Actin and myosin II modulate differentiation of pluripotent stem cells

Efficient Differentiation of hiPSCs into hMSC-like Cells under Chemically Defined Conditions on Temperature-Sensitive Micropatterned Surfaces

The fairness of long-term self-renewal and robust cell proliferation limits the applications of human mesenchymal stem cells (hMSCs) in regenerative medicine. Inducing hMSCs from human-induced pluripotent stem cells (hiPSCs), which have the advantages of autogenous and no cell number issues, is highly valuable. However, current induction methods using FBS-containing mesenchymal culture medium have problems, including immunogenicity, microbial contamination, and low efficiency. To solve these problems, we propose a chemically defined induction protocol incorporating transforming growth factor-beta 1 and retinoic acid (RA) additives in serum-free E6 medium for the suspension induction of embryoid bodies in hiPSCs. Additionally, microgroove-patterned polydimethylsiloxane surfaces coated with temperature-sensitive N-isopropylacrylamide (PNIPAAm) were prepared for efficient harvesting and purification of induced hiPSC-derived hMSCs (hiPSC-MSCs). The results showed that both supplementation with RA and patterned microgrooves with a width of 20 μm could accelerate the induction of hiPSC-MSCs, realizing the promising scalable production of homogeneous cells. This study successfully established a chemically defined induction protocol and utilized patterned surfaces to obtain clinically applicable hiPSC-MSCs, which show great promise in tissue engineering, gene therapy, and cell transplantation.

ZO-1 boosts the in vitro self-renewal of pre-haematopoietic stem cells from OCT4-reprogrammed human hair follicle mesenchymal stem cells through cytoskeleton remodeling

BACKGROUND

The challenge of expanding haematopoietic stem/progenitor cells (HSPCs) in vitro has limited their clinical application. Human hair follicle mesenchymal stem cells (hHFMSCs) can be reprogrammed to generate intermediate stem cells by transducing OCT4 (hHFMSCsOCT4) and pre-inducing with FLT3LG/SCF, and differentiated into erythrocytes. These intermediate cells exhibit gene expression patterns similar to pre-HSCs, making them promising for artificial haematopoiesis. However, further investigation is required to elucidate the in vitro proliferation ability and mechanism underlying the self-renewal of pre-HSCs derived from hHFMSCs.

METHODS

hHFMSCsOCT4 were pre-treated with FLT3LG and SCF cytokines, followed by characterization and isolation of the floating cell subsets for erythroid differentiation through stimulation with hematopoietic cytokines and nutritional factors. Cell adhesion was assessed through disassociation and adhesion assays. OCT4 expression levels were measured using immunofluorescence staining, RT-qPCR, and Western blotting. RNA sequencing and Gene Ontology (GO) enrichment analysis were then conducted to identify proliferation-related biological processes. Proliferative capacity was evaluated through CCK-8, colony formation assays, Ki67 index, and cell cycle analysis. Cytoskeleton was observed through Wright‒Giemsa, Coomassie brilliant blue, and phalloidin staining. Expression of adherens junction (AJ) core members was confirmed through RT‒qPCR, Western blotting, and immunofluorescence staining before and after ZO-1 knockdown. A regulatory network was constructed to determine relationships among cytoskeleton, proliferation, and the AJ pathway. Student's t tests (GraphPad Prism 8.0.2) were used for group comparisons. The results were considered significant at P < 0.05.

RESULTS

Pre-treatment of hHFMSCsOCT4 with FLT3LG and SCF leads to the emergence of floating cell subsets exhibiting small, globoid morphology, suspended above adherent cells, forming colonies, and displaying minimal expression of CD45. Excessive OCT4 expression weakens adhesion in floating hHFMSCsOCT4. Floating cells moderately enhanced proliferation and undergo cytoskeleton remodelling, with increased contraction and aggregation of F-actin near the nucleus. The upregulation of ZO-1 could impact the expressions of F-actin, E-cadherin, and β-catenin genes, as well as the nuclear positioning of β-catenin, leading to variations in the cytoskeleton and cell cycle. Finally, a regulatory network revealed that the AJ pathway cored with ZO-1 critically bridges cytoskeletal remodelling and haematopoiesis-related proliferation in a β-catenin-dependent manner.

