Wh. Stoothoff et Gvw. Johnson, Hyperosmotic stress-induced apoptosis and tau phosphorylation in human neuroblastoma cells, J NEUROSC R, 65(6), 2001, pp. 573-582
A characteristic hallmark of Alzheimer's disease brain is the presence of h
yperphosphorylated tau; however, the mechanisms responsible for the aberran
t tau phosphorylation are unknown. Recently, it has been shown that apoptot
ic-like processes may be involved in some of the neuronal loss in Alzheimer
's disease. In consideration of these findings, the relationship between ta
u phosphorylation and apoptosis was examined in human neuroblastoma SH-SY5Y
cells that were subjected to hyperosmotic stress. In this model caspase 3
activity, which served as an indicator of apoptosis, was increased by 30 mi
n of osmotic stress and remained elevated through 4 hr. Hyperosmotic stress
also resulted in a robust increase in tau phosphorylation at both Ser/Pro
and non-Ser/Pro sites. Phosphorylation of Ser262/356 (12E8) and Ser396/404
(PHF-1) increased by 5 min and remained elevated for at least 1 hr. In cont
rast, phosphorylation within the Tau-1 epitope did not increase (as evidenc
ed by decreased immunoreactivity) until 30 min after treatment but remained
elevated for a much greater period of time. Treatment with insulin-like gr
owth factor-1 delayed but did not prevent apoptotic cell death induced by o
smotic stress and attenuated the increase in phosphorylation at the Tau-1 e
pitope. Li+, an inhibitor of glycogen synthase kinase 3 beta, had no effect
on osmotic stress-induced caspase activation, but reduced phosphorylation
at the Tau-1 epitope. Complete inhibition of osmotic stress-induced caspase
activation with DEVD-CHO had no effect on the increases in tau phosphoryla
tion. The results of these studies demonstrate that tau phosphorylation is
increased at the specific epitopes during apoptosis. However, the changes i
n tau phosphorylation likely do not significantly impact the apoptotic proc
ess but rather occur concurrently as a result of inappropriate activation o
f specific protein kinases. Nonetheless, there is increasing evidence of a
dysregulation of protein kinases that occurs in Alzheimer's disease brain t
hat may be part of the events of apoptosis, which could contribute to aberr
ant increases in tau phosphorylation. J. Neurosci. Res. 65:573-582, 2001. (
C) 2001 Wiley-Liss, Inc.