Metabolic mechanisms controlling lymphatic vessel formation

PROJECT SUMMARY/ABSTRACT Lymphatic vessels play critical roles in regulating tissue fluid drainage, dietary fat absorption, and reverse cholesterol transport. Fulfilling these important physiological functions requires proper development of the lymphatic vasculature, which is mainly driven by vascular endothelial growth factor C (VEGF-C). VEGF-C signaling also stimulates pathological lymphangiogenesis in tumors and organ transplantation, which may, in turn, promote cancer metastasis and allograft rejection respectively. Therefore, elucidating the mechanisms by which VEGF-C signaling drives lymphangiogenesis will not only enhance the fundamental understanding of physiological processes regulated by lymphatics, but also facilitate the development of novel anti- lymphangiogenic strategies for disease treatments. We previously discovered that lymphatic endothelial cells (LECs), even when grown in an oxygen-rich environment, preferentially convert glucose to lactate. This unique metabolic feature is termed the Warburg effect. Despite this finding, it remains unclear whether and how the Warburg effect is regulated by VEGF-C signaling for promoting developmental and pathological lymphangiogenesis. Lactate dehydrogenase A (LDHA) catalyzes the reduction of pyruvate to lactate and the regeneration of oxidized nicotinamide adenine dinucleotide (NAD+) from its reduced form NADH. Our preliminary studies suggest that LDHA mediates the Warburg effect in LECs. We also found that genetic ablation of Ldha in mice impairs LEC proliferation and migration during lymphatic vascular development. Moreover, VEGF-C enhances LDHA transcription and lactate generation in LECs. These data collectively support our central hypothesis that LDHA couples VEGF-C signaling with cellular metabolism to drive lymphangiogenesis, which will be tested through two Specific Aims. Aim 1 will use genetic mouse models and cultured LECs to determine the molecular mechanisms by which VEGF-C signaling induces LDHA expression during lymphatic vessel formation. Aim 2 will combine several advanced analytical tools to elucidate the mechanisms by which LDHA controls cellular metabolism to promote lymphangiogenesis. Taken together, our proposed studies will identify LDHA as a novel mechanistic link between VEGF-C signaling and metabolic processes critical for lymphatic vessel formation. Our work may also suggest an innovative strategy, i.e., targeting the Warburg effect via LDHA inhibition, for suppressing VEGF-C-induced pathological lymphangiogenesis.