Loss of Rab27 function results in abnormal lung epithelium structure in mice

Rab27a-mediated exosome secretion in anterior cingulate cortex contributes to colorectal visceral pain in adult mice with neonatal maternal deprivation

Chronic visceral pain is a common symptom of irritable bowel syndrome (IBS). Exosomes are involved in the development of pain. Rab27a can mediate the release of exosomes. The purpose of this study is to investigate how Rab27a-mediated exosome secretion in the anterior cingulate cortex (ACC) regulates visceral hyperalgesia induced with neonatal maternal deprivation (NMD) in adult mice. The colorectal distension method was adopted to measure visceral pain. The BCA protein assay kit was applied to detect the exosome protein concentration. Western blotting, quantitative PCR, and immunofluorescence technique were adopted to detect the expression of Rab27a and the markers of exosomes. Exosomes extracted from ACC were more in NMD mice than in control (CON) mice. Injection of the exosome-specific inhibitor GW4869 in ACC attenuated colorectal visceral pain of NMD mice. Injection of NMD-derived exosomes produced colorectal visceral pain in CON mice. Rab27a was upregulated in ACC of NMD mice. Rab27a was highly expressed in ACC neurons of NMD mice, rather than astrocytes and microglia. Injection of Rab27a-siRNA reduced the release of exosomes and attenuated the colorectal visceral pain in NMD mice. This study suggested that overexpression of Rab27a increased exosome secretion in ACC neurons, thus contributing to visceral hyperalgesia in NMD mice.NEW & NOTEWORTHY This work demonstrated that the expression of Rab27a in the anterior cingulate cortex was upregulated, which mediated multivesicular bodies trafficking to the plasma membrane and led to the increased release of neuronal exosomes, thus contributing to colorectal visceral pain in neonatal maternal deprivation (NMD) mice. Blocking the release of exosomes or downregulation of Rab27a could alleviate colorectal visceral pain in NMD mice. These data may provide a promising strategy for the treatment of visceral pain in irritable bowel syndrome patients.

Deletion in chromosome 6 spanning alpha-synuclein and multimerin1 loci in the Rab27a/b double knockout mouse

We report an incidental 358.5 kb deletion spanning the region encoding for alpha-synuclein (αsyn) and multimerin1 (Mmrn1) in the Rab27a/Rab27b double knockout (DKO) mouse line previously developed by Tolmachova and colleagues in 2007. Western blot and RT-PCR studies revealed lack of αsyn expression at either the mRNA or protein level in Rab27a/b DKO mice. PCR of genomic DNA from Rab27a/b DKO mice demonstrated at least partial deletion of the Snca locus using primers targeted to exon 4 and exon 6. Most genes located in proximity to the Snca locus, including Atoh1, Atoh2, Gm5570, Gm4410, Gm43894, and Grid2, were shown not to be deleted by PCR except for Mmrn1. Using whole genomic sequencing, the complete deletion was mapped to chromosome 6 (60,678,870–61,037,354), a slightly smaller deletion region than that previously reported in the C57BL/6J substrain maintained by Envigo. Electron microscopy of cortex from these mice demonstrates abnormally enlarged synaptic terminals with reduced synaptic vesicle density, suggesting potential interplay between Rab27 isoforms and αsyn, which are all highly expressed at the synaptic terminal. Given this deletion involving several genes, the Rab27a/b DKO mouse line should be used with caution or with appropriate back-crossing to other C57BL/6J mouse substrain lines without this deletion.

Exophilin-5 regulates allergic airway inflammation by controlling IL-33-mediated Th2 responses

A common variant in the RAB27A gene in adults was recently found to be associated with the fractional exhaled nitric oxide level, a marker of eosinophilic airway inflammation. The small GTPase Rab27 is known to regulate intracellular vesicle traffic, although its role in allergic responses is unclear. We demonstrated that exophilin-5, a Rab27-binding protein, was predominantly expressed in both of the major IL-33 producers, lung epithelial cells, and the specialized IL-5 and IL-13 producers in the CD44hiCD62LloCXCR3lo pathogenic Th2 cell population in mice. Exophilin-5 deficiency increased stimulant-dependent damage and IL-33 secretion by lung epithelial cells. Moreover, it enhanced IL-5 and IL-13 production in response to TCR and IL-33 stimulation from a specific subset of pathogenic Th2 cells that expresses a high level of IL-33 receptor, which exacerbated allergic airway inflammation in a mouse model of asthma. Mechanistically, exophilin-5 regulates extracellular superoxide release, intracellular ROS production, and phosphoinositide 3-kinase activity by controlling intracellular trafficking of Nox2-containing vesicles, which seems to prevent the overactivation of pathogenic Th2 cells mediated by IL-33. This is the first report to our knowledge to establish the significance of the Rab27-related protein exophilin-5 in the development of allergic airway inflammation, and provides insights into the pathophysiology of asthma.

