Brain mitochondrial diversity and network organization predict anxiety-like behavior in male mice

Abstract

The brain and behavior are under energetic constraints, limited by mitochondrial energy transformation capacity. However, the mitochondria-behavior relationship has not been systematically studied at a brain-wide scale. Here we examined the association between multiple features of mitochondrial respiratory chain capacity and stress-related behaviors in male mice with diverse behavioral phenotypes. Miniaturized assays of mitochondrial respiratory chain enzyme activities and mitochondrial DNA (mtDNA) content were deployed on 571 samples across 17 brain areas, defining specific patterns of mito-behavior associations. By applying multi-slice network analysis to our brain-wide mitochondrial dataset, we identified three large-scale networks of brain areas with shared mitochondrial signatures. A major network composed of cortico-striatal areas exhibited the strongest mitochondria-behavior correlations, accounting for up to 50% of animal-to-animal behavioral differences, suggesting that this mito-based network is functionally significant. The mito-based brain networks also overlapped with regional gene expression and structural connectivity, and exhibited distinct molecular mitochondrial phenotype signatures. This work provides convergent multimodal evidence anchored in enzyme activities, gene expression, and animal behavior that distinct, behaviorally-relevant mitochondrial phenotypes exist across the male mouse brain.

A Human Brain Map of Mitochondrial Respiratory Capacity and Diversity

“…There are 100-1,000s of these organelles per neuron or glial cell 17 . Mitochondria molecularly specialize to meet specific cellular demands, direct subcellular activities 5,6,[17][18][19] , and provide the necessary energy to support brain activity. Beyond energetics, mitochondria also participate in other critical functions including cell-cell signaling 20 and regulation of neuronal excitability 21 , neurotransmitter release 22 and modulation of inflammatory processes 23,24 .…”

“…The average voxel weight was 26.2±4.5 mg (mean±SD; predicted weight = 27 mg from 3x3x3 mm voxel dimensions at aqueous volumetric density). Such small tissue samples require high-sensitivity assays for both mitochondrial density and enzymatic activities of the respiratory chain (also known as the electron transport chain, ETC) 5 . Mitochondrial density was assessed using a combination of two mitochondrial markers: citrate synthase (CS) activity and mitochondrial DNA (mtDNA) density.…”

“…For robustness, OxPhos enzymatic activities were quantified using two independent assays in different laboratories: a miniaturized colorimetric assay optimized for brain tissue 5 and frozentissue respirometry 32,33 (Extended Data Fig. 3).…”

“…Mitochondrial DNA copy number (mtDNAcn), which reflects the number of mtDNA genomes per cell nucleus, is also presented (Extended Data Fig. 7b) but is influenced by cellularity and therefore comparison between brain regions cannot be straightforward 5 .…”

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Mitochondrial oxidative phosphorylation (OxPhos) powers brain activity 1,2 , and mitochondrial defects are linked to neurodegenerative and neuropsychiatric disorders 3,4 , underscoring the need to define the brain's molecular energetic landscape [5][6][7][8][9][10] . To bridge the cognitive neuroscience and cell biology scale gap, we developed a physical voxelization approach to partition a frozen human coronal hemisphere section into 703 voxels comparable to neuroimaging resolution (3x3x3 mm).In each cortical and subcortical brain voxel, we profiled mitochondrial phenotypes including OxPhos enzyme activities, mitochondrial DNA and volume density, and mitochondria-specific respiratory capacity.

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