Insights into the post-transcriptional regulation of the mitochondrial electron transport chain

Divergent effects of the antiretroviral drugs, dolutegravir, tenofovir alafenamide, and tenofovir disoproxil fumarate, on human adipocyte function

Combined antiretroviral therapy (cART) has been associated with increased body weight accompanied by metabolic alterations in people living with human immunodeficiency virus (PLWH). To gain insight into the combined effects of cART components on adipocyte dysfunction, we assessed whether and how treatment of human adipocytes with dolutegravir (DTG) and the nucleotide-analog reverse-transcriptase inhibitors (NRTIs), tenofovir alafenamide (TAF) and tenofovir disoproxil fumarate (TDF), alone and in combination, altered biological processes related to adipose tissue dysfunction. DTG, TAF, and TDF were applied to human Simpson-Golabi-Behmel syndrome (SGBS) adipose cells during differentiation (day 10) and ensuing differentiation (day 14). Expression of selected marker genes was determined by qPCR, the release of adipokines and inflammatory cytokines to the culture media was assessed, and cell respiration was measured. Adipogenesis was not altered by the combined treatment of human adipocytes. However, DTG at the highest dose repressed adipogenesis marker genes expression, and TAF and TDF appeared to mitigate this effect. DTG repressed the expression of adiponectin and the release of adiponectin and leptin in differentiating adipocytes, and these effects were mantained in combination with TAF and TDF. DTG plus TAF or TDF on human adipocytes enhanced inflammation and stress and increased the release of proinflammatory cytokines to the culture media. Together, our results show that combined therapy with these drugs can alter inflammation, cellular stress, and fibrosis in human adipocytes. These findings may improve our understanding and management of the effects of cART on body adiposity and metabolic dysregulation in PLWH.

Anti-Müllerian hormone (AMH) treatment enhances oocyte quality, embryonic development and live birth rate

Anti-Müllerian hormone (AMH) produced by the granulosa cells of growing follicles is critical for folliculogenesis and is clinically used as a diagnostic and/or prognostic marker of female fertility. Previous studies report that AMH-pretreatment in mice creates a pool of quiescent follicles that are released following superovulation, resulting in increased number of ovulated oocytes. However, the quality and developmental competency of oocytes derived from AMH-induced accumulated follicles as well as the effect of AMH treatment on live birth are not known. This study reports that AMH priming positively affects oocyte maturation and early embryonic development culminating in higher number of live births. Our results show that AMH treatment results in good quality oocytes with higher developmental competence that enhances embryonic development resulting in blastocysts with greater gene expression. Transcriptome analysis of oocytes from AMH-primed compared to control mice reveal that AMH upregulates a large number of genes and pathways associated with oocyte quality and embryonic development. Mitochondrial function is the most affected pathway by AMH priming, that is supported by higher number of active mitochondria, mitochondrial DNA content and ATP levels in oocytes and embryos isolated from AMH-primed compared to control animals. These studies for the first time provide an insight into the overall impact of AMH on female fertility and highlight critical knowledge necessary to develop AMH as a therapeutic option to improve female fertility.

Ketogenesis controls mitochondrial gene expression and rescues mitochondrial bioenergetics after cervical spinal cord injury in rats

A better understanding of the secondary injury mechanisms that occur after traumatic spinal cord injury (SCI) is essential for the development of novel neuroprotective strategies linked to the restoration of metabolic deficits. We and others have shown that Ketogenic diet (KD), a high fat, moderate in proteins and low in carbohydrates is neuroprotective and improves behavioural outcomes in rats with acute SCI. Ketones are alternative fuels for mitochondrial ATP generation, and can modulate signaling pathways via targeting specific receptors. Here, we demonstrate that ad libitum administration of KD for 7 days after SCI rescued mitochondrial respiratory capacity, increased parameters of mitochondrial biogenesis, affected the regulation of mitochondrial-related genes, and activated the NRF2-dependent antioxidant pathway. This study demonstrates that KD improves post-SCI metabolism by rescuing mitochondrial function and supports the potential of KD for treatment of acute SCI in humans.

Evaluation of mitochondria in mouse oocytes following cisplatin exposure

BACKGROUND

Cisplatin is a platinum-based chemotherapeutic that damages genomic DNA leading to cell death. It also damages mitochondrial DNA and induces high levels of mitochondrial reactive oxygen species (mtROS), further sensitising cells to apoptosis. Notably, immature oocytes are particularly vulnerable to cisplatin treatment, a common side effect of which is depletion of the primordial follicle reserve, leading to infertility and early menopause. Cisplatin is known to damage the DNA of oocytes, but the possibility that cisplatin also compromises oocyte survival and quality by damaging mitochondria, has not been investigated. To begin to address this question, neonatal mice were treated with saline or cisplatin (2 mg/kg or 4 mg/kg) and the short and long-term impacts on mitochondria in oocytes were characterised.

