SIRT6 regulates obesity-induced oxidative stress via ENDOG/SOD2 signaling in the heart.

The sirtuin 6 (SIRT6) participates in regulating glucose and lipid homeostasis. However, the function of SIRT6 in the process of cardiac pathogenesis caused by obesity-associated lipotoxicity remains to be unveiled. This study was designed to elucidate the role of SIRT6 in the pathogenesis of cardiac injury due to nutrition overload-induced obesity and explore the downstream signaling pathways affecting oxidative stress in the heart. In this study, we used Sirt6 cardiac-specific knockout murine models treated with a high-fat diet (HFD) feeding to explore the function and mechanism of SIRT6 in the heart tissue during HFD-induced obesity. We also took advantage of neonatal cardiomyocytes to study the role and downstream molecules of SIRT6 during HFD-induced injury in vitro, in which intracellular oxidative stress and mitochondrial content were assessed. We observed that during HFD-induced obesity, Sirt6 loss-of-function aggravated cardiac injury including left ventricular hypertrophy and lipid accumulation. Our results evidenced that upon increased fatty acid uptake, SIRT6 positively regulated the expression of endonuclease G (ENDOG), which is a mitochondrial-resident molecule that plays an important role in mitochondrial biogenesis and redox homeostasis. Our results also showed that SIRT6 positively regulated superoxide dismutase 2 (SOD2) expression post-transcriptionally via ENDOG. Our study gives a new sight into SIRT6 beneficial role in mitochondrial biogenesis of cardiomyocytes. Our data also show that SIRT6 is required to reduce intracellular oxidative stress in the heart triggered by high-fat diet-induced obesity, involving the control of ENDOG/SOD2.

AKT2 regulates development and metabolic homeostasis via AMPK-depedent pathway in skeletal muscle.

Skeletal muscle is responsible for the majority of glucose disposal in the body. Insulin resistance in the skeletal muscle accounts for 85-90% of the impairment of total glucose disposal in patients with type 2 diabetes (T2D). However, the mechanism remains controversial. The present study aims to investigate whether AKT2 deficiency causes deficits in skeletal muscle development and metabolism, we analyzed the expression of molecules related to skeletal muscle development, glucose uptake and metabolism in mice of 3- and 8-months old. We found that AMP-activated protein kinase (AMPK) phosphorylation and myocyte enhancer factor 2 (MEF2) A (MEF2A) expression were down-regulated in AKT2 knockout (KO) mice, which can be inverted by AMPK activation. We also observed reduced mitochondrial DNA (mtDNA) abundance and reduced expression of genes involved in mitochondrial biogenesis in the skeletal muscle of AKT2 KO mice, which was prevented by AMPK activation. Moreover, AKT2 KO mice exhibited impaired AMPK signaling in response to insulin stimulation compared with WT mice. Our study establishes a new and important function of AKT2 in regulating skeletal muscle development and glucose metabolism via AMPK-dependent signaling.

Interleukin-6 deficiency facilitates myocardial dysfunction during high fat diet-induced obesity by promoting lipotoxicity and inflammation.

OBJECTIVE: Obesity is associated with metabolic disorder and chronic inflammation that plays a crucial role in cardiovascular diseases. IL-6 is involved in regulating obesity-related lipid metabolism and inflammation. In this study, we sought to determine the role of IL-6 in high-fat diet (HFD)-induced cardiomyopathy and explore the signaling pathway. METHODS: Female, 5-week-old IL-6 knockout (KO) and littermate mice were fed a normal diet (ND, 10% fat) or HFD (45% fat) for 14 weeks. At the end of treatment, cardiac function was assessed by echocardiography. Adipose tissues and plasma were collected for further measurement. Immunohistology of CD68 was performed to detect inflammation in the heart. Masson's trichrome staining and Oil Red O staining was applied to evaluated cardiac fibrosis and lipid accumulation. Real-time PCR and Western immunoblotting analyses on heart tissue were used to explore the underlying mechanism. RESULTS: IL-6 KO mice displayed increased insulin resistance compared to WT mice at baseline. When fed HFD, IL-6 KO mice showed decreased gains in body weight and fat mass, increased insulin resistance relative to IL-6 KO mice feed ND. Furthermore, IL-6 KO mice developed cardiac dysfunction during HFD-induced obesity. Histological analysis suggested increased lipid accumulation, fibrosis and inflammation without affecting cardiac morphology during HFD treatment in the heart of IL-6 KO mice. Finally, IL-6 deficiency increased the phosphorylation of AMPK and ACC in the heart during HFD-induced obesity. CONCLUSION: Our results suggest that IL-6 contributes to limit lipid metabolic disorder, cardiac hypertrophy, fibrosis, inflammation and myocardium lipotoxicity during HFD-induced obesity.

