Myogenic Characteristics Research Articles

Abstract 1095: Prox1 transcription factor and its downstream signaling - A new therapeutic target for rhabdomyosarcoma

Abstract Rhabdomyosarcoma (RMS) stands as the predominant soft tissue sarcoma in children, characterized by a high-grade neoplasm composed of cells resembling skeletal myoblasts. Despite being prevalent, patients with metastatic or recurrent rhabdomyosarcoma still experience poor outcomes, underscoring the necessity for novel treatments. We have recently shown that PROX1 is a critical factor in RMS tumor growth and myogenic characteristics (Gizaw NY, et al. PNAS 2022). As PROX1 has previously been associated with tumor metabolism in colorectal cancer, we investigated further its role in RMS metabolism. Our findings demonstrate that PROX1 plays a crucial role in regulating RMS cell metabolism. Specifically, silencing of PROX1 resulted in decreased lipid and oxidative metabolism, which was accompanied by an increase in glycolysis and triglyceride accumulation. RNA sequencing and Gene Set Enrichment Analysis revealed downregulation of all genes involved in the cholesterol synthesis pathway in PROX1-silenced RMS cells. Our studies further reveal that inhibiting cholesterol synthesis, akin to PROX1 silencing, can effectively inhibit RMS cell growth. Our results provide novel insights into the role of PROX1 in RMS metabolism and highlight the potential of PROX1-regulated metabolic pathways as promising targets for the development of novel RMS therapies. Citation Format: Nebeyu Y. Gizaw, Tom Böhling, Mika Sampo, Kari Alitalo, Riikka M. Kivela. Prox1 transcription factor and its downstream signaling - A new therapeutic target for rhabdomyosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1095.

Resident muscle stem cell myogenic characteristics in postnatal muscle growth impairments in children with cerebral palsy.

Children with cerebral palsy (CP), a perinatal brain alteration, have impaired postnatal muscle growth, with some muscles developing contractures. Functionally, children are either able to walk or primarily use wheelchairs. Satellite cells are muscle stem cells (MuSCs) required for postnatal development and source of myonuclei. Only MuSC abundance has been previously reported in contractured muscles, with myogenic characteristics assessed only in vitro. We investigated whether MuSC myogenic, myonuclear, and myofiber characteristics in situ differ between contractured and noncontractured muscles, across functional levels, and compared with typically developing (TD) children with musculoskeletal injury. Open muscle biopsies were obtained from 36 children (30 CP, 6 TD) during surgery; contracture correction for adductors or gastrocnemius, or from vastus lateralis [bony surgery in CP, anterior cruciate ligament (ACL) repair in TD]. Muscle cross sections were immunohistochemically labeled for MuSC abundance, activation, proliferation, nuclei, myofiber borders, type-1 fibers, and collagen content in serial sections. Although MuSC abundance was greater in contractured muscles, primarily in type-1 fibers, their myogenic characteristics (activation, proliferation) were lower compared with noncontractured muscles. Overall, MuSC abundance, activation, and proliferation appear to be associated with collagen content. Myonuclear number was similar between all muscles, but only in contractured muscles were there associations between myonuclear number, MuSC abundance, and fiber cross-sectional area. Puzzlingly, MuSC characteristics were similar between ambulatory and nonambulatory children. Noncontractured muscles in children with CP had a lower MuSC abundance compared with TD-ACL injured children, but similar myogenic characteristics. Contractured muscles may have an intrinsic deficiency in developmental progression for postnatal MuSC pool establishment, needed for lifelong efficient growth and repair.

Effects of sheep slaughter age on myogenic characteristics in skeletal muscle satellite cells.

