STAGE-SPECIFIC EFFECTS OF PITX2 INACTIVATION DURING SKELETAL MYOGENESIS

Durante el desarrollo embrionario, estructuras transitorias llamadas somitos dan lugar al dermomiotomo epitelial, origen de los precursores de la musculatura esquelética del tronco. Las células progenitoras musculares multipo- tentes (MPC) que expresan Pax3 surgen del dermomiotomo y adquieren su identidad definitiva a través de los factores reguladores miogénicos (MRF) Myf5, Mrf4 y MyoD. Además, las células madre musculares (células satélite) del cuerpo y las extremidades también surgen de somitos, en común con el músculo con el que están asociadas. Evidencias previas han revelado que el factor de transcripción Pitx2 podría ser un factor clave dentro de las vías moleculares que controlan el destino de los progenitores musculares derivados de somitos. Sin embargo, la posición jerárquica ocupada por Pitx2 dentro de la cascada genética que controla la miogénesis derivada de los somitos sigue sin resolverse. Para obtener información sobre este problema, hemos generado dos ratones mutantes condicionales para inactivar específicamente Pitx2 en progenitores musculares multipotentes Pax3+ (Pax3Cre+/Pitx2loxp/loxp) y en los progenitores comprometidos miogénicos (Myf5Cre+/Pitx2loxp / loxp). Nuestros análisis revelaron que la inacti- vación de Pitx2 en los precursores de Pax3+ conduce a una miogénesis deteriorada, mientras que la pérdida de Pitx2 en las células miogénicas Myf5+ tiene un impacto en el número de células madre satélite musculares que alcanzan su nicho en el músculo adulto con graves consecuencias en la regeneración muscular.During embryonic development, transitory structures called somites give rise to an epithelial dermomyotome, the source of skeletal muscles precursors of the trunk. Multipotent muscle progenitor cells (MPCs) that express Pax3 arise from the dermomyotome and acquire their definitive identity via the myogenic regulatory factors (MRFs) Myf5, Mrf4, and MyoD. Moreover, the muscle stem cells (satellite cells) of the body and limbs also arise from somites, in common with the muscle that they are associated with. Previous evidences have revealed that the transcription factor Pitx2 might be a player within the molecular pathways controlling somite-derived muscle progenitors’ fate. However, the hierarchical position occupied by Pitx2 within the genetic cascade that control somite-derived myogenesis remain unsolved. To get insight into this issue, we have differentially generated two conditional Pitx2 mutant mice to specifically inactivate Pitx2 in multipotent Pax3+ muscle progenitors (Pax3Cre+/Pitx2loxp/loxp mice) and in myogenic committed progenitors (Myf5Cre+/Pitx2loxp/loxp mice). Our analyses revealed that Pitx2 inactivation in Pax3+ precursors lead to impaired myogenesis while the loss of Pitx2 in Myf5+ myogenic cells have an impact in the number of muscle satellite stem cells that reach their niche in the adult muscle with severe consequences in muscle regeneration.Tesis Univ. Jaén. Departamento de Biología Experimenta

Muscle Satellite Cell Heterogeneity: Does Embryonic Origin Matter?

Funding This work was partially supported by grants PID2019-10 7492GB-I00 (Ministerio de Ciencia e Innovacion, Spain) and 06030050P1 PROY I + D + I. FEDER ANDALUCIA (Junta de Andalucia, Spain). LR-O is recipient of a FPU grant (FPU17/03843).Muscle regeneration is an important homeostatic process of adult skeletal muscle that recapitulates many aspects of embryonic myogenesis. Satellite cells (SCs) are the main muscle stem cells responsible for skeletal muscle regeneration. SCs reside between the myofiber basal lamina and the sarcolemma of the muscle fiber in a quiescent state. However, in response to physiological stimuli or muscle trauma, activated SCs transiently re-enter the cell cycle to proliferate and subsequently exit the cell cycle to differentiate or self-renew. Recent evidence has stated that SCs display functional heterogeneity linked to regenerative capability with an undifferentiated subgroup that is more prone to self-renewal, as well as committed progenitor cells ready for myogenic differentiation. Several lineage tracing studies suggest that such SC heterogeneity could be associated with different embryonic origins. Although it has been established that SCs are derived from the central dermomyotome, how a small subpopulation of the SCs progeny maintain their stem cell identity while most progress through the myogenic program to construct myofibers is not well understood. In this review, we synthesize the works supporting the different developmental origins of SCs as the genesis of their functional heterogeneity.Spanish Government PID2019-10 7492GB-I00FEDER ANDALUCIA (Junta de Andalucia, Spain) 06030050P1 PROY I + D + ISpanish Government FPU17/0384

Pitx2 Differentially Regulates the Distinct Phases of Myogenic Program and Delineates Satellite Cell Lineages During Muscle Development