CONCLUSIONS

ZO-1 improved the self-renewal of pre-HSCs from OCT4-overexpressing hHFMSCs by remodeling the cytoskeleton via the ZO-1-regulated AJ pathway, suggesting floating hHFMSCsOCT4 as the promising seed cells for artificial hematopoiesis.

Nuclear actin is a critical regulator of Drosophila female germline stem cell maintenance

Nuclear actin has been implicated in regulating cell fate, differentiation, and cellular reprogramming. However, its roles in development and tissue homeostasis remain largely unknown. Here we uncover the role of nuclear actin in regulating stemness using Drosophila ovarian germline stem cells (GSCs) as a model. We find that the localization and structure of nuclear actin is dynamic in the early germ cells. Nuclear actin recognized by anti-actin C4 is found in both the nucleoplasm and nucleolus of GSCs. The polymeric nucleoplasmic C4 pool is lost after the 2-cell stage, whereas the monomeric nucleolar pool persists to the 8-cell stage, suggesting that polymeric nuclear actin may contribute to stemness. To test this idea, we overexpressed nuclear targeted actin constructs to alter nuclear actin polymerization states in the GSCs and early germ cells. Increasing monomeric nuclear actin, but not polymerizable nuclear actin, causes GSC loss that ultimately results in germline loss. This GSC loss is rescued by simultaneous overexpression of monomeric and polymerizable nuclear actin. Together these data reveal that GSC maintenance requires polymeric nuclear actin. This polymeric nuclear actin likely plays numerous roles in the GSCs, as increasing monomeric nuclear actin disrupts nuclear architecture causing nucleolar hypertrophy, distortion of the nuclear lamina, and heterochromatin reorganization; all factors critical for GSC maintenance and function. These data provide the first evidence that nuclear actin, and in particular, its ability to polymerize, are critical for stem cell function and tissue homeostasis in vivo.

Nanofiber-microwell cell culture system for spatially patterned differentiation of pluripotent stem cells in 3D

The intricate interplay between biochemical and physical cues dictates pluripotent stem cell (PSC) differentiation to form various tissues. While biochemical modulation has been extensively studied, the role of biophysical microenvironments in early lineage commitment remains elusive. Here, we introduce a novel 3D cell culture system combining electrospun nanofibers with microfabricated polydimethylsiloxane (PDMS) patterns. This system enables the controlled formation of semispherical human induced pluripotent stem cell (hiPSC) colonies, facilitating the investigation of local mechanical stem cell niches on mechano-responsive signaling and lineage specification. Our system unveiled spatially organized RhoA activity coupled with actin-myosin cable formation, suggesting mechano-dependent hiPSC behaviors. Nodal network analysis of RNA-seq data revealed RhoA downstream regulation of YAP signaling, DNA histone modifications, and patterned germ layer specification. Notably, altering colony morphology through controlled PDMS microwell shaping effectively modulated the spatial distribution of mechano-sensitive mediators and subsequent differentiation. This study provides a cell culture platform to decipher the role of biophysical cues in early embryogenesis, offering valuable insights for material design in tissue engineering and regenerative medicine applications.

