Distinct differences in rates of oxygen consumption and ATP synthesis of regionally isolated non‐synaptic mouse brain mitochondria

Abstract

Brain mitochondrial dysfunction has been implicated in several neurodegenerative diseases. The distribution and efficiency of mitochondria display large heterogeneity throughout the regions of the brain. This may imply that the selective regional susceptibility of neurodegenerative diseases could be mediated through inherent differences in regional mitochondrial function. To investigate regional cerebral mitochondrial energetics, the rates of oxygen consumption and adenosine‐5′‐triphosphate (ATP) synthesis were assessed in isolated non‐synaptic mitochondria of the cerebral cortex, hippocampus, and striatum of the male mouse brain. Oxygen consumption rates were assessed using a Seahorse XFe96 analyzer and ATP synthesis rates were determined by an online luciferin‐luciferase coupled luminescence assay. Complex I‐ and complex II‐driven respiration and ATP synthesis, were investigated by applying pyruvate in combination with malate, or succinate, as respiratory substrates, respectively. Hippocampal mitochondria exhibited the lowest basal and adenosine‐5′‐diphosphate (ADP)‐stimulated rate of oxygen consumption when provided pyruvate and malate. However, hippocampal mitochondria also exhibited an increased proton leak and an elevated relative rate of oxygen consumption in response to the uncoupler carbonyl cyanide 4‐(trifluoromethoxy)phenylhydrazone (FCCP), showing a large capacity for uncoupled respiration in the presence of pyruvate. When the complex II‐linked substrate succinate was provided, striatal mitochondria exhibited the highest respiration and ATP synthesis rate, whereas hippocampal mitochondria had the lowest. However, the mitochondrial efficiency, determined as ATP produced/O2 consumed, was similar between the three regions. This study reveals inherent differences in regional mitochondrial energetics and may serve as a tool for further investigations of regional mitochondrial function in relation to neurodegenerative diseases.

Targeting of reactive isolevuglandins in mitochondrial dysfunction and inflammation

“…To define the specific role of complex I mediated respiration we performed measurements in the presence of complex II inhibitor malonate (5 mM). We have measured basal respiration in the presence of mitochondria plus substrates, coupled respiration after addition of ADP (2 mM), proton leak following addition of oligomycin A (2.5 μM), uncoupled respiration after supplementation of CCCP (1 μM), and non-mitochondrial respiration with mixture of antimycin A and rotenone (1 μM) [32]. Mitochondrial studies where independently verified in two labs using Oroboros O2k high-resolution respirometry and Fluorescence Lifetime Micro Oxygen Monitoring System (Instech Laboratories, Inc).…”

Soluble adenylyl cyclase‐mediated cAMP signaling and the putative role of PKA and EPAC in cerebral mitochondrial function

“…Mitochondrial diversity is reported between species, tissues, and even within different regions of the brain (Andersen et al, 2019;Johnson, Harris, French, et al, 2007;Phillips et al, 2012). Due to this diversity, findings in mitochondria from one tissue should only be extrapolated to mitochondria in other tissues if there is experimental data to support it.…”

“…Data shown represent means ± SD (unless otherwise noted), with individual data points plotted. Sample sizes were estimated based on previous experiments(Andersen, Jakobsen, Waagepetersen, & Aldana, 2019;Jakobsen et al, 2018). For each assay, n equals the number of experiments where each individual experiment is equivalent to a single animal.…”

Hippocampal Disruptions of Synaptic and Astrocyte Metabolism are Primary Events of Early Amyloid Pathology in the 5xFAD Mouse Model of Alzheimer's Disease

“…An important, but often overlooked, aspect of brain mitochondrial function is the region of origin. Individual brain regions display distinct differences in metabolic capacity making it crucial to investigate mitochondrial functionality with respect to the specific brain regions [60,61]. Here, we found maintained non-synaptic mitochondrial oxygen consumption in both the hippocampus and cerebral cortex of 4 mo old 5xFAD mice.…”