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Rhabdomyosarcomas (RMS) are the most common soft tissue cancer among children and are characterized by their expression of the myogenic regulatory factors MyoD and myogenin. Yet RMS cells cannot undergo normal myogenesis and are caught between the proliferation program and the terminal differentiation program. Many questions still remain about the defects present in rhabdomyosarcoma cells. In this work, we set out to understand the role of myogenin in these cells. To begin, we found that myogenin and its co-factors were present in rhabdomyosarcoma cells at levels that should support terminal differentiation. We examined the expression profile of several myogenin target genes in rhabdomyosarcoma cells and then assayed for myogenin activity using luciferase reporter constructs that contain myogenin dependent promoters to test for myogenin function. Many myogenin target genes were down regulated in RMS cells but that the target promoters on the luciferase constructs were activated. Terminal differentiation is a complicated process that involves many proteins. In cancer cells, it is important to compare the levels proteins with known functions to those levels in wild-type cells at the protein and RNA levels. Establishing the defect of rhabdomyosarcoma cells can lead to further insights into normal myogenesis, and may also lead to new therapeutic approaches in the treatment of this childhood cancer.

Rhabdomyosarcoma (RMS) is a highly malignant pediatric cancer that is the most common form of soft tissue tumors in children. RMS cells have many features of skeletal muscle cells, yet do not differentiate. Thus, our studies have focused on the molecular defects present in these cells that block myogenesis. We have found MEF2D is absent in RMS cell lines representing both major subtypes of RMS and primary cells derived from an embryonal RMS mice model. We have shown that the down regulation of MEF2D is a major cause for the failure of RMS cells to differentiate. We find MEF2D cannot bind to muscle specific gene promoters. Exogenous expression of MEF2D activates muscle specific luciferase constructs, upregulates p21 expression and increases muscle specific gene expression including the expression of myosin heavy chain, a marker for skeletal muscle differentiation. Restoring expression of MEF2D also inhibits proliferation, cell motility, anchorage independent growth in vitro, and tumor growth in vivo by xenograft assay. We also have found MEF2C is deregulated in rhabdomyosarcoma with the aberrant alternative splicing. We have shown that exon α in MEF2C is aberrantly alternatively spliced in RMS cells, with the ratio of α2/α1 being highly downregulated in RMS cells compared with normal myoblasts. We find that MEF2Cα1 is the ubiquitously expressed isoform which exhibits no myogenic activity and that MEF2Cα2, the muscle specific MEF2C isoform, is required for efficient differentiation. Compared with MEF2Cα2, MEF2Cα1 more strongly interacts with and recruits HDAC5 to myogenic gene promoters to repress muscle specific genes. Overexpression of the MEF2Cα2 isoform in RMS cells increases myogenic activity and promotes differentiation in RMS cells. We have also identified a serine protein kinase, SRPK3, which is downregulated in RMS cells and found that expression of SRPK3 promoted the splicing of the MEF2Cα2 isoform and induced differentiation. Restoration of either MEF2Cα2 or SPRK3 inhibited both proliferation and anchorage independent growth of RMS cells. The NAC complex performs many diverse biological functions, and the deregulation of its subunits has been correlated with many cancers. We sought to understand the function of the NAC complex in normal myogenesis and tumor progression in rhabdomyosarcoma cells. We found that the muscle specific subunit of the NAC complex, skNAC, which is the alternatively spliced isoform of NACα, was induced in normal cells and downregulated in RMS cells, while BTF3, also known as NACβ, was induced in normal cells and severely downregulated in RMS cells. We also showed that skNAC associated with muscle specific promoters together with BTF3 in differentiated normal cells, and this association was dependent on the expression of BTF3. We further investigated the involvement of skNAC in RMS progression. We found that the muscle specific expressed methyltransferase Smyd1 was nuclear localized in RMS cells and its interaction partner skNAC was switched with corepressors (HDAC1 and TBX2). We also confirmed the expression of skNAC was regulated by the splicing factor kinase SRPK3 and overexpression of SPRK3 induced skNAC expression and muscle differentiation in RMS cells. We also confirmed the overexpression of BTF3 in patient RMS tumors and depletion of BTF3 induced apoptosis in RMS cells and decrease RMS cell survival. BTF3 depletion also sensitized TRAIL induced cell apoptosis in RMS cells. However, BTF3 played a different role in normal cells. Deletion of BTF3 in C2C12 cells does not induce cell apoptosis, which suggests BTF3 functions as an anti-apoptosis factor in RMS cells and could be used as a cancer specific therapeutic target in RMS cells.

