression. Several studies have performed transplantation of rudimentary bioengineered lung scaffolds in animal models with limited, short-term functionality but much further study is needed.

Gene expression profile of A549 cells from tissue of 4D model predicts poor prognosis in lung cancer patients

The tumor microenvironment plays an important role in regulating cell growth and metastasis. Recently, we developed an ex vivo lung cancer model (four dimensional, 4D) that forms perfusable tumor nodules on a lung matrix that mimics human lung cancer histopathology and protease secretion pattern. We compared the gene expression profile (Human OneArray v5 chip) of A549 cells, a human lung cancer cell line, grown in a petri dish (two-dimensional, 2D), and of the same cells grown in the matrix of our ex vivo model (4D). Furthermore, we obtained gene expression data of A549 cells grown in a petri dish (2D) and matrigel (three-dimensional, 3D) from a previous study and compared the 3D expression profile with that of 4D. Expression array analysis showed 2,954 genes differentially expressed between 2D and 4D. Gene ontology (GO) analysis showed upregulation of several genes associated with extracellular matrix, polarity and cell fate and development. Moreover, expression array analysis of 2D vs. 3D showed 1,006 genes that were most differentially expressed, with only 36 genes (4%) having similar expression patterns as observed between 2D and 4D. Finally, the differential gene expression signature of 4D cells (vs. 2D) correlated significantly with poor survival in patients with lung cancer (n = 1,492), while the expression signature of 3D vs. 2D correlated with better survival in lung cancer patients with lung cancer. As patients with larger tumors have a worse rate of survival, the ex vivo 4D model may be a good mimic of natural progression of tumor growth in lung cancer patients.

Human lung cancer cells grown in an ex vivo 3D lung model produce matrix metalloproteinases not produced in 2D culture

We compared the growth of human lung cancer cells in an ex vivo three-dimensional (3D) lung model and 2D culture to determine which better mimics lung cancer growth in patients. A549 cells were grown in an ex vivo 3D lung model and in 2D culture for 15 days. We measured the size and formation of tumor nodules and counted the cells after 15 days. We also stained the tissue/cells for Ki-67, and Caspase-3. We measured matrix metalloproteinase (MMP) levels in the conditioned media and in blood plasma from patients with adenocarcinoma of the lung. Organized tumor nodules with intact vascular space formed in the ex vivo 3D lung model but not in 2D culture. Proliferation and apoptosis were greater in the ex vivo 3D lung model compared to the 2D culture. After 15 days, there were significantly more cells in the 2D culture than the 3D model. MMP-1, MMP-9, and MMP-10 production were significantly greater in the ex vivo 3D lung model. There was no production of MMP-9 in the 2D culture. The patient samples contained MMP-1, MMP-2, MMP-9, and MMP-10. The human lung cancer cells grown on ex vivo 3D model form perfusable nodules that grow over time. It also produced MMPs that were not produced in 2D culture but seen in human lung cancer patients. The ex vivo 3D lung model may more closely mimic the biology of human lung cancer development than the 2D culture.

Human lung cancer cells grown on acellular rat lung matrix create perfusable tumor nodules

BACKGROUND

Extracellular matrix allows lung cancer to form its shape and grow. Recent studies on organ reengineering for orthotopic transplantation have provided a new avenue for isolating purified native matrix to use for growing cells. Whether human lung cancer cells grown in a decellularized rat lung matrix would create perfusable human lung cancer nodules was tested.

METHODS

Rat lungs were harvested and native cells were removed using sodium dodecyl sulfate and Triton X-100 in a decellularization chamber to create a decellularized rat lung matrix. Human A549, H460, or H1299 lung cancer cells were placed into the decellularized rat lung matrix and grown in a customized bioreactor with perfusion of oxygenated media for 7 to 14 days.

RESULTS

Decellularized rat lung matrix showed preservation of matrix architecture devoid of all rat cells. All three human lung cancer cell lines grown in the bioreactor developed tumor nodules with intact vasculature. Moreover, the lung cancer cells developed a pattern of growth similar to the original human lung cancer.

CONCLUSIONS

Overall, this study shows that human lung cancer cells form perfusable tumor nodules in a customized bioreactor on a decellularized rat lung matrix created by a customized decellularization chamber. The lung cancer cells grown in the matrix had features similar to the original human lung cancer. This ex vivo model can be used potentially to gain a deeper understanding of the biologic processes involved in human lung cancer.

