Thèse Rôle du Métabolisme Adipocytaire de la Lysine dans la Croissance Tumorale en Condition d'Obésité H/F - Doctorat.Gouv.Fr

Établissement : Université de Montpellier École doctorale : Sciences Chimiques et Biologiques pour la Santé Laboratoire de recherche : IRCM - Institut de Recherche en Cancérologie de Montpellier Direction de la thèse : Patrick JOUANDIN ORCID 0000000286567694 Début de la thèse : 2026-10-01 Date limite de candidature : 2026-05-11T23:59:59 L'obésité constitue un facteur de risque majeur de cancer et est associée à un mauvais pronostic dans de nombreux types tumoraux. Elle se caractérise par des altérations profondes du tissu adipeux, incluant une inflammation chronique, une sécrétion dérégulée et un déséquilibre métabolique systémique. Dans ce contexte, le tissu adipeux dysfonctionnel favorise la croissance tumorale en fournissant nutriments, lipides, adipokines et cytokines pro-inflammatoires, tout en induisant une résistance à l'insuline et une hyperinsulinémie compensatoire qui stimulent la prolifération et la survie des cellules cancéreuses.

La voie du mévalonate, impliquée dans la synthèse du cholestérol et des isoprénoïdes, joue un rôle central dans la biologie des adipocytes et est activée dans l'obésité. Ses produits sont essentiels à la prénylation des protéines et à la signalisation intracellulaire, également requises pour l'activation oncogénique. Cela suggère que l'activation de cette voie dans l'obésité pourrait contribuer à la progression tumorale. Bien que les statines ciblent cette voie, leur efficacité clinique limitée souligne la nécessité d'identifier de nouvelles stratégies thérapeutiques.

En utilisant la drosophile, nous avons identifié la lysine comme une source majeure alimentant la voie du mévalonate dans le tissu adipeux. Ce projet vise à déterminer si ce lien métabolique est conservé chez les adipocytes de mammifères et s'il contribue à la croissance tumorale en contexte d'obésité. Le premier objectif sera d'évaluer la contribution du catabolisme de la lysine à la voie du mévalonate dans des adipocytes « obèses ». Le second objectif sera d'analyser l'impact du métabolisme de la lysine sur la signalisation, la sécrétion et les fonctions pro-tumorales des adipocytes en co-culture avec des cellules cancéreuses. Enfin, nous étudierons l'effet de cet axe métabolique sur la croissance tumorale in vivo chez la drosophile.

Ce projet permettra d'identifier un nouvel axe métabolique lysine-mévalonate reliant dysfonction adipocytaire et progression tumorale, et de proposer de nouvelles cibles thérapeutiques.
Aim 1. Determine whether lysine catabolism promotes the dysregulation of adipocytes during obesity.

Our results in Drosophila indicate that lysine degradation is a major carbon source for the mevalonate pathway. Whether lysine fuels mevalonate metabolism to control adipocytes dysregulation in obese-like adipocytes remains unknown. Therefore, we aim to quantify lysine flux into the mevalonate pathway during adipocyte dysregulation through isotope tracing. Using high-resolution mass spectrometry available at the Mamma Platon platform (IRCM), we will measure the intermediates of the lysine and mevalonate degradation pathways in control and in obese-like adipocytes. We will use different adipocyte models, including differentiated mouse 3T3-L1 cells and human SGBS cells (Selvaraju et al., 2025). To mimic obesity at the cellular level In these cells, we will use lipid overload in the cell culture media through elevating the concentration of free fatty acids (specifically palmitate), which leads to triglyceride accumulation, adipocyte hypertrophy, and increased secretion of pro-inflammatory mediators (Newton et al., 2011). In addition, we will use chronic stimulation with cytokines (such as TNF-) as an alternative model commonly used to reproduces key features of dysfunctional adipose tissue observed in obesity, including ***** resistance and low-grade inflammation (Ajuwon et al., 2005).

Methods to measure CoAs and mevalonate intermediates have been developed during the work in Drosophila and have already been validated for mammary cell lines. A ¹³C-lysine tracer (in substitution of 12C-lysine) will be used to investigate the contribution of lysine-derived carbon into downstream metabolites of the mevalonate pathway by quantifying isotopologue distribution in control adipocytes versus obese-like adipocytes.
Interestingly, our preliminary results show that statins block the differentiation of MEF to adipocytes, as demonstrated by a decrease of ORO staining after treatment with simvastatin, atorvastatin and lovastatin. We will also perform rescue experiments with mevalonate or other upstream metabolic intermediates.
In order to identify key enzymatic steps linking lysine catabolism to the mevalonate pathway, we will systematically target (siRNA-mediated knockdown) all the enzymes of the lysine degradation pathway in control adipocytes and evaluate the effects on their dysregulation in obese-like adipocytes (through lipid accumulation and/or PPAR/C/EBP expression). Efficient silencing will be validated by Western blotting using previously characterized antibodies.

Aim 2. Determine how lysine metabolism shapes obese-like adipocyte communication with tumor cells

The mevalonate pathway is essential for adipocyte differentiation and function, notably through the production of isoprenoids that regulate protein prenylation, intracellular trafficking, and secretion. However, the contribution of lysine in this process remains unknown, limiting our understanding of how metabolic rewiring in obesity shapes adipocyte signaling and their pro-tumorigenic functions.
Based on our preliminary data and Aim 1, we hypothesize that lysine catabolism sustains mevalonate pathway activity in obese-like adipocytes, thereby controlling prenylation-dependent signaling and the secretion of adipokines and extracellular matrix components. Disruption of this metabolic axis is expected to impair adipocyte functional output and alter their communication with the tumor microenvironment.

