Gpr18 agonist dampens inflammation, enhances myogenesis, and restores muscle function in models of Duchenne muscular dystrophy

Introduction: Muscle wasting in Duchenne Muscular Dystrophy is caused by myofiber fragility and poor regeneration that lead to chronic inflammation and muscle replacement by fibrofatty tissue. Our recent findings demonstrated that Resolvin-D2, a bioactive lipid derived from omega-3 fatty acids, has the capacity to dampen inflammation and stimulate muscle regeneration to alleviate disease progression. This therapeutic avenue has many advantages compared to glucocorticoids, the current gold-standard treatment for Duchenne Muscular Dystrophy. However, the use of bioactive lipids as therapeutic drugs also faces many technical challenges such as their instability and poor oral bioavailability.Methods: Here, we explored the potential of PSB-KD107, a synthetic agonist of the resolvin-D2 receptor Gpr18, as a therapeutic alternative for Duchenne Muscular Dystrophy.Results and discussion: We showed that PSB-KD107 can stimulate the myogenic capacity of patient iPSC-derived myoblasts in vitro. RNAseq analysis revealed an enrichment in biological processes related to fatty acid metabolism, lipid biosynthesis, small molecule biosynthesis, and steroid-related processes in PSB-KD107-treated mdx myoblasts, as well as signaling pathways such as Peroxisome proliferator-activated receptors, AMP-activated protein kinase, mammalian target of rapamycin, and sphingolipid signaling pathways. In vivo, the treatment of dystrophic mdx mice with PSB-KD107 resulted in reduced inflammation, enhanced myogenesis, and improved muscle function. The positive impact of PSB-KD107 on muscle function is similar to the one of Resolvin-D2. Overall, our findings provide a proof-of concept that synthetic analogs of bioactive lipid receptors hold therapeutic potential for the treatment of Duchenne Muscular Dystrophy

Clearance of defective muscle stem cells by senolytics reduces the expression of senescence-associated secretory phenotype and restores myogenesis in myotonic dystrophy type 1

Muscle weakness and atrophy are clinical hallmarks of myotonic dystrophy type 1 (DM1). Muscle stem cells, which contribute to skeletal muscle growth and repair, are also affected in this disease. However, the molecular mechanisms leading to this defective activity and the impact on the disease severity are still elusive. Here, we explored through an unbiased approach the molecular signature leading to myogenic cell defects in DM1. Single cell RNAseq data revealed the presence of a specific subset of DM1 myogenic cells expressing a senescence signature, characterized by the high expression of genes related to senescence-associated secretory phenotype (SASP). This profile was confirmed using different senescence markers in vitro and in situ. Accumulation of intranuclear RNA foci in senescent cells, suggest that RNA-mediated toxicity contribute to senescence induction. High expression of IL-6, a prominent SASP cytokine, in the serum of DM1 patients was identified as a biomarker correlating with muscle weakness and functional capacity limitations. Drug screening revealed that the BCL-XL inhibitor (A1155463), a senolytic drug, can specifically target senescent DM1 myoblasts to induce their apoptosis and reduce their SASP. Removal of senescent cells re-established the myogenic function of the non-senescent DM1 myoblasts, which displayed improved proliferation and differentiation capacity in vitro; and enhanced engraftment following transplantation in vivo. Altogether this study presents a well-defined senescent molecular signature in DM1 untangling part of the pathological mechanisms observed in the disease; additionally, we demonstrate the therapeutic potential of targeting these defective cells with senolytics to restore myogenesis

