Traditional lifespan curves that are observed in other animals don‘t appear to apply in NMR (naked mole rats). After three months of age, mortality rates do not change with aging, and death frequency appears to be similar in every adult age group throughout life (Buffenstein, 2008). During its long lifespan they experience very little decline in many of the characteristics that usually comes with aging. Adults are rarely sick, and it can be very difficult to decipher young from old animals by physical appearance alone. Body composition, bone density, gastrointestinal absorption rate, metabolic rate, and neuron number stay constant until at least the age of 24 years (Buffstein, 2008; O‘Conner et al. 2002). These delayed declines with age are supported by transcriptome analyses (Kim et al., 2011), which revealed that gene expression is also unchaged in the liver, brain and kidney tissues that were examined from 4-20 year old animals.
NMR brains show no signs of neurodegeneration, neuron number is retained well into their third decade and there are also no signs of plaques and tangles (Edrey et. al., 2013). One key protective factor in this regard is the sustained high hlevels of neuregulin-1, a neurotrophic growth factor that commonly declines early in the aging process.
Unlike most mammals, NRM do not show age related declines in fertility, neither in males or females (Buffstein, 2005). Naked mole rats, like other naturally long-lived species and experimentally manipulated organisms with extended lifespans, show pronounced resistance to a broad spectrum of toxins both in vivo and in cells in culture, includeing heavy metals, heat, and chemotherapeutic/DNA-damaging compounds (Kapahi et al., 1999; Salmon et al., 2008; Lewis et al., 2012).
One of the most publicized characteristics of the NMR in the last years has been their impressive resistance to not only spontaneous cancers, but also to induced cancers. It is extremely rare to find a small mammal that does not die from or with signs of cancer (Leroi et al., 2003). Commonly approximately 70% of laboratory mouse autopsies show signs of tumors or lesions and even longer lived captive wild derived mice die primarily of neoplasia (Harper et al., 2006; Ikeno et al., 2003). Many of the unique characteristics described above of the NMR have been also found to contribute to aging and longevity. Long lived animals and species have notably lower incidences of cancer, can be very resistant to different toxic compounds and also show delayed frailty during their long lifespan. Naked mole rats are exhibiting unusual longevity (Buffstein and Jarvis, 2002). They are the oldest documented rodents with a maximum life span that can exceed 31 years in captivity, more than eight times longer than similar sized mice.
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