Naked mole-rat TMEM2 lacks physiological hyaluronan-degrading activity.

Mouse transmembrane protein 2 (mTMEM2) has been identified as a hyaluronidase, which has extracellularly G8 and GG domains and PbH1 repeats; however, our previously study showed that human TMEM2 (hTMEM2) is not a catalytic hyaluronidase due to the absence of the critical amino acid residues (His248/Ala303) in the GG domain. Naked mole-rats (NMRs) accumulate abundant high-molecular weight hyaluronan (HA) in their tissues, suggesting decreased HA degradation. Therefore, we aimed to evaluate the HA-degrading activity of NMR TMEM2 (nmrTMEM2) and compare it with those of mTMEM2 and hTMEM2. The amino acid residues of nmrTMEM2 (Asn247/Val302) are similar to Asn248/Phe303 of hTMEM2, and nmrTMEM2-expressing HEK293T cells showed negligible activity. We confirmed the significance of these amino acid residues using an inactive chimeric TMEM2 with the human GG domain, which acquired catalytic activity when Asn248/Phe303 was substituted with His248/Ala303. Semi-quantitative comparison of the activities of the membrane-fractions derived from m/h/nmrTMEM2-expressing HEK293T cells revealed that at least 20- and 14-fold higher amounts of nmr/hTMEM2 were required to degrade HA to the same extent as by mTMEM2. Thus, unlike mTMEM2, nmrTMEM2 is not a physiological hyaluronidase. The inability of nmrTMEM2 to degrade HA might partially account for the high-molecular-weight HA accumulation in NMR tissues.

Naked mole-rats resist the accumulation of hypoxia-induced oxidative damage.

Naked mole-rats are among the few mammals with the ability to endure severe hypoxia. These unique rodents use metabolic rate depression along with various molecular mechanisms to successfully overcome the challenges of oxygen-limitation, which they experience in their underground borrows. While studies have reported that naked mole-rats exhibit inherently higher levels of oxidative damage across their lifespan as compared to mice, it has yet to be determined whether naked mole-rats are vulnerable to oxidative damage during periods of low oxygen exposure. To investigate this phenomenon, we examined cellular oxidative damage markers of macromolecules: DNA oxidation determined as 8-oxo-2'deoxyguanosine (8-OHdG8) levels, RNA oxidation as 8-hydroxyguanosine (8-OHG), protein carbonylation, and lipid peroxidation in normoxic (control), acute (4 h at 7% O2), and chronic (24 h at 7% O2) hypoxia-exposed naked mole-rats. Brain appears to be the most resilient to hypoxia-induced oxidative damage, with both brain and heart exhibiting enhanced antioxidant capacity during hypoxia. Levels of DNA and RNA oxidation were minimally changed in all tissues and no changes were observed in protein carbonylation. Most tissues experienced lipid peroxidation, with liver displaying a 9.6-fold increase during hypoxia. Concomitantly, levels of DNA damage repair proteins were dynamically regulated in a tissue-specific manner, with white adipose displaying a significant reduction during hypoxia. Our findings show that naked mole-rats largely avoid hypoxia-induced oxidative damage, possibly due to their high tolerance to redox stress, or to reduced oxidative requirements made possible during their hypometabolic response when oxygen supply is limited.

Acute Hypoxia Alters Extracellular Vesicle Signatures and the Brain Citrullinome of Naked Mole-Rats (Heterocephalus glaber).

