Single-cell RNA-seq analysis of Mesp1-induced skeletal myogenic development

Advancing skeletal health and disease research with single-cell RNA sequencing

Orthopedic conditions have emerged as global health concerns, impacting approximately 1.7 billion individuals worldwide. However, the limited understanding of the underlying pathological processes at the cellular and molecular level has hindered the development of comprehensive treatment options for these disorders. The advent of single-cell RNA sequencing (scRNA-seq) technology has revolutionized biomedical research by enabling detailed examination of cellular and molecular diversity. Nevertheless, investigating mechanisms at the single-cell level in highly mineralized skeletal tissue poses technical challenges. In this comprehensive review, we present a streamlined approach to obtaining high-quality single cells from skeletal tissue and provide an overview of existing scRNA-seq technologies employed in skeletal studies along with practical bioinformatic analysis pipelines. By utilizing these methodologies, crucial insights into the developmental dynamics, maintenance of homeostasis, and pathological processes involved in spine, joint, bone, muscle, and tendon disorders have been uncovered. Specifically focusing on the joint diseases of degenerative disc disease, osteoarthritis, and rheumatoid arthritis using scRNA-seq has provided novel insights and a more nuanced comprehension. These findings have paved the way for discovering novel therapeutic targets that offer potential benefits to patients suffering from diverse skeletal disorders.

Producing Engraftable Skeletal Myogenic Progenitors from Pluripotent Stem Cells via Teratoma Formation

Generating engraftable skeletal muscle progenitor cells is a promising cell therapy approach to treating degenerating muscle diseases. Pluripotent stem cell (PSC) is an ideal cell source for cell therapy because of its unlimited proliferative capability and potential to differentiate into multiple lineages. Approaches such as ectopic overexpression of myogenic transcription factors and growth factors-directed monolayer differentiation, while able to differentiate PSCs into the skeletal myogenic lineage in vitro, are limited in producing muscle cells that reliably engraft upon transplantation. Here we present a novel method to differentiate mouse PSCs into skeletal myogenic progenitors without genetic modification or monolayer culture. We make use of forming a teratoma, in which skeletal myogenic progenitors can be routinely obtained. We first inject mouse PSCs into the limb muscle of an immuno-compromised mouse. Within 3-4 weeks, α7-integrin+ VCAM-1+ skeletal myogenic progenitors are purified by fluorescent-activated cell sorting. We further transplant these teratoma-derived skeletal myogenic progenitors into dystrophin-deficient mice to assess engraftment efficiency. This teratoma formation strategy is capable of generating skeletal myogenic progenitors with high regenerative potency from PSCs without genetic modifications or growth factors supplementation.

Targeting the histone demethylase LSD1 prevents cardiomyopathy in a mouse model of laminopathy

LMNA mutations in patients are responsible for a dilated cardiomyopathy. Molecular mechanisms underlying the origin and development of the pathology are unknown. Herein, using mouse pluripotent embryonic stem cells (ESCs) and a mouse model both harboring the p.H222P Lmna mutation, we found early defects in cardiac differentiation of mutated ESCs and dilatation of mutated embryonic hearts at E13.5, pointing to a developmental origin of the disease. Using mouse ESCs, we demonstrated that cardiac differentiation of LmnaH222P/+ was impaired at the mesodermal stage. Expression of Mesp1, a mesodermal cardiogenic gene involved in epithelial-to-mesenchymal transition of epiblast cells, as well as Snai1 and Twist expression, was decreased in LmnaH222P/+ cells compared with WT cells in the course of differentiation. In turn, cardiomyocyte differentiation was impaired. ChIP assay of H3K4me1 in differentiating cells revealed a specific decrease of this histone mark on regulatory regions of Mesp1 and Twist in LmnaH222P/+ cells. Downregulation or inhibition of LSD1 that specifically demethylated H3K4me1 rescued the epigenetic landscape of mesodermal LmnaH222P/+ cells and in turn contraction of cardiomyocytes. Inhibition of LSD1 in pregnant mice or neonatal mice prevented cardiomyopathy in E13.5 LmnaH222P/H222P offspring and adults, respectively. Thus, LSD1 appeared to be a therapeutic target to prevent or cure dilated cardiomyopathy associated with a laminopathy.

Dual TGFβ and Wnt inhibition promotes Mesp1-mediated mouse pluripotent stem cell differentiation into functional cardiomyocytes

Efficient derivation of cardiomyocytes from mouse pluripotent stem cells has proven challenging, and existing approaches rely on expensive supplementation or extensive manipulation. Mesp1 is a transcription factor that regulates cardiovascular specification during embryo development, and its overexpression has been shown to promote cardiogenesis. Here, we utilize a doxycycline-inducible Mesp1-expressing mouse embryonic stem cell system to develop an efficient differentiation protocol to generate functional cardiomyocytes. Our cardiac differentiation method involves transient Mesp1 induction following by subsequent dual inhibition of TGFβ and Wnt signaling pathways using small molecules. We discovered that whereas TGFβ inhibition promoted Mesp1-induced cardiac differentiation, Wnt inhibition was ineffective. Nevertheless, a combined inhibition of both pathways was superior to either inhibition alone in generating cardiomyocytes. These observations suggested a potential interaction between TGFβ and Wnt signaling pathways in the context of Mesp1-induced cardiac differentiation. Using a step-by-step approach, we have further optimized the windows of Mesp1 induction, TGFβ inhibition and Wnt inhibition to yield a maximal cardiomyocyte output - Mesp1 was induced first, followed by dual inhibition of TGFβ and Wnt signaling. Our protocol is capable of producing approximately 50% of cardiomyocytes in 12 days, which is comparable to existing methods, and have the advantages of being technically simple and inexpensive. Moreover, cardiomyocytes thus derived are functional, displaying intrinsic contractile capacity and contraction in response to electric stimulus. Derivation of mouse cardiomyocytes without the use of growth factors or other costly supplementation provides an accessible cell source for future applications.

Integrative Methods and Practical Challenges for Single-Cell Multi-omics

Fast-developing single-cell multimodal omics (scMulti-omics) technologies enable the measurement of multiple modalities, such as DNA methylation, chromatin accessibility, RNA expression, protein abundance, gene perturbation, and spatial information, from the same cell. scMulti-omics can comprehensively explore and identify cell characteristics, while also presenting challenges to the development of computational methods and tools for integrative analyses. Here, we review these integrative methods and summarize the existing tools for studying a variety of scMulti-omics data. The various functionalities and practical challenges in using the available tools in the public domain are explored through several case studies. Finally, we identify remaining challenges and future trends in scMulti-omics modeling and analyses.