Intestinal phenotype of variable-weight cystic fibrosis knockout mice

Impaired intestinal free fatty acid transport followed by chylomicron malformation, not pancreatic insufficiency, cause metabolic defects in cystic fibrosis

Intestinal disease is one of the earliest manifestations of cystic fibrosis (CF) in children and is closely tied to deficits in growth and nutrition, both of which are directly linked to future mortality. Patients are treated aggressively with pancreatic enzyme replacement therapy and a high-fat diet to circumvent fat malabsorption, but this does not reverse growth and nutritional defects. We hypothesized that defects in chylomicron production could explain why CF body weights and nutrition are so resistant to clinical treatments. We used gold standard intestinal lipid absorption and metabolism approaches, including mouse mesenteric lymph cannulation, in vivo chylomicron secretion kinetics, transmission electron microscopy, small intestinal organoids, and chylomicron metabolism assays to test this hypothesis. In mice expressing the G542X mutation in cystic fibrosis transmembrane conductance regulator (CFTR-/- mice), we find that defective FFA trafficking across the epithelium into enterocytes drives a chylomicron formation defect. Furthermore, G542X mice secrete small, triglyceride-poor chylomicrons into the lymph and blood. These defective chylomicrons are cleared into extraintestinal tissues at ∼10-fold faster than WT chylomicrons. This defect in FFA absorption resulting in dysfunctional chylomicrons cannot be explained by steatorrhea or pancreatic insufficiency and is maintained in primary small intestinal organoids treated with micellar lipids. These studies suggest that the ultrahigh-fat diet that most people with CF are counselled to follow may instead make steatorrhea and malabsorption defects worse by overloading the absorptive capacity of the CF small intestine.

Goblet cell hyperplasia is not epithelial-autonomous in the Cftr knockout intestine

Goblet cell hyperplasia is an important manifestation of cystic fibrosis (CF) disease in epithelial-lined organs. Explants of CF airway epithelium show normalization of goblet cell numbers; therefore, we hypothesized that small intestinal enteroids from Cftr knockout (KO) mice would not exhibit goblet cell hyperplasia. Toll-like receptors 2 and 4 (Tlr2 and Tlr4) were investigated as markers of inflammation and influence on goblet cell differentiation. Ex vivo studies found goblet cell hyperplasia in Cftr KO jejunum compared with wild-type (WT) mice. IL-13, SAM pointed domain-containing ETS transcription factor (Spdef), Tlr2, and Tlr4 protein expression were increased in Cftr KO intestine relative to WT. In contrast, WT and Cftr KO enteroids did not exhibit differences in basal or IL-13-stimulated goblet cell numbers, or differences in expression of Tlr2, Tlr4, and Spdef. Ileal goblet cell numbers in Cftr KO/Tlr4 KO and Cftr KO/Tlr2 KO mice were not different from Cftr KO mice, but enumeration was confounded by altered mucosal morphology. Treatment with Tlr4 agonist LPS did not affect goblet cell numbers in WT or Cftr KO enteroids, whereas the Tlr2 agonist Pam3Csk4 stimulated goblet cell hyperplasia in both genotypes. Pam3Csk4 stimulation of goblet cell numbers was associated with suppression of Notch1 and Neurog3 expression and upregulated determinants of goblet cell differentiation. We conclude that goblet cell hyperplasia and inflammation of the Cftr KO small intestine are not exhibited by enteroids, indicating that this manifestation of CF intestinal disease is not epithelial-automatous but secondary to the altered CF intestinal environment.NEW & NOTEWORTHY Studies of small intestinal organoids from cystic fibrosis (CF) mice show that goblet cell hyperplasia and increased Toll-like receptor 2/4 expression are not primary manifestations of the CF intestine. Intestinal goblet cell hyperplasia in the CF mice was not strongly altered by genetic ablation of Tlr2 and Tlr 4, but could be induced in both wild-type and CF intestinal organoids by a Tlr2-dependent suppression of Notch signaling.

