Metabolic regulation by the PGC-1α and PGC-1β coactivators in larval zebrafish (Danio rerio)

The peroxisome proliferator activated receptor gamma coactivator-1 (PGC-1) family is composed of three coactivators whose role in regulating mammalian bioenergetics regulation is clear, but is much less certain in other vertebrates. Current evidence suggests that in fish, PGC-1 alpha and PGC-1 beta may exhibit much less redundancy in the control of fatty acid oxidation and mitochondrial biogenesis compared to mammals. To assess these roles directly, we knocked down PGC-1 alpha and PGC-1 beta expression with morpholinos in zebrafish embryos, and we investigated the resulting molecular and physiological phenotypes. First, we found no effects of either morpholinos on larval hatching, heart rates and oxygen consumption over the first few days of development. Next, at 3 days post fertilization (dpf), we confirmed by real time PCR a specific knock down of both coactivators, that resulted in a significant reduction in the transcript levels of citrate synthase (CS), 3-hydroxyacyl-CoA dehydrogenase (HOAD), and medium-chain acyl-coenzyme A dehydrogenase (MCAD) in both morphant groups. However, there was no effect on transcription factors' gene expression except for a marked reduction in estrogen related receptor a (ERR alpha) transcripts in PGC-1 alpha morphants. Finally, we assessed whole embryonic enzyme activity for CS, cytochrome oxidase (COX), HOAD and carnitine palmitoyltransferase I (CPT-1) at 4 dpf. The only significant effect of the knockdown was a reduced CS activity in PGC-1 alpha morphants and a counterintuitive increase of cytochrome oxidase activity in PGC-1 beta morphants. Overall, our results indicate that in larval zebrafish, PGC-1 alpha and PGC-1 beta both play a role in regulating expression of important mitochondrial genes potentially through ERRa.