Peptidylarginine deiminases (PADs) and extracellular vesicles (EVs) may be indicative biomarkers of physiological and pathological status and adaptive responses, including to diseases and disorders of the central nervous system (CNS) and related to hypoxia. While these markers have been studied in hypoxia-intolerant mammals, in vivo investigations in hypoxia-tolerant species are lacking. Naked mole-rats (NMR) are among the most hypoxia-tolerant mammals and are thus a good model organism for understanding natural and beneficial adaptations to hypoxia. Thus, we aimed to reveal CNS related roles for PADs in hypoxia tolerance and identify whether circulating EV signatures may reveal a fingerprint for adaptive whole-body hypoxia responses in this species. We found that following in vivo acute hypoxia, NMR: (1) plasma-EVs were remodelled, (2) whole proteome EV cargo contained more protein hits (including citrullinated proteins) and a higher number of associated KEGG pathways relating to the total proteome of plasma-EVs Also, (3) brains had a trend for elevation in PAD1, PAD3 and PAD6 protein expression, while PAD2 and PAD4 were reduced, while (4) the brain citrullinome had a considerable increase in deiminated protein hits with hypoxia (1222 vs. 852 hits in normoxia). Our findings indicate that circulating EV signatures are modified and proteomic content is reduced in hypoxic conditions in naked mole-rats, including the circulating EV citrullinome, while the brain citrullinome is elevated and modulated in response to hypoxia. This was further reflected in elevation of some PADs in the brain tissue following acute hypoxia treatment. These findings indicate a possible selective role for PAD-isozymes in hypoxia response and tolerance.

Hypoxic naked mole-rat brains use microRNA to coordinate hypometabolic fuels and neuroprotective defenses.

Naked mole-rats are among the mammalian champions of hypoxia tolerance. They evolved adaptations centered around reducing metabolic rate to overcome the challenges experienced in their underground burrows. In this study, we used next-generation sequencing to investigate one of the factors likely supporting hypoxia tolerance in naked mole-rat brains, posttranscriptional microRNAs (miRNAs). Of the 212 conserved miRNAs identified using small RNA sequencing, 18 displayed significant differential expression during hypoxia. Bioinformatic enrichment revealed that hypoxia-mediated miRNAs were suppressing energy expensive processes including de novo protein translation and cellular proliferation. This suppression occurred alongside the activation of neuroprotective and neuroinflammatory pathways, and the induction of central signal transduction pathways including HIF-1α and NFκB via miR-335, miR-101, and miR-155. MiRNAs also coordinated anaerobic glycolytic fuel sources, where hypoxia-upregulated miR-365 likely suppressed protein levels of ketohexokinase, the enzyme responsible for catalyzing the first committed step of fructose catabolism. This was further supported by a hypoxia-mediated reduction in glucose transporter 5 proteins that import fructose into the cell. Yet, messenger RNA and protein levels of lactate dehydrogenase, which converts pyruvate to lactate in the absence of oxygen, were elevated during hypoxia. Together, this demonstrated the induction of anaerobic glycolysis despite a lack of reliance on fructose as the primary fuel source, suggesting that hypoxic brains are metabolically different than anoxic naked mole-rat brains that were previously found to shift to fructose-based glycolysis. Our findings contribute to the growing body of oxygen-responsive miRNAs "OxymiRs" that facilitate natural miRNA-mediated mechanisms for successful hypoxic exposures.

Bone remodeling in the longest living rodent, the naked mole-rat: Interelement variation and the effects of reproduction.