Base teórica: A osteoartrite é uma doença crônica cuja principal característica é a degradação progressiva da cartilagem articular. Além do acometimento articular, frequentemente, os pacientes com osteoartrite apresentam fraqueza e atrofia dos músculos periarticulares. Apesar disso, os mecanismos moleculares envolvidos na perda muscular relacionada à osteoartrite não são conhecidos. Os principais mecanismos já estudados, em outras condições, estão relacionados ao aumento da degradação e à redução da síntese de proteínas musculares e a déficits na ativação das células-satélite, responsáveis pela regeneração muscular. A miostatina, um importante regulador negativo do crescimento da massa muscular, estimula o aumento da degradação e a redução da síntese de proteínas musculares. Por outro lado, MyoD e miogenina, são marcadores de proliferação e de diferenciação de células-satélite, respectivamente. Objetivos: Investigar os mecanismos moleculares envolvidos na perda muscular em um modelo animal de osteoartrite induzida por transecção do ligamento cruzado anterior em ratas. Métodos: Ratas Wistar fêmeas foram alocadas em dois grupos: OA (submetidas à cirurgia de transecção do ligamento cruzado anterior do joelho direito) e SHAM (submetidas à cirurgia fictícia do joelho direito). Durante o período experimental de 12 semanas foram avaliados, semanalmente, o peso corporal e a locomoção exploratória espontânea. Após a eutanásia, foram coletadas as articulações do joelho direito para confirmação do desenvolvimento da doença. Os músculos gastrocnêmio, tibial-anterior e sóleo, da pata posterior direita, foram dissecados, pesados e congelados. O músculo gastrocnêmio foi utilizado para a avaliação da atrofia muscular, através da análise da área seccional da miofibra, e para análise da expressão proteica de miostatina, MyoD e miogenina. Resultados: A locomoção exploratória espontânea, o peso corporal e o peso dos músculos gastrocnêmio, tibial-anterior e sóleo não apresentaram diferença significativa entre os grupos OA e SHAM. A histopatologia da articulação do joelho confirmou o desenvolvimento da doença nos animais do grupo OA. A área do músculo gastrocnêmio demonstrou redução de aproximadamente 10% no grupo OA, em comparação com o grupo SHAM. O grupo OA apresentou aumento na expressão proteica de miostatina e redução na expressão proteica de miogenina. A expressão proteica de MyoD não apresentou diferença entre os grupos. Conclusão: A atrofia do músculo gastrocnêmio presente na osteoartrite induzida por transecção do ligamento cruzado anterior envolve aumento na expressão de miostatina e redução na expressão de miogenina. Nesse modelo, a perda muscular pode estar relacionada à proteólise induzida pelos níveis aumentados de miostatina e ao déficit na diferenciação das células-satélite devido à redução na expressão de miogenina. / Background: Osteoarthritis is a chronic joint disease primarily characterized by cartilage loss. In addition to joint impairment, patients with osteoarthritis often suffer from weakness and atrophy of the periarticular muscles. However, the molecular mechanisms involved in osteoarthritis-related muscle wasting are not known. The main mechanisms studied, in other conditions, are related to increased degradation and reduced synthesis of muscle protein and to deficits in the activation of satellitecells, which are responsible for muscle regeneration. Myostatin, an important negative regulator of muscle growth, stimulates the increase of degradation and the reduction of synthesis of muscle protein. Moreover, MyoD and