Alpha-Synuclein Levels in Blood Plasma Decline with Healthy Aging

There is unequivocal evidence that alpha-synuclein plays a pivotal pathophysiological role in neurodegenerative diseases, and in particular in synucleinopathies. These disorders present with a variable extent of cognitive impairment and alpha-synuclein is being explored as a biomarker in CSF, blood serum and plasma. Considering key events of aging that include proteostasis, alpha-synuclein may not only be useful as a marker for differential diagnosis but also for aging per se. To explore this hypothesis, we developed a highly specific ELISA to measure alpha-synuclein. In healthy males plasma alpha-synuclein levels correlated strongly with age, revealing much lower concentrations in older (avg. 58.1 years) compared to younger (avg. 27.6 years) individuals. This difference between the age groups was enhanced after acidification of the plasmas (p<0.0001), possibly reflecting a decrease of alpha-synuclein-antibody complexes or chaperone activity in older individuals. Our results support the concept that alpha-synuclein homeostasis may be impaired early on, possibly due to disturbance of the proteostasis network, a key component of healthy aging. Thus, alpha-synuclein may be a novel biomarker of aging, a factor that should be considered when analyzing its presence in biological specimens.Fil: Koehler, Niklas K. U.. Eberhard-Karls-University Tübingen. Department of Psychiatry and Psychotherapy; Alemania. German Center for Neurodegenerative Diseases; AlemaniaFil: Stransky, Elle. Eberhard-Karls-University Tübingen. Department of Psychiatry and Psychotherapy; AlemaniaFil: Meyer, Mirjam. Eberhard-Karls-University Tübingen. Department of Psychiatry and Psychotherapy; AlemaniaFil: Gaertner, Susanne. Eberhard-Karls-University Tübingen. Department of Psychiatry and Psychotherapy; AlemaniaFil: Shing, Mona. Eberhard-Karls-University Tübingen. Department of Psychiatry and Psychotherapy; AlemaniaFil: Schnaidt, Martina. Zentrum für Klinische Transfusionsmedizin; AlemaniaFil: Celej, Maria Soledad. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Quimica Biológica; Argentina. Institute for Biophysical Chemistry. Laboratory for Cellular Dynamics, Max-Planck; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Química Biológica de Córdoba (p); ArgentinaFil: Jovin, Thomas M.. Institute for Biophysical Chemistry. Laboratory for Cellular Dynamics, Max-Planck; AlemaniaFil: Leyhe, Thomas. Eberhard-Karls-University Tübingen. Department of Psychiatry and Psychotherapy; Alemania. Psychiatric University Hospital. Center of Old Age Psychiatry; AlemaniaFil: Laske, Christoph . Eberhard-Karls-University Tübingen. Department of Psychiatry and Psychotherapy; Alemania. German Center for Neurodegenerative Diseases; AlemaniaFil: Batra, Anil. Eberhard-Karls-University Tübingen. Department of Psychiatry and Psychotherapy; AlemaniaFil: Buchkremer, Gerhard. Eberhard-Karls-University Tübingen. Department of Psychiatry and Psychotherapy; AlemaniaFil: Fallgatter, Andreas J.. Eberhard-Karls-University Tübingen. Department of Psychiatry and Psychotherapy; AlemaniaFil: Wernet, Dorothee. Zentrum für Klinische Transfusionsmedizin; AlemaniaFil: Richartz Salzburger, Elke. Eberhard-Karls-University Tübingen. Department of Psychiatry and Psychotherapy; Alemani

Altered serum IgG levels to α-synuclein in dementia with Lewy bodies and Alzheimer's disease.

Natural self-reactive antibodies in the peripheral blood may play a considerable role in the control of potentially toxic proteins that may otherwise accumulate in the aging brain. The significance of serum antibodies reactive against α-synuclein is not well known. We explored serum IgG levels to monomeric α-synuclein in dementia with Lewy bodies (DLB) and Alzheimer's disease (AD) with a novel and validated highly sensitive ELISA assay. Antibody levels revealed stark differences in patients compared to healthy subjects and were dependent on diagnosis, disease duration and age. Anti-α-synuclein IgG levels were increased in both patient groups, but in early DLB to a much greater extent than in AD. Increased antibody levels were most evident in younger patients, while with advanced age relatively low levels were observed, similar to healthy individuals, exhibiting stable antibody levels independent of age. Our data show the presence of differentially altered IgG levels against α-synuclein in DLB and AD, which may relate to a disturbed α-synuclein homeostasis triggered by the disease process. These observations may foster the development of novel, possibly preclinical biomarkers and immunotherapeutic strategies that target α-synuclein in neurodegenerative disease

Concentration of an alpha-synuclein standard solution decreases with preincubation.

<p>Incubation of freshly diluted alpha-synuclein at 6 ng/ml in PBS for 3, 18 and 32 h at 37°C decreased ELISA-measured alpha-synuclein levels by 21, 66 and 78%, respectively.</p

Box plots* of alpha-synuclein levels in native and acidified plasma.

<p>(a) Younger in comparison to older individuals revealed higher alpha-synuclein levels, highly significant by Mann Whitney test for native, p = 0,0005 and acidified plasmas, p<0.0001. (b) Plasma acidification increased alpha-synuclein concentrations in both age groups, highly significant by a one-tailed Wilcoxon matched pairs test, p<0.0001. The additional horizontal short line in the box represents the mean.</p

ELISA standard curve for alpha-synuclein.

<p>Detection limit of the assay was set at 300 pg/ml (described in results). SD bars are from duplicate measurements.</p

Linear regression of age with alpha-synuclein concentration in native and acidified plasma.

<p>Alpha-synuclein decreased with age and was enhanced by acidification. Spearman correlation was very significant for native samples, p = 0.0093, r = -0.3, after acidification, p = 0.0019, r = -0.34.</p

Dissociation factor after plasma acidification young vs. old.

<p>Box plots* of dissociation factors, calculated by dividing the acidified and native plasma alpha-synuclein concentration of each individual sample. Lower dissociation factors were observed in older individuals, very significant by Mann Whitney test, p = 0.0093.</p

Spike and recovery.

<p>Eight native plasmas were spiked with 5 ng/ml alpha-synuclein, recoveries are illustrated in a box plot*, mean recovery was 70.4%.* The boxes upper and lower borders represent the 25th and 75th percentile, whiskers indicate the 10 to 90 percentile, lines within the box mark the median (thin line) and the mean (bold line).</p

Alpha-synuclein concentration in native and acidified plasma in a younger and older group of healthy males.

<p>Data are shown as mean (median) +/- SE. SE = standard error, CI = 95% confidence interval of the mean, n = number of individuals, y = years.</p><p>Alpha-synuclein concentration in native and acidified plasma in a younger and older group of healthy males.</p