Effects of Cell-Derived Microparticles on Immune Cells and Potential Implications in Clinical Medicine

In the past few years, interest has increased in cell-derived microparticles (MPs), which are defined by their size of from 0.1 to 1 μm, and can be derived from various cell types, including endothelial cells, leukocytes, red blood cells (RBCs), and platelets. These MPs carry negatively charged phosphatidylserine (PS) on their surfaces and proteins packaged from numerous cellular components. MPs that have been shed by the body can play important roles in the pathophysiology of diseases and can affect various biological systems. Among these systems, the immune components have been shown to be modulated by MPs. Therefore, understanding the roles of MPs in the immune system is crucial to developing alternative therapeutic treatments for diseases. This review describes the effects of MPs on various immune cells and provides plausible potential applications of the immune-modulating properties of MPs in clinical medicine.

Rab27a Contributes to the Processing of Inflammatory Pain in Mice

Tissue injury and inflammation may result in chronic pain, a severe debilitating disease that is associated with great impairment of quality of life. An increasing body of evidence indicates that members of the Rab family of small GTPases contribute to pain processing; however, their specific functions remain poorly understood. Here, we found using immunofluorescence staining and in situ hybridization that the small GTPase Rab27a is highly expressed in sensory neurons and in the superficial dorsal horn of the spinal cord of mice. Rab27a mutant mice, which carry a single-nucleotide missense mutation of Rab27a leading to the expression of a nonfunctional protein, show reduced mechanical hyperalgesia and spontaneous pain behavior in inflammatory pain models, while their responses to acute noxious mechanical and thermal stimuli is not affected. Our study uncovers a previously unrecognized function of Rab27a in the processing of persistent inflammatory pain in mice.

Use of induced pluripotent stem cell models to probe the pathogenesis of Choroideremia and to develop a potential treatment

Choroideremia (CHM) is a rare monogenic, X-linked recessive inherited retinal degeneration resulting from mutations in the Rab Escort Protein-1 (REP1) encoding CHM gene. The primary retinal cell type leading to CHM is unknown. In this study, we explored the utility of induced pluripotent stem cell-derived models of retinal pigmented epithelium (iPSC-RPE) to study disease pathogenesis and a potential gene-based intervention in four different genetically distinct forms of CHM. A number of abnormal cell biologic, biochemical, and physiologic functions were identified in the CHM mutant cells. We then identified a recombinant adeno-associated virus (AAV) serotype, AAV7m8, that is optimal for both delivering transgenes to iPSC-RPEs as well as to appropriate target cells (RPE cells and rod photoreceptors) in the primate retina. To establish the proof of concept of AAV7m8 mediated CHM gene therapy, we developed AAV7m8.hCHM, which delivers the human CHM cDNA under control of CMV-enhanced chicken β-actin promoter (CßA). Delivery of AAV7m8.hCHM to CHM iPSC-RPEs restored protein prenylation, trafficking and phagocytosis. The results confirm that AAV-mediated delivery of the REP1-encoding gene can rescue defects in CHM iPSC-RPE regardless of the type of disease-causing mutation. The results also extend our understanding of mechanisms involved in the pathophysiology of choroideremia.

A common variant in RAB27A gene is associated with fractional exhaled nitric oxide levels in adults

BACKGROUND

Exhaled nitric oxide (FeNO) is a biomarker for eosinophilic inflammation in the airways and for responsiveness to corticosteroids in asthmatics.

OBJECTIVE

We sought to identify in adults the genetic determinants of fractional exhaled nitric oxide (FeNO) levels and to assess whether environmental and disease-related factors influence these associations.

METHODS

We performed a genome-wide association study of FeNO through meta-analysis of two independent discovery samples of European ancestry: the outbred EGEA study (French Epidemiological study on the Genetics and Environment of Asthma, N = 610 adults) and the Hutterites (N = 601 adults), a founder population living on communal farms. Replication of main findings was assessed in adults from an isolated village in Sardinia (Talana study, N = 450). We then investigated the influence of asthma, atopy and tobacco smoke exposure on these genetic associations, and whether they were also associated with FeNO values in children of the EAGLE (EArly Genetics & Lifecourse Epidemiology, N = 8858) consortium.

RESULTS

We detected a common variant in RAB27A (rs2444043) associated with FeNO that reached the genome-wide significant level (P = 1.6 × 10(-7) ) in the combined discovery and replication adult data sets. This SNP belongs to member of RAS oncogene family (RAB27A) and was associated with an expression quantitative trait locus for RAB27A in lymphoblastoid cell lines from asthmatics. A second suggestive locus (rs2194437, P = 8.9 × 10(-7) ) located nearby the sodium/calcium exchanger 1 (SLC8A1) was mainly detected in atopic subjects and influenced by inhaled corticosteroid use. These two loci were not associated with childhood FeNO values.

