Mechanobiology of human pluripotent stem cells

Neighbor-specific gene expression revealed from physically interacting cells during mouse embryonic development

Development of multicellular organisms is orchestrated by persistent cell-cell communication between neighboring partners. Direct interaction between different cell types can induce molecular signals that dictate lineage specification and cell fate decisions. Current single-cell RNA-seq technology cannot adequately analyze cell-cell contact-dependent gene expression, mainly due to the loss of spatial information. To overcome this obstacle and resolve cell-cell contact-specific gene expression during embryogenesis, we performed RNA sequencing of physically interacting cells (PIC-seq) and assessed them alongside similar single-cell transcriptomes derived from developing mouse embryos between embryonic day (E) 7.5 and E9.5. Analysis of the PIC-seq data identified gene expression signatures that were dependent on the presence of specific neighboring cell types. Our computational predictions, validated experimentally, demonstrated that neural progenitor (NP) cells upregulate Lhx5 and Nkx2-1 genes, when exclusively interacting with definitive endoderm (DE) cells. Moreover, there was a reciprocal impact on the transcriptome of DE cells, as they tend to upregulate Rax and Gsc when in contact with NP cells. Using individual cell transcriptome data, we formulated a means of computationally predicting the impact of one cell type on the transcriptome of its neighboring cell types. We have further developed a distinctive spatial-t-distributed stochastic neighboring embedding to display the pseudospatial distribution of cells in a 2-dimensional space. In summary, we describe an innovative approach to study contact-specific gene regulation during embryogenesis.

Surface Engineering of Auxetic Scaffolds for Neural and Vascular Differentiation from Human Pluripotent Stem Cells

Auxetic materials are the materials that can display negative Poisson's ratio that describes the degree to which a material contracts (or expands) transversally when axially strained. Human stem cells sense the mechanical properties of the microenvironment, including material surface properties, stiffness, and Poisson's ratio. In this study, six different auxetic polyurethane (PU) foams with different elastic modulus (0.7-1.8 kPa) and Poisson's ratio (-0.1 to -0.5) are used to investigate lineage specification of human induced pluripotent stem cells (hiPSCs). The surfaces of the foams are modified with chitosan or heparin to enhance the adhesion and proliferation of hiPSCs. Then, the vascular and neural differentiation of hiPSCs are investigated on different foams with distinct elastic modulus and Poisson's ratio. With different auxetic foams, cells show differential adherent density and differentiation capacity. Chitosan and heparin surface functionalization promote the hindbrain and hippocampal markers, but not forebrain markers during neural patterning of hiPSCs. Properly surface engineered auxetic scaffolds can also promote vascular differentiation of hiPSCs. This study represents a versatile and multifunctional scaffold fabrication approach and can lead to a suitable system for establishing hiPSC culture models in applications of neurovascular disease modeling and drug screening.

Single-Use Bioreactors for Human Pluripotent and Adult Stem Cells: Towards Regenerative Medicine Applications

Research on human stem cells, such as pluripotent stem cells and mesenchymal stromal cells, has shown much promise in their use for regenerative medicine approaches. However, their use in patients requires large-scale expansion systems while maintaining the quality of the cells. Due to their characteristics, bioreactors have been regarded as ideal platforms to harbour stem cell biomanufacturing at a large scale. Specifically, single-use bioreactors have been recommended by regulatory agencies due to reducing the risk of product contamination, and many different systems have already been developed. This review describes single-use bioreactor platforms which have been used for human stem cell expansion and differentiation, along with their comparison with reusable systems in the development of a stem cell bioprocess for clinical applications.

