Single-Cell Atlas Reveals Fatty Acid Metabolites Regulate the Functional Heterogeneity of Mesenchymal Stem Cells

Unveiling the functional heterogeneity of cytokine-primed human umbilical cord mesenchymal stem cells through single-cell RNA sequencing

BACKGROUND

Mesenchymal stem cells (MSCs) hold immense promise for use in immunomodulation and regenerative medicine. However, their inherent heterogeneity makes it difficult to achieve optimal therapeutic outcomes for a specific clinical disease. Primed MSCs containing a certain cytokine can enhance their particular functions, thereby increasing their therapeutic potential for related diseases. Therefore, understanding the characteristic changes and underlying mechanisms of MSCs primed by various cytokines is highly important.

RESULTS

In this study, we aimed to reveal the cellular heterogeneity, functional subpopulations, and molecular mechanisms of MSCs primed with IFN-γ, TNF-α, IL-4, IL-6, IL-15, and IL-17 using single-cell RNA sequencing (scRNA-seq). Our results demonstrated that cytokine priming minimized the heterogeneity of the MSC transcriptome, while the expression of MSC surface markers exhibited only slight changes. Notably, compared to IL-6, IL-15, and IL-17; IFN-γ, TNF-α, and IL-4 priming, which stimulated a significantly greater number of differentially expressed genes (DEGs). Functional analysis, which included Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses, indicated that IFN-γ, TNF-α, and IL-4-primed hUC-MSCs are involved in interferon-mediated immune-related processes, leukocyte migration, chemotaxis potential, and extracellular matrix and cell adhesion, respectively. Moreover, an investigation of various biological function scores demonstrated that IFN-γ-primed hUC-MSCs exhibit strong immunomodulatory ability, TNF-α-primed hUC-MSCs exhibit high chemotaxis potential, and IL-4-primed hUC-MSCs express elevated amounts of collagen. Finally, we observed that cytokine priming alters the distribution of functional subpopulations of MSCs, and these subpopulations exhibit various potential biological functions. Taken together, our study revealed the distinct regulatory effects of cytokine priming on MSC heterogeneity, biological function, and functional subpopulations at the single-cell level.

CONCLUSIONS

These findings contribute to a comprehensive understanding of the inflammatory priming of MSCs, paving the way for their precise treatment in clinical applications.

Lipids and the cancer stemness regulatory system in acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous disease of impaired myeloid differentiation and a caricature of normal hematopoiesis. Leukemic stem cells (LSCs) are responsible for long-term clonal propagation in AML just as hematopoietic stem cells (HSCs) sustain lifelong hematopoiesis. LSCs are often resistant to standard chemotherapy and are responsible for clinical relapse. Although AML is highly heterogeneous, determinants of stemness are prognostic for AML patient survival and can predict AML drug sensitivity. Therefore, one way to overcome challenges preventing efficacious treatment outcomes is to target LSC stemness. Metabolomic and lipidomic studies of serum and cells from AML patients are emerging to complement genomic, transcriptomic, epigenetic, and proteomic data sets to characterize and stratify AML. Recent studies have shown the value of fractionating LSCs versus blasts when characterizing metabolic pathways and implicate the importance of lipid balance to LSCs function. As more extensive metabolic studies coupled to functional in vivo assays are conducted on highly purified HSCs, bulk AML, and LSCs, the similarities and differences in lipid homeostasis in stem-like versus more mature AML subtypes as well as from normal HSCs are emerging. Here, we discuss the latest findings from studies of lipid function in LSCs, with a focus on sphingolipids (SLs) as stemness/lineage fate mediators in AML, and the balance of fatty acid anabolism and catabolism fueling metabolic flexibility and drug resistance in AML. We also discuss how designing successful strategies to target lipid vulnerabilities and improve AML patient survival should take into consideration the hierarchical nature of AML.