Mechanotransduction in tissue engineering: Insights into the interaction of stem cells with biomechanical cues

Stem cells in their natural microenvironment are exposed to biochemical and biophysical cues emerging from the extracellular matrix (ECM) and neighboring cells. In particular, biomechanical forces modulate stem cell behavior, biological fate, and early developmental processes by sensing, interpreting, and responding through a series of biological processes known as mechanotransduction. Local structural changes in the ECM and mechanics are driven by reciprocal activation of the cell and the ECM itself, as the initial deposition of matrix proteins sequentially affects neighboring cells. Recent studies on stem cell mechanoregulation have provided insight into the importance of biomechanical signals on proper tissue regeneration and function and have shown that precise spatiotemporal control of these signals exists in stem cell niches. Against this background, the aim of this work is to review the current understanding of the molecular basis of mechanotransduction by analyzing how biomechanical forces are converted into biological responses via cellular signaling pathways. In addition, this work provides an overview of advanced strategies using stem cells and biomaterial scaffolds that enable precise spatial and temporal control of mechanical signals and offer great potential for the fields of tissue engineering and regenerative medicine will be presented.

Cell Behavioral Dynamics as a Cue in Optimizing Culture Stabilization in the Bioprocessing of Pluripotent Stem Cells

Pluripotent stem cells (PSCs) are important for future regenerative medicine therapies. However, in the production of PSCs and derivatives, the control of culture-induced fluctuations in the outcome of cell quality remains challenging. A detailed mechanistic understanding of how PSC behaviors are altered in response to biomechanical microenvironments within a culture is necessary for rational bioprocessing optimization. In this review, we discuss recent insights into the role of cell behavioral and mechanical homeostasis in modulating the states and functions of PSCs during culture processes. We delineate promising ways to manipulate the culture variability through regulating cell behaviors using currently developed tools. Furthermore, we anticipate their potential implementation for designing a culture strategy based on the concept of Waddington's epigenetic landscape that may provide a feasible solution for tuning the culture quality and stability in the bioprocessing space.

Emerging interplay of cytoskeletal architecture, cytomechanics and pluripotency

Pluripotent stem cells (PSCs) are capable of differentiating into all three germ layers and trophoblasts, whereas tissue-specific adult stem cells have a more limited lineage potency. Although the importance of the cytoskeletal architecture and cytomechanical properties in adult stem cell differentiation have been widely appreciated, how they contribute to mechanotransduction in PSCs is less well understood. Here, we discuss recent insights into the interplay of cellular architecture, cell mechanics and the pluripotent states of PSCs. Notably, the distinctive cytomechanical and morphodynamic profiles of PSCs are accompanied by a number of unique molecular mechanisms. The extent to which such mechanobiological signatures are intertwined with pluripotency regulation remains an open question that may have important implications in developmental morphogenesis and regenerative medicine.

A novel alveolar epithelial cell sheet fabricated under feeder-free conditions for potential use in pulmonary regenerative therapy

Introduction

Methods

Results

Conclusions

•

Alveolar epithelial cells were cultured and expanded under feeder-free conditions.

•

Alveolar epithelial cell sheets were generated using temperature-responsive dishes.

•

Alveolar epithelial cell sheets engrafted after transplantation onto rat lung.

•

The sheets retained alveolar epithelial cell characteristics after transplantation.

•

These cell sheets potentially could be used for pulmonary regenerative therapy.

A lysine-rich cluster in the N-BAR domain of ARF GTPase-activating protein ASAP1 is necessary for binding and bundling actin filaments

Actin filament maintenance is critical for both normal cell homeostasis and events associated with malignant transformation. The ADP-ribosylation factor GTPase-activating protein ASAP1 regulates the dynamics of filamentous actin-based structures, including stress fibers, focal adhesions, and circular dorsal ruffles. Here, we have examined the molecular basis for ASAP1 association with actin. Using a combination of structural modeling, mutagenesis, and in vitro and cell-based assays, we identify a putative-binding interface between the N-Bin-Amphiphysin-Rvs (BAR) domain of ASAP1 and actin filaments. We found that neutralization of charges and charge reversal at positions 75, 76, and 79 of ASAP1 reduced the binding of ASAP1 BAR-pleckstrin homology tandem to actin filaments and abrogated actin bundle formation in vitro. In addition, overexpression of actin-binding defective ASAP1 BAR-pleckstrin homology [K75, K76, K79] mutants prevented cellular actin remodeling in U2OS cells. Exogenous expression of [K75E, K76E, K79E] mutant of full-length ASAP1 did not rescue the reduction of cellular actin fibers consequent to knockdown of endogenous ASAP1. Taken together, our results support the hypothesis that the lysine-rich cluster in the N-BAR domain of ASAP1 is important for regulating actin filament organization.

