Although multiple CHCHD10 mutations are associated with the spectrum of familial and sporadic frontotemporal dementia–amyotrophic lateral sclerosis (FTD–ALS) diseases, neither the normal function of endogenous CHCHD10 nor its role in the pathological milieu (that is, TDP-43 pathology) of FTD/ALS have been investigated. In this study, we made a series of observations utilizing Caenorhabditis elegans models, mammalian cell lines, primary neurons and mouse brains, demonstrating that CHCHD10 normally exerts a protective role in mitochondrial and synaptic integrity as well as in the retention of nuclear TDP-43, whereas FTD/ALS-associated mutations (R15L and S59L) exhibit loss of function phenotypes in C. elegans genetic complementation assays and dominant negative activities in mammalian systems, resulting in mitochondrial/synaptic damage and cytoplasmic TDP-43 accumulation. As such, our results provide a pathological link between CHCHD10-associated mitochondrial/synaptic dysfunction and cytoplasmic TDP-43 inclusions.

Neurodegeneration associated with amyloid b (Ab) peptide accumulation, synaptic loss, neuroinflammation, tauopathy, and memory impairments encompass the pathophysiological features of Alzheimer's disease (AD). We previously reported that the scaffolding protein RanBP9, which is overall increased in brains of AD patients, simultaneously promotes Ab generation and focal adhesion disruption by accelerating the endocytosis of amyloid precursor protein (APP) and b1-integrin, respectively. Here, we show that RanBP9 protein levels are increased by fourfold in FAD mutant APP transgenic mice. Accordingly, RanBP9 transgenic mice demonstrate significantly increased synapse loss, neurodegeneration, gliosis, and spatial memory deficits. RanBP9 overexpression promotes apoptosis and potentiates Ab-induced neurotoxicity independent of its capacity to promote Ab generation. Conversely, RanBP9 reduction by siRNA or gene dosage mitigates Ab-induced neurotoxicity. Importantly, RanBP9 activates/dephosphorylates cofilin, a key regulator of actin dynamics and mitochondria-mediated apoptosis, and siRNA knockdown of cofilin abolishes both Ab and RanBP9-induced apoptosis. These findings implicate the RanBP9-cofilin pathway as critical therapeutic targets not only for stemming Ab generation but also antagonizing Ab-induced neurotoxicity. Cell Death and Differentiation (2012) 19, 1413-1423; doi:10.1038/cdd.2012.14; published online 24 February 2012Alzheimer's disease (AD) is a neurodegenerative disorder characterized by accumulations of the amyloid b (Ab) -peptide and hyperphosphorylated tau in senile plaques and neurofibrillary tangles, respectively. Ab is a neurotoxic peptide derived from b-and g-secretase cleavages of the amyloid precursor protein (APP) and is thought to be a critical early player in AD pathogenesis. 1 In addition to the accumulation of Ab and tau, abnormalities in the actin cytoskeleton are detected earlier during the course of AD and other neurodegenerative diseases. 2 Indeed, it has been demonstrated that Ab can induce actin/cofilin pathology associated with hyperphosphorylated tau in primary neurons and in vivo. [3][4][5] We recently demonstrated that the scaffolding protein RanBP9 interacts with the cytoplasmic tails of LRP, APP, and BACE1, and functions as a scaffold upon which APP is brought together with BACE1 and LRP. Such interactions of RanBP9 promote the endocytosis of APP and strongly increase BACE1 cleavage of APP to generate Ab in vitro and in vivo. 6,7 Conversely, siRNA knockdown of RanBP9 reduces BACE1 cleavage of APP and Ab generation, indicating that endogenous RanBP9 normally functions in this capacity. 6 In addition, a 60-kD proteolytic fragment of RanBP9 is increased by more than sixfold in brains of AD patients, and this fragment potentiates Ab generation via BACE1 processing of APP. 8 In addition to promoting Ab generation by accelerating APP endocytosis, RanBP9 also potently disrupts integrin-dependent focal adhesion signaling and assembly by accelerating b1-integrin and LRP endocytosis. 9 In th...

