ABSTRACT
Amyloid-ß (Aß) is thought to be neuronally derived in Alzheimer's disease (AD). However, transcripts of amyloid precursor protein (APP) and amyloidogenic enzymes are equally abundant in oligodendrocytes (OLs). By cell-type-specific deletion of Bace1 in a humanized knock-in AD model, APPNLGF, we demonstrate that OLs and neurons contribute to Aß plaque burden. For rapid plaque seeding, excitatory projection neurons must provide a threshold level of Aß. Ultimately, our findings are relevant for AD prevention and therapeutic strategies.
ABSTRACT
Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impaired social interactions, communication deficits and repetitive behaviors. A study of autistic human subjects has identified RFWD2 as a susceptibility gene for autism, and autistic patients have 3 copies of the RFWD2 gene. The role of RFWD2 as an E3 ligase in neuronal functions, and its contribution to the pathophysiology of ASD, remain unknown. We generated RFWD2 knockin mice to model the human autistic condition of high gene dosage of RFWD2. We found that heterozygous knockin (Rfwd2+/-) male mice exhibited the core symptoms of autism. Rfwd2+/- male mice showed deficits in social interaction and communication, increased repetitive and anxiety-like behavior, and spatial memory deficits, whereas Rfwd2+/- female mice showed subtle deficits in social communication and spatial memory but were normal in anxiety-like, repetitive, and social behaviors. These autistic-like behaviors in males were accompanied by a reduction in dendritic spine density and abnormal synaptic function on layer II/III pyramidal neurons in the prelimbic area of the medial prefrontal cortex (mPFC), as well as decreased expression of synaptic proteins. Impaired social behaviors in Rfwd2+/- male mice were rescued by the expression of ETV5, one of the major substrates of RFWD2, in the mPFC. These findings indicate an important role of RFWD2 in the pathogenesis of autism.
ABSTRACT
Alzheimer's Disease (AD) pathogenesis is thought to begin up to 20 years before cognitive symptoms appear, suggesting the need for more sensitive diagnostic biomarkers of AD. In this report, we demonstrated pathological changes in retinal Müller glia significantly earlier than amyloid pathology in AD mouse models. By utilizing the knock-in NLGF mouse model, we surprisingly discovered an increase in reticulon 3 (RTN3) protein levels in the NLGF retina as early as postnatal day 30 (P30). Despite RTN3 being a canonically neuronal protein, this increase was noted in the retinal Müller glia, confirmed by immunohistochemical characterization. Further unbiased transcriptomic assays of the P30 NLGF retina revealed that retinal Müller glia were the most sensitive responding cells in this mouse retina, compared with other cell types including photoreceptor cells and ganglion neurons. Pathway analyses of differentially expressed genes in glia cells showed activation of ER stress response via the upregulation of unfolded protein response (UPR) proteins such as ATF4 and CHOP. Early elevation of RTN3 in response to challenges by toxic Aß likely facilitated UPR. Altogether, these findings suggest that Müller glia act as a sentinel for AD pathology in the retina and should aid for both intervention and diagnosis.
Subject(s)
Alzheimer Disease , Animals , Mice , Alzheimer Disease/pathology , Retina , Neurons/metabolism , Disease Models, Animal , Amyloidogenic Proteins/metabolism , Neuroglia/metabolism , Brain/metabolism , Ependymoglial Cells/metabolismABSTRACT
Alzheimer's disease (AD) is characterized by the formation ß-amyloid (Aß) deposited neuritic plaques. Recent evidence suggests that abnormal lipid metabolism and accumulation could serve as biomarkers for neurodegenerative diseases, including AD. Tubular endoplasmic reticulum protein, reticulon 3 (RTN3), plays a crucial role in the development of neuritic plaque and lipid metabolism in AD brains. In present study, we sought to investigate a potential association between neutral lipid accumulation and AD pathology. BODIPY 500/510 dye was used to label neutral lipid surrounding Aß plaques in APPNL-G-F mouse and AD postmortem brains samples. Immunofluorescent images were captured using confocal microscope and co-localization between lipid metabolism proteins and neutral lipids were evaluated. Lipid accumulation in Aß plaque surrounding dystrophic neurites (DNs) was observed in the cortical region of AD mouse models and human AD brain samples. The neutral lipid staining was not co-localized with IBA1-labeled microglia or GFAP-labeled astrocytes, but it was co-labeled with VAMP2 and neurofilament. We further showed that neutral lipids were accumulated in RTN3 immunoreactive DNs. Both the neutral lipids accumulation and RIDNs formation showed age-dependent patterns in surrounding amyloid plaques. Mechanistic studies revealed that RTN3 likely contributes to the enrichment of neutral lipids near plaques by interacting with heat shock cognate protein 70 (HSC70) and diminishing its function in chaperone-mediated lipophagy. Our study provides immunohistochemical evidence of neutral lipids being enriched in DNs near amyloid plaques. Our findings shed light on RTN3-mediaed lipid accumulation in AD neuropathology and provide fresh insights into the role of RTN3 in neurodegenerative diseases.