The pattern of bone remodeling of one of the most peculiar mammals in the world, the naked mole-rat (NMR), was assessed. NMRs are known for their long lifespans among rodents and for having low metabolic rates. We assessed long-term in vivo bone labeling of subordinate individuals, as well as the patterns of bone resorption and bone remodeling in a large sample including reproductive and non-reproductive individuals (n = 70). Over 268 undecalcified thin cross-sections from the midshaft of humerus, ulna, femur and tibia were analyzed with confocal fluorescence and polarized light microscopy. Fluorochrome analysis revealed low osteogenesis, scarce bone resorption and infrequent formation of secondary osteons (Haversian systems) (i.e., slow bone turnover), thus most likely reflecting the low metabolic rates of this species. Secondary osteons occurred regardless of reproductive status. However, considerable differences in the degree of bone remodeling were found between breeders and non-breeders. Pre-reproductive stages (subordinates) exhibited quite stable skeletal homeostasis and bone structure, although the attainment of sexual maturity and beginning of reproductive cycles in female breeders triggered a series of anabolic and catabolic processes that up-regulate bone turnover, most likely associated with the increased metabolic rates of reproduction. Furthermore, bone remodeling was more frequently found in stylopodial elements compared to zeugopodial elements. Despite the limited bone remodeling observed in NMRs, the variation in the pattern of skeletal homeostasis (interelement variation) reported here represents an important aspect to understand the skeletal dynamics of a small mammal with low metabolic rates. Given the relevance of the remodeling process among mammals, this study also permitted the comparison of such process with the well-documented histomorphology of extinct therapsids (i.e., mammalian precursors), thus evidencing that bone remodeling and its endocortical compartmentalization represent ancestral features among the lineage that gave rise to mammals. It is concluded that other factors associated with development (and not uniquely related to biomechanical loading) can also have an important role in the development of bone remodeling.

Long bone histomorphogenesis of the naked mole-rat: Histodiversity and intraspecific variation.

Lacking fur, living in eusocial colonies and having the longest lifespan of any rodent, makes naked mole-rats (NMRs) rather peculiar mammals. Although they exhibit a high degree of polymorphism, skeletal plasticity and are considered a novel model to assess the effects of delayed puberty on the skeletal system, scarce information on their morphogenesis exists. Here, we examined a large ontogenetic sample (n = 76) of subordinate individuals to assess the pattern of bone growth and bone microstructure of fore- and hindlimb bones by using histomorphological techniques. Over 290 undecalcified thin cross-sections from the midshaft of the humerus, ulna, femur, and tibia from pups, juveniles and adults were analyzed with polarized light microscopy. Similar to other fossorial mammals, NMRs exhibited a systematic cortical thickening of their long bones, which clearly indicates a conserved functional adaptation to withstand the mechanical strains imposed during digging, regardless of their chisel-tooth predominance. We describe a high histodiversity of bone matrices and the formation of secondary osteons in NMRs. The bones of pups are extremely thin-walled and grow by periosteal bone formation coupled with considerable expansion of the medullary cavity, a process probably tightly regulated and adapted to optimize the amount of minerals destined for skeletal development, to thus allow the female breeder to produce a higher number of pups, as well as several litters. Subsequent cortical thickening in juveniles involves high amounts of endosteal bone apposition, which contrasts with the bone modeling of other mammals where a periosteal predominance exists. Adults have bone matrices predominantly consisting of parallel-fibered bone and lamellar bone, which indicate intermediate to slow rates of osteogenesis, as well as the development of poorly vascularized lamellar-zonal tissues separated by lines of arrested growth (LAGs) and annuli. These features reflect the low metabolism, low body temperature and slow growth rates reported for this species, as well as indicate a cyclical pattern of osteogenesis. The presence of LAGs in captive individuals was striking and indicates that postnatal osteogenesis and its consequent cortical stratification most likely represents a plesiomorphic thermometabolic strategy among endotherms which has been suggested to be regulated by endogenous rhythms. However, the generalized presence of LAGs in this and other subterranean taxa in the wild, as well as recent investigations on variability of environmental conditions in burrow systems, supports the hypothesis that underground environments experience seasonal fluctuations that may influence the postnatal osteogenesis of animals by limiting the extension of burrow systems during the unfavorable dry seasons and therefore the finding of food resources. Additionally, the intraspecific variation found in the formation of bone tissue matrices and vascularization suggested a high degree of developmental plasticity in NMRs, which may help explaining the polymorphism reported for this species. The results obtained here represent a valuable contribution to understanding the relationship of several aspects involved in the morphogenesis of the skeletal system of a mammal with extraordinary adaptations.

MicroRNA-mediated inhibition of AMPK coordinates tissue-specific downregulation of skeletal muscle metabolism in hypoxic naked mole-rats.