Mechanotranduction Pathways in the Regulation of Mitochondrial Homeostasis in Cardiomyocytes

Mitochondria are one of the most important organelles in cardiomyocytes. Mitochondrial homeostasis is necessary for the maintenance of normal heart function. Mitochondria perform four major biological processes in cardiomyocytes: mitochondrial dynamics, metabolic regulation, Ca2+ handling, and redox generation. Additionally, the cardiovascular system is quite sensitive in responding to changes in mechanical stress from internal and external environments. Several mechanotransduction pathways are involved in regulating the physiological and pathophysiological status of cardiomyocytes. Typically, the extracellular matrix generates a stress-loading gradient, which can be sensed by sensors located in cellular membranes, including biophysical and biochemical sensors. In subsequent stages, stress stimulation would regulate the transcription of mitochondrial related genes through intracellular transduction pathways. Emerging evidence reveals that mechanotransduction pathways have greatly impacted the regulation of mitochondrial homeostasis. Excessive mechanical stress loading contributes to impairing mitochondrial function, leading to cardiac disorder. Therefore, the concept of restoring mitochondrial function by shutting down the excessive mechanotransduction pathways is a promising therapeutic strategy for cardiovascular diseases. Recently, viral and non-viral protocols have shown potentials in application of gene therapy. This review examines the biological process of mechanotransduction pathways in regulating mitochondrial function in response to mechanical stress during the development of cardiomyopathy and heart failure. We also summarize gene therapy delivery protocols to explore treatments based on mechanical stress-induced mitochondrial dysfunction, to provide new integrative insights into cardiovascular diseases.

Mapping the Mechanome-A Protocol for Simultaneous Live Imaging and Quantitative Analysis of Cell Mechanoadaptation and Ingression

Mechanomics, the mechanics equivalent of genomics, is a burgeoning field studying mechanical modulation of stem cell behavior and lineage commitment. Analogous to mechanical testing of a living material as it adapts and evolves, mapping of the mechanome necessitates the development of new protocols to assess changes in structure and function in live stem cells as they adapt and differentiate. Previous techniques have relied on imaging of cellular structures in fixed cells and/or live cell imaging of single cells with separate studies of changes in mechanical and biological properties. Here we present two complementary protocols to study mechanobiology and mechanoadaptation of live stem cells in adherent and motile contexts. First, we developed and tested live imaging protocols for simultaneous visualization and tracking of actin and tubulin mechanoadaptation as well as shape and volume of cells and their nuclei in adherent model embryonic murine mesenchymal stem cells (C3H/10T1/2) and in a neuroblastoma cell line. Then we applied the protocol to enable quantitative study of primary human mesenchymal stem cells in a motile state, e.g., ingression in a three-dimensional, in vitro cell culture model. Together, these protocols enable study of emergent structural mechanoadaptation of the cell's own cytoskeletal machinery while tracking lineage commitment using phenotypic (quantitative morphology measures) and genotypic (e.g., reverse transcription Polymerase Chain Reaction, rtPCR) methods. These tools are expected to facilitate the mapping of the mechanome and incipient mechanistic understanding of stem cell mechanobiology, from the cellular to the tissue and organ length scales.

Force Spectrum Microscopy Using Mitochondrial Fluctuations of Control and ATP-Depleted Cells

A single-cell assay of active and passive intracellular mechanical properties of mammalian cells could give significant insight into cellular processes. Force spectrum microscopy (FSM) is one such technique, which combines the spontaneous motion of probe particles and the mechanical properties of the cytoskeleton measured by active microrheology using optical tweezers to determine the force spectrum of the cytoskeleton. A simpler and noninvasive method to perform FSM would be very useful, enabling its widespread adoption. Here, we develop an alternative method of FSM using measurement of the fluctuating motion of mitochondria. Mitochondria of the C3H-10T1/2 cell line were labeled and tracked using confocal microscopy. Mitochondrial probes were selected based on morphological characteristics, and their mean-square displacement, creep compliance, and distributions of directional change were measured. We found that the creep compliance of mitochondria resembles that of particles in viscoelastic media. However, comparisons of creep compliance between controls and cells treated with pharmacological agents showed that perturbations to the actomysoin network had surprisingly small effects on mitochondrial fluctuations, whereas microtubule disruption and ATP depletion led to a significantly decreased creep compliance. We used properties of the distribution of directional change to identify a regime of thermally dominated fluctuations in ATP-depleted cells, allowing us to estimate the viscoelastic parameters for a range of timescales. We then determined the force spectrum by combining these viscoelastic properties with measurements of spontaneous fluctuations tracked in control cells. Comparisons with previous measurements made using FSM revealed an excellent match.

