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Abnormal axonal trajectories in FE65 À / À ; FE65L1 À / À mouse cortex. Silver-stained coronal sections of 10-week-old WT ( A, C ), 12- week-old FE65 À / À ; FE65L1 À / À ( B, D ) and 9-week-old ( E ) FE65 À / À ; FE65L1 À / À mouse brain sections. An intact corpus callosum, well- developed fimbria and mossy fiber axons emanating from dentate granule cells are observed in the WT mouse brain (A). In the FE65 À / À ; FE65L1 À / À mice, cortical projection neurons fail to cross the midline, forming Probst bundles, and fimbria are reduced in size and medially displaced (B). Higher magnification (boxed in A, B) reveals the absence of the infrapyramidal mossy fibers in FE65 À / À ; FE65L1 À / À hippocampi (D) compared to WT (C). Aberrant fiber bundles are present in the cortical plate of adult (E) and E18.5 FE65 À / À ; FE65L1 À / À mice ( F ). E18.5 brain slices were stained with Tuj1 (red) and counterstained with DAPI (blue) (F). Arrows indicate the position of fiber bundles and arrowheads indicate breaks in the marginal zone where DAPI-positive cells have invaded and migrated into the subarachnoid space. cc, corpus callosum; dg, dentate gyrus; f, fimbria; mf, mossy fibers; spmf, suprapyramidal mossy fibers; ipmf, infrapyramidal mossy fibers; P, Probst bundle. Scale bar, 250 m m (A).
Source publication
Targeted deletion of two members of the FE65 family of adaptor proteins, FE65 and FE65L1, results in cortical dysplasia. Heterotopias resembling those found in cobblestone lissencephalies in which neuroepithelial cells migrate into superficial layers of the developing cortex, aberrant cortical projections and loss of infrapyramidal mossy fibers ari...
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... projection defects are varied in the FE65 À/À ; FE65L1 À/À mice Several axonal projection pathways are aberrant in FE65 À/À ; FE65L1 À/À brains. Reduced size and medial shifting of the fimbria were observed in FE65 À/À ; FE65L1 À/À mice when compared to WT coronal sections at similar rostro-caudal positions, possibly due to a reduction in the number of efferent fibers from the hippocampus (Figure 5A and B). Silver staining of coronal sections also revealed defects in the mossy fiber pathway formed by dentate granule cell axons. ...
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... staining of coronal sections also revealed defects in the mossy fiber pathway formed by dentate granule cell axons. In WT hippocampi, mossy fiber bundles extend from dentate granule cells and run through the hilus of the dentate, above (suprapyramidal) and below (infrapyramidal) the pyr- amidal cell layer of the CA3 region ( Figure 5C). By contrast, the infrapyramidal blade of the dentate gyrus in the FE65 À/À ; FE65L1 À/À mice (n ¼ 4) is foreshortened, deflected toward the thalamus and lacks mossy fiber axons ( Figure 5D). ...
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... WT hippocampi, mossy fiber bundles extend from dentate granule cells and run through the hilus of the dentate, above (suprapyramidal) and below (infrapyramidal) the pyr- amidal cell layer of the CA3 region ( Figure 5C). By contrast, the infrapyramidal blade of the dentate gyrus in the FE65 À/À ; FE65L1 À/À mice (n ¼ 4) is foreshortened, deflected toward the thalamus and lacks mossy fiber axons ( Figure 5D). This does not occur in FE65 þ /À ; FE65L1 À/À or FE65 À/À ; FE65L1 þ /À hippocampi (data not shown). ...
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... major axonal projection pathway joining the two hemispheres, the corpus callosum, is also disrupted in FE65 À/À ; FE65L1 À/À mice ( Figure 5A). Agenesis of the corpus callosum was observed in all adult (n ¼ 5) and E18.5 (n ¼ 3) FE65 À/À ; FE65L1 À/À mouse brains that were examined for this defect ( Figure 5B). ...
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... major axonal projection pathway joining the two hemispheres, the corpus callosum, is also disrupted in FE65 À/À ; FE65L1 À/À mice ( Figure 5A). Agenesis of the corpus callosum was observed in all adult (n ¼ 5) and E18.5 (n ¼ 3) FE65 À/À ; FE65L1 À/À mouse brains that were examined for this defect ( Figure 5B). However, no callosal abnormalities were detected in WT (n ¼ 6) mice, single knockout mice (FE65 À/À n ¼ 2; FE65L1 À/À n ¼ 3) or mice lacking three of the four FE65 and FE65L1 alleles (E18.5, n ¼ 2; adult, n ¼ 4). ...