RESULTS

At 6 and 24 h after treatment, mitochondrial localisation, mass and ATP content in immature oocytes were similar between groups. However, TMRM staining intensity, a marker of mitochondrial membrane potential, was decreased in immature oocytes from cisplatin treated mice compared to saline treated controls, consistent with the induction of apoptosis. When mice were super ovulated 5 weeks after exposure, the number of mature oocytes harvested from cisplatin treated mice was significantly lower than controls. Mitochondrial localisation, mass, membrane potential and ATP levels showed no differences between groups.

CONCLUSIONS

These findings suggest that mitochondrial dysfunction may contribute to the depletion of the ovarian reserve caused by cisplatin, but long-term impacts on mitochondria may be minimal as those immature oocytes that survive cisplatin treatment develop into mature oocytes with normal mitochondrial parameters.

Mitochondrial miR-181a-5p promotes glucose metabolism reprogramming in liver cancer by regulating the electron transport chain

Liver cancer and other malignant tumor cells rely on the glycolytic pathway to obtain energy (i.e. the Warburg effect); however, the underlying mechanism is unclear. Mitochondria are sites of oxidative phosphorylation and adenosine triphosphate (ATP) production. The 13 constituent respiratory chain proteins encoded by the mitochondrial genome (namely, mtDNA) play essential roles. We found that in human hepatocellular carcinoma (HCC) tissues, 11 out of the 13 mtDNA-encoded genes exhibited decreased mRNA levels and 5 genes displayed decreased protein levels, including the cytochrome B (mt-CYB) and cytochrome C oxidase II (mt-CO2) genes. Mitochondrial gene sequencing revealed abnormalities in the levels of a large number of mitochondrial miRNAs (mitomiRs). MicroRNA-181a-5p (mir-181a-5p), which potentially targets genes encoding mt-CYB and mt-CO2 protein, was screened out from 549 downregulated mitomiRs via bioinformatic analysis. After overexpression of mitomiR-181a-5p, mt-CYB and mt-CO2 levels were reduced in HCC cells, and the mitochondrial membrane potential (MMP) maintained by the electron transport chain (ETC) was decreased. Furthermore, the expression of hexokinase 2 (HK2) and glucose transporter type 1 (GLUT1) was upregulated, accompanied by elevated glucose, lactic acid release, and activity of lactate dehydrogenase (LDH). In vivo experiments confirmed that constitutive mitomiR-181a-5p expression caused reprogramming of glucose metabolism and promoted tumor growth and early lung metastasis in liver cancer. In summary, the present study reveals the important role of mitomiRs in glucose metabolism reprogramming in liver cancer, which is of considerable value in exploring new therapeutic targets for HCC.

Requirement of splicing factor hnRNP A2B1 for tumorigenesis of melanoma stem cells

Background

Cancer stem cells play essential roles in tumorigenesis, thus forming an important target for tumor therapy. The hnRNP family proteins are important splicing factors that have been found to be associated with tumor progression. However, the influence of hnRNPs on cancer stem cells has not been extensively explored.

Methods

Quantitative real-time PCR and Western blot were used to examine gene expressions. RNA immunoprecipitation assays were conducted to identify the RNAs interacted with hnRNP A2B1. The in vivo assays were performed in nude mice.

Results

In this study, the results showed that out of 19 evaluated hnRNPs, hnRNP A2B1 was significantly upregulated in melanoma stem cells compared with non-stem cells, suggesting an important role of hnRNP A2B1 in cancer stem cells. Silencing of hnRNP A2B1 triggered cell cycle arrest in G2 phase, leading to apoptosis of melanoma stem cells. The results also revealed that hnRNP A2B1 could bind to the precursor mRNAs of pro-apoptosis genes (DAPK1, SYT7, and RNF128) and anti-apoptosis genes (EIF3H, TPPP3, and DOCK2) to regulate the splicing of these 6 genes, thus promoting the expressions of anti-apoptosis genes and suppressing the expressions of pro-apoptosis genes. The in vivo data indicated that hnRNP A2B1 was required for tumorigenesis by affecting the splicing of TPPP3, DOCK2, EIF3H, RNF128, DAPK1, and SYT7, thus suppressing apoptosis of melanoma stem cells.

Conclusion

Our findings showed the requirement of hnRNP A2B1 for tumorigenesis, thus presenting novel molecular insights into the role of hnRNPs in cancer stem cells.