Naked mole-rats reduce their metabolic requirements to tolerate severe hypoxia. However, the regulatory mechanisms that underpin this metabolic suppression have yet to be elucidated. 5'-AMP-activated protein kinase (AMPK) is the cellular 'master' energy effector and we hypothesized that alterations in the AMPK pathway contribute to metabolic reorganization in hypoxic naked mole-rat skeletal muscle. To test this hypothesis, we exposed naked mole-rats to 4 h of normoxia (21% O2) or severe hypoxia (3% O2), while indirectly measuring whole-animal metabolic rate and fuel preference. We then isolated skeletal muscle and assessed protein expression and post-translational modification of AMPK, and downstream changes in key glucose and fatty acid metabolic proteins mediated by AMPK, including acetyl-CoA carboxylase (ACC1), glycogen synthase (GS) and glucose transporters (GLUTs) 1 and 4. We found that in hypoxic naked mole-rats (1) metabolic rate decreased ∼80% and fuel use switched to carbohydrates, and that (2) levels of activated phosphorylated AMPK and GS, and GLUT4 expression were downregulated in skeletal muscle, while ACC1 was unchanged. To explore the regulatory mechanism underlying this hypometabolic state, we used RT-qPCR to examine 55 AMPK-associated microRNAs (miRNAs), which are short non-coding RNA post-transcriptional silencers. We identified changes in 10 miRNAs (three upregulated and seven downregulated) implicated in AMPK downregulation. Our results suggest that miRNAs and post-translational mechanisms coordinately reduce AMPK activity and downregulate metabolism in naked mole-rat skeletal muscle during severe hypoxia. This novel mechanism may support tissue-specific prioritization of energy for more essential organs in hypoxia.

Managed Care of Naked Mole-Rats.

Naked mole-rats are a burgeoning model species in the field of biomedical research and are also housed at many zoos throughout the world. These mammals possess many traits that have a large impact on the way that they are kept in captivity such as their eusociality, thermolability and lack of need for drinking water. This chapter outlines the captive care and unusual housing needs of these animals. Providing information and examples from our own experiences while working with naked mole-rats for many decades. While this chapter serves as a good framework for the captive care of this mammal species, it is in no way all-encompassing but simply reflects the way in which we have managed over many years to successfully sustain our colony of thousands of animals.

The Idiosyncratic Physiological Traits of the Naked Mole-Rat; a Resilient Animal Model of Aging, Longevity, and Healthspan.

The subterranean-dwelling naked mole-rat (Heterocephalus glaber) is an extremophilic rodent, able to thrive in the harsh underground conditions of sub-Saharan Northeast Africa. This pelage-free mammal exhibits numerous unusual ecophysiological features including pronounced tolerance of thermolability, hypoxia, hypercapnia and noxious substances. As a mammal, the naked mole-rat provides a proof-of-concept that age-related changes in physiology are avoidable. At ages far beyond their expected lifespans given both their body size and/or the timing of early developmental milestones, naked mole-rats fail to exhibit meaningful changes in physiological health or demographic mortality. Lack of physiological deterioration with age is also evident in lean and fat mass, bone quality, and reproductive capacity. Rather, regardless of age, under basal conditions naked mole-rats appear to "idle on low" with their "shields up" as is manifested by low body temperature, metabolic rate, cardiac output and kidney concentrating ability, enabling better protection of organs and cellular function. When needed, they can nevertheless ramp up these functions, increasing cardiac output and metabolism 2-5 fold. Here we review many unusual aspects of their physiology and examine how these attributes facilitate both tolerance of the diverse suite of hostile conditions encountered in their natural milieu as well as contribute to their extraordinary longevity and resistance to common, age-related chronic diseases.

Differential protein phosphorylation is responsible for hypoxia-induced regulation of the Akt/mTOR pathway in naked mole rats.

