Numerous stem cell niches are present in the different tissues and organs of the adult human body. Among these tissues, dental pulp, entrapped within the ‘sealed niche’ of the pulp chamber, is an extremely rich site for collecting stem cells. In this study, we demonstrate that the isolation of human dental pulp stem cells by the explants culture method (hD-DPSCs) allows the recovery of a population of dental mesenchymal stem cells that exhibit an elevated proliferation potential. Moreover, we highlight that hD-DPSCs are not only capable of differentiating into osteoblasts and chondrocytes but are also able to switch their genetic programme when co-cultured with murine myoblasts. High levels of MyoD expression were detected, indicating that muscle-specific genes in dental pulp cells can be turned on through myogenic fusion, confirming thus their multipotency. A perivascular niche may be the potential source of hD-DPSCs, as suggested by the consistent Ca2+ release from these cells in response to endothelin-1 (ET-1) treatment, which is also able to significantly increase cell proliferation. Moreover, response to ET-1 has been found to be superior in hD-DPSCs than in DPSCs, probably due to the isolation method that promotes release of stem/progenitor cells from perivascular structures. The ability to isolate, expand and direct the differentiation of hD-DPSCs into several lineages, mainly towards myogenesis, offers an opportunity for the study of events associated with cell commitment and differentiation. Therefore, hD-DPSCs display enhanced differentiation abilities when compared to DPSCs, and this might be of relevance for their use in therapy.

Arg8-vasopressin (AVP) promotes the differentiation of myogenic cell lines and mouse primary satellite cells by mechanisms involving the transcriptional activation of myogenic bHLH regulatory factors and myocyte enhancer factor 2 (MEF2). We here report that AVP treatment of L6 cells results in the activation of calcineurin-dependent differentiation, increased expression of MEF2 and GATA2, and nuclear translocation of the calcineurin target NFATc1. Interaction of these three factors occurs at MEF2 sites of muscle specific genes. The different kinetics of AVP-dependent expression of early (myogenin) and late (MCK) muscle-specific genes correlate with different acetylation levels of histones at their MEF2 sites. The cooperative role of calcineurin and Ca2+/calmodulin-dependent kinase (CaMK) in AVP-dependent differentiation is demonstrated by the effect of inhibitors of the two pathways. We show here, for the first time, that AVP, a "novel" myogenesis promoting factor, activates both the calcineurin and the CaMK pathways, whose combined activation leads to the formation of multifactor complexes and is required for the full expression of the differentiated phenotype. Although MEF2-NFATc1 complexes appear to regulate the expression of an early muscle-specific gene product (myogenin), the activation of late muscle-specific gene expression (MCK) involves the formation of complexes including GATA2.

NSAIDs have a beneficial effect on mdx muscle morphology, pointing to a crucial role of inflammation in the progression of DMD.

Conflicting data have been reported on cyclooxygenase (COX)-1 and COX-2 expression and activity in striated muscles, including skeletal muscles and myocardium, in particular it is still unclear whether muscle cells are able to produce prostaglandins (PGs). We characterized the expression and enzymatic activity of COX-1 and COX-2 in the skeletal muscles and in the myocardium of mice, rats and humans. By RT-PCR, COX-1 and COX-2 mRNAs were observed in homogenates of mouse and rat hearts, and in different types of skeletal muscles from all different species. By Western blotting, COX-1 and -2 proteins were detected in skeletal muscles and hearts from rodents, as well as in skeletal muscles from humans. Immunoperoxidase stains showed that COX-1 and -2 were diffusely expressed in the myocytes of different muscles and in the myocardiocytes from all different species. In the presence of arachidonic acid, which is the COX enzymatic substrate, isolated skeletal muscle and heart samples from rodents released predominantly PGE(2). The biosynthesis of PGE(2) was reduced between 50 and 80% (P < 0.05 vs. vehicle) in the presence of either COX-1- or COX-2-selective blockers, demonstrating that both isoforms are enzymatically active. Exogenous PGE(2) added to isolated skeletal muscle preparations from rodents did not affect contraction, whereas it significantly fastened relaxation of a slow type muscle, such as soleus. In conclusion, COX-1 and COX-2 are expressed and enzymatically active in myocytes of skeletal muscles and hearts of rodents and humans. PGE(2) appears to be the main product of COX activity in striated muscles.

The neurohypophyseal nonapeptide Arg8 vasopressin (AVP) promotes differentiation of cultured L6 and L5 myogenic cell lines and mouse primary satellite cells. Here, we investigated the molecular mechanism involved in the induction of the myogenic program by AVP. In L6 cells, AVP treatment rapidly induces Myf-5, myogenin, and myocyte enhancer factor 2 (MEF2) mRNAs, without affecting the expression of known myogenic growth factors such as IGF-I, IGF-II, or their receptors. In the presence of cycloheximide, AVP up-regulates the expression of MEF2, but not of myogenin, indicating that the synthesis of a protein intermediate is not necessary for MEF2 induction. Notably, AVP treatment activates a calcium/calmodulin kinase signaling pathway that induces cytosolic compartmentalization of the histone deacetylase 4, a mechanism related to the transcriptional activation of MEF2. The activity of chloramphenicol acetyltransferase reporter constructs carrying the Myo184 and Myo84 fragments of the myogenin promoter is also induced by AVP. Mutation of the MEF2 site completely abolishes the response to AVP, whereas deletion of the E1 site present in pMyo84 does not impair this response. Together, these results show that AVP induces myogenic differentiation through the transcriptional activation of MEF2, a mechanism that is critical for myogenesis.