Bioengineered human myobundles mimic clinical responses of skeletal muscle to drugs

Direct extrusion of multifascicle prevascularized human skeletal muscle for volumetric muscle loss surgery

Skeletal muscle is composed of multiple fascicles, which are parallel bundles of muscle fibers surrounded by connective tissues that contain blood vessels and nerves. Here, we fabricated multifascicle human skeletal muscle scaffolds that mimic the natural structure of human skeletal muscle bundles using a seven-barrel nozzle. For the core material to form the fascicle structure, human skeletal myoblasts were encapsulated in Matrigel with calcium chloride. Meanwhile, the shell that plays a role as the connective tissue, human fibroblasts and human umbilical vein endothelial cells within a mixture of porcine muscle decellularized extracellular matrix and sodium alginate at a 95:5 ratio was used. We assessed four types of extruded scaffolds monolithic-monoculture (Mo-M), monolithic-coculture (Mo-C), multifascicle-monoculture (Mu-M), and multifascicle-coculture (Mu-C) to determine the structural effect of muscle mimicking scaffold. The Mu-C scaffold outperformed other scaffolds in cell proliferation, differentiation, vascularization, mechanical properties, and functionality. In an in vivo mouse model of volumetric muscle loss, the Mu-C scaffold effectively regenerated the tibialis anterior muscle defect, demonstrating its potential for volumetric muscle transplantation. Our nozzle will be further used to produce other volumetric functional tissues, such as tendons and peripheral nerves.

Optogenetic stimulation and simultaneous optical mapping of membrane potential and calcium transients in human engineered cardiac spheroids

Optogenetic stimulation combined with optical mapping of membrane potential (Vm) and calcium transients (CaT) is a powerful electrophysiological tool. We developed a novel experimental platform in which tissue is stimulated optogenetically while Vm and CaT are imaged simultaneously. The Vm indicator is an organic dye, while the CaT indicator is genetically encoded. We used cardiac spheroids containing cardiomyocytes and fibroblasts differentiated from human induced pluripotent stem cells as model tissue. The spheroids were genetically encoded with an optogenetic actuator, CheRiff, and the calcium indicator jRCaMP1b. The Vm indicator was the organic dye RH237. CheRiff was excited using blue light (450 nm), and both RH237 and jRCaMP1b were excited using a single band of green light (either 525-575 nm or 558-575 nm). Fluorescence emission was split and imaged by two cameras (CaT: 595-665 nm; Vm: >700 nm). The spheroids were successfully stimulated optogenetically and Vm and CaT were recorded simultaneously without cross-talk using both excitation light bands. The 525-575 nm band produced higher signal-to-noise ratios than the 558-575 nm band, but caused a slight increase in tissue excitability because of CheRiff activation. The optogenetic actuator and CaT indicator are genetically encoded and can be expressed in engineered tissue constructs. In contrast, the Vm indicator is an organic dye that can stain any tissue. This system is well-suited for studying coupling between engineered tissue grafts and host tissue because the two tissue types can be stimulated independently, and tissue activation can be unambiguously attributed to either graft or host.

Engineering large-scale hiPSC-derived vessel-integrated muscle-like lattices for enhanced volumetric muscle regeneration

Engineering biomimetic tissue implants with human induced pluripotent stem cells (hiPSCs) holds promise for repairing volumetric tissue loss. However, these implants face challenges in regenerative capability, survival, and geometric scalability at large-scale injury sites. Here, we present scalable vessel-integrated muscle-like lattices (VMLs), containing dense and aligned hiPSC-derived myofibers alongside passively perfusable vessel-like microchannels inside an endomysium-like supporting matrix using an embedded multimaterial bioprinting technology. The contractile and millimeter-long myofibers are created in mechanically tailored and nanofibrous extracellular matrix-based hydrogels. Incorporating vessel-like lattice enhances myofiber maturation in vitro and guides host vessel invasion in vivo, improving implant integration. Consequently, we demonstrate successful de novo muscle formation and muscle function restoration through a combinatorial effect between improved graft-host integration and its increased release of paracrine factors within volumetric muscle loss injury models. The proposed modular bioprinting technology enables scaling up to centimeter-sized prevascularized hiPSC-derived muscle tissues with custom geometries for next-generation muscle regenerative therapies.

Actuating Extracellular Matrices Decouple the Mechanical and Biochemical Effects of Muscle Contraction on Motor Neurons

Emerging in vivo evidence suggests that repeated muscle contraction, or exercise, impacts peripheral nerves. However, the difficulty of isolating the muscle-specific impact on motor neurons in vivo, as well as the inability to decouple the biochemical and mechanical impacts of muscle contraction in this setting, motivates investigating this phenomenon in vitro. This study demonstrates that tuning the mechanical properties of fibrin enables longitudinal culture of highly contractile skeletal muscle monolayers, enabling functional characterization of and long-term secretome harvesting from exercised tissues. Motor neurons stimulated with exercised muscle-secreted factors significantly upregulate neurite outgrowth and migration, with an effect size dependent on muscle contraction intensity. Actuating magnetic microparticles embedded within fibrin hydrogels enable dynamically stretching motor neurons and non-invasively mimicking the mechanical effects of muscle contraction. Interestingly, axonogenesis is similarly upregulated in both mechanically and biochemically stimulated motor neurons, but RNA sequencing reveals different transcriptomic signatures between groups, with biochemical stimulation having a greater impact on cell signaling related to axonogenesis and synapse maturation. This study leverages actuating extracellular matrices to robustly validate a previously hypothesized role for muscle contraction in regulating motor neuron growth and maturation from the bottom-up through both mechanical and biochemical signaling.

In vitro vascularization improves in vivo functionality of human engineered cardiac tissues

Engineered human cardiac tissues hold great promise for disease modeling, drug development, and regenerative therapy. For regenerative applications, successful engineered tissue engraftment in vivo requires rapid vascularization and blood perfusion post-implantation. In the present study, we engineered highly functional, vascularized cardiac tissues ("cardiopatches") by co-culturing human induced pluripotent stem cell-derived cardiomyocytes (hiPSCCMs) and endothelial cells (hiPSC-ECs) in optimized serum-free media. The vascularized cardiopatches displayed stable capillary networks over 4 weeks of culture, the longest reported in the field, while maintaining high contractile stress (>15 mN/mm2) and fast conduction velocity (>20 cm/s). Robustness of the method was confirmed using two distinct hiPSC-EC sources. Upon implantation into dorsal-skinfold chambers in immunocompromised mice, in vitro vascularized cardiopatches exhibited improved angiogenesis compared to avascular implants. Significant lumenization of the engineered human vasculature and anastomosis with host mouse vessels yielded the formation of hybrid human-mouse capillaries and robust cardiopatch perfusion by blood. Moreover, compared to avascular tissues, the implanted vascularized cardiopatches exhibited significantly higher conduction velocity and Ca2+ transient amplitude, longitudinally monitored in live mice for the first time. Overall, we demonstrate successful 4-week vascularization of engineered human cardiac tissues without loss of function in vitro, which promotes tissue functionality upon implantation in vivo. STATEMENT OF SIGNIFICANCE: Complex interactions between cardiac muscle fibers and surrounding capillaries are critical for everyday function of the heart. Tissue engineering is a powerful method to recreate functional cardiac muscle and its vascular network, which are both lost during a heart attack. Our study demonstrates in vitro engineering of dense capillary networks within highly functional engineered heart tissues that successfully maintain the structure, electrical, and mechanical function long-term. In mice, human capillaries from these engineered tissues integrate with host mouse capillaries to allow blood perfusion and support improved implant function. In the future, the developed vascularized engineered heart tissues will be used for in vitro studies of cardiac development and disease and as a potential regenerative therapy for heart attack.

Engineered Cardiac Tissues as a Platform for CRISPR-Based Mitogen Discovery

Improved understanding of cardiomyocyte (CM) cell cycle regulation may allow researchers to stimulate pro-regenerative effects in injured hearts or promote maturation of human stem cell-derived CMs. Gene therapies, in particular, hold promise to induce controlled proliferation of endogenous or transplanted CMs via transient activation of mitogenic processes. Methods to identify and characterize candidate cardiac mitogens in vitro can accelerate translational efforts and contribute to the understanding of the complex regulatory landscape of CM proliferation and postnatal maturation. In this study, A CRISPR knockout-based screening strategy using in vitro neonatal rat ventricular myocyte (NRVM) monolayers is established, followed by candidate mitogen validation in mature 3-D engineered cardiac tissues (ECTs). This screen identified knockout of the purine metabolism enzyme adenosine deaminase (ADA-KO) as an effective pro-mitogenic stimulus. RNA-sequencing of ECTs further reveals increased pentose phosphate pathway (PPP) activity as the primary driver of ADA-KO-induced CM cycling. Inhibition of the pathway's rate limiting enzyme, glucose-6-phosphate dehydrogenase (G6PD), prevented ADA-KO induced CM cycling, while increasing PPP activity via G6PD overexpression increased CM cycling. Together, this study demonstrates the development and application of a genetic/tissue engineering platform for in vitro discovery and validation of new candidate mitogens affecting regenerative or maturation states of cardiomyocytes.