Endonuclease G is a novel determinant of cardiac hypertrophy and mitochondrial function.

Left ventricular mass (LVM) is a highly heritable trait and an independent risk factor for all-cause mortality. So far, genome-wide association studies have not identified the genetic factors that underlie LVM variation, and the regulatory mechanisms for blood-pressure-independent cardiac hypertrophy remain poorly understood. Unbiased systems genetics approaches in the rat now provide a powerful complementary tool to genome-wide association studies, and we applied integrative genomics to dissect a highly replicated, blood-pressure-independent LVM locus on rat chromosome 3p. Here we identified endonuclease G (Endog), which previously was implicated in apoptosis but not hypertrophy, as the gene at the locus, and we found a loss-of-function mutation in Endog that is associated with increased LVM and impaired cardiac function. Inhibition of Endog in cultured cardiomyocytes resulted in an increase in cell size and hypertrophic biomarkers in the absence of pro-hypertrophic stimulation. Genome-wide network analysis unexpectedly implicated ENDOG in fundamental mitochondrial processes that are unrelated to apoptosis. We showed direct regulation of ENDOG by ERR-α and PGC1α (which are master regulators of mitochondrial and cardiac function), interaction of ENDOG with the mitochondrial genome and ENDOG-mediated regulation of mitochondrial mass. At baseline, the Endog-deleted mouse heart had depleted mitochondria, mitochondrial dysfunction and elevated levels of reactive oxygen species, which were associated with enlarged and steatotic cardiomyocytes. Our study has further established the link between mitochondrial dysfunction, reactive oxygen species and heart disease and has uncovered a role for Endog in maladaptive cardiac hypertrophy.

AKT2 Blocks Nucleus Translocation of Apoptosis-Inducing Factor (AIF) and Endonuclease G (EndoG) While Promoting Caspase Activation during Cardiac Ischemia.

The AKT (protein kinase B, PKB) family has been shown to participate in diverse cellular processes, including apoptosis. Previous studies demonstrated that protein kinase B2 (AKT2-/-) mice heart was sensitized to apoptosis in response to ischemic injury. However, little is known about the mechanism and apoptotic signaling pathway. Here, we show that AKT2 inhibition does not affect the development of cardiomyocytes but increases cell death during cardiomyocyte ischemia. Caspase-dependent apoptosis of both the extrinsic and intrinsic pathway was inactivated in cardiomyocytes with AKT2 inhibition during ischemia, while significant mitochondrial disruption was observed as well as intracytosolic translocation of cytochrome C (Cyto C) together with apoptosis-inducing factor (AIF) and endonuclease G (EndoG), both of which are proven to conduct DNA degradation in a range of cell death stimuli. Therefore, mitochondria-dependent cell death was investigated and the results suggested that AIF and EndoG nucleus translocation causes cardiomyocyte DNA degradation during ischemia when AKT2 is blocked. These data are the first to show a previous unrecognized function and mechanism of AKT2 in regulating cardiomyocyte survival during ischemia by inducing a unique mitochondrial-dependent DNA degradation pathway when it is inhibited.

Studies on the role of apoptosis after transient myocardial ischemia: genetic deletion of the executioner caspases-3 and -7 does not limit infarct size and ventricular remodeling.

