Author
Andrew S. Brack
Other affiliations: University of California, Berkeley, Harvard University, Medical Research Council ...read more
Bio: Andrew S. Brack is an academic researcher from University of California, San Francisco. The author has contributed to research in topics: Stem cell & Skeletal muscle. The author has an hindex of 27, co-authored 47 publications receiving 7526 citations. Previous affiliations of Andrew S. Brack include University of California, Berkeley & Harvard University.
Papers
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TL;DR: It is shown that this approach can reprogram multiple human cell types to pluripotency with efficiencies that greatly surpass established protocols and represents a safe, efficient strategy for somatic cell reprogramming and directing cell fate that has broad applicability for basic research, disease modeling, and regenerative medicine.
2,627 citations
TL;DR: It is shown that muscle stem cells from aged mice tend to convert from a myogenic to a fibrogenic lineage as they begin to proliferate and that this conversion is mediated by factors in the systemic environment of the old animals.
Abstract: The regenerative potential of skeletal muscle declines with age, and this impairment is associated with an increase in tissue fibrosis. We show that muscle stem cells (satellite cells) from aged mice tend to convert from a myogenic to a fibrogenic lineage as they begin to proliferate and that this conversion is mediated by factors in the systemic environment of the old animals. We also show that this lineage conversion is associated with an activation of the canonical Wnt signaling pathway in aged myogenic progenitors and can be suppressed by Wnt inhibitors. Furthermore, components of serum from aged mice that bind to the Frizzled family of proteins, which are Wnt receptors, may account for the elevated Wnt signaling in aged cells. These results indicate that the Wnt signaling pathway may play a critical role in tissue-specific stem cell aging and an increase in tissue fibrosis with age.
1,389 citations
TL;DR: It is demonstrated that the aged muscle stem cell niche, the muscle fibre, expresses Fgf2 under homeostatic conditions, driving a subset of satellite cells to break quiescence and lose their self-renewing capacity.
Abstract: The niche is a conserved regulator of stem cell quiescence and function. During ageing, stem cell function declines. To what extent and by what means age-related changes within the niche contribute to this phenomenon are unknown. Here we demonstrate that the aged muscle stem cell niche, the muscle fibre, expresses Fgf2 under homeostatic conditions, driving a subset of satellite cells to break quiescence and lose their self-renewing capacity. We show in mice that relatively dormant aged satellite cells robustly express sprouty 1 (Spry1), an inhibitor of fibroblast growth factor (FGF) signalling. Increasing FGF signalling in aged satellite cells under homeostatic conditions by removing Spry1 results in the loss of quiescence, satellite cell depletion and diminished regenerative capacity. Conversely, reducing niche-derived FGF activity through inhibition of Fgfr1 signalling or overexpression of Spry1 in satellite cells prevents their depletion. These experiments identify an age-dependent change in the stem cell niche that directly influences stem cell quiescence and function. The expression of fibroblast growth factor in aged muscle fibre, the muscle stem cell niche, is shown to cause satellite cells to lose the capacity for self-renewal, and is thus an age-dependent change that directly influences stem cell quiescence and function. The efficiency of stem-cell maintenance declines with age, but it is not clear whether the stem-cell niche itself plays a part in this decline. Here, Andrew Brack and colleagues report that as mice age, the skeletal-muscle niche becomes more mitogenic — meaning more cells undergo mitosis and differentiation — and less capable of maintaining the quiescence of the skeletal-muscle stem cells. This results in the loss of capacity for stem-cell self-renewal. The protein FGF2 is a key mitogenic factor in the aged niche, although a small number of muscle stem cells express SPRY1, an inhibitor of FGF signalling, and maintain some quiescence in aged skeletal-muscle fibres.
690 citations
TL;DR: It is demonstrated that the temporal balance between Notch and Wnt signaling orchestrates the precise progression of muscle precursor cells along the myogenic lineage pathway, through stages of proliferative expansion and then differentiation, during postnatal myogenesis.
586 citations
TL;DR: A GDF11-specific immunoassay is developed and a trend toward increased GDF 11 levels in sera of aged rats and humans is shown and GDF12 could be a target for pharmacologic blockade to treat age-related sarcopenia.
443 citations
Cited by
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TL;DR: Nine tentative hallmarks that represent common denominators of aging in different organisms are enumerated, with special emphasis on mammalian aging, to identify pharmaceutical targets to improve human health during aging, with minimal side effects.
9,980 citations
TL;DR: An update of the core Wnt/β-catenin signaling pathway is provided, how its various components contribute to disease, and outstanding questions to be addressed in the future are discussed.
4,561 citations
TL;DR: It is shown that this approach can reprogram multiple human cell types to pluripotency with efficiencies that greatly surpass established protocols and represents a safe, efficient strategy for somatic cell reprogramming and directing cell fate that has broad applicability for basic research, disease modeling, and regenerative medicine.
2,627 citations
TL;DR: Recent evidence supports the possible contribution of adult stem cells in the muscle regeneration process and in particular, bone marrow-derived and muscle-derived stem cells contribute to new myofiber formation and to the satellite cell pool after injury.
Abstract: Charge, Sophie B. P., and Michael A. Rudnicki. Cellular and Molecular Regulation of Muscle Regeneration. Physiol Rev 84: 209–238, 2004; 10.1152/physrev.00019.2003.—Under normal circumstances, mamma...
2,497 citations
TL;DR: The nematode Caenorhabditis elegans ages and dies in a few weeks, but humans can live for 100 years or more, which means that over evolutionary time mutations have increased lifespan more than 2,000-fold.
Abstract: The nematode Caenorhabditis elegans ages and dies in a few weeks, but humans can live for 100 years or more. Assuming that the ancestor we share with nematodes aged rapidly, this means that over evolutionary time mutations have increased lifespan more than 2,000-fold. Which genes can extend lifespan? Can we augment their activities and live even longer? After centuries of wistful poetry and wild imagination, we are now getting answers, often unexpected ones, to these fundamental questions.
2,466 citations