A Micromanipulation-Actuated Large-Scale Screening to Identify Optimized Microphysiological Model Parameters in Skeletal Muscle Regeneration

Hydrogel-based 3D cell cultures are extensively utilized to create biomimetic cellular microstructures. However, there is still lack of effective method for both evaluation of the complex interaction of cells with hydrogel and the functionality of the resulting micro-structures. This limitation impedes the further application of these microstructures as microphysiological models (microPMs) for the screening of potential culture condition combinations to enhance the skeletal muscle regeneration. This paper introduces a two-probe micromanipulation method for the large-scale assessment of viscoelasticity and contractile force (CF) of skeletal muscle microPMs, which are produced in high-throughput via microfluidic spinning and 96-well culture. The collected data demonstrate that viscoelasticity parameters (E* and tanδ) and CF both measured in a solution environment are indicative of the formation of cellular structures without hydrogel residue and the subsequent generation of myotubes, respectively. This study have developed screening criterias that integrate E*, tanδ, and CF to examine the effects of multifactorial interactions on muscle fiber repair under hypoxic conditions and within bioprinted bipennate muscle structures. This approach has improved the quality of hypoxic threshold evaluation and aligned cell growth in 3D. The proposed method is useful in exploring the role of different factors in muscle tissue regeneration with limited resources.

Interferon-β-Induced Injury During Pediatric Muscle Differentiation: Insight Into Juvenile Dermatomyositis Pathogenesis

OBJECTIVE

Juvenile dermatomyositis (JDM) involves up-regulated type I interferons (IFNs), including IFNβ, yet pathologic mechanisms remain poorly understood. We aimed to characterize the functional and structural effects of IFNβ on in vitro human pediatric myoblast growth and differentiation in a three-dimensional skeletal muscle model (myobundles).

METHODS

Myobundles fabricated from myoblasts of a healthy pediatric donor were exposed to IFNβ at 0 to 5,600 IU/mL during growth (days 1-4), differentiation (days 4-11), and/or mature (days 11-18) periods. To assess myobundle structure and function, contractile force, kinetics, and fatigue were measured at day 18 with subsequent immunohistochemistry.

RESULTS

Myobundles were not functionally affected by IFNβ exposure during growth period alone. However, when IFNβ exposure continued through differentiation, myobundles became dysfunctional (P < 0.0001). IFNβ during differentiation or mature periods alone resulted in dose-dependent decreases in contractility, with greater decrease in the differentiation alone group (P < 0.0001). Twitch kinetics and fatigue remained largely unchanged when myobundles were exposed to IFNβ only during growth, yet twitch time slowed (P < 0.005) and fatigue decreased (P < 0.002) when myobundles were exposed during differentiation or mature stages alone. Nuclei density and myofiber size and organization also decreased when IFNβ was added during differentiation period alone.

CONCLUSION

IFNβ decreases pediatric myobundle contractile function most significantly during differentiation of myoblasts to myotubes. Function is not affected when IFNβ exposure is limited to myoblast proliferation alone. These findings implicate a pathologic role for IFNβ in JDM by impairing myoblast differentiation, leading to subsequent loss of function and ongoing need for muscle regeneration and repair.

Rodent model intervention for prevention and optimal management of sarcopenia: A systematic review on the beneficial effects of nutrients & non-nutrients and exercise to improve skeletal muscle health

Sarcopenia is a common musculoskeletal disorder characterized by degenerative processes and is strongly linked to an increased susceptibility to falls, fractures, physical limitations, and mortality. Several models have been used to explore therapeutic and preventative measures as well as to gain insight into the molecular mechanisms behind sarcopenia. With novel experimental methodologies emerging to design foods or novel versions of conventional foods, understanding the impact of nutrition on the prevention and management of sarcopenia has become important. This review provides a thorough assessment of the use of rodent models of sarcopenia for understanding the aging process, focusing the effects of nutrients, plant extracts, exercise, and combined interventions on skeletal muscle health. According to empirical research, nutraceuticals and functional foods have demonstrated potential benefits in enhancing physical performance. In preclinical investigations, the administration of herbal extracts and naturally occurring bioactive compounds yielded advantageous outcomes such as augmented muscle mass and strength generation. Furthermore, herbal treatments exhibited inhibitory effects on muscle atrophy and sarcopenia. A substantial body of information establishes a connection between diet and the muscle mass, strength, and functionality of older individuals. This suggests that nutrition has a major impact in both the prevention and treatment of sarcopenia.

Engineered myovascular tissues for studies of endothelial/satellite cell interactions

In native skeletal muscle, capillaries reside in close proximity to muscle stem cells (satellite cells, SCs) and regulate SC numbers and quiescence through partially understood mechanisms that are difficult to study in vivo. This challenge could be addressed by the development of a 3-dimensional (3D) in vitro model of vascularized skeletal muscle harboring both a pool of quiescent SCs and a robust network of capillaries. Still, studying interactions between SCs and endothelial cells (ECs) within a tissue-engineered muscle environment has been hampered by the incompatibility of commercially available EC media with skeletal muscle differentiation. In this study, we first optimized co-culture media and cellular ratios to generate highly functional vascularized human skeletal muscle tissues ("myovascular bundles") with contractile properties (∼10 mN/mm2) equaling those of avascular, muscle-only tissues ("myobundles"). Within one week of muscle differentiation, ECs in these tissues formed a dense network of capillaries that co-aligned with muscle fibers and underwent initial lumenization. Incorporating vasculature within myobundles increased the total SC number by 82%, with SC density and quiescent signature being increased proximal (≤20μm) to EC networks. In vivo, at two weeks post-implantation into dorsal window chambers in nude mice, vascularized myobundles exhibited improved calcium handling compared to avascular implants. In summary, we engineered highly functional myovascular tissues that enable studies of the roles of EC-SC crosstalk in human muscle development, physiology, and disease. STATEMENT OF SIGNIFICANCE: In native skeletal muscle, intricate relationships between vascular cells and muscle stem cells ("satellite cells") play critical roles in muscle growth and regeneration. Current methods for in vitro engineering of contractile skeletal muscle do not recreate capillary networks present in vivo. Our study for the first time generates in vitro robustly vascularized, highly functional engineered human skeletal muscle tissues. Within these tissues, satellite cells are more abundant and, similar to in vivo, they are more dense and less proliferative proximal to endothelial cells. Upon implantation in mice, vascularized engineered muscles show improved calcium handling compared to muscle-only implants. We expect that this versatile in vitro system will enable studies of muscle-vasculature crosstalk in human development and disease.

Biogenic derived nanoparticles modulate mitochondrial function in cardiomyocytes

Preservation of mitochondrial functionality is essential for heart hemostasis and cardiovascular diseases treatment. However, the current nanomedicines including liposomes, polymers and inorganic nanomaterials are severely hindered by poor stability, high manufacturing costs and potential biotoxicity. In this research, we present novel polyphenolic nanoparticles (NPs) derived from naturally occurring pomegranate peel (PP, labelled as PPP NPs), which exhibit potent antioxidative and anti-inflammatory properties, serving as a modulator of mitochondrial function. PPP NPs have been identified to improve survival rates in models of mitochondrial depletion through enhancement of cardiomyocyte proliferation and the reduction of DNA damage. Moreover, PPP NPs can effectively inhibit the production of reactive oxygen species and inflammatory mediators in lipopolysaccharide (LPS)-induced mitochondrial damage. Utilizing human engineered heart tissue and mice models, PPP NPs were found to significantly improve contractile function and alleviate inflammation activities after LPS treatment. Mechanically, PPP NPs regulated inflammatory responses via a m6A dependent manner, as determined using RNA-seq and MeRIP-seq analyses. Collectively, these insights underscore the potential of PPP NPs as a novel therapeutic approach for mitochondrial dysfunction.

