Effects of extracellular matrix and neighboring cells on induction of human embryonic stem cells into retinal or retinal pigment epithelial progenitors

Characterizing Bruch's membrane: State-of-the-art imaging, computational segmentation, and biologic models in retinal disease and health

The Bruch's membrane (BM) is an acellular, extracellular matrix that lies between the choroid and retinal pigment epithelium (RPE). The BM plays a critical role in retinal health, performing various functions including biomolecule diffusion and RPE support. The BM is also involved in many retinal diseases, and insights into BM dysfunction allow for further understanding of the pathophysiology of various chorioretinal pathologies. Thus, characterization of the BM serves as an important area of research to further understand its involvement in retinal disease. In this article, we provide a review of various advancements in characterizing and visualizing the BM. We provide an overview of the BM in retinal health, as well as changes observed in aging and disease. We then describe current state-of-the-art imaging modalities and advances to further visualize the BM including various types of optical coherence tomography imaging, near-infrared reflectance (NIR), and autofluorescence imaging and tissue matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS). Following advances in imaging of the BM, we describe animal, cellular, and synthetic models that have been developed to further visualize the BM. Following this section, we provide an overview of deep learning in retinal imaging and describe advances in computational and artificial intelligence (AI) techniques to provide automated segmentation of the BM and BM opening. We conclude this section considering the clinical implications of these segmentation techniques. Ultimately, the diverse advances aimed to further characterize the BM may allow for deeper insights into the involvement of this critical structure in retinal health and disease.

Retina-on-chip: engineering functional in vitro models of the human retina using organ-on-chip technology

The retina is a complex and highly metabolic tissue in the back of the eye essential for human vision. Retinal diseases can lead to loss of vision in early and late stages of life, significantly affecting patients' quality of life. Due to its accessibility for surgical interventions and its isolated nature, the retina is an attractive target for novel genetic therapies and stem cell-based regenerative medicine. Understanding disease mechanisms and evaluating new treatments require relevant and robust experimental models. Retina-on-chip models are microfluidic organ-on-chip systems based on human tissue that capture multi-cellular interactions and tissue-level functions in vitro. Various retina-on-chip models have been described in literature. Some of them capture basic retinal barrier functions while others replicate key events underlying vision. In addition, some of these cellular systems have also been used in studies to explore their added value in retinal disease modeling. Most existing retina-on-chip models capture limited aspects of the phenotypic complexity of human diseases. This limitation arises primarily from the challenges related to controlled recapitulation of retinal function, including the relevant multi-cellular interactions and functional read-outs. In this review, we provide an update on recent advancements in the field of retina-on-chip, and we discuss the biotechnical strategies to further enhance the physiological relevance of the models. We emphasize that developers and researchers should prioritize the incorporation of the full spectrum of retinal complexity to effectuate a direct impact of retina-on-chip models in disease modeling and development of therapeutic strategies.

Decellularization of various tissues and organs through chemical methods

Due to the increase in demand for donor organs and tissues during the past 20 years, new approaches have been created. These methods include, for example, tissue engineering in vitro and the production of regenerative biomaterials for transplantation. Applying the natural extracellular matrix (ECM) as a bioactive biomaterial for clinical applications is a unique approach known as decellularization technology. Decellularization is the process of eliminating cells from an extracellular matrix while preserving its natural components including its structural and functional proteins and glycosaminoglycan. This can be achieved by physical, chemical, or biological processes. A naturally formed three-dimensional structure with a biocompatible and regenerative structure is the result of the decellularization process. Decreasing the biological factors and antigens at the transplant site reduces the risk of adverse effects including inflammatory responses and immunological rejection. Regenerative medicine and tissue engineering applications can benefit from the use of decellularization, a promising approach that provides a biomaterial that preserves its extracellular matrix.

Biomaterial engineering strategies for modeling the Bruch's membrane in age-related macular degeneration

Age-related macular degeneration, a multifactorial inflammatory degenerative retinal disease, ranks as the leading cause of blindness in the elderly. Strikingly, there is a scarcity of curative therapies, especially for the atrophic advanced form of age-related macular degeneration, likely due to the lack of models able to fully recapitulate the native structure of the outer blood retinal barrier, the prime target tissue of age-related macular degeneration. Standard in vitro systems rely on 2D monocultures unable to adequately reproduce the structure and function of the outer blood retinal barrier, integrated by the dynamic interaction of the retinal pigment epithelium, the Bruch's membrane, and the underlying choriocapillaris. The Bruch's membrane provides structural and mechanical support and regulates the molecular trafficking in the outer blood retinal barrier, and therefore adequate Bruch's membrane-mimics are key for the development of physiologically relevant models of the outer blood retinal barrier. In the last years, advances in the field of biomaterial engineering have provided novel approaches to mimic the Bruch's membrane from a variety of materials. This review provides a discussion of the integrated properties and function of outer blood retinal barrier components in healthy and age-related macular degeneration status to understand the requirements to adequately fabricate Bruch's membrane biomimetic systems. Then, we discuss novel materials and techniques to fabricate Bruch's membrane-like scaffolds for age-related macular degeneration in vitro modeling, discussing their advantages and challenges with a special focus on the potential of Bruch's membrane-like mimics based on decellularized tissue.

The mechanics of the retina: Müller glia role on retinal extracellular matrix and modelling

The retina is a highly heterogeneous tissue, both cell-wise but also regarding its extracellular matrix (ECM). The stiffness of the ECM is pivotal in retinal development and maturation and has also been associated with the onset and/or progression of numerous retinal pathologies, such as glaucoma, proliferative vitreoretinopathy (PVR), age-related macular degeneration (AMD), epiretinal membrane (ERM) formation or uveitis. Nonetheless, much remains unknown about the biomechanical milieu of the retina, and specifically the role that Müller glia play as principal mechanosensors and major producers of ECM constituents. So far, new approaches need to be developed to further the knowledge in the field of retinal mechanobiology for ECM-target applications to arise. In this review, we focus on the involvement of Müller glia in shaping and altering the retinal ECM under both physiological and pathological conditions and look into various biomaterial options to more accurately replicate the impact of matrix stiffness in vitro.

Extracellular Matrix: The Unexplored Aspects of Retinal Pathologies and Regeneration

Nearly a billion people worldwide are affected by vision-impairing conditions, with retinal degenerative diseases being a major cause of blindness. Unfortunately, such diseases are often permanent and progressive, resulting in further degeneration and loss of sight, due to the human retina possessing little, if any, regenerative capacity. Despite numerous efforts and great progress being made to understand the molecular mechanisms of these diseases and possible therapies, the majority of investigations focused on cell-intrinsic factors. However, the microenvironment surrounding retinal cells throughout these processes also plays an important role, though our current understanding of its involvement remains limited. Here we present a brief overview of the current state of the field of extracellular matrix studies within the retina and its potential roles in retinal diseases and potential therapeutic approaches.

