| Popis: |
Satellite cells represent a heterogeneous population of muscle stem cells responsible for post-hatch muscle hypertrophic growth and the regeneration of injured muscle. As multipotential stem cells, satellite cells with appropriate extrinsic stimuli have the plasticity to convert to an adipocyte-like lineage. Different satellite cell populations can express different cell surface markers, of which syndecan-4 and CD44 can mediate the function and fate of satellite cells. During the first week after hatch, satellite cells have the peak mitotic activity, and their function and fate are highly responsive to environmental thermal stress. Changes in satellite cell function and fate during thermal stress are regulated by signal transduction pathways. Mechanistic target of rapamycin (mTOR) pathway and wingless-type mouse mammary tumor virus integration site family/planar cell polarity (Wnt/PCP) pathway were among the most affected pathways during both thermal stress and growth selection in turkey pectoralis major (p. major) muscle satellite cells. The central hypothesis of this study was both hot and cold thermal stress would differentially affect mTOR and Wnt/PCP pathways altering the function, fate, and expression of syndecan-4 and CD44 in different populations of satellite cells isolated from the p. major muscle of 1-week faster-growing modern-commercial (NC) turkeys and 1-week slower-growing historic Randombred Control Line 2 (RBC2) turkeys. The objective of specific aim 1 and 2 was to determine the effects of thermal stress and growth selection on the proliferation, differentiation, and adipogenic potential of 1-week-old turkey p. major muscle satellite cells. The NC line satellite cells have increased proliferation, differentiation, and lipid accumulation compared to the RBC2 line. Heat stress of 43°C further increased the proliferation, differentiation, and lipid accumulation in both lines compared to the control temperature of 38°C, while cold stress of 33°C had an inhibitory effect on these cellular responses. Satellite cell function and fate were more responsive to thermal stress during proliferation than during differentiation, and the NC line satellite cells were more sensitive to thermal stress compared to the RBC2 line. Increases in satellite cell proliferation and differentiation are associated with muscle hypertrophic growth, while elevated lipid accumulation in satellite cells is linked to increased fat deposition in the p. major muscle. These results suggest that thermal stress during satellite cell mitotic activity may change poultry p. major muscle development, growth, structure, and protein to fat ratio, in part, by altering the function and fate of satellite cells. In specific aim 3, 4, and 5, the effects of thermal stress, growth selection, mTOR pathway, and Wnt/PCP pathway on the proliferation, myogenesis, adipogenesis, and the expression of syndecan-4 and CD44 in 1-week-old turkey p. major muscle satellite cells were investigated. The NC line satellite cells had increased proliferation, differentiation, and lipid content accompanied by the elevated activity of the mTOR and Wnt/PCP pathway compared to the RBC2 line. Heat stress further increased the proliferation, myogenesis, and adipogenesis and increased the activity of mTOR and Wnt/PCP pathway in both line satellite cells, whereas cold stress showed an inhibitory effect on these cellular responses. Hot and cold thermal stress differentially changed the expression of syndecan-4 and CD44 in different populations of satellite cells, and the NC line satellite cell population was more responsive to both hot and cold thermal stress compared to the RBC2 line. Furthermore, inhibiting the activity of either mTOR or Wnt/PCP pathway by knocking down the expression of pivotal gene mTOR or Frizzled-7 not only suppressed satellite cell proliferation, myogenesis, and adipogenesis but also differentially changed the expression of syndecan-4 and CD44 in both lines at all the temperatures. These data indicate that thermal stress-induced changes in satellite cell function, fate, and expression of syndecan-4 and CD44 are mediated by the mTOR and Wnt/PCP pathways in a growth-dependent manner. Results of the current study can be used for the development of temperature manipulation strategies to improve poultry breast muscle growth while maintaining high-quality lean meat by increasing satellite cell-mediated muscle hypertrophy and suppressing satellite cell-mediated fat production. |