Localization of collagen in the rat lung: biochemical quantitation of types I and III collagen in small airways, vessels, and parenchyma

The marked insolubility of pulmonary collagen has limited its accurate biochemical quantitation in small samples of lung and other tissues. We have recently developed a microassay based on radioisotope dilution techniques that we have used for the accurate determination of types I and III collagen in extremely small tissue samples. By applying this method to carefully dissected small airways and vessels and samples of parenchymal tissue of rat lungs, we have localized and quantitated biochemically the type I and III structural collagens of the lung. Large pulmonary arteries are the units richest in these interstitial collagen types on the basis of dried tissue weight (50 micrograms/100 micrograms dried tissue). Amounts of both types I and III collagen are considerably lower in the alveolar domain than in vessels and airways of the rat lung. The proportion of tissue composed of these collagen types decreases centripetally in rat pulmonary arteries, but increases in the bronchial tree. The relative proportions of type I and type III remain constant in all the structures tested. The higher total amount of collagen in the nonalveolar domain has implications for biochemical studies based on whole lung samples.

Detecting proteoglycans immobilized on positively charged nylon

Proteoglycans (PG) immobilized on positively charged Nylon 66 are detected readily by staining with Alcian blue. With the exception of hyaluronic acid, free glycosaminoglycans appear unreactive when treated similarly. Immobilization was performed by dot blotting or by electrophoretic transblotting from various gel supports. When transblotted to positively charged Nylon 66 from large-pore agarose-acrylamide gels, levels of 10-50 ng of PG could be detected by Alcian blue staining. This procedure appeared to be nearly 10(2) times more sensitive than staining of gels with toluidine blue. The transblot and staining procedure also appears to be effective with PG separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and was applied to a preparation enriched in basement membrane components.

Cytochemistry of the gas-exchange area in vertebrate lungs

Considerable progress has been made in the localization of chemical substances within the gas-exchange zones of vertebrate lungs since cytochemical techniques suitable for use with the electron microscope have been developed. The light microscope, an instrument with an effective resolution limit of about 0.2 micron, is ill-suited for studying regions such as these where small tissue elements are arranged in a complex manner. A wide range of acid hydrolases have been detected in the vacuoles and dense bodies of alveolar macrophages by means of cytochemical techniques. The enzymes demonstrated in this way include acid phosphatase, aryl sulphatase, cathepsin D, beta-glucuronidase, acetyl glucosaminidase, nonspecific esterase, dipeptidyl peptidase II and dipeptidyl peptidase IV. Such enzymes are, of course, to be expected in the lysosomes of cells which have a primary phagocytic role. Nevertheless, it must be confessed that very little is yet known about the actual mechanism of phagocytosis or of the fate of the digested material. It is fortunate, however, that some of the tools which are likely to be of value in research on these aspects of macrophage function are currently being developed. Of particular interest in this connection are the immunocytochemical techniques which permit the localization of surface-associated antigens and intracellular contractile proteins. It must be emphasized that phagocytosis is not the only function of macrophages in the gas-exchange zone of the lung. These cells are thought to be involved in the presentation of exogenous antigenic material to the reactive cells of the lymphoid system. Recent research has also indicated that mammalian alveolar macrophages synthesize a diverse range of substances. Furthermore, the elastases associated with pulmonary macrophages are now thought to be involved in the pathogenesis of emphysema. All of the above-mentioned activities are of great biological and clinical significance and, consequently, merit the cytochemists' attention in future. The epithelial lining of the greater part of the pulmonary gas-exchange area is composed of type I pneumonocytes. In terms of ultrastructure, these are very specialized cells; their extensive and highly-attenuated cytoplasmic processes form the outer layer of the air-blood barrier. No special carrier systems have been identified within type I pneumonocytes and this is in keeping with the claims that oxygen is transferred across the alveolar tissue barrier by a process of simple diffusion. Type II pneumonocytes, in contrast, have considerable metabolic activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Repopulation of a human alveolar matrix by adult rat type II pneumocytes in vitro. A novel system for type II pneumocyte culture

