Progress 12/01/03 to 11/30/07
Outputs
Growth rate of domestic animals has improved markedly over the past few decades, but environmental and nutritional refinements still have the potential to afford further improvement. It has been estimated the 85% of postnatal animal growth is driven by the growth hormone - insulin-like growth factor (IGF) axis, emphasizing the importance of optimizing this axis. The IGF's are expressed within all tissues of the body, including expression by mature and precursor cells of skeletal muscle. Similarly, the signal transducing receptor for the IGFs, IGF-1R or its closely related homologous insulin receptor appear to be expressed by most if not all cells of the body. Considering the absolute requirement of IGF-1R activity for normal growth and well-being, mechanisms must exist to control IGF activity. Work supported by this USDA grant has characterized two distinct mechanisms that positively (zinc) and negatively (proinflammatory cytokines TNFα and IL-1B) modulate IGF
activity and that interact to offset each others effects. Our results clearly indicate that zinc acts to enhance muscle cell survival, proliferation and metabolism partially by enhancing IGF activity. This particular aspect of the project was performed using cultured skeletal muscle precursor cells (myoblasts) and differentiated myotubes. The mechanism by which zinc works is at least three fold; first, zinc maintains IGF in an active state by diminishing IGF association with inhibitor molecules (IGF binding proteins); second, zinc directly strengthens IGF binding to the IGF-1R; and third zinc prevents the ability of the proinflammatory cytokine, TNFα, to depress IGF activity. None of these novel interactions with zinc have been previously described. The data clearly suggest that circulating levels of zinc in domestic animals (20uM) is not optimal for stimulation of animal growth or preventing the growth inhibitory activities of proinflammatory cytokines that are present during
inflammation, since optimal zinc activity for muscle cells is about 2-fold higher (40-50uM). This higher level of zinc blocks the inhibition of IGF activity elicited by the presence of TNFα. This is the first data showing that zinc blocks the inhibitory effect of TNFα on muscle and provides a novel mechanism that may be very useful to improve the performance of sick livestock by blocking the growth inhibition that occurs during inflammation. In addition to this interaction, the requirement of IGF-1R activity for muscle cell survival was defined. New inhibitors of the IGF-1R became available for in vitro studies that were originally described by their anti-cancer capacity; a cyclolignan picropodophyllin and a tyrphostin AG1024. Using these inhibitors to depress basal IGF-1R activity, studies have shown that muscle cell survival and global rate of protein synthesis is intricately controlled by and dependent on basal IGF-1R activity. These reagents provide extremely sensitive
and specific tools to further delineate the role of the IGF system during animal growth and development. These inhibitors act similar to cytokines; acting to limit the growth promoting activities of the IGF system.
Impacts
Growth rate of domestic animals is determined by a complex interaction between genetic potential, management practices, disease and proper nutrition. The findings from this research illustrate the importance of the interaction between micronutrients, zinc in particular, and the endocrine system that regulate growth efficiency. The data should provide a basis to define the optimal nutritional allowances needed for maximal health and growth of agriculturally important animals.
Publications
- Huey, K., McCusker, R.H. and Kelley, K.W. 2008. Exaggerated expression of skeletal muscle-derived interleukin-6 in mice lacking interleukin-10. J. Neuroimmuno. (Under Review).
- Strle, K., McCusker, R.H., Zunich, S.M., Johnson, R.W., Dantzer, R. and Kelley, K.W. 2008. The prototypical anti-inflammatory cytokine, IL-10, prevents loss of IGF-I-induced myogenin caused by IL-1B. Amer. J. Physiology (Accepted).
- O'Connor, J.C., McCusker, R.H., Strle, K., Johnson, R.W., Dantzer, R. and Kelley, K.W.. 2008. Regulation of IGF-I function by proinflammatory cytokines: At the interface of immunology and endocrinology. Cellular Immunology (In Press).
- Strle, K., McCusker, R.H., Tran, L., King, A., Johnson, R.W., Freund, G.G., Dantzer, R. and Kelley, K.W. 2007. Novel activity of an anti-inflammatory cytokine: IL-10 prevents TNFα-induced resistance to IGF-I in myoblasts. J. Neuroimmunology, 188:48-55.