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... no callosal abnormalities were detected in WT (n ¼ 6) mice, single knockout mice (FE65 À/À n ¼ 2; FE65L1 À/À n ¼ 3) or mice lacking three of the four FE65 and FE65L1 alleles (E18.5, n ¼ 2; adult, n ¼ 4). Probst bundles, which consist of callosal axonal projections that have grown toward but have failed to cross the midline ( Ozaki and Wahlsten, 1993), were visualized in several FE65 À/À ; FE65L1 À/À mouse brains (see Figure 5B). A variable frequency of callosal agenesis has been reported for the 129 inbred strain background, depending on the substrain ( Magara et al, 1999). ...
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... connections are established at the time of neuronal migration during cortical development. Ectopic axon bundles were observed in FE65 À/À ; FE65L1 À/À adult (n ¼ 2) and embryonic (n ¼ 3) brains ( Figure 5E and F, respectively). Silver-stained coronal sections of 10-week-old WT (A, C), 12- week-old FE65 À/À ; FE65L1 À/À (B, D) and 9-week-old (E) FE65 À/À ; FE65L1 À/À mouse brain sections. ...
Citations
... Neuronal migration is essential for the establishment of the nervous system as the process allocates newly differentiated neurons to form functional neuronal layers and circuitry. FE65 -/-/FE65L1 -/double knockout mice show cortical dysplasia, which indicates the role of FE65 in guiding neuronal migration and positioning during cortical development (Guenette et al., 2006). However, controversial roles have been reported for the complex in regulating KAI1 expression. ...
... It is noteworthy that mice lacking both FE65 and FE65L1 exhibit a similar defect in neuronal positioning as in App -/-/Aplp1 −/− /Aplp2 −/− tripleknockout mice (Guenette et al., 2006). Given that APP interacts with FE65, the above knockout mouse studies suggest the two proteins influence the same signaling pathway(s). ...
... One of them is the triple mutant in app family genes app/aplp1/2 (Herms et al., 2004). Another is a related double mutant in apbb1/2, which encode a family of adaptors binding to the cytoplasmic domain of APP (Guenette et al., 2006). The similarity of these phenotypes raises the possibility that inappropriate microglial activation may also be responsible for ectopia formation in these app-related mutants. ...
Microglia, the resident immune cell of the brain, play critical roles in brain development, function, and disease. However, how microglial activity is regulated in this process remains to be elucidated. Here we report an amyloid precursor protein (APP) and heterotrimeric G protein-mediated pathway that negatively regulates microglial inflammatory activation during cerebral cortex development. Disruption of this pathway results in dysregulated microglial activity, excessive extracellular matrix proteinase production, cortical basement membrane breach, and laminar assembly disruption. We further show that this pathway is activated by amyloid β (Aβ), the cleavage product of APP that accumulates in large quantities as plaques in the Alzheimer's disease brain. Specifically, we find Aβ monomers potently suppress inflammatory cytokine transcription and secretion by brain microglia, in an APP and heterotrimeric G protein-dependent manner. These results discover a previously unknown activity of Aβ as a negative regulator of brain microglia as well as a new pathway that mediates the signal transduction. They shed new light on the cell-cell communication mechanisms that regulate brain immune homeostasis and may facilitate further insight into Alzheimer's disease pathogenesis.
... Additionally, APP-FE65 interaction is suggested to influence APPs effect on neuronal migration. FE65 −/− /FE65-like 1 (FE65L1) −/− double knockout mice display focal neuronal ectopia and loss of CR neurons, of which the phenotypes overlap with those observed in App −/− /Aplp1 −/− /Aplp2 −/− triple-knockout mice [46]. ...
Amyloid precursor protein (APP) is a key molecule in the pathogenesis of Alzheimer's disease (AD) as the pathogenic amyloid-β peptide is derived from it. Two closely related APP family proteins (APPs) have also been identified in mammals. Current knowledge, including genetic analyses of gain- and loss-of-function mutants, highlights the importance of APPs in various physiological functions. Notably, APPs consist of multiple extracellular and intracellular protein-binding regions/domains. Protein-protein interactions are crucial for many cellular processes. In past decades, many APPs interactors have been identified which assist the revelation of the putative roles of APPs. Importantly, some of these interactors have been shown to influence several APPs-mediated neuronal processes which are found defective in AD and other neurodegenerative disorders. Studying APPs-interactor complexes would not only advance our understanding of the physiological roles of APPs but also provide further insights into the association of these processes to neurodegeneration, which may lead to the development of novel therapies. In this mini-review, we summarize the roles of APPs-interactor complexes in neurodevelopmental processes including neurogenesis, neurite outgrowth, axonal guidance and synaptogenesis.
