HERPUD1 governs tumor cell mitochondrial function via inositol 1,4,5-trisphosphate receptor-mediated calcium signaling.

The intricate relationship between calcium (Ca2+) homeostasis and mitochondrial function is crucial for cellular metabolic adaptation in tumor cells. Ca2+-initiated signaling maintains mitochondrial respiratory capacity and ATP synthesis, influencing critical cellular processes in cancer development. Previous studies by our group have shown that the homocysteine-inducible ER Protein with Ubiquitin-Like Domain 1 (HERPUD1) regulates inositol 1,4,5-trisphosphate receptor (ITPR3) levels and intracellular Ca2+ signals in tumor cells. This study explores the role of HERPUD1 in regulating mitochondrial function and tumor cell migration by controlling ITPR3-dependent Ca2+ signals. We found HERPUD1 levels correlated with mitochondrial function in tumor cells, with HERPUD1 deficiency leading to enhanced mitochondrial activity. HERPUD1 knockdown increased intracellular Ca2+ release and mitochondrial Ca2+ influx, which was prevented using the ITPR3 antagonist xestospongin C or the Ca2+ chelator BAPTA-AM. Furthermore, HERPUD1 expression reduced tumor cell migration by controlling ITPR3-mediated Ca2+ signals. HERPUD1-deficient cells exhibited increased migratory capacity, which was attenuated by treatment with xestospongin C or BAPTA-AM. Additionally, HERPUD1 deficiency led to reactive oxygen species-dependent activation of paxillin and FAK proteins, which are associated with enhanced cell migration. Our findings highlight the pivotal role of HERPUD1 in regulating mitochondrial function and cell migration by controlling intracellular Ca2+ signals mediated by ITPR3. Understanding the interplay between HERPUD1 and mitochondrial Ca2+ regulation provides insights into potential therapeutic targets for cancer treatment and other pathologies involving altered energy metabolism.

Myristate induces mitochondrial fragmentation and cardiomyocyte hypertrophy through mitochondrial E3 ubiquitin ligase MUL1.

Introduction: Cardiovascular diseases, especially metabolic-related disorders, are progressively growing worldwide due to high-fat-containing foods, which promote a deleterious response at the cellular level, termed lipotoxicity, or lipotoxic stress. At the cardiac level, saturated fatty acids have been directly associated with cardiomyocyte lipotoxicity through various pathological mechanisms involving mitochondrial dysfunction, oxidative stress, and ceramide production, among others. However, integrative regulators connecting saturated fatty acid-derived lipotoxic stress to mitochondrial and cardiomyocyte dysfunction remain elusive. Methods: Here, we worked with a cardiomyocyte lipotoxicity model, which uses the saturated fatty acid myristate, which promotes cardiomyocyte hypertrophy and insulin desensitization. Results: Using this model, we detected an increase in the mitochondrial E3 ubiquitin ligase, MUL1, a mitochondrial protein involved in the regulation of growth factor signaling, cell death, and, notably, mitochondrial dynamics. In this context, myristate increased MUL1 levels and induced mitochondrial fragmentation, associated with the decrease of the mitochondrial fusion protein MFN2, and with the increase of the mitochondrial fission protein DRP1, two targets of MUL1. Silencing of MUL1 prevented myristate-induced mitochondrial fragmentation and cardiomyocyte hypertrophy. Discussion: These data establish a novel connection between cardiomyocytes and lipotoxic stress, characterized by hypertrophy and fragmentation of the mitochondrial network, and an increase of the mitochondrial E3 ubiquitin ligase MUL1.

GDF-11 prevents cardiomyocyte hypertrophy by maintaining the sarcoplasmic reticulum-mitochondria communication.

Growth differentiation factor 11 (GDF11) is a novel factor with controversial effects on cardiac hypertrophy both in vivo and in vitro. Although recent evidence has corroborated that GDF11 prevents the development of cardiac hypertrophy, its molecular mechanism remains unclear. In our previous work, we showed that norepinephrine (NE), a physiological pro-hypertrophic agent, increases cytoplasmic Ca2+ levels accompanied by a loss of physical and functional communication between sarcoplasmic reticulum (SR) and mitochondria, with a subsequent reduction in the mitochondrial Ca2+ uptake and mitochondrial metabolism. In order to study the anti-hypertrophic mechanism of GDF11, our aim was to investigate whether GDF11 prevents the loss of SR-mitochondria communication triggered by NE. Our results show that: a) GDF11 prevents hypertrophy in cultured neonatal rat ventricular myocytes treated with NE. b) GDF11 attenuates the NE-induced loss of contact sites between both organelles. c) GDF11 increases oxidative mitochondrial metabolism by stimulating mitochondrial Ca2+ uptake. In conclusion, the GDF11-dependent maintenance of physical and functional communication between SR and mitochondria is critical to allow Ca2+ transfer between both organelles and energy metabolism in the cardiomyocyte and to avoid the activation of Ca2+-dependent pro-hypertrophic signaling pathways.