Effect of mechanical vibration stress in cell culture on human induced pluripotent stem cells

The development of induced pluripotent stem cell (iPSC) techniques has solved various limitations in cell culture including cellular proliferation and potency. Hence, the expectations on wider applications and the quality of manufactured iPSCs are rapidly increasing. To answer such growing expectations, enhancement of technologies to improve cell-manufacturing efficiency is now a challenge for the bioengineering field. Mechanization of conventional manual operations, aimed at automation of cell manufacturing, is quickly advancing. However, as more processes are being automated in cell manufacturing, it is need to be more critical about influential parameters that may not be as important in manual operations. As a model of such parameters, we focused on the effect of mechanical vibration, which transmits through the vessel to the cultured iPSCs. We designed 7 types of vertical vibration conditions in cell culture vessels using a vibration calibrator. These conditions cover a wide range of potential situations in cell culture, such as tapping or closing an incubator door, and examined their effects by continuous passaging (P3 to P5). Detailed evaluation of cells by time-course image analysis revealed that vibrations can enhance cell growth as an early effect but can negatively affect cell adhesion and growth profile after several passages as a delayed effect. Such unexpected reductions in cell quality are potentially critical issues in maintaining consistency in cell manufacturing. Therefore, this work reveals the importance of continuous examination across several passages with detailed, temporal, quantitative measurements obtained by non-invasive image analysis to examine when and how the unknown parameters will affect the cell culture processes.

Physiological Microenvironmental Conditions in Different Scalable Culture Systems for Pluripotent Stem Cell Expansion and Differentiation

Human Pluripotent Stem Cells (PSCs) are a valuable cell type that has a wide range of biomedical applications because they can differentiate into many types of adult somatic cell. Numerous studies have examined the clinical applications of PSCs. However, several factors such as bioreactor design, mechanical stress, and the physiological environment have not been optimized. These factors can significantly alter the pluripotency and proliferation properties of the cells, which are important for the mass production of PSCs. Nutritional mass transfer and oxygen transfer must be effectively maintained to obtain a high yield. Various culture systems are currently available for optimum cell propagation by maintaining the physiological conditions necessary for cell cultivation. Each type of culture system using a different configuration with various advantages and disadvantages affecting the mechanical conditions in the bioreactor, such as shear stress. These factors make it difficult to preserve the cellular viability and pluripotency of PSCs. Additional limitations of the culture system for PSCs must also be identified and overcome to maintain the culture conditions and enable large-scale expansion and differentiation of PSCs. This review describes the different physiological conditions in the various culture systems and recent developments in culture technology for PSC expansion and differentiation.

Vascular differentiation from pluripotent stem cells in 3-D auxetic scaffolds

Auxetic scaffolds, that is, scaffolds that can display negative Poisson's ratio, have unique physical properties and can expand transversally when axially strained or contract under compression. Auxetic materials have been used for bioprostheses and artery stents due to the enhanced compressive strength and shear stiffness. In vascular tissue engineering, auxetic scaffolds allow the widening of blood vessels when blood flows through (creating compressive stress) to prevent the blockage. However, the influence of auxetic materials on the cellular fate decision in local environment is unclear. In this study, auxetic polyurethane foams were used to support vascular differentiation from pluripotent stem cells. The expression of alkaline phosphatase, Oct-4, and Nanog was lower after 4 days of differentiation for the cells grown in auxetic scaffolds. Higher expression of vascular markers CD31 and VE-cadherin was observed for the cells from auxetic scaffolds compared with those from the scaffolds before auxetic conversion. Little influence on the expression of cardiac marker α-actinin was observed. The vascular cells secreted extracellular matrix proteins vitronectin and laminin and expressed membrane-bound matrix metalloproteinase 9. The examination of Yes-associated protein expression indicated more cytoplasmic retention in the cells from auxetic scaffolds compared with those from regular scaffolds, suggesting that the auxetic scaffolds may affect cellular contraction. This study demonstrates a novel 3-D culture based on auxetic scaffolds for vascular differentiation and provides a platform to study the influence of biophysical microenvironments on differentiation of pluripotent stem cells. The outcome of this study has implications for regenerative medicine and drug discovery.

