The PPARβ/δ-AMPK Connection in the Treatment of Insulin Resistance

The current treatment options for type 2 diabetes mellitus do not adequately control the disease in many patients. Consequently, there is a need for new drugs to prevent and treat type 2 diabetes mellitus. Among the new potential pharmacological strategies, activators of peroxisome proliferator-activated receptor (PPAR)β/δ show promise. Remarkably, most of the antidiabetic effects of PPARβ/δ agonists involve AMP-activated protein kinase (AMPK) activation. This review summarizes the recent mechanistic insights into the antidiabetic effects of the PPARβ/δ-AMPK pathway, including the upregulation of glucose uptake, muscle remodeling, enhanced fatty acid oxidation, and autophagy, as well as the inhibition of endoplasmic reticulum stress and inflammation. A better understanding of the mechanisms underlying the effects resulting from the PPARβ/δ-AMPK pathway may provide the basis for the development of new therapies in the prevention and treatment of insulin resistance and type 2 diabetes mellitus

IDENTIFICACIÓN Y CUANTIFICACIÓN DE LA EXPRESIÓN GÉNICA DE RECEPTORES DE MELATONINA EN EL TRACTO REPRODUCTOR DE MORUECO

La hormona melatonina es una de las sustancias biológicamente activas más antiguas de los organismos vivos y desempeña una gran variedad de funciones. Una gran parte de estas funciones las ejerce principalmente interaccionando con los receptores transmembrana acoplados a proteína G, MT1 y MT2, los cuales intervienen en diferentes vías de transducción de señal. La melatonina se sintetiza principalmente en la glándula pineal durante la noche, y, como consecuencia de ello, sus niveles en plasma sanguíneo son prácticamente inexistentes durante el día. Sin embargo, recientes estudios de nuestro grupo de investigación han demostrado la presencia de melatonina en plasma seminal ovino, que mantiene niveles constantes a lo largo del día aunque menores que los nocturnos. Asimismo, en dichos estudios también se ha verificado la existencia de enzimas responsables de la síntesis de melatonina en el tracto reproductor de morueco. Una cuestión interesante sería determinar si la melatonina puede ejercer alguna acción directa sobre los tejidos del tracto genital masculino. Con este fin, en este trabajo se analizó la existencia de los dos receptores principales de melatonina, MT1 y MT2, en los distintos tejidos del aparato reproductor del morueco (testículo, epidídimo y glándulas accesorias). Mediante PCR con transcriptasa inversa (RT-PCR) se demostró la expresión génica de dichos receptores en todos los tejidos estudiados, y además la real time-PCR (q-PCR) permitió cuantificar las diferencias existentes en los niveles de expresión en cada uno de los tejidos. Asimismo, se demostró la presencia de estos receptores, mediante Western-Blot, en la mayoría de los tejidos en mayor o menor medida. La relevancia de dichos resultados radica en que la presencia de los dos receptores de melatonina en el tracto reproductor masculino indicaría la existencia de mecanismos de modulación de posibles vías de trasducción de señal asociadas a ellos. Las respuestas producidas podrían incidir de algún modo en el control de los eventos de maduración, desarrollo, transporte y almacenamiento de las células espermáticas, pudiendo influenciar la calidad seminal y, consecuentemente, la capacidad fecundante de los eyaculados

A positive feedback loop between AMPK and GDF15 promotes metformin antidiabetic effects

