Comparison of MSCs and Muse cells: the possible use for healthspan optimization.

The exploration for safe, effective intervention strategies to improve longevity and aging-related diseases is attracting attention to prolong the healthy lifespan. Since aging is based on cellular changes, including telomere attrition, DNA damage, and mitochondrial dysfunction, therapies related to stem cells are expected to be a rational strategy for solving aging problems at the cellular level. Mesenchymal stem cells (MSCs) are an easily accessible, safe candidate, as they supply paracrine factors and extracellular vesicles to deliver pleiotropic effects for aging tissues. Multilineage-differentiating stress enduring (Muse) cells represent endogenous, reparative macrophage-like/pluripotent-like stem cells distributed in various tissues, including extraembryonic tissues such as the umbilical cord, and are also found in MSCs as a small percentage of the total population. Muse cell characteristics are different from those of MSCs. Intravenously injected Muse cells sharply sense the universal damage signal sphingosine-1-P and selectively migrate to damaged tissue rather than being trapped in the lung, phagocytose damaged/apoptotic cells in the tissue and directly differentiate into the same cell type. Muse cells then repair the three dimensional structure of the tissue by replacing multiple tissue component with healthy cells through pluripotent-like differentiation. Clinical trials have shown that HLA-mismatched donor Muse cells escape immune rejection and survive in the recipient tissue for an extended period without immunosuppressant treatment. Therefore, the pleiotropic bystander effects of Muse cells are more potent than those of MSCs. Due to heterogeneity, the properties of MSCs are still not fully understood; they have limited differentiation ability into osteogenic, chondrogenic, and adipogenic cells, and the main biological action in vivo is bystander effects. Muse cells are key, not only to the medical benefits of MSCs, but also to their potential use in anti-aging therapy. Enriching and purifying Muse cells will significantly enhance the therapeutic effect of MSCs, leading to further expansion of the use of MSCs. This review discusses the fundamental differences between MSCs and Muse cells and their potential applications in anti-aging therapy.