Resistance exercise in early-stage ALS patients, ALSFRS-R, Sickness Impact Profile ALS-19, and muscle transcriptome: a pilot study.

Amyotrophic lateral sclerosis (ALS) patients lack effective treatments to maintain motor and neuromuscular function. This study aimed to evaluate the effect of a home-based exercise program on muscle strength, ALS scores, and transcriptome in ALS patients, Clinical Trials.gov #NCT03201991 (28/06/2017). An open-label, non-randomized pilot clinical trial was conducted in seven individuals with early-stage ALS. Participants were given 3 months of home-based resistance exercise focusing on the quadriceps muscles. The strength of exercised muscle was evaluated using bilateral quadriceps strength with manual muscle testing, handheld dynamometers, five times sit-to-stand, and Timed-Up-and-Go before and after the exercise program. In addition, changes in the Sickness Impact Profile ALS-19 (SIP/ALS-19) as the functional outcome measure and the transcriptome of exercised muscles were compared before and after the exercise. The primary outcome of muscle strength did not change significantly by the exercise program. The exercise program maintained the SIP/ALS-19 and the ALS Functional Rating Scale-Revised (ALSFRS-R). Transcriptome analysis revealed that exercise reverted the expression level of genes decreased in ALS, including parvalbumin. Three months of moderately intense strength and conditioning exercise maintained muscle strength of the exercised muscle and ALSFRS-R scores and had a positive effect on patients' muscle transcriptome.

O-GlcNAc impacts mitophagy via the PINK1-dependent pathway.

Background: The accumulation of dysfunctional mitochondria is an early feature of Alzheimer's disease (AD). The impaired turnover of damaged mitochondria increases reactive oxygen species production and lowers ATP generation, leading to cellular toxicity and neurodegeneration. Interestingly, AD exhibits a disruption in the global post-translational modification ß-N-acetylglucosamine (O-GlcNAc). O-GlcNAc is a ubiquitous single sugar modification found in the nuclear, cytoplasmic, and mitochondrial proteins. Cells maintain a homeostatic level of O-GlcNAc by cycling the addition and removal of the sugar by O-GlcNAc transferase (OGT) or O-GlcNAcase (OGA), respectively. Methods: We used patient-derived induced pluripotent stem cells, a transgenic mouse model of AD, SH-SY5Y neuroblastoma cell lines to examine the effect of sustained O-GlcNAcase inhibition by Thiamet-G (TMG) or OGT deficiency on mitophagy using biochemical analyses. Results: Here, we established an essential role for O-GlcNAc in regulating mitophagy (mitochondria-selective autophagy). Stimulating mitophagy using urolithin A (UA) decreases cellular O-GlcNAc and elevates mitochondrial O-GlcNAc. Sustained elevation in O-GlcNAcylation via pharmacologically inhibiting OGA using Thiamet-G (TMG) increases the mitochondrial level of mitophagy protein PTEN-induced kinase 1 (PINK1) and autophagy-related protein light chain 3 (LC3). Moreover, we detected O-GlcNAc on PINK1 and TMG increases its O-GlcNAcylation level. Conversely, decreasing cellular O-GlcNAcylation by knocking down OGT decreases both PINK1 protein expression and LC3 protein expression. Mitochondria isolated from CAMKII-OGT-KO mice also had decreased PINK1 and LC3. Moreover, human brain organoids treated with TMG showed significant elevation in LC3 compared to control. However, TMG-treated AD organoids showed no changes in LC3 expression. Conclusion: Collectively, these data demonstrate that O-GlcNAc plays a crucial role in the activation and progression of mitophagy, and this activation is disrupted in AD.

The reciprocal relationship between amyloid precursor protein and mitochondrial function.