Differentiating Human Pluripotent Stem Cells to Cardiomyocytes Using Purified Extracellular Matrix Proteins

Human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) can be differentiated into cardiomyocytes (hESC-CMs and iPSC-CMs, respectively), which hold great promise for cardiac regenerative medicine and disease modeling efforts. However, the most widely employed differentiation protocols require undefined substrates that are derived from xenogeneic (animal) products, contaminating resultant hESC- and iPSC-CM cultures with xenogeneic proteins and limiting their clinical applicability. Additionally, typical hESC- and iPSC-CM protocols produce CMs that are significantly contaminated by non-CMs and that are immature, requiring lengthy maturation procedures. In this review, we will summarize recent studies that have investigated the ability of purified extracellular matrix (ECM) proteins to support hESC- and iPSC-CM differentiation, with a focus on commercially available ECM proteins and coatings to make such protocols widely available to researchers. The most promising of the substrates reviewed here include laminin-521 with laminin-221 together or Synthemax (a synthetic vitronectin-based peptide coating), which both resulted in highly pure CM cultures. Future efforts are needed to determine whether combinations of specific purified ECM proteins or derived peptides could further improve CM maturation and culture times, and significantly improve hESC- and iPSC-CM differentiation protocols.

Bioengineering approaches for modelling retinal pathologies of the outer blood-retinal barrier

Alterations of the junctional complex of the outer blood-retinal barrier (oBRB), which is integrated by the close interaction of the retinal pigment epithelium, the Bruch's membrane, and the choriocapillaris, contribute to the loss of neuronal signalling and subsequent vision impairment in several retinal inflammatory disorders such as age-related macular degeneration and diabetic retinopathy. Reductionist approaches into the mechanisms that underlie such diseases have been hindered by the absence of adequate in vitro models using human cells to provide the 3D dynamic architecture that enables expression of the in vivo phenotype of the oBRB. Conventional in vitro cell models are based on 2D monolayer cellular cultures, unable to properly recapitulate the complexity of living systems. The main drawbacks of conventional oBRB models also emerge from the cell sourcing, the lack of an appropriate Bruch's membrane analogue, and the lack of choroidal microvasculature with flow. In the last years, the advent of organ-on-a-chip, bioengineering, and stem cell technologies is providing more advanced 3D models with flow, multicellularity, and external control over microenvironmental properties. By incorporating additional biological complexity, organ-on-a-chip devices can mirror physiologically relevant properties of the native tissue while offering additional set ups to model and study disease. In this review we first examine the current understanding of oBRB biology as a functional unit, highlighting the coordinated contribution of the different components to barrier function in health and disease. Then we describe recent advances in the use of pluripotent stem cells-derived retinal cells, Bruch's membrane analogues, and co-culture techniques to recapitulate the oBRB. We finally discuss current advances and challenges of oBRB-on-a-chip technologies for disease modelling.

Application of Collagen I and IV in Bioengineering Transparent Ocular Tissues

Collagens represent a major group of structural proteins expressed in different tissues and display distinct and variable properties. Whilst collagens are non-transparent in the skin, they confer transparency in the cornea and crystalline lens of the eye. There are 28 types of collagen that all share a common triple helix structure yet differ in the composition of their α-chains leading to their different properties. The different organization of collagen fibers also contributes to the variable tissue morphology. The important ability of collagen to form different tissues has led to the exploration and application of collagen as a biomaterial. Collagen type I (Col-I) and collagen type IV (Col-IV) are the two primary collagens found in corneal and lens tissues. Both collagens provide structure and transparency, essential for a clear vision. This review explores the application of these two collagen types as novel biomaterials in bioengineering unique tissue that could be used to treat a variety of ocular diseases leading to blindness.

Mechanistic dissection of diabetic retinopathy using the protein-metabolite interactome

Purpose

The current study aims to determine the molecular mechanisms of diabetic retinopathy (DR) using the protein-protein interactome and metabolome map. We examined the protein network of novel biomarkers of DR for direct (physical) and indirect (functional) interactions using clinical target proteins in different models.

Methods

We used proteomic tools including 2-dimensional gel electrophoresis, mass spectrometry analysis, and database search for biomarker identification using in vivo murine and human model of diabetic retinopathy and in vitro model of oxidative stress. For the protein interactome and metabolome mapping, various bioinformatic tools that include STRING and OmicsNet were used.

Results

We uncovered new diabetic biomarkers including prohibitin (PHB), dynamin 1, microtubule-actin crosslinking factor 1, Toll-like receptor (TLR 7), complement activation, as well as hypothetical proteins that include a disintegrin and metalloproteinase (ADAM18), vimentin III, and calcium-binding C2 domain-containing phospholipid-binding switch (CAC2PBS) using a proteomic approach. Proteome networks of protein interactions with diabetic biomarkers were established using known DR-related proteome data. DR metabolites were interconnected to establish the metabolome map. Our results showed that mitochondrial protein interactions were changed during hyperglycemic conditions in the streptozotocin-treated murine model and diabetic human tissue.

Conclusions

Our interactome mapping suggests that mitochondrial dysfunction could be tightly linked to various phases of DR pathogenesis including altered visual cycle, cytoskeletal remodeling, altered lipid concentration, inflammation, PHB depletion, tubulin phosphorylation, and altered energy metabolism. The protein-metabolite interactions in the current network demonstrate the etiology of retinal degeneration and suggest the potential therapeutic approach to treat DR.

Fabrication of Biomolecule-Loaded Composite Scaffolds Carried by Extracellular Matrix Hydrogel

Fabrication of multifunctional scaffolds with biomimicking physical and biological signals play an important role in enhancing tissue regeneration. Multifunctional features come from the composite scaffold with various bioactive molecules. However, simple, biocompatible, and controllable hybridization strategy is still lacking. In this study, we leverage naturally derived extracellular matrix (ECM) as chemically controllable hydrogel carrier to effectively load functional biomolecules. The use of ECM hydrogel takes advantage of both native functionality of ECM components and tunability of hydrogel in controlling release of loaded molecules. As a proof of concept, porous acellular bone scaffold was selected as the solid pristine scaffold to be composited with BMP-2 and VEGF, which are loaded by spinal cord-derived ECM (SC-ECM) hydrogel. Crosslinking degree of SC-ECM hydrogel is tuned by changing genipin concentration, which renders the control over release kinetics of BMP-2 and VEGF. The mechanical strength of scaffold maintained after hybridization and is not significantly decreased in wet condition. In vitro evaluations of scaffolds cocultured with osteoblasts and mesenchymal stem cells (MSCs) demonstrate the biocompatible and bioactive features resulting from the composite scaffolds. Evidenced by alkaline phosphatase test, immunofluorescence, and real-time polymerase chain reaction, differentiation of MSCs towards osteoblast lineage is significantly enhanced by composite scaffolds. Therefore, our strategy in fabricating composite scaffold enabled by biomolecule-loaded ECM hydrogel holds great promise in regenerating diverse tissue types by appropriate combinations of solid pristine scaffolds, ECM, and bioactive molecules. Impact statement We developed a bioactive molecule (e.g., growth factor, protein) loading method using extracellular matrix hydrogel as a carrier. It brings a new strategy to fabricate composite scaffolds with unique biofunctions.

Oxidative stress and mitochondrial transfer: A new dimension towards ocular diseases

Ocular cells like, retinal pigment epithelium (RPE) is a highly specialized pigmented monolayer of post-mitotic cells, which is located in the posterior segment of the eye between neuro sensory retina and vascular choroid. It functions as a selective barrier and nourishes retinal visual cells. As a result of high-level oxygen consumption of retinal cells, RPE cells are vulnerable to chronic oxidative stress and an increased level of reactive oxygen species (ROS) generated from mitochondria. These oxidative stress and ROS generation in retinal cells lead to RPE degeneration. Various sources including mtDNA damage could be an important factor of oxidative stress in RPE. Gene therapy and mitochondrial transfer studies are emerging fields in ocular disease research. For retinal degenerative diseases stem cell-based transplantation methods are developed from basic research to preclinical and clinical trials. Translational research contributions of gene and cell therapy would be a new strategy to prevent, treat and cure various ocular diseases. This review focuses on the effect of oxidative stress in ocular cell degeneration and recent translational researches on retinal degenerative diseases to cure blindness.

