Abstract
In humans, alterations of circadian rhythms and autophagy are linked to metabolic, cardiovascular and neurological dysfunction. Autophagy constitutes a specific form of cell recycling in many eukaryotic cells. Aging is the principal risk factor for the development of neurodegenerative diseases. Thus, we assume that both the circadian clock and autophagy are indispensable to counteract aging. We have previously shown that the hippocampus of Per1−/−-mice exhibits a reduced autophagy and higher neuronal susceptibility to ischemic insults compared to wild type (WT). Therefore, we chose to study the link between aging and loss of clock gene Per1−/−-mice. Young and aged C3H- and Per1−/−-mice were used as models to analyze the hippocampal distribution of Aβ42, lipofuscin, presenilin, microglia, synaptophysin and doublecortin. We detected several changes in the hippocampus of aged Per1−/−-mice compared to their wild type littermates. Our results show significant alterations of microglia morphology, an increase in Aβ42 deposition, overexpression of presenilin, decrease in synaptophysin levels and massive accumulation of lipofuscin in the hippocampus of 24-month-old Per1−/−-mice, without alteration of adult neurogenesis. We suggest that the marked lipofuscin accumulation, Aβ42 deposition, and overexpression of presenilin-2 observed in our experiments may be some of the consequences of the slowed autophagy in the hippocampus of aged Per1−/−-mice. This may lead during aging to excessive accumulation of misfolded proteins which may, consequently, result in higher neuronal vulnerability.
Highlights
We hypothesized that the defective autophagy in the hippocampus of Per1−/− -mice may lead during aging to excessive accumulation of misfolded proteins, which may result in higher neuronal vulnerability
We found a significant decrease in the protein levels of lysosome-associated membrane protein 1 (LAMP-1) and cathepsin-B in aged Per1−/− -mice, which could potentially be responsible for lipofuscin accumulation
Our findings show several changes in the hippocampus of aged Per1−/− -mice compared to aged wild type (WT) mice
Summary
Several forms of circadian disruption are common symptoms of aging and neurodegeneration. It has been shown that disruption of circadian rhythms accelerates the aging process [1,2]. The mammalian clock gene Period (Per1) is a central element of the circadian oscillator and has diverse extra-clock functions including cell cycle regulation, DNA damage response, and epigenetic regulation [3]. The ubiquitous expression of Per in many brain regions including the cerebral cortex, hippocampus and amygdala suggests that Per is likely involved in other processes [3,4,5,6,7,8]. It has recently been shown that down-regulation of clock genes might initiate the development of neurological disorders [9]
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