Common and rare variants of EGF increase the genetic risk of Alzheimer's disease as revealed by targeted sequencing of growth factors in Han Chinese

Homocysteine decreases VEGF, EGF, and TrkB levels and increases CCL5/RANTES in the hippocampus: Neuroprotective effects of rivastigmine and ibuprofen

Homocysteine (Hcy) is produced through methionine transmethylation. Elevated Hcy levels are termed Hyperhomocysteinemia (HHcy) and represent a risk factor for neurodegenerative conditions such as Alzheimer's disease. This study aimed to explore the impact of mild HHcy and the neuroprotective effects of ibuprofen and rivastigmine via immunohistochemical analysis of glial markers (Iba-1 and GFAP). Additionally, we assessed levels of vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), chemokine ligand 5 (CCL5/RANTES), CX3C chemokine ligand 1 (CX3CL1), and the NGF/p75NTR/tropomyosin kinase B (TrkB) pathway in the hippocampus of adult rats. Mild chronic HHcy was induced chemically in Wistar rats by subcutaneous administration of Hcy (4 mg/kg body weight) twice daily for 30 days. Rivastigmine (0.5 mg/kg) and ibuprofen (40 mg/kg) were administered intraperitoneally once daily. Results revealed elevated levels of CCL5/RANTES and reduced levels of VEGF, EGF, and TrkB in the hippocampus of HHcy-exposed rats. Rivastigmine mitigated the neurotoxic effects of HHcy by increasing TrkB and VEGF levels. Conversely, ibuprofen attenuated CCL5/RANTES levels against the neurotoxicity of HHcy, significantly reducing this chemokine's levels. HHcy-induced neurochemical impairment in the hippocampus may jeopardize neurogenesis, synapse formation, axonal transport, and inflammatory balance, leading to neurodegeneration. Treatments with rivastigmine and ibuprofen alleviated some of these detrimental effects. Reversing HHcy-induced damage through these compounds could serve as a potential neuroprotective strategy against brain damage.

Convergent transcriptomic and genomic evidence supporting a dysregulation of CXCL16 and CCL5 in Alzheimer's disease

BACKGROUND

Neuroinflammatory factors, especially chemokines, have been widely reported to be involved in the pathogenesis of Alzheimer's disease (AD). It is unclear how chemokines are altered in AD, and whether dysregulation of chemokines is the cause, or the consequence, of the disease.

METHODS

We initially screened the transcriptomic profiles of chemokines from publicly available datasets of brain tissues of AD patients and mouse models. Expression alteration of chemokines in the blood from AD patients was also measured to explore whether any chemokine might be used as a potential biomarker for AD. We further analyzed the association between the coding variants of chemokine genes and genetic susceptibility of AD by targeted sequencing of a Han Chinese case-control cohort. Mendelian randomization (MR) was performed to infer the causal association of chemokine dysregulation with AD development.

RESULTS

Three chemokine genes (CCL5, CXCL1, and CXCL16) were consistently upregulated in brain tissues from AD patients and the mouse models and were positively correlated with Aβ and tau pathology in AD mice. Peripheral blood mRNA expression of CXCL16 was upregulated in mild cognitive impairment (MCI) and AD patients, indicating the potential of CXCL16 as a biomarker for AD development. None of the coding variants within any chemokine gene conferred a genetic risk to AD. MR analysis confirmed a causal role of CCL5 dysregulation in AD mediated by trans-regulatory variants.

CONCLUSIONS

In summary, we have provided transcriptomic and genomic evidence supporting an active role of dysregulated CXCL16 and CCL5 during AD development.