Altered Proteolysis in Fibroblasts of Alzheimer Patients with Predictive Implications for Subjects at Risk of Disease

Abstract

There is great interest in developing reliable biomarkers to support antemortem diagnosis of late-onset Alzheimer's disease (AD). Early prediction and diagnosis of AD might be improved by the detection of a proteolytic dysfunction in extracts from cultured AD fibroblasts, producing altered isoelectrophoretic forms of the enzyme transketolase (TK-alkaline bands). The TK profile and apolipoprotein E (APOE) genotype were examined in fibroblasts from 36 clinically diagnosed probable late-onset sporadic AD patients and 38 of their asymptomatic relatives, 29 elderly healthy individuals, 12 neurological non-AD patients, and 5 early-onset AD patients. TK alterations occurred in (i) several probable AD patients regardless of age-of-onset and severity of disease; (ii) all early-onset AD patients and APOE ε4/4 carriers; and (iii) nearly half of asymptomatic AD relatives. Normal subjects and non-AD patients were all negative. Notably, culture conditions promoting TK alterations were also effective in increasing active BACE1 levels. Overall, the TK assay might represent a low-cost laboratory tool useful for supporting AD differential diagnosis and identifying asymptomatic subjects who are at greater risk of AD and who should enter a follow-up study. Moreover, the cultured fibroblasts were confirmed as a useful in vitro model for further studies on the pathogenetic process of AD.

Upregulation of Glycolytic Enzymes, Mitochondrial Dysfunction and Increased Cytotoxicity in Glial Cells Treated with Alzheimer’s Disease Plasma

“…Transketolase is a thiamine-dependent enzyme which catalyses the first reaction in the pentose phosphate pathway. Transketolase alterations have been previously identified in (i) several probable AD patients regardless of age-of-onset and severity of disease; (ii) all early-onset AD patients and APOE ε4/4 carriers; and (iii) nearly half of asymptomatic AD relatives [ 80 ]. Increased transketolase activity has also been correlated with increased levels of BACE1, the key rate-limiting enzyme for the production of the Aβ peptide [ 80 ].…”

In silico Analysis of Gamma-Secretase-Complex Mutations in Hidradenitis Suppurativa Demonstrates Disease-Specific Substrate Recognition and Cleavage Alterations

“…The GSC cleaves up to 69 individual substrates (5), the most well-known being amyloid precursor protein (APP) associated with AlzD (6) pathogenesis. Of interest, altered GSC substrate proteolysis is seen in non-neural tissues (including cutaneous fibroblasts) in AlzD (6) suggesting that peripheral tissues such as cutaneous fibroblasts can be analyzed for diagnostic and predictive biomarkers of disease (6).…”

Alzheimer's disease mechanisms in peripheral cells: Promises and challenges

“…While the majority of work on biomarker discovery for AD was traditionally conducted in biofluids [78,79], the utilization of fibroblasts as a source of biomarkers for AD has also been proposed [80]. One of the examples includes the identification of a proteolytic dysfunction in AD cells that produces altered isoelectrophoretic forms of the enzyme transketolase (TK‐alkaline bands) that could be used for an early diagnosis [81]. The TK profile conducted in fibroblasts from clinically diagnosed probable LOAD patients, their asymptomatic relatives, neurological non‐AD patients, early‐onset AD patients, and control individuals demonstrated the usefulness of cultured fibroblasts as an excellent in vitro model for the study of the pathogenic processes of AD and as a low‐cost laboratory tool useful for supporting AD differential diagnosis [81].…”

“…One of the examples includes the identification of a proteolytic dysfunction in AD cells that produces altered isoelectrophoretic forms of the enzyme transketolase (TK‐alkaline bands) that could be used for an early diagnosis [81]. The TK profile conducted in fibroblasts from clinically diagnosed probable LOAD patients, their asymptomatic relatives, neurological non‐AD patients, early‐onset AD patients, and control individuals demonstrated the usefulness of cultured fibroblasts as an excellent in vitro model for the study of the pathogenic processes of AD and as a low‐cost laboratory tool useful for supporting AD differential diagnosis [81]. Similarly, AD fibroblasts were found to have the upregulation of the lysosomal system including increased levels of glycohydrolases (α‐D‐mannosidase, β‐D‐hexosaminidase, and β‐D‐galactosidase).…”