... cell migration. It has been reported that FE65/FE65L1 KO mice show cortical dysplasia which is caused by defective neuroblast migration [40]. Noteworthy, ARF6-ARNO has been shown to stimulate Rac-mediated cell motility via ELMO-DOCK180 [39]. ...
ADP-ribosylation factor 6 (ARF6) is a small GTPase that has a variety of neuronal functions including stimulating neurite outgrowth, a crucial process for the establishment and maintenance of neural connectivity. As impaired and atrophic neurites are often observed in various brain injuries and neurological diseases, understanding the intrinsic pathways that stimulate neurite outgrowth may provide insights into developing strategies to trigger the reconnection of injured neurons. The neuronal adaptor FE65 has been shown to interact with ARF6 and potentiate ARF6-mediated neurite outgrowth. However, the precise mechanism that FE65 activates ARF6 remains unclear, as FE65 does not possess a guanine nucleotide exchange factor (GEF) domain/function. Here, we show that FE65 interacts with the ARF6 GEF, namely the ARF nucleotide-binding site opener (ARNO). Moreover, a complex consisting of ARNO, ARF6 and FE65 is detected. Notably, FE65 potentiates the stimulatory effect of ARNO on ARF6-mediated neurite outgrowth, and the effect of FE65 is abrogated by an FE65 mutation that disrupts FE65–ARNO interaction. Additionally, the intramolecular interaction for mediating the autoinhibited conformation of ARNO is attenuated by FE65. Moreover, FE65 potentiates the effects of wild-type ARNO, but not the monomeric mutant, suggesting an association between FE65 and ARNO dimerization. Collectively, we demonstrate that FE65 binds to and activates ARNO and, consequently, potentiates ARF6-mediated neurite outgrowth.
... Important insights into the Fe65 function were gained by analyses of genetically modified mice [15,[166][167][168][169]. In addition to the Fe65 family KO mice, mice overexpressing Fe65 together with APP or APP fragments, such as AICD, were also analyzed [170,171]. ...
... Interestingly, some key features, observed in Fe65 KO mice were also found in mice lacking the APP or Mena/VASP family (Table 2). Thus, Fe65/Fe65L1 DKO as well as APP and Mena/VASP TKO mice all exhibit abnormal ectopic accumulations of neuroblasts, migrating through the basal lamina and pial membrane during brain development [76,167,172], resembling a cobblestone or type II lissencephaly [173][174][175]. Additionally, they all represent failures in axon tract formation and reduction or displacement of Cajal Retzius (CR) cells, resulting in disruption of cortical/meningeal layering. ...
... Mena/VASP TKO mice exhibit exencephaly that is also found in two out of 31 APP TKO mice [76,172]. The cause for cortical malformation in APP and Fe65 KO mice is not yet understood but could be well explained by defects in actin cytoskeleton regulation, possibly causing problems in glial endfoot formation, lamination, neuronal migration, or defective recognition of stop signals [75,76,167,172]. Fe65 and its interacting ABPs were also shown to positively influence dendritic and axonal outgrowth by elevation of actin polymerization [54,58,72,75,76,145,167,[176][177][178]. ...
The scaffolding protein family Fe65, composed of Fe65, Fe65L1, and Fe65L2, was identified as an interaction partner of the amyloid precursor protein (APP), which plays a key function in Alzheimer’s disease. All three Fe65 family members possess three highly conserved interaction domains, forming complexes with diverse binding partners that can be assigned to different cellular functions, such as transactivation of genes in the nucleus, modulation of calcium homeostasis and lipid metabolism, and regulation of the actin cytoskeleton. In this article, we rule out putative new intracellular signaling mechanisms of the APP-interacting protein Fe65 in the regulation of actin cytoskeleton dynamics in the context of various neuronal functions, such as cell migration, neurite outgrowth, and synaptic plasticity.
... Triple KO animals for all three APP family members are also lethal after birth and show important anatomical abnormalities including focal dysplasia, cortical loss of Cajal-Retzius cells, cranial problems and impaired position of the cellular migration 177 . Similar phenotypes have been reported in aTable 1 -Summary of the in vivo and ex vivo functions of APP fragments.Fe65/Fe65L1 KO model, which are protein interactors of APP, suggesting that the complexes formed between these proteins mediate similar functions related to normal brain development178,179 . The combination of these models with KI alleles expressing extra or intracellular truncations of APP has been a powerful model to delineate the function of the different APP products and domains in vivo. ...
