Biology subjects

Levy, G.

Publications and source records attributed to Levy, G..

4 recordsLinked to original sources

bioRxiv2026

The hepatic sinusoid is a site of microvascular complications of hyperglycemia

Diabetes is the strongest independent predictor of progression of metabolic dysfunction-associated steatotic liver disease (MASLD) to cirrhosis and hepatocellular carcinoma, yet how glucose injures the liver is poorly understood. In the retina and kidney, hyperglycemia damages the microvascular endothelium through a shared mechanism in which unrestricted glucose entry inhibits glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and diverts glycolytic intermediates into the four major pathways of glucotoxicity. The liver sinusoidal endothelial cell (LSEC) is the first cell exposed to portal blood, which carries glucose from the gut at concentrations higher than the systemic circulation reaches, for years before diabetes is diagnosed. LSEC capillarization, the loss of fenestrae and transition to a continuous capillary, precedes steatohepatitis and fibrosis. Here we show that the LSEC is a target of the same glucotoxic mechanism that underlies the classical diabetic complications. Hyperglycemia inhibited GAPDH in primary mouse LSECs and induced capillarization cell-autonomously, and inhibition of GAPDH alone reproduced the defenestration. Of the four glucotoxicity pathways, flux through the hexosamine pathway to protein O-GlcNAcylation was necessary for defenestration under high glucose and su[ff]icient to induce it under low glucose. O-GlcNAcylation of endothelial nitric oxide synthase suppressed nitric oxide production, driving defenestration through cGMP and protein kinase G signaling and Rho kinase-driven actomyosin contraction. Intervening at any step of the cascade reversed the defenestration. Hyaluronan, cleared by the LSEC and normally catabolized through glycolysis, supplied a second, GFAT-independent input to protein O-GlcNAcylation under hyperglycemia. Loss of LSEC nitric oxide was su[ff]icient to increase hepatocyte lipid accumulation in coculture. In mice with established diet-induced steatohepatitis, inhibiting O-GlcNAc transferase restored sinusoidal fenestrae and attenuated fibrosis. The hepatic sinusoid is therefore a site of microvascular complications of hyperglycemia, alongside the retina, kidney and peripheral nerve.

cell biology↗

bioRxiv2025

Human mitochondrial DNA variants influence telomere length: evidence from a transmitochondrial cybrid model

Telomere shortening is a hallmark of aging, yet telomere length (TL) varies considerably among individuals and is strongly influenced by inheritance. In mice, efficient mitochondrial function-characterized by low reactive oxygen species (ROS) production-is critical for telomere elongation during early embryogenesis. Since mitochondrial DNA (mtDNA) encodes several subunits of the electron transport chain, it may influence TL at birth by regulating mitochondrial function in utero. To explore the relationship between mtDNA and TL in human, we used a transmitochondrial cybrid approach, introducing mitochondria from donor platelets with varying telomere lengths into mtDNA-depleted cells. This revealed an inverse correlation between donor blood TL and mitochondrial ROS levels measured in the resulting cybrids, suggesting that specific mtDNA variants may contribute to the maintenance of long telomeres in humans by enhancing mitochondrial fitness. During in vitro cybrid formation, a transient phase of oxidative stress precedes cellular adaptation. In this specific window, mtDNA variants associated with reduced complex I (CI) activity induced rapid telomere shortening--an effect rescued by antioxidant and NAD precursor supplementation. While these variants occur naturally in certain individuals with long telomeres, our data suggest that, at least under in vitro conditions of acute oxidative stress, CI is critical to support PARP1 activity by maintaining the NAD/NADH balance, thereby preserving telomere integrity. Collectively, these findings solidify the link between mtDNA variants and human TL regulation, highlighting potential therapeutic opportunities for mitochondrial replacement strategies. Significance StatementTelomere length at birth influences aging trajectories and disease risk later in life, yet the mechanisms governing this trait remain incompletely understood. Using a transmitochondrial cybrid approach, we show that single-nucleotide variants in the mitochondrial genome of healthy donors directly affect mitochondrial metabolism and reactive oxygen species production. In addition, mitochondrial ROS levels measured in cybrids inversely correlate with blood cell telomere length in donors. During cybrid formation, mitochondrial DNA variants associated with reduced CI activity promote telomere shortening. Attrition was reversed by antioxidant and NAD precursor supplementation, pointing to an essential role for robust CI function in sustaining telomere length during acute oxidative stress, at least under in vitro conditions. Together, these findings establish a direct link between mitochondrial genetics, redox homeostasis, and telomere maintenance in human cells.

cell biology↗

bioRxiv2022

Constitutive Activation and Oncogenicity Are Mediated by Loss of Helical Structure at the Cytosolic Boundary of the Thrombopoietin Receptor

Dimerization of the thrombopoietin receptor (TpoR) is necessary for receptor activation and downstream signaling through activated Janus kinase 2. We have shown previously that different orientations of the transmembrane (TM) helices within a receptor dimer can lead to different signaling outputs. Here we addressed the structural basis of activation for receptor mutations S505N and W515K that induce myeloproliferative neoplasms. We show using in vivo bone marrow reconstitution experiments that ligand-independent activation of TpoR by TM asparagine (Asn) substitutions is proportional to the proximity of the mutation to the intracellular membrane surface. Solid-state NMR experiments on TM peptides indicate a progressive loss of helical structure in the juxtamembrane (JM) R/KWQFP motif with either proximity of Asn substitutions to the cytosolic boundary or mutation of W515 in the motif. Mutational studies in the TpoR cytosolic JM region show that the helical loss by itself can induce activation, but is localized to a maximum of 6 amino acids downstream of W515, the rest of the region until Box 1 requiring helicity for receptor function. The constitutive activation of TpoR mutants S505N and W515K can be inhibited by rotation of TM helices within the TpoR dimer, which also restores helicity around W515. Together these data allow us to develop a general model for activation and to explain the critical role of the JM W515 residue in the regulation of receptor activity. (Total manuscript without References and Figure Legends 6507 words, main text (without methods and materials):)

molecular biology↗

bioRxiv2019

Lithium treatment reverses irradiation-induced changes in rodent neural progenitors

Cranial radiotherapy in children has detrimental effects on cognition, mood, and social competence in young cancer survivors. Treatments harnessing hippocampal neurogenesis are currently of great relevance in this context, and we previously showed that voluntary running introduced long after irradiation rescued hippocampal neurogenesis in young mice (Naylor et al. 2008a). Lithium, a well-known mood stabilizer, has both neuroprotective, pro-neurogenic as well as anti-tumor effects, and in the current study we introduced lithium treatment 4 weeks after irradiation, analogous to the voluntary running study. Female mice received a single 4 Gy whole-brain irradiation dose at postnatal day (PND) 21 and were randomized to 0.24% Li2CO3 chow or normal chow from PND 49 to 77. Hippocampal neurogenesis was assessed at PND 77, 91 and 105. We found that lithium treatment had a pro-proliferative effect on neural progenitors and promoted neuronal integration upon its discontinuation. Gene expression profiling and DNA methylation analysis identified two novel factors related to the observed effects, Tppp, associated with proliferation, and GAD2/65, associated with neuronal signaling. Our results show that lithium treatment reverses irradiation-induced impairment of hippocampal neurogenesis even when introduced long after the injury. We propose that lithium treatment should be intermittent in order to first make neural progenitors proliferate and then, upon discontinuation, allow them to differentiate. Our findings suggest that pharmacological treatment of cognitive so-called late effects in childhood cancer survivors is possible.

neuroscience↗