HIF-1 regulates insect lifespan extension by inhibiting c-Myc-TFAM signaling and mitochondrial biogenesis

Transcriptional Control of Lipid Metabolism

Transcriptional control of lipid metabolism uses a framework that parallels the control of lipid metabolism at the protein or enzyme level, via feedback and feed-forward mechanisms. Increasing the substrates for an enzyme often increases enzyme gene expression, for example. A paucity of product can likewise potentiate transcription or stability of the mRNA encoding the enzyme or enzymes needed to produce it. In addition, changes in second messengers or cellular energy charge can act as on/off switches for transcriptional regulators to control transcript (and protein) abundance. Insects use a wide range of DNA-binding transcription factors (TFs) that sense changes in the cell and its environment to produce the appropriate change in transcription at gene promoters. These TFs work together with histones, spliceosomes, and additional RNA processing factors to ultimately regulate lipid metabolism. In this chapter, we will first focus on the important TFs that control lipid metabolism in insects. Next, we will describe non-TF regulators of insect lipid metabolism such as enzymes that modify acetylation and methylation status, transcriptional coactivators, splicing factors, and microRNAs. To conclude, we consider future goals for studying the mechanisms underlying the control of lipid metabolism in insects.

The protease Lon prolongs insect lifespan by responding to reactive oxygen species and degrading mitochondrial transcription factor A

Diapause is a widespread adaptation of insects that enables them to survive during unfavorable seasons and is characterized by suppressed metabolism and increased lifespan. Previous works have demonstrated that high levels of reactive oxygen species (ROS) and hypoxia-inducible factor-1α (HIF-1α) in the pupal brain of the moth Helicoverpa armigera induce diapause and extend lifespan by downregulating mitochondrial transcription factor A (TFAM). However, the molecular mechanisms of ROS-HIF-1α regulating metabolic activity to extend lifespan are still poorly understood. Here, we show that the mitochondrial abundance in diapause-type pupal brains is markedly lower than that in their nondiapause-type pupae, suggesting that ROS-HIF-1α signaling negatively regulates the number of mitochondria. The protease Lon, a major mitochondrial matrix protease, can respond to ROS signals. It is activated by transcription factor HIF-1α, which specifically binds the LON promoter to promote its expression. A high level of LON mediates the degradation of TFAM, which is a crucial factor in regulating mitochondrial abundance and metabolic activity. We believe this is the first report that a previously unrecognized regulatory pathway, ROS-HIF-1α-LON-TFAM, reduces mitochondrial activity to induce diapause, extending insect lifespan.

Molecular signatures of diapause in the Asian longhorned beetle: Gene expression

Most previous studies on gene expression during insect diapause do not address among-tissue variation in physiological processes. We measured transcriptomic changes during larval diapause in the Asian longhorned beetle, Anoplophora glabripennis (Coleoptera: Cerambycidae). We conducted RNA-seq on fat body, the supraesophageal ganglion, midgut, hindgut, and Malpighian tubules during pre-diapause, diapause maintenance, post-diapause quiescence, and post-diapause development. We observed a small, but consistent, proportion of genes within each gene expression profile that were shared among tissues, lending support for a core set of diapause-associated genes whose expression is tissue-independent. We evaluated the overarching hypotheses that diapause would be associated with cell cycle arrest, developmental arrest, and increased stress tolerance and found evidence of repressed TOR and insulin signaling, reduced cell cycle activity and increased capacity of stress response via heat shock protein expression and remodeling of the cytoskeleton. However, these processes varied among tissues, with the brain and fat body appearing to maintain higher levels of cellular activity during diapause than the midgut or Malpighian tubules. We also observed temperature-dependent changes in gene expression during diapause maintenance, particularly in genes related to the heat shock response and MAPK, insulin, and TOR signaling pathways. Additionally, we provide evidence for epigenetic reorganization during the diapause/post-diapause quiescence transition and expression of genes involved in post-translational modification, highlighting the need for investigations of the protein activity of these candidate genes and processes. We conclude that diapause development is coordinated via diverse tissue-specific gene expression profiles and that canonical diapause phenotypes vary among tissues.