BACKGROUND AND AIMS: Metformin, the most prescribed drug for the treatment of type 2 diabetes mellitus, has been recently reported to promote weight loss by upregulating the anorectic cytokine growth differentiation factor 15 (GDF15). Since the antidiabetic effects of metformin are mostly mediated by the activation of AMPK, a key metabolic sensor in energy homeostasis, we examined whether the activation of this kinase by metformin was dependent on GDF15. METHODS: Cultured hepatocytes and myotubes, and wild-type and Gdf15(-/-) mice were utilized in a series of studies to investigate the involvement of GDF15 in the activation of AMPK by metformin. RESULTS: A low dose of metformin increased GDF15 levels without significantly reducing body weight or food intake, but it ameliorated glucose intolerance and activated AMPK in the liver and skeletal muscle of wild-type mice but not Gdf15(-/-) mice fed a high-fat diet. Cultured hepatocytes and myotubes treated with metformin showed AMPK-mediated increases in GDF15 levels independently of its central receptor GFRAL, while Gdf15 knockdown blunted the effect of metformin on AMPK activation, suggesting that AMPK is required for the metformin-mediated increase in GDF15, which in turn is needed to sustain the full activation of this kinase independently of the CNS. CONCLUSION: Overall, these findings uncover a novel mechanism through which GDF15 upregulation by metformin is involved in achieving and sustaining full AMPK activation by this drug independently of the CNS

GDF15 mediates the metabolic effects of PPARβ/δ by activating AMPK

Peroxisome proliferator-activated receptor β/ (PPARβ/) activates AMP-activated protein kinase (AMPK) and plays a crucial role in glucose and lipid metabolism. Here, we examined whether the beneficial effects of PPARβ/δ activation depended on growth differentiation factor 15 (GDF15), a stress response cytokine that regulates energy metabolism. Pharmacological PPARβ/δ activation increased GDF15 levels and ameliorated glucose intolerance, fatty acid oxidation, endoplasmic reticulum stress, inflammation and activated AMPK in HFD-fed mice, whereas these effects were abrogated by the injection of a GDF15 neutralizing antibody and in Gdf15-/- mice. The AMPK-p53 pathway was involved in the PPARβ/δ-mediated increase in GDF15, which in turn activated again AMPK. Finally, Gdf15-/- mice showed reduced AMPK activation in skeletal muscle, whereas GDF15 administration resulted in AMPK activation in this organ. Collectively, these data reveal a novel mechanism by which PPARβ/δ activation increases the levels of GDF15 via AMPK and p53, which in turn mediates the metabolic effects of PPARβ/δ by sustaining AMPK activation. Abbreviations: Acadm, acyl-CoA dehydrogenase medium chain; Acox, acyl-CoA oxidase; AMPK, AMP-activated protein kinase; ATF4, activating transcription factor 4; BiP/GRP78, Binding immunoglobulin protein/78-kDa glucose-regulated protein; CC, compound C; Chop, C/EBP homologous protein; Cpt-1, carnitine palmitoyl-transferase 1; eIF2eukaryotic translation initiation factor 2 ER, endoplasmic reticulum; ERK, extracellular signal-regulated kinase; FGF21, fibroblast growth factor 21; GDF15, growth differentiation factor 15; GFRAL, glial-derived neurotrophic factor receptor α-like; HFD, high-fat diet; Pdk4, pyruvate dehydrogenase kinase 4; IRS, insulin receptor substrate; PGC-1PPAR co-activator 1 PPAR peroxisome proliferator-activated receptor; SOCS3, suppressor of cytokine signaling 3; STAT3, signal transducer and activator of transcription 3; Vldlr, very-low density lipoprotein receptor

