Bio-Metal Dyshomeostasis-Associated Acceleration of Aging and Cognitive Decline in Down Syndrome

Abstract

Down syndrome (DS), which is caused by triplication of human chromosome 21 (Hsa21), exhibits some physical signs of accelerated aging, such as graying hair, wrinkles and menopause at an unusually young age. Development of early-onset Alzheimer’s disease, which is frequently observed in adults with DS, is also suggested to occur due to accelerated aging of the brain. Several Hsa21 genes are suggested to be responsible for the accelerated aging in DS. In this review, we summarize these candidate genes and possible molecular mechanisms, and discuss the related key factors. In particular, we focus on copper, an essential trace element, as a key factor in the accelerated aging in DS. In addition, the physiological significance of brain copper accumulation in cognitive impairment is discussed. We herein provide our hypothesis on the copper dyshomeostasis-based pathophysiology of DS.

1. INTRODUCTION

Down syndrome (DS), which is caused by triplication of human chromosome 21 (Hsa21), is the most common aneuploidy, with an incidence of approximately 1/700 live births.¹⁾ DS is the most common genetic cause of intellectual disability, and numerous other generalized features, such as cataract, early-onset Alzheimer-like dementia (ALD), congenital heart defects, and leukemia also develop with higher incidence in individuals with DS in comparison to individuals without DS.^1,2) In the clinical observation, adults with DS show some features of accelerated aging, such as premature skin wrinkling, greying of the hair, hypogonadism, early menopause, hypothyroidism, a declining immune function, and early-onset ALD.³⁾ In addition, the assessment of bio-markers, (e.g., epigenetic markers),^4,5) metabolic biomarkers (including plasma N-glycomic changes),⁶⁾ or predicted brain age (assessed by the degree of amyloid β (Aβ) accumulation and the cognitive function) indicate accelerated aging in DS.⁷⁾ The oxidative stress theory of aging is a structural damage-based hypothesis that age-associated functional losses are caused by the accumulation of oxidative damage to macromolecules, such as lipids, DNA, and proteins induced by reactive oxygen and nitrogen species.⁸⁾ Oxidative stress markers are consistently reported to increase in the brain and urine from individuals with DS, suggesting that enhanced oxidative stress accelerates aging in DS.^7,9,10) Thus, the hypothesis that accelerated aging contributes to numerous features in DS has been widely accepted.

The long arm of Hsa21 encodes 164 classical protein-coding genes and 49 members of the gene family of keratin-associated proteins (KRTAPs).¹¹⁾ KRTAP genes are mainly expressed in the skin and the family may include many pseudogenes; thus, these genes are excluded when considering the brain pathophysiology of DS. Mouse models have made major contributions to effective investigations to understand the pathophysiology of DS. Since Hsa21 genes are coded in three murine chromosomal regions: 102 protein-coding genes in the approx. 28 Mb of the telomeric region of mouse chromosome (Mmu) 16, 19 protein-coding genes in an internal approx. 1.5 Mb segment of Mmu17, and 37 protein-coding genes in an internal approx. 3 Mb segment of Mmu10,¹²⁾ many kinds of mice carrying a triplicated partial or whole syntenic region have been established as mouse models of DS¹³⁾ (Fig. 1). Some DS mouse models exhibit an impaired cognitive function,^14,15) and enhanced oxidative stress in the brain.^16,17) Thus, the mouse models of DS are useful for understanding the molecular mechanisms underlying accelerated aging-based DS features.

Fig. 1. The Trisomic Regions of Mouse Models of DS

Enumerated genes are mouse genes syntenic to Hsa21 genes with the exception of Keratin-related genes. Genes indicated with underline and bold font are suggested to be related to enhanced oxidative stress in DS (Fig. 2).

In this review, we introduce potential candidates that cause oxidative stress in brains and consequent cognitive decline in DS, ALD, and old age.