Although it is widely accepted that apoptosis may contribute to cell death in myocardial infarction, experimental evidence suggests that adult cardiomyocytes repress the expression of the caspase-dependent apoptotic pathway. The aim of this study was to analyze the contribution of caspase-mediated apoptosis to myocardial ischemia-reperfusion injury. Cardiac-specific caspase-3 deficient/full caspase-7-deficient mice (Casp3/7DKO) and wild type control mice (WT) were subjected to in situ ischemia by left anterior coronary artery ligation for 45 min followed by 24 h or 28 days of reperfusion. Heart function was assessed using M-mode echocardiography. Deletion of caspases did not modify neither infarct size determined by triphenyltetrazolium staining after 24 h of reperfusion (40.0 ± 5.1 % in WT vs. 36.2 ± 3.6 % in Casp3/7DKO), nor the scar area measured by pricosirius red staining after 28 days of reperfusion (41.1 ± 5.4 % in WT vs. 44.6 ± 8.7 % in Casp3/7DKO). Morphometric and echocardiographic studies performed 28 days after the ischemic insult revealed left ventricular dilation and severe cardiac dysfunction without statistically significant differences between WT and Casp3/7DKO groups. These data demonstrate that the executioner caspases-3 and -7 do not significantly contribute to cardiomyocyte death induced by transient coronary occlusion and provide the first evidence obtained in an in vivo model that argues against a relevant role of apoptosis through the canonical caspase pathway in this context.

A pathway involving HDAC5, cFLIP and caspases regulates expression of the splicing regulator polypyrimidine tract binding protein in the heart.

Polypyrimidine tract binding protein (PTB) regulates pre-mRNA splicing, having special relevance for determining gene expression in the differentiating muscle. We have previously shown that PTB protein abundance is progressively reduced during heart development without reduction of its own transcript. Simultaneous reduction of histone deacetylase (HDAC) expression prompted us to investigate the potential link between these events. HDAC5-deficient mice have reduced cardiac PTB protein abundance, and HDAC inhibition in myocytes causes a reduction in endogenous expression of cellular FLICE-like inhibitory protein (cFLIP) and caspase-dependent cleavage of PTB. In agreement with this, cardiac PTB expression is abnormally high in mice with cardiac-specific executioner caspase deficiency, and cFLIP overexpression prevents PTB cleavage in vitro. Caspase-dependent cleavage triggers further fragmentation of PTB, and these fragments accumulate in the presence of proteasome inhibitors. Experimental modification of the above processes in vivo and in vitro results in coherent changes in the alternative splicing of genes encoding tropomyosin-1 (TPM1), tropomyosin-2 (TPM2) and myocyte enhancer factor-2 (MEF2). Thus, we report a pathway connecting HDAC, cFLIP and caspases regulating the progressive disappearance of PTB, which enables the expression of the adult variants of proteins involved in the regulation of contraction and transcription during cardiac muscle development.

FAIM-L is an IAP-binding protein that inhibits XIAP ubiquitinylation and protects from Fas-induced apoptosis.

The neuronal long isoform of Fas Apoptotic Inhibitory Molecule (FAIM-L) protects from death receptor (DR)-induced apoptosis, yet its mechanism of protection remains unknown. Here, we show that FAIM-L protects rat neuronal Type II cells from Fas-induced apoptosis. XIAP has previously emerged as a molecular discriminator that is upregulated in Type II and downregulated in Type I apoptotic signaling. We demonstrate that FAIM-L requires sustained endogenous levels of XIAP to protect Type II cells as well as murine cortical neurons from Fas-induced apoptosis. FAIM-L interacts with the BIR2 domain of XIAP through an IAP-binding motif, the mutation of which impairs the antiapoptotic function of FAIM-L. Finally, we report that FAIM-L inhibits XIAP auto-ubiquitinylation and maintains its stability, thus conferring protection from apoptosis. Our results bring new understanding of the regulation of endogenous XIAP by a DR antagonist, pointing out at FAIM-L as a promising therapeutic tool for protection from apoptosis in pathological situations where XIAP levels are decreased.

Translation of Myocyte Enhancer Factor-2 is induced by hypertrophic stimuli in cardiomyocytes through a Calcineurin-dependent pathway.

