Expression patterns of SLIT/ROBO mRNAs reveal a characteristic feature in the entorhinal-hippocampal area of macaque monkeys

African ancestry GWAS of dementia in a large military cohort identifies significant risk loci

While genome wide association studies (GWASs) of Alzheimer's Disease (AD) in European (EUR) ancestry cohorts have identified approximately 83 potentially independent AD risk loci, progress in non-European populations has lagged. In this study, data from the Million Veteran Program (MVP), a biobank which includes genetic data from more than 650,000 US Veteran participants, was used to examine dementia genetics in an African descent (AFR) cohort. A GWAS of Alzheimer's disease and related dementias (ADRD), an expanded AD phenotype including dementias such as vascular and non-specific dementia that included 4012 cases and 18,435 controls age 60+ in AFR MVP participants was performed. A proxy dementia GWAS based on survey-reported parental AD or dementia (n = 4385 maternal cases, 2256 paternal cases, and 45,970 controls) was also performed. These two GWASs were meta-analyzed, and then subsequently compared and meta-analyzed with the results from a previous AFR AD GWAS from the Alzheimer's Disease Genetics Consortium (ADGC). A meta-analysis of common variants across the MVP ADRD and proxy GWASs yielded GWAS significant associations in the region of APOE (p = 2.48 × 10-101), in ROBO1 (rs11919682, p = 1.63 × 10-8), and RNA RP11-340A13.2 (rs148433063, p = 8.56 × 10-9). The MVP/ADGC meta-analysis yielded additional significant SNPs near known AD risk genes TREM2 (rs73427293, p = 2.95 × 10-9), CD2AP (rs7738720, p = 1.14 × 10-9), and ABCA7 (rs73505251, p = 3.26 × 10-10), although the peak variants observed in these genes differed from those previously reported in EUR and AFR cohorts. Of the genes in or near suggestive or genome-wide significant associated variants, nine (CDA, SH2D5, DCBLD1, EML6, GOPC, ABCA7, ROS1, TMCO4, and TREM2) were differentially expressed in the brains of AD cases and controls. This represents the largest AFR GWAS of AD and dementia, finding non-APOE GWAS-significant common SNPs associated with dementia. Increasing representation of AFR participants is an important priority in genetic studies and may lead to increased insight into AD pathophysiology and reduce health disparities.

Roles and Mechanisms of Axon-Guidance Molecules in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease that is characterized by progressive memory decline and cognitive dysfunctions. Although the causes of AD have not yet been established, many mechanisms have been proposed. Axon-guidance molecules play the roles in the occurrence and development of AD by participating in different mechanisms. Therefore, what roles do axon-guidance molecules play in AD? This study aimed at elucidating how axon-guidance molecules Netrins, Slits, Semaphorins, and Ephrins regulate the levels of Aβ, hyperphosphorylation of tau protein, Reelin, and other ways through different signaling pathways, in order to show the roles of axon-guidance molecules in the occurrence and development of AD. And it is hoped that this study can provide a theoretical basis and new perspectives in the search for new therapeutic targets for AD.

Depression-/Anxiety-Like Behavior Alterations in Adult Slit2 Transgenic Mice

Background: Slit2 is a member of the Slit family of secreted glycoproteins that plays highly conserved roles in neuronal axon guidance and cellular migration. Our previous experimental results showed Alzheimer's disease-like alterations and increased permeability of the blood–brain barrier in Slit2-overexpressing transgenic (Slit2-Tg) mice aged 8–9 months. Nevertheless, relatively little is known about behavioral alterations in adult Slit2-Tg mice (2–6 months of age). To observe the age-related behavioral effects of Slit2 overexpression in adult mice, we performed a battery of behavioral tests with adult Slit2-Tg mice at 2–6 months of age.

Results: The body weight of Slit2-Tg mice was lower than that of the wild-type mice from 15 weeks of age. Compared with the control mice, depression-like behaviors were found in Slit2-Tg mice from 15 to 21 weeks of age in the sucrose preference test, although Slit2-Tg mice were hyperactive in the tail suspension test. The anxiety-like behaviors were found in Slit2-Tg mice in the open field test, as well as increased locomotor activity. The anxiety-like behaviors were also found in adult Slit2-Tg mice in the elevated plus maze. Compared to wild-type mice at 23 weeks old, impairment of the hippocampal neurons were found in Slit2-Tg mice at the same age in hematoxylin–eosin staining (H&E), including some eccentric dispersion and expansion of neuronal bodies. In addition, the messenger RNA (mRNA) expression of TNF-α was elevated in the hippocampus of adult Slit2-Tg mice.

Conclusions: Slit2 overexpression causes depression-/anxiety-like behaviors in adult mice that may be related to an increase in inflammatory factors and damage to hippocampal neurons.

White matter abnormalities in fetal alcohol spectrum disorders: Focus on axon growth and guidance

Fetal Alcohol Spectrum Disorders (FASDs) describe a range of deficits, affecting physical, mental, cognitive, and behavioral function, arising from prenatal alcohol exposure. FASD causes widespread white matter abnormalities, with significant alterations of tracts in the cerebral cortex, cerebellum, and hippocampus. These brain regions present with white-matter volume reductions, particularly at the midline. Neural pathways herein are guided primarily by three guidance cue families: Semaphorin/Neuropilin, Netrin/DCC, and Slit/Robo. These guidance cue/receptor pairs attract and repulse axons and ensure that they reach the proper target to make functional connections. In several cases, these signals cooperate with each other and/or additional molecular partners. Effects of alcohol on guidance cue mechanisms and their associated effectors include inhibition of growth cone response to repellant cues as well as changes in gene expression. Relevant to the corpus callosum, specifically, developmental alcohol exposure alters GABAergic and glutamatergic cell populations and glial cells that serve as guidepost cells for callosal axons. In many cases, deficits seen in FASD mirror aberrancies in guidance cue/receptor signaling. We present evidence for the need for further study on how prenatal alcohol exposure affects the formation of neural connections which may underlie disrupted functional connectivity in FASD.