2. HSA21 GENES CONTRIBUTING TO ENHANCED OXIDATIVE STRESS IN DS

Some Hsa21 genes coding Aβ-protein precursor (APP), Copper/Zinc (Cu/Zn)-superoxide dismutase 1 (SOD1), and BTB, CNC Homolog 1 (BACH1) and so on are suggested to enhance oxidative stress. Cleavage of APP by β- and γ-secretases produces the more aggregation-prone 42-residue Aβ (Aβ_1-42) and the major secreted 40-residue Aβ (Aβ_1-40). It has been shown that metal ions, including iron (Fe), Zn, and Cu are detected at higher level in the core of senile plaques with Aβ fibrils.¹⁸⁾ Among the metal ions, Cu-bound Aβ is suggested to produce hydrogen peroxide,^19,20) and superoxide anions,²¹⁾ and hydroxy radicals²²⁾ (Fig. 2). It is, therefore, probable that an increased copy number of the APP gene results in the overproduction of Cu-Aβ, which can enhance oxidative stress. Furthermore, it is suggested that Cu-Aβ affects the oligomerization and/or aggregation of Aβ peptide,²³⁾ meaning that Cu plays a role in Aβ-related neurotoxicity. SOD1, which is a metalloenzyme with Cu and Zn, produces hydrogen peroxide (H₂O₂), an important precursor of toxic hydroxyl radical. Since H₂O₂ is neutralized to water and oxygen through the actions of glutathione peroxidase (GPx) and/or catalase (CAT),²⁴⁾ the triplication of only SOD1 gene results in an imbalance in the SOD1/CAT levels and in the SOD1/GPx levels, with an accumulation of H₂O₂. In the presence of Fe(II) or Cu(I), accumulated H₂O₂ is led to hydroxyl radical production by a Fenton(-like) reaction that damages membrane lipids, proteins, and nucleic acids.²⁵⁾ It is of interest that an altered SOD1/GPx activity ratio has been observed in various tissues with DS,²⁴⁾ that may partially explain the enhanced oxidative stress in DS. In particular, the expression levels of CAT and GPx in the brain are lower in comparison to other tissues, the effects of the altered SOD1/GPx ratio may contribute to increasing levels of H₂O₂ in the brain with DS.²⁶⁾ Thus, triplication of the SOD1 gene is a potent candidate for enhancing oxidative stress in DS. BACH1 suppresses the transcription of target genes, including heme oxygenase 1 (HO-1), a typical enzyme with antioxidant properties by converting toxic heme into antioxidants, and ferritin, a major iron storage protein.^27,28) BACH1 competes with nuclear factor (erythroid-derived 2)-like-2 (NRF2) for binding to the Maf recognition elements (MAREs) in oxidative stress-response genes such as Hmox gene coding HO-1 and FTH1/FTL1 genes coding Ferritin, suggesting that increased BACH1 levels lead to enhanced oxidative stress and ferroptosis through the increased cellular Fe²⁺ pool.^29,30) These facts allow us to consider that triplication of the BACH1 gene is also a candidate responsible gene for the enhanced oxidative stress in DS. Thus, APP, SOD1, and BACH1 are suggested to be candidate genes responsible for the enhanced oxidative stress in DS. These three genes are included in the trisomic region of Dp(16)1Yey/Dp1Tyb and Ts65Dn/Ts2Cje mice, but not in that of Ts1Cje and Ts1Rhr mice (Fig. 1). However, we have found that lipid peroxidation is enhanced in the brains of Ts1Cje mice and Ts2Cje mice, suggesting that triplicated gene(s) in the trisomic region of Ts1Cje mice other than the three candidates could be responsible for the enhanced oxidative stress in DS.¹⁶⁾

Fig. 2. Hypothetical Mechanism Underlying the Enhanced Oxidative Stress in the Brain with DS

APP, BACH1, SOD1, and interferon receptor-associated genes (IFN-Rs) are candidates for enhancing the oxidative stress (OS) and neurotoxicity by ferroptosis. An increased level of APP caused by triplication of the APP gene leads to the overproduction of Aβ peptides (Aβ_1-40/Aβ_1-42). Cu-bound Aβ peptides produce hydroxyl radical and Aβ-Cu oligomers, which show neurotoxicity. The gene-dosage dependent overexpression of SOD1 produces an increased level of hydroxy peroxide, resulting in an increase in hydroxyl radicals. The accumulation of hydroxyl radical is a cause of enhanced OS in DS. BACH1 and IFN-Rs (activation of IFN signaling) suppresses the transcriptional activity of ARF2 by inhibiting the ARF2-MAF complex, resulting in the decreased transcription of target genes, such as HO-1 and ferritin. Decreased HO-1, which has anti-OS activity, enhances OS in DS, and decreased ferritin, which stores iron, results in an increased level of labile iron, which will lead to ferroptosis.

As shown in Fig. 1, the trisomic region of Ts1Cje mice encodes a gene cluster for interferon (IFN) signaling, Ifnar1, Ifnar2, Ifngr2, and Il10rg. IFNAR1 and IFNAR2 are two subunits of type I IFN receptor. IFNGR2 and IL10RB are a type II IFN receptor and type III IFN receptor, respectively. In addition, IL10RB is a subunit of receptors for three interleukins (IL-10, IL-22, and IL-26). Indeed, more constitutive activation of the IFN transcriptional response (all types) is detected in fibroblasts and lymphoblastoid cells with trisomy 21.³¹⁾ It is suggested that accelerated aging was detected by the activation of the type I IFN signaling in mitochondrial DNA mutated mice.³²⁾ Furthermore, activated IFN signaling suppresses the Nrf2 in the presence of mitochondrial dysfunction,³²⁾ so it is possible that the elevated the IFN response induced by the increased expression of four IFN-related Hsa21 genes may contribute to the enhanced oxidative stress in DS (Fig. 2). In the trisomic region genes in Ts1Cje mice, the regulator of calcineurin 1 (Rcan1) gene is worth considering as an inducer of oxidative stress. RCAN1 is induced under oxidative stress,³³⁾ and RCAN1 null mice exhibit less oxidative damage than wild-type mice after an acute oxidative insult.³⁴⁾ Increased copy number of transcription factor Ets2 gene, which is coded in the trisomic region of Ts1Cje mice, is also suggested to be associated with the enhancement of oxidative stress.³⁵⁾ Although the molecular mechanisms of enhanced oxidative stress induced by the overexpression of the Rcan1 and Ets2 genes remains to be clarified, these genes can be candidates as responsible genes for the enhanced oxidative stress and accelerated aging in DS.

