Brain cortex mitochondrial bioenergetics in synaptosomes and non-synaptic mitochondria during aging

Abstract

Alterations in mitochondrial bioenergetics have been associated with brain aging. In order to evaluate the susceptibility of brain cortex synaptosomes and non-synaptic mitochondria to aging-dependent dysfunction, male Swiss mice of 3 or 17 months old were used. Mitochondrial function was evaluated by oxygen consumption, mitochondrial membrane potential and respiratory complexes activity, together with UCP-2 protein expression. Basal respiration and respiration driving proton leak were decreased by 26 and 33 % in synaptosomes from 17-months old mice, but spare respiratory capacity was not modified by aging. Succinate supported state 3 respiratory rate was decreased by 45 % in brain cortex non-synaptic mitochondria from 17-month-old mice, as compared with young animals, but respiratory control was not affected. Synaptosomal mitochondria would be susceptible to undergo calcium-induced depolarization in 17 months-old mice, while non-synaptic mitochondria would not be affected by calcium overload. UCP-2 was significantly up-regulated in both synaptosomal and submitochondrial membranes from 17-months old mice, compared to young animals. UCP-2 upregulation seems to be a possible mechanism by which mitochondria would be resistant to suffer oxidative damage during aging.

Mitochondrial dysfunction in the APP/PSEN1 mouse model of Alzheimer’s disease and a novel protective role for ascorbate

“…Nevertheless, it is important to note that while respirometry measures how much oxygen is consumed, this design does not describe the fate of that oxygen, and whether it contributes to ATP or ROS production. We therefore assessed the efficiency of the electron transport chain in mitochondrial isolates from the SVCT2 +/− and the APP/PSEN1 mice by measuring mitochondrial membrane potential and ATP/ADP ratios to identify individual contributions of each mutation [21,51,59]. We used dihydrofluorescein to measure of ROS production given that disruption of the electron transport chain leads to oxidative stress.…”

“…Freshly isolated cortical mitochondria were assayed at 0.5mg protein/ml MiR05 respiration buffer to a final volume of 2mL per chamber in an O2K Oxygraph (Oroboros, Innsbruck, Austria). Baseline oxygen uptake was established over 10 minutes and oxygen flux was measured and normalized to protein concentration under State 4 respiration in the presence of glutamate (10mM), and malate (2mM) and State 3 respiration was determined by the addition of ADP (2mM) [49–51] over a 10-minute time-span for each. We calculated a “pseudo” respiratory control ratio by normalizing oxygen consumed by isolated mitochondria after the addition of ADP (State 3) to the oxygen consumed at baseline in the absence of substrate or inhibitor (State 4).…”

Hallmarks of Brain Aging: Adaptive and Pathological Modification by Metabolic States

“…They include analysis of mitochondria-specific proteins, functional interrogation of isolated mitochondria or mitochondria in synaptosome preparations, and manipulation of genes that encode mitochondrial proteins (Grimm and Eckert, 2017). Comparisons of mitochondria isolated from brain tissue of animals reveal numerous age-related alterations, including mitochondrial enlargement or fragmentation (Stahon et al, 2016; Morozov et al, 2017), increased oxidative damage to mitochondrial DNA (Kim and Chan, 2001; Santos et al, 2013), impaired function of the electron transport chain (ETC) (Yao et al, 2010; Pandya et al, 2015, 2016; Pollard et al, 2016), increased numbers of mitochondria with depolarized membranes (Lores-Arnaiz et al, 2016), impaired Ca 2+ handling (Leslie et al, 1985; Pandya et al, 2015), and a reduced threshold for triggering mPTP formation (Brown et al, 2004). The decrement in mitochondrial function during brain aging involves a decline in cellular NAD + levels and the NAD:NADH ratio (Braidy et al, 2014), which would be expected to compromise the activities of NAD + -dependent enzymes critical for neuronal function and viability, including protein deacetylases of the sirtuin family (Fang et al, 2017).…”

The path from mitochondrial ROS to aging runs through the mitochondrial permeability transition pore

“…Mather & Rottenberg, ), different types of cells from the same tissue (cf. LaFrance et al ., ; Bambrick et al ., ; Picard et al ., ; Lores‐Arnaiz et al ., ), and even between mitochondria from different locations in the cell (Brown et al ., ). This variability probably results from the large differences in the expression and activity of the proteins that control activation of the mPTP such as ANT1 (Stepien et al ., ), CyPD (Hazelton et al ., ), the MCU complex (Paillard et al ., ), and probably other proteins.…”