ROS elevate HIF-1α phosphorylation for insect lifespan through the CK2-MKP3-p38 pathway

Diapause in insects is akin to dauer in Caenorhabditis elegans and hibernation in vertebrates, characterized by metabolic depression and lifespan extension. Previous studies have shown that reactive oxygen species (ROS) and hypoxia-inducible factor-1α (HIF-1α) in brains of diapause-destined pupae are more abundant than those in nondiapause-destined pupae in Helicoverpa armigera, but the ROS regulating HIF-1α activity remain unknown. Here, we showed that high ROS levels in brains of diapause-destined pupae resulted in low casein kinase 2 (CK2) activity and that downregulation of CK2 caused low expression of mitogen-activated protein kinase phosphatase 3 (MKP3), which is an inhibitor of p-p38. Thus, high p-p38 levels accumulate to improve HIF-1α activity via activating HIF-1α phosphorylation at the S732 residue to regulate insect diapause. This is the first report showing that a new pathway, ROS-CK2-MKP3-p38, regulates HIF-1α activity for lifespan in insects.

CBR1 decreases protein carbonyl levels via the ROS/Akt/CREB pathway to extend lifespan in the cotton bollworm, Helicoverpa armigera

Reactive oxygen species (ROS) are considered a major cause of ageing and ageing-related diseases through protein carbonylation. Little is known about the molecular mechanisms that confer protection against ROS. Here, we observed that, compared with nondiapause-destined pupae, high protein carbonyl levels are present in the brains of diapause-destined pupae, which is a 'non-ageing' phase in the moth Helicoverpa armigera. Protein carbonyl levels respond to ROS and decrease metabolic activity to induce diapause in order to extend lifespan. However, protein carbonylation in the brains of diapause-destined pupae still occurs at a physiological level compared to young adult brains. We find that ROS activate Akt, and Akt then phosphorylates the transcription factor CREB to facilitate its nuclear import. CREB binds to the promoter of carbonyl reductase 1 (CBR1) and regulates its expression. High CBR1 levels reduce protein carbonyl levels to maintain physiological levels. This is the first report showing that the moth brain can naturally control protein carbonyl levels through a distinct ROS-Akt-CREB-CBR1 pathway to extend lifespan.

Timing of Diapause Initiation and Overwintering Conditions Alter Gene Expression Profiles in Megachile rotundata

Within the United States and Canada, the primary pollinator of alfalfa is the alfalfa leafcutting bee (ALCB), Megachile rotundata. Our previous findings showed that overwintering conditions impacted gene expression profile in ALCB prepupae that entered diapause early in the season. However, ALCB are a bivoltine species, which begs the question of whether bees entering diapause later in the season also show this trend. To better understand the effects of the timing of diapause initiation, we analyzed mRNA copy number of genes known to be involved in diapause regulation in early and late season diapausing ALCB that were overwintered in field conditions or using current agricultural management conditions. We hypothesized that overwintering conditions for late diapausing bees also affects gene expression profiles. Our results showed that expression profiles were altered by both overwintering condition and timing of diapause initiation, with bees that entered diapause earlier in the season showing different expression patterns than those that entered diapause later in the season. This trend was seen in expression of members of the cyclin family and several targets of the insulin signaling pathway, including forkhead box protein O (FOXO), which is known to be important for diapause regulation and stress responses. But, of the genes screened, the proto-oncogene, Myc, was the most impacted by the timing of diapause initiation. Under field conditions, there were significant differences in Myc expression between the early and late season samples in all months except for November and February. This same general trend in Myc expression was also seen in the laboratory-maintained bees with significant difference in expression in all months except for November, February, and May. These results support previous conclusions from our research showing that the molecular regulation of diapause development in ALCB is not a simple singular cascade of gene expression but a highly plastic response that varies between bees depending upon their environmental history.

Chromosomal-Level Genome Assembly of a True Bug, Aspongopus chinensis Dallas, 1851 (Hemiptera: Dinidoridae)

The true bug, Aspongopus chinensis Dallas, 1851 (Hemiptera: Dinidoridae), is a fascinating insect with prolonged diapause and medicinal properties but also a notorious pest. However, because of the lack of genomic resources, an in-depth understanding of its biological characteristics is lacking. Here, we report the first genome assembly of A. chinensis anchored to 10 pseudochromosomes, which was achieved by combining PacBio long reads and Hi-C sequencing data. This chromosome-level genome assembly was 1.55 Gb in size with a scaffold N50 of 156 Mb. The benchmarking universal single-copy ortholog (BUSCO) analysis of the assembly captured 96.6% of the BUSCO genes. A total of 686,888,052 bp of repeat sequences, 18,511 protein-coding genes, and 1,749 noncoding RNAs were annotated. By comparing the A. chinensis genome with that of 8 homologous insects and 2 model organisms, 213 rapidly evolving gene families were identified, including 83 expanded and 130 contracted gene families. The functional enrichment of Gene Ontology and KEGG pathways showed that the significantly expanded gene families were primarily involved in metabolism, immunity, detoxification, and DNA/RNA replication associated with stress responses. The data reported here shed light on the ecological adaptation of A. chinensis and further expanded our understanding of true bug evolution in general.