Role of the Nucleus as a Sensor of Cell Environment Topography

The proper integration of biophysical cues from the cell vicinity is crucial for cells to maintain homeostasis, cooperate with other cells within the tissues, and properly fulfill their biological function. It is therefore crucial to fully understand how cells integrate these extracellular signals for tissue engineering and regenerative medicine. Topography has emerged as a prominent component of the cellular microenvironment that has pleiotropic effects on cell behavior. This progress report focuses on the recent advances in the understanding of the topography sensing mechanism with a special emphasis on the role of the nucleus. Here, recent techniques developed for monitoring the nuclear mechanics are reviewed and the impact of various topographies and their consequences on nuclear organization, gene regulation, and stem cell fate is summarized. The role of the cell nucleus as a sensor of cell-scale topography is further discussed.

Tissue-engineered magnetic cell sheet patches for advanced strategies in tendon regeneration

Tendons are powerful 3D biomechanically structures combining a few cells in an intrincated and highly hierarchical niche environment. When tendon homeostasis is compromised, restoration of functionality upon injury is limited and requires alternatives to current augmentation or replacement strategies. Cell sheet technologies are a powerful tool for the fabrication of living extracellular-rich patches towards regeneration of tenotopic defects. Thus, we originally propose the development of magnetically responsive tenogenic patches through magnetic cell sheet (magCSs) technology that enable the remote control upon implantation of the tendon-mimicking constructs. A Tenomodulin positive (TNMD⁺) subpopulation of cells sorted from a crude population of human adipose stem cells (hASCs) previously identified as being prone to tenogenesis was selected for the magCSs patch construction. We investigated the stability, the cellular co-location of the iron oxide nanoparticles (MNPs), as well as the morphology and mechanical properties of the developed magCSs. Moreover, the expression of tendon markers and collagenous tendon-like matrix were further assessed under the actuation of an external magnetic field. Overall, this study confirms the potential to bioengineer tendon patches using a magnetic cell sheet construction with magnetic responsiveness, good mechanoelastic properties and a tenogenic prone stem cell population envisioning cell-based functional therapies towards tendon regeneration.

STATEMENT OF SIGNIFICANCE

The concept of magnetic force-based tissue engineering may assist the development of innovative solutions to treat tendon (or other tissues) disorders upon remote control of biological processes as cell migration or differentiation. Herein, we originally fabricated magnetic responsive cell sheets (magCSs) with a Tenomodulin positive subpopulation of adipose tissue derived stem cells identified to commit to the tenogenic lineage. To the best of authors knowledge, this is the first time a tendon oriented strategy resorting on magCSsis reported. Moreover, the promising role of tenogenic living constructs fabricated as magnetically responsive ECM-rich patches is highlighted, envisioning the stimulation of endogenous regenerative mechanisms. Altogether, these findings contribute to future stem cell studies and their translation toward tendon therapies.

Non-Washed Resorbable Blasting Media (NWRBM) on Titanium Surfaces could Enhance Osteogenic Properties of MSCs through Increase of miRNA-196a And VCAM1

Surface topography of Titanium (Ti) dental implants strongly influences osseointegration. In the present work, we have analyzed the influence of two Ti implant surfaces characterized by similar microtopography but different nanotopography and chemistry on the osteoblastic phenotype of Dental Pulp Stem Cells (DPSCs). The effect on osteogenic differentiation, extracellular matrix (ECM) and cell adhesion molecules production have been evaluated by means of molecular biology analyses. The morphology of the cells grown onto these surfaces has been analyzed with SEM and immunofluorescence (IF), and the safety of the surfaces has been tested by using karyotype analysis, Ames test and hemocompatibility assay. Results showed that starting from 15 days of DPSCs culture, a substantial expression of osteoblast specific markers and a strong increase of cell adhesion molecules can be detected. In particular, when DPSCs are seeded on the Ti implants expression of microRNA (miRNA)-196a, which is involved in osteoblastic commitment of stem cells, and of Vascular Cell Adhesion Molecule 1 (VCAM1), a factor involved in angiogenesis, is strongly enhanced.

