Faculty Bibliography

Inflammation of human bronchial epithelia (HBE) activates the endoplasmic reticulum (ER) stress transducer inositol-requiring enzyme 1 (IRE1)alpha, resulting in IRE1alpha-mediated cytokine production. Previous studies demonstrated ubiquitous expression of IRE1alpha and gut-restricted expression of IRE1beta. We found that IRE1beta is also expressed in HBE, is absent in human alveolar cells, and is upregulated in cystic fibrosis and asthmatic HBE. Studies with Ire1beta(-/-) mice and Calu-3 airway epithelia exhibiting IRE1beta knockdown or overexpression revealed that IRE1beta is expressed in airway mucous cells, is functionally required for airway mucin production, and this function is specific for IRE1beta vs. IRE1alpha. IRE1beta-dependent mucin production is mediated, at least in part, by activation of the transcription factor X-box binding protein-1 (XBP-1) and the resulting XBP-1-dependent transcription of anterior gradient homolog 2, a gene implicated in airway and intestinal epithelial mucin production. These novel findings suggest that IRE1beta is a potential mucous cell-specific therapeutic target for airway diseases characterized by mucin overproduction.

MicroRNAs (miRNAs) are small, ~22 nucleotide (nt) sequences of RNA that regulate gene expression at posttranscriptional level. These endogenous gene expression inhibitors were primarily described in cancer but recent exciting findings have also demonstrated a key role in cardiovascular diseases (CVDs), including atherosclerosis. MiRNAs control endothelial cell (EC), vascular smooth muscle cell (VSMC), and macrophage functions, and thereby regulate the progression of atherosclerosis. MiRNA expression is modulated by different stimuli involved in every stage of atherosclerosis, and conversely miRNAs modulates several pathways implicated in plaque development such as cholesterol metabolism. In the present review, we focus on the importance of miRNAs in atherosclerosis, and we further discuss their potential use as biomarkers and therapeutic targets in CVDs.

Eukaryotic cells respond to stress caused by the accumulation of unfolded/misfolded proteins in the endoplasmic reticulum by activating the intracellular signaling pathways referred to as the unfolded protein response (UPR). In metazoans, UPR consists of three parallel branches, each characterized by its stress sensor protein, IRE1, ATF6, and PERK, respectively. In Drosophila, IRE1/XBP1 pathway is considered to function as a major branch of UPR; however, its physiological roles during the normal development and homeostasis remain poorly understood. To visualize IRE1/XBP1 activity in fly tissues under normal physiological conditions, we modified previously reported XBP1 stress sensing systems (Souid et al., Dev Genes Evol 217: 159-167, 2007; Ryoo et al., EMBO J 26: 242-252, 2007), based on the recent reports regarding the unconventional splicing of XBP1/HAC1 mRNA (Aragon et al., Nature 457: 736-740, 2009; Yanagitani et al., Mol Cell 34: 191-200, 2009; Science 331: 586-589, 2011). The improved XBP1 stress sensing system allowed us to detect new IRE1/XBP1 activities in the brain, gut, Malpighian tubules, and trachea of third instar larvae and in the adult male reproductive organ. Specifically, in the larval brain, IRE1/XBP1 activity was detected exclusively in glia, although previous reports have largely focused on IRE1/XBP1 activity in neurons. Unexpected glial IRE1/XBP1 activity may provide us with novel insights into the brain homeostasis regulated by the UPR.

OBJECTIVE: Emerging evidence suggests that neuronal guidance cues, typically expressed during development, are involved in both physiological and pathological immune responses. We hypothesized that endothelial expression of such guidance cues may regulate leukocyte trafficking into the vascular wall during atherogenesis. Approach and Results- We demonstrate that members of the netrin, semaphorin, and ephrin family of guidance molecules are differentially regulated under conditions that promote or protect from atherosclerosis. Netrin-1 and semaphorin3A are expressed by coronary artery endothelial cells and potently inhibit chemokine-directed migration of human monocytes. Endothelial expression of these negative guidance cues is downregulated by proatherogenic factors, including oscillatory shear stress and proinflammatory cytokines associated with monocyte entry into the vessel wall. Furthermore, we show using intravital microscopy that inhibition of netrin-1 or semaphorin3A using blocking peptides increases leukocyte adhesion to the endothelium. Unlike netrin-1 and semaphorin3A, the guidance cue ephrinB2 is upregulated under proatherosclerotic flow conditions and functions as a chemoattractant, increasing leukocyte migration in the absence of additional chemokines. CONCLUSIONS: The concurrent regulation of negative and positive guidance cues may facilitate leukocyte infiltration of the endothelium through a balance between chemoattraction and chemorepulsion. These data indicate a previously unappreciated role for axonal guidance cues in maintaining the endothelial barrier and regulating leukocyte trafficking during atherogenesis.