Nucleus-cytoskeleton communication impacts on OCT4-chromatin interactions in embryonic stem cells

BACKGROUND

The cytoskeleton is a key component of the system responsible for transmitting mechanical cues from the cellular environment to the nucleus, where they trigger downstream responses. This communication is particularly relevant in embryonic stem (ES) cells since forces can regulate cell fate and guide developmental processes. However, little is known regarding cytoskeleton organization in ES cells, and thus, relevant aspects of nuclear-cytoskeletal interactions remain elusive.

RESULTS

We explored the three-dimensional distribution of the cytoskeleton in live ES cells and show that these filaments affect the shape of the nucleus. Next, we evaluated if cytoskeletal components indirectly modulate the binding of the pluripotency transcription factor OCT4 to chromatin targets. We show that actin depolymerization triggers OCT4 binding to chromatin sites whereas vimentin disruption produces the opposite effect. In contrast to actin, vimentin contributes to the preservation of OCT4-chromatin interactions and, consequently, may have a pro-stemness role.

CONCLUSIONS

Our results suggest roles of components of the cytoskeleton in shaping the nucleus of ES cells, influencing the interactions of the transcription factor OCT4 with the chromatin and potentially affecting pluripotency and cell fate.

Heading towards a dead end: The role of DND1 in germ line differentiation of human iPSCs

The DND microRNA-mediated repression inhibitor 1 (DND1) is a conserved RNA binding protein (RBP) that plays important roles in survival and fate maintenance of primordial germ cells (PGCs) and in the development of the male germline in zebrafish and mice. Dead end was shown to be expressed in human pluripotent stem cells (PSCs), PGCs and spermatogonia, but little is known about its specific role concerning pluripotency and human germline development. Here we use CRISPR/Cas mediated knockout and PGC-like cell (PGCLC) differentiation in human iPSCs to determine if DND1 (1) plays a role in maintaining pluripotency and (2) in specification of PGCLCs. We generated several clonal lines carrying biallelic loss of function mutations and analysed their differentiation potential towards PGCLCs and their gene expression on RNA and protein levels via RNA sequencing and mass spectrometry. The generated knockout iPSCs showed no differences in pluripotency gene expression, proliferation, or trilineage differentiation potential, but yielded reduced numbers of PGCLCs as compared with their parental iPSCs. RNAseq analysis of mutated PGCLCs revealed that the overall gene expression remains like non-mutated PGCLCs. However, reduced expression of genes associated with PGC differentiation and maintenance (e.g., NANOS3, PRDM1) was observed. Together, we show that DND1 iPSCs maintain their pluripotency but exhibit a reduced differentiation to PGCLCs. This versatile model will allow further analysis of the specific mechanisms by which DND1 influences PGC differentiation and maintenance.

Emerging roles of cytoskeletal proteins in regulating gene expression and genome organization during differentiation

In the eukaryotic cell nucleus, cytoskeletal proteins are emerging as essential players in nuclear function. In particular, actin regulates chromatin as part of ATP-dependent chromatin remodeling complexes, it modulates transcription and it is incorporated into nascent ribonucleoprotein complexes, accompanying them from the site of transcription to polyribosomes. The nuclear actin pool is undistinguishable from the cytoplasmic one in terms of its ability to undergo polymerization and it has also been implicated in the dynamics of chromatin, regulating heterochromatin segregation at the nuclear lamina and maintaining heterochromatin levels in the nuclear interiors. One of the next frontiers is, therefore, to determine a possible involvement of nuclear actin in the functional architecture of the cell nucleus by regulating the hierarchical organization of chromatin and, thus, genome organization. Here, we discuss the repertoire of these potential actin functions and how they are likely to play a role in the context of cellular differentiation.