Amyloid precursor protein (APP), secretase enzymes, and amyloid beta (Aß) have been extensively studied in the context of Alzheimer's disease (AD). Despite this, the function of these proteins and their metabolism is not understood. APP, secretase enzymes, and APP processing products (Aß and C-terminal fragments) localize to endosomes, mitochondria, endoplasmic reticulum (ER), and mitochondrial/ER contact sites. Studies implicate significant relationships between APP, secretase enzyme function, APP metabolism, and mitochondrial function. Mitochondrial dysfunction is a key pathological hallmark of AD and is intricately linked to proteostasis. Here, we review studies examining potential functions of APP, secretase enzymes, and APP metabolites in the context of mitochondrial function and bioenergetics. We discuss implications and limitations of studies and highlight knowledge gaps that remain in the field.

Intrinsic aerobic capacity modulates Alzheimer's disease pathological hallmarks, brain mitochondrial function and proteome during aging.

Low aerobic capacity is strongly associated with all-cause mortality and risk for Alzheimer's disease (AD). Individuals with early dementia and AD have lower aerobic capacity compared to age-matched controls. The mechanism by which aerobic capacity influences AD risk is unknown but is likely mediated by sexual dimorphism and tissue-level differences in mitochondrial energetics. Here, we used rats selectively bred for large differences in intrinsic aerobic exercise capacity. Brain tissue from 18-month and 24-month-old female and male low-capacity runner (LCR) and high-capacity runner (HCR) rats were analyzed for markers of mitochondrial function and AD-associated pathologies. LCR rats, irrespective of sex, exhibited a greater increase in brain amyloid beta (Aß42) and tau hyperphosphorylation (pTauthr181/total tau) with aging. In female LCR rats, brain mitochondrial respiration at states 3, 4, and FCCP-induced uncoupling, when stimulated with pyruvate/malate, was reduced at 18 and 24 months, leading to lower ATP-linked mitochondrial respiration compared to mitochondria from HCR rats. Male LCR rats also showed reduced complex II-stimulated mitochondrial respiration (succinate + rotenone) at 24 months compared to HCR rats. Differences in mitochondrial respiration were associated with tau hyperphosphorylation and Aß42 alterations in both HCR and LCR strains. Proteomic analysis unveiled a distinct difference in the mitochondrial proteome, wherein female LCR rats displayed diminished mitochondrial translation and oxidative phosphorylation (OXPHOS) proteins at 18 months compared to female HCR rats. Conversely, male LCR rats exhibited increased OXPHOS protein abundance but reduced tricarboxylic acid (TCA) cycle proteins compared to male HCR rats. These findings underscore a robust association between intrinsic aerobic exercise capacity, brain mitochondrial function, and AD pathologies during aging.

Proteome profiling of cerebrospinal fluid using machine learning shows a unique protein signature associated with APOE4 genotype.

INTRODUCTION: Proteome changes associated with APOE4 variant carriage that are independent of Alzheimer's disease (AD) pathology and diagnosis are unknown. This study investigated APOE4 proteome changes in people with AD, mild cognitive impairment, and no impairment. METHODS: Clinical, APOE genotype, and cerebrospinal fluid (CSF) proteome and AD biomarker data was sourced from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. Proteome profiling was done using supervised machine learning. RESULTS: We found an APOE4-specific proteome signature that was independent of cognitive diagnosis and AD pathological biomarkers, and increased risk of progression to cognitive impairment. Proteins were enriched in brain regions including the caudate and cortex and cells including endothelial cells, oligodendrocytes, and astrocytes. Enriched peripheral immune cells included T cells, macrophages, and B cells. DISCUSSION: APOE4 carriers have a unique CSF proteome signature associated with a strong brain and peripheral immune and inflammatory phenotype that likely underlies APOE4 carriers' vulnerability to cognitive decline and AD.

Traumatic Brain Injury Alters the Trajectory of Age-Related Mitochondrial Change.

