OXPHOS complex impairment and mitochondrial DNA depletion modify hypoxia signaling pathway activity in zebrafish.

Mitochondria are essential for cell survival and health, utilizing about 90% of the oxygen we breath for OXPHOS. Previous studies showed a strong relationship between mitochondrial alterations and hypoxia signaling pathway, an interesting aspect to be investigated. POLG-related disorders are a group of diseases characterized by the dysfunction of DNA polymerase gamma, an enzyme crucial for mtDNA replication, repair and stability. Danio rerio (zebrabish) is an ideal vertebrate model of human mitochondrial diseases because of its high conservation of physiological processes and genomic structure, transgenic lines availability and embryonic transparency. Using zebrabish embryos, we have performed a transient knock-down of the polg gene, inducing a dilated cardiomyopathy and an increased heart bit rate. Moreover, we have developed a transgenic line able to show in vivo the activation of hypoxia-inducible factor 1 (Hif1) signaling. Taking advantage of this reporter line, we established that Hypoxia pathway is up-regulated in polg morphants. In addition, using a pharmacological approach targeting OXPHOS complexes NADH:ubiquinone reductase (Complex I) and Succinate dehydrogenase (Complex II), we have investigated the effect of mitochondrial dysfunctions on the Hypoxia pathway. We established that Hypoxia pathway is signibicantly reduced, both in normoxia and in hypoxia conditions, perhaps due to an increase in ROS production. In conclusion, our data suggest the existence of cross-talk mechanisms sensing mitochondrial dysfunction and changing Hypoxia signaling. In addition, our results on polg transient inactivation incourage the use of zebrabish as a suitable model to perform CRISPR/Cas9-mediated mutagenesis of DNA polymerase gamma, an ongoing project in our laboratory.