Caracterización del papel del succinato y su receptor SUCNR1 en la fisiopatología de la obesidad y la diabetes de tipo 2

L’eix succinat-SUCNR1 ha cobrat especial interès per la seva implicació en diverses patologies inflamatòries cròniques, com l'obesitat i la diabetis tipus 2 (T2D). Diverses condicions d'estrès metabòlic s'han relacionat amb un augment del succinat extracel·lular, i l’activació específica del seu receptor SUCNR1. Dintre de les funcions de senyalització del succinat es troba l'activació de la resposta immunitària, motiu pel qual durant molt de temps se li va considerar com a un simple intermediari de la inflamació. En aquest context, aquesta tesi doctoral s’ha centrat en l'estudi de la via succinat-SUCNR1 en el macròfag, i la seva implicació en la fisiopatologia de la inflamació associada a l'obesitat i la T2D. A més, proposem la utilitat dels nivells circulants de succinat com a potencial biomarcador de l'estat metabòlic del pacient, comportant una nova eina clínica en el maneig de ambdues condicions. Amb aquests objectius, vam generar un model murí deficient en SUCNR1 en la línia mieloide, que ens permetés estudiar l'impacte d'aquesta via en el metabolisme. D'altra banda, mitjançant una cohort de pacients obesos i T2D, en un estudi prospectiu aleatoritzat unicentro, vam determinar els nivells de succinat circulant, i diversos paràmetres bioquímics i antropomètrics, tant previs a cirurgia bariàtrica, com després d'un any. Resultats que van ser validats en una segona cohort independent. Els nostres resultats demostren que la via succinat-SUCNR1 resulta fonamental per l'adequada resposta inflamatòria tant aguda com crònica, així com en la resolució natural de la inflamació; a l’hora que determina la importància d'aquest eix en el manteniment i funcionalitat dels macròfags; i en la relació obesitat i nivells elevats de succinat, on existeix un estat de resistència als seus efectes antiinflamatoris. Finalment, destaca l'enorme potencial d'aquesta ruta des d'un punt de vista transnacional en el context de desenvolupar aproximacions clíniques enfocades al maneig de la malaltia metabòlica.El eje succinato-SUCNR1 ha cobrado especial interés por su demostrada implicación en diversas patologías inflamatorias crónicas, como la obesidad y la diabetes tipo 2 (T2D). Condiciones de estrés metabólico se han relacionado con aumento de succinato extracelular, y activación específica de su receptor SUCNR1. Entre las funciones señalizadoras del succinato se encuentra la activación de la respuesta inmune, motivo por el que durante mucho tiempo se le consideró un mero mediador de la inflamación. En este contexto, esta tesis doctoral se centra en el estudio de la vía succinato-SUCNR1 en el macrófago, y su implicación en la fisiopatología de la inflamación asociada a la obesidad y T2D. Además, proponemos los niveles circulantes de succinato como biomarcador del estado metabólico del paciente, y herramienta clínica en el manejo de ambas condiciones. Para ello, generamos un modelo murino deficiente en SUCNR1 en la línea mieloide, donde estudiar el impacto de esta vía a nivel metabólico. Por otro lado, empleamos una cohorte de pacientes obesos y T2D, en un estudio prospectivo aleatorizado unicentro, donde determinamos succinato circulante, y parámetros bioquímicos y antropométricos, pre-cirugía bariátrica y tras un año, validándose en una segunda cohorte independiente. Nuestros resultados revelan que la vía succinato-SUCNR1 resulta fundamental en la adecuada respuesta inflamatoria aguda y crónica, así como en el curso natural de su resolución; la importancia de este eje en el mantenimiento y funcionalidad de los macrófagos; y la relación entre obesidad, niveles elevados de succinato y resistencia a sus efectos antiinflamatorios. Finalmente, destaca el enorme potencial de esta ruta desde un punto de vista traslacional en el contexto de enfermedades metabólicas, en el empleo de los niveles de succinato como biomarcador, aplicable en el manejo y pronóstico de la patología metabólica.The succinate-SUCNR1 axis has emerged as relevant molecular pathway implicated in the development of inflammatory chronic conditions, such as obesity and type 2 diabetes (T2D). Elevated amounts of circulating succinate occur in some pathologies related with an increased cardiovascular risk. Activation of SUCNR1 by extracellular succinate has been associated with a broad range of effects, especially in the context of inflammation and immune response. Accordingly, this doctoral thesis focuses on the study of succinate-SUCNR1 signaling pathway in macrophages, and its effect in the development of the inflammatory status underlying obesity and T2D. Furthermore, we propose circulating succinate levels as a biomarker of metabolic status, that could apply in clinical and therapeutic management of these pathologies. For this purpose, we generated mice with myeloid-cell-specific SUCNR1 deficiency and study the metabolic effect of this specific depletion. On the other hand, a prospective single-center, nonblinded, randomized controlled trial including obese patients with T2D, were employed to determine circulating succinate levels, anthropometrical and biochemical parameters, before and 1 year after bariatric surgery. The results were externally validated in a second cohort based on clinical criteria. Our study reveals succinate-SUCNR1 axis as crucial factor to adequately develop chronic and acute inflammatory response, as well as contributing to the resolution of inflammation; we note the relevance of this pathway in the maintenance and function of macrophages; and exposes obesity as a succinate-resistant state with loss of its anti-inflammatory properties. Finally, we highlight the potential of the succinate-SUCNR1 route from a translational point of view in the development of clinical approach focused on metabolic patholog