Subject(s)
Alzheimer Disease , Mice , Animals , Humans , Alzheimer Disease/metabolism , Neurites/pathology , Plaque, Amyloid/metabolism , Mice, Transgenic , Nerve Tissue Proteins/metabolism , LipidsABSTRACT
Alzheimer's disease (AD) increases the risk for seizures and sleep disorders. We show here that germline deletion of ß-site amyloid precursor protein (APP) cleaving enzyme-1 (BACE1) in neurons, but not in astrocytes, increased epileptiform activity. However, Bace1 deletion at adult ages did not alter the normal EEG waveform, indicating less concern for BACE1 inhibition in patients. Moreover, we showed that deletion of Bace1 in the adult was able to reverse epileptiform activity in 5xFAD mice. Intriguingly, treating 5xFAD and APPNL-G-F/NL-G-F (APP KI) mice of either sex with one BACE1 inhibitor Lanabecestat (AZD3293) dramatically increased epileptiform spiking, likely resulting from an off-target effect. We also monitored sleep-wake pathologies in these mice and showed increased wakefulness, decreased non-rapid eye movement sleep, and rapid eye movement sleep in both 5xFAD and APP KI mice; BACE1 inhibition in the adult 5xFAD mice reversed plaque load and sleep disturbances, but this was not seen in APP KI mice. Further studies with and without BACE1 inhibitor treatment showed different levels of plaque-associated microgliosis and activated microglial proteins in 5xFAD mice compared with APP KI mice. Together, BACE1 inhibition should be developed to avoid off-target effect for achieving benefits in reducing epileptic activity and sleep disturbance in Alzheimer's patients.SIGNIFICANCE STATEMENT BACE1 is widely recognized as a therapeutic target for treating Alzheimer's disease patients. However, BACE1 inhibitors failed in clinical trials because of inability to show cognitive improvement in patients. Here we show that BACE1 inhibition actually reduces sleep disturbances and epileptic seizures; both are seen in AD patients. We further showed that one of clinically tested BACE1 inhibitors does have off-target effects, and development of safer BACE1 inhibitors will be beneficial to AD patients. Results from this study will provide useful guidance for additional drug development.
Subject(s)
Alzheimer Disease , Sleep Wake Disorders , Mice , Animals , Alzheimer Disease/complications , Alzheimer Disease/drug therapy , Alzheimer Disease/genetics , Mice, Transgenic , Amyloid Precursor Protein Secretases/metabolism , Aspartic Acid Endopeptidases/genetics , Aspartic Acid Endopeptidases/metabolism , Plaque, Amyloid , Seizures , Sleep Wake Disorders/etiology , Sleep Wake Disorders/genetics , Sleep , Amyloid beta-Protein Precursor/genetics , Amyloid beta-Protein Precursor/metabolism , Amyloid beta-Peptides/metabolism , Disease Models, AnimalABSTRACT
Reticulon (RTN) proteins are a family of proteins biochemically identified for shaping tubular endoplasmic reticulum, a subcellular structure important for vesicular transport and cell-to-cell communication. In our recent study of mice with knockout of both reticulon 1 (Rtn1) and Rtn3, we discovered that Rtn1-/-;Rtn3-/- (brief as R1R3dKO) mice exhibited neonatal lethality, despite the fact that mice deficient in either RTN1 or RTN3 alone exhibit no discernible phenotypes. This has been the first case to find early lethality in animals with deletion of partial members of RTN proteins. The complete penetrance for neonatal lethality can be attributed to multiple defects including the impaired neuromuscular junction found in the diaphragm. We also observed significantly impaired axonal growth in a regional-specific manner, detected by immunohistochemical staining with antibodies to neurofilament light chain and neurofilament medium chain. Ultrastructural examination by electron microscopy revealed a significant reduction in synaptic active zone length in the hippocampus. Mechanistic exploration by unbiased proteomic assays revealed reduction of proteins such as FMR1, Staufen2, Cyfip1, Cullin-4B and PDE2a, which are known components in the fragile X mental retardation pathway. Together, our results reveal that RTN1 and RTN3 are required to orchestrate neurofilament organization and intact synaptic structure of the central nervous system.
