Lipid homeostasis and mitochondrial fitness in LAM pathogenesis and therapy

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Abstract Lymphangioleiomyomatosis (LAM) is a rare multisystem disease of women, characterized by progressive cystic lung destruction and diffuse proliferation of smooth muscle-like cells. LAM cells harbor inactivating mutations in the TSC1 or TSC2 tumor suppressor gene, which results in hyperactivation of mammalian target of rapamycin complex 1 (mTORC1). Rapamycin is an FDA-approved treatment for LAM; however, clinical response is heterogeneous across patients, and disease progression resumes once treatment is stopped. New therapies to improve the rate and durability of response remain a critical unmet need in LAM. Furthermore, the lack of imaging or other quantitative biomarkers of disease progression (beyond pulmonary function) limits clinical progress. mTORC1 promotes metabolic reprogramming and uncontrolled cell growth. We have identified a novel metabolic hallmark of LAM cells: a deregulation of the Randle cycle, a competitive interplay between fatty acids and glucose as substrates for mitochondrial oxidation, that promotes metabolic fitness and viability. Genetic inhibition of carnitine palmitoyltransferase 1A (CPT1A), the rate-limiting enzyme of fatty acid β-oxidation (FAO) suppressed in vivo tumorigenesis of TSC2-deficient cells by 50%, and inhibition of pyruvate dehydrogenase (PDH, a key mediator in the Randle cycle) and the tricarboxylic (TCA) cycle by a first-in-class mitochondrial inhibitor suppressed tumorigenesis by 90%, highlighting the translational potential of this project. Moreover, supplementation of exogenous fats stimulated the proliferation of LAM cells, in vitro and in vivo. Our central hypothesis is that PDH and CPT1 promote LAM cell fitness and proliferation via regulation of mitochondrial bioenergetics and lipid homeostasis. A key translational corollary of this hypothesis is that these biochemical pathways will provide opportunities for therapeutic interventions and the development of imaging biomarkers. Our central hypothesis will be tested in two Aims: Aim 1. To determine the metabolic derangements underlying lipid homeostasis and mitochondrial bioenergetics in TSC2-deficient cells. We will test the working hypotheses that LAM cells enhance mitochondrial efficiency by deregulating the Randle cycle and promoting utilization of exogenous fats, and that this metabolic asset supports LAM cell growth. Aim 2. To elucidate the PDH and CPT1A-dependent tumorigenic mechanisms in preclinical models of LAM in vivo. We will test the working hypothesis that PDH and lipid homeostasis are critical to LAM tumorigenesis. Our approaches will include stable isotope-labeled nutrients (glucose and palmitate) and deuterated water-based tracing experiments, and [18F]fluorothia-6-heptadecanoic acid (FTHA) micro-PET (positron emission tomography) imaging to probe LAM cell metabolism in vivo. The long-term objectives of this project are to harness the distinctive bioenergetic vulnerabilities of LAM cells to improve therapies and develop effective imaging strategies for women with LAM.