Accumulation Of Amyloid Precursor Protein Research Articles

Spatiotemporal development of the neuronal accumulation of amyloid precursor protein and the amyloid plaque formation in the brain of 3xTg-AD mice

The amyloid plaque is a hallmark of Alzheimer's disease. The accumulation of the amyloid precursor protein (APP) in the neuronal structure is assumed to lead to amyloid plaque formation through the excessive production of β-amyloid protein. To study the relationship between the neuronal accumulation of APP and amyloid plaque formation, we histologically analyzed their development in the different brain regions in 3xTg-AD mice, which express Swedish mutated APP (APPSWE) in the neurons. Observation throughout the brain revealed APPSWE-positive somata in the broad regions. Quantitative model analysis showed that the somatic accumulation of APPSWE developed firstly in the hippocampus from a very early age (<1 month) and proceeded slower in the isocortex. In line with this, the hippocampus was the first region to form amyloid plaques at the age of 9–12 months, while amyloid plaques were rarely observed in the isocortex. Females had more APPSWE-positive somata and plaques than males. Furthermore, amyloid plaques were observed in the lateral septum and pontine grey, which did not contain APPSWE-positive somata but only the APPSWE-positive fibers. These results suggested that neuronal accumulation of APPSWE, both in somatodendritic and axonal domains, is closely related to the formation of amyloid plaques.

Abstract 3969: Alzheimer's disease-associated amyloid precursor protein improves anti-tumor immunity by inhibiting ceramide-mediated lethal mitophagy and restoring mitochondrial fumarate metabolism in aging T-cells

Abstract The association between Alzheimer’s disease (AD) and lower cancer incidence has been observed in several epidemiological studies without much mechanistic insight. We aimed to understand this cancer resistance mechanism linked to AD and exploit it for broader cancer therapies. A hallmark of AD is the accumulation of amyloid precursor protein (APP) in neuronal mitochondria, inhibiting mitophagy, abrogating the clearance of dysfunctional mitochondria, and contributing to AD pathology. In addition to neurons, mitophagy plays an important role in T-cells, where excessive ceramide-dependent mitophagy in aging T-cells inhibits their energy metabolism and limits their anti-tumor functions. Thus, attenuation of ceramide-dependent mitophagy plays a favorable role in enhancing aging T-cell anti-tumor function. Given that APP is also processed in T-cells, we hypothesized that APP accumulates aberrantly in aging Alzheimer’s T-cells, inhibiting mitophagy and enhancing T-cell anti-tumor activity. Employing techniques of lipidomics, metabolomics, imaging, molecular biology, and genetic models, we show that AD T-cells from a mouse model and human patients are protected against aging-associated ceramide-dependent mitophagy, which enhanced their secretion of inflammatory anti-tumor cytokines. The excessive localization of APP to the T-cell mitochondria, where it inhibits the accumulation of ceramide synthase 6 (CerS6) and C14/C16-ceramides, attenuated the levels of mitophagy and protected the Alzheimer’s T-cells from metabolic defects observed in aging, namely protecting against the exhaustion of fumarate pools. Both in vitro and in vivo re-supplementation of fumarate to aging WT mouse T-cells effectively rescued their viability, cytokine production, and tumor killing capacity both in vitro and in adoptive T-cell transfers to mice with melanoma, functionally mimicking the AD phenotype. The fumarate supplementation also led to a decrease in ceramide-dependent mitophagy in the WT aging T-cells, indicating an interplay between ceramide-dependent mitophagy and fumarate metabolism which contributes to the protection of the anti-tumor function in aging AD T-cells. Moreover, we show that Alzheimer’s mice that express APP in the brain and T-cells, but not AD mice that express APP only in the brain, are protected against the growth of both carcinogen-induced and allografted tumors. Finally, transfer of mitochondria from AD T-cells to aging WT T-cells improved their metabolic fitness and anti-cancer functions. In summary, we show that AD-associated APP improves anti-tumor immunity of aging T-cells by inhibiting ceramide-mediated lethal mitophagy and restoring mitochondrial fumarate metabolism. These data provide a novel mechanism to explain reduced cancer incidences in AD patients. Citation Format: Mohamed Faisal Kassir, Han G. Lee, Natalia Oleinik, Wyatt Wofford, Chase Walton, F. Cansu Atilgan, Paramita Chakraborty, Kubra Calisir, Ozgur Sahin, Shikhar Mehrotra, Besim Ogretmen. Alzheimer's disease-associated amyloid precursor protein improves anti-tumor immunity by inhibiting ceramide-mediated lethal mitophagy and restoring mitochondrial fumarate metabolism in aging T-cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3969.

