Physiological Replication of the Human Glomerulus Using a Triple Culture Microphysiological System.

The function of the glomerulus depends on the complex cell-cell/matrix interactions and replication of this in vitro would aid biological understanding in both health and disease. Previous models do not fully reflect all cell types and interactions present as they overlook mesangial cells within their 3D matrix. Herein, the development of a microphysiological system that contains all resident renal cell types in an anatomically relevant manner is presented. A detailed transcriptomic analysis of the contributing biology of each cell type, as well as functionally appropriate albumin retention in the system, is demonstrated. The important role of mesangial cells is shown in promoting the health and maturity of the other cell types. Additionally, a comparison of the incremental advances that each individual cell type brings to the phenotype of the others demonstrates that glomerular cells in simple 2D culture exhibit a state more reflective of the dysfunction observed in human disease than previously recognized. This in vitro model will expand the capability to investigate glomerular biology in a more translatable manner by the inclusion of the important mesangial cell compartment.

Human iPSCs and Genome Editing Technologies for Precision Cardiovascular Tissue Engineering.

Induced pluripotent stem cells (iPSCs) originate from the reprogramming of adult somatic cells using four Yamanaka transcription factors. Since their discovery, the stem cell (SC) field achieved significant milestones and opened several gateways in the area of disease modeling, drug discovery, and regenerative medicine. In parallel, the emergence of clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein 9 (CRISPR-Cas9) revolutionized the field of genome engineering, allowing the generation of genetically modified cell lines and achieving a precise genome recombination or random insertions/deletions, usefully translated for wider applications. Cardiovascular diseases represent a constantly increasing societal concern, with limited understanding of the underlying cellular and molecular mechanisms. The ability of iPSCs to differentiate into multiple cell types combined with CRISPR-Cas9 technology could enable the systematic investigation of pathophysiological mechanisms or drug screening for potential therapeutics. Furthermore, these technologies can provide a cellular platform for cardiovascular tissue engineering (TE) approaches by modulating the expression or inhibition of targeted proteins, thereby creating the possibility to engineer new cell lines and/or fine-tune biomimetic scaffolds. This review will focus on the application of iPSCs, CRISPR-Cas9, and a combination thereof to the field of cardiovascular TE. In particular, the clinical translatability of such technologies will be discussed ranging from disease modeling to drug screening and TE applications.

Both Specific Endothelial and Proximal Tubular Adam17 Deletion Protect against Diabetic Nephropathy.

ADAM17 is a disintegrin and metalloproteinase capable of cleaving the ectodomains of a diverse variety of molecules including TNF-α, TGF-α, L-selectin, and ACE2. We have previously demonstrated that renal ADAM17 is upregulated in diabetic mice. The role of endothelial (eAdam17) and proximal tubular (tAdam17) Adam17 deletion in renal histology, modulation of the renin angiotensin system (RAS), renal inflammation, and fibrosis was studied in a mouse model of type 1 Diabetes Mellitus. Moreover, the effect of Adam17 deletion in an in vitro 3D cell culture from human proximal tubular cells under high glucose conditions was evaluated. eAdam17 deletion attenuates renal fibrosis and inflammation, whereas tAdam17 deletion decreases podocyte loss, attenuates the RAS, and decreases macrophage infiltration, α-SMA and collagen accumulation. The 3D in vitro cell culture reinforced the findings obtained in tAdam17KO mice with decreased fibrosis in the Adam17 knockout spheroids. In conclusion, Adam17 deletion either in the endothelial or the tubular cells mitigates kidney injury in the diabetic mice by targeting different pathways. The manipulation of Adam17 should be considered as a therapeutic strategy for treating DN.

Human Cardiac Organoids for Modeling Genetic Cardiomyopathy.

