Damage-Free Shortening of Telomeres Is a Potential Strategy Supporting Blind Mole-Rat Longevity

Telomere shortening or loss of shelterin components activates DNA damage response (DDR) pathways, leading to a replicative senescence that is usually coupled with a senescence-associated secretory phenotype (SASP). Recent studies suggested that telomere aberration that activates DDR may occur, irrespective of telomere length or loss of shelterin complex. The blind mole-rat (Spalax) is a subterranean rodent with exceptional longevity, and its cells demonstrate an uncoupling of senescence and SASP inflammatory components. Herein, we evaluated Spalax relative telomere length, telomerase activity, and shelterin expression, along with telomere-associated DNA damage foci (TAFs) levels with cell passage. We show that telomeres shorten in Spalax fibroblasts similar to the process in rats, and that the telomerase activity is lower. Moreover, we found lower DNA damage foci at the telomeres and a decline in the mRNA expression of two shelterin proteins, known as ATM/ATR repressors. Although additional studies are required for understanding the underling mechanism, our present results imply that Spalax genome protection strategies include effective telomere maintenance, preventing early cellular senescence induced by persistent DDR, thereby contributing to its longevity and healthy aging.

Cancer-free aging: Insights from Spalax ehrenbergi superspecies

Cancer and ageing can be regarded as two different manifestations of the same underlying process-accumulation of cellular damage-and therefore both are closely linked. Nowadays, the ageing of populations worldwide is leading to an unprecedented increase in cancer cases and fatalities, and therefore the understanding of links between cancer and ageing is more important than ever. Spalax is considered an excellent model for ageing and, additionally, for cancer research, due to not show clear age-related phenotypic changes and not develop spontaneous tumours, despite its relatively long lifespan (∼20 years in captivity). Thereby, the purpose of this review is to summarize the recent knowledge on Spalax, with a particular emphasis on the molecular mechanisms associated with their longevity and cancer resistance.

They live in the land down under: thyroid function and basal metabolic rate in the Blind Mole Rat, Spalax

The Israeli blind subterranean mole rat (Spalax ehrenbergi superspecies) lives in sealed underground burrows under extreme, hypoxic conditions. The four Israeli Spalax allospecies have adapted to different climates, the cool-humid (Spalax galili, 2 n = 52 chromosomes), semihumid (S. golani, 2 n = 54) north regions, warm-humid (S. carmeli, 2 n = 58) central region and the warm-dry S. judaei, 2 n = 60) southern regions. A dramatic interspecies decline in basal metabolic rate (BMR) from north to south, even after years of captivity, indicates a genetic basis for this BMR trait. We examined the possibility that the genetically-conditioned interspecies BMR difference was expressed via circulating thyroid hormone. An unexpected north to south increase in serum free thyroxine (FT4) and total 3, 5, 3'-triiodo-L-thyronine (T3) (p < 0.02) correlated negatively with previously published BMR measurements. The increases in serum FT4 and T3 were symmetrical, so that the T3:FT4 ratio - interpretable as an index of conversion of T4 to T3 in nonthyroidal tissues - did not support relative decrease in production of T3 as a contributor to BMR. Increased north-to-south serum FT4 and T3 levels also correlated negatively with hemoglobin/hematocrit. North-to-south adaptations in spalacids include decreased BMR and hematocrit/hemoglobin in the face of increasing thyroid hormone levels, arguing for independent control of hormone secretion and BMR/hematocrit/hemoglobin. But the significant inverse relationship between thyroid hormone levels and BMR/hematocrit/hemoglobin is also consistent with a degree of cellular resistance to thyroid hormone action that protects against hormone-induced increase in oxygen consumption in a hostile, hypoxic environment.

Adaptation of pelage color and pigment variations in Israeli subterranean blind mole rats, Spalax ehrenbergi [corrected]

Background

Concealing coloration in rodents is well established. However, only a few studies examined how soil color, pelage color, hair-melanin content, and genetics (i.e., the causal chain) synergize to configure it. This study investigates the causal chain of dorsal coloration in Israeli subterranean blind mole rats, Spalax ehrenbergi.

