the melas mutation m 3243a g promotes reactivation of fetal cardiac genes and an epithelial mesenchymal transition like program via dysregulation of mirnas

Abstract The pathomechanisms underlying oxidative phosphorylation (OXPHOS) diseases are not well-understood, but they involve maladaptive changes in mitochondria-nucleus communication. Many studies on the mitochondria-nucleus cross-talk triggered by mitochondrial dysfunction have focused on the role played by regulatory proteins, while the participation of miRNAs remains poorly explored. MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) is mostly caused by mutation m.3243A>G in mitochondrial tRNALeu(UUR) gene. Adverse cardiac and neurological events are the commonest causes of early death in m.3243A>G patients. Notably, the incidence of major clinical features associated with this mutation has been correlated to the level of m.3243A>G mutant mitochondrial DNA (heteroplasmy) in skeletal muscle. In this work, we used a transmitochondrial cybrid model of MELAS (100% m.3243A>G mutant mitochondrial DNA) to investigate the participation of miRNAs in the mitochondria-nucleus cross-talk associated with OXPHOS dysfunction. High-throughput analysis of small-RNA-Seq data indicated that expression of 246 miRNAs was significantly altered in MELAS cybrids. Validation of selected miRNAs, including miR-4775 and miR-218-5p, in patient muscle samples revealed miRNAs whose expression declined with high levels of mutant heteroplasmy. We show that miR-218-5p and miR-4775 are direct regulators of fetal cardiac genes such as NODAL, RHOA, ISL1 and RXRB, which are up-regulated in MELAS cybrids and in patient muscle samples with heteroplasmy above 60%. Our data clearly indicate that TGF-β superfamily signaling and an epithelial-mesenchymal transition-like program are activated in MELAS cybrids, and suggest that down-regulation of miRNAs regulating fetal cardiac genes is a risk marker of heart failure in patients with OXPHOS diseases

The African striped mouse Lemniscomys barbarus as a model for aggression. Brain areas activated by agonistic encounters

During agonistic behavior several brain areas became differentially activated depending on the role the subject is taking. Several areas are mostly activated during the offender role and several others are activated if the subject plays a defensive role. The main goal of this work is to study in detail the anatomic areas involved in agonistic behavior using a novel animal model, the striped mouse Lemniscomys barbarus, a North African diurnal rodent well known by its natural high aggressiveness toward conspecifics. After social encounters, neural activation in brain areas related to agonistic behavior was measured by c-fos immunostaining. The encounters were recorded and behaviors related to the encounter were analyzed. We differentiated between the aggressive behavior (offender) and escape behavior (defender or defeated). Our results showed that conspecific confrontation induced general c-fos activation in both offender and defender in all measured areas in comparison with non-confronted control. Differences in neural activity between offender and defender were observed specifically in the lateral, cortical and medial amygdala, suprachiasmatic nucleus and the nucleus incertus, suggesting a potential role of these areas in displaying different kinds of behavior during conspecific confrontation. We found that, while in the lateral, medial and cortical amygdala defenders express significantly more c-fos than offenders, in the nucleus incertus of the brainstem the differential activation is just the opposite, Additionally, defenders display significantly more freezing than offenders. This work provides data showing that Lemniscomys barbarus is a widely useful model to study the anatomic background supporting agonistic behavior.This research was supported by the following grants: 51 0935-Tempus-1-2010, TEMPUS IV EU (RB), Generalitat Valenciana AICO/2015/042; Universitat Jaume I P1·1A2014-06 (AMS)

The MELAS mutation m.3243A>G alters the expression of mitochondrial tRNA fragments

