Impairment of the ubiquitin-proteasome system associated with extracellular transthyretin aggregates in familial amyloidotic polyneuropathy

The ubiquitin-proteasome system (UPS) has been associated with neurodegenerative disorders of intracellular protein aggregation. We have studied the UPS in familial amyloidotic polyneuropathy (FAP), a neurodegenerative disorder caused by extracellular deposition of mutant transthyretin (TTR). The studies were conducted in TTR-synthesizing and non-synthesizing tissues from affected individuals, in transgenic mouse models for FAP, and in neuronal or Schwannoma cell lines cultured with TTR aggregates. In human FAP tissues presenting extracellular TTR aggregates, ubiquitin-protein conjugates were up-regulated, the proteasome levels were decreased and parkin and alpha-synuclein expression were both decreased. A similar response was detected in mouse models for TTR V30M or L55P. On the other hand, the liver, which normally synthesizes variant TTR V30M, did not show this response. Furthermore, transgenic mice immunized to decrease TTR deposition showed a significant reduction in ubiquitin levels and an increase in parkin and alpha-synuclein levels in comparison to control mice. Studies performed in cell lines with aggregates in the medium resulted in increased ubiquitin and decreased parkin levels. The overall results are indicative of TTR deposition as an external stimulus to an intracellular UPS response in FAP.

Enlarged ventricles, astrogliosis and neurodegeneration in heat shock factor 1 null mouse brain

Heat shock transcription factors mediate the regulation of the organism physiological maintenance and adaptation. We investigated the morphology and cellular expression of selected genes in brains of transgenic mice lacking the heat shock transcription factor 1, HSF1, the main transactivator under stress conditions. All HSF1 null mice displayed major brain morphological alterations: the lateral ventricles were markedly enlarged and the white matter reduced, as in ventriculomegaly. Heterozygous mice for the HSF1 gene also had these abnormalities albeit to a lower extent in comparison to the wild type, indicating a gene dosage effect. Cell loss, vacuolisation, amorphous eosinophilic cytoplasm and pyknotic nucleus were evident in the white matter, especially in periventricular regions. These areas also exhibited astrogliosis and neurodegeneration. The expression of heat shock protein hsp 27 was up-regulated whereas alpha B-crystallin was down-regulated in different areas of HSF1 null mouse brain in comparison to control mice. These data implicate HSF1 in maintaining the postnatal mammalian brain under non-stress conditions.