The Myocyte Enhancer Factor-2 (MEF2) family of transcription factors regulates gene expression during cardiomyocyte differentiation and adaptation of the myocardium to stress. MEF2 activity is enhanced by increasing its transcription and by MAPK-dependent phosphorylation, and is reduced by binding to class-II Histone Deacetylases and by miR-1-mediated degradation of its transcript. Here we show that MEF2 protein abundance is regulated at the translational level, determining myocyte size, during hypertrophy. In order to reduce MEF2 protein expression, its silencing through RNA interference required serum deprivation and, even in this condition, MEF2 protein abundance recovered to basal levels in presence of phenylephrine. Hypertrophic agonist stimulation of neonatal ventricular cardiomyocytes increased Mef2 expression by enhancing its translation, without changing its transcription or blocking degradation of the protein. MEF2 abundance was increased by Calcineurin overexpression in vivo and was reduced by Calcineurin inhibition in vitro, without affecting Mef2 mRNA levels. Calcineurin activity influenced expression of Polypyrimidine Tract Protein (PTB), contributing to MEF2 translation. Thus, our results show a previously unrecognized but relevant level of MEF2 activity regulation through the control of its translation that involves Calcineurin and PTB.

Cost-effectiveness of upper extremity dry needling in the rehabilitation of patients with stroke.

INTRODUCTION: Dry needling (DN) has been shown to be effective for the treatment of upper extremity hypertonia in patients with stroke. PURPOSE: To evaluate the cost-effectiveness of DN in patients with stroke. METHODS: A cost-effectiveness analysis was performed in a research study conducted at a Spanish public hospital where patients were classified into two groups with or without DN. Hypertonia was measured using the Modified Modified Ashworth Scale (MMAS), and quality of life (QOL) was assessed using the EuroQoL 5-dimension questionnaire. Data regarding the effects and costs of physiotherapy were presented by calculating the mean and 95% confidence interval. The health outcomes were evaluated considering the rate of responders to the treatment based on the MMAS. Spanish preference weights were used to estimate quality-adjusted life years (QALYs). The incremental cost-effectiveness ratio (ICER) and incremental cost-utility ratio (ICUR) were calculated to determine the economic value of DN. RESULTS: Eighty patients with stroke in the subacute stage of recovery were selected to participate in this study. Based on the rate of responders, the ICER of the DN group was very low. Despite the sensitivity analysis performed, the results of the ICUR were not encouraging. DISCUSSION: Cost-effectiveness with responder rate results were favourable for the DN group and were confirmed by the sensitivity analysis according to levels of care. In addition, our findings revealed that 4 weeks of treatment could be more cost-effective than 8 weeks. DN treatment of the upper extremity appears to be cost-effective based on the rate of responders measured using the MMAS scale.

Cardiac fibroblasts display endurance to ischemia, high ROS control and elevated respiration regulated by the JAK2/STAT pathway.

Cardiovascular diseases are the leading cause of death globally and more than four out of five cases are due to ischemic events. Cardiac fibroblasts (CF) contribute to normal heart development and function, and produce the post-ischemic scar. Here, we characterize the biochemical and functional aspects related to CF endurance to ischemia-like conditions. Expression data mining showed that cultured human CF (HCF) express more BCL2 than pulmonary and dermal fibroblasts. In addition, gene set enrichment analysis showed overrepresentation of genes involved in the response to hypoxia and oxidative stress, respiration and Janus kinase (JAK)/Signal transducer and Activator of Transcription (STAT) signaling pathways in HCF. BCL2 sustained survival and proliferation of cultured rat CF, which also had higher respiration capacity and reactive oxygen species (ROS) production than pulmonary and dermal fibroblasts. This was associated with higher expression of the electron transport chain (ETC) and antioxidant enzymes. CF had high phosphorylation of JAK2 and its effectors STAT3 and STAT5, and their inhibition reduced viability and respiration, impaired ROS control and reduced the expression of BCL2, ETC complexes and antioxidant enzymes. Together, our results identify molecular and biochemical mechanisms conferring survival advantage to experimental ischemia in CF and show their control by the JAK2/STAT signaling pathway. The presented data point to potential targets for the regulation of cardiac fibrosis and also open the possibility of a general mechanism by which somatic cells required to acutely respond to ischemia are constitutively adapted to survive it.

