Biology subjects

Ouellet, M.

Publications and source records attributed to Ouellet, M..

6 recordsLinked to original sources

bioRxiv2024

Mitochondrial Dysfunction alters Early Endosome Distribution and Cargo Trafficking via ROS-Mediated Microtubule Reorganization

Mitochondria are essential for bioenergetic functions and various cellular processes, including differentiation and immunity, their dysfunction leading to several pathologies. While these pathologies have traditionally been associated with ATP deficits, mitochondrial dysfunction also leads to reactive oxygen species (ROS) generation, inflammation, and alterations the function of other organelles. While the negative impact of mitochondrial dysfunction on lysosomal activity has been established, the relationship between mitochondria and the rest of the endocytic compartment remains poorly understood. Here, we show that inhibiting mitochondrial activity through genetic and chemical approaches causes early endosome (EE) perinuclear aggregation and impairs cargo delivery to lysosomes. This impairment is due to altered microtubule architecture and centrosome dynamics, mediated by ROS. Antioxidants can rescue these EE defects, underlying the pivotal role of mitochondria in maintaining cellular activities through ROS regulation of microtubule networks. Our findings highlight the significance of mitochondria beyond ATP production, emphasizing their critical involvement in endocytic trafficking and cellular homeostasis. These insights emphasize mitochondrias critical involvement in cellular activities and suggest novel targets for therapies to mitigate the effects of mitochondrial dysfunction.

cell biology↗

bioRxiv2024

Endothelial SHP-1 regulates diabetes-induced abnormal collateral vessel formation and endothelial cell senescence

ObjectiveIschemia due to narrowing of the femoral artery and distal vessels is a major cause of peripheral arterial disease and morbidity affecting patients with diabetes. Diabetes-induced premature senescence of endothelial cells (EC) has been proposed as a mechanism leading to impaired ischemia-driven angiogenesis. Importantly, our previous work has shown that hyperglycemia reduced vascular endothelial growth factor (VEGF) activity in ischemic muscle of diabetic mice, which was associated with increased expression of the protein tyrosine phosphatase Src homology region 2 domain-containing phosphatase-1 (SHP-1). Here, we evaluate the impact of SHP-1 deletion on EC function and senescence. Approach and ResultsLigation of the femoral artery was performed in nondiabetic (NDM) and 3 months diabetic (DM) mice with EC-specific deletion of SHP-1 and blood flow reperfusion was measured for 4 weeks. Blood flow reperfusion and limb function during voluntary wheel running were reduced by 43% and 82%, respectively in DM mice as compared to NDM mice. EC-specific deletion of SHP-1 in DM mice restored blood flow reperfusion by 60%, limb function by 86%, while capillary density was similar to NDM mice. Moreover, ablation of SHP-1 in EC prevented diabetes-induced expression of the senescence markers p53 and p21 and counteracted Nrf2 downregulation. In cultured EC, overexpression of dominant negative of SHP-1 prevented HG-induced inhibition of proliferation, migration, tubule formation and VEGFR2/Akt phosphorylation following VEGF stimulation. In addition, the expression of senescence markers and suppression of Nrf2 in EC exposed to HG levels were reversed by overexpression of dominant negative SHP-1. ConclusionSHP-1 in ECs is a central effector of diabetes-induced senescence that blocks VEGF action, and induces aberrant collateral vessel formation and blood flow reperfusion. Reduced SHP-1 expression counteracts these pathologic features suggesting the notion that it represents a promising therapeutic target. HIGHLIGHTSO_LIEndothelial specific deletion of SHP-1 (Scr homology 2-containing phosphatase-1) improves blood flow reperfusion, limb motricity and vessel density in the diabetic ischemic limb. C_LIO_LIDiabetes-induced SHP-1 protein expression inhibits VEGF proangiogenic actions and promotes endothelial senescence. C_LIO_LIEndothelial specific deletion of SHP-1 restores VEGF proangiogenic actions and prevents senescence in ischemic muscle and artery of diabetic mice and patients. C_LI

cell biology↗

bioRxiv2022

Myelination and excitation-inhibition balance synergistically shape structure-function coupling across the human cortex

Recent work has demonstrated that the relationship between structural and functional connectivity varies regionally across the human brain, with reduced coupling emerging along the sensory-association cortical hierarchy. The biological underpinnings driving this expression, however, remain largely unknown. Here, we postulated that intracortical myelination and excitation-inhibition (EI) balance mediate the heterogeneous expression of structure-function coupling (SFC) and its temporal variance across the cortical hierarchy. We employed atlas-and voxel-based connectivity approaches to analyze neuroimaging data acquired from two groups of healthy participants. Our findings were consistent across processing pipelines: 1) increased myelination and lower EI-ratio associated with more rigid SFC and restricted moment-to-moment SFC fluctuations; 2) a gradual shift from EI-ratio to myelination as the principal predictor of SFC occurred when traversing from granular to agranular cortical regions. Collectively, our work delivers a novel framework to conceptualize structure-function relationships in the human brain, paving the way for an improved understanding of how demyelination and/or EI-imbalances induce reorganization in brain disorders.