3. DYSHOMEOSTASIS OF COPPER IN DS AND OTHER DISORDERS, INCLUDING AD

Enhanced oxidative stress is assumed to cause the accelerated aging in DS, resulting in the development of early-onset ALD. The increased expression of APP caused by the triplicated APP gene is believed to play a role in the manifestation of AD in DS.^36–38) In contrast, it is also suggested that the increased expression of APP alone may be insufficient for early-onset AD to develop. In fact, APP protein levels are not increased in the young adult brain in a mouse model of DS, Ts65Dn.³⁹⁾ Therefore, factors other than an increased copy-number of the APP gene are thought to be present in DS. As a candidate, dysregulation of some bio-metals, such as iron and Cu, may be associated with the development of early-onset ALD, because bio-metals play a role in oxidative stress and neurotoxicity in DS (Fig. 2). To evaluate this bio-metals dyshomeostasis hypothesis, we performed a comparative metallomic analysis, and found a higher level of Cu in the brain of Ts1Cje mice in comparison to wild-type mice.⁴⁰⁾ The increased Cu level causes the enhancement of oxidative stress and accumulation of hyperphosphorylated Tau protein (pTau).⁴¹⁾ Accumulation of pTau, which is also a typical hallmark of AD, is suggested to result in neural damage by affecting mitochondrial functions.^41,42) In addition, Cu seems to be associated with Aβ-mediated neurotoxicity, as mentioned above (Fig. 2). Thus, the accumulation of Cu in the brain is a potent candidate factor that accelerates ageing and disturbs the cognitive function, and may be linked to AD in DS.

Several reports have shown Cu dyshomeostasis in AD. Serum Cu levels in AD patients are approximately 1.5-fold higher than those in healthy controls, suggesting Cu dyshomeostasis in AD.⁴³⁾ High Cu levels are detected in Aβ plaques in the dentate gyrus subregion (DG) of the hippocampus of a mouse AD model,⁴⁴⁾ whereas Cu levels of the whole hippocampus and amygdale areas are significantly reduced in AD patients in comparison to age-matched controls.^45,46) Furthermore, the increased level of Cu in the brain caused by mutation of the ATP7b transporter, which is associated with Wilson’s disease, reduces the number of amyloid plaques and diminishes plasma Aβ levels in transgenic CRND8 amyloid precursor protein mice, which exhibit robust Aβ deposition, supporting a hypothesis that AD results in the deficiency of Cu in the brain.⁴⁷⁾ These findings indicate that Cu dyshomeostasis in AD is characterized by extracellular excess and intracellular deficiency. Recently, correlations between higher brain Cu levels and cognitive decline have been shown, suggesting that a lower concentration of Cu in the brain may exacerbate or indicate disease severity.⁴⁸⁾ However, the mechanism through which lower Cu levels suppress the formation of amyloid plaques and are associated with cognitive decline remains unclear. Of note, it has recently been shown that some differences are detected between AD and DS in the neuropathic spread of Aβ and Tau.⁴⁹⁾ Experiments assessing the infectivity of Aβ and Tau prions to cultured cells demonstrated significant trends of increased Aβ and Tau prions in individuals with DS in an age-dependent manner, in contrast, the Aβ and Tau prions tend to decrease in individuals with AD who lived longer.⁴⁹⁾ Cu has also been implicated in the pathogenesis of prion disease. In fact, there is a case report describing the comorbidity in Wilson’s disease, characterized by the accumulation of Cu in tissue and in Creutzfeldt-Jakob disease caused by misfolding of the neuronal prion protein (PrP^SC), suggesting a possible association of Cu metabolism with the pathogenesis of Creutzfeldt-Jakob disease.⁵⁰⁾ PrP^SC which consists of 253 amino acids, is highly expressed in neurons. Cellular prion perotein (PrP^C) binds to Cu, and it is suggested is that Cu coordination affects the conversion from PrP^C to PrP^SC and may affect the infectivity of PrP^SC.⁵¹⁾ The brain Cu level may play a role in the infectivity of Aβ and Tau prions and may be able to partially explain the differences in the neuropathic spread of Aβ and Tau between AD and DS.

4. RELATIONSHIP BETWEEN COPPER AND THE COGNITIVE FUNCTION

Cu is an important cofactor for a variety of enzymes, such as SOD1, in the oxidation-reduction reactions of biological processes. As mentioned above, Cu can induce a Fenton-like reaction causing oxidative stress,²⁵⁾ and the oxidative stress theory is widely considered to be a mechanism underlying age-related cognitive decline.⁵²⁾ Given that the Cu levels in several brain regions increase with age,^53,54) and that the chronic administration of Cu induces oxidative stress and impairs spatial learning,^55,56) Cu-induced oxidative stress might mediate age-related cognitive decline. Moreover, the intraperitoneal administration of high dose of Cu(OAc)₂ increases the total amount of Cu in the hippocampus as well as the levels of glutamate (Glu) and Glu/γ-aminobutyric acid (GABA) ratio, and leads to spatial learning deficits.⁵⁶⁾ Since Cu suppresses and promotes the biosynthesis of neurotransmitters and synaptic neurotransmission,^56–58) dysregulation of the biphasic effects of Cu on synaptic transmission might also shape the age-related impairment of the brain function, including cognition, memory, and learning. Of note, our recent study demonstrated that high levels of Cu in the brain mediates oxidative stress in DS mice.⁴⁰⁾ We also found that the Glu levels and Glu/GABA ratio in the hippocampus of DS mice were higher in comparison to those in wild-type mice (unpublished data). Therefore, excess Cu in the brain is most likely a central factor in the redox dysregulation and excitatory/inhibitory imbalance in DS.

