Tension-loaded bone marrow stromal cells potentiate the paracrine osteogenic signaling of co-cultured vascular endothelial cells

Physical and biological advances in endothelial cell-based engineered co-culture model systems

Scientific knowledge in the field of cell biology and mechanobiology heavily leans on cell-based in vitro experiments and models that favor the examination and comprehension of certain biological processes and occurrences across a variety of environments. Cell culture assays are an invaluable instrument for a vast spectrum of biomedical and biophysical investigations. The quality of experimental models in terms of simplicity, reproducibility, and combinability with other methods, and in particular the scale at which they depict cell fate in native tissues, is critical to advancing the knowledge of the comprehension of cell-cell and cell-matrix interactions in tissues and organs. Typically, in vitro models are centered on the experimental tinkering of mammalian cells, most often cultured as monolayers on planar, two-dimensional (2D) materials. Notwithstanding the significant advances and numerous findings that have been accomplished with flat biology models, their usefulness for generating further new biological understanding is constrained because the simple 2D setting does not reproduce the physiological response of cells in natural living tissues. In addition, the co-culture systems in a 2D stetting weakly mirror their natural environment of tissues and organs. Significant advances in 3D cell biology and matrix engineering have resulted in the creation and establishment of a new type of cell culture shapes that more accurately represents the in vivo microenvironment and allows cells and their interactions to be analyzed in a biomimetic approach. Contemporary biomedical and biophysical science has novel advances in technology that permit the design of more challenging and resilient in vitro models for tissue engineering, with a particular focus on scaffold- or hydrogel-based formats, organotypic cultures, and organs-on-chips, which cover the purposes of co-cultures. Even these complex systems must be kept as simplified as possible in order to grasp a particular section of physiology too very precisely. In particular, it is highly appreciated that they bridge the space between conventional animal research and human (patho)physiology. In this review, the recent progress in 3D biomimetic culturation is presented with a special focus on co-cultures, with an emphasis on the technological building blocks and endothelium-based co-culture models in cancer research that are available for the development of more physiologically relevant in vitro models of human tissues under normal and diseased conditions. Through applications and samples of various physiological and disease models, it is possible to identify the frontiers and future engagement issues that will have to be tackled to integrate synthetic biomimetic culture systems far more successfully into biomedical and biophysical investigations.

Endothelial Cells Promote Osteogenesis by Establishing a Functional and Metabolic Coupling With Human Mesenchymal Stem Cells

Bone formation involves a complex crosstalk between endothelial cells (EC) and osteodifferentiating stem cells. This functional interplay is greatly mediated by the paracrine and autocrine action of soluble factors released at the vasculature-bone interface. This study elucidates the molecular and functional responses triggered by this intimate interaction. In this study, we showed that human dermal microvascular endothelial cells (HMEC) induced the expression of pro-angiogenic factors in stem cells from human exfoliated deciduous teeth (SHED) and sustain their osteo-differentiation at the same time. In contrast, osteodifferentiating SHED increased EC recruitment and promoted the formation of complex vascular networks. Moreover, HMEC enhanced anaerobic glycolysis in proliferating SHED without compromising their ability to undergo the oxidative metabolic shift required for adequate osteo-differentiation. Taken together, these findings provide novel insights into the molecular mechanism underlying the synergistic cooperation between EC and stem cells during bone tissue renewal.

Mechanical Stimulation on Mesenchymal Stem Cells and Surrounding Microenvironments in Bone Regeneration: Regulations and Applications

Treatment of bone defects remains a challenge in the clinic. Artificial bone grafts are the most promising alternative to autologous bone grafting. However, one of the limiting factors of artificial bone grafts is the limited means of regulating stem cell differentiation during bone regeneration. As a weight-bearing organ, bone is in a continuous mechanical environment. External mechanical force, a type of biophysical stimulation, plays an essential role in bone regeneration. It is generally accepted that osteocytes are mechanosensitive cells in bone. However, recent studies have shown that mesenchymal stem cells (MSCs) can also respond to mechanical signals. This article reviews the mechanotransduction mechanisms of MSCs, the regulation of mechanical stimulation on microenvironments surrounding MSCs by modulating the immune response, angiogenesis and osteogenesis, and the application of mechanical stimulation of MSCs in bone regeneration. The review provides a deep and extensive understanding of mechanical stimulation mechanisms, and prospects feasible designs of biomaterials for bone regeneration and the potential clinical applications of mechanical stimulation.

Recent Advances on Cell-Based Co-Culture Strategies for Prevascularization in Tissue Engineering

Currently, the fabrication of a functional vascular network to maintain the viability of engineered tissues is a major bottleneck in the way of developing a more advanced engineered construct. Inspired by vasculogenesis during the embryonic period, the in vitro prevascularization strategies have focused on optimizing communications and interactions of cells, biomaterial and culture conditions to develop a capillary-like network to tackle the aforementioned issue. Many of these studies employ a combination of endothelial lineage cells and supporting cells such as mesenchymal stem cells, fibroblasts, and perivascular cells to create a lumenized endothelial network. These supporting cells are necessary for the stabilization of the newly developed endothelial network. Moreover, to optimize endothelial network development without impairing biomechanical properties of scaffolds or differentiation of target tissue cells, several other factors, including target tissue, endothelial cell origins, the choice of supporting cell, culture condition, incorporated pro-angiogenic factors, and choice of biomaterial must be taken into account. The prevascularization method can also influence the endothelial lineage cell/supporting cell co-culture system to vascularize the bioengineered constructs. This review aims to investigate the recent advances on standard cells used in in vitro prevascularization methods, their co-culture systems, and conditions in which they form an organized and functional vascular network.