Genetic cardiomyopathies are characterized by changes in the function and structure of the myocardium. The development of a novel in vitro model could help to better emulate healthy and diseased human heart conditions and may improve the understanding of disease mechanisms. In this study, for the first time, we demonstrated the generation of cardiac organoids using a triculture approach of human induced pluripotent stem-cell-derived cardiomyocytes (hiPS-CMs)-from healthy subjects and cardiomyopathy patients-human cardiac microvascular endothelial cells (HCMECs) and human cardiac fibroblasts (HCFs). We assessed the organoids' suitability as a 3D cellular model for the representation of phenotypical features of healthy and cardiomyopathic hearts. We observed clear differences in structure and beating behavior between the organoid groups, depending on the type of hiPS-CMs (healthy versus cardiomyopathic) used. Organoids may thus prove a promising tool for the design and testing of patient-specific treatments as well as provide a platform for safer and more efficacious drug development.

Cleavable cellulosic sponge for functional hepatic cell culture and retrieval.

Interconnected macroporous hydrogel is hydrophilic; it exhibits soft tissue-like mechanical property and aqueous-stable macroporosity for 3D spheroid culture. There is an unmet need to develop cleavable macroporous hydrogel, for the ease of retrieving functional spheroids for further in vitro and in vivo applications. We have developed and comprehensively characterized a hydroxypropyl-cellulose-disulfide sponge by systematically identifying strategies and synthesis schemes to confer cleavability to the sponge under cell-friendly conditions. It preserved the essential advantages of the macroporous hydrogel to support 3D spheroid formation and maintenance of sensitive hepatocytes while allowing rapid cleavage and retrieval of functional spheroids. By culturing HepaRG as spheroids in the cleavable sponge, we have accelerated HepaRG differentiation to 9 days compared to 28 days in 2D culture. Cytochrome P450 basal activity reached significantly higher level, while albumin secretion and fluorescein diacetate staining indicated the same at day 5. The purity of albumin+ hepatocytes reached 92.9% versus 7.1% of CK19+ cholangiocytes at day 9, a much stronger preference for hepatocytes than the 60% albumin+ hepatocytes purity in 2D culture. HepaRG differentiated hepatocytes were retrieved by cleaving the sponge with 10 mM tris-(2-carboxyethyl)-phosphine (TCEP) within 30 min preserving viability, plateability and positive albumin staining of the hepatocyte spheroids. This cleavable macroporous hydrogel sponge will support the rapid development of various 3D spheroid- or organoid-based applications in basic research and drug testing.

Human Cardiac Organoids for Disease Modeling.

Human cardiac drug discovery and disease modeling face challenges in recapitulating cellular complexity and animal-to-human translation due to the limitations of conventional 2D cell culture and animal models. The development of human cardiac organoid technologies could help in stimulating and maintaining differentiated cell functions for extended periods of time. By closely mimicking in vivo organ functions in vitro they could thereby help in overcoming the obstacles mentioned above. Through the construction of human cardiac organoids from pluripotent stem cell-derived cells, derived from patients with specific known genotypes and phenotypes, more complex and robust in vitro tools have recently become available for disease modeling. In this review, we will describe the relevance and importance of evolving organoid platforms in disease biology. We further provide examples of cardiac organoid platforms, which may lead the way toward future personalized medicine and drug discovery.

Monitoring and manipulating cellular crosstalk during kidney fibrosis inside a 3D in vitro co-culture.

In pharmacological research the development of promising lead compounds requires a detailed understanding of the dynamics of disease progression. However, for many diseases, such as kidney fibrosis, gaining such understanding requires complex real-time, multi-dimensional analysis of diseased and healthy tissue. To allow for such studies with increased throughput we established a dextran hydrogel-based in vitro 3D co-culture as a disease model for kidney fibrosis aimed at the discovery of compounds modulating the epithelial/mesenchymal crosstalk. This platform mimics a simplified pathological renal microenvironment at the interface between tubular epithelial cells and surrounding quiescent fibroblasts. We combined this 3D technology with epithelial reporter cell lines expressing fluorescent biomarkers in order to visualize pathophysiological cell state changes resulting from toxin-mediated chemical injury. Epithelial cell damage onset was robustly detected by image-based monitoring, and injured epithelial spheroids induced myofibroblast differentiation of co-cultured quiescent human fibroblasts. The presented 3D co-culture system therefore provides a unique model system for screening of novel therapeutic molecules capable to interfere and modulate the dialogue between epithelial and mesenchymal cells.