Recent evidences highlight the importance of mitochondria-nucleus communication for the clinical phenotype of oxidative phosphorylation (OXPHOS) diseases. However, the participation of small non-coding RNAs (sncRNAs) in this communication has been poorly explored. We asked whether OXPHOS dysfunction alters the production of a new class of sncRNAs, mitochondrial tRNA fragments (mt tRFs), and, if so, whether mt tRFs play a physiological role and their accumulation is controlled by the action of mt tRNA modification enzymes. To address these questions, we used a cybrid model of MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes), an OXPHOS disease mostly caused by mutation m.3243A>G in the mitochondrial tRNALeu(UUR) gene. High-throughput analysis of small-RNA-Seq data indicated that m.3243A>G significantly changed the expression pattern of mt tRFs. A functional analysis of potential mt tRFs targets (performed under the assumption that these tRFs act as miRNAs) indicated an association with processes that involve the most common affected tissues in MELAS. We present evidences that mt tRFs may be biologically relevant, as one of them (mt i-tRF GluUUC), likely produced by the action of the nuclease Dicer and whose levels are Ago2 dependent, down-regulates the expression of mitochondrial pyruvate carrier 1 (MPC1), promoting the build-up of extracellular lactate. Therefore, our study underpins the idea that retrograde signaling from mitochondria is also mediated by mt tRFs. Finally, we show that accumulation of mt i-tRF GluUUC depends on the modification status of mt tRNAs, which is regulated by the action of stress-responsive miRNAs on mt tRNA modification enzymes.This work has been supported by grant BFU2014-58673-P from the Spanish Ministry of Economy and Competitiveness to M.-E.A

Defects in the mitochondrial-tRNA modification enzymes MTO1 and GTPBP3 promote different metabolic reprogramming through a HIF-PPARγ-UCP2-AMPK axis

18 páginas 8 figuras. Supplementary information accompanies this paper at https://doi.org/10.1038/s41598-018-19587-5.Human proteins MTO1 and GTPBP3 are thought to jointly catalyze the modification of the wobble uridine in mitochondrial tRNAs. Defects in each protein cause infantile hypertrophic cardiomyopathy with lactic acidosis. However, the underlying mechanisms are mostly unknown. Using fibroblasts from an MTO1 patient and MTO1 silenced cells, we found that the MTO1 deficiency is associated with a metabolic reprogramming mediated by inactivation of AMPK, down regulation of the uncoupling protein 2 (UCP2) and transcription factor PPARγ, and activation of the hypoxia inducible factor 1 (HIF-1). As a result, glycolysis and oxidative phosphorylation are uncoupled, while fatty acid metabolism is altered, leading to accumulation of lipid droplets in MTO1 fibroblasts. Unexpectedly, this response is different from that triggered by the GTPBP3 defect, as GTPBP3-depleted cells exhibit AMPK activation, increased levels of UCP2 and PPARγ, and inactivation of HIF-1. In addition, fatty acid oxidation and respiration are stimulated in these cells. Therefore, the HIF-PPARγ-UCP2-AMPK axis is operating differently in MTO1- and GTPBP3-defective cells, which strongly suggests that one of these proteins has an additional role, besides mitochondrial-tRNA modification. This work provides new and useful information on the molecular basis of the MTO1 and GTPBP3 defects and on putative targets for therapeutic intervention.Tis work has been supported by grants from the Spanish Ministry of Economy and Competitiveness (grants BFU2010-19737 and BFU2014-58673-P to M.-E.A.; and SAF2016-75004-R to M.C.), Instituto de Salud Carlos III (FIS-ISCIII PI 14/0431 to M.A.M) and Generalitat Valenciana (ACOMP/2012/065 and PROMETEO/2012/061 to M.-E.A. Contribution to COST Action CA15203 MITOEAGLE. R.B. is a recipient of a fellowship from the Generalitat Valenciana (grant GRISOLIA/2014/038). Te authors thank Dr. E. Knecht and Dr. C. Aguado (CIPF, Valencia, Spain) for their valuable advice and for providing facilities in our research work, and Dr. M. Morán (Hospital 12 de Octubre, Madrid, Spain) for growth and maintenance of patient fbroblasts.Peer reviewe