Controlling stem cell behavior with decellularized extracellular matrix scaffolds

Decellularized tissues have become a common regenerative medicine platform with multiple materials being researched in academic laboratories, tested in animal studies, and used clinically. Ideally, when a tissue is decellularized the native cell niche is maintained with many of the structural and biochemical cues that naturally interact with the cells of that particular tissue. This makes decellularized tissue materials an excellent platform for providing cells with the signals needed to initiate and maintain differentiation into tissue-specific lineages. The extracellular matrix (ECM) that remains after the decellularization process contains the components of a tissue specific microenvironment that is not possible to create synthetically. The ECM of each tissue has a different composition and structure and therefore has unique properties and potential for affecting cell behavior. This review describes the common methods for preparing decellularized tissue materials and the effects that decellularized materials from different tissues have on cell phenotype.

The cytoprotective capacity of processed human cardiac extracellular matrix

Freshly isolated human cardiac extracellular matrix sheets (cECM) have been shown to support stem cell proliferation and tissue-specific lineage commitment. We now developed a protocol for standardized production of durable, bio-functional hcECM microparticles and corresponding hydrogel, and tested its cytoprotective effects on contractile cells subjected to ischemia-like conditions. Human ventricular myocardium was decellularized by a 3-step protocol, including Tris/EDTA, SDS and serum incubation (cECM). Following snap-freezing and lyophilization, microparticles were created and characterized by laser diffraction, dynamic image analysis (DIA), and mass spectrometry. Moreover, cECM hydrogel was produced by pepsin digestion. Baseline cell-support characteristics were determined using murine HL-1 cardiomyocytes, and the cytoprotective effects of ECM products were tested under hypoxia and glucose/serum deprivation. In cECM, glycoproteins (thrombospondin 1, fibronectin, collagens and nidogen-1) and proteoglycans (dermatopontin, lumican and mimecan) were preserved, but residual intracellular and blood-borne proteins were also detected. The median particle feret diameter was 66 μm (15-157 μm) by laser diffraction, and 57 μm (20-182 μm) by DIA with crystal violet staining. HL-1 cells displayed enhanced metabolic activity (39 ± 12 %, P < 0.05) and proliferation (16 ± 3 %, P < 0.05) when grown on cECM microparticles in normoxia. During simulated ischemia, cECM microparticles exerted distinct cytoprotective effects (MTS conversion, 240 ± 32 %; BrdU uptake, 45 ± 14 %; LDH release, -72 ± 7 %; P < 0.01, each). When cECM microparticles were solubilized to form a hydrogel, the cytoprotective effect was initially abolished. However, modifying the preparation process (pepsin digestion at pH 2 and 25 °C, 1 mg/ml final cECM concentration) restored the cytoprotective cECM activity. Extracellular matrix from human myocardium can be processed to yield standardized durable microparticles that exert specific cytoprotective effects on cardiomyocyte-like cells. The use of processed cECM may help to optimize future clinical-grade myocardial tissue engineering approaches.

Rebuilding the Damaged Heart: Mesenchymal Stem Cells, Cell-Based Therapy, and Engineered Heart Tissue

Mesenchymal stem cells (MSCs) are broadly distributed cells that retain postnatal capacity for self-renewal and multilineage differentiation. MSCs evade immune detection, secrete an array of anti-inflammatory and anti-fibrotic mediators, and very importantly activate resident precursors. These properties form the basis for the strategy of clinical application of cell-based therapeutics for inflammatory and fibrotic conditions. In cardiovascular medicine, administration of autologous or allogeneic MSCs in patients with ischemic and nonischemic cardiomyopathy holds significant promise. Numerous preclinical studies of ischemic and nonischemic cardiomyopathy employing MSC-based therapy have demonstrated that the properties of reducing fibrosis, stimulating angiogenesis, and cardiomyogenesis have led to improvements in the structure and function of remodeled ventricles. Further attempts have been made to augment MSCs' effects through genetic modification and cell preconditioning. Progression of MSC therapy to early clinical trials has supported their role in improving cardiac structure and function, functional capacity, and patient quality of life. Emerging data have supported larger clinical trials that have been either completed or are currently underway. Mechanistically, MSC therapy is thought to benefit the heart by stimulating innate anti-fibrotic and regenerative responses. The mechanisms of action involve paracrine signaling, cell-cell interactions, and fusion with resident cells. Trans-differentiation of MSCs to bona fide cardiomyocytes and coronary vessels is also thought to occur, although at a nonphysiological level. Recently, MSC-based tissue engineering for cardiovascular disease has been examined with quite encouraging results. This review discusses MSCs from their basic biological characteristics to their role as a promising therapeutic strategy for clinical cardiovascular disease.

