Citations

Abstract Oxidative phosphorylation (OXPHOS) is a central function and a key indicator of mitochondrial fitness, yet studies in human tissue remain limited. Inclusion body myositis (IBM) is a progressive myopathy that lies at the intersection of aging, inflammation and mitochondrial dysfunction. We aimed to perform a comprehensive profiling of mitochondrial respiration in muscle tissue from patients with IBM. A wide battery of complementary approaches from RNA level to high-resolution respirometry on permeabilized muscle fibers was employed. The relationship between mitochondrial respiration, mitochondrial content, mitochondrial DNA (mtDNA) abnormalities and mitophagy was examined, along with the correlation with various clinical parameters to determine their clinical relevance. The study included a total of 67 patients with IBM and 45 controls. On high resolution respirometry of permeabilized muscle fibers, IBM samples exhibited reduced maximal mitochondrial respiration per tissue weight in State 3 (high substrates, high ADP) and uncoupled state with decreased coupling efficiency and higher leak control ratios. When adjusting for citrate synthase reflecting mitochondrial content, male patients had decreased State 3 intrinsic respiration, whereas female patients had greater intrinsic respiration under leak states. Complex I activity was decreased mainly in female patients, in whom complex II control ratio positively correlated with disease duration and severity. IBM was further associated with decreased RNA levels of all complexes, and lower protein expression of complex I, III, IV and V, likely related to the lower mtDNA content seen in IBM samples. Regarding the production of reactive oxygen species, IBM samples exhibited lower maximal H2O2 emission, accompanied by a higher total antioxidant capacity that positively correlated with disease duration in female patients. Lastly, correlation analyses suggested that impaired mitochondrial respiration, altered mitophagy, and reduced mtDNA content are interconnected in IBM and maybe of clinical significance. IBM is characterized by multifaceted, clinically relevant impairments in mitochondrial respiration. Future studies should further explore underlying pathomechanisms and the variation of mitochondrial respiration by disease stage.

Abstract Mitochondrial dysfunction and lipid dysregulation are among the earliest abnormalities in Alzheimer’s disease (AD), yet their mechanistic interplay and therapeutic potential remain poorly understood. Here, we investigated whether restoration of mitochondrial function can reverse metabolic dysfunction and promote resilience in advanced-stage AD. Female APP/PS1 mice were treated with the brain-penetrant mitochondrial complex I (mtCI) modulator CP2 beginning at 19 months of age, when pathology and cognitive deficits were well established. To define the metabolic mechanisms underlying therapeutic response, we developed iMiceBrain , the first brain-specific genome-scale metabolic model of the mouse brain, and integrated transcriptomics, targeted metabolomics, lipidomics, and metabolic network analyses. CP2 treatment broadly reprogrammed AD-associated molecular signatures and restored pathways involved in mitochondrial function, glucose utilization, lipid metabolism, synaptic activity, and cellular stress responses. Metabolic modeling identified enhanced mitochondrial substrate flexibility, activation of fatty acid utilization, restoration of pyruvate dehydrogenase flux, and normalization of cholesterol metabolism as key features of the therapeutic response. Lipidomic analyses further demonstrated correction of disease-associated alterations in cholesteryl esters, phospholipids, and sphingolipids. Together, these findings demonstrate that mild mtCI modulation restores metabolic resilience by coordinating mitochondrial and lipid metabolism, establishing it as a disease-modifying therapeutic strategy for AD.

