Our previous studies have implicated
perlecan, a specific
heparan sulfate proteoglycan, in the pathogenesis of fibrillar
beta-amyloid protein (A beta) accumulation and persistence in
Alzheimer's disease (AD) brain. In the present investigation, we determined if
perlecan mRNA was present in rodent and human brain tissue and whether
perlecan persistence in A
beta amyloid deposits in AD hippocampus may be partly due to increased
perlecan expression and/or decreased
perlecan degradation. To detect and to quantify low-abundance
perlecan mRNA in rodent and postmortem human brain tissue, regions of
perlecan domain I (503 and 366 bp) containing the unique
heparan sulfate glycosaminoglycan attachment sites were analyzed by reverse transcription (RT) and polymerase chain reaction (PCR).
Perlecan mRNA was detected in rodent brain, kidney, and liver and in human AD and normal aged frontal cortex. Different-size transcripts of
perlecan domain I were found, suggesting the existence of alternatively spliced variants of
perlecan or closely related gene products. Quantitative competitive RT-PCR using a mutant
perlecan domain I internal standard was used to determine
perlecan mRNA levels in total
RNA isolated from the hippocampus of 10 AD (mean +/- SEM duration of illness, 11.3 +/- 1.4 years) and 10 normal aged controls. No significant difference in
perlecan mRNA levels from the hippocampus of AD (1.12 +/- 0.29 amol/500 ng of total
RNA) versus normal aged controls (1.09 +/- 0.30 amol/500 ng of total
RNA) was found, indicating that
perlecan expression remained at steady-state levels. These results therefore suggest that
perlecan persistence in A
beta-amyloid deposits in late-stage AD may be primarily due to decreased
perlecan degradation and removal.