Mucosal injuries due to ribosome-inactivating stress and the compensatory responses of the intestinal epithelial barrier

Stress-responsive Gdf15 counteracts renointestinal toxicity via autophagic and microbiota reprogramming

The integrated stress response (ISR) plays a pivotal role in the cellular stress response, primarily through global translational arrest and the upregulation of cellular adaptation-linked molecules. Growth differentiation factor 15 (Gdf15) is a potent stress-responsive biomarker of clinical inflammatory and metabolic distress in various types of diseases. Herein, we assess whether ISR-driven cellular stress contributes to pathophysiological outcomes by modulating Gdf15. Clinical transcriptome analysis demonstrates that PKR is positively associated with Gdf15 expression in patients with renal injury. Gdf15 expression is dependent on protein kinase R (PKR)-linked ISR during acute renointestinal distress in mice and genetic ablation of Gdf15 aggravates chemical-induced lesions in renal tissues and the gut barrier. An in-depth evaluation of the gut microbiota indicates that Gdf15 is associated with the abundance of mucin metabolism-linked bacteria and their enzymes. Moreover, stress-responsive Gdf15 facilitates mucin production and cellular survival via the reorganization of the autophagy regulatory network. Collectively, ISR-activated Gdf15 counteracts pathological processes via the protective reprogramming of the autophagic network and microbial community, thereby providing robust predictive biomarkers and interventions against renointestinal distress.

Enterocyte-innate lymphoid cell crosstalk drives early IFN-γ-mediated control of Cryptosporidium

The intestinal parasite, Cryptosporidium, is a major contributor to global child mortality and causes opportunistic infection in immune deficient individuals. Innate resistance to Cryptosporidium, which specifically invades enterocytes, is dependent on the production of IFN-γ, yet whether enterocytes contribute to parasite control is poorly understood. In this study, utilizing a mouse-adapted strain of C. parvum, we show that epithelial-derived IL-18 synergized with IL-12 to stimulate innate lymphoid cell (ILC) production of IFN-γ required for early parasite control. The loss of IFN-γ-mediated STAT1 signaling in enterocytes, but not dendritic cells or macrophages, antagonized early parasite control. Transcriptional profiling of enterocytes from infected mice identified an IFN-γ signature and enrichment of the anti-microbial effectors IDO, GBP, and IRG. Deletion experiments identified a role for Irgm1/m3 in parasite control. Thus, enterocytes promote ILC production of IFN-γ that acts on enterocytes to restrict the growth of Cryptosporidium.

Post-translational protein deimination signatures in sea lamprey (Petromyzon marinus) plasma and plasma-extracellular vesicles