The useful agent to have an ideal biological scaffold

Tissue engineering which is applied in regenerative medicine has three basic components: cells, scaffolds and growth factors. This multidisciplinary field can regulate cell behaviors in different conditions using scaffolds and growth factors. Scaffolds perform this regulation with their structural, mechanical, functional and bioinductive properties and growth factors by attaching to and activating their receptors in cells. There are various types of biological extracellular matrix (ECM) and polymeric scaffolds in tissue engineering. Recently, many researchers have turned to using biological ECM rather than polymeric scaffolds because of its safety and growth factors. Therefore, selection the right scaffold with the best properties tailored to clinical use is an ideal way to regulate cell behaviors in order to repair or improve damaged tissue functions in regenerative medicine. In this review we first divided properties of biological scaffold into intrinsic and extrinsic elements and then explain the components of each element. Finally, the types of scaffold storage methods and their advantages and disadvantages are examined.

Investigation of multiphasic 3D-bioplotted scaffolds for site-specific chondrogenic and osteogenic differentiation of human adipose-derived stem cells for osteochondral tissue engineering applications

Osteoarthritis is a degenerative joint disease that limits mobility of the affected joint due to the degradation of articular cartilage and subchondral bone. The limited regenerative capacity of cartilage presents significant challenges when attempting to repair or reverse the effects of cartilage degradation. Tissue engineered medical products are a promising alternative to treat osteochondral degeneration due to their potential to integrate into the patient's existing tissue. The goal of this study was to create a scaffold that would induce site-specific osteogenic and chondrogenic differentiation of human adipose-derived stem cells (hASC) to generate a full osteochondral implant. Scaffolds were fabricated using 3D-bioplotting of biodegradable polycraprolactone (PCL) with either β-tricalcium phosphate (TCP) or decellularized bovine cartilage extracellular matrix (dECM) to drive site-specific hASC osteogenesis and chondrogenesis, respectively. PCL-dECM scaffolds demonstrated elevated matrix deposition and organization in scaffolds seeded with hASC as well as a reduction in collagen I gene expression. 3D-bioplotted PCL scaffolds with 20% TCP demonstrated elevated calcium deposition, endogenous alkaline phosphatase activity, and osteopontin gene expression. Osteochondral scaffolds comprised of hASC-seeded 3D-bioplotted PCL-TCP, electrospun PCL, and 3D-bioplotted PCL-dECM phases were evaluated and demonstrated site-specific osteochondral tissue characteristics. This technique holds great promise as cartilage morbidity is minimized since autologous cartilage harvest is not required, tissue rejection is minimized via use of an abundant and accessible source of autologous stem cells, and biofabrication techniques allow for a precise, customizable methodology to rapidly produce the scaffold.

Optimizing The Cell Seeding Protocol to Human Decellularized Ovarian Scaffold: Application of Dynamic System for Bio-Engineering

Objective

Decellularized tissue scaffolds provide an extracellular matrix to control stem cells differentiation toward specific lineages. The application of mesenchymal stem cells for artificial ovary production may enhance ex vivo functions of the ovary. On the other hand, the scaffold needs interaction and integration with cells. Thus, the development of ovarian engineered constructs (OVECs) requires the use of efficient methods for seeding of the cells into the ovarian and other types of scaffolds. The main goal of the present study was to develop an optimized culture system for efficient seeding of peritoneum mesenchymal stem cells (PMSCs) into human decellularized ovarian scaffold.

Materials and Methods

In this experimental study, three methods were used for cellular seeding including rotational (spinner flask) and static (conventional and injection) seeding cultures. OVECs were evaluated with Hematoxylin and Eosin staining and viability analyses for the seeded PMSCs. Then, immunohistochemistry analysis was performed using the best method of cellular seeding for primordial germ cell-like cells, mesenchymal stem cells and proliferation markers. Stereology analysis was also performed for the number of penetrated cells into the OVECs.

Results

Our results showed that rotational seeding increases the permeability of PMSCs into the scaffold and survival rate of the seeded PMSCs, comparing to the other methods. On the other hand, rotationally seeded PMSCs had a more favorable capability of proliferation with Ki67 expression and differentiation to ovarian specific cells with expression of primordial germ cell line markers without mesenchymal stem cells markers production. Furthermore, stereology showed a more favorable distribution of PMSCs along the outer surfaces of the OVEC with further distribution at the central part of the scaffold. The average total cell values were determined 2142187 cells/mm³ on each OVEC.

Conclusion

The rotational seeding method is a more favorable approach to cell seeding into ovarian decellularized tissue than static seeding.

A Defective Crosstalk Between Neurons and Müller Glial Cells in the rd1 Retina Impairs the Regenerative Potential of Glial Stem Cells

Müller glial cells (MGC) are stem cells in the retina. Although their regenerative capacity is very low in mammals, the use of MGC as stem cells to regenerate photoreceptors (PHRs) during retina degenerations, such as in retinitis pigmentosa, is being intensely studied. Changes affecting PHRs in diseased retinas have been thoroughly investigated; however, whether MGC are also affected is still unclear. We here investigated whether MGC in retinal degeneration 1 (rd1) mouse, an animal model of retinitis pigmentosa, have impaired stem cell properties or structure. rd1 MGC showed an altered morphology, both in culture and in the whole retina. Using mixed neuron-glial cultures obtained from newborn mice retinas, we determined that proliferation was significantly lower in rd1 than in wild type (wt) MGC. Levels of stem cell markers, such as Nestin and Sox2, were also markedly reduced in rd1 MGC compared to wt MGC in neuron-glial cultures and in retina cryosections, even before the onset of PHR degeneration. We then investigated whether neuron-glial crosstalk was involved in these changes. Noteworthy, Nestin expression was restored in rd1 MGC in co-culture with wt neurons. Conversely, Nestin expression decreased in wt MGC in co-culture with rd1 neurons, as occurred in rd1 MGC in rd1 neuron-glial mixed cultures. These results imply that MGC proliferation and stem cell markers are reduced in rd1 retinas and might be restored by their interaction with “healthy” PHRs, suggesting that alterations in rd1 PHRs lead to a disruption in neuron-glial crosstalk affecting the regenerative potential of MGC.

The combination of bFGF and CHIR99021 maintains stable self-renewal of mouse adult retinal progenitor cells

BACKGROUND

Millions of people are affected with retinal diseases that eventually cause blindness, and retinal progenitor cell (RPC) transplantation is a promising therapeutic avenue. However, RPC expansion and the underlying regulation mechanisms remain elusive.

METHODS

Adult mouse neural RPCs (mNRPCs) were isolated and amplified with the combination of basic fibroblast growth factor (bFGF) and glycogen synthase kinase 3 (GSK3) inhibitor CHIR99021. The progenitor characteristics were evaluated with RT-PCR, immunocytochemistry (ICC), western blot, flow cytometry, and transcriptome analysis prior to transplantation. By treating cells with or without bFGF and CHIR99021 at different time points, the mechanism for mNRPCs' self-renewal was investigated by transcriptome analysis and western blot assay.

