Collaborative Research: IntBIO: Micro level oxygen transport mechanisms in elite diving mammals: Capillary RBC to myofiber

National Marine Mammal Foundation, San Diego CA

Investigators

Abstract

For mammals, oxygen is essential to breathe and fuel daily activities. However, some marine mammals have specialized adaptations that allow them to spend long time periods underwater on a single breath. One adaptation that is not well understood is how red blood cells travel and oxygen is delivered to working muscles during a long duration dive. Further, not all marine mammals have evolved with the same adaptations and genes. One genetic difference is the loss of a gene that encodes for the enzyme CMP-Neu5AC hydroxylase in pinnipeds (e.g., sea lions) but not cetaceans (e.g., dolphins). CMP-Neu5AC hydroxylase modifies sugar residues coating the surface of cells, which could significantly affect oxygen transport. This project brings together a team of researchers with expertise in marine mammal biology, hemoglobin protein structure, spectroscopy, and cell and molecular biology to test the hypothesis that there are differences between pinnipeds and cetaceans in how oxygen-carrying red blood cells reach active skeletal muscles, how oxygen is unloaded from red blood cells and how oxygen is transferred across cell membranes. Unique training opportunities will be provided for next generation scientists as they perform experiments in diverse research settings and draw from several specialized fields to answer a complex biological question. By partnering with education development experts and training teachers who serve underrepresented students, we will integrate research-based content from our oxygen transport work on diving mammals into science lessons that meet Next Generation Science Standards and will be shared with teachers locally and nationally. O2 store management studies in air-breathing marine mammals demonstrate that diving mammals not only tolerate very low O2 environments, but actually thrive under these conditions. Part of their success derives from a well-defined dive response at the systemic level (bradycardia and vasoconstriction). However, O2 exchange at the peripheral microvessel-myocyte level is not well understood. Further, there may be differences in peripheral O2 transport due to the loss of a gene in pinnipeds but not cetaceans. This gene encodes for CMP-Neu5AC hydroxylase (CMAH) which alters cell surfaces including red blood cells, potentially affecting peripheral O2 transport. Our central hypothesis is that Pinnipeds and Cetaceans have distinct peripheral morphological adaptations and O2 regulatory mechanisms for extended diving. This hypothesis will be tested by investigators with complementary expertise in marine mammal biology, Hb/Mb protein structure, advanced spectroscopy/EPR, and cell/molecular O2 models using three approaches: 1. Evaluate and model in vivo O2 delivery in California sea lions (CaSL, Pinniped, Cmah-) and bottlenose dolphins (BD, Cetacean, Cmah+) during and immediately after a simulated dive. 2. Elucidate and model the biochemical mechanisms regulating RBC Hb-O2 off-loading kinetics in Pinnipeds and Cetaceans. 3. Elucidate O2 storage and diffusion parameters in CaSL and BD skeletal muscle endothelial cells +/- CMAH overexpression or sialic acid modulation. This project spans multiple organizational levels and will uncover adaptive mechanisms by which marine mammals push physiological limits during dives. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.