ObjectiveThe objective of this study was to investigate the effects of sheep slaughter age on myogenic characteristics in skeletal muscle satellite cells (SMSCs).MethodsPrimary SMSCs were isolated from hind leg biceps femoris muscles of Wurank lambs (slaughtered at three months, Mth-3) and adults (slaughtered at fifteen months, Mth-15). SMSCs were selected by morphological observation and fluorescence staining. Myogenic regulatory factors (MRF) and myosin heavy chain (MyHC) expressions of SMSCs were analyzed on days 1, 3, 4, and 5.ResultsThe expressions of myogenic factor 5 (Myf5), myogenic differentiation (MyoD), Myf6, and myogenin (MyoG) in Mth-15 were significantly higher in Mth-15 than in Mth-3 on days 1, 3, and 4 (p<0.05). However, MyoG expression in Mth-15 was significantly lower than in Mth-3 on day 5 (p<0.05). The expressions of MyHC I, MyHC IIa, and MyHC IIx in Mth-15 were significantly higher than in Mth-3 on days 1 and 3 (p<0.05), and MyHC IIb were significantly lower than in Mth-3 on days 3 and 4 (p<0.05). In contrast, the expression of MyHC IIx in Mth-15 was significantly lower and MyHC IIb was significantly higher than in Mth-3 on days 5 (p<0.05).ConclusionThe slaughter age altered the expression of MRFs and MyHCs in SMSCs while differentiation, which caused the variation of myogenic characteristics, and thus may affect the meat quality of Wurank sheep.

Bovine Satellite Cells Isolated after 2 and 5 Days of Tissue Storage Maintain the Proliferative and Myogenic Capacity Needed for Cultured Meat Production.

Cultured meat is an emerging alternative food technology which aims to deliver a more ethical, sustainable, and healthy muscle-tissue-derived food item compared to conventional meat. As start-up companies are rapidly forming and accelerating this technology, many aspects of this multi-faceted science have still not been investigated in academia. In this study, we investigated if bovine satellite cells with the ability to proliferate and undergo myogenic differentiation could be isolated after extended tissue storage, for the purpose of increasing the practicality for cultured meat production. Proliferation of bovine satellite cells isolated on the day of arrival or after 2 and 5 days of tissue storage were analyzed by metabolic and DNA-based assays, while their myogenic characteristics were investigated using RT-qPCR and immunofluorescence. Extended tissue storage up to 5 days did not negatively affect proliferation nor the ability to undergo fusion and create myosin heavy chain-positive myotubes. The expression patterns of myogenic and muscle-specific genes were also not affected after tissue storage. In fact, the data indicated a positive trend in terms of myogenic potential after tissue storage, although it was non-significant. These results suggest that the timeframe of which viable myogenic satellite cells can be isolated and used for cultured meat production can be greatly extended by proper tissue storage.

The PAX-FOXO1s trigger fast trans-differentiation of chick embryonic neural cells into alveolar rhabdomyosarcoma with tissue invasive properties limited by S phase entry inhibition.

The chromosome translocations generating PAX3-FOXO1 and PAX7-FOXO1 chimeric proteins are the primary hallmarks of the paediatric fusion-positive alveolar subtype of Rhabdomyosarcoma (FP-RMS). Despite the ability of these transcription factors to remodel chromatin landscapes and promote the expression of tumour driver genes, they only inefficiently promote malignant transformation in vivo. The reason for this is unclear. To address this, we developed an in ovo model to follow the response of spinal cord progenitors to PAX-FOXO1s. Our data demonstrate that PAX-FOXO1s, but not wild-type PAX3 or PAX7, trigger the trans-differentiation of neural cells into FP-RMS-like cells with myogenic characteristics. In parallel, PAX-FOXO1s remodel the neural pseudo-stratified epithelium into a cohesive mesenchyme capable of tissue invasion. Surprisingly, expression of PAX-FOXO1s, similar to wild-type PAX3/7, reduce the levels of CDK-CYCLIN activity and increase the fraction of cells in G1. Introduction of CYCLIN D1 or MYCN overcomes this PAX-FOXO1-mediated cell cycle inhibition and promotes tumour growth. Together, our findings reveal a mechanism that can explain the apparent limited oncogenicity of PAX-FOXO1 fusion transcription factors. They are also consistent with certain clinical reports indicative of a neural origin of FP-RMS.

