Coculture in Musculoskeletal Tissue Regeneration

Revolutionizing bone healing: the role of 3D models

The increasing incidence of bone diseases has driven research towards Bone Tissue Engineering (BTE), an innovative discipline that uses biomaterials to develop three-dimensional (3D) scaffolds capable of mimicking the natural environment of bone tissue. Traditional approaches relying on two-dimensional (2D) models have exhibited significant limitations in simulating cellular interactions and the complexity of the bone microenvironment. In response to these challenges, 3D models such as organoids and cellular spheroids have emerged as effective tools for studying bone regeneration. Adult mesenchymal stem cells have proven crucial in this context, as they can differentiate into osteoblasts and contribute to bone tissue repair. Furthermore, the integration of composite biomaterials has shown substantial potential in enhancing bone healing. Advanced technologies like microfluidics offer additional opportunities to create controlled environments for cell culture, facilitating more detailed studies on bone regeneration. These advancements represent a fundamental step forward in the treatment of bone pathologies and the promotion of skeletal health. In this review, we report on the evolution of in vitro culture models applied to the study of bone healing/regrowth, starting from 2 to 3D cultures and microfluids. The different methodologies of in vitro model generation, cells and biomaterials are presented and discussed.

Regulation and mechanistic insights into tensile strain in mesenchymal stem cell osteogenic differentiation

Bone marrow mesenchymal stem cells (BMSCs) are integral to bone remodeling and homeostasis, as they are capable of differentiating into osteogenic and adipogenic lineages. This differentiation is substantially influenced by mechanosensitivity, particularly to tensile strain, which is a prevalent mechanical stimulus known to enhance osteogenic differentiation. This review specifically examines the effects of various cyclic tensile stress (CTS) conditions on BMSC osteogenesis. It delves into the effects of different loading devices, magnitudes, frequencies, elongation levels, dimensionalities, and coculture conditions, providing a comparative analysis that aids identification of the most conducive parameters for the osteogenic differentiation of BMSCs. Subsequently, this review delineates the signaling pathways activated by CTS, such as Wnt/β-catenin, BMP, Notch, MAPK, PI3K/Akt, and Hedgehog, which are instrumental in mediating the osteogenic differentiation of BMSCs. Through a detailed examination of these pathways, this study elucidates the intricate mechanisms whereby tensile strain promotes osteogenic differentiation, offering valuable guidance for optimizing therapeutic strategies aimed at enhancing bone regeneration.

Artificial Taste Buds: Bioorthogonally Ligated Gustatory-Neuronal Multicellular Hybrids Enabling Intercellular Taste Signal Transmission

Heterogeneous tissue models require the assembly and co-culture of multiple types of cells. Our recent work demonstrated taste signal transmission from gustatory cells to neurons by grafting single-stranded DNA into the cell membrane to construct multicellular assemblies. However, the weak DNA linkage and low grafting density allowed the formation of large gustatory cell self-aggregates that cannot communicate with neurons efficiently. This article presents the construction of artificial taste buds exhibiting active intercellular taste signal transmission through the hybridization of gustatory-neuronal multicellular interfaces using bioorthogonal click chemistry. Hybrid cell clusters were formed by the self-assembly of neonatal gustatory cells displaying tetrazine with a precultured embryonic hippocampal neuronal network displaying trans-cyclooctene. A bitter taste signal transduction was provoked in gustatory cells using denatonium benzoate and transmitted to neurons as monitored by intracellular calcium ion sensing. In the multicellular hybrids, the average number of signal transmissions was five to six peaks per cell, and the signal transmission lasted for ∼5 min with a signal-to-signal gap time of 10-40 s. The frequent and extended intercellular signal transmission suggests that the cell surface modification by the bioorthogonal click chemistry is a promising approach to fabricating functional multicellular hybrid clusters potentially useful for cell-based biosensors, toxicity assays, and tissue regeneration.