RESULTS

mNRPCs were self-renewing in the presence of bFGF and CHIR99021 and showed prominent RPC characteristics. bFGF was essential in promoting cell cycle by facilitating G1/S and G2/M transitions. bFGF combined with CHIR99021 activated the non-canonical Wnt5A/Ca2+ pathway and form a calcium homeostasis. In addition, the self-renewing mNRPCs could differentiate into rod photoreceptor-like cells and retinal pigment epithelium (RPE)-like cells by in vitro induction. When green fluorescent protein (GFP)-labeled cells were transplanted into the subretinal space (SRS) of Pde6b (rd1) mice (also known as RD1 mice, or rodless mice), the cells survived for more than 12 weeks and migrated into the retina. Parts of the recipient retina showed positive expression of photoreceptor marker rhodopsin. Transplanted cells can migrate into the retina, mainly into the inner cell layer (INL) and ganglion cell layer (GCL). Some cells can differentiate into astrocytes and amacrine cells. Cultured mNRPCs did not form tumors after transplanted into NOD/SCID mice for 6 months.

CONCLUSIONS

Present study developed an approach to maintain long-term self-renewal of RPCs from adult retinal tissues and revealed that activation of the non-canonical Wnt5A/Ca2+ pathway may participate in regulating RPC self-renewal in vitro. This study presents a very promising platform to expand RPCs for future therapeutic application.

Advanced glycation end products-related modulation of cathepsin L and NF-κB signalling effectors in retinal pigment epithelium lead to augmented response to TNFα

The retinal pigment epithelium (RPE) plays a central role in neuroretinal homoeostasis throughout life. Altered proteolysis and inflammatory processes involving RPE contribute to the pathophysiology of age‐related macular degeneration (AMD), but the link between these remains elusive. We report for the first time the effect of advanced glycation end products (AGE)—known to accumulate on the ageing RPE's underlying Bruch's membrane in situ—on both key lysosomal cathepsins and NF‐κB signalling in RPE. Cathepsin L activity and NF‐κB effector levels decreased significantly following 2‐week AGE exposure. Chemical cathepsin L inhibition also decreased total p65 protein levels, indicating that AGE‐related change of NF‐κB effectors in RPE cells may be modulated by cathepsin L. However, upon TNFα stimulation, AGE‐exposed cells had significantly higher ratio of phospho‐p65(Ser536)/total p65 compared to non‐AGEd controls, with an even higher fold increase than in the presence of cathepsin L inhibition alone. Increased proportion of active p65 indicates an AGE‐related activation of NF‐κB signalling in a higher proportion of cells and/or an enhanced response to TNFα. Thus, NF‐κB signalling modulation in the AGEd environment, partially regulated via cathepsin L, is employed by RPE cells as a protective (para‐inflammatory) mechanism but renders them more responsive to pro‐inflammatory stimuli.

Extracellular matrix component expression in human pluripotent stem cell-derived retinal organoids recapitulates retinogenesis in vivo and reveals an important role for IMPG1 and CD44 in the development of photoreceptors and interphotoreceptor matrix

The extracellular matrix (ECM) plays an important role in numerous processes including cellular proliferation, differentiation, migration, maturation, adhesion guidance and axonal growth. To date, there has been no detailed analysis of the ECM distribution during retinal ontogenesis in humans and the functional importance of many ECM components is poorly understood. In this study, the expression of key ECM components in adult mouse and monkey retina, developing and adult human retina and retinal organoids derived from human pluripotent stem cells was studied. Our data indicate that basement membrane ECMs (Fibronectin and Collagen IV) were expressed in Bruch's membrane and the inner limiting membrane of the developing human retina, whilst the hyalectins (Versican and Brevican), cluster of differentiation 44 (CD44), photoreceptor-specific ECMs Interphotoreceptor Matrix Proteoglycan 1 (IMPG1) and Interphotoreceptor Matrix Proteoglycan 2 (IMPG2) were detected in the developing interphotoreceptor matrix (IPM). The expression of IMPG1, Versican and Brevican in the developing IPM was conserved between human developing retina and human pluripotent stem cell-derived retinal organoids. Blocking the action of CD44 and IMPG1 in pluripotent stem cell derived retinal organoids affected the development of photoreceptors, their inner/outer segments and connecting cilia and disrupted IPM formation, with IMPG1 having an earlier and more significant impact. Together, our data suggest an important role for IMPG1 and CD44 in the development of photoreceptors and IPM formation during human retinogenesis.

STATEMENT OF SIGNIFICANCE

The expression and the role of many extracellular matrix (ECM) components during human retinal development is not fully understood. In this study, expression of key ECM components (Collagen IV, Fibronectin, Brevican, Versican, IMPG1 and IMPG2) was investigated during human retinal ontogenesis. Collagen IV and Fibronectin were expressed in Bruch's membrane; whereas Brevican, Versican, IMPG1 & IMPG2 in the developing interphotoreceptor matrix (IPM). Retinal organoids were successfully generated from pluripotent stem cells. The expression of ECM components was examined in the retinal organoids and found to recapitulate human retinal development in vivo. Using functional blocking experiments, we were able to highlight an important role for IMPG1 and CD44 in the development of photoreceptors and IPM formation.

An investigation on the correlation between the mechanical property change and the alterations in composition and microstructure of a porcine vascular tissue underwent trypsin-based decellularization treatment

PURPOSE

The nonlinear pseudoelastic behavior of a native/decellularized vascular tissue is closely related to the detailed composition and microstructure of the extracellular matrix and is important in maintaining the patency of a small-caliber vascular graft. A commonly used enzyme-detergent based decellularization protocol is effective in cell component removal but it also changes the microstructure and composition of the decellularized tissues. Previous studies provide limited information to correlate the mechanical property change with the alterations in composition and microstructure in a decellularization process. In this study, the correlations were studied by implementing a previously established fiber-progressive-engagement model to describe the nonlinear pseudoelastic behavior of a vascular tissue and to evaluate the effects of trypsin concentration and exposure duration on porcine coronary artery decellularization RESULTS: Results showed that tissue length and width increased and thickness and wet weight decreased with the exposure of trypsin. The effects of trypsin exposure times on the four mechanical parameters, i.e. initial strain, turning strain, initial modulus and stiffness modulus, in the longitudinal and circumferential directions were similar, but stronger in the circumferential direction. Major components of the extracellular matrix were vulnerable to the trypsin-based decellularization process. The decreases in initial and turning strain and the increase in initial modulus in circumferential direction were correlated with the significant decrease of collagen and glycosaminoglycans in the media layer.

CONCLUSIONS

Although trypsin-based decellularization achieved cell component removal and preservation of ultimate tensile stress, the microstructure and composition changed with alterations in the pseudoelastic behavior of the porcine coronary artery. Taken together, the current observations suggested less waviness, early engagement, or re-alignment of insoluble collagen fibers in the media layer, which resulted in turning from anisotropic into isotropic uniaxial mechanical property of porcine vascular tissue. Selecting the proper trypsin concentration (< 0.03-0.5%) and duration (< 12 h) of trypsin exposure in combination with other methods will achieve optimal porcine coronary artery decellularization.