myogenin are markers of proliferation and differentiation of satellite-cells, respectively. Objective: To investigate the pathways involved in muscle wasting in a model of osteoarthritis induced by anterior cruciate ligament transection (ACL) in rats. Methods: Female Wistar rats were allocated into two groups: OA (submitted to the ACL transection) and SHAM (submitted to surgical procedures without ACL transection). The spontaneous exploratory locomotion and the body weight of animals were evaluated weekly. In the twelfth week after the induction of disease, animals were euthanized and the right knee joints were collected for further confirmation of the disease by histopathology. Gastrocnemius, tibialis-anterior and soleus muscles from right hind paw were dissected, weighed and frozen. Gastrocnemius was used for evaluation of muscle atrophy, by cross-sectional area measurement, and protein expression of myostatin, MyoD and myogenin. Results: Spontaneous exploratory locomotion, body weight and weight of muscles showed no difference between OA and SHAM groups. The histopathology of the knee joints confirmed the development of the disease in animals from OA group. Gastrocnemius area of animals from OA group had a reduction of about 10% compared to animals from SHAM group. Protein expression of myostatin was increased in animals from OA group, while myogenin expression was decreased. MyoD expression was similar in both OA and SHAM groups. Conclusion: Gastrocnemius atrophy in osteoarthritis induced by ACL transection involves increased protein expression of myostatin and decreased protein expression of myogenin. In this model, muscle wasting may be linked to myostatininduced proteolysis and to deficits in satellite-cell differentiation due to decreased expression of myogenin.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 83-97).

Skeletal muscle injury results in functional deficits that can take several weeks to fully recover. Ultimate recovery of function is dependent on the muscle’s ability to regenerate, a highly coordinated process that involves transient muscle inflammation and the replacement of damaged myofibers. Instrumental in the inflammatory response, is the pro-inflammatory cytokine TNF-α. Expression of TNF-α is thought to be regulated, in part, by the stress sensing 70 kDa heat shock protein (Hsp70). However, it remains unclear how Hsp70 alters TNF-α following injury, and if so, how these changes affect skeletal muscle repair. Therefore, we up-regulated Hsp70 expression using 17-allylamino-17-demethoxygeldanamycin (17-AAG) prior to and following BaCl2-induced injury, and assessed TNF-α and myogenin content. Regenerating fiber cross-sectional area (CSA) and in vivo isometric torque were also analyzed in the weeks following the injury. Treatment of 17-AAG resulted in a ~5 fold increase in Hsp70 of the uninjured muscle, but did not affect any other biochemical, morphological or functional variables compared to controls. In the days following the injury, TNF-α and myogenin were elevated and directly correlated. At these earlier time points (≤7 days), treatment of 17-AAG increased TNF-α above that of the injured controls and resulted in a sustained increase in myogenin. However, no differences were observed in regenerating fiber CSA or in vivo torque production between the groups. Together, these data suggest that Hsp70 induction increases TNF-α and myogenin content following BaCl2-induced injury, but does not appear to alter skeletal muscle regeneration or attenuate functional deficits in otherwise healthy young mice.

