Welcome to the AD/PD™ 2024 Interactive Program
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EARLY LOCUS COERULEUS SYSTEM DEGENERATION DRIVES OLFACTORY DYSFUNCTION IN ALZHEIMER’S DISEASE
Abstract
Aims
The locus coeruleus (LC) is the primary source of noradrenaline in the forebrain and one of the earliest brain regions affected in Alzheimer's disease (AD). Patients with AD often experience olfactory deficits decades before the onset of cognitive impairments, highlighting the potential of early diagnosis for effective treatment. Here, we seek to better understand the mechanisms underlying the vulnerability of the LC in the context of olfaction.
Methods
We used wild-type (C57BL/6J) mice and transgenic APPNL-G-F mice, aged between 1 and 12 month. We employed a range of in vitro and in vivo techniques including immunohistochemistry, behavioural experiments, slice electrophysiology, optogenetics, positron emission tomography (PET) scans in mice and humans and analysis of human post-mortem brain tissue.
Results
Our findings reveal an early loss of LC-noradrenergic axons exclusive to the olfactory bulb (OB) that coincides with olfactory dysfunction. Inhibiting noradrenaline release in the OB by optogenetics recapitulates the olfactory phenotype. Importantly, we confirm early LC axon decline also in human post-mortem tissue and find patients with prodromal AD to show hyposmia. Finally, we identify microglia phagocytosing LC axons as the underlying mechanism of LC axon loss.
Conclusions
Our study highlights early-onset loss of LC axons in the OB of mice and humans to underlie olfactory dysfunction. We propose neuro-circuit analysis as a critical tool for the early diagnosis of AD and thereby identify the earliest possible time point for therapeutic intervention aiming at slowing or halting the disease progression.
NEURONAL ACE1 REGULATES THE HIPPOCAMPAL RENIN ANGIOTENSIN SYSTEM AND MAINTAINS CEREBROVASCULAR INTEGRITY IN MICE
Abstract
Aims
Angiotensin I converting enzyme (ACE1) maintains blood pressure homeostasis by converting angiotensin I (angI) into angiotensin II (angII) in the renin-angiotensin system (RAS). The brain expresses ACE1, and an intrinsic, central RAS regulates cardiovascular homeostasis as well as more complex cognitive functions such as learning and memory. ACE1 has been implicated in neurodegenerative disorders including Alzheimer’s disease (AD) and Parkinson’s disease (PD), but the mechanisms remain incompletely understood.
Methods
To gain a deeper understanding of the function of neuronal ACE1, we generated ACE1 conditional knockout (cKO) mice lacking ACE1 expression specifically in forebrain neurons.
Results
Total ACE1 levels in the hippocampus and cortex were significantly reduced in ACE cKO mice showing that neurons are the predominant cell type producing and shedding ACE1. However, RAS components were dysregulated in the hippocampus only and ACE cKO mice exhibited hippocampus-dependent memory impairment. Cerebrovascular defects appeared in the hippocampus, but not cortex, of ACE cKO mice with age. A subpopulation of interneurons that highly express ACE1 and tightly associate with hippocampal capillaries was identified. Uncoupling of ACE1+ interneurons and capillaries was observed in ACE1 cKO mice and in wild-type mice treated with a brain penetrant ACE1 inhibitor, suggesting a possible mechanism underlying local hippocampal cerebrovascular deficits and memory impairment in ACE1 cKO mice.
Conclusions
We reveal a novel role for neuronal ACE1 in maintaining hippocampal microvascular integrity and show selective vulnerability of the hippocampus to ACE1 inhibition and RAS dysregulation. Our results provide important insights into the function of ACE1 in the brain and demonstrate a connection between neuronal ACE and cerebrovascular function in the hippocampus.