Subject(s)
Axons , Cytoskeleton , Hippocampus , Nerve Tissue Proteins , Animals , Mice , Genes, Lethal , Mice, Knockout , Axons/metabolism , Axons/pathology , Cytoskeleton/metabolism , Cytoskeleton/pathology , Nerve Tissue Proteins/metabolism , Endoplasmic Reticulum/metabolism , Synapses , Hippocampus/metabolism , Hippocampus/pathologyABSTRACT
BACKGROUND: Abnormal accumulation of amyloid beta peptide (Aß) in the brain induces a cascade of pathological changes in Alzheimer's disease (AD), and inhibiting BACE1, which is required for Aß generation, is therefore being explored for the treatment of AD by reducing Aß accumulation. As Bace1 knockout mice exhibit increased number of reactive astrocytes and AD brains have reactive astrocytes that surround amyloid plaques, we investigated the role of BACE1 in astrocytes and determined whether BACE1 regulates astrocytic functions. METHODS: We conducted unbiased single cell RNA-seq (scRNA-seq) using purified astrocytes from Bace1 KO mice and wild type control littermates. Similar scRNA-seq was also conducted using AD mice with conditional deletion of Bace1 in the adult stage (5xFAD;Bace1fl/fl;UBC-creER compared to 5xFAD;Bace1fl/fl controls). We compared the transcriptomes of astrocyte and reactive astrocyte clusters and identified several differentially expressed genes, which were further validated using Bace1 KO astrocyte cultures. Mice with astrocyte-specific Bace1 knockout in 5xFAD background were used to compare amyloid deposition. Mechanistic studies using cultured astrocytes were used to identify BACE1 substrates for changes in gene expression and signaling activity. RESULTS: Among altered genes, Clusterin (Clu) and Cxcl14 were significantly upregulated and validated by measuring protein levels. Moreover, BACE1 deficiency enhanced both astrocytic Aß uptake and degradation, and this effect was significantly attenuated by siRNA knockdown of Clu. Mechanistic study suggests that BACE1 deficiency abolishes cleavage of astrocytic insulin receptors (IR), and this may enhance expression of Clu and Cxcl14. Acutely isolated astrocytes from astrocyte-specific knockout of Bace1 mice (Bace1 fl/fl;Gfap-cre) show similar increases in CLU and IR. Furthermore, astrocyte-specific knockout of Bace1 in a 5xFAD background resulted in a significant attenuation in cortical Aß plaque load through enhanced clearance. CONCLUSION: Together, our study suggests that BACE1 in astrocytes regulates expression of Clu and Cxcl14, likely via the control of insulin receptor pathway, and inhibition of astrocytic BACE1 is a potential alternative strategy for enhancing Aß clearance.
Subject(s)
Alzheimer Disease , Amyloid beta-Peptides , Animals , Mice , Alzheimer Disease/metabolism , Amyloid beta-Peptides/metabolism , Amyloid beta-Protein Precursor/metabolism , Amyloid Precursor Protein Secretases/metabolism , Aspartic Acid Endopeptidases/metabolism , Astrocytes/metabolism , Clusterin/metabolism , Mice, Knockout , Mice, TransgenicABSTRACT
Klotho (KL) is a glycosyl hydrolase and aging-suppressor gene. Stress is a risk factor for depression and anxiety, which are highly comorbid with each other. The aim of this study is to determine whether KL is regulated by estrogen and plays an important role in sex differences in stress resilience. Our results showed that KL is regulated by estrogen in rat hippocampal neurons in vivo and in vitro and is essential for the estrogen-mediated increase in the number of presynaptic vesicular glutamate transporter 1 (Vglut1)-positive clusters on the dendrites of hippocampal neurons. The role of KL in sex differences in stress response was examined in rats using 3-week chronic unpredictable mild stress (CUMS). CUMS produced a deficit in spatial learning and memory, anhedonic-like behaviors, and anxiety-like behaviors in male but not female rats, which was accompanied by a reduction in KL protein levels in the hippocampus of male but not female rats. This demonstrated the resilience of female rats to CUMS. Interestingly, the knockdown of KL protein levels in the rat hippocampus of both sexes caused a decrease in stress resilience in both sexes, especially in female rats. These results suggest that the regulation of KL by estrogen plays an important role in estrogen-mediated synapse formation and that KL plays a critical role in the sex differences in cognitive deficit, anhedonic-like behaviors, and anxiety-like behaviors induced by chronic stress in rats, highlighting an important role of KL in sex differences in stress resilience.
