BCL9 is an essential component of canonical Wnt signaling that mediates the differentiation of myogenic progenitors during muscle regeneration

Michel Aguet
Elsevier, 2009
Article

Résumé

Muscle stem cells and their progeny play a fundamental role in the regeneration of adult skeletal muscle. We have previously shown that activation of the canonical Wnt/beta-catenin signaling pathway in adult myogenic progenitors is required for their transition from rapidly dividing transient amplifying cells to more differentiated progenitors. Whereas Wnt signaling in Drosophila is dependent on the presence of the co-regulator Legless, previous studies of the mammalian ortholog of Legless, BCL9 (and its homolog, BCL9-2), have not revealed an essential role of these proteins in Wnt signaling in specific tissues during development. Using Cre-lox technology to delete BCL9 and BCL9-2 in the myogenic lineage in vivo and RNAi technology to knockdown the protein levels in vitro, we show that BCL9 is required for activation of the Wnt/beta-catenin cascade in adult mammalian myogenic progenitors. We observed that the nuclear localization of beta-catenin and downstream TCF/LEF-mediated transcription, which are normally observed in myogenic progenitors upon addition of exogenous Wnt and during muscle regeneration, were abrogated when BCL9/9-2 levels were reduced. Furthermore, reductions of BCL9/9-2 inhibited the promotion of myogenic differentiation by Wnt and the normal regenerative response of skeletal muscle. These results suggest a critical role of BCL9/9-2 in the Wnt-mediated regulation of adult, as opposed to embryonic, myogenic progenitors.

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https://infoscience.epfl.ch/record/151920?ln=fr

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Michel Aguet
Elsevier, 2009
Article

Résumé

Official source

https://infoscience.epfl.ch/record/151920?ln=fr

À propos de ce résultat

Concepts associés (16)

Wnt est une famille de glycoprotéines intervenant dans l'embryogenèse et le cancer. Le nom Wnt (prononcez « winnt ») est la réunion de Wg (, en français « sans aile ») et Int (, en français « site d'i

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vignette|Cellules souches embryonnaires de souris en culture. En biologie cellulaire, une cellule souche est une cellule indifférenciée capable, à la fois, de générer des cellules spécialisées par di

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Bioengineering the Human Muscle Stem-Cell Niche for Therapeutic Applications

Omid Mashinchian

In spite of decades of research, no feasible method for obtaining sufficient numbers of uncommitted muscle stem cells (MuSCs) for therapy of degenerative muscle diseases exists. One of the most fundamental problems associated with stem cell therapy of muscle is that removal of MuSCs from their tissue microenvironment and expansion in conventional culture induces their terminal commitment to myogenic differentiation. This in-vitro loss of stemness impairs the long-term engraftment potential of MuSCs and renders them unsuitable for stem cell therapy. In another disease relevant context, aging, dramatic changes in the functionality of MuSCs have been shown to depend on an altered composition of their microenvironment. Thus, muscle progenitors are fundamentally dependent on their local environment, commonly known as the âstem cell niche", and a better understanding of its role in guiding stem cell function is highly relevant for the development of therapies for aging and muscle diseases. The muscle stem cell niche is composed of diverse cellular and acellular elements, including different supportive cell types, growth factors and extracellular matrix, and as outlined above, is critical for maintaining healthy stem cell characteristics such as the capacity for self-renewal, commitment, and differentiation. Using molecular biology approaches, we decided to interrogate (I) the role of the cellular environment on stem cell commitment, (II) to test whether, in a physiological context, the systemic circulation has niche-independent effects on MuSC stemness, and (III) to study a population of MuSC-supportive cells that is affected by the aging process. In the first study of this thesis, we have successfully developed an organoid-like-approach for the scalable derivation of uncommitted MuSCs from human induced pluripotent stem cells (iPSCs) in a biologically faithful cellular 3D-environment in suspension embryoids. To this end, we employed human iPSCs and a spectrum of immortalized cell lines to screen for 3D-aggregation conditions promoting mesoderm formation and subsequent specification to the myogenic lineage without the parallel upregulation of myogenic commitment markers. Compared to myogenic cells derived from adult human skeletal muscle, this niche-mimetic embryoid derived progenitors display significantly enhanced engraftment into the muscle stem cell position peripheral to muscle fibers, and restoration of dystrophin expression when transplanted into muscles of a mouse model of Duchenne muscular dystrophy. In a second study, we present a novel method for encapsulation of human muscle progenitors in highly diffusible polyethersulfone hollow fiber capsules to identify highly specific "transcriptional-signature" induced by systemic aging in-vivo. This technique allows to study the systemic circulation in health, disease and aging at an unprecedented level in human cell types of choice. Finally, in our third study, we investigated the cellular cross-talk between muscle stem cells and non-myogenic niche-based cell type, called fibro/adipogenic progenitors (FAPs). Interestingly, the support-function and the cross-talk with stem cells are dramatically impaired in aged FAPs. We demonstrate that this mechanism can be targeted to rejuvenate myogenesis. Taken together, "mimicking" the physicochemical-interactions of MuSCs with their niche-resident cell types, represents a powerful opportunity to manipulate MuSC function in aging and disease.

