The transcriptome landscape of the carcinogenic treatment response in the blind mole rat: insights into cancer resistance mechanisms

Activity of DNA Repair Systems in the Cells of Long-Lived Rodents and Bats

Damages of various origin accumulated in the genomic DNA can lead to the breach of genome stability, and are considered to be one of the main factors involved in cellular senescence. DNA repair systems in mammalian cells ensure effective damage removal and repair of the genome structure, therefore, activity of these systems is expected to be correlated with high maximum lifespan observed in the long-lived mammals. This review discusses current results of the studies focused on determination of the DNA repair system activity and investigation of the properties of its key regulatory proteins in the cells of long-lived rodents and bats. Based on the works discussed in the review, it could be concluded that the long-lived rodents and bats in general demonstrate high efficiency in functioning and regulation of DNA repair systems. Nevertheless, a number of questions around the study of DNA repair in the cells of long-lived rodents and bats remain poorly understood, answers to which could open up new avenues for further research.

The Naked Mole-Rat as a Model for Healthy Aging

Naked mole-rats (NMRs, Heterocephalus glaber) are the longest-lived rodents with a maximum life span exceeding 37 years. They exhibit a delayed aging phenotype and resistance to age-related functional decline/diseases. Specifically, they do not display increased mortality with age, maintain several physiological functions until nearly the end of their lifetime, and rarely develop cancer and Alzheimer's disease. NMRs live in a hypoxic environment in underground colonies in East Africa and are highly tolerant of hypoxia. These unique characteristics of NMRs have attracted considerable interest from zoological and biomedical researchers. This review summarizes previous studies of the ecology, hypoxia tolerance, longevity/delayed aging, and cancer resistance of NMRs and discusses possible mechanisms contributing to their healthy aging. In addition, we discuss current issues and future perspectives to fully elucidate the mechanisms underlying delayed aging and resistance to age-related diseases in NMRs.

Beyond the Lab: What We Can Learn about Cancer from Wild and Domestic Animals

Cancer research has benefited immensely from the use of animal models. Several genetic tools accessible in rodent models have provided valuable insight into cellular and molecular mechanisms linked to cancer development or metastasis and various lines are available. However, at the same time, it is important to accompany these findings with those from alternative or non-model animals to offer new perspectives into the understanding of tumor development, prevention, and treatment. In this review, we first discuss animals characterized by little or no tumor development. Cancer incidence in small animals, such as the naked mole rat, blind mole rat and bats have been reported as almost negligible and tumor development may be inhibited by increased defense and repair mechanisms, altered cell cycle signaling and reduced rates of cell migration to avoid tumor microenvironments. On the other end of the size spectrum, large animals such as elephants and whales also appear to have low overall cancer rates, possibly due to gene replicates that are involved in apoptosis and therefore can inhibit uncontrolled cell cycle progression. While it is important to determine the mechanisms that lead to cancer protection in these animals, we can also take advantage of other animals that are highly susceptible to cancer, especially those which develop tumors similar to humans, such as carnivores or poultry. The use of such animals does not require the transplantation of malignant cancer cells or use of oncogenic substances as they spontaneously develop tumors of similar presentation and pathophysiology to those found in humans. For example, some tumor suppressor genes are highly conserved between humans and domestic species, and various tumors develop in similar ways or because of a common environment. These animals are therefore of great interest for broadening perspectives and techniques and for gathering information on the tumor mechanisms of certain types of cancer. Here we present a detailed review of alternative and/or non-model vertebrates, that can be used at different levels of cancer research to open new perspectives and fields of action.

Transcriptomics and Proteomics Analyses Reveal JAK Signaling and Inflammatory Phenotypes during Cellular Senescence in Blind Mole Rats: The Reflections of Superior Biology

Simple Summary

Blind mole rats (BMR) (Spalax, Nannospalax sp.) are extraordinary organisms with cancer resistance and a long lifespan for their size. Cellular senescence is a condition in which cells cease dividing irreversibly and secrete proinflammatory cytokines. To understand the mechanisms behind their superior traits, we utilized transcriptomics and proteomics tools in senescent BMR cells to compare them to similarly sized mice. The results revealed the alterations in Janus kinase (JAK) signaling and the cytokine-mediated pathway during the cellular senescence process in BMRs. These findings might reveal the novel mechanisms behind the unique biology of BMRs through cytokine-mediated adaptations.