Endothelial-mesenchymal transition in skeletal muscle: Opportunities and challenges from 3D microphysiological systems

Fibrosis is a pathological condition that in the muscular context is linked to primary diseases such as dystrophies, laminopathies, neuromuscular disorders, and volumetric muscle loss following traumas, accidents, and surgeries. Although some basic mechanisms regarding the role of myofibroblasts in the progression of muscle fibrosis have been discovered, our knowledge of the complex cell-cell, and cell-matrix interactions occurring in the fibrotic microenvironment is still rudimentary. Recently, vascular dysfunction has been emerging as a key hallmark of fibrosis through a process called endothelial-mesenchymal transition (EndoMT). Nevertheless, no effective therapeutic options are currently available for the treatment of muscle fibrosis. This lack is partially due to the absence of advanced in vitro models that can recapitulate the 3D architecture and functionality of a vascularized muscle microenvironment in a human context. These models could be employed for the identification of novel targets and for the screening of potential drugs blocking the progression of the disease. In this review, we explore the potential of 3D human muscle models in studying the role of endothelial cells and EndoMT in muscle fibrotic tissues and identify limitations and opportunities for optimizing the next generation of these microphysiological systems. Starting from the biology of muscle fibrosis and EndoMT, we highlight the synergistic links between different cell populations of the fibrotic microenvironment and how to recapitulate them through microphysiological systems.

Genetic changes from type I interferons and JAK inhibitors: clues to drivers of juvenile dermatomyositis

OBJECTIVE

To better understand the pathogenesis of juvenile dermatomyositis (JDM), we examined the effect of the cytokines type I interferons (IFN I) and JAK inhibitor drugs (JAKi) on gene expression in bioengineered pediatric skeletal muscle.

METHODS

Myoblasts from three healthy pediatric donors were used to create three-dimensional skeletal muscle units termed myobundles. Myobundles were treated with IFN I, either IFNα or IFNβ. A subset of IFNβ-exposed myobundles was treated with JAKi tofacitinib or baricitinib. RNA sequencing analysis was performed on all myobundles.

RESULTS

Seventy-six myobundles were analysed. Principal component analysis showed donor-specific clusters of gene expression across IFNα and IFNβ-exposed myobundles in a dose-dependent manner. Both cytokines upregulated interferon response and proinflammatory genes; however, IFNβ led to more significant upregulation. Key downregulated pathways involved oxidative phosphorylation, fatty acid metabolism and myogenesis genes. Addition of tofacitinib or baricitinib moderated the gene expression induced by IFNβ, with partial reversal of upregulated inflammatory and downregulated myogenesis pathways. Baricitinib altered genetic profiles more than tofacitinib.

CONCLUSION

IFNβ leads to more pro-inflammatory gene upregulation than IFNα, correlating to greater decrease in contractile protein gene expression and reduced contractile force. JAK inhibitors, baricitinib more so than tofacitinib, partially reverse IFN I-induced genetic changes. Increased IFN I exposure in healthy bioengineered skeletal muscle leads to IFN-inducible gene expression, inflammatory pathway enrichment, and myogenesis gene downregulation, consistent with what is observed in JDM.

Dynamic and Static Workout of In Vitro Skeletal Muscle Tissue through a Weight Training Device

Enhancing muscle strength through workouts is a key factor in improving physical activity and maintaining metabolic profiles. The controversial results concerning the impacts of weight training often arise from clinical experiments that require controlled experimental conditions. In this study, a weight training system for a muscle development model is presented, which is capable of performing weight training motions with adjustable weight loads. Through the implementation of cultured skeletal muscle tissue with floating structures and a flexible ribbon, both isotonic (dynamic change in muscle length) and isometric (static in muscle length) exercises can be performed without the deflection of the tissue. Quantitative analysis of contraction force, changes in metabolic processes, and muscle morphology under different weight training conditions demonstrates the effectiveness of the proposed system. Our proposed system holds potential for establishing effective muscle development and for further applications in rehabilitation training methods.

Development of a skeletal muscle sheet with direct reprogramming-induced myoblasts on a nanogel-cross-linked porous freeze-dried gel scaffold in a mouse gastroschisis model

PURPOSE

In this study, we attempted to create skeletal muscle sheets made of directly converted myoblasts (dMBs) with a nanogel scaffold on a biosheet using a mouse gastroschisis model.

METHODS

dMBs were prepared by the co-transfection of MYOD1 and MYCL into human fibroblasts. Silicon tubes were implanted under the skin of NOG/SCID mice, and biosheets were formed. The nanogel was a nanoscale hydrogel based on cholesterol-modified pullulan, and a NanoClip-FD gel was prepared by freeze-drying the nanogel. 7 mm in length was created in the abdominal wall of NOG/SCID mice as a mouse gastroschisis model. Matrigel or NanoCliP-FD gel seeded with dMBs was placed on the biosheet and implanted on the model mice.

RESULTS

Fourteen days after surgery, dMBs with Matrigel showed a small amount of coarse aggregations of muscle-like cells. In contrast, dMBs with NanoCliP-FD gel showed multinucleated muscle-like cells, which were expressed as desmin and myogenin by fluorescent immunostaining.

CONCLUSION

Nanogels have a porous structure and are useful as scaffolds for tissue regeneration by supplying oxygen and nutrients supply to the cells. Combining dMBs and nanogels on the biosheets resulted in the differentiation and engraftment of skeletal muscle, suggesting the possibility of developing skeletal muscle sheets derived from autologous cells and tissues.

Lamin A/C deficiency-mediated ROS elevation contributes to pathogenic phenotypes of dilated cardiomyopathy in iPSC model

Mutations in the nuclear envelope (NE) protein lamin A/C (encoded by LMNA), cause a severe form of dilated cardiomyopathy (DCM) with early-onset life-threatening arrhythmias. However, molecular mechanisms underlying increased arrhythmogenesis in LMNA-related DCM (LMNA-DCM) remain largely unknown. Here we show that a frameshift mutation in LMNA causes abnormal Ca2+ handling, arrhythmias and disformed NE in LMNA-DCM patient-specific iPSC-derived cardiomyocytes (iPSC-CMs). Mechanistically, lamin A interacts with sirtuin 1 (SIRT1) where mutant lamin A/C accelerates degradation of SIRT1, leading to mitochondrial dysfunction and oxidative stress. Elevated reactive oxygen species (ROS) then activates the Ca2+/calmodulin-dependent protein kinase II (CaMKII)-ryanodine receptor 2 (RYR2) pathway and aggravates the accumulation of SUN1 in mutant iPSC-CMs, contributing to arrhythmias and NE deformation, respectively. Taken together, the lamin A/C deficiency-mediated ROS disorder is revealed as central to LMNA-DCM development. Manipulation of impaired SIRT1 activity and excessive oxidative stress is a potential future therapeutic strategy for LMNA-DCM.

Bioengineered Model of Human LGMD2B Skeletal Muscle Reveals Roles of Intracellular Calcium Overload in Contractile and Metabolic Dysfunction in Dysferlinopathy

Dysferlin is a multi-functional protein that regulates membrane resealing, calcium homeostasis, and lipid metabolism in skeletal muscle. Genetic loss of dysferlin results in limb girdle muscular dystrophy 2B/2R (LGMD2B/2R) and other dysferlinopathies - rare untreatable muscle diseases that lead to permanent loss of ambulation in humans. The mild disease severity in dysferlin-deficient mice and diverse genotype-phenotype relationships in LGMD2B patients have prompted the development of new in vitro models for personalized studies of dysferlinopathy. Here the first 3-D tissue-engineered hiPSC-derived skeletal muscle ("myobundle") model of LGMD2B is described that exhibits compromised contractile function, calcium-handling, and membrane repair, and transcriptomic changes indicative of impaired oxidative metabolism and mitochondrial dysfunction. In response to the fatty acid (FA) challenge, LGMD2B myobundles display mitochondrial deficits and intracellular lipid droplet (LD) accumulation. Treatment with the ryanodine receptor (RyR) inhibitor dantrolene or the dissociative glucocorticoid vamorolone restores LGMD2B contractility, improves membrane repair, and reduces LD accumulation. Lastly, it is demonstrated that chemically induced chronic RyR leak in healthy myobundles phenocopies LGMD2B contractile and metabolic deficit, but not the loss of membrane repair capacity. Together, these results implicate intramyocellular Ca2+ leak as a critical driver of dysferlinopathic phenotype and validate the myobundle system as a platform to study LGMD2B pathogenesis.