High MEK/ERK signalling is a key regulator of diapause maintenance in the cotton bollworm, Helicoverpa armigera

MEK/ERK signalling has been identified as a key factor that terminates diapause in Sarcophaga crassipalpis and Bombyx mori. Paradoxically, high p-MEK/p-ERK signalling induces diapause in pupae of the moth Helicoverpa armigera; however, the regulatory mechanism is unknown. In the present study, we show that p-MEK and p-ERK are elevated in the brain of diapause-destined pupae and suppression of MEK/ERK activity terminates diapause progress. Reactive oxygen species (ROS) activate MEK/ERK signalling, causing large-scale phosphorylation of downstream proteins. The levels of ubiquitin-conjugated proteins are also significantly reduced when ROS or p-ERK level decreased. Moreover, terminated diapause progress by 20-hydroxyecdysone injection significantly decreases p-MEK, p-ERK and phospho-ribosomal S6 kinase levels, while phospho-MAPK substrates and ubiquitin-conjugated protein levels increase. Our data demonstrate that high MEK/ERK signalling mediated by ROS promotes diapause maintenance via increasing phosphorylation and degradation of downstream substrates. The results of this study may provide important information for understanding the regulatory mechanisms during insect diapause.

Hypoxia-Inducible Factor (HIF) in Ischemic Stroke and Neurodegenerative Disease

Hypoxia is one of the most common pathological conditions, which can be induced by multiple events, including ischemic injury, trauma, inflammation, tumors, etc. The body's adaptation to hypoxia is a highly important phenomenon in both health and disease. Most cellular responses to hypoxia are associated with a family of transcription factors called hypoxia-inducible factors (HIFs), which induce the expression of a wide range of genes that help cells adapt to a hypoxic environment. Basic mechanisms of adaptation to hypoxia, and particularly HIF functions, have being extensively studied over recent decades, leading to the 2019 Nobel Prize in Physiology or Medicine. Based on their pivotal physiological importance, HIFs are attracting increasing attention as a new potential target for treating a large number of hypoxia-associated diseases. Most of the experimental work related to HIFs has focused on roles in the liver and kidney. However, increasing evidence clearly demonstrates that HIF-based responses represent an universal adaptation mechanism in all tissue types, including the central nervous system (CNS). In the CNS, HIFs are critically involved in the regulation of neurogenesis, nerve cell differentiation, and neuronal apoptosis. In this mini-review, we provide an overview of the complex role of HIF-1 in the adaptation of neurons and glia cells to hypoxia, with a focus on its potential involvement into various neuronal pathologies and on its possible role as a novel therapeutic target.

ROS and hypoxia signaling regulate periodic metabolic arousal during insect dormancy to coordinate glucose, amino acid, and lipid metabolism

Metabolic suppression is a hallmark of animal dormancy that promotes overall energy savings. Some diapausing insects and some mammalian hibernators have regular cyclic patterns of substantial metabolic depression alternating with periodic arousal where metabolic rates increase dramatically. Previous studies, largely in mammalian hibernators, have shown that periodic arousal is driven by an increase in aerobic mitochondrial metabolism and that many molecules related to energy metabolism fluctuate predictably across periodic arousal cycles. However, it is still not clear how these rapid metabolic shifts are regulated. We first found that diapausing flesh fly pupae primarily use anaerobic glycolysis during metabolic depression but engage in aerobic respiration through the tricarboxylic acid cycle during periodic arousal. Diapausing pupae also clear anaerobic by-products and regenerate many metabolic intermediates depleted in metabolic depression during arousal, consistent with patterns in mammalian hibernators. We found that decreased levels of reactive oxygen species (ROS) induced metabolic arousal and elevated ROS extended the duration of metabolic depression. Our data suggest ROS regulates the timing of metabolic arousal by changing the activity of two critical metabolic enzymes, pyruvate dehydrogenase and carnitine palmitoyltransferase I by modulating the levels of hypoxia inducible transcription factor (HIF) and phosphorylation of adenosine 5'-monophosphate-activated protein kinase (AMPK). Our study shows that ROS signaling regulates periodic arousal in our insect diapasue system, suggesting the possible importance ROS for regulating other types of of metabolic cycles in dormancy as well.

