Protein histidine methylation is a rare post-translational modification of unknown biochemical importance. In vertebrates, only a few methylhistidine-containing proteins have been reported, including β-actin as an essential example. The evolutionary conserved methylation of β-actin H73 is catalyzed by an as yet unknown histidine N-methyltransferase. We report here that the protein SETD3 is the actin-specific histidine N-methyltransferase. In vitro, recombinant rat and human SETD3 methylated β-actin at H73. Knocking-out SETD3 in both human HAP1 cells and in Drosophila melanogaster resulted in the absence of methylation at β-actin H73 in vivo, whereas β-actin from wildtype cells or flies was > 90% methylated. As a consequence, we show that Setd3-deficient HAP1 cells have less cellular F-actin and an increased glycolytic phenotype. In conclusion, by identifying SETD3 as the actin-specific histidine N-methyltransferase, our work pioneers new research into the possible role of this modification in health and disease and questions the substrate specificity of SET-domain-containing enzymes.

The proper functioning of tissues and organs depends on their ability to self-renew and repair. Some of the tissues, like epithelia, renew almost constantly while in the others this process is induced by injury or diseases. The stem or progenitor cells responsible for tissue homeostasis have been identified in many organs. Some of them, such as hematopoietic or intestinal epithelium stem cells, are multipotent and can differentiate into various cell types. Others are unipotent. The skeletal muscle tissue does not self-renew spontaneously, however, it presents unique ability to regenerate in response to the injury or disease. Its repair almost exclusively relies on unipotent satellite cells. However, multiple lines of evidence document that some progenitor cells present in the muscle can be supportive for skeletal muscle regeneration. Here, we summarize the current knowledge on the complicated landscape of stem and progenitor cells that exist in skeletal muscle and support its regeneration. We compare the cells from two model organisms, i.e., mouse and human, documenting their similarities and differences and indicating methods to test their ability to undergo myogenic differentiation.

Background: The skeletal muscle reconstruction occurs thanks to unipotent stem cells, i.e., satellite cells. The satellite cells remain quiescent and localized between myofiber sarcolemma and basal lamina. They are activated in response to muscle injury, proliferate, differentiate into myoblasts, and recreate myofibers. The stem and progenitor cells support skeletal muscle regeneration, which could be disturbed by extensive damage, sarcopenia, cachexia, or genetic diseases like dystrophy. Many lines of evidence showed that the level of oxygen regulates the course of cell proliferation and differentiation. Methods: In the present study, we analyzed hypoxia impact on human and pig bone marrow-derived mesenchymal stromal cell (MSC) and mouse myoblast proliferation, differentiation, and fusion. Moreover, the influence of the transplantation of human bone marrow-derived MSCs cultured under hypoxic conditions on skeletal muscle regeneration was studied. Results: We showed that bone marrow-derived MSCs increased VEGF expression and improved myogenesis under hypoxic conditions in vitro. Transplantation of hypoxia preconditioned bone marrow-derived MSCs into injured muscles resulted in the improved cell engraftment and formation of new vessels. Conclusions: We suggested that SDF-1 and VEGF secreted by hypoxia preconditioned bone marrow-derived MSCs played an essential role in cell engraftment and angiogenesis. Importantly, hypoxia preconditioned bone marrow-derived MSCs more efficiently engrafted injured muscles; however, they did not undergo myogenic differentiation.

β-escin is a mixture of triterpene saponins isolated from the horse chestnut seeds (Aesculus hippocastanum L.). The anti-edematous, anti-inflammatory and venotonic properties of β-escin have been the most extensively clinically investigated effects of this plant-based drug and randomized controlled trials have proved the efficacy of β-escin for the treatment of chronic venous insufficiency. However, despite the clinical recognition of the drug its pharmacological mechanism of action still remains largely elusive. To determine the cellular and molecular basis for the therapeutic effectiveness of β-escin we performed discovery and targeted proteomic analyses and in vitro evaluation of cellular and molecular responses in human endothelial cells under inflammatory conditions. Our results demonstrate that in endothelial cells β-escin potently induces cholesterol synthesis which is rapidly followed with marked fall in actin cytoskeleton integrity. The concomitant changes in cell functioning result in a significantly diminished responses to TNF-α stimulation. These include reduced migration, alleviated endothelial monolayer permeability, and inhibition of NFκB signal transduction leading to down-expression of TNF-α—induced effector proteins. Moreover, the study provides evidence for novel therapeutic potential of β-escin beyond the current vascular indications.