Lampreys are a jawless vertebrate species belonging to an ancient vertebrate lineage that diverged from a common ancestor with humans ~500 million years ago. The sea lamprey (Petromyzon marinus) has a filter feeding ammocoete larval stage that metamorphoses into a parasitic adult, feeding both on teleost and elasmobranch fish. Lampreys are a valuable comparative model species for vertebrate immunity and physiology due to their unique phylogenetic position, unusual adaptive immune system, and physiological adaptions such as tolerance to salinity changes and urea. Peptidylarginine deiminases (PADs) are a phylogenetically conserved enzyme family which catalyses post-translational deimination/citrullination in target proteins, enabling proteins to gain new functions (moonlighting). The identification of deiminated protein targets in species across phylogeny may provide novel insights into post-translational regulation of physiological and pathophysiological processes. Extracellular vesicles (EVs) are membrane vesicles released from cells that carry cargos of small molecules and proteins for cellular communication, involved in both normal and pathological processes. The current study identified deimination signatures in proteins of both total plasma and plasma-EVs in sea lamprey and furthermore reports the first characterisation of plasma-EVs in lamprey. EVs were poly-dispersed in the size range of 40-500 nm, similar to what is observed in other taxa, positive for CD63 and Flotillin-1. Plasma-EV morphology was confirmed by transmission electron microscopy. Assessment of deimination/citrullination signatures in lamprey plasma and plasma-EVs, revealed 72 deimination target proteins involved in immunity, metabolism and gene regulation in whole plasma, and 37 target proteins in EVs, whereof 24 were shared targets. Furthermore, the presence of deiminated histone H3, indicative of gene-regulatory mechanisms and also a marker of neutrophil extracellular trap formation (NETosis), was confirmed in lamprey plasma. Functional protein network analysis revealed some differences in KEGG and GO pathways of deiminated proteins in whole plasma compared with plasma-EVs. For example, while common STRING network clusters in plasma and plasma-EVs included Peptide chain elongation, Viral mRNA translation, Glycolysis and gluconeogenesis, STRING network clusters specific for EVs only included: Cellular response to heat stress, Muscle protein and striated muscle thin filament, Nucleosome, Protein processing in endoplasmic reticulum, Nucleosome and histone deacetylase complex. STRING network clusters specific for plasma were: Adipokinetic hormone receptor activity, Fibrinogen alpha/beta chain family, peptidase S1A, Glutathione synthesis and recycling-arginine, Fructose 1,6-bisphosphate metabolic process, Carbon metabolism and lactate dehydrogenase activity, Post-translational protein phosphorylation, Regulation of insulin-like growth factor transport and clotting cascade. Overall, for the EV citrullinome, five STRING network clusters, 10 KEGG pathways, 15 molecular GO pathways and 29 Reactome pathways were identified, compared with nine STRING network clusters, six KEGG pathways, two Molecular GO pathways and one Reactome pathway specific for whole plasma; while further pathways were shared. The reported findings indicate that major pathways relevant for immunity and metabolism are targets of deimination in lamprey plasma and plasma-EVs, with some differences, and may help elucidating roles for the conserved PAD enzyme family in regulation of immune and metabolic function throughout phylogeny.

Extracellular Vesicle Signatures and Post-Translational Protein Deimination in Purple Sea Urchin (Strongylocentrotus purpuratus) Coelomic Fluid-Novel Insights into Echinodermata Biology

The purple sea urchin (Strongylocentrotus purpuratus) is a marine invertebrate of the class Echinoidea that serves as an important research model for developmental biology, cell biology, and immunology, as well as for understanding regenerative responses and ageing. Peptidylarginine deiminases (PADs) are calcium-dependent enzymes that mediate post-translational protein deimination/citrullination. These alterations affect protein function and may also play roles in protein moonlighting. Extracellular vesicles (EVs) are membrane-bound vesicles that are released from cells as a means of cellular communication. Their cargo includes a range of protein and RNA molecules. EVs can be isolated from many body fluids and are therefore used as biomarkers in physiological and pathological responses. This study assessed EVs present in the coelomic fluid of the purple sea urchin (Strongylocentrotus purpuratus), and identified both total protein cargo as well as the deiminated protein cargo. Deiminated proteins in coelomic fluid EVs were compared with the total deiminated proteins identified in coelomic fluid to assess putative differences in deiminated protein targets. Functional protein network analysis for deiminated proteins revealed pathways for immune, metabolic, and gene regulatory functions within both total coelomic fluid and EVs. Key KEGG and GO pathways for total EV protein cargo furthermore showed some overlap with deimination-enriched pathways. The findings presented in this study add to current understanding of how post-translational deimination may shape immunity across the phylogeny tree, including possibly via PAD activity from microbiota symbionts. Furthermore, this study provides a platform for research on EVs as biomarkers in sea urchin models.

