Biology subjects

Brazhe, N.

Publications and source records attributed to Brazhe, N..

4 recordsLinked to original sources

bioRxiv2026

Mitochondrial cytochrome c accumulation accompanies reduced electron flux through complex IV without enhancing cell sensitivity to apoptosis

We show that chronic impairment of mitochondrial respiration is associated with marked accumulation of cytochrome c (Cytc) protein. Using SCO2-deficient HCT116 cells lacking functional cytochrome c oxidase and wild-type cells exposed to sustained hypoxia, we found that substantial mitochondrial Cytc accumulation parallels reduced electron flux through Cytc. SCO2-deficient cells exhibited equally elevated Cytc levels under normoxia (19% O2) and hypoxia (0.1-3% O2). Wild-type cells under sustained hypoxia accumulated Cytc, reaching levels comparable to those in SCO2-deficient cells. This effect was reversible upon reoxygenation. Increased Cytc protein levels were also observed in other cell models, including primary cortical neurons cultured under chronic hypoxia and in cerebral cortex tissue from hypoxia-exposed mice. Cytc accumulation occurred independently of CYCS transcription, mRNA translation, HIF activation, ROS production and changes in mitochondrial network. Pharmacological inhibition of complex III was likewise accompanied by increased Cytc levels, whereas mitochondrial uncoupling had no effect, suggesting that impaired electron transfer rather than membrane depolarisation per se underlies this association. Raman spectroscopy revealed enrichment of reduced Cytc and an increased Cytc-to-cytochrome b ratio in respiration-deficient cells. Further supporting a stabilisation-based mechanism, the fraction of membrane-unbound ferro-Cytc was decreased in SCO2-deficient cells, consistent with moderate cardiolipin enrichment, which is known to enhance retention of Cytc at the inner mitochondrial membrane. Despite elevated mitochondrial Cytc content, SCO2-deficient cells were less susceptible to apoptosis induced by intermittent hypoxia or dichloroacetate. Together, these findings indicate that reduced electron flux through complex IV is associated with Cytc accumulation through increased protein stability and membrane retention without enhancing apoptotic sensitivity.

Cell Biology↗

bioRxiv2024

Cerebral perfusion and metabolic response of astrocytes and neurons during locomotion

The hemodynamic response links neural oxidative metabolism changes to increased cerebral blood flow during brain activity1. Although Roy and Sherrington introduced this concept over a century ago (1890), the exact cellular mechanisms remain unclear. This study demonstrates how local blood supply increases correlate with the metabolic response of individual brain cells during locomotion. Using Raman microspectroscopy, we observed an elevation in oxygen saturation levels (sO2) in cortical venules but not in arterioles, which were already near saturation. The increased sO2 in the venules was accompanied by vasodilation, indicating blood oversupply in the local brain area, a phenomenon known as functional hyperemia. We then analyzed the metabolic response of individual neurons and astrocytes to locomotion. In neurons, the levels of reduced cytochromes of c and b types [cyt c,b (Fe2+)] rapidly decreased at the onset of locomotion. This suggests an increase in the activity of the mitochondrial respiratory chain (electron transport chain, ETC) in response to heightened energy demands in these cells2. In contrast, because astrocytes rely less on oxidative phosphorylation for their energy metabolism than neurons3, we did not observe an initial decrease in reduced cytochromes in these cells. However, as locomotion continued, the cyt c,b (Fe2+) levels steadily increased in both cell types. In neurons, this led to a slow recovery from the initial drop, while in astrocytes, the increase exceeded baseline levels. Consequently, we observed an overload of electrons in the astrocytic ETC. The distinct responses of astrocytic and neuronal mitochondria to locomotion may reflect differences in the organization of the ETC in the two cell types4. Furthermore, astrocytes may shift to glycolysis under increased neuronal activity5,6. This difference also resulted in hydrogen peroxide (H202) production in astrocytic mitochondria but not neuronal mitochondria. Since H202 is a signaling molecule critical for cognitive function in the brain7, we speculate that astrocytic mitochondria act as signaling hubs during exercise.

neuroscience↗

bioRxiv2022

Aging impairs astrocytes in the human cerebral cortex

How aging affects cellular components of the human brain active milieu remains largely unknown. We analyzed astrocytes and neurons in the neocortical access tissue of younger (22 - 50 years) and older (51 - 72 years) adult patients who underwent glioma resection. Aging decreased the amount of reduced mitochondrial cytochromes in astrocytes but not neurons. The total amount of protein was decreased in astrocytes and increased in neurons. Aged astrocytes showed morphological dystrophy quantified by the decreased length of branches, decreased volume fraction of leaflets, and shrinkage of the anatomical domain. Dystrophy correlated with the loss of gap junction coupling between astrocytes and increased input resistance. Aging was accompanied by the upregulation of glial fibrillary acidic protein (GFAP) and downregulation of membrane-cytoskeleton linker Ezrin associated with leaflets. No significant changes in neuronal excitability or spontaneous inhibitory postsynaptic signaling were observed. Thus, brain aging is associated with the impaired morphological presence and mitochondrial malfunction of astrocytes, but not neurons.

neuroscience↗

bioRxiv2021

A high-fat diet changes astrocytic metabolism to enhance synaptic plasticity and promote exploratory behavior

A high-fat diet (HFD) is generally considered to negatively influence the body, the brain, and cognitive abilities. On the other hand, fat and fatty acids are essential for nourishing and constructing brain tissue. Astrocytes are central for lipolysis and fatty acids metabolism. Here we show that exposure of young mice to one month of HFD elevates lipid content and increases the relative amount of reduced cytochromes in astrocytes but not in neurons. Metabolic changes were paralleled with an enlargement of astrocytic territorial domains due to an increased outgrowth of branches and leaflets. Astrocyte remodeling was associated with an increase in expression of ezrin and with no changes in glial fibrillary acidic protein (GFAP), glutamate transporter-1 (GLT-1), and glutamine synthetase (GS). Such physiological (non-reactive) enlargement of astrocytes in the brain active milieu promoted glutamate clearance and long-term potentiation. These changes translated into improved exploratory behavior. Thus, dietary fat intake is not invariably harmful and might exert beneficial effects depending on the biological context. In BriefA high-fat diet stimulates the metabolism and growth of astrocytes, which improves glutamate clearance, synaptic plasticity, and exploratory behavior in young mice. Thus, dietary fat arguably is an essential component of the diet for children and young adults, supporting the optimal development of the brain. HighlightsO_LIExposure of young mice to a high-fat diet elevated lipid content and increased amount of reduced cytochromes in astrocytes but not in neurons. C_LIO_LIMetabolic changes were paralleled with an enlargement of astrocytic territorial domains due to an increased outgrowth of branches and leaflets. C_LIO_LIAstrocytic enlargement was associated with increased expression of ezrin but not GFAP, hence was not reactive but physiological C_LIO_LIExpansion of astrocytes in the brain active milieu improved glutamate clearance and long-term potentiation. C_LIO_LIThe high-fat diet improved exploratory behavior in young mice. C_LI

neuroscience↗