Accelerated FASTK mRNA degradation induced by oxidative stress is responsible for the destroyed myocardial mitochondrial gene expression and respiratory function in alcoholic cardiomyopathy

Chronic alcoholism disrupts mitochondrial function and often results in alcoholic cardiomyopathy (ACM). Fas-activated serine/threonine kinase (FASTK) is newly recognized as a key post-transcriptional regulator of mitochondrial gene expression. However, the modulatory role of FASTK in cardiovascular pathophysiology remains totally unknown. In experimental ACM models, cardiac FASTK expression markedly declined. Ethanol directly suppressed FASTK expression at post-transcriptional level through NADPH oxidase-derived reactive oxygen species (ROS). Ethanol destabilized FASTK mRNA 3'-untranslated region (3'-UTR) and accelerated its decay, which was blocked by the clearance of ROS. Regnase-1 (Reg1), a ribonuclease regulating mRNA stability, was induced by ROS in ethanol-stimulated cardiomyocytes. Reg1 directly bound to FASTK mRNA 3'-UTR and promoted its degradation, whereas silencing of Reg1 reversed ethanol-induced FASTK downregulation. Compared to wild type control, alcohol-related myocardial morphological (hypertrophy, fibrosis and cardiomyocyte apoptosis) and functional (reduced ejection fraction and compromised cardiomyocyte contraction) anomalies were worsened in FASTK deficient mice. Mechanistically, FASTK ablation repressed NADH dehydrogenase subunit 6 (MTND6, a mitochondrial gene encoding a subunit of complex I) mRNA production and reduced complex I-supported respiration. Importantly, cardiomyocyte-specific upregulation of FASTK through intra-cardiac AAV9-cTNT injection mitigated myocardial mitochondrial dysfunction and restrained ACM progression. In vitro study showed that overexpression of FASTK ameliorated ethanol-induced MTND6 mRNA downregulation, complex I inactivation, and cardiomyocyte death, whereas these beneficial effects were counteracted by rotenone, a complex I inhibitor. Collectively, ROS-accelerated FASTK mRNA degradation via Reg1 underlies chronic ethanol ingestion-associated mitochondrial dysfunction and cardiomyopathy. Restoration of FASTK expression through genetic approaches might be a promising therapeutic strategy for ACM.

High-fat diet affects skeletal muscle mitochondria comparable to pressure overload-induced heart failure

In heart failure, high-fat diet (HFD) may exert beneficial effects on cardiac mitochondria and contractility. Skeletal muscle mitochondrial dysfunction in heart failure is associated with myopathy. However, it is not clear if HFD affects skeletal muscle mitochondria in heart failure as well. To induce heart failure, we used pressure overload (PO) in rats fed normal chow or HFD. Interfibrillar mitochondria (IFM) and subsarcolemmal mitochondria (SSM) from gastrocnemius were isolated and functionally characterized. With PO heart failure, maximal respiratory capacity was impaired in IFM but increased in SSM of gastrocnemius. Unexpectedly, HFD affected mitochondria comparably to PO. In combination, PO and HFD showed additive effects on mitochondrial subpopulations which were reflected by isolated complex activities. While PO impaired diastolic as well as systolic cardiac function and increased glucose tolerance, HFD did not affect cardiac function but decreased glucose tolerance. We conclude that HFD and PO heart failure have comparable effects leading to more severe impairment of IFM. Glucose tolerance seems not causally related to skeletal muscle mitochondrial dysfunction. The additive effects of HFD and PO may suggest accelerated skeletal muscle mitochondrial dysfunction when heart failure is accompanied with a diet containing high fat.

Identification of key genes and pathways associated with feed efficiency of native chickens based on transcriptome data via bioinformatics analysis

BACKGROUND

Improving feed efficiency is one of the important breeding targets for poultry industry. The aim of current study was to investigate the breast muscle transcriptome data of native chickens divergent for feed efficiency. Residual feed intake (RFI) value was calculated for 1008 closely related chickens. The 5 most efficient (LRFI) and 5 least efficient (HRFI) birds were selected for further analysis. Transcriptomic data were generated from breast muscle collected post-slaughter.

RESULTS

The differently expressed genes (DEGs) analysis showed that 24 and 325 known genes were significantly up- and down-regulated in LRFI birds. An enrichment analysis of DEGs showed that the genes and pathways related to inflammatory response and immune response were up-regulated in HRFI chickens. Moreover, Gene Set Enrichment Analysis (GSEA) was also employed, which indicated that LRFI chickens increased expression of genes related to mitochondrial function. Furthermore, protein network interaction and function analyses revealed ND2, ND4, CYTB, RAC2, VCAM1, CTSS and TLR4 were key genes for feed efficiency. And the 'phagosome', 'cell adhesion molecules (CAMs)', 'citrate cycle (TCA cycle)' and 'oxidative phosphorylation' were key pathways contributing to the difference in feed efficiency.