OBJECTIVE: The persistence of myeloid-derived cells in the artery wall is a characteristic of advanced atherosclerotic plaques. However, the mechanisms by which these cells are retained are poorly understood. Semaphorins, a class of neuronal guidance molecules, play a critical role in vascular patterning and development, and recent studies suggest that they may also have immunomodulatory functions. The present study evaluates the expression of Semaphorin 3E (Sema3E) in settings relevant to atherosclerosis and its contribution to macrophage accumulation in plaques. Approach and Results- Immunofluorescence staining of Sema3E, and its receptor PlexinD1, demonstrated their expression in macrophages of advanced atherosclerotic lesions of Apoe(-/-) mice. Notably, in 2 different mouse models of atherosclerosis regression, Sema3E mRNA was highly downregulated in plaque macrophages, coincident with a reduction in plaque macrophage content and an enrichment in markers of reparative M2 macrophages. In vitro, Sema3E mRNA was highly expressed in inflammatory M1 macrophages and in macrophages treated with physiological drivers of plaque progression and inflammation, such as oxidized low-density lipoprotein and hypoxia. To explore mechanistically how Sema3E affects macrophage behavior, we treated macrophages with recombinant protein in the presence/absence of chemokines, including CCL19, a chemokine implicated in the egress of macrophages from atherosclerotic plaques. Sema3E blocked actin polymerization and macrophage migration stimulated by the chemokines, suggesting that it may immobilize these cells in the plaque. CONCLUSIONS: Sema3E is upregulated in macrophages of advanced plaques, is dynamically regulated by multiple atherosclerosis-relevant factors, and acts as a negative regulator of macrophage migration, which may promote macrophage retention and chronic inflammation in vivo.

Sharply delineated domains of cell types arise in developing tissues under instruction of inductive signal (morphogen) gradients, which specify distinct cell fates at different signal levels. The translation of a morphogen gradient into discrete spatial domains relies on precise signal responses at stable cell positions. However, cells in developing tissues undergoing morphogenesis and proliferation often experience complex movements, which may affect their morphogen exposure, specification, and positioning. How is a clear pattern achieved with cells moving around? Using in toto imaging of the zebrafish neural tube, we analyzed specification patterns and movement trajectories of neural progenitors. We found that specified progenitors of different fates are spatially mixed following heterogeneous Sonic Hedgehog signaling responses. Cell sorting then rearranges them into sharply bordered domains. Ectopically induced motor neuron progenitors also robustly sort to correct locations. Our results reveal that cell sorting acts to correct imprecision of spatial patterning by noisy inductive signals.

Laboratory-reared Caenorhabditis elegans eat Escherichia coli. A new study demonstrates a strong diet-gene interaction: worms with reduced nhr-114 activity are fertile when fed E. coli K-12 strains but are sterile on E. coli B. Surprisingly, tryptophan supplementation of E. coli B restores worm fertility.

Why patients with chronic kidney disease have elevated cardiovascular risk remains elusive. In this issue of Immunity, Speer et al. (2013) show that natural modification of high density lipoprotein promotes hypertension through a toll-like receptor-dependent mechanism.

Endosomal sorting of the Alzheimer amyloid precursor protein (APP) plays a key role in the biogenesis of the amyloid-beta (Abeta) peptide. Genetic lesions underlying Alzheimer's disease (AD) can act by interfering with this physiological process. Specifically, proteins involved in trafficking between endosomal compartments and the trans-Golgi network (TGN) [including the retromer complex (Vps35, Vps26) and its putative receptors (sortilin, SorL1, SorCS1)] have been implicated in the molecular pathology of late-onset AD. Previously, we demonstrated a role for SorCS1 in APP metabolism and Abeta production and, while we implicated a role for the retromer in this regulation, the underlying mechanism remained poorly understood. Here, we provide evidence for a motif within the SorCS1c cytoplasmic tail that, when manipulated, results in perturbed sorting of APP and/or its fragments to endosomal compartments, decreased retrograde TGN trafficking, and increased Abeta production in H4 neuroglioma cells. These perturbations apparently do not involve turnover of the cell surface APP pool, but rather they involve intracellular APP and/or its fragments, downstream of APP endocytosis.