Fabrication of micro/nanoporous collagen/dECM/silk-fibroin biocomposite scaffolds using a low temperature 3D printing process for bone tissue regeneration

Biomaterials must be biocompatible, biodegradable, and mechanically stable to be used for tissue engineering applications. Among various biomaterials, a natural-based biopolymer, collagen, has been widely applied in tissue engineering because of its outstanding biocompatibility. However, due to its low mechanical properties, collagen has been a challenge to build a desired/complex 3D porous structure with appropriate mechanical strength. To overcome this problem, in this study, we used a low temperature printing process to create a 3D porous scaffold consisting of collagen, decellularized extracellular matrix (dECM) to induce high cellular activities, and silk-fibroin (SF) to attain the proper mechanical strength. To show the feasibility of the scaffold, pre-osteoblast (MC3T3-E1) cells were grown on the fabricated scaffold. Various in vitro cellular activities (cell-viability, MTT assay, and osteogenic activity) for pure collagen, collagen/dECM, and collagen/SF/dECM scaffolds were compared.

Advances in the Knowledge about Kidney Decellularization and Repopulation

End-stage renal disease (ESRD) is characterized by the progressive deterioration of renal function that may compromise different tissues and organs. The major treatment indicated for patients with ESRD is kidney transplantation. However, the shortage of available organs, as well as the high rate of organ rejection, supports the need for new therapies. Thus, the implementation of tissue bioengineering to organ regeneration has emerged as an alternative to traditional organ transplantation. Decellularization of organs with chemical, physical, and/or biological agents generates natural scaffolds, which can serve as basis for tissue reconstruction. The recellularization of these scaffolds with different cell sources, such as stem cells or adult differentiated cells, can provide an organ with functionality and no immune response after in vivo transplantation on the host. Several studies have focused on improving these techniques, but until now, there is no optimal decellularization method for the kidney available yet. Herein, an overview of the current literature for kidney decellularization and whole-organ recellularization is presented, addressing the pros and cons of the actual techniques already developed, the methods adopted to evaluate the efficacy of the procedures, and the challenges to be overcome in order to achieve an optimal protocol.

Isolation, culture and characterization of primary mouse RPE cells

Mouse models are powerful tools for the study of ocular diseases. Alterations in the morphology and function of the retinal pigment epithelium (RPE) are common features shared by many ocular disorders. We report a detailed protocol to collect, seed, culture and characterize RPE cells from mice. We describe a reproducible method that we previously developed to collect and culture murine RPE cells on Transwells as functional polarized monolayers. The collection of RPE cells takes ∼3 h, and the cultures mimic in vivo RPE cell features within 1 week. This protocol also describes methods to characterize the cells on Transwells within 1-2 weeks by transmission and scanning electron microscopy (TEM and SEM, respectively), immunostaining of vibratome sections and flat mounts, and measurement of transepithelial electrical resistance. The RPE cell cultures are suitable to study the biology of the RPE from wild-type and genetically modified strains of mice between the ages of 10 d and 12 months. The RPE cells can also be manipulated to investigate molecular mechanisms underlying the RPE pathology in the numerous mouse models of ocular disorders. Furthermore, modeling the RPE pathology in vitro represents a new approach to testing drugs that will help accelerate the development of therapies for vision-threatening disorders such as macular degeneration (MD).

Matrigel and Activin A promote cell-cell contact and anti-apoptotic activity in cultured human retinal pigment epithelium cells

Age-related macular degeneration (AMD) is a leading cause of blindness among the aging population. Currently, replacement of diseased retinal pigment epithelium (RPE) cells with transplanted healthy RPE cells could be a feasible approach for AMD therapy. However, maintaining cell-cell contact and good viability of RPE cells cultured in vitro is difficult and fundamentally determines the success of RPE cell transplantation. This study was conducted to examine the role of Matrigel and Activin A (MA) in regulating cell-cell contact and anti-apoptotic activity in human RPE (hRPE) cells, as assessed by atomic force microscopy (AFM), scanning electron microscope (SEM), immunofluorescence staining, quantitative polymerase chain reaction (qPCR) analysis, Annexin V/propidium iodide (PI) analysis, mitochondrial membrane potential (△Ψ m) assays, intracellular reactive oxygen species (ROS) assays and Western blotting. hRPE cells cultured in vitro could maintain their epithelioid morphology after MA treatment over at least 4 passages. The contact of N-cadherin to the lateral cell border was promoted in hRPE cells at P2 by MA. MA treatment also enhanced the expression of tight junction-associated genes and proteins, such as Claudin-1, Claudin-3, Occludin and ZO-1, as well as polarized ZO-1 protein distribution and barrier function, in cultured hRPE cells. Moreover, MA treatment decreased apoptotic cells, ROS and Bax and increased △Ψ m and Bcl2 in hRPE cells under serum withdrawal-induced apoptosis. In addition, MA treatment elevated the protein expression levels of β-catenin and its target proteins, including Cyclin D1, c-Myc and Survivin, as well as the gene expression levels of ZO-1, β-catenin, Survivin and TCF-4, all of which could be down-regulated by the Wnt/β-catenin pathway inhibitor XAV-939. Taken together, MA treatment could effectively promote cell-cell contact and anti-apoptotic activity in hRPE cells, partly involving the Wnt/β-catenin pathway. This study will benefit the understanding of hRPE cells and future cell therapy.

Chondroinduction from Naturally Derived Cartilage Matrix: A Comparison Between Devitalized and Decellularized Cartilage Encapsulated in Hydrogel Pastes

Hydrogel precursors are liquid solutions that are prone to leaking after surgical placement. This problem was overcome by incorporating either decellularized cartilage (DCC) or devitalized cartilage (DVC) microparticles into traditional photocrosslinkable hydrogel precursors in an effort to achieve a paste-like hydrogel precursor. DCC and DVC were selected specifically for their potential to induce chondrogenesis of stem cells, given that materials that are chondroinductive on their own without growth factors are a revolutionary goal in orthopedic medicine. We hypothesized that DVC, lacking the additional chemical processing steps in DCC to remove cell content, would lead to a more chondroinductive hydrogel with rat bone marrow-derived mesenchymal stem cells. Hydrogels composed of methacrylated hyaluronic acid (MeHA) and either DCC or DVC microparticles were tested with and without exposure to transforming growth factor (TGF)-β3 over a 6 week culture period, where swelling, mechanical analysis, and gene expression were observed. For collagen II, Sox-9, and aggrecan expression, MeHA precursors containing DVC consistently outperformed the DCC-containing groups, even when the DCC groups were exposed to TGF-β3. DVC consistently outperformed all TGF-β3-exposed groups in aggrecan and collagen II gene expression as well. In addition, when the same concentrations of MeHA with DCC or DVC microparticles were evaluated for yield stress, the yield stress with the DVC microparticles was 2.7 times greater. Furthermore, the only MeHA-containing group that exhibited shape retention was the group containing DVC microparticles. DVC appeared to be superior to DCC in both chondroinductivity and rheological performance of hydrogel precursors, and therefore DVC microparticles may hold translational potential for cartilage regeneration.

Extracellular Matrix Components Regulate Cellular Polarity and Tissue Structure in the Developing and Mature Retina

While genetic networks and other intrinsic mechanisms regulate much of retinal development, interactions with the extracellular environment shape these networks and modify their output. The present review has focused on the role of one family of extracellular matrix molecules and their signaling pathways in retinal development. In addition to their effects on the developing retina, laminins play a role in maintaining Müller cell polarity and compartmentalization, thereby contributing to retinal homeostasis. This article which is intended for the clinical audience, reviews the fundamentals of retinal development, extracellular matrix organization and the role of laminins in retinal development. The role of laminin in cortical development is also briefly discussed.