Harnessing nerve-muscle cell interactions for biomaterials-based skeletal muscle regeneration

Nerve cells secrete neurotrophic factors that play a critical role in neuronal survival, proliferation, and regeneration. However, their role in regulating myoblast behavior and skeletal muscle repair remains largely unexplored. In the present study, we investigated the effects of PC12 secreted signaling factors in modulating C2C12 myoblast behavior under physiologically relevant conditions. We showed that PC12 conditioned media modulated myoblast proliferation and differentiation in both 2D culture and 3D aligned electrospun fiber scaffold system in a dose-dependent manner. We further developed a biomimetic, tunable hydrogel consisting of hyaluronic acid, chondroitin sulfate, and polyethylene glycol as a 3D matrix encapsulating PC12 cells. The hydrogel-encapsulated PC12 cells promoted survival and proliferation of myoblasts in co-culture. Further proteomics analysis identified a total of 2,088 proteins from the secretome of the encapsulated PC12 cells and revealed the biological role and overlapping functions of nerve-secreted proteins for skeletal muscle regeneration, potentially through regulating myoblast behavior, nerve function, and angiogenesis. These experiments provide insights into the nerve-muscle interactions and pave the way for developing advanced biomaterials strategies incorporating nerve cell secretome for accelerated skeletal muscle regeneration.

Fluid shear stress and endothelial cells synergistically promote osteogenesis of mesenchymal stem cells via integrin β1-FAK-ERK1/2 pathway

Prevascularization and mechanical stimulation have been reported as effective methods for the construction of functional bone tissue. However, their combined effects on osteogenic differentiation and its mechanism remain to be explored. Here, the effects of fluid shear stress (FSS) on osteogenic differentiation of rat bone-marrow-derived mesenchymal stem cells (BMSCs) when cocultured with human umbilical vein endothelial cells (HUVECs) were investigated, and underlying signaling mechanisms were further explored. FSS stimulation for 1-4 h/day increased alkaline phosphatase (ALP) activity and calcium deposition in coculture systems and promoted the proliferation of cocultured cells. FSS stimulation for 2 h/day was selected as the optimized protocol according to osteogenesis in the coculture. In this situation, the mRNA levels of ALP, runt-related transcriptional factor 2 (Runx2) and osteocalcin (OCN), and protein levels of OCN and osteopontin (OPN) in BMSCs were upregulated. Furthermore, FSS and coculture with HUVECs synergistically increased integrin β1 expression in BMSCs and further activated focal adhesion kinases (FAKs) and downstream extracellular signal-related kinase (ERK), leading to the enhancement of Runx2 expression. Blocking the phosphorylation of FAK abrogated FSS-induced ERK phosphorylation and inhibited osteogenesis of cocultured BMSCs. These results revealed that FSS and coculture with HUVECs synergistically promotes the osteogenesis of BMSCs, which was mediated by the integrin β1-FAK-ERK signaling pathway.

A novel method to improve the osteogenesis capacity of hUCMSCs with dual-directional pre-induction under screened co-culture conditions

OBJECTIVES

Mesenchymal stem cells (MSCs) based therapy for bone regeneration has been regarded as a promising method in the clinic. However, hBMSCs with invasive harvesting process and undesirable proliferation rate hinder the extensive usage. HUCMSCs of easier access and excellent performances provide an alternative for the fabrication of tissue-engineered bone construct. Evidence suggested the osteogenesis ability of hUCMSCs was weaker than that of hBMSCs. To address this issue, a co-culture strategy of osteogenically and angiogenically induced hUCMSCs has been proposed since thorough vascularization facilitates the blood-borne nutrition and oxygen to transport in the scaffold, synergistically expediting the process of ossification.

MATERIALS AND METHODS

Herein, we used osteogenic- and angiogenic-differentiated hUCMSCs for co-culture in screened culture medium to elevate the osteogenic capacity with in vitro studies and finally coupled with 3D TCP scaffold to repair rat's critical-sized calvarial bone defect. By dual-directional induction, hUCMSCs could differentiate into osteoblasts and endothelial cells, respectively. To optimize the co-culture condition, gradient ratios of dual-directional differentiated hUCMSCs co-cultured under different medium were studied to determine the appropriate condition.

RESULTS

It revealed that the osteogenic- and angiogenic-induced hUCMSCs mixed with the ratio of 3:1 co-cultured in the mixed medium of osteogenic induction medium to endothelial cell induction medium of 3:1 possessed more mineralization nodules. Similarly, ALP and osteogenesis/angiogenesis-related genes expressions were relatively higher. Further evidence of bone defect repair with 3D printed TCP of 3:1 group exhibited better restoration outcomes.

