Fabricating Muscle–Neuron Constructs with Improved Contractile Force Generation

The Adrenal Pheochromocytoma Cell Line PC12 Efficiently Promotes the Regeneration Capability of Adipose Tissue-Derived Mesenchymal Stem Cells in Myogenesis: A Particular Approach to Improving Skeletal Muscle Cell Regeneration

Background

Researchers are looking for a way to improve the myogenic differentiation of stem cells. Adipose-derived stem cells (ADSCs), known for their multipotency and regenerative capabilities, have been extensively studied for their therapeutic potential. Meanwhile, PC12 cells, derived from rat pheochromocytoma, have been found pivotal in neuroscience research, particularly as a neuronal model system. The current study investigated the effect of the PC12 adrenal pheochromocytoma cell line on the myogenic differentiation of ADSCs.

Methods

This experimental study was conducted during 2019-2022 (Ahvaz, Iran). Differentiation of ADSCs was induced by using 3 μg/mL 5-azacytidine for 24 hours. Then, the culture media was changed with Dulbecco's Modified Eagle-High Glucose (DMEM-HG) containing 5% horse serum (HS) and kept for 7 days. Different percentages of differentiated ADSCs and PC12 (100:0, 70:30, 50:50, 30:70) were cocultured for 7 days in DMEM-HG containing 5% HS. PC12 was labeled with cell tracker C7000. The real-time polymerase chain reaction and Western blotting techniques were utilized to assess gene and protein expression. All experiments were repeated three times. Data were analyzed using GraphPad Prism 8.0.2 software with a one-way analysis of variance. P<0.05 was considered statistically significant.

Results

PC12 visualization confirmed the accuracy of the co-culture process. The differentiated cells showed an aligned, multinucleated shape. The differentiated ADSCs revealed significantly elevated levels of Myh1, Myh2, and Chrn-α1 gene expression compared with undifferentiated ADSCs (P<0.0001). The ADSCs cocultured with PC12 cells showed significantly higher Myh1, Myh2, and Chrn-α1 gene expression than differentiated ADSCs (P<0.001). ADSCs cocultured with 50% PC12 revealed significantly higher MYH and nAchR protein expression than the differentiated group (P<0.01 and P<0.001).

Conclusion

Coculturing PC12 cells and ADSCs improves the efficiency of myogenic differentiation. However, the effectiveness of myogenic differentiation depends on the proportions of administered PC12 cells.

Upscaled Skeletal Muscle Engineered Tissue with In Vivo Vascularization and Innervation Potential

Engineering functional tissues of clinically relevant size (in mm-scale) in vitro is still a challenge in tissue engineering due to low oxygen diffusion and lack of vascularization. To address these limitations, a perfusion bioreactor was used to generate contractile engineered muscles of a 3 mm-thickness and a 8 mm-diameter. This study aimed to upscale the process to 50 mm in diameter by combining murine skeletal myoblasts (SkMbs) with human adipose-derived stromal vascular fraction (SVF) cells, providing high neuro-vascular potential in vivo. SkMbs were cultured on a type-I-collagen scaffold with (co-culture) or without (monoculture) SVF. Large-scale muscle-like tissue showed an increase in the maturation index over time (49.18 ± 1.63% and 76.63 ± 1.22%, at 9 and 11 days, respectively) and a similar force of contraction in mono- (43.4 ± 2.28 µN) or co-cultured (47.6 ± 4.7 µN) tissues. Four weeks after implantation in subcutaneous pockets of nude rats, the vessel length density within the constructs was significantly higher in SVF co-cultured tissues (5.03 ± 0.29 mm/mm²) compared to monocultured tissues (3.68 ± 0.32 mm/mm²) (p < 0.005). Although no mature neuromuscular junctions were present, nerve-like structures were predominantly observed in the engineered tissues co-cultured with SVF cells. This study demonstrates that SVF cells can support both in vivo vascularization and innervation of contractile muscle-like tissues, making significant progress towards clinical translation.