The accumulation of amyloid-β protein (Aβ) is an early event associated with synaptic and mitochondrial damage in Alzheimer's disease (AD). Recent studies have implicated the filamentous actin (F-actin) severing protein, Cofilin, in synaptic remodeling, mitochondrial dysfunction, and AD pathogenesis. However, whether Cofilin is an essential component of the AD pathogenic process and how Aβ impinges its signals to Cofilin from the neuronal surface are unknown. In this study, we found that Aβ42 oligomers (Aβ42O, amyloid-β protein 1–42 oligomers) bind with high affinity to low or intermediate activation conformers of β1-integrin, resulting in the loss of surface β1-integrin and activation of Cofilin via Slingshot homology-1 (SSH1) activation. Specifically, conditional loss of β1-integrin prevented Aβ42O-induced Cofilin activation, and allosteric modulation or activation of β1-integrin significantly reduced Aβ42O binding to neurons while blocking Aβ42O-induced reactive oxygen species (ROS) production, mitochondrial dysfunction, depletion of F-actin/focal Vinculin, and apoptosis. Cofilin, in turn, was required for Aβ42O-induced loss of cell surface β1-integrin, disruption of F-actin/focal Talin–Vinculin, and depletion of F-actin-associated postsynaptic proteins. SSH1 reduction, which mitigated Cofilin activation, prevented Aβ42O-induced mitochondrial Cofilin translocation and apoptosis, while AD brain mitochondria contained significantly increased activated/oxidized Cofilin. In mechanistic support in vivo, AD mouse model (APP (amyloid precursor protein)/PS1) brains contained increased SSH1/Cofilin and decreased SSH1/14-3-3 complexes, indicative of SSH1–Cofilin activation via release of SSH1 from 14-3-3. Finally, genetic reduction in Cofilin rescued APP/Aβ-induced synaptic protein loss and gliosis in vivo as well as deficits in long-term potentiation (LTP) and contextual memory in APP/PS1 mice. These novel findings therefore implicate the essential involvement of the β1-integrin–SSH1–Cofilin pathway in mitochondrial and synaptic dysfunction in AD.

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.

Mitochondrial dysfunction and synaptic damage are critical early features of Alzheimer's disease (AD) associated with amyloid b (Ab) and s. We previously reported that the scaffolding protein RanBP9, which is overall increased in AD, simultaneously promotes Ab generation and focal adhesion disruption by accelerating the endocytosis of APP and b1-integrin, respectively. Moreover, RanBP9 induces neurodegeneration in vitro and in vivo and mediates Ab-induced neurotoxicity. However, little is known regarding the mechanisms underlying such neurotoxic processes. Here, we show that RanBP9 induces the loss of mitochondrial membrane potential and increase in mitochondrial superoxides associated with decrease in Bcl-2, increase in Bax protein and oligomerization, fragmentation of mitochondria, and cytochrome c release. RanBP9-induced neurotoxic changes are significantly prevented by the mitochondrial fission inhibitor Mdivi-1 and by classical inhibitors of the mitochondrial apoptosis, XIAP, Bcl-2, and Bcl-xl. RanBP9 physically interacts with the tumor suppressor p73 and increases endogenous p73a levels at both transcriptional and post-translational levels;moreover, the knockdown of endogenous p73 by siRNA effectively blocks RanBP9 and Ab1-42-induced mitochondria-mediated cell death. Conversely, siRNA knockdown of endogenous RanBP9 also suppresses p73-induced apoptosis, suggesting that RanBP9 and p73 have cooperative roles in inducing cell death. Taken together, these finding implicate the RanBP9/p73 complex in mitochondria-mediated apoptosis in addition to its role in enhancing Ab generation. The accumulations of amyloid b (Ab) peptide and hyperphosphorylated t are the major pathological hallmarks of Alzheimer's disease (AD). Mounting evidence clearly indicates that mitochondrial dysfunction is a critical early component of AD and related neurodegenerative disorders.

