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RanBP9 at the intersection between cofilin and Aβ pathologies: rescue of neurodegenerative changes by RanBP9 reduction.

Woo JA, Boggess T, Uhlar C, Wang X, Khan H, Cappos G, Joly-Amado A, De Narvaez E, Majid S, Minamide LS, Bamburg JR, Morgan D, Weeber E, Kang DE - Cell Death Dis (2015)

Bottom Line: In this study, we found that endogenous RanBP9 positively regulates SSH1 levels and mediates Aβ-induced translocation of cofilin to mitochondria and induction of cofilin-actin pathology in cultured cells, primary neurons, and in vivo.Endogenous level of RanBP9 was also required for Aβ-induced collapse of growth cones in immature neurons (days in vitro 9 (DIV9)) and depletion of synaptic proteins in mature neurons (DIV21).Therefore, these results underscore the critical importance of endogenous RanBP9 not only in Aβ accumulation but also in mediating the neurotoxic actions of Aβ at the level of synaptic plasticity, mitochondria, and cofilin-actin pathology via control of the SSH1-cofilin pathway in vivo.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Medicine, USF Health Byrd Alzheimer's Institute, Tampa, FL, USA.

ABSTRACT
Molecular pathways underlying the neurotoxicity and production of amyloid β protein (Aβ) represent potentially promising therapeutic targets for Alzheimer's disease (AD). We recently found that overexpression of the scaffolding protein RanBP9 increases Aβ production in cell lines and in transgenic mice while promoting cofilin activation and mitochondrial dysfunction. Translocation of cofilin to mitochondria and induction of cofilin-actin pathology require the activation/dephosphorylation of cofilin by Slingshot homolog 1 (SSH1) and cysteine oxidation of cofilin. In this study, we found that endogenous RanBP9 positively regulates SSH1 levels and mediates Aβ-induced translocation of cofilin to mitochondria and induction of cofilin-actin pathology in cultured cells, primary neurons, and in vivo. Endogenous level of RanBP9 was also required for Aβ-induced collapse of growth cones in immature neurons (days in vitro 9 (DIV9)) and depletion of synaptic proteins in mature neurons (DIV21). In vivo, amyloid precursor protein (APP)/presenilin-1 (PS1) mice exhibited 3.5-fold increased RanBP9 levels, and RanBP9 reduction protected against cofilin-actin pathology, synaptic damage, gliosis, and Aβ accumulation associated with APP/PS1 mice. Brains slices derived from APP/PS1 mice showed significantly impaired long-term potentiation (LTP), and RanBP9 reduction significantly enhanced paired pulse facilitation and LTP, as well as partially rescued contextual memory deficits associated with APP/PS1 mice. Therefore, these results underscore the critical importance of endogenous RanBP9 not only in Aβ accumulation but also in mediating the neurotoxic actions of Aβ at the level of synaptic plasticity, mitochondria, and cofilin-actin pathology via control of the SSH1-cofilin pathway in vivo.