Remote Magnetic Microengineering and Alignment of Spheroids into 3D Cellular Fibers

Developing in vitro models that recapitulate the in vivo organization of living cells in a 3D microenvironment is one of the current challenges in the field of tissue engineering. In particular for anisotropic tissues where alignment of precursor cells is required for them to create functional structures. Herein, a new method is proposed that allows aligning in the direction of a uniform magnetic field both individual cells (muscle, stromal, and stem cells) or spheroids in a thermoresponsive collagen hydrogel. In an all‐in‐one approach, spheroids are generated at high throughput by magnetic engineering using microfabricated micromagnets and are used as building blocks to create 3D anisotropic tissue structures of different scales. The magnetic cells and spheroids alignment process is optimized in terms of magnetic cell labeling, concentration, and size. Anisotropic structures are induced to form fibers in the direction of the magnetic alignment, with the respective roles of the magnetic field, the mechanical stretching of hydrogel or co‐culture of the aligned cells with non‐magnetic stromal cells, being investigated. Over days, spheroids fuse into 3D tubular structures, oriented in the direction of the magnetic alignment. Moreover, in the case of the muscle cells model, multinucleated cells can be observed within the fibers.

Recellularization of Bioengineered Scaffolds for Vascular Composite Allotransplantation

Traumatic injuries or cancer resection resulting in large volumetric soft tissue loss requires surgical reconstruction. Vascular composite allotransplantation (VCA) is an emerging reconstructive option that transfers multiple, complex tissues as a whole subunit from donor to recipient. Although promising, VCA is limited due to side effects of immunosuppression. Tissue-engineered scaffolds obtained by decellularization and recellularization hold great promise. Decellularization is a process that removes cellular materials while preserving the extracellular matrix architecture. Subsequent recellularization of these acellular scaffolds with recipient-specific cells can help circumvent adverse immune-mediated host responses and allow transplantation of allografts by reducing and possibly eliminating the need for immunosuppression. Recellularization of acellular tissue scaffolds is a technique that was first investigated and reported in whole organs. More recently, work has been performed to apply this technique to VCA. Additional work is needed to address barriers associated with tissue recellularization such as: cell type selection, cell distribution, and functionalization of the vasculature and musculature. These factors ultimately contribute to achieving tissue integration and viability following allotransplantation. The present work will review the current state-of-the-art in soft tissue scaffolds with specific emphasis on recellularization techniques. We will discuss biological and engineering process considerations, technical and scientific challenges, and the potential clinical impact of this technology to advance the field of VCA and reconstructive surgery.

Schwann Cells Promote Myogenic Differentiation of Myoblasts and Adipogenic Mesenchymal Stromal Cells on Poly-ɛ-Caprolactone-Collagen I-Nanofibers

For the purpose of skeletal muscle tissue engineering, different cell types have been investigated regarding their myogenic differentiation potential, including co-cultured myoblasts and adipogenic mesenchymal stromal cells (Mb/ADSC). As neural cells enhance synaptic junction formation, the aim of this study was to co-culture Schwann cells (SCs) with Mb/ADSC on biocompatible electrospun aligned poly-ε-polycaprolacton (PCL)-collagen I-nanofibers. It was hypothesized that SCs, as part of the peripheral nervous system, promote the myogenic differentiation of Mb/ADSC co-cultures. Mb/ADSC were compared to Mb/ADSC/SC regarding their capacity for myogenic differentiation via immunofluorescent staining and gene expression of myogenic markers. Mb/ADSC/SC showed more myotubes after 28 days of differentiation (p ≤ 0.05). After 28 days of differentiation on electrospun aligned PCL-collagen I-nanofibers, gene expression of myosin heavy chains (MYH2) and myogenin (MYOG) was upregulated in Mb/ADSC/SC compared to Mb/ADSC (p ≤ 0.01 and p ≤ 0.05, respectively). Immunofluorescent staining for MHC showed highly aligned multinucleated cells as possible myotube formation in Mb/ADSC/SC. In conclusion, SCs promote myogenic differentiation of Mb/ADSC. The co-culture of primary Mb/ADSC/SC on PCL-collagen I-nanofibers serves as a physiological model for skeletal muscle tissue engineering, applicable to future clinical applications.

The Evolution of Complex Muscle Cell In Vitro Models to Study Pathomechanisms and Drug Development of Neuromuscular Disease

Many neuromuscular disease entities possess a significant disease burden and therapeutic options remain limited. Innovative human preclinical models may help to uncover relevant disease mechanisms and enhance the translation of therapeutic findings to strengthen neuromuscular disease precision medicine. By concentrating on idiopathic inflammatory muscle disorders, we summarize the recent evolution of the novel in vitro models to study disease mechanisms and therapeutic strategies. A particular focus is laid on the integration and simulation of multicellular interactions of muscle tissue in disease phenotypes in vitro. Finally, the requirements of a neuromuscular disease drug development workflow are discussed with a particular emphasis on cell sources, co-culture systems (including organoids), functionality, and throughput.