SPIN90 Deficiency Ameliorates Amyloid ß Accumulation by Regulating APP Trafficking in AD Model Mice

AbstractBackgroundAlzheimer’s disease (AD), a common form of dementia, is caused in part by the aggregation and accumulation in the brain of amyloid ß (Aß), a product of the proteolytic cleavage of amyloid precursor protein (APP) in endosomes. Trafficking of APP, such as surface‐intracellular recycling, is an early critical step required for Aβ generation. Less is known, however, about the molecular mechanism regulating APP trafficking. This study investigated the mechanism by which SPIN90, along with Rab11, modulates APP trafficking, Aβ motility and accumulation, and synaptic functionalityMethodThis study utilized live‐imaging technology with molecular, cellular and 5xFAD model mice system.ResultBrain Aβ deposition was lower in the progeny of 5xFAD‐SPIN90KO mice than in 5xFAD‐SPIN90WT mice. Analysis of APP distribution and trafficking showed that the surface fraction of APP was locally distinct in axons and dendrites, with these distributions differing significantly in 5xFAD‐SPIN90WT and 5xFAD‐SPIN90KO mice, and that neural activity‐driven APP trafficking to the surface and intracellular recycling were more actively mobilized in 5xFAD‐SPIN90KO neurons. In addition, SPIN90 was found to be cotrafficked with APP via axons, with ablation of SPIN90 reducing the intracellular accumulation of APP in axons. Finally, synaptic transmission was restored over time in 5xFAD‐SPIN90KO but not in 5xFAD‐SPIN90WT neuronsConclusionThe interaction of SPIN90 and Rab11 is implicated in Aβ production through the regulation of APP trafficking.

Mitochondrial Localized Amyloid Precursor Protein Alters Mitochondrial Function and Mitophagy

AbstractBackgroundMitochondrial dysfunction and Aβ accumulation are hallmarks of Alzheimer’s disease (AD). Decades of research describe a relationship between mitochondrial function and Aβ production. Amyloid precursor protein (APP), from which Aβ is generated, is found in mitochondria. APP and Aβ alter mitochondrial function, while mitochondrial function alters Aβ production from APP. How these interactions contribute to AD pathology and progression are unknown. Here we interrogated the association of full‐length APP with mitochondria, mitochondrial function, and AD pathological hallmarks.MethodND (n = 5, without DS) and DS with dementia (DSD, n = 5) postmortem brain tissue was obtained from the University of California Irvine. A human iPSC line underwent Crispr/Cas9 genome editing to mutate three amino acids in APP and generate a 3M APP model, with reduced mitochondrial APP localization. We also leveraged a human iPSC line with triplication of the APP gene. iPSC models were differentiated into neurons using StemCell Technologies reagents and protocols. We examined mitochondrial function using a Seahorse XF analyzer. We measured full‐length APP protein levels in whole cell extracts and mitochondrial fractions via Western Blotting. We measured Aβ levels with ELISA kits from ThermoFisher. Mitophagy and mitochondrial mass/biogenesis was measured using MitoTimer and EGFP‐Cox8 adenoviral constructs.ResultiPSC derived neurons showed alterations to Aβ production. 3M APP models had reduced Aβ production while APP triplication models had increased production. 3M APP models had reduced mitochondrial APP levels and APP triplication models had increased mitochondrial APP levels. 3M APP models had reduced mitophagy, increased mitochondrial biogenesis, and increased mitochondrial mass. APP triplication models had increased mitophagy and reduced mitochondrial mass. Mitochondrial respiratory function was reduced in both 3M APP and APP triplication models. DSD postmortem brain tissue had reduced mitochondrial function in females. Full‐length APP levels were significantly higher in mitochondrial fractions in DSD brain tissue. Full‐length APP levels in mitochondrial fractions correlated with mitochondrial function. Higher mitochondrial APP (full‐length) levels associated with lower mitochondrial function.ConclusionWe describe a relationship between mitochondrial APP accumulation, mitochondrial function, and Aβ. These data support a centralized role for mitochondrial function in APP physiology and APP may play a role in modulating mitophagy.

Identifying the Phenotypes of Diffuse Axonal Injury Following Traumatic Brain Injury.