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RanBP9 mediates AβO-induced translocation of cofilin to mitochondria and lowers cofilin activation via SSH1. (a) Freshly solubilized Aβ1-42 monomers (Aβ42M) or Aβ1-42 oligomer preparation (Aβ42O) subjected to SDS-PAGE and immunoblotted for Aβ. Note the monomer (M), dimers (Di), trimmers (Tri), and tetramemers (Tet) in the oligomer preparation. (b and c) Hippocampus-derived HT22 cells transiently transfected with control or RanBP9 siRNA for 48 h, treated with/without Aβ1-42O for 2 h, separated for mitochondrial and cytosol fractions, and subjected to immunoblotting for the indicated proteins. A representative experiment is shown. Notice the reduction phospho-cofilin upon Aβ42O treatment but mitigated response in RanBP9 siRNA knocked down cells. (c) Quantitation of mitochondrial cofilin (ANOVA, post-hoc Tukey, **P<0.005, n=3 replicates). (d and e) Hippocampal extracts from 3-month-old APP/PS1 and APP/PS1;RanBP9+/− mice subjected to separation of mitochondrial and cytosol fractions and immunoblotted for the indicated proteins. Note the reduced level of cofilin in mitochondrial fraction of APP/PS1;RanBP9+/− brain. (e) Quantitation of mitochondrial cofilin (t-test, **P<0.005, n=4 mice per genotype). (f-h) Hippocampal extracts from 3-month-old WT and littermate RanBP9+/− (Ran9+/−) mice subjected to immunoblotting for the indicated proteins. Representative experiment showing increase in phospho-cofilin (P-cofilin) and decrease in SSH1 in RanBP9+/− brain. (g) Quantitation of P-cofilin in hippocampus (t=2.74, P=0.022, *P<0.05, n=5 mice per genotype). (h) Quantitation of SSH1 (t-test, **P=0.0016, n=4 mice per genotype). (i and j) HT22 cells transiently transfected with vector control (Vec) or Flag-RanBP9 and immunoblotted for the indicated proteins. Note the increase in SSH1 but not LIMK1 by RanBP9 overexpression. (j) Quantitation of SSH1 (t-test, ***P<0.0001, n=4 replicates). Error bars represent S.E.M. on graphs. (k) Cortex (CTX) and hippocampus (HIPP) homogenates of 6-month-old WT or littermate Flag-RanBP9 transgenic (TG) mice immunoprecipitated for SSH1 and/or immunoblotted for the indicated proteins. Note the increase in SSH1-RanBP9 complex in Flag-RanBP9 transgenic mice (TG). (l) HT22 cells transiently transfected with/without RanBP9 siRNA and treated with/without Aβ42O (1 μM) for 2 h followed by immunoprecipitation for SSH1 and/or immunoblotting for the indicated proteins. Note that RanBP9 siRNA reduces SSH1 levels and decreases Aβ42O-induced enhancement of cofilin–SSH1 interaction. (m) Quantitation of SSH1 protein levels with/without RanBP9 siRNA transfection in HT22 cells (t-test, ***P=0.0008, n=4 replicates). (n) DIV18 cortical primary neurons treated with or without Aβ42O (1 μM) for 2 h, subjected to immunoprecipitation for SSH1, and/or immunoblotting for the indicated proteins. Note the increase in RanBP9-SSH1 and cofilin-SSH1 complex formation with Aβ42O treatment. (o) HT22 cells transiently transfected with control, RanBP9 siRNA, or RanBP9 and subjected to cycloheximide (CHX) treatment for the indicated times followed by immunoblotting for SSH1 or actin. Representative blots adjusted to show similar signal at time 0. Note that RanBP9 siRNA and overexpression accelerates and delays SSH1 turnover, respectively