Naked mole rats (NMRs, Heterocephalus glaber) are among the most hypoxia-tolerant mammals known. They can reduce their metabolic rate (>85%) under severe hypoxia, remain moderately active and recover with no obvious signs of damage. Hence, NMRs are an excellent model for studying mammalian hypoxia tolerance. The current study characterized the involvement of posttranslational modifications in regulating the Akt/mTOR pathway that regulates protein synthesis, and the responses of key ribosomal proteins in order to assess tissue-specific responses to 4 h exposure to 7% O2 (compared to controls at 21% O2). Results showed a tissue-specific regulation of the Akt/mTOR pathway via differential phosphorylation. Relative amounts of p-TSC(S939) in brain and of p-TSC(S939), p-Akt(473) and p-PTEN(S380) in liver increased under hypoxia, whereas levels of IGF1R(Y1135/1136) in liver decreased. In skeletal muscle, levels of p-Akt(S473) and p-PTEN(S380) decreased during hypoxia, whereas lungs showed an increase in p-mTOR(S2884) content but a decrease in p-RPS6(S235-236) under the same conditions. Analysis of the phosphorylation states of ribosomal proteins revealed increases in p-4E-BP1(T37/46) content in brain and lungs under hypoxia, as well as a rise in total 4E-BP1 protein level in liver. Phosphorylated eIF-4B(S422) content also increased in liver while levels of p-eIF-2α(S51), and eIF-4E(S209) decreased during hypoxia in liver. Overall, hypoxia altered the Akt/mTOR pathway, which correlated with a general decrease in activity of the ribosomal protein biosynthesis machinery in muscle, lung, and brain of NMRs. However, the increase in eIF-4B in liver suggests the potential promotion of cap-independent mRNA translation mechanism operating under hypoxic stress.

ANESTHETIC EFFECT OF DEXMEDETOMIDINE-KETAMINEMIDAZOLAM COMBINATION ADMINISTERED INTRAMUSCULARLY TO ZOO-HOUSED NAKED MOLE-RATS (HETEROCEPHALUS GLABER).

In this study, adult intact male and female (n = 10) naked mole-rats (Heterocephalus glaber) were anesthetized using a combination of dexmedetomidine (0.06 mg/kg intramuscularly [IM]), ketamine (20 mg/kg IM), and midazolam (1.0 mg/kg IM). Atipamezole (1.0 mg/kg IM) and flumazenil (0.1 mg/kg IM) were administered 40 min after induction. Induction and recovery times were monitored and recorded. Vital parameters, including heart rate, respiratory rate, and SpO2, and reflexes were monitored every 5 min during the anesthetic period. Anesthetic induction was smooth and rapid. All monitored reflexes were lost within a median time of 60 sec (interquartile range, 15 sec). Heart rate and respiratory rate were significantly decreased from baseline, whereas there was no difference in SpO2 over the anesthetic period. The mean time to recovery was 15 ± 7 min (mean ± SD). One animal was found dead 40 min after apparent recovery, which is suspected to be an anesthetic-related death. Based on these findings, dexmedetomidine-ketamine-midazolam anesthesia is an effective anesthetic protocol in naked mole rats that provides a consistent anesthetic plane but should be used with caution in animals with underlying conditions.

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.

Renal Pathology in a Nontraditional Aging Model: The Naked Mole-Rat (Heterocephalus glaber).

