Comparative Effects of Basic Fibroblast Growth Factor Delivery or Voluntary Exercise on Muscle Regeneration after Volumetric Muscle Loss

Combinatorial extracellular matrix cues with mechanical strain induce differential effects on myogenesis in vitro

Skeletal muscle regeneration remains a clinical unmet need for volumetric muscle loss and atrophy where muscle function cannot be restored to prior capacity. Current experimental approaches do not account for the complex microenvironmental factors that modulate myogenesis. In this study we developed a biomimetic tissue chip platform to systematically study the combined effects of the extracellular matrix (ECM) microenvironment and mechanical strain on myogenesis of murine myoblasts. Using stretchable tissue chips composed of collagen I (C), fibronectin (F) and laminin (L), as well as their combinations thereof, we tested the addition of mechanical strain regimens on myogenesis at the transcriptomic and translational levels. Our results show that ECMs have a significant effect on myotube formation in C2C12 murine myoblasts. Under static conditions, laminin substrates induced the longest myotubes, whereas fibronectin produced the widest myotubes. Combinatorial ECMs showed non-intuitive effects on myotube formation. Genome-wide analysis revealed the upregulation in actin cytoskeletal related genes that are suggestive of myogenesis. When mechanical strain was introduced to C + F + L combinatorial ECM substrates in the form of constant or intermittent uniaxial strain at low (5%) and high (15%) levels, we observed synergistic enhancements in myotube width, along with transcriptomic upregulation in myosin heavy chain genes. Together, these studies highlight the complex role of microenvironmental factors such as ECM interactions and strain on myotube formation and the underlying signaling pathways.

Biocompatible Macroion/Growth Factor Assemblies for Medical Applications

Growth factors are a class of proteins that play a role in the proliferation (the increase in the number of cells resulting from cell division) and differentiation (when a cell undergoes changes in gene expression becoming a more specific type of cell) of cells. They can have both positive (accelerating the normal healing process) and negative effects (causing cancer) on disease progression and have potential applications in gene therapy and wound healing. However, their short half-life, low stability, and susceptibility to degradation by enzymes at body temperature make them easily degradable in vivo. To improve their effectiveness and stability, growth factors require carriers for delivery that protect them from heat, pH changes, and proteolysis. These carriers should also be able to deliver the growth factors to their intended destination. This review focuses on the current scientific literature concerning the physicochemical properties (such as biocompatibility, high affinity for binding growth factors, improved bioactivity and stability of the growth factors, protection from heat, pH changes or appropriate electric charge for growth factor attachment via electrostatic interactions) of macroions, growth factors, and macroion-growth factor assemblies, as well as their potential uses in medicine (e.g., diabetic wound healing, tissue regeneration, and cancer therapy). Specific attention is given to three types of growth factors: vascular endothelial growth factors, human fibroblast growth factors, and neurotrophins, as well as selected biocompatible synthetic macroions (obtained through standard polymerization techniques) and polysaccharides (natural macroions composed of repeating monomeric units of monosaccharides). Understanding the mechanisms by which growth factors bind to potential carriers could lead to more effective delivery methods for these proteins, which are of significant interest in the diagnosis and treatment of neurodegenerative and civilization diseases, as well as in the healing of chronic wounds.

Effects of Adjunct Antifibrotic Treatment within a Regenerative Rehabilitation Paradigm for Volumetric Muscle Loss

The use of a rehabilitation approach that promotes regeneration has the potential to improve the efficacy of pro-regenerative therapies and maximize functional outcomes in the treatment of volumetric muscle loss (VML). An adjunct antifibrotic treatment could further enhance functional gains by reducing fibrotic scarring. This study aimed to evaluate the potential synergistic effects of losartan, an antifibrotic pharmaceutical, paired with a voluntary wheel running rehabilitation strategy to enhance a minced muscle graft (MMG) pro-regenerative therapy in a rodent model of VML. The animals were randomly assigned into four groups: (1) antifibrotic with rehabilitation, (2) antifibrotic without rehabilitation, (3) vehicle treatment with rehabilitation, and (4) vehicle treatment without rehabilitation. At 56 days, the neuromuscular function was assessed, and muscles were collected for histological and molecular analysis. Surprisingly, we found that the losartan treatment decreased muscle function in MMG-treated VML injuries by 56 days, while the voluntary wheel running elicited no effect. Histologic and molecular analysis revealed that losartan treatment did not reduce fibrosis. These findings suggest that losartan treatment as an adjunct therapy to a regenerative rehabilitation strategy negatively impacts muscular function and fails to promote myogenesis following VML injury. There still remains a clinical need to develop a regenerative rehabilitation treatment strategy for traumatic skeletal muscle injuries. Future studies should consider optimizing the timing and duration of adjunct antifibrotic treatments to maximize functional outcomes in VML injuries.