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fig1: RanBP9 mediates AβO-induced translocation of cofilin to mitochondria and lowers cofilin activation via SSH1. (a) Freshly solubilized Aβ1-42 monomers (Aβ42M) or Aβ1-42 oligomer preparation (Aβ42O) subjected to SDS-PAGE and immunoblotted for Aβ. Note the monomer (M), dimers (Di), trimmers (Tri), and tetramemers (Tet) in the oligomer preparation. (b and c) Hippocampus-derived HT22 cells transiently transfected with control or RanBP9 siRNA for 48 h, treated with/without Aβ1-42O for 2 h, separated for mitochondrial and cytosol fractions, and subjected to immunoblotting for the indicated proteins. A representative experiment is shown. Notice the reduction phospho-cofilin upon Aβ42O treatment but mitigated response in RanBP9 siRNA knocked down cells. (c) Quantitation of mitochondrial cofilin (ANOVA, post-hoc Tukey, **P<0.005, n=3 replicates). (d and e) Hippocampal extracts from 3-month-old APP/PS1 and APP/PS1;RanBP9+/− mice subjected to separation of mitochondrial and cytosol fractions and immunoblotted for the indicated proteins. Note the reduced level of cofilin in mitochondrial fraction of APP/PS1;RanBP9+/− brain. (e) Quantitation of mitochondrial cofilin (t-test, **P<0.005, n=4 mice per genotype). (f-h) Hippocampal extracts from 3-month-old WT and littermate RanBP9+/− (Ran9+/−) mice subjected to immunoblotting for the indicated proteins. Representative experiment showing increase in phospho-cofilin (P-cofilin) and decrease in SSH1 in RanBP9+/− brain. (g) Quantitation of P-cofilin in hippocampus (t=2.74, P=0.022, *P<0.05, n=5 mice per genotype). (h) Quantitation of SSH1 (t-test, **P=0.0016, n=4 mice per genotype). (i and j) HT22 cells transiently transfected with vector control (Vec) or Flag-RanBP9 and immunoblotted for the indicated proteins. Note the increase in SSH1 but not LIMK1 by RanBP9 overexpression. (j) Quantitation of SSH1 (t-test, ***P<0.0001, n=4 replicates). Error bars represent S.E.M. on graphs. (k) Cortex (CTX) and hippocampus (HIPP) homogenates of 6-month-old WT or littermate Flag-RanBP9 transgenic (TG) mice immunoprecipitated for SSH1 and/or immunoblotted for the indicated proteins. Note the increase in SSH1-RanBP9 complex in Flag-RanBP9 transgenic mice (TG). (l) HT22 cells transiently transfected with/without RanBP9 siRNA and treated with/without Aβ42O (1 μM) for 2 h followed by immunoprecipitation for SSH1 and/or immunoblotting for the indicated proteins. Note that RanBP9 siRNA reduces SSH1 levels and decreases Aβ42O-induced enhancement of cofilin–SSH1 interaction. (m) Quantitation of SSH1 protein levels with/without RanBP9 siRNA transfection in HT22 cells (t-test, ***P=0.0008, n=4 replicates). (n) DIV18 cortical primary neurons treated with or without Aβ42O (1 μM) for 2 h, subjected to immunoprecipitation for SSH1, and/or immunoblotting for the indicated proteins. Note the increase in RanBP9-SSH1 and cofilin-SSH1 complex formation with Aβ42O treatment. (o) HT22 cells transiently transfected with control, RanBP9 siRNA, or RanBP9 and subjected to cycloheximide (CHX) treatment for the indicated times followed by immunoblotting for SSH1 or actin. Representative blots adjusted to show similar signal at time 0. Note that RanBP9 siRNA and overexpression accelerates and delays SSH1 turnover, respectively

Mentions: We assessed whether Aβ oligomers alter cofilin translocation to mitochondria and whether siRNA knockdown of RanBP9 may influence this phenotype. We prepared Aβ1-42 oligomers precisely as previously characterized,21 which contained sodium dodecyl sulfate (SDS)-resistant dimers, trimers, and tetramers (Aβ1-42 oligomers (Aβ42O)), whereas freshly dissolved Aβ1-42 only contained monomers (Aβ42M) (Figure 1a). All stated Aβ42O concentrations heretofore are based on the monomer concentration. Hippocampus-derived HT22 cells were transiently transfected with control or RanBP9 siRNA for 48 h and subjected to treatment with or without Aβ42O (1 μM) for 2 h, followed by separation of intact mitochondria and cytosol fractions. Aβ42O treatment increased both cofilin and