The naked mole-rat (NMR; Heterocephalus glaber) is growing in popularity as a model for aging research due to its extreme longevity (up to 30 years), highly adapted physiology, and resistance to cancer, particularly when compared with traditional aging models such as laboratory mice and rats. Despite the NMR's seemingly lengthy health span, several age-related lesions have been documented. During a 15-year retrospective evaluation of a zoo-housed population, histologic changes in the kidneys were reported in 127 of 138 (92%) adult NMRs. Of these, renal tubular mineralization was very common (115 of 127; 90.6%) and found in NMRs without concurrent renal lesions (36 of 127; 28.3%). Many of the other described lesions were considered progressive stages of a single process, generally referred to as chronic nephritis or nephropathy, and diagnosed in 73 of 127 (57.5%), while end-stage renal disease was reported in only 12 (9.4%) NMRs. Renal lesions of these NMRs were comparable to disease entities reported in laboratory rats and certain strains of inbred and noninbred mice. Although many lesions of NMR kidneys were similar to those found in aged laboratory rodents, some common urinary diseases were not represented in the examined colonies. The goal of this study was to describe renal lesions in NMRs from a zoologic setting to familiarize investigators and pathologists with an apparently common and presumably age-related disease in this nontraditional model.

Initial Case Reports of Cancer in Naked Mole-rats (Heterocephalus glaber).

Naked mole-rats (NMRs;Heterocephalus glaber) are highly adapted, eusocial rodents renowned for their extreme longevity and resistance to cancer. Because cancer has not been formally described in this species, NMRs have been increasingly utilized as an animal model in aging and cancer research. We previously reported the occurrence of several age-related diseases, including putative pre-neoplastic lesions, in zoo-housed NMR colonies. Here, we report for the first time 2 cases of cancer in zoo-housed NMRs. In Case No. 1, we observed a subcutaneous mass in the axillary region of a 22-year-old male NMR, with histologic, immunohistochemical (pancytokeratin positive, rare p63 immunolabeling, and smooth muscle actin negative), and ultrastructural characteristics of an adenocarcinoma possibly of mammary or salivary origin. In Case No. 2, we observed a densely cellular, poorly demarcated gastric mass of polygonal cells arranged in nests with positive immunolabeling for synaptophysin and chromogranin indicative of a neuroendocrine carcinoma in an approximately 20-year-old male NMR. We also include a brief discussion of other proliferative growths and pre-cancerous lesions diagnosed in 1 zoo colony. Although these case reports do not alter the longstanding observation of cancer resistance, they do raise questions about the scope of cancer resistance and the interpretation of biomedical studies in this model. These reports also highlight the benefit of long-term disease investigations in zoo-housed populations to better understand naturally occurring disease processes in species used as models in biomedical research.

Temperature preferences of African mole-rats (family Bathyergidae).

Many animals are able to detect small temperature differences and show strong temperature preferences during periods of rest and activity. Mammals inhabiting the subterranean ecotope can adapt their digging and foraging activity in shallow tunnels temporarily to periods with favourable ambient air and soil temperatures. Moreover, subterranean mammals have the unique opportunity to select for their nests in soil depths with certain, daily and seasonally constant temperatures. Our knowledge on nest temperatures in several species of subterranean mammals is based on measurements of temperatures in empty nests. We can expect, however, that the temperature in an occupied nest is higher (due to the "igloo effect"). We performed two experiments regarding the temperature preference in five species of African mole-rats (Bathyergidae, Rodentia: Fukomys anselli, F. mechowii, F. micklemi, Heliophobius argenteocinereus, and Heterocephalus glaber). In a first experiment, the animals were tested pairwise (except for the solitary silvery mole-rats, H. argenteocinereus, that were tested singly) in an apparatus consisting of seven chambers with a temperature gradient ranging between 16 and 37°C (air temperature). While the smaller species (<110g; F. anselli, F. micklemi, H. glaber) chose chambers with average air temperatures around 29°C, the larger mole-rats rested preferably at lower temperatures of approximately 25.6°C (F. mechowii) and 27.7°C (H. argenteocinereus). A strong negative correlation between body mass and preferred air temperature was detected across species. Thus, the results comply with the surface-volume-rule. Contrary to expectations, temperature preference of naked mole-rats (H. glaber) did not deviate from those of furred small mole-rats, but followed the general trend with smaller species preferring higher temperatures. In a second experiment, Ansell's mole-rats (F. anselli) were tested in groups of four, six and nine animals and the preferred temperatures were compared to the values obtained for pairs. The preferred mean air temperatures did not differ among the groups of different sizes. We discuss our findings in the light of ecophysiological adaptations to cope with the ambient conditions proposed by the "thermal stress hypothesis". Furthermore, we suggest that while soil temperature is decisive during digging as the mole-rats warm up or cool due to tight contact between body and soil (conduction), resting animals prevent heat loss through conduction by building a nest.