Investigating the choriocapillaris and choroidal vasculature with new optical coherence tomography technologies

The body of knowledge of in vivo investigation of the choroid has been markedly enhanced by recent technological advances in optical coherence tomography (OCT). New insights elucidating the morphological features of the choriocapillaris and choroidal vasculature, in both physiological and pathological conditions, indicate that the choroid plays a pivotal role in many posterior segment diseases. In this article, a review of the histological characteristics of the choroid, which must be considered for the proper interpretation of in vivo imaging, is followed by a comprehensive discussion of fundamental principles of the current state-of-the-art in OCT, including cross-sectional OCT, en face OCT, and OCT angiography using both spectral domain OCT and swept source OCT technologies. A detailed review of the tomographic features of the choroid in the normal eye is followed by relevant findings in prevalent chorioretinal diseases, focusing on major causes of vision loss such as typical early and advanced age-related macular degeneration, polypoidal choroidal vasculopathy, central serous chorioretinopathy, pachychoroid spectrum disorders, diabetic choroidopathy, and myopia.

Reprint of: Extracellular matrix as a biological scaffold material: Structure and function

Biological scaffold materials derived from the extracellular matrix (ECM) of intact mammalian tissues have been successfully used in a variety of tissue engineering/regenerative medicine applications both in preclinical studies and in clinical applications. Although it is recognized that the materials have constructive remodeling properties, the mechanisms by which functional tissue restoration is achieved are not well understood. There is evidence to support essential roles for both the structural and functional characteristics of the biological scaffold materials. This paper provides an overview of the composition and structure of selected ECM scaffold materials, the effects of manufacturing methods upon the structural properties and resulting mechanical behavior of the scaffold materials, and the in vivo degradation and remodeling of ECM scaffolds with an emphasis on tissue function.

Development of decellularized scaffolds for stem cell-driven tissue engineering

Organ transplantation is an effective treatment for chronic organ dysfunctioning conditions. However, a dearth of available donor organs for transplantation leads to the death of numerous patients waiting for a suitable organ donor. The potential of decellularized scaffolds, derived from native tissues or organs in the form of scaffolds has been evolved as a promising approach in tissue-regenerative medicine for translating functional organ replacements. In recent years, donor organs, such as heart, liver, lung and kidneys, have been reported to provide acellular extracellular matrix (ECM)-based scaffolds through the process called 'decellularization' and proved to show the potential of recellularization with selected cell populations, particularly with stem cells. In fact, decellularized stem cell matrix (DSCM) has also emerged as a potent biological scaffold for controlling stem cell fate and function during tissue organization. Despite the proven potential of decellularized scaffolds in tissue engineering, the molecular mechanism responsible for stem cell interactions with decellularized scaffolds is still unclear. Stem cells interact with, and respond to, various signals/cues emanating from their ECM. The ability to harness the regenerative potential of stem cells via decellularized ECM-based scaffolds has promising implications for tissue-regenerative medicine. Keeping these points in view, this article reviews the current status of decellularized scaffolds for stem cells, with particular focus on: (a) concept and various methods of decellularization; (b) interaction of stem cells with decellularized scaffolds; (c) current recellularization strategies, with associated challenges; and (iv) applications of the decellularized scaffolds in stem cell-driven tissue engineering and regenerative medicine. Copyright © 2015 John Wiley & Sons, Ltd.

Generation of three-dimensional retinal tissue with functional photoreceptors from human iPSCs

Many forms of blindness result from the dysfunction or loss of retinal photoreceptors. Induced pluripotent stem cells (iPSCs) hold great potential for the modelling of these diseases or as potential therapeutic agents. However, to fulfill this promise, a remaining challenge is to induce human iPSC to recreate in vitro key structural and functional features of the native retina, in particular the presence of photoreceptors with outer-segment discs and light sensitivity. Here we report that hiPSC can, in a highly autonomous manner, recapitulate spatiotemporally each of the main steps of retinal development observed in vivo and form three-dimensional retinal cups that contain all major retinal cell types arranged in their proper layers. Moreover, the photoreceptors in our hiPSC-derived retinal tissue achieve advanced maturation, showing the beginning of outer-segment disc formation and photosensitivity. This success brings us one step closer to the anticipated use of hiPSC for disease modelling and open possibilities for future therapies.

Enhancing RPE Cell-Based Therapy Outcomes for AMD: The Role of Bruch's Membrane

Age-related macular degeneration (AMD) is the leading cause of legal blindness in older people in the developed world. The disease involves damage to the part of the retina responsible for central vision. Degeneration of retinal pigment epithelial (RPE) cells, photoreceptors, and choriocapillaris may contribute to visual loss. Over the past decades, scientists and clinicians have tried to replace lost RPE cells in patients with AMD using cells from different sources. In recent years, advances in generating RPE cells from stem cells have been made and clinical trials are currently evaluating the safety and efficiency of replacing the degenerated RPE cell layer with stem cell-derived RPE cells. However, the therapeutic success of transplantation of stem cell-derived RPE cells may be limited unless the transplanted cells can adhere and survive in the long term in the diseased eye. One hallmark of AMD is the altered extracellular environment of Bruch's membrane to which the grafted cells have to adhere. Here, we discuss recent approaches to overcome the inhibitory environment of the diseased eye and to enhance the survival rate of transplanted RPE cells. Our aim is to highlight novel approaches that may have the potential to improve the efficacy of RPE transplantation for AMD in the future.

Lab generated retina: realizing the dream

Blindness represents an increasing global problem with significant social and economic impact upon affected patients and society as a whole. In Europe, approximately one in 30 individuals experience sight loss and 75% of those are unemployed, a social burden which is very likely to increase as the population of Europe ages. Diseases affecting the retina account for approximately 26% of blindness globally and 70% of blindness in the United Kingdom. To date, there are no treatments to restore lost retinal cells and improve visual function, highlighting an urgent need for new therapeutic approaches. A pioneering breakthrough has demonstrated the ability to generate synthetic retina from pluripotent stem cells under laboratory conditions, a finding with immense relevance for basic research, in vitro disease modeling, drug discovery, and cell replacement therapies. This review summarizes the current achievements in pluripotent stem cell differentiation toward retinal cells and highlights the steps that need to be completed in order to generate human synthetic retinae with high efficiency and reproducibly from patient-specific pluripotent stem cells.

Renal bioengineering with scaffolds generated from rat and pig kidneys

BACKGROUND

Chronic kidney disease (CKD) is a global public health issue with an estimated prevalence of 8-16% worldwide. End-stage renal disease eventually develops every year in 0.15-0.2% of patients with overt CKD, and renal replacement therapy (RRT) with dialysis or transplantation is required. Although approximately 2 million people worldwide are currently on RRT to sustain life, this likely represents less than 10% of those who need it. The kidney transplant approach is also seriously impaired by limited graft survival and by the scarce availability of donors. Innovative tissue-engineering strategies have been recently proposed to overcome these challenges. It is anticipated that these novel approaches will also be cost-effective in the long term. Although the initial setup of these innovative technologies could be quite expensive, there would be a single application for each patient, with no additional costs thereafter, compared to the lifelong costs of dialysis or immunosuppressive medications required for transplantation. One of the most innovative tools currently being investigated in experimental models is based on the idea of using decellularized kidneys to engineer a new functional organ as a potential future treatment option for end-stage renal disease.