Derivation and Characterization of Immortalized Human Muscle Satellite Cell Clones from Muscular Dystrophy Patients and Healthy Individuals.

In Duchenne muscular dystrophy (DMD) patients, absence of dystrophin causes muscle wasting by impacting both the myofiber integrity and the properties of muscle stem cells (MuSCs). Investigation of DMD encompasses the use of MuSCs issued from human skeletal muscle. However, DMD-derived MuSC usage is restricted by the limited number of divisions that human MuSCs can undertake in vitro before losing their myogenic characteristics and by the scarcity of human material available from DMD muscle. To overcome these limitations, immortalization of MuSCs appears as a strategy. Here, we used CDK4/hTERT expression in primary MuSCs and we derived MuSC clones from a series of clinically and genetically characterized patients, including eight DMD patients with various mutations, four congenital muscular dystrophies and three age-matched control muscles. Immortalized cultures were sorted into single cells and expanded as clones into homogeneous populations. Myogenic characteristics and differentiation potential were tested for each clone. Finally, we screened various promoters to identify the preferred gene regulatory unit that should be used to ensure stable expression in the human MuSC clones. The 38 clonal immortalized myogenic cell clones provide a large collection of controls and DMD clones with various genetic defects and are available to the academic community.

Effect of cell-extracellular matrix interaction on myogenic characteristics and artificial skeletal muscle tissue

Although various types of artificial skeletal muscle tissue have been reported, the contractile forces generated by tissue-engineered artificial skeletal muscles remain to be improved for biological model and clinical applications. In this study, we investigated the effects of extracellular matrix (ECM) and supplementation of a small molecule, which has been reported to enhance α7β1 integrin expression (SU9516), on cell migration speed, cell fusion rate, myoblast (mouse C2C12cells) differentiation and contractile force generation of tissue-engineered artificial skeletal muscles. When cells were cultured on varying ECM coated-surfaces, we observed significant enhancement in the migration speed, while the myotube formation (differentiation ratio) decreased in all except for cells cultured on Matrigel coated-surfaces. In contrast, SU9516 supplementation resulted in an increase in both the myotube width and differentiation ratio. Following combined culture with a Matrigel-coated surface and SU9516 supplementation, myotube width was further increased. Additionally, contractile forces produced by the tissue-engineered artificial skeletal muscles was augmented following combined culture. These findings indicate that regulation of the cell-ECM interaction is a promising approach to improve the function of tissue-engineered artificial skeletal muscles.

Pathway-specific reporter genes to study stem cell biology.

Little is known on the phenotypic characteristics of stem cells (SCs) after they are transplanted to the myocardium, in part due to lack of noninvasive platforms to study SCs directly in the living subject. Reporter gene imaging has played a valuable role in the noninvasive assessment of cell fate in vivo. In this study, we validated a pathway-specific reporter gene that can be used to noninvasively image the phenotype of SCs transplanted to the myocardium. Rat mesenchymal SCs (MSCs) were studied for phenotypic evidence of myogenic characteristics under in vitro conditions. After markers of myogenic characteristics were identified, we constructed a reporter gene sensor, comprising the firefly luciferase (Fluc) reporter gene driven by the troponin T (TnT) promoter (cardio MSCs had threefold expression in polymerase chain reaction compared to control MSCs) using a two-step signal amplification strategy. MSCs transfected with TnT-Fluc were studied and validated under in vitro conditions, showing a strong signal after MSCs acquired myogenic characteristics. Lastly, we observed that cardio MSCs had higher expression of the reporter sensor compared to control cells (0.005 ± 0.0005 vs 0.0025 ± 0.0008 Tnt-Fluc/ubiquitin-Fluc, P < .05), and that this novel sensor can detect the change in the phenotype of MSCs directly in the living subject. Pathway-specific reporter gene imaging allows assessment of changes in the phenotype of MSCs after delivery to the ischemic myocardium, providing important information on the phenotype of these cells. Imaging sensors like the one described here are critical to better understanding of the changes that SCs undergo after transplantation.