Peripheral administration of oxytocin increases social affiliation in the naked mole-rat (Heterocephalus glaber).

The neuropeptide oxytocin regulates a wide variety of social behaviors across diverse species. However, the types of behaviors that are influenced by this hormone are constrained by the species in question and the social organization that a particular species exhibits. Therefore, the present experiments investigated behaviors regulated by oxytocin in a eusocial mammalian species by using the naked mole-rat (Heterocephalus glaber). In Experiment 1, adult non-breeding mole-rats were given intraperitoneal injections of either oxytocin (1mg/kg or 10mg/kg) or saline on alternate days. Animals were then returned to their colony and behavior was recorded for minutes 15-30 post-injection. Both doses of oxytocin increased huddling behavior during this time period. In Experiment 2, animals received intraperitoneal injections of either oxytocin (1mg/kg), an oxytocin-receptor antagonist (0.1mg/kg), a cocktail of oxytocin and the antagonist, or saline across 4 testing days in a counterbalanced design. Animals were placed in either a 2-chamber arena with a familiar conspecific or in a small chamber with 1week old pups from their home colony and behaviors were recorded for minutes 15-30 post-injection. Oxytocin increased investigation of, and time spent in close proximity to, a familiar conspecific; these effects were blocked by the oxytocin antagonist. No effects were seen on pup-directed behavior. These data suggest that oxytocin is capable of modulating affiliative-like behavior in this eusocial species.

Naked mole-rat hyaluronan.

Naked mole rats (NMRs) are renowned for their exceptional longevity and remarkable maintenance of health throughout their lifetime. Their subterranean lifestyle has led to adaptations that have resulted in elevated levels of a very high molecular weight hyaluronan in their tissues. Hyaluronan, a glycosaminoglycan, is a key component of the extracellular matrix, which plays a critical role in maintaining tissue structure and regulating cell signaling pathways. This phenomenon in NMRs is attributed to a higher processing and production capacity by some of their hyaluronan synthases, along with lower degradation by certain hyaluronidases. Furthermore, this adaptation indirectly confers several advantages to NMRs, such as the preservation of skin elasticity and youthful appearance, accelerated wound healing, protection against oxidative stress, and resistance to conditions such as cancer and arthritis, largely attributable to CD44 signaling and other intricate mechanisms. Thus, the main objective of this study was to conduct a comprehensive study of the distinctive features of NMR hyaluronan, particularly emphasizing the currently known molecular mechanisms that contribute to its beneficial properties. Furthermore, this research delves into the potential applications of NMR hyaluronan in both cosmetic and therapeutic fields, as well as the challenges involved.

In-silico structural analysis of Heterocephalus glaber amyloid beta: an anti-Alzheimer's peptide.

Heterocephalus glaber, known as the Naked mole-rat, has an extraordinary immunity to Alzheimer's disease. The pathological hallmark of Alzheimer's disease is cerebral accumulations of plaques, consisting of self-aggregated amyloid beta peptides. Homo sapiens and H. glaber amyloid beta peptides are different in only one amino acid. Herein, computational structural analyses were carried out to determine whether plaque development in H. glaber is prevented by the replacement of His13 with Arg13 in the amyloid beta peptide. AlphaFold2 was used to predict the structure of the H. glaber amyloid beta peptide. HADDOCK and Hex were used to self-dock the peptides and dock ions on peptides, respectively. Illustrations were made by PyMol and ChimeraX. Using VMD, we calculated the radius of gyration. The phylogenetic analysis was conducted by Mega. The results showed an accurate structure with two alpha helices separated by a short coil for H. glaber. Self-docking of the two amyloid beta peptides demonstrated a globular conformation in the H. glaber dimer, implying the unlikeliness of amyloid beta peptides' self-aggregation to form fibrillar structures. This conformational state resulted in lower electrostatic energy compared to H. sapiens, contributing to H. glaber's lower tendency for fibril and, ultimately, plaque formation. Phylogenetic analysis confirmed that amyloid precursor protein is highly conserved in each taxon of rodentia and primata. This study provides insight into the connection between the structure of H. glaber amyloid beta and its plaque formation properties, showing that the Arg13 in H. glaber leads to fibril instability, and might prevent senile plaque accumulation.

