Increased β-synuclein (Sncb) expression has been described in the aging visual system.
Sncb functions as the physiological antagonist of α-synuclein (Snca), which is involved in
the development of neurodegenerative diseases, such as Parkinson’s and Alzheimer’s
diseases. However, the exact function of Sncb remains unknown. The aim of this study was
to elucidate the age-dependent role of Sncb in brain microvascular endothelial cells
(BMECs). BMECs were isolated from the cortices of 5- to 9-d-old Sprague-Dawley rats and
were cultured with different concentrations of recombinant Sncb (rSncb) up to 72 h
resembling to some degree age-related as well as pathophysiological conditions. Viability,
apoptosis, expression levels of Snca, and the members of phospholipase D2
(Pld2)/p53/ Mouse double minute 2 homolog (Mdm2)/p19(Arf) pathway,
response in RAC-alpha serine/threonine-protein kinase (Akt), and stress-mediating factors
such as heme oxygenase (decycling) 1 (Hmox) and Nicotinamide adenine dinucleotide
phosphate oxygenase 4 (Nox4) were examined. rSncb-induced effects were confirmed through
Sncb small interfering RNA (siRNA) knockdown in BMECs. We demonstrated
that the viability decreases, while the rate of apoptosis underly dose-dependent
alterations. For example, apoptosis increases in BMECs following the treatment with higher
dosed rSncb. Furthermore, we observed a decrease in Snca immunostaining and messenger RNA
(mRNA) levels following the exposure to higher rScnb concentrations. Akt was shown to be
downregulated and pAkt upregulated by this treatment, which was accompanied by a
dose-independent increase in p19(Arf) levels and enhanced intracellular Mdm2 translocation
in contrast to a dose-dependent p53 activation. Moreover, Pld2 activity
was shown to be induced in rSncb-treated BMECs. The expression of Hmox and Nox4 after Sncb
treatment was altered on BEMCs. The obtained results demonstrate dose-dependent effects of
Sncb on BMECs in vitro. For example, the p53-mediated and Akt-independent
apoptosis together with the stress-mediated response of BMECs related to exposure of
higher SNCB concentrations may reflect the increase in Sncb with duration of culture as
well as its impact on cell decay. Further studies, expanding on the role of Sncb, may help
understand its role in the neurodegenerative diseases.