Chronic cerebral hypoperfusion upregulates leptin receptor expression in astrocytes and tau phosphorylation in tau transgenic mice

The Bidirectional Role of Hypoxia-Inducible Factor 1 Alpha in Vascular Dementia Caused by Chronic Cerebral Hypoperfusion

Chronic cerebral hypoperfusion (CCH) is a critical indicator of cognitive impairment and dementia, especially vascular dementia. Cerebral blood flow disturbance alters the properties of neurons and glial cells as a result of a deficit in energy sources. Hypoxia-inducible factor 1 alpha (HIF- 1α) is a transcription factor that controls gene activity in response to low oxygen levels. It regulates a complex network of cellular adaptations to improve oxygenation, metabolic reprogramming, and cell survival in hypoxic situations. However, recent research suggests that HIF- 1α plays a role not only in neuroprotection but also in brain injury. It is therefore critical to fully comprehend the mechanisms behind these disorders. This review highlights the dual role of HIF- 1α in CCH-induced VaD. Initially, HIF- 1α provides a neuroprotection by promoting angiogenesis through vascular endothelial growth factor (VEGF) signaling. However, prolonged activation can detrimentally effects, including oxidative stress, neuroinflammation, blood-brain barrier dysfunction, and cognitive impairment. Evidence suggests that HIF- 1α exerts its protective effects in acute ischemic/hypoxic-induced VaD through pathways such as PI3 K/AKT/mTOR and MAPK/p-c-Jun signaling. However, its dysregulation in chronic stages of CCH contributes to cognitive decline and disease progression. Understanding the complex role of HIF- 1α and its interactions with other molecular pathways is crucial for developing effective therapeutic strategies. Therefore, an informed, in-depth discussion of its involvement in these pathologic processes is necessary, as a precise contribution of HIF- 1α to CCH-induced VaD remains to be established and requires further investigation.

Neurofibrillary tangles predict dementia in patients with carotid stenosis

OBJECTIVE

There is growing appreciation that extracranial carotid atherosclerotic disease (ECAD) is associated with increased dementia risk. Despite this, clinical management of ECAD does not involve evaluation for cognitive outcomes or risk stratification for dementia. One impediment to studying and improving clinical care for this cohort (roughly 10% of adults aged >60 years) is that factors to identify patients with ECAD at risk for dementia are not known.

METHODS

Our prospective clinicopathologic study, the Arizona Study of Aging and Neurodegenerative Disorders study, evaluated clinical and histopathologic factors for dementia in subjects with ECAD. The primary outcome (dementia) was defined as a composite of Alzheimer's disease and/or vascular dementia based on a clinical/neuropathologic diagnosis. Of 1234 subjects, those with dementia other than Alzheimer's disease and/or vascular dementia were excluded; there remained 111 subjects with ECAD to be evaluated. Logistic regression analysis was performed to examine the association of key risk factors for dementia including age, sex, cardiovascular risk factors, apolipoprotein E4 (APOE4) genetic status, and dementia biomarkers. A precision recall curve was also generated to evaluate the diagnostic accuracy of dementia prediction models.

RESULTS

Individuals with dementia compared with those without had significantly increased levels of stroke, APOE4 genotype, and dementia biomarkers, neurofibrillary tangles (NFTs), and amyloid plaques. Models of multiple combined risk factors were little or no better than NFTs alone, which showed a 96.9% positive predictive value at an NFT threshold of 10.

CONCLUSIONS

Although we hypothesized that a combination of clinical and histopathologic biomarkers would result in the strongest predictive model for dementia, we found that NFTs alone had the highest association and positive predictive value for dementia risk in patients with ECAD. As blood-based assays for NFT quantification become more clinically reliable and available, these data support the possibility that NFT quantification may help identify patients with ECAD at increased risk for dementia.

Prolonged Chronic Cerebral Hypoperfusion Does not Exacerbate Tau Pathology in a Tauopathy Mouse Model

BACKGROUND

Several preclinical studies have reported elevated levels of tau following the induction of chronic cerebral hypoperfusion (CCH) in Alzheimer's disease mouse models. The objective of this study was to first induce CCH in a mouse model of tauopathy over an extended period of up to 6 months and to subsequently investigate the effects of CCH on tau accumulation and alterations in the transcriptome.