CETP INHIBITOR EVACETRAPIB PREVENTS MEMORY DECLINE IN ALZHEIMER’S DISEASE MOUSE MODEL
Abstract
Aims
Genetic studies looking at risk factors in Alzheimer’s disease (AD) show growing evidence that perturbation in lipid metabolism may be a central component of the neurodegenerative disease. High plasma cholesterol levels increase the risk of Alzheimer’s disease (AD). Epidemiological and genetic studies have linked the cholesteryl ester transfer protein (CETP), which increases cholesterol levels in low-density lipoproteins, has been associated with decreased AD risk.Thus, CETP emerges as an interesting pharmacological target for AD. CETP activity can be inhibited by the cardiovascular drug evacetrapib. However, whether CETP inhibition can delay or prevent the onset of AD has not yet been investigated in preclinical mouse models of AD.
Methods
Wildtype (WT), McGill-Thy1-hAPP (APPtg), CETPtg, and double-transgenic (APP/CETPtg) mice fed a high cholesterol diet were injected daily i.p. with 30 mg/kg of evacetrapib or vehicle at 11-weeks of age for 10-weeks. Behaviour analyses and biochemical analyses were performed at 21-weeks of age.
Results
Our findings reveal that CETP inhibition by evacetrapib maintained memory in APPtg/CETPtg mice independently of APP expression or amyloid-beta (Ab) accumulation in the brain. However, we found regional changes in the free cholesterol content of the brain, more specifically in the hippocampus. We further found changes in ApoA-I- and ApoB-associated particles size and lipidation in plasma induced by evacetrapib treatment. Memory was significantly positively correlated to the levels of high-density lipoprotein while significantly negatively correlated with low-density lipoprotein.
Conclusions
This study provides preclinical evidence that repurposing of CETP inhibitors such as evacetrapib could delay or prevent AD. Our findings add to the ever-growing evidence that lipid metabolism modulates AD risk and that CETP inhibition is an effective therapeutic avenue.
EARLY DISRUPTION OF MITOCHONDRIAL RESPONSE TO NUTRIENTS IN THE APP KNOCK-IN MICE
Abstract
Aims
Mitochondrial dysfunction, oxidative stress and mTOR dysregulation features Alzheimer’s disease (AD). We discovered ‘Nutrient-induced Mitochondrial Activity’ (NiMA), an inter-organelle signaling pathway whereby insulin stimulation of lysosomal mTORC1 regulates oxidative phosphorylation in perikaryal mitochondria in neurons in culture. We also reported NiMA to be downregulated by extracellular amyloid-β oligomers (xcAβOs; DOI: 10.15252/embj.2018100241). The mechanism involves xcAβO activation of mTORC1 at the neuronal plasma membrane (DOI: 10.1016/j.jalz.2016.08.015) and upregulation of superoxide dismutase 1, a major regulator of cellular redox (SOD1; DOI: 10.1016/j.nbd.2022.105737). How these processes mechanistically promote neurodegeneration remain elusive.
Methods
Proximity-dependent biotin identification (BioID) followed by mass spectrometry were used to identify SOD1 interacting partners. A lentiviral-mediated shRNA screen targeting 96 mTOR substrates was performed to seek regulators of the NiMA pathway in NPC-derived human neurons. Live mitochondrial metabolism in APP knock-in mouse brain (APPKI) was recorded with two-photon fluorescence lifetime imaging.
Results
We found NiMA to be downregulated in 4-month-old APPKI mice and completely blocked in 6-month-old animals. Disruption of NiMA, thus occurs ~2-3 month before microgliosis, cognitive decline and other pathological AD features detected in this amyloid-β mouse model. Mechanistically, we found that GSK3β signals through mTORC1 to regulate SOD1 and mitochondrial activity. Pharmacological inhibition of GSK3β in 4-month-old APPKI mice partially restored mitochondrial functioning, suggesting that a GSK3β-mediated regulation of NiMA may control SOD1 interaction with cytosolic regulators. BioID identified PDE4D5 as a potential regulator of NiMA. Seventeen mTOR substrates were found to regulate NiMA, including AKAP1, a mitochondrial regulator of PKA activity. Thus, we are unveiling a fundamental mechanism connecting nutrient sensing, mTORC1 kinase activity, cytosolic redox regulation and PKA activity to mitochondrial functioning in neurons.