Inferred inactivation of the Cftr gene in the duodena of mice exposed to hexavalent chromium (Cr(VI)) in drinking water supports its tumor-suppressor status and implies its potential role in Cr(VI)-induced carcinogenesis of the small intestines

Carcinogenicity of hexavalent chromium [Cr (VI)] has been supported by a number of epidemiological and animal studies; however, its carcinogenic mode of action is still incompletely understood. To identify mechanisms involved in cancer development, we analyzed gene expression data from duodena of mice exposed to Cr(VI) in drinking water. This analysis included (i) identification of upstream regulatory molecules that are likely responsible for the observed gene expression changes, (ii) identification of annotated gene expression data from public repositories that correlate with gene expression changes in duodena of Cr(VI)-exposed mice, and (iii) identification of hallmark and oncogenic signature gene sets relevant to these data. We identified the inactivated CFTR gene among the top scoring upstream regulators, and found positive correlations between the expression data from duodena of Cr(VI)-exposed mice and other datasets in public repositories associated with the inactivation of the CFTR gene. In addition, we found enrichment of signatures for oncogenic signaling, sustained cell proliferation, impaired apoptosis and tissue remodeling. Results of our computational study support the tumor-suppressor role of the CFTR gene. Furthermore, our results support human relevance of the Cr(VI)-mediated carcinogenesis observed in the small intestines of exposed mice and suggest possible groups that may be more vulnerable to the adverse outcomes associated with the inactivation of CFTR by hexavalent chromium or other agents. Lastly, our findings predict, for the first time, the role of CFTR inactivation in chemical carcinogenesis and expand the range of plausible mechanisms that may be operative in Cr(VI)-mediated carcinogenesis of intestinal and possibly other tissues.

Secretion of Acid Sphingomyelinase and Ceramide by Endothelial Cells Contributes to Radiation-Induced Intestinal Toxicity

Ceramide-induced endothelial cell apoptosis boosts intestinal stem cell radiosensitivity. However, the molecular connection between these two cellular compartments has not been clearly elucidated. Here we report that ceramide and its related enzyme acid sphingomyelinase (ASM) are secreted by irradiated endothelial cells and act as bystander factors to enhance the radiotoxicity of intestinal epithelium. Ceramide and the two isoforms of ASM were acutely secreted in the blood serum of wild-type mice after 15 Gy radiation dose, inducing a gastrointestinal syndrome. Interestingly, serum ceramide was not enhanced in irradiated ASMKO mice, which are unable to develop intestinal failure injury. Because ASM/ceramide were secreted by primary endothelial cells, their contribution was studied in intestinal epithelium dysfunction using coculture of primary endothelial cells and intestinal T84 cells. Adding exogenous ASM or ceramide enhanced epithelial cell growth arrest and death. Conversely, blocking their secretion by endothelial cells using genetic, pharmacologic, or immunologic approaches abolished intestinal T84 cell radiosensitivity. Use of enteroid models revealed ASM and ceramide-mediated deleterious mode-of-action: when ceramide reduced the number of intestinal crypt-forming enteroids without affecting their structure, ASM induced a significant decrease of enteroid growth without affecting their number. Identification of specific and different roles for ceramide and ASM secreted by irradiated endothelial cells opens new perspectives in the understanding of intestinal epithelial dysfunction after radiation and defines a new class of potential therapeutic radiomitigators. SIGNIFICANCE: This study identifies secreted ASM and ceramide as paracrine factors enhancing intestinal epithelial dysfunction, revealing a previously unknown class of mediators of radiosensitivity.

A BAC Transgene Expressing Human CFTR under Control of Its Regulatory Elements Rescues Cftr Knockout Mice

Small-molecule modulators of cystic fibrosis transmembrane conductance regulator (CFTR) biology show promise in the treatment of cystic fibrosis (CF). A Cftr knockout (Cftr KO) mouse expressing mutants of human CFTR would advance in vivo testing of new modulators. A bacterial artificial chromosome (BAC) carrying the complete hCFTR gene including regulatory elements within 40.1 kb of DNA 5' and 25 kb of DNA 3' to the gene was used to generate founder mice expressing hCFTR. Whole genome sequencing indicated a single integration site on mouse chromosome 8 (8qB2) with ~6 gene copies. hCFTR+ offspring were bred to murine Cftr KO mice, producing hCFTR+/mCftr- (H+/m-) mice, which had normal survival, growth and goblet cell function as compared to wild-type (WT) mice. Expression studies showed hCFTR protein and transcripts in tissues typically expressing mCftr. Functionally, nasal potential difference and large intestinal short-circuit (Isc) responses to cAMP stimulation were similar in magnitude to WT mice, whereas small intestinal cAMP ΔIsc responses were reduced. A BAC transgenic mouse with functional hCFTR under control of its regulatory elements has been developed to enable the generation of mouse models of hCFTR mutations by gene editing for in vivo testing of new CF therapies.

