Masatoshi Suzuki, DVM, PhD – Slide of the Week

Title: A novel in vitro model of the human myotendinous junction

Legend: The myotendinous junction (MTJ) is an integrated structure that transduces force across the muscle-tendon boundary, making the region vulnerable to strain injury. Despite the clinical relevance, previous in vitro models of the MTJ lack the structure and mechanical accuracy of the native tissue and have difficulty transmitting force across the cell-cell interface. This study demonstrates an in vitro model of the MTJ, using spatially restrictive cues to inform human myocyte-tenocyte interactions and architecture. The model expressed MTJ markers and developed anisotropic myocyte-tenocyte integrations that resemble the native tissue and allow for force transduction from contracting myocytes to passive tenocyte regions. As such, this study presents a system capable of investigating development, injury, and pathology in the human MTJ.

Citation:  Josvai, M., Polyak, E., Kalluri, M., Robertson, S., Crone, W. C., & Suzuki, M. (2024). An engineered in vitro model of the human myotendinous junction. Acta biomaterialia, S1742-7061(24)00180-6. Advance online publication.

Abstract: The myotendinous junction (MTJ) is a vulnerable region at the interface of skeletal muscle and tendon that forms an integrated mechanical unit. This study presents a technique for the spatially restrictive co-culture of human embryonic stem cell (hESC)-derived skeletal myocytes and primary tenocytes for two-dimensional modeling of the MTJ. Micropatterned lanes of extracellular matrix and a 2-well culture chamber define the initial regions of occupation. On day 1, both lines occupy less than 20% of the initially vacant interstitial zone, referred to henceforth as the junction. Myocyte-tenocyte interdigitations are observed by day 7. Immunocytochemistry reveals enhanced organization and alignment of patterned myocyte and tenocyte features, as well as differential expression of multiple MTJ markers. On day 24, electrically stimulated junction myocytes demonstrate negative contractile strains, while positive tensile strains are exhibited by mechanically passive tenocytes at the junction. Unpatterned tenocytes distal to the junction experience significantly decreased strains in comparison to cells at the interface. Unpatterned myocytes have impaired organization and uncoordinated contractile behavior. These findings suggest that this platform is capable of inducing myocyte-tenocyte junction formation and mechanical coupling similar to the native MTJ, showing transduction of force across the cell-cell interface.

Masatoshi Suzuki, DVM, PhD
Masatoshi Suzuki, DVM, PhD

Investigator: Masatoshi Suzuki, DVM, PhD

About the Lab: The Suzuki group has demonstrated the therapeutic benefits of ex vivo gene therapy (stem cell-based growth/trophic factor delivery) targeting the skeletal muscle to prevent degeneration of motor neurons and associated neuromuscular junctions during ALS. Although most ALS research has focused on mechanisms of motor neuron cell death, degeneration is also observed in skeletal muscle, particularly at the neuromuscular connection. Glial cell line-derived neurotrophic factor and vascular endothelial growth factor (VEGF) promote survival of motor neurons and their neuromuscular junctions in neuromuscular disorders, such as ALS. Most recently, the lab delivered a combination of GDNF and/or VEGF to muscles using hMSCs; the hMSCs survive and synthesize and release growth factors, which slow disease progression in familial ALS model rats.

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