Miniaturized skeletal muscle tissue fabrication for measuring contractile activity

The contractile function of skeletal muscle is essential for maintaining the vital activity of life. Muscular diseases such as muscular dystrophy severely compromise the quality of life of patients and ultimately lead to death. There is therefore an urgent need to develop therapeutic agents for these diseases. In a previous study, we showed that three-dimensional skeletal muscle tissues fabricated using the magnetic force-based tissue engineering technique exhibited contractile activity, and that drug effects could be evaluated based on the contractile activity of the skeletal muscle tissues. However, the reported method requires a large number of cells and the tissue preparation procedure is complex. It is therefore necessary to improve the tissue preparation method. In this study, a miniature device made of polydimethylsiloxane was used to simplify the production of contracting skeletal muscle tissues applicable to high-throughput screening. The effects of model drugs on the contractile force generation of skeletal muscle tissues prepared from mouse C2C12 myoblast and human induced pluripotent stem cells were evaluated using the miniature muscle device. The results indicated that the muscle device system could provide a useful tool for drug screening.

Next Stage Approach to Tissue Engineering Skeletal Muscle

Large-scale muscle injury in humans initiates a complex regeneration process, as not only the muscular, but also the vascular and neuro-muscular compartments have to be repaired. Conventional therapeutic strategies often fall short of reaching the desired functional outcome, due to the inherent complexity of natural skeletal muscle. Tissue engineering offers a promising alternative treatment strategy, aiming to achieve an engineered tissue close to natural tissue composition and function, able to induce long-term, functional regeneration after in vivo implantation. This review aims to summarize the latest approaches of tissue engineering skeletal muscle, with specific attention toward fabrication, neuro-angiogenesis, multicellularity and the biochemical cues that adjuvate the regeneration process.

Systemic Actions of Breast Cancer Facilitate Functional Limitations

Breast cancer is a disease of a specific organ, but its effects are felt throughout the body. The systemic effects of breast cancer can lead to functional limitations in patients who suffer from muscle weakness, fatigue, pain, fibromyalgia, or many other dysfunctions, which hasten cancer-associated death. Mechanistic studies have identified quite a few molecular defects in skeletal muscles that are associated with functional limitations in breast cancer. These include circulating cytokines such as TNF-α, IL-1, IL-6, and TGF-β altering the levels or function of myogenic molecules including PAX7, MyoD, and microRNAs through transcriptional regulators such as NF-κB, STAT3, and SMADs. Molecular defects in breast cancer may also include reduced muscle mitochondrial content and increased extracellular matrix deposition leading to energy imbalance and skeletal muscle fibrosis. This review highlights recent evidence that breast cancer-associated molecular defects mechanistically contribute to functional limitations and further provides insights into therapeutic interventions in managing functional limitations, which in turn may help to improve quality of life in breast cancer patients.

Engineered topographical structure to control spatial cell density using cell migration

Control of the spatial distribution of various cell types is required to construct functional tissues. Here, we report a simple topographical structure changed the spatial cell density. A concave curved boundary was designed, which allowed the spatial descent moving of cells and the change in spatial distributions of co-cultured cells. We utilized the difference in cell motility between myoblast cells (C2C12) and neuronal cells (PC12) to demonstrate the feasibility of spontaneous change in spatial cell density. Without the curved boundaries, high motility cells (C2C12) did not migrate to the adjacent area, which resulted in a slight temporal change (< 15%) in the spatial cell distribution. In contrast, with the curved boundaries, the cell density of the high motility cells in the groove to those cells on the ridge showed an increase exceeding 45%. On the other hand, the temporal change in the spatial cell distribution of low motility cells (PC12) was below 15% with or without the curved boundaries. In addition, as groove width increased, both cells displayed more initially gathering in groove. Importantly, these cell-type dependent results were also maintained under co-culture conditions. Our results suggest that designing topographical interfaces changes spatial cell density without any manipulation and is useful for multi-cellular constructs.