Short-term CFTR inhibition reduces islet area in C57BL/6 mice

Cystic fibrosis-related diabetes (CFRD) worsens CF lung disease leading to early mortality. Loss of beta cell area, even without overt diabetes or pancreatitis is consistently observed. We investigated whether short-term CFTR inhibition was sufficient to impact islet morphology and function in otherwise healthy mice. CFTR was inhibited in C57BL/6 mice via 8-day intraperitoneal injection of CFTRinh172. Animals had a 7-day washout period before measures of hormone concentration or islet function were performed. Short-term CFTR inhibition increased blood glucose concentrations over the course of the study. However, glucose tolerance remained normal without insulin resistance. CFTR inhibition caused marked reductions in islet size and in beta cell and non-beta cell area within the islet, which resulted from loss of islet cell size rather than islet cell number. Significant reductions in plasma insulin concentrations and pancreatic insulin content were also observed in CFTR-inhibited animals. Temporary CFTR inhibition had little long-term impact on glucose-stimulated, or GLP-1 potentiated insulin secretion. CFTR inhibition has a rapid impact on islet area and insulin concentrations. However, islet cell number is maintained and insulin secretion is unaffected suggesting that early administration of therapies aimed at sustaining beta cell mass may be useful in slowing the onset of CFRD.

Animal Models in the Pathophysiology of Cystic Fibrosis

Our understanding of the multiorgan pathology of cystic fibrosis (CF) has improved impressively during the last decades, but we still lack a full comprehension of the disease progression. Animal models have greatly contributed to the elucidation of specific mechanisms involved in CF pathophysiology and the development of new therapies. Soon after the cloning of the CF transmembrane conductance regulator (CFTR) gene in 1989, the first mouse model was generated and this model has dominated in vivo CF research ever since. Nonetheless, the failure of murine models to mirror human disease severity in the pancreas and lung has led to the generation of larger animal models such as pigs and ferrets. The following review presents and discusses data from the current animal models used in CF research.

SLC6A14, an amino acid transporter, modifies the primary CF defect in fluid secretion

The severity of intestinal disease associated with Cystic Fibrosis (CF) is variable in the patient population and this variability is partially conferred by the influence of modifier genes. Genome-wide association studies have identified SLC6A14, an electrogenic amino acid transporter, as a genetic modifier of CF-associated meconium ileus. The purpose of the current work was to determine the biological role of Slc6a14, by disrupting its expression in CF mice bearing the major mutation, F508del. We found that disruption of Slc6a14 worsened the intestinal fluid secretion defect, characteristic of these mice. In vitro studies of mouse intestinal organoids revealed that exacerbation of the primary defect was associated with reduced arginine uptake across the apical membrane, with aberrant nitric oxide and cyclic GMP-mediated regulation of the major CF-causing mutant protein. Together, these studies highlight the role of this apical transporter in modifying cellular nitric oxide levels, residual function of the major CF mutant and potentially, its promise as a therapeutic target.

Cystic fibrosis mouse model-dependent intestinal structure and gut microbiome

Mice with a null mutation in the cystic fibrosis transmembrane conductance regulator (Cftr) gene show intestinal structure alterations and bacterial overgrowth. To determine whether these changes are model-dependent and whether the intestinal microbiome is altered in cystic fibrosis (CF) mouse models, we characterized the ileal tissue and intestinal microbiome of mice with the clinically common ΔF508 Cftr mutation (FVB/N Cftr(tm1Eur)) and with Cftr null mutations (BALB/c Cftr(tm1UNC) and C57BL/6 Cftr(tm1UNC)). Intestinal disease in 12-week-old CF mice, relative to wild-type strain controls, was measured histologically. The microbiome was characterized by pyrosequencing of the V4-V6 region of the 16S rRNA gene and intestinal load was measured by RT-PCR of the 16S rRNA gene. The CF-associated increases in ileal crypt to villus axis distention, goblet cell hyperplasia, and muscularis externa thickness were more severe in the BALB/c and C57BL/6 Cftr(tm1UNC) mice than in the FVB/N Cftr(tm1Eur) mice. Intestinal bacterial load was significantly increased in all CF models, compared to levels in controls, and positively correlated with circular muscle thickness in CF, but not wild-type, mice. Microbiome profiling identified Bifidobacterium and groups of Lactobacillus to be of altered abundance in the CF mice but overall bacterial frequencies were not common to the three CF strains and were not correlative of major histological changes. In conclusion, intestinal structure alterations, bacterial overgrowth, and dysbiosis were each more severe in BALB/c and C57BL/6 Cftr(tm1UNC) mice than in the FVB/N Cftr(tm1Eur) mice. The intestinal microbiome differed among the three CF mouse models.