METHODS

Three-month-old P301S tauopathy mice were randomly allocated to either a Sham or CCH group. The common carotid arteries (CCAs) of the CCH group were bilaterally implanted using 0.75-mm inner diameter ameroid constrictors. Prior to surgery, Doppler ultrasound imaging was acquired, with follow-up imaging at 1, 3, and 6 months postoperatively. Brain tissue samples were obtained, and hemispheres were dissected and divided for separate analysis.

RESULT

No significant differences in phosphorylated and total tau protein levels were found in either Sham or CCH left cortical hemispheres or hippocampal lysates. Immunohistochemical staining of phosphorylated tau in the right hemisphere revealed similar findings. Compared with the Sham group, transcriptomic deconvolution revealed a significant reduction of memory B cells in the CCH group (p = 0.029).

CONCLUSION

To clarify the effects of chronic hypoperfusion on tau pathology, more than one surgical method of hypoperfusion should be used in future studies.

Cerebral hypoperfusion reduces tau accumulation

OBJECTIVE

Alzheimer's disease (AD) often coexists with cerebrovascular diseases. However, the impact of cerebrovascular diseases such as stroke on AD pathology remains poorly understood.

METHODS

This study examines the correlation between cerebrovascular diseases and AD pathology. The research was carried out using clinical and neuropathological data collected from the National Alzheimer's Coordinating Center (NACC) database and an animal model in which bilateral common carotid artery stenosis surgery was performed, following the injection of tau seeds into the brains of wild-type mice.

RESULTS

Analysis of the NACC database suggests that clinical stroke history and lacunar infarcts are associated with lower neurofibrillary tangle pathology. An animal model demonstrates that chronic cerebral hypoperfusion reduces tau pathology, which was observed in not only neurons but also astrocytes, microglia, and oligodendrocytes. Furthermore, we found that astrocytes and microglia were activated in response to tau pathology and chronic cerebral hypoperfusion. Additionally, cerebral hypoperfusion increased a lysosomal enzyme, cathepsin D.

INTERPRETATION

These data together indicate that cerebral hypoperfusion reduces tau accumulation likely through an increase in microglial phagocytic activity towards tau and an elevation in degradation through cathepsin D. This study contributes to understanding the relationship between tau pathology and cerebrovascular diseases in older people with multimorbidity.

Aberrant vascular architecture in the hippocampus correlates with tau burden in mild cognitive impairment and Alzheimer's disease

Cerebrovascular dysfunction is a significant contributor to Alzheimer's disease (AD) progression. AD mouse models show altered capillary morphology, density, and diminished blood flow in areas of tau and beta-amyloid accumulation. The purpose of this study was to examine alterations in vascular structure and their contributions to perfusion deficits in the hippocampus in AD and mild cognitive impairment (MCI). Seven individuals with AD and MCI (1 AD/6 MCI), nine cognitively intact older healthy adults, and seven younger healthy adults underwent pseudo-continuous arterial spin labeling (PCASL) and gradient-echo/spin-echo (GESE) dynamic susceptibility contrast (DSC) MRI. Cerebral blood flow (CBF), cerebral blood volume, relative vessel size index (rVSI), and mean vessel density were calculated from model fitting. Lower CBF from PCASL and SE DSC MRI was observed in the hippocampus of AD/MCI group. rVSI in the hippocampus of the AD/MCI group was larger than that of the two healthy groups (FDR-P = 0.02). No difference in vessel density was detected between the groups. We also explored relationship of tau burden from 18F-flortaucipir positron emission tomography and vascular measures from MRI. Tau burden was associated with larger vessel size and lower CBF in the hippocampus. We postulate that larger vessel size may be associated with vascular alterations in AD/MCI.

Effect of ferroptosis on chronic cerebral hypoperfusion in vascular dementia

Vascular dementia (VaD) is the second most prevalent type of dementia after Alzheimer's disease and is caused by impaired nerve cell function resulting from cerebrovascular disease and vascular risk factors. Chronic cerebral hypoperfusion (CCH) is a common pathological and physiological state that may result from cerebral ischemia and hypoxia, causing widespread diffuse lesions in the brain parenchyma which leads to progressive nerve damage. Transferrin (TF) and transferrin receptor 1 (TfR1), two proteins involved in iron uptake, were upregulated by CCH, whereas ferroprotein (FPN), a protein involved in iron efflux, was downregulated. This process may involve various mechanisms including tau and iron regulatory proteins (IRP). CCH can also exacerbate lipid peroxidation caused by an iron imbalance by inhibiting glutathione peroxidase 4 (Gpx4) synthesis and some Gpx4 independent pathways through cystine/glutamate transporters (system Xc-), ultimately leading to ferroptosis in nerve cells and accelerating the progression of VaD.

