MDT-15 Mediates Enhanced Immunity in C. Elegans Against S. Gordonii

Objectives: Mitis group streptococci are an understudied group of opportunistic pathogens that reside in the oral cavity and are capable of producing hydrogen peroxide as major contributor to their pathogenesis. We previously demonstrated pretreatment of the nematode Caenorhabditis. elegans with metformin activates SKN-1/Nrf-2 via the p38 MAPK pathway and mediates protection from streptococcal infections. In addition, we have shown MDT-15, a transcription co-regulator is required for SKN-1 activation in response to metformin. In this study we investigated if MDT-15 activates the oxidative stress response and enhances survival of the worms on S. gordonii a representative of the mitis group.
Methods: To confirm the metformin enhanced survival of the worms is mediated by skn-1, we compared survival of skn-1 mutant worms on Streptococcus gordonii in the presence or absence of metformin. To further confirm the activation of SKN-1 is mediated by MDT-15 in response to metformin, we observed the expression of skn-1-dependent genes gcs-1 and gst-4 fused to green fluorescent protein (GFP) in mdt-15 knockdown worms relative to vector control treated worms by epifluorescence microscopy. Finally, we determine if the enhanced survival of the worms is mediated by mdt-15 by comparing the survival of mdt-15 mutant worms on S. gordonii in the presence or absence of metformin.
Results: No significant difference was observed in skn-1 mutant worms in the presence or absence of metformin. gcs-1::GFP and gst-4::GFP expression significantly decreased in mdt-15 knockdown worms compared to the vector control treated worms. Furthermore, no significant decrease in survival of mdt-15 mutant worms was observed in the presence or absence of metformin.
Conclusions: MDT-15 in addition to the p38 MAPK pathway is required for the metformin enhanced protection of the worms. We will further investigate if these mechanisms are conserved using mammalian cell lines.