Spheroid formation and modulation of tenocyte-specific gene expression under simulated microgravity

Equine tendon mechanical behaviour: Prospects for repair and regeneration applications

Tendons are dense connective tissues that play an important role in the biomechanical function of the musculoskeletal system. The mechanical forces have been implicated in every aspect of tendon biology. Tendon injuries are frequently occurring and their response to treatments is often unsatisfactory. A better understanding of tendon biomechanics and mechanobiology can help develop treatment options to improve clinical outcomes. Recently, tendon tissue engineering has gained more attention as an alternative treatment due to its potential to overcome the limitations of current treatments. This review first provides a summary of tendon mechanical properties, focusing on recent findings of tendon mechanobiological responses. In the next step, we highlight the biomechanical parameters of equine energy-storing and positional tendons. The final section is devoted to how mechanical loading contributes to tenogenic differentiation using bioreactor systems. This study may help develop novel strategies for tendon injury prevention or accelerate and improve tendon healing.

Three-Dimensional Cell Culture System for Tendon Tissue Engineering

Tendon, connective tissue between bone and muscle has unique component of the musculoskeletal system. It plays important role for transporting mechanical stress from muscle to bone and enabling locomotive motion of the body. There are some restoration capacities in the tendon tissue, but the injured tendons are not completely regenerated after acute and chronic tendon injury. At this point, the treatment options for tendon injuries are limited and not that successful. Therefore, biomedical engineering approaches are emerged to cope with this issue. Among them, three-dimensional cell culture platforms provided similarity to in vivo conditions and suggested opportunities for new therapeutic approaches for treatment of tendon injuries. In this review, we focus on the characteristics of tendon tissue and tendon pathologies which can be targets for tendon tissue engineering strategies. Then proof-of-concept and pre-clinical studies leveraging advanced 3-dimensional cell culture platforms for tendon tissue regeneration have been discussed.

Three-Dimensional Growth of Prostate Cancer Cells Exposed to Simulated Microgravity

Prostate cancer metastasis has an enormous impact on the mortality of cancer patients. Factors involved in cancer progression and metastasis are known to be key players in microgravity (µg)-driven three-dimensional (3D) cancer spheroid formation. We investigated PC-3 prostate cancer cells for 30 min, 2, 4 and 24 h on the random positioning machine (RPM), a device simulating µg on Earth. After a 24 h RPM-exposure, the cells could be divided into two groups: one grew as 3D multicellular spheroids (MCS), the other one as adherent monolayer (AD). No signs of apoptosis were visible. Among others, we focused on cytokines involved in the events of metastasis and MCS formation. After 24 h of exposure, in the MCS group we measured an increase in ACTB, MSN, COL1A1, LAMA3, FN1, TIMP1, FLT1, EGFR1, IL1A, IL6, CXCL8, and HIF1A mRNA expression, and in the AD group an elevation of LAMA3, COL1A1, FN1, MMP9, VEGFA, IL6, and CXCL8 mRNAs compared to samples subjected to 1 g conditions. Significant downregulations in AD cells were detected in the mRNA levels of TUBB, KRT8, IL1B, IL7, PIK3CB, AKT1 and MTOR after 24 h. The release of collagen-1α1 and fibronectin protein in the supernatant was decreased, whereas the secretion of IL-6 was elevated in 24 h RPM samples. The secretion of IL-1α, IL-1β, IL-7, IL-2, IL-8, IL-17, TNF-α, laminin, MMP-2, TIMP-1, osteopontin and EGF was not significantly altered after 24 h compared to 1 g conditions. The release of soluble factors was significantly reduced after 2 h (IL-1α, IL-2, IL-7, IL-8, IL-17, TNF-α, collagen-1α1, MMP-2, osteopontin) and elevated after 4 h (IL-1β, IL-2, IL-6, IL-7, IL-8, TNF-α, laminin) in RPM samples. Taken together, simulated µg induced 3D growth of PC-3 cancer cells combined with a differential expression of the cytokines IL-1α, IL-1β, IL-6 and IL-8, supporting their involvement in growth and progression of prostate cancer cells.

Minispheroids as a Tool for Ligament Tissue Engineering: Do the Self-Assembly Techniques and Spheroid Dimensions Influence the Cruciate Ligamentocyte Phenotype?

