Biology subjects

Stepanova, A.

Publications and source records attributed to Stepanova, A..

6 recordsLinked to original sources

bioRxiv2026

Calcium dysregulation amplifies fibrotic responses to TGFβ in human Friedreich's ataxia fibroblasts

Friedreich's ataxia (FA) is an inherited disease caused by loss of frataxin (FXN) and characterized by neurodegeneration and fatal cardiomyopathy. Cardiac fibrosis contributes to cardiomyopathy by stiffening the heart wall, yet the underlying mechanisms remain unknown. Here, we investigated pro-fibrotic predisposition in FA patient-derived fibroblasts, focusing on the role of cytosolic calcium (Ca) in TGF{beta}-driven fibroblast-to-myofibroblast transition (FMT). We found pro-fibrotic transcriptional priming in FA fibroblasts, alongside elevated expression of genes controlled by the Ca-responsive transcription factor NFAT. Upon FMT, FA myofibroblasts showed amplified induction of pro-fibrotic (CCN2, NOX4) and suppression of anti-fibrotic (CCN3) genes, which were inversely correlated with residual FXN. Mechanistically, FA fibroblasts exhibited elevated cytosolic Ca and strongly downregulated expression of the Na-Ca exchanger NCX1, which directly correlated with FXN. Furthermore, NCX1 inhibition in control fibroblasts recapitulated FA Ca phenotypes, whereas NCX1 transduction in FA fibroblasts normalized Ca dynamics and blunted CCN2 induction in FMT. These findings highlight NCX1 as a modulator of fibrotic reprogramming in FA and identify Ca dyshomeostasis as an intrinsic mechanism of fibrosis that could be targeted therapeutically.

molecular biology↗

bioRxiv2025

A mouse model of CHCHD10 p.R15L familial ALS presents mild, age-related motor neuron degeneration without protein instability or mitochondrial dysfunction

Mutations in the mitochondrial protein CHCHD10 (D10) cause a spectrum of hereditary neurodegenerative disorders. Among these, the p.R15L variant is linked to a slowly progressive, late-onset familial form of amyotrophic lateral sclerosis (ALS) with unclear pathogenic mechanisms. To better understand this, we investigated a knock-in (KI) mouse model carrying the p.R15L mutation in the endogenous protein. Unlike previously described mutant D10 KI models, p.R15L KI mice exhibited normal D10 protein levels, with no evidence of large protein aggregates. Mitochondrial respiration and hydrogen peroxide emission in mitochondria isolated from muscle and brain were unaltered. Similarly, fibroblasts from human p.R15L carriers exhibited normal D10 levels and unchanged oxidative phosphorylation function. Histochemical analyses of p.R15L KI muscle revealed mild increases in mitochondrial enzymatic activity in a subset of muscle fibers and muscle transcriptomics showed elevated expression of PGC-1, suggesting enhanced mitochondrial biogenesis. p.R15L KI mice developed subtle, late-onset phenotypes, including reduced body weight and motor activity and increased anxiety-like behavior. Importantly, in aged mice electrophysiological studies demonstrated decreased amplitude of the compound muscle action potential, commensurate with a moderate loss of spinal cord motor neurons and elevated serum neurofilament light levels, indicative of neurodegeneration. Together, these results indicate that the p.R15L mutation produces a mild, late-onset motor neuron phenotype in mice, partially recapitulating the human disease, without mitochondrial functional or morphological alterations. The findings indicate that p.R15L D10 selectively impairs mouse motor neurons through a gain-of-function mechanism, providing a genetically accurate yet mild in vivo model of familial ALS.