Impact of Passaging Primary Skeletal Muscle Cell Isolates on the Engineering of Skeletal Muscle

Volumetric muscle loss (VML) is a clinical state that results in impaired skeletal muscle function. Engineered skeletal muscle can serve as a treatment for VML. Currently, large biopsies are required to achieve the cells necessary for the fabrication of engineered muscle, leading to donor-site morbidity. Amplification of cell numbers using cell passaging may increase the usefulness of a single muscle biopsy for engineering muscle tissue. In this study, we evaluated the impact of passaging cells obtained from donor muscle tissue by analyzing characteristics of in vitro cellular growth and tissue-engineered skeletal muscle unit (SMU) structure and function. Human skeletal muscle cell isolates from three separate donors (P0-Control) were compared with cells passaged once (P1), twice (P2), or three times (P3) by monitoring SMU force production and determining muscle content and structure using immunohistochemistry. Data indicated that passaging decreased the number of satellite cells and increased the population doubling time. P1 SMUs had slightly greater contractile force and P2 SMUs showed statistically significant greater force production compared with P0 SMUs with no change in SMU muscle content. In conclusion, human skeletal muscle cells can be passaged twice without negatively impacting SMU muscle content or contractile function, providing the opportunity to potentially create larger SMUs from smaller biopsies, thereby producing clinically relevant sized grafts to aid in VML repair.

Developing engineered muscle tissues utilizing standard cell culture plates and mesenchymal stem cell-conditioned medium

The construction of engineered muscle tissues that resemble the function and microstructure of human muscles holds significant promise for various applications, including disease modeling, regenerative medicine, and biological machines. However, current muscle tissue engineering approaches often rely on complex equipment which may limit their accessibility and practicality. Herein, we present a convenient approach using a standard 24-well cell culture plate to construct a platform to facilitate engineered muscle tissues formation and culture. Using this platform, engineered muscle tissue with differentiation characteristics can be manufactured in large quantities. Additionally, the mesenchymal stem cell conditioned medium was utilized to promote the formation and functionality of the engineered muscle tissues. The resulting tissues comprised a higher cell density and a better differentiation effect in the tissues. Taken together, this study provides a simple, convenient, and effective platform for studying muscle tissue engineering.

Pillar electrodes embedded in the skeletal muscle tissue for selective stimulation of biohybrid actuators with increased contractile distance

Electrodes are crucial for controlling the movements of biohybrid robots, but their external placement outside muscle tissue often leads to inefficient and non-selective stimulation of nearby biohybrid actuators. To address this, we propose embedding pillar electrodes within the skeletal muscle tissue, resulting in enhanced contraction of the target muscle without affecting the neighbor tissue with a 4 mm distance. We use finite element method simulations to establish a selectivity model, correlating the VIE(volume integration of electric field intensity within muscle tissue) with actual contractile distances under different amplitudes of electrical pulses. The simulated selective index closely aligns with experimental results, showing the potential of pillar electrodes for effective and selective biohybrid actuator stimulation. In experiments, we validated that the contractile distance and selectivity achieved with these pillar electrodes exceed conventional Au rod electrodes. This innovation has promising implications for building biohybrid robots with densely arranged muscle tissue, ultimately achieving more human-like movements. Additionally, our selectivity model offers valuable predictive tools for assessing electrical stimulation effects with different electrode designs.

Organoid-guided precision hepatology for metabolic liver disease

Metabolic dysfunction-associated steatotic liver disease affects millions of people worldwide. Progress towards a definitive cure has been incremental and treatment is currently limited to lifestyle modification. Hepatocyte-specific lipid accumulation is the main trigger of lipotoxic events, driving inflammation and fibrosis. The underlying pathology is extraordinarily heterogenous, and the manifestations of steatohepatitis are markedly influenced by metabolic communications across non-hepatic organs. Synthetic human tissue models have emerged as powerful platforms to better capture the mechanistic diversity in disease progression, while preserving person-specific genetic traits. In this review, we will outline current research efforts focused on integrating multiple synthetic tissue models of key metabolic organs, with an emphasis on organoid-based systems. By combining functional genomics and population-scale en masse profiling methodologies, human tissues derived from patients can provide insights into personalised genetic, transcriptional, biochemical, and metabolic states. These collective efforts will advance our understanding of steatohepatitis and guide the development of rational solutions for mechanism-directed diagnostic and therapeutic investigation.

Complex or not too complex? One size does not fit all in next generation microphysiological systems

In the attempt to overcome the increasingly recognized shortcomings of existing in vitro and in vivo models, researchers have started to implement alternative models, including microphysiological systems. First examples were represented by 2.5D systems, such as microfluidic channels covered by cell monolayers as blood vessel replicates. In recent years, increasingly complex microphysiological systems have been developed, up to multi-organ on chip systems, connecting different 3D tissues in the same device. However, such an increase in model complexity raises several questions about their exploitation and implementation into industrial and clinical applications, ranging from how to improve their reproducibility, robustness, and reliability to how to meaningfully and efficiently analyze the huge amount of heterogeneous datasets emerging from these devices. Considering the multitude of envisaged applications for microphysiological systems, it appears now necessary to tailor their complexity on the intended purpose, being academic or industrial, and possibly combine results deriving from differently complex stages to increase their predictive power.

Simulated microgravity attenuates myogenesis and contractile function of 3D engineered skeletal muscle tissues

While the effects of microgravity on inducing skeletal muscle atrophy have been extensively studied, the impacts of microgravity on myogenesis and its mechanisms remain unclear. In this study, we developed a microphysiological system of engineered muscle tissue (EMT) fabricated using a collagen / Matrigel composite hydrogel and murine skeletal myoblasts. This 3D EMT model allows non-invasive quantitative assessment of contractile function. After applying a 7-day differentiation protocol to induce myotube formation, the EMTs clearly exhibited sarcomerogenesis, myofilament formation, and synchronous twitch and tetanic contractions with electrical stimuli. Using this 3D EMT system, we investigated the effects of simulated microgravity at 10-3 G on myogenesis and contractile function utilizing a random positioning machine. EMTs cultured for 5 days in simulated microgravity exhibited significantly reduced contractile forces, myofiber size, and differential expression of muscle contractile, myogenesis regulatory, and mitochondrial biogenesis-related proteins. These results indicate simulated microgravity attenuates myogenesis, resulting in impaired muscle function.

Time-dependent effects of BRAF-V600E on cell cycling, metabolism, and function in engineered myocardium

Candidate cardiomyocyte (CM) mitogens such as those affecting the extracellular signal-regulated kinase (ERK) signaling pathway represent potential targets for functional heart regeneration. We explored whether activating ERK via a constitutively active mutant of B-raf proto-oncogene (BRAF), BRAF-V600E (caBRAF), can induce proproliferative effects in neonatal rat engineered cardiac tissues (ECTs). Sustained CM-specific caBRAF expression induced chronic ERK activation, substantial tissue growth, deficit in sarcomeres and contractile function, and tissue stiffening, all of which persisted for at least 4 weeks of culture. caBRAF-expressing CMs in ECTs exhibited broad transcriptomic changes, shift to glycolytic metabolism, loss of connexin-43, and a promigratory phenotype. Transient, doxycycline-controlled caBRAF expression revealed that the induction of CM cycling is rapid and precedes functional decline, and the effects are reversible only with short-lived ERK activation. Together, direct activation of the BRAF kinase is sufficient to modulate CM cycling and functional phenotype, offering mechanistic insights into roles of ERK signaling in the context of cardiac development and regeneration.

Profiling of plasma extracellular vesicles identifies proteins that strongly associate with patient's global assessment of disease activity in rheumatoid arthritis

Background

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic synovial inflammation and cartilage/bone damage. Intercellular messengers such as IL-1 and TNF play a crucial role in the pathophysiology of RA but have limited diagnostic and prognostic values. Therefore, we assessed whether the protein content of the recently discovered extracellular vesicles (EVs), which have gained attention in the pathogenesis of RA, correlates with disease activity parameters in RA patients.

Methods

We identified and quantified proteins in plasma-derived EVs (pEVs), isolated by size exclusion chromatography from 17 RA patients by mass spectrophotometry (MS). Quantified protein levels were correlated with laboratory and clinical parameters and the patient's own global assessment of their disease activity (PGA-VAS). In a second MS run, the pEV proteins of nine other RA patients were quantified and compared to those from nine healthy controls (HC).

Results

No differences were observed in the concentration, size, and protein content of pEVs from RA patients. Proteomics revealed >95% overlapping proteins in RA-pEVs, compared to HC-pEVs (data are available via ProteomeXchange with identifier PXD046058). Remarkably, in both runs, the level of far more RA-pEV proteins correlated positively to PGA-VAS than to either clinical or laboratory parameters. Interestingly, all observed PGA-VAS positively correlated RA-pEV proteins were associated with the actin-cytoskeleton linker proteins, ezrin, and moesin.

