Mitochondrial bioenergetic deficit precedes Alzheimer's pathology in female mouse model of Alzheimer's disease

Abstract

Mitochondrial dysfunction has been proposed to play a pivotal role in neurodegenerative diseases, including Alzheimer's disease (AD). To address whether mitochondrial dysfunction precedes the development of AD pathology, we conducted mitochondrial functional analyses in female triple transgenic Alzheimer's mice (3xTg-AD) and age-matched nontransgenic (nonTg). Mitochondrial dysfunction in the 3xTg-AD brain was evidenced by decreased mitochondrial respiration and decreased pyruvate dehydrogenase (PDH) protein level and activity as early as 3 months of age. 3xTg-AD mice also exhibited increased oxidative stress as manifested by increased hydrogen peroxide production and lipid peroxidation. Mitochondrial amyloid beta (A␤) level in the 3xTg-AD mice was significantly increased at 9 months and temporally correlated with increased level of A␤ binding to alcohol dehydrogenase (ABAD). Embryonic neurons derived from 3xTg-AD mouse hippocampus exhibited significantly decreased mitochondrial respiration and increased glycolysis. Results of these analyses indicate that compromised mitochondrial function is evident in embryonic hippocampal neurons, continues unabated in females throughout the reproductive period, and is exacerbated during reproductive senescence. In nontransgenic control mice, oxidative stress was coincident with reproductive senescence and accompanied by a significant decline in mitochondrial function. Reproductive senescence in the 3xTg-AD mouse brain markedly exacerbated mitochondrial dysfunction. Collectively, the data indicate significant mitochondrial dysfunction occurs early in AD pathogenesis in a female AD mouse model. Mitochondrial dysfunction provides a plausible mechanistic rationale for the hypometabolism in brain that precedes AD diagnosis and suggests therapeutic targets for prevention of AD.ABAD ͉ aging ͉ bioenergetics ͉ brain hypometabolism ͉ mitochondria T he essential role of mitochondria in cellular bioenergetics and survival has been well established (1-3). Previous studies have suggested that mitochondrial dysfunction plays a central role in the pathogenesis of neurodegenerative disorders, including Alzheimer's disease (AD) (1, 4). Alzheimer's pathology is accompanied by a decrease in expression and activity of enzymes involved in mitochondrial bioenergetics, which would be expected to lead to compromised electron transport chain complex activity and reduced ATP synthesis (5). Further, in AD there is a generalized shift from glycolytic energy production toward use of an alternative fuel, ketone bodies. This is evidenced by a 45% reduction in cerebral glucose utilization in AD patients (6), which is paralleled by decrease in the expression of glycolytic enzymes coupled to a decrease in the activity of the pyruvate dehydrogenase (PDH) complex (5). Patients with incipient AD exhibit a utilization ratio of 2:1 glucose to alternative fuel, whereas comparably aged controls exhibit a ratio of 29:1, whereas young controls exclusively use glucose as with a ratio of 100:0 ratio (7). In addition to t...

No Consistent Bioenergetic Defects in Presynaptic Nerve Terminals Isolated from Mouse Models of Alzheimer's Disease

“…1 describes eight different respiratory variables that test an extensive range of mitochondrial respiratory functions in situ (Brand and Nicholls, 2011), determined by automated multi-well plate format respirometry in a Seahorse XF Extracellular Flux Analyzer (Seahorse Bioscience). Surprisingly, contrary to existing literature on respiratory defects in isolated mitochondria (Gillardon et al, 2007, Hauptmann et al, 2009, Yao et al, 2009, Du et al, 2010), we observed no consistent defects in any of the synaptosomal respiratory variables (Table 1). Basal respiration, non-mitochondrial respiration, respiration driving ATP synthesis, respiration driving proton leak, maximum respiration, cell respiratory control (defined here as the ratio between the maximal and leak respiration), coupling efficiency and spare respiratory capacity (defined here as the ratio between maximal and basal respiration) were compared between transgenic mice and appropriate age-matched controls (Table 1A-C).…”

“…Our results do not support existing indirect evidence for impaired mitochondrial function in nerve termini as a cause or consequence of the initiation or progression of AD-like symptoms in mice (Begley et al., 1999, Yao et al, 2009, Du et al, 2010, Varghese et al, 2011). The reported mitochondrial respiration changes in AD are minor (~20% decrease in state III respiration, see above), but large enough to have registered in our assays.…”

“…Alternatively, it could be that the dysfunction is present only in a small subpopulation of nerve terminal types, or manifests only postsynaptically, or in cell body but not terminal mitochondria. In contrast to the synaptic mitochondria-specific bioenergetic decline shown by Du et al 2010, Yao et al (2009) reported lower mitochondrial respiration in whole brain mitochondria and primary hippocampal neurons from transgenic mice with AD-like phenotypes when compared to WT, which may imply weaker mitochondrial capacity in postsynaptic terminals of AD-mice rather than in the presynaptic synaptosomes investigated here. Our results also do not exclude the possibility of mitochondrial dysfunction in sporadic AD.…”