neuroscience↗

bioRxiv2022

Asymmetric Signaling Across the Hierarchy of Cytoarchitecture within the Human Connectome

Cortical variations in cytoarchitecture form a sensory-fugal axis that systematically shapes regional profiles of extrinsic connectivity. Additionally, this axis is thought to guide signal propagation and integration across the cortical hierarchy. While human neuroimaging work has shown that this axis constrains local properties of the human connectome, it remains unclear whether it also shapes the asymmetric signaling that arises from higher-order connectome topology. Here, we used network control theory to examine the amount of energy required to propagate dynamics across the sensory-fugal axis. Our results revealed an asymmetry in this energy indicating that bottom-up transitions were easier to complete compared to top-down transitions. Supporting analyses demonstrated that this asymmetry was underpinned by a connectome topology that is wired to support efficient bottom-up signaling. Finally, we found that this asymmetry correlated with changes in intrinsic neuronal timescales and lessened throughout youth. Our results show that cortical variation in cytoarchitecture may guide the formation of macroscopic connectome topology.

neuroscience↗

bioRxiv2021

Introduction of loxP sites by electroporation in the mouse genome; a simple approach for conditional allele generation in complex targeting loci.

BackgroundThe discovery of the CRISPR-Cas9 system and its applicability in mammalian embryos has revolutionized the way we generate genetically engineered animal models. To date, models harbouring conditional alleles (i.e.: two loxP sites flanking an exon or a critical DNA sequence of interest) remain the most challenging to generate as they require simultaneous cleavage of the genome using two guides in order to properly integrate the repair template. In the current manuscript, we describe a modification of the sequential electroporation procedure described by Horii et al (2017). We demonstrate production of conditional allele mouse models for eight different genes via one of two alternative strategies: either by consecutive sequential electroporation (strategy A) or non-consecutive sequential electroporation (strategy B). ResultsBy using strategy A, we demonstrated successful generation of conditional allele models for three different genes (Icam1, Lox, and Sar1b), with targeting efficiencies varying between 5 to 13%. By using strategy B, we generated five conditional allele models (Loxl1, Pard6a, Pard6g, Clcf1, and Mapkapk5), with targeting efficiencies varying between 3 to 25%. ConclusionOur modified electroporation-based approach, involving one of the two alternative strategies, allowed the production of conditional allele models for eight different genes via two different possible paths. This reproducible method will serve as another reliable approach in addition to other well-established methodologies in the literature for conditional allele mouse model generation.

molecular biology↗

bioRxiv2021

Mitochondrial fission is required for proper nucleoid distribution within mitochondrial networks

Mitochondrial DNA (mtDNA) maintenance is essential to sustain a functionally healthy population of mitochondria within cells. Proper mtDNA replication and distribution within mitochondrial networks are essential to maintain mitochondrial homeostasis. However, the fundamental basis of mtDNA segregation and distribution within mitochondrial networks is still unclear. To address these questions, we developed an algorithm, Mitomate tracker to unravel the global distribution of nucleoids within mitochondria. Using this tool, we decipher the semi-regular spacing of nucleoids across mitochondrial networks. Furthermore, we show that mitochondrial fission actively regulates mtDNA distribution by controlling the distribution of nucleoids within mitochondrial networks. Specifically, we found that primary cells bearing disease-associated mutations in the fission proteins DRP1 and MYH14 show altered nucleoid distribution, and acute enrichment of enlarged nucleoids near the nucleus. Further analysis suggests that the altered nucleoid distribution observed in the fission mutants is the result of both changes in network structure and nucleoid density. Thus, our study provides novel insights into the role of mitochondria fission in nucleoid distribution and the understanding of diseases caused by fission defects. Significance statementMutation or deletion of mitochondrial DNA (mtDNA) is associated with a large number of human diseases. However, the mechanisms controlling mtDNA replication and segregation are still poorly understood. Here, we have developed a new computational method to quantify the distribution of nucleoids (mtDNA with associated proteins) and define how nucleoid distribution is affected by changes in mitochondrial network structure. We demonstrate that mitochondrial fission is required for the proper distribution of nucleoids across mitochondrial networks, cells from patients with fission defects showing irregular nucleoid distribution and perinuclear accumulation. Nonetheless, each fission mutant behaved in a distinct manner, indicating a complex relationship between mitochondrial dynamics and nucleoid distribution.

cell biology↗