Conclusion

Our observation suggests that PGA-VAS (loss of vitality) may have a different underlying pathological mechanism in RA, possibly related to enhanced muscle actin-cytoskeleton activity. Furthermore, our study contributes to the growing awareness and evidence that pEVs contain valuable biomarkers for diseases, with added value for RA patients.

Generation of Mature Toxoplasma gondii Bradyzoites in Human Immortalized Myogenic KD3 Cells

Toxoplasma gondii is a zoonotic protozoan parasite and one of the most successful foodborne pathogens. Upon infection and dissemination, the parasites convert into the persisting, chronic form called bradyzoites, which reside within cysts in muscle and brain tissue. Despite their importance, bradyzoites remain difficult to investigate directly, owing to limited in vitro models. In addition, the need for new drugs targeting the chronic stage, which is underlined by the lack of eradicating treatment options, remains difficult to address since in vitro access to drug-tolerant bradyzoites remains limited. We recently published the use of a human myotube-based bradyzoite cell culture system and demonstrated its applicability to investigate the biology of T. gondii bradyzoites. Encysted parasites can be functionally matured during long-term cultivation in these immortalized cells and possess many in vivo-like features, including pepsin resistance, oral infectivity, and antifolate resistance. In addition, the system is scalable, enabling experimental approaches that rely on large numbers, such as metabolomics. In short, we detail the cultivation of terminally differentiated human myotubes and their subsequent infection with tachyzoites, which then mature to encysted bradyzoites within four weeks at ambient CO2 levels. We also discuss critical aspects of the procedure and suggest improvements. Key features • This protocol describes a scalable human myotube-based in vitro system capable of generating encysted bradyzoites featuring in vivo hallmarks. • Bradyzoite differentiation is facilitated through CO2 depletion but without additional artificial stress factors like alkaline pH. • Functional maturation occurs over four weeks.

Effect of type I interferon on engineered pediatric skeletal muscle: a promising model for juvenile dermatomyositis

OBJECTIVE

To investigate pathogenic mechanisms underlying JDM, we defined the effect of type I IFN, IFN-α and IFN-β, on pediatric skeletal muscle function and expression of myositis-related proteins using an in vitro engineered human skeletal muscle model (myobundle).

METHODS

Primary myoblasts were isolated from three healthy pediatric donors and used to create myobundles that mimic functioning skeletal muscle in structural architecture and physiologic function. Myobundles were exposed to 0, 5, 10 or 20 ng/ml IFN-α or IFN-β for 7 days and then functionally tested under electrical stimulation and analyzed immunohistochemically for structural and myositis-related proteins. Additionally, IFN-β-exposed myobundles were treated with Janus kinase inhibitors (JAKis) tofacitinib and baricitinib. These myobundles were also analyzed for contractile force and immunohistochemistry.

RESULTS

IFN-β, but not IFN-α, was associated with decreased contractile tetanus force and slowed twitch kinetics. These effects were reversed by tofacitinib and baricitinib. Type I IFN paradoxically reduced myobundle fatigue, which did not reverse after JAKi. Additionally, type I IFN correlated with MHC I upregulation, which normalized after JAKi treatment, but expression of myositis-specific autoantigens Mi-2, melanocyte differentiation-associated protein 5 and the endoplasmic reticulum stress marker GRP78 were variable and donor specific after type I IFN exposure.

CONCLUSION

IFN-α and IFN-β have distinct effects on pediatric skeletal muscle and these effects can partially be reversed by JAKi treatment. This is the first study illustrating effective use of a three-dimensional human skeletal muscle model to investigate JDM pathogenesis and test novel therapeutics.

Genome-wide epigenetic dynamics during postnatal skeletal muscle growth in Hu sheep

Hypertrophy and fiber transformation are two prominent features of postnatal skeletal muscle development. However, the role of epigenetic modifications is less understood. ATAC-seq, whole genome bisulfite sequencing, and RNA-seq were applied to investigate the epigenetic dynamics of muscle in Hu sheep at 3 days, 3 months, 6 months, and 12 months after birth. All 6865 differentially expressed genes were assigned into three distinct tendencies, highlighting the balanced protein synthesis, accumulated immune activities, and restrained cell division in postnatal development. We identified 3742 differentially accessible regions and 11799 differentially methylated regions that were associated with muscle-development-related pathways in certain stages, like D3-M6. Transcription factor network analysis, based on genomic loci with high chromatin accessibility and low methylation, showed that ARID5B, MYOG, and ENO1 were associated with muscle hypertrophy, while NR1D1, FADS1, ZFP36L2, and SLC25A1 were associated with muscle fiber transformation. Taken together, these results suggest that DNA methylation and chromatin accessibility contributed toward regulating the growth and fiber transformation of postnatal skeletal muscle in Hu sheep.

Highly contractile 3D tissue engineered skeletal muscles from human iPSCs reveal similarities with primary myoblast-derived tissues

Skeletal muscle research is transitioning toward 3D tissue engineered in vitro models reproducing muscle's native architecture and supporting measurement of functionality. Human induced pluripotent stem cells (hiPSCs) offer high yields of cells for differentiation. It has been difficult to differentiate high-quality, pure 3D muscle tissues from hiPSCs that show contractile properties comparable to primary myoblast-derived tissues. Here, we present a transgene-free method for the generation of purified, expandable myogenic progenitors (MPs) from hiPSCs grown under feeder-free conditions. We defined a protocol with optimal hydrogel and medium conditions that allowed production of highly contractile 3D tissue engineered skeletal muscles with forces similar to primary myoblast-derived tissues. Gene expression and proteomic analysis between hiPSC-derived and primary myoblast-derived 3D tissues revealed a similar expression profile of proteins involved in myogenic differentiation and sarcomere function. The protocol should be generally applicable for the study of personalized human skeletal muscle tissue in health and disease.

Mimicking sarcolemmal damagein vitro: a contractile 3D model of skeletal muscle for drug testing in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is the most prevalent neuromuscular disease diagnosed in childhood. It is a progressive and wasting disease, characterized by a degeneration of skeletal and cardiac muscles caused by the lack of dystrophin protein. The absence of this crucial structural protein leads to sarcolemmal fragility, resulting in muscle fiber damage during contraction. Despite ongoing efforts, there is no cure available for DMD patients. One of the primary challenges is the limited efficacy of current preclinical tools, which fail in modeling the biological complexity of the disease. Human-based three-dimensional (3D) cell culture methods appear as a novel approach to accelerate preclinical research by enhancing the reproduction of pathophysiological processes in skeletal muscle. In this work, we developed a patient-derived functional 3D skeletal muscle model of DMD that reproduces the sarcolemmal damage found in the native DMD muscle. These bioengineered skeletal muscle tissues exhibit contractile functionality, as they responded to electrical pulse stimulation. Sustained contractile regimes induced the loss of myotube integrity, mirroring the pathological myotube breakdown inherent in DMD due to sarcolemmal instability. Moreover, damaged DMD tissues showed disease functional phenotypes, such as tetanic fatigue. We also evaluated the therapeutic effect of utrophin upregulator drug candidates on the functionality of the skeletal muscle tissues, thus providing deeper insight into the real impact of these treatments. Overall, our findings underscore the potential of bioengineered 3D skeletal muscle technology to advance DMD research and facilitate the development of novel therapies for DMD and related neuromuscular disorders.

Optimization of Culture Media and Cell Ratios for 3D In Vitro Skeletal Muscle Tissues with Endothelial Cells

A major challenge of engineering larger macroscale tissues in vitro is the limited diffusion of nutrients and oxygen to the interior. For skeletal muscle, this limitation results in millimeter scale outcomes to avoid necrosis. One method to address this constraint may be to vascularize in vitro-grown muscle tissue, to support nutrient (culture media) flow into the interior of the structure. In this exploratory study, we examine culture conditions that enable myogenic development and endothelial cell survival within tissue engineered 3D muscles. Myoblasts (C2C12s), endothelial cells (HUVECs), and endothelial support cells (C3H 10T1/2s) were seeded into Matrigel-fibrin hydrogels and cast into 3D printed frames to form 3D in vitro skeletal muscle tissues. Our preliminary results suggest that the simultaneous optimization of culture media formulation and cell concentrations is necessary for 3D cultured muscles to exhibit robust myosin heavy chain expression and GFP expression from GFP-transfected endothelial cells. The ability to form differentiated 3D muscles containing endothelial cells is a key step toward achieving vascularized 3D muscle tissues, which have potential use as tissue for implantation in a medical setting, as well as for future foods such as cultivated meats.