Abstract

The blind mole rat (BMR), a long-living subterranean rodent, is an exceptional model for both aging and cancer research since they do not display age-related phenotypes or tumor formation. The Janus kinase–signal transducer and activator of transcription (JAK–STAT) signaling is a cytokine-stimulated pathway that has a crucial role in immune regulation, proliferation, and cytokine production. Therefore, the pathway has recently attracted interest in cellular senescence studies. Here, by using publicly available data, we report that JAK–STAT signaling was suppressed in the BMR in comparison to the mouse. Interestingly, our experimental results showed upregulated Jak1/2 expressions in BMR fibroblasts during the replicative senescence process. The transcriptomic analysis using publicly available data also demonstrated that various cytokines related to JAK–STAT signaling were upregulated in the late passage cells, while some other cytokines such as MMPs and SERPINs were downregulated, representing a possible balance of senescence-associated secretory phenotypes (SASPs) in the BMR. Finally, our proteomics data also confirmed cytokine-mediated signaling activation in senescent BMR fibroblasts. Together, our findings suggest the critical role of JAK–STAT and cytokine-mediated signaling pathways during cellular senescence, pointing to the possible contribution of divergent inflammatory factors to the superior resistance of aging and cancer in BMRs.

Resistance to chemical carcinogenesis induction via a dampened inflammatory response in naked mole-rats

Naked mole-rats (NMRs) have a very low spontaneous carcinogenesis rate, which has prompted studies on the responsible mechanisms to provide clues for human cancer prevention. However, it remains unknown whether and how NMR tissues respond to experimental carcinogenesis induction. Here, we show that NMRs exhibit extraordinary resistance against potent chemical carcinogenesis induction through a dampened inflammatory response. Although carcinogenic insults damaged skin cells of both NMRs and mice, NMR skin showed markedly lower immune cell infiltration. NMRs harbour loss-of-function mutations in RIPK3 and MLKL genes, which are essential for necroptosis, a type of necrotic cell death that activates strong inflammation. In mice, disruption of Ripk3 reduced immune cell infiltration and delayed carcinogenesis. Therefore, necroptosis deficiency may serve as a cancer resistance mechanism via attenuating the inflammatory response in NMRs. Our study sheds light on the importance of a dampened inflammatory response as a non-cell-autonomous cancer resistance mechanism in NMRs.

Naked mole rats are found to be resistant to cancer development through dampened inflammatory response due to genetically determined impaired necroptosis, with essential necroptosis genes RIPK3 and MLKL containing mutations causing premature stop codons.

Gut Microbiome Alterations and Hepatic Metabolic Flexibility in the Gansu Zokor, Eospalax cansus: Adaptation to Hypoxic Niches

The Gansu zokor (Eospalax cansus), a typical subterranean rodent endemic to the Chinese Loess Plateau, spends almost its whole life in its self-constructed underground burrows and has strong adaptability to ambient hypoxia. Energy adaptation is the key to supporting hypoxia tolerance, and recent studies have shown that the intestinal microbiota has an evident effect on energy metabolism. However, how the gut microbiome of Gansu zokor will change in response to hypoxia and the metabolic role played by the microbiome have not been reported. Thus, we exposed Gansu zokors to severe hypoxia of 6.5% of O2 (6 or 44 h) or moderate hypoxia of 10.5% of O2 (44 h or 4 weeks), and then analyzed 16S rRNA sequencing, metagenomic sequencing, metagenomic binning, liver carbohydrate metabolites, and the related molecular levels. Our results showed that the hypoxia altered the microbiota composition of Gansu zokor, and the relative contribution of Ileibacterium to carbohydrate metabolism became increased under hypoxia, such as glycolysis and fructose metabolism. Furthermore, Gansu zokor liver enhanced carbohydrate metabolism under the short-term (6 or 44 h) hypoxia but it was suppressed under the long-term (4 weeks) hypoxia. Interestingly, under all hypoxia conditions, Gansu zokor liver exhibited enhanced fructose-driven metabolism through increased expression of the GLUT5 fructose transporter, ketohexokinase (KHK), aldolase B (ALDOB), and aldolase C (ALDOC), as well as increased KHK enzymatic activity and fructose utilization. Overall, our results suggest that the altered gut microbiota mediates the carbohydrate metabolic pattern under hypoxia, possibly contributing to the hepatic metabolic flexibility in Gansu zokor, which leads to better adaptation to hypoxic environments.

The hypoxia adaptation of small mammals to plateau and underground burrow conditions

Oxygen is one of the important substances for the survival of most life systems on the earth, and plateau and underground burrow systems are two typical hypoxic environments. Small mammals living in hypoxic environments have evolved different adaptation strategies, which include increased oxygen delivery, metabolic regulation of physiological responses and other physiological responses that change tissue oxygen utilization. Multi-omics predictions have also shown that these animals have evolved different adaptations to extreme environments. In particular, vascular endothelial growth factor (VEGF) and erythropoietin (EPO), which have specific functions in the control of O2 delivery, have evolved adaptively in small mammals in hypoxic environments. Naked mole-rats and blind mole-rats are typical hypoxic model animals as they have some resistance to cancer. This review primarily summarizes the main living environment of hypoxia tolerant small mammals, as well as the changes of phenotype, physiochemical characteristics and gene expression mode of their long-term living in hypoxia environment.