Defective goblet cell exocytosis contributes to murine cystic fibrosis-associated intestinal disease

Cystic fibrosis (CF) intestinal disease is associated with the pathological manifestation mucoviscidosis, which is the secretion of tenacious, viscid mucus that plugs ducts and glands of epithelial-lined organs. Goblet cells are the principal cell type involved in exocytosis of mucin granules; however, little is known about the exocytotic process of goblet cells in the CF intestine. Using intestinal organoids from a CF mouse model, we determined that CF goblet cells have altered exocytotic dynamics, which involved intrathecal granule swelling that was abruptly followed by incomplete release of partially decondensated mucus. Some CF goblet cells exhibited an ectopic granule location and distorted cellular morphology, a phenotype that is consistent with retrograde intracellular granule movement during exocytosis. Increasing the luminal concentration of bicarbonate, which mimics CF transmembrane conductance regulator-mediated anion secretion, increased spontaneous degranulation in WT goblet cells and improved exocytotic dynamics in CF goblet cells; however, there was still an apparent incoordination between granule decondensation and exocytosis in the CF goblet cells. Compared with those within WT goblet cells, mucin granules within CF goblet cells had an alkaline pH, which may adversely affect the polyionic composition of the mucins. Together, these findings indicate that goblet cell dysfunction is an epithelial-autonomous defect in the CF intestine that likely contributes to the pathology of mucoviscidosis and the intestinal manifestations of obstruction and inflammation.

Digestive system dysfunction in cystic fibrosis: challenges for nutrition therapy

Cystic fibrosis can affect food digestion and nutrient absorption. The underlying mutation of the cystic fibrosis trans-membrane regulator gene depletes functional cystic fibrosis trans-membrane regulator on the surface of epithelial cells lining the digestive tract and associated organs, where Cl(-) secretion and subsequently secretion of water and other ions are impaired. This alters pH and dehydrates secretions that precipitate and obstruct the lumen, causing inflammation and the eventual degradation of the pancreas, liver, gallbladder and intestine. Associated conditions include exocrine pancreatic insufficiency, impaired bicarbonate and bile acid secretion and aberrant mucus formation, commonly leading to maldigestion and malabsorption, particularly of fat and fat-soluble vitamins. Pancreatic enzyme replacement therapy is used to address this insufficiency. The susceptibility of pancreatic lipase to acidic and enzymatic inactivation and decreased bile availability often impedes its efficacy. Brush border digestive enzyme activity and intestinal uptake of certain disaccharides and amino acids await clarification. Other complications that may contribute to maldigestion/malabsorption include small intestine bacterial overgrowth, enteric circular muscle dysfunction, abnormal intestinal mucus, and intestinal inflammation. However, there is some evidence that gastric digestive enzymes, colonic microflora, correction of fatty acid abnormalities using dietary n-3 polyunsaturated fatty acid supplementation and emerging intestinal biomarkers can complement nutrition management in cystic fibrosis.

MicroRNA profiling implicates the insulin-like growth factor pathway in bleomycin-induced pulmonary fibrosis in mice

BACKGROUND

Idiopathic pulmonary fibrosis is a disease characterized by alveolar epithelial cell injury, inflammatory cell infiltration and deposition of extracellular matrix in lung tissue. As mouse models of bleomycin-induced pulmonary fibrosis display many of the same phenotypes observed in patients with idiopathic pulmonary fibrosis, they have been used to study various aspects of the disease, including altered expression of microRNAs.

