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Skeletal muscle fibers form in overlapping, but distinct phases that depend on the generation of temporally different lineages of myogenic cells. During primary myogenesis (E10.5–E12.5 in the mouse), embryonic myoblasts fuse homotypically to generate primary fibers, whereas during later development (E14.5–E17.5), fetal myoblasts differentiate into secondary fibers. How these myogenic waves are regulated remains largely unknown. Studies have been hampered by the lack of markers which would distinguish embryonic from fetal myoblast populations. We show here that the homeobox gene Arx is strongly expressed in differentiating embryonic muscle, downstream of myogenic basic helix–loop–helix (bHLH) genes. Its expression progressively decreases during development. When overexpressed in the C2C12 myogenic cell line, Arx enhances differentiation. Accordingly, it stimulates the transcriptional activity from the Myogenin promoter and from multimerized E-boxes when co-expressed with MyoD and Mef2C in CH310T1/2. Furthermore, Arx co-immunoprecipitates with Mef2C, suggesting that it participates in the transcriptional regulatory network acting in embryonic muscle. Finally, embryonic myoblasts isolated from Arx-deficient embryos show a delayed differentiation in vivo together with an enhanced clonogenic capacity in vitro. We propose here that Arx acts as a novel positive regulator of embryonic myogenesis by synergizing with Mef2C and MyoD and by establishing an activating loop with Myogenin.Cell Death and Differentiation (2008) 15, 94–104; doi:10.1038/sj.cdd.4402230; published online 12 October 2007 [ABSTRACT FROM AUTHOR]

A first-line gene therapy for type 1 diabetes should be based on a safe procedure to engineer an accessible tissue for insulin release. We evaluated the ability of the skeletal muscle to release human insulin after electrotransfer (ET)-enhanced plasmid DNA injection in mice. A furin-cleavable proinsulin cDNA under the CMV or the MFG promoter was electrotransferred to immune-incompetent mice with STZ-induced severe diabetes. At 1 week, mature human insulin was detected in the serum of 17/20 mice. After an initial peak of 68.5 ± 34.9 μU/ml, insulin was consistently detected at significant levels up to 6 weeks after gene transfer. Importantly, untreated diabetic animals died within 3 weeks after STZ, whereas treated mice survived up to 10 weeks. Fed blood glucose (BG) was reduced in correspondence with the insulin peak. Fasting BG was near-normalized when insulin levels were 12.9 ± 5.3 (CMV group, 2 weeks) and 7.7 ± 2.6 μU/ml (MFG group, 4 weeks), without frank hypoglycemia. These data indicate that ET-enhanced DNA injection in muscle leads to the release of biologically active insulin, with restoration of basal insulin levels, and lowering of fasting BG with increased survival in severe diabetes. Therefore the skeletal muscle can be considered as a platform for basal insulin secretion.Gene Therapy 2002 9, 1429–1437. doi:10.1038/sj.gt.3301804 [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to investigate the in vitro effect of different concentrations of blood on the morphological and biochemical properties of engineered cartilage. Previous studies have demonstrated a negative effect of blood on native cartilage; however, the effect of the contact of blood on engineered cartilage is unclear. Methods: Articular chondrocytes were isolated from swine joints, expanded in monolayer culture, and seeded onto collagen membranes. The seeded membranes were cultured for 3 days in the presence of different concentrations of peripheral blood. Some samples were retrieved at the end of the blood contact, others after 21 additional days of standard culture conditions, in order to investigate the 'long-term effect' of the blood contact. Results: All seeded samples showed an increase in the weight and an evident cartilage-like matrix production. A concentration-dependent reduction in the mitochondrial activity due to blood contact was shown at the earlier culture time, followed by a partial recover at the longer culture time. Conclusion: A blood contact of 3 days affected the chondrocytes' activity and determined a delay in the maturation of the engineered cartilage. These findings have clinical relevance, as autologous chondrocytes seeded onto biological scaffolds has become an established surgical method for articular cartilage repair. Therefore, further investigation into material sciences should be encouraged for the development of scaffold protecting the reparative cells from the blood insult. [ABSTRACT FROM AUTHOR]

The use of autologous chondrocytes seeded onto a biological scaffold represents a current valid tool for cartilage repair. However, the effect of the contact of blood to the engineered construct is unknown. The aim of this work was to investigate in vitro the effect of blood on the morphological, biochemical and biomechanical properties of engineered cartilage. Articular chondrocytes were enzymatically isolated from swine joints, expanded in monolayer culture and seeded onto collagen membranes for 2 weeks. Then, the seeded membranes were placed for 3 days in contact with peripheral blood, which was obtained from animals of the same species and diluted with a standard medium. As controls, some samples were left in the standard medium. After the 3 days' contact, some samples were retrieved for analysis; others were returned to standard culture conditions for 21 additional days, in order to investigate the "long-term effect" of the blood contact. Upon retrieval, all seeded samples showed increasing sizes and weights over time. However, the samples exposed to blood presented lower values with respect to the controls. Biochemical evaluation demonstrated a reduction in the mitochondrial activity due to blood contact at the early culture time (3 days post blood contact), followed by a partial recovery at the longer culture time (21 days post blood contact). Histological evaluation demonstrated evident cartilage-like matrix production for both groups. Biomechanical data showed a reduction of the values, followed by stabilization, regardless of the presence of blood. Based on the data obtained in this study, we can conclude that blood contact affects the chondrocyte activity and determines a delay in the dimensional growth of the engineered cartilage; however, at the experimental times utilized in this study, this delay did not affect the histological pattern and the biomechanical properties of the construct. [ABSTRACT FROM AUTHOR]