Abstract Weak inhibition of mitochondrial complex I (mtCI) has been shown to have neuroprotective effects in cellular and animal models of Alzheimer’s and Huntington’s diseases, at least in part by enhancing mitochondrial biogenesis and function. Mitochondrial dysfunction has also been demonstrated in schizophrenia patients and mouse models of schizophrenia. We tested whether weak inhibition of mtCI would ameliorate mitochondrial and behavioral phenotypes in a mouse model of schizophrenia. In mice with four copies of the Gldc gene, 8 weeks of treatment with the weak mtCI inhibitor, the small-molecule tricyclic pyrone compound CP2, reversed spontaneous alternation deficits in the Y maze, startle habituation deficits, and social novelty deficits in the three-chamber social interaction test. Consistent with the mechanism of action, Western blots revealed that CP2 reverses the reduced expression of PGC-1α, a master regulator of mitochondrial biogenesis, and of the VDAC1, a primary gatekeeper for the exchange of metabolites, ions, and ATP between mitochondria and the cytosol. These findings suggest that the improvement of mitochondrial function may represent a novel strategy to reverse pathophysiological and behavioral deficits in schizophrenia.

Abstract Alzheimer’s disease (AD) is characterized by diminished capacity to mount adaptive cellular stress responses required to maintain energy homeostasis and proteostasis. An emerging therapeutic strategy is to restore adaptive stress responses by inducing mild energetic stress through inhibition of mitochondrial complex I (mtCI). However, pharmacological inhibition of the respiratory chain has remained challenging, as it can induce bioenergetic failure rather than beneficial signaling. Here, we describe C273, a brain-penetrant small molecule that delivers controlled, weak attenuation of mtCI activity to therapeutically restore endogenous adaptive stress pathways. This work establishes a first-in-class mechanism in which calibrated activation of multifaceted adaptive mechanisms enhances cellular resilience, rather than impairing mitochondrial function. Structure-activity relationship optimization yielded a compound with high potency against Aβ-induced cellular toxicity, strong selectivity for mtCI, and favorable drug-like properties. C273 demonstrated excellent oral bioavailability, metabolic stability in mouse, rat, and human microsomes, minimal CYP liabilities, and a clean ancillary pharmacology profile in the Eurofins CEREP44 panel. In vivo , C273 readily crosses the blood-brain barrier and activates AMP-activated protein kinase (AMPK), initiating a coordinated hormetic response characterized by enhanced antioxidant defenses, suppression of inflammatory signaling, induction of autophagy, and increased mitochondrial biogenesis and turnover. Genetic deletion of AMPKα1/α2 abolished these responses, establishing AMPK as a critical mediator of C273 activity. Pharmacological competition experiments further confirmed the target, as pretreatment with non-toxic concentrations of rotenone blocked C273 interaction with the quinone-binding site of mtCI and eliminated its neuroprotective effects. Repeated oral administration of C273 (20-80 mg/kg/day) to wild-type mice for one month produced no detectable cardiac or hepatic toxicity, indicating a favorable in vivo safety margin. Importantly, C273 activated these mechanisms and reduced Aβ and p-Tau levels in induced pluripotent stem cell-derived cerebral organoids from patients with sporadic AD. Collectively, these results establish controlled mtCI modulation as a therapeutic strategy and position C273 as a promising disease-modifying candidate for AD.

Abstract Background Oxidative phosphorylation (OXPHOS) is a central function and a key indicator of mitochondrial fitness, yet studies in human tissue remain limited. Inclusion body myositis (IBM) is a progressive myopathy that lies at the intersection of aging, inflammation and mitochondrial dysfunction. We aimed to perform a comprehensive profiling of mitochondrial respiration in muscle tissue from patients with IBM. Methods A wide battery of complementary tests from RNA level to high-resolution respirometry on permeabilized muscle fibers was performed. The relationship between respiration, mitochondrial content, mitochondrial DNA (mtDNA) abnormalities and mitophagy was examined, along with the correlation with various clinical parameters to determine the clinical significance of the findings. Results The study included a total of 67 patients with IBM and 45 controls. IBM muscle tissue exhibited reduced maximal respiration per tissue weight in State 3 (high substrates, high ADP) and uncoupled state with decreased coupling efficiency and higher leak control ratios. When adjusting for citrate synthase reflecting mitochondrial content, males had decreased State 3 intrinsic respiration, whereas females had greater intrinsic respiration in leak states. Complex II control ratio strongly correlated with disease duration and severity only in females. IBM was associated with decreased RNA and protein expression of OXPHOS complexes. Complex I activity was decreased mainly in females. IBM samples exhibited lower maximal H 2 O 2 emission, accompanied by a higher total antioxidant capacity that correlated with disease duration in females. In IBM, there was decreased mtDNA content, and impaired mitophagy, both of which strongly correlated with respirometry measures and markers of disease severity, indicating these pathways are likely interconnected and of clinical significance. Conclusion IBM is characterized by multilevel impairments in mitochondrial coupling efficiency, revealing several potential therapeutic targets to improve mitochondrial fitness, while accounting for sex-specific differences.