Spontaneous histologic lesions of the adult naked mole rat (Heterocephalus glaber): a retrospective survey of lesions in a zoo population.

Naked mole rats (NMRs; Heterocephalus glaber) are highly adapted, subterranean, eusocial rodents from semiarid regions of the eastern horn of Africa and the longest-living rodent known with a maximum life span of up to 30 years. They are a unique model for aging research due to their physiology, extreme longevity, and, when compared to mice and rats, resistance to cancer. Published surveys of disease in NMRs are sparse. Captive colonies in zoological collections provide an opportunity to monitor spontaneous disease over time in a seminatural environment. This retrospective study describes common lesions of a zoo population over a 15-year period during which 138 adult NMRs were submitted for gross and histologic evaluation. Of these, 61 (44.2%) were male, 77 (55.8%) female, 45 (32.6%) died, and 93 (67.4%) were euthanized. The most frequent cause of death or reason for euthanasia was conspecific trauma (bite wounds) and secondary complications. Some common histologic lesions and their prevalence were renal tubular mineralization (82.6%), hepatic hemosiderosis (64.5%), bite wounds (63.8%), chronic progressive nephropathy (52.9%), and calcinosis cutis (10.1%). In sum, 104 (75.4%) NMRs had more than one of the most prevalent histologic lesions. No malignant neoplasms were noted; however, there was a case of renal tubular adenomatous hyperplasia with nuclear atypia and compression that in rats is considered a preneoplastic lesion. This retrospective study confirms the NMR's relative resistance to cancer in spite of development of other degenerative diseases and highlights the utility of zoological databases for baseline pathological data on nontraditional animal models.

Duplications of Human Longevity-Associated Genes Across Placental Mammals.

Natural selection has shaped a wide range of lifespans across mammals, with a few long-lived species showing negligible signs of ageing. Approaches used to elucidate the genetic mechanisms underlying mammalian longevity usually involve phylogenetic selection tests on candidate genes, detections of convergent amino acid changes in long-lived lineages, analyses of differential gene expression between age cohorts or species, and measurements of age-related epigenetic changes. However, the link between gene duplication and evolution of mammalian longevity has not been widely investigated. Here, we explored the association between gene duplication and mammalian lifespan by analyzing 287 human longevity-associated genes across 37 placental mammals. We estimated that the expansion rate of these genes is eight times higher than their contraction rate across these 37 species. Using phylogenetic approaches, we identified 43 genes whose duplication levels are significantly correlated with longevity quotients (False Discovery Rate (FDR) < 0.05). In particular, the strong correlation observed for four genes (CREBBP, PIK3R1, HELLS, FOXM1) appears to be driven mainly by their high duplication levels in two ageing extremists, the naked mole rat (Heterocephalus glaber) and the greater mouse-eared bat (Myotis myotis). Further sequence and expression analyses suggest that the gene PIK3R1 may have undergone a convergent duplication event, whereby the similar region of its coding sequence was independently duplicated multiple times in both of these long-lived species. Collectively, this study identified several candidate genes whose duplications may underlie the extreme longevity in mammals, and highlighted the potential role of gene duplication in the evolution of mammalian long lifespans.