Constrained spheroids for prolonged hepatocyte culture.

Liver-specific functions in primary hepatocytes can be maintained over extended duration in vitro using spheroid culture. However, the undesired loss of cells over time is still a major unaddressed problem, which consequently generates large variations in downstream assays such as drug screening. In static culture, the turbulence generated by medium change can cause spheroids to detach from the culture substrate. Under perfusion, the momentum generated by Stokes force similarly results in spheroid detachment. To overcome this problem, we developed a Constrained Spheroids (CS) culture system that immobilizes spheroids between a glass coverslip and an ultra-thin porous Parylene C membrane, both surface-modified with poly(ethylene glycol) and galactose ligands for optimum spheroid formation and maintenance. In this configuration, cell loss was minimized even when perfusion was introduced. When compared to the standard collagen sandwich model, hepatocytes cultured as CS under perfusion exhibited significantly enhanced hepatocyte functions such as urea secretion, and CYP1A1 and CYP3A2 metabolic activity. We propose the use of the CS culture as an improved culture platform to current hepatocyte spheroid-based culture systems.

Scalable spheroid model of human hepatocytes for hepatitis C infection and replication.

Developing effective new drugs against hepatitis C (HCV) virus has been challenging due to the lack of appropriate small animal and in vitro models recapitulating the entire life cycle of the virus. Current in vitro models fail to recapitulate the complexity of human liver physiology. Here we present a method to study HCV infection and replication on spheroid cultures of Huh 7.5 cells and primary human hepatocytes. Spheroid cultures are constructed using a galactosylated cellulosic sponge with homogeneous macroporosity, enabling the formation and maintenance of uniformly sized spheroids. This facilitates easy handling of the tissue-engineered constructs and overcomes limitations inherent of traditional spheroid cultures. Spheroids formed in the galactosylated cellulosic sponge show enhanced hepatic functions in Huh 7.5 cells and maintain liver-specific functions of primary human hepatocytes for 2 weeks in culture. Establishment of apical and basolateral polarity along with the expression and localization of all HCV specific entry proteins allow for a 9-fold increase in viral entry in spheroid cultures over conventional monolayer cultures. Huh 7.5 cells cultured in the galactosylated cellulosic sponge also support replication of the HCV clone, JFH (Japanese fulminant hepatitis)-1 at higher levels than in monolayer cultures. The advantages of our system in maintaining liver-specific functions and allowing HCV infection together with its ease of handling make it suitable for the study of HCV biology in basic research and pharmaceutical R&D.

Hepatic stellate cell-targeted delivery of hepatocyte growth factor transgene via bile duct infusion enhances its expression at fibrotic foci to regress dimethylnitrosamine-induced liver fibrosis.

Liver fibrosis generates fibrotic foci with abundant activated hepatic stellate cells and excessive collagen deposition juxtaposed with healthy regions. Targeted delivery of antifibrotic therapeutics to hepatic stellate cells (HSCs) might improve treatment outcomes and reduce adverse effects on healthy tissue. We delivered the hepatocyte growth factor (HGF) gene specifically to activated hepatic stellate cells in fibrotic liver using vitamin A-coupled liposomes by retrograde intrabiliary infusion to bypass capillarized hepatic sinusoids. The antifibrotic effects of DsRed2-HGF vector encapsulated within vitamin A-coupled liposomes were validated by decreases in fibrotic markers in vitro. Fibrotic cultures transfected with the targeted transgene showed a significant decrease in fibrotic markers such as transforming growth factor-ß1. In rats, dimethylnitrosamine-induced liver fibrosis is manifested by an increase in collagen deposition and severe defenestration of sinusoidal endothelial cells. The HSC-targeted transgene, administered via retrograde intrabiliary infusion in fibrotic rats, successfully reduced liver fibrosis markers alpha-smooth muscle actin and collagen, accompanied by an increase in the expression of DsRed2-HGF near the fibrotic foci. Thus, targeted delivery of HGF gene to hepatic stellate cells increased the transgene expression at the fibrotic foci and strongly enhanced its antifibrotic effects.