Cost-Effectiveness of Upper Extremity Dry Needling in Chronic Stroke.

INTRODUCTION: Dry needling is a non-pharmacological approach that has proven to be effective in different neurological conditions. OBJECTIVE: The aim of this study was to evaluate the cost-effectiveness of a single dry needling session in patients with chronic stroke. METHODS: A cost-effectiveness analysis was performed based on a randomized controlled clinical trial. The results obtained from the values of the EuroQol-5D questionnaire and the Modified Modified Ashworth Scale were processed in order to obtain the percentage of treatment responders and the quality-adjusted life years (QALYs) for each alternative. The cost analysis was that of the hospital, clinic, or health center, including the equipment and physiotherapist. The cost per respondent and the incremental cost-effectiveness ratio of each alternative were assessed. RESULTS: Twenty-three patients with stroke were selected. The cost of DN treatment was EUR 14.96, and the data analysis showed a favorable cost-effectiveness ratio of both EUR/QALY and EUR/responder for IG, although the sensitivity analysis using limit values did not confirm the dominance (higher effectiveness with less cost) of the dry needling over the sham dry needling. CONCLUSIONS: Dry needling is an affordable alternative with good results in the cost-effectiveness analysis-both immediately, and after two weeks of treatment-compared to sham dry needling in persons with chronic stroke.

A comparative study of treatment interventions for patellar tendinopathy: a secondary cost-effectiveness analysis.

OBJECTIVE: To compare the cost-effectiveness of three patellar tendinopathy treatments. DESIGN: Secondary (cost-effectiveness) analysis of a blinded, randomised controlled trial, with follow-up at 10 and 22 weeks. SETTINGS: Recruitment was performed in sport clubs. The diagnosis and the intervention were carried out at San Jorge University. PARTICIPANTS: The participants were adults between 18 and 45 years (n = 48) with patellar tendinopathy. INTERVENTIONS: Participants received percutaneous needle electrolysis, dry needling or sham needling, all of which were combined with eccentric exercise. MAIN OUTCOME MEASURES: Costs, quality-adjusted life years and incremental cost-effectiveness ratio were calculated for each group. RESULTS: The total cost per session was similar in the three groups: €9.46 for the percutaneous needle electrolysis group; €9.44 for the dry needling group; and €8.96 for the sham group. The percutaneous needle electrolysis group presented better cost-effectiveness in terms of quality-adjusted life years and 96% and 93% probability of being cost-effective compared to the sham and dry needling groups, respectively. CONCLUSION: Our study shows that percutaneous needle electrolysis has a greater probability of being cost-effective than sham or dry needling treatment.

Ubiquitination of TrkA by Nedd4-2 regulates receptor lysosomal targeting and mediates receptor signaling.

The nerve growth factor receptor TrkA (tropomyosin-related kinase receptor) participates in the survival and differentiation of several neuronal populations. The C-terminal tail of TrkA contains a PPXY motif, the binding site of the E3 ubiquitin-ligase Nedd4-2 (neural precursor cell expressed, developmentally down-regulated 4-2). In order to analyze the role of Nedd4-2 ubiquitination on TrkA function, we generated three TrkA mutants, by introducing point mutations on conserved hydrophobic amino acids - Leu784 and Val790 switched to Ala. TrkA mutants co-localized and co-immunoprecipitated more efficiently with Nedd4-2 and consequently a strong increase in the basal multimonoubiquitination of the mutant receptors was observed. In addition, we found a decrease in TrkA abundance because of the preferential sorting of mutant receptors towards the late endosome/lysosome pathway instead of recycling back to the plasma membrane. Despite the reduction in the amount of membrane receptor caused by the C-terminal changes, TrkA mutants were able to activate signaling cascades and were even more efficient in promoting neurite outgrowth than the wild-type receptor. Our results demonstrate that the C-terminal tail hydrophobicity of TrkA regulates Nedd4-2 binding and activity and therefore controls receptor turnover. In addition, TrkA multimonoubiquitination does not interfere with the activation of signaling cascades, but rather potentiates receptor signaling leading to differentiation.