Muscle Specific Promotors for Gene Therapy - A Comparative Study in Proliferating and Differentiated Cells

BACKGROUND

Depending on the therapy approach and disease background, the heterogeneity of muscular tissues complicates the development of targeted gene therapy, where either expression in all muscle types or restriction to only one muscle type is warranted. Muscle specificity can be achieved using promotors mediating tissue specific and sustained physiological expression in the desired muscle types but limited activity in non-targeted tissue. Several muscle specific promotors have been described, but direct comparisons between them are lacking.

OBJECTIVE

Here we present a direct comparison of muscle specific Desmin-, MHCK7, microRNA206- and Calpain3 promotor.

METHODS

To directly compare these muscle specific promotors we utilized transfection of reporter plasmids using an in vitro model based on electrical pulse stimulation (EPS) to provoke sarcomere formation in 2D cell culture for quantification of promotor activities in far differentiated mouse and human myotubes.

RESULTS

We found that Desmin- and MHCK7 promotors showed stronger reporter gene expression levels in proliferating and differentiated myogenic cell lines than miR206 and CAPN3 promotor. However, Desmin and MHCK7 promotor promoted gene expression also cardiac cells whereas miR206 and CAPN3 promotor expression was restricted to skeletal muscle.

CONCLUSIONS

Our results provides direct comparison of muscle specific promotors with regard to expression strengths and specificity as this is important feature to avoid undesired transgene expression in non-target muscle cells for a desired therapy approach.

3D human induced pluripotent stem cell-derived bioengineered skeletal muscles for tissue, disease and therapy modeling

Skeletal muscle is a complex tissue composed of multinucleated myofibers responsible for force generation that are supported by multiple cell types. Many severe and lethal disorders affect skeletal muscle; therefore, engineering models to reproduce such cellular complexity and function are instrumental for investigating muscle pathophysiology and developing therapies. Here, we detail the modular 3D bioengineering of multilineage skeletal muscles from human induced pluripotent stem cells, which are first differentiated into myogenic, neural and vascular progenitor cells and then combined within 3D hydrogels under tension to generate an aligned myofiber scaffold containing vascular networks and motor neurons. 3D bioengineered muscles recapitulate morphological and functional features of human skeletal muscle, including establishment of a pool of cells expressing muscle stem cell markers. Importantly, bioengineered muscles provide a high-fidelity platform to study muscle pathology, such as emergence of dysmorphic nuclei in muscular dystrophies caused by mutant lamins. The protocol is easy to follow for operators with cell culture experience and takes between 9 and 30 d, depending on the number of cell lineages in the construct. We also provide examples of applications of this advanced platform for testing gene and cell therapies in vitro, as well as for in vivo studies, providing proof of principle of its potential as a tool to develop next-generation neuromuscular or musculoskeletal therapies.

Bioengineered 3D Skeletal Muscle Model Reveals Complement 4b as a Cell-Autonomous Mechanism of Impaired Regeneration with Aging

A mechanistic understanding of cell-autonomous skeletal muscle changes after injury can lead to novel interventions to improve functional recovery in an aged population. However, major knowledge gaps persist owing to limitations of traditional biological aging models. 2D cell culture represents an artificial environment, while aging mammalian models are contaminated by influences from non-muscle cells and other organs. Here, a 3D muscle aging system is created to overcome the limitations of these traditional platforms. It is shown that old muscle constructs (OMC) manifest a sarcopenic phenotype, as evidenced by hypotrophic myotubes, reduced contractile function, and decreased regenerative capacity compared to young muscle constructs. OMC also phenocopy the regenerative responses of aged muscle to two interventions, pharmacological and biological. Interrogation of muscle cell-specific mechanisms that contribute to impaired regeneration over time further reveals that an aging-induced increase of complement component 4b (C4b) delays muscle progenitor cell amplification and impairs functional recovery. However, administration of complement factor I, a C4b inactivator, improves muscle regeneration in vitro and in vivo, indicating that C4b inhibition may be a novel approach to enhance aged muscle repair. Collectively, the model herein exhibits capabilities to study cell-autonomous changes in skeletal muscle during aging, regeneration, and intervention.

A 3D cell culture system for bioengineering human neuromuscular junctions to model ALS

The signals that coordinate and control movement in vertebrates are transmitted from motoneurons (MNs) to their target muscle cells at neuromuscular junctions (NMJs). Human NMJs display unique structural and physiological features, which make them vulnerable to pathological processes. NMJs are an early target in the pathology of motoneuron diseases (MND). Synaptic dysfunction and synapse elimination precede MN loss suggesting that the NMJ is the starting point of the pathophysiological cascade leading to MN death. Therefore, the study of human MNs in health and disease requires cell culture systems that enable the connection to their target muscle cells for NMJ formation. Here, we present a human neuromuscular co-culture system consisting of induced pluripotent stem cell (iPSC)-derived MNs and 3D skeletal muscle tissue derived from myoblasts. We used self-microfabricated silicone dishes combined with Velcro hooks to support the formation of 3D muscle tissue in a defined extracellular matrix, which enhances NMJ function and maturity. Using a combination of immunohistochemistry, calcium imaging, and pharmacological stimulations, we characterized and confirmed the function of the 3D muscle tissue and the 3D neuromuscular co-cultures. Finally, we applied this system as an in vitro model to study the pathophysiology of Amyotrophic Lateral Sclerosis (ALS) and found a decrease in neuromuscular coupling and muscle contraction in co-cultures with MNs harboring ALS-linked SOD1 mutation. In summary, the human 3D neuromuscular cell culture system presented here recapitulates aspects of human physiology in a controlled in vitro setting and is suitable for modeling of MND.

Engineered Human Muscle Tissue from Multilayered Aligned Myofiber Sheets for Studies of Muscle Physiology and Predicting Drug Response

In preclinical drug testing, human muscle tissue models are critical to understanding the complex physiology, including drug effects in the human body. This study reports that a multilayering approach to cell sheet-based engineering produces an engineered human muscle tissue with sufficient contractile force suitable for measurement. A thermoresponsive micropatterned substrate regulates the biomimetic alignment of myofiber structures enabling the harvest of the aligned myofibers as a single cell sheet. The functional muscle tissue is produced by layering multiple myofiber sheets on a fibrin-based gel. This gel environment promotes myofiber maturation, provides the tissue an elastic platform for contraction, and allows the attachment of a measurement device. Since this multilayering approach is effective in enhancing the contractile ability of the muscle tissue, this muscle tissue generates a significantly high contractile force that can be measured quantitatively. The multilayered muscle tissue shows unidirectional contraction from electrical and chemical stimulation. In addition, their physiological responses to representative drugs can be determined quantitatively in real time by changes in contractile force and fatigue resistance. These physiological properties indicate that the engineered muscle tissue can become a promising tissue model for preclinical in vitro studies in muscle physiology and drug discovery.

Bioengineering a miniaturized in vitro 3D myotube contraction monitoring chip to model muscular dystrophies

Quantification of skeletal muscle functional contraction is essential to assess the outcomes of therapeutic procedures for neuromuscular disorders. Muscle three-dimensional "Organ-on-chip" models usually require a substantial amount of biological material, which rarely can be obtained from patient biopsies. Here, we developed a miniaturized 3D myotube culture chip with contraction monitoring capacity at the single cell level. Optimized micropatterned substrate design enabled to obtain high culture yields in tightly controlled microenvironments, with myotubes derived from primary human myoblasts displaying spontaneous contractions. Analysis of nuclear morphology confirmed similar myonuclei structure between obtained myotubes and in vivo myofibers, as compared to 2D monolayers. LMNA-related Congenital Muscular Dystrophy (L-CMD) was modeled with successful development of diseased 3D myotubes displaying reduced contraction. The miniaturized myotube technology can thus be used to study contraction characteristics and evaluate how diseases affect muscle organization and force generation. Importantly, it requires significantly fewer starting materials than current systems, which should substantially improve drug screening capability.

Impaired muscle stem cell function and abnormal myogenesis in acquired myopathies

Skeletal muscle possesses a high plasticity and a remarkable regenerative capacity that relies mainly on muscle stem cells (MuSCs). Molecular and cellular components of the MuSC niche, such as immune cells, play key roles to coordinate MuSC function and to orchestrate muscle regeneration. An abnormal infiltration of immune cells and/or imbalance of pro- and anti-inflammatory cytokines could lead to MuSC dysfunctions that could have long lasting effects on muscle function. Different genetic variants were shown to cause muscular dystrophies that intrinsically compromise MuSC function and/or disturb their microenvironment leading to impaired muscle regeneration that contributes to disease progression. Alternatively, many acquired myopathies caused by comorbidities (e.g., cardiopulmonary or kidney diseases), chronic inflammation/infection, or side effects of different drugs can also perturb MuSC function and their microenvironment. The goal of this review is to comprehensively summarize the current knowledge on acquired myopathies and their impact on MuSC function. We further describe potential therapeutic strategies to restore MuSC regenerative capacity.

