The expression of presenilin-1 mRNA in skin fibroblasts from Alzheimer's disease

Accumulation of neutral lipids in peripheral blood mononuclear cells as a distinctive trait of Alzheimer patients and asymptomatic subjects at risk of disease

BACKGROUND

Alzheimer's disease is the most common progressive neurodegenerative disease. In recent years, numerous progresses in the discovery of novel Alzheimer's disease molecular biomarkers in brain as well as in biological fluids have been made. Among them, those involving lipid metabolism are emerging as potential candidates. In particular, an accumulation of neutral lipids was recently found by us in skin fibroblasts from Alzheimer's disease patients. Therefore, with the aim to assess whether peripheral alterations in cholesterol homeostasis might be relevant in Alzheimer's disease development and progression, in the present study we analyzed lipid metabolism in plasma and peripheral blood mononuclear cells from Alzheimer's disease patients and from their first-degree relatives.

METHODS

Blood samples were obtained from 93 patients with probable Alzheimer's disease and from 91 of their first-degree relatives. As controls we utilized 57, cognitively normal, over-65 year-old volunteers and 113 blood donors aged 21-66 years, respectively. Data are reported as mean +/- standard error. Statistical calculations were performed using the statistical analysis software Origin 8.0 version. Data analysis was done using the Student t-test and the Pearson test.

RESULTS

Data reported here show high neutral lipid levels and increased ACAT-1 protein in about 85% of peripheral blood mononuclear cells freshly isolated (ex vivo) from patients with probable sporadic Alzheimer's disease compared to about 7% of cognitively normal age-matched controls. A significant reduction in high density lipoprotein-cholesterol levels in plasma from Alzheimer's disease blood samples was also observed. Additionally, correlation analyses reveal a negative correlation between high density lipoprotein-cholesterol and cognitive capacity, as determined by Mini Mental State Examination, as well as between high density lipoprotein-cholesterol and neutral lipid accumulation. We observed great variability in the neutral lipid-peripheral blood mononuclear cells data and in plasma lipid analysis of the subjects enrolled as Alzheimer's disease-first-degree relatives. However, about 30% of them tend to display a peripheral metabolic cholesterol pattern similar to that exhibited by Alzheimer's disease patients.

CONCLUSION

We suggest that neutral lipid-peripheral blood mononuclear cells and plasma high density lipoprotein-cholesterol determinations might be of interest to outline a distinctive metabolic profile applying to both Alzheimer's disease patients and asymptomatic subjects at higher risk of disease.

How frequent is altered gene expression among susceptibility genes to human complex disorders?

It is regularly thought that human complex disorder susceptibility genes show differences in gene expression between normal and pathologic tissues. Thus, differences of transcript amounts could be indicative of complex disorder susceptibility loci and, therefore, be used for the discovery or the validation of human susceptibility genes to complex disorders/traits. Whether human complex disorder susceptibility genes effectively display differences in transcript amounts was tested by meta-analysis of the published literature comparing transcript amounts of well-validated human susceptibility genes to complex traits/disorders. A total of 94 gene-disease associations, which were studied in at least three independent studies and showed strong evidence of positive association, were analyzed. For 23 out of these 94 well-validated gene-disease associations, 120 gene expression studies comparing normal and pathologic human tissues were found. For 60 out of these 120 gene expression studies, the difference of level expression between normal and pathologic human tissues was statistically significant. This result was highly significant, as only 6 significant results were expected randomly under the null hypothesis (P < 10(-112)). A large excess of replication studies were also found, which were in agreement with the original report (P = 6 x 10(-4)). However, the overall level of expression change between normal and pathologic human tissues was relatively moderate, because only 36 (60%) and 19 (31.6%) out of the 62 statistically significant gene expression studies reached 2- or 3-fold changes in expression level, respectively. The present meta-analysis confirms statistical differences of expression levels between normal and pathologic human tissues for human susceptibility genes to complex traits/disorders. However, the levels of differences in transcript amounts appear to be relatively weak. These findings rationalize the use of gene expression for the discovery/validation of human susceptibility genes, but the weak differences of expression typically found should be taken into account for the design of such studies.

The expression of presenilin 1 mRNA in skin fibroblasts and brains from sporadic Alzheimer's disease

We examined the expression of presenilin 1 (PS-1) mRNA in cultured skin fibroblasts taken from living patients with Alzheimer's disease (AD) and human brains taken postmortem from AD patients by RT-PCR analysis. The donors of fibroblasts consisted of 28 cases with AD and 19 neurological patient without dementia (CTL). The brains came from 17 cases with AD and 23 cases with CTL. We found that PS-1 mRNA levels in skin fibroblasts of AD patients were significantly higher than those of CTL patients (p < 0.0001). Moreover, we found that PS-1 mRNA levels in human brains with AD were significantly higher than in those with CTL (p < 0.0001). These findings suggest that high levels of PS-1 mRNA in AD may play an important role in developing AD and that the examination of PS-1 mRNA in skin fibroblasts may be helpful for the diagnosis of AD.

Specific downregulation of presenilin 2 gene expression is prominent during early stages of sporadic late-onset Alzheimer's disease

Mutations in the presenilin genes PS1 and PS2 cause familial Alzheimer's disease (AD). In a previous study, we reported that PS2 mRNA levels are decreased in the hippocampus, frontal cortex and basal forebrain of subjects with late-onset sporadic AD. In this study, we examined whether this downregulation occurs as the disease progresses from mild to severe stages or whether downregulation of PS2 expression is an early event in AD. We used in situ hybridization histochemistry to quantify the level of expression of PS2 message in the hippocampus of normal subjects and subjects with mild, moderate or severe AD. Several regions of the hippocampus which are sequentially susceptible to AD neuropathology as the disease progresses in severity were analyzed. We demonstrate that specific downregulation of PS2 expression is as severe in subjects with mild AD as it is in subjects in late stages of the disease. In addition, we show that hippocampal regions that are relatively free of AD neuropathology during early stages of the disease exhibit severely compromised PS2 mRNA levels even in mild AD cases. In contrast, PS2 is expressed at normal levels in the cerebellum, a region which succumbs to significantly fewer AD-related insults even at very advanced stages of the disease. These results suggest that the specific downregulation of PS2 gene expression is an early event in sporadic late-onset AD.