In vivo experience with natural scaffolds for myocardial infarction: the times they are a-changin'

Treating a myocardial infarction (MI), the most frequent cause of death worldwide, remains one of the most exciting medical challenges in the 21st century. Cardiac tissue engineering, a novel emerging treatment, involves the use of therapeutic cells supported by a scaffold for regenerating the infarcted area. It is essential to select the appropriate scaffold material; the ideal one should provide a suitable cellular microenvironment, mimic the native myocardium, and allow mechanical and electrical coupling with host tissues. Among available scaffold materials, natural scaffolds are preferable for achieving these purposes because they possess myocardial extracellular matrix properties and structures. Here, we review several natural scaffolds for applications in MI management, with a focus on pre-clinical studies and clinical trials performed to date. We also evaluate scaffolds combined with different cell types and proteins for their ability to promote improved heart function, contractility and neovascularization, and attenuate adverse ventricular remodeling. Although further refinement is necessary in the coming years, promising results indicate that natural scaffolds may be a valuable translational therapeutic option with clinical impact in MI repair.

Bioengineering Human Myocardium on Native Extracellular Matrix

RATIONALE

More than 25 million individuals have heart failure worldwide, with ≈4000 patients currently awaiting heart transplantation in the United States. Donor organ shortage and allograft rejection remain major limitations with only ≈2500 hearts transplanted each year. As a theoretical alternative to allotransplantation, patient-derived bioartificial myocardium could provide functional support and ultimately impact the treatment of heart failure.

OBJECTIVE

The objective of this study is to translate previous work to human scale and clinically relevant cells for the bioengineering of functional myocardial tissue based on the combination of human cardiac matrix and human induced pluripotent stem cell-derived cardiomyocytes.

METHODS AND RESULTS

To provide a clinically relevant tissue scaffold, we translated perfusion-decellularization to human scale and obtained biocompatible human acellular cardiac scaffolds with preserved extracellular matrix composition, architecture, and perfusable coronary vasculature. We then repopulated this native human cardiac matrix with cardiomyocytes derived from nontransgenic human induced pluripotent stem cells and generated tissues of increasing 3-dimensional complexity. We maintained such cardiac tissue constructs in culture for 120 days to demonstrate definitive sarcomeric structure, cell and matrix deformation, contractile force, and electrical conduction. To show that functional myocardial tissue of human scale can be built on this platform, we then partially recellularized human whole-heart scaffolds with human induced pluripotent stem cell-derived cardiomyocytes. Under biomimetic culture, the seeded constructs developed force-generating human myocardial tissue and showed electrical conductivity, left ventricular pressure development, and metabolic function.

CONCLUSIONS

Native cardiac extracellular matrix scaffolds maintain matrix components and structure to support the seeding and engraftment of human induced pluripotent stem cell-derived cardiomyocytes and enable the bioengineering of functional human myocardial-like tissue of multiple complexities.

Porous, Ventricular Extracellular Matrix-Derived Foams as a Platform for Cardiac Cell Culture

To more closely mimic the native cellular microenvironment, 3D scaffolds derived from the extracellular matrix (ECM) are being developed as alternatives to conventional 2D culture systems. In the present study, we established methods to fabricate nonchemically cross-linked 3D porous foams derived entirely from decellularized porcine left ventricle (DLV) for use as an in vitro cardiac cell culture platform. Furthermore, we explored the effects of physically preprocessing the DLV through mechanical mincing versus cryomilling, as well as varying the ECM concentration on the structure, composition, and physical properties of the foams. Our results indicate that the less highly processed minced foams had a more cohesive and complex network of ECM components, enhanced mechanical properties, and improved stability under simulated culturing conditions. To validate the DLV foams, a proof-of-concept study was conducted to explore the early cardiomyogenic differentiation of pericardial fat adipose-derived stem/stromal cells (pfASCs) on the minced DLV foams relative to purified collagen I gel controls. Differentiation was induced using a modified cardiomyogenic medium (MCM) or through stimulation with 5-azacytidine (5-aza), and cardiomyocyte marker expression was characterized by immunohistochemistry and real-time reverse transcriptase-polymerase chain reaction. Our results indicate that early markers of cardiomyogenic differentiation were significantly enhanced on the DLV foams cultured in MCM, suggesting a synergistic effect of the cardiac ECM-derived scaffolds and the culture medium on the induction of pfASC differentiation. Furthermore, in analyzing the response in the noninduced control groups, the foams were observed to provide a mildly inductive microenvironment for pfASC cardiomyogenesis, supporting the rationale for using tissue-specific ECM as a substrate for cardiac cell culture applications.