RESULTS

In this work, microRNA expression profiling of the lungs from treated C57BL/6J mice, relative to that of untreated controls, was undertaken to determine which alterations in microRNAs could in part regulate the fibrosis phenotype induced by bleomycin delivered through mini-osmotic pumps. We identified 11 microRNAs, including miR-21 and miR-34a, to be significantly differentially expressed (P < 0.01) in lungs of bleomycin treated mice and confirmed these data with real time PCR measurements. In situ hybridization of both miR-21 and miR-34a indicated that they were expressed in alveolar macrophages. Using a previously reported gene expression profile, we identified 195 genes to be both predicted targets of the 11 microRNAs and of altered expression in bleomycin-induced lung disease of C57BL/6J mice. Pathway analysis with these 195 genes indicated that altered microRNA expression may be associated with hepatocyte growth factor signaling, cholecystokinin/gastrin-mediated signaling, and insulin-like growth factor (IGF-1) signaling, among others, in fibrotic lung disease. The relevance of the IGF-1 pathway in this model was then demonstrated by showing lung tissue of bleomycin treated C57BL/6J mice had increased expression of Igf1 and that increased numbers of Igf-1 positive cells, predominantly in macrophages, were detected in the lungs.

CONCLUSIONS

We conclude that altered microRNA expression in macrophages is a feature which putatively influences the insulin-like growth factor signaling component of bleomycin-induced pulmonary fibrosis.

Recent advances in small bowel diseases: Part II

As is the case in all areas of gastroenterology and hepatology, in 2009 and 2010 there were many advances in our knowledge and understanding of small intestinal diseases. Over 1000 publications were reviewed, and the important advances in basic science as well as clinical applications were considered. In Part II we review six topics: absorption, short bowel syndrome, smooth muscle function and intestinal motility, tumors, diagnostic imaging, and cystic fibrosis.

Vitamin D bioavailability in cystic fibrosis: a cause for concern?

Despite the inclusion of extra vitamin D in their regimen of fat-soluble vitamin supplementation, cystic fibrosis patients remain chronically depleted of vitamin D. The persistence of suboptimal vitamin D status is often blamed on the maldigestion and malabsorption of fat. However, the mitigated success of recent clinical trials with high-dose vitamin D supplementation suggests that vitamin D bioavailability might be impaired in these patients. Given the growing understanding of the importance of this vitamin in the regulation of multiple biological functions beyond skeletal health, the present review analyzes the current literature by addressing each step of vitamin D metabolism and action in the context of this life-limiting pathology. In addition, it highlights the importance of vitamin D in relation to organs and or conditions affected by cystic fibrosis.

Insulin production and resistance in cystic fibrosis: effect of age, disease activity, and genotype

AIM

To assess the major determinants of glucose tolerance between age, genotype, and clinical status in cystic fibrosis (CF) patients, and study if defects of insulin secretion and insulin sensitivity were associated with the onset of CF-related diabetes (CFRD).

SUBJECTS AND METHODS

One hundred and nineteen patients, in stable clinical condition were studied. They were subdivided into 3 groups based on age, and 2 groups based on Schwachman-Kulczycki clinical score. All patients were genotyped, and subsequently divided into 3 groups. Ninety-four healthy normal-weight controls, comparable for sex and age were also studied. All subjects had baseline blood samples taken for glucose and insulin, C-peptide, and glycated hemoglobin. Homeostasis model assessment of insulin resistance (HOMA-IR), fasting glucose/insulin ratio (FGIR) were calculated as indices of IR and insulinogenic index as a marker of pancreatic β-cell function. All patients underwent an oral glucose tolerance test, and 57 underwent an IVGTT for the calculation of first-phase (FPIR) and acute insulin responses (AIR).

RESULTS

The F508del homozygous patients had an increased chance of developing impaired glucose tolerance (IGT) and significantly lower FPIR, decreased HOMA-IR, and insulinogenic index. Heterozygote F508del patients had an increased chance of having normal glucose tolerance. HOMA-IR, FGIR, and insulinogenic index did not change with age or clinical score. HOMAIR correlated with FPIR. FPIR correlated positively with insulinogenic index. AIR correlated negatively with FGIR, and positively with C-reactive protein. In multiple linear regression analyses, glucose tolerance was related to the agegroup, and to the HOMA-IR and insulinogenic indexes.