Subject(s)
Depression , Sex Characteristics , Rats , Animals , Male , Female , Depression/metabolism , Anxiety , Anxiety Disorders/metabolism , Hippocampus/metabolism , Stress, Psychological/metabolism , Disease Models, Animal , Estrogens/metabolismABSTRACT
Beta amyloid cleaving enzyme 1 (BACE1) is largely expressed by neurons and is the sole ß-secretase for initiating the production of neuronal ß-amyloid peptides (Aß). To fully understand the physiological functions of neuronal BACE1, we used mouse genetic approach coupled with unbiased single nucleus RNA sequencing (snRNAseq) to investigate how targeted deletion of Bace1 in neurons, driven by Thy-1-Cre recombinase, would affect functions in the nervous system. Our transcriptome results revealed that BACE1 is essential for maturation of neural precursor cells and oligodendrocytes in mice. RNA velocity analysis confirmed deficit in the trajectory of neuroblasts in reaching the immature granule neuron state in young Bace1fl/fl; Thy1-cre mice. Further analysis of differential gene expression indicated changes in genes important for SNARE signaling, tight junction signaling, synaptogenesis and insulin secretion pathways. Morphological studies revealed a hypomyelination in Bace1fl/fl;Thy1-cre sciatic nerves, but no detectable myelination changes in the corpus callosum, despite clear reduction in myelination proteins in the brain. Functional studies showed reduction in long-term potential, defects in synaptogenesis and learning behavioral. Altogether, our results show that neuronal BACE1 is critical for optimal development of central and peripheral nervous system, and inhibition of neuronal BACE1 will result in deficits in synaptic functions and cognitive behaviors.
Subject(s)
Alzheimer Disease , Neural Stem Cells , Mice , Animals , Amyloid Precursor Protein Secretases/genetics , Amyloid Precursor Protein Secretases/metabolism , Aspartic Acid Endopeptidases/genetics , Aspartic Acid Endopeptidases/metabolism , Neural Stem Cells/metabolism , Neurons/metabolism , Amyloid beta-Peptides/metabolism , Oligodendroglia/metabolism , Amyloid beta-Protein Precursor/metabolism , Alzheimer Disease/metabolismABSTRACT
Despite the importance of the endothelium in the regulation of the blood brain barrier (BBB) in aging and neurodegenerative disease, difficulties in extracting endothelial cell (EC) nuclei have limited analysis of these cells. In addition, nearly all Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Degeneration (FTD), and a large portion of Alzheimer's Disease (AD) exhibit neuronal TDP-43 aggregation, leading to loss of nuclear function, but whether TDP-43 is similarly altered in human BBB ECs is unknown. Here we utilize a novel technique for the enrichment of endothelial and microglial nuclei from human cortical brain tissues, combined with inCITE-seq, to analyze nuclear proteins and RNA transcripts in a large cohort of healthy and diseased donors. Our findings reveal a unique transcriptional signature in nearly half of the capillary endothelial cells across neurodegenerative states, characterized by reduced levels of nuclear ß-Catenin and canonical downstream genes, and an increase in TNF/NF-kB target genes. We demonstrate that this does not correlate with increased nuclear p65/NF-kB, but rather a specific loss of nuclear TDP-43 in these disease associated ECs. Comparative analysis in animal models with targeted disruption of TDP-43 shows that this is sufficient to drive these transcriptional alterations. This work reveals that TDP-43 is a critical governor of the transcriptional output from nuclear p65/NF-kB, which has paradoxical roles in barrier maintenance and also barrier compromising inflammatory responses, and suggests that disease specific loss in ECs contributes to BBB defects observed in the progression of AD, ALS and FTD.