RanBP9 translocation to mitochondria (Figure 1b). However, siRNA knockdown of endogenous RanBP9 mitigated AβO-induced cofilin mitochondrial translocation (Figures 1b and c). Aβ42 monomer exposure (1 μM, 2 h) neither promoted cofilin translocation to mitochondria nor altered cofilin activation (Supplementary Figure S1A). In vivo, RanBP9 levels were greatly decreased in the hippocampus of 3-month-old APP/PS1;RanBP9+/− mice in both cytosol and mitochondrial fractions compared with APP/PS1 mice22 (Figure 1d). Although cofilin levels were unchanged in the cytosol fraction between the genotypes, cofilin was significantly reduced in the hippocampal mitochondrial fraction of APP/PS1;RanBP9+/− mice compared with APP/PS1 mice (Figures 1d and e), indicating that endogenous RanBP9 facilitates translocation of cofilin to mitochondria in vivo. As expected, 3-month-old RanBP9+/− mice exhibited reduced RanBP9 protein together with significantly increased inactive phospho-cofilin without altering total cofilin (Figures 1f and g), which was accompanied by significantly decreased SSH1 protein in RanBP9+/− mice (Figures 1f and h), indicating that RanBP9 positively regulates SSH1 levels. Indeed, SSH1 but not LIMK1 levels were significantly increased secondary to RanBP9 overexpression in HT22 cells (Figures 1I and j). Consistent with these observations, RanBP9 not only markedly increased SSH1 but also co-immunoprecipitated with SSH1 in brain (Figure 1k). Accordingly, siRNA knockdown of RanBP9 in HT22 cells strongly reduced the enhancement of cofilin-SSH1 complex induced by Aβ42O treatment (Figure 1l), while significantly decreasing SSH1 levels (Figures 1I and m). In days in vitro 21 (DIV21) primary cortical neurons, Aβ42O (2 h) markedly increased RanBP9-SSH1 and cofilin-SSH1 complexes (Figure 1n), suggesting that RanBP9 not only increases SSH1 levels but may also serve to facilitate cofilin-SSH1 interaction upon Aβ42O exposure. To determine whether the RanBP9-SSH1 complex alters SSH1 protein stability, we performed cycloheximide turnover experiments. Indeed, RanBP9 siRNA and overexpression markedly accelerated and delayed the turnover of SSH1, respectively (Figure 1o), confirming that RanBP9 positively regulates SSH1 protein stability.


RanBP9 at the intersection between cofilin and Aβ pathologies: rescue of neurodegenerative changes by RanBP9 reduction.

Woo JA, Boggess T, Uhlar C, Wang X, Khan H, Cappos G, Joly-Amado A, De Narvaez E, Majid S, Minamide LS, Bamburg JR, Morgan D, Weeber E, Kang DE - Cell Death Dis (2015)

RanBP9 mediates AβO-induced translocation of cofilin to mitochondria and lowers cofilin activation via SSH1. (a) Freshly solubilized Aβ1-42 monomers (Aβ42M) or Aβ1-42 oligomer preparation (Aβ42O) subjected to SDS-PAGE and immunoblotted for Aβ. Note the monomer (M), dimers (Di), trimmers (Tri), and tetramemers (Tet) in the oligomer preparation. (b and c) Hippocampus-derived HT22 cells transiently transfected with control or RanBP9 siRNA for 48 h, treated with/without Aβ1-42O for 2 h, separated for mitochondrial and cytosol fractions, and subjected to immunoblotting for the indicated proteins. A representative experiment is shown. Notice the reduction phospho-cofilin upon Aβ42O treatment but mitigated response in RanBP9 siRNA knocked down cells. (c) Quantitation of mitochondrial cofilin (ANOVA, post-hoc Tukey, **P<0.005, n=3 replicates). (d and e) Hippocampal extracts from 3-month-old APP/PS1 and APP/PS1;RanBP9+/− mice subjected to separation of mitochondrial and cytosol fractions and immunoblotted for the indicated proteins. Note the reduced level of cofilin in mitochondrial fraction of APP/PS1;RanBP9+/− brain. (e) Quantitation of mitochondrial cofilin (t-test, **P<0.005, n=4 mice per genotype). (f-h) Hippocampal extracts from 3-month-old WT and littermate RanBP9+/− (Ran9+/−) mice subjected to immunoblotting for the indicated proteins. Representative experiment showing increase in phospho-cofilin (P-cofilin) and decrease in SSH1 in RanBP9+/− brain. (g) Quantitation of P-cofilin in hippocampus (t=2.74, P=0.022, *P<0.05, n=5 mice per genotype). (h) Quantitation of SSH1 (t-test, **P=0.0016, n=4 mice per genotype). (i and j) HT22 cells transiently transfected with vector control (Vec) or Flag-RanBP9 and immunoblotted for the indicated proteins. Note the increase in SSH1 but not LIMK1 by RanBP9 overexpression. (j) Quantitation of SSH1 (t-test, ***P<0.0001, n=4 replicates). Error bars represent S.E.M. on graphs. (k) Cortex (CTX) and hippocampus (HIPP) homogenates of 6-month-old WT or littermate Flag-RanBP9 transgenic (TG) mice immunoprecipitated for SSH1 and/or immunoblotted for the indicated proteins. Note the increase in SSH1-RanBP9 complex in Flag-RanBP9 transgenic mice (TG). (l) HT22 cells transiently transfected with/without RanBP9 siRNA and treated with/without Aβ42O (1 μM) for 2 h followed by immunoprecipitation for SSH1 and/or immunoblotting for the indicated proteins. Note that RanBP9 siRNA reduces SSH1 levels and decreases Aβ42O-induced enhancement of cofilin–SSH1 interaction. (m) Quantitation of SSH1 protein levels with/without RanBP9 siRNA transfection in HT22 cells (t-test, ***P=0.0008, n=4 replicates). (n) DIV18 cortical primary neurons treated with or without Aβ42O (1 μM) for 2 h, subjected to immunoprecipitation for SSH1, and/or immunoblotting for the indicated proteins. Note the increase in RanBP9-SSH1 and cofilin-SSH1 complex formation with Aβ42O treatment. (o) HT22 cells transiently transfected with control, RanBP9 siRNA, or RanBP9 and subjected to cycloheximide (CHX) treatment for the indicated times followed by immunoblotting for SSH1 or actin. Representative blots adjusted to show similar signal at time 0. Note that RanBP9 siRNA and overexpression accelerates and delays SSH1 turnover, respectively
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fig1: RanBP9 mediates AβO-induced translocation of cofilin to mitochondria and lowers cofilin activation via SSH1. (a) Freshly solubilized Aβ1-42 monomers (Aβ42M) or Aβ1-42 oligomer preparation (Aβ42O) subjected to SDS-PAGE and immunoblotted for Aβ. Note the monomer (M), dimers (Di), trimmers (Tri), and tetramemers (Tet) in the oligomer preparation. (b and c) Hippocampus-derived HT22 cells transiently transfected with control or RanBP9 siRNA for 48 h, treated with/without Aβ1-42O for 2 h, separated for mitochondrial and cytosol fractions, and subjected to immunoblotting for the indicated proteins. A representative experiment is shown. Notice the reduction phospho-cofilin upon Aβ42O treatment but mitigated response in RanBP9 siRNA knocked down cells. (c) Quantitation of mitochondrial cofilin (ANOVA, post-hoc Tukey, **P<0.005, n=3 replicates). (d and e) Hippocampal extracts from 3-month-old APP/PS1 and APP/PS1;RanBP9+/− mice subjected to separation of mitochondrial and cytosol fractions and immunoblotted for the indicated proteins. Note the reduced level of cofilin in mitochondrial fraction of APP/PS1;RanBP9+/− brain. (e) Quantitation of mitochondrial cofilin (t-test, **P<0.005, n=4 mice per genotype). (f-h) Hippocampal extracts from 3-month-old WT and littermate RanBP9+/− (Ran9+/−) mice subjected to immunoblotting for the indicated proteins. Representative experiment showing increase in phospho-cofilin (P-cofilin) and decrease in SSH1 in RanBP9+/− brain. (g) Quantitation of P-cofilin in hippocampus (t=2.74, P=0.022, *P<0.05, n=5 mice