CONCLUSIONS

IGT and CFRD were related mainly to genotype, although, as expected, the prevalence increased with age. The data suggested a possible combined contribution of insulin deficiency, β-cell function, and reduced insulin sensitivity to the onset of CFRD; however, further studies are warranted to better elucidate this aspect.

Strain-dependent airway hyperresponsiveness and a chromosome 7 locus of elevated lymphocyte numbers in cystic fibrosis transmembrane conductance regulator-deficient mice

We previously observed the lungs of naive BALB/cJ Cftr(tm1UNC) mice to have greater numbers of lymphocytes, by immunohistochemical staining, than did BALB wild type littermates or C57BL/6J Cftr(tm1UNC) mice. In the present study, we initially investigated whether this mutation in Cftr alters the adaptive immunity phenotype by measuring the lymphocyte populations in the lungs and spleens by FACS and by evaluating CD3-stimulated cytokine secretion, proliferation, and apoptosis responses. Next, we assessed a potential influence of this lymphocyte phenotype on lung function through airway resistance measures. Finally, we mapped the phenotype of pulmonary lymphocyte counts in BALB × C57BL/6J F2 Cftr(tm1UNC) mice and reviewed positional candidate genes. By FACS analysis, both the lungs and spleens of BALB Cftr(tm1UNC) mice had more CD3(+) (both CD4(+) and CD8(+)) cells than did littermates or C57BL/6J Cftr(tm1UNC) mice. Cftr(tm1UNC) and littermate mice of either strain did not differ in anti-CD3-stimulated apoptosis or proliferation levels. Lymphocytes from BALB Cftr(tm1UNC) mice produced more IL-4 and IL-5 and reduced levels of IFN-γ than did littermates, whereas lymphocytes from C57BL/6J Cftr(tm1UNC) mice demonstrated increased Il-17 secretion. BALB Cftr(tm1UNC) mice presented an enhanced airway hyperresponsiveness to methacholine challenge compared with littermates and C57BL/6J Cftr(tm1UNC) mice. A chromosome 7 locus was identified to be linked to lymphocyte numbers, and genetic evaluation of the interval suggests Itgal and Il4ra as candidate genes for this trait. We conclude that the pulmonary phenotype of BALB Cftr(tm1UNC) mice includes airway hyperresponsiveness and increased lymphocyte numbers, with the latter trait being influenced by a chromosome 7 locus.

Cystic fibrosis growth retardation is not correlated with loss of Cftr in the intestinal epithelium

Maldigestion due to exocrine pancreatic insufficiency leads to intestinal malabsorption and consequent malnutrition, a mechanism proposed to cause growth retardation associated with cystic fibrosis (CF). However, although enzyme replacement therapy combined with increased caloric intake improves weight gain, the effect on stature is not significant, suggesting that growth retardation has a more complex etiology. Mouse models of CF support this, since these animals do not experience exocrine pancreatic insufficiency yet are growth impaired. Cftr absence from the intestinal epithelium has been suggested as a primary source of growth retardation in CF mice, a concept we directly tested by generating mouse models with Cftr selectively inactivated or restored in intestinal epithelium. The relationship between growth and functional characteristics of the intestines, including transepithelial electrophysiology, incidence of intestinal obstruction, and histopathology, were assessed. Absence of Cftr exclusively from intestinal epithelium resulted in loss of cAMP-stimulated short-circuit current, goblet cell hyperplasia, and occurrence of intestinal obstructions but only slight and transient impaired growth. In contrast, specifically restoring Cftr to the intestinal epithelium resulted in restoration of ion transport and completely protected against obstruction and histopathological anomalies, but growth was indistinguishable from CF mice. These results indicate that absence of Cftr in the intestinal epithelium is an important contributor to the intestinal obstruction phenotype in CF but does not correlate with the observed growth reduction in CF.