Base teórica: A osteoartrite é uma doença crônica cuja principal característica é a degradação progressiva da cartilagem articular. Além do acometimento articular, frequentemente, os pacientes com osteoartrite apresentam fraqueza e atrofia dos músculos periarticulares. Apesar disso, os mecanismos moleculares envolvidos na perda muscular relacionada à osteoartrite não são conhecidos. Os principais mecanismos já estudados, em outras condições, estão relacionados ao aumento da degradação e à redução da síntese de proteínas musculares e a déficits na ativação das células-satélite, responsáveis pela regeneração muscular. A miostatina, um importante regulador negativo do crescimento da massa muscular, estimula o aumento da degradação e a redução da síntese de proteínas musculares. Por outro lado, MyoD e miogenina, são marcadores de proliferação e de diferenciação de células-satélite, respectivamente. Objetivos: Investigar os mecanismos moleculares envolvidos na perda muscular em um modelo animal de osteoartrite induzida por transecção do ligamento cruzado anterior em ratas. Métodos: Ratas Wistar fêmeas foram alocadas em dois grupos: OA (submetidas à cirurgia de transecção do ligamento cruzado anterior do joelho direito) e SHAM (submetidas à cirurgia fictícia do joelho direito). Durante o período experimental de 12 semanas foram avaliados, semanalmente, o peso corporal e a locomoção exploratória espontânea. Após a eutanásia, foram coletadas as articulações do joelho direito para confirmação do desenvolvimento da doença. Os músculos gastrocnêmio, tibial-anterior e sóleo, da pata posterior direita, foram dissecados, pesados e congelados. O músculo gastrocnêmio foi utilizado para a avaliação da atrofia muscular, através da análise da área seccional da miofibra, e para análise da expressão proteica de miostatina, MyoD e miogenina. Resultados: A locomoção exploratória espontânea, o peso corporal e o peso dos músculos gastrocnêmio, tibial-anterior e sóleo não apresentaram diferença significativa entre os grupos OA e SHAM. A histopatologia da articulação do joelho confirmou o desenvolvimento da doença nos animais do grupo OA. A área do músculo gastrocnêmio demonstrou redução de aproximadamente 10% no grupo OA, em comparação com o grupo SHAM. O grupo OA apresentou aumento na expressão proteica de miostatina e redução na expressão proteica de miogenina. A expressão proteica de MyoD não apresentou diferença entre os grupos. Conclusão: A atrofia do músculo gastrocnêmio presente na osteoartrite induzida por transecção do ligamento cruzado anterior envolve aumento na expressão de miostatina e redução na expressão de miogenina. Nesse modelo, a perda muscular pode estar relacionada à proteólise induzida pelos níveis aumentados de miostatina e ao déficit na diferenciação das células-satélite devido à redução na expressão de miogenina. / Background: Osteoarthritis is a chronic joint disease primarily characterized by cartilage loss. In addition to joint impairment, patients with osteoarthritis often suffer from weakness and atrophy of the periarticular muscles. However, the molecular mechanisms involved in osteoarthritis-related muscle wasting are not known. The main mechanisms studied, in other conditions, are related to increased degradation and reduced synthesis of muscle protein and to deficits in the activation of satellitecells, which are responsible for muscle regeneration. Myostatin, an important negative regulator of muscle growth, stimulates the increase of degradation and the reduction of synthesis of muscle protein. Moreover, MyoD and myogenin are markers of proliferation and differentiation of satellite-cells, respectively. Objective: To investigate the pathways involved in muscle wasting in a model of osteoarthritis induced by anterior cruciate ligament transection (ACL) in rats. Methods: Female Wistar rats were allocated into two groups: OA (submitted to the ACL transection) and SHAM (submitted to surgical procedures without ACL transection). The spontaneous exploratory locomotion and the body weight of animals were evaluated weekly. In the twelfth week after the induction of disease, animals were euthanized and the right knee joints were collected for further confirmation of the disease by histopathology. Gastrocnemius, tibialis-anterior and soleus muscles from right hind paw were dissected, weighed and frozen. Gastrocnemius was used for evaluation of muscle atrophy, by cross-sectional area measurement, and protein expression of myostatin, MyoD and myogenin. Results: Spontaneous exploratory locomotion, body weight and weight of muscles showed no difference between OA and SHAM groups. The histopathology of the knee joints confirmed the development of the disease in animals from OA group. Gastrocnemius area of animals from OA group had a reduction of about 10% compared to animals from SHAM group. Protein expression of myostatin was increased in animals from OA group, while myogenin expression was decreased. MyoD expression was similar in both OA and SHAM groups. Conclusion: Gastrocnemius atrophy in osteoarthritis induced by ACL transection involves increased protein expression of myostatin and decreased protein expression of myogenin. In this model, muscle wasting may be linked to myostatininduced proteolysis and to deficits in satellite-cell differentiation due to decreased expression of myogenin.