SUMMARY

In the last 5 years, several interesting observations have been reported regarding the possibility of using an acellular matrix from the whole kidney and the attempt to recellularize this scaffold using stem or differentiated cells. This review provides an overview of the decellularization methods tested so far and their effects on the resulting extracellular matrix structure and composition. In addition, we also discuss methods recently described by us and others for the perfusion of kidney scaffolds for recellularization.

KEY MESSAGES

Despite difficulties in achieving the import goal of kidney engineering in the laboratory, we discuss the problems with and limits of the experimental results obtained so far and point out the strategies that need to be adopted in order for this line of research to advance.

Barrier properties of cultured retinal pigment epithelium

The principal function of an epithelium is to form a dynamic barrier that regulates movement between body compartments. Each epithelium is specialized with barrier functions that are specific for the tissues it serves. The apical surface commonly faces a lumen, but the retinal pigment epithelium (RPE) appears to be unique by a facing solid tissue, the sensory retina. Nonetheless, there exists a thin (subretinal) space that can become fluid filled during pathology. RPE separates the subretinal space from the blood supply of the outer retina, thereby forming the outer blood-retinal barrier. The intricate interaction between the RPE and sensory retina presents challenges for learning how accurately culture models reflect native behavior. The challenge is heightened by findings that detail the variation of RPE barrier proteins both among species and at different stages of the life cycle. Among the striking differences is the expression of claudin family members. Claudins are the tight junction proteins that regulate ion diffusion across the spaces that lie between the cells of a monolayer. Claudin expression by RPE varies with species and life-stage, which implies functional differences among commonly used animal models. Investigators have turned to transcriptomics to supplement functional studies when comparing native and cultured tissue. The most detailed studies of the outer blood-retinal barrier have focused on human RPE with transcriptome and functional studies reported for human fetal, adult, and stem-cell derived RPE.

Structure and barrier properties of human embryonic stem cell-derived retinal pigment epithelial cells are affected by extracellular matrix protein coating

Extracellular matrix (ECM) interactions play a vital role in cell morphology, migration, proliferation, and differentiation of cells. We investigated the role of ECM proteins on the structure and function of human embryonic stem cell-derived retinal pigment epithelial (hESC-RPE) cells during their differentiation and maturation from hESCs into RPE cells in adherent differentiation cultures on several human ECM proteins found in native human Bruch's membrane, namely, collagen I, collagen IV, laminin, fibronectin, and vitronectin, as well as on commercial substrates of xeno-free CELLstart™ and Matrigel™. Cell pigmentation, expression of RPE-specific proteins, fine structure, as well as the production of basal lamina by hESC-RPE on different protein coatings were evaluated after 140 days of differentiation. The integrity of hESC-RPE epithelium and barrier properties on different coatings were investigated by measuring transepithelial resistance. All coatings supported the differentiation of hESC-RPE cells as demonstrated by early onset of cell pigmentation and further maturation to RPE monolayers after enrichment. Mature RPE phenotype was verified by RPE-specific gene and protein expression, correct epithelial polarization, and phagocytic activity. Significant differences were found in the degree of RPE cell pigmentation and tightness of epithelial barrier between different coatings. Further, the thickness of self-assembled basal lamina and secretion of the key ECM proteins found in the basement membrane of the native RPE varied between hESC-RPE cultured on compared protein coatings. In conclusion, this study shows that the cell culture substrate has a major effect on the structure and basal lamina production during the differentiation and maturation of hESC-RPE potentially influencing the success of cell integrations and survival after cell transplantation.

Noninvasive sorting of stem cell aggregates based on intrinsic markers

Noninvasive biomarkers hold important potential for the characterization and purification of stem cells because the addition of exogenous labels, probes, or reporters, as well as the disruption of cell-cell and cell-extracellular matrix interactions, can unintentionally but dramatically alter stem cell state. We recently showed that intensity of the intrinsically fluorescent metabolite, nicotinamide adenine dinucleotide (NADH), fluctuates predictably with changes in stem cell viability and differentiation state. Here, we use multiphoton flow cytometry developed in our laboratory to rapidly and noninvasively characterize and purify populations of intact stem cell aggregates based on NADH intensity and assessed the differentiation capacity of sorted populations. We found removal of aggregates with NADH intensity indicative of cell death resulted in a remaining population of aggregates significantly more likely to produce beating cardiomyocytes (26% vs. 8%, P < 0.05). Similarly, we found isolation of stem cell aggregates with NADH intensity indicative of future cardiac differentiation gave rise to more aggregates with beating cardiomyocytes at later time points (50% vs. 28%, P < 0.05). Further, coupling NADH intensity with gating based on size, enhances the enrichment for EBs capable of giving rise to cardiomyocytes (59% vs. 27%, P < 0.05). Thus, we demonstrate that endogenous properties of cell aggregates, such as NADH and size, can serve as gating parameters for large particle sorting devices to purify populations of stem cells or their progeny in a noninvasive manner, leading the way for improved therapeutic applications.

Topographical control of ocular cell types for tissue engineering

Visual impairment affects over 285 million people worldwide and has a major impact on an individual's quality of life. Tissue engineering has the potential to increase the quality of life for many of these patients by preventing vision loss or restoring vision using cell-based therapies. However, these strategies will require an understanding of the microenvironmental factors that influence cell behavior. The eye is a well-organized organ whose structural complexity is essential for proper function. Interactions between ocular cells and their highly ordered extracellular matrix are necessary for maintaining key tissue properties including corneal transparency and retinal lamination. Therefore, it is not surprising that culturing these cells in vitro on traditional flat substrates result in irregular morphology. Instead, topographically patterned biomaterials better mimic native extracellular matrix and have been shown to elicit in vivo-like morphology and gene expression which is essential for tissue engineering. Herein we review multiple methods for producing well-controlled topography and discuss optimal biomaterial scaffold design for cells of the cornea, retina, and lens.

Perfusion decellularization of human and porcine lungs: bringing the matrix to clinical scale

BACKGROUND

Organ engineering is a theoretical alternative to allotransplantation for end-stage organ failure. Whole-organ scaffolds can be created by detergent perfusion via the native vasculature, generating an acellular matrix suitable for recellularization with selected cell types. We aimed to up-scale this process, generating biocompatible scaffolds of a clinically relevant scale.

METHODS

Rat, porcine, and human lungs were decellularized by detergent perfusion at constant pressures. Collagen, elastin, and glycosaminoglycan content of scaffolds were quantified by colorimetric assays. Proteomic analysis was performed by microcapillary liquid chromatography tandem mass spectrometry. Extracellular matrix (ECM) slices were cultured with human umbilical vein endothelial cells (HUVEC), small airway epithelial cells (SAEC), or pulmonary alveolar epithelial cells (PAECs) and evaluated by time-lapse live cell microscopy and MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay. Whole-organ culture was maintained under constant-pressure media perfusion after seeding with PAECs.

RESULTS

Rat lungs were decellularized using: (1) sodium dodecyl sulfate (SDS), (2) sodium deoxycholate (SDC), or (3) 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS). Resulting scaffolds showed comparable loss of DNA but greatest preservation of ECM components in SDS-decellularized lungs. Porcine (n = 10) and human (n = 7) lungs required increased SDS concentration, perfusion pressures, and time to achieve decellularization as determined by loss of DNA, with preservation of intact matrix composition and lung architecture. Proteomic analysis of human decellularized lungs further confirmed ECM preservation. Recellularization experiments confirmed scaffold biocompatibility when cultured with mature cell phenotypes and scaffold integrity for the duration of biomimetic culture.