Mechanical compaction directly modulates the dynamics of bile canaliculi formation.

Homeostatic pressure-driven compaction is a ubiquitous mechanical force in multicellular organisms and is proposed to be important in the maintenance of multicellular tissue integrity and function. Previous cell-free biochemical models have demonstrated that there are cross-talks between compaction forces and tissue structural functions, such as cell-cell adhesion. However, its involvement in physiological tissue function has yet to be directly demonstrated. Here, we use the bile canaliculus (BC) as a physiological example of a multicellular functional structure in the liver, and employ a novel 3D microfluidic hepatocyte culture system to provide an unprecedented opportunity to experimentally modulate the compaction states of primary hepatocyte aggregates in a 3D physiological-mimicking environment. Mechanical compaction alters the physical attributes of the hepatocyte aggregates, including cell shape, cell packing density and cell-cell contact area, but does not impair the hepatocytes' remodeling and functional capabilities. Characterization of structural and functional polarity shows that BC formation in compact hepatocyte aggregates is accelerated to as early as 12 hours post-seeding; whereas non-compact control requires 48 hours for functional BC formation. Further dynamic immunofluorescence imaging and gene expression profiling reveal that compaction accelerated BC formation is accompanied by changes in actin cytoskeleton remodeling dynamics and transcriptional levels of hepatic nuclear factor 4α and Annexin A2. Our report not only provides a novel strategy of modeling BC formation for in vitro hepatology research, but also shows a first instance that homeostatic pressure-driven compaction force is directly coupled to the higher-order multicellular functions.

Tethered spheroids as an in vitro hepatocyte model for drug safety screening.

Hepatocyte spheroids mimic many in vivo liver-tissue phenotypes but increase in size during extended culture which limits their application in drug testing applications. We have developed an improved hepatocyte 3D spheroid model, namely tethered spheroids, on RGD and galactose-conjugated membranes using an optimized hybrid ratio of the two bioactive ligands. Cells in the spheroid configuration maintained 3D morphology and uncompromised differentiated hepatocyte functions (urea and albumin production), while the spheroid bottom was firmly tethered to the substratum maintaining the spheroid size in multi-well plates. The oblate shape of the tethered spheroids, with an average height of 32 µm, ensured efficient nutrient, oxygen and drug access to all the cells within the spheroid structure. Cytochrome P450 induction by prototypical inducers was demonstrated in the tethered spheroids and was comparable or better than that observed with hepatocyte sandwich cultures. These data suggested that tethered 3D hepatocyte spheroids may be an excellent alternative to 2D hepatocyte culture models for drug safety applications.

Influence of cell culture configuration on the post-cryopreservation viability of primary rat hepatocytes.

Cryopreservation has been identified as a necessary barrier to overcome in the production of tissue engineered products for clinical application. Liver engineering and bioartificial liver assisting devices are on the forefront of tissue engineering research due to its high demand and clinical potential. In this study we propose that the cryopreservation of primary mammalian hepatocytes yields better results when these cells are in a tissue-like culture configuration since cell attachment is essential for cell survival in this cell type. We used two different tissue-engineered culture configurations: monolayers and spheroid culture; and two different concepts of cryopreservation, namely vitrification and freezing. Cell suspensions were also cryopreserved using both approaches and results were compared to the engineered cultures. Both engineered configurations and suspension were cryopreserved using both conventional freezing (cooling at 1 °C/minute using 10% DMSO in foetal calf serum) and vitrification (using 40% ethylene glycol 0.6 m sucrose supplemented with 9% Ficoll). These two approaches differ on the degree of mechanical stress they inflict on the material to be cryopreserved. The maintenance of cell-to-cell and the integrity of the actin cytoskeleton were assessed using scanning electron microscopy and immunohistochemistry respectively. Results showed that while there was no significant difference between the degree of integrity shown between vitrified and control engineered cultures, the same did not happen to the frozen engineered constructs. The disruption of the cytoskeletal structure correlated with increased levels of apoptotic markers. With cryopreserved suspensions there was evidence of disruption of the cytoskeletal structure. This study concluded that cell-to-cell contact is beneficial in the maintenance of viability post-cryopreservation and that the vitrification approach was far superior to those of conventional freezing when applied to 2D and 3D hepatocyte based engineered cultures.