Diffuse axonal injury (DAI) is a significant feature of traumatic brain injury (TBI) across all injury severities and is driven by the primary mechanical insult and secondary biochemical injury phases. Axons comprise an outer cell membrane, the axolemma which is anchored to the cytoskeletal network with spectrin tetramers and actin rings. Neurofilaments act as space-filling structural polymers that surround the central core of microtubules, which facilitate axonal transport. TBI has differential effects on these cytoskeletal components, with axons in the same white matter tract showing a range of different cytoskeletal and axolemma alterations with different patterns of temporal evolution. These require different antibodies for detection in post-mortem tissue. Here, a comprehensive discussion of the evolution of axonal injury within different cytoskeletal elements is provided, alongside the most appropriate methods of detection and their temporal profiles. Accumulation of amyloid precursor protein (APP) as a result of disruption of axonal transport due to microtubule failure remains the most sensitive marker of axonal injury, both acutely and chronically. However, a subset of injured axons demonstrate different pathology, which cannot be detected via APP immunoreactivity, including degradation of spectrin and alterations in neurofilaments. Furthermore, recent work has highlighted the node of Ranvier and the axon initial segment as particularly vulnerable sites to axonal injury, with loss of sodium channels persisting beyond the acute phase post-injury in axons without APP pathology. Given the heterogenous response of axons to TBI, further characterization is required in the chronic phase to understand how axonal injury evolves temporally, which may help inform pharmacological interventions.

Butyrate acts as a G-protein-coupled receptor ligand that prevents high glucose-induced amyloidogenesis in N2a cells through the protein kinase B/glycogen synthase kinase-3β pathway.

Butyrate acts as a G-protein-coupled receptor ligand that prevents high glucose-induced amyloidogenesis in N2a cells through the protein kinase B/glycogen synthase kinase-3β pathway.

Toll-like receptor 4-mediated microglial inflammation exacerbates early white matter injury following experimental subarachnoid hemorrhage.

Neuroinflammation has been reported to be associated with white matter injury (WMI) after subarachnoid hemorrhage (SAH). As the main resident immune cells of the brain, microglia can be activated into proinflammatory and anti-inflammatory phenotypes. Toll-like receptor 4 (TLR4), expressed on the surface of the microglia, plays a key role in microglial inflammation. However, the relationship between TLR4, microglial polarization, and WMI following SAH remains unclear. In this study, a total of 121 male adult C57BL/6 wild-type (WT) mice, 20 WT mice at postnatal day 1 (P1), and 41 male adult TLR4 gene knockout (TLR4-/-) mice were used to investigate the potential role of TLR4-induced microglial polarization in early WMI after SAH by radiological, histological, microstructural, transcriptional, and cytological evidence. The results indicated that microglial inflammation was associated with myelin loss and axon damage, shown as a decrease in myelin basic protein (MBP), as well as increase in degraded myelin basic protein (dMBP) and amyloid precursor protein (APP). Gene knockout of TLR4 revised microglial polarization toward the anti-inflammatory phenotype and protected the white matter at an early phase after SAH (24 h), as shown through reduction of toxic metabolites, preservation of myelin, reductions in APP accumulation, reductions in white matter T2 hyperintensity, and increases in FA values. Cocultures of microglia and oligodendrocytes, the cells responsible for myelin production and maintenance, were established to further elucidate the relationship between microglial polarization and WMI. In vitro, TLR4 inhibition decreased the expression of microglial MyD88 and phosphorylated NF-κB, thereby inhibiting M1 polarization and mitigating inflammation. Decrease in TLR4 in the microglia increased preservation of neighboring oligodendrocytes. In conclusion, microglial inflammation has dual effects on early WMI after experimental SAH. Future explorations on more clinically relevant methods for modulating neuroinflammation are warranted to combat stroke with both WMI and gray matter destruction.

Familial Alzheimer’s Disease‐linked Swedish mutation impairs APP axonal transport