Mucosal ribosomal stress-induced PRDM1 promotes chemoresistance via stemness regulation

The majorities of colorectal cancer (CRC) cases are sporadic in origin and a large proportion of etiologies are associated with environmental stress responses. In response to external and internal stress, the ribosome stands sentinel and stress-driven ribosomal dysfunction triggers the cellular decision pathways via transcriptional reprogramming. In the present study, PR domain zinc finger protein (PRDM) 1, a master transcriptional regulator, was found to be closely associated with ribosomal actions in patients with CRC and the murine models. Stress-driven ribosomal dysfunction enhanced PRDM1 levels in intestinal cancer cells, which contributed to their survival and enhanced cancer cell stemness against cancer treatment. Mechanistically, PRDM1 facilitated clustering modulation of insulin-like growth factor (IGF) receptor-associated genes, which supported cancer cell growth and stemness-linked features. Ribosomal dysfunction-responsive PRDM1 facilitated signaling remodeling for the survival of tumor progenitors, providing compelling evidence for the progression of sporadic CRC.

Caveolar communication with xenobiotic-stalled ribosomes compromises gut barrier integrity

In response to internal and external insults, the intestinal lining undergoes various types of epithelial adaptation or pathologic distress via stress-responsive eIF2α kinase signaling and subsequent cellular reprogramming. As a vital platform for growth factor-linked adaptive signaling, caveolae were evaluated for epithelial modulation of the insulted gut. Patients under ulcerative insult displayed enhanced expression of caveolin-1, the main structural component of caveolae, which was positively associated with expression of protein kinase R (PKR), the ribosomal stress-responsive eIF2α kinase. PKR-linked biological responses were simulated in experimental gut models of ribosome-inactivating stress using mice and Caenorhabditis elegans. Caveolar activation counteracted the expression of wound-protective epidermal growth factor receptor (EGFR) and its target genes, such as chemokines that were pivotal for epithelial integrity in the ribosome-inactivated gut. Mechanistic findings regarding ribosomal inactivation-associated disorders in the gut barrier provide crucial molecular evidence for detrimental caveolar actions against EGFR-mediated epithelial protection in patients with IBD.

Post-translational protein deimination in cod (Gadus morhua L.) ontogeny novel roles in tissue remodelling and mucosal immune defences?

Peptidylarginine deiminases (PADs) are calcium dependent enzymes with physiological and pathophysiological roles conserved throughout phylogeny. PADs promote post-translational deimination of protein arginine to citrulline, altering the structure and function of target proteins. Deiminated proteins were detected in the early developmental stages of cod from 11 days post fertilisation to 70 days post hatching. Deiminated proteins were present in mucosal surfaces and in liver, pancreas, spleen, gut, muscle, brain and eye during early cod larval development. Deiminated protein targets identified in skin mucosa included nuclear histones; cytoskeletal proteins such as tubulin and beta-actin; metabolic and immune related proteins such as galectin, mannan-binding lectin, toll-like receptor, kininogen, Beta2-microglobulin, aldehyde dehydrogenase, bloodthirsty and preproapolipoprotein A-I. Deiminated histone H3, a marker for anti-pathogenic neutrophil extracellular traps, was particularly elevated in mucosal tissues in immunostimulated cod larvae. PAD-mediated protein deimination may facilitate protein moonlighting, allowing the same protein to exhibit a range of biological functions, in tissue remodelling and mucosal immune defences in teleost ontogeny.

Ribosomal alteration-derived signals for cytokine induction in mucosal and systemic inflammation: noncanonical pathways by ribosomal inactivation

Ribosomal inactivation damages 28S ribosomal RNA by interfering with its functioning during gene translation, leading to stress responses linked to a variety of inflammatory disease processes. Although the primary effect of ribosomal inactivation in cells is the functional inhibition of global protein synthesis, early responsive gene products including proinflammatory cytokines are exclusively induced by toxic stress in highly dividing tissues such as lymphoid tissue and epithelia. In the present study, ribosomal inactivation-related modulation of cytokine production was reviewed in leukocyte and epithelial pathogenesis models to characterize mechanistic evidence of ribosome-derived cytokine induction and its implications for potent therapeutic targets of mucosal and systemic inflammatory illness, particularly those triggered by organellar dysfunctions.