Alzheimer’s disease (AD) is a progressive neurodegenerative disease which affects 47 million people worldwide, being the most prominent type of dementia. The etiology of the disease is unknown but genetic evidence from the familial form of the disease indicates that the amyloid precursor protein (APP) plays a key role in the pathology. Importantly, APP is the substrate in the proteolytic reaction producing Aβ peptides which compose the amyloid plaques, one of the main pathological hallmarks in AD brain. In addition, APP is ubiquitously expressed by neurons where it interacts with multiple presynaptic proteins but the role of these interactions is elusive.The aim of my thesis was to study the physiological and pathological functions of APP related to its location at the presynapse. First, we studied the consequences on presynaptic mechanisms of the genetic deletion of presenilin, the catalytic subunit of γ-secretase, the intramembrane protease which cleaves APP. We observed that in absence of presenilin, APP accumulates in axons. By combining optogenetic to electrophysiology, we assessed synaptic transmission and plasticity in the CA3 region of the hippocampus. The presynaptic facilitation, the increase in synaptic vesicle release during repetitive stimulation, was altered whereas the basal neurotransmission was not. The impairment of presynaptic mechanisms was due to the accumulation of APP Cter, which decreases the abundancy of synaptotagmin-7, a calcium sensor essential for facilitation. Using a similar approach, we investigated the consequences of the genetic deletion of APP itself and observed again an impairment of presynaptic facilitation. Together, these results demonstrate the importance of APP homeostasis in presynaptic plasticity.I then investigated possible alterations of APP, other than the amyloid peptides, in the AD brain. I discovered that APP dramatically accumulates together with presynaptic proteins around dense-core amyloid plaques in human AD brain. In addition, the Nter domain, but not the Cter domain of APP is enriched in the core of amyloid plaques uncovering a potential pathological role of the secreted APP Nter in dense-core plaques. Ultrastructural analysis of APP accumulations reveals abundant multivesicular bodies containing presynaptic vesicle proteins and autophagosomal built-up of APP. Finally, we observed that outside the APP accumulations, presynaptic proteins were downregulated, in the neuropil area of the outer molecular layer of the dentate gyrus. Altogether, the data I collected during my thesis supports a role of presynaptic APP in physiology and in AD pathology and highlights APP accumulations as a pathological site where presynaptic proteins are mis-distributed.
... 14 Congenital brain defects and aberrant axonal trajectories are seen in FE65/FE65L1 knockout (KO) mice. 15 Additionally, significant learning and memory defects are found in FE65 KO mice. 16 Previously, we demonstrated that FE65 promotes Rac1-mediated neurite outgrowth by recruiting ELMO1 and facilitating the trafficking of ELMO1 to the plasma membrane (PM), 7 where Rac1 activation predominantly occurs. ...
... For instance, altered neuronal migration is reported in FE65/FE65L1 double KO mice. 15 Moreover, overexpression of FE65 has been shown to stimulate MDCK cell movement. 69 Similarly, active ARF6 dramatically enhances the migration of MDCK cells. ...
Ras‐related C3 botulinum toxin substrate 1 (Rac1) is a member of the Rho family of GTPases that functions as a molecular switch to regulate many important cellular events including actin cytoskeleton remodeling during neurite outgrowth. Engulfment and cell motility 1 (ELMO1)‐dedicator of cytokinesis 1 (DOCK180) is a bipartite guanine nucleotide exchange factor (GEF) complex that has been reported to activate Rac1 on the plasma membrane (PM). Emerging evidence suggests that the small GTPase ADP ribosylation factor 6 (ARF6) activates Rac1 via the ELMO1/DOCK180 complex. However, the exact mechanism by which ARF6 triggers ELMO1/DOCK180‐mediated Rac1 signaling remains unclear. Here, we report that the neuronal scaffold protein FE65 serves as a functional link between ARF6 and ELMO1, allowing the formation of a multimeric signaling complex. Interfering with formation of this complex by transfecting either FE65‐binding‐defective mutants or FE65 siRNA attenuates both ARF6‐ELMO1‐mediated Rac1 activation and neurite elongation. Notably, the PM trafficking of ELMO1 is markedly decreased in cells with suppressed expression of either FE65 or ARF6. Likewise, this process is attenuated in the FE65‐binding‐defective mutants transfected cells. Moreover, overexpression of FE65 increases the amount of ELMO1 in the recycling endosome, an organelle responsible for returning proteins to the PM, whereas knockout of FE65 shows opposite effect. Together, our data indicates that FE65 potentiates ARF6‐Rac1 signaling by orchestrating ARF6 and ELMO1 to promote the PM trafficking of ELMO1 via the endosomal recycling pathway, and thus, promotes Rac1‐mediated neurite outgrowth.