To test this, we will inhibit lysine degradation and assess the consequences on mevalonate pathway activity, including levels of cholesterol and isoprenoid intermediates, in a breast cancer-adipocyte co-culture system (Dirat et al., 2011, Afrin et al., 2023, Cai et al., 2019 and Hoy et al., 2017). We will investigate how lysine metabolism affects obese-like adipocyte secretory programs, including adipokine production and extracellular protein synthesis. Human Adipokine Array (R&D systems) and quantitative proteomics on conditioned media from co-colture will be used to profile adipokines and secreted factors (Zaoui et al., 2022), while confocal microscopy will assess protein localization and trafficking. To evaluate the effects of adipokines and secreted factor from obese-like' adipocytes on breast cancer cells, we will evaluate breast cancer cell proliferation, migration and invasion. Breast cancer cells in control medium will be added to the upper well of the chemotaxis plates (IncuCyte). Control media or adipocyte conditioned media will be used as chemoattractant in the lower chambers.
These analyses will determine whether lysine-dependent mevalonate metabolism regulates the production and secretion of factors from obese-like adipocytes known to influence tumor growth. Rescue experiments with mevalonate or upstream intermediates will confirm that the observed effects are mediated through the mevalonate pathway.
This aim will establish whether lysine-dependent fueling of the mevalonate pathway controls adipocyte secretory and signaling programs, thereby defining a metabolic mechanism through which obese adipocytes promote tumor progression.

Aim 3. Investigate how adipose lysine metabolism regulates tumor growth in an in vivo model of obesity

Whether lysine-dependent mevalonate synthesis in adipose tissue influences tumor progression in obese animals remains unknown. We hypothesize that lysine catabolism in the fat body sustains mevalonate pathway activity, that in turns promotes the secretion of systemic signals that promote tumor growth in obese animals.
To test this, we will use an experimental set up in vivo in Drosophila to address the role of adipose lysine-mevalonate on epithelial tumors in obese animals.
We will work with well characterized and established epithelial tumor models in Drosophila, whereby the expression of oncogenic Ras combined with loss of polarity genes (for example scribble) in imaginal discs promotes the development of epithelial tumors. Tumor growth will be assessed by size, cell proliferation and cell death using confocal microscopy (Zhu et al., 2016). We will then induce obesity through control diet or (Birse et al., 2010 and Musselman et al., 2011) and this will allow the comparison between normal and obese tumor bearing Drosophila. diet-fed Drosophila larvae display reduced body size and delayed development (Musselman et al., 2011). Both High-sugar diet-induced metabolic dysfunction and oncogenic growth (Ras^V12; scrib/ tumors) in Drosophila are associated with delayed larval development, thereby extending the larval stage and providing a prolonged window for tumor progression and systemic adipocytes-tumor interplay.
In this context, we will genetically manipulate lysine degradation in the adipose tissue to downregulate key enzymes of the lysine pathway and we will inhibit the mevalonate pathway (statins) in order to compare the following conditions: Control, Tumor in normal Drosophila, Tumor in obesity condition, Tumor with lysine metabolism inhibition and Tumor in obesity condition with lysine metabolism inhibition. In these conditions, we will perform metabolomics experiment to measure metabolic intermediates of lysine degradation and mevalonate pathway, as well as stable isotope tracing. Moreover, we will evaluate the tumor growth, proliferation rate and apoptosis. Rescue experiments with mevalonate or upstream metabolic intermediates will confirm that these effects are mediated through the lysine degradation pathway.
Murine 3T3-L1 and human SGBS preadipocytes will be differentiated into mature adipocytes. Obese-like adipocytes will be generated via chronic palmitate exposure or TNF- stimulation to induce lipid accumulation, hypertrophy, and low-grade inflammation. ^13C-labeled lysine will replace natural lysine to trace its incorporation into mevalonate pathway intermediates (HMG-CoA, mevalonate, FPP, GGPP) using high-resolution mass spectrometry. Key enzymes of the lysine degradation pathway will be inhibited by siRNA and using Crispr-Cas9 mediated gene editing, with rescue experiments using mevalonate or additional downstream intermediates to confirm specificity.

Obese-like adipocytes will be co-cultured with breast cancer cells to assess adipocyte-tumor crosstalk. Secreted factors will be profiled using Human Adipokine Arrays and quantitative proteomics, while confocal microscopy will evaluate protein localization and trafficking. Effects on breast cancer cell proliferation, migration, and invasion will be assessed using chemotaxis plates (IncuCyte).

In vivo, Drosophila epithelial tumors will be induced by Ras^V12 expression with scribble^/ loss in imaginal discs. Larvae will be fed standard or high-sugar diets to model obesity; HSD-fed larvae show delayed development, extending the larval stage and allowing prolonged tumor-adipose interaction. Lysine degradation in the fat body will be genetically manipulated, and the mevalonate pathway inhibited using statins. Tumor growth, proliferation, and apoptosis will be quantified by confocal microscopy, and metabolomics combined with ^13C-lysine tracing will assess pathway activity.

All experiments will be performed with 3 biological replicates, and statistical significance determined by t-tests or ANOVA (p<0.05).

Nous recruterons un·e doctorant·e hautement motivé·e, doté·e d'un esprit collaboratif. Le·la candidat·e devra avoir une expérience des méthodes de biologie moléculaire et de biochimie de base. Nous recherchons également toute expertise en technologies d'édition génomique, métabolomique, fluxomique, bioinformatique, protéomique ou imagerie. Une expérience en génétique de la drosophile est appréciée mais n'est pas nécessaire.