Loss of full-length dystrophin expression results in major cell-autonomous abnormalities in proliferating myoblasts

Duchenne muscular dystrophy (DMD) affects myofibers and muscle stem cells, causing progressive muscle degeneration and repair defects. It was unknown whether dystrophic myoblasts—the effector cells of muscle growth and regeneration—are affected. Using transcriptomic, genome-scale metabolic modelling and functional analyses, we demonstrate, for the first time, convergent abnormalities in primary mouse and human dystrophic myoblasts. In Dmd(mdx) myoblasts lacking full-length dystrophin, the expression of 170 genes was significantly altered. Myod1 and key genes controlled by MyoD (Myog, Mymk, Mymx, epigenetic regulators, ECM interactors, calcium signalling and fibrosis genes) were significantly downregulated. Gene ontology analysis indicated enrichment in genes involved in muscle development and function. Functionally, we found increased myoblast proliferation, reduced chemotaxis and accelerated differentiation, which are all essential for myoregeneration. The defects were caused by the loss of expression of full-length dystrophin, as similar and not exacerbated alterations were observed in dystrophin-null Dmd(mdx-βgeo) myoblasts. Corresponding abnormalities were identified in human DMD primary myoblasts and a dystrophic mouse muscle cell line, confirming the cross-species and cell-autonomous nature of these defects. The genome-scale metabolic analysis in human DMD myoblasts showed alterations in the rate of glycolysis/gluconeogenesis, leukotriene metabolism, and mitochondrial beta-oxidation of various fatty acids. These results reveal the disease continuum: DMD defects in satellite cells, the myoblast dysfunction affecting muscle regeneration, which is insufficient to counteract muscle loss due to myofiber instability. Contrary to the established belief, our data demonstrate that DMD abnormalities occur in myoblasts, making these cells a novel therapeutic target for the treatment of this lethal disease

Quantitative atomic force microscopy provides new insight into matrix vesicle mineralization

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Biomimetic generation of the strongest known biomaterial found in limpet tooth

The biomaterial with the highest known tensile strength is a unique composite of chitin and goethite (α-FeO(OH)) present in teeth from the Common Limpet (Patella vulgata). A biomimetic based on limpet tooth, with corresponding high-performance mechanical properties is highly desirable. Here we report on the replication of limpet tooth developmental processes ex vivo, where isolated limpet tissue and cells in culture generate new biomimetic structures. Transcriptomic analysis of each developmental stage of the radula, the organ from which limpet teeth originate, identifies sequential changes in expression of genes related to chitin and iron processing. We quantify iron and chitin metabolic processes in the radula and grow isolated radula cells in vitro. Bioinspired material can be developed with electrospun chitin mineralised by conditioned media from cultured radula cells. Our results inform molecular processes behind the generation of limpet tooth and establish a platform for development of a novel biomimetic with comparable properties

Whole-body clearing, staining and screening of calcium deposits in the mdx mouse model of Duchenne muscular dystrophy

Abstract Background Duchenne muscular dystrophy (DMD) is a fatal, X-linked genetic disorder. Although DMD is the most common form of muscular dystrophy, only two FDA-approved drugs were developed to delay its progression. In order to assess therapies for treating DMD, several murine models have recently been introduced. As the wide variety of murine models enlighten mechanisms underlying DMD pathology, the question on how to monitor the progression of the disease within the entire musculoskeletal system still remains to be answered. One considerable approach to monitor such progression is histological evaluation of calcium deposits within muscle biopsies. Although accurate, histology is limited to small tissue area and cannot be utilized to evaluate systemic progression of DMD. Therefore, we aimed to develop a methodology suitable for rapid and high-resolution screening of calcium deposits within the entire murine organism. Methods Procedures were performed on adult male C57BL/10-mdx and adult male C57BL mice. Animals were sacrificed, perfused, paraformaldehyde-fixed, and subjected to whole-body clearing using optimized perfusion-based CUBIC protocol. Next, cleared organisms were stained with alizarin red S to visualize calcium deposits and subjected to imaging. Results Study revealed presence of calcium deposits within degenerated muscles of the entire C57BL/10-mdx mouse organism. Calcified deposits were observed within skeletal muscles of the forelimb, diaphragm, lumbar region, pelvic region, and hindlimb. Calcified deposits found in quadriceps femoris, triceps brachii, and spinalis pars lumborum were characterized. Analysis of cumulative frequency distribution showed different distribution characteristics of calcified deposits in quadriceps femoris muscle in comparison to triceps brachii and spinalis pars lumborum muscles (p < 0.001) and quadriceps femoris vs spinalis pars lumborum (p < 0.001). Differences between the number of calcified deposits in selected muscles, their volume, and average volume were statistically significant. Conclusions In aggregate, we present new methodology to monitor calcium deposits in situ in the mouse model of Duchenne muscular dystrophy. Sample imaging with the presented setup is feasible and applicable for whole-organ/body imaging. Accompanied by the development of custom-made LSFM apparatus, it allows targeted and precise characterization of calcium deposits in cleared muscles. Hence, presented approach might be broadly utilized to monitor degree to which muscles of the entire organism are affected by the necrosis and how is it altered by the treatment or physical activity of the animal. We believe that this would be a valuable tool for studying organs alternations in a wide group of animal models of muscle dystrophy and bone-oriented diseases