AbstractBackgroundIt is well‐established that most familial Alzheimer’s disease (AD) mutations alter processing of the amyloid precursor protein (APP) and perturb the balance between its proteolytic fragments. Considering different APP fragments play a role in its axonal transport, we here ask whether familial APP mutations impair axonal transport and homeostasis.MethodStem cells‐derived human neurons were transduced with either APPwt_GFP or APPswe_tRFP. Time‐lapse movies were analyzed using tracking algorithms to describe axonal transport parameters. Immunocytochemistry was performed to assess APP localization. To evaluate the impact of APPswe on other cargoes we also studied axonal transport of Rab5 endosomes.ResultProportions of movement, velocity, and distances of APPswe particles were decreased in anterograde direction compared to wt, while increased pauses and reversions were found. Accumulation of APP at the soma compared to neurite was found for APP mutant vs wt. Moreover, effect of APPswe resulted in the enlargement of Rab5 endosomes vs ctrl. Furthermore, to validate other effects of the APP mutant on Rab5, we studied its transport and found changes in some parameters compared with the ctrl.ConclusionThis work shows that APPswe impairs axonal transport. The change found on anterograde transport of APPswe, goes in hand with its accumulation at the soma vs neurite. Moreover, our results suggest that the Swedish mutation affects other proteins linked with APP, as described for the early‐endosome protein, Rab5. In line with many studies conducted on APP, our data suggest once more the importance of understanding as many mechanisms as possible involved in the biology of this protein.

Abstract TP210: Small Extracellular Vesicle-derived Micrornas Differentiate Ischemic Stroke And Intracerebral Hemorrhage: A Pilot Study

Investigating the short and long-term signaling mechanisms via small extracellular vesicles (sEVs) in peripheral blood following human Ischemic Stroke (IS) and Intracerebral Hemorrhage (ICH) is of great interest. The sEV’s cargo can induce distant responses which can be used to derive potential novel therapeutic targets and biomarkers to differentiate the two brain pathologies. Thus, we sequenced the miRNA cargo derived from peripheral blood sEVs in IS (n=3), ICH (n=3), and Vascular Risk Factor-matched Control (VRFC; n=3) subjects. Subjects were divided into contrast groups (IS vs VRFC, ICH vs VRFC, ICH vs IS), and log2 transformed expression underwent Kruskal-Wallis tests to identify differentially expressed (DE; p&lt;0.05) miRNAs. We found 55 DE miRNAs in IS vs VRFC, 38 in ICH vs VRFC, and 45 in ICH vs IS ( Fig. 1A ). The combination of these miRNAs differentiated the three groups on Principal Components Analysis ( Fig. 1B ). IS associated miRNA included miR-30a, miR-30b, and miR-144. miR-30a is involved in hematopoietic stem cell self-renewal and can impair B cell differentiation. miR-30b may be an immune suppressor via Notch1. In male mice, miR-144 is protective against atherosclerosis. ICH associated miRNA included miR-195, miR-1-3p, and miR-20b-5p. miR-195 can inhibit the pro-inflammatory roles of macrophages. miR-1-3p is involved in cardiomyocyte development, can target TLR1 (Toll-Like Receptor 1), and may regulate autophagy. miR-20b-5p reduces Amyloid Precursor Protein (APP) mRNA and protein levels; vascular accumulation of APP is one cause of Lobar ICH. We show differential expression of sEV-derived miRNAs in peripheral blood of human IS and ICH patients that are involved in relevant signaling processes. sEV cargo profiles pose a largely underexplored intercellular signaling mechanism in IS and ICH with the potential to better characterize long distance signaling from injured brain to peripheral blood leukocytes in these brain disorders.

Effects of experimental glaucoma in Lama1nmf223 mutant mice

To identify changes in response to experimental intraocular pressure (IOP) elevation associated with the laminin α1 nmf223 mutation in mice.Laminin mutant (LM) mice (Lama1nmf223) and C57BL/6J (B6) mice in two age groups each (4–5 months and >1 year) underwent intracameral microbead injections to produce unilaterally elevated IOP. We assessed axonal transport block of immunofluorescently labeled amyloid precursor protein (APP) after 3 days and retinal ganglion cell (RGC) axon loss after 6 weeks. Light, electron and fluorescent microscopy was used to study baseline anatomic differences and effects of 3-day IOP elevation in younger LM mice.In younger mice of both LM and B6 strains, elevated IOP led to increased APP block in the retina, prelaminar optic nerve head (preONH), unmyelinated optic nerve (UON), and myelinated optic nerve (MON). APP blockade not significantly different between younger B6 and LM mouse strains. Older LM mice had greater APP accumulation in both control and glaucoma eyes compared to older B6, however, accumulation was not significantly greater in LM glaucoma eyes compared to LM controls. Axon loss at 6 weeks was 12.2% in younger LM and 18.7% in younger B6 mice (difference between strains, p = 0.22, Mann Whitney test). Untreated LM optic nerve area was lower compared to B6 (nerve area, p < 0.0001, t-test). Aberrant axon bundles, as well as defects, thickening and reduplication of pia mater, were seen in the optic nerves of younger LM mice.Axonal transport blockade significantly differed between old B6 and old LM mice in control and glaucoma eyes, and younger LM mice had abnormal axon paths and lower optic nerve area.

