Decline in mitochondrial bioenergetics and shift to ketogenic profile in brain during reproductive senescenceIntroductionMaterials and methodsTransgenic miceBrain tissue preparation and mitochondrial isolationRespiratory measurementEnzyme activity assayLipid peroxidationWestern blot analysisStatisticsResultsReproductive senescence paralleled significant decrease in mitochondrial respirationAccelerated decline in metabolic enzyme activity with reproductive senescence.Increased enzyme expression in ketogenic pathway with reproductive senescenceOxidative stress is mainly associated with aging rather thanreproductive senescenceBioenergetic phenotypes emerge from the reproductive senescence transitionDiscussionAcknowledgmentsReferencesDecline in mitochondrial bioenergetics and shift to ketogenic profile in brain duringreproductive senescenceJia Yaoa, Ryan T. Hamiltona, Enrique Cadenasa, Roberta Diaz Brintona,b,⁎aDepartment of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, CA 90033, United StatesbProgram in Neuroscience, University of Southern California, Los Angeles, CA 90089, United Statesabstractarticle infoArticle history:Received 28 April 2010Received in revised form 30 May 2010Accepted 2 June 2010Available online xxxxKeywords:MitochondriaBioenergeticsReproductive senescenceAlzheimer's diseaseEstrogenBackground: We have previously demonstrated that mitochondrial bioenergetic deficits precede Alzheimer'spathology in the female triple transgenic Alzheimer's (3xTgAD) mouse model. Herein, we sought todetermine the impact of reproductive senescence on mitochondrial function in the normal non-transgenic(nonTg) and 3xTgAD female mouse model of AD.Methods: Both nonTg and 3xTgAD female mice at 3, 6, 9, and 12 months of age were sacrificed andmitochondrial bioenergetic profile as well as oxidative stress markers were analyzed.Results: In both nonTg and 3xTgAD mice, reproductive senescence paralleled a significant decline in PDH, andComplex IV cytochrome c oxidase activity and mitoch ondrial respiration. During the reproductivesenescence transition, both nonTg and 3xTgAD mice exhibited greater individual variability in bioenergeticparameters suggestive of divergent bioenerget ic phenotypes. Following transition through reproductivesenescence, enzymes required for long-chain fatty acid (HADHA) and ketone body (SCOT) metabolism weresignificantly increased and variability in cytochrome c oxidase (Complex IV) collapsed to cluster at a ∼ 40%decline in both the nonTg and 3xTgAD brain which was indicative of alternative fuel generation withconcomitant decline in ATP generation.Conclusions: These data indicate that reproductive senescence in the normal nonTg female brain parallels theshift to ketogenic/fatty acid substrate phenotype with concomitant decline in mitochondrial function andexacerbation of bioenergetic deficits in the 3xTgAD brain.General significance: These findings provide a plausible mechanism for increased life-time risk of AD inpostmenopausal women and suggest an optimal window of opportunity to prevent or delay decline inbioenergetics during reproductive senescence.© 2010 Elsevier B.V. All rights reserved.1. IntroductionThe essential role of mitochondria in cellular bioenergetics andsurvival has been well established [1–3]. Further, mitochondrialdysfunction has been suggested to play a pivotal role in neurodegen-erative disorders, including Alzheimer's disease (AD) [1,4,5]. It hasbeen shown that brain metabolism is declined in AD patients at least adecade before disease diagnosis [1,6–9]. Dysfunction in glucosemetabolism, bioenergetics and mitochondrial function are consistentantecedents to development of Alzheimer pathology [10–18]. Re-cently we demonstrated that mitochondrial bioenergetic deficitsprecede Alzheimer's pathology in the female triple transgenic mousemodel of Alzheimer's disease (3xTgAD) [7]. These antecedent declinesin brain metabolism indicate a potential causal role of mitochondrialbioenergetics in AD pathogenesis and disease progression.Basic science analyses indicate that the endogenous estrogen, 17β-estradiol (E2), significantly increased glucose uptake, glucose metab-olism, insulin growth factor signaling and the energetic capacity ofbrain mitochondria by maximizing aerobic glycolysis (oxidativephosphorylation coupled to pyruvate metabolism) [1,6,19].Theenhanced aerobic glycolysis in the aging brain would be predictedto prevent conversion of the brain to using alternative sources of fuelsuch as the ketone body pathway characteristic of AD [1,6]. The abilityof estrogen to sustain glucose as the primary fuel source in brain byenhancing glucose transport, uptake and aerobic glycolysis (oxidativephosphorylation coupled to pyruvate metabolism) is likely linked toits ability to prevent age-associated metabolic decline in brain andthus could be a key mechanism whereby estrogen reduces the risk ofAD in postmenopausal women [1,6,19–24].Reproductive senescence is a multifactorial process with a highdegree of interpersonal variability and subject to a host of beneficialor detrimental influences. As such, reproductive senescence is anBiochimica et Biophysica Acta xxx (2010) xxx–xxxAbbreviations: AD, Alzheimer's disease; 3xTgAD, triple transgenic Alzheimer'sdisease; nonTg, non-transgenic; E2, 17β-estradiol; PDH, pyruvate dehydrogenase; COX,cytochrome c oxidase⁎ Corresponding author. Pharmacology & Pharmaceutical Sciences, University ofSouthern California, Pharmaceutical Sciences Center, 1985 Zonal Avenue PSC502, LosAngeles, CA 90089, United States. Tel.: +323 442 1428; fax: +323 442 1489.E-mail address: [email protected] (R.D. Brinton).BBAGEN-26896; No. of pages: 6; 4C:0304-4165/$ – see front matter © 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.bbagen.2010.06.002Contents lists available at ScienceDirectBiochimica et Biophysica Actajournal homepage: www.elsevier.com/locate/bbagenPlease cite this article as: J. Yao, et al., Decline in mitochondrial bioenergetics and shift to ketogenic profile in brain during reproductivesenescence, Biochim. Biophys. Acta (2010), doi:10.1016/j.bbagen.2010.06.002illustrative example of both the aging process and of modifiers ofaging, such as ovarian hormone status, which both contribute toalteration in brain metabolic profile. In the current study, we sought todetermine the impact of loss of ovarian hormones associated