Figure 5. hLf inhibits APP phosphorylation via p38 and PP2Ac
interaction-mediated upregulation of PP2A activity. (A) Aβ oligomer
treatment increased the expression and secretion of Lf in the mouse
primary astrocytes from WT mice. n = 5; one-way ANOVA. (B) Conditional
astrocytic medium from Astro-Lf mice inhibited p-APP expression in
N2a-sw cells. n = 3; Student’s t -test. (C) hLf treatment reduced
the expressions of p-APP and sAPPβ, but not APP in N2a-sw cells. n = 5;
one-way ANOVA. (D) hLf treatment diminished the Aβ42 content in the
medium. n = 5; one-way ANOVA. (E) Double immunostaining showing the
fluorescent intensities of Aβ and p-APP in control N2a-sw cells and
hLf-treated N2a-sw cells. The Aβ intensities were both positively
correlated with p-APP intensities in control N2a-sw cells (E1) and
hLf-treated N2a-sw cells (E2), and the intensities of Aβ (E3) and p-APP
(E4) were both decreased in hLf-treated N2a-sw cells. n >
25; Student’s t -test. (F) hLf treatment increased the expression
of p-p38 but had no effects on the expressions of p38, p-CDK5, CDK5,
p-GSK3α/β, GSK3α/β and PP2Ac in N2a-sw cells. n = 5; one-way ANOVA. (G)
The PP2A activity was increased in hLf-treated N2a-sw cells. n = 5;
one-way ANOVA. (H) Inhibition of p38 activity promoted p-APP expression,
and also abrogated hLf-induced downregulation of p-APP in N2a-sw cells.
n = 5; Two-way ANOVA followed by the Bonferroni’s post hoc test. (I)
Activation of PP2A activity rescued the p38 inhibition-induced
upregulation of p-APP in N2a-sw cells. n = 5; Two-way ANOVA followed by
the Bonferroni’s post hoc test. (J) Inhibition of PP2A activity
abrogated hLf-induced downregulation of p-APP in N2a-sw cells. n = 5;
Two-way ANOVA followed by the Bonferroni’s post hoc test. (K) hLf
treatment induced the interaction of PP2Ac and p38, while inhibition of
p38 activity inhibited the interaction of PP2Ac and p38, and also
abrogated the hLf-induced interaction of PP2Ac and p38 in N2a-sw cells.
n = 5; Two-way ANOVA followed by the Bonferroni’s post hoc test. (L)
Inhibition of p38 activity reduced the PP2A activity and abrogated the
hLf-induced upregulation of PP2A activity in N2a-sw cells. n = 5;
Two-way ANOVA followed by the Bonferroni’s post hoc test. (M-N)
Overexpression of p38 enhanced the PP2A activity without changing the
expression of PP2Ac in N2a-sw cells. n = 5; Student’s t -test. (O)
Overexpression of p38 slightly reduced the APP expression, but sharply
decreased the expressions of p-APP and sAPPβ in N2a-sw cells. n = 5;
Student’s t -test. (P) LRP1 siRNA effectively knocked down the
expression of LRP1 in N2a-sw cells. n = 3; Student’s t -test. (Q)
LRP1 silence largely inhibited the hLf-induced upregulation of p-p38 and
subsequently rescued the hLf-induced downregulation of p-APP in N2a-sw
cells. n = 5; Two-way ANOVA followed by the Bonferroni’s post hoc test.
*P < 0.05, **P < 0.01.