Spheroid culture might stabilize the ligamentocyte phenotype. Therefore, the phenotype of lapine cruciate ligamentocyte (L-CLs) minispheroids prepared either by hanging drop (HD) method or by using a novel spheroid plate (SP) and the option of methyl cellulose (MC) for tuning spheroid formation was tested. A total of 250 and 1000 L-CLs per spheroid were seeded as HDs or on an SP before performing cell viability assay, morphometry, gene expression (qRT-PCR) and protein immunolocalization after 7 (HD/SP) and 14 (SP) days. Stable and viable spheroids of both sizes could be produced with both methods, but more rapidly with SP. MC accelerated the formation of round spheroids (HD). Their circular areas decreased significantly during culturing. After 7 days, the diameters of HD-derived spheroids were significantly larger compared to those harvested from the SP, with a tendency of lower circularity suggesting an ellipsoid shape. Gene expression of decorin increased significantly after 7 days (HD, similar trend in SP), tenascin C tended to increase after 7 (HD/SP) and 14 days (SP), whereas collagen type 1 decreased (HD/SP) compared to the monolayer control. The cruciate ligament extracellular matrix components could be localized in all mini-spheroids, confirming their conserved expression profile and their suitability for ligament tissue engineering.

Maintenance of Ligament Homeostasis of Spheroid-Colonized Embroidered and Functionalized Scaffolds after 3D Stretch

Anterior cruciate ligament (ACL) ruptures are usually treated with autograft implantation to prevent knee instability. Tissue engineered ACL reconstruction is becoming promising to circumvent autograft limitations. The aim was to evaluate the influence of cyclic stretch on lapine (L) ACL fibroblasts on embroidered scaffolds with respect to adhesion, DNA and sulphated glycosaminoglycan (sGAG) contents, gene expression of ligament-associated extracellular matrix genes, such as type I collagen, decorin, tenascin C, tenomodulin, gap junctional connexin 43 and the transcription factor Mohawk. Control scaffolds and those functionalized by gas phase fluorination and cross-linked collagen foam were either pre-cultured with a suspension or with spheroids of LACL cells before being subjected to cyclic stretch (4%, 0.11 Hz, 3 days). Stretch increased significantly the scaffold area colonized with cells but impaired sGAGs and decorin gene expression (functionalized scaffolds seeded with cell suspension). Stretching increased tenascin C, connexin 43 and Mohawk but decreased decorin gene expression (control scaffolds seeded with cell suspension). Pre-cultivation of functionalized scaffolds with spheroids might be the more suitable method for maintaining ligamentogenesis in 3D scaffolds compared to using a cell suspension due to a significantly higher sGAG content in response to stretching and type I collagen gene expression in functionalized scaffolds.

Cyclically stretched ACL fibroblasts emigrating from spheroids adapt their cytoskeleton and ligament-related expression profile

Mechanical stress of ligaments varies; hence, ligament fibroblasts must adapt their expression profile to novel mechanomilieus to ensure tissue resilience. Activation of the mechanoreceptors leads to a specific signal transduction, the so-called mechanotransduction. However, with regard to their natural three-dimensional (3D) microenvironment cell reaction to mechanical stimuli during emigrating from a 3D spheroid culture is still unclear. This study aims to provide a deeper understanding of the reaction profile of anterior cruciate ligament (ACL)-derived fibroblasts exposed to cyclic uniaxial strain in two-dimensional (2D) monolayer culture and during emigration from 3D spheroids with respect to cell survival, cell and cytoskeletal orientation, distribution, and expression profile. Monolayers and spheroids were cultured in crosslinked polydimethyl siloxane (PDMS) elastomeric chambers and uniaxially stretched (14% at 0.3 Hz) for 48 h. Cell vitality, their distribution, nuclear shape, stress fiber orientation, focal adhesions, proliferation, expression of ECM components such as sulfated glycosaminoglycans, collagen type I, decorin, tenascin C and cell-cell communication-related gap junctional connexin (CXN) 43, tendon-related markers Mohawk and tenomodulin (myodulin) were analyzed. In contrast to unstretched cells, stretched fibroblasts showed elongation of stress fibers, cell and cytoskeletal alignment perpendicular to strain direction, less rounded cell nuclei, increased numbers of focal adhesions, proliferation, amplified CXN43, and main ECM component expression in both cultures. The applied cyclic stretch protocol evoked an anabolic response and enhanced tendon-related marker expression in ACL-derived fibroblasts emigrating from 3D spheroids and seems also promising to support in future tissue formation in ACL scaffolds seeded in vitro with spheroids.