Elevated circulating levels of succinate in human obesity are linked to specific gut microbiota

Gut microbiota-related metabolites are potential clinical biomarkers for cardiovascular disease (CVD). Circulating succinate, a metabolite produced by both microbiota and the host, is increased in hypertension, ischemic heart disease, and type 2 diabetes. We aimed to analyze systemic levels of succinate in obesity, a major risk factor for CVD, and its relationship with gut microbiome. We explored the association of circulating succinate with specific metagenomic signatures in cross-sectional and prospective cohorts of Caucasian Spanish subjects. Obesity was associated with elevated levels of circulating succinate concomitant with impaired glucose metabolism. This increase was associated with specific changes in gut microbiota related to succinate metabolism: a higher relative abundance of succinate-producing Prevotellaceae (P) and Veillonellaceae (V), and a lower relative abundance of succinate-consuming Odoribacteraceae (O) and Clostridaceae (C) in obese individuals, with the (P + V/O + C) ratio being a main determinant of plasma succinate. Weight loss intervention decreased (P + V/O + C) ratio coincident with the reduction in circulating succinate. In the spontaneous evolution after good dietary advice, alterations in circulating succinate levels were linked to specific metagenomic signatures associated with carbohydrate metabolism and energy production with independence of body weight change. Our data support the importance of microbe-microbe interactions for the metabolite signature of gut microbiome and uncover succinate as a potential microbiota-derived metabolite related to CVD risk

Crohn's Disease Disturbs the Immune Properties of Human Adipose-Derived Stem Cells Related to Inflammasome Activation

Crohn's disease (CD) is characterized by the expansion of mesenteric fat, also known as “creeping fat.” We explored the plasticity and immune properties of adipose-derived stem cells (ASCs) in the context of CD as potential key players in the development of creeping fat. Mesenteric CD-derived ASCs presented a more proliferative, inflammatory, invasive, and phagocytic phenotype than equivalent cells from healthy donors, irrespective of the clinical stage. Remarkably, ASCs from the subcutaneous depot of patients with CD also showed an activated immune response that was associated with a reduction in their immunosuppressive properties. The invasive phenotype of mesenteric CD ASCs was governed by an inflammasome-mediated inflammatory state since blocking inflammasome signaling, mainly the secretion of interleukin-1β, reversed this characteristic. Thus, CD alters the biological functions of ASCs as adipocyte precursors, but also their immune properties. Selection of ASCs with the best immunomodulatory properties is advocated for the success of cell-based therapies

