Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 115 (2), 373-84

β-Amyloid Regulates Leptin Expression and Tau Phosphorylation Through the mTORC1 Signaling Pathway

Affiliations

β-Amyloid Regulates Leptin Expression and Tau Phosphorylation Through the mTORC1 Signaling Pathway

Gurdeep Marwarha et al. J Neurochem.

Abstract

High levels of the adipocytokine leptin are associated with reduced risk of Alzheimer's disease. Leptin treatment also reduces β-amyloid (Aβ) levels in in vivo and in vitro models of Alzheimer's disease. Aβ and leptin interact with the Akt/mammalian target of rapamycin complex 1 (mTORC1) signaling pathway. Akt/mTORC1 activation reduces tau phosphorylation through the inhibition of the downstream enzyme GSK-3β. mTORC1 also regulates translation of many proteins including leptin. While Aβ has been shown to inactivate Akt, inhibit mTORC1, and facilitate the phosphorylation of tau, leptin activates both Akt and mTORC1 and reduces tau phosphorylation. However, the extent to which Aβ may modulate leptin expression and increase tau phosphorylation involving Akt/mTORC1 has not been determined. In this study, we show that incubation of organotypic slices from rabbit hippocampus with Aβ down-regulates leptin expression, inhibits Akt, activates GSK-3β, increases tau phosphorylation, and inactivates mTORC1. Leptin treatment reverses Aβ effects by alleviating Akt inhibition, preventing GSK-3β activation, reducing tau phosphorylation, and activating mTORC1. On the other hand, Rapamycin, an allosteric inhibitor of mTORC1, down-regulates leptin expression, increases tau phosphorylation, and does not affect Akt and GSK-3β. Our results demonstrate for the first time that Aβ regulates leptin expression and tau phosphorylation through mTORC1.

Conflict of interest statement

All authors report no biomedical financial interests or potential conflicts of interest.

