Intra- and Inter-cellular Rewiring of the Human Colon during Ulcerative Colitis.

Genome-wide association studies (GWAS) have revealed risk alleles for ulcerative colitis (UC). To understand their cell type specificities and pathways of action, we generate an atlas of 366,650 cells from the colon mucosa of 18 UC patients and 12 healthy individuals, revealing 51 epithelial, stromal, and immune cell subsets, including BEST4+ enterocytes, microfold-like cells, and IL13RA2+IL11+ inflammatory fibroblasts, which we associate with resistance to anti-TNF treatment. Inflammatory fibroblasts, inflammatory monocytes, microfold-like cells, and T cells that co-express CD8 and IL-17 expand with disease, forming intercellular interaction hubs. Many UC risk genes are cell type specific and co-regulated within relatively few gene modules, suggesting convergence onto limited sets of cell types and pathways. Using this observation, we nominate and infer functions for specific risk genes across GWAS loci. Our work provides a framework for interrogating complex human diseases and mapping risk variants to cell types and pathways.

A missense variant in SLC39A8 confers risk for Crohn's disease by disrupting manganese homeostasis and intestinal barrier integrity.

Common genetic variants interact with environmental factors to impact risk of heritable diseases. A notable example of this is a single-nucleotide variant in the Solute Carrier Family 39 Member 8 (SLC39A8) gene encoding the missense variant A391T, which is associated with a variety of traits ranging from Parkinson's disease and neuropsychiatric disease to cardiovascular and metabolic diseases and Crohn's disease. The remarkable extent of pleiotropy exhibited by SLC39A8 A391T raises key questions regarding how a single coding variant can contribute to this diversity of clinical outcomes and what is the mechanistic basis for this pleiotropy. Here, we generate a murine model for the Slc39a8 A391T allele and demonstrate that these mice exhibit Mn deficiency in the colon associated with impaired intestinal barrier function and epithelial glycocalyx disruption. Consequently, Slc39a8 A391T mice exhibit increased sensitivity to epithelial injury and pathological inflammation in the colon. Taken together, our results link a genetic variant with a dietary trace element to shed light on a tissue-specific mechanism of disease risk based on impaired intestinal barrier integrity.

QRICH1 dictates the outcome of ER stress through transcriptional control of proteostasis.

Tissue homeostasis is perturbed in a diversity of inflammatory pathologies. These changes can elicit endoplasmic reticulum (ER) stress, protein misfolding, and cell death. ER stress triggers the unfolded protein response (UPR), which can promote recovery of ER proteostasis and cell survival or trigger programmed cell death. Here, we leveraged single-cell RNA sequencing to define dynamic transcriptional states associated with the adaptive versus terminal UPR in the mouse intestinal epithelium. We integrated these transcriptional programs with genome-scale CRISPR screening to dissect the UPR pathway functionally. We identified QRICH1 as a key effector of the PERK-eIF2α axis of the UPR. QRICH1 controlled a transcriptional program associated with translation and secretory networks that were specifically up-regulated in inflammatory pathologies. Thus, QRICH1 dictates cell fate in response to pathological ER stress.

C1orf106 is a colitis risk gene that regulates stability of epithelial adherens junctions.

Polymorphisms in C1orf106 are associated with increased risk of inflammatory bowel disease (IBD). However, the function of C1orf106 and the consequences of disease-associated polymorphisms are unknown. Here we demonstrate that C1orf106 regulates adherens junction stability by regulating the degradation of cytohesin-1, a guanine nucleotide exchange factor that controls activation of ARF6. By limiting cytohesin-1-dependent ARF6 activation, C1orf106 stabilizes adherens junctions. Consistent with this model, C1orf106-/- mice exhibit defects in the intestinal epithelial cell barrier, a phenotype observed in IBD patients that confers increased susceptibility to intestinal pathogens. Furthermore, the IBD risk variant increases C1orf106 ubiquitination and turnover with consequent functional impairments. These findings delineate a mechanism by which a genetic polymorphism fine-tunes intestinal epithelial barrier integrity and elucidate a fundamental mechanism of cellular junctional control.

