Satellite cell-derived TRIM28 is pivotal for mechanical load- and injury-induced myogenesis.

Satellite cells are skeletal muscle stem cells that contribute to postnatal muscle growth, and they endow skeletal muscle with the ability to regenerate after a severe injury. Here we discover that this myogenic potential of satellite cells requires a protein called tripartite motif-containing 28 (TRIM28). Interestingly, different from the role reported in a previous study based on C2C12 myoblasts, multiple lines of both in vitro and in vivo evidence reveal that the myogenic function of TRIM28 is not dependent on changes in the phosphorylation of its serine 473 residue. Moreover, the functions of TRIM28 are not mediated through the regulation of satellite cell proliferation or differentiation. Instead, our findings indicate that TRIM28 regulates the ability of satellite cells to progress through the process of fusion. Specifically, we discover that TRIM28 controls the expression of a fusogenic protein called myomixer and concomitant fusion pore formation. Collectively, the outcomes of this study expose the framework of a novel regulatory pathway that is essential for myogenesis.

The role of satellite cell-derived TRIM28 in mechanical load- and injury-induced myogenesis.

Satellite cells are skeletal muscle stem cells that contribute to postnatal muscle growth, and they endow skeletal muscle with the ability to regenerate after a severe injury. Here we discovered that this myogenic potential of satellite cells requires a protein called tripartite motif-containing 28 (TRIM28). Unexpectedly, multiple lines of both in vitro and in vivo evidence revealed that the myogenic function of TRIM28 is not dependent on changes in the phosphorylation of its serine 473 residue. Moreover, the functions of TRIM28 were not mediated through the regulation of satellite cell proliferation or differentiation. Instead, our findings indicate that TRIM28 regulates the ability of satellite cells to progress through the process of fusion. Specifically, we discovered that TRIM28 controls the expression of a fusogenic protein called myomixer and concomitant fusion pore formation. Collectively, the outcomes of this study expose the framework of a novel regulatory pathway that is essential for myogenesis.

Retinoic Acid Signaling Modulates Recipient Gut Barrier Integrity and Microbiota After Allogeneic Hematopoietic Stem Cell Transplantation in Mice.

Graft-versus-host disease (GVHD) remains a major complication after allogeneic hematopoietic stem cell transplantation (HSCT). An impaired intestinal epithelial barrier is an important component of GVHD pathogenesis. However, contributing host factors that modulate mucosal barrier integrity during GVHD are poorly defined. We hypothesized that vitamin A and retinoic acid (RA) exert positive impacts on maintaining intestinal barrier function after HSCT, thus preventing or dampening GVHD severity. Unexpectedly, we found that exogenous RA increased intestinal permeability of recipient mice after allogeneic HSCT. Serum bacterial endotoxin levels were significantly higher in GVHD mice fed a vitamin A-high (VAH) diet compared to those fed a vitamin A-normal (VAN) diet, indicating a more compromised intestinal barrier function. Furthermore, VAH mice showed more severe lung GVHD with increased donor T cell infiltration in this tissue and died significantly faster than VAN recipients. 16S rRNA sequencing of fecal samples revealed significant differences in the diversity and composition of gut microbiota between VAN and VAH transplant recipients. Collectively, we show that retinoic acid signaling may negatively impact intestinal barrier function during GVHD. Mild vitamin A supplementation is associated with increased lung GVHD and more profound gut dysbiosis. Micronutrients such as vitamin A could modulate complications of allogeneic HSCT, which may be mediated by shaping gut microbiota.