CONCLUSIONS

In summary, a series of key genes and pathways were identified via bioinformatics analysis. These key genes may influence feed efficiency through deep involvement in ROS production and inflammatory response. Our results suggested that LRFI chickens may synthesize ATP more efficiently and control reactive oxygen species (ROS) production more strictly by enhancing the mitochondrial function in skeletal muscle compared with HRFI chickens. These findings provide some clues for understanding the molecular mechanism of feed efficiency in birds and will be a useful reference data for native chicken breeding.

Mitochondrial noncoding RNA-regulatory network in cardiovascular disease

Mitochondrial function and integrity are vital for the maintenance of cellular homeostasis, particularly in high-energy demanding cells. Cardiomyocytes have a large number of mitochondria, which provide a continuous and bulk supply of the ATP necessary for cardiac mechanical function. More than 90% of the ATP consumed by the heart is derived from the mitochondrial oxidative metabolism. Decreased energy supply as the main consequence of mitochondrial dysfunction is closely linked to cardiovascular disease (CVD). The discovery of noncoding RNA (ncRNAs) in the mitochondrial compartment has changed the traditional view of molecular pathways involved in the regulatory network of CVD. Mitochondrial ncRNAs participate in controlling cardiovascular pathogenesis by regulating glycolysis, mitochondrial energy status, and the expression of genes involved in mitochondrial metabolism. Understanding the underlying mechanisms of the association between impaired mitochondrial function resulting from fluctuation in expression levels of ncRNAs and specific disease phenotype can aid in preventing and treating CVD. This review presents an overview of the role of mitochondrial ncRNAs in the complex regulatory network of the cardiovascular pathology. We will summarize and discuss (1) mitochondrial microRNAs (mitomiRs) and long noncoding RNAs (lncRNAs) encoded either by nuclear or mitochondrial genome which are involved in the regulation of mitochondrial metabolism; (2) the role of mitomiRs and lncRNAs in the pathogenesis of several CVD such as hypertension, cardiac hypertrophy, acute myocardial infarction and heart failure; (3) the biomarker and therapeutic potential of mitochondrial ncRNAs in CVD; (4) and the challenges inherent to their translation into clinical application.

Selecting Appropriate Reference Genes for Quantitative Real-Time Polymerase Chain Reaction Studies in Isolated and Cultured Ocular Surface Epithelia

The introduction of tissue engineering has allowed scientists to push the boundaries and treat seriously damaged ocular surface epithelia. They have managed to do this through the development of biological substitutes that restore, maintain or improve tissue function. To ensure the generation of a therapeutically safe and effective graft, knowledge on the transcriptional profile of native and cultured ocular surface epithelia is of undeniable value. Gene expression studies are, however, only as reliable as their proper selection of internal reaction controls or reference genes. In this study, we determined the expression stability of a number of reference genes: 18s rRNA, ACTB, ATP5B, CyC1, EIF4A2, GAPDH, RPL13A, SDHA, TOP1, UBC, and YWHAZ in primary isolates as well as in ex vivo cultured ocular surface epithelia explants (day 0 and/or day 14). Expression stability of the reference genes was assessed with both the geNorm and NormFinder software that use a pairwise comparison and a model-based approach, respectively. Our results extend the general recommendation of using multiple reference genes for normalization purposes to our model systems and provide an overview of several references genes that are likely to be stable in similar culture protocols.

The long non-coding RNA Cerox1 is a post transcriptional regulator of mitochondrial complex I catalytic activity

To generate energy efficiently, the cell is uniquely challenged to co-ordinate the abundance of electron transport chain protein subunits expressed from both nuclear and mitochondrial genomes. How an effective stoichiometry of this many constituent subunits is co-ordinated post-transcriptionally remains poorly understood. Here we show that Cerox1, an unusually abundant cytoplasmic long noncoding RNA (lncRNA), modulates the levels of mitochondrial complex I subunit transcripts in a manner that requires binding to microRNA-488-3p. Increased abundance of Cerox1 cooperatively elevates complex I subunit protein abundance and enzymatic activity, decreases reactive oxygen species production, and protects against the complex I inhibitor rotenone. Cerox1 function is conserved across placental mammals: human and mouse orthologues effectively modulate complex I enzymatic activity in mouse and human cells, respectively. Cerox1 is the first lncRNA demonstrated, to our knowledge, to regulate mitochondrial oxidative phosphorylation and, with miR-488-3p, represent novel targets for the modulation of complex I activity.