Intrinsic Myogenic Potential of Skeletal Muscle-Derived Pericytes from Patients with Myotonic Dystrophy Type 1

Pericytes are multipotent, vessel-associated progenitors that exhibit high proliferative capacity, can cross the blood-muscle barrier, and have the ability to home to muscle tissue and contribute to myogenesis. Consequently, pericyte-based therapies hold great promise for muscular dystrophies. A complex multi-system disorder exhibiting muscular dystrophy for which pericytes might be a valuable cell source is myotonic dystrophy type 1 (DM1). DM1 is caused by an unstable (CTG)n repeat in the DMPK gene and characterized by skeletal muscle weakness, muscle wasting, and myotonia. We have successfully isolated alkaline phosphatase-positive pericytes from skeletal muscle of DM1 patients and a transgenic mouse model. Intranuclear (CUG)n RNA foci, a pathogenic DM1 hallmark, were identified in human and mouse pericytes. Notably, pericytes from DM1 patients maintained similar growth parameters and innate myogenic characteristics in vitro compared to cells from unaffected controls. Our in vitro results thus demonstrate the potential of pericytes to ameliorate muscle features in DM1 in a therapeutic setting.

P.498 - Dystrophin Dp427 is lost due to multiple DMD intron retentions in rhabdomyosarcoma CRL-2061 cells

Dystrophin inactivation, responsible for Duchenne muscular dystrophy (DMD), is recently implicated as an anti-tumor suppressor factor in cancers with myogenic characteristics. Rhabdomyosarcoma (RMS), a mesodermal cancer, shows myogenic features and occurs at a higher frequency in mdx mouse, a DMD model mouse. In humans, as the clinical management of DMD advances to increase the life expectancy of patients, a subsequent issue is anticipated to be that of addressing other complications such as RMS. RMS, although displays myogenic properties, has not yet been fully evaluated for dystrophin expression. Here, we used reverse transcription PCR and western blotting to analyze dystrophin in RMS CRL-2061 cells. The 14 kb DMD transcript was fully amplified as 20 fragments as in skeletal muscle. Alternatively, spliced transcripts including 3 intron retentions and 2 exons skipping events were disclosed. In one fragment extending from exon 70 to 79, no normally spliced product was obtained. Instead, 6 alternatively spliced products including a new product deleting exon 73 were identified, and exon 78 deleted products was most abundant. However, dystrophin Dp427 was not detected by western blotting. Remarkably, analysis of 9 short DMD introns indicated retention of introns 40, 58 and 70. These intron retentions occupied 75, 15 and 20 % of the total PCR amplified products, respectively, indicating the possibility of every DMD transcript to carry an intron retention event. Multiple intron retentions in the DMD transcript are suggested to hamper translation of the Dp427 isoform and promote tumorigenesis in RMS. This study exemplifies the important significance of DMD intron retention in tumorigenesis in RMS.

Isolation of myogenic progenitor cell population from human placenta: A pilot study

PurposeThe purpose of this study was to demonstrate a method of isolating myogenic progenitor cells from human placenta chorionic villi and to confirm the myogenic characteristics of the isolated cells. MethodsCells were isolated from chorionic villi of a second trimester male placenta via a combined enzymatic digestion and explant culture. A morphologically distinct subpopulation of elongated and multinucleated cells was identified. This subpopulation was manually passaged from the explant culture, expanded, and analyzed by fluorescence in situ hybridization (FISH) assay, immunocytochemistry, and flow cytometry. Myogenic characteristics including alignment and fusion were tested by growing these cells on aligned polylactic acid microfibrous scaffold in a fusion media composed of 2% horse serum in Dulbecco's modified Eagle medium/high glucose. ResultsThe expanded subpopulation was uniformly positive for integrin α-7. Presence of Y-chromosome by FISH analysis confirmed chorionic villus origin rather than maternal cell contamination. Isolated cells grew, aligned, and fused on the microfibrous scaffold, and they expressed myogenin, desmin, and MHC confirming their myogenic identity. ConclusionMyogenic progenitor cells can be isolated from human chorionic villi. This opens the possibility for translational and clinical applications using autologous myogenic cells for possible engraftment in treatment of chest and abdominal wall defects.