MicroRNA profiling of cystic fibrosis intestinal disease in mice

Cystic fibrosis (CF) intestinal disease is characterized by alterations in processes such as proliferation and apoptosis which are known to be regulated in part by microRNAs. Herein, we completed microRNA expression profiling of the intestinal tissue from the cystic fibrosis mouse model of cystic fibrosis transmembrane conductance regulator (Cftr) deficient mice (BALBc/J Cftr(tm1UNC)), relative to that of wildtype littermates, to determine whether changes in microRNA expression level are part of this phenotype. We identified 24 microRNAs to be significantly differentially expressed in tissue from CF mice compared to wildtype, with the higher expression in tissue from CF mice. These data were confirmed with real time PCR measurements. A comparison of the list of genes previously reported to have decreased expression in the BALB×C57BL/6J F2 CF intestine to that of genes putatively targeted by the 24 microRNAs, determined from target prediction software, revealed 155 of the 759 genes of the expression profile (20.4%) to overlap with predicted targets, which is significantly more than the 100 genes expected by chance (p=1×10(-8)). Pathway analysis identified these common genes to function in phosphatase and tensin homolog-, protein kinase A-, phosphoinositide-3 kinase/Akt- and peroxisome proliferator-activated receptor alpha/retinoid X receptor alpha signaling pathways, among others, and through real time PCR experiments genes of these pathways were demonstrated to have lower expression in the BALB CF intestine. We conclude that altered microRNA expression is a feature which putatively influences both metabolic abnormalities and the altered tissue homeostasis component of CF intestinal disease.

IGF binding protein-3 treatment alters intestinal cell proliferation but not body weight of adult cystic fibrosis transmembrane conductance regulator deficient mice

The intestinal phenotype of cystic fibrosis (CF) transmembrane conductance regulator deficient mice includes altered cell homeostasis and a distended crypt-villus axis, which, in previous work, was inversely proportional to body weight. To investigate this correlation, herein, we treated CF mice with IGF binding protein-3 (IGFBP-3), a protein which, as it has potent effects on cell proliferation and apoptosis, we hypothesized would alter the intestinal cell homeostasis, and assessed body weight. Six-week-old C57BL/6JxBALB F2 CF and WT mice received recombinant human IGFBP-3 (rhIGFBP-3, 20 mg/kg) or vehicle treatment, and weight gain, serum protein levels, and intestinal histology were assessed. Administration of rhIGFBP-3 to CF mice significantly increased the number of Igfbp-3 positive cells in the intestine and partially reversed the hyperproliferative phenotype of intestinal crypts and muscularis externa, while not affecting apoptosis. Serum Igfbp-3 levels were increased, and Igf-I, albumin, and triglycerides measures were decreased in CF compared with WT mice. rhIGFBP-3 treatment significantly increased serum albumin and triglycerides but did not affect weight gain in CF mice. We have identified rhIGFBP-3 treatment to reduce intestinal cell proliferation, resulting in decreases in crypt depth and muscularis externa thickness in CF mice.

Listeria monocytogenes exploits cystic fibrosis transmembrane conductance regulator (CFTR) to escape the phagosome

Virulence of the intracellular pathogen Listeria monocytogenes (Listeria) requires escape from the phagosome into the host cytosol, where the bacteria replicate. Phagosomal escape is a multistep process characterized by perforation, which is dependent on the pore-forming toxin listeriolysin O (LLO), followed by rupture. The contribution of host factors to Listeria phagosomal escape is incompletely defined. Here we show that the cystic fibrosis transmembrane conductance regulator (CFTR) facilitates Listeria cytosolic entry. CFTR inhibition or mutation suppressed Listeria vacuolar escape in culture, and inhibition of CFTR in wild-type mice before oral inoculation of Listeria markedly decreased systemic infection. We provide evidence that high chloride concentrations may facilitate Listeria vacuolar escape by enhancing LLO oligomerization and lytic activity. We propose that CFTR transiently increases phagosomal chloride concentration after infection, potentiating LLO pore formation and vacuole lysis. Our studies suggest that Listeria exploits mechanisms of cellular ion homeostasis to escape the phagosome and emphasize host ion-channel function as a key parameter of bacterial virulence.