ABSTRACT
Loss of nuclear TDP-43 occurs in a wide range of neurodegenerative diseases, and specific mutations in the TARDBP gene that encodes the protein are linked to familial Frontal Temporal Lobar Dementia (FTD), and Amyotrophic Lateral Sclerosis (ALS). Although the focus has been on neuronal cell dysfunction caused by TDP-43 variants, TARDBP mRNA transcripts are expressed at similar levels in brain endothelial cells (ECs). Since increased permeability across the blood brain barrier (BBB) precedes cognitive decline, we postulated that altered functions of TDP-43 in ECs contributes to BBB dysfunction in neurodegenerative disease. To test this hypothesis, we examined EC function and BBB properties in mice with either knock-in mutations found in ALS/FTLD patients (TARDBPG348C and GRNR493X) or EC-specific deletion of TDP-43 throughout the endothelium (Cdh5(PAC)CreERT2; Tardbpff) or restricted to brain endothelium (Slco1c1(BAC)CreERT2; Tardbpff). We found that TARDBPG348C mice exhibited increased permeability to 3kDa Texas Red dextran and NHS-biotin, relative to their littermate controls, which could be recapitulated in cultured brain ECs from these mice. Nuclear levels of TDP-43 were reduced in vitro and in vivo in ECs from TARDBPG348C mice. This coincided with a reduction in junctional proteins VE-cadherin, claudin-5 and ZO-1 in isolated ECs, supporting a cell autonomous effect on barrier function through a loss of nuclear TDP-43. We further examined two models of Tardbp deletion in ECs, and found that the loss of TDP-43 throughout the endothelium led to systemic endothelial activation and permeability. Deletion specifically within the brain endothelium acutely increased BBB permeability, and eventually led to hallmarks of FTD, including fibrin deposition, microglial and astrocyte activation, and behavioral defects. Together, these data show that TDP-43 dysfunction specifically within brain ECs would contribute to the BBB defects observed early in the progression of ALS/FTLD.
ABSTRACT
CX3CL1, also known as fractalkine, is best known for its signaling activity through interactions with its cognate receptor CX3CR1. However, its intrinsic function that is independent of interaction with CX3CR1 remains to be fully understood. We demonstrate that the intracellular domain of CX3CL1 (CX3CL1-ICD), generated upon sequential cleavages by α-/ß-secretase and γ-secretase, initiates a back signaling activity, which mediates direct signal transmission to gene expression in the nucleus. To study this, we fused a synthetic peptide derived from CX3CL1-ICD, named Tet34, with a 13-amino acid tetanus sequence at the N terminus to facilitate translocation into neuronal cells. We show that treatment of mouse neuroblastoma Neuro-2A cells with Tet34, but not its scrambled control (Tet34s), induced cell proliferation, as manifested by changes in protein levels of transcription factors and progrowth molecules cyclin D1, PCNA, Sox5, and Cdk2. Further biochemical assays reveal elevation of phosphorylated insulin receptor ß subunit, insulin-like growth factor-1 receptor ß subunit, and insulin receptor substrates as well as activation of proliferation-linked kinase AKT. In addition, transgenic mice overexpressing membrane-anchored C-terminal CX3CL1 also exhibited activation of insulin/insulin-like growth factor-1 receptor signaling. Remarkably, we found that this Tet34 peptide, but not Tet34s, protected against endoplasmic reticulum stress and cellular apoptosis when Neuro-2A cells were challenged with toxic oligomers of ß-amyloid peptide or hydrogen peroxide. Taken together, our results suggest that CX3CL1-ICD may have translational potential for neuroprotection in Alzheimer's disease and for disorders resulting from insulin resistance.