Bioengineered Pancreas-Liver Crosstalk in a Microfluidic Coculture Chip Identifies Human Metabolic Response Signatures in Prediabetic Hyperglycemia

Aberrant glucose homeostasis is the most common metabolic disturbance affecting one in ten adults worldwide. Prediabetic hyperglycemia due to dysfunctional interactions between different human tissues, including pancreas and liver, constitutes the largest risk factor for the development of type 2 diabetes. However, this early stage of metabolic disease has received relatively little attention. Microphysiological tissue models that emulate tissue crosstalk offer emerging opportunities to study metabolic interactions. Here, a novel modular multitissue organ-on-a-chip device is presented that allows for integrated and reciprocal communication between different 3D primary human tissue cultures. Precisely controlled heterologous perfusion of each tissue chamber is achieved through a microfluidic single "synthetic heart" pneumatic actuation unit connected to multiple tissue chambers via specific configuration of microchannel resistances. On-chip coculture experiments of organotypic primary human liver spheroids and intact primary human islets demonstrate insulin secretion and hepatic insulin response dynamics at physiological timescales upon glucose challenge. Integration of transcriptomic analyses with promoter motif activity data of 503 transcription factors reveals tissue-specific interacting molecular networks that underlie β-cell stress in prediabetic hyperglycemia. Interestingly, liver and islet cultures show surprising counter-regulation of transcriptional programs, emphasizing the power of microphysiological coculture to elucidate the systems biology of metabolic crosstalk.

Tissue Engineering Applied to Skeletal Muscle: Strategies and Perspectives

Muscle tissue is formed by elongated and contractile cells with specific morphofunctional characteristics. Thus, it is divided into three basic types: smooth muscle tissue, cardiac striated muscle tissue and skeletal striated muscle tissue. The striated skeletal muscle tissue presents high plasticity, regeneration and growth capacity due to the presence of satellite cells, quiescent myoblasts that are activated in case of injury to the tissue and originate new muscle fibers when they differentiate. In more severe deficiencies or injuries there is a loss of their regenerative capacity, thus compromising the body's functionality at different levels. Tissue engineering studies the development of biomaterials capable of stimulating the recovery of cellular activity in injured body tissues, as well as the activity of cells with muscle differentiation potential in injury repair. However, the need for three-dimensional re-assembly in a complex organization makes it difficult to mimic this tissue and fully regenerate it for the sake of precise and effective movements. Thus, this article aims to provide a narrative review of tissue engineering strategies applied to the regeneration of skeletal muscle, in a critical evaluation of research, whether aimed at injury or atrophies such as spinal muscular atrophy.

Organotypic cultures as aging associated disease models

Aging remains a primary risk factor for a host of diseases, including leading causes of death. Aging and associated diseases are inherently multifactorial, with numerous contributing factors and phenotypes at the molecular, cellular, tissue, and organismal scales. Despite the complexity of aging phenomena, models currently used in aging research possess limitations. Frequently used in vivo models often have important physiological differences, age at different rates, or are genetically engineered to match late disease phenotypes rather than early causes. Conversely, routinely used in vitro models lack the complex tissue-scale and systemic cues that are disrupted in aging. To fill in gaps between in vivo and traditional in vitro models, researchers have increasingly been turning to organotypic models, which provide increased physiological relevance with the accessibility and control of in vitro context. While powerful tools, the development of these models is a field of its own, and many aging researchers may be unaware of recent progress in organotypic models, or hesitant to include these models in their own work. In this review, we describe recent progress in tissue engineering applied to organotypic models, highlighting examples explicitly linked to aging and associated disease, as well as examples of models that are relevant to aging. We specifically highlight progress made in skin, gut, and skeletal muscle, and describe how recently demonstrated models have been used for aging studies or similar phenotypes. Throughout, this review emphasizes the accessibility of these models and aims to provide a resource for researchers seeking to leverage these powerful tools.

W. Lo E, Lim H, Dias S, Wagner KR, Mao HQ, Cahan P, Lee G, Grayson WL. Engineering Skeletal Muscle Grafts with PAX7::GFP-Sorted Human Pluripotent Stem Cell-Derived Myogenic Progenitors on Fibrin Microfiber Bundles for Tissue Regeneration

Tissue engineering strategies that combine human pluripotent stem cell-derived myogenic progenitors (hPDMs) with advanced biomaterials provide promising tools for engineering 3D skeletal muscle grafts to model tissue development in vitro and promote muscle regeneration in vivo. We recently demonstrated (i) the potential for obtaining large numbers of hPDMs using a combination of two small molecules without the overexpression of transgenes and (ii) the application of electrospun fibrin microfiber bundles for functional skeletal muscle restoration following volumetric muscle loss. In this study, we aimed to demonstrate that the biophysical cues provided by the fibrin microfiber bundles induce hPDMs to form engineered human skeletal muscle grafts containing multinucleated myotubes that express desmin and myosin heavy chains and that these grafts could promote regeneration following skeletal muscle injuries. We tested a genetic PAX7 reporter line (PAX7::GFP) to sort for more homogenous populations of hPDMs. RNA sequencing and gene set enrichment analyses confirmed that PAX7::GFP-sorted hPDMs exhibited high expression of myogenic genes. We tested engineered human skeletal muscle grafts derived from PAX7::GFP-sorted hPDMs within in vivo skeletal muscle defects by assessing myogenesis, engraftment and immunogenicity using immunohistochemical staining. The PAX7::GFP-sorted groups had moderately high vascular infiltration and more implanted cell association with embryonic myosin heavy chain (eMHC) regions, suggesting they induced pro-regenerative microenvironments. These findings demonstrated the promise for the use of PAX7::GFP-sorted hPDMs on fibrin microfiber bundles and provided some insights for improving the cell-biomaterial system to stimulate more robust in vivo skeletal muscle regeneration.

Organ-On-A-Chip Database Revealed-Achieving the Human Avatar in Silicon

Organ-on-a-chip (OOC) provides microphysiological conditions on a microfluidic chip, which makes up for the shortcomings of traditional in vitro cellular culture models and animal models. It has broad application prospects in drug development and screening, toxicological mechanism research, and precision medicine. A large amount of data could be generated through its applications, including image data, measurement data from sensors, ~omics data, etc. A database with proper architecture is required to help scholars in this field design experiments, organize inputted data, perform analysis, and promote the future development of novel OOC systems. In this review, we overview existing OOC databases that have been developed, including the BioSystics Analytics Platform (BAP) developed by the University of Pittsburgh, which supports study design as well as data uploading, storage, visualization, analysis, etc., and the organ-on-a-chip database (Ocdb) developed by Southeast University, which has collected a large amount of literature and patents as well as relevant toxicological and pharmaceutical data and provides other major functions. We used examples to overview how the BAP database has contributed to the development and applications of OOC technology in the United States for the MPS consortium and how the Ocdb has supported researchers in the Chinese Organoid and Organs-On-A-Chip society. Lastly, the characteristics, advantages, and limitations of these two databases were discussed.

Translating musculoskeletal bioengineering into tissue regeneration therapies

Musculoskeletal injuries and disorders are the leading cause of physical disability worldwide and a considerable socioeconomic burden. The lack of effective therapies has driven the development of novel bioengineering approaches that have recently started to gain clinical approvals. In this review, we first discuss the self-repair capacity of the musculoskeletal tissues and describe causes of musculoskeletal dysfunction. We then review the development of novel biomaterial, immunomodulatory, cellular, and gene therapies to treat musculoskeletal disorders. Last, we consider the recent regulatory changes and future areas of technological progress that can accelerate translation of these therapies to clinical practice.