Abstract Background Mitochondrial dysfunction in Alzheimer's Disease (AD) is characterized by impaired energy production, oxidative stress, and disrupted calcium homeostasis, which collectively contribute to neuronal damage, synaptic dysfunction, and the progression of AD pathology. A significant knowledge gap in studying mitochondrial dysfunction in Alzheimer's Disease (AD) lies in understanding the precise molecular mechanisms linking mitochondrial metabolic alterations to neuronal damage, particularly how sex‐specific and cell‐type‐specific mitochondrial processes contribute to the progression of AD pathology. Method This study integrates multiple datasets, post‐mortem brain RNAseq from ROSMAP, Mayo Clinic brain bank and Mount Sinai Brain Bank cohort data available via AD Knowledge Portal hosted by Sage Bionetworks), Human Protein Atlas (HPA), MitoCarta3, genome‐scale human metabolic reconstruction, mitochondriome analysis, and brain & blood metabolomics data (data generated by the Alzheimer's Disease Metabolomics Consortium (ADMC)) to identify mitochondrial genes associated with disrupted metabolism in AD. Additionally, biodomain analysis was used to identify key processes associated with pathology. Result A total of 62 common genes were identified across these approaches, highlighting their potential significance in mitochondrial processes. We also developed the framework to perform metabolite‐gene correlation analyses revealing key mitochondrial‐metabolic interactions (eg. homocysteine and MTHFR gene; acetyl‐CoA and PDHA1 gene). Integrated in silico metabolic analysis identified reaction fluxes, uncovering sex‐specific differences in mitochondrial transport and tricarboxylic acid (TCA) cycle subsystems, with notable alterations in females. Biodomain enrichment analysis focused on mitochondrial processes, identifying disruptions in pathways critical for energy production and redox homeostasis. Additionally, we analyzed datasets related to metformin and complex I inhibitors, linking mitochondrial complex I modulation with metabolic alterations in AD. This analysis identified druggable targets and potential therapeutic candidates for mitochondrial metabolic pathways. Conclusion Our findings integrate multiple data sources to provide a systems‐level understanding of mitochondrial metabolism in AD. Sex‐specific differences associated with mitochondrial dysfunction in AD were identified. We identify important mitochondrial transport proteins and metabolites that could potentially be used as druggable targets in AD.