No Consistent Bioenergetic Defects in Presynaptic Nerve Terminals Isolated from Mouse Models of Alzheimer's Disease

“…1 describes eight different respiratory variables that test an extensive range of mitochondrial respiratory functions in situ (Brand and Nicholls, 2011), determined by automated multi-well plate format respirometry in a Seahorse XF Extracellular Flux Analyzer (Seahorse Bioscience). Surprisingly, contrary to existing literature on respiratory defects in isolated mitochondria (Gillardon et al, 2007, Hauptmann et al, 2009, Yao et al, 2009, Du et al, 2010), we observed no consistent defects in any of the synaptosomal respiratory variables (Table 1). Basal respiration, non-mitochondrial respiration, respiration driving ATP synthesis, respiration driving proton leak, maximum respiration, cell respiratory control (defined here as the ratio between the maximal and leak respiration), coupling efficiency and spare respiratory capacity (defined here as the ratio between maximal and basal respiration) were compared between transgenic mice and appropriate age-matched controls (Table 1A-C).…”

“…Our results do not support existing indirect evidence for impaired mitochondrial function in nerve termini as a cause or consequence of the initiation or progression of AD-like symptoms in mice (Begley et al., 1999, Yao et al, 2009, Du et al, 2010, Varghese et al, 2011). The reported mitochondrial respiration changes in AD are minor (~20% decrease in state III respiration, see above), but large enough to have registered in our assays.…”

“…Alternatively, it could be that the dysfunction is present only in a small subpopulation of nerve terminal types, or manifests only postsynaptically, or in cell body but not terminal mitochondria. In contrast to the synaptic mitochondria-specific bioenergetic decline shown by Du et al 2010, Yao et al (2009) reported lower mitochondrial respiration in whole brain mitochondria and primary hippocampal neurons from transgenic mice with AD-like phenotypes when compared to WT, which may imply weaker mitochondrial capacity in postsynaptic terminals of AD-mice rather than in the presynaptic synaptosomes investigated here. Our results also do not exclude the possibility of mitochondrial dysfunction in sporadic AD.…”

Decline in mitochondrial bioenergetics and shift to ketogenic profile in brain during reproductive senescence

“…To investigate the impact of reproductive senescence on PDH and COX activity, we assessed PDH and COX activity in mitochondria isolated from whole forebrain of the same set of 3xTg-AD and nonTg mice utilized for the mitochondrial respiration. Similary to our previous findings[7], 3xTgAD mice had significant lower PDH and COX activity compared to age-matched nonTg mice at 9 and 12 month. More importantly, in both nonTg and 3xTgAD mice, reproductive senescence paralleled a significant decline in PDH and COX activity (Fig.…”

Ovarian hormone loss induces bioenergetic deficits and mitochondrial β-amyloid

“…Consistent with our previous findings, in the Sham-OVX groups, 3xTgAD mice exhibited lower respiratory control ratio (RCR) relative to nonTg mice (Fig. 1B and 1D) (Yao, et al, 2009). More importantly, relative to ovary-intact mice (Sham-OVX), RCR was significantly decreased by OVX in both nonTg (~30%) and 3xTgAD (~40%) group (Fig.1, P<0.05, compared to Sham-OVX group, n=7).…”

No Consistent Bioenergetic Defects in Presynaptic Nerve Terminals Isolated from Mouse Models of Alzheimer's Disease

“…1 describes eight different respiratory variables that test an extensive range of mitochondrial respiratory functions in situ (Brand and Nicholls, 2011), determined by automated multi-well plate format respirometry in a Seahorse XF Extracellular Flux Analyzer (Seahorse Bioscience). Surprisingly, contrary to existing literature on respiratory defects in isolated mitochondria (Gillardon et al, 2007, Hauptmann et al, 2009, Yao et al, 2009, Du et al, 2010), we observed no consistent defects in any of the synaptosomal respiratory variables (Table 1). Basal respiration, non-mitochondrial respiration, respiration driving ATP synthesis, respiration driving proton leak, maximum respiration, cell respiratory control (defined here as the ratio between the maximal and leak respiration), coupling efficiency and spare respiratory capacity (defined here as the ratio between maximal and basal respiration) were compared between transgenic mice and appropriate age-matched controls (Table 1A-C).…”

“…Our results do not support existing indirect evidence for impaired mitochondrial function in nerve termini as a cause or consequence of the initiation or progression of AD-like symptoms in mice (Begley et al., 1999, Yao et al, 2009, Du et al, 2010, Varghese et al, 2011). The reported mitochondrial respiration changes in AD are minor (~20% decrease in state III respiration, see above), but large enough to have registered in our assays.…”

