New familial forms of cerebral amyloid and dementia

Characterization of amyloid deposits in neurodegenerative diseases

The extracellular accumulation of insoluble fibrillar peptides in brain parenchyma and vessel walls as amyloid is the hallmark of neurodegenerative diseases, such as Alzheimer's disease and Prion diseases. Regardless their amino acid sequences, all amyloid peptides adopt an insoluble, highly ordered beta sheet structure when aggregated. Amyloid is homogeneous and eosinophilic and, common to most cross-beta-type structures; it is generally identified by apple-green birefringence when stained with Congo red and seen under polarized light. Amyloid can also be identified by an apple green color when stained with thioflavine-S and seen under a fluorescence microscope. By electron microscopy, the typical fibrillar ultrastructure of amyloid deposits is revealed. The biochemical nature of the amyloid subunits present in the deposits can be recognized by immunohistochemistry using specific antibodies or by amino acid sequencing analysis, western blot, and mass spectrometry after isolation of parenchymal or vascular amyloid proteins.

Modeling familial British and Danish dementia

Familial British dementia (FBD) and familial Danish dementia (FDD) are two autosomal dominant neurodegenerative diseases caused by mutations in the BRI ( 2 ) gene. FBD and FDD are characterized by widespread cerebral amyloid angiopathy (CAA), parenchymal amyloid deposition, and neurofibrillary tangles. Transgenic mice expressing wild-type and mutant forms of the BRI(2) protein, Bri ( 2 ) knock-in mutant mice, and Bri ( 2 ) gene knock-out mice have been developed. Transgenic mice expressing a human FDD-mutated form of the BRI ( 2 ) gene have partially reproduced the neuropathological lesions observed in FDD. These mice develop extensive CAA, parenchymal amyloid deposition, and neuroinflammation in the central nervous system. These animal models allow the study of the molecular mechanism(s) underlying the neuronal dysfunction in these diseases and allow the development of potential therapeutic approaches for these and related neurodegenerative conditions. In this review, a comprehensive account of the advances in the development of animal models for FBD and FDD and of their relevance to the study of Alzheimer disease is presented.

Neurodegeneration Caused by Proteins with an Aberrant Carboxyl-Terminus

In recent years, 2 groups of hereditary neurodegenerative diseases have been recognized in which different genetic defects lead to the accumulation of proteins that contain a carboxyl-terminus that is abnormal in length and primary sequence. In this paper, we review the current knowledge on the molecular basis of diseases from these 2 groups. The first group includes familial British and Danish dementias, in which the molecular genetic defect resides in the BRI2 gene located on chromosome 13. In this group, carboxyl-terminal proteolytic products of the mutant BRI2 proteins aggregate in the extracellular space of the brain and in blood vessels. The second group includes 2 recently described ferritinopathies, in which the molecular genetic defect resides in the ferritin light polypeptide gene located on chromosome 19. In this group, full-length ferritin polypeptides aggregate intracellularly. The study of these conditions has led to the discovery of the BRI2 gene and to the finding of an unsuspected role for ferritin in neurodegeneration. These diseases provide new models in which to study the relationship between abnormal protein aggregation, neuronal cell death, and dementia.