Suppression of oxidative phosphorylation confers resistance against bevacizumab in experimental glioma

Although bevacizumab initially shows high response rates in gliomas and other tumours, therapy resistance usually develops later. Because anti‐angiogenic agents are supposed to induce hypoxia, we asked whether rendering glioma cells independent of oxidative phosphorylation modulates their sensitivity against hypoxia and bevacizumab. LNT‐229 glioma cells without functional mitochondria (rho⁰) and control (rho⁺) cells were generated. LNT‐229 rho⁰‐cells displayed reduced expression of oxidative phosphorylation‐related genes and diminished oxygen consumption. Conversely, glycolysis was up‐regulated in these cells, as shown by increased lactate production and stronger expression of glucose transporter‐1 and lactate dehydrogenase‐A. However, hypoxia‐induced cell death in vitro was nearly completely abolished in the LNT‐229 rho⁰‐cells, these cells were more sensitive towards glucose restriction and the treatment with the glycolysis inhibitor 2‐deoxy‐D‐glucose. In an orthotopic mouse xenograft experiment, bevacizumab induced hypoxia as reflected by elevated Hypoxia‐inducible factor 1‐alpha staining in both, rho⁺‐ and rho⁰‐tumours. However, it prolonged survival only in the mice bearing rho⁺‐tumours (74 days vs. 105 days, p  = 0.024 log‐rank test) and had no effect on survival in mice carrying LNT‐229 rho⁰‐tumours (75 days vs. 70 days, p  = 0.52 log‐rank test). Interestingly, inhibition of glycolysis in vivo with 2‐deoxy‐D‐glucose re‐established sensitivity of rho⁰‐tumours against bevacizumab (98 days vs. 80 days, p  = 0.0001). In summary, ablation of oxidative phosphorylation in glioma cells leads to a more glycolytic and hypoxia‐resistant phenotype and is sufficient to induce bevacizumab‐refractory tumours. These results add to increasing evidence that a switch towards glycolysis is one mechanism how tumour cells may evade anti‐angiogenic treatments and suggest anti‐glycolytic strategies as promising approaches to overcome bevacizumab resistance.

     

Comparative study of sequence aligners for detecting antibiotic resistance in bacterial metagenomes

We aim to compare the performance of Bowtie2 , bwa‐mem , blastn and blastx when aligning bacterial metagenomes against the Comprehensive Antibiotic Resistance Database (CARD). Simulated reads were used to evaluate the performance of each aligner under the following four performance criteria: correctly mapped, false positives, multi‐reads and partials. The optimal alignment approach was applied to samples from two wastewater treatment plants to detect antibiotic resistance genes using next generation sequencing. blastn mapped with greater accuracy among the four sequence alignment approaches considered followed by Bowtie2 . blastx generated the greatest number of false positives and multi‐reads when aligned against the CARD. The performance of each alignment tool was also investigated using error‐free reads. Although each aligner mapped a greater number of error‐free reads as compared to Illumina‐error reads, in general, the introduction of sequencing errors had little effect on alignment results when aligning against the CARD. Given each performance criteria, blastn was found to be the most favourable alignment tool and was therefore used to assess resistance genes in sewage samples. Beta‐lactam and aminoglycoside were found to be the most abundant classes of antibiotic resistance genes in each sample.

Significance and Impact of the Study

Antibiotic resistance genes (ARGs) are pollutants known to persist in wastewater treatment plants among other environments, thus methods for detecting these genes have become increasingly relevant. Next generation sequencing has brought about a host of sequence alignment tools that provide a comprehensive look into antimicrobial resistance in environmental samples. However, standardizing practices in ARG metagenomic studies is challenging since results produced from alignment tools can vary significantly. Our study provides sequence alignment results of synthetic, and authentic bacterial metagenomes mapped against an ARG database using multiple alignment tools, and the best practice for detecting ARGs in environmental samples.     

Mechanisms of resistance in the rice cultivar Manikpukha to the rice stem nematode Ditylenchus angustus

The incompatible interaction between the rice cultivar Manikpukha and the rice stem nematode Ditylenchus angustus has been reported recently. This research focuses on the underlying mechanisms of resistance in Manikpukha. Invasion, post‐infection development and reproduction of D. angustus were compared in compatible and incompatible interactions to identify the stage in which resistance occurs. The results indicate that resistance in Manikpukha is associated with reduced development and reproduction, implying that resistance acts post‐invasion. We studied the possible involvement of three classical defence hormones, salicylic acid (SA), jasmonic acid (JA) and ethylene (ET), in response to infection in a compatible interaction using biosynthesis/signalling‐deficient transgenic rice lines. All three hormones appear to have an influence on the basal defence of Nipponbare against the stem nematode. Although hormone application increases basal defences, expression studies and hormone analyses after nematode infection in Manikpukha did not show a clear involvement of the hormone defense pathways for SA, ET and JA. However, it seems that OsPAL1 plays a pivotal role in resistance, indicating that the phenylpropanoid pathway and its products might be key players in the incompatible interaction. Lignin measurement showed that, although basal levels are similar, Manikpukha had a significantly higher lignin content on nematode infection, whereas it was decreased in the susceptible cultivar. The results presented here show that SA, ET and JA are involved in basal defences, but the resistance of Manikpukha against D. angustus probably relies on products of the phenylpropanoid pathway.     

