Biology subjects

Katina, C.

Publications and source records attributed to Katina, C..

3 recordsLinked to original sources

bioRxiv2026

Epithelial MHC II antigen presentation dynamically informs intestinal homeostasis and injury

The intestinal epithelium plays a pivotal role in balancing immune tolerance and inflammation, yet how it communicates tissue state to the adaptive immune system remains unclear. Here, we show that intestinal epithelial cells (IECs) encode tissue identity and injury into the major histocompatibility complex class II (MHC II) ligandome. We employed integrated single cell transcriptomics, quantitative proteomics, and high-depth in vivo immunopeptidomics to map the MHC class II self-peptidome of the mouse small intestine across epithelial and immune compartments. Mature enterocytes and intestinal stem cells (ISCs) emerged as the dominant epithelial antigen-presenting cells (APCs), displaying a compartmentalized repertoire of endogenous self-immunopeptides reflecting epithelial differentiation and function. Disruption of epithelial MHC II expression led to loss of antigenic compartmentalization, immune infiltration, extracellular matrix remodeling, and emergence of inflammation-associated immune ligands, demonstrating that epithelial MHC II is required to maintain homeostasis. Functionally, a subset of ISC-derived self-immunopeptides preferentially promotes regulatory CD4{square} T cell responses, linking epithelial antigen presentation and peripheral tolerance. During gut inflammation, the epithelial MHC II landscape shifted toward damage-associated antigens. Together, these findings establish epithelial MHC II presentation as a context-dependent tissue-immune communication system that promotes tolerance in homeostasis and alerts to tissue injury during inflammation.

immunology↗

bioRxiv2025

Two opposing redox signals mediated by 2-Cys peroxiredoxin shape the redox proteome during photosynthetic induction

Photosynthetic induction, characterized by the lag in CO2 assimilation rates typically observed upon plant transition from darkness to light, has traditionally been attributed to Rubisco activase activity and stomatal opening. Yet, the faster induction of photosynthesis in the 2-Cys peroxiredoxins (Prxs) mutant (2cpab) highlighted the critical role of chloroplast redox state in regulating photosynthetic rates during this phase. Since 2-Cys Prxs are involved in transmission of oxidative signals to target enzymes, it was hypothesized that it slows down photosynthesis during the induction phase. SPEAR, a redox proteomics approach for simultaneous protein expression and redox analysis, was used to systematically map redox changes occurring at the proteome level during photosynthesis induction and to unravel the role of 2-Cys Prxs in shaping these redox alterations. No significant difference was observed in protein expression levels between WT and 2cpab plants, suggesting that protein abundance does not account for the 2cpab phenotype. During the transition from dark to low light, 82 and 54 cysteine-containing peptides were reduced or oxidized, respectively, in WT plants. Most redox-regulated cysteines in photosynthetic proteins were found oxidized in the dark and became reduced in response to light, including ATP synthase gamma chain 1 (ATPC1) and glyceraldehyde-3-phosphate dehydrogenase (GAPB). A reverse pattern was observed among redox-regulated cysteines in proteins involved in starch degradation and chloroplast glycolysis, which shifted from a reduced to an oxidized state in response to light. These findings demonstrate the initiation of two opposing redox responses, affecting distinct sets of metabolic proteins during the induction phase. Remarkably, a significantly lower number of cysteines were reduced or oxidized in 2cpab plants, highlighting the crucial role 2-Cys Prxs play in shaping both signals. Taken together, rotational shifts between metabolic pathways during the photosynthesis induction phase are regulated by two opposing redox signals mediated by 2-Cys Prx activity.

plant biology↗

bioRxiv2021

SPEAR: a proteomics approach for simultaneous protein expression and redox analysis

Oxidation and reduction of protein cysteinyl thiols serve as molecular switches, which is considered the most central mechanism for redox regulation of biological processes, altering protein structure, biochemical activity, subcellular localization, and binding affinity. Redox proteomics allows for the global identification of redox-modified cysteine (Cys) sites and quantification of their oxidation/reduction responses, serving as a hypothesis-generating platform to stimulate redox biology mechanistic research. Here, we developed Simultaneous Protein Expression and Redox (SPEAR) analysis, a new redox-proteomics approach based on differential labeling of oxidized and reduced cysteines with light and heavy isotopic forms of commercially available isotopically-labeled N-ethylmaleimide (NEM). The presented method does not require enrichment for labeled peptides, thus enabling simultaneous quantification of Cys oxidation state and protein abundance. Using SPEAR, we were able to quantify the in-vivo oxidation state of thousands of cysteines across the Arabidopsis proteome under steady-state and oxidative stress conditions. Functional assignment of the identified redox-sensitive proteins demonstrated the widespread effect of oxidative conditions on various cellular functions and highlighted the enrichment of chloroplast-targeted proteins. SPEAR provides a simple, straightforward, and cost-effective means of studying redox proteome dynamics. The presented data provide a global quantitative view of cysteine oxidation of well-known redox-regulated active sites and many novel redox-sensitive sites whose role in plant acclimation to stress conditions remains to be further explored.

biochemistry↗