Neurogenesis occurs in particular brain regions, such as the DG and subventricular zone (SVZ). Adult neurogenesis in the DG and SVZ is suggested to play a role in the cognitive function, spatial memory, fear contextual memory, and pattern separation, where newborn neurons are incorporated into the existing neuronal circuits.^59–61) Growing evidence suggests that adult hippocampal and SVZ neurogenesis is reduced with age and AD, which is associated with cognitive decline.^61,62) We have clarified that DS mice show reduced adult neurogenesis in the DG and SVZ in comparison to wild-type mice.⁶³⁾ It is noted that SVZ is the one of the brain regions that shows high levels of Cu accumulation with age and the increase in Cu levels in SVZ is inversely associated with a marker of neuroblasts.⁵⁴⁾ Cu suppresses the growth of neurospheres derived from adult mouse SVZ,⁶⁴⁾ suggesting an important role of Cu as a modulator of neurogenesis in the SVZ. In addition, Cu dyshomeostasis induced by short-term feeding of a cuprizone-containing diet reduces hippocampal neurogenesis resulting in cognitive deficits.⁶⁵⁾ Considering that short-term feeding of a cuprizone-containing diet increases the levels of Cu in the brain, although the mechanism of the increase is unclear,⁶⁶⁾ excess Cu possibly suppresses hippocampal neurogenesis. Taken together, dysregulation of Cu metabolism in DS might be a critical factor for the impaired adult neurogenesis in SVZ and DG, as well as oxidative stress and abnormal synaptic transmission, leading to accelerated brain aging (Fig. 3).

Fig. 3. High Level of Cu as a Potential Factor for the Enhanced Oxidative Stress, Reduced Neurogenesis, and Consequent Cognitive Decline in DS

Excess Cu in the brain caused by metal dyshomeostasis induces oxidative stress, abnormal synaptic transmission, and reduced neurogenesis. As Cu suppresses neurogenesis in SVZ, hippocampal neurogenesis is possibly reduced by the accumulation of Cu in DS and aged adults, resulting in cognitive decline. LV: lateral ventricle.

5. CONCLUDING REMARKS

It has been more than six decades since the cause of DS was found to be trisomy of Hsa21. However, the molecular mechanism underlying the cognitive dysfunction of DS is still not fully understood. Consequently, there is no pharmacotherapy. In the past two decades, preclinical trials using mouse models of DS have been conducted with the aim of improving the cognitive dysfunction of DS.⁶⁷⁾ Based on the outcome of the preclinical investigation using Ts65Dn mice, more than 20 drugs have been suggested to rescue neurobiological and/or cognitive defects.^67,68) Although some of the candidates have advanced to human clinical trials, most have failed to show significant therapeutic effects thus far.⁶⁹⁾ In particular, trials for a compound targeting GABAergic signaling, basmisanil, which is a highly selective orally active α subunit-containing GABA_A receptors, have been expected to restore the cognitive impairments in DS, since increased inhibitory neuronal transmission is observed in Ts65Dn mice.^70,71) Although the compounds improve multiple pathological features, including cellular, behavioral, and electrophysiological deficits in Ts65Dn mice,^72,73) basmisanil failed to show efficacy in improving the cognitive functions of individuals with DS (trials: NCT02024789xiv, NCT01436955xv, NCT01667367xvi, NCT02484703xvii). As considerable findings, the GABA concentration is reported to decrease in human frontal and temporal cortices with DS,^74,75) suggesting impaired neurogenesis and/or migration of GABAergic interneurons.⁷⁶⁾ Such controversial observations about GABAergic interneurons in DS between the mouse model and humans may be a possible cause of the lack of efficacy in the trials of basmisanil. Therefore, we would like to make a point that the accumulation of Cu in DS should be confirmed in the human brain with DS. This confirmation will strongly support that lowering Cu strategy is a promising target for pharmacotherapy for DS.

Acknowledgments

KI’s research is funded by JSPS KAKENHI (20H05521, 22H04822, and 22K07033).

Conflict of Interest

The authors declare no conflict of interest.