Figures

Figure 1
Figure 1
Efects of Aβ on leptin expression levels in organotypic slices from rabbit hippocampus. (a) Representative Western blot and densitometric analysis demonstrate that treatment with 10 μM soluble Aβ42 or fibrillar Aβ42 (fAβ42) for 72 hours significantly decreases protein levels of leptin compared to untreated slices. (b) Quantitative determination of leptin concentrations by ELISA shows that Aβ treatments reduce leptin concentrations in organotypic slices. (c) Real Time RT- PCR analysis demonstrates that treatment with soluble Aβ42 and fibrillar Aβ42 (fAβ42) for 72 hours significantly decreases mRNA expression of leptin compared to untreated slices. Data is presented as mean values ± S.E.M. *p<0.05, **p<0.01, ***p<0.001 versus control.
Figure 2
Figure 2
Effects of leptin treatment on leptin receptor phosphorylation and leptin concentrations. (a) Representative Western blot and densitometric analysis demonstrating that treatment of organotypic slices with 125nM leptin elicits an increase in leptin receptor phosphorylation (p-Tyr1138 ObRb) compared to untreated organotypic slices or slices treated with 31.25 or 62.5 nM. (b) Quantitative determination of leptin concentrations by ELISA in organotypic slices demonstrates that 125nM but not 31.25nM or 62.5 nM leptin elicits an increase in leptin concentrations in organotypic slice tissue. (c) Representative Western blot and densitometric analysis showing that treatment of organotypic slices with soluble Aβ42 and fAβ42 for 72 hours significantly decreases levels of phosphorylated leptin receptor (p-ObRb) at Tyr1138 residue. Leptin (125nM) treatment reverses the effects of soluble Aβ42 and fAβ42 on levels of p-Tyr1138 ObRb. Treatment of slices with leptin (125nM) alone increased p-Tyr1138 Ob-Rb. Data is presented as mean values ± S.E.M. **p<0.01, ***p<0.001 versus control. †† p<0.01, ††† p<0.001 versus soluble Aβ42 or fibrillar Aβ42.
Figure 3
Figure 3
Representative Western blot and densitometric analysis showing that treatment of organotypic slices with soluble Aβ42 and fAβ42 for 72 hours significantly increases levels of the phosphatase SOCS-3. Leptin (125nM) treatment does not affect levels of SOCS-3. Data is presented as mean values ± S.E.M. * p<0.05 versus control.
Figure 4
Figure 4
Western blot, ELISA and Real Time RT- PCR analysis demonstrating the involvement of mTOR in leptin expression. (a) Representative Western blot and densitometric analysis show that treatment of organotypic slices with the mTOR inhibitor rapamycin for 72 hours significantly decreases protein levels of leptin compared to control slices. (b) Quantitative measurement of leptin levels using ELISA demonstrate that treatment of organotypic slices with rapamycin significantly decreases leptin concentrations. (c) Real Time RT- PCR analysis shows that treatment of organotypic slices with rapamycin significantly also decreases leptin mRNA expression. Data is presented as mean values ± S.E.M. **p<0.01, ***p<0.001 versus control.
Figure 5
Figure 5
Effect of Aβ, rapamycin and leptin treatment on mTOR phosphorylation and activation. (a) Treatment of organotypic slices with soluble Aβ42 or fAβ42 for 72 hours significantly decreases phosphorylation of mTOR at Ser2448 residue. The mTOR inhibitor rapamycin does not affect mTOR phosphorylation. Leptin treatment, either alone or in association with soluble Aβ and rapamycin, dramatically increases p-Ser2448 mTOR to levels higher than basal levels. However, leptin only partially reversed the decrease in levels of p-Ser2448 mTOR induced by fAβ42. (b) Treatment of organotypic slices with soluble Aβ42, fAβ42 and rapamycin for 72 hours significantly reduces phosphorylation of p70S6K1 (p-Thr389 p70S6K1). Leptin treatment, either alone or in association with soluble Aβ increases p-Thr389 p70S6K1to levels higher than basal levels. Leptin also prevented the decrease in p-Thr389 p70S6K1 induced by fAβ42. However, leptin fails to prevent the inhibition of p-Thr389 p70S6K1 caused by rapamycin. Data is presented as mean values ± S.E.M. *p<0.05, **p<0.01 and ***p<0.001 versus control, p<0.05 and ††† p<0.001 versus soluble Aβ42 or fAβ42, ‡ ‡ ‡ p<0.001 versus rapamycin.
Figure 6
Figure 6
Representative Western blots and densitometric analysis demonstrating the effect of Aβ, rapamycin and leptin treatments on tau levels. Treatment of organotypic slices with soluble Aβ42, fAβ42 or rapamycin for 72 hours significantly increases phosphorylation of tau at the Ser202 and Thr205 residues as detected by CP13 antibody. Leptin treatment decreases both basal levels, soluble Aβ42 and rapamycin-induced, but not fAβ42 -induced, phosphorylated Ser202 and Thr205 tau. fAβ42 and rapamycin, but not soluble Aβ42, increased levels of tau phosphorylated at Ser396 and Ser404 residues as detected by PHF-1 antibody. Leptin treatment, while reduces basal levels and fAβ42 - induced phosphorylated Ser396 and Ser404 tau levels, fails to reduce rapamycin-induced increase in levels of phosphorylated tau at Ser396 and Ser404. Data is presented as mean values ± S.E.M. *p<0.05 and **p<0.01 versus control, p<0.05 versus soluble Aβ42 or fAβ42, p<0.05 versus rapamycin
Figure 7
Figure 7
Effects of Aβ, rapamycin and leptin treatments on p- Ser473 AkT, p- Ser9 GSK-3β, and p- Tyr216 GSK-3β levels. (a) Treatment of organotypic slices for 72 hours with soluble Aβ42 or fAβ42, but not with rapamycin, significantly decreases phosphorylation of AkT at Ser473. Leptin treatment, either alone or in association with Aβ or rapamycin, markedly increases p-Ser473 AkT to levels higher than the basal levels. (b) Treatment of organotypic slices for 72 hours with soluble Aβ42 or fAβ42 reduces p-Ser9 GSK-3β levels and increases p-Tyr216 GSK-3β levels. Rapamycin does not affect p-Ser9 GSK-3β or p-Tyr216 GSK-3β levels. Leptin treatment increases p-Ser9 GSK-3β alone or in the presence of Aβ but does not affect p-Tyr216 GSK-3β levels. Data is presented as mean values ± S.E.M. *p<0.05, **p<0.01 and ***p<0.001 versus control; p<0.05 and †† p<0.01 versus soluble Aβ42 or fAβ42; p<0.05 versus rapamycin.
Figure 7
Figure 7
Effects of Aβ, rapamycin and leptin treatments on p- Ser473 AkT, p- Ser9 GSK-3β, and p- Tyr216 GSK-3β levels. (a) Treatment of organotypic slices for 72 hours with soluble Aβ42 or fAβ42, but not with rapamycin, significantly decreases phosphorylation of AkT at Ser473. Leptin treatment, either alone or in association with Aβ or rapamycin, markedly increases p-Ser473 AkT to levels higher than the basal levels. (b) Treatment of organotypic slices for 72 hours with soluble Aβ42 or fAβ42 reduces p-Ser9 GSK-3β levels and increases p-Tyr216 GSK-3β levels. Rapamycin does not affect p-Ser9 GSK-3β or p-Tyr216 GSK-3β levels. Leptin treatment increases p-Ser9 GSK-3β alone or in the presence of Aβ but does not affect p-Tyr216 GSK-3β levels. Data is presented as mean values ± S.E.M. *p<0.05, **p<0.01 and ***p<0.001 versus control; p<0.05 and †† p<0.01 versus soluble Aβ42 or fAβ42; p<0.05 versus rapamycin.
Figure 8
Figure 8
Aβ attenuates mTORC1 signaling by reducing the phosphorylation of mTOR (1), thus causing a decrease in the expression of leptin (2). Reduced expression levels of leptin are accompanied by a reduction in phosphorylation of leptin receptor (p-Tyr1138 ObRb) (3). Aβ also increases SOCS-3 expression levels (4), an effect that may also cause a reduction in levels of p-Tyr1138 ObRb (5). Reduced levels p-Tyr1138 ObRb leads to decreased activation of AkT (6), subsequently resulting in the activation of GSK-3β (7). Activation of GSK-3β results in increased phosphorylation of tau (p-tau) (8). Attenuated AkT activation can also reduce mTORC1 activation (9), an effect that may further reduce leptin expression (2). It is also possible that Aβ regulates leptin signaling via other mechanisms independent of mTORC1 and SOCS-3.

Similar articles

See all similar articles

Cited by 18 PubMed Central articles

See all "Cited by" articles

Publication types

MeSH terms

Feedback