Morphological and biomolecular targets in retina and vitreous from Reelin-deficient mice (Reeler): Potential implications for age-related macular degeneration in Alzheimer’s dementia

The neurosensory retina is an outgrowth of the Central Nervous System (CNS), and the eye is considered "a window to the brain." Reelin glycoprotein is directly involved in neurodevelopment, in synaptic plasticity, learning and memory. Consequently, abnormal Reelin signaling has been associated with brain neurodegeneration but its contributing role in ocular degeneration is still poorly explored. To this aim, experimental procedures were assayed on vitreous or retinas obtained from Reeler mice (knockout for Reelin protein) at different postnatal days (p) p14, p21 and p28. At p28, a significant increase in the expression of Amyloid Precursor Protein (APP) and its amyloidogenic peptide (Aβ1-42 along with truncated tau fragment (i.e., NH2htau)- three pathological hallmarks of Alzheimer's disease (AD)-were found in Reeler mice when compared to their age-matched wild-type controls. Likewise, several inflammatory mediators, such as Interleukins, or crucial biomarkers of oxidative stress were also found to be upregulated in Reeler mice by using different techniques such as ELLA assay, microchip array or real-time PCR. Taken together, these findings suggest that a dysfunctional Reelin signaling enables the expression of key pathological features which are classically associated with AD neurodegenerative processes. Thus, this work suggests that Reeler mouse might be a suitable animal model to study not only the pathophysiology of developmental processes but also several neurodegenerative diseases, such as AD and Age-related Macular Degeneration (AMD), characterized by accumulation of APP and/or Aβ1-42, NH2htau and inflammatory markers.

Concussion leads to widespread axonal sodium channel loss and disruption of the node of Ranvier.

Despite being a major health concern, little is known about the pathophysiological changes that underly concussion. Nonetheless, emerging evidence suggests that selective damage to white matter axons, or diffuse axonal injury (DAI), disrupts brain network connectivity and function. While voltage-gated sodium channels (NaChs) and their anchoring proteins at the nodes of Ranvier (NOR) on axons are key elements of the brain's network signaling machinery, changes in their integrity have not been studied in context with DAI. Here, we utilized a clinically relevant swine model of concussion that induces evolving axonal pathology, demonstrated by accumulation of amyloid precursor protein (APP) across the white matter. Over atwo-week follow-uppost-concussion with this model, we found widespread loss of NaCh isoform 1.6 (Nav1.6), progressive increases in NOR length, the appearance of void and heminodes and loss of βIV-spectrin, ankyrin G, and neurofascin 186 or their collective diffusion into the paranode. Notably, these changes were in close proximity, yet distinct from APP-immunoreactive swollen axonal profiles, potentially representing a unique, newfound phenotype of axonal pathology in DAI. Since concussion in humans is non-fatal, the clinical relevance of these findings was determined through examination of post-mortem brain tissue from humans with higher levels of acute traumatic brain injury. Here, a similar loss of Nav1.6 and changes in NOR structures in brain white matterwere observed as foundin the swine model of concussion. Collectively, this widespread and progressive disruption of NaChs and NOR appears to be a form of sodium channelopathy, which may represent an important substrate underlying brain network dysfunction after concussion.

SPIN90 Deficiency Ameliorates Amyloid β Accumulation by Regulating APP Trafficking in AD Model Mice.

Alzheimer’s disease (AD), a common form of dementia, is caused in part by the aggregation and accumulation in the brain of amyloid β (Aβ), a product of the proteolytic cleavage of amyloid precursor protein (APP) in endosomes. Trafficking of APP, such as surface-intracellular recycling, is an early critical step required for Aβ generation. Less is known, however, about the molecular mechanism regulating APP trafficking. This study investigated the mechanism by which SPIN90, along with Rab11, modulates APP trafficking, Aβ motility and accumulation, and synaptic functionality. Brain Aβ deposition was lower in the progeny of 5xFAD-SPIN90KO mice than in 5xFAD-SPIN90WT mice. Analysis of APP distribution and trafficking showed that the surface fraction of APP was locally distinct in axons and dendrites, with these distributions differing significantly in 5xFAD-SPIN90WT and 5xFAD-SPIN90KO mice, and that neural activity-driven APP trafficking to the surface and intracellular recycling were more actively mobilized in 5xFAD-SPIN90KO neurons. In addition, SPIN90 was found to be cotrafficked with APP via axons, with ablation of SPIN90 reducing the intracellular accumulation of APP in axons. Finally, synaptic transmission was restored over time in 5xFAD-SPIN90KO but not in 5xFAD-SPIN90WT neurons, suggesting SPIN90 is implicated in Aβ production through the regulation of APP trafficking.