per genotype). (h) Quantitation of SSH1 (t-test, **P=0.0016, n=4 mice per genotype). (i and j) HT22 cells transiently transfected with vector control (Vec) or Flag-RanBP9 and immunoblotted for the indicated proteins. Note the increase in SSH1 but not LIMK1 by RanBP9 overexpression. (j) Quantitation of SSH1 (t-test, ***P<0.0001, n=4 replicates). Error bars represent S.E.M. on graphs. (k) Cortex (CTX) and hippocampus (HIPP) homogenates of 6-month-old WT or littermate Flag-RanBP9 transgenic (TG) mice immunoprecipitated for SSH1 and/or immunoblotted for the indicated proteins. Note the increase in SSH1-RanBP9 complex in Flag-RanBP9 transgenic mice (TG). (l) HT22 cells transiently transfected with/without RanBP9 siRNA and treated with/without Aβ42O (1 μM) for 2 h followed by immunoprecipitation for SSH1 and/or immunoblotting for the indicated proteins. Note that RanBP9 siRNA reduces SSH1 levels and decreases Aβ42O-induced enhancement of cofilin–SSH1 interaction. (m) Quantitation of SSH1 protein levels with/without RanBP9 siRNA transfection in HT22 cells (t-test, ***P=0.0008, n=4 replicates). (n) DIV18 cortical primary neurons treated with or without Aβ42O (1 μM) for 2 h, subjected to immunoprecipitation for SSH1, and/or immunoblotting for the indicated proteins. Note the increase in RanBP9-SSH1 and cofilin-SSH1 complex formation with Aβ42O treatment. (o) HT22 cells transiently transfected with control, RanBP9 siRNA, or RanBP9 and subjected to cycloheximide (CHX) treatment for the indicated times followed by immunoblotting for SSH1 or actin. Representative blots adjusted to show similar signal at time 0. Note that RanBP9 siRNA and overexpression accelerates and delays SSH1 turnover, respectively
Mentions: We assessed whether Aβ oligomers alter cofilin translocation to mitochondria and whether siRNA knockdown of RanBP9 may influence this phenotype. We prepared Aβ1-42 oligomers precisely as previously characterized,21 which contained sodium dodecyl sulfate (SDS)-resistant dimers, trimers, and tetramers (Aβ1-42 oligomers (Aβ42O)), whereas freshly dissolved Aβ1-42 only contained monomers (Aβ42M) (Figure 1a). All stated Aβ42O concentrations heretofore are based on the monomer concentration. Hippocampus-derived HT22 cells were transiently transfected with control or RanBP9 siRNA for 48 h and subjected to treatment with or without Aβ42O (1 μM) for 2 h, followed by separation of intact mitochondria and cytosol fractions. Aβ42O treatment increased both cofilin and RanBP9 translocation to mitochondria (Figure 1b). However, siRNA knockdown of endogenous RanBP9 mitigated AβO-induced cofilin mitochondrial translocation (Figures 1b and c). Aβ42 monomer exposure (1 μM, 2 h) neither promoted cofilin translocation to mitochondria nor altered cofilin activation (Supplementary Figure S1A). In vivo, RanBP9 levels were greatly decreased in the hippocampus of 3-month-old APP/PS1;RanBP9+/− mice in both cytosol and mitochondrial fractions compared with APP/PS1 mice22 (Figure 1d). Although cofilin levels were unchanged in the cytosol fraction between the genotypes, cofilin was significantly reduced in the hippocampal mitochondrial fraction of APP/PS1;RanBP9+/− mice compared with APP/PS1 mice (Figures 1d and e), indicating that endogenous RanBP9 facilitates translocation of cofilin to mitochondria in vivo. As expected, 3-month-old RanBP9+/− mice exhibited reduced RanBP9 protein together with significantly increased inactive phospho-cofilin without altering total cofilin (Figures 1f and g), which was accompanied by significantly decreased SSH1 protein in RanBP9+/− mice (Figures 1f and h), indicating that RanBP9 positively regulates SSH1 levels. Indeed, SSH1 but not LIMK1 levels were