H. Michael Tucker

The expression of key oxidative stress-handling genes in different brain regions in alzheimer’s disease

Alzheimer’s disease (AD) has been hypothesized to be associated with oxidative stress. In this study, the expression of key oxidative stress-handling genes was studied in hippocampus, inferior parietal lobule, and cerebellum of 10 AD subjects and 10 control subjects using reverse transcriptase-polymerase chain reaction (RT-PCR). The content of Mn-, Cu,Zn-superoxide dismutases (Mn- and Cu,Zn-SOD), catalase (CAT), glutathione peroxidase (GSH-Px), and glutathione reductase (GSSG-R) mRNAs, and the “marker genes” (β-actin and cyclophilin) mRNAs was determined. This study suggests that gene responses to oxidative stress can be significantly modulated by the general decrease of transcription in the AD brain. To determine if the particular oxidative stress handling gene transcription was induced or suppressed in AD, the “oxidative stress-handling gene/β-actin” ratios were quantified and compared with control values in all brain regions studied. The Mn-SOD mRNA/β-actin mRNA ratio was unchanged in all regions of the AD brain studied, but an increase of the Cu,Zn-SOD mRNA/β-actin mRNA ratio was observed in the AD inferior parietal lobule. The levels of peroxidation handling (CAT, GSH-Px, and GSSG-R) mRNAs normalized to β-actin mRNA level were elevated in hippocampus and inferior parietal lobule, but not in cerebellum of AD patients, which may reflect the protective gene response to the increased peroxidation in the brain regions showing severe AD pathology. The results of this study suggest that region-specific differences of the magnitude of ROS-mediated injury rather than primary deficits of oxidative stress handling gene transcription are likely to contribute to the variable intensity of neurodegeneration in different areas of AD brain.

Tissue Plasminogen Activator Requires Plasminogen to Modulate Amyloid-β Neurotoxicity and Deposition

Abstract: Tissue plasminogen (plgn) activator (tPA) modulates neuronal death in models of stroke, excitotoxicity, and oxidative stress. Amyloid‐β (Aβ) appears central to Alzheimers disease and is neurotoxic to neurons in vitro. Here, we evaluate tPA effects on Aβ toxicity. We report that tPA alone had no effect on Aβ toxicity. However, in combination with plgn, tPA reduced Aβ toxicity in a robust fashion. Moreover, the combined tPA and plgn treatment markedly inhibited Aβ accumulation. The addition of phenylmethylsulfonyl fluoride, a serine protease inhibitor, to a sample of tPA, plgn, and Aβ resulted in a marked reduction of Aβ degradation. We interpret the actions of tPA and plgn within the context of the ability of plasmin to degrade Aβ.

Urokinase‐type plasminogen activator inhibits amyloid‐β neurotoxicity and fibrillogenesis via plasminogen

Amyloid‐β (Aβ) appears central to Alzheimers disease (AD), aggregates spontaneously, and is neurotoxic to neurons in vitro. Recently, several groups reported a familial AD locus on chromosome 10. Here, we note that urokinase‐type plasminogen activator (uPA) is located within this locus. Previously, we reported that uPA and its functional homolog, tissue‐type plasminogen activator, are induced by Aβ treatment of neurons in vitro as well as in a mouse model of Aβ accumulation in vivo. Moreover, the target of plasminogen activators, plasmin, degraded nonaggregated and aggregated Aβ and modulated Aβ toxicity and deposition. Here, we have evaluated the effects of uPA and plasminogen on Aβ fibril formation and neurotoxicity. We report that the combination of uPA and plasminogen, but neither alone, inhibits Aβ toxicity, reduces Aβ deposition in vitro, and inhibits Aβ fibrillogenesis. We interpret these observations as suggesting that uPA represents a possible candidate gene for the chromosome 10 familial AD locus.

Plasmin deficiency does not alter endogenous murine amyloid beta levels in mice.

Deposition of amyloid beta (A beta) into extracellular plaques is a pathologic characteristic of Alzheimers disease. Plasmin, neprilysin, endothelin-converting enzyme and insulin-degrading enzyme (IDE) have each been implicated in A beta degradation; data supporting the role of the latter three enzymes have included increased levels of endogenous murine A beta in mice genetically deficient for the respective enzyme. In this study, we sought to determine if plasminogen deficiency increases endogenous A beta. We report that plasminogen deficiency did not result in an A beta increase in the brain or in the plasma of adult mice. Hence, although plasmin is potentially important in the degradation of A beta aggregates, we interpret these data as suggesting that plasmin does not regulate steady-state A beta levels in non-pathologic conditions.

c‐Jun Contributes to Amyloid β‐Induced Neuronal Apoptosis but Is Not Necessary for Amyloid β‐Induced c‐jun Induction

Abstract : The role of gene expression in neuronal apoptosis may be cell‐ and apoptotic stimulus‐specific. Previously, we and others showed that amyloid β (Aβ)‐induced neuronal apoptosis is accompanied by c‐jun induction. Moreover, c‐Jun contributes to neuronal death in several apoptosis paradigms involving survival factor withdrawal. To evaluate the role of c‐Jun in Aβ toxicity, we compared Aβ‐induced apoptosis in neurons from murine fetal littermates that were deficient or wild‐type with respect to c‐Jun. We report that neurons deficient for c‐jun are relatively resistant to Aβ toxicity, suggesting that c‐Jun contributes to apoptosis in this model. When changes in gene expression were quantified in neurons treated in parallel, we found that Aβ treatment surprisingly led to an apparent activation of the c‐jun promoter in both c‐jun‐deficient and wild‐type neurons, suggesting that c‐Jun is not necessary for activation of the c‐jun promoter. Indeed, several genes induced by Aβ in wild‐type neurons were also induced in c‐jun‐deficient neurons, including c‐fos, fosB, ngfi‐B, and iκB. In summary, these results indicate that c‐Jun contributes to Aβ‐induced neuronal death but that c‐Jun is not necessary for c‐jun induction.

Evolution and the scientific method

Alzheimer’s disease (AD) is a devastating age related disease that currently effects as many as 4 million Americans. It has, and as the “graying” of America proceeds, will continue to have a dramatic impact on our social, health and economic capabilities. Although we have made immense progress in the understanding of the disease, its cure has yet to be realized. In 1906 Alois Alzheimer described unusual clumps and tangled fibers in the brain of a deceased woman. These clumps and tangles are now known to be deposits of amyloid(A ) and neurofibrillary tangles (NFT) of hyperphosphorylated tau respectively. These features remain the defining characteristics of the AD brain and understanding their relationship to the progression of the disease will almost certainly be key to finding a cure for AD. Deposits of A , or plaques, in addition to being a key morphologic feature of the AD brain, have been a driving force guiding much of the AD research of the past several decades. This body of work has led to what is now known as the “amyloid hypothesis.” This hypothesis states that progressive accumulation of A within the brain initiates a complicated cascade of events that ultimately results in neuronal dysfunction and loss [14]. This cascade involves multiple cell types and signal transduction pathways that result in a wide variety of functional and structural changes in the brain. In this review, Robinson and Bishop take an alternative look at the existing data and propose a “bioflocculant hypothesis” for the function of A in normal aging as well as in the AD brain. This hypothesis proposes that A functions as a neuroprotectant by binding to extracellular neurotoxic solutes. A then precipitates into plaques thereby capturing these toxic agents and presenting them for efficient phagocytic removal. Much of the review and criticism of the data supporting the amyloid hypothesis presented by Robinson and Bishop focuses on the role of mature A plaques in the pathogenesis of AD. However, as the amyloid hypothesis has evolved, focus into the toxic role of A has turned from these mature