Co-culture systems of osteoblasts and osteoclasts: Simulating in vitro bone remodeling in regenerative approaches

Bone is an extremely dynamic tissue, undergoing continuous remodeling for its whole lifetime, but its regeneration or augmentation due to bone loss or defects are not always easy to obtain. Bone tissue engineering (BTE) is a promising approach, and its success often relies on a "smart" scaffold, as a support to host and guide bone formation through bone cell precursors. Bone homeostasis is maintained by osteoblasts (OBs) and osteoclasts (OCs) within the basic multicellular unit, in a consecutive cycle of resorption and formation. Therefore, a functional scaffold should allow the best possible OB/OC cooperation for bone remodeling, as happens within the bone extracellular matrix in the body. In the present work OB/OC co-culture models, with and without scaffolds, are reviewed. These experimental systems are intended for different targets, including bone remodeling simulation, drug testing and the assessment of biomaterials and 3D scaffolds for BTE. As a consequence, several parameters, such as cell type, cell ratio, culture medium and inducers, culture times and setpoints, assay methods, etc. vary greatly. This review identifies and systematically reports the in vitro methods explored up to now, which, as they allow cellular communication, more closely resemble bone remodeling and/or the regeneration process in the framework of BTE. STATEMENT OF SIGNIFICANCE: Bone is a dynamic tissue under continuous remodeling, but spontaneous healing may fail in the case of excessive bone loss which often requires valid alternatives to conventional treatments to restore bone integrity, like bone tissue engineering (BTE). Pre-clinical evaluation of scaffolds for BTE requires in vitro testing where co-cultures combining innovative materials with osteoblasts (OBs) and osteoclasts (OCs) closely mimic the in vivo repair process. This review considers the direct and indirect OB/OC co-cultures relevant to BTE, from the early mouse-cell models to the recent bone regenerative systems. The co-culture modeling of bone microenvironment provides reliable information on bone cell cross-talk. Starting from improved knowledge on bone remodeling, bone disease mechanisms may be understood and new BTE solutions are designed.

DFMG attenuates the activation of macrophages induced by co‑culture with LPC‑injured HUVE‑12 cells via the TLR4/MyD88/NF‑κB signaling pathway

7‑difluoromethoxy‑5,4'‑dimethoxy‑genistein (DFMG) is a novel active chemical entity, which modulates the function and signal transduction of endothelial cells and macrophages (MPs), and is essential in the prevention of atherosclerosis. In the present study, the activity and molecular mechanism of DFMG on MPs was investigated using a Transwell assay to construct a non‑contact co‑culture model. Human umbilical vein endothelial cells (HUVE‑12), which were incubated with lysophosphatidylcholine (LPC), were seeded in the upper chambers, whereas PMA‑induced MPs were grown in the lower chambers. The generation of reactive oxygen species (ROS) and the release of lactate dehydrogenase (LDH) were measured using the corresponding assay kits. The proliferation and migration were assessed using 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide and wound healing assays, respectively. Foam cell formation was examined using oil red O staining and a total cholesterol assay. The protein expression levels of Toll‑like receptor 4 (TLR4), myeloid differentiation factor 88 (MyD88) and nuclear factor (NF)‑κB p65 were detected by western immunoblotting. The secretion of interleukin (IL)‑1β was examined using an enzyme‑linked immunosorbent assay. It was found that LPC significantly increased the generation of ROS and the release of LDH in HUVE‑12 cells. The LPC‑injured HUVE‑12 cells activated MPs under co‑culture conditions and this process was inhibited by DFMG treatment. LPC upregulated the expression levels of TLR4, MyD88 and NF‑κB p65, and the secretion of IL‑1β in the supernatant of the co‑cultured HUVE‑12 cells and MPs. These effects were reversed by the application of DFMG. Furthermore, CLI‑095 and IL‑1Ra suppressed the activation of MPs that was induced by co‑culture with injured HUVE‑12 cells. These effects were further enhanced by co‑treatment with DFMG, and DFMG exhibited synergistic effects with a TLR4‑specific inhibitor. Take together, these findings revealed that DFMG attenuated the activation of MP induced by co‑culture with LPC‑injured HUVE‑12 cells. This process was mediated via inhibition of the TLR4/MyD88/NF‑κB signaling pathway in HUVE‑12 cells.