REFERENCES

• 1) Presson AP, Partyka G, Jensen KM, Devine OJ, Rasmussen SA, McCabe LL, McCabe ER. Current estimate of Down syndrome population prevalence in the United States. J. Pediatr., 163, 1163–1168 (2013).
• 2) Antonarakis SE, Skotko BG, Rafii MS, Strydom A, Pape SE, Bianchi DW, Sherman SL, Reeves RH. Down syndrome. Nat. Rev. Dis. Primers, 6, 9 (2020).
• 3) Patterson D, Cabelof DC. Down syndrome as a model of DNA polymerase beta haploinsufficiency and accelerated aging. Mech. Ageing Dev., 133, 133–137 (2012).
• 4) Horvath S, Garagnani P, Bacalini MG, Pirazzini C, Salvioli S, Gentilini D, Di Blasio AM, Giuliani C, Tung S, Vinters HV, Franceschi C. Accelerated epigenetic aging in Down syndrome. Aging Cell, 14, 491–495 (2015).
• 5) Obeid R, Hübner U, Bodis M, Geisel J. Plasma amyloid beta 1-42 and DNA methylation pattern predict accelerated aging in young subjects with Down syndrome. Neuromolecular Med., 18, 593–601 (2016).
• 6) Borelli V, Vanhooren V, Lonardi E, Reiding KR, Capri M, Libert C, Garagnani P, Salvioli S, Franceschi C, Wuhrer M. Plasma N-glycome signature of Down syndrome. J. Proteome Res., 14, 4232–4245 (2015).
• 7) Nunomura A, Perry G, Pappolla MA, Friedland RP, Hirai K, Chiba S, Smith MA. Neuronal oxidative stress precedes amyloid-beta deposition in Down syndrome. J. Neuropathol. Exp. Neurol., 59, 1011–1017 (2000).
• 8) Beckman KB, Ames BN. The free radical theory of aging matures. Physiol. Rev., 78, 547–581 (1998).
• 9) Jovanovic SV, Clements D, MacLeod K. Biomarkers of oxidative stress are significantly elevated in Down syndrome. Free Radic. Biol. Med., 25, 1044–1048 (1998).
• 10) Praticò D, Iuliano L, Amerio G, Tang LX, Rokach J, Sabatino G, Violi F. Down’s syndrome is associated with increased 8,12-iso-iPF2alpha-VI levels: evidence for enhanced lipid peroxidation in vivo. Ann. Neurol., 48, 795–798 (2000).
• 11) Gupta M, Dhanasekaran AR, Gardiner KJ. Mouse models of Down syndrome: gene content and consequences. Mamm. Genome, 27, 538–555 (2016).
• 12) Davisson MT, Bechtel LJ, Akeson EC, Fortna A, Slavov D, Gardiner K. Evolutionary breakpoints on human chromosome 21. Genomics, 78, 99–106 (2001).
• 13) Ishihara K. Genes associated with disturbed cerebral neurogenesis in the embryonic brain of mouse models of Down syndrome. Genes, 12, 1598 (2021).
• 14) Reeves RH, Irving NG, Moran TH, Wohn A, Kitt C, Sisodia SS, Schmidt C, Bronson RT, Davisson MT. A mouse model for Down syndrome exhibits learning and behaviour deficits. Nat. Genet., 11, 177–184 (1995).
• 15) Sago H, Carlson EJ, Smith DJ, Kilbridge J, Rubin EM, Mobley WC, Epstein CJ, Huang TT. Ts1Cje, a partial trisomy 16 mouse model for Down syndrome, exhibits learning and behavioral abnormalities. Proc. Natl. Acad. Sci. U.S.A., 95, 6256–6261 (1998).
• 16) Ishihara K, Amano K, Takaki E, Ebrahim AS, Shimohata A, Shibazaki N, Inoue I, Takaki M, Ueda Y, Sago H, Epstein CJ, Yamakawa K. Increased lipid peroxidation in Down’s syndrome mouse models. J. Neurochem., 110, 1965–1976 (2009).
• 17) Shichiri M, Yoshida Y, Ishida N, Hagihara Y, Iwahashi H, Tamai H, Niki E. α-Tocopherol suppresses lipid peroxidation and behavioral and cognitive impairments in the Ts65Dn mouse model of Down syndrome. Free Radic. Biol. Med., 50, 1801–1811 (2011).
• 18) Beauchemin D, Kisilevsky R. A method based on ICP-MS for the analysis of Alzheimer’s amyloid plaques. Anal. Chem., 70, 1026–1029 (1998).
• 19) Curtain CC, Ali F, Volitakis I, Cherny RA, Norton RS, Beyreuther K, Barrow CJ, Masters CL, Bush AI, Barnham KJ. Alzheimer’s disease amyloid-beta binds copper and zinc to generate an allosterically ordered membrane-penetrating structure containing superoxide dismutase-like subunits. J. Biol. Chem., 276, 20466–20473 (2001).
• 20) Opazo C, Huang X, Cherny RA, Moir RD, Roher AE, White AR, Cappai R, Masters CL, Tanzi RE, Inestrosa NC, Bush AI. Metalloenzyme-like activity of Alzheimer’s disease beta-amyloid. Cu-dependent catalytic conversion of dopamine, cholesterol, and biological reducing agents to neurotoxic H₂O₂. J. Biol. Chem., 277, 40302–40308 (2002).