Background: Some epidemiologic studies associate traumatic brain injury (TBI) with Alzheimer's disease (AD). Objective: To test whether a TBI-induced acceleration of age-related mitochondrial change could potentially mediate the reported TBI-AD association. Methods: We administered unilateral controlled cortical impact (CCI) or sham injuries to 5-month-old C57BL/6J and tau transgenic rTg4510 mice. In the non-transgenics, we assessed behavior (1-5 days, 1 month, and 15 months), lesion size (1 and 15 months), respiratory chain enzymes (1 and 15 months), and mitochondrial DNA copy number (mtDNAcn) (1 and 15 months) after CCI/sham. In the transgenics we quantified post-injury mtDNAcn and tangle burden. Results: In the non-transgenics CCI caused acute behavioral deficits that improved or resolved by 1-month post-injury. Protein-normalized complex I and cytochrome oxidase activities were not significantly altered at 1 or 15 months, although complex I activity in the CCI ipsilesional cortex declined during that period. Hippocampal mtDNAcn was not altered by injury at 1 month, increased with age, and rose to the greatest extent in the CCI contralesional hippocampus. In the injured then aged transgenics, the ipsilesional hippocampus contained less mtDNA and fewer tangles than the contralesional hippocampus; mtDNAcn and tangle counts did not correlate. Conclusions: As mice age their brains increase mtDNAcn as part of a compensatory response that preserves mitochondrial function, and TBI enhances this response. TBI may, therefore, increase the amount of compensation required to preserve late-life mitochondrial function. If TBI does modify AD risk, altering the trajectory or biology of aging-related mitochondrial changes could mediate the effect.

Protocol for a single-arm, pilot trial of creatine monohydrate supplementation in patients with Alzheimer's disease.

BACKGROUND: Impaired brain bioenergetics is a pathological hallmark of Alzheimer's disease (AD) and is a compelling target for AD treatment. Patients with AD exhibit dysfunction in the brain creatine (Cr) system, which is integral in maintaining bioenergetic flux. Recent studies in AD mouse models suggest Cr supplementation improves brain mitochondrial function and may be protective of AD peptide pathology and cognition. AIMS: The Creatine to Augment Bioenergetics in Alzheimer's disease (CABA) study is designed to primarily assess the feasibility of supplementation with 20 g/day of creatine monohydrate (CrM) in patients with cognitive impairment due to AD. Secondary aims are designed to generate preliminary data investigating changes in brain Cr levels, cognition, peripheral and brain mitochondrial function, and muscle strength and size. METHODS: CABA is an 8-week, single-arm pilot study that will recruit 20 patients with cognitive impairment due to AD. Participants attend five in-person study visits: two visits at baseline to conduct screening and baseline assessments, a 4-week visit, and two 8-week visits. Outcomes assessment includes recruitment, retention, and compliance, cognitive testing, magnetic resonance spectroscopy of brain metabolites, platelet and lymphocyte mitochondrial function, and muscle strength and morphology at baseline and 8 weeks. DISCUSSION: CABA is the first study to investigate CrM as a potential treatment in patients with AD. The pilot data generated by this study are pertinent to inform the design of future large-scale efficacy trials. TRIAL REGISTRATION: ClinicalTrials.gov, NCT05383833 , registered on 20 May 2022.

Blood-Based Transcriptomic Biomarkers Are Predictive of Neurodegeneration Rather Than Alzheimer's Disease.

Alzheimer's disease (AD) is a growing global health crisis affecting millions and incurring substantial economic costs. However, clinical diagnosis remains challenging, with misdiagnoses and underdiagnoses being prevalent. There is an increased focus on putative, blood-based biomarkers that may be useful for the diagnosis as well as early detection of AD. In the present study, we used an unbiased combination of machine learning and functional network analyses to identify blood gene biomarker candidates in AD. Using supervised machine learning, we also determined whether these candidates were indeed unique to AD or whether they were indicative of other neurodegenerative diseases, such as Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS). Our analyses showed that genes involved in spliceosome assembly, RNA binding, transcription, protein synthesis, mitoribosomes, and NADH dehydrogenase were the best-performing genes for identifying AD patients relative to cognitively healthy controls. This transcriptomic signature, however, was not unique to AD, and subsequent machine learning showed that this signature could also predict PD and ALS relative to controls without neurodegenerative disease. Combined, our results suggest that mRNA from whole blood can indeed be used to screen for patients with neurodegeneration but may be less effective in diagnosing the specific neurodegenerative disease.

Cell type and sex specific mitochondrial phenotypes in iPSC derived models of Alzheimer's disease.