Paraneoplastic Cerebellar Degeneration With P/Q-VGCC vs Yo Autoantibodies.

Background and ObjectivesParaneoplastic cerebellar degeneration (PCD) is characterized by a widespread loss of Purkinje cells (PCs) and may be associated with autoantibodies against intracellular antigens such as Yo or cell surface neuronal antigens such as the P/Q-type voltage-gated calcium channel (P/Q-VGCC). Although the intracellular location of the target antigen in anti–Yo-PCD supports a T cell–mediated pathology, the immune mechanisms in anti–P/Q-VGCC-PCD remain unclear. In this study, we compare neuropathologic characteristics of PCD with anti–P/Q-VGCC and anti-Yo autoantibodies in an archival autopsy cohort.MethodsWe performed neuropathology, immunohistochemistry, and multiplex immunofluorescence on formalin-fixed and paraffin-embedded brain tissue of 1 anti–P/Q-VGCC, 2 anti–Yo-PCD autopsy cases and controls.ResultsAnti–Yo-PCD revealed a diffuse and widespread PC loss together with microglial nodules with pSTAT1+ and CD8+granzymeB+ T cells and neuronal upregulation of major histocompatibility complex (MHC) Class I molecules. Some neurons showed a cytoplasmic immunoglobulin G (IgG) staining. In contrast, PC loss in anti–P/Q-VGCC-PCD was focal and predominantly affected the upper vermis, whereas caudal regions and lateral hemispheres were spared. Inflammation was characterized by scattered CD8+ T cells, single CD20+/CD79a+ B/plasma cells, and an IgG staining of the neuropil in the molecular layer of the cerebellar cortex and neuronal cytoplasms. No complement deposition or MHC-I upregulation was detected. Moreover, synaptophysin was reduced, and neuronal P/Q-VGCC was downregulated. In affected areas, axonal spheroids and the accumulation of amyloid precursor protein and glucose-regulated protein 78 in PCs indicate endoplasmatic reticulum stress and impairment of axonal transport. In both PCD types, calbindin expression was reduced or lost in the remaining PCs.DiscussionAnti–Yo-PCD showed characteristic features of a T cell–mediated pathology, whereas this was not observed in 1 case of anti–P/Q-VGCC-PCD. Our findings support a pathogenic role of anti–P/Q-VGCC autoantibodies in causing neuronal dysfunction, probably due to altered synaptic transmission resulting in calcium dysregulation and subsequent PC death. Because disease progression may lead to irreversible PC loss, anti–P/Q-VGCC-PCD patients could benefit from early oncologic and immunologic therapies.

CLSTN3 gene variant associates with obesity risk and contributes to dysfunction in white adipose tissue

ObjectiveWhite adipose tissue (WAT) possesses the remarkable remodeling capacity, and maladaptation of this ability contributes to the development of obesity and associated comorbidities. Calsyntenin-3 (CLSTN3) is a transmembrane protein that promotes synapse development in brain. Even though this gene has been reported to be associated with adipose tissue, its role in the regulation of WAT function is unknown yet. We aim to further assess the expression pattern of CLSTN3 gene in human adipose tissue, and investigate its regulatory impact on WAT function. MethodsIn our study, we observed the expression pattern of Clstn3/CLSTN3 gene in mouse and human WAT. Genetic association study and expression quantitative trait loci analysis were combined to identify the phenotypic effect of CLSTN3 gene variant in humans. This was followed by mouse experiments using adeno-associated virus-mediated human CLSTN3 overexpression in inguinal WAT. We investigated the effect of CLSTN3 on WAT function and overall metabolic homeostasis, as well as the possible underlying molecular mechanism. ResultsWe observed that CLSTN3 gene was routinely expressed in human WAT and predominantly enriched in adipocyte fraction. Furthermore, we identified that the variant rs7296261 in the CLSTN3 locus was associated with a high risk of obesity, and its risk allele was linked to an increase in CLSTN3 expression in human WAT. Overexpression of CLSTN3 in inguinal WAT of mice resulted in diet-induced local dysfunctional expansion, liver steatosis, and systemic metabolic deficiency. In vivo and ex vivo lipolysis assays demonstrated that CLSTN3 overexpression attenuated catecholamine-stimulated lipolysis. Mechanistically, CLSTN3 could interact with amyloid precursor protein (APP) in WAT and increase APP accumulation in mitochondria, which in turn impaired adipose mitochondrial function and promoted obesity. ConclusionTaken together, we provide the evidence for a novel role of CLSTN3 in modulating WAT function, thereby reinforcing the fact that targeting CLSTN3 may be a potential approach for the treatment of obesity and associated metabolic diseases.