This paper describes the preparation of lung acellular alveolar matrix fragments and culture of rat type II pneumocytes directly on the alveolar epithelial basement membrane, thereby permitting study of the effect of lung basement membrane on the morphology and function of type II cells. Collagen types I, III, IV and V, laminin and fibronectin were located by immunofluorescence in the lung matrix with the same patterns as those described for the normal human lung. Transmission electron microscopy (TEM) of the fragments revealed intact epithelial and endothelial basement membranes. The matrix maintained the normal three-dimensional alveolar architecture. Glycosaminoglycans were still present by Alcian Blue staining. Isolated adult rat type II pneumocytes cultured on 150 micron thick fragments of acellular human alveolar extracellular matrix undergo gradual cytoplasmic flattening, with loss of lamellar bodies, mitochondria, and surface microvilli. These changes are similar to the in vivo differentiation of type II pneumocytes into type I pneumocytes. The type II pneumocyte behaviour on the lung epithelial basement membrane contrasted sharply with that of the same cell type cultured on a human amnionic basement membrane. On the latter surface the cells retained their cuboidal shape, lamellar bodies and surface microvilli for up to 8 days. These observations suggest that the basement membranes from different organ systems exert differing influences on the morphology and function of type II pneumocytes and that the alveolar and amnionic basement membranes may have differing three-dimensional organizations. The technique of direct culture of type II cells on the lung basement membrane provides a useful tool for studying the modulating effect of the basement membrane on alveolar epithelial cells.

The involvement of type IV collagen in Goodpasture's syndrome

Goodpasture's syndrome, involving lung and kidney, is considered to be caused by autoantibodies to basement membranes. This paper has described the isolation and identification of the antigen, which is isolated from collagenase digests of glomerular basement membrane, as a monomer protein of 26,000 daltons and two dimers of about 50,000 daltons. Further analyses indicated that the antigenic protein is derived from the globular domain of type IV collagen corresponding to the NCl peptide. All 22 patients with Goodpasture's syndrome studied had circulating antibodies to this antigen, a few had additional antibodies to laminin, and only one also had antibodies to the 7S collagen domain. No other patient with glomerulonephritis had circulating antibodies to the antigen. The isolated protein can therefore be used in an assay specific for Goodpasture's syndrome. Interestingly the protein antigen could be identified in glomerular, lung, and placenta basement membranes, although the components reacting with the antibodies represented different proportions of the preparations.

Isolation and characterization of a rat lung fraction enriched in alveolar wall basement membranes

Separation of lung alveolar basement membranes from interstitial connective tissue protein has proved difficult, and a pure preparation of alveolar wall basement membranes (AWBM) is not available. We have modified a technique employing the detergent Triton X-100 for isolating AWBM from rat lungs by adding a step utilizing human skin collagenase (HSC), a highly purified enzyme obtained from skin fibroblasts that specifically cleaves non-basement membrane collagens. Triton extraction of both lungs yields 15-20 mg of basement membrane-enriched material referred to as crude fraction (CF). Ultrastructural studies show that CF includes both epithelial and endothelial basement membranes that appear similar to their in vivo counterparts and contain heparan sulfate proteoglycans. Extraction of type IV collagen is documented by the appearance of highly glycosylated hydroxylysine. This CF contains minimal amounts of contaminating elastin but significant amounts of interstitial collagens. CF was further purified for biochemical studies by incubation with HSC. HSC solubilized 20% of CF hydroxyproline resulting in a final fraction highly enriched in AWBM. Lung minces incubated in tritiated lysine produced a CF extract rich in newly formed type IV collagen, showing that lung tissue synthesizes AWBM collagen in vitro.

Preparation of cell-free extracellular matrix from human peripheral nerve

The extracellular matrix of human peripheral nerve, which is mainly basement membrane and fibrillar collagen, has been prepared by a procedure involving extensive detergent extraction of isolated endoneurium and perineurium obtained from various nerves. The ultrastructure of the isolated nerve extracellular matrix was indistinguishable from that seen in sections of intact nerve, indicating that the extraction procedure preserved the morphological integrity of these connective tissue components. The amino acid and carbohydrate compositions of the nerve extracellular matrix preparations were typically collagenous in nature containing a high content of glycine, proline, 4-hydroxyproline, and alanine and significant amounts of lysine and hydroxylysine. The preparations contained virtually no 3-hydroxyproline and low content of glucose and galactose compared to pure basement membranes, indicating that interstitial rather than basement membrane collagens predominated. This preparation appears well-suited to both the ultrastructural and biochemical study of the extracellular matrix of peripheral nerve.