Conclusions
Our results suggest that NiMA disruption is an early event in AD pathogenesis.
THE NEUROPROTECTIVE RESPONSE OF EXERCISE IN ALZHEIMER’S DISEASE AT THE SINGLE-CELL LEVEL
Abstract
Aims
Exercise’s neuroprotective effects are well recognized in AD, but cell-specific contributions and molecular mechanisms of such effects remain unclear.
Methods
We used single-nuclei RNA-sequencing (snRNA-seq) to systematically dissect the adaptive neuroprotective response in the neurogenic stem cell niche within the dentate gyrus. AD mice and wild-type (WT) littermates were either sedentary or exercised with running wheels resulting in improved cognitive flexibility.
Results
snRNA-seq revealed that exercise responses differed between AD and WT mice, most prominent in adult hippocampal neurogenesis. Additionally, exercise restored a proportion of AD-dysregulated genes with unique signatures varying by cell type. Notably, we discovered an astrocyte subpopulation that was reduced in AD and induced with exercise, that the expression of disease-associated microglia genes is enhanced with exercise and an Apoe-high subcluster of mature granule cells that responds to exercise. Interestingly, transcriptional rescue was the greatest in oligodendrocytes precursor cells and oligodendrocytes.
Conclusions
Taken together, our data presents a unique resource for comprehensively understanding neuroprotective exercise pathways in AD.
ABCA7 DEFICIENCY ALTERS MITOCHONDRIAL LIPID METABOLISM AND CAUSES NEURONAL DYSREGULATION
Abstract
Aims
Loss-of-function variants of ABCA7 gene encoding ATP-binding cassette sub-family A member 7 are associated with the increased risk of Alzheimer’s disease (AD). Although ABCA7 is thought to primarily transport lipids and other lipophilic molecules, the mechanisms by which ABCA7 loss-of-function contributes to the pathogenesis of AD are not fully understood. There we aim to determine how ABCA7 deficiency impacts neuronal homeostasis.
Methods
We generated the neuron-specific ABCA7 knock-out mice with 5XFAD background by crossing Abca7-floxed mice with Camk2a-Cre mice and 5xFAD mice to investigate how the loss of neuronal ABCA7 affects AD pathogenesis. Using ABCA7 knockout human iPSC models generated with CRISPR/Cas9, we also investigated the impacts of ABCA7 deficiency on neuronal metabolism and function.
Results
While neuronal ABCA7 deficiency exacerbated brain amyloid-β accumulation and neuritic dystrophy in 5xFAD mice at the age of 10-12 months, we found impaired mitochondrial function and synaptic protein reductions in the synaptosomes isolated from the neuron-specific ABCA7 knock-out mice. Consistently, lipidomics revealed that mitochondria-related phospholipids were reduced in the ABCA7-deficient iPSC-derived cortical organoids. ABCA7 deficiency induced alterations of mitochondrial morphology accompanied by reduced ATP synthase activity and exacerbated oxidative damage in the organoids. Furthermore, ABCA7-deficient iPSC-derived neurons showed compromised mitochondrial respiration and excess ROS generation, as well as enlarged mitochondrial morphology compared to the isogenic controls. ABCA7 deficiency also decreased spontaneous synaptic firing and network formation in iPSC-derived neurons.
Conclusions
Our results provide evidence that ABCA7 loss-of-function contributes to AD risk by modulating mitochondria lipid metabolism. Restoring ABCA7 function may be a potential therapeutic target to treat AD.