Biomedical Applications of Collagen

Extracellular matrix proteins (ECMs) provide structural support and dynamic signaling cues that regulate cell behavior and tissue morphogenesis [...].

Early initiation of electrical stimulation paired with range of motion after a volumetric muscle loss injury does not benefit muscle function

NEW FINDINGS

What is the central question of this study? First, how does physical rehabilitation influence recovery from traumatic muscle injury? Second, how does physical activity impact the rehabilitation response for skeletal muscle function and whole-body metabolism? What is the main finding and its importance? The most salient findings were that rehabilitation impaired muscle function and range of motion, while restricting activity mitigated some negative effects but also impacted whole-body metabolism. These data suggest that first, work must continue to explore treatment parameters, including modality, time, type, duration and intensity, to find the best rehabilitation approaches for volumetric muscle loss injuries; and second, restricting activity acutely might enhance rehabilitation response, but whole-body co-morbidities should continue to be considered.

ABSTRACT

Volumetric muscle loss (VML) injury occurs when a substantial volume of muscle is lost by surgical removal or trauma, resulting in an irrecoverable deficit in muscle function. Recently, it was suggested that VML impacts whole-body and muscle-specific metabolism, which might contribute to the inability of the muscle to respond to treatments such as physical rehabilitation. The aim of this work was to understand the complex relationship between physical activity and the response to rehabilitation after VML in an animal model, evaluating the rehabilitation response by measurement of muscle function and whole-body metabolism. Adult male mice (n = 24) underwent a multi-muscle, full-thickness VML injury to the gastrocnemius, soleus and plantaris muscles and were randomized into one of three groups: (1) untreated; (2) rehabilitation (i.e., combined electrical stimulation and range of motion, twice per week, beginning 72 h post-injury, for ∼8 weeks); or (3) rehabilitation and restriction of physical activity. There was a lack of positive adaption associated with electrical stimulation and range of motion intervention alone; however, maximal isometric torque of the posterior muscle group was greater in mice receiving treatment with activity restriction (P = 0.008). Physical activity and whole-body metabolism were measured ∼6 weeks post-injury; metabolic rate decreased (P = 0.001) and respiratory exchange ratio increased (P = 0.022) with activity restriction. Therefore, restricting physical activity might enhance an intervention delivered to the injured muscle group but impair whole-body metabolism. It is possible that restricting activity is important initially post-injury to protect the muscle from excess demand. A gradual increase in activity throughout the course of treatment might optimize muscle function and whole-body metabolism.

Engineering Spatiotemporal Control in Vascularized Tissues

A major challenge in engineering scalable three-dimensional tissues is the generation of a functional and developed microvascular network for adequate perfusion of oxygen and growth factors. Current biological approaches to creating vascularized tissues include the use of vascular cells, soluble factors, and instructive biomaterials. Angiogenesis and the subsequent generation of a functional vascular bed within engineered tissues has gained attention and is actively being studied through combinations of physical and chemical signals, specifically through the presentation of topographical growth factor signals. The spatiotemporal control of angiogenic signals can generate vascular networks in large and dense engineered tissues. This review highlights the developments and studies in the spatiotemporal control of these biological approaches through the coordinated orchestration of angiogenic factors, differentiation of vascular cells, and microfabrication of complex vascular networks. Fabrication strategies to achieve spatiotemporal control of vascularization involves the incorporation or encapsulation of growth factors, topographical engineering approaches, and 3D bioprinting techniques. In this article, we highlight the vascularization of engineered tissues, with a focus on vascularized cardiac patches that are clinically scalable for myocardial repair. Finally, we discuss the present challenges for successful clinical translation of engineered tissues and biomaterials.