Analysis of Minerals Produced by hFOB 1.19 and Saos-2 Cells Using Transmission Electron Microscopy with Energy Dispersive X-ray Microanalysis

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Additional file 1: of Whole-body clearing, staining and screening of calcium deposits in the mdx mouse model of Duchenne muscular dystrophy

Figure S1. Implementation of apparatus for macroscopic imaging using light-sheet illumination. (a) General view. (b) Side view. (c) Front view. (1) camera, (2) stepper motor, (3) z-axis line module (here light microscope body, Zeiss), (4) base holder, (5) glass container, (6) line lasers, (7) metal block, (8) laser power supply. Figure S2. Perfusion-based CUBIC cleared rat organs stained with propidium iodide. Bright field images of whole rat organs (a) intestine, (b) kidney, (c) heart, (d) cerebellum and (e) spleen. Single squares in all panels - 5 × 5 mm. This figure has been adapted from the original article “Optimized perfusion-based CUBIC protocol for the efficient whole-body clearing and imaging of rat organs” by P. Matryba et al., J Biophotonics 2017, doi./10.1002/jbio.201700248 . Reproduced with permission 4358370973288. Figure S3. Comparison between optical and standard histopathology sectioning of Alizarin red S stained mdx mouse muscles. (a) Representative optical sections acquired during imaging with custom-made LSFM. Control animals present no staining-positive tissue. (b) Representative histopathology 4 μm sections observed with low and (c) high magnification. It has to be noted that histopathology images stay in line with optical sectioning, presenting petite deposits in triceps brachii and similar amount of deposits between quadriceps femoris and spinalis pars lumborum. White scale bar, 1 mm, black scale bar, 200 μm. Figure S4. Quantitative volume analysis of calcified deposits in mdx mouse. (a) Triceps brachii muscles from left and right side of the animals were compared. Differences between left vs. right side presented as % mineralization of muscle volume were not statistically significant (Wilcoxon test (W = 0.0, number of pairs = 3), p > 0.999). (b) Analysis of volume of muscles replaced by calcific deposits. Percent of mineralization in triceps brachii, quadriceps femoris and spinalis pars lumborum muscles was significantly different (Kruskal-Wallis test (K-W statistic = 5.6), p = 0.05, n = 3 per each muscle group). Figure S5. Perfusion-based CUBIC clearing does not alter microstructure of muscle. Perfusion-based CUBIC cleared triceps brachii and quadriceps femoris muscles of mdx and C57BL/10 control animals were subjected to standard hematoxylin and eosin histological staining. Low (10×) and high (20×) magnification representative images present microstructure preservation. It has to be noted that centrally positioned nuclei, a prominent feature of dystrophy, is maintained during mdx clearing. Scale bar, 100 μm. (ZIP 12014 kb

Annexins A2, A6 and Fetuin-A Affect the Process of Mineralization in Vesicles Derived from Human Osteoblastic hFOB 1.19 and Osteosarcoma Saos-2 Cells

