Mechanisms determining characteristic age of onset for neurological diseases are largely unknown. Normal brain aging associates with robust and progressive transcriptome changes (“molecular aging”), but the intersection with disease pathways is mostly uncharacterized. Here, using cross-cohort microarray analysis of four human brain areas, we show that neurological disease pathways largely overlap with molecular aging and that subjects carrying a newly-characterized low-expressing polymorphism in a putative longevity gene (Sirtuin5; SIRT5prom2) have older brain molecular ages. Specifically, molecular aging was remarkably conserved across cohorts and brain areas, and included numerous developmental and transcription-regulator genes. Neurological disease-associated genes were highly overrepresented within age-related genes and changed almost unanimously in pro-disease directions, together suggesting an underlying genetic “program” of aging that progressively promotes disease. To begin testing this putative pathway, we developed and used an age-biosignature to assess five candidate longevity gene polymorphisms association with molecular aging rates. Most robustly, aging was accelerated in cingulate, but not amygdala, of subjects carrying a SIRT5 promoter polymorphism (+9yrs, p=0.004), in concordance with cingulate-specific decreased SIRT5 expression. This effect was driven by a set of core transcripts (+24 yrs, p=0.0004), many of which were mitochondrial, including Parkinson’s disease genes, PINK1 and DJ1/PARK7, hence suggesting that SIRT5prom2 may represent a risk factor for mitochondrial dysfunction-related diseases, including Parkinson s, through accelerated molecular aging of disease-related genes. Based on these results we speculate that a “common mechanism” may underlie age of onset across several neurological diseases. Confirming this pathway and its regulation by common genetic variants would provide new strategies for predicting, delaying, and treating neurological diseases.

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Aging of the human brain is associated with "normal" functional, structural, and molecular changes that underlie alterations in cognition, memory, mood and motor function, amongst other processes. Normal aging also imposes a robust constraint on the onset of many neurological diseases, ranging from late onset neurodegenerative diseases, such as Alzheimer's (AD) and Parkinson's diseases (PD), to early onset psychiatric disorders, such as bipolar disorder (BPD) and schizophrenia (SCZ). The molecular mechanisms and genetic underpinnings of age-related changes in the brain are understudied, and, while they share some overlap with peripheral mechanisms of aging, many are unique to the largely non-mitotic brain. Hence, understanding mechanisms of brain aging and identifying associated modulators may have profound consequences for the prevention and treatment of age-related impairments and diseases. Here we review current knowledge on age-related functional and structural changes, their molecular and genetic underpinnings, and discuss how these pathways may contribute to the vulnerability to develop age-related neurological diseases. We highlight recent findings from human postmortem brain microarray studies, which we hypothesize, point to a potential genetically-controlled transcriptional program underlying molecular changes and age-gating of neurological diseases. Finally, we discuss the implications of this model for understanding basic mechanisms of brain aging and for the future investigation of therapeutic approaches.

Parkinson’s disease is characterized by progressive death of dopaminergic neurons, leading to motor and cognitive dysfunction. Epidemiological studies consistently show that the use of tobacco reduces the risk of Parkinson’s. We report that nicotine reduces the abundance of SIRT6 in neuronal culture and brain tissue. We find that reduction of SIRT6 is partly responsible for neuroprotection afforded by nicotine. Additionally, SIRT6 abundance is greater in Parkinson’s patient brains, and decreased in the brains of tobacco users. We also identify SNPs that promote SIRT6 expression and simultaneously associate with an increased risk of Parkinson’s. Furthermore, brain-specific SIRT6 knockout mice are protected from MPTP-induced Parkinson’s, while SIRT6 overexpressing mice develop more severe pathology. Our data suggest that SIRT6 plays a pathogenic and pro-inflammatory role in Parkinson’s and that nicotine can provide neuroprotection by accelerating its degradation. Inhibition of SIRT6 may be a promising strategy to ameliorate Parkinson’s and neurodegeneration.Electronic supplementary materialThe online version of this article (10.1186/s40478-018-0625-y) contains supplementary material, which is available to authorized users.

Normal aging of the brain differs from pathological conditions and is associated with increased risk for psychiatric and neurological disorders. In addition to its role in the etiology and treatment of mood disorders, altered serotonin (5-HT) signaling is considered a contributing factor to aging; however, no causative role has been identified in aging. We hypothesized that a deregulation of the 5-HT system would reveal its contribution to agerelated processes and investigated behavioral and molecular changes throughout adult life in mice lacking the regulatory presynaptic 5-HT 1B receptor (5-HT 1B R), a candidate gene for 5-HTmediated age-related functions. We show that the lack of 5-HT 1B R (Htr1b KO mice) induced an early age-related motor decline and resulted in decreased longevity. Analysis of life-long transcriptome changes revealed an early and global shift of the gene expression signature of aging in the brain of Htr1b KO mice. Moreover, molecular changes reached an apparent maximum effect at 18-months in Htr1b KO mice, corresponding to the onset of early death in that group. A comparative analysis with our previous characterization of aging in the human brain revealed a phylogenetic conservation of age-effect from mice to humans, and confirmed the early onset of molecular aging in Htr1b KO mice. Potential mechanisms appear independent of known central mechanisms (Bdnf, inflammation), but may include interactions with previously identified age-related systems (IGF-1, sirtuins). In summary, our findings suggest that the onset of age-related events can be influenced by altered 5-HT function, thus identifying 5-HT as a modulator of brain aging, and suggesting age-related consequences to chronic manipulation of 5-HT.