Pluripotency of embryonic stem cells lacking clathrin-mediated endocytosis cannot be rescued by restoring cellular stiffness

Mouse embryonic stem cells (mESCs) display unique mechanical properties, including low cellular stiffness in contrast to differentiated cells, which are stiffer. We have previously shown that mESCs lacking the clathrin heavy chain (Cltc), an essential component for clathrin-mediated endocytosis (CME), display a loss of pluripotency and an enhanced expression of differentiation markers. However, it is not known whether physical properties such as cellular stiffness also change upon loss of Cltc, similar to what is seen in differentiated cells, and if so, how these altered properties specifically impact pluripotency. Using atomic force microscopy (AFM), we demonstrate that mESCs lacking Cltc display higher Young's modulus, indicative of greater cellular stiffness, compared with WT mESCs. The increase in stiffness was accompanied by the presence of actin stress fibers and accumulation of the inactive, phosphorylated, actin-binding protein cofilin. Treatment of Cltc knockdown mESCs with actin polymerization inhibitors resulted in a decrease in the Young's modulus to values similar to those obtained with WT mESCs. However, a rescue in the expression profile of pluripotency factors was not obtained. Additionally, whereas WT mouse embryonic fibroblasts could be reprogrammed to a state of pluripotency, this was inhibited in the absence of Cltc. This indicates that the presence of active CME is essential for the pluripotency of embryonic stem cells. Additionally, whereas physical properties may serve as a simple readout of the cellular state, they may not always faithfully recapitulate the underlying molecular fate.

Spheroid Fabrication Using Concave Microwells Enhances the Differentiation Efficacy and Function of Insulin-Producing Cells via Cytoskeletal Changes

Pancreatic islet transplantation is the fundamental treatment for insulin-dependent diabetes; however, donor shortage is a major hurdle in its use as a standard treatment. Accordingly, differentiated insulin-producing cells (DIPCs) are being developed as a new islet source. Differentiation efficiency could be enhanced if the spheroid structure of the natural islets could be recapitulated. Here, we fabricated DIPC spheroids using concave microwells, which enabled large-scale production of spheroids of the desired size. We prepared DIPCs from human liver cells by trans-differentiation using transcription factor gene transduction. Islet-related gene expression and insulin secretion levels were higher in spheroids compared to those in single-cell DIPCs, whereas actin-myosin interactions significantly decreased. We verified actin-myosin-dependent insulin expression in single-cell DIPCs by using actin-myosin interaction inhibitors. Upon transplanting cells into the kidney capsule of diabetic mouse, blood glucose levels decreased to 200 mg/dL in spheroid-transplanted mice but not in single cell-transplanted mice. Spheroid-transplanted mice showed high engraftment efficiency in in vivo fluorescence imaging. These results demonstrated that spheroids fabricated using concave microwells enhanced the engraftment and functions of DIPCs via actin-myosin-mediated cytoskeletal changes. Our strategy potentially extends the clinical application of DIPCs for improved differentiation, glycemic control, and transplantation efficiency of islets.