The mineralization process is initiated by osteoblasts and chondrocytes during intramembranous and endochondral ossifications, respectively. Both types of cells release matrix vesicles (MVs), which accumulate Pi and Ca2+ and form apatites in their lumen. Tissue non-specific alkaline phosphatase (TNAP), a mineralization marker, is highly enriched in MVs, in which it removes inorganic pyrophosphate (PPi), an inhibitor of apatite formation. MVs then bud from the microvilli of mature osteoblasts or hypertrophic chondrocytes and, thanks to the action of the acto-myosin cortex, become released to the extracellular matrix (ECM), where they bind to collagen fibers and propagate mineral growth. In this report, we compared the mineralization ability of human fetal osteoblastic cell line (hFOB 1.19 cells) with that of osteosarcoma cell line (Saos-2 cells). Both types of cells were able to mineralize in an osteogenic medium containing ascorbic acid and beta glycerophosphate. The composition of calcium and phosphate compounds in cytoplasmic vesicles was distinct from that in extracellular vesicles (mostly MVs) released after collagenase-digestion. Apatites were identified only in MVs derived from Saos-2 cells, while MVs from hFOB 1.19 cells contained amorphous calcium phosphate complexes. In addition, AnxA6 and AnxA2 (nucleators of mineralization) increased mineralization in the sub-membrane region in strongly mineralizing Saos-2 osteosarcoma, where they co-localized with TNAP, whereas in less mineralizing hFOB 1.19 osteoblasts, AnxA6, and AnxA2 co-localizations with TNAP were less visible in the membrane. We also observed a reduction in the level of fetuin-A (FetuA), an inhibitor of mineralization in ECM, following treatment with TNAP and Ca channels inhibitors, especially in osteosarcoma cells. Moreover, a fraction of FetuA was translocated from the cytoplasm towards the plasma membrane during the stimulation of Saos-2 cells, while this displacement was less pronounced in stimulated hFOB 19 cells. In summary, osteosarcoma Saos-2 cells had a better ability to mineralize than osteoblastic hFOB 1.19 cells. The formation of apatites was observed in Saos-2 cells, while only complexes of calcium and phosphate were identified in hFOB 1.19 cells. This was also evidenced by a more pronounced accumulation of AnxA2, AnxA6, FetuA in the plasma membrane, where they were partly co-localized with TNAP in Saos-2 cells, in comparison to hFOB 1.19 cells. This suggests that both activators (AnxA2, AnxA6) and inhibitors (FetuA) of mineralization were recruited to the membrane and co-localized with TNAP to take part in the process of mineralization

Src and ROCK Kinases Differentially Regulate Mineralization of Human Osteosarcoma Saos-2 Cells

Osteoblasts initiate bone mineralization by releasing matrix vesicles (MVs) into the extracellular matrix (ECM). MVs promote the nucleation process of apatite formation from Ca2+ and Pi in their lumen and bud from the microvilli of osteoblasts during bone development. Tissue non-specific alkaline phosphatase (TNAP) as well as annexins (among them, AnxA6) are abundant proteins in MVs that are engaged in mineralization. In addition, sarcoma proto-oncogene tyrosine-protein (Src) kinase and Rho-associated coiled-coil (ROCK) kinases, which are involved in vesicular transport, may also regulate the mineralization process. Upon stimulation in osteogenic medium containing 50 &mu;g/mL of ascorbic acid (AA) and 7.5 mM of &beta;-glycerophosphate (&beta;-GP), human osteosarcoma Saos-2 cells initiated mineralization, as evidenced by Alizarin Red-S (AR-S) staining, TNAP activity, and the partial translocation of AnxA6 from cytoplasm to the plasma membrane. The addition of 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo [3,4-d] pyrimidine (PP2), which is an inhibitor of Src kinase, significantly inhibited the mineralization process when evaluated by the above criteria. In contrast, the addition of (R)-(+)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexane carboxamide hydrochloride (Y-27632), which is an inhibitor of ROCK kinase, did not affect significantly the mineralization induced in stimulated Saos-2 cells as denoted by AR-S and TNAP activity. In conclusion, mineralization by human osteosarcoma Saos-2 cells seems to be differently regulated by Src and ROCK kinases