A brief overview of a mouse model of cerebral hypoperfusion by bilateral carotid artery stenosis

Vascular cognitive impairment (VCI) refers to all forms of cognitive disorder related to cerebrovascular diseases, including vascular mild cognitive impairment, post-stroke dementia, multi-infarct dementia, subcortical ischemic vascular dementia (SIVD), and mixed dementia. Among the causes of VCI, more attention has been paid to SIVD because the causative cerebral small vessel pathologies are frequently observed in elderly people and because the gradual progression of cognitive decline often mimics Alzheimer's disease. In most cases, small vessel diseases are accompanied by cerebral hypoperfusion. In mice, prolonged cerebral hypoperfusion is induced by bilateral carotid artery stenosis (BCAS) with surgically implanted metal micro-coils. This cerebral hypoperfusion BCAS model was proposed as a SIVD mouse model in 2004, and the spreading use of this mouse SIVD model has provided novel data regarding cognitive dysfunction and histological/genetic changes by cerebral hypoperfusion. Oxidative stress, microvascular injury, excitotoxicity, blood-brain barrier dysfunction, and secondary inflammation may be the main mechanisms of brain damage due to prolonged cerebral hypoperfusion, and some potential therapeutic targets for SIVD have been proposed by using transgenic mice or clinically used drugs in BCAS studies. This review article overviews findings from the studies that used this hypoperfused-SIVD mouse model, which were published between 2004 and 2021.

Gray matter hypoperfusion is a late pathological event in the course of Alzheimer's disease

Several studies have shown decreased cerebral blood flow (CBF) in Alzheimer's disease (AD). However, the role of hypoperfusion in the disease pathogenesis remains unclear. Combining arterial spin labeling MRI, PET, and CSF biomarkers, we investigated the associations between gray matter (GM)-CBF and the key mechanisms in AD including amyloid-β (Aβ) and tau pathology, synaptic and axonal degeneration. Further, we applied a disease progression modeling to characterize the temporal sequence of different AD biomarkers. Lower perfusion was observed in temporo-occipito-parietal cortex in the Aβ-positive cognitively impaired compared to both Aβ-negative and Aβ-positive cognitively unimpaired individuals. In participants along the AD spectrum, GM-CBF was associated with tau, synaptic and axonal dysfunction, but not Aβ in similar cortical regions. Axonal degeneration was further associated with hypoperfusion in cognitively unimpaired individuals. Disease progression modeling revealed that GM-CBF disruption Followed the abnormality of biomarkers of Aβ, tau and brain atrophy. These findings indicate that tau tangles and neurodegeneration are more closely connected with GM-CBF changes than Aβ pathology. Although subjected to the sensitivity of the employed neuroimaging techniques and the modeling approach, these findings suggest that hypoperfusion might not be an early event associated with the build-up of Aβ in preclinical phase of AD.

Honokiol prevents chronic cerebral hypoperfusion induced astrocyte A1 polarization to alleviate neurotoxicity by targeting SIRT3-STAT3 axis

Alzheimer's Dementia (AD) and Vascular Dementia (VaD) are two main types of dementias for which no specific treatment is available. Chronic Cerebral Hypoperfusion (CCH) is a pathogenesis underlying AD and VaD that promotes neuroinflammatory responses and oxidative stress. Honokiol (HNK) is a natural compound isolated from magnolia leaves that can easily cross blood brain barrier and has anti-inflammatory and antioxidant effects. In the present study, the effects of HNK on astrocyte polarization and neurological damage in in vivo and in vitro models of chronic cerebral hypoperfusion were explored. We found that HNK was able to inhibit the phosphorylation and nuclear translocation of STAT3, A1 polarization, and reduce conditioned medium's neuronal toxicity of astrocyte under chronic hypoxia induced by cobalt chloride; STAT3 phosphorylation inhibitor C188-9 was able to mimic the above effects of HNK, suggesting that HNK may inhibit chronic hypoxia-induced A1 polarization in astrocytes via STAT3. SIRT3 inhibitor 3-TYP reversed, while Sirt3 overexpression mimicked the inhibitory effects of HNK on oxidative stress, STAT3 phosphorylation and nuclear translocation, A1 polarization and neuronal toxicity of astrocyte under chronic hypoxic conditions. For in vivo research, continuous intraperitoneal injection of HNK (1mg/kg) for 21 days ameliorated the decrease in SIRT3 activity and oxidative stress, inhibited astrocytic STAT3 nuclear translocation and A1 polarization, and prevented neuron and synaptic loss in the hippocampal of CCH rats. Besides, HNK application improved the spatial memory impairment of CCH rats, as assessed with Morris Water Maze. In conclusion, these results suggest that the phytochemical HNK can inhibit astrocyte A1 polarization via regulating SIRT3-STAT3 axis, thus improving CCH-induced neurological damage. These results highlight HNK as novel treatment for dementia with underlying vascular mechanisms.

