Evaluating the Role of Peroxisome Proliferator-Activated Receptor Gama Coactivator-1 Alpha in Mitochondrial Biogenesis in Goldfish
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The production of ATP is of the utmost importance to cell survival. To maintain energy homeostasis, cells regulate mitochondrial content through the control of degradative and synthetic processes. Mitochondrial biogenesis is primarily controlled through a small number of transcriptional regulators, primarily nuclear respiratory factor-1 (NRF-1), NRF-2, and peroxisome proliferator-activated receptors (PPARs). DNA-binding proteins regulate genes encoding the machinery of oxidative phosphorylation. In addition to these DNA-binding proteins, the coactivator PPAR gamma coactivator-1 alpha (PGC-1α) is central to control of mitochondrial genes, so much so that it has been dubbed a “master controller” of energy homeostasis in mammalian muscle tissues. Though well studied in mammals, previous studies suggest that this NRF-1-PGC1α axis may be disrupted in fish. The response to treatments such as temperature and diet cause reciprocal effects on NRF-1 and PGC-1α. A serine-rich insertion into the NRF-1 binding domain of PGC-1α most likely disrupts this interaction. In this study I looked at the ability for the goldfish PGC-1α gene to interact with the PGC-1α binding domain of NRF-1. I have found that goldfish PGC-1α does not physically bind NRF-1, which would suggest that the PGC-1α-NRF-1 axis in fish is disrupted. To further explore the role of PGC-1α in fish we looked at the role of AMP-activated kinase (AMPK) to phosphorylate goldfish, zebrafish, and human PGC-1α. The results from this analysis show that AMPK in a zebrafish embryonic cell line (ZEB2J) have their AMPK activated by the AMPK activator AICAR. This response was shown to be both dose and time dependent. Transcript data was generated looking at typical AMPK responsive targets in the mammalian system. The target of ramapamycin (TOR) gene responded with a decrease as is expected in mammals. Hexokinase 2 (HK2), PGC-1α, and NRF-1 all decreased which is opposite of the typical mammalian response. COX7C a downstream target of the PGC-1α-NRF-1 axis did not respond to treatment. Indicating a disruption in the AMPK- PGC-1α-NRF-1 pathway.