Decellularized amniotic membrane attenuates postinfarct left ventricular remodeling

BACKGROUND

Placenta and amnion have been suggested as sources of juvenile cells and tissues for use in surgical regenerative medicine. We previously determined the impact of amniotic epithelial cells induced to undergo epithelial-to-mesenchymal transition (EMT) on myocardial remodeling processes and now evaluated the effects of naïve and processed amniotic membrane (AM) on postischemic left ventricular (LV) geometry and function.

METHODS

Human AM was used in unmodified form (AM), after EMT induction by transforming growth factor β (EMT-AM), and after decellularization (Decell-AM). After characterization by histology, electron microscopy, splenocyte proliferation assay, and cytokine release, myocardial infarction was induced in 6-8-week old male BALB/c mice by permanent left anterior descending coronary occlusion, and AM patches were sutured to the anterior LV surface (n = 10 per group). Infarcted hearts without AM or sham-operated mice were used as controls (n = 10 each). After 4 weeks, LV pressure-volume curves were recorded using a conductance catheter before the animals were sacrificed and the hearts analyzed by histology.

RESULTS

TGF-ß treatment induced EMT-like changes in amniotic epithelial cells but increased AM xenoreactivity in vitro (splenocyte proliferation) and in vivo (CD4+ cell invasion). Moreover, in vitro interleukin-6 release from AM and from cardiac fibroblasts co-incubated with AM was 300- or 100-fold higher than that of interleukin-10, whereas Decell-AM did not release any cytokines. AM- and Decell-AM-treated hearts had smaller infarct size and greater infarct scar thickness than infarct control hearts, but there was no difference in myocardial capillary density or the number of TUNEL positive apoptotic cells. LV contractile function was better in the AM and EMT-AM groups than in infarcted control hearts, but dP/dt max, dP/dt min, stroke work, and cardiac output were best preserved in mice treated with Decell-AM. Volume-based parameters (LV end-systolic and end-diastolic volume as well as LV ejection fraction) did not differ between AM and Decell-AM.

CONCLUSIONS

Decellularized AM supports postinfarct ventricular dynamics independent of the actual regeneration processes. As a cell-free approach to support the infarcted heart, this concept warrants further investigation.

Bioengineering for Organ Transplantation: Progress and Challenges

Organ transplantation can offer a curative option for patients with end stage organ failure. Unfortunately the treatment is severely limited by the availability of donor organs. Organ bioengineering could provide a solution to the worldwide critical organ shortage. The majority of protocols to date have employed the use of decellularization-recellularization technology of naturally occurring tissues and organs with promising results in heart, lung, liver, pancreas, intestine and kidney engineering. Successful decellularization has provided researchers with suitable scaffolds to attempt cell reseeding. Future work will need to focus on the optimization of organ specific recellularization techniques before organ bioengineering can become clinically translatable. This review will examine the current progress in organ bioengineering and highlight future challenges in the field.

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.

Novel xeno-free human heart matrix-derived three-dimensional scaffolds

Rationale

Myocardial infarction (MI) results in damaged heart tissue which can progress to severely reduce cardiac function, leading to death. Recent studies have injected dissociated, suspended cardiac cells into coronary arteries to restore function with limited results attributed to poor cell retention and cell death. Extracellular matrix (ECM) injected into damaged cardiac tissue sites show some promising effects. However, combined use of human cardiac ECM and cardiac cells may produce superior benefits to restore cardiac function.

Objective

This study was designed to assess use of new three-dimensional human heart ECM-derived scaffolds to serve as vehicles to deliver cardiac-derived cells directly to damaged heart tissue and improve cell retention at these sites while also providing biomechanical support and attracting host cell recruitment.

Methods and Results

ECM-derived porous protein scaffolds were fabricated from human heart tissues. These scaffolds were designed to carry, actively promote and preserve cardiac cell phenotype, viability and functional retention in tissue sites. ECM scaffolds were optimized and were seeded with human cardiomyocytes, cultured and subsequently implanted ex vivo onto infarcted murine epicardium. Seeded human cardiomyocytes readily adhered to human cardiac-derived ECM scaffolds and maintained representative phenotypes including expression of cardiomyocyte-specific markers, and remained electrically synchronous within the scaffold in vitro. Ex vivo, cardiomyocyte-seeded ECM scaffolds spontaneously adhered and incorporated into murine ventricle.

