Addolorata Pisconti

Duchenne muscular dystrophy (DMD) is a genetic disorder characterized by muscle wasting, and leading to premature death. The pathogenesis of DMD is complex. It is triggered by loss of the cytoskeletal protein dystrophin, which causes muscle fiber instability and damage, followed by chronic inflammation and fibrotic replacement of damaged muscle tissue. Here we investigated the hypothesis that inhibition of neutrophil elastase, which is increased in dystrophic mice and impairs myogenesis, could provide a therapeutic effect in DMD. While neutrophil elastase inhibition, via the orally bioavailable compound Alvelestat, enhances myogenesis both in vitro and in vivo and reduces muscle damage and fibrosis, it does not produce a significant beneficial effect on the functional outcomes. However, when co- administered with the standard of care Prednisolone, Alvelestat dramatically enhances Prednisolone efficacy in a mouse model of DMD. In key functional tests, the performance of mice co-dosed with Alvelestat and Prednisolone is almost three times better than that of mice treated with Prednisolone alone. Additionally, co-administration of Alvelestat and Prednisolone reduces Prednisolone’s negative effects on muscle mass and resistance to fatigue. These findings are consistent with the finding that Prednisolone induces neutrophil elastase expression in patients affected by DMD. Our data support a beneficial role for neutrophil elastase inhibition in a mouse model of DMD that is also treated with Prednisolone, suggesting that a combinatorial therapy for DMD including a corticosteroid and a neutrophil elastase inhibitor could be trialed in humans. Graphical

The molecular mechanisms underlying the activation of muscle stem cells in response to skeletal muscle injury are complex and only beginning to be elucidated since new tools were developed in the last decade. The immune response to tissue injury, often referred to as sterile inflammation, is a known key contributor to the mechanisms supporting muscle stem cell proliferation and differentiation in the muscle stem cell niche, but it is unclear whether muscle stem cell activation is also affected by the immune response. Here we show that neutrophil elastase, released in abundance during the first two days after muscle injury by infiltrating neutrophils, contributes to muscle stem cell re-entry into the cell cycle and commitment to the myogenic program. When neutrophil elastase is genetically ablated in mice, muscle stem cell activation is impaired, and muscle regeneration is delayed. Additionally, we identified cMet/mTOR and FGFR/ERK1/2 as two pathways activated by elastase in two different in vitro systems, via elastase-mediated cleavage and activation of pro-HGF and via elastase-mediated cleavage of extracellular matrix and release of bioactive FGF, respectively. While chronic exposure to neutrophil elastase impairs myoblast survival and differentiation, ultimately causing muscle regeneration defects, its transient presence in injured muscle during the first 24-48 hours post injury is beneficial and necessary. Thus, our results emphasize the importance of a tight regulation of the immune response for successful muscle regeneration, and provide strong evidence in support of a role for neutrophil elastase that is mainly to promote muscle healing in response to injury. Mechanistically, we highlight a key role for the cross-talk between neutrophils and muscle stem cells in muscle stem cell activation that involves neutrophil-derived elastase-mediated activation of mTOR and ERK1/2 via cMet and FGFR in muscle stem cells. Abstract Figure:

Background: Type II diabetes (T2DM) is one of the most prevalent metabolic disorders, and its multisystemic health consequences are widely known. Due to skeletal muscle's ability to sequester a vast amount of glucose, muscle function and exercise have become a subject of much research into strategies to prevent and treat T2DM. Myokines are bioactive molecules released by muscle during contraction and involved in several biological processes such as metabolism, inflammation and behaviour. Irisin, a recently discovered myokine, has been implicated in a vast array of physiological roles, including the ability to induce fat beiging. Since beige and brown fat both serve important roles in metabolic regulation, irisin's role in the context of T2DM is the subject of ongoing investigations.Methods: We systematically reviewed articles indexed in PubMed, Scopus and Web of Science that were published between 2011 and 2024 and compared circulating irisin levels in patients affected by T2DM and healthy subjects. As part of our systematic review of the literature, we performed meta‐analysis of the data across all included articles, as well as stratified by body mass index (BMI), country of origin and by average irisin concentration in the control group.Results: We discovered great variability across the included studies in the average irisin levels detected, which spanned four orders of magnitude, hence the attempt at reducing variability by stratifying based on average levels in the control group. While the statistical power of our meta‐analysis was decreased by the great variability in reported irisin concentrations, we nonetheless detected a consistent trend of decreased irisin concentration in T2DM patients compared with healthy controls, regardless of BMI, country of origin or average irisin concentration in the control group.Conclusions: With almost 60 articles included, ours is the first extensive systematic review and meta‐analysis of irisin in T2DM, yet a highly statistically significant association between circulating irisin levels and T2DM could not be established due to the great variability of the data across include articles. Nonetheless, we noticed a trend that is independent of BMI, suggesting a direct relationship between T2DM and irisin that is likely not secondary to diabetic sarcopenia. While our work encourages further research into irisin's potential role in T2DM pathogenesis, the reproducibility of irisin detection methods in biological samples should be determined and standardized protocols should be made available to the research and clinical communities.

Background: Type II diabetes (T2DM) is one of the most prevalent metabolic disorders, and its multisystemic health consequences are widely known. Due to skeletal muscle’s ability to sequester a vast amount of glucose, muscle function and exercise have become a subject of much research into strategies to prevent and treat T2DM. Myokines are bioactive molecules released by muscle during contraction and involved in several biological processes such as metabolism, inflammation and behavior. Irisin, a recently discovered myokine, has been implicated in a vast array of physiological roles, including the ability to induce fat beiging. Since beige and brown fat both serve important roles in metabolic regulation, irisin’s role in the context of T2DM is the subject of ongoing investigations. Methods: We systematically reviewed articles indexed in PubMed, Scopus and Web of Science that were published between 2011 and 2024, and compared circulating irisin levels in patients affected by T2DM and healthy subjects. As part of our systematic review of the literature, we performed meta-analysis of the data across all included articles, as well as stratified by body mass index (BMI), country of origin and by average irisin concentration in the control group. Results: We discovered great variability across the included studies in the average irisin levels detected, which spanned four orders of magnitude, hence the attempt at reducing variability by stratifying based on average levels in the control group. While the statistical power of our meta-analysis was decreased by the great variability in reported irisin concentrations, we nonetheless detected a consistent trend of decreased irisin concentration in T2DM patients compared with healthy controls, regardless of BMI, country of origin or average irisin concentration in the control group. Conclusion: With almost 60 articles included, ours is the first extensive systematic review and meta-analysis of irisin in T2DM, yet a highly statistically significant association between circulating irisin levels and T2DM could not be established due to the great variability of the data across include articles. Nonetheless we noticed a trend that is independent of BMI, suggesting a direct relationship between T2DM and irisin that is likely not secondary to diabetic sarcopenia. While our work encourages further research into irisin’s potential role in T2DM pathogenesis, the reproducibility of irisin detection methods in biological samples should be determined and standardized protocols should be made available to the research and clinical communities.

Osteoporosis is the most common age‐related metabolic bone disorder, which is characterized by low bone mass and deterioration in bone architecture, with a propensity to fragility fractures. The best treatment for osteoporosis relies on stimulation of osteoblasts to form new bone and restore bone structure, however, anabolic therapeutics are few and their use is time restricted. Here, we report that Syndecan‐3 increases new bone formation through enhancement of WNT signaling in osteoblasts. Young adult Sdc3 ^−/− mice have low bone volume, reduced bone formation, increased bone marrow adipose tissue, increased bone fragility, and a blunted anabolic bone formation response to mechanical loading. This premature osteoporosis‐like phenotype of Sdc3 ^−/− mice is due to delayed osteoblast maturation and impaired osteoblast function, with contributing increased osteoclast‐mediated bone resorption. Indeed, overexpressing Sdc3 in osteoblasts using the Col1a1 promoter rescues the low bone volume phenotype of the Sdc3 ^−/− mice, and also increases bone volume in WT mice. Mechanistically, SDC3 enhances canonical WNT signaling in osteoblasts through stabilization of Frizzled 1, making SDC3 an attractive target for novel bone anabolic drug development.