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Progress 01/01/06 to 12/31/06
Outputs
Growth rate of domestic animals has improved markedly over the past few decades, but environmental and nutritional refinements still have the potential to afford further improvement. It has been estimated that 85% of postnatal animal growth is driven by the growth hormone - insulin-like growth factor (IGF) axis, emphasizing the importance of optimizing this axis. The IGF's are expressed within all tissues of the body, including expression by mature and precursor cells of skeletal muscle. Similarly, the signal transducing receptor for the IGFs, IGF-1R or its closely related homologous insulin receptor appear to be expressed by most if not all cells of the body. Considering the absolute requirement of IGF-1R activity for normal growth and well-being, mechanisms must exist to control IGF activity. Work supported by this USDA grant has characterized two distinct mechanisms that positively (zinc) and negatively (proinflammatory cytokines TNF Alpha and IL-1B) modulate IGF
activity and that interact to offset each others effects. Our results clearly indicate that zinc acts to enhance muscle cell survival, proliferation and metabolism partially by enhancing IGF activity. This particular aspect of the project was performed using cultured skeletal muscle precursor cells (myoblasts) and differentiated myotubes. The mechanism by which zinc works is at least three fold: First, zinc maintains IGF in an active state by diminishing IGF association with inhibitor molecules (IGF binding proteins); second, zinc directly strengthens IGF binding to the IGF-1R, and third zinc prevents the ability of the proinflammatory cytokine, TNF Alpha, to depress IGF activity. None of these novel interactions with zinc have been previously described. The data clearly indicate that circulating levels of zinc in domestic animals (20uM) is not optimal for stimulation of animal growth or preventing the growth inhibitory activities of proinflammatory cytokines that are present during
inflammation, since optimal zinc activity for muscle cells is about 2-fold higher (40-50uM). This higher level of zinc blocks the inhibition of IGF activity elicited by the presence of TNF Alpha. This is the first data showing that zinc blocks the inhibitory effect of TNF Alpha on muscle and provides a novel mechanism that may be very useful to improve performance of sick livestock by blocking the growth inhibition that occurs during inflammation. In addition to this interaction, the requirement of IGF-1R activity for muscle cell survival was defined. New inhibitors of the IGF-1R became available for in vitro studies that were originally described by their anti-cancer capacity; a cyclolignan picropodophyllin and a tyrphostin AG1024. Using these inhibitors to depress basal IGF-1R activity, studies have shown that muscle cell survival and global rate of protein synthesis is intricately controlled by and dependent on basal IGF-1R activity. These reagents provide extremely sensitive and
specific tools to further delineate the role of the IGF system during animal growth and development. These inhibitors act similar to cytokines; acting to limit the growth promoting activities of the IGF system.
Impacts
Development of mechanisms to optimize the IGF system has long been seen as a promising means to increase the rate and efficiency for muscle growth of livestock. Optimizing IGF activity will help meet the future demands that will be placed on livestock production industry. The work described here strongly suggest that current dietary zinc supplementation methods are not adequate to optimize body zinc levels and thus not adequate to optimize growth rate. Despite its importance, optimal zinc requirement for growth, development and health is not known nor is the mechanism by which zinc promotes these processes well defined. We are currently describing a mechanism by which zinc increases growth and defining optimal extracellular levels of zinc that are necessary for this activity. A novel interaction between zinc, TNF alpha and IGF-I indicates that optimizing zinc levels within the body would markedly enhance IGF activity, markedly depress the inhibitory actions of TNF
alpha and increase the ability of livestock species to thrive during periods of stress due to inflammation and sickness.
Publications
- Strle, K., Broussard, S.R., McCusker, R.H., Shen, W.H., Lecleir, J.M., Johnson, R.W., Freund, G.G., Dantzer, R. and Kelley, K.W. 2006. C-jun N-terminal kinase mediates tumor necrosis factor-alpha suppression of differentiation in myoblasts. Endocrinology, 147:4363-4373.
- McCusker, R.H., Strle, K., Broussard, S.R., Dantzer, R., Bluthe, R.M. and Kelley, K.W. 2006. Crosstalk Between Insulin-like Growth Factors and Pro-Inflammatory Cytokines. In: Psychoneuroimmunology, 4th Edition, Chapter 7, Ed. Adler, R., Dantzer, R., Glaser, R., Heijnen, C., Irwin, M., Padgett, D. and Sheridan, J. Academic Press, pp 171-191.