An intermittent rocking platform for integrated expansion and differentiation of human pluripotent stem cells to cardiomyocytes in suspended microcarrier cultures

The development of novel platforms for large scale production of human embryonic stem cells (hESC) derived cardiomyocytes (CM) becomes more crucial as the demand for CMs in preclinical trials, high throughput cardio toxicity assays and future regenerative therapeutics rises. To this end, we have designed a microcarrier (MC) suspension agitated platform that integrates pluripotent hESC expansion followed by CM differentiation in a continuous, homogenous process. Hydrodynamic shear stresses applied during the hESC expansion and CM differentiation steps drastically reduced the capability of the cells to differentiate into CMs. Applying vigorous stirring during pluripotent hESC expansion on Cytodex 1 MC in spinner cultures resulted in low CM yields in the following differentiation step (cardiac troponin-T (cTnT): 22.83±2.56%; myosin heavy chain (MHC): 19.30±5.31%). Whereas the lower shear experienced in side to side rocker (wave type) platform resulted in higher CM yields (cTNT: 47.50±7.35%; MHC: 42.85±2.64%). The efficiency of CM differentiation is also affected by the hydrodynamic shear stress applied during the first 3days of the differentiation stage. Even low shear applied continuously by side to side rocker agitation resulted in very low CM differentiation efficiency (cTnT<5%; MHC<2%). Simply by applying intermittent agitation during these 3days followed by continuous agitation for the subsequent 9days, CM differentiation efficiency can be substantially increased (cTNT: 65.73±10.73%; MHC: 59.73±9.17%). These yields are 38.3% and 39.3% higher (for cTnT and MHC respectively) than static culture control. During the hESC expansion phase, cells grew on continuously agitated rocker platform as pluripotent cell/MC aggregates (166±88×10(5)μm(2)) achieving a cell concentration of 3.74±0.55×10(6)cells/mL (18.89±2.82 fold expansion) in 7days. These aggregates were further differentiated into CMs using a WNT modulation differentiation protocol for the subsequent 12days on a rocking platform with an intermittent agitation regime during the first 3days. Collectively, the integrated MC rocker platform produced 190.5±58.8×10(6) CMs per run (31.75±9.74 CM/hESC seeded). The robustness of the system was demonstrated by using 2 cells lines, hESC (HES-3) and human induced pluripotent stem cell (hiPSC) IMR-90. The CM/MC aggregates formed extensive sarcomeres that exhibited cross-striations confirming cardiac ontogeny. Functionality of the CMs was demonstrated by monitoring the effect of inotropic drug, Isoproterenol on beating frequency. In conclusion, we have developed a simple robust and scalable platform that integrates both hESC expansion and CM differentiation in one unit process which is capable of meeting the need for large amounts of CMs.

Generating size-controlled embryoid bodies using laser direct-write

Embryonic stem cells (ESCs) have the potential to self-renew and differentiate into any specialized cell type. One common method to differentiate ESCs in vitro is through embryoid bodies (EBs), three-dimensional cellular aggregates that spontaneously self-assemble and generally express markers for the three germ layers, endoderm, ectoderm, and mesoderm. It has been previously shown that both EB size and 2D colony size each influence differentiation. We hypothesized that we could control the size of the EB formed by mouse ESCs (mESCs) by using a cell printing method, laser direct-write (LDW), to control both the size of the initial printed colony and the local cell density in printed colonies. After printing mESCs at various printed colony sizes and printing densities, two-way ANOVAs indicated that the EB diameter was influenced by printing density after three days (p = 0.0002), while there was no effect of the printed colony diameter on the EB diameter at the same timepoint (p = 0.74). There was no significant interaction between these two factors. Tukey's honestly significant difference test showed that high-density colonies formed significantly larger EBs, suggesting that printed mESCs quickly aggregate with nearby cells. Thus, EBs can be engineered to a desired size by controlling printing density, which will influence the design of future differentiation studies. Herein, we highlight the capacity of LDW to control the local cell density and colony size independently, at prescribed spatial locations, potentially leading to better stem cell maintenance and directed differentiation.