Base teórica: A osteoartrite é uma doença crônica cuja principal característica é a degradação progressiva da cartilagem articular. Além do acometimento articular, frequentemente, os pacientes com osteoartrite apresentam fraqueza e atrofia dos músculos periarticulares. Apesar disso, os mecanismos moleculares envolvidos na perda muscular relacionada à osteoartrite não são conhecidos. Os principais mecanismos já estudados, em outras condições, estão relacionados ao aumento da degradação e à redução da síntese de proteínas musculares e a déficits na ativação das células-satélite, responsáveis pela regeneração muscular. A miostatina, um importante regulador negativo do crescimento da massa muscular, estimula o aumento da degradação e a redução da síntese de proteínas musculares. Por outro lado, MyoD e miogenina, são marcadores de proliferação e de diferenciação de células-satélite, respectivamente. Objetivos: Investigar os mecanismos moleculares envolvidos na perda muscular em um modelo animal de osteoartrite induzida por transecção do ligamento cruzado anterior em ratas. Métodos: Ratas Wistar fêmeas foram alocadas em dois grupos: OA (submetidas à cirurgia de transecção do ligamento cruzado anterior do joelho direito) e SHAM (submetidas à cirurgia fictícia do joelho direito). Durante o período experimental de 12 semanas foram avaliados, semanalmente, o peso corporal e a locomoção exploratória espontânea. Após a eutanásia, foram coletadas as articulações do joelho direito para confirmação do desenvolvimento da doença. Os músculos gastrocnêmio, tibial-anterior e sóleo, da pata posterior direita, foram dissecados, pesados e congelados. O músculo gastrocnêmio foi utilizado para a avaliação da atrofia muscular, através da análise da área seccional da miofibra, e para análise da expressão proteica de miostatina, MyoD e miogenina. Resultados: A locomoção exploratória espontânea, o peso corporal e o peso dos músculos gastrocnêmio, tibial-anterior e sóleo não apresentaram diferença significativa entre os grupos OA e SHAM. A histopatologia da articulação do joelho confirmou o desenvolvimento da doença nos animais do grupo OA. A área do músculo gastrocnêmio demonstrou redução de aproximadamente 10% no grupo OA, em comparação com o grupo SHAM. O grupo OA apresentou aumento na expressão proteica de miostatina e redução na expressão proteica de miogenina. A expressão proteica de MyoD não apresentou diferença entre os grupos. Conclusão: A atrofia do músculo gastrocnêmio presente na osteoartrite induzida por transecção do ligamento cruzado anterior envolve aumento na expressão de miostatina e redução na expressão de miogenina. Nesse modelo, a perda muscular pode estar relacionada à proteólise induzida pelos níveis aumentados de miostatina e ao déficit na diferenciação das células-satélite devido à redução na expressão de miogenina. / Background: Osteoarthritis is a chronic joint disease primarily characterized by cartilage loss. In addition to joint impairment, patients with osteoarthritis often suffer from weakness and atrophy of the periarticular muscles. However, the molecular mechanisms involved in osteoarthritis-related muscle wasting are not known. The main mechanisms studied, in other conditions, are related to increased degradation and reduced synthesis of muscle protein and to deficits in the activation of satellitecells, which are responsible for muscle regeneration. Myostatin, an important negative regulator of muscle growth, stimulates the increase of degradation and the reduction of synthesis of muscle protein. Moreover, MyoD and myogenin are markers of proliferation and differentiation of satellite-cells, respectively. Objective: To investigate the pathways involved in muscle wasting in a model of osteoarthritis induced by anterior cruciate ligament transection (ACL) in rats. Methods: Female Wistar rats were allocated into two groups: OA (submitted to the ACL transection) and SHAM (submitted to surgical procedures without ACL transection). The spontaneous exploratory locomotion and the body weight of animals were evaluated weekly. In the twelfth week after the induction of disease, animals were euthanized and the right knee joints were collected for further confirmation of the disease by histopathology. Gastrocnemius, tibialis-anterior and soleus muscles from right hind paw were dissected, weighed and frozen. Gastrocnemius was used for evaluation of muscle atrophy, by cross-sectional area measurement, and protein expression of myostatin, MyoD and myogenin. Results: Spontaneous exploratory locomotion, body weight and weight of muscles showed no difference between OA and SHAM groups. The histopathology of the knee joints confirmed the development of the disease in animals from OA group. Gastrocnemius area of animals from OA group had a reduction of about 10% compared to animals from SHAM group. Protein expression of myostatin was increased in animals from OA group, while myogenin expression was decreased. MyoD expression was similar in both OA and SHAM groups. Conclusion: Gastrocnemius atrophy in osteoarthritis induced by ACL transection involves increased protein expression of myostatin and decreased protein expression of myogenin. In this model, muscle wasting may be linked to myostatininduced proteolysis and to deficits in satellite-cell differentiation due to decreased expression of myogenin.