Central Ghrelin Resistance Permits the Overconsolidation of Fear Memory.

BACKGROUND: There are many contradictory findings about the role of the hormone ghrelin in aversive processing, with studies suggesting that ghrelin signaling can both inhibit and enhance aversion. Here, we characterize and reconcile the paradoxical role of ghrelin in the acquisition of fearful memories. METHODS: We used enzyme-linked immunosorbent assay to measure endogenous acyl-ghrelin and corticosterone at time points surrounding auditory fear learning. We used pharmacological (systemic and intra-amygdala) manipulations of ghrelin signaling and examined several aversive and appetitive behaviors. We also used biotin-labeled ghrelin to visualize ghrelin binding sites in coronal brain sections of amygdala. All work was performed in rats. RESULTS: In unstressed rodents, endogenous peripheral acyl-ghrelin robustly inhibits fear memory consolidation through actions in the amygdala and accounts for virtually all interindividual variability in long-term fear memory strength. Higher levels of endogenous ghrelin after fear learning were associated with weaker long-term fear memories, and pharmacological agonism of the ghrelin receptor during the memory consolidation period reduced fear memory strength. These fear-inhibitory effects cannot be explained by changes in appetitive behavior. In contrast, we show that chronic stress, which increases both circulating endogenous acyl-ghrelin and fear memory formation, promotes profound loss of ghrelin binding sites in the amygdala and behavioral insensitivity to ghrelin receptor agonism. CONCLUSIONS: These studies provide a new link between stress, a novel type of metabolic resistance, and vulnerability to excessive fear memory formation and reveal that ghrelin can regulate negative emotionality in unstressed animals without altering appetite.

Stress Enables Reinforcement-Elicited Serotonergic Consolidation of Fear Memory.

BACKGROUND: Prior exposure to stress is a risk factor for developing posttraumatic stress disorder (PTSD) in response to trauma, yet the mechanisms by which this occurs are unclear. Using a rodent model of stress-based susceptibility to PTSD, we investigated the role of serotonin in this phenomenon. METHODS: Adult mice were exposed to repeated immobilization stress or handling, and the role of serotonin in subsequent fear learning was assessed using pharmacologic manipulation and western blot detection of serotonin receptors, measurements of serotonin, high-speed optogenetic silencing, and behavior. RESULTS: Both dorsal raphe serotonergic activity during aversive reinforcement and amygdala serotonin 2C receptor (5-HT2CR) activity during memory consolidation were necessary for stress enhancement of fear memory, but neither process affected fear memory in unstressed mice. Additionally, prior stress increased amygdala sensitivity to serotonin by promoting surface expression of 5-HT2CR without affecting tissue levels of serotonin in the amygdala. We also showed that the serotonin that drives stress enhancement of associative cued fear memory can arise from paired or unpaired footshock, an effect not predicted by theoretical models of associative learning. CONCLUSIONS: Stress bolsters the consequences of aversive reinforcement, not by simply enhancing the neurobiological signals used to encode fear in unstressed animals, but rather by engaging distinct mechanistic pathways. These results reveal that predictions from classical associative learning models do not always hold for stressed animals and suggest that 5-HT2CR blockade may represent a promising therapeutic target for psychiatric disorders characterized by excessive fear responses such as that observed in PTSD.

Restoration of hippocampal growth hormone reverses stress-induced hippocampal impairment.

Though growth hormone (GH) is synthesized by hippocampal neurons, where its expression is influenced by stress exposure, its function is poorly characterized. Here, we show that a regimen of chronic stress that impairs hippocampal function in rats also leads to a profound decrease in hippocampal GH levels. Restoration of hippocampal GH in the dorsal hippocampus via viral-mediated gene transfer completely reversed stress-related impairment of two hippocampus-dependent behavioral tasks, auditory trace fear conditioning, and contextual fear conditioning, without affecting hippocampal function in unstressed control rats. GH overexpression reversed stress-induced decrements in both fear acquisition and long-term fear memory. These results suggest that loss of hippocampal GH contributes to hippocampal dysfunction following prolonged stress and demonstrate that restoring hippocampal GH levels following stress can promote stress resilience.