Introduction: Mitochondrial dysfunction is observed in Alzheimer's disease (AD). Altered mitochondrial respiration, cytochrome oxidase (COX) Vmax, and mitophagy are observed in human subjects and animal models of AD. Models derived from induced pluripotent stem cells (iPSCs) may not recapitulate these phenotypes after reprogramming from differentiated adult cells. Methods: We examined mitochondrial function across iPSC derived models including cerebral organoids, forebrain neurons, and astrocytes. iPSCs were reprogrammed from fibroblasts either from the University of Kansas Alzheimer's Disease Research Center (KU ADRC) cohort or purchased from WiCell. A total of four non-demented and four sporadic AD iPSC lines were examined. Models were subjected to mitochondrial respiration analysis using Seahorse XF technology, spectrophotometric cytochrome oxidase (COX) Vmax assays, fluorescent assays to determine mitochondrial mass, mitochondrial membrane potential, calcium, mitochondrial dynamics, and mitophagy levels. AD pathological hallmarks were also measured. Results: iPSC derived neurons and cerebral organoids showed reduced COX Vmax in AD subjects with more profound defects in the female cohort. These results were not observed in astrocytes. iPSC derived neurons and astrocytes from AD subjects had reduced mitochondrial respiration parameters with increased glycolytic flux. iPSC derived neurons and astrocytes from AD subjects showed sex dependent effects on mitochondrial membrane potential, mitochondrial superoxide production, and mitochondrial calcium. iPSC derived neurons from AD subjects had reduced mitochondrial localization in lysosomes with sex dependent effects on mitochondrial mass, while iPSC derived astrocytes from female AD subjects had increased mitochondrial localization to lysosomes. Both iPSC derived neurons and astrocytes from AD subjects showed altered mitochondrial dynamics. iPSC derived neurons had increased secreted Aß, and sex dependent effects on total APP protein expression. iPSC derived astrocytes showed sex dependent changes in GFAP expression in AD derived cells. Conclusion: Overall, iPSC derived models from AD subjects show mitochondrial phenotypes and AD pathological hallmarks in a cell type and sex dependent manner. These results highlight the importance of sex as a biological variable in cell culture studies.

Mitochondria Profoundly Influence Apolipoprotein E Biology.

BACKGROUND: Mitochondria can trigger Alzheimer's disease (AD)-associated molecular phenomena, but how mitochondria impact apolipoprotein E (APOE; apoE) is not well known. OBJECTIVE: Consider whether and how mitochondrial biology influences APOE and apoE biology. METHODS: We measured APOE expression in human SH-SY5Y neuronal cells with different forms of mitochondrial dysfunction including total, chronic mitochondrial DNA (mtDNA) depletion (ρ0 cells); acute, partial mtDNA depletion; and toxin-induced mitochondrial dysfunction. We further assessed intracellular and secreted apoE protein levels in the ρ0 cells and interrogated the impact of transcription factors and stress signaling pathways known to influence APOE expression. RESULTS: SH-SY5Y ρ0 cells exhibited a 65-fold increase in APOE mRNA, an 8-fold increase in secreted apoE protein, and increased intracellular apoE protein. Other models of primary mitochondrial dysfunction including partial mtDNA-depletion, toxin-induced respiratory chain inhibition, and chemical-induced manipulations of the mitochondrial membrane potential similarly increased SH-SY5Y cell APOE mRNA. We explored potential mediators and found in the ρ0 cells knock-down of the C/EBPα and NFE2L2 (Nrf2) transcription factors reduced APOE mRNA. The activity of two mitogen-activated protein kinases, JNK and ERK, also strongly influenced ρ0 cell APOE mRNA levels. CONCLUSION: Primary mitochondrial dysfunction either directly or indirectly activates APOE expression in a neuronal cell model by altering transcription factors and stress signaling pathways. These studies demonstrate mitochondrial biology can influence the biology of the APOE gene and apoE protein, which are implicated in AD.

Interactions between amyloid, amyloid precursor protein, and mitochondria.