Strategies for utrophin upregulation

Duchenne Muscular Dystrophy (DMD) is the most common X-linked lethal disorder caused by a genetic defect in the dystrophin gene. A substantial, ectopic expression of utrophin, which is a close analogue of dystrophin, in the extra-synaptic sarcolemma of dystrophin-deficient muscle fibers, can prevent deleterious effects of dystrophin deficiency. Our aim is to up-regulate the expression of this dystrophin-related gene in DMD, thereby complementing the lack of dystrophin function. To achieve utrophin up-regulation, we engineered several zinc finger proteins (ZFPs), and tested their ability to target and upregulate the human utrophin A promoter. In parallel, we used genome editing tools, such as the zinc fingers nuclease (ZFN), and the Clustered, Regularly Interspersed, Short Palindromic Repeats (CRISPR), to target and modify the endogenous utrophin A promoter. Although results of ZFPs coupled to the trans-activator domain VP16 have shown a moderate up-regulation of the endogenous utrophin in HEK 293T cells, the screening of ZFN and CRISPR/Cas9 systems have shown these to have a great efficacy in inducing DNA double-strand breaks at utrophin A promoter. The co-transfection of HEK 293T cells with the CRISPR/Cas9 system and a donor plasmid harboring the Cytomegalovirus and chicken beta actin (CAG) promoter flanked between utrophin A arms triggered the integration of the CAG promoter sequence into the endogenous human utrophin A promoter region through a homology-directed repair mechanism. Integration of the CAG promoter within the utrophin A promoter region led to a substantial up-regulation of the endogenous utrophin gene in these cells.La Dystrophie Musculaire de Duchenne (DMD) est une maladie létale causée par le dysfonctionnement du gène codant pour la dystrophine située sur le chromosome X. La surexpression de l'utrophine (protéine analogue à la dystrophine) dans les muscles déficients de la dystrophine, peut prévenir l'effet néfaste liée à cette anomalie. Notre but est de sur-exprimer l'utrophine chez des patients atteints de la DMD afin de défier l'absence de la dystrophine. Pour cela, des protéines à doigts de zinc (ZFP) ont été synthétisées et leur capacité à activer le promoteur A de l'utrophine a été testé. En même temps, la nucléase à doigts de zinc (outils de correction génomique) ainsi que le système 'Courtes répétitions palindromiques groupées et régulièrement espacées' (CRISPR) ont été utilisés pour modifier le promoteur A de l'utrophin endogène. Bien que le ZFP couplé au domaine trans-activateur de VP16 a montré une surexpression modérée de l'utrophine endogène dans les cellules HEK 293T, le criblage de ZFN et le système CRISPR/Cas9 a démontré quant à lui une grande efficacité à induire des cassures sur le double brin d'ADN au niveau du promoteur A de l'utrophine. La co-transfection des cellules HEK 293T avec le système CRSIPR/Cas9 ainsi que le plasmide donneur possédant le promoteur chimère de la β-actine de poulet fusionné a l'enhancer du promoteur précoce de cytomégalovirus (CAG) flanqué entre les deux bras du promoteur A de l'utrophine induit la voie de la réparation homologue dirigée qui induit à son tour l'intégration du CAG dans le promoteur A de l'utrophine humaine endogène. Les résultats ont confirmé que l'intégration de CAG au niveau du promoteur A de l'utrophine, permet une surexpression stable de l'utrophine endogène

Desalination with a solar-assisted heat pump : an economic optimization

The solar-assisted heat pump (SAHP) desalination, based on the Rankin cycle, operates in low temperature and utilizes both solar and ambient energy. An experimental SAHP desalination system has been constructed at the National University of Singapore, Singapore. The system consisted of two main sections: an SAHP and a water distillation section. Experiments were carried out under the different meteorological condition of Singapore and results showed that the system had a performance ratio close to 1.3. The heat pump has a coefficient of performance of about 8, with solar collector efficiencies of 80% and 60% for evaporator and liquid collectors, respectively. Economic analysis showed that at a production rate of 900 L/day and an evaporator collector area of around 70m2 will have a payback period of about 3.5 years

Performance of Photovoltaic Systems with Solar Tracking in Singapore

Photovoltaic technology enables direct conversion of solar irradiation into electricity. This project investigated the performance of a single-axis active solar tracking system by constructing and testing. From the results, it was observed that the output current varied almost instantaneously with the irradiation whilst the output voltage remained fairly constant even with huge fluctuations in irradiation. The efficiency of the solar panels was found to be 11.9% for the tracking configuration. This represented a 33.6% increase in efficiency when using the single-axis tracking system over the fixed ones