CONCLUSIONS

Our work demonstrated a favourable and convenient approach of dual-directional differentiated hUCMSCs co-culture to improve the osteogenesis, establishing a novel way to fabricate tissue-engineered bone graft with 3D TCP for large bone defect augmentation.

Enhanced bone tissue regeneration of a biomimetic cellular scaffold with co-cultured MSCs-derived osteogenic and angiogenic cells

OBJECTIVES

The bone tissue engineering primarily focuses on three-dimensional co-culture systems, which physical and biological properties resemble the cell matrix of actual tissues. The complex dialogue between bone-forming and endothelial cells (ECs) in a tissue-engineered construct will directly regulate angiogenesis and bone regeneration. The purpose of this study was to investigate whether co-culture between osteogenic and angiogenic cells derived by bone mesenchymal stem cells (MSCs) could affect cell activities and new bone formation.

MATERIALS AND METHODS

Mesenchymal stem cells were dually induced to differentiate into osteogenic cells (OMSCs) and ECs; both cell types were co-cultured at different ratios to investigate their effects and underlying mechanisms through ELISA, RT-qPCR and MTT assays. The selected cell mixture was transplanted onto a nano-hydroxyapatite/polyurethane (n-HA/PU) scaffold to form a cell-scaffold construct that was implanted in the rat femoral condyles. Histology and micro-CT were examined for further verification.

RESULTS

ELISA and gene expression studies revealed that co-cultured OMSCs/ECs (0.5/1.5) significantly elevated the transcription levels of osteogenic genes such as ALP, Col-I and OCN, as well as transcription factors Msx2, Runx2 and Osterix; it also upregulated angiogenic factors of vascular endothelial growth factor (VEGF) and CD31 when compared with cells cultured alone or in other ratios. The optimized OMSCs/ECs group had more abundant calcium phosphate crystal deposition, further facilitated their bone formation in vivo.

CONCLUSIONS

The OMSCs/ECs-scaffold constructs at an optimal cell ratio (0.5/1.5) achieved enhanced osteogenic and angiogenic factor expression and biomineralization, which resulted in more effective bone formation.

[Vascular endothelial growth factor/polylactide-polyethyleneglycol-polylactic acid copolymer/basic fibroblast growth factor mixed microcapsules in promoting angiogenic differentiation of rat bone marrow mesenchymal stem cells in vitro]

Objective

To observe the effect of vascular endothelial growth factor/polylactide-polyethyleneglycol-polylactic acid copolymer/basic fibroblast growth factor (VEGF/PELA/bFGF) mixed microcapsules in promoting the angiogenic differentiation of rat bone marrow mesenchymal stem cells (BMSCs) in vitro.

Methods

The BMSCs were isolated by the method of whole bone marrow adherent, and sub-cultured. The passage 3 BMSCs were identified by Wright-Giemsa staining and flow cytometry, and used for subsequent experiments. VEGF/PELA/bFGF (group A), PELA/bFGF (group B), VEGF/PELA (group C), and PELA (group D) microcapsules were prepared. The biodegradable ability and cytotoxicity of PELA microcapsule were determined，and the slow-released ability of VEGF/PELA/bFGF mixed microcapsules was measured. The passage 3 BMSCs were co-cultured with the extracts of groups A, B, C, and D, separately. At 1, 3, 7, 14, and 20 days after being cultured, the morphological changes of induced BMSCs were recorded. At 21 days, the induced BMSCs were tested for DiI-labeled acetylated low density lipoprotein (Dil-ac-LDL) and FITC-labeled ulex europaeus agglutinin I (FITC-UEA-I) uptake ability. The tube-forming ability of the induced cells on Matrigel was also verified. The differences of the vascularize indexes in nodes, master junctions, master segments, and tot.master segments length in 4 groups were summarized and analyzed.

Results

The isolated and cultured cells were identified as BMSCs. The degradation time of PELA was more than 20 days. There was no significant effect on cell viability under co-culture conditions. At 20 days, the cumulative release of VEGF in the mixed microcapsules exceeded 95%, and the quantity of bFGF exceeded 80%. The morphology of cells in groups A, B, and C were changed. The cells in groups A and B showed the typical change of cobble-stone morphology. The numbers of double fluorescent labeled cells observed by fluorescence microscope were the most in group A, and decreases from group B and group C, with the lowest in group D. The cells in groups A and B formed a grid-like structure on Matrigel. Quantitative analysis showed that the differences in the number of nodes, master junctions, master segments, and tot.master segments length between groups A, B and groups C, D were significant ( P<0.05). The number of nodes and the tot.master segments length of group A were more than those of group B ( P<0.05). There was no significant differences in the number of master junctions and master segments between group A and group B ( P>0.05).

Conclusion

VEGF/PELA/bFGF mixed microcapsules have significantly ability to promote the angiogenic differentiation of rat BMSCs in vitro.