CONCLUSIONS

SDS-based perfusion decellularization can be applied to whole porcine and human lungs to generate biocompatible organ scaffolds with preserved ECM composition and architecture.

Process-induced extracellular matrix alterations affect the mechanisms of soft tissue repair and regeneration

Extracellular matrices derived from animal tissues for human tissue repairs are processed by various methods of physical, chemical, or enzymatic decellularization, viral inactivation, and terminal sterilization. The mechanisms of action in tissue repair vary among bioscaffolds and are suggested to be associated with process-induced extracellular matrix modifications. We compared three non-cross-linked, commercially available extracellular matrix scaffolds (Strattice, Veritas, and XenMatrix), and correlated extracellular matrix alterations to in vivo biological responses upon implantation in non-human primates. Structural evaluation showed significant differences in retaining native tissue extracellular matrix histology and ultrastructural features among bioscaffolds. Tissue processing may cause both the condensation of collagen fibers and fragmentation or separation of collagen bundles. Calorimetric analysis showed significant differences in the stability of bioscaffolds. The intrinsic denaturation temperature was measured to be 51°C, 38°C, and 44°C for Strattice, Veritas, and XenMatrix, respectively, demonstrating more extracellular matrix modifications in the Veritas and XenMatrix scaffolds. Consequently, the susceptibility to collagenase degradation was increased in Veritas and XenMatrix when compared to their respective source tissues. Using a non-human primate model, three bioscaffolds were found to elicit different biological responses, have distinct mechanisms of action, and yield various outcomes of tissue repair. Strattice permitted cell repopulation and was remodeled over 6 months. Veritas was unstable at body temperature, resulting in rapid absorption with moderate inflammation. XenMatrix caused severe inflammation and sustained immune reactions. This study demonstrates that extracellular matrix alterations significantly affect biological responses in soft tissue repair and regeneration. The data offer useful insights into the rational design of extracellular matrix products and bioscaffolds of tissue engineering.

Study in vivo intraocular biocompatibility of in situ gelation hydrogels: poly(2-ethyl oxazoline)-block-poly(ε-caprolactone)-block-poly(2-ethyl oxazoline) copolymer, matrigel and pluronic F127

The long term in vivo biocompatibility is an essential feature for the design and development of sustained drug release carriers. In the recent intraocular drug delivery studies, hydrogels were suggested as sustained release carriers. The biocompatibility test for these hydrogels, however, was commonly performed only through in vitro cell culture examination, which is insufficient before the clinical applications. We compared three thermosensitive hydrogels that have been suggested as the carriers for drugs by their gel-solution phase-change properties. A new block terpolymer (PEOz-PCL-PEOz, ECE) and two commercial products (Matrigel® and Pluronic F127) were studied. The results demonstrated that the ocular media remained translucent for ECE and Pluronic F127 in the first 2 weeks, but cataract formation for Matrigel occurred in 2 weeks and for Pluronic F127 in 1 month, while turbid media was observed for both Matrigel and Pluronic F127 in 2 months. The electrophysiology examinations showed significant neuroretinal toxicity of Matrigel and Pluronic F127 but good biocompatibility of ECE. The neuroretinal toxicity of Matrigel and Pluronic F127 and superior biocompatibility of ECE hydrogel suggests ECE as more appropriate biomaterial for use in research and potentially in intraocular application.

A simple and scalable process for the differentiation of retinal pigment epithelium from human pluripotent stem cells

Age-related macular degeneration (AMD), the leading cause of irreversible vision loss and blindness among the elderly in industrialized countries, is associated with the dysfunction and death of the retinal pigment epithelial (RPE) cells. As a result, there has been significant interest in developing RPE culture systems both to study AMD disease mechanisms and to provide substrate for possible cell-based therapies. Because of their indefinite self-renewal, human pluripotent stem cells (hPSCs) have the potential to provide an unlimited supply of RPE-like cells. However, most protocols developed to date for deriving RPE cells from hPSCs involve time- and labor-consuming manual steps, which hinder their use in biomedical applications requiring large amounts of differentiated cells. Here, we describe a simple and scalable protocol for the generation of RPE cells from hPSCs that is less labor-intensive. After amplification by clonal propagation using a myosin inhibitor, differentiation was induced in monolayers of hPSCs, and the resulting RPE cells were purified by two rounds of whole-dish single-cell passage. This approach yields highly pure populations of functional hPSC-derived RPE cells that display many characteristics of native RPE cells, including proper pigmentation and morphology, cell type-specific marker expression, polarized membrane and vascular endothelial growth factor secretion, and phagocytic activity. This work represents a step toward mass production of RPE cells from hPSCs.

Extracellular matrix scaffolds for cartilage and bone regeneration

Regenerative medicine approaches based on decellularized extracellular matrix (ECM) scaffolds and tissues are rapidly expanding. The rationale for using ECM as a natural biomaterial is the presence of bioactive molecules that drive tissue homeostasis and regeneration. Moreover, appropriately prepared ECM is biodegradable and does not elicit adverse immune responses. Successful clinical application of decellularized tissues has been reported in cardiovascular, gastrointestinal, and breast reconstructive surgery. At present, the use of ECM for osteochondral tissue engineering is attracting interest. Recent data underscore the great promise for future application of decellularized ECM for osteochondral repair. This review describes the rationale for using ECM-based approaches for different regenerative purposes and details the application of ECM for cartilage or osteochondral repair.

Embryonic stem cell-derived microvesicles induce gene expression changes in Müller cells of the retina

Cell-derived microvesicles (MVs), recognized as important components of cell-cell communication, contain mRNAs, miRNAs, proteins and lipids and transfer their bioactive contents from parent cells to cells of other origins. We have studied the effect that MVs released from embryonic stem cells (ESMVs) have on retinal progenitor Müller cells. Cultured human Müller cells were exposed to mouse ESMVs every 48 hours for a total of 9 treatments. Morphological changes were observed by light microscopy in the treated cells, which grew as individual heterogeneous cells, compared to the uniform, spindle-like adherent cellular sheets of untreated cells. ESMVs transferred to Müller cells embryonic stem cell (ESC) mRNAs involved in the maintenance of pluripotency, including Oct4 and Sox2, and the miRNAs of the 290 cluster, important regulators of the ESC-specific cell cycle. Moreover, ESMV exposure induced up-regulation of the basal levels of endogenous human Oct4 mRNA in Müller cells. mRNA and miRNA microarrays of ESMV-treated vs. untreated Müller cells revealed the up-regulation of genes and miRNAs involved in the induction of pluripotency, cellular proliferation, early ocular genes and genes important for retinal protection and remodeling, as well as the down-regulation of inhibitory and scar-related genes and miRNAs involved in differentiation and cell cycle arrest. To further characterize the heterogeneous cell population of ESMV-treated Müller cells, their expression of retinal cell markers was compared to that in untreated control cells by immunocytochemistry. Markers for amacrine, ganglion and rod photoreceptors were present in treated but not in control Müller cells. Together, our findings indicate that ESMs induce de-differentiation and pluripotency in their target Müller cells, which may turn on an early retinogenic program of differentiation.