Simulated Microgravity Remodels Extracellular Matrix of Osteocommitted Mesenchymal Stromal Cells

The extracellular matrix (ECM) is the principal structure of bone tissue. Long-term spaceflights lead to osteopenia, which may be a result of the changes in composition as well as remodeling of the ECM by osteogenic cells. To elucidate the cellular effects of microgravity, human mesenchymal stromal cells (MSCs) and their osteocommitted progeny were exposed to simulated microgravity (SMG) for 10 days using random positioning machine (RPM). After RPM exposure, an imbalance of MSC collagen/non-collagen ratio at the expense of a decreased level of collagenous proteins was detected. At the same time, the secretion of proteases (cathepsin A, cathepsin D, MMP3) was increased. No significant effects of SMG on the expression of stromal markers and cell adhesion molecules on the MSC surface were noted. Upregulation of COL11A1, CTNND1, TIMP3, and TNC and downregulation of HAS1, ITGA3, ITGB1, LAMA3, MMP1, and MMP11 were detected in RPM exposed MSCs. ECM-associated transcriptomic changes were more pronounced in osteocommitted progeny. Thus, 10 days of SMG provokes a decrease in the collagenous components of ECM, probably due to the decrease in collagen synthesis and activation of proteases. The presented data demonstrate that ECM-associated molecules of both native and osteocommitted MSCs may be involved in bone matrix reorganization during spaceflight.

The Lack of a Representative Tendinopathy Model Hampers Fundamental Mesenchymal Stem Cell Research

Overuse tendon injuries are a major cause of musculoskeletal morbidity in both human and equine athletes, due to the cumulative degenerative damage. These injuries present significant challenges as the healing process often results in the formation of inferior scar tissue. The poor success with conventional therapy supports the need to search for novel treatments to restore functionality and regenerate tissue as close to native tendon as possible. Mesenchymal stem cell (MSC)-based strategies represent promising therapeutic tools for tendon repair in both human and veterinary medicine. The translation of tissue engineering strategies from basic research findings, however, into clinical use has been hampered by the limited understanding of the multifaceted MSC mechanisms of action. In vitro models serve as important biological tools to study cell behavior, bypassing the confounding factors associated with in vivo experiments. Controllable and reproducible in vitro conditions should be provided to study the MSC healing mechanisms in tendon injuries. Unfortunately, no physiologically representative tendinopathy models exist to date. A major shortcoming of most currently available in vitro tendon models is the lack of extracellular tendon matrix and vascular supply. These models often make use of synthetic biomaterials, which do not reflect the natural tendon composition. Alternatively, decellularized tendon has been applied, but it is challenging to obtain reproducible results due to its variable composition, less efficient cell seeding approaches and lack of cell encapsulation and vascularization. The current review will overview pros and cons associated with the use of different biomaterials and technologies enabling scaffold production. In addition, the characteristics of the ideal, state-of-the-art tendinopathy model will be discussed. Briefly, a representative in vitro tendinopathy model should be vascularized and mimic the hierarchical structure of the tendon matrix with elongated cells being organized in a parallel fashion and subjected to uniaxial stretching. Incorporation of mechanical stimulation, preferably uniaxial stretching may be a key element in order to obtain appropriate matrix alignment and create a pathophysiological model. Together, a thorough discussion on the current status and future directions for tendon models will enhance fundamental MSC research, accelerating translation of MSC therapies for tendon injuries from bench to bedside.

Effect of Muscle Cell Preservation on Viability and Differentiation of Hamstring Tendon Graft In Vitro

Muscle tissue is often removed during hamstring tendon graft preparation for anterior cruciate ligament (ACL) reconstruction. The purpose of the study was to test whether preservation of muscle remnants on a tendon graft is beneficial to the graft healing process following ACL reconstruction. Co-culturing of tendon-derived cells (TDCs) and muscle-derived cells (MDCs) was performed at various ratios, and their potential for cell viability and multilineage differentiation was compared to a single TDC cell group. Ligamentous and chondrogenic differentiation was most enhanced when a small population of MDCs was co-cultured with TDCs (6:2 co-culture group). Cell viability and osteogenic differentiation were proportionally enhanced with increasing MDC population size. MDCs co-cultured with TDCs possess both the ability to enhance cell viability and differentiate into other cell lineages.

Extracellular Matrix Proteins and Transcription of Matrix-Associated Genes in Mesenchymal Stromal Cells during Modeling of the Effects of Microgravity

We studied the effects of simulated microgravity (10 days) on the production of extracellular matrix proteins and expression of extracellular matrix-associated genes in human mesenchymal stem cells. A decrease in collagen production, reduced expression of TIMP-1, TIMP-3, and MMP-11 genes, and enhanced expression of tenascin and laminin subunit were revealed. The results attest to activation of proteolytic processes in the matrix of mesenchymal stromal cells and weakening of cell adhesion to extracellular matrix under conditions of simulated microgravity.