Methods

We examined pelage coloration of 128 adult animals from 11 populations belonging to four species of Spalax ehrenbergi superspecies (Spalax galili, Spalax golani, Spalax carmeli, and Spalax judaei) and the corresponding coloration of soil samples from the collection sites using a digital colorimeter. Additionally, we quantified hair-melanin contents of 67 animals using HPLC and sequenced the MC1R gene in 68 individuals from all four mole rat species.

Results

Due to high variability of soil colors, the correlation between soil and pelage color coordinates was weak and significant only between soil hue and pelage lightness. Multiple stepwise forward regression revealed that soil lightness was significantly associated with all pelage color variables. Pelage color lightness among the four species increased with the higher southward aridity in accordance to Gloger's rule (darker in humid habitats and lighter in arid habitats). Darker and lighter pelage colors are associated with darker basalt and terra rossa, and lighter rendzina soils, respectively. Despite soil lightness varying significantly, pelage lightness and eumelanin converged among populations living in similar soil types. Partial sequencing of the MC1R gene identified three allelic variants, two of which were predominant in northern species (S. galili and S. golani), and the third was exclusive to southern species (S. carmeli and S. judaei), which might have caused the differences found in pheomelanin/eumelanin ratio.

Conclusion/Significance

Darker dorsal pelage in darker basalt and terra rossa soils in the north and lighter pelage in rendzina and loess soils in the south reflect the combined results of crypsis and thermoregulatory function following Gloger's rule.

Methionine sulfoxide reductases and methionine sulfoxide in the subterranean mole rat (Spalax): characterization of expression under various oxygen conditions

The blind subterranean mole rat (Spalax ehrenbergi) exhibits a relatively long life span, which is attributed to an efficient antioxidant defense affording protection against accumulation of oxidative modifications of proteins. Methionine residues can be oxidized to methionine sulfoxide (MetO) and then enzymatically reduced by the methionine sulfoxide reductase (Msr) system. In the current study we have isolated the cDNA sequences of the Spalax Msr genes as well as 23 additional selenoproteins and monitored the activities of Msr enzymes in liver and brain of rat (Rattus norvegicus), Spalax galili, and Spalax judaei under normoxia, hypoxia, and hyperoxia. Under normoxia, the Msr activity was lower in S. galili in comparison to S. judaei and R. norvegicus especially in the brain. The pattern of Msr activity of the three species was similar throughout the tested conditions. However, exposure of the animals to hypoxia caused a significant enhancement of Msr activity, especially in S. galili. Hyperoxic exposure showed a highly significant induction of Msr activity compared with normoxic conditions for R. norvegicus and S. galili brain. It was concluded that among all species examined, S. galili appears to be more responsive to oxygen tension changes and that the Msr system is upregulated mainly by severe hypoxia.

Tissue-specific activity of the blind mole rat and the two nucleotide-mutated mouse alphaB-crystallin promoter in transgenic mice

The alphaB-crystallin and HspB2 genes are located approximately 0.9 kb apart in a head-to-head arrangement in mammals. Previous experiments have shown that a truncated -668/+45 alphaB-crystallin enhancer/promoter fragment from blind mole rats (Spalax ehrenbergi), which have nonfunctional lenses, lacks lens activity and has enhanced muscle activity in transgenic mice. Here we show that the full-length mole rat alphaB-crystallin intergenic region behaves similarly in transgenic mice. A two-nucleotide mutation ((-273)CA-->G) in the mouse alphaB-crystallin enhancer/promoter fragment mimicking the wild-type mole rat sequence functionally converted the mouse promoter fragment to that of the wild-type mole rat promoter when tested in transgenic mice. The reciprocal mutation in the mole rat promoter fragment ((-272)G-->CA) did not affect its activity. Oligonucleotides from the wild-type mouse and mole rat alphaB-crystallin promoter region under study formed distinct complexes with nuclear proteins from cultured cells. The mouse mutant sequence lost binding ability, whereas the mutated mole rat sequence gained the ability to form a complex similar in size to that of the wild-type mouse oligonucleotide. Our data support the idea that blind mole rats' alphaB-crystallin promoter activity was modified during the evolution of subterranean life and shows that tissue-specific promoter activity can be modulated by changing as few as two apparently neutral nucleotides in the mouse alphaB-crystallin enhancer region, implying the importance of the context of regulatory sequences for promoter activity.