Elevated circulating levels of succinate in human obesity are linked to specific gut microbiota

Gut microbiota-related metabolites are potential clinical biomarkers for cardiovascular disease (CVD). Circulating succinate, a metabolite produced by both microbiota and the host, is increased in hypertension, ischemic heart disease, and type 2 diabetes. We aimed to analyze systemic levels of succinate in obesity, a major risk factor for CVD, and its relationship with gut microbiome. We explored the association of circulating succinate with specific metagenomic signatures in cross-sectional and prospective cohorts of Caucasian Spanish subjects. Obesity was associated with elevated levels of circulating succinate concomitant with impaired glucose metabolism. This increase was associated with specific changes in gut microbiota related to succinate metabolism: a higher relative abundance of succinate-producing Prevotellaceae (P) and Veillonellaceae (V), and a lower relative abundance of succinate-consuming Odoribacteraceae (O) and Clostridaceae (C) in obese individuals, with the (P + V/O + C) ratio being a main determinant of plasma succinate. Weight loss intervention decreased (P + V/O + C) ratio coincident with the reduction in circulating succinate. In the spontaneous evolution after good dietary advice, alterations in circulating succinate levels were linked to specific metagenomic signatures associated with carbohydrate metabolism and energy production with independence of body weight change. Our data support the importance of microbe-microbe interactions for the metabolite signature of gut microbiome and uncover succinate as a potential microbiota-derived metabolite related to CVD risk

SUCNR1 controls an anti-inflammatory program in macrophages to regulate the metabolic response to obesity

Succinate is a signaling metabolite sensed extracellularly by succinate receptor 1 (SUNCR1). The accumulation of succinate in macrophages is known to activate a pro-inflammatory program; however, the contribution of SUCNR1 to macrophage phenotype and function has remained unclear. Here we found that activation of SUCNR1 had a critical role in the anti-inflammatory responses in macrophages. Myeloid-specific deficiency in SUCNR1 promoted a local pro-inflammatory phenotype, disrupted glucose homeostasis in mice fed a normal chow diet, exacerbated the metabolic consequences of diet-induced obesity and impaired adipose-tissue browning in response to cold exposure. Activation of SUCNR1 promoted an anti-inflammatory phenotype in macrophages and boosted the response of these cells to type 2 cytokines, including interleukin-4. Succinate decreased the expression of inflammatory markers in adipose tissue from lean human subjects but not that from obese subjects, who had lower expression of SUCNR1 in adipose-tissue-resident macrophages. Our findings highlight the importance of succinate-SUCNR1 signaling in determining macrophage polarization and assign a role to succinate in limiting inflammation.This study was supported by grants from the Spanish Ministry of Science, Innovation and Universities (PI14/00228 and PI17/01503 to J.V., SAF2015-65019-R to S.F.-V., SAF2014-56819-R and SAF2015-71878-REDT to A.C., BFU2016-78951-R to G.M.-M., PI15/00143 to C.S. and PI15/01562 to A.M., BFU2015-70454-REDT and BFU2017-90578-REDT to S.F.-V. and G.M.-M.) co-financed by the European Regional Development Fund (ERDF). The Spanish Biomedical Research Center in Diabetes and Associated Metabolic Disorders (CIBERDEM) (CB07708/0012) is an initiative of the Instituto de Salud Carlos III. N.K. is recipient of a predoctoral fellowship from MINECO, Spain (FPI, BES-2016-077745). C.S. acknowledges support from the ‘Ramón y Cajal’ program from MINECO (RYC2013-13186) and S.F.-V. the Miguel Servet tenure-track program (CP10/00438 and CPII16/00008) from the Fondo de Investigación Sanitaria, co-financed by the ERDF.Peer reviewe