CDK5 and MAPT Gene Expression in Alzheimer's Disease Brain Samples

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by extracellular amyloid plaque and neurofibrillary tangles in the brain. Studies have shown that neurons are able to re-enter the cell cycle, but not enough to enable full replication. This leads to cell death and consequent neurodegeneration.

OBJECTIVE

This study aimed to characterize the expression of the MAPT gene and CDK5 (the gene involved in cell cycle regulation) in brain samples from patients with AD and controls.

METHOD

The real-time-PCR technique was used to characterize 150 samples from three areas of the brain (entorhinal cortex, auditory cortex, and hippocampus) of 26 AD patients and 24 healthy elderly subjects.

RESULTS

When the brain samples were analyzed collectively, a decrease in CDK5 and MAPT gene expression was found in AD patients. When each groups' samples were separated by area of the brain and compared, significant differences were found in CDK5 expression in the hippocampus and the entorhinal cortex. In both cases, mRNA was lower in the AD group (p=0.0001); however, the same analysis using the MAPT gene revealed no significant statistical differences. No statistical differences were found when gene expression was compared between the different regions of the brain within each group.

CONCLUSION

These results may contribute to a better understanding of the involvement of CDK5 and MAPT genes in AD in that they consider different areas of the brain that are affected differently based on disease progression. The main challenge is to establish an effective therapy for this debilitating disease in the future.

Differential Expression of Ribosomal Genes in Brain and Blood of Alzheimer's Disease Patients

Changes in rRNA and rDNA expression have been associated with cellular and organism aging and have been linked to Alzheimer's disease (AD) pathogenesis. In this study, we investigated the mRNA expression of ribosomal genes (28S/18S) and β-amyloid precursor protein (APP) in different post mortem brain tissue regions (the entorhinal and auditory cortices and the hippocampus) of AD patients and elderly control subjects and also evaluated the extent of expression in peripheral blood from young, healthy, elderly, and Alzheimer's disease patients in order to investigate whether these individuals experienced the effects of aging. The comparative threshold cycle (CT) method via Real Time Polymerase Chain Reaction and the Polymerase Chain Reaction- Restriction Fragment Length Polymorphism (PCR-RFLP) were used to analyze gene expression and the Apolipoprotein E (APOE) genotype, respectively. When the brain areas were analyzed collectively, we observed a significant decrease in APP expression and a significant increase in levels of mRNA of 18S and 28S in Alzheimer's disease patients compared to healthy elderly individuals. Furthermore, there was a significant upregulation of 28SrRNA in the entorhinal cortex and hippocampus, but not in the auditory cortex of patients with AD. On the other hand, tests of blood samples verified a decreased expression of 28S rRNA in patients with AD. These results support the hypothesis that changes in rRNA are present in AD patients, are tissue-specific, and seem to occur independently and differently in each tissue. However, the next challenge is to discover the mechanisms responsible for the differences in expression observed in the blood and the brain in both healthy elderly individuals and Alzheimer's disease patients, as well as the impact of these genes on AD pathogenesis.

Characterization of Cerebellum-Specific Ribosomal DNA Epigenetic Modifications in Alzheimer's Disease: Should the Cerebellum Serve as a Control Tissue After All?

Alzheimer's disease (AD) is a neurodegenerative disease, known as the most common form of dementia. In AD onset, abnormal rRNA expression has been reported to be linked in pathogenesis. Although region-specific expression patterns have previously been reported in AD, it is not until recently that the cerebellum has come under the spotlight. Specifically, it is unclear whether DNA methylation is the mechanism involved in rRNA expression regulation in AD. Hence, we sought to explore the rDNA methylation pattern of two different brain regions - auditory cortex and cerebellum - from AD and age-/sex-matched controls. Our results showed differential hypermethylation at an upstream CpG region to the rDNA promoter when comparing cerebellum controls to auditory cortex controls. This suggests a possible regulatory region from rDNA expression regulation. Moreover, when comparing between AD and control cerebellum samples, we observed hypermethylation of the rDNA promoter region as well as an increase in rDNA content. In addition, we also observed increased rRNA levels in AD compared to control cerebellum. Although still considered a pathology-free brain region, there are growing findings that continue to suggest otherwise. Indeed, cerebellum from AD has been recently described as affected by the disease, presenting a unique pattern of molecular alterations. Given that we observed that increased rDNA promoter methylation did not silence rDNA gene expression, we suggest that rDNA promoter hypermethylation is playing a protective role in rDNA genomic stability and, therefore, increasing rRNA levels in AD cerebellum.