Myoepithelial carcinoma with RB1 mutation: remarkable chemosensitivity to carcinoma of unknown origin therapy

BackgroundMyoepithelial carcinoma of soft tissue is a rare, malignant neoplasm that is morphologically and immunophenotypically similar to its counterpart in salivary gland. It demonstrates myoepithelial differentiation, possessing both epithelial and myogenic characteristics. Thought to be chemotherapy insensitive, the optimal treatment regimen of this tumor has yet to be established and only a select few cases in the literature discuss treatment efficacy in detail.Case presentationHere we present a case of a young adult with metastatic myoepithelial carcinoma with an initial excellent response to systemic therapy utilizing carboplatin and paclitaxel with continued complete response after 3 years. The patient also underwent complete surgical excision and received adjuvant radiation to the primary site of disease. Exome sequencing revealed an inactivating mutation in RB1 which we believe to be the first such mutation to be reported in this cancer type.ConclusionsGiven increasing evidence suggesting RB1 loss is associated with responsiveness to conventional chemotherapies, particularly platinum-based regimens, we hypothesize that this genetic feature predisposed chemosensitivity in our patient’s tumor.

Mammalian Skeletal Muscle Fibres Promote Non-Muscle Stem Cells and Non-Stem Cells to Adopt Myogenic Characteristics

Skeletal muscle fibres are unique cells in large animals, often composed of thousands of post-mitotic nuclei. Following skeletal muscle damage, resident stem cells, called satellite cells, commit to myogenic differentiation and migrate to carry out repair. Satellite stem cells migrate on muscle fibres through amoeboid movement, which relies on dynamic cell membrane extension and retraction (blebbing). It is not known whether blebbing is due to the intrinsic properties of satellite cells, or induced by features of the myofibre surface. Here, we determined the influence of the muscle fibre matrix on two important features of muscle regeneration: the ability to migrate and to differentiate down a myogenic lineage. We show that the muscle fibre is able to induce amoeboid movement in non-muscle stem cells and non-stem cells. Secondly, we show that prolonged co-culture on myofibres caused amniotic fluid stem cells and breast cancer cells to express MyoD, a key myogenic determinant. Finally, we show that amniotic fluid stem cells co-cultured on myofibres are able to fuse and make myotubes that express Myosin Heavy Chain.

MP8-01 THE ESTABLISHMENT OF AN UNDERACTIVE BLADDER MODEL FOLLOWING A HYSTERECTOMY IN MONKEY

INTRODUCTION AND OBJECTIVES: Underactive bladder (UAB) syndrome describes a dysfunctional condition of the bladder where patients are unable to produce an effective voiding contraction. To date a pathophysiological mechanisms are not fully understood. To address this issue, we established on underactive bladder model in monkeys after having a hysterectomy. METHODS: Female cynomolgus monkeys were anesthetized with ketamine chloride and pentobarbital sodium. The uterine corpus was then surgically removed while preserving the uterine cervix. Days after surgery, conscious animals were placed on chairs to monitor natural urination after oral administration of 150 mL water (uroflowmetry, UFM). In addition to this, in order to confirm the detrusor underactivity, pressure flow study (PFS) was conducted in the conscious animals. An in vitro muscle strip study was also performed. RESULTS: Monkeys showed typical detrusor underactivity in PFS. Maximum flow rate (Qmax), average flow rate (Qave) and voided volume per micturition were significantly decreased at 2, 4, 6, 8, 21, 60 days after surgery compared with before surgery. On the contrary, voiding time per micturition was significantly increased. Sham-operated group did not show any changes. In muscle strip studies, there was significant decrease in maximum response to potassium chloride (KCl) in the 2 months group but not in the 2 weeks group compared with the sham group. There was a significant decrease in the response to carbachol (CCh) and electric field stimulation (EFS) in both the 2 weeks and 2 months group. CONCLUSIONS: This is the first report on UAB model following a hysterectomy in monkeys. This model had an acutely neurogenic but chronically neurogenic and myogenic characteristics. It seems to be useful in the pathophysiological elucidation of UAB and have potential for assessment of pharmacotherapy of UAB. Source of Funding: none

A high salt diet alters pressure-induced mechanical activity of the rat lymphatics with enhancement of myogenic characteristics.