Subject(s)
Chemokine CX3CL1 , Neuroprotection , Receptor, Insulin , Receptors, Somatomedin , Animals , Mice , Amyloid Precursor Protein Secretases/genetics , Amyloid Precursor Protein Secretases/metabolism , Chemokine CX3CL1/genetics , Chemokine CX3CL1/metabolism , CX3C Chemokine Receptor 1 , Mice, Transgenic , Receptor, Insulin/genetics , Receptor, Insulin/metabolism , Receptors, Somatomedin/genetics , Receptors, Somatomedin/metabolismABSTRACT
BACKGROUND: In Alzheimer's disease (AD), synaptic dysfunction is thought to occur many years before the onset of cognitive decline. OBJECTIVE: Detecting synaptic dysfunctions at the earliest stage of AD would be desirable in both clinic and research settings. METHODS: Population voltage imaging allows monitoring of synaptic depolarizations, to which calcium imaging is relatively blind. We developed an AD mouse model (APPswe/PS1dE9 background) expressing a genetically-encoded voltage indicator (GEVI) in the neocortex. GEVI was restricted to the excitatory pyramidal neurons (unlike the voltage-sensitive dyes). RESULTS: Expression of GEVI did not disrupt AD model formation of amyloid plaques. GEVI expression was stable in both AD model mice and Control (healthy) littermates (CTRL) over 247 days postnatal. Brain slices were stimulated in layer 2/3. From the evoked voltage waveforms, we extracted several parameters for comparison AD versus CTRL. Some parameters (e.g., temporal summation, refractoriness, and peak latency) were weak predictors, while other parameters (e.g., signal amplitude, attenuation with distance, and duration (half-width) of the evoked transients) were stronger predictors of the AD condition. Around postnatal age 150 days (P150) and especially at P200, synaptically-evoked voltage signals in brain slices were weaker in the AD groups versus the age- and sex-matched CTRL groups, suggesting an AD-mediated synaptic weakening that coincides with the accumulation of plaques. However, at the youngest ages examined, P40 and P80, the AD groups showed differentially stronger signals, suggesting "hyperexcitability" prior to the formation of plaques. CONCLUSION: Our results indicate bidirectional alterations in cortical physiology in AD model mice; occurring both prior (P40-80), and after (P150-200) the amyloid deposition.
Subject(s)
Alzheimer Disease , Cognitive Dysfunction , Alzheimer Disease/metabolism , Amyloid beta-Peptides/metabolism , Amyloid beta-Protein Precursor/genetics , Amyloid beta-Protein Precursor/metabolism , Animals , Disease Models, Animal , Mice , Mice, Transgenic , Plaque, Amyloid/metabolismABSTRACT
Abnormal accumulation of ß-amyloid (Aß) peptides is a culprit in Alzheimer's disease (AD); blocking Aß generation is therefore being explored as a logical approach for AD treatment. Here, we demonstrate that targeted inhibition of ß-site amyloid precursor protein (APP) cleaving enzyme-1 (BACE-1) in microglia has unique advantages. When Bace-1 was deleted in Alzheimer's 5xFAD microglia, fewer amyloid plaques developed, and this reduction was not due to changes in APP processing but rather to enhanced Aß clearance, in line with the increase in a microglial gene signature favoring phagocytosis. Moreover, deletion of Bace-1 in microglia enhances functions of autophagolysosomes and Aß-induced metabolic reprogramming necessary for Aß degradation by favoring phosphorylation of mammalian target of rapamycin complex (mTOR) at Ser2448 and modulating the PI3K-mTOR-HIF-1α signaling pathways. Mice with deletion of Bace-1 in microglia showed no reduction in long-term potentiation, unlike global deletion of Bace-1. Our results suggest that targeted inhibition of BACE-1 in microglia is a superior strategy for AD treatment.
Subject(s)
Alzheimer Disease , Amyloid Precursor Protein Secretases/metabolism , Aspartic Acid Endopeptidases/metabolism , Microglia , Alzheimer Disease/drug therapy , Alzheimer Disease/genetics , Alzheimer Disease/metabolism , Amyloid , Amyloid beta-Peptides/metabolism , Amyloid beta-Protein Precursor/genetics , Animals , Cognition , Mammals/metabolism , Mice , Microglia/metabolism , TOR Serine-Threonine KinasesABSTRACT
BACE-1 is required for generating ß-amyloid (Aß) peptides in Alzheimer's disease (AD). Here, we report that microglial BACE-1 regulates the transition of homeostatic to stage 1 disease-associated microglia (DAM-1) signature. BACE-1 deficiency elevated levels of transcription factors including Jun, Jund, Btg2, Erg1, Junb, Fos, and Fosb in the transition signature, which transition from more homeostatic to highly phagocytic DAM-1. Consistently, similar transition-state microglia in human AD brains correlated with lowered levels of BACE-1 expression. Targeted deletion of Bace-1 in adult 5xFAD mice microglia elevated these phagocytic microglia, correlated with significant reduction in amyloid plaques without synaptic toxicity. Silencing or pharmacologically inhibiting BACE-1 in cultured microglia-derived cells shows higher phagocytic function in microglia. Mechanistic exploration suggests that abolished cleavage of IL-1R2 and Toll-like receptors via BACE-1 inhibition contributes to the enhanced signaling via the PI3K and p38 MAPK kinase pathway. Together, targeted inhibition of BACE-1 in microglia may offer AD treatment.
