Toll-Like Receptor 4-Independent Carbon Tetrachloride-Induced Fibrosis and Lipopolysaccharide-Induced Acute Liver Injury in Mice: Role of Hepatic Stellate Cells

Gram-negative bacterial endotoxin lipopolysaccharide (LPS) is implicated in acute and chronic liver injury; its effects are mediated predominantly via the membrane receptor Toll-like receptor 4 (TLR4). However, TLR4-independent effects of LPS may play important role in hepatic pathophysiology. We investigated carbon tetrachloride (CCl₄)-induced fibrosis and LPS-induced acute liver injury in wild-type (WT) and B6.B10ScN-Tlr4^lps-del/JthJ [TLR4-knockout (KO)] mice. Effects of LPS on fibrogenic hepatic stellate cells (HSCs) from WT and TLR4-KO mice were assessed in vitro. CCl₄ produced similar fibrosis and necroinflammation and increased the mRNA and protein expression of cytokines and chemokines in WT and TLR4-KO mice. However, circulating LPS concentration did not increase in CCl₄-treated mice. Interestingly, LPS down-modulated α-smooth muscle actin (activated HSC marker) and collagen 1 in both WT and TLR4-KO HSCs. LPS induced similar activation of NF-κB, and stimulated the expression of cytokines and chemokines in WT and TLR4-KO HSCs. Finally, LPS caused similar inflammation and injury in previously untreated WT and TLR4-KO mice. The results provide evidence of the TLR4/LPS-independent mechanisms of liver fibrosis and also indicate that TLR4 is not entirely critical to LPS-induced acute liver injury. The results further indicate that LPS signaling in activated HSCs might be a mechanism of limiting liver fibrosis.

The dendritic cell-T helper 17-macrophage axis controls cholangiocyte injury and disease progression in murine and human biliary atresia

Biliary atresia (BA) is a fibroinflammatory obstruction of the extrahepatic biliary tree in neonates. While intrahepatic bile duct proliferation is universal at diagnosis, bile duct paucity develops later. We hypothesized that polarized T helper lymphocyte responses orchestrate progression of intrahepatic biliary injury in this disease. Interleukin 17A (IL-17A)-green fluorescent protein, cluster of differentiation 11c (CD11c)/diphtheria toxin receptor, and IL-17 receptor A^-/- mice were used to examine T-lymphocyte polarization, inflammatory leukocyte recruitment, and biliary injury in rhesus rotavirus-induced BA. Multiparameter flow cytometry and automated image analysis of immunostaining were applied to liver tissue samples from infants with BA. In the mouse model, activated CD4⁺ lymphocytes started to emerge in the liver on day 8 after viral challenge, while innate immune responses were waning. Plasma IL-17A levels rose concomitantly with hepatic accumulation of T helper 17 lymphocytes and myeloid dendritic cells. Targeted depletion of CD11c⁺ dendritic cells diminished hepatic IL-17A production and ameliorated intrahepatic bile duct injury. Recombinant IL-17A induced expression of chemokine (C-C motif) ligand 2 in neonatal cholangiocytes in vitro, and blockade of the corresponding chemokine (C-C motif) receptor 2 reduced recruitment of inflammatory macrophages to the liver in vivo. Genetic disruption of IL-17A signaling was associated with down-regulation of hepatic Ccl2/Ccr2 messenger RNA expression, reduced infiltration of the liver with inflammatory Ly6C^hi macrophages, and improved survival. In the liver of infants with BA, cholangiocytes were found to express IL-17 receptor A, and the prevalence of IL-17A⁺ cells was positively correlated with the degree of CD68⁺ macrophage infiltration at diagnosis. Hepatic CD4⁺ lymphocytes were chief producers of IL-17A in patients with progressive disease undergoing liver transplantation.

CONCLUSION

These findings identify the dendritic cell-T helper 17-macrophage axis as a target for the development of strategies to block progression of intrahepatic bile duct injury in patients with BA. (Hepatology 2017;65:174-188).

Delivery of bevacizumab to atheromatous porcine carotid tissue using echogenic liposomes

Ultrasound is both a valuable diagnostic tool and a promoter of beneficial tissue bioeffects for the treatment of cardiovascular disease. Vascular effects can be mediated by mechanical oscillations of circulating microbubbles that may also encapsulate and shield therapeutic agents in the bloodstream. Here, the effect of color-Doppler ultrasound exposure on bevacizumab-loaded liposome delivery into the vascular bed was assessed in atheromatous porcine carotids. Bevacizumab, an anti-angiogenic antibody to vascular endothelial growth factor (VEGF-A), was loaded into echogenic liposomes (BEV-ELIP) and confirmed to be immunoreactive. BEV-ELIP flowing within the lumen were exposed to color-Doppler ultrasound at three acoustic pressures for 3.5 min during treatment at physiologic temperature and fluid pressure. To confirm the presence of bubble activity, cavitation was detected within the lumen by a single-element passive cavitation detector. After treatment, the artery was fixed at physiologic pressure and subjected to immunohistochemical analysis to assess the penetration of bevacizumab within the carotid wall. The results suggest that other factors may more strongly influence the deposition of bevacizumab into carotid tissue than color-Doppler ultrasound and cavitation. In both sets of arteries, preferential accumulation of bevacizumab occurred in locations associated with atheroma progression and neointimal thickening: fibrous tissue, necrotic plaque and areas near macrophage infiltration. The delivery of bevacizumab to carotid vascular tissue correlated with the properties of the tissue bed, such as permeability, or affinity for growth-factor binding. Future investigations using this novel therapeutic strategy may focus on characterizing the spatial extent of delivery and bevacizumab colocalization with biochemical markers of atheroma.