Actomyosin and the MRTF-SRF pathway downregulate FGFR1 in mesenchymal stromal cells

Both biological and mechanical signals are known to influence cell proliferation. However, biological signals are mostly studied in two-dimensions (2D) and the interplay between these different pathways is largely unstudied. Here, we investigated the influence of the cell culture environment on the response to bFGF, a widely studied and important proliferation growth factor. We observed that human mesenchymal stromal cells (hMSCs), but not fibroblasts, lose the ability to respond to soluble or covalently bound bFGF when cultured on microfibrillar substrates. This behavior correlated with a downregulation of FGF receptor 1 (FGFR1) expression of hMSCs on microfibrillar substrates. Inhibition of actomyosin or the MRTF/SRF pathway decreased FGFR1 expression in hMSCs, fibroblasts and MG63 cells. To our knowledge, this is the first time FGFR1 expression is shown to be regulated through a mechanosensitive pathway in hMSCs. These results add to the sparse literature on FGFR1 regulation and potentially aid designing tissue engineering constructs that better control cell proliferation.

ROCK inhibitor combined with Ca2+ controls the myosin II activation and optimizes human nasal epithelial cell sheets

The proliferation and differentiation of cultured epithelial cells may be modified by Rho-associated kinase (ROCK) inhibition and extracellular Ca²⁺ concentration. However, it was not known whether a combination would influence the behavior of cultured epithelial cells through changes in the phosphorylation of non-muscle myosin light chain II (MLC). Here we show that the combination of ROCK inhibition with Ca²⁺ elevation regulated the phosphorylation of MLC and improved both cell expansion and cell–cell adhesion during the culture of human nasal mucosal epithelial cell sheets. During explant culture, Ca²⁺ enhanced the adhesion of nasal mucosal tissue, while ROCK inhibition downregulated MLC phosphorylation and promoted cell proliferation. During cell sheet culture, an elevation of extracellular Ca²⁺ promoted MLC phosphorylation and formation of cell–cell junctions, allowing the harvesting of cell sheets without collapse. Moreover, an in vitro grafting assay revealed that ROCK inhibition increased the expansion of cell sheets three-fold (an effect maintained when Ca²⁺ was also elevated), implying better wound healing potential. We suggest that combining ROCK inhibition with elevation of Ca²⁺ could facilitate the fabrication of many types of cell graft.

Phenyl Saligenin Phosphate Disrupts Cell Morphology and the Actin Cytoskeleton in Differentiating H9c2 Cardiomyoblasts and Human-Induced Pluripotent Stem-Cell-Derived Cardiomyocyte Progenitor Cells

We have previously shown that phenyl saligenin phosphate (PSP), an organophosphorus compound which is classed as a weak inhibitor of acetylcholinesterase, triggered cytotoxicity in mitotic and differentiated H9c2 cardiomyoblasts. The aim of this study was to assess whether sublethal concentrations of PSP could disrupt the morphology of differentiating rat H9c2 cardiomyoblasts and human-induced pluripotent stem-cell-derived cardiomyocyte progenitor cells (hiPSC-CMs) and to assess the underlying cytoskeletal changes. PSP-induced changes in protein expression were monitored via Western blotting, immunocytochemistry, and proteomic analysis. PSP-mediated cytotoxicity was determined by measuring MTT reduction, LDH release, and caspase-3 activity. Sublethal exposure to PSP (3 μM) induced morphological changes in differentiating H9c2 cells (7, 9, and 13 days), reflected by reduced numbers of spindle-shaped cells. Moreover, this treatment (7 days) attenuated the expression of the cytoskeletal proteins cardiac troponin I, tropomyosin-1, and α-actin. Further proteomic analysis identified nine proteins (e.g., heat shock protein 90-β and calumenin) which were down-regulated by PSP exposure in H9c2 cells. To assess the cytotoxic effects of organophosphorus compounds in a human cell model, we determined their effects on human-induced pluripotent stem-cell-derived cardiomyocyte progenitor cells. Chlorpyrifos and diazinon-induced cytotoxicity (48 h) was evident only at concentrations >100 μM. By contrast, PSP exhibited cytotoxicity in hiPSC-CMs at a concentration of 25 μM following 48 h exposure. Finally, sublethal exposure to PSP (3 μM; 7 days) induced morphological changes and decreased the expression of cardiac troponin I, tropomyosin-1, and α-actin in hiPSC-CMs. In summary, our data suggest cardiomyocyte morphology is disrupted in both cell models by sublethal concentrations of PSP via modulation of cytoskeletal protein expression.