High-throughput profiling of diapause regulated genes from Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae)

Background

The parasitoid wasp, Trichogramma dendrolimi, can enter diapause at the prepupal stage. Thus, diapause is an efficient preservation method during the mass production of T. dendrolimi. Previous studies on diapause have mainly focused on ecological characteristics, so the molecular basis of diapause in T. dendrolimi is unknown. We compared transcriptomes of diapause and non-diapause T. dendrolimi to identify key genes and pathways involved in diapause development.

Results

Transcriptome sequencing was performed on diapause prepupae, pupae after diapause, non-diapause prepupae, and pupae. Analysis yielded a total of 87,022 transcripts with an average length of 1604 bp. By removing redundant sequences and those without significant BLAST hits, a non-redundant dataset was generated, containing 7593 sequences with an average length of 3351 bp. Among them, 5702 genes were differentially expressed. The result of Gene Ontology (GO) enrichment analysis revealed that regulation of transcription, DNA-templated, oxidation-reduction process, and signal transduction were significantly affected. Ten genes were selected for validation using quantitative real-time PCR (qPCR). The changes showed the same trend as between the qPCR and RNA-Seq results. Several genes were identified as involved in diapause, including ribosomal proteins, zinc finger proteins, homeobox proteins, forkhead box proteins, UDP-glucuronosyltransferase, Glutathione-S-transferase, p53, and DNA damage-regulated gene 1 (pdrg1). Genes related to lipid metabolism were also included.

Conclusions

We generated a large amount of transcriptome data from T. dendrolimi, providing a resource for future gene function research. The diapause-related genes identified help reveal the molecular mechanisms of diapause, in T. dendrolimi, and other insect species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07285-4.

COXIV and SIRT2-mediated G6PD deacetylation modulate ROS homeostasis to extend pupal lifespan

Previous studies have shown that high physiological levels of reactive oxygen species (ROS) in the brain promote pupal diapause, which extends the pupal lifespan. However, the molecular mechanisms of ROS generation are unclear. In this paper, we found that mitochondrial ROS (mtROS) levels in the brains of Helicoverpa armigera diapause-destined pupae (DP) were higher and that the expression of cytochrome oxidase subunit IV (COXIV) was lower than in NP. In addition, downregulating COXIV caused mitochondrial dysfunction which elevated mtROS levels. Protein kinase A (PKA) was downregulated in DP, which led to the downregulated expression of the mitochondrial transcription factor TFAM. Low TFAM activity failed to promote COXIV expression and resulted in the high ROS levels that induced diapause. In addition, low sirtuin 2 expression suppressed glucose-6-phosphate dehydrogenase (G6PD) deacetylation at K382, which led to reduced G6PD activity and low NADPH levels, thereby maintaining high levels of ROS. Two proteins, COXIV and G6PD, thus play key roles in the elevated accumulation of ROS that induce diapause and extend the pupal lifespan.

Special Significance of Non-Drosophila Insects in Aging

Aging is the leading risk factor of human chronic diseases. Understanding of aging process and mechanisms facilitates drug development and the prevention of aging-related diseases. Although many aging studies focus on fruit fly as a canonical insect system, minimal attention is paid to the potentially significant roles of other insects in aging research. As the most diverse group of animals, insects provide many aging types and important complementary systems for aging studies. Insect polyphenism represents a striking example of the natural variation in longevity and aging rate. The extreme intraspecific variations in the lifespan of social insects offer an opportunity to study how aging is differentially regulated by social factors. Insect flight, as an extremely high-intensity physical activity, is suitable for the investigation of the complex relationship between metabolic rate, oxidative stress, and aging. Moreover, as a "non-aging" state, insect diapause not only slows aging process during diapause phase but also affects adult longevity during/after diapause. In the past two decades, considerable progress has been made in understanding the molecular basis of aging regulation in insects. Herein, the recent research progress in non-Drosophila insect aging was reviewed, and its potential utilization in aging in the future was discussed.

