Role of lactate dehydrogenase A in endothelial metabolism and angiogenesis

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The blood vascular system is an extensive network that provides tissues with oxygen, nutrients, and a variety of angiocrine factors. It is formed mainly through angiogenesis, a process in which new blood vessels grow from the existing vasculature. Angiogenesis is vital for embryonic development, tissue growth, and regeneration, and is also involved in the pathogenesis of many human diseases. For example, proliferative diabetic retinopathy (PDR) and retinopathy of prematurity (ROP) are eye disorders that may lead to vision loss in diabetic patients and premature babies respectively. Both of these ocular diseases are characterized by excessive retinal angiogenesis, which causes intravitreal hemorrhage, macular edema, and even retinal detachment. However, current treatment strategies to inhibit aberrant blood vessel formation in PDR and ROP only have limited efficacy and may elicit undesirable side effects. Therefore, understanding the mechanisms that drive blood vessel formation is important because it may facilitate the development of better therapies for treating these severe eye diseases. Formation of new blood vessels through angiogenesis involves proliferation, migration, and several other energy-consuming endothelial cell (EC) behaviors. Recent studies have shown that proliferating ECs preferentially convert glucose to lactate and generate ~85% of ATP through glycolysis rather than glucose oxidation via the TCA cycle, even when the ECs are grown in an oxygen-rich environment. This metabolic feature is also seen in cancer cells and is termed the Warburg effect. However, it remains unclear at the molecular level why lactate instead of metabolites in the TCA cycle are favorably produced from glucose in proliferating ECs. Pilot studies from the applicant’s lab suggest that lactate dehydrogenase A (LDHA), an enzyme catalyzing the conversion of pyruvate to lactate and the regeneration of NAD+ from NADH, is a potentially key driver of the Warburg effect in ECs. The central hypothesis of this application is that LDHA controls the metabolic fate of glucose and sustains angiogenesis by regulating glycolytic flux in ECs. We will test this hypothesis through two Specific Aims. Aim 1 will use various metabolic assays and endothelial-specific Ldha knockout mice to determine the roles of LDHA in regulating the Warburg effect and developmental and pathological angiogenesis in the retina. By combining mouse genetic models, molecular and biochemical approaches, and advanced analytical tools, Aim 2 will identify the upstream regulator that controls LDHA expression in ECs and will elucidate the mechanism by which LDHA regulates endothelial growth. Collectively, our proposal will advance the understanding of the link between endothelial metabolism and blood vessel formation, and it will provide concrete steps towards developing new strategies for inhibiting angiogenesis in human ocular diseases.