The lymphatic system has become a new player for pathogenesis in salt-sensitive hypertension animals. A high salt diet (HSD) evokes accumulation of Na(+) in the skin of rodents. In response to increase in Na(+)-proteoglycan complex, infiltrated macrophages stimulate secretion of vascular endothelial growth factor (VEGF)-C. Macrophage-derived VEGF-C increases density of the dermal lymph capillaries, indicating that lymphangiogenesis is advantageous to hypertensive animals by buffering elevated blood pressure. However, the effects of a high salt diet (HSD) on changes in mechanical activity of collecting lymph vessels, which directly connect with lymph capillaries, have not yet been determined. Changes in mechanical activity of isolated collecting lymphatics in normal salt diet (NSD) and HSD rats in response to increase in intraluminal pressures were measured by video-microscopy. HSD vessels had smaller % active diameters (maximum and minimum) and higher amplitude compared with NSD vessels. The frequency of lymphatic oscillation was better maintained in HSD rats than in NSD. Lymphatic pump efficiency including stroke volume index (SVI), frequency times SVI, and amplitude times frequency in HSD rats were significantly higher than those of NSD. Thus, a HSD enhances the resistance to pressure-induced decreases in lymphatic pump efficiency. The present ex vivo study suggest that collecting lymphatics of rats enhance myogenic activity and lymphatic pump efficiency to compensate for increase in lymph flow and/or pressure after 2 weeks salt loading.

Effects of type IV collagen on myogenic characteristics of IGF-I gene-engineered myoblasts

Skeletal muscle regeneration requires migration, proliferation and fusion of myoblasts to form multinucleated myotubes. In our previous study, we showed that insulin-like growth factor (IGF)-I gene delivery stimulates the proliferation and differentiation of mouse myoblast C2C12 cells and promotes the contractile force generated by tissue-engineered skeletal muscles. The aim of this study was to investigate the effects of the extracellular matrix on IGF-I gene-engineered C2C12 cells in vitro. Retroviral vectors for doxycycline (Dox)-inducible expression of the IGF-I gene were transduced into C2C12 cells. When cultured on a type IV collagen-coated surface, we observed significant increases in the migration speed and number of IGF-I gene-engineered C2C12 cells with Dox addition, designated as C2C12/IGF (+) cells. Co-culture of C2C12/IGF (+) cells and parental C2C12 cells, which had been cultured in differentiation medium for 3 days, greatly enhanced myotube formation. Moreover, type IV collagen supplementation promoted the fusion of C2C12/IGF (+) cells with differentiated C2C12 cells and increased the number of myotubes with striations. Myotubes formed by C2C12/IGF (+) cells cultured on type IV collagen showed a dynamic contractile activity in response to electrical pulse stimulation. These findings indicate that type IV collagen promotes skeletal muscle regeneration mediated by IGF-I-expressing myoblasts, which may have important clinical implications in the design of myoblast-based therapies.

