P. 68

October 11, 2022, 17:40 - 19:00
Background: Accumulating evidence has indicated cerebral glucose hypometabolism is associated with many neurodegenerative diseases (e.g. Alzheimer's disease) and neuropsychiatric symptoms. The current approach to assessing cerebral glucose metabolism relies on 18F-fluorodeoxyglucose-position-emission tomography (18F-FDG-PET) which is not a cell-specific approach to studying the associated pathophysiological functions. Therefore, the type of cell with changes in glucose uptake and the underlying mechanism involved in dementia remain largely unknown. Moreover, studying cerebral glucose metabolism in mouse models requires high-resolution PET scan instruments and trained staff that may not be available in every laboratory. Therefore, we attempt to establish a quantitative method to evaluate cell-specific cerebral glucose uptake in AD mouse models. Methods: To measure the neural and glial cells' glucose uptake level, 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG), a fluorescent D-glucose derivative, was delivered to the hippocampus of 5xFAD mice or C57BL/6J (WT) mice through stereotaxic injection. Upon dissociation and myelin removal, hippocampal neurons were isolated using magnetic depletion of all non-neuronal cells. The frequency of 2-NBDG+ neurons and glia was then determined by flow cytometry.
Results: Using this method, we quantified 37.2% of neuronal and non- neuronal glucose uptake in 5xFAD mice while 46% of neuronal and non-neuronal glucose uptake were detected in WT mice. Both glucose uptake level of neuronal and non-neuronal cells was significantly reduced in 5xFAD mice. Surprisingly, our data show that the reduction of glucose uptake level in glia is even more drastic than in neurons. Conclusion: We have developed a novel quantitative method for measuring cell-specific glucose metabolic changes in mouse brains using 2-NBDG. The assay is rapid, reliable, and highly reproducible, without a requirement for any specialized MRI/PET instrument, and should be easy to adapt for use in most research laboratory settings.
attenuated in AD cell and animal models with unknown mechanisms [1]. Materials & Method: We used human SH-SY5Y neuroblastoma transduced wild-type or mutant PS1 and fibroblasts collected from familial AD patients as cellular models, and 5xFAD mice as in vivo models to dissect the mechanism for mitophagy impairment in AD. Results: We found that the underlying cause of impaired PINK1- dependent mitophagy in AD may be due to disrupted intracellular calcium (Ca2+) homeostasis. Our in vitro and in vivo data demonstrated an exaggerated Ca2+ release from the endoplasmic reticulum (ER). In addition, there was enhanced mitochondrial-ER microdomains in AD models that leading to mitochondrial Ca2+ overloading. We further demonstrated that the elevated mitochondrial Ca2+ contributes to the MPP- and PARL-mediated PINK1 cleavage that impairing mitophagy initiation. Knock-out of MICU1 to enhance the mitochondrial uniporter (MCU) activity recapitulates impaired mitophagy found in AD, while preventing excessive Ca2+ shuffling into mitochondrial by Ru360 restores impaired mitophagy and respiratory function. Importantly, our in vivo study shows that Ru360 treatment rescued mitochondria deformity, AD pathologies, and cognitive function in 5xFAD mice. Conclusion & Discussion: Taken together, we conclude that mitochondrial Ca2+ overload impairs mitophagy in AD, and employing MCU blockers to prevent mitochondrial Ca2+ overloading may become a novel therapeutic strategy for AD. Yet, whether direct targeting of the MCU could exhibit beneficial effect in AD patients requires further investigation.
Keywords: Alzheimer’s disease, mitochondria, Calcium, mitophagy, PINK1
By 2050 more than 115 million people worldwide will be living with Alzheimer’s disease (AD). Preclinical research has established a role for the brain region known as the nucleus incertus (NI) in contextual memory by elucidating the strong neural communication between the NI and the septohippocampal system (SHS), which is central to learning and memory. Specifically, the NI contains a major population of relaxin-3 (RLN3)-producing GABAergic neurons which project heavily to limbic circuits that are vulnerable to degeneration in dementia, including the SHS, which expresses abundant RLN3 receptors (RXFP3) in rat brain. Therefore, overactivity or degeneration of these NI inputs may have adverse consequences for memory formation and recall and may contribute to its dysregulation in dementia. Here, we aimed to elucidate the localization and role of the RLN3/RXFP3 signaling system in the NI- hippocampus network, in experimental rat models and in postmortem human brain. We used viral-based, neural tract-tracing to label NI- originating fibers in the hippocampus of male rats (n=4). Fluorescent multiplex in situ hybridization was used to localize RXFP3 mRNA in relation to the expression of vesicular GABA transporter (vGAT), and vesicular glutamate transporter (vGLUT) or somatostatin (SST) mRNA, in male Sprague-Dawley rat brain (n=3), and in post-mortem human brain tissues from male subjects (n=3) without a history of dementia. Tract- tracing in rats revealed a high-density of NI-originating fibers within the polymorph layer of the dentate gyrus (DG), with the majority being RLN3-immunopositive. In rat brain, a majority of vGAT mRNA-positive neurons in the ventral hippocampus (vHPC) expressed RXFP3 mRNA. In human hippocampus, we observed neuronal co-expression of vGAT, SST, and RXFP3 mRNA. These results indicate that the NI influences information processing in rat vHPC by modulation of the DG, and RXFP3 activation may underlie some of these processes. RLN3/RXFP3 signaling may also influence similar circuits in human brain.
Glial and vascular contributions to neurodegenerative diseases
Establishing a cell type-specific quantitative method to study glucose uptake in the brain of AD mouse model
Ka Fai Oscar Ma1, Chun Laam Roy Ng1
1Department of Medicine, Li Ka Shing Faculty of Medicine, the University of Hong Kong, Hong Kong, Hong Kong
The relaxin-3/RXFP3 signaling system in the hippocampus and memory – rat and human studies
Camila de Avila1, Anna Gugula2, Aleksandra Trenk2, Anna Blasiak2, Andrew Gundlach3, John Fryer1
1Dept of Neurosci., Mayo Clinic, Scottsdale, USA, 2Dept. of Neurophysiol. and Chronobiol., Jagiellonian Univ., Krakow, Poland, 3Florey Inst. Neurosci. Mental Hlth., Melbourne, Australia
Mitochondrial Ca2+ overloading contributes PINK1 cleavage to disrupt mitophagy in Alzheimer’s Disease models
Aston Jiaxi WU1, Benjamin Chun-Kit TONG1, Alexis Shiying HUANG1, Olivia Ka-Yi HO1, Anna Hau-Yee KONG1, Sravan Gopalkrishnashetty SREENIVASMURTHY1, Zhou ZHU1, Chengfu SU1, Jia LIU1, Ashok IYASWAMY1, Juxian SONG1,2, Min LI1, King-ho CHEUNG1
1School of Chinese Medicine, Hong Kong Baptist University, Hong Kong, China , 2Medical College of Acupuncture-Moxibustion and Rehabilitation, Guangzhou University of Chinese Medicine, Guangzhou, China
 Background: Alzheimer’s disease (AD) is the most common form of dementia, but current therapies against beta-amyloid (Aβ) and tau pathologies have failed in clinical trials. Thus, the identification of novel pathogenic targets is urgently needed. Despite the pathological origin of AD remains elusive, studies have shown that mitophagy promotion could mitigate Aβ and tau pathologies as well as memory deficits. Studies also show that PINK1-dependent mitophagy is significantly
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