The mTORC1/eIF4E/HIF-1α Pathway Mediates Glycolysis to Support Brain Hypoxia Resistance in the Gansu Zokor, Eospalax cansus

The Gansu zokor (Eospalax cansus) is a subterranean rodent species that is unique to China. These creatures inhabit underground burrows with a hypoxia environment. Metabolic energy patterns in subterranean rodents have become a recent focus of research; however, little is known about brain energy metabolism under conditions of hypoxia in this species. The mammalian (mechanistic) target of rapamycin complex 1 (mTORC1) coordinates eukaryotic cell growth and metabolism, and its downstream targets regulate hypoxia inducible factor-1α (HIF-1α) under conditions of hypoxia to induce glycolysis. In this study, we compared the metabolic characteristics of hypoxia-tolerant subterranean Gansu zokors under hypoxic conditions with those of hypoxia-intolerant Sprague-Dawley rats with a similar-sized surface area. We exposed Gansu zokors and rats to hypoxia I (44 h at 10.5% O₂) or hypoxia II (6 h at 6.5% O₂) and then measured the transcriptional levels of mTORC1 downstream targets, the transcriptional and translational levels of glycolysis-related genes, glucose and fructose levels in plasma and brain, and the activity of key glycolysis-associated enzymes. Under hypoxia, we found that hif-1α transcription was upregulated via the mTORC1/eIF4E pathway to drive glycolysis. Furthermore, Gansu zokor brain exhibited enhanced fructose-driven glycolysis under hypoxia through increased expression of the GLUT5 fructose transporter and ketohexokinase (KHK), in addition to increased KHK enzymatic activity, and utilization of fructose; these changes did not occur in rat. However, glucose-driven glycolysis was enhanced in both Gansu zokor and rat under hypoxia II of 6.5% O₂ for 6 h. Overall, our results indicate that on the basis of glucose as the main metabolic substrate, fructose is used to accelerate the supply of energy in Gansu zokor, which mirrors the metabolic responses to hypoxia in this species.

Distinct organization of adaptive immunity in the long-lived rodent Spalax galili

A balanced immune response is a cornerstone of healthy aging. Here, we uncover distinctive features of the long-lived blind mole-rat (Spalax spp.) adaptive immune system, relative to humans and mice. The T-cell repertoire remains diverse throughout the Spalax lifespan, suggesting a paucity of large long-lived clones of effector-memory T cells. Expression of master transcription factors of T-cell differentiation, as well as checkpoint and cytotoxicity genes, remains low as Spalax ages. The thymus shrinks as in mice and humans, while interleukin-7 and interleukin-7 receptor expression remains high, potentially reflecting the sustained homeostasis of naive T cells. With aging, immunoglobulin hypermutation level does not increase and the immunoglobulin-M repertoire remains diverse, suggesting shorter B-cell memory and sustained homeostasis of innate-like B cells. The Spalax adaptive immune system thus appears biased towards sustained functional and receptor diversity over specialized, long-lived effector-memory clones-a unique organizational strategy that potentially underlies this animal's extraordinary longevity and healthy aging.

Transcriptome analysis of the response provided by Lasiopodomys mandarinus to severe hypoxia includes enhancing DNA repair and damage prevention

Background

Severe hypoxia induces a series of stress responses in mammals; however, subterranean rodents have evolved several adaptation mechanisms of energy metabolisms and O₂ utilization for hypoxia. Mammalian brains show extreme aerobic metabolism. Following hypoxia exposure, mammals usually experience irreversible brain damage and can even develop serious diseases, such as hypoxic ischemic encephalopathy and brain edema. To investigate mechanisms underlying the responses of subterranean rodents to severe hypoxia, we performed a cross-species brain transcriptomic analysis using RNA sequencing and identified differentially expressed genes (DEGs) between the subterranean rodent Lasiopodomys mandarinus and its closely related aboveground species L. brandtii under severe hypoxia (5.0% O₂, 6 h) and normoxia (20.9% O₂, 6 h).