- Strle, K., McCusker, R.H., Tran, L., King, A., Johnson, R.W., Freund, G.G., Dantzer, R. and Kelley, K.W. 2006. IL-10 inactivates c-Jun NH(2)-terminal kinase and overcomes TNF alpha-induced inhibition of myogenesis. FASEB J. (Submitted).
- McCusker, R.H., Strle, K., Dantzer, R., Bluthe, R.-M., Zunich, S., McCrea, K., Neuhaus, M., Choi, S., Berkowitz, D.B. and Kelley, K.W. 2006. Insulin-like growth factor type 1 receptor activity promotes survival and inhibits glutamate-induced excitotoxicity of cortical neurons. J. NeuroImmunol. (Submitted).
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Progress 01/01/05 to 12/31/05
Outputs
An interaction between zinc and the insulin-like growth factor system appears critical for normal growth and development. A dietary deficiency of zinc decreases growth and development of domestic animals and humans; with a particular depression of muscle mass. The amount of zinc needed by the body for optimal muscle growth has not been defined. With this in mind, we are currently trying to determine the amount of zinc that muscle requires for optimal growth and development. Most of this work is being performed with cell culture models wherein we can precisely control the amount of zinc that is available to the muscle cell and then quantify cell survival, cell number and degree of development (differentiation). Initially we were able to show that zinc, at levels 3 to 5-fold higher than those found in serum, is necessary for maximal growth of muscle cells. Recent work now shows that zinc and insulin-like growth factor-I act together to promote muscle cell survival by
overcoming the deleterious effect of a potent pro-inflammatory cytokine, tumor necrosis factor-alpha. Tumor necrosis factor-alpha is released and acts on muscle during infections and wasting diseases and it acts to decrease muscle mass and growth. Zinc alone or insulin-like growth factor-I alone cannot optimize cell survival; they are both necessary to maximally keep muscle cells alive in the presence of tumor necrosis factor-alpha. This work is scheduled to be submitted and presented at a 2006 meeting (McCusker, R.H., Broussard, S.B., Strle, K. and Kelley, K.W.; Insulin-like growth factor-I, zinc and pyruvate interact to enhance C2C12 myoblast survival; counter-effective actions with those of tumor necrosis factor-alpha; scheduled for the Endocrine Society meeting; deadline Jan 17, 2006; meetings June 24-27, Boston). Part of our work also defining the interaction between insulin-like growth factor and tumor necrosis factor-alpha has already been submitted for publication (see
publications). Besides the cell culture models, we are using biochemical methods to define how zinc and insulin-like growth factor interact to promote cell number and survival. Two manuscripts are being prepared for 2006 publication in this area (1: McCusker, R.H.; Zinc depresses insulin-like growth factor binding to IGFBP-5 and IGFBP-4 but not IGFBP-2; and 2: McCusker, R.H.; Zinc increases insulin-like growth factor binding by targeting IGFBP-5, IGFBP-2 and IGFBP-4 to the surface of muscle cells; both for submission to Endocrinology). The data indicate that zinc enhances insulin-like growth factor activity by depressing the action of insulin-like growth factor-specific inhibitors. The data shows that zinc decreases the ability of insulin-like growth factor binding proteins to bind insulin-like growth factor. These are the first studies with muscle suggesting that insulin-like growth factor and zinc act together to promote muscle cell survival, growth and development. However, future
studies are needed to determine if the effects seen with cultured cells can be used to promote muscle growth in live animals. Two such studies were conducted and conclusions await analysis of the samples.
Impacts
Zinc is an important nutrient from both an agricultural and human standpoint. It is estimated that 25 percent of the world's human population is zinc deficient. Also, domestic animal growth rate and production efficiency are associated with zinc levels in the diet. Despite its importance, optimal zinc requirement for growth, development and health is not known nor is the mechanism by which zinc promotes these processes well defined. Over 20 years ago, an extracellular role for zinc during growth was proposed, albeit no such function has been described. Our work is currently defining both the optimal extracellular zinc concentrations needed for muscle growth and they are describing a novel mechanism responsible for extracellular zincs ability to promote growth. We have found that zinc levels in normal blood are less than half that needed for optimal growth and survival of muscle cells grown in culture. These findings suggest that zinc availability to muscle is not
optimal during current animal production practices and that even a larger portion of the human population my not have enough zinc because of inadequate levels in the body. The findings from this work should lead to new mechanisms both to promote domestic animal growth rate and growth efficiency and they should lead to novel means of clinical intervention to reverse the adverse effects of nutritional deficiencies involving zinc.