Muscle stem cells (MuSCs) are indispensable for muscle regeneration. A multitude of extracellular stimuli direct MuSC fate decisions from quiescent progenitors to differentiated myocytes. The activity of these signals is modulated by coreceptors such as syndecan-3 (SDC3). We investigated the global landscape of SDC3-mediated regulation of myogenesis using a phosphoproteomics approach which revealed, with the precision level of individual phosphosites, the large-scale extent of SDC3-mediated regulation of signal transduction in MuSCs. We then focused on INSR/AKT/mTOR as a key pathway regulated by SDC3 during myogenesis and mechanistically dissected SDC3-mediated inhibition of insulin signaling in MuSCs. SDC3 interacts with INSR limiting insulin signal transduction via AKT/mTOR. Both knockdown of INSR and inhibition of AKT rescue Sdc3 ^-/- MuSC differentiation to wild type levels. Since SDC3 is rapidly downregulated at the onset of differentiation, our study suggests that SDC3 acts a timekeeper to restrain proliferating MuSC response to insulin and prevent premature differentiation.

Background: Extracellular matrix (ECM) remodeling is essential for skeletal muscle development and adaption in response to environmental cues such as exercise and injury. The cell surface proteoglycan syndecan-4 has been reported to be essential for muscle differentiation, but few molecular mechanisms are known. Syndecan-4^–/– mice are unable to regenerate damaged muscle, and display deficient satellite cell activation, proliferation, and differentiation. A reduced myofiber basal lamina has also been reported in syndecan-4^–/– muscle, indicating possible defects in ECM production. To get a better understanding of the underlying molecular mechanisms, we have here investigated the effects of syndecan-4 genetic ablation on molecules involved in ECM remodeling and muscle growth, both under steady state conditions and in response to exercise. Methods: Tibialis anterior (TA) muscles from sedentary and exercised syndecan-4^–/– and WT mice were analyzed by immunohistochemistry, real-time PCR and western blotting. Results: Compared to WT, we found that syndecan-4^–/– mice had reduced body weight, reduced muscle weight, muscle fibers with a smaller cross-sectional area, and reduced expression of myogenic regulatory transcription factors. Sedentary syndecan-4^–/– had also increased mRNA levels of syndecan-2, decorin, collagens, fibromodulin, biglycan, and LOX. Some of these latter ECM components were reduced at protein level, suggesting them to be more susceptible to degradation or less efficiently translated when syndecan-4 is absent. At the protein level, TRPC7 was reduced, whereas activation of the Akt/mTOR/S6K1 and Notch/HES-1 pathways were increased. Finally, although exercise induced upregulation of several of these components in WT, a further upregulation of these molecules was not observed in exercised syndecan-4^–/– mice. Conclusion: Altogether our data suggest an important role of syndecan-4 in muscle development.

1 Rheumatoid arthritis (RA) is a debilitating and painful inflammatory autoimmune disease characterised by the accumulation of leukocytes in the synovium, cartilage destruction and bone erosion. The immunomodulatory effects of bone marrow derived mesenchymal stem cells (MSCs) has been widely studied and the recent observations that syndecan-3 (SDC3) is selectively pro-inflammatory in the joint led us to hypothesise that SDC3 might play an important role in MSC biology. MSCs isolated from bone marrow of wild type and Sdc3 ^−/− mice were used to assess immunophenotype, differentiation, adhesion and migration properties and cell signalling pathways. While both cell types show similar differentiation potential and forward scatter values, the cell complexity in wild type MSCs was significantly higher than in Sdc3 ^−/− cells and was accompanied by lower spread surface area. Moreover, Sdc3 ^−/− MSCs adhered more rapidly to collagen type I and showed a dramatic increase in AKT phosphorylation, accompanied by a decrease in ERK1/2 phosphorylation compared with control cells. In a mouse model of antigen-induced inflammatory arthritis, intraarticular injection of Sdc3 ^−/− MSCs yielded enhanced recovery compared to injection of wild type MSCs. In conclusion, our data suggest that syndecan-3 regulates MSC adhesion and efficacy in inflammatory arthritis, likely via induction of the AKT pathway.