... Data Analysis-Quantification of cortical plate and phosphorylated histone H3-positive (pHH3 ϩ ) cells was performed as described previously (26). Briefly, the quantification of cortical plate was determined in hematoxylin-and eosin-stained E14.5 cerebral cortex sections throughout rostral, intermediate, and caudal levels (40,41). The length of a line, measured by the ImageJ program, from the ventricular surface to the pial surface served as the total cortical thickness. ...
... The ATM-BRCA1 pathway of HR not only plays a role in AD through the management of DSB repair but also may affect AD indirectly. FE65 is an adaptor protein with its expression enriched in the brain [94,95]. It binds the APP intracellular domain (AICD), the c-terminal fragment of Aβ, contributes to ACID-derived transcription activities in mice, and likely plays a role in AD [94,96]. ...
... FE65 is an adaptor protein with its expression enriched in the brain [94,95]. It binds the APP intracellular domain (AICD), the c-terminal fragment of Aβ, contributes to ACID-derived transcription activities in mice, and likely plays a role in AD [94,96]. FE65 interacts with Tip60 and has an important role in DNA damage response (DDR) in SK-N-SH neuroblastoma cells [97]. ...
Alzheimer’s disease (AD) is the most common type of neurodegenerative disease. Its typical pathology consists of extracellular amyloid-β (Aβ) plaques and intracellular tau neurofibrillary tangles. Mutations in the APP, PSEN1, and PSEN2 genes increase Aβ production and aggregation, and thus cause early onset or familial AD. Even with this strong genetic evidence, recent studies support AD to result from complex etiological alterations. Among them, aging is the strongest risk factor for the vast majority of AD cases: Sporadic late onset AD (LOAD). Accumulation of DNA damage is a well-established aging factor. In this regard, a large amount of evidence reveals DNA damage as a critical pathological cause of AD. Clinically, DNA damage is accumulated in brains of AD patients. Genetically, defects in DNA damage repair resulted from mutations in the BRAC1 and other DNA damage repair genes occur in AD brain and facilitate the pathogenesis. Abnormalities in DNA damage repair can be used as diagnostic biomarkers for AD. In this review, we discuss the association, the causative potential, and the biomarker values of DNA damage in AD pathogenesis.
... Amyloid precursor protein (APP) is a transmembrane protein with a large extracellular N-terminal domain and a short cytoplasmic tail. Because APP is expressed within microglia, astrocytes, oligodendrocytes, and neurites of the brain and is primarily responsible for cell adhesion and axon pruning (Chasseigneaux and Allinquant, 2012), its regulation is critical to maintaining normal neuronal development and homeostasis (Hartmann et al., 1999;Herms et al., 2004;Guénette et al., 2006;Chasseigneaux and Allinquant, 2012). APP can be metabolized through two distinct processing pathways, the amyloidogenic and non-amyloidogenic processing pathways. ...
Fragile X syndrome (FXS) is the most common inherited form of intellectual disability and is associated with increased risk for autism spectrum disorder (ASD), anxiety, ADHD, and epilepsy. While our understanding of FXS pathophysiology has improved, a lack of validated blood-based biomarkers of disease continues to impede bench-to-bedside efforts. To meet this demand, there is a growing effort to discover a reliable biomarker to inform treatment discovery and evaluate treatment target engagement. Such a marker, amyloid-beta precursor protein (APP), has shown potential dysregulation in the absence of fragile X mental retardation protein (FMRP) and may therefore be associated with FXS pathophysiology. While APP is best understood in the context of Alzheimer disease, there is a growing body of evidence suggesting the molecule and its derivatives play a broader role in regulating neuronal hyperexcitability, a well-characterized phenotype in FXS. To evaluate the viability of APP as a peripheral biological marker in FXS, we conducted an exploratory ELISA-based evaluation of plasma APP-related species involving 27 persons with FXS (mean age: 22.0 ± 11.5) and 25 age- and sex-matched persons with neurotypical development (mean age: 21.1 ± 10.7). Peripheral levels of both Aβ(1–40) and Aβ(1–42) were increased, while sAPPα was significantly decreased in persons with FXS as compared to control participants. These results suggest that dysregulated APP processing, with potential preferential β-secretase processing, may be a readily accessible marker of FXS pathophysiology.
