Faculty Bibliography

The pathogenesis of neurofibrillary tangles (NFTs) in Alzheimer's disease (AD) is poorly understood, but changes in the expression of specific messenger RNAs (mRNAs) may reflect mechanisms underlying the formation of NFTs and their consequences in affected neurons. For these reasons, we compared the relative abundance of multiple mRNAs in tangle-bearing versus normal CA1 neurons aspirated from sections of AD and control brains. Amplified antisense RNA expression profiling was performed on individual isolated neurons for analysis of greater than 18,000 expressed sequence tagged complementary DNAs (cDNAs) with cDNA microarrays, and further quantitative analyses were performed by reverse Northern blot analysis on 120 selected mRNAs on custom cDNA arrays. Relative to normal CA1 neurons, those harboring NFTs in AD brains showed significant reductions in several classes of mRNAs that are known to encode proteins implicated in AD neuropathology, including phosphatases/kinases, cytoskeletal proteins, synaptic proteins, glutamate receptors, and dopamine receptors. Because cathepsin D mRNA was upregulated in NFT-bearing CA1 neurons in AD brains, we performed immunohistochemical studies that demonstrated abundant cathepsin D immunoreactivity in the same population of tangle-bearing CA1 neurons. In addition, levels of mRNAs encoding proteins not previously implicated in AD were reduced in CA1 tangle-bearing neurons, suggesting that these proteins (eg, activity-regulated cytoskeleton-associated protein, focal adhesion kinase, glutaredoxin, utrophin) may be novel mediators of NFT formation or degeneration in affected neurons. Thus, the profile of mRNAs differentially expressed by tangle-bearing CA1 neurons may represent a 'molecular fingerprint' of these neurons, and we speculate that mRNA expression profiles of diseased neurons in AD may suggest new directions for AD research or identify novel targets for developing more effective AD therapies

To evaluate whether in vivo accumulations of heparan sulfate caused by inborn errors in the metabolism of glycosaminoglycans lead to the formation of neurofibrillary tangles and/or senile plaques, as seen in Alzheimer disease (AD), we studied postmortem brains from 9 patients, ages 1 to 42 years, with mucopolysaccharidosis (MPS). The brains of patients with Hurler's syndrome (MPS I: n = 5) and Sanfilippo's syndrome (MPS III; n = 4) as well as from caprine MPS IIID and murine MPS VII models were evaluated by thioflavine-S staining and by immunohistochemistry using antibodies directed against heparan sulfate proteoglycans, hyperphosphorylated tau, amyloid-beta peptide precursor proteins (APP), and amyloid-beta peptides (A beta [1-40], and A beta [1-42]). A two-site sandwich enzyme-linked immunosorbent assay (ELISA) was also utilized to compare levels of total soluble and insoluble A beta (1-40) and A beta (1-42) obtained from temporal cortex of MPS patients. Although no neurofibrillary tangles, senile plaques, or tau-positive lesions were detected in any of the MPS brains studied here, antibodies directed against A beta (1-40) intensely and diffusely stained the cytoplasm of cells throughout the brains of the MPS patients and the caprine MPS model. The ELISA assay also demonstrated a significant 3-fold increase in the level of soluble A beta (1-40) in the MPS brains compared with normal control brains. Thus, at least some of the metabolic defects that lead to accumulations of glycosaminoglycans in MPS also are associated with an increase in immunoreactive A beta (1-40) within the cytoplasmic compartment where they could contribute to the dysfunction and death of affected cells in these disorders, but not induce the formation of plaques and tangles. Models of MPS may enable mechanistic studies of the role A beta and glycosaminoglycans play in the amyloidosis that is a neuropathological feature of AD

The sequestration of RNA in Alzheimer's disease (AD) senile plaques (SPs) and the production of intraneuronal amyloid-beta peptides (Abeta) prompted analysis of the mRNA profile in single immunocytochemically identified SPs in sections of AD hippocampus. By using amplified RNA expression profiling, polymerase chain reaction, and in situ hybridization, we assessed the presence and abundance of 51 mRNAs that encode proteins implicated in the pathogenesis of AD. The mRNAs in SPs were compared with those in individual CA1 neurons and the surrounding neuropil of control subjects. The remarkable demonstration here, that neuronal mRNAs predominate in SPs, implies that these mRNAs are nonproteinaceous components of SPs, and, moreover, that mRNAs may interact with Abeta protein and that SPs form at sites where neurons degenerate in the AD brain

Fimbria-fornix transection produces neuronal injury in the septum. This cellular pathology is characterized by somatodendritic vacuolar abnormalities in neurons. Because these cellular changes are reminiscent of some of the morphological abnormalities seen with glutamate receptor-mediated excitoxicity, we tested whether excitotoxic injury to the septal complex of adult rats mimics the degeneration observed within the dorsolateral septal nucleus and medial septal nucleus following fimbria-fornix transection. The septal complex was evaluated at various time-points (6 h to 14 days) by light and electron microscopy following unilateral injection of the N-methyl-D-aspartate receptor agonist quinolinate or the non-N-methyl-D-aspartate receptor agonist kainate, and the morphological changes observed were compared to those abnormalities in the medial septal nucleus and dorsolateral septal nucleus at three to 14 days after fimbria-fornix transection. The patterns of cytoplasmic abnormalities and vacuolar injury were morphologically similar in the somatodendritic compartment of neurons following excitotoxicity and axotomy paradigms. These similarities were most evident when comparing the persistently injured neurons in the penumbral regions of the excitotoxic lesions at one to 14 days recovery to neurons in the medial septal nucleus and dorsolateral septal nucleus at seven and 14 days after fimbria-fornix transection. Pretreatment with the N-methyl-D-aspartate receptor antagonist dizocilpine maleate prior to unilateral fimbria-fornix transection attenuated the somatodentritic vacuolar damage found within the ipsilateral dorsolateral and medial septal nuclei at 14 days recovery. Because glutamate is the principal transmitter of hippocampal efferents within the fimbria-fornix, we conclude that postsynaptic glutamate receptor activation participates in the evolution of septal neuron injury following fimbria-fornix transection. Thus, excitotoxicity is a possible mechanism for transneuronal degeneration following central nervous system axotomy.