Aβ Assemblies Promote Amyloidogenic Processing of APP and Intracellular Accumulation of Aβ42 Through Go/Gβγ Signaling.

Alzheimer’s disease (AD) is characterized by the deposition of aggregated species of amyloid beta (Aβ) in the brain, which leads to progressive cognitive deficits and dementia. Aβ is generated by the successive cleavage of the amyloid precursor protein (APP), first by β-site APP cleaving enzyme 1 (BACE1) and subsequently by the γ-secretase complex. Those conditions which enhace or reduce its clearance predispose to Aβ aggregation and the development of AD. In vitro studies have demonstrated that Aβ assemblies spark a feed-forward loop heightening Aβ production. However, the underlying mechanism remains unknown. Here, we show that oligomers and fibrils of Aβ enhance colocalization and physical interaction of APP and BACE1 in recycling endosomes of human neurons derived from induced pluripotent stem cells and other cell types, which leads to exacerbated amyloidogenic processing of APP and intracellular accumulation of Aβ42. In cells that are overexpressing the mutant forms of APP which are unable to bind Aβ or to activate Go protein, we have found that treatment with aggregated Aβ fails to increase colocalization of APP with BACE1 indicating that Aβ-APP/Go signaling is involved in this process. Moreover, inhibition of Gβγ subunit signaling with βARKct or gallein prevents Aβ-dependent interaction of APP and BACE1 in endosomes, β-processing of APP, and intracellular accumulation of Aβ42. Collectively, our findings uncover a signaling mechanism leading to a feed-forward loop of amyloidogenesis that might contribute to Aβ pathology in the early stages of AD and suggest that gallein could have therapeutic potential.

An adult-stage transcriptional program for survival of serotonergic connectivity.

SUMMARYNeurons must function for decades of life, but how these non-dividing cells are preserved is poorly understood. Using mouse serotonin (5-HT) neurons as a model, we report an adult-stage transcriptional program specialized to ensure the preservation of neuronal connectivity. We uncover a switch in Lmx1b and Pet1 transcription factor function from controlling embryonic axonal growth to sustaining a transcriptomic signature of 5-HT connectivity comprising functionally diverse synaptic and axonal genes. Adult-stage deficiency of Lmx1b and Pet1 causes slowly progressing degeneration of 5-HT synapses and axons, increased susceptibility of 5-HT axons to neurotoxic injury, and abnormal stress responses. Axon degeneration occurs in a die back pattern and is accompanied by accumulation of α-synuclein and amyloid precursor protein in spheroids and mitochondrial fragmentation without cell body loss. Our findings suggest that neuronal connectivity is transcriptionally protected by maintenance of connectivity transcriptomes; progressive decay of such transcriptomes may contribute to age-related diseases of brain circuitry.

Proteasome activity modulates amyloid toxicity.

Alzheimer's disease (AD) is responsible for 60%-80% of identified cases of dementia. While the generation and accumulation of amyloid precursor protein (APP) fragments is accepted as a key step in AD pathogenesis, the precise role of these fragments remains poorly understood. To overcome this deficit, we induced the expression of the soluble C-terminal fragment of APP (C99), the rate-limiting peptide for the generation of amyloid fragments, in yeast that contain thermosensitive mutations in genes encoding proteasome subunits. Our previous work with this system demonstrated that these proteasome-deficient yeast cells, expressing C99 when proteasome activity was blunted, generated amyloid fragments similar to those observed in AD patients. We now report the phenotypic repercussions of inducing C99 expression in proteasome-deficient cells. We show increased levels of protein aggregates, cellular stress and chaperone expression, electron-dense accumulations in the nuclear envelope/ER, abnormal DNA condensation, and an induction of apoptosis. Taken together, these findings suggest that the generation of C99 and its associated fragments in yeast cells with compromised proteasomal activity results in phenotypes that may be relevant to the neuropathological processes observed in AD patients. These data also suggest that this yeast model should be useful for testing therapeutics that target AD-associated amyloid, since it allows for the assessment of the reversal of the perturbed cellular physiology observed when degradation pathways are dysfunctional.