Abstract Background Despite recent approval of monoclonal antibodies that reduce amyloid (Ab) accumulation, the development of disease‐modifying strategies targeting the underlying mechanisms of Alzheimer’s Disease (AD) are urgently needed. We identified mitochondrial complex I (mtCI) as a small‐molecule druggable target for AD. Using cryo‐EM, we previously demonstrated that the neuroprotective tool compound CP2 directly binds to the Q‐site of mtCI and weakly inhibits its activity. Method Rational design and extensive structure‐activity relationship studies using CP2 as a tool compound allowed the development of novel classes of partial mtCI inhibitors with high selectivity, specificity, safety, and improved drug‐like properties. Target engagement, selectivity, efficacy, safety and the direct binding to mtCI were demonstrated using multiple in vitro assays. Efficacy in vivo was established using APP/PS1 mice. The best new leads, C458 and C273, were evaluated as preclinical candidates. Result Like CP2, C458 and C273 weakly inhibit mtCI, leading to AMPK activation, which triggers a neuroprotective stress response. This response enhances oxidative stress protection, promotes autophagy, and increases mitochondrial biogenesis and turnover, ultimately protecting against Aβ toxicity. Pretreatment with the irreversible mtCI inhibitor rotenone (at non‐toxic concentrations) blocked C458 and C273 from binding to mtCI and abrogated their protection against Aβ toxicity. Both C458 and C273 exhibited excellent bioavailability, blood–brain barrier penetrance, and a clean safety profile in the CEREP 44 safety panel. Chronic administration of C458 (25 mg/kg/day in drinking water ad lib ) to APP/PS1 mice for 7 months preserved cognition, improved long‐term potentiation, reduced oxidative stress and inflammation, and enhanced mitochondrial biogenesis. Similarly, C273 (20, 50, or 80 mg/kg/day) administered to C57BL/6 mice for one month showed no detectable side effects or toxicity in the heart or liver. Conclusion Mechanistic studies revealed that C458 and C273 activate a mitochondrial stress response, augmenting mitochondrial biogenesis, antioxidant signaling, and autophagy, which collectively provided protection against Aβ toxicity in multiple in vitro and in vivo models of AD. These findings demonstrate that weak mtCI inhibition by novel compounds C458 and C273, with improved drug‐like properties, is neuroprotective. This supports the feasibility of developing safe and efficacious mtCI inhibitors as a disease‐modifying strategy for AD.

Abstract Background There is a critical need for novel treatment strategies addressing key features of Alzheimer's disease (AD) pathogenesis. Therapies targeting individual hallmarks yield little benefit. Low‐dose whole brain radiation is a non‐pharmacological approach that has shown promise in AD animal models, reducing amyloid plaques and neuroinflammation, and improving cognitive performance. These findings have initiated small clinical trials. However, even low doses (2 Gray per treatment) can cause adverse effects like vascular damage and reduced neurogenesis in the hippocampus. Minibeam radiation therapy (MBRT) which delivers radiation in an alternating pattern of submillimeter‐wide high (“peak”) and low (“valley”) dose regions can potentially mitigate these negative effects. It has proven to reduce toxicity in a variety of normal tissues including the brain. Therefore, the objective of this study is to determine whether MBRT can safely and effectively address multiple AD mechanisms including amyloid deposition, neuroinflammation and brain energy metabolism while significantly reducing radiation exposure to the brain. Method The study aims to develop an MBRT treatment paradigm to investigate its efficacy in targeting biochemical and cognitive hallmarks of AD. This includes assessing amyloid plaque burden, cognitive function, optimal treatment age, radiation dose, and duration of effect. In a preliminary study, 6‐month‐old 5XFAD mice were irradiated with MBRT (2 Gy peak and 0.3 Gy valley) or conventional irradiation (2 Gy) for a total of 5 daily treatments. Tissue was collected 4 weeks later for analysis of soluble and insoluble amyloid beta by ELISA and microscopic assessment of plaques stained with thioflavin S. Spontaneous alternation in the Y‐maze was assessed 4 weeks post‐irradiation. Result Trends showing reductions in insoluble Aβ were observed in the brains of irradiated 5XFAD mice 4 weeks following MBRT. Although plaque burden is high in untreated 5XFAD mice, cognitive decline was not yet apparent at this age. Conclusion Given these preliminary results, we will define optimal treatment parameters and assess efficacy when MBRT is administered after the onset of cognitive deficits.