CONCLUSIONS AND CLINICAL RELEVANCE

This study identified a common variant located in RAB27A gene influencing FeNO levels specifically in adults and with a biological relevance to the regulation of FeNO levels. This study provides new insight into the biological mechanisms underlying FeNO levels in adults.

MicroRNA-containing T-regulatory-cell-derived exosomes suppress pathogenic T helper 1 cells

Foxp3(+) T regulatory (Treg) cells prevent inflammatory disease but the mechanistic basis of suppression is not understood completely. Gene silencing by RNA interference can act in a cell-autonomous and non-cell-autonomous manner, providing mechanisms of intercellular regulation. Here, we demonstrate that non-cell-autonomous gene silencing, mediated by miRNA-containing exosomes, is a mechanism employed by Treg cells to suppress T-cell-mediated disease. Treg cells transferred microRNAs (miRNA) to various immune cells, including T helper 1 (Th1) cells, suppressing Th1 cell proliferation and cytokine secretion. Use of Dicer-deficient or Rab27a and Rab27b double-deficient Treg cells to disrupt miRNA biogenesis or the exosomal pathway, respectively, established a requirement for miRNAs and exosomes for Treg-cell-mediated suppression. Transcriptional analysis and miRNA inhibitor studies showed that exosome-mediated transfer of Let-7d from Treg cell to Th1 cells contributed to suppression and prevention of systemic disease. These studies reveal a mechanism of Treg-cell-mediated suppression mediated by miRNA-containing exosomes.

Reduced expression level of the cyclic adenosine monophosphate response element-binding protein contributes to lung aging

Lung aging is associated with morphological and physiological changes in which alterations in transcription factors, including the cyclic adenosine monophosphate response element-binding protein (CREB), could play a role. We studied CREB in lung tissue from mice at different ages and in response to known age-related factors (e.g., cellular senescence and matrix modifications with advanced glycation end-products [AGEs]). Our study shows that protein but not mRNA levels of CREB are reduced in the lungs of old mice. CREB reduction was also observed in senescent human lung fibroblasts (WI-38, LuFi) and human lung epithelial cells (A549) cultured on AGE-modified collagen matrix. Reduction of CREB protein is partially based on pre- and posttranslational modifications as exhibited by an increase in the CREB-regulating microRNA 34b and CREB ubiquitination. Permanent down-regulation of CREB in lung cells impaired cell proliferation and viability and increased the number of cells with senescence-associated β-galactosidase activity. CREB down-regulation was accompanied by the reduced expression of 165 genes in WI-38 fibroblasts and A549 epithelial cells, of which 15 genes showed a reduced expression in lung tissues of old mice. The CREB-dependent reduction in RAB27A coding for the Ras-related protein Rab27A and IGFBP3 coding for the insulin-like growth factor-binding protein 3 has been confirmed for aged lung tissue, senescent fibroblasts, and lung epithelial cells on AGE-modified collagen. Our data demonstrate that the reduced protein expression of CREB might play a significant role in lung aging by modifying the transcription of RAB27A, IGFBP3, and other target genes.

Persistence of LPS-induced lung inflammation in surfactant protein-C-deficient mice

Pulmonary surfactant protein-C (SP-C) gene-targeted mice (Sftpc(-/-)) develop progressive lung inflammation and remodeling. We hypothesized that SP-C deficiency reduces the ability to suppress repetitive inflammatory injury. Sftpc(+/+) and Sftpc(-/-) mice given three doses of bacterial LPS developed airway and airspace inflammation, which was more intense in the Sftpc(-/-) mice at 3 and 5 days after the final dose. Compared with Sftpc(+/+)mice, inflammatory injury persisted in the lungs of Sftpc(-/-) mice 30 days after the final LPS challenge. Sftpc(-/-) mice showed LPS-induced airway goblet cell hyperplasia with increased detection of Sam pointed Ets domain and FoxA3 transcription factors. Sftpc(-/-) type II alveolar epithelial cells had increased cytokine expression after LPS exposure relative to Sftpc(+/+) cells, indicating that type II cell dysfunction contributes to inflammatory sensitivity. Microarray analyses of isolated type II cells identified a pattern of enhanced expression of inflammatory genes consistent with an intrinsic low-level inflammation resulting from SP-C deficiency. SP-C-containing clinical surfactant extract (Survanta) or SP-C/phospholipid vesicles blocked LPS signaling through the LPS receptor (Toll-like receptor [TLR] 4/CD14/MD2) in human embryonic kidney 293T cells, indicating that SP-C blocks LPS-induced cytokine production by a TLR4-dependent mechanism. Phospholipid vesicles alone did not modify the TLR4 response. In vivo deficiency of SP-C leads to inflammation, increased cytokine production by type II cells, and persistent inflammation after repetitive LPS stimulation.