ABSTRACT
Reticulon 3 (RTN3) is an endoplasmic reticulum protein that has previously been shown to play roles in neurodegenerative diseases, but little is known about its function in the kidneys. The aim of the present study was to clarify the roles of RTN3 in chronic kidney disease (CKD) and kidney fibrosis. In this study, RTN3 levels were measured in kidney tissues from healthy controls and CKD or kidney fibrosis patients. An RTN3-null mouse model was generated to explore the pathophysiological roles of RTN3 in the kidneys. The underlying mechanisms were studied in primary proximal tubular epithelial cells and HEK293 cells in vitro. The results showed that (1) a reduction in RTN3 in mice induces CKD and kidney fibrosis; (2) decreased RTN3 expression is found in patients with CKD; (3) RTN3 plays critical roles in regulating collagen biosynthesis and mitochondrial function; and (4) mechanistically, RTN3 regulates these phenotypes by interacting with GC-Rich Promoter Binding Protein 1 (GPBP1), which activates the IGF2-JAK2-STAT3 pathway. Our study indicates that RTN3 might play crucial roles in CKD and kidney fibrosis and that a reduction in RTN3 in the kidneys might be a risk factor for CKD and kidney fibrosis.
Subject(s)
Membrane Proteins , Nerve Tissue Proteins , Renal Insufficiency, Chronic , Animals , Blood Proteins/genetics , Blood Proteins/metabolism , Carrier Proteins/genetics , Carrier Proteins/metabolism , DNA-Binding Proteins , Epithelial Cells/metabolism , Fibrosis , HEK293 Cells , Humans , Insulin-Like Growth Factor II/genetics , Insulin-Like Growth Factor II/metabolism , Janus Kinase 2/genetics , Janus Kinase 2/metabolism , Kidney/metabolism , Membrane Proteins/genetics , Membrane Proteins/metabolism , Mice , Nerve Tissue Proteins/genetics , Nerve Tissue Proteins/metabolism , Phenotype , Renal Insufficiency, Chronic/geneticsABSTRACT
AIMS: While most Alzheimer's disease (AD) research emphasizes cognitive and behavioral abnormalities, lower urinary tract symptoms (LUTS) are observed in a third of AD patients, contributing to morbidity, poor quality of life, and need for institutionalization. Alzheimer's disease-associated urinary dysfunction (ADUD) has been assumed to be due to cognitive decline alone. While mouse studies have suggested that bladder innervation and voiding behavior may be altered in AD models, technical challenges precluded voiding reflex assessments. This study seeks to establish a mouse model of ADUD, and it seeks to characterize the noncognitive sequelae involved in AD-pathology associated alterations in the voiding reflex. METHODS: Having developed techniques permitting the assessment of bladder volume, pressure, and flow in mice, we now provide evidence of alterations in involuntary bladder control and increased response heterogeneity in a transgenic amyloidosis mouse model of AD using cystometry and tissue pharmacomyography. Tg-APP/PS1DE9 (PA) mice and their wild-type (WT) littermates (n = 6-8 per group) were used before plaque onset in the PA mice (4-6 months) and after plaque accumulation in the PA mice (8-10 months) in comparison to their WT control littermates. RESULTS: Novel findings include data suggestive of sphincteric discoordination, with pharmacological evidence of altered adrenergic mechanisms. CONCLUSIONS: Together, these data highlight the importance of addressing noncognitive sequelae of AD and offer novel translational insights into the debilitating impact of AD on LUTS and incontinence.