Abstract Background Although novel treatments targeting amyloid‐beta (Aβ) have been recently approved by the FDA, there remains a critical need for alternative therapeutic strategies to delay the onset and progression of Alzheimer's disease (AD). Mitochondrial dysfunction and disrupted brain energy homeostasis are key hallmarks of early‐stage AD. Developing treatments that address these deficits could offer substantial benefits. We identified mitochondrial complex I (mtCI) as a druggable target and demonstrated that its mild inhibition using the small molecule CP2 improves brain energy homeostasis, restores synaptic and cognitive function, and activates neuroprotective signaling in AD mouse models. However, the mechanistic link between mtCI inhibition, glucose metabolism, and energy homeostasis remains unclear. Methods Cellular energy metabolism was assessed in neuroblastoma SH‐SY5Y cells expressing mutant human APP protein (APPswe) and in control cells. Glycolytic function, mitochondrial energetics, and fatty acid β‐oxidation (FAO) were measured using a Seahorse Analyzer. Glucose transporter (GLUT) translocation to the cell surface was evaluated using flow cytometry and immunofluorescence staining. Protein expression changes were analyzed via Western blot, and glucose uptake was quantified with the Glucose Uptake‐Glo™ assay. Additionally, metabolic flux analysis using 13C‐labeled glucose and targeted metabolomics by mass spectrometry were performed to measure specific metabolites. Results APPswe cells displayed significant reductions in glycolysis and spare respiratory capacity, indicative of impaired mitochondrial energy production under stress. These deficits were accompanied by reduced glucose uptake, which was partially compensated by an increase in FAO. At concentrations relevant to in vivo treatments, CP2 acutely enhanced GLUT translocation to the cell surface, increasing glucose uptake within one hour. Enhanced glucose utilization in OXPHOS machinery was confirmed by inhibition of PDH phosphorylation and increased conversion of pyruvate to acetyl‐CoA, fueling the TCA cycle and generating critical signaling metabolites essential for gene regulation. These mechanisms were mediated by AMPK. Conclusion Our findings suggest that mild inhibition of mtCI activates multiple neuroprotective mechanisms, including improved glucose metabolism and energy homeostasis. These consistent results in human cells and AD mouse models highlight the translational potential of this therapeutic approach for AD.

Abstract Background Early mechanisms of neuronal damage in Alzheimer's Disease (AD) include mitochondrial dysfunction and abnormal energy homeostasis. AD‐associated mitochondrial signaling was shown to occur upstream of amyloid precursor protein processing, Ab production, apolipoprotein E (APOE) expression, and tau pathology. However, whether alterations in mitochondrial function are sufficient to instigate AD remains unclear. Mitochondrial complex I (mtCI) is a rate‐limiting enzyme in the oxidative phosphorylation (OXPHOS) machinery. Changes in mtCI activity influence ATP and ROS production, cellular energy and redox homeostasis. We examined how reduced activity of mtCI due to a knockout of one of its accessory subunits Ndufs4 in mice affects transcriptional networks in the brain. We also determined whether reduced activity of mtCI abrogates neuroprotective properties of a small molecule CP2. Method RNA‐sequencing of the brain tissue was performed using Ndufs4 ‐/‐ and control mice ( n = 3–5 per group). The co‐expression modules of differentially expressed genes were compared to the AMP‐AD patient cohort data. Key mechanisms, including mitophagy signaling, were confirmed using ELISA and western blot analyses; the effect on mtCI activity was confirmed using functional assays. Results In Ndufs4 ‐/‐ mice, a residual activity of mtCI was ∼50% of the control. This loss of function led to a global disruption of mitochondrial homeostasis, energy metabolism, synaptic function, significant increase in mitophagy and a reduction in biogenesis. Transcriptomic signatures in brain tissue of male and female Ndufs4 ‐/‐ mice overlapped with changer reported for AD patients and AD mouse models with Ab and p ‐tau pathologies. These changes were partially rescued by a neuroprotective mitochondria‐targeting small molecule CP2. Consistent with studies in AD mice, CP2 treatment in Ndufs4 ‐/‐ mice augmented the expression of genes associated with mitochondrial biogenesis and turnover, synaptic activity, autophagy, redox balance, and reduced expression of genes related to inflammation. Sex‐specific differences included better adaptation to a reduced activity of mtCI and to CP2 treatment in female mice. Conclusion Reduced mtCI activity was sufficient to induce the AD‐like transcriptomic changes in brain. Residual mtCI function was sufficient to mediate neuroprotective effect of CP2, emphasizing a key role of mitochondria in AD development and treatment.