Elafibranor upregulates the EMT-inducer S100A4 via PPARβ/δ

Elafibranor is a dual peroxisome proliferator-activated receptor (PPAR)α and β/δ agonist that has reached a phase III clinical trial for the treatment of metabolic dysfunction-associated steatotic liver disease (MASLD). Here, we examined the effects of elafibranor in mice fed a choline-deficient high-fat diet (CD-HFD), a model of metabolic dysfunction-associated steatohepatitis (MASH) that presents obesity and insulin resistance. Our findings revealed that elafibranor treatment ameliorated steatosis, inflammation, and fibrogenesis in the livers of CD-HFD-fed mice. Unexpectedly, elafibranor also increased the levels of the epithelial-mesenchymal transition (EMT)-promoting protein S100A4 via PPARβ/δ activation. The increase in S100A4 protein levels caused by elafibranor was accompanied by changes in the levels of markers associated with the EMT program. The S100A4 induction caused by elafibranor was confirmed in the BRL-3A rat liver cells and a mouse primary hepatocyte culture. Furthermore, elafibranor reduced the levels of ASB2, a protein that promotes S100A4 degradation, while ASB2 overexpression prevented the stimulating effect of elafibranor on S100A4. Collectively, these findings reveal an unexpected hepatic effect of elafibranor on increasing S100A4 and promoting the EMT program.This study was partly supported by the grants RTI2018-093999-B-I00 and PID2021-122116OB-I00 (M.V-C.), PID2021-122766OB-I00 (A.M.V.), and PID2019-105989RB-I00 (J.B.) from MCIN/AEI/10.13039/501100011033 and “ERDF, A Way of Making Europe”. CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM) is a Carlos III Health Institute project. Support was also received from the CERCA Programme/Generalitat de Catalunya. Meijian Zhang was supported by a grant from the China Scholarship Council (CSC) (202007565030).Peer reviewe

GDF15, a novel regulator of the AMPK-mediated antidiabetic actions of PPARβ/δ and metformin

