Methods for Observing and Quantifying Muscle Satellite Cell Motility and Invasion In Vitro.
TL;DR: Three protocols developed in the group for quantitatively analyzing satellite cell motility over time are described, which allow identification and longitudinal evaluation of individual cells over time and quantification of variations in motility due to intrinsic or extrinsic factors.
Abstract: Motility and/or chemotaxis of satellite cells has been suggested or observed in multiple in vitro and in vivo contexts. Satellite cell motility also affects the efficiency of muscle regeneration, particularly in the context of engrafted exogenous cells. Consequently, there is keen interest in determining what cell-autonomous and environmental factors influence satellite cell motility and chemotaxis in vitro and in vivo. In addition, the ability of activated satellite cells to relocate in vivo would suggest that they must be able to invade and transit through the extracellular matrix (ECM), which is supported by studies in which alteration or addition of matrix metalloprotease (MMP) activity enhanced the spread of engrafted satellite cells. However, despite its potential importance, analysis of satellite cell motility or invasion quantitatively even in an in vitro setting can be difficult; one of the most powerful techniques for overcoming these difficulties is timelapse microscopy. Identification and longitudinal evaluation of individual cells over time permits not only quantification of variations in motility due to intrinsic or extrinsic factors, it permits observation and analysis of other (frequently unsuspected) cellular activities as well. We describe here three protocols developed in our group for quantitatively analyzing satellite cell motility over time in two dimensions on purified ECM substrates, in three dimensions on a living myofiber, and in three dimensions through an artificial matrix.
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TL;DR: Background in the field is provided and recent advances in the understanding of muscle stem cell function and dysfunction are discussed, particularly in the case of aging, and the potential involvement of Muscle stem cells in genetic diseases such as the muscular dystrophies are discussed.
Abstract: Skeletal muscle stem cells, originally termed satellite cells for their position adjacent to differentiated muscle fibers, are absolutely required for the process of skeletal muscle repair and regeneration. In the last decade, satellite cells have become one of the most studied adult stem cell systems and have emerged as a standard model not only in the field of stem cell-driven tissue regeneration but also in stem cell dysfunction and aging. Here, we provide background in the field and discuss recent advances in our understanding of muscle stem cell function and dysfunction, particularly in the case of aging, and the potential involvement of muscle stem cells in genetic diseases such as the muscular dystrophies.
7 citations
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TL;DR: This review will highlight the origin and unique markers of the satellite cell population, the regulation by growth factors, and the response to physiological and pathological stimuli, and identify future research goals for the study of satellite cell biology.
Abstract: Adult skeletal muscle has a remarkable ability to regenerate following myotrauma. Because adult myofibers are terminally differentiated, the regeneration of skeletal muscle is largely dependent on a small population of resident cells termed satellite cells. Although this population of cells was identified 40 years ago, little is known regarding the molecular phenotype or regulation of the satellite cell. The use of cell culture techniques and transgenic animal models has improved our understanding of this unique cell population; however, the capacity and potential of these cells remain ill-defined. This review will highlight the origin and unique markers of the satellite cell population, the regulation by growth factors, and the response to physiological and pathological stimuli. We conclude by highlighting the potential therapeutic uses of satellite cells and identifying future research goals for the study of satellite cell biology.
1,647 citations
TL;DR: It is demonstrated that MT-MMP–expressing cells can penetrate and remodel type I collagen-rich tissues by using membrane-anchored metalloproteinases as pericellular collagenases.
