Mitochondrial E3 ubiquitin ligase 1 (MUL1) as a novel therapeutic target for diseases associated with mitochondrial dysfunction.

Mitochondrial E3 ubiquitin ligase 1 (MUL1) is a mitochondrial outer membrane-anchored protein-containing transmembrane domain in its N- and C-terminal regions, where both are exposed to the cytosol. Interestingly the C-terminal region has a RING finger domain responsible for its E3 ligase activity, as ubiquitin or in SUMOylation, interacting with proteins related to mitochondrial fusion and fission, cell survival, and tumor suppressor process, such as Akt. Therefore, MUL1 is involved in various cellular processes, such as mitochondrial dynamics, inter-organelle communication, proliferation, mitophagy, immune response, inflammation and cell apoptosis. MUL1 is expressed at a higher basal level in the heart, immune system organs, and blood. Here, we discuss the role of MUL1 in mitochondrial dynamics and its function in various pathological models, both in vitro and in vivo. In this context, we describe the role of MUL1 in: (1) the inflammatory response, by regulating NF-κB activity; (2) cancer, by promoting cell death and regulating exonuclear function of proteins, such as p53; (3) neurological diseases, by maintaining communication with other organelles and interacting with proteins to eliminate damaged organelles and; (4) cardiovascular diseases, by maintaining mitochondrial fusion/fission homeostasis. In this review, we summarize the latest advances in the physiological and pathological functions of MUL1. We also describe the different substrates of MUL1, acting as a positive or negative regulator in various pathologies associated with mitochondrial dysfunction. In conclusion, MUL1 could be a potential key target for the development of therapies that focus on ensuring the functionality of the mitochondrial network and, furthermore, the quality control of intracellular components by synchronously modulating the activity of different cellular mechanisms involved in the aforementioned pathologies. This, in turn, will guide the development of targeted therapies.

Skeletal muscle type-specific mitochondrial adaptation to high-fat diet relies on differential autophagy modulation.

In obesity, skeletal muscle mitochondrial activity changes to cope with increased nutrient availability. Autophagy has been proposed as an essential mechanism involved in the regulation of mitochondrial metabolism. Still, the contribution of autophagy to mitochondrial adaptations in skeletal muscle during obesity is unknown. Here, we show that in response to high-fat diet (HFD) feeding, distinct skeletal muscles in mice exhibit differentially regulated autophagy that may modulate mitochondrial activity. We observed that after 4 and 40 weeks of high-fat diet feeding, OXPHOS subunits and mitochondrial DNA content increased in the oxidative soleus muscle. However, in gastrocnemius muscle, which has a mixed fiber-type composition, the mitochondrial mass increased only after 40 weeks of HFD feeding. Interestingly, fatty acid-supported mitochondrial respiration was enhanced in gastrocnemius, but not in soleus muscle after a 4-week HFD feeding. This increased metabolic profile in gastrocnemius was paralleled by preserving autophagy flux, while autophagy flux in soleus was reduced. To determine the role of autophagy in this differential response, we used an autophagy-deficient mouse model with partial deletion of Atg7 specifically in skeletal muscle (SkM-Atg7+/- mice). We observed that Atg7 reduction resulted in diminished autophagic flux in skeletal muscle, alongside blunting the HFD-induced increase in fatty acid-supported mitochondrial respiration observed in gastrocnemius. Remarkably, SkM-Atg7+/- mice did not present increased mitochondria accumulation. Altogether, our results show that HFD triggers specific mitochondrial adaptations in skeletal muscles with different fiber type compositions, and that Atg7-mediated autophagy modulates mitochondrial respiratory capacity but not its content in response to an obesogenic diet.

The aging of ER-mitochondria communication: A journey from undifferentiated to aged cells.

The complex physiology of eukaryotic cells requires that a variety of subcellular organelles perform unique tasks, even though they form highly dynamic communication networks. In the case of the endoplasmic reticulum (ER) and mitochondria, their functional coupling relies on the physical interaction between their membranes, mediated by domains known as mitochondria-ER contacts (MERCs). MERCs act as shuttles for calcium and lipid transfer between organelles, and for the nucleation of other subcellular processes. Of note, mounting evidence shows that they are heterogeneous structures, which display divergent behaviors depending on the cell type. Furthermore, MERCs are plastic structures that remodel according to intra- and extracellular cues, thereby adjusting the function of both organelles to the cellular needs. In consonance with this notion, the malfunction of MERCs reportedly contributes to the development of several age-related disorders. Here, we integrate current literature to describe how MERCs change, starting from undifferentiated cells, and their transit through specialization, malignant transformation (i.e., dedifferentiation), and aging/senescence. Along this journey, we will review the function of MERCs and their relevance for pivotal cell types, such as stem and cancer cells, cardiac, skeletal, and smooth myocytes, neurons, leukocytes, and hepatocytes, which intervene in the progression of chronic diseases related to age.

