Although sphingosine 1-phosphate (S1P) has been considered a potent regulator of skeletal muscle biology, acting as a physiological anti-mitogenic and prodifferentiating agent, its downstream effectors are poorly known. In the present study, we provide experimental evidence for a novel mechanism by which S1P regulates skeletal muscle differentiation through the regulation of gap junctional protein connexin (Cx) 43. Indeed, the treatment with S1P greatly enhanced Cx43 expression and gap junctional intercellular communication during the early phases of myoblast differentiation, whereas the down-regulation of Cx43 by transfection with short interfering RNA blocked myogenesis elicited by S1P. Moreover, calcium and p38 MAPK-dependent pathways were required for S1P-induced increase in Cx43 expression. Interestingly, enforced expression of mutated Cx43^Δ130–136reduced gap junction communication and totally inhibited S1P-induced expression of the myogenic markers, myogenin, myosin heavy chain, caveolin-3, and myotube formation. Notably, in S1P-stimulated myoblasts, endogenous or wild-type Cx43 protein, but not the mutated form, coimmunoprecipitated and colocalized with F-actin and cortactin in a p38 MAPK-dependent manner. These data, together with the known role of actin remodeling in cell differentiation, strongly support the important contribution of gap junctional communication, Cx43 expression and Cx43/cytoskeleton interaction in skeletal myogenesis elicited by S1P.

Tissue damage, irrespective from the underlying etiology, destroys tissue structure and, eventually, function. In attempt to achieve a morpho-functional recover of the damaged tissue, reparative/regenerative processes start in those tissues endowed with regenerative potential, mainly mediated by activated resident stem cells. These cells reside in a specialized niche that includes different components, cells and surrounding extracellular matrix (ECM), which, reciprocally interacting with stem cells, direct their cell behavior. Evidence suggests that ECM stiffness represents an instructive signal for the activation of stem cells sensing it by various mechanosensors, able to transduce mechanical cues into gene/protein expression responses. The actin cytoskeleton network dynamic acts as key mechanotransducer of ECM signal. The identification of signaling pathways influencing stem cell mechanobiology may offer therapeutic perspectives in the regenerative medicine field. Sphingosine 1-phosphate (S1P)/S1P receptor (S1PR) signaling, acting as modulator of ECM, ECM-cytoskeleton linking proteins and cytoskeleton dynamics appears a promising candidate. This review focuses on the current knowledge on the contribution of S1P/S1PR signaling in the control of mechanotransduction in stem/progenitor cells. The potential contribution of S1P/S1PR signaling in the mechanobiology of skeletal muscle stem cells will be argued based on the intriguing findings on S1P/S1PR action in this mechanically dynamic tissue.

Skeletal muscle regeneration is severely compromised in the case of extended damage. The current challenge is to find factors capable of limiting muscle degeneration and/or potentiating the inherent regenerative program mediated by a specific type of myoblastic cells, the satellite cells. Recent studies from our groups and others have shown that the bioactive lipid, sphingosine 1-phosphate (S1P), promotes myoblast differentiation and exerts a trophic action on denervated skeletal muscle fibres. In the present study, we examined the effects of S1P on eccentric contraction (EC)-injured extensor digitorum longus muscle fibres and resident satellite cells. After EC, skeletal muscle showed evidence of structural and biochemical damage along with significant electrophysiological changes, i.e. reduced plasma membrane resistance and resting membrane potential and altered Na⁺ and Ca²⁺ current amplitude and kinetics. Treatment with exogenous S1P attenuated the EC-induced tissue damage, protecting skeletal muscle fibre from apoptosis, preserving satellite cell viability and affecting extracellular matrix remodelling, through the up-regulation of matrix metalloproteinase 9 (MMP-9) expression. S1P also promoted satellite cell renewal and differentiation in the damaged muscle. Notably, EC was associated with the activation of sphingosine kinase 1 (SphK1) and with increased endogenous S1P synthesis, further stressing the relevance of S1P in skeletal muscle protection and repair/regeneration. In line with this, the treatment with a selective SphK1 inhibitor during EC, caused an exacerbation of the muscle damage and attenuated MMP-9 expression. Together, these findings are in favour for a role of S1P in skeletal muscle healing and offer new clues for the identification of novel therapeutic approaches to counteract skeletal muscle damage and disease.

Surface Plasmon Resonance (SPR) has proven to be one of the most effective technologies in terms of specificity, affinity, and determination of kinetic parameters for evaluating interactions between macromolecules. The focus of this tutorial is to give an overview of the recent advances and applications of SPR biosensors in biomedicine that are presented emphasizing the potentiality for the detection of very low abundant compounds, which, in recent years, have assumed great importance for prevention and early diagnosis of various diseases in biomedicine. The real-time detection of important biomarkers such as tumor markers, viruses, and toxins but also of compounds of interest such as drugs and hormones allows point-of-care analysis and monitoring of disease progression quickly and in a less invasive manner. Over the past years, several technical innovations have been introduced to SPR devices, which have gone through a process of miniaturization, portability, flexibility, and cost reduction. These characteristics are in line with the advantages of SPR biosensors over other biosensing techniques, i.e., to be label-free detection systems and their capacity to observe in real-time the interactions between a variety of molecules of interest at the metal surface. Recent advances in SPR sensor technology, such as LSPR, SPRi, and SPRM, attempted to improve the sensitivity and performance of molecule detection.

Sphingosine-1-phosphate (S1P) is a bioactive lipid that is characterized by a peculiar mechanism of action. In fact, S1P, which is produced inside the cell, can act as an intracellular mediator, whereas after its export outside the cell, it can act as ligand of specific G-protein coupled receptors, which were initially named endothelial differentiation gene (Edg) and eventually renamed sphingosine 1-phosphate receptors (S1PRs). Among the five S1PR subtypes, S1PR1, S1PR2 and S1PR3 isoforms show broad tissue gene expression, while S1PR4 is primarily expressed in immune system cells, and S1PR5 is expressed in the central nervous system. There is accumulating evidence for the important role of S1P as a mediator of many processes, such as angiogenesis, carcinogenesis and immunity, and, ultimately, fibrosis. After a tissue injury, the imbalance between the production of extracellular matrix (ECM) and its degradation, which occurs due to chronic inflammatory conditions, leads to an accumulation of ECM and, consequential, organ dysfunction. In these pathological conditions, many factors have been described to act as pro- and anti-fibrotic agents, including S1P. This bioactive lipid exhibits both pro- and anti-fibrotic effects, depending on its site of action. In this review, after a brief description of sphingolipid metabolism and signaling, we emphasize the involvement of the S1P/S1PR axis and the downstream signaling pathways in the development of fibrosis. The current knowledge of the therapeutic potential of S1PR subtype modulators in the treatment of the cardiac functions and fibrinogenesis are also examined.