[eng] Type 2 diabetes (T2D) is a multifactorial disease that comprises metabolic defects in multiple organs. Several studies have shown that the presence of a chronic low-state inflammatory process induces the development of insulin resistance, a pathology in which the organism fails to respond to the hormone insulin. This condition precedes and predicts the development of T2D. Likewise, the presence of endoplasmic reticulum (ER) stress induced by a lipid overload in obesity states contributes to the development of insulin resistance through multiple processes, including the activation of inflammatory pathways. At present, T2D has become a chronic disease that affects more than 400 million people worldwide, reaching epidemiological rates. In addition to the metabolic defects, T2D progression can lead to further complications, including blindness, cardiovascular disease, kidney failure, or limb amputation. Despite its growing incidence, the current available drugs for the treatment of T2D show a limited efficacy and significant side effects that are not fully controlled. For that reason, there is an urgent need to discover new therapeutic targets that can control the complexity of the disease. In this regard, PPARβ/δ agonists have been proven effective as a therapy against insulin resistance and T2D, by improving lipid-induced ER stress and inflammation, as well as glucose and lipid homeostasis. However, PPARβ/δ agonists are not currently available for clinical therapy. On the other hand, metformin has been the most prescribed oral drug for T2D in the past years. Nevertheless, the molecular mechanisms by which this drug exerts its antidiabetic actions are not fully understood. Interestingly, many of the antidiabetic effects of PPARβ/δ activation and metformin on lipid metabolism, inflammation or insulin signalling rely on AMPK activation, and present similarities with the actions of growth differentiation factor 15 (GDF15), a stress response cytokine that regulates energy metabolism through different mechanisms. In the present thesis, we show that pharmacological PPARβ/δ activation increases GDF15 levels, which contribute to the antidiabetic effects of PPARβ/δ on glucose intolerance, fatty acid oxidation, ER stress, inflammation and insulin signalling. Additionally, we report that the AMPK-p53 pathway is involved in the PPARβ/δ-mediated increase in GDF15, which in turn is necessary to maintain the activation of AMPK. Similarly, metformin treatment increases GDF15 levels through an AMPK-ATF3 pathway. Interestingly, we report that GDF15 mediates the AMPK- mediated antidiabetic effects of metformin on fatty acid oxidation, inflammation and insulin signalling independently of changes in food intake or body weight. Importantly, one of the most remarkable findings is that GDF15 activates AMPK in skeletal muscle independently of central nervous system or the glial cell line- derived neurotrophic factor (GDNF) family receptor α-like (GFRAL), the neuronal receptor for GDF15. Overall, the results of the present doctoral thesis shed light on the mechanism of action of two well-known antidiabetic agents and indicate that GDF15 may become a new therapeutic target for the potential treatment of metabolic disorders.[spa] La diabetes tipo 2 es una enfermedad multifactorial que engloba defectos metabólicos en múltiples órganos. Diversos estudios ponen de manifiesto que la presencia de un proceso inflamatorio crónico de baja intensidad induce el desarrollo de la resistencia a insulina, una patología metabólica en la cual el organismo no responde correctamente a la hormona insulina. Esta condición precede y predice el desarrollo de la diabetes tipo 2. Asimismo, la presencia de estrés en el retículo endoplásmico (RE) inducida por una sobrecarga lipídica en estados de obesidad contribuye al desarrollo de la resistencia a insulina a través de múltiples procesos, incluyendo la activación de vías inflamatorias. En la actualidad, la diabetes tipo 2 se ha convertido en una enfermedad crónica que afecta a más de 400 millones de personas en todo el mundo, alcanzando tasas epidemiológicas. Además de los defectos metabólicos inherentes a la enfermedad, la progresión de ésta puede desembocar en futuras complicaciones, incluyendo ceguera, enfermedades cardiovasculares, fallo renal, o amputación de extremidades. A pesar del crecimiento de su incidencia, los fármacos actualmente disponibles para el tratamiento de la diabetes tipo 2 muestran una eficacia limitada y efectos secundarios significativos que no están completamente controlados. Por esta razón, existe una urgente necesidad de definir nuevas dianas terapéuticas que permitan controlar la complejidad de esta enfermedad. En este sentido, los agonistas de PPARβ/δ han demostrado ser una terapia eficaz contra la resistencia a insulina y la diabetes tipo 2, mejorando la inflamación y el estrés del RE inducido por lípidos, así como la homeostasis glucídica y lipídica. Sin embargo, los agonistas de PPARβ/δ no están actualmente disponibles para la terapia clínica. Por otro lado, la metformina ha sido el fármaco oral más prescrito contra la diabetes tipo 2 en los últimos años. A pesar de ello, los mecanismos moleculares por los que este fármaco ejerce sus funciones antidiabéticas no están completamente descritas. Resulta interesante que varios de los efectos antidiabéticos de la activación de PPARβ/δ y de la metformina sobre el metabolismo lipídico, la inflamación, o la señalización de la insulina dependen de la activación de AMPK, y presentan similitudes con las acciones de GDF15 (growth differentiation factor 15), una citoquina de respuesta a estrés que regula el metabolismo energético a través de diferentes mecanismos. En la presente tesis, demostramos que la activación farmacológica de PPARβ/δ aumenta los niveles de GDF15, y que este aumento contribuye a los efectos antidiabéticos de PPARβ/δ sobre la intolerancia a la glucosa, la oxidación de ácidos grasos, el estrés del RE, la inflamación y la señalización de la insulina. Además, reportamos que la vía AMPK-p53 está involucrada en el aumento de GDF15 mediado por PPARβ/δ, y que este aumento de GDF15 es necesario para mantener la activación de AMPK. De modo similar, el tratamiento con metformina aumenta los niveles de GDF15 a través de la vía AMPK-ATF3. Asimismo, este aumento de GDF15 media los efectos antidiabéticos de la metformina regulados por AMPK sobre la oxidación de ácidos grasos, la inflamación y la señalización de la insulina en ausencia de cambios en la ingesta de comida o en el peso corporal. Finalmente, uno de los descubrimientos más relevantes es que GDF15 activa AMPK en el músculo esquelético independientemente del receptor neuronal de GDF15 GFRAL (GDNF family receptor α-like) y sin mediación del sistema nervioso central. En resumen, los resultados obtenidos en la presente tesis doctoral permiten definir en mayor profundidad el mecanismo de acción de dos agentes antidiabéticos ampliamente conocidos e indican que GDF15 podría constituir una nueva diana terapéutica para el potencial tratamiento de distintas enfermedades metabólicas