ENDOG Impacts on Tumor Cell Proliferation and Tumor Prognosis in the Context of PI3K/PTEN Pathway Status.

EndoG influences mitochondrial DNA replication and is involved in somatic cell proliferation. Here, we investigated the effect of ENDOG/Endog expression on proliferation in different tumor models. Noteworthy, ENDOG deficiency reduced proliferation of endometrial tumor cells expressing low PTEN/high p-AKT levels, and Endog deletion blunted the growth of PTEN-deficient 3D endometrial cultures. Furthermore, ENDOG silencing reduced proliferation of follicular thyroid carcinoma and glioblastoma cell lines with high p-AKT expression. High ENDOG expression was associated with a short time to treatment in a cohort of patients with chronic lymphocytic leukemia (CLL), a B-cell lymphoid neoplasm with activation of PI3K/AKT. This clinical impact was observed in the less aggressive CLL subtype with mutated IGHV in which high ENDOG and low PTEN levels were associated with worse outcome. In summary, our results show that reducing ENDOG expression hinders growth of some tumors characterized by low PTEN activity and high p-AKT expression and that ENDOG has prognostic value for some cancer types.

A trans locus causes a ribosomopathy in hypertrophic hearts that affects mRNA translation in a protein length-dependent fashion.

BACKGROUND: Little is known about the impact of trans-acting genetic variation on the rates with which proteins are synthesized by ribosomes. Here, we investigate the influence of such distant genetic loci on the efficiency of mRNA translation and define their contribution to the development of complex disease phenotypes within a panel of rat recombinant inbred lines. RESULTS: We identify several tissue-specific master regulatory hotspots that each control the translation rates of multiple proteins. One of these loci is restricted to hypertrophic hearts, where it drives a translatome-wide and protein length-dependent change in translational efficiency, altering the stoichiometric translation rates of sarcomere proteins. Mechanistic dissection of this locus across multiple congenic lines points to a translation machinery defect, characterized by marked differences in polysome profiles and misregulation of the small nucleolar RNA SNORA48. Strikingly, from yeast to humans, we observe reproducible protein length-dependent shifts in translational efficiency as a conserved hallmark of translation machinery mutants, including those that cause ribosomopathies. Depending on the factor mutated, a pre-existing negative correlation between protein length and translation rates could either be enhanced or reduced, which we propose to result from mRNA-specific imbalances in canonical translation initiation and reinitiation rates. CONCLUSIONS: We show that distant genetic control of mRNA translation is abundant in mammalian tissues, exemplified by a single genomic locus that triggers a translation-driven molecular mechanism. Our work illustrates the complexity through which genetic variation can drive phenotypic variability between individuals and thereby contribute to complex disease.

Involvement of the mitochondrial nuclease EndoG in the regulation of cell proliferation through the control of reactive oxygen species.

The apoptotic nuclease EndoG is involved in mitochondrial DNA replication. Previous results suggested that, in addition to regulate cardiomyocyte hypertrophy, EndoG could be involved in cell proliferation. Here, by using in vivo and cell culture models, we investigated the role of EndoG in cell proliferation. Genetic deletion of Endog both in vivo and in cultured cells or Endog silencing in vitro induced a defect in rodent and human cell proliferation with a tendency of cells to accumulate in the G1 phase of cell cycle and increased reactive oxygen species (ROS) production. The defect in cell proliferation occurred with a decrease in the activity of the AKT/PKB-GSK-3ß-Cyclin D axis and was reversed by addition of ROS scavengers. EndoG deficiency did not affect the expression of ROS detoxifying enzymes, nor the expression of the electron transport chain complexes and oxygen consumption rate. Addition of the micropeptide Humanin to EndoG-deficient cells restored AKT phosphorylation and proliferation without lowering ROS levels. Thus, our results show that EndoG is important for cell proliferation through the control of ROS and that Humanin can restore cell division in EndoG-deficient cells and counteracts the effects of ROS on AKT phosphorylation.