Cell-Engineered Nanovesicle as a Surrogate Inducer of Contact-Dependent Stimuli

Heterotypic interactions between cells are crucial in various biological phenomena. Particularly, stimuli that regulate embryonic stem cell (ESC) fate are often provided from neighboring cells. However, except for feeder cultures, no practical methods are identified that can provide ESCs with contact-dependent cell stimuli. To induce contact-dependent cell stimuli in the absence of living cells, a novel method that utilizes cell-engineered nanovesicles (CNVs) that are made by extruding living cells through microporous membranes is described. Protein compositions of CNVs are similar to their originating cells, as well as freely diffusible and precisely scalable. Treatment of CNVs produced from three different stromal cells successfully induces the same effect as feeder cultures. The results suggest that the effects of CNVs are mainly mediated by membrane-associated components. The use of CNVs might constitute a novel and efficient tool for ESC research.

Next Generation Tissue Engineering of Orthopedic Soft Tissue-to-Bone Interfaces

Soft tissue-to-bone interfaces are complex structures that consist of gradients of extracellular matrix materials, cell phenotypes, and biochemical signals. These interfaces, called entheses for ligaments, tendons, and the meniscus, are crucial to joint function, transferring mechanical loads and stabilizing orthopedic joints. When injuries occur to connected soft tissue, the enthesis must be re-established to restore function, but due to structural complexity, repair has proven challenging. Tissue engineering offers a promising solution for regenerating these tissues. This prospective review discusses methodologies for tissue engineering the enthesis, outlined in three key design inputs: materials processing methods, cellular contributions, and biochemical factors.

Novel Platform of Cardiomyocyte Culture and Coculture via Fibroblast-Derived Matrix-Coupled Aligned Electrospun Nanofiber

For cardiac tissue engineering, much attention has been given to the artificial cardiac microenvironment in which anisotropic design of scaffold and extracellular matrix (ECM) are the major cues. Here we propose poly(l-lactide-co-caprolactone) and fibroblast-derived ECM (PLCL/FDM), a hybrid scaffold that combines aligned electrospun PLCL fibers and FDM. Fibroblasts were grown on the PLCL fibers for 5-7 days and subsequently decellularized to produce PLCL/FDM. Various analyses confirmed aligned, FDM-deposited PLCL fibers. Compared to fibronectin (FN)-coated electrospun PLCL fibers (control), H9c2 cardiomyoblast differentiation was significantly effective, and neonatal rat cardiomyocyte (CM) phenotype and maturation was improved on PLCL/FDM. Moreover, a coculture platform was created using multilayer PLCL/FDM in which two different cells make indirect or direct cell-cell contacts. Such coculture platforms demonstrate their feasibility in terms of higher cell viability, efficiency of target cell harvest (>95% in noncontact; 85% in contact mode), and molecular diffusion through the PLCL/FDM layer. Coculture of primary CMs and fibroblasts exhibited much better CM phenotype and improvement of CM maturity upon either direct or indirect interactions, compared to the conventional coculture systems (transwell insert and tissue culture plate (TCP)). Taken together, our platform should be very useful and have significant contributions in investigating some scientific or practical issues of crosstalks between multiple cell types.

PHBV/bioglass composite scaffolds with co-cultures of endothelial cells and bone marrow stromal cells improve vascularization and osteogenesis for bone tissue engineering

PHBV + 10% BG composite scaffolds stimulated osteogenic differentiation and angiogenic differentiation of co-cultures of HBMSCs and HUVECs by enhancing paracrine effects between the two types of cells.

The Use of Silk as a Scaffold for Mature, Sustainable Unilocular Adipose 3D Tissue Engineered Systems

There is a critical need for monitoring physiologically relevant, sustainable, human adipose tissues in vitro to gain new insights into metabolic diseases. To support long-term culture, a 3D silk scaffold assisted culture system is developed that maintains mature unilocular adipocytes ex vivo in coculture with preadipocytes, endothelial cells, and smooth muscle cells obtained from small volumes of liquefied adipose samples. Without the silk scaffold, adipose tissue explants cannot be sustained in long-term culture (3 months) due to their fragility. Adjustments to media components are used to tune lipid metabolism and proliferation, in addition to responsiveness to an inflammatory stimulus. Interestingly, patient specific responses to TNFα stimulation are observed, providing a proof-of-concept translational technique for patient specific disease modeling in the future. In summary, this novel 3D scaffold assisted approach is required for establishing physiologically relevant, sustainable, human adipose tissue systems from small volumes of lipoaspirate, making this methodology of great value to studies of metabolism, adipokine-driven diseases, and other diseases where the roles of adipocytes are only now becoming uncovered.