The PPARβ/δ-AMPK Connection in the Treatment of Insulin Resistance

International audienceThe current treatment options for type 2 diabetes mellitus do not adequately control the disease in many patients. Consequently, there is a need for new drugs to prevent and treat type 2 diabetes mellitus. Among the new potential pharmacological strategies, activators of peroxisome proliferator-activated receptor (PPAR)β/δ show promise. Remarkably, most of the antidiabetic effects of PPARβ/δ agonists involve AMP-activated protein kinase (AMPK) activation. This review summarizes the recent mechanistic insights into the antidiabetic effects of the PPARβ/δ-AMPK pathway, including the upregulation of glucose uptake, muscle remodeling, enhanced fatty acid oxidation, and autophagy, as well as the inhibition of endoplasmic reticulum stress and inflammation. A better understanding of the mechanisms underlying the effects resulting from the PPARβ/δ-AMPK pathway may provide the basis for the development of new therapies in the prevention and treatment of insulin resistance and type 2 diabetes mellitus

A positive feedback loop between AMPK and GDF15 promotes metformin antidiabetic effects

[Background and aims]: Metformin, the most prescribed drug for the treatment of type 2 diabetes mellitus, has been recently reported to promote weight loss by upregulating the anorectic cytokine growth differentiation factor 15 (GDF15). Since the antidiabetic effects of metformin are mostly mediated by the activation of AMPK, a key metabolic sensor in energy homeostasis, we examined whether the activation of this kinase by metformin was dependent on GDF15. [Methods]: Cultured hepatocytes and myotubes, and wild-type and Gdf15-/- mice were utilized in a series of studies to investigate the involvement of GDF15 in the activation of AMPK by metformin. [Results]: A low dose of metformin increased GDF15 levels without significantly reducing body weight or food intake, but it ameliorated glucose intolerance and activated AMPK in the liver and skeletal muscle of wild-type mice but not Gdf15-/- mice fed a high-fat diet. Cultured hepatocytes and myotubes treated with metformin showed AMPK-mediated increases in GDF15 levels independently of its central receptor GFRAL, while Gdf15 knockdown blunted the effect of metformin on AMPK activation, suggesting that AMPK is required for the metformin-mediated increase in GDF15, which in turn is needed to sustain the full activation of this kinase independently of the CNS. [Conclusion]: Overall, these findings uncover a novel mechanism through which GDF15 upregulation by metformin is involved in achieving and sustaining full AMPK activation by this drug independently of the CNS.This research was supported by CIBER-Consorcio Centro de Investigación Biomédica en Red- (CB07/08/0003), Instituto de Salud Carlos III, Ministerio de Ciencia e Innovación. CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM) is a Carlos III Health Institute project. CERCA Programme/Generalitat de Catalunya. Meijian Zhang was supported by a grant from the China Scholarship Council (CSC) (202007565030)

Elafibranor upregulates the EMT-inducer S100A4 via PPARβ/δ

Elafibranor is a dual peroxisome proliferator-activated receptor (PPAR)α and β/δ agonist that has reached a phase III clinical trial for the treatment of metabolic dysfunction-associated steatotic liver disease (MASLD). Here, we examined the effects of elafibranor in mice fed a choline-deficient high-fat diet (CD-HFD), a model of metabolic dysfunction-associated steatohepatitis (MASH) that presents obesity and insulin resistance. Our findings revealed that elafibranor treatment ameliorated steatosis, inflammation, and fibrogenesis in the livers of CD-HFD-fed mice. Unexpectedly, elafibranor also increased the levels of the epithelial-mesenchymal transition (EMT)-promoting protein S100A4 via PPARβ/δ activation. The increase in S100A4 protein levels caused by elafibranor was accompanied by changes in the levels of markers associated with the EMT program. The S100A4 induction caused by elafibranor was confirmed in the BRL-3A rat liver cells and a mouse primary hepatocyte culture. Furthermore, elafibranor reduced the levels of ASB2, a protein that promotes S100A4 degradation, while ASB2 overexpression prevented the stimulating effect of elafibranor on S100A4. Collectively, these findings reveal an unexpected hepatic effect of elafibranor on increasing S100A4 and promoting the EMT program