Galactosylated cellulosic sponge for multi-well drug safety testing.

Hepatocyte spheroids can maintain mature differentiated functions, but collide to form bulkier structures when in extended culture. When the spheroid diameter exceeds 200 µm, cells in the inner core experience hypoxia and limited access to nutrients and drugs. Here we report the development of a thin galactosylated cellulosic sponge to culture hepatocytes in multi-well plates as 3D spheroids, and constrain them within a macroporous scaffold network to maintain spheroid size and prevent detachment. The hydrogel-based soft sponge conjugated with galactose provided suitable mechanical and chemical cues to support rapid formation of hepatocyte spheroids with a mature hepatocyte phenotype. The spheroids tethered in the sponge showed excellent maintenance of 3D cell morphology, cell-cell interaction, polarity, metabolic and transporter function and/or expression. For example, cytochrome P450 (CYP1A2, CYP2B2 and CYP3A2) activities were significantly elevated in spheroids exposed to ß-naphthoflavone, phenobarbital, or pregnenolone-16α-carbonitrile, respectively. The sponge also exhibits minimal drug absorption compared to other commercially available scaffolds. As the cell seeding and culture protocols are similar to various high-throughput 2D cell-based assays, this platform is readily scalable and provides an alternative to current hepatocyte platforms used in drug safety testing applications.

Rapid construction of mechanically- confined multi- cellular structures using dendrimeric intercellular linker.

Tissue constructs that mimic the in vivo cell-cell and cell-matrix interactions are especially useful for applications involving the cell- dense and matrix- poor internal organs. Rapid and precise arrangement of cells into functional tissue constructs remains a challenge in tissue engineering. We demonstrate rapid assembly of C3A cells into multi- cell structures using a dendrimeric intercellular linker. The linker is composed of oleyl- polyethylene glycol (PEG) derivatives conjugated to a 16 arms- polypropylenimine hexadecaamine (DAB) dendrimer. The positively charged multivalent dendrimer concentrates the linker onto the negatively charged cell surface to facilitate efficient insertion of the hydrophobic oleyl groups into the cellular membrane. Bringing linker- treated cells into close proximity to each other via mechanical means such as centrifugation and micromanipulation enables their rapid assembly into multi- cellular structures within minutes. The cells exhibit high levels of viability, proliferation, three- dimensional (3D) cell morphology and other functions in the constructs. We constructed defined multi- cellular structures such as rings, sheets or branching rods that can serve as potential tissue building blocks to be further assembled into complex 3D tissue constructs for biomedical applications.

Control of in vitro neural differentiation of mesenchymal stem cells in 3D macroporous, cellulosic hydrogels.

BACKGROUND: Mesenchymal stem cells (MSCs) are multipotent cells that can be induced to differentiate into multiple cell lineages, including neural cells. They are a good cell source for neural tissue-engineering applications. Cultivation of human (h)MSCs in 3D scaffolds is an effective means for the development of novel neural tissue-engineered constructs, and may serve as a promising strategy in the treatment of nerve injury. AIM: This study presents the in vitro growth and neural differentiation of hMSCs in 3D macroporous, cellulosic hydrogels. RESULTS: The number of hMSCs cultivated in the 3D scaffolds increased by more than 14-fold after 7 days. After 2 days induction, most of the hMSCs in the 3D scaffolds were positive for nestin, a marker of neural stem cells. After 7 days induction, most of the hMSCs in the 3D scaffolds showed glial fibrillary acidic protein, tubulin or neurofilament M-positive reaction and a few hMSCs were positive for nestin. After 14 days induction, hMSCs in the 3D scaffolds could completely differentiate into neurons and glial cells. The neural differentiation of hMSCs in the 3D scaffolds was further demonstrated by real-time PCR. CONCLUSION: These results show that the 3D macroporous cellulosic hydrogel could be an appropriate substrate for neural differentiation of hMSCs and its possible applications in neural tissue engineering are discussed.