Alzheimer disease models and human neuropathology: similarities and differences

Animal models aim to replicate the symptoms, the lesions or the cause(s) of Alzheimer disease. Numerous mouse transgenic lines have now succeeded in partially reproducing its lesions: the extracellular deposits of Aβ peptide and the intracellular accumulation of tau protein. Mutated human APP transgenes result in the deposition of Aβ peptide, similar but not identical to the Aβ peptide of human senile plaque. Amyloid angiopathy is common. Besides the deposition of Aβ, axon dystrophy and alteration of dendrites have been observed. All of the mutations cause an increase in Aβ 42 levels, except for the Arctic mutation, which alters the Aβ sequence itself. Overexpressing wild-type APP alone (as in the murine models of human trisomy 21) causes no Aβ deposition in most mouse lines. Doubly (APP × mutated PS1) transgenic mice develop the lesions earlier. Transgenic mice in which BACE1 has been knocked out or overexpressed have been produced, as well as lines with altered expression of neprilysin, the main degrading enzyme of Aβ. The APP transgenic mice have raised new questions concerning the mechanisms of neuronal loss, the accumulation of Aβ in the cell body of the neurons, inflammation and gliosis, and the dendritic alterations. They have allowed some insight to be gained into the kinetics of the changes. The connection between the symptoms, the lesions and the increase in Aβ oligomers has been found to be difficult to unravel. Neurofibrillary tangles are only found in mouse lines that overexpress mutated tau or human tau on a murine tau −/− background. A triply transgenic model (mutated APP, PS1 and tau) recapitulates the alterations seen in AD but its physiological relevance may be discussed. A number of modulators of Aβ or of tau accumulation have been tested. A transgenic model may be analyzed at three levels at least (symptoms, lesions, cause of the disease), and a reading key is proposed to summarize this analysis

Observations in APP Bitransgenic Mice Suggest that Diffuse and Compact Plaques Form via Independent Processes in Alzheimer's Disease

Studies of familial Alzheimer's disease suggest that misfolding and aggregation of amyloid-β (Aβ) peptides initiate the pathogenesis. The Arctic mutation of Aβ precursor protein (APP) results in AD, and Arctic Aβ is more prone to form Aβ protofibrils and extracellular deposits. Herein is demonstrated that the burden of diffuse Aβ deposits but not compact plaques is increased when tg-Swe mice are crossed with tg-ArcSwe mice synthesizing low levels of Arctic Aβ. The diffuse deposits in bitransgenic mice, which contain primarily wild-type Aβ42, accumulate in regions both with and without transgene expression. However, APP processing, when compared with tg-Swe, remains unchanged in young bitransgenic mice, whereas wild-type Aβ42 aggregation is accelerated and fibril architecture is altered in vitro and in vivo when a low level of Arctic Aβ42 is introduced. Thus, the increased number of diffuse deposits is likely due to physical interactions between Arctic Aβ and wild-type Aβ42. The selective increase of a single type of parenchymal Aβ deposit suggests that different pathways lead to formation of diffuse and compact plaques. These findings could have general implications for Alzheimer's disease pathogenesis and particular relevance to patients heterozygous for the Arctic APP mutation. Moreover, it further illustrates how Aβ neuropathologic features can be manipulated in vivo by mechanisms similar to those originally conceptualized in prion research

The reverse metabolic syndrome in the elderly: Is it a “catabolic” syndrome?

Traditional risk factors of cardiovascular death in the general population, including body mass index (BMI), serum cholesterol, and blood pressure are also found to relate to outcomes in the geriatric population, but in a differing direction. A higher body mass index, hypercholesterolemia and hypertension are not harmful but even permit better survival at advancing age. This phenomenon is called "reverse epidemiology" or "risk factor paradox" and is also detected in a variety of chronic disease states such as chronic heart failure. Accordingly, a low BMI, blood pressure and cholesterol values are associated with a worse prognosis. Several possible causes are hypothesized to explain this elderly paradox, but this phenomenon remains controversial and its underlying reasons are poorly understood. The aim of this review is to recognize the factors behind this intriguing phenomenon and analyse the consequences that it can bring in the management of the cardiovascular therapy in elderly patient. Finally, a new phenotype identified as "catabolic syndrome" has been postulated