The death receptor antagonist FAIM promotes neurite outgrowth by a mechanism that depends on ERK and NF-kapp B signaling.

Fas apoptosis inhibitory molecule (FAIM) is a protein identified as an antagonist of Fas-induced cell death. We show that FAIM overexpression fails to rescue neurons from trophic factor deprivation, but exerts a marked neurite growth-promoting action in different neuronal systems. Whereas FAIM overexpression greatly enhanced neurite outgrowth from PC12 cells and sympathetic neurons grown with nerve growth factor (NGF), reduction of endogenous FAIM levels by RNAi decreased neurite outgrowth in these cells. FAIM overexpression promoted NF-kappa B activation, and blocking this activation by using a super-repressor I kappa B alpha or by carrying out experiments using cortical neurons from mice that lack the p65 NF-kappa B subunit prevented FAIM-induced neurite outgrowth. The effect of FAIM on neurite outgrowth was also blocked by inhibition of the Ras-ERK pathway. Finally, we show that FAIM interacts with both Trk and p75 neurotrophin receptor NGF receptors in a ligand-dependent manner. These results reveal a new function of FAIM in promoting neurite outgrowth by a mechanism involving activation of the Ras-ERK pathway and NF-kappa B.

Nrf2 deficiency aggravates Angiotensin II-induced cardiac injury by increasing hypertrophy and enhancing IL-6/STAT3-dependent inflammation.

BACKGROUND: NF-E2-related factor 2 (Nrf2) is a transcription factor playing cytoprotective effects in various pathological processes including oxidative stress and cardiac hypertrophy. Despite being a potential therapeutic target to treat several cardiomyopathies, the signaling underlying Nrf2-dependent cardioprotective action remains largely uncharacterized. AIM: This study aimed to explore the signaling mediating the role of Nrf2 in the development of hypertensive cardiac pathogenesis by analyzing the response to Angiotensin II (Ang II) in the presence or absence of Nrf2 expression, both in vivo and in vitro. RESULTS: Our results indicated that Nrf2 deficiency exacerbated cardiac damage triggered by Ang II infusion. Mechanistically, our study shows that Ang II-triggered hypertrophy and inflammation is exacerbated in the absence of Nrf2 expression and points to the involvement of the IL-6/STAT3 signaling pathway in this event. Indeed, our results show that IL-6 abundance triggered by Ang II is increased in the absence of Nrf2 and demonstrate the requirement of IL-6 in STAT3 activation and cardiac inflammation induced by Ang II. CONCLUSION: Our results show that Nrf2 is important for the protection of the heart against Ang II-induced cardiac hypertrophy and inflammation by mechanisms involving the regulation of IL-6/STAT3-dependent signaling.

Tyr-701 is a new regulatory site for neurotrophin receptor TrkA trafficking and function.

Tropomyosin-related kinase A (TrkA) receptor mediates the effects exerted by nerve growth factor on several subpopulations of neuronal cells. Ligand binding to TrkA induces receptor autophosphorylation on several tyrosine residues and the activation of signaling cascades. In this study, we describe a new site relevant for TrkA regulation, the tyrosine 701 (Y701), which is important for receptor trafficking and activation. Y701 replacement by aspartate or phenylalanine reduces receptor internalization rate and decreases the colocalization and association of TrkA with clathrin heavy chain, demonstrating that Y701 constitutes a YxxPhi (YRKF701-704) trafficking motif relevant for the regulation of receptor endocytosis. In accordance with this hypothesis, the colocalization of Y701 mutant receptors with a lysosomal marker is also reduced giving support to the involvement of the YRKF701-704 motif in the lysosomal targeting of TrkA receptors. Contrary to what was expected, substitution of Y701 for an Asp in order to mimic phosphorylation, impairs TrkA ability to mediate nerve growth factor-induced differentiation, although the mutant receptor retains its in vitro kinase activity. This is the first evidence that a Tyr residue can simultaneously regulate TrkA receptor trafficking and activity.