Post-transcriptional regulatory patterns revealed by protein-RNA interactions

The coordination of the synthesis of functionally-related proteins can be achieved at the post-transcriptional level by the action of common regulatory molecules, such as RNA–binding proteins (RBPs). Despite advances in the genome-wide identification of RBPs and their binding transcripts, the protein–RNA interaction space is still largely unexplored, thus hindering a broader understanding of the extent of the post-transcriptional regulation of related coding RNAs. Here, we propose a computational approach that combines protein–mRNA interaction networks and statistical analyses to provide an inferred regulatory landscape for more than 800 human RBPs and identify the cellular processes that can be regulated at the post-transcriptional level. We show that 10% of the tested sets of functionally-related mRNAs can be post-transcriptionally regulated. Moreover, we propose a classification of (i) the RBPs and (ii) the functionally-related mRNAs, based on their distinct behaviors in the functional landscape, hinting towards mechanistic regulatory hypotheses. In addition, we demonstrate the usefulness of the inferred functional landscape to investigate the cellular role of both well-characterized and novel RBPs in the context of human diseases.

Effects of Xingpi Kaiyu Fang on ATP, Na/K-ATPase, and Respiratory Chain Complexes of Hippocampus and Gastrocnemius Muscle in Depressed Rats

Objective

To clarify the effectiveness and mechanism of the Chinese herbal formula Xingpi Kaiyu Fang (XPKYF) which is composed of American ginseng (Xi-Yang-shen), Radix curcumae (Yu-Jin), Acori tatarinowii rhizoma (Shi-Chang-pu), and Hypericum perforatum (Guan-Ye-lian-qiao) in depressed rats.

Methods

The rat model of depression was established by chronic unpredictable mild stress (CUMS) method for 6 weeks. Rats were randomly divided into six groups: control group, CUMS group, CUMS+XPKYF (3.6g/kg/d, 7.2g/kg/d, 14.4g/kg/d) groups, and CUMS+sertraline (4.5mg/kg/d) group. The sucrose preference test and the forced swimming test were performed to assess the rats' depression behavior. Mitochondrial ultrastructure was observed by transmission electron microscope and adenosine triphosphate (ATP) content, sodium potassium ATPase (Na/K-ATPase) activity, and mitochondrial respiratory chain complexes activities in hippocampus and gastrocnemius muscle were measured at the 14^th and 42^nd day.

Results

Rats subjected to six weeks of CUMS exhibited decreased sucrose preference ratio and prolonged immobility time. CUMS reduced ATP content in hippocampus, decreased Na/K-ATPase activity and respiratory chain complex I, III, and IV activities in hippocampus and gastrocnemius muscle, and damaged mitochondrial ultrastructure of hippocampus and gastrocnemius muscle. XPKYF at 14.4g/kg, the efficacy trend of which was better than the other drug groups, could prevent the stress-induced depressed behavior changes, inhibit the decrease of Na/K-ATPase activity in hippocampus, inhibit the decrease of respiratory chain complex III activities in hippocampus and gastrocnemius muscle, and protect mitochondria from ultrastructural damage.

Conclusions

Energy deficiency and damaged mitochondrial ultrastructure were found in hippocampus and gastrocnemius muscle of depressed rats established by CUMS. XPKYF could partly reverse alterations in ATP, Na/K-ATPase, and respiratory chain complexes of hippocampus and gastrocnemius muscle and protect mitochondria from ultrastructural damage. This provides another experimental evidence for the clinical application of XPKYF in the treatment of depression.

Differentiation and cell density upregulate cytochrome c levels in megakaryoblastic cell lines: Implications for analysis of CYCS-associated thrombocytopenia

Mutations in the cytochrome c gene (CYCS) cause autosomal dominant thrombocytopenia by an unknown mechanism. While attempting to generate megakaryoblastic cell lines exogenously expressing cytochrome c variants, we discovered that endogenous cytochrome c expression increased both upon induction of differentiation with the phorbol ester phorbol 12-myristate 13-acetate (PMA), and as cell density increased. A concomitant increase in cytochrome c oxidase subunit II in response to PMA, but not cell higher cell density, suggests upregulation of the mitochondrial respiratory chain may be a specific feature of differentiation. These results highlight the likely importance of cytochrome c in both differentiating and proliferating cells, and illustrate the unsuitability of megakaryoblastic lines for modeling CYCS-associated thrombocytopenia.