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia. While the accumulation of Aβ is pivotal to the etiology of AD, both the microtubule-associated protein tau (MAPT) and the F-actin severing protein cofilin are necessary for the deleterious effects of Aβ. However, the molecular link between tau and cofilin remains unclear. In this study, we found that cofilin competes with tau for direct microtubule binding in vitro, in cells, and in vivo, which inhibits tau-induced microtubule assembly. Genetic reduction of cofilin mitigates tauopathy and synaptic defects in Tau-P301S mice and movement deficits in tau transgenic C. elegans. The pathogenic effects of cofilin are selectively mediated by activated cofilin, as active but not inactive cofilin selectively interacts with tubulin, destabilizes microtubules, and promotes tauopathy. These results therefore indicate that activated cofilin plays an essential intermediary role in neurotoxic signaling that promotes tauopathy.

Bitter taste receptors (TAS2Rs) are expressed on human airway smooth muscle (HASM) and evoke marked relaxation. Agonist interaction with TAS2Rs activates phospholipase C and increases compartmentalized intracellular Ca ([Ca]) via inositol 1,4,5 triphosphate. In taste cells, the G protein gustducin couples TAS2R to phospholipase C; however, we find very low levels of G mRNA or protein in HASM. We hypothesized that another G protein in HASM transmits TAS2R function. TAS2R signaling to [Ca], extracellular signal-regulated kinase (ERK) 1/2, and physiologic relaxation was sensitive to pertussis toxin, confirming a role for a member of the G family. α subunit expression in HASM was G > G = G > G ≈ G, with G and G at the limits of detection (>100-fold lower than G). Small interfering RNA knockdowns in HASM showed losses of [Ca] and ERK1/2 signaling when G, G, or G were reduced. G and G knockdowns had no effect on [Ca] and a minimal, transient effect on ERK1/2 phosphorylation. Furthermore, G and G knockdowns did not affect any TAS2R signaling. In overexpression experiments in human embryonic kidney-293T cells, we confirmed an agonist-dependent physical interaction between TAS2R14 and G. ASM cells from transgenic mice expressing a peptide inhibitor of G had attenuated relaxation to TAS2R agonist. These data indicate that, unlike in taste cells, TAS2Rs couple to the prevalent G proteins, G, G, and G, with no evidence for functional coupling to G. This absence of function for the "canonical" TAS2R G protein in HASM may be due to the very low expression of G, indicating that TAS2Rs can optionally couple to several G proteins in a cell type-dependent manner contingent upon G protein expression.

The defining pathological hallmarks of Alzheimer's disease (AD) are proteinopathies marked by the amyloid-␤ (A␤) peptide and hyperphosphorylated tau. In addition, Hirano bodies and cofilin-actin rods are extensively found in AD brains, both of which are associated with the actin cytoskeleton. The actin-binding protein cofilin known for its actin filament severing, depolymerizing, nucleating, and bundling activities has emerged as a significant player in AD pathogenesis. In this review, we discuss the regulation of cofilin by multiple signaling events impinging on LIM kinase-1 (LIMK1) and/or Slingshot homolog-1 (SSH1) downstream of A␤. Such pathophysiological signaling pathways impact actin dynamics to regulate synaptic integrity, mitochondrial translocation of cofilin to promote neurotoxicity, and formation of cofilin-actin pathology. Other intracellular signaling proteins, such as ␤-arrestin, RanBP9, Chronophin, PLD1, and 14-3-3 also impinge on the regulation of cofilin downstream of A␤. Finally, we discuss the role of activated cofilin as a bridge between actin and microtubule dynamics by displacing tau from microtubules, thereby destabilizing tau-induced microtubule assembly, missorting tau, and promoting tauopathy.