Orientadores: Daniela Cristina Carvalho de Abreu, Alberto Cliquet Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas / Made available in DSpace on 2018-08-22T07:19:52Z (GMT). No. of bitstreams: 1 Brunelli_RobertadeMatos_M.pdf: 1872583 bytes, checksum: 5ce843f202a01778398ee2807e19dd08 (MD5) Previous issue date: 2013 / Resumo: O objetivo deste estudo foi verificar os efeitos da laserterapia de baixa potência no comprimento de onda ?=780nm entre diferentes períodos de tratamento 7, 14 e 21 dias e verificar a dose (10J/cm2 ou 50J/cm2) que promove melhor reparo muscular através das análises histopatológicas e imunohistoquímicas. Foram utilizados 54 ratos machos divididos em 3 grupos: GC: grupo controle (criolesão, sem tratamento); G10: criolesão do músculo tibial anterior (TA) e tratados com laser dose 10J/cm² e G50: criolesão do músculo TA e tratados com laser dose 50J/cm² que foram subdivididos em 3 subgrupos (n=6): 7, 14 e 21 dias de tratamento. Os achados histopatológicos revelaram maior organização das fibras musculares dos grupos tratados com laser 10J/cm² e 50J/cm² durante os períodos 7 e 14 dias em relação ao grupo controle; no período 21 dias os grupos apresentaram semelhanças na reparação tecidual. Em relação à área da lesão os grupos tratados com laser 10J/cm² e 50J/cm² durante 7 dias obtiveram diminuição significativa (p ? 0.05) da área da lesão em relação ao grupo controle, sendo que os grupos 14 e 21 dias não apresentaram diferenças significativas entre eles. Na contagem dos vasos o grupo tratado com laser 10J/cm² no 14° dia apresentou aumento dos vasos em relação ao grupo tratado com dose 50J/cm², mas não em relação ao grupo controle. Nos tempos de 7 e 21 dias os grupos não apresentaram diferença significativa entre si. Com relação às análises imunohistoquímicas da myoD no período de 7 dias os grupos tratados com laser 10J/cm² e 50J/cm² apresentaram maior imunomarcação comparada com o grupo controle, no período 14 e 21 dias a imunomarcação estava ausente. A imunomarcação da miogenina estava presente de forma semelhante nos períodos 7 e 14 dias para os três grupos analisados e no período 21 dias a imunomarcação da miogenina estava ausente em todos os grupos experimentais. Os resultados mostraram que o laser possui efeitos positivos no reparo muscular / Abstract: The objective of this study was to assess the effects of 780nm low-level laser therapy at different periods of 7, 14 and 21 days after cryolesion, including the dose (10 or 50J/cm2) to promote a better muscle repair evidenced by histopathological and immumohistochemical analyses. Fifty-four male rats were divided into three groups: injured control group (CG) - injured animals without any treatment; injured 780nm laser treated group, at 10 J/cm² (G10) and injured 780nm laser treated group, at 50 J/cm² (G50). Each group was divided into 3 subgroups (n=6): 7, 14 and 21 days post-injury. Histopathological findings revealed better-organized muscle fibers in the G10 and G50 during the periods of 7 and 14 days compared to CG. The G10 and G50 during 7 days showed a significant reduction (p? 0.05) of lesion area compared to CG, without differences between groups treated for 14 and 21 days. The G10 showed an increase of the amount of vessels after 14 days compared to the G50, but not in relation to controls. With regard to the immumohistochemical analyses of the MyoD factor, The G10 and G50 during 7 days showed higher concentrations of immunomarkers than controls. Myogenin immunomarkers were similarly observed at days 7 and 14 in all three groups analyzed, whereas immunomarkers were found in none of the groups after 21 days of laser therapy. The results showed that laser has positive effects on muscle repair / Mestrado / Fisiopatologia Cirúrgica / Mestra em Ciências