neuroscience↗

bioRxiv2025

Rescuing Ischemic Brain Injury by Rewiring Mitochondrial Electron Flow

Mitochondrial metabolic flux alterations are critical drivers of acute ischemia-reperfusion (IR) brain injury. Reverse electron transfer (RET), defined as the upstream flow of electrons from the quinone pool to complex I, is a major source of pathological reactive oxygen species (ROS) under stress conditions. In an in vivo brain IR model, oxygen deprivation induces the buildup of RET-supporting substrates, with glycerol 3-phosphate identified as the dominant contributor in addition to succinate. Rapid oxidation of these substrates by brain mitochondria upon reoxygenation drives massive ROS production, while also leading to over-reduction and dissociation of the complex I flavin mononucleotide (FMN) cofactor. The resulting FMN-deficient complex I becomes catalytically impaired, unable to oxidize NADH or to produce ROS. To mitigate RET and preserve complex I function, we used transgenic mice xenotopically expressing alternative oxidase (AOX). This enzyme bypasses complexes III and IV by directly oxidizing the reduced quinone pool and passing electrons onto molecular oxygen. AOX expression did not alter complex I abundance, supercomplexes assembly, or basal respiration rates, but effectively diverted electrons from the quinone pool, decreasing RET flux via complex I and limiting ROS generation during IR. For the first time we showed that AOX expression and attenuation of RET preserved complex I FMN binding, suppressed oxidative stress, and conferred neuroprotection in vivo. Our findings reveal a novel strategy for rewiring mitochondrial electron flux to mitigate initial IR brain injury, highlighting modulation of the quinone pool by AOX as a potential therapeutic strategy for IR.

biochemistry↗

bioRxiv2022

Cell-specific expression of key mitochondrial enzymes precludes OXPHOS in astrocytes of the adult human neocortex and hippocampal formation

The astrocyte-to-neuron lactate shuttle hypothesis entails that glycolytically derived pyruvate in astrocytes is converted to lactate instead of being catabolized in mitochondria. The mechanism of this metabolic rewiring is unclear. Here we show that astrocytes of the adult human neocortex and hippocampal formation do not express mitochondrial proteins critical for performing oxidative phosphorylation (OXPHOS) to a detectable degree, including cytochrome c and complex IV. Without OXPHOS, human brain astrocytes are bound to produce lactate to avoid interruption of glycolysis.

neuroscience↗

bioRxiv2022

Altered MAM function shifts mitochondrial metabolism in SOD1-mutant models of ALS

Mitochondrial defects are a common hallmark of familial and sporadic forms of amyotrophic lateral sclerosis (ALS). However, the origin of these defects, including reduced pyruvate metabolism and reduced oxygen consumption, is poorly understood. These metabolic functions are regulated in specialized endoplasmic reticulum (ER) domains in close contact with mitochondria, called mitochondrial-associated ER membranes (MAM). Recently it has been shown that MAM domains are disrupted in ALS, but the connection between MAM dysregulation and mitochondrial defects in ALS cells remains unclear. Using human embryonic stem cell (ESC)-derived motor neurons (hMNs) and mouse models with ALS-pathogenic mutations in superoxide dismutase 1 (SOD1), we found that the glycolytic deficiency in ALS is a direct consequence of the progressive disruption of MAM structure and function that hinders the use of glucose-derived pyruvate as a mitochondrial fuel and triggers a shift in mitochondrial substrates from pyruvate to fatty acids. This glycolytic deficiency, over time, induces significant alterations in mitochondrial electron flow and in the active/dormant (A/D) status of complex I in spinal cord, but not in brain. These data agree with a role for MAM in the maintenance and regulation of cellular glucose metabolism and suggest that MAM disruption in ALS could be the underlying cause of the bioenergetic deficits observed in the disease.

molecular biology↗

bioRxiv2020

Partial inhibition of mitochondrial complex I attenuates neurodegeneration and restores energy homeostasis and synaptic function in a symptomatic Alzheimers mouse model

We demonstrate that mitochondrial respiratory chain complex I is an important small molecule druggable target in Alzheimers Disease (AD). Partial inhibition of complex I triggers the AMP-activated protein kinase-dependent signaling network leading to neuroprotection in symptomatic APP/PS1 mice, a translational model of AD. Treatment of APP/PS1 mice with complex I inhibitor after the onset of AD-like neuropathology improved energy homeostasis, synaptic activity, long-term potentiation, dendritic spine maturation, cognitive function and proteostasis, and reduced oxidative stress and inflammation in brain and periphery, ultimately blocking the ongoing neurodegeneration. Therapeutic efficacy in vivo was monitored using translational biomarkers FDG-PET, 31P NMR, and metabolomics. Cross-validation of the mouse and the human AMP-AD transcriptomic data demonstrated that pathways improved by the treatment in APP/PS1 mice, including the immune system response and neurotransmission, represent mechanisms essential for therapeutic efficacy in AD patients.

neuroscience↗