Clearance of defective muscle stem cells by senolytics restores myogenesis in myotonic dystrophy type 1

Abstract Muscle stem cells, the engine of muscle repair, are affected in myotonic dystrophy type 1 (DM1); however, the underlying molecular mechanism and the impact on the disease severity are still elusive. Here, we show using patients’ samples that muscle stem cells/myoblasts exhibit signs of cellular senescence in vitro and in situ. Single cell RNAseq uncovers a subset of senescent myoblasts expressing high levels of genes related to the senescence-associated secretory phenotype (SASP). We show that the levels of interleukin-6, a prominent SASP cytokine, in the serum of DM1 patients correlate with muscle weakness and functional capacity limitations. Drug screening revealed that the senolytic BCL-XL inhibitor (A1155463) can specifically remove senescent DM1 myoblasts by inducing their apoptosis. Clearance of senescent cells reduced the expression of SASP, which rescued the proliferation and differentiation capacity of DM1 myoblasts in vitro and enhanced their engraftment following transplantation in vivo. Altogether, this study identifies the pathogenic mechanism associated with muscle stem cell defects in DM1 and opens a therapeutic avenue that targets these defective cells to restore myogenesis

Biallelic variants in the transcription factor PAX7 are a new genetic cause of myopathy

Skeletal muscle growth and regeneration rely on muscle stem cells, called satellite cells. Specific transcription factors, particularly PAX7, are key regulators of the function of these cells. Knockout of this factor in mice leads to poor postnatal survival; however, the consequences of a lack of PAX7 in humans have not been established. Purpose Skeletal muscle growth and regeneration rely on muscle stem cells, called satellite cells. Specific transcription factors, particularly PAX7, are key regulators of the function of these cells. Knockout of this factor in mice leads to poor postnatal survival; however, the consequences of a lack of PAX7 in humans have not been established. Methods Here, we study five individuals with myopathy of variable severity from four unrelated consanguineous couples. Exome sequencing identified pathogenic variants in the PAX7 gene. Clinical examination, laboratory tests, and muscle biopsies were performed to characterize the disease. Results The disease was characterized by hypotonia, ptosis, muscular atrophy, scoliosis, and mildly dysmorphic facial features. The disease spectrum ranged from mild to severe and appears to be progressive. Muscle biopsies showed the presence of atrophic fibers and fibroadipose tissue replacement, with the absence of myofiber necrosis. A lack of PAX7 expression was associated with satellite cell pool exhaustion; however, the presence of residual myoblasts together with regenerating myofibers suggest that a population of PAX7-independent myogenic cells partially contributes to muscle regeneration. Conclusion These findings show that biallelic variants in the master transcription factor PAX7 cause a new type of myopathy that specifically affects satellite cell survival.German Bundesministerium für Bildung und Forschung through the Juniorverbund in der Systemmedizin “mitOmics” (FKZ01ZX1405C to T.B.H.) and Horizon2020 through the E-Rare project GENOMIT (01GM1603 and 01GM1207 for H.P. and FWFI2741B26 for J.A.M.) and the Deutsche Forschungsgemeinschaft (SCHO754/52 to L.S. and BA2427/22 to P.B.) as well as the Vereinigung zur Förderung Pädiatrischer Forschung und Fortbildung Salzburg, the EU FP7 Mitochondrial European Educational Training Project (317433 to H.P. and J.A.M.), and the EU Horizon2020 Collaborative Research Project SOUND (633974 to H.P.). N.A.D. is supported by grants from the Fonds de recherche du Québec–Santé (35015), Canadian Institutes of Health Research (388296), Rare Disease Foundation (2301), and CHU Sainte-Justine Foundation. N.A.D. acknowledges the support of ThéCell and Stem Cell Netwo