significantly increased secondary to RanBP9 overexpression in HT22 cells (Figures 1I and j). Consistent with these observations, RanBP9 not only markedly increased SSH1 but also co-immunoprecipitated with SSH1 in brain (Figure 1k). Accordingly, siRNA knockdown of RanBP9 in HT22 cells strongly reduced the enhancement of cofilin-SSH1 complex induced by Aβ42O treatment (Figure 1l), while significantly decreasing SSH1 levels (Figures 1I and m). In days in vitro 21 (DIV21) primary cortical neurons, Aβ42O (2 h) markedly increased RanBP9-SSH1 and cofilin-SSH1 complexes (Figure 1n), suggesting that RanBP9 not only increases SSH1 levels but may also serve to facilitate cofilin-SSH1 interaction upon Aβ42O exposure. To determine whether the RanBP9-SSH1 complex alters SSH1 protein stability, we performed cycloheximide turnover experiments. Indeed, RanBP9 siRNA and overexpression markedly accelerated and delayed the turnover of SSH1, respectively (Figure 1o), confirming that RanBP9 positively regulates SSH1 protein stability.

Bottom Line: In this study, we found that endogenous RanBP9 positively regulates SSH1 levels and mediates Aβ-induced translocation of cofilin to mitochondria and induction of cofilin-actin pathology in cultured cells, primary neurons, and in vivo.Endogenous level of RanBP9 was also required for Aβ-induced collapse of growth cones in immature neurons (days in vitro 9 (DIV9)) and depletion of synaptic proteins in mature neurons (DIV21).Therefore, these results underscore the critical importance of endogenous RanBP9 not only in Aβ accumulation but also in mediating the neurotoxic actions of Aβ at the level of synaptic plasticity, mitochondria, and cofilin-actin pathology via control of the SSH1-cofilin pathway in vivo.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Medicine, USF Health Byrd Alzheimer's Institute, Tampa, FL, USA.

ABSTRACT
Molecular pathways underlying the neurotoxicity and production of amyloid β protein (Aβ) represent potentially promising therapeutic targets for Alzheimer's disease (AD). We recently found that overexpression of the scaffolding protein RanBP9 increases Aβ production in cell lines and in transgenic mice while promoting cofilin activation and mitochondrial dysfunction. Translocation of cofilin to mitochondria and induction of cofilin-actin pathology require the activation/dephosphorylation of cofilin by Slingshot homolog 1 (SSH1) and cysteine oxidation of cofilin. In this study, we found that endogenous RanBP9 positively regulates SSH1 levels and mediates Aβ-induced translocation of cofilin to mitochondria and induction of cofilin-actin pathology in cultured cells, primary neurons, and in vivo. Endogenous level of RanBP9 was also required for Aβ-induced collapse of growth cones in immature neurons (days in vitro 9 (DIV9)) and depletion of synaptic proteins in mature neurons (DIV21). In vivo, amyloid precursor protein (APP)/presenilin-1 (PS1) mice exhibited 3.5-fold increased RanBP9 levels, and RanBP9 reduction protected against cofilin-actin pathology, synaptic damage, gliosis, and Aβ accumulation associated with APP/PS1 mice. Brains slices derived from APP/PS1 mice showed significantly impaired long-term potentiation (LTP), and RanBP9 reduction significantly enhanced paired pulse facilitation and LTP, as well as partially rescued contextual memory deficits associated with APP/PS1 mice. Therefore, these results underscore the critical importance of endogenous RanBP9 not only in Aβ accumulation but also in mediating the neurotoxic actions of Aβ at the level of synaptic plasticity, mitochondria, and cofilin-actin pathology via control of the SSH1-cofilin pathway in vivo.

Show MeSH
Related in: MedlinePlus