Abstract: During tissue-invasive events, migrating cells penetrate type I collagen-rich interstitial tissues by mobilizing undefined proteolytic enzymes. To screen for members of the matrix metalloproteinase (MMP) family that mediate collagen-invasive activity, an in vitro model system was developed wherein MDCK cells were stably transfected to overexpress each of ten different MMPs that have been linked to matrix remodeling states. MDCK cells were then stimulated with scatter factor/hepatocyte growth factor (SF/HGF) to initiate invasion and tubulogenesis atop either type I collagen or interstitial stroma to determine the ability of MMPs to accelerate, modify, or disrupt morphogenic responses. Neither secreted collagenases (MMP-1 and MMP-13), gelatinases (gelatinase A or B), stromelysins (MMP-3 and MMP-11), or matrilysin (MMP-7) affected SF/HGF-induced responses. By contrast, the membrane-anchored metalloproteinases, membrane-type 1 MMP, membrane-type 2 MMP, and membrane-type 3 MMP (MT1-, MT2-, and MT3-MMP) each modified the morphogenic program. Of the three MT-MMPs tested, only MT1-MMP and MT2-MMP were able to directly confer invasion-incompetent cells with the ability to penetrate type I collagen matrices. MT-MMP–dependent invasion proceeded independently of proMMP-2 activation, but required the enzymes to be membrane-anchored to the cell surface. These findings demonstrate that MT-MMP–expressing cells can penetrate and remodel type I collagen-rich tissues by using membrane-anchored metalloproteinases as pericellular collagenases.
600 citations
TL;DR: Results suggest that purified pericytes and endothelium-related cells demonstrate high myogenic potential in culture and in vivo, and suggest their ultimate origin in blood vessel walls.
570 citations
TL;DR: Greater understanding of these mechanisms will increase the possibility of total muscle recovery from severe injury or disease and have particular application to the production of meat animals and to a greater understanding of the growth process in general.
Abstract: Since the first reports of satellite cells in 1961, considerable knowledge has accumulated concerning their phylogenetic distribution and their location, morphology, and function. There is no doubt that satellite cells are capable of undergoing mitosis and that they have considerable motility. These cells function as the progenitors of the myofiber nuclei that must be added during normal (postnatal) growth of muscle. In muscle undergoing or attempting to undergo regeneration, the satellite cell functions as a myogenic stem cell to produce myoblasts that line up and fuse within the scaffolding of the remnant basal lamina or migrate into the interstitium to produce neofibers . A number of problems remain to be solved concerning the regulation of satellite cell function. At this time it is equivocable whether or not the presumptive myoblast and the satellite cell are functionally identical and at the same stage of myogenic differentiation. Apparently there is species variation in terms of the ability of myotubes from embryonic myogenic cells and satellite cells to synthesize protein. The mechanism(s) by which a wide variety of stimuli activate satellite cells is not known, nor is the mechanism(s) by which satellite cells become inactive during the latter stages of growth and adulthood known. Mitogenic factors are present in damaged muscle; but the specific characteristics of these factors and their mechanism of activation are also unknown. Hormones are certainly involved in the regulation of proliferation and differentiation of myogenic cells, but whether presumptive myoblasts and satellite cells or their myotubes respond similarly to hormones in culture has not been adequately examined. Greater understanding of these mechanisms will increase the possibility of total muscle recovery from severe injury or disease. Such knowledge would also have particular application to the production of meat animals and to a greater understanding of the growth process in general.
510 citations
TL;DR: In the present review, studies will be examined that focus on the origin, gene expression, and coordinated regulation of stem cell populations to highlight the regenerative capacity of skeletal muscle and emphasize the challenges for this field.
Abstract: Somatic stem cell populations participate in the development and regeneration of their host tissues. Skeletal muscle is capable of complete regeneration due to stem cells that reside in skeletal muscle and nonmuscle stem cell populations. However, in severe myopathic diseases such as Duchenne Muscular Dystrophy, this regenerative capacity is exhausted. In the present review, studies will be examined that focus on the origin, gene expression, and coordinated regulation of stem cell populations to highlight the regenerative capacity of skeletal muscle and emphasize the challenges for this field. Intense interest has focused on cell-based therapies for chronic, debilitating myopathic diseases. Future studies that enhance our understanding of stem cell biology and repair mechanisms will provide a platform for therapeutic applications directed toward these chronic, life-threatening diseases.
502 citations