Microarray analysis of hippocampal CA1 neurons implicates early endosomal dysfunction during Alzheimer's disease progression.
BACKGROUND
Endocytic dysfunction and neurotrophin signaling deficits may underlie the selective vulnerability of hippocampal neurons during the progression of Alzheimer's disease (AD), although there is little direct in vivo and biochemical evidence to support this hypothesis.


METHODS
Microarray analysis of hippocampal CA1 pyramidal neurons acquired via laser capture microdissection was performed using postmortem brain tissue. Validation was achieved using real-time quantitative polymerase chain reaction and immunoblot analysis. Mechanistic studies were performed using human fibroblasts subjected to overexpression with viral vectors or knockdown via small interference RNA.


RESULTS
Expression levels of genes regulating early endosomes (rab5) and late endosomes (rab7) are selectively upregulated in homogeneous populations of CA1 neurons from individuals with mild cognitive impairment and AD. The levels of these genes are selectively increased as antemortem measures of cognition decline during AD progression. Hippocampal quantitative polymerase chain reaction and immunoblot analyses confirmed increased levels of these transcripts and their respective protein products. Elevation of select rab GTPases regulating endocytosis paralleled the downregulation of genes encoding the neurotrophin receptors TrkB and TrkC. Overexpression of rab5 in cells suppressed TrkB expression, whereas knockdown of TrkB expression did not alter rab5 levels, suggesting that TrkB downregulation is a consequence of endosomal dysfunction associated with elevated rab5 levels in early AD.


CONCLUSIONS
These data support the hypothesis that neuronal endosomal dysfunction is associated with preclinical AD. Increased endocytic pathway activity, driven by elevated rab GTPase expression, may result in long-term deficits in hippocampal neurotrophic signaling and represent a key pathogenic mechanism underlying AD progression.
Ginsberg
Stephen D
SD
Center for Dementia Research, Nathan Kline Institute, New York University Langone Medical Center, Orangeburg, NY 10962, USA. ginsberg@nki.rfmh.org
Alldred
Melissa J
MJ
Counts
Scott E
SE
Cataldo
Anne M
AM
Neve
Rachael L
RL
Jiang
Ying
Y
Wuu
Joanne
J
Chao
Moses V
MV
Mufson
Elliott J
EJ
Nixon
Ralph A
RA
Che
Shaoli
S
D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000235:genetics* / Q000378:metabolism*; D056547:CA1 Region, Hippocampal / Q000378:metabolism*; D002461:Cell Line, Transformed; D018450:Disease Progression; D015536:Down-Regulation; D011992:Endosomes / Q000378:metabolism*; D005260:Female; D020869:Gene Expression Profiling / Q000379:methods; D055785:Gene Knockdown Techniques / Q000379:methods; D006801:Humans; D008297:Male; D009474:Neurons / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis / Q000379:methods*; D020813:Receptor, trkB / Q000378:metabolism; D020812:Receptor, trkC / Q000378:metabolism; D015854:Up-Regulation; D020691:rab GTP-Binding Proteins / Q000378:metabolism; D020696:rab5 GTP-Binding Proteins / Q000378:metabolism; D000090802:rab7 GTP-Binding Proteins
D000090802:rab7 GTP-Binding Proteins; C000716463:rab7 GTP-binding proteins, human; D020813:Receptor, trkB; D020812:Receptor, trkC; D020691:rab GTP-Binding Proteins; D020696:rab5 GTP-Binding Proteins