Author Correction: Caveolin-1 impairs PKA-DRP1-mediated remodelling of ER-mitochondria communication during the early phase of ER stress.

Following publication of the article, the authors wrote to point out the following mistake.

Caveolin-1 impairs PKA-DRP1-mediated remodelling of ER-mitochondria communication during the early phase of ER stress.

Close contacts between endoplasmic reticulum and mitochondria enable reciprocal Ca2+ exchange, a key mechanism in the regulation of mitochondrial bioenergetics. During the early phase of endoplasmic reticulum stress, this inter-organellar communication increases as an adaptive mechanism to ensure cell survival. The signalling pathways governing this response, however, have not been characterized. Here we show that caveolin-1 localizes to the endoplasmic reticulum-mitochondria interface, where it impairs the remodelling of endoplasmic reticulum-mitochondria contacts, quenching Ca2+ transfer and rendering mitochondrial bioenergetics unresponsive to endoplasmic reticulum stress. Protein kinase A, in contrast, promotes endoplasmic reticulum and mitochondria remodelling and communication during endoplasmic reticulum stress to promote organelle dynamics and Ca2+ transfer as well as enhance mitochondrial bioenergetics during the adaptive response. Importantly, caveolin-1 expression reduces protein kinase A signalling, as evidenced by impaired phosphorylation and alterations in organelle distribution of the GTPase dynamin-related protein 1, thereby enhancing cell death in response to endoplasmic reticulum stress. In conclusion, caveolin-1 precludes stress-induced protein kinase A-dependent remodelling of endoplasmic reticulum-mitochondria communication.

Nanoparticles for diagnosis and therapy of atherosclerosis and myocardial infarction: evolution toward prospective theranostic approaches.

Cardiovascular diseases are the leading cause of death worldwide. Despite preventive efforts, early detection of atherosclerosis, the common pathophysiological mechanism underlying cardiovascular diseases remains elusive, and overt coronary artery disease or myocardial infarction is often the first clinical manifestation. Nanoparticles represent a novel strategy for prevention, diagnosis, and treatment of atherosclerosis, and new multifunctional nanoparticles with combined diagnostic and therapeutic capacities hold the promise for theranostic approaches to this disease. This review focuses on the development of nanosystems for therapy and diagnosis of subclinical atherosclerosis, coronary artery disease, and myocardial infarction and the evolution of nanosystems as theranostic tools. We also discuss the use of nanoparticles in noninvasive imaging, targeted drug delivery, photothermal therapies together with the challenges faced by nanosystems during clinical translation.

Herpud1 impacts insulin-dependent glucose uptake in skeletal muscle cells by controlling the Ca2+-calcineurin-Akt axis.

Skeletal muscle plays a central role in insulin-controlled glucose homeostasis. The molecular mechanisms related to insulin resistance in this tissue are incompletely understood. Herpud1 is an endoplasmic reticulum membrane protein that maintains intracellular Ca2+ homeostasis under stress conditions. It has recently been reported that Herpud1-knockout mice display intolerance to a glucose load without showing altered insulin secretion. The functions of Herpud1 in skeletal muscle also remain unknown. Based on these findings, we propose that Herpud1 is necessary for insulin-dependent glucose disposal in skeletal muscle. Here we show that Herpud1 silencing decreased insulin-dependent glucose uptake, GLUT4 translocation to the plasma membrane, and Akt Ser473 phosphorylation in cultured L6 myotubes. A decrease in insulin-induced Akt Ser473 phosphorylation was observed in soleus but not in extensor digitorum longus muscle samples from Herpud1-knockout mice. Herpud1 knockdown increased the IP3R-dependent cytosolic Ca2+ response and the activity of Ca2+-dependent serine/threonine phosphatase calcineurin in L6 cells. Calcineurin decreased insulin-dependent Akt phosphorylation and glucose uptake. Moreover, calcineurin inhibition restored the insulin response in Herpud1-depleted L6 cells. Based on these findings, we conclude that Herpud1 is necessary for adequate insulin-induced glucose uptake due to its role in Ca2+/calcineurin regulation in L6 myotubes.