“…Alternatively, it could be that the dysfunction is present only in a small subpopulation of nerve terminal types, or manifests only postsynaptically, or in cell body but not terminal mitochondria. In contrast to the synaptic mitochondria-specific bioenergetic decline shown by Du et al 2010, Yao et al (2009) reported lower mitochondrial respiration in whole brain mitochondria and primary hippocampal neurons from transgenic mice with AD-like phenotypes when compared to WT, which may imply weaker mitochondrial capacity in postsynaptic terminals of AD-mice rather than in the presynaptic synaptosomes investigated here. Our results also do not exclude the possibility of mitochondrial dysfunction in sporadic AD.…”

Decline in mitochondrial bioenergetics and shift to ketogenic profile in brain during reproductive senescence

“…To investigate the impact of reproductive senescence on PDH and COX activity, we assessed PDH and COX activity in mitochondria isolated from whole forebrain of the same set of 3xTg-AD and nonTg mice utilized for the mitochondrial respiration. Similary to our previous findings[7], 3xTgAD mice had significant lower PDH and COX activity compared to age-matched nonTg mice at 9 and 12 month. More importantly, in both nonTg and 3xTgAD mice, reproductive senescence paralleled a significant decline in PDH and COX activity (Fig.…”

Ovarian hormone loss induces bioenergetic deficits and mitochondrial β-amyloid

“…Consistent with our previous findings, in the Sham-OVX groups, 3xTgAD mice exhibited lower respiratory control ratio (RCR) relative to nonTg mice (Fig. 1B and 1D) (Yao, et al, 2009). More importantly, relative to ovary-intact mice (Sham-OVX), RCR was significantly decreased by OVX in both nonTg (~30%) and 3xTgAD (~40%) group (Fig.1, P<0.05, compared to Sham-OVX group, n=7).…”

No Consistent Bioenergetic Defects in Presynaptic Nerve Terminals Isolated from Mouse Models of Alzheimer's Disease

“…1 describes eight different respiratory variables that test an extensive range of mitochondrial respiratory functions in situ (Brand and Nicholls, 2011), determined by automated multi-well plate format respirometry in a Seahorse XF Extracellular Flux Analyzer (Seahorse Bioscience). Surprisingly, contrary to existing literature on respiratory defects in isolated mitochondria (Gillardon et al, 2007, Hauptmann et al, 2009, Yao et al, 2009, Du et al, 2010), we observed no consistent defects in any of the synaptosomal respiratory variables (Table 1). Basal respiration, non-mitochondrial respiration, respiration driving ATP synthesis, respiration driving proton leak, maximum respiration, cell respiratory control (defined here as the ratio between the maximal and leak respiration), coupling efficiency and spare respiratory capacity (defined here as the ratio between maximal and basal respiration) were compared between transgenic mice and appropriate age-matched controls (Table 1A-C).…”

“…Our results do not support existing indirect evidence for impaired mitochondrial function in nerve termini as a cause or consequence of the initiation or progression of AD-like symptoms in mice (Begley et al., 1999, Yao et al, 2009, Du et al, 2010, Varghese et al, 2011). The reported mitochondrial respiration changes in AD are minor (~20% decrease in state III respiration, see above), but large enough to have registered in our assays.…”

“…Alternatively, it could be that the dysfunction is present only in a small subpopulation of nerve terminal types, or manifests only postsynaptically, or in cell body but not terminal mitochondria. In contrast to the synaptic mitochondria-specific bioenergetic decline shown by Du et al 2010, Yao et al (2009) reported lower mitochondrial respiration in whole brain mitochondria and primary hippocampal neurons from transgenic mice with AD-like phenotypes when compared to WT, which may imply weaker mitochondrial capacity in postsynaptic terminals of AD-mice rather than in the presynaptic synaptosomes investigated here. Our results also do not exclude the possibility of mitochondrial dysfunction in sporadic AD.…”

Decline in mitochondrial bioenergetics and shift to ketogenic profile in brain during reproductive senescence

“…To investigate the impact of reproductive senescence on PDH and COX activity, we assessed PDH and COX activity in mitochondria isolated from whole forebrain of the same set of 3xTg-AD and nonTg mice utilized for the mitochondrial respiration. Similary to our previous findings[7], 3xTgAD mice had significant lower PDH and COX activity compared to age-matched nonTg mice at 9 and 12 month. More importantly, in both nonTg and 3xTgAD mice, reproductive senescence paralleled a significant decline in PDH and COX activity (Fig.…”

Ovarian hormone loss induces bioenergetic deficits and mitochondrial β-amyloid

“…Consistent with our previous findings, in the Sham-OVX groups, 3xTgAD mice exhibited lower respiratory control ratio (RCR) relative to nonTg mice (Fig. 1B and 1D) (Yao, et al, 2009). More importantly, relative to ovary-intact mice (Sham-OVX), RCR was significantly decreased by OVX in both nonTg (~30%) and 3xTgAD (~40%) group (Fig.1, P<0.05, compared to Sham-OVX group, n=7).…”