Sodium butyrate inhibits osteogenesis in human periodontal ligament stem cells by suppressing smad1 expression

Background

Butyrate is a major subgingival microbial metabolite that is closely related to periodontal disease. It affects the proliferation and differentiation of mesenchymal stem cells. However, the mechanisms by which butyrate affects the osteogenic differentiation of periodontal ligament stem cells (PDLSCs) remain unclear. Here, we investigated the effect of sodium butyrate (NaB) on the osteogenic differentiation of human PDLSCs.

Methods

PDLSCs were isolated from human periodontal ligaments and treated with various concentrations of NaB in vitro. The cell counting kit-8 assay and flow cytometric analysis were used to assess cell viability. The osteogenic differentiation capabilities of PDLSCs were evaluated using the alkaline phosphatase activity assay, alizarin red staining, RT-PCR, western blotting and in vivo transplantation.

Results

NaB decreased PDLSC proliferation and induced apoptosis in a dose- and time-depend manner. Additionally, 1 mM NaB reduced alkaline phosphatase activity, mineralization ability, and the expression of osteogenic differentiation-related genes and proteins. Treatment with a free fatty acids receptor 2 (FFAR2) antagonist and agonist indicated that NaB inhibited the osteogenic differentiation capacity of PDLSCs by affecting the expression of Smad1.

Conclusion

Our findings suggest that NaB inhibits the osteogenic differentiation of PDLSCs by activating FFAR2 and decreasing the expression of Smad1.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-022-02255-6.

Resident Fibroblast MKL1 Is Sufficient to Drive Pro-fibrogenic Response in Mice

Fibrosis is an evolutionarily conserved pathophysiological process serving bifurcated purposes. On the one hand, fibrosis is essential for wound healing and contributes to the preservation of organ function. On the other hand, aberrant fibrogenic response may lead to tissue remodeling and precipitate organ failure. Recently lineage tracing studies have shown that resident fibroblasts are the primary mediator of fibrosis taking place in key organs such as the heart, the lungs, and the kidneys. Megakaryocytic leukemia 1 (MKL1) is transcriptional regulator involved in tissue fibrosis. Here we generated resident fibroblast conditional MKL1 knockout (CKO) mice by crossing the Mkl1^f/f mice to the Col1a2-Cre^ERT2 mice. Models of cardiac fibrosis, pulmonary fibrosis, and renal fibrosis were reproduced in the CKO mice and wild type (WT) littermates. Compared to the WT mice, the CKO mice displayed across-the-board attenuation of fibrosis in different models. Our data cement the pivotal role MKL1 plays in tissue fibrosis but point to the cellular origin from which MKL1 exerts its pro-fibrogenic effects.

Single-cell Transcriptomic Analysis Reveals the Cellular Heterogeneity of Mesenchymal Stem Cells

Ex vivo-expanded mesenchymal stem cells (MSCs) have been demonstrated to be a heterogeneous mixture of cells exhibiting varying proliferative, multipotential, and immunomodulatory capacities. However, the exact characteristics of MSCs remain largely unknown. By single-cell RNA sequencing of 61,296 MSCs derived from bone marrow and Wharton’s jelly, we revealed five distinct subpopulations. The developmental trajectory of these five MSC subpopulations was mapped, revealing a differentiation path from stem-like active proliferative cells (APCs) to multipotent progenitor cells, followed by branching into two paths: 1) unipotent preadipocytes or 2) bipotent prechondro-osteoblasts that were subsequently differentiated into unipotent prechondrocytes. The stem-like APCs, expressing the perivascular mesodermal progenitor markers CSPG4/MCAM/NES, uniquely exhibited strong proliferation and stemness signatures. Remarkably, the prechondrocyte subpopulation specifically expressed immunomodulatory genes and was able to suppress activated CD3⁺ T cell proliferation in vitro, supporting the role of this population in immunoregulation. In summary, our analysis mapped the heterogeneous subpopulations of MSCs and identified two subpopulations with potential functions in self-renewal and immunoregulation. Our findings advance the definition of MSCs by identifying the specific functions of their heterogeneous cellular composition, allowing for more specific and effective MSC application through the purification of their functional subpopulations.