Conclusions

Decellularized human cardiac tissue-derived 3D ECM scaffolds are effective delivery vehicles for human cardiac cells to directly target ischemic heart tissue and warrant further studies to assess their therapeutic potential in restoring essential cardiac functions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0559-0) contains supplementary material, which is available to authorized users.

From cardiac tissue engineering to heart-on-a-chip: beating challenges

The heart is one of the most vital organs in the human body, which actively pumps the blood through the vascular network to supply nutrients to as well as to extract wastes from all other organs, maintaining the homeostasis of the biological system. Over the past few decades, tremendous efforts have been exerted in engineering functional cardiac tissues for heart regeneration via biomimetic approaches. More recently, progress has been made toward the transformation of knowledge obtained from cardiac tissue engineering to building physiologically relevant microfluidic human heart models (i.e. heart-on-chips) for applications in drug discovery. The advancement in stem cell technologies further provides the opportunity to create personalized in vitro models from cells derived from patients. Here, starting from heart biology, we review recent advances in engineering cardiac tissues and heart-on-a-chip platforms for their use in heart regeneration and cardiotoxic/cardiotherapeutic drug screening, and then briefly conclude with characterization techniques and personalization potential of the cardiac models.

Engineered heart slices for electrophysiological and contractile studies

A major consideration in the design of engineered cardiac tissues for the faithful representation of physiological behavior is the recapitulation of the complex topography and biochemistry of native tissue. In this study we present engineered heart slices (EHS), which consist of neonatal rat ventricular cells (NRVCs) seeded onto thin slices of decellularized cardiac tissue that retain important aspects of native extracellular matrix (ECM). To form EHS, rat or pig ventricular tissue was sectioned into 300 μm-thick, 5 to 16 mm-diameter disks, which were subsequently decellularized using detergents, spread on coverslips, and seeded with NRVCs. The organized fiber structure of the ECM remained after decellularization and promoted cell elongation and alignment, resulting in an anisotropic, functional tissue that could be electrically paced. Contraction decreased at higher pacing rates, and optical mapping revealed electrical conduction that was anisotropic with a ratio of approximately 2.0, rate-dependent shortening of the action potential and slowing of conduction, and slowing of conduction by the sodium channel blocker lidocaine. Reentrant arrhythmias could also be pace-induced and terminated. EHS constitute an attractive in vitro cardiac tissue in which cardiac cells are cultured on thin slices of decellularized cardiac ECM that provide important biochemical, structural, and mechanical cues absent in traditional cell cultures.

Human cardiac extracellular matrix supports myocardial lineage commitment of pluripotent stem cells

OBJECTIVES

Cross-talk between organ-specific extracellular matrix (ECM) and stem cells is often assumed but has not been directly demonstrated. We developed a protocol for the preparation of human cardiac ECM (cECM) and studied whether cECM has effects on pluripotent stem cell differentiation that may be useful for future cardiac regeneration strategies in patients with end-stage heart failure.

METHODS

Of note, 0.3 mm-thick cECM slices were prepared from samples of myocardium from patients with end-stage non-ischaemic dilated cardiomyopathy, using a three-step protocol involving hypotonic lysis buffer, sodium dodecyl sulphate (SDS) and foetal bovine serum (FBS). Murine embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs) and mesenchymal stromal cells (MSCs) were seeded and grown in standard culture, on cECM or on non-specific ECM preparations (Matrigel® or Geltrex®). Cell attachment, apoptosis induction (Caspase 3/7 activity) and metabolic activity (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium conversion) were followed. Transcriptional activation of genes involved in pluripotency; early and late myocardial development; and endothelial, ectodermal or endodermal commitment were monitored by quantitative real-time polymerase chain reaction (rtPCR). Protein expression of selected markers was confirmed by immunohistology.

RESULTS

cECM supported the proliferation of ESCs and iPSCs, and Caspase 3/7 activity was significantly lower compared with standard culture. Cardiac lineage commitment was favoured when ESCs or iPSCs were grown on cECM, as evidenced by the significantly increased mRNA expression of cardiac alpha myosin heavy polypeptide 6 (Myh6), cardiac troponin T2 (Tnnt2) and NK2 homeobox 5 (Nkx2.5) as well as positive immunohistology for cardiac troponin T and heavy-chain cardiac myosin protein. In contrast, Matrigel or Geltrex did not induce cardiac-specific markers. MSCs showed no evidence of cardiomyocyte differentiation.

CONCLUSIONS

Human cardiac ECM seems to direct differentiation of pluripotent stem cells towards a cardiomyocyte phenotype. This phenomenon supports the use of cardiac ECM preparations for guided stem cell differentiation and myocardial repair, and may ultimately increase the therapeutic efficacy of cell therapy in heart failure patients.