Mifepristone enhances insulin-stimulated Akt phosphorylation and glucose uptake in skeletal muscle cells.

Mifepristone is the only FDA-approved drug for glycaemia control in patients with Cushing's syndrome and type 2 diabetes. Mifepristone also has beneficial effects in animal models of diabetes and patients with antipsychotic treatment-induced obesity. However, the mechanisms through which Mifepristone produces its beneficial effects are not completely elucidated. PURPOSE: To determine the effects of mifepristone on insulin-stimulated glucose uptake on a model of L6 rat-derived skeletal muscle cells. RESULTS: Mifepristone enhanced insulin-dependent glucose uptake, GLUT4 translocation to the plasma membrane and Akt Ser473 phosphorylation in L6 myotubes. In addition, mifepristone reduced oxygen consumption and ATP levels and increased AMPK Thr172 phosphorylation. The knockdown of AMPK prevented the effects of mifepristone on insulin response. CONCLUSIONS: Mifepristone enhanced insulin-stimulated glucose uptake through a mechanism that involves a decrease in mitochondrial function and AMPK activation in skeletal muscle cells.

Herpud1 negatively regulates pathological cardiac hypertrophy by inducing IP3 receptor degradation.

Cardiac hypertrophy is an adaptive response triggered by pathological stimuli. Regulation of the synthesis and the degradation of the Ca2+ channel inositol 1,4,5-trisphosphate receptor (IP3R) affects progression to cardiac hypertrophy. Herpud1, a component of the endoplasmic reticulum-associated degradation (ERAD) complex, participates in IP3R1 degradation and Ca2+ signaling, but the cardiac function of Herpud1 remains unknown. We hypothesize that Herpud1 acts as a negative regulator of cardiac hypertrophy by regulating IP3R protein levels. Our results show that Herpud1-knockout mice exhibit cardiac hypertrophy and dysfunction and that decreased Herpud1 protein levels lead to elevated levels of hypertrophic markers in cultured rat cardiomyocytes. In addition, IP3R levels were elevated both in Herpud1-knockout mice and Herpud1 siRNA-treated rat cardiomyocytes. The latter treatment also led to elevated cytosolic and nuclear Ca2+ levels. In summary, the absence of Herpud1 generates a pathological hypertrophic phenotype by regulating IP3R protein levels. Herpud1 is a novel negative regulator of pathological cardiac hypertrophy.

Increased C-reactive protein plasma levels are not involved in the onset of post-operative atrial fibrillation.

BACKGROUND: Increased inflammation biomarkers plasma levels, including C-reactive protein (CRP), have been associated with the initiation and perpetuation of atrial fibrillation (AF). However, it is not known whether an increased CRP plasma level, without concomitant inflammation, is sufficient to induce AF. We investigated whether higher CRP plasma levels, determined by the presence of +219G>A CRP gene polymorphism, is associated with an increased risk of post-operative AF. METHODS: One hundred and fifteen adult patients submitted to elective coronary surgery were genotyped for the CRP +219G>A polymorphism. CRP plasma levels were determined by enzyme-linked immunosorbent assay. RESULTS: CRP plasma levels before surgery were higher in GG than in GA+AA patients (3.4±3.1 vs. 1.7±1.8, p<0.015). Thirteen percent of the patients presented post-operative AF. Despite the positive correlation between the polymorphism and CRP levels, there was no significant difference in the occurrence of post-operative AF between the different genotypes. CONCLUSIONS: These results suggest that increased CRP plasma levels that are not associated with an inflammatory process are not sufficient to trigger AF after cardiac surgery.

HERPUD1 protects against oxidative stress-induced apoptosis through downregulation of the inositol 1,4,5-trisphosphate receptor.