Estrogen signaling as a bridge between the nucleus and mitochondria in cardiovascular diseases.

Cardiovascular diseases (CVDs) are the leading cause of morbidity and mortality worldwide. Epidemiological studies indicate that pre-menopausal women are more protected against the development of CVDs compared to men of the same age. This effect is attributed to the action/effects of sex steroid hormones on the cardiovascular system. In this context, estrogen modulates cardiovascular function in physiological and pathological conditions, being one of the main physiological cardioprotective agents. Here we describe the common pathways and mechanisms by which estrogens modulate the retrograde and anterograde communication between the nucleus and mitochondria, highlighting the role of genomic and non-genomic pathways mediated by estrogen receptors. Additionally, we discuss the presumable role of bromodomain-containing protein 4 (BRD4) in enhancing mitochondrial biogenesis and function in different CVD models and how this protein could act as a master regulator of estrogen protective activity. Altogether, this review focuses on estrogenic control in gene expression and molecular pathways, how this activity governs nucleus-mitochondria communication, and its projection for a future generation of strategies in CVDs treatment.

Novel Insights Into the Pathogenesis of Diabetic Cardiomyopathy and Pharmacological Strategies.

Diabetic cardiomyopathy (DCM) is a severe complication of diabetes developed mainly in poorly controlled patients. In DCM, several clinical manifestations as well as cellular and molecular mechanisms contribute to its phenotype. The production of reactive oxygen species (ROS), chronic low-grade inflammation, mitochondrial dysfunction, autophagic flux inhibition, altered metabolism, dysfunctional insulin signaling, cardiomyocyte hypertrophy, cardiac fibrosis, and increased myocardial cell death are described as the cardinal features involved in the genesis and development of DCM. However, many of these features can be associated with broader cellular processes such as inflammatory signaling, mitochondrial alterations, and autophagic flux inhibition. In this review, these mechanisms are critically discussed, highlighting the latest evidence and their contribution to the pathogenesis of DCM and their potential as pharmacological targets.

Mecanismo sensor y de adaptación a los niveles de oxígeno y su implicancia en las enfermedades cardiovasculares: a propósito del Premio Nobel de Fisiología-Medicina 2019 / Role of hypoxia-inducible factor-1 (HIF-1) in the adaptacion to oxygen levels: Nobel Prize in physiology-medicine 2019

RESUMEN: El Premio Nobel 2019 en Fisiología-Medicina se confirió a los Profesores Gregg Semenza, William Kaelin y Sir Peter Ratcliffe por sus investigaciones en la maquinaria molecular que regula la expresión de genes sensibles a los cambios en los niveles de oxígeno. La síntesis de eritropoyetina inducida por la disminución de los niveles sanguíneos de oxígeno condujo al estudio del gen de la eritropoyetina y descubrimiento de los elementos de respuesta a hipoxia (HRE) en la región promotora y posteriormente al factor transcripcional inducible por hipoxia tipo 1 (HIF-1). Este factor consta de dos subunidades: HIF-1α, sensible al oxígeno, y HIF-1β, expresada constitutivamente. HIF1 activa la transcripción de genes que codifican enzimas, transportadores y proteínas mitocondriales que disminuyen la utilización de oxígeno al cambiar el metabolismo oxidativo al metabolismo glicolítico y además aquellos involucrados en la angiogénesis y diferenciación celular. Las investigaciones paralelas en la enfermedad von Hippel-Lindau (VHL), un desorden autosómico dominante, permitieron descubrir el mecanismo de degradación de HIF1 en condiciones de normoxia y como se estabiliza bajo hipoxia. El impacto de HIF en clínica radica en el establecimiento de nuevas dianas terapéuticas para combatir la anemia y diversas enfermedades cardiovasculares. HIF promueve la angiogénesis a través de la expresión del factor de crecimiento vascular endotelial (VEGF), agente cardioprotector con potencial para tratar la isquemia/reperfusión, hipertrofia patológica e insuficiencia cardíaca.

