Early-life stress elicits peripheral and brain immune activation differently in wild type and 5xFAD mice in a sex-specific manner.

BACKGROUND: The risk of developing Alzheimer's disease (AD) is modulated by genetic and environmental factors. Early-life stress (ELS) exposure during critical periods of brain development can impact later brain function and health, including increasing the risk of developing AD. Microglial dysfunction and neuroinflammation have been implicated as playing a role in AD pathology and may be modulated by ELS. To complicate matters further, sex-specific effects have been noted in response to ELS and in the incidence and progression of AD. METHODS: Here, we subjected male and female mice with either a wild type or 5xFAD familial AD-model background to maternal separation (MS) from postnatal day 2 to 14 to induce ELS. RESULTS: We detected hippocampal neuroinflammatory alterations already at postnatal day 15. By 4 months of age, MS mice presented increased immobility time in the forced swim test and a lower discrimination index in the novel object recognition memory test compared to controls. We found altered Bdnf and Arc expression in the hippocampus and increased microglial activation in the prefrontal cortex due to MS in a sex-dependent manner. In 5xFAD mice specifically, MS exacerbated amyloid-beta deposition, particularly in females. In the periphery, the immune cell population was altered by MS exposure. CONCLUSION: Overall, our results demonstrate that MS has both short- and long-term effects on brain regions related to memory and on the inflammatory system, both in the brain and periphery. These ELS-related effects that are detectable even in adulthood may exacerbate pathology and increase the risk of developing AD via sex-specific mechanisms.

The fetal thymus has a unique genomic copy number profile resulting from physiological T cell receptor gene rearrangement.

Somatic mosaicism, the presence of genetically distinct cells within an organism, has been increasingly associated with human morbidity, ranging from being a cause of rare syndromes to a risk factor for common disorders such as malignancy and cardiovascular disease. Previous studies interrogating the normal prevalence of somatic mosaicism have focused on adults. We here present an estimate of the baseline frequency of somatic mosaic copy number variation (CNV) at the time around birth, by sampling eight different organs from a total of five fetuses and newborns. Overall we find a significantly lower frequency of organ specific (i.e. mosaic) CNVs as compared to adults (p = 0.003; Mann-Whitney U-test). The rate of somatic CNV in adults has been estimated to around 2.2 CNV per organ assayed. In contrast, after stringent filtering, we found no organ-private CNVs in fetuses or newborns with exception of the thymus. This organ exhibited a specific genome profile in the form of deletions resulting from polyclonal T-cell receptor rearrangements. This implies that somatic non-immune related CNVs, if present at birth, are typically confined to very small cell populations within organs.