• 21) Reybier K, Ayala S, Alies B, Rodrigues JV, Bustos Rodriguez S, La Penna G, Collin F, Gomes CM, Hureau C, Faller P. Free superoxide is an intermediate in the production of H₂O₂ by Copper(I)-Aβ Peptide and O₂. Angew. Chem. Int. Ed. Engl., 55, 1085–1089 (2016).
• 22) Guilloreau L, Combalbert S, Sournia-Saquet A, Mazarguil H, Faller P. Redox chemistry of copper-amyloid-beta: the generation of hydroxyl radical in the presence of ascorbate is linked to redox-potentials and aggregation state. ChemBioChem, 8, 1317–1325 (2007).
• 23) Pedersen JT, Østergaard J, Rozlosnik N, Gammelgaard B, Heegaard NH. Cu(II) mediates kinetically distinct, non-amyloidogenic aggregation of amyloid-beta peptides. J. Biol. Chem., 286, 26952–26963 (2011).
• 24) Michiels C, Raes M, Toussaint O, Remacle J. Importance of Se-glutathione peroxidase, catalase, and Cu/Zn-SOD for cell survival against oxidative stress. Free Radic. Biol. Med., 17, 235–248 (1994).
• 25) Sankarapandi S, Zweier JL. Evidence against the generation of free hydroxyl radicals from the interaction of copper, zinc-superoxide dismutase and hydrogen peroxide. J. Biol. Chem., 274, 34576–34583 (1999).
• 26) Zana M, Janka Z, Kálmán J. Oxidative stress: a bridge between Down’s syndrome and Alzheimer’s disease. Neurobiol. Aging, 28, 648–676 (2007).
• 27) Sun J, Hoshino H, Takaku K, Nakajima O, Muto A, Suzuki H, Tashiro S, Takahashi S, Shibahara S, Alam J, Taketo MM, Yamamoto M, Igarashi K. Hemoprotein Bach1 regulates enhancer availability of heme oxygenase-1 gene. EMBO J., 21, 5216–5224 (2002).
• 28) Hintze KJ, Katoh Y, Igarashi K, Theil EC. Bach1 repression of ferritin and thioredoxin reductase1 is heme-sensitive in cells and in vitro and coordinates expression with heme oxygenase1, beta-globin, and NADP(H) quinone (oxido) reductase1. J. Biol. Chem., 282, 34365–34371 (2007).
• 29) Ogawa K, Sun J, Taketani S, Nakajima O, Nishitani C, Sassa S, Hayashi N, Yamamoto M, Shibahara S, Fujita H, Igarashi K. Heme mediates derepression of Maf recognition element through direct binding to transcription repressor Bach1. EMBO J., 20, 2835–2843 (2001).
• 30) Nishizawa H, Matsumoto M, Shindo T, Saigusa D, Kato H, Suzuki K, Sato M, Ishii Y, Shimokawa H, Igarashi K. Ferroptosis is controlled by the coordinated transcriptional regulation of glutathione and labile iron metabolism by the transcription factor BACH1. J. Biol. Chem., 295, 69–82 (2020).
• 31) Sullivan KD, Lewis HC, Hill AA, Pandey A, Jackson LP, Cabral JM, Smith KP, Liggett LA, Gomez EB, Galbraith MD, DeGregori J, Espinosa JM. Trisomy 21 consistently activates the interferon response. eLife, 5, e16220 (2016).
• 32) Lei Y, Guerra Martinez C, Torres-Odio S, Bell SL, Birdwell CE, Bryant JD, Tong CW, Watson RO, West LC, West AP. Elevated type I interferon responses potentiate metabolic dysfunction, inflammation, and accelerated aging in mtDNA mutator mice. Sci. Adv., 7, eabe7548 (2021).
• 33) Crawford DR, Leahy KP, Abramova N, Lan L, Wang Y, Davies KJ. Hamster adapt78 mRNA is a Down syndrome critical region homologue that is inducible by oxidative stress. Arch. Biochem. Biophys., 342, 6–12 (1997).
• 34) Lloret A, Monllor P, Fuchsberger T, Giraldo E, Perluigi M, Vina J. Increased basal antioxidant levels in RCAN1-deficient mice lowers oxidative injury after acute paraquat insult. Free Radic. Res., 54, 442–454 (2020).
• 35) Helguera P, Pelsman A, Pigino G, Wolvetang E, Head E, Busciglio J. ets-2 promotes the activation of a mitochondrial death pathway in Down’s syndrome neurons. J. Neurosci., 25, 2295–2303 (2005).
• 36) Prasher VP, Farrer MJ, Kessling AM, Fisher EM, West RJ, Barber PC, Butler AC. Molecular mapping of Alzheimer-type dementia in Down’s syndrome. Ann. Neurol., 43, 380–383 (1998).
• 37) Korbel JO, Tirosh-Wagner T, Urban AE, et al. The genetic architecture of Down syndrome phenotypes revealed by high-resolution analysis of human segmental trisomies. Proc. Natl. Acad. Sci. U.S.A., 106, 12031–12036 (2009).
• 38) Doran E, Keator D, Head E, Phelan MJ, Kim R, Totoiu M, Barrio JR, Small GW, Potkin SG, Lott IT. Down syndrome, partial trisomy 21, and absence of Alzheimer’s disease: the role of APP. J. Alzheimers Dis., 56, 459–470 (2017).
