Youngah Shin

The Co-chaperone Carboxyl Terminus of Hsp70-interacting Protein (CHIP) Mediates α-Synuclein Degradation Decisions between Proteasomal and Lysosomal Pathways

α-Synuclein is a major component of Lewy bodies, the pathological hallmark of Parkinson disease, dementia with Lewy bodies, and related disorders. Misfolding and aggregation of α-synuclein is thought to be a critical cofactor in the pathogenesis of certain neurodegenerative diseases. In the current study, we investigate the role of the carboxyl terminus of Hsp70-interacting protein (CHIP) in α-synuclein aggregation. We demonstrate that CHIP is a component of Lewy bodies in the human brain, where it colocalizes with α-synuclein and Hsp70. In a cell culture model, endogenous CHIP colocalizes with α-synuclein and Hsp70 in intracellular inclusions, and overexpression of CHIP inhibits α-synuclein inclusion formation and reduces α-synuclein protein levels. We demonstrate that CHIP can mediate α-synuclein degradation by two discrete mechanisms that can be dissected using deletion mutants; the tetratricopeptide repeat domain is critical for proteasomal degradation, whereas the U-box domain is sufficient to direct α-synuclein toward the lysosomal degradation pathway. Furthermore, α-synuclein, synphilin-1, and Hsp70 all coimmunoprecipitate with CHIP, raising the possibility of a direct α-synuclein-CHIP interaction. The fact that the tetratricopeptide repeat domain is required for the effects of CHIP on α-synuclein inclusion morphology, number of inclusions, and proteasomal degradation as well as the direct interaction of CHIP with Hsp70 implicates a cooperation of CHIP and Hsp70 in these processes. Taken together, these data suggest that CHIP acts a molecular switch between proteasomal and lysosomal degradation pathways.

Clinical and biochemical correlates of insoluble α-synuclein in dementia with Lewy bodies

Abstractα-Synuclein is a major constituent of Lewy bodies, the fibrillar aggregates that form within neurons in Parkinson’s disease and dementia with Lewy bodies (DLB). Recent biochemical data show that α-synuclein accumulates in Parkinson’s disease in a detergent insoluble form. We now examine the relationship between detergent insoluble α-synuclein and the presence of Lewy bodies, clinical measures of dementia and biochemical parameters in a series of individuals with DLB. We found that Triton X-100 insoluble α-synuclein enriched nearly twofold in the temporal cortex of patients with DLB compared to age-matched controls. By contrast the total amount of α-synuclein protein was unchanged. Surprisingly, the degree of Triton X-100 insoluble α-synuclein did not correlate with either the duration of illness or the number of Lewy bodies counted using stereological methods from an adjacent block of tissue. However, the Triton X-100 soluble fraction of α-synuclein did correlate strongly with the expression of several heat shock proteins (HSPs) in DLB but not control cases, suggesting a coordinated HSP response in DLB neocortex.

Hemorrhagic stroke associated with the Iowa amyloid precursor protein mutation.

The authors searched for mutations in the β-amyloid precursor protein in a Spanish family with a hereditary syndrome of hemorrhagic stroke, dementia, leukoencephalopathy, and occipital calcifications. DNA from two affected members demonstrated the Iowa amyloid precursor protein mutation previously identified as a cause of severe amyloid angiopathy without hemorrhagic stroke. These data point to other genetic or environmental factors that may determine the occurrence of symptomatic hemorrhage in amyloid angiopathy.

Aβ species, including IsoAsp23 Aβ, in Iowa-type familial cerebral amyloid angiopathy

Abstract. Mutations within the Aβ sequence of the AβPP gene are associated with familial forms of cerebral amyloid angiopathy (CAA). One mutation, Aβ D23N, was identified in a family in Iowa with a clinical history of early-onset dementia. We analyzed the pattern of Aβ deposition in the hippocampus of an individual with Iowa CAA. In addition to strong amyloid angiopathy, we found unusual diffuse Aβ deposits in the CA4, and in the parenchyma near amyloid-laden vessels. ELISA of cortical brain extracts showed that Aβ40 was nearly 20-fold higher than Aβ42, in both soluble and insoluble fractions. We identified an Aβ antibody that recognized wild-type Aβ but not Iowa Aβ. With this antibody, we found that wild-type Aβ was present in the Aβ deposits, but limited to the strongest deposits in the cerebrovasculature. Previous in vitro studies suggested that the presence of an asparagine at position 23 of Aβ favored formation of an isoAsp residue, which was associated with increased Aβ fibrillogenesis. Using isoAsp-specific antibodies in immunohistochemical studies, we examined the distribution of isoAsp Aβ in the Iowa brain. IsoAsp7 Aβ was present in both the parenchymal and vascular deposits, whereas isoAsp23 Aβ was present only in vascular deposits. These data suggest that alteration of Aβ Asn23 to isoAsp may be an important determinant in the deposition of Aβ in cerebral blood vessels.

Genotyping of Apolipoprotein E: Comparative Evaluation of Different Protocols

Disease‐associated gene polymorphisms provide both scientific insight into pathophysiological mechanisms and clinical information regarding risk and progression. Of special interest is the ɛ4 allele of the apolipoprotein E gene, which has emerged as a substantial risk factor for late‐onset forms of Alzheimer disease and also influences the risk of cardiovascular disease. Genotyping of apolipoprotein E can be performed by several methods; presented here are a quality and cost‐benefit analysis of four different protocols on a cohort of 42 clinical samples is included in the unit. Each method resulted in genotyping with a high sensitivity and specificity. The newer microtiter‐plate‐based high‐throughput techniques, fluorescence polarization and SNaPshot analysis, were as reliable as the traditional techniques of restriction fragment length polymorphism analysis and reverse hybridization. The reverse hybridization method tends to be more cost‐ and time‐effective when the number of analyses is limited, although economy of scale favors fluorescence polarization or SNaPshot analysis in larger studies. The latter approaches also provide the flexibility to investigate other polymorphic disease markers.

Vascular Changes in Iowa-Type Hereditary Cerebral Amyloid Angiopathy

Abstract: Vascular dysfunction due to cerebral amyloid angiopathy (CAA) may contribute to cognitive impairment. The Iowa D694N amyloid precursor protein mutation, a recently identified cause of hereditary CAA with dementia, offers an opportunity to explore the anatomic basis of CAA‐related vascular dysfunction. Examination by immunolabeling and confocal microscopy demonstrated extensive loss of smooth muscle cells in affected segments as well as a perivascular inflammatory reaction of astrocytes and microglia. On 3‐D reconstruction, vessels appeared tortuous with twiglike projections that may represent areas of vascular degeneration. The observed changes in the Iowa brain suggest pathophysiologic mechanisms for vascular dysfunction in CAA and possible approaches to treatment of CAA‐related cognitive impairment.