Das Chemokine SDF-1α und sein Rezeptor CXCR4 sind in eine Vielzahl biologischer Prozesse, wie der Organogenese, der Hämatopoese und der Immunantwort involviert. Die Entdeckung des alternativen SDF-1α-Rezeptors CXCR7 bewirkte eine erneute Untersuchung der Funktion des SDF-1-Systems in diesen Vorgängen. CXCR7 ist in der Lage, je nach Gewebe- oder Zelltyp, als \"Scavenger\"-Rezeptor, Modulator des CXCR4 oder selbstständig aktiver Rezeptor zu agieren. In dieser Arbeit wurde untersucht, inwiefern beide Rezeptoren im Verlauf der Entwicklung der Muskulatur exprimiert werden, welche Aufgabe sie dabei übernehmen und ob sich Rückschlüsse auf die Muskelregeneration daraus ableiten lassen. Hierfür erfolgten in vitro-Untersuchungen an C2C12-Zellen und die anschließende Analyse der Expression von CXCR4, CXCR7 und SDF-1α in der sich entwickelnden Gliedmaßenmuskulatur von Wildtyp- und mdx-Mäusen. Die Untersuchung von C2C12-Zellen zeigte in allen Differenzierungsstadien eine detektierbare Menge von CXCR4 und eine zunehmende Expression des CXCR7. Die Behandlung der Zellen mit SDF-1α führte zu einer Phosphorylierung von Erk1/2 und PKCζ/λ und hemmte gleichzeitig deren Differenzierung. Nach einer Blockierung des CXCR4 mit seinem pharmakologischen Antagonist AMD3100 oder nach Hemmung der Expression durch spezifische siRNA blieb die Aktivierung des Signalweges aus und der hemmende Einfluss des SDF-1α auf die Differenzierung verschwand vollständig. Im Gegensatz dazu blieben nach der pharmakologischen Blockierung oder durch siRNA vermittelten Expressionshemmung des CXCR7 alle SDF-1α induzierten Effekte vollständig erhalten. Eine Untersuchung des Signalweges am dritten Tag der Differenzierung zeigte keine Aktivierung von Erk1/2. Ebenso blieb Erk1/2 nach einer Hemmung der Expression des CXCR4 unphosphoryliert. Im Gegensatz dazu fand nach einer Hemmung der Expression des CXCR7 mit spezifischer siRNA erneut eine Aktivierung des Signalweges statt. Weiterhin konnte in vivo festgestellt werden, dass die Expression des CXCR4 in der Muskulatur während der embryonalen Entwicklung am höchsten ist und bereits kurz nach der Geburt stark abnimmt, wenn die sekundäre Muskelentwicklung abgeschlossen ist. Die Expression des CXCR7 hingegen steigt perinatal an und bleibt bis zum Erwachsenenalter bestehen. Zusammengefasst zeigen diese Ergebnisse, dass CXCR4 aktiv das Signalgeschehen von SDF-1α in der Myogenese vermittelt und somit zur Differenzierungshemmung von Myoblasten beiträgt. CXCR7 hingegen wirkt als passiver SDF-1α-Scavenger und induziert somit durch eine Modulierung der extrazellulären SDF-1α-Konzentration die Differenzierung. In Übereinstimmung mit der Rolle des SDF-1α-Systems bei der Muskelentwicklung, konnte eine kontinuierliche SDF-1α- Expression im Bindegewebe um pränatale und im Endomysium von postnatalen und adulten Muskelfasern festgestellt werden. Diese SDF-1α-Expression stieg ebenso wie die CXCR4-Expression bei der Analyse der Muskulatur von dystrophin-defizienten Mäusen an und zeigte somit, dass dieses System auch für die Proliferation von Muskelvorläuferzellen in der regenerativen Muskulatur eine wichtige Rolle