Toll-like receptor-4 genotype influences the survival of cystic fibrosis mice

Toll-like receptor (Tlr) 4 is a lipopolysaccharide (LPS) receptor that contributes to the regulation of intestinal cell homeostasis, a condition that is altered in the intestines of cystic fibrosis mice. Herein, we assessed whether Tlr4 genotype influences cystic fibrosis intestinal disease by producing and phenotyping 12-wk (adult)- and 4-day (neonate)-old mice derived from BALB cystic fibrosis transmembrane conductance regulator, Cftr(+/tm1Unc) and C.C3-Tlr4(Lps-d)/J (Tlr4(-/-)), progenitors. Intestinal disease was assayed through mouse survival, crypt-villus axis (CVA) length, cell proliferation, bacterial load, bacterial classification, inflammatory cell infiltrate, and mucus content measures. Of the 77 Cftr(-/-) (CF) mice produced, only one Cftr/Tlr4 double-mutant mouse lived to the age of 12 wk while the majority of the remainder succumbed at approximately 4 days of age. The survival of CF Tlr4(+/-) mice exceeded that of both CF Tlr4(+/+) and Cftr/Tlr4 double-mutant mice. Adult CF mice presented increased Tlr4 expression, CVA length, crypt cell proliferation, and bacterial load relative to non-CF mice, but no differences were detected in Tlr4(+/-) compared with Tlr4(+/+) CF mice. The double-mutant neonates did not differ from Tlr4(+/+) or Tlr4(+/-) CF mice by intestinal CVA length or bacterial load, but fewer Tlr4(+/-) CF neonates presented with luminal mucus obstruction in the distal ileum, and the intestinal mast cell increase of CF mice was not evident in double-mutant neonates. We conclude that Tlr4 deficiency reduces the survival, but does not alter the intestinal phenotypes, of extended CVA or increased bacterial load in BALB CF mice.

Gene expression profiling distinguishes radiation-induced fibrosing alveolitis from alveolitis in mice

Thoracic cavity radiotherapy is limited by the development of alveolitis and fibrosis in susceptible patients. To define the response to 18 Gy pulmonary irradiation in mice at the gene expression level and to identify pathways that may influence the alveolitis and fibrosis phenotypes, expression profiling was undertaken. Male mice of three strains, A/J (late alveolitis response), C3H/HeJ (C3H, early alveolitis response) and C57BL/6J (B6, fibrosis response), were exposed to thoracic radiation and euthanized when moribund, and lung tissue gene expression was assessed with microarrays. The responses of A/J and C3H mice were more similar to each other (60% of differentially expressed genes detected in both strains) than to that of B6 mice (17% overlap). Pathway analysis revealed the expression of complement and of B-cell proliferation and activation genes to distinguish fibrosis from the alveolitis response and cytokine interactions and intracellular signaling differed between A/J and C3H mice. A genomic approach was used to identify specific pathways that likely contribute to the lung response to radiation as fibrosis or alveolitis in mice.

CFTR knockdown stimulates lipid synthesis and transport in intestinal Caco-2/15 cells

Cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel highly expressed in epithelial cells of the gastrointestinal tract. Mutations in the CFTR gene cause cystic fibrosis (CF), a disease characterized by pancreatic insufficiency, fat malabsorption, and steatorrhea. Despite the administration of pancreatic enzymes to normalize malabsorption, CF patients still experienced lipid fecal loss, nutritional deficiencies, and abnormalities in serum lipid profile, suggesting the presence of intrinsic defects in the intestinal handling of nutrients. The objective of the present study was to assess the impact of CFTR gene knockdown on intracellular lipid metabolism of the intestinal Caco-2/15 cell line. Partial CFTR gene inactivation led to cellular lipid accretion of phospholipids, triglycerides, and cholesteryl esters. Likewise, secretion of these lipid fractions was significantly increased following CFTR gene manipulation. As expected from these findings, the output of triglyceride-rich lipoproteins showed the same increasing pattern. Investigation of the mechanisms underlying these changes revealed that CFTR knockdown resulted in raised levels of apolipoproteins in cells and media and microsomal transfer protein activity, two important factors for the efficient assembly and secretion of lipoproteins. Similarly, scrutiny of the enzymatic monoacylglycerol acyltransferase and diacylglycerol acyltransferase, which exhibit dynamic function in triacylglycerol resynthesis and chylomicron formation in enterocytes, revealed a significant augmentation in their activity. Conversely, cholesterol uptake mediated by Niemann-Pick C1 like 1, Scavenger Receptor Class B Type I, and ATP-binding cassette G8 remains unaffected by genetic modification of CFTR. Collectively, these results highlight the role played by CFTR in intestinal handling of lipids and may suggest that factors other than defective CFTR are responsible for the abnormal intracellular events leading to fat malabsorption in CF patients.