Fluorescence-based actin turnover dynamics of stem cells as a profiling method for stem cell functional evolution, heterogeneity and phenotypic lineage parsing

Stem cells are widely explored in regenerative medicine as a source to produce diverse cell types. Despite the wide usage of stem cells like mesenchymal stem cells (MSCs) and induced pluripotent stem cells (iPSCs), there is a lack of robust methods to rapidly discern the phenotypic and functional heterogeneity of stem cells. The organization of actin cytoskeleton has been previously used to discern divergent stem cell differentiation pathways. In this paper, we highlight the versatility of a cell profiling method for actin turnover dynamics. Actin filaments in live stem cells are labeled using SiR-actin, a cell permeable fluorogenic probe, to determine the endogenous actin turnover. Live MSC imaging after days of induction successfully demonstrated lineage specific change in actin turnover. Next, we highlighted the differences in the cellular heterogeneity of actin dynamics during adipogenic or osteogenic MSC differentiation. Next, we applied the method to differentiating iPSCs in culture, and detected a progressive slowdown in actin turnover during differentiation upon stimulation with neural or cardiac media. Finally, as a proof of concept, the actin dynamic profiling was used to isolate MSCs via flow cytometry prior to sorting into three distinct sub-populations with low, intermediate or high actin dynamics. A greater fraction of MSCs with more rapid actin dynamics demonstrated increased inclination for adipogenesis, whereas, slower actin dynamics correlated with increased osteogenesis. Together, these results show that actin turnover can serve as a versatile biomarker to not only track cellular phenotypic heterogeneity but also harvest live cells with potential for differential phenotypic fates.

Mechanical Roles of F-Actin in the Differentiation of Stem Cells: A Review

In the development and differentiation of stem cells, mechanical forces associated with filamentous actin (F-actin) play a crucial role. The present review aims to reveal the relationship among the chemical components, microscopic structures, mechanical properties, and biological functions of F-actin. Particular attention is given to the functions of the cytoplasmic and nuclear microfilament cytoskeleton and their regulation mechanisms in the differentiation of stem cells. The distributions of different types of actin monomers in mammal cells and the functions of actin-binding proteins are summarized. We discuss how the fate of stem cells is regulated by intra/extracellular mechanical and chemical cues associated with microfilament-related proteins, intercellular adhesion molecules, etc. In addition, we also address the differentiation-induced variation in the stiffness of stem cells and the correlation between the fate and geometric shape change of stem cells. This review not only deepens our understanding of the biophysical mechanisms underlying the fates of stem cells under different culture conditions but also provides inspirations for the tissue engineering of stem cells.

Keratinocytes are mechanoresponsive to the microflow-induced shear stress

Here, we have reported that keratinocytes respond to the microflow-induced shear stress both at the collective and individual cell level. Using a microfluidic setup, we categorically showed that low shear stress of magnitude 0.06 dyne/cm² could induce morphological variation and cytoskeletal reorganization in keratinocyte, whereas higher shear stress (6 dyne/cm² ) resulted in cellular disruption. Using a series of blocker molecules specific to different mechanotransducers, we demonstrated the pivotal role of actin network in keratinocyte mechanoresponsiveness in conjugation with myosin and lipid rafts. Flow-induced shear stress also induced significant elevation in E-cadherin and Zonula occludens-1 (ZO-1) expression levels. We further showed that under the influence of shear stress, the extent of colocalization of E-cadherin and ZO-1 was more at the cell-cell junction that indicates an improvement in the epithelial phenotype. An increase in the expression of nuclear lamin was also observed in the sheared cells that suggest the transmission of mechanical signals to the nucleus. It is envisioned that this study may find its application in basic and applied organogenesis of the epidermis.