Page 49 - ebook

Circulating Proteasome Activity in Plasma
as a Novel Biomarker in Mild Cognitive Impairment
with Chronic Tinnitus

1,2
Yejin Yun , Sumin Kim 1,2 , Dawon Jeong 1,2 , and Min Jae Lee 1,2 ,*
1 Department of Biochemistry and Molecular Biology, Seoul National University College of Medicine, Korea,
2 Department of Biomedical Sciences, Seoul National University College of Medicine, Korea

Abstract
The proteasome is the major proteolytic enzyme complex involved in the maintenance of protein quality
control in the cell. Although the existence of proteasomes in human blood, termed circulating proteasomes
(c-proteasomes), has been reported previously, their origin and pathophysiological functions remain largely
unknown. Over the course of biochemically characterizing c-proteasomes, we observed that the catalytic
activity of c-proteasomes was significantly reduced in multiple lines of Alzheimer’s disease model mice. Given
that a relatively high frequency of mild cognitive impairment (MCI) is accompanied by chronic tinnitus in
aged patients, we examined whether c-proteasome activity in human plasma was associated with cognitive
function in patients with chronic tinnitus (N = 55). The activity of c-proteasome was significantly lower in
patients with chronic tinnitus and MCI (p = 0.042), whereas activities of other plasma enzymes showed little
correlation with c-proteasome activity. In addition, c-proteasome activity was negatively associated with the
level of plasma beta-amyloids and was directly dependent on its own concentration in the plasma of patients
with chronic tinnitus.
Result 1 Result 2
a b a
Patient selection and analysis of
clinical characteristics between
MCI and non-MCI
a) Flow chart of patient selection. b,c)
Difference in demographics (b) and clinical
characteristics (c) between the MCI (Montreal
cognitive assessment (MoCA) score, ≤22) and
non-MCI (MoCA score, >23) groups from
patients with chronic (more than 6 months)
tinnitus. None of them reached a statistically
significant difference, except for the visual
c analogue scale (VAS) annoyance. PHQ,
patient health questionnaire-9; IADL,
instrumental activities of daily living (IADL);
d
THI, tinnitus handicap index. d) Comparison
of MoCA scores at each domain between two
groups. d) Comparison of c-proteasome
activity between the MCI and non-MCI
groups. Data indicate means ± SD. *p < 0.05
(total N = 55, Welch’s t-test).
b c d
Characterization of the circulating proteasome in mouse blood plasma
a) Proteasome activity from wild type male mouse plasma b) Purified human 26S proteasomes,
mouse plasma after removal of IgG, and cell extracts from MEFs were subjected to native PAGE,
followed by in-gel suc-LLVY-AMC hydrolysis or by immunoblotting against the 20S subunit to
visualize the proteasomes. c) As in (a), except that the purified 19S complex was added to the suc-
LLVY-AMC hydrolysis reaction. Elevated proteasome activity upon the addition of the 19S subunit
indicates direct association of the 19S with the 20S complex in the plasma. d) Reduced c-
proteasome activity was detected from different lines of AD model mice.

Result 3 Conclusion
a b To the best of our knowledge, the present study is the first
Significant association between to explore the role of c-proteasome activity and its
concentration in determining the presence of MCI among
c-proteasome activity and the
patients with chronic tinnitus. Notably, the findings
levels of Ab 40 or c-proteasomes presented herein replicate those of mouse AD models
from chronic tinnitus patients overexpressing mutant tau, demonstrating that c-
with MCI proteasome activity from patients with chronic tinnitus and
MCI was significantly reduced. What merited our attention
a) Comparison of c-proteasome activity was the fact that c-proteasome activity in patients with
between the MCI and non-MCI groups. b) chronic tinnitus was largely dependent on its concentration
Spearman’s correlation analysis revealed a in blood plasma.
strong positive correlation between c-
proteasome activity and proteasome level in
c d the plasma from patients with chronic References
tinnitus. s (N = 55, ρ = 0.366, p = 0.006) c)
1. Yun Y, Lee, SY Choi WH, Park JC, Lee DH, Kim YK, Lee JH,
Significant negative correlation between Ab 40 Lee JY, Lee MJ, Kim YH (2020) Proteasome Activity in the
concentration and c-proteasome activity in Plasma as a Novel Biomarker in Mild Cognitive Impairment
the plasma. (Spearman’s correlation: total N with Chronic Tinnitus. J. Alzheimer’s Dis 78, 195–205.
.
= 55, ρ = –0.266, p = 0.049). d) Negative 2. Lee SY, Lee JY, Han SY, Seo Y, Shim YJ, Kim YH (2020)
correlation between Ab 40 and c-proteasome Neurocognition of aged patients with chronic tinnitus: Focus
levels in the plasma from patients with on mild cognitive impairment. Clin Exp Otorhinolaryngol. 13,
chronic tinnitus. (N = 55, ρ = –0.380, p = 8-14.
0.004)
3. Keller JN, Hanni KB, Markesbery WR (2000) Impaired
proteasome function in Alzheimer’s disease. J Neurochem 75,
436-439.