Alzheimer Disease: van Laar T

van Laar T, van der Eb AJ, Terleth C. · MGC-Department of Radiation Genetics and Chemical Mutagenesis, P. O. Box 9503, 2300 RA Leiden, the Netherlands. · Curr Protein Pept Sci. · Pubmed #12370023 No free full text.

Abstract: Eukaryotic cells have three different mechanisms to deal with the accumulation of unfolded proteins in the endoplasmic reticulum: (1) In cells in which unfolded polypeptides accumulate, translation initiation is inhibited to prevent further accumulation of unfolded proteins. (2) Expression of proteins involved in polypeptide folding is strongly enhanced by a process called the Unfolded Protein Response (UPR). (3) Proteins missing the proper tertiary structure are degraded by the ER-Associated protein Degradation (ERAD) mechanism. Recent studies in S. cerevisiae have shown that the processes of UPR and ERAD are functionally linked to each other. Cells lacking a functional ERAD show a constitutive activation of UPR. In addition, many of the components of ERAD are under the direct transcriptional control of UPR. Finally, while neither UPR nor ERAD are essential for cell viability, deletion of both pathways results in severe growth impairment. UPR and ERAD are conserved between yeast and mammalian cells. One of the components of mammalian UPR is the protease presenilin-1. Mutations in the gene for presenilin-1 cause early-onset familial Alzheimer disease. Interestingly, inhibition of proteolysis by the ubiquitin-26S proteasome system has also been described for Alzheimer s disease. This suggests a link between UPR and ERAD in mammalian cells. The recently identified gene Mif1 is a possible candidate to form a direct link between UPR and ERAD in mammalian cells. The Mif1 gene is under the direct control of UPR. Mif1 is a trans-ER-membrane protein, with both the N- and the C-termini facing the cytoplasmic side of the ER membrane. It contains an N-terminal ubiquitin-like domain. It is anticipated that Mif1 may associate through its ubiquitin-like domain with the 26S proteasome, in this way connecting the protein degradation machinery to the ER membrane and resulting in an efficient ERAD.

Barone P, Burn DJ, van Laar T, Hsu C, Poewe W, Lane RM. · Dipartimento di Scienze Neurologiche, Università Federico II di Napoli, Naples, Italy. · Mov Disord. · Pubmed #18581467 No free full text.

Abstract: The effects of rivastigmine versus placebo in Parkinson's disease dementia (PDD) patients with elevated or normal/low plasma homocysteine were determined. In this prospective analysis of a 24-week, randomly assigned, placebo-controlled study of rivastigmine in PDD, subpopulations comprised patients with plasma homocysteine >or=14 micromol/L (elevated) or <14 micromol/L (normal/low). Coprimary outcomes were the Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-cog) and Alzheimer Disease Cooperative Society-Clinical Global Impression of Change (ADCS-CGIC). Secondary outcomes included additional measures of cognition, including attention and executive function, daily function, and neuropsychiatric symptoms. Adverse events (AEs) were monitored. In total, 342 of 541 patients provided samples for analysis, from which 72% had elevated plasma homocysteine. Hyperhomocysteinemic patients showed treatment differences (rivastigmine vs. placebo) of 4.0 on ADAS-cog and 0.7 on ADCS-CGIC (both P < 0.01), and significant treatment differences on secondary outcomes. Rivastigmine- and placebo-treated hyperhomocysteinemic patients (16.5% and 14.6%) discontinued the study because of AEs. Patients with normal/low homocysteine showed no treatment differences on primary or secondary outcomes (1.4 on the ADAS-cog and 0.1 on ADCS-CGIC, both P = ns); 16.7% and 10.3% rivastigmine- and placebo-treated patients discontinued because of AEs. Elevated homocysteine was associated with greater rivastigmine treatment differences than normal/low homocysteine.