Mitochondrial dysfunction and Aß accumulation are hallmarks of Alzheimer's disease (AD). Decades of research describe a relationship between mitochondrial function and Aß production. Amyloid precursor protein (APP), of which Aß is generated from, is found within mitochondria. Studies suggest Aß can be generated in mitochondria and imported into mitochondria. APP and Aß alter mitochondrial function, while mitochondrial function alters Aß production from APP. The role these interactions contribute to AD pathology and progression are unknown. Here, we discuss prior research, the rigor of those studies, and the critical knowledge gaps of relationships between APP, Aß, and mitochondria.

Amyloid precursor protein and mitochondria.

Amyloid Precursor Protein (APP) processing to amyloid beta (Aß) is a major hallmark of Alzheimer's disease (AD). The amyloid cascade hypothesis postulates that Aß accumulation and aggregation causes AD, however many therapeutics targeting Aß have failed recently. Decades of research describe metabolic deficits in AD. Mitochondrial dysfunction is observed in AD subjects within the brain and systemically. APP and γ-secretase are localized to mitochondria. APP can be processed within mitochondria and its localization to mitochondria affects function. Here we discuss the evidence showing APP and γ-secretase localize to mitochondria. We also discuss the implications for the function of APP and its cleavage products in regulating mitochondrial function.

ß-Hydroxybutyrate preferentially enhances neuron over astrocyte respiration while signaling cellular quiescence.

While ketone bodies support overall brain energy metabolism, it is increasingly clear specific brain cell types respond differently to ketone body availability. Here, we characterized how SH-SY5Y neuroblastoma cell, primary neuron, and primary astrocyte bioenergetics and nutrient sensing pathways respond to ß-hydroxybutyrate (ßOHB). SH-SY5Y cells and primary neurons, but not astrocytes, exposed to ßOHB increased respiration and decreased PI3K-Akt-mTOR signaling. Despite increased carbon availability and respiration, SH-SY5Y cells treated with ßOHB reduced their overall metabolic activity and cell cycling rate. Levels of the quiescence-regulating Yamanaka factors increased to a broader extent in SH-SY5Y cells and primary neurons. We propose a ßOHB-induced increase in neuron respiration, accompanied by activation of quiescence associated pathways, could alleviate bioenergetic stress and limit cell senescence. This in turn could potentially benefit conditions, including brain aging and neurodegenerative diseases, that feature bioenergetic decline and cell senescence.

The Role of Bioenergetics in Neurodegeneration.

Bioenergetic and mitochondrial dysfunction are common hallmarks of neurodegenerative diseases. Decades of research describe how genetic and environmental factors initiate changes in mitochondria and bioenergetics across Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). Mitochondria control many cellular processes, including proteostasis, inflammation, and cell survival/death. These cellular processes and pathologies are common across neurodegenerative diseases. Evidence suggests that mitochondria and bioenergetic disruption may drive pathological changes, placing mitochondria as an upstream causative factor in neurodegenerative disease onset and progression. Here, we discuss evidence of mitochondrial and bioenergetic dysfunction in neurodegenerative diseases and address how mitochondria can drive common pathological features of these diseases.

Mitochondrial function and Aß in Alzheimer's disease postmortem brain.

INTRODUCTION: Mitochondrial dysfunction is observed in Alzheimer's disease (AD). However, the relationship between functional mitochondrial deficits and AD pathologies is not well established in human subjects. METHODS: Post-mortem human brain tissue from 11 non-demented (ND) and 12 AD subjects was used to examine mitochondrial electron transport chain (ETC) function. Data were analyzed by neuropathology diagnosis and Apolipoprotein E (APOE) genotype. Relationships between AD pathology and mitochondrial function were determined. RESULTS: AD subjects had reductions in brain cytochrome oxidase (COX) function and complex II Vmax. APOE ε4 carriers had COX, complex II and III deficits. AD subjects had reduced expression of Complex I-III ETC proteins, no changes were observed in APOE ε4 carriers. No correlation between p-Tau Thr 181 and mitochondrial outcomes was observed, although brains from non-demented subjects demonstrated positive correlations between Aß concentration and COX Vmax. DISCUSSION: These data support a dysregulated relationship between brain mitochondrial function and Aß pathology in AD.

