Biology subjects

Byrnes, C.

Publications and source records attributed to Byrnes, C..

3 recordsLinked to original sources

bioRxiv2025

1-Deoxysphingolipids Require Very-Long-Chain Ceramide Synthesis to Induce ER Stress and Neurotoxicity

Sphingolipids play key roles in cellular systems both as membrane components and as signaling molecules. Their biosynthesis, which occurs in the endoplasmic reticulum (ER), begins with the condensation of an amino acid, typically serine, and a fatty acyl-CoA. Under certain pathological conditions, alanine can be substituted for serine in the condensation reaction, producing 1-deoxysphingolipids, which lack the 1-hydroxyl group on the sphingoid base. Unlike typical sphingolipids, 1-deoxysphingolipids are unable to accept a head group modification, which alters their metabolic processing and prevents their canonical degradation. The accumulation of these "headless" 1-deoxysphingolipids causes neurotoxicity in various neurological and metabolic disorders. Here, we conducted a genome-wide CRISPR-Cas9 screen to identify pathways leading to 1-deoxysphinganine-induced toxicity in SH-SY5Y cells, a model used to study neurotoxic responses. Our top genetic hits highlighted the pathway involved in synthesizing ceramides with very-long-chain fatty acids (C22-C26). Using CRISPR-Cas9-modified SH-SY5Y cells with loss-of-function (LOF) mutations in the TECR or CERS2 genes--both critical for producing very-long-chain ceramides--we validated that this pathway was essential for 1-deoxysphinganine-mediated toxicity. Furthermore, we demonstrated that the ceramide synthesis pathway is required for 1-deoxysphinganine to trigger ER stress, as evidenced by significantly increased expression of the unfolded protein response in WT, but not TECR or CERS2 LOF mutant, SH-SY5Y cells exposed to 1-deoxysphinganine. Collectively, these findings identify a specific metabolic pathway for 1-deoxysphinganine leading to very-long-chain 1-deoxyceramide production that culminates in ER stress and toxicity. The findings highlight potential therapeutic targets for neuropathological diseases caused by 1-deoxysphingolipid accumulation.

biochemistry↗

bioRxiv2024

No cardiac phase bias for threat perception under naturalistic conditions in immersive virtual reality

Previous studies have found that threatening stimuli are more readily perceived and more intensely experienced when presented during cardiac systole compared to diastole. Also, threatening stimuli are judged as physically closer than neutral ones. In a pre-registered study, we tested these effects and their interaction using a naturalistic (interactive, 3D) experimental design in immersive virtual reality: We briefly displayed threatening and non-threatening animals (four each) at varying distances (1.5-5.5 meters) to a group of young, healthy participants (n = 41), while recording their ECGs (electrocardiograms). Participants then pointed to the location where they had seen the animal (ca. 29k trials in total). Our pre-registered analyses indicated that perceived distances to both threatening and non-threatening animals did not differ significantly between cardiac phases - with Bayesian analysis supporting the null hypothesis. There was also no evidence for an association between subjective fear and perceived proximity to threatening animals. These results contrast with previous findings that used verbal or declarative distance measures in less naturalistic experimental conditions. Furthermore, our findings suggest that the cardiac phase-related variation in threat processing may not generalize across different paradigms and may be less relevant in naturalistic scenarios than under more abstract experimental conditions. Impact statementTo our knowledge, this is the first study to assess the influence of interoceptive cardiac signals on visual perception using naturalistic stimuli in immersive virtual reality. We based the design of our experiment on previous reports about threat processing biases and the role of the cardiac cycle but did not observe the expected effects. This poses the question of their generalizability from abstract settings to more naturalistic setups, featuring greater behavioral engagement and a richer sensory environment.

physiology↗

bioRxiv2019

Use of dual electron probes reveals role of ferritin in erythropoiesis

Much is known about the finely regulated process of mammalian erythropoiesis that occurs in the bone marrow, whereby erythropoietic stem cells undergo terminal differentiation accompanied by enormous morphological changes to generate highly functional specialized red blood cells. However, a crucial step in erythropoiesis, the labile iron pool and its transport to mitochondria for heme production, is not well understood1. We apply a dual 3D imaging and spectroscopic technique, based on scanned electron probes, to measure distributions of ferritin iron-storage protein in ex vivo human erythropoietic stem cells, and to determine how those distributions change during terminal differentiation. After seven days of differentiation, the cells display a highly specialized architecture of organelles with anchored clustering of mitochondria and massive accumulation of Fe3+ in loaded ferritin cores localized to lysosomal storage depots, providing an iron source for heme production. Macrophages are not present in our ex vivo cultures, so they cannot be the source of the ferritin2. We suggest that lysosomal iron depots are required by developing reticulocytes while terminally differentiating and continuing to produce heme and globin, which assemble and concentrate to fill the cytoplasm after much of the cellular machinery is expelled.

cell biology↗