The Target of Rapamycin Signalling Pathway in Ageing and Lifespan Regulation

Ageing is a complex trait controlled by genes and the environment. The highly conserved mechanistic target of rapamycin signalling pathway (mTOR) is a major regulator of lifespan in all eukaryotes and is thought to be mediating some of the effects of dietary restriction. mTOR is a rheostat of energy sensing diverse inputs such as amino acids, oxygen, hormones, and stress and regulates lifespan by tuning cellular functions such as gene expression, ribosome biogenesis, proteostasis, and mitochondrial metabolism. Deregulation of the mTOR signalling pathway is implicated in multiple age-related diseases such as cancer, neurodegeneration, and auto-immunity. In this review, we briefly summarise some of the workings of mTOR in lifespan and ageing through the processes of transcription, translation, autophagy, and metabolism. A good understanding of the pathway's outputs and connectivity is paramount towards our ability for genetic and pharmacological interventions for healthy ageing and amelioration of age-related disease.

P-S6K is associated with insect diapause via the ROS/AKT/ S6K/CREB/HIF-1 pathway in the cotton bollworm, Helicoverpa armigera

Diapause is a complex physiological response that allows insects to survive unfavorable environmental conditions, and many signaling pathways participate in regulating this process. However, little is known about TOR signaling in the regulation of diapause. In this study, we found that the TOR pathway-related proteins TOR and Raptor are expressed at low levels in the brains of diapause-destined pupae of Helicoverpa armigera, consistent with a previous report that TOR signaling is associated with development. Interestingly, another TOR signaling-related protein, p-S6K, was increased in the brains of diapause-destined pupae. Our results showed that p-S6K in the brains of diapause-destined pupae can respond to the upstream signals reactive oxygen species (ROS) and AKT and that S6K activates the level of CREB, which binds to the HIF-1α promoter and increases its expression. Previous study has shown that HIF-1α levels elevated by ROS in the brains of diapause-destined pupae cause low mitochondrial activity for insect diapause. Thus, p-S6K in response to ROS/AKT regulates HIF-1α via activating transcription factor CREB for diapause initiation.

FUBP1 promotes neuroblastoma proliferation via enhancing glycolysis-a new possible marker of malignancy for neuroblastoma

Background

Neuroblastoma (NB) is one of the deadliest paediatric solid tumours due to its rapid proliferative characteristics. Amplified copies of MYCN are considered the most important marker for the prediction of tumour relapse and progression in NB, but they were only detected in 20–30% of NB patients, indicating there might be other oncogenes in the development of NB. The far upstream element binding protein 1 (FUBP1) was first identified as a transcriptional regulator of the proto-oncogene MYC. However, the expression and role of FUBP1 in NB have not been documented.

Methods

FUBP1 expression was analysed from GEO database and verified by immunohistochemistry (IHC) and western blotting (WB) in NB tissues and cell lines. Cell proliferation and apoptosis were detected by Cell Counting Kit-8, Colony formation assay, EDU, TUNEL staining and flow cytometric analysis. Several glycolytic metabolites production was confirmed by ELISA and oxygen consuming rate (OCR). Luciferase assay, WB, chromatin immunoprecipitation (CHIP) were used to explore the mechanisms of the effect of FUBP1 on NB.

Results

FUBP1 mRNA levels were increased along with the increase in International Neuroblastoma Staging System (INSS) stages. High expression of FUBP1 with low N-Myc expression accounted for 44.6% of NB patient samples (n = 65). In addition, FUBP1 protein levels were remarkably increased with NB malignancy in the NB tissue microarray (NB: n = 65; ganglioneuroblastoma: n = 31; ganglioneuroma: n = 27). Furthermore, FUBP1 expression was negatively correlated with patient survival rate but positively correlated with ki67 content. In vitro experiments showed that FUBP1 promotes NB cell proliferation and inhibits cell apoptosis via enhancing glycolysis and ATP production. Mechanistically, FUBP1 inhibited the degradation of HIF1α via downregulation of Von Hippel-Lindau (VHL), the E3 ligase for HIF1α, resulting in upregulation of lactate dehydrogenase isoform B (LDHB) expression to enhance glycolysis. Overexpressed or silenced N-Myc could not regulate FUBP1 or LDHB levels.

Conclusions

Taken together, our findings demonstrate for the first time that elevated FUBP1 promotes NB glycolysis and growth by targeting HIF1α rather than N-Myc, suggesting that FUBP1 is a novel and powerful oncogene in the development of NB independent of N-Myc and may have potential in the diagnosis and treatment of NB.