EPFL2019

Chargement

Wnt signaling is essential for embryogenesis and adult tissue homeostasis and contributes to cancer development, especially in the colon. A new essential pathway component, legless, was identified in Drosophila melanogaster. Mice with Cre/loxP-mediated conditional ablation of the legless homologues Bcl9 and Bcl9l in the intestinal epithelium were generated to assess the contribution of the genes to Wnt signaling and their potential suitability as therapeutic drug targets. Initial analysis had revealed that both genes were not required for self-renewal of the intestinal epithelium during homeostasis, but for regeneration of experimentally induced colon wounds. Furthermore, formation of chemically induced colon tumors was not impaired and Bcl9/Bcl9-mutant tumors were morphologically indistinguishable from wild-type tumors and displayed hallmarks of active Wnt signaling. This study aimed at further investigating the molecular processes involving Bcl9 and Bcl9l in wound regeneration and tumorigenesis in the colon, and in particular relatedness of the genes to Wnt signaling. To this end, transcriptomes of laser microdissected wound regions were analyzed by microarray-based gene expression profiling and realtime quantitative PCR, but did not reveal significant changes in gene expression at the time point chosen for analysis. However, expression profiling of homeostatic colon epithelium revealed a reduced expression of several intestinal stem cell marker genes in Bcl9/Bcl9l-mutant colon epithelium, suggesting that the regeneration deficit has been caused by functional impairment of intestinal stem cells. This stem cell deficiency did not differ between young and old mice and was also weakly detectable in small intestinal epithelium. To verify that tumors originated from cells in which complete deletion of all four Bcl9 and Bcl9l alleles had occurred and to assess Wnt signaling activity more comprehensively, laser microdissected tumor regions were profiled using microarrays and realtime quantitative PCR. This analysis confirmed that Bcl9 and Bcl9l were not required for colon tumorigenesis and revealed that despite the morphological similarity, transcriptional profiles of Bcl9/Bcl9l-mutant tumors were very different from wild-type tumors. Notably, loss of Bcl9 and Bcl9l caused reduced expression of a subset of direct Wnt target genes, genes related to epithelial-mesenchymal transition (EMT) and intestinal stem cell traits. While wild-type tumor epithelium appeared to be in a metastable state, characterized by co-expression of epithelial and mesenchymal traits, Bcl9/Bcl9l-mutant tumor epithelium predominantly expressed epithelial traits. In addition, a marked reduction in expression of several genes associated with malignant tumor properties was observed in Bcl9/Bcl9l-mutant tumors. This was highlighted by the preservation of an intact basement membrane around Bcl9/Bcl9l-mutant tumor epithelium, which was absent in wild-type tumors, and indicated that loss of Bcl9/Bcl9l decreased tumor aggressiveness. Of note, EMT and stemness traits are correlated to tumor resistance to therapy and thus interfering with Bcl9/Bcl9l function might restore drug responsiveness. As a proof of concept, it was shown that the malignant traits mediated by Bcl9/Bcl9l could be abrogated in wild-type tumors by inducing deletion of the genes. These findings suggest that targeting Bcl9 and Bcl9l with therapeutic drugs has the potential to attenuate the malignancy of colon tumors.

EPFL2011

Chargement

Metabolic rescue of muscle and muscle stem cells in muscle disease

Peiling Luan

Duchenne muscular dystrophy (DMD), caused by the mutation of dystrophin gene, is an X-linked disorder that affects 1 in 3500 males, leading to progressive muscle degeneration and eventually resulting in premature death. Increasing evidence indicates that DMD and age-related sarcopenia share clinical hallmarks, such as decreased metabolic activity of both myofibers and muscle stem cells (MuSCs), which results in defective MuSC function and impaired muscle regeneration. In my Ph.D. thesis, I focused on manipulating mitochondrial function, such as mitophagy, and lipid metabolism, particularly sphingolipid metabolic pathways, to restore muscle and MuSC functions in DMD and age-associated sarcopenia. My thesis consists of three projects: Rescue of mitophagy improves muscle function in DMD. In this project, we identified defective mitophagy as a hallmark of muscular dystrophy. Rescue of dysfunctional mitophagy by dietary supplementation of Urolithin A (UA), a metabolite present in fruit extracts and a potent activator of mitophagy, improved muscle function in mdx mice. The beneficial effects of mitophagy restoration observed in dystrophic animals were attributed to the improvement in mitochondrial function, structural integrity of muscles, restoration of MuSC activity, and reduction in general inflammation and fibrosis. Sphingolipid depletion improves muscle regeneration during ageing. We first established the link between sphingolipid metabolism and ageing by demonstrating that sphingolipids accumulate in skeletal muscle upon aging. We reduced skeletal muscle sphingolipid accumulation by treating aged mice with myriocin, a selective inhibitor of serine pamitoyltransferase (SPT), the first and rate-limiting enzyme of sphingolipid de novo synthesis pathway. Sphingolipid depletion increased MuSC regenerative ability through enhancing the proliferation and differentiation capacities of MuSCs, ultimately leading to the prevention of age-related decline in muscle mass and function. Inhibition of sphingolipid synthesis reverts muscular dystrophy. By studying skeletal muscle transcript profiles of human muscular dystrophies, we identified upregulation of sphingolipid biosynthetic pathway as a universal feature of human patients affected with muscular dystrophy. To rescue the aberrant sphingolipid metabolism, we treated mdx mice with myriocin and showed that inhibition of sphingolipid generation enhanced muscle function, leading to amelioration of DMD. Furthermore, we uncovered a novel role of sphingolipid depletion in macrophage polarization and in reconstruction of the mdx MuSC niche, resulting in improved regenerative capacity of MuSCs. In summary, our work establishes the essential roles of mitophagy and sphingolipid metabolism in maintaining muscle and MuSC function. Restoration of mitophagy and blockade of sphingolipid generation could therefore be attractive treatment strategies to delay the progression of DMD and age-related sarcopenia.

EPFL2020

Chargement

Bioengineering the Human Muscle Stem-Cell Niche for Therapeutic Applications

Omid Mashinchian

EPFL2019

EPFL2011

Metabolic rescue of muscle and muscle stem cells in muscle disease

Peiling Luan

EPFL2020