Association of Tooth Loss with Alzheimer's Disease Tau Pathologies Assessed by Positron Emission Tomography

BACKGROUND

Deterioration of the oral environment is one of the risk factors for dementia. A previous study of an Alzheimer's disease (AD) model mouse suggests that tooth loss induces denervation of the mesencephalic trigeminal nucleus and neuroinflammation, possibly leading to accelerated tau dissemination from the nearby locus coeruleus (LC).

OBJECTIVE

To elucidate the relevance of oral conditions and amyloid-β (Aβ) and tau pathologies in human participants.

METHODS

We examined the number of remaining teeth and the biofilm-gingival interface index in 24 AD-spectrum patients and 19 age-matched healthy controls (HCs). They also underwent positron emission tomography (PET) imaging of Aβ and tau with specific radiotracers, 11C-PiB and 18F-PM-PBB3, respectively. All AD-spectrum patients were Aβ-positive, and all HCs were Aβ-negative. We analyzed the correlation between the oral parameters and radiotracer retention.

RESULTS

No differences were found in oral conditions between the AD and HC groups. 11C-PiB retentions did not correlate with the oral indices in either group. In AD-spectrum patients, brain-wide, voxel-based image analysis highlighted several regions, including the LC and associated brainstem substructures, as areas where 18F-PM-PBB3 retentions negatively correlated with the remaining teeth and revealed the correlation of tau deposits in the LC (r = -0.479, p = 0.018) primarily with the hippocampal and neighboring areas. The tau deposition in none of the brain regions was associated with the periodontal status.

CONCLUSIONS

Our findings with previous preclinical evidence imply that tooth loss may enhance AD tau pathogenesis, promoting tau spreading from LC to the hippocampal formation.

Fecal microbiota transplantation and replenishment of short-chain fatty acids protect against chronic cerebral hypoperfusion-induced colonic dysfunction by regulating gut microbiota, differentiation of Th17 cells, and mitochondrial energy metabolism

BACKGROUND

Little is known about the association between gut microbiota and intestinal injury under a state of chronic cerebral hypoperfusion (CCH). Here, the effects of gut microbiota and short-chain fatty acids (SCFAs), as important metabolic products, on intestinal function and potential mechanisms after CCH were investigated.

METHODS

Rats were subjected to bilateral common carotid artery occlusion (BCCAo) to induce CCH. The gut microbiota and metabolites of SCFAs were assessed by 16S rRNA sequencing and targeted metabolomics, respectively. Transcriptomic analysis of colon tissues was also conducted. Subsequently, potential molecular pathways and differentially expressed genes were verified by western blot, immunoprecipitation, and immunofluorescence analyses. Furthermore, the integrity of the colonic barrier was evaluated by hematoxylin and eosin and mucin 2 staining and expression levels of tight junction proteins. Besides, colonic inflammation was further assessed by flow cytometry and expression levels of inflammatory cytokines. In addition, colonic mitochondrial dysfunction was analyzed via membrane potential, reactive oxygen species, electron transport chain (ETC) activities, adenosine triphosphate content, and mitochondrial ultrastructure.

RESULTS

CCH modified gut microbial composition and microbial metabolism of SCFAs, which may be associated with inhibition of mitochondrial ETC activities and oxidative phosphorylation, leading to dysregulation of mitochondrial energy metabolism. Furthermore, CCH induced differentiation of pathogenic Th17 cells, promoted the formation of complexes of interferon regulatory factor 4 and signal transducer and activator of transcription 3 (STAT3), and increased the phosphorylation of STAT3. This was associated with an impairment of colonic barrier function and chronic colonic inflammation. In contrast, FMT and SCFA replenishment ameliorated CCH-induced gut microbial dysbiosis by increasing the intestinal content of Ruminococcus_sp_N15_MGS_57 and modulating microbial metabolism of SCFAs by increasing acetic acid contents associated with an improvment of the balance between Tregs and Th17 cells, mitochondrial ETC activities, and oxidative phosphorylation to prevent colonic inflammation and dysregulation of mitochondrial energy metabolism.

