Biology subjects

Verginadis, I.

Publications and source records attributed to Verginadis, I..

3 recordsLinked to original sources

bioRxiv2026

Decreased Damage for proton FLASH vs Conventional Dose Rates in Mouse Jejunum Shown by Quantitative Assessment of γ-H2AX

Purpose: FLASH radiation with ultra-high dose rate delivery is less damaging to normal tissue than conventional radiation ( <1 Gy/s). Since radiation depletes oxygen (ROD), this damage reduction might occur via the oxygen effect. ROD experiments have shown an oxygen-independent reduction in dose effectiveness at FLASH dose rates. However, prior in vivo ROD measurements relied on extracellular oxygen probes that could not penetrate cell membranes, leaving intracellular effects unresolved. To investigate the ROD hypothesis more directly, we developed a novel three-component immunohistochemical assay with algorithmic image processing to quantitatively compare DNA damage following FLASH and conventional irradiation in mouse jejunum. Methods: Mice received intravenous EF5 2 hours before proton irradiation at FLASH (103.63 +/- 17.2 Gy/s) or conventional (0.73 +/- 0.1 Gy/s) dose rates of 2.5 Gy or 5 Gy, with unirradiated controls. Mice were euthanized 30 minutes post-irradiation, and 10 cm of jejunum was frozen as a 'Swiss Roll', sectioned, stained, and imaged. Tissue sections were stained for {gamma}-H2AX, DRAQ5, and EF5 to assess DNA double-strand breaks, total DNA content, and hypoxia, respectively. An in-house algorithm identified individual cell nuclei and registered each nucleus with its corresponding {gamma}-H2AX and EF5 signals, enabling quantitative measurement of DNA damage as a function of local tissue hypoxia. Results: Hypoxia was greatest in the villi and, to a lesser extent, the outer jejunal musculature, with substantial inter-animal variation. DNA damage decreased in hypoxic regions. FLASH enhanced the hypoxia-associated reduction in DNA damage compared with conventional dose rate and, separately, revealed an oxygen-independent reduction in DNA damage, suggesting an additional FLASH sparing mechanism. Conclusion: Current results suggest that FLASH compared to conventional dose rate radiation caused less DNA damage with increasing effect at low oxygen levels, a result consistent with ROD as a mechanism. Pronounced tissue heterogeneity in murine jejunum requires further studies to segment the effect for each tissue type.

biophysics↗

bioRxiv2024

Brown adipose tissue thermogenesis rhythms are driven by the SCN independent of adipocyte clocks

Circadian misalignment has been associated with obesity both in rodents and humans. Brown adipose tissue (BAT) thermogenesis contributes to energy expenditure and can be activated in adults to reduce body weight. Although previous studies suggest control of BAT thermogenesis by the circadian clock, the site and mechanisms of regulation remain unclear. We used mice with genetic disruption of the circadian clock in the suprachiasmatic nucleus (SCN) and peripheral tissues to delineate their role in BAT thermogenesis. Global post-natal deletion of Bmal1 in adult mice (Bmal1-/-) abolishes the rhythms of interscapular BAT temperature, a measure of thermogenesis, while normal locomotor activity rhythms are maintained under a regular 12h light-12h dark schedule. Activation of thermogenesis either by exposure to cold or adrenergic stimulation of BAT displays a diurnal rhythm with higher activation during the active period. Both the rhythm and the magnitude of the thermogenic response is preserved in Bmal1-/- mice. In contrast to mice with global deletion of Bmal1, mice with brown adipocyte (Ucp1-Bmal1-/-) or brown and white adipocyte (Ad-Bmal1-/-) deletion of Bmal1 show intact rhythms of BAT thermogenic activity. The capacity of Ucp1-Bmal1-/- mice to activate thermogenesis in response to exposure to cold is identical to WT mice, independent of time of stimulation. Circadian rhythmicity of interscapular BAT temperature is lost in mice with SCN deletion of Bmal1 (SCN-Bmal1-/-), indicating control of BAT thermogenesis rhythms by the SCN. Control mice exhibit rhythmic BAT glucose and fatty acid uptake - a rhythm that is not recapitulated in Bmal1-/- and SCN-Bmal1-/- mice but is present in Ucp1-Bmal1-/- and Ad-Bmal1-/- mice. BAT cAMP and phosphorylated hormone-sensitive lipase (pHSL) is reduced during the active period in Bmal1-/- and SCN-Bmal1-/- mice consistent with reduced sympathetic tone. Furthermore, sympathetic denervation of BAT ablates BAT temperature rhythms in WT mice. Taken together, our findings suggest that the SCN drives rhythms of BAT thermogenesis through adipocyte clock-independent, sympathetic signaling to the BAT.

physiology↗

bioRxiv2023

p53 promotes revival stem cells in the regenerating intestine after severe radiation injury

Ionizing radiation induces cell death in the gastrointestinal (GI) epithelium by activating p53. However, p53 also prevents animal lethality caused by radiation-induced GI injury. Through single-cell RNA-sequencing of the irradiated mouse intestine, we find that p53 target genes are specifically enriched in stem cells of the regenerating epithelium, including revival stem cells that promote animal survival after GI damage. Accordingly, in mice with p53 deleted specifically in the GI epithelium, ionizing radiation fails to induce revival stem cells. Using intestinal organoids, we show that transient p53 expression is required for the induction of revival stem cells that is controlled by an Mdm2-mediated negative feedback loop. These results suggest that p53 suppresses severe radiation-indued GI injury by promoting intestinal epithelial cell reprogramming. One-Sentence SummaryAfter severe radiation injury to the intestine, transient p53 activity induces revival stem cells to promote regeneration.

cell biology↗