Effective tolerance based on resource reallocation is a virus‐specific defence in Arabidopsis thaliana

Plant viruses often harm their hosts, which have developed mechanisms to prevent or minimize the effects of virus infection. Resistance and tolerance are the two main plant defences to pathogens. Although resistance to plant viruses has been studied extensively, tolerance has received much less attention. Theory predicts that tolerance to low‐virulent parasites would be achieved through resource reallocation from growth to reproduction, whereas tolerance to high‐virulent parasites would be attained through shortening of the pre‐reproductive period. We have shown previously that the tolerance of Arabidopsis thaliana to Cucumber mosaic virus (CMV), a relatively low‐virulent virus in this host, accords to these predictions. However, whether other viruses trigger the same response, and how A. thaliana copes with highly virulent virus infections remains unexplored. To address these questions, we challenged six A. thaliana wild genotypes with five viruses with different genomic structures, life histories and transmission modes. In these plants, we quantified virus multiplication, virulence, and the effects of infection on plant growth and reproduction, and on the developmental schedule. Our results indicate that virus multiplication varies according to the virus × host genotype interaction. Conversely, effective tolerance is observed only on CMV infection, and is associated with resource reallocation from growth to reproduction. Tolerance to the other viruses is observed only in specific host–virus combinations and, at odds with theoretical predictions, is linked to longer pre‐reproductive periods. These findings only partially agree with theoretical predictions, and contribute to a better understanding of pathogenic processes in plant–virus interactions.     

Virulence properties of Campylobacter jejuni are enhanced by displaying a mycobacterial TlyA methylation pattern in its rRNA

Campylobacter jejuni is a bacterial pathogen that is generally acquired as a zoonotic infection from poultry and animals. Adhesion of C. jejuni to human colorectal epithelial cells is weakened after loss of its cj0588 gene. The Cj0588 protein belongs to the type I group of TlyA (TlyA^I) enzymes, which 2′‐O‐methylate nucleotide C1920 in 23S rRNA. Slightly longer TlyA^II versions of the methyltransferase are found in actinobacterial species including Mycobacterium tuberculosis, and methylate not only C1920 but also nucleotide C1409 in 16S rRNA. Loss of TlyA function attenuates virulence of both M. tuberculosis and C. jejuni. We show here that the traits impaired in C. jejuni null strains can be rescued by complementation not only with the original cj0588 (tlyA ^I) but also with a mycobacterial tlyA ^II gene. There are, however, significant differences in the recombinant phenotypes. While cj0588 restores motility, biofilm formation, adhesion to and invasion of human epithelial cells and stimulation of IL‐8 production in a C. jejuni null strain, several of these properties are further enhanced by the mycobacterial tlyA ^II gene, in some cases to twice the original wild‐type level. These findings strongly suggest that subtle changes in rRNA modification patterns can affect protein synthesis in a manner that has serious consequences for bacterial pathogenicity.     

miR‐126 reduces trastuzumab resistance by targeting PIK3R2 and regulating AKT/mTOR pathway in breast cancer cells

MicroRNAs (miRNAs) have been found to play a key role in drug resistance. In the current study, we aimed to explore the potential role of miR‐126 in trastuzumab resistance in breast cancer cells. We found that the trastuzumab‐resistant cell lines SKBR3/TR and BT474/TR had low expression of miR‐126 and increased ability to migrate and invade. The resistance, invasion and mobilization abilities of the cells resistant to trastuzumab were reduced by ectopic expression of miR‐126 mimics. In comparison, inhibition of miR‐126 in SKBR3 parental cells had the opposite effect of an increased resistance to trastuzumab as well as invasion and migration. It was also found that miR‐126 directly targets PIK3R2 in breast cancer cells. PIK3R2‐knockdown cells showed decreased resistance to trastuzumab, while overexpression of PIK3R2 increased trastuzumab resistance. In addition, our finding showed that overexpression of miR‐126 reduced resistance to trastuzumab in the trastuzumab‐resistant cells and that inhibition of the PIK3R2/PI3K/AKT/mTOR signalling pathway was involved in this effect. SKBR3/TR cells also showed increased sensitivity to trastuzumab mediated by miR‐126 in vivo. In conclusion, the above findings demonstrated that overexpression of miR‐126 or down‐regulation of its target gene may be a potential approach to overcome trastuzumab resistance in breast cancer cells.     

Biology and pathological implications of brown adipose tissue: promises and caveats for the control of obesity and its associated complications

The discovery of metabolically active brown adipose tissue (BAT) in adult humans has fuelled the research of diverse aspects of this previously neglected tissue. BAT is solely present in mammals and its clearest physiological role is non‐shivering thermogenesis, owing to the capacity of brown adipocytes to dissipate metabolic energy as heat. Recently, a number of other possible functions have been proposed, including direct regulation of glucose and lipid homeostasis and the secretion of a number of factors with diverse regulatory actions. Herein, we review recent advances in general biological knowledge of BAT and discuss the possible implications of this tissue in human metabolic health. In particular, we confront the claimed thermogenic potential of BAT for human energy balance and body mass regulation, mostly based on animal studies, with the most recent quantifications of human BAT.