CONCLUSION

These findings indicate that FMT and SCFA replenishment present a promising therapeutic strategy against colonic dysfunction under a state of chronic cerebral ischemia.

Extracranial carotid atherosclerosis is associated with increased neurofibrillary tangle accumulation

OBJECTIVE

We sought to determine whether extracranial carotid atherosclerotic disease (ECAD) is associated with increased key neurodegenerative pathology such as neurofibrillary tangle (NFT), beta-amyloid plaque, or cerebral amyloid angiopathy (CAA) accumulation, findings associated with Alzheimer's disease (AD) and other dementias.

METHODS

Our prospective, longitudinal, clinicopathologic study, the AZSAND (Arizona study of aging and neurodegenerative disorders) and Brain and Body Donation Program, recorded the presence or absence of clinically diagnosed ECAD and performed semiquantitative density estimates of NFT, beta-amyloid plaque, and CAA at death. After adjusting for potential confounding factors determined by logistic regression analysis, histopathology density scores were evaluated in individuals with ECAD (n = 66) and those without ECAD (n = 125).

RESULTS

We found that the presence of ECAD was associated with a 21% greater NFT burden at death compared with no ECAD (P = .02). Anatomically, an increased NFT burden was seen throughout the brain regions evaluated but was significant in the temporal lobe (P < .05) and entorhinal cortex (P = .02). In addition, we found that subjects who had undergone carotid endarterectomy (CEA), the surgical treatment of ECAD (n = 32), had decreased NFT densities compared with those with ECAD who had not undergone CEA (n = 66; P = .04). In contrast to NFT, ECAD was not associated with beta-amyloid plaques or CAA density.

CONCLUSIONS

These findings indicate that ECAD is associated with the NFT burden in the temporal lobe and entorhinal cortex, which has clinical significance for AD and non-AD dementias and cognitive dysfunction. Further understanding of whether ECAD increases the risk of neurodegenerative brain changes is highly relevant because ECAD is a treatable disease that has not, otherwise, been evaluated for nor specifically treated as a dementia risk factor.

Vascular Hypothesis of Alzheimer Disease: Topical Review of Mouse Models

[Figure: see text].

Deciphering Alzheimer's Disease Pathogenic Pathway: Role of Chronic Brain Hypoperfusion on p-Tau and mTOR

This review examines new biomolecular findings that lend support to the hemodynamic role played by chronic brain hypoperfusion (CBH) in driving a pathway to Alzheimer's disease (AD). CBH is a common clinical feature of AD and the current topic of intense investigation in AD models. CBH is also the basis for the vascular hypothesis of AD which we originally proposed in 1993. New biomolecular findings reveal the interplay of CBH in increasing tau phosphorylation (p-Tau) in the hippocampus and cortex of AD mice, damaging fast axonal transport, increasing signaling of mammalian target of rapamycin (mTOR), impairing learning-memory function, and promoting the formation of neurofibrillary tangles, a neuropathologic hallmark of AD. These pathologic elements have been singularly linked with neurodegeneration and AD but their abnormal, collective participation during brain aging have not been fully examined. The format for this review will provide a consolidated analysis of each pathologic phase contributing to cognitive decline and AD onset, summarized in nine chronological steps. These steps galvanize each factor's active participation and contribution in constructing a biomolecular pathway to AD onset generated by CBH.

Associations between Vascular Function and Tau PET Are Associated with Global Cognition and Amyloid