Investigating and Resolving Cardiotoxicity Induced by COVID-19 Treatments using Human Pluripotent Stem Cell-Derived Cardiomyocytes and Engineered Heart Tissues

Coronavirus disease 2019 continues to spread worldwide. Given the urgent need for effective treatments, many clinical trials are ongoing through repurposing approved drugs. However, clinical data regarding the cardiotoxicity of these drugs are limited. Human pluripotent stem cell-derived cardiomyocytes (hCMs) represent a powerful tool for assessing drug-induced cardiotoxicity. Here, by using hCMs, it is demonstrated that four antiviral drugs, namely, apilimod, remdesivir, ritonavir, and lopinavir, exhibit cardiotoxicity in terms of inducing cell death, sarcomere disarray, and dysregulation of calcium handling and contraction, at clinically relevant concentrations. Human engineered heart tissue (hEHT) model is used to further evaluate the cardiotoxic effects of these drugs and it is found that they weaken hEHT contractile function. RNA-seq analysis reveals that the expression of genes that regulate cardiomyocyte function, such as sarcomere organization (TNNT2, MYH6) and ion homeostasis (ATP2A2, HCN4), is significantly altered after drug treatments. Using high-throughput screening of approved drugs, it is found that ceftiofur hydrochloride, astaxanthin, and quetiapine fumarate can ameliorate the cardiotoxicity of remdesivir, with astaxanthin being the most prominent one. These results warrant caution and careful monitoring when prescribing these therapies in patients and provide drug candidates to limit remdesivir-induced cardiotoxicity.

Differential microRNA profiles of intramuscular and secreted extracellular vesicles in human tissue-engineered muscle

Exercise affects the expression of microRNAs (miR/s) and muscle-derived extracellular vesicles (EVs). To evaluate sarcoplasmic and secreted miR expression in human skeletal muscle in response to exercise-mimetic contractile activity, we utilized a three-dimensional tissue-engineered model of human skeletal muscle ("myobundles"). Myobundles were subjected to three culture conditions: no electrical stimulation (CTL), chronic low frequency stimulation (CLFS), or intermittent high frequency stimulation (IHFS) for 7 days. RNA was isolated from myobundles and from extracellular vesicles (EVs) secreted by myobundles into culture media; miR abundance was analyzed by miRNA-sequencing. We used edgeR and a within-sample design to evaluate differential miR expression and Pearson correlation to evaluate correlations between myobundle and EV populations within treatments with statistical significance set at p < 0.05. Numerous miRs were differentially expressed between myobundles and EVs; 116 miRs were differentially expressed within CTL, 3 within CLFS, and 2 within IHFS. Additionally, 25 miRs were significantly correlated (18 in CTL, 5 in CLFS, 2 in IHFS) between myobundles and EVs. Electrical stimulation resulted in differential expression of 8 miRs in myobundles and only 1 miR in EVs. Several KEGG pathways, known to play a role in regulation of skeletal muscle, were enriched, with differentially overrepresented miRs between myobundle and EV populations identified using miEAA. Together, these results demonstrate that in vitro exercise-mimetic contractile activity of human engineered muscle affects both their expression of miRs and number of secreted EVs. These results also identify novel miRs of interest for future studies of the role of exercise in organ-organ interactions in vivo.

Development of a simple and versatile in vitro method for production, stimulation, and analysis of bioengineered muscle

In recent years, 3D in vitro modeling of human skeletal muscle has emerged as a subject of increasing interest, due to its applicability in basic studies or screening platforms. These models strive to recapitulate key features of muscle architecture and function, such as cell alignment, maturation, and contractility in response to different stimuli. To this end, it is required to culture cells in biomimetic hydrogels suspended between two anchors. Currently available protocols are often complex to produce, have a high rate of breakage, or are not adapted to imaging and stimulation. Therefore, we sought to develop a simplified and reliable protocol, which still enabled versatility in the study of muscle function. In our method, we have used human immortalized myoblasts cultured in a hydrogel composed of MatrigelTM and fibrinogen, to create muscle strips suspended between two VELCROTM anchors. The resulting muscle constructs show a differentiated phenotype and contractile activity in response to electrical, chemical and optical stimulation. This activity is analyzed by two alternative methods, namely contraction analysis and calcium analysis with Fluo-4 AM. In all, our protocol provides an optimized version of previously published methods, enabling individual imaging of muscle bundles and straightforward analysis of muscle response with standard image analysis software. This system provides a start-to-finish guide on how to produce, validate, stimulate, and analyze bioengineered muscle. This ensures that the system can be quickly established by researchers with varying degrees of expertise, while maintaining reliability and similarity to native muscle.

Harvest of quality-controlled bovine myogenic cells and biomimetic bovine muscle tissue engineering for sustainable meat production

Alternative technology for meat production holds the potential to alleviate ethical, environmental, and public health concerns associated with conventional meat production. Cultured meat produced using cell culture technology promises to become a viable alternative to animal-raised meat for the future of the food industry. In this study, biomimetic bovine muscle tissue was artificially fabricated from myogenic cells extracted from bovine meat. Our primary culture method relies on three key factors; a sequential digesting process, enzymatic treatment with pronase, and coating with laminin fragment on culture dishes. This method allows the efficient collection of large numbers of primary cells from bovine cheek meat, purifies the myogenic cells from the cell mixture, and then continuously grows the myogenic cells in vitro. In addition, using our "quality control" methods, we were able to determine the "cell quality", including the proliferative and differentiation capability in each step of the primary culture. Furthermore, to mimic native bovine meat, the quality-controlled bovine myogenic cells were cultured on a micropatterned thermoresponsive substrate stimulating a native-like aligned structure of cells, which were then transferred onto a fibrin-based gel. This gel-based culture environment promoted structural and functional maturation of the myogenic cells, resulting in the production of bovine muscle tissues with sarcomere structures, native-like membrane structures, and contractile ability. We believe that these biomimetic features of "tissue-engineered meat" are important for the production of future cultured meat, which will need native-like nutrients, texture and taste. Therefore, our meat production approach will provide a new platform to produce more native biomimetic tissue-engineered meat in the near future.

Microphysiological system for studying contractile differences in young, active, and old, sedentary adult derived skeletal muscle cells

Microphysiological systems (MPS), also referred to as tissue chips, incorporating 3D skeletal myobundles are a novel approach for physiological and pharmacological studies to uncover new medical treatments for sarcopenia. We characterize a MPS in which engineered skeletal muscle myobundles derived from donor-specific satellite cells that model aged phenotypes are encapsulated in a perfused tissue chip platform containing platinum electrodes. Our myobundles were derived from CD56+ myogenic cells obtained via percutaneous biopsy of the vastus lateralis from adults phenotyped by age and physical activity. Following 17 days differentiation including 5 days of a 3 V, 2 Hz electrical stimulation regime, the myobundles exhibited fused myotube alignment and upregulation of myogenic, myofiber assembly, signaling and contractile genes as demonstrated by gene array profiling and localization of key components of the sarcomere. Our results demonstrate that myobundles derived from the young, active (YA) group showed high intensity immunofluorescent staining of α-actinin proteins and responded to electrical stimuli with a ~1 μm displacement magnitude compared with non-stimulated myobundles. Myobundles derived from older sedentary group (OS) did not display a synchronous contraction response. Hypertrophic potential is increased in YA-derived myobundles in response to stimulation as shown by upregulation of insulin growth factor (IGF-1), α-actinin (ACTN3, ACTA1) and fast twitch troponin protein (TNNI2) compared with OS-derived myobundles. Our MPS mimics disease states of muscle decline and thus provides an aged system and experimental platform to investigate electrical stimulation mimicking exercise regimes and may be adapted to long duration studies of compound efficacy and toxicity for therapeutic evaluation against sarcopenia.

Contractile force assessment methods for in vitro skeletal muscle tissues

Over the last few years, there has been growing interest in measuring the contractile force (CF) of engineered muscle tissues to evaluate their functionality. However, there are still no standards available for selecting the most suitable experimental platform, measuring system, culture protocol, or stimulation patterns. Consequently, the high variability of published data hinders any comparison between different studies. We have identified that cantilever deflection, post deflection, and force transducers are the most commonly used configurations for CF assessment in 2D and 3D models. Additionally, we have discussed the most relevant emerging technologies that would greatly complement CF evaluation with intracellular and localized analysis. This review provides a comprehensive analysis of the most significant advances in CF evaluation and its critical parameters. In order to compare contractile performance across experimental platforms, we have used the specific force (sF, kN/m2), CF normalized to the calculated cross-sectional area (CSA). However, this parameter presents a high variability throughout the different studies, which indicates the need to identify additional parameters and complementary analysis suitable for proper comparison. We propose that future contractility studies in skeletal muscle constructs report detailed information about construct size, contractile area, maturity level, sarcomere length, and, ideally, the tetanus-to-twitch ratio. These studies will hopefully shed light on the relative impact of these variables on muscle force performance of engineered muscle constructs. Prospective advances in muscle tissue engineering, particularly in muscle disease models, will require a joint effort to develop standardized methodologies for assessing CF of engineered muscle tissues.