Effects of ciliary neutrophic factor (CNTF) on protein turnover in cultured L8 rat muscle cells Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/g158bm13p

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  • Skeletal muscle proteins are the largest amino acid pool in animal body and are continuously degraded and resynthesized. Dozens of factors have been shown to influence the balance between synthesis and degradation and thereby regulate muscle growth and function. It is now know that one of the major regulatory bases of muscle metabolism is neuron-muscle interaction. A neurogenic factor, ciliary neurotrophic factor (CNTF), is proposed to exert myotrophic actions and could possible be a mediator of neuron-muscle interactions. The goal of this study was to investigate the effects of CNTF on muscle protein turnover in an in vitro system. CNTF was applied to differentiated cultured muscle cells (L8 cell line). Radiochemical labeled amino acids were added to the culture medium to determine the rate of incorporation or release by the cells as indexes of protein synthesis and protein degradation, respectively. Total protein was measured as an index of change in total protein accretion. Twelve hours of CNTF treatment increased myofibrillar protein synthesis by 10%. However, longer CNTF treatment (24 hours) reduced non-myofibrillar protein synthesis. CNTF (1 ng/ml) decreased protein degradation but higher doses (20 ng/ml) accelerated protein degradation. These changes in protein turnover resulted from changes in the myofibrillar protein fraction rather than from changes in turnover of the non-myofibrillar fraction. The change in protein synthesis and protein degradation resulted in an increase in total protein accretion of about 6%. Compared with the myotrophic studies on the effects of CNTF in vivo, the action of CNTF were relatively small. Reverse transcription polymerase chain reaction (RT-PCR) analysis showed that CNTF receptor alpha subunit (CNTFRα) mRNA expression is lower than which is expressed in muscle tissue. This could explain the reason why CNTF exerted smaller effects in vitro compared to those reported in vivo. Overall, CNTF exerts a small but statistically significant anabolic actions in cultured skeletal muscle and the actions were highly dose-dependent. The limited action of CNTF in vitro may be related to its low receptor density in the L8 cell (compared to in vivo). Because actions may be highly dose-dependent, a challenging series of studies are ahead for anyone wishing to identify the signal transduction mechanisms which account for CNTF's actions.
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  • description.provenance : Made available in DSpace on 2012-09-20T20:38:25Z (GMT). No. of bitstreams: 1 WangMei-Chuan1998.pdf: 5675882 bytes, checksum: cca9e182acfcc71fc0b528ece407a29b (MD5) Previous issue date: 1997-12-02
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