• 39) Choi JH, Berger JD, Mazzella MJ, Morales-Corraliza J, Cataldo AM, Nixon RA, Ginsberg SD, Levy E, Mathews PM. Age-dependent dysregulation of brain amyloid precursor protein in the Ts65Dn Down syndrome mouse model. J. Neurochem., 110, 1818–1827 (2009).
• 40) Ishihara K, Kawashita E, Shimizu R, Nagasawa K, Yasui H, Sago H, Yamakawa K, Akiba S. Copper accumulation in the brain causes the elevation of oxidative stress and less anxious behavior in Ts1Cje mice, a model of Down syndrome. Free Radic. Biol. Med., 134, 248–259 (2019).
• 41) Vossel KA, Zhang K, Brodbeck J, Daub AC, Sharma P, Finkbeiner S, Cui B, Mucke L. Tau reduction prevents Abeta-induced defects in axonal transport. Science, 330, 198 (2010).
• 42) Shahpasand K, Uemura I, Saito T, Asano T, Hata K, Shibata K, Toyoshima Y, Hasegawa M, Hisanaga S. Regulation of mitochondrial transport and inter-microtubule spacing by tau phosphorylation at the sites hyperphosphorylated in Alzheimer’s disease. J. Neurosci., 32, 2430–2441 (2012).
• 43) Li DD, Zhang W, Wang ZY, Zhao P. Serum copper, zinc, and iron levels in patients with Alzheimer’s disease: a meta-analysis of case-control studies. Front. Aging Neurosci., 9, 300 (2017).
• 44) James SA, Churches QI, de Jonge MD, Birchall IE, Streltsov V, McColl G, Adlard PA, Hare DJ. Iron, copper, and zinc concentration in Aβ plaques in the APP/PS1 mouse model of Alzheimer’s disease correlates with metal levels in the surrounding neuropil. ACS Chem. Neurosci., 8, 629–637 (2017).
• 45) Deibel MA, Ehmann WD, Markesbery WR. Copper, iron, and zinc imbalances in severely degenerated brain regions in Alzheimer’s disease: possible relation to oxidative stress. J. Neurol. Sci., 143, 137–142 (1996).
• 46) Schrag M, Mueller C, Oyoyo U, Smith MA, Kirsch WM. Iron, zinc and copper in the Alzheimer’s disease brain: a quantitative meta-analysis. Some insight on the influence of citation bias on scientific opinion. Prog. Neurobiol., 94, 296–306 (2011).
• 47) Phinney AL, Drisaldi B, Schmidt SD, Lugowski S, Coronado V, Liang Y, Horne P, Yang J, Sekoulidis J, Coomaraswamy J, Chishti MA, Cox DW, Mathews PM, Nixon RA, Carlson GA, St George-Hyslop P, Westaway D. In vivo reduction of amyloid-beta by a mutant copper transporter. Proc. Natl. Acad. Sci. U.S.A., 100, 14193–14198 (2003).
• 48) Agarwal P, Ayton S, Agrawal S, Dhana K, Bennett DA, Barnes LL, Leurgans SE, Bush AI, Schneider JA. Brain copper may protect from cognitive decline and Alzheimer’s disease pathology: a community-based study. Mol. Psychiatry, 27, 4307–4313 (2022).
• 49) Condello C, Maxwell AM, Castillo E, Aoyagi A, Graff C, Ingelsson M, Lannfelt L, Bird TD, Keene CD, Seeley WW, Perl DP, Head E, Prusiner SB. Aβ and tau prions feature in the neuropathogenesis of Down syndrome. Proc. Natl. Acad. Sci. U.S.A., 119, e2212954119 (2022).
• 50) Koutsouraki E, Michmizos D, Patsi O, Tzartos J, Spilioti M, Arnaoutoglou M, Tsolaki M. A probable role of copper in the comorbidity in Wilson’s and Creutzfeldt-Jakob’s diseases: a case report. Virol. J., 17, 35 (2020).
• 51) Legname G. Copper coordination modulates prion conversion and infectivity in mammalian prion proteins. Prion, 17, 1–6 (2023).
• 52) Pamplona R, Borras C, Jové M, Pradas I, Ferrer I, Viña J. Redox lipidomics to better understand brain aging and function. Free Radic. Biol. Med., 144, 310–321 (2019).
• 53) Palm R, Wahlström G, Hallmans G. Age related changes in weight and the concentrations of zinc and copper in the brain of the adult rat. Lab. Anim., 24, 240–245 (1990).
• 54) Fu S, Jiang W, Zheng W. Age-dependent increase of brain copper levels and expressions of copper regulatory proteins in the subventricular zone and choroid plexus. Front. Mol. Neurosci., 8, 22 (2015).
• 55) Lamtai M, Zghari O, Ouakki S, Marmouzi I, Mesfioui A, El Hessni A, Ouichou A. Chronic copper exposure leads to hippocampus oxidative stress and impaired learning and memory in male and female rats. Toxicol. Res., 36, 359–366 (2020).
• 56) Opazo CM, Greenough MA, Bush AI. Copper: from neurotransmission to neuroproteostasis. Front. Aging Neurosci., 6, 143 (2014).
• 57) Zhang Y, Lu W, Han M, Li H, Luo H, Li W, Luo W, Lin Z. Biphasic effects of copper on rat learning and memory in the Morris water maze. Ann. Clin. Lab. Sci., 46, 346–352 (2016).
