Biology subjects

Ritz, S.

Publications and source records attributed to Ritz, S..

4 recordsLinked to original sources

bioRxiv2024

The role of the synaptic vesicle protein SV2A in regulating mitochondrial morphology and autophagy.

The synaptic vesicle glycoprotein 2A (SV2A) is a transmembrane protein of synaptic vesicles. It is involved in key functions of neurons, focused on the regulation of neurotransmitter release. Here we report three novel findings suggesting a completely new role of SV2A. First, we demonstrate that SV2A is localized at the outer mitochondrial membrane (OMM) using confocal and super-resolution microscopy. Second, Inactivation of SV2A in our cell and animal models leads to fragmented mitochondria. In addition, SV2A also affects the basal autophagic flux as well as mitophagy. Third, using proteomics analysis we demonstrate that SV2A interacts with the fission factor DRP1 and the autophagy factor ATG9A. Using AlphaFold3 we provide a first glimpse of the molecular interaction between DRP1 and SV2A. Our findings demonstrate that SV2A is not only a vesicular protein but also a mitochondrial protein in the OMM with defined functions regulating mitochondrial morphology and autophagy.

molecular biology↗

bioRxiv2023

Recovery of fibroblasts from membrane attack by S. aureus α-toxin does not depend on acid sphingomyelinase but involves macropinocytosis

Damage of the plasma membrane by mechanical stress or pore forming proteins, like streptolysin O, may trigger Ca2+ influx-dependent repair mechanisms. Ca2+ influx-dependent lysosomal exocytosis, leading to release of acid sphingomyelinase, remodeling of the plasma membrane and caveolar endocytosis of membrane lesions, is reportedly involved in membrane repair after both mechanical damage or perforation by streptolysin O. Although the small {beta}-barrel pore forming S. aureus -toxin may also increase cytosolic Ca2+ concentration in certain cell types, and reportedly lead to release of acid sphingomyelinase from endothelial cells, evidence for a role of this response for membrane repair after attack by -toxin is lacking. We exploited fibroblasts expressing dysfunctional acid sphingomyelinase to investigate whether this enzyme is required for membrane repair after S. aureus -toxin attack. Because -toxin-dependent loss of cellular ATP and externalization of phosphatidylserine were reversible, membrane damage by this pore former triggered an effective repair response in these cells. Although -toxin depolarized the plasma membrane, it did not cause a simultaneous increase of [Ca2+]i. Consistently, there was no release of {beta}-hexosaminidase, a marker of lysosomal exocytosis. Acid sphingomyelinase-deficient fibroblasts internalized -toxin, which however did not co-localize with caveolin-1, but with FITC-dextran 70kDa, a cargo of macropinosomes. Inhibition of actin polymerization or sterol synthesis prevented recovery from -toxin-dependent membrane damage. Therefore, we conclude that defense of fibroblasts against -toxin does not depend on rapid calcium-influx, lysosomal exocytosis, and functional acid sphingomyelinase, but involves ongoing cholesterol synthesis and macropinocytosis.

cell biology↗

bioRxiv2021

GDAP1 loss of function inhibits the mitochondrial pyruvate dehydrogenase complex by altering the actin cytoskeleton

Charcot-Marie-Tooth (CMT) disease 4A is an autosomal-recessive polyneuropathy caused by mutations of ganglioside-induced differentiation-associated protein 1 (GDAP1), a putative glutathione transferase, which affects mitochondrial shape and alters cellular Ca2+ homeostasis. Here, we identify the underlying mechanism. We found that patient-derived motoneurons and GDAP1 knockdown SH-SY5Y cells display two phenotypes: more tubular mitochondria and a metabolism characterized by glutamine dependence and fewer cytosolic lipid droplets. GDAP1 interacts with the actin-depolymerizing protein Cofilin-1 in a redoxdependent manner, suggesting a role for actin signaling. Consistently, GDAP1 loss causes less F-actin close to mitochondria, which restricts mitochondrial localization of the fission factor dynamin-related protein 1, instigating tubularity. Changes in the actin cytoskeleton also disrupt mitochondria-ER contact sites. This results in lower mitochondrial Ca2+ levels and inhibition of the pyruvate dehydrogenase complex, explaining the metabolic changes upon GDAP1 loss of function. Together, these findings reconcile GDAP1-associated phenotypes and implicate disrupted actin signaling in CMT4A pathophysiology.

neuroscience↗

bioRxiv2021

NECAB2 orchestrates an endosomal pathway of mitochondrial quality control at striatal synapses

Synaptic signaling depends on ATP generated by mitochondria. Due to extensive connectivity, the striatum is especially vulnerable to mitochondrial dysfunction and thus requires efficient mitochondrial quality control and repair. We found that global knockout of the neuronal calcium-binding protein 2 (NECAB2) in the mouse causes loss of striatal synapses and behavioral phenotypes related to striatal dysfunction such as reduced motivation and altered sensory gating. Striatal mitochondria from Necab2 knockout mice are more abundant and smaller. They are characterized by increased respiration and superoxide production resulting in oxidative stress. This accumulation of dysfunctional mitochondria is caused by a defective assembly of mitochondria with early endosomes in a pathway that involves the small GTPase Rab5 and its guanine nucleotide exchange factor Alsin/ALS2. NECAB2 therefore participates in an endosomal pathway of mitochondrial stress response and repair important for striatal function.

neuroscience↗