Podophyllotoxin (PPT) is a plant natural product that serves as a precursor for the synthesis of many well-known chemotherapeutic drugs. The limited availability and high demand for the source plants of PPT have led to the exploration of alternative sources for this compound. In this study, we utilized the endophytic fungus Phialocephala podophylli (strain PPE7) that we isolated from the rhizomes of Podophyllum peltatum and is known to produce detectable amounts of PPT in broth culture. To date, the complete PPT biosynthetic pathway has yet to be determined in any species. Since fungi are well known for clustering genes that belong to secondary metabolite pathways, use of a fungal system for investigation of the PPT biosynthesis genes may ultimately lead to elucidation of the entire pathway. In this study, we investigated the secoisolariciresinol dehydrogenase (SD) gene that facilitates the dehydrogenation of secoisolariciresinol to form matairesinol, a mid-pathway intermediate product in PPT biosynthesis. We utilized PCR amplification to acquire the complete SD gene sequence in PPE7 and opted to synthesize the P. peltatum SD sequence for expression. Through western blotting, we confirmed the expression of the recombinant SD (PpSD) and verified protein functionality with a bioconversion assay followed by HPLC and LC-MS analyses. Here, we report the identification of the SD gene in PPE7; this is the first report of the SD gene in an endophytic fungus. Additionally, we established the groundwork for the future expression of the complete PPT biosynthetic pathway in the heterologous host Pichia pastoris.
Concussion is associated with a myriad of deleterious immediate and long-term consequences. Yet the molecular mechanisms and genetic targets promoting the selective vulnerability of different neural subtypes to dysfunction and degeneration remain unclear. Translating experimental models of blunt force trauma in C. elegans to concussion in mice, we identify a conserved neuroprotective mechanism in which reduction of mitochondrial electron flux through complex IV suppresses trauma-induced degeneration of the highly vulnerable dopaminergic neurons. Reducing cytochrome C oxidase function elevates mitochondrial-derived reactive oxygen species, which signal through the cytosolic hypoxia inducing transcription factor, Hif1a, to promote hyperphosphorylation and inactivation of the pyruvate dehydrogenase, PDHE1α. This critical enzyme initiates the Warburg shunt, which drives energetic reallocation from mitochondrial respiration to astrocyte-mediated glycolysis in a neuroprotective manner. These studies demonstrate a conserved process in which glycolytic preconditioning suppresses Parkinson-like hypersensitivity of dopaminergic neurons to trauma-induced degeneration via redox signaling and the Warburg effect.
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