• 58) Zhang G, Li Q, Gao W, Liu S, Wu R, Shen Z, Liu W, Chen Y. Copper chloride dose-dependently alters spatial learning and memory, and glutamate levels, in the hippocampus of rats. Mol. Med. Rep., 17, 4074–4082 (2018).
• 59) Kozareva DA, Cryan JF, Nolan YM. Born this way: Hippocampal neurogenesis across the lifespan. Aging Cell, 18, e13007 (2019).
• 60) Yin BK, Lázaro D, Wang ZQ. TRRAP-mediated acetylation on Sp1 regulates adult neurogenesis. Comput. Struct. Biotechnol. J., 21, 472–484 (2022).
• 61) Chen Q, Song H, Liu C, Xu J, Wei C, Wang W, Han F. The Interaction of EphA4 with PDGFRβ regulates proliferation and neuronal differentiation of neural progenitor cells in vitro and promotes neurogenesis in vivo. Front. Aging Neurosci., 12, 7 (2020).
• 62) Kim HS, Shin SM, Kim S, Nam Y, Yoo A, Moon M. Relationship between adult subventricular neurogenesis and Alzheimer’s disease: pathologic roles and therapeutic implications. Front. Aging Neurosci., 14, 1002281 (2022).
• 63) Ishihara K, Amano K, Takaki E, Shimohata A, Sago H, Epstein CJ, Yamakawa K. Enlarged brain ventricles and impaired neurogenesis in the Ts1Cje and Ts2Cje mouse models of Down syndrome. Cereb. Cortex, 20, 1131–1143 (2010).
• 64) Liu LL, van Rijn RM, Zheng W. Copper modulates adult neurogenesis in brain subventricular zone. Int. J. Mol. Sci., 23, 9888 (2022).
• 65) Ohgomori T, Jinno S. Signal transducer and activator of transcription 3 activation in hippocampal neural stem cells and cognitive deficits in mice following short-term cuprizone exposure. Neuroscience, 472, 90–102 (2021).
• 66) Tezuka T, Tamura M, Kondo MA, Sakaue M, Okada K, Takemoto K, Fukunari A, Miwa K, Ohzeki H, Kano S, Yasumatsu H, Sawa A, Kajii Y. Cuprizone short-term exposure: astrocytic IL-6 activation and behavioral changes relevant to psychosis. Neurobiol. Dis., 59, 63–68 (2013).
• 67) Gardiner KJ. Pharmacological approaches to improving cognitive function in Down syndrome: current status and considerations. Drug Des. Devel. Ther., 9, 103–125 (2014).
• 68) Costa AC, Scott-McKean JJ. Prospects for improving brain function in individuals with Down syndrome. CNS Drugs, 27, 679–702 (2013).
• 69) Lee SE, Duran-Martinez M, Khantsis S, Bianchi DW, Guedj F. Challenges and opportunities for translation of therapies to improve cognition in Down syndrome. Trends Mol. Med., 26, 150–169 (2020).
• 70) Best TK, Siarey RJ, Galdzicki Z. Ts65Dn, a mouse model of Down syndrome, exhibits increased GABAB-induced potassium current. J. Neurophysiol., 97, 892–900 (2007).
• 71) Kleschevnikov AM, Belichenko PV, Villar AJ, Epstein CJ, Malenka RC, Mobley WC. Hippocampal long-term potentiation suppressed by increased inhibition in the Ts65Dn mouse, a genetic model of Down syndrome. J. Neurosci., 24, 8153–8160 (2004).
• 72) Martínez-Cué C, Martínez P, Rueda N, Vidal R, García S, Vidal V, Corrales A, Montero JA, Pazos Á, Flórez J, Gasser R, Thomas AW, Honer M, Knoflach F, Trejo JL, Wettstein JG, Hernández MC. Reducing GABAA α5 receptor-mediated inhibition rescues functional and neuromorphological deficits in a mouse model of down syndrome. J. Neurosci., 33, 3953–3966 (2013).
• 73) Braudeau J, Delatour B, Duchon A, Pereira PL, Dauphinot L, de Chaumont F, Olivo-Marin JC, Dodd RH, Hérault Y, Potier MC. Specific targeting of the GABA-A receptor α5 subtype by a selective inverse agonist restores cognitive deficits in Down syndrome mice. J. Psychopharmacol., 25, 1030–1042 (2011).
• 74) Whittle N, Sartori SB, Dierssen M, Lubec G, Singewald N. Fetal Down syndrome brains exhibit aberrant levels of neurotransmitters critical for normal brain development. Pediatrics, 120, e1465–e1471 (2007).
• 75) Śmigielska-Kuzia J, Boćkowski L, Sobaniec W, Kułak W, Sendrowski K. Amino acid metabolic processes in the temporal lobes assessed by proton magnetic resonance spectroscopy (1H MRS) in children with Down syndrome. Pharmacol. Rep., 62, 1070–1077 (2010).
• 76) Rissman RA, Mobley WC. Implications for treatment: GABAA receptors in aging, Down syndrome and Alzheimer’s disease. J. Neurochem., 117, 613–622 (2011).