Tenocyte-imprinted substrate: a topography-based inducer for tenogenic differentiation in adipose tissue-derived mesenchymal stem cells

Tendon tissue engineering based on stem cell differentiation has attracted a great deal of attention in recent years. Previous studies have examined the effect of cell-imprinted polydimethylsiloxane (PDMS) substrate on induction differentiation in stem cells. In this study, we used tenocyte morphology as a positive mold to create a tenocyte-imprinted substrate on PDMS. The morphology and topography of this tenocyte replica on PDMS was evaluated with scanning electron microscopy (SEM) and atomic force microscopy. The tenogenic differentiation induction capacity of the tenocyte replica in adipose tissue-derived mesenchymal stem cells (ADSCs) was then investigated and compared with other groups, including tissue replica (which was produced similarly to the tenocyte replica and was evaluated by SEM), decellularized tendon, and bone morphogenic protein (BMP)-12, as other potential inducers. This comparison gives us an estimate of the ability of tenocyte-imprinted PDMS (called cell replica in the present study) to induce differentiation compared to other inducers. For this reason, ADSCs were divided into five groups, including control, cell replica, tissue replica, decellularized tendon and BMP-12. ADSCs were seeded on each group separately and investigated by the real-time reverse transcription polymerase chain reaction (RT-PCR) technique after seven and 14 days. Our results showed that in spite of the higher effect of the growth factor on tenogenic differentiation, the cell replica can also induce tenocyte marker expression (scleraxis and tenomodulin) in ADSCs. Moreover, the tenogenic differentiation induction capacity of the cell replica was greater than tissue replica. Immunocytochemistry analysis revealed that ADSCs seeding on the cell replica for 14 days led to scleraxis and tenomodulin expression at the protein level. In addition, immunohistochemistry indicated that contrary to the promising results in vitro, there was little difference between ADSCs cultured on tenocyte-imprinted PDMS and untreated ADSCs. The results of such studies could lead to the production of inexpensive cell culture plates or biomaterials that can induce differentiation in stem cells without growth factors or other supplements.

SV40 Transfected Human Anterior Cruciate Ligament Derived Ligamentocytes-Suitable as a Human in Vitro Model for Ligament Reconstruction?

Cultured human primary cells have a limited lifespan undergoing dedifferentiation or senescence. Anterior cruciate ligaments (ACL) are hypocellular but tissue engineering (TE) requires high cell numbers. Simian virus (SV) 40 tumor (T) antigen expression could extend the lifespan of cells. This study aimed to identify cellular changes induced by SV40 expression in human ACL ligamentocytes by comparing them with non-transfected ligamentocytes and tissue of the same donor to assess their applicability as TE model. Human ACL ligamentocytes (40-year-old female donor after ACL rupture) were either transfected with a SV40 plasmid or remained non-transfected (control) before monitored for SV40 expression, survival, and DNA content. Protein expression of cultured ligamentocytes was compared with the donor tissue. Ligamentocyte spheroids were seeded on scaffolds embroidered either from polylactic acid (PLA) threads solely or combined PLA and poly (L-lactide-co-ε-caprolactone) (P(LA-CL)) threads. These scaffolds were further functionalized with fluorination and fibrillated collagen foam. Cell distribution and survival were monitored for up to five weeks. The transfected cells expressed the SV40 antigen throughout the entire observation time, but often exhibited random and incomplete cell divisions with significantly more dying cells, significantly more DNA and more numerous nucleoli than controls. The expression profile of non-transfected and SV40-positive ligamentocytes was similar. In contrast to controls, SV40-positive cells formed larger spheroids, produced less vimentin and focal adhesions and died on the scaffolds after 21 d. Functionalized scaffolds supported human ligamentocyte growth. SV40 antigen expressing ligamentocytes share many properties with their non-transfected counterparts suggesting them as a model, however, applicability for TE is limited.