Results

We obtained 361 million clean reads, including 69,611 unigenes in L. mandarinus and 69,360 in L. brandtii. We identified 359 and 515 DEGs by comparing the hypoxic and normoxia groups of L. mandarinus and L. brandtii, respectively. Gene Ontology (GO) analysis showed that upregulated DEGs in both species displayed similar terms in response to severe hypoxia; the main difference is that GO terms of L. brandtii were enriched in the immune system. However, in the downregulated DEGs, GO terms of L. mandarinus were enriched in cell proliferation and protein transport and those of L. brandtii were enriched in nuclease and hydrolase activities, particularly in terms of developmental functions. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that upregulated DEGs in L. mandarinus were associated with DNA repair and damage prevention as well as angiogenesis and metastasis inhibition, whereas downregulated DEGs were associated with neuronal synaptic transmission and tumor-associated metabolic pathways. In L. brandtii, upregulated KEGG pathways were enriched in the immune, endocrine, and cardiovascular systems and particularly in cancer-related pathways, whereas downregulated DEGs were associated with environmental information processing and misregulation in cancers.

Conclusions

L. mandarinus has evolved hypoxia adaptation by enhancing DNA repair, damage prevention, and augmenting sensing, whereas L. brandtii showed a higher risk of tumorigenesis and promoted innate immunity toward severe hypoxia. These results reveal the hypoxic mechanisms of L. mandarinus to severe hypoxia, which may provide research clues for hypoxic diseases.

Downregulation of the inflammatory network in senescent fibroblasts and aging tissues of the long-lived and cancer-resistant subterranean wild rodent, Spalax

The blind mole rat (Spalax) is a wild, long‐lived rodent that has evolved mechanisms to tolerate hypoxia and resist cancer. Previously, we demonstrated high DNA repair capacity and low DNA damage in Spalax fibroblasts following genotoxic stress compared with rats. Since the acquisition of senescence‐associated secretory phenotype (SASP) is a consequence of persistent DNA damage, we investigated whether cellular senescence in Spalax is accompanied by an inflammatory response. Spalax fibroblasts undergo replicative senescence (RS) and etoposide‐induced senescence (EIS), evidenced by an increased activity of senescence‐associated beta‐galactosidase (SA‐β‐Gal), growth arrest, and overexpression of p21, p16, and p53 mRNAs. Yet, unlike mouse and human fibroblasts, RS and EIS Spalax cells showed undetectable or decreased expression of the well‐known SASP factors: interleukin‐6 (IL6), IL8, IL1α, growth‐related oncogene alpha (GROα), SerpinB2, and intercellular adhesion molecule (ICAM‐1). Apparently, due to the efficient DNA repair in Spalax, senescent cells did not accumulate the DNA damage necessary for SASP activation. Conversely, Spalax can maintain DNA integrity during replicative or moderate genotoxic stress and limit pro‐inflammatory secretion. However, exposure to the conditioned medium of breast cancer cells MDA‐MB‐231 resulted in an increase in DNA damage, activation of the nuclear factor κB (NF‐κB) through nuclear translocation, and expression of inflammatory mediators in RS Spalax cells. Evaluation of SASP in aging Spalax brain and intestine confirmed downregulation of inflammatory‐related genes. These findings suggest a natural mechanism for alleviating the inflammatory response during cellular senescence and aging in Spalax, which can prevent age‐related chronic inflammation supporting healthy aging and longevity.

Post-Translational Deimination of Immunological and Metabolic Protein Markers in Plasma and Extracellular Vesicles of Naked Mole-Rat (Heterocephalus glaber)

Naked mole-rats are long-lived animals that show unusual resistance to hypoxia, cancer and ageing. Protein deimination is an irreversible post-translational modification caused by the peptidylarginine deiminase (PAD) family of enzymes, which convert arginine into citrulline in target proteins. Protein deimination can cause structural and functional protein changes, facilitating protein moonlighting, but also leading to neo-epitope generation and effects on gene regulation. Furthermore, PADs have been found to regulate cellular release of extracellular vesicles (EVs), which are lipid-vesicles released from cells as part of cellular communication. EVs carry protein and genetic cargo and are indicative biomarkers that can be isolated from most body fluids. This study was aimed at profiling deiminated proteins in plasma and EVs of naked mole-rat. Key immune and metabolic proteins were identified to be post-translationally deiminated, with 65 proteins specific for plasma, while 42 proteins were identified to be deiminated in EVs only. Using protein-protein interaction network analysis, deiminated plasma proteins were found to belong to KEEG (Kyoto Encyclopedia of Genes and Genomes) pathways of immunity, infection, cholesterol and drug metabolism, while deiminated proteins in EVs were also linked to KEEG pathways of HIF-1 signalling and glycolysis. The mole-rat EV profiles showed a poly-dispersed population of 50-300 nm, similar to observations of human plasma. Furthermore, the EVs were assessed for three key microRNAs involved in cancer, inflammation and hypoxia. The identification of post-translational deimination of critical immunological and metabolic markers contributes to the current understanding of protein moonlighting functions, via post-translational changes, in the longevity and cancer resistance of naked mole-rats.