Role of extracellular matrix signaling cues in modulating cell fate commitment for cardiovascular tissue engineering

It is generally agreed that engineered cardiovascular tissues require cellular interactions with the local milieu. Within the microenvironment, the extracellular matrix (ECM) is an important support structure that provides dynamic signaling cues in part through its chemical, physical, and mechanical properties. In response to ECM factors, cells activate biochemical and mechanotransduction pathways that modulate their survival, growth, migration, differentiation, and function. This Review describes the role of ECM chemical composition, spatial patterning, and mechanical stimulation in the specification of cardiovascular lineages, with a focus on stem cell differentiation, direct transdifferentiation, and endothelial-to-mesenchymal transition. The translational application of ECMs is discussed in the context of cardiovascular tissue engineering and regenerative medicine.

Influence of the microenvironment on cell fate determination and migration

Several critical cell functions are influenced not only by internal cellular machinery but also by external mechanical and biochemical cues from the surrounding microenvironment. Slight changes to the microenvironment can result in dramatic changes to the cell's phenotype; for example, a change in the nutrients or pH of a tumor microenvironment can result in increased tumor metastasis. While cellular fate and the regulators of cell fate have been studied in detail for several decades now, our understanding of the extracellular regulators remains qualitative and far from comprehensive. In this review, we discuss the microenvironment influence on cell fate in terms of adhesion, migration, and differentiation and focus on both developments in experimental and computation tools to analyze cellular fate.

Neural differentiation from pluripotent stem cells: The role of natural and synthetic extracellular matrix

Neural cells differentiated from pluripotent stem cells (PSCs), including both embryonic stem cells and induced pluripotent stem cells, provide a powerful tool for drug screening, disease modeling and regenerative medicine. High-purity oligodendrocyte progenitor cells (OPCs) and neural progenitor cells (NPCs) have been derived from PSCs recently due to the advancements in understanding the developmental signaling pathways. Extracellular matrices (ECM) have been shown to play important roles in regulating the survival, proliferation, and differentiation of neural cells. To improve the function and maturation of the derived neural cells from PSCs, understanding the effects of ECM over the course of neural differentiation of PSCs is critical. During neural differentiation of PSCs, the cells are sensitive to the properties of natural or synthetic ECMs, including biochemical composition, biomechanical properties, and structural/topographical features. This review summarizes recent advances in neural differentiation of human PSCs into OPCs and NPCs, focusing on the role of ECM in modulating the composition and function of the differentiated cells. Especially, the importance of using three-dimensional ECM scaffolds to simulate the in vivo microenvironment for neural differentiation of PSCs is highlighted. Future perspectives including the immediate applications of PSC-derived neural cells in drug screening and disease modeling are also discussed.

Technological progress and challenges towards cGMP manufacturing of human pluripotent stem cells based therapeutic products for allogeneic and autologous cell therapies

Recent technological advances in the generation, characterization, and bioprocessing of human pluripotent stem cells (hPSCs) have created new hope for their use as a source for production of cell-based therapeutic products. To date, a few clinical trials that have used therapeutic cells derived from hESCs have been approved by the Food and Drug Administration (FDA), but numerous new hPSC-based cell therapy products are under various stages of development in cell therapy-specialized companies and their future market is estimated to be very promising. However, the multitude of critical challenges regarding different aspects of hPSC-based therapeutic product manufacturing and their therapies have made progress for the introduction of new products and clinical applications very slow. These challenges include scientific, technological, clinical, policy, and financial aspects. The technological aspects of manufacturing hPSC-based therapeutic products for allogeneic and autologous cell therapies according to good manufacturing practice (cGMP) quality requirements is one of the most important challenging and emerging topics in the development of new hPSCs for clinical use. In this review, we describe main critical challenges and highlight a series of technological advances in all aspects of hPSC-based therapeutic product manufacturing including clinical grade cell line development, large-scale banking, upstream processing, downstream processing, and quality assessment of final cell therapeutic products that have brought hPSCs closer to clinical application and commercial cGMP manufacturing.