P53 in blind subterranean mole rats – loss-of-function versus gain-of-function activities on newly cloned Spalax target genes

A tumor suppressor gene, p53, controls cellular responses to a variety of stress conditions, including DNA damage and hypoxia, leading to growth arrest and/or apoptosis. Recently, we demonstrated that in blind subterranean mole rats, Spalax, a model organism for hypoxia tolerance, the p53 DNA-binding domain contains a specific Arg174Lys amino acid substitution. This substitution reduces the p53 effect on the transcription of apoptosis genes (apaf1, puma, pten and noxa) and enhances it on human cell cycle arrest and p53 stabilization/homeostasis genes (mdm2, pten, p21 and cycG). In the current study, we cloned Spalax apaf1 promoter and mdm2 intronic regions containing consensus p53-responsive elements. We compared the Spalax-responsive elements to those of human, mouse and rat and investigated the transcriptional activity of Spalax and human Arg174Lys-mutated p53 on target genes of both species. Spalax and human-mutated p53 lost induction of apaf1 transcription, and increased induction of mdm2 transcription. We conclude that Spalax evolved hypoxia-adaptive mechanisms, analogous to the alterations acquired by cancer cells during tumor development, with a bias against apoptosis while favoring cell arrest and DNA repair.

Differential expression profiling of the blind subterranean mole rat Spalax ehrenbergi superspecies: bioprospecting for hypoxia tolerance

The blind subterranean mole rat of the Spalax ehrenbergi superspecies, living underground and exposed to fluctuating oxygen and carbon dioxide levels, is an excellent model of hypoxic tolerance. Unique structural and functional adaptations of the cardiovascular and respiratory systems allow these underground mammals to survive at severely reduced oxygen tension. Elucidation of the natural variation and evolutionary changes under hypoxia within this superspecies may have biomedical applications in ischemic syndromes and cancer. In this study, we have compared expression profiles of muscle tissue at normoxic (21%) and hypoxic (3%) levels of oxygen concentration between two allospecies of the S. ehrenbergi superspecies exhibiting differential hypoxia tolerance in accordance with their ecological regimes. Profiling was performed by cross-species hybridization using a mouse cDNA array containing 15,000 gene elements. Results uncover species-specific responses to hypoxic stress among numerous genes involved in angiogenesis, apoptosis, and oxidative stress management. Among the most striking results are differential expressions of cardiac ankyrin repeat protein ( Carp), activating transcription factor 3 ( Atf3), LIM and cysteine-rich domains 1 ( Lmcd1), cysteine and glycine-rich protein 2 ( Csrp2), and ras homolog gene family, member B ( RhoB). These findings support the hypothesis that allospecies of the S. ehrenbergi superspecies are variably adapted to fluctuating oxygen tension. Differences may involve specific metabolic pathways and functional adaptations at the structural and molecular levels.

Adaptive evolution of heparanase in hypoxia-tolerant Spalax: gene cloning and identification of a unique splice variant

Heparan sulfate (HS) side chains of HS proteoglycans bind to and assemble extracellular matrix proteins and play important roles in cell-cell and cell-extracellular matrix interactions. HS chains bind a multitude of bioactive molecules and thereby function in the control of multiple normal and pathological processes. Enzymatic degradation of HS by heparanase, a mammalian endoglycosidase, affects the integrity and functional state of tissues and is involved in, among other processes, inflammation, angiogenesis, and cancer metastasis. Here, we report the cloning of heparanase from four Israeli species of the blind subterranean mole rat (Spalax ehrenbergi superspecies), 85% homologous to the human enzyme. Unlike its limited expression in human tissues, heparanase is highly expressed in diverse Spalax tissues. Moreover, we have identified a unique splice variant of the Spalax enzyme lacking 16 aa encoded by exon 7. This deletion resulted in a major defect in trafficking and processing of the heparanase protein, leading to a loss of its enzymatic activity. Interspecies variation was noted in the sequence and in the expression of the splice variant of the heparanase gene in blind mole rats living under different ecogeographical stresses, indicating a possible role in adaptation to stress in Spalax evolution.