The Role of C-X-C Chemokine Receptor Type 4 (CXCR4) in Cell Adherence and Spheroid Formation of Human Ewing's Sarcoma Cells under Simulated Microgravity

We studied the behavior of Ewing's Sarcoma cells of the line A673 under simulated microgravity (s-µg). These cells express two prominent markers-the oncogene EWS/FLI1 and the chemokine receptor CXCR4, which is used as a target of treatment in several types of cancer. The cells were exposed to s-µg in a random-positioning machine (RPM) for 24 h in the absence and presence of the CXCR4 inhibitor AMD3100. Then, their morphology and cytoskeleton were examined. The expression of selected mutually interacting genes was measured by qRT-PCR and protein accumulation was determined by western blotting. After 24 h incubation on the RPM, a splitting of the A673 cell population in adherent and spheroid cells was observed. Compared to 1 g control cells, EWS/FLI1 was significantly upregulated in the adherent cells and in the spheroids, while CXCR4 and CD44 expression were significantly enhanced in spheroids only. Transcription of CAV-1 was upregulated and DKK2 and VEGF-A were down-regulated in both, adherent in spheroid cells, respectively. Regarding, protein accumulation EWS/FLI1 was enhanced in adherent cells only, but CD44 decreased in spheroids and adherent cells. Inhibition of CXCR4 did not change spheroid count, or structure. Under s-µg, the tumor marker EWS/FLI1 is intensified, while targeting CXCR4, which influences adhesion proteins, did not affect spheroid formation.

Alteration of Cytoskeleton Morphology and Gene Expression in Human Breast Cancer Cells under Simulated Microgravity

Objective

Weightlessness simulation due to the simulated microgravity has been shown to considerably affect behavior of tumor cells. It is aim of this study to evaluate characteristics of human breast cancer cells in this scaffoldfree 3D culture model.

Materials and Methods

In this experimental study, the cells were exposed to simulated microgravity in a randompositioning machine (RPM) for five days. Morphology was observed under phase-contrast and confocal microscopy. Cytofilament staining was performed and changes in expression level of cytofilament genes, proliferation/differentiation genes, oncogenes and tumor suppressor genes were detected by quantitative reverse transcription polymerase chain reaction (qRT-PCR), followed by western blot confirmation.

Results

After five days, distinct spheroid formation was observed. Rearrangement of the cytoskeleton into spherical shape was visible. VIM gene expression was significantly up-regulated for adherent cells and spheroids (3.3x and 3.6x respectively, P<0.05 each). RHOA also showed significant gene up-regulation for adherent cells and spheroids (3.2x and 3.9x respectively, P<0.05 each). BRCA showed significant gene up-regulation in adherent cells and spheroids (2.1x and 4.1x respectively, P<0.05 each). ERBB2 showed significant gene up-regulation (2.4x, P<0.05) in the spheroids, but not in the adherent cells. RAB27A showed no significant alteration in gene expression. MAPK) showed significant gene up-regulation in adherent cells and spheroids (3.2x, 3.0x, P<0.05 each). VEGF gene expression was down-regulated under simulated microgravity, without significance. Alterations of gene expressions could be confirmed on protein level for vimentin and MAPK1. Protein production was not increased for BRCA1, human epidermal growth factor receptor 2 (HER2) and VEGF. Contradictory changes were determined for RHOA and its related protein.

Conclusion

Microgravity provides an easy-to handle, scaffold-free 3D-culture model for human breast cancer cells. There were considerable changes in morphology, cytoskeleton shape and gene expressions. Identification of the underlying mechanisms could provide new therapeutic options.

Apoptosis Induction and Alteration of Cell Adherence in Human Lung Cancer Cells under Simulated Microgravity

BACKGROUND

Lung cancer cells are known to change proliferation and migration under simulated microgravity. In this study, we sought to evaluate cell adherence, apoptosis, cytoskeleton arrangement, and gene expression under simulated microgravity.

METHODS

Human lung cancer cells were exposed to simulated microgravity in a random-positioning machine (RPM). Cell morphology and adherence were observed under phase-contrast microscopy, cytoskeleton staining was performed, apoptosis rate was determined, and changes in gene and protein expression were detected by real-time PCR with western blot confirmation.

RESULTS

Three-dimensional (3D)-spheroid formation was observed under simulated microgravity. Cell viability was not impaired. Actin filaments showed a shift in alignment from longitudinal to spherical. Apoptosis rate was significantly increased in the spheroids compared to the control. TP53, CDKN2A, PTEN, and RB1 gene expression was significantly upregulated in the adherent cells under simulated microgravity with an increase in corresponding protein production for p14 and RB1. SOX2 expression was significantly upregulated in the adherent cells, but protein was not. Gene expressions of AKT3, PIK3CA, and NFE2L2 remained unaltered.

CONCLUSION

Simulated microgravity induces alteration in cell adherence, increases apoptosis rate, and leads to upregulation of tumor suppressor genes in human lung cancer cells.