The knowledge of the molecular mechanisms that regulate embryonic myogenesis from early myogenic progenitors to myoblasts, as well as the emergence of adult satellite stem cells (SCs) during development, are key concepts to understanding the genesis and regenerative abilities of the skeletal muscle. Several previous pieces of evidence have revealed that the transcription factor Pitx2 might be a player within the molecular pathways controlling somite-derived muscle progenitors’ fate and SC behavior. However, the role exerted by Pitx2 in the progression from myogenic progenitors to myoblasts including SC precursors remains unsolved. Here, we show that Pitx2 inactivation in uncommitted early myogenic precursors diminished cell proliferation and migration leading to muscle hypotrophy and a low number of SCs with decreased myogenic differentiation potential. However, the loss of Pitx2 in committed myogenic precursors gave rise to normal muscles with standard amounts of SCs exhibiting high levels of Pax7 expression. This SC population includes few MYF5+ SC-primed but increased amount of less proliferative miR-106b+cells, and display myogenic differentiation defects failing to undergo proper muscle regeneration. Overall our results demonstrate that Pitx2 is required in uncommitted myogenic progenitors but it is dispensable in committed precursors for proper myogenesis and reveal a role for this transcription factor in the generation of diverse SC subpopulations.BFU2015-67131 (Spanish Ministery of Economy and Competitiveness)PID2019- 107492GB-100 (Spanish Ministry of Science and Innovation

Regulation of Epicardial Cell Fate during Cardiac Development and Disease: An Overview

This work was partially supported by grants BFU2015-67131 (Spanish Ministry of Economy and Competitiveness) and PID2019-107492GB-100 (Spanish Ministry of Science and Innovation).The epicardium is the outermost cell layer in the vertebrate heart that originates during development from mesothelial precursors located in the proepicardium and septum transversum. The epicardial layer plays a key role during cardiogenesis since a subset of epicardial-derived cells (EPDCs) undergo an epithelial–mesenchymal transition (EMT); migrate into the myocardium; and differentiate into distinct cell types, such as coronary vascular smooth muscle cells, cardiac fibroblasts, endothelial cells, and presumably a subpopulation of cardiomyocytes, thus contributing to complete heart formation. Furthermore, the epicardium is a source of paracrine factors that support cardiac growth at the last stages of cardiogenesis. Although several lineage trace studies have provided some evidence about epicardial cell fate determination, the molecular mechanisms underlying epicardial cell heterogeneity remain not fully understood. Interestingly, seminal works during the last decade have pointed out that the adult epicardium is reactivated after heart damage, re-expressing some embryonic genes and contributing to cardiac remodeling. Therefore, the epicardium has been proposed as a potential target in the treatment of cardiovascular disease. In this review, we summarize the previous knowledge regarding the regulation of epicardial cell contribution during development and the control of epicardial reactivation in cardiac repair after damage.Spanish Government BFU2015-67131 PID2019-107492GB-10

MiRNAs and Muscle Regeneration: Therapeutic Targets in Duchenne Muscular Dystrophy

This research was funded by Duchenne Parent Project Espana grants 2016, 2018 and 2019.microRNAs (miRNAs) are small non-coding RNAs required for the post-transcriptional control of gene expression. MicroRNAs play a critical role in modulating muscle regeneration and stem cell behavior. Muscle regeneration is affected in muscular dystrophies, and a critical point for the development of effective strategies for treating muscle disorders is optimizing approaches to target muscle stem cells in order to increase the ability to regenerate lost tissue. Within this framework, miRNAs are emerging as implicated in muscle stem cell response in neuromuscular disorders and new methodologies to regulate the expression of key microRNAs are coming up. In this review, we summarize recent advances highlighting the potential of miRNAs to be used in conjunction with gene replacement therapies, in order to improve muscle regeneration in the context of Duchenne Muscular Dystrophy (DMD).Duchenne Parent Project Espana grant 2016Duchenne Parent Project Espana grant 2018Duchenne Parent Project Espana grant 201

Understanding Epicardial Cell Heterogeneity during Cardiogenesis and Heart Regeneration

The outermost layer of the heart, the epicardium, is an essential cell population that contributes, through epithelial-to-mesenchymal transition (EMT), to the formation of different cell types and provides paracrine signals to the developing heart. Despite its quiescent state during adulthood, the adult epicardium reactivates and recapitulates many aspects of embryonic cardiogenesis in response to cardiac injury, thereby supporting cardiac tissue remodeling. Thus, the epicardium has been considered a crucial source of cell progenitors that offers an important contribution to cardiac development and injured hearts. Although several studies have provided evidence regarding cell fate determination in the epicardium, to date, it is unclear whether epicardium-derived cells (EPDCs) come from specific, and predetermined, epicardial cell subpopulations or if they are derived from a common progenitor. In recent years, different approaches have been used to study cell heterogeneity within the epicardial layer using different experimental models. However, the data generated are still insufficient with respect to revealing the complexity of this epithelial layer. In this review, we summarize the previous works documenting the cellular composition, molecular signatures, and diversity within the developing and adult epicardium