Proinflammatory role of epithelial cell-derived exosomes in allergic airway inflammation

BACKGROUND

Exosomes are nanovesicles involved in intercellular communication. Their roles in various diseases are often contextual, depending on the cell type producing them. Although few studies hint toward the proinflammatory role of bronchoalveolar lavage fluid-derived exosomes in asthmatic progression, the cell types in lungs associated with exosome-mediated crosstalk and their resultant effects remain unexplored.

OBJECTIVE

It is well established that exosome-mediated cellular communication can influence disease phenotypes. This study explores exosome-mediated cellular crosstalk between structural and immune cells in asthma pathogenesis.

METHODS

Exosomes were isolated and detected from bronchoalveolar lavage fluid of control and asthmatic mice and were quantified by using a bead-based assay. Involvement of epithelial cells and macrophages were established by using immunohistochemical techniques in lung tissue sections. The role of IL-13 in exosome production was ascertained by using various in vitro and in vivo techniques. Exosome secretion was blocked in in vitro and in vivo settings by using a chemical inhibitor, and the effects on various asthmatic features were studied.

RESULTS

Using combinatorial in vitro and in vivo approaches, we found that exosome secretion and production of exosome-associated proteins are higher in lungs of asthmatic mice compared with that seen in sham mice. Asthma is marked by enhanced secretion of exosomes by epithelial cells, but not macrophages, under the influence of IL-13. These epithelial cell exosomes induce proliferation and chemotaxis of undifferentiated macrophages. On the other hand, GW4869, which inhibited exosome production, resulted in a reduced population of proliferating monocytes and alleviation of various asthmatic features.

CONCLUSION

Under the influence of IL-13, epithelial cell-derived exosomes can induce enhanced proliferation and chemotaxis of undifferentiated macrophages in the lungs during asthmatic inflammatory conditions.

Synaptotagmin-like proteins control the formation of a single apical membrane domain in epithelial cells

The formation of epithelial tissues requires both the generation of apical-basal polarity and the coordination of this polarity between neighbouring cells to form a central lumen. During de novo lumen formation, vectorial membrane transport contributes to the formation of a singular apical membrane, resulting in the contribution of each cell to only a single lumen. Here, from a functional screen for genes required for three-dimensional epithelial architecture, we identify key roles for synaptotagmin-like proteins 2-a and 4-a (Slp2-a/4-a) in the generation of a single apical surface per cell. Slp2-a localizes to the luminal membrane in a PtdIns(4,5)P(2)-dependent manner, where it targets Rab27-loaded vesicles to initiate a single lumen. Vesicle tethering and fusion is controlled by Slp4-a, in conjunction with Rab27/Rab3/Rab8 and the SNARE syntaxin-3. Together, Slp2-a/4-a coordinate the spatiotemporal organization of vectorial apical transport to ensure that only a single apical surface, and thus the formation of a single lumen, occurs per cell.

PI3K p110α/Akt signaling negatively regulates secretion of the intestinal peptide neurotensin through interference of granule transport

Neurotensin (NT), an intestinal peptide secreted from N cells in the small bowel, regulates a variety of physiological functions of the gastrointestinal tract, including secretion, gut motility, and intestinal growth. The class IA phosphatidylinositol 3-kinase (PI3K) family, which comprised of p110 catalytic (α, β and δ) and p85 regulatory subunits, has been implicated in the regulation of hormone secretion from endocrine cells. However, the underlying mechanisms remain poorly understood. In particular, the role of PI3K in intestinal peptide secretion is not known. Here, we show that PI3K catalytic subunit, p110α, negatively regulates NT secretion in vitro and in vivo. We demonstrate that inhibition of p110α, but not p110β, induces NT release in BON, a human endocrine cell line, which expresses NT mRNA and produces NT peptide in a manner analogous to N cells, and QGP-1, a pancreatic endocrine cell line that produces NT peptide. In contrast, overexpression of p110α decreases NT secretion. Consistently, p110α-inhibition increases plasma NT levels in mice. To further delineate the mechanisms contributing to this effect, we demonstrate that inhibition of p110α increases NT granule trafficking by up-regulating α-tubulin acetylation; NT secretion is prevented by overexpression of HDAC6, an α-tubulin deacetylase. Moreover, ras-related protein Rab27A (a small G protein) and kinase D-interacting substrate of 220 kDa (Kidins220), which are associated with NT granules, play a negative and positive role, respectively, in p110α-inhibition-induced NT secretion. Our findings identify the critical role and novel mechanisms for the PI3K signaling pathway in the control of intestinal hormone granule transport and release.