Pharmacologic enrichment of exosome yields and mitochondrial cargo.

In studies with human participants, exosome-based biospecimens can facilitate unique biomarker assessments. As exosome cargos can include mitochondrial components, there is interest in using exosomes to inform the status of an individual's mitochondria. Here, we evaluated whether targeted pharmacologic manipulations could influence the quantity of exosomes shed by cells, and whether these manipulations could impact their mitochondrial cargos. We treated human SH-SY5Y cells with bafilomycin A1, which interferes with general autophagy and mitophagy by inhibiting lysosome acidification and lysosome-autophagosome fusion; deferiprone (DFP), which enhances receptor-mediated mitophagy; or both. Exosome fractions from treated cells were harvested from the cell medium and analyzed for content including mitochondria-derived components. We found bafilomycin increased particle yields, and a combination of bafilomycin plus DFP consistently increased particle yields and mitochondria-associated content. Specifically, the exosome fractions from the bafilomycin plus DFP-treated cells contained more mitochondrial DNA (mtDNA), mtDNA-derived mRNA transcripts, and citrate synthase protein. Our data suggest pharmacologic manipulations that enhance mitophagy initiation, while inhibiting the lysosomal digestion of autophagosomes and multivesicular bodies, could potentially enhance the sensitivity of exosome-based biomarker assays intended to inform the status of an individual's mitochondria.

Apolipoprotein E and Alzheimer's disease.

Genetic variation in apolipoprotein E (APOE) influences Alzheimer's disease (AD) risk. APOE ε4 alleles are the strongest genetic risk factor for late onset sporadic AD. The AD risk is dose dependent, as those carrying one APOE ε4 allele have a 2-3-fold increased risk, while those carrying two ε4 alleles have a 10-15-fold increased risk. Individuals carrying APOE ε2 alleles have lower AD risk and those carrying APOE ε3 alleles have neutral risk. APOE is a lipoprotein which functions in lipid transport, metabolism, and inflammatory modulation. Isoform specific effects of APOE within the brain include alterations to Aß, tau, neuroinflammation, and metabolism. Here we review the association of APOE with AD, the APOE isoform specific effects within brain and periphery, and potential therapeutics.

Mitochondrial Targeting of Amyloid-ß Protein Precursor Intracellular Domain Induces Hippocampal Cell Death via a Mechanism Distinct from Amyloid-ß.

BACKGROUND: Amyloid-ß (Aß) is a principal cleavage product of amyloid-ß protein precursor (AßPP) and is widely recognized as a key pathogenic player in Alzheimer's disease (AD). Yet, there is increasing evidence of a neurotoxic role for the AßPP intracellular domain (AICD) which has been proposed to occur through its nuclear function. Intriguingly, there is a γ-secretase resident at the mitochondria which could produce AICD locally. OBJECTIVE: We examined the potential of AICD to induce neuronal apoptosis when targeted specifically to the mitochondria and compared its mechanism of neurotoxicity to that of Aß. METHODS: We utilized transient transfection of HT22 neuronal cells with bicistronic plasmids coding for DsRed and either empty vector (Ires), Aß, AICD59, or mitochondrial-targeted AICD (mitoAICD) in combination with various inhibitors of pathways involved in apoptosis. RESULTS: AICD induced significant neuronal apoptosis only when targeted to the mitochondria. Apoptosis required functional mitochondria as neither Aß nor mitoAICD induced significant toxicity in cells devoid of mitochondrial DNA. Both glutathione and a Bax inhibitor protected HT22 cells from either peptide. However, inhibition of the mitochondrial permeability transition pore only protected from Aß, while pan-caspase inhibitors uniquely rescued cells from mitoAICD. CONCLUSION: Our results show that AICD displays a novel neurotoxic function when targeted to mitochondria. Moreover, mitoAICD induces apoptosis via a mechanism that is distinct from that of Aß. These findings suggest that AICD produced locally at mitochondria via organelle-specific γ-secretase could act in a synergistic manner with Aß to cause mitochondrial dysfunction and neuronal death in AD.