spielt. Bemerkenswerter Weise hatte diese Muskeldystrophie keinen Einfluss auf die Expression des CXCR7 und beeinflusst vermutlich dessen Funktion über einen anderen Mechanismus. Durch die offensichtlich enge Kontrolle von Muskelentwicklung und Regeneration durch CXCR4, CXCR7 und deren Liganden SDF-1α, bilden diese ein vielversprechendes therapeutisches Ziel für bestimmte Muskelerkrankungen. / The chemokine, SDF-1α, and its receptor, CXCR4, are assumed to control a multitude of biological processes such as organogenesis, haematopoesis, and immune responses. The previous demonstration that SDF-1α additionally binds to the chemokine receptor, CXCR7, currently urges a re-evaluation of the function of the SDF-1 system in these processes. In fact, depending on the tissue and cell type, CXCR7 either acts as a scavenger receptor, a modulator of CXCR4 or an independent active receptor. This thesis is dedicated to answer the following questions: Are both SDF-1α receptors expressed during muscle development? What is the actual function of these receptors during myogenesis? Is there a role of the SDF-1 system in muscle regeneration? To adress these issues both in vitro studies with the myoblast cell line, C2C12, as well as in vivo analyses on the expression of CXCR4, CXCR7 and SDF-1α in developing and regenerating limb muscles have been performed. At all stages of differentiation, C2C12 cells exhibited measurable amounts of CXCR4. In addition, in the course of differentiation C2C12 cells showed increasing expression levels of CXCR7. Treatment of the cells with SDF-1α resulted in the phosphorylation of Erk1/2 and PKCζ/λ and subsequently blocked their myogenic differentiation. Following inactivation of CXCR4 either by its antagonist, AMD3100, or by specific siRNA, SDF-1α failed to activate both pathways and in addition no longer inhibited the myogenic differentiation of C2C12 cells. By contrast, inactivation of CXCR7 remained without effects on SDF-1α-induced cell signalling and resulting inhibitory effects on myogenic differentiation. Interestingly, SDF-1α also failed to activate Erk1/2 signalling in differentiated C2C12 cells. Cell signalling in differentiated C2C12 cells was, however, restored following inhibition of CXCR7 expression, but not following inhibition of CXCR4 expression. The in vivo analysis further revealed that in limb muscles expression of the CXCR4 is highest during embryonic development with a decrease in expression levels shortly after birth when secondary muscle development is completed. Vice versa, expression levels of CXCR7 increased perinatally and remained high into adulthood. In summary, these findings unravel that CXCR4 actively mediates SDF-1α-signalling during myogenesis. The findings further provide evidence that CXCR7 acts as a scavenger receptor during myogenesis which controls myogenic differentiation by modulating extracellular SDF-1α concentration. In further agreement with a major role of SDF-1α in muscle development, SDF-1α is continously expressed by the endomysium of postnatal and adult muscle fibers. Moreover, expression of SDF-1α as well as CXCR4 is massively increased in muscles of dystrophin-deficient mice further implying that the SDF-1 system plays an equally important role during muscle development and regeneration. The pivotal role of SDF-1α in muscle development and regeneration points to the SDF-1 system as a promising therapeutical target for certain muscle diseases.