The Klotho protein is a β-glucuronidase, and its overexpression is associated with life extension. Its mechanism of action is not fully understood, although it has been recently reported that αKlotho improves synaptic and cognitive functions, and it may also influence a variety of structures and functions during CNS maturation and aging. The αKlotho gene has two transcripts, one encoding a transmembrane isoform (m-KL), and the other a putative secreted isoform (s-KL). Unfortunately, little is known about the secreted αKlotho isoform, since available antibodies cannot discriminate s-KL from the KL1 domain cleaved from the transmembrane isoform. This study shows, for the first time, that the klotho transcript produced by alternative splicing generates a stable protein (70 kDa), and that in contrast to the transmembrane Klotho isoform, it is ten times more abundant in the brain than in the kidney suggesting that the two isoforms may have different functions. We also studied whether klotho expression in the CNS was influenced by aging, Alzheimer's disease (AD), or a healthy lifestyle, such as voluntary moderate continuous exercise. We observed a strong correlation between high expression levels of the two klotho transcripts and the healthy status of the animals. Expression of Klotho in brain areas decayed more rapidly in the 3xTg-AD model of AD than in healthy animals, whilst moderate continuous exercise in adulthood prevents the decline in expression of both klotho transcripts.

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New evidence reveals a high degree of heterogeneity in Alzheimer’s disease (AD) clinical and temporal patterns, supporting the existence of several subgroups of patients. Prognosticators of end-of-life dementia specific to elderly patients are necessary to address this heterogeneity. Among 3xTg-AD mice, a widely-used model for AD, a very small number of animals overcome advanced neuropathological stages of disease beyond 18 months of age. They are usually females, which reach longevity in spite of worse neuropathological status as compared to males (the morbidity/mortality paradox). We posit that 3xTg-AD long-term survivors could serve to model end-of-life dementia but also aware about the mortality selection bias. In the present study, we performed behavioral and functional phenotype in long-term survivors, 18-month-old female 3xTg-AD mice and age-matched wildtype undergoing normal aging. Animals were followed up until natural death to correlate survival with phenotype assessments. Strong similarity of their behavioral profiles in all the variables analyzed (e.g. reflexes, sensorimotor functions, locomotion, exploration, emotionality, and anxiety-like behaviors) was found, with the exception of memory impairment, which was a salient trait in old 3xTg-AD survivors. The two groups showed similar mean life expectancy and had behavioral correlates among lifespan, neophobia and long-term memory in common, with some distinctions in 3xTg-AD, supporting recent studies in end-of-life patients. In spite of the small sample size, this brief report presents an interesting scenario to further study heterogeneity and survival in Alzheimer’s disease. 3xTg-AD survivors may be a model to gain insight into the frailty/survival paradigm in normal and pathological aging.