Publications
- Strle, K., Broussard, S.B., McCusker, R.H., Shen, W.H., Johnson, R.W., Freund, G.G., Dantzer, R. and Kelley, K.W. 2006. JNK mediates TNFa suppression of differentiation in myoblasts. Endocrinology (Submitted).
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Progress 01/01/04 to 12/31/04
Outputs
Zinc is a required dietary ingredient. Zinc deficiency is expressed as decreased growth and development of domestic animals (swine, cattle, sheep and poultry) and humans. Despite several decades of work, the body's optimal zinc requirement for growth has not been defined; requirement being the amount needed by the body not the amount present in the diet. The amount of zinc the body needs for optimal growth and development is probably much higher than that currently defined by dietary recommendations. Zinc requirements have, to date, only been defined by determining those amounts of zinc needed within a diet that support a given rate of growth. Due to limitations in the current ability to add additional available zinc to diets without causing copper deficiency, optimal zinc requirements are not known for any mammalian species. Our project is designed to determine the amount of zinc a cell requires for optimal growth and the mechanism by which zinc promotes cell growth.
With this information we will then use animal models to determine if meeting these amounts optimizes animal growth. IGF, along with its major stimulant growth hormone, are responsible for approximately 85% of postnatal growth. Many of zinc's actions occur intracellularly by its binding to proteins within the cell. However, it is quite clear that zinc has an extracellular role during animal growth and development. In particular, we are working to determine the extracellular impact of zinc on insulin-like growth factor (IGF)-driven growth to define the optimal amount of extracellular zinc that is needed for cellular proliferation. We have determined that zinc directly enhances the growth of muscle progenitor cells (myoblasts). Zinc increases myoblast proliferation independent of added growth factors by an as yet undescribed mechanism. We also have recently found that zinc acts synergistically with IGF-I to further enhance myoblast proliferation. The amount of extracellular zinc that
results in maximal cell proliferation is 3 to 5-fold higher than that found in fluids within the body. This finding indicates that cells within the body are always bathed in suboptimal zinc concentrations and that domestic animal growth rate should be enhanced by elevating extracellular zinc. Although most of these studies use in vitro cell culture models to define the physiological interaction between zinc and IGF-I, there is another component of our work designed to characterize the biochemical interaction between zinc and the IGF system. Our previous work demonstrated that zinc activated IGF-I; i.e. suppressed the activity of inhibitory IGF-binding proteins (IGFBPs) while simultaneously elevating the activity of the stimulatory receptor (IGF-1R). We have now completed work that confirms the IGFBP effect using purified proteins. Also, by quantifying the binding of zinc to IGFBP-3 and the IGF-1R, we have now shown that zinc directly interacts with both of these proteins outside of
cells thus describing a novel and direct extracellular growth promoting action for zinc. Thus, zinc acts in the extracellular environment to enhance IGF-driven growth by its interaction with members of the IGF system.
Impacts
Zinc is an important nutrient from both an agricultural and humane standpoint. It's estimated that 25% of the world's human population is overtly zinc deficient. Also, domestic animal growth rate and production efficiency are associated with zinc levels in the diet. Despite its importance, optimal zinc requirement for growth, development and health is not known nor is the mechanism by which zinc promotes these processes well defined. Over 20 years ago, an extracellular role for zinc during growth was proposed, albeit no such function has been described. Our work is currently defining both the optimal extracellular zinc concentrations needed for muscle growth and describing a novel mechanism responsible for extracellular zinc's ability to promote growth. We have found that zinc levels in normal blood are less than half that needed for optimal growth of muscle cells grown in culture and that the effect of zinc involves activation of the major growth promoting hormone
found in serum: the growth hormone-dependent insulin-like growth factor-I. These findings indicate that the action of zinc during growth is by no means optimal during current animal production practices and that even a larger portion of the human population are growing at a suboptimal rate because of inadequate zinc levels in the body. The findings from this work should lead to new mechanisms both to promote domestic animal growth rate and growth efficiency and they should lead to novel means of clinical intervention to reverse the adverse effects of nutritional deficiencies involving zinc.
Publications
- No publications reported this period
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