Tau pathology and vascular dysfunction are important contributors to Alzheimer's disease (AD), but vascular-tau associations and their effects on cognition are poorly understood. We investigated these associations in male and female humans by conducting voxelwise comparisons between cerebral blood flow (CBF) and tau positron emission tomography (PET) images in independent discovery [cognitively normal (CN), 19; mild cognitive impairment (MCI) risk, 43; MCI, 6] and replication (CN,73; MCI, 45; AD, 20) cohorts. In a subgroup, we assessed relationships between tau and soluble platelet-derived growth factor β (sPDGFRβ), a CSF marker of pericyte injury. We tested whether CBF/sPDGFRβ-tau relationships differed based on Montreal Cognitive Assessment (MoCA) global cognition performance, or based on amyloid burden. Mediation analyses assessed relationships among CBF/sPDGFRβ, tau, and cognition. Negative CBF-tau correlations were observed predominantly in temporal-parietal regions. In the replication cohort, early negative CBF-tau correlations increased in spatial extent and in strength of correlation with increased disease severity. Stronger CBF-tau and sPDGFRβ-tau correlations were observed in participants with greater amyloid burden and lower MoCA scores. Importantly, when stratifying by amyloid status, stronger CBF-tau relationships in individuals with lower MoCA scores were driven by amyloid+ participants. Tau PET was a significant mediator CBF/sPDGFRβ-MoCA relationships in numerous regions. Our results demonstrate vascular-tau associations across the AD spectrum and suggest that early vascular-tau associations are exacerbated in the presence of amyloid, consistent with a two-hit model of AD on cognition. Combination treatments targeting vascular health, as well as amyloid-β and tau levels, may preserve cognitive function more effectively than single-target therapies.SIGNIFICANCE STATEMENT Emerging evidence demonstrates a role for vascular dysfunction as a significant contributor to Alzheimer's pathophysiology. However, associations between vascular dysfunction and tau pathology, and their effects on cognition remain poorly understood. Multimodal neuroimaging data from two independent cohorts were analyzed to provide novel in vivo evidence of associations between cerebral blood flow (CBF), an MRI measure of vascular health, and tau pathology using PET. CBF-tau associations were related to cognition and driven in part by amyloid burden. Soluble platelet-derived growth factor β, an independent CSF vascular biomarker, confirmed vascular-tau associations in a subgroup analysis. These results suggest that combination treatments targeting vascular health, amyloid-β, and tau levels may more effectively preserve cognitive function than single-target therapies.

Clinical Features and Experimental Models of Cerebral Small Vessel Disease

Cerebral small vessel disease (SVD) refers to a group of disease conditions affecting the cerebral small vessels, which include the small arteries, arterioles, capillaries, and postcapillary venules in the brain. SVD is the primary cause of vascular cognitive impairment and gait disturbances in aged people. There are several types of SVD, though arteriolosclerosis, which is mainly associated with hypertension, aging, and diabetes mellitus, and cerebral amyloid angiopathy (CAA) comprise most SVD cases. The pathology of arteriolosclerosis-induced SVD is characterized by fibrinoid necrosis and lipohyalinosis, while CAA-associated SVD is characterized by progressive deposition of amyloid beta (Aβ) protein in the cerebral vessels. Brain magnetic resonance imaging (MRI) has been used for examination of SVD lesions; typical lesions are characterized by white matter hyperintensity, lacunar infarcts, enlargement of perivascular spaces (EPVS), microbleeds, cortical superficial siderosis (cSS), and cortical microinfarcts. The microvascular changes that occur in the small vessels are difficult to identify clearly; however, these consequent image findings can represent the SVD. There are two main strategies for prevention and treatment of SVD, i.e., pharmacotherapy and lifestyle modification. In this review, we discuss clinical features of SVD, experimental models replicating SVD, and treatments to further understand the pathological and clinical features of SVD.

Neuroprotective actions of leptin facilitated through balancing mitochondrial morphology and improving mitochondrial function

Mitochondrial dysfunction has a recognised role in the progression of Alzheimer's disease (AD) pathophysiology. Cerebral perfusion becomes increasingly inefficient throughout ageing, leading to unbalanced mitochondrial dynamics. This effect is exaggerated by amyloid β (Aβ) and phosphorylated tau, two hallmark proteins of AD pathology. A neuroprotective role for the adipose-derived hormone, leptin, has been demonstrated in neuronal cells. However, its effects with relation to mitochondrial function in AD remain largely unknown. To address this question, we have used both a glucose-serum-deprived (CGSD) model of ischaemic stroke in SH-SY5Y cells and a Aβ_1-42 -treatment model of AD in differentiated hippocampal cells. Using a combination of 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide (JC-1) and MitoRed staining techniques, we show that leptin prevents depolarisation of the mitochondrial membrane and excessive mitochondrial fragmentation induced by both CGSD and Aβ_1-42 . Thereafter, we used ELISAs and a number of activity assays to reveal the biochemical underpinnings of these processes. Specifically, leptin was seen to inhibit up-regulation of the mitochondrial fission protein Fis1 and down-regulation of the mitochondrial fusion protein, Mfn2. Furthermore, leptin was seen to up-regulate the expression and activity of the antioxidant enzyme, monoamine oxidase B. Herein we provide the first demonstration that leptin is sufficient to protect against aberrant mitochondrial dynamics and resulting loss of function induced by both CGSD and Aβ_1-42 . We conclude that the established neuroprotective actions of leptin may be facilitated through regulation of mitochondrial dynamics.