ABSTRACT: The Nobel Prize in Physiology-Medicine was awarded to Drs. Gregg Semenza, William Kaelin and Sir Peter Ratcliffe for their research in the molecular machinery that regulates the expression of genes sensitive to the change in oxygen levels. The synthesis of erythropoietin induced by the decrease levels of oxygen in the blood led to investigate the promoter of the erythropoietin gene where the so-called hypoxia response elements (HRE) were described. Semenza et al. described a protein that binds to HREs and called it hypoxia-inducible transcriptional factor (HIF) that regulates gene expression among those involved in angiogenesis, cell differentiation and glycolytic enzymes. HIF presents two oxygen-sensitive subunits HIF-1α and HIF-1β constitutively expressed. In parallel, Kaelin et al. investigated von Hippel-Lindau disease (VHL), an autosomal dominant disorder, discovering a mutation of this protein generated a behavior similar to hypoxia. The impact of HIF-1α lies in the search for new strategies such as hydrolase inhibitors to combat prevalent diseases, including anemia and cardiovascular diseases These compounds promote the expression of vascular endothelial growth factor (VEGF), a cardioprotective agent with potential use in pre- and post-conditioning therapy, cardiac hypertrophy and heart failure.

Enfermedades cardiovasculares y cáncer: ¿dos entidades mutuamente relacionadas? / Cardiovascular diseases and cancer: ¿mutually related entities?

Resumen: Las enfermedades cardiovasculares y el cáncer son enfermedades crónicas transmisibles culturalmente, y las dos causas principales de mortalidad en el mundo. Además del gran impacto sobre la mortalidad y morbilidad, estas enfermedades han mostrado un alto grado de relación entre ellas debido, entre otras razones, a que comparten factores de riesgo y mecanismos biológicos. La alta incidencia de enfermedad cardiovascular en pacientes con cáncer es un fenómeno conocido que ha orientado el desarrollo del campo interdisciplinario de la cardio-oncología. Sin embargo, en la última década han surgido evidencias que muestran el papel que desempeñan las enfermedades cardiovasculares en el desarrollo de cáncer. Un estudio reciente publicado por Meijers y cols, en agosto de 2018 en Circulation, mostró que la insuficiencia cardiaca post-infarto del miocardio contribuye significativamente al desarrollo del cáncer de colón, apoyando lo obtenido en estudios epidemiológicos anteriores. Este estudio también sugiere que el crecimiento tumoral podría producirse por factores secretados por el corazón insuficiente abriendo un amplio grupo de posibilidades de investigación en lo que sería un nuevo campo de la medicina cuyo propósito sería el desarrollo de nuevas estrategias para el seguimiento y tratamiento del cáncer en pacientes con enfermedades cardiovasculares. El presente artículo revisa los factores de riesgo, y mecanismos celulares y moleculares, que son comunes en las enfermedades cardiovasculares y el cáncer, la contribución del trabajo de Meijers y cols hacia un mayor entendimiento de la interrelación entre estas patologías y las perspectivas futuras con respecto a los nuevos hallazgos.

Abstracts: Cardiovascular diseases and cancer are culturally transmitted chronic diseases and the two main causes of death globally. In addition to their high morbidity and mortality, these diseases are closely related, due to their common risk factors and biological mechanisms. The high incidence of cardiovascular diseases in cancer patients is widely known phenomenon, which has oriented the development of the interdisciplinary field of cardio-oncology Nonetheless, there is emerging evidence in the last decade suggesting a potential role for cardiovascular diseases in the onset of cancer. A recent publication by Meijers et al in the scientific cardiovascular journal Circulation showed that heart failure significantly contributes to tumor growth, confirming previous epidemiological findings suggesting this hypothesis. Moreover, this study indicates that tumor growth may be stimulated by the secretion of factors from the failing heart, opening a wide spectrum of research areas in what may be suggested as a new field in medicine that would seek to develop new strategies to treat and prevent cancer in patients with cardiovascular diseases. This article will review shared risk factor and common cellular and molecular pathways in cardiovascular diseases and cancer, the contribution of Meijers et al to a better understanding of the connection of these diseases and future perspectives in light of the new evidence.