The long term objectives are to elucidate the molecular mechanisms involved in skeletal muscle catabolism during excess/deficit of hormones, injury and diseases . Secretion of cytokines such as tumor necrosis factor (TNF- alpha), interleukin-1 (IL-1) and Il-6 from activated macrophages and lymphocytes during fever, sepsis, severe injury, trauma, burns or cancer has been implicated in the induciton of protein loss from various types of skeletal muscles. Both acute and chronic Tumor necrosis factor-alpha excess has been shown to inhibit total protein synthesis in fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus. However, there is no information on the effect of TNF-alpha; a) on the synthesis of specific myofibrillar proteins such as myosin light chain, myosin heavy chain and alpha-actin, or b) on the expression, stability, and translation of their mRNAs in different skeletal muscle types. Since impairment of protein synthesis induced by TNF can aggravate the primary disease or injury, elucidation of the molecular mechanisms involved in this reduced protein synthesis has appreciable biomedical significance. To elucidate these molecular mechanisms, the proposed study, using rats as a model system, will focus on the following specific aims. a) To evaluate the effect of TNF-alpha on the synthesis of total and specific myofibrillar proteins in EDL and soleus. b) To evaluate athe effect of TNF-alpha treatment on the expression and stability of mRNA of specific myofibrillar proteins in EDL and soleus. c) To evaluate the effect of TNF-alpha treatment on total protein translation by examining polysomal aggregation and peptide-chain initiation or elongation in EDL and soleus. Protein synthesis will be measured by the incorporation of 3H-tyrosine into muscle protein. Western blot analysis and Northern blot analysis will be done to evaluate abundance of specific myofibrillar proteins and transcription of their mRNA respectively. Polysomal aggregation and impairment of peptide-chain initiation or elongation will be examined by the analysis of sucrose density gradient profiles of polysomes and ribosomes extracted from muscles. Future work will be focused on the identification of TNF responsive kinases and their cellular substrates involved in signal transduction responsible for TNP's actions on myofibrillar proteins.
| Cheema, Ijaz R; Jones, Donald L (2003) TNF-alpha and cortisone impair peptide chain initiation by altering the availability of initiation factor EIF-4E. Front Biosci 8:s1051-5 |