Homocysteine-inducible, endoplasmic reticulum (ER) stress-inducible, ubiquitin-like domain member 1 (HERPUD1), an ER resident protein, is upregulated in response to ER stress and Ca(2+) homeostasis deregulation. HERPUD1 exerts cytoprotective effects in various models, but its role during oxidative insult remains unknown. The aim of this study was to investigate whether HERPUD1 contributes to cytoprotection in response to redox stress and participates in mediating stress-dependent signaling pathways. Our data showed that HERPUD1 protein levels increased in HeLa cells treated for 30 min with H2O2 or angiotensin II and in aortic tissue isolated from mice treated with angiotensin II for 3 weeks. Cell death was higher in HERPUD1 knockdown (sh-HERPUD1) HeLa cells treated with H2O2 in comparison with control (sh-Luc) HeLa cells. This effect was abolished by the intracellular Ca(2+) chelating agent BAPTA-AM or the inositol 1,4,5-trisphosphate receptor (ITPR) antagonist xestospongin B, suggesting that the response to H2O2 was dependent on intracellular Ca(2+) stores and the ITPR. Ca(2+) kinetics showed that sh-HERPUD1 HeLa cells exhibited greater and more sustained cytosolic and mitochondrial Ca(2+) increases than sh-Luc HeLa cells. This higher sensitivity of sh-HERPUD1 HeLa cells to H2O2 was prevented with the mitochondrial permeability transition pore inhibitor cyclosporine A. We concluded that the HERPUD1-mediated cytoprotective effect against oxidative stress depends on the ITPR and Ca(2+) transfer from the ER to mitochondria.

Defective insulin signaling and mitochondrial dynamics in diabetic cardiomyopathy.

Diabetic cardiomyopathy (DCM) is a common consequence of longstanding type 2 diabetes mellitus (T2DM) and encompasses structural, morphological, functional, and metabolic abnormalities in the heart. Myocardial energy metabolism depends on mitochondria, which must generate sufficient ATP to meet the high energy demands of the myocardium. Dysfunctional mitochondria are involved in the pathophysiology of diabetic heart disease. A large body of evidence implicates myocardial insulin resistance in the pathogenesis of DCM. Recent studies show that insulin signaling influences myocardial energy metabolism by impacting cardiomyocyte mitochondrial dynamics and function under physiological conditions. However, comprehensive understanding of molecular mechanisms linking insulin signaling and changes in the architecture of the mitochondrial network in diabetic cardiomyopathy is lacking. This review summarizes our current understanding of how defective insulin signaling impacts cardiac function in diabetic cardiomyopathy and discusses the potential role of mitochondrial dynamics.

Mitochondrial fragmentation impairs insulin-dependent glucose uptake by modulating Akt activity through mitochondrial Ca2+ uptake.

Insulin is a major regulator of glucose metabolism, stimulating its mitochondrial oxidation in skeletal muscle cells. Mitochondria are dynamic organelles that can undergo structural remodeling in order to cope with these ever-changing metabolic demands. However, the process by which mitochondrial morphology impacts insulin signaling in the skeletal muscle cells remains uncertain. To address this question, we silenced the mitochondrial fusion proteins Mfn2 and Opa1 and assessed insulin-dependent responses in L6 rat skeletal muscle cells. We found that mitochondrial fragmentation attenuates insulin-stimulated Akt phosphorylation, glucose uptake and cell respiratory rate. Importantly, we found that insulin induces a transient rise in mitochondrial Ca(2+) uptake, which was attenuated by silencing Opa1 or Mfn2. Moreover, treatment with Ruthenium red, an inhibitor of mitochondrial Ca(2+) uptake, impairs Akt signaling without affecting mitochondrial dynamics. All together, these results suggest that control of mitochondrial Ca(2+) uptake by mitochondrial morphology is a key event for insulin-induced glucose uptake.

Regulation of cardiac autophagy by insulin-like growth factor 1.

Insulin-like growth factor-1 (IGF-1) signaling is a key pathway in the control of cell growth and survival. Three critical nodes in the IGF-1 signaling pathway have been described in cardiomyocytes: protein kinase Akt/mammalian target of rapamycin (mTOR), Ras/Raf/extracellular signal-regulated kinase (ERK), and phospholipase C (PLC)/inositol 1,4,5-triphosphate (InsP3 )/Ca(2+) . The Akt/mTOR and Ras/Raf/ERK signaling arms govern survival in the settings of cardiac stress and hypertrophic growth. By contrast, PLC/InsP3 /Ca(2+) functions to regulate metabolic adaptability and gene transcription. Autophagy is a catabolic process involved in protein degradation, organelle turnover, and nonselective breakdown of cytoplasmic components during nutrient starvation or stress. In the heart, autophagy is observed in a variety of human pathologies, where it can be either adaptive or maladaptive, depending on the context. We proposed the hypothesis that IGF-1 protects the heart by rescuing the mitochondrial metabolism and the energetics state, reducing cell death and controls the potentially exacerbate autophagic response to nutritional stress. In light of the importance of IGF-1 and autophagy in the heart, we review here IGF-1 signaling and autophagy regulation in the context of cardiomyocyte nutritional stress.