Alternative splicing and expression analysis of HSF1 in diapause pupal brains in the cotton bollworm, Helicoverpa armigera

BACKGROUND

Diapause is the arrest of the development of insects and can be used for the development of effective agricultural pest management strategies. Heat shock protein 70 (Hsp70) is reported to be up-regulated during diapause to maintain survival in some insect species. However, its regulatory mechanism is unknown.

RESULTS

Expression of hsp70 in Helicoverpa armigera was found to be up-regulated in diapause pupal brains. To elucidate the molecular regulatory mechanisms of hsp70, we focused our attention on its transcription factor, heat shock factor 1 (HSF1). Four alternative splicing variants of HSF1 from pupal brains of H. armigera were identified, and subcellular localization analysis indicated that these variants were exclusively expressed in the nucleus. Real-time PCR analysis showed that all of these variants were up-regulated in diapause pupal brains, and their expression patterns were consistent with that of hsp70. Finally, promoter activity assay and Western blotting detection demonstrated that hsp70 was activated and up-regulated by these variants.

CONCLUSION

Expression of hsp70 in H. armigera during diapause is regulated by multiple alternatively spliced isoforms of HSF1. The results of this study may provide important information for understanding the regulatory mechanisms of hsps during insect diapause. © 2018 Society of Chemical Industry.

PTEN expression responds to transcription factor POU and regulates p-AKT levels during diapause initiation in the cotton bollworm, Helicoverpa armigera

Diapause is a complex physiological response accompanied by many signaling pathways participating in the process. Previous studies have shown that p-AKT levels in brains of diapause-destined pupae are elevated by ROS, and the activated AKT promotes Glut expression for glucose uptake during diapause entry in Helicoverpa armigera. However, the mechanism by which ROS activate AKT is still unclear. Here, we show that PTEN, a PI3K/p-AKT signaling inhibitor, was significantly lower in the brains of diapause-destined pupae and that p-AKT levels were elevated by a lack of PTEN dephosphorylating PIP3. In addition, POU was identified as a transcription factor that binds to the PTEN promoter and regulates its expression. POU expression was enhanced by ecdysone but suppressed by ROS, suggesting that POU/PTEN plays a central role in responding to ROS signaling and regulating p-AKT levels. These results suggest that ecdysone and ROS participate together in the regulation of insect diapause through downregulation of POU/PTEN, which elevates p-AKT levels.

Impact of Drosophila Models in the Study and Treatment of Friedreich's Ataxia

Drosophila melanogaster has been for over a century the model of choice of several neurobiologists to decipher the formation and development of the nervous system as well as to mirror the pathophysiological conditions of many human neurodegenerative diseases. The rare disease Friedreich’s ataxia (FRDA) is not an exception. Since the isolation of the responsible gene more than two decades ago, the analysis of the fly orthologue has proven to be an excellent avenue to understand the development and progression of the disease, to unravel pivotal mechanisms underpinning the pathology and to identify genes and molecules that might well be either disease biomarkers or promising targets for therapeutic interventions. In this review, we aim to summarize the collection of findings provided by the Drosophila models but also to go one step beyond and propose the implications of these discoveries for the study and cure of this disorder. We will present the physiological, cellular and molecular phenotypes described in the fly, highlighting those that have given insight into the pathology and we will show how the ability of Drosophila to perform genetic and pharmacological screens has provided valuable information that is not easily within reach of other cellular or mammalian models.

HuR stabilizes TFAM mRNA in an ATM/p38-dependent manner in ionizing irradiated cancer cells

Mitochondrial transcription factor A (TFAM) plays key roles in transcription and maintenance of mtDNA. It has been reported that TFAM could promote the proliferation and tumorigenesis of cells under stressed conditions. Previous evidence showed ionizing radiation stimulated the expression of TFAM, the replication of mtDNA, and the activity of mtDNA‐encoded cytochrome C oxidase. However, little is known about the mechanism of TFAM regulation in irradiated cells. In this article, we explored the role of mRNA stability in regulating TFAM expression in irradiated cancer cells. Our results showed that radiation stimulated the levels of TFAM mRNA and protein. RNA‐binding protein HuR associated and stabilized TFAM mRNA to facilitate the expression of TFAM, which was enhanced by radiation. Furthermore, radiation‐activated ataxia‐telangiectasia mutated kinase/p38 signaling positively contributed to the nucleus to cytosol translocation of HuR, its binding and stabilization of TFAM mRNA, without affecting the transcription and the stability of TFAM. Our current work proposed a new mechanism of DNA damage response‐regulated mitochondrial function variations, and indicated that TFAM might be a potential target for increasing the sensitization of cancer cells to radiotherapy.