Accumulation of amyloid beta (Aβ) and amyloid precursor protein (APP) in tumors formed by a mouse xenograft model of inflammatory breast cancer.

Accumulation of amyloid in breast cancer is a well‐known phenomenon, but only immunoglobulin light‐chain amyloidosis (AL) or transthyretin (TTR) amyloid had been detected in human breast tumor samples previously. We recently reported that another amyloidogenic peptide, amyloid beta (Aβ), is present in an aggregated form in animal and human high‐grade gliomas and suggested that it originates systemically from the blood, possibly generated by platelets. To study whether breast cancers are also associated with these Aβ peptides and in what form, we used a nude mouse model inoculated with triple‐negative inflammatory breast cancer cell (SUM‐149) xenografts, which develop noticeable tumors. Immunostaining with two types of specific antibodies for Aβ identified the clear presence of Aβ peptides associated with (a) carcinoma cells and (b) extracellular aggregated amyloid (also revealed by Congo red and thioflavin S staining). Aβ peptides, in both cells and in aggregated amyloid, were distributed in clear gradients, with maximum levels near blood vessels. We detected significant presence of amyloid precursor protein (APP) in the walls of blood vessels of tumor samples, as well as in carcinoma cells. Finally, we used ELISA to confirm the presence of elevated levels of mouse‐generated Aβ40 in tumors. We conclude that Aβ in inflammatory breast cancer tumors, at least in a mouse model, is always present and is concentrated near blood vessels. We also discuss here the possible pathways of Aβ accumulation in tumors and whether this phenomenon could represent the specific signature of high‐grade cancers.

Amyloidogenic Processing of Amyloid Precursor Protein Drives Stretch-Induced Disruption of Axonal Transport in hiPSC-Derived Neurons.

Traumatic brain injury (TBI) results in disrupted brain function following impact from an external force and is a risk factor for sporadic Alzheimer's disease (AD). Although neurologic symptoms triggered by mild traumatic brain injuries (mTBI), the most common form of TBI, typically resolve rapidly, even an isolated mTBI event can increase the risk to develop AD. Aberrant accumulation of amyloid β peptide (Aβ), a cleaved fragment of amyloid precursor protein (APP), is a key pathologic outcome designating the progression of AD following mTBI and has also been linked to impaired axonal transport. However, relationships among mTBI, amyloidogenesis, and axonal transport remain unclear, in part because of the dearth of human models to study the neuronal response following mTBI. Here, we implemented a custom-microfabricated device to deform neurons derived from human-induced pluripotent stem cells, derived from a cognitively unimpaired male individual, to mimic the mild stretch experienced by neurons during mTBI. Although no cell lethality or cytoskeletal disruptions were observed, mild stretch was sufficient to stimulate rapid amyloidogenic processing of APP. This processing led to abrupt cessation of APP axonal transport and progressive formation of aberrant axonal accumulations that contained APP, its processing machinery, and amyloidogenic fragments. Consistent with this sequence of events, stretch-induced defects were abrogated by reducing amyloidogenesis either pharmacologically or genetically. In sum, we have uncovered a novel and manipulable stretch-induced amyloidogenic pathway directly responsible for APP axonal transport dysregulation. Our findings may help to understand and ultimately mitigate the risk of developing AD following mTBI.SIGNIFICANCE STATEMENT Mild traumatic brain injury is a risk factor for sporadic Alzheimer's disease (AD). Increased amyloid β peptide generation after injury may drive this risk. Here, by using a custom-built device to impose mild stretch to human neurons, we found that stretch triggers amyloid precursor protein (APP) cleavage, and thus amyloid β peptide generation, consequently disrupting APP axonal transport. Compellingly, protecting APP from cleavage was sufficient to spare axonal transport dysregulation and the consequent aberrant axonal accumulation of APP. Supporting such protective mechanism, the expression of the AD-protective APPA673T genetic variant conferred protection against stretch-induced APP axonal transport phenotypes. Our data reveal potential subcellular pathways contributing to the development of AD-associated phenotypes following mild traumatic brain injury, and putative strategies for intervening in these pathways.