SENOLYTIC INTERVENTION IMPROVED COGNITIVE, METABOLIC, AND ADIPOSE DEPOTS IN FEMALE APPNL-F/NL-F MICE
Abstract
Aims
Senescent cells accumulate in numerous organs, contributing to functional alterations associated with aging and Alzheimer’s disease (AD). Senescent cells contribute to neuronal loss, and decreasing their burden led to functional improvements in the brain of AD mouse models. However, it is unclear if disease stage at intervention or sex play a role in treatment response. Our objective was to determine the effects of prodromal senolytic intervention on glucose metabolism, energy metabolism, and cognition in the APPNL-F/NL-F knock-in mouse model of AD.
Methods
Male and female APPNL-F/NL-F mice received oral administration of Fisetin (100 mg/kg BW), Dasatinib (5 mg/kg BW) plus Quercetin (50 mg/kg BW) (D+Q), or vehicle control beginning at 4 months of age, prior to amyloid plaque deposition. Treatments were administered monthly until study completion. Beginning at 12 months of age, mice underwent glucose and insulin tolerance testing to examine glucose metabolism, indirect calorimetry to determine energy metabolism, and the Morris water maze to assess cognition.
Results
Senolytic intervention did not alter glucose metabolism. Sexual dimorphic energy metabolic responses were observed with D+Q increasing oxygen consumption and energy expenditure in female APPNL-F/NL-F mice accompanied with significant reduction of visceral adipose tissues, whereas Fisetin decreased respiratory quotient in male APPNL-F/NL-F mice. Importantly, D+Q treatments in female APPNL-F/NL-F mice led to improved long-term spatial memory recall. Ongoing studies will assess cerebral plaque load and neuroinflammatory markers.
Conclusions
These data support improved spatial learning and memory in D+Q treated female APPNL-F/NL-F mice that coincides with enhanced peripheral energy metabolism and decreased abdominal adiposity. This work was supported by the NIH (R01 AG057767, R01 AG061937), Smith Alzheimer’s Center, and Kenneth Stark Endowment.
TT-P34: A NOVEL FIRST-IN-CLASS PEPTIDE DRUG FOR TREATMENT OF HUNTINGTON’S DISEASE
Abstract
Aims
TT-P34 is a novel peptide drug which has been developed by Teitur Trophics, a biotech company based in Aarhus, Denmark. The cyclic peptide induces activation of transcription factor CREB to increase both mitochondrial and lysosomal biogenesis and neurotrophic support through upregulation of master regulators PGC1a and TFEB and neurotrophin BDNF. One key hallmark in Huntington’s Disease (HD) is the dysfunction in the cortico-striatal BDNF-signaling, which leads to loss of CREB activity and ultimately striatal degeneration. Here, we assessed the therapeutic effects of TT-P34 in the zQ175 mouse model of HD. The aim of the study was to investigate the potential of TT-P34 to protect the proteome and as a result halt or delay disease progression.
Methods
Over a 9 months period of once daily-treatment, we evaluated a variety of motor behavior tests and performed home-cage analysis as a measure of quality of life. We further investigated the molecular effects of TT-P34 on the striatum of zQ175 using unbiased proteomics and metabolomics to correlate behavioral readout with changes in the proteome.
Results
Treatment with TT-P34 (0.2 mg/kg) led to a complete rescue of the HD phenotype measured across 12 behavioral outputs in home-cage analysis in addition to significant improvement in motor-coordination in the transverse beam-test. Proteomics and metabolomics of the striatum revealed extensive protection and upregulation of mitochondrial and synaptic proteins of both dopaminergic, GABAergic, and glutamatergic synapses, as well as increased dopamine and GABA levels.
Conclusions
This demonstrates that TT-P34 drives key cellular pathways affected in HD, which protects against loss of synaptic content. Taken together, this validates the therapeutic efficacy of TT-P34 as a novel and first-in-class drug for HD and potentially other neurodegenerative diseases with mitochondrial and lysosomal deficits.