The role of declining adaptive homeostasis in ageing

Adaptive homeostasis is "the transient expansion or contraction of the homeostatic range for any given physiological parameter in response to exposure to sub-toxic, non-damaging, signalling molecules or events, or the removal or cessation of such molecules or events" (Davies, 2016). Adaptive homeostasis enables biological systems to make continuous short-term adjustments for optimal functioning despite ever-changing internal and external environments. Initiation of adaptation in response to an appropriate signal allows organisms to successfully cope with much greater, normally toxic, stresses. These short-term responses are initiated following effective signals, including hypoxia, cold shock, heat shock, oxidative stress, exercise-induced adaptation, caloric restriction, osmotic stress, mechanical stress, immune response, and even emotional stress. There is now substantial literature detailing a decline in adaptive homeostasis that, unfortunately, appears to manifest with ageing, especially in the last third of the lifespan. In this review, we present the hypothesis that one hallmark of the ageing process is a significant decline in adaptive homeostasis capacity. We discuss the mechanistic importance of diminished capacity for short-term (reversible) adaptive responses (both biochemical and signal transduction/gene expression-based) to changing internal and external conditions, for short-term survival and for lifespan and healthspan. Studies of cultured mammalian cells, worms, flies, rodents, simians, apes, and even humans, all indicate declining adaptive homeostasis as a potential contributor to age-dependent senescence, increased risk of disease, and even mortality. Emerging work points to Nrf2-Keap1 signal transduction pathway inhibitors, including Bach1 and c-Myc, both of whose tissue concentrations increase with age, as possible major causes for age-dependent loss of adaptive homeostasis.

Cathepsin L participates in the remodeling of the midgut through dissociation of midgut cells and activation of apoptosis via caspase-1

The larval midgut in holometabolous insects must undergo a remodeling process during metamorphosis to form the pupal-adult midgut. However, the molecular mechanism of larval midgut cell dissociation remains unknown. Here, we show that the expression and activity of Helicoverpa armigera cathepsin L (Har-CatL) are high in the midgut at the mid-late stage of the 6th-instar larvae and are responsive to the upstream hormone ecdysone. Immunocytochemistry shows that signals for Har-CatL-like are localized in midgut cells, and an inhibitor experiment demonstrates that Har-CatL functions in the dissociation of midgut epithelial cells. Mechanistically, Har-CatL can cleave pro-caspase-1 into the mature peptide, thereby increasing the activity of caspase-1, which plays a key role in apoptosis, indicating that Har-CatL is also involved in the apoptosis of midgut cells by activating caspase-1. We believe that this is the first report that Har-CatL regulates the dissociation and apoptosis of the larval midgut epithelium for midgut remodeling.

Characterization of Bombyx mori mitochondrial transcription factor A, a conserved regulator of mitochondrial DNA

In the present study, we initially cloned and characterized a mitochondrial transcription factor A (Tfam) homologue in the silkworm, Bombyx mori. Bombyx mori TFAM (BmTFAM) localized to mitochondria in cultured silkworm and human cells, and co-localized with mtDNA nucleoids in human HeLa cells. In an immunoprecipitation analysis, BmTFAM was found to associate with human mtDNA in mitochondria, indicating its feature as a non-specific DNA-binding protein. In spite of the low identity between BmTFAM and human TFAM (26.5%), the expression of BmTFAM rescued mtDNA copy number reductions and enlarged mtDNA nucleoids in HeLa cells, which were induced by human Tfam knockdown. Thus, BmTFAM compensates for the function of human TFAM in HeLa cells, demonstrating that the mitochondrial function of TFAM is highly conserved between silkworms and humans. BmTfam mRNA was strongly expressed in early embryos. Through double-stranded RNA (dsRNA)-based RNA interference (RNAi) in silkworm embryos, we found that the knockdown of BmTFAM reduced the amount of mtDNA and induced growth retardation at the larval stage. Collectively, these results demonstrate that BmTFAM is a highly conserved mtDNA regulator and may be a good candidate for investigating and modulating mtDNA metabolism in this model organism.