Myogenic characteristics of the afferent arteriole in papillectomized and in Cx40 deficient mice (678.1)

Glomerular flow is regulated through diameter changes in the afferent arteriole (AA). In turn diameter of the AA is regulated primarily by the myogenic response and by the tubuloglomerular feedback (TGF) mechanism constituting renal autoregulation. Connexin 40 (Cx40) is the main connexin of endothelial gap junctions in AA and it has been shown previously that Cx40 knock‐out (Cx40KO) mice lack TGF. In the present study we investigated whether absence of functional Cx40 in the endothelium also affects the properties of the myogenic response in the AA. We compared the diameter changes of the AA to an increase in renal perfusion pressure, which elicits an autoregulatory AA contraction induced by the myogenic response and TGF. We compared papillectomized wildtype mice (lacking TGF, but with intact intracellular communication in the endothelial layer) versus Cx40KO mice (lacking TGF and with deficient intracellular communication in the endothelium). We found no differences between the two groups indicating that the level of myogenic tone is largely determined by the local pressure, independent of longitudinal endothelial communication. In addition we modeled the observed myogenic response and estimated the characteristic relation between circumferential stress and vessel wall activation leading to the observed myogenic behavior.

Biophysical cues enhance myogenesis of human adipose derived stem/stromal cells

Adipose-derived stem/stromal cell (ASC)-based tissue engineered muscle grafts could provide an effective alternative therapy to autografts – which are limited by their availability – for the regeneration of damaged muscle. However, the current myogenic potential of ASCs is limited by their low differentiation efficiency into myoblasts. The aim of this study was to enhance the myogenic response of human ASCs to biochemical cues by providing biophysical stimuli (11% cyclic uniaxial strain, 0.5Hz, 1h/day) to mimic the cues present in the native muscle microenvironment. ASCs elongated and fused upon induction with myogenic induction medium alone. Yet, their myogenic characteristics were significantly enhanced with the addition of biophysical stimulation; the nuclei per cell increased approximately 4.5-fold by day 21 in dynamic compared to static conditions (23.3±7.3 vs. 5.2±1.6, respectively), they aligned at almost 45° to the direction of strain, and exhibited significantly higher expression of myogenic proteins (desmin, myoD and myosin heavy chain). These results demonstrate that mimicking the biophysical cues inherent to the native muscle microenvironment in monolayer ASC cultures significantly improves their differentiation along the myogenic lineage.

Generation of Isogenic D4Z4 Contracted and Noncontracted Immortal Muscle Cell Clones from a Mosaic Patient: A Cellular Model for FSHD

In most cases facioscapulohumeral muscular dystrophy (FSHD) is caused by contraction of the D4Z4 repeat in the 4q subtelomere. This contraction is associated with local chromatin decondensation and derepression of the DUX4 retrogene. Its complex genetic and epigenetic cause and high clinical variability in disease severity complicate investigations on the pathogenic mechanism underlying FSHD. A validated cellular model bypassing the considerable heterogeneity would facilitate mechanistic and therapeutic studies of FSHD. Taking advantage of the high incidence of somatic mosaicism for D4Z4 repeat contraction in de novo FSHD, we have established a clonal myogenic cell model from a mosaic patient. Individual clones are genetically identical except for the size of the D4Z4 repeat array, being either normal or FSHD sized. These clones retain their myogenic characteristics, and D4Z4 contracted clones differ from the noncontracted clones by the bursts of expression of DUX4 in sporadic nuclei, showing that this burst-like phenomenon is a locus-intrinsic feature. Consequently, downstream effects of DUX4 expression can be observed in D4Z4 contracted clones, like differential expression of DUX4 target genes. We also show their participation to in vivo regeneration with immunodeficient mice, further expanding the potential of these clones for mechanistic and therapeutic studies. These cell lines will facilitate pairwise comparisons to identify FSHD-specific differences and are expected to create new opportunities for high-throughput drug screens.

In Situ Implantation Preserves Myogenic and Neuronal Characteristics of Intrinsically Innervated Bioengineered Human Internal Anal Sphincter (IAS)

G A A b st ra ct s younger on average (65.5 ±10.7) than bleeding cases (70.0±11.4; p = 0.056). Conclusions: 1. The rate of gastrointestinal bleeding among patients on dual antiplatelet therapy after PCI with PPI co-therapy is 1.8 cases per 100 patient-years. 2. Most bleeding events occur during the first year of follow-up and are located in the lower GI tract. 3. Risk factors predictive of a bleeding event are co-therapy with warfarin, age and a peptic ulcer history.