Integrated Genomic Analysis of Diverse Induced Pluripotent Stem Cells from the Progenitor Cell Biology Consortium

The rigorous characterization of distinct induced pluripotent stem cells (iPSC) derived from multiple reprogramming technologies, somatic sources, and donors is required to understand potential sources of variability and downstream potential. To achieve this goal, the Progenitor Cell Biology Consortium performed comprehensive experimental and genomic analyses of 58 iPSC from ten laboratories generated using a variety of reprogramming genes, vectors, and cells. Associated global molecular characterization studies identified functionally informative correlations in gene expression, DNA methylation, and/or copy-number variation among key developmental and oncogenic regulators as a result of donor, sex, line stability, reprogramming technology, and cell of origin. Furthermore, X-chromosome inactivation in PSC produced highly correlated differences in teratoma-lineage staining and regulator expression upon differentiation. All experimental results, and raw, processed, and metadata from these analyses, including powerful tools, are interactively accessible from a new online portal at https://www.synapse.org to serve as a reusable resource for the stem cell community.

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Comprehensive portal for diverse iPSC, protocols, metadata, and genomic assays

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Recurrent CNV occur during reprogramming, impact oncogenes and tumor suppressors

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DNA methylation is influenced by cell of origin in iPSC

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PSC X-chromosome inactivation impacts lineage differentiation outcomes

Pharmacological inhibition of apical sodium-dependent bile acid transporter changes bile composition and blocks progression of sclerosing cholangitis in multidrug resistance 2 knockout mice

Deficiency of multidrug resistance 2 (mdr2), a canalicular phospholipid floppase, leads to excretion of low-phospholipid "toxic" bile causing progressive cholestasis. We hypothesize that pharmacological inhibition of the ileal, apical sodium-dependent bile acid transporter (ASBT), blocks progression of sclerosing cholangitis in mdr2(-/-) mice. Thirty-day-old, female mdr2(-/-) mice were fed high-fat chow containing 0.006% SC-435, a minimally absorbed, potent inhibitor of ASBT, providing, on average, 11 mg/kg/day of compound. Bile acids (BAs) and phospholipids were measured by mass spectrometry. Compared with untreated mdr2(-/-) mice, SC-435 treatment for 14 days increased fecal BA excretion by 8-fold, lowered total BA concentration in liver by 65%, reduced total BA and individual hydrophobic BA concentrations in serum by >98%, and decreased plasma alanine aminotransferase, total bilirubin, and serum alkaline phosphatase levels by 86%, 93%, and 55%, respectively. Liver histology of sclerosing cholangitis improved, and extent of fibrosis decreased concomitant with reduction of hepatic profibrogenic gene expression. Biliary BA concentrations significantly decreased and phospholipids remained low and unchanged with treatment. The phosphatidylcholine (PC)/BA ratio in treated mice corrected toward a ratio of 0.28 found in wild-type mice, indicating decreased bile toxicity. Hepatic RNA sequencing studies revealed up-regulation of putative anti-inflammatory and antifibrogenic genes, including Ppara and Igf1, and down-regulation of several proinflammatory genes, including Ccl2 and Lcn2, implicated in leukocyte recruitment. Flow cytometric analysis revealed significant reduction of frequencies of hepatic CD11b(+) F4/80(+) Kupffer cells and CD11b(+) Gr1(+) neutrophils, accompanied by expansion of anti-inflammatory Ly6C(-) monocytes in treated mdr2(-/-) mice.

CONCLUSION

Inhibition of ASBT reduces BA pool size and retention of hydrophobic BA, favorably alters the biliary PC/BA ratio, profoundly changes the hepatic transcriptome, attenuates recruitment of leukocytes, and abrogates progression of murine sclerosing cholangitis.

Placenta growth factor augments airway hyperresponsiveness via leukotrienes and IL-13

Airway hyperresponsiveness (AHR) affects 55%-77% of children with sickle cell disease (SCD) and occurs even in the absence of asthma. While asthma increases SCD morbidity and mortality, the mechanisms underlying the high AHR prevalence in a hemoglobinopathy remain unknown. We hypothesized that placenta growth factor (PlGF), an erythroblast-secreted factor that is elevated in SCD, mediates AHR. In allergen-exposed mice, loss of Plgf dampened AHR, reduced inflammation and eosinophilia, and decreased expression of the Th2 cytokine IL-13 and the leukotriene-synthesizing enzymes 5-lipoxygenase and leukotriene-C4-synthase. Plgf-/- mice treated with leukotrienes phenocopied the WT response to allergen exposure; conversely, anti-PlGF Ab administration in WT animals blunted the AHR. Notably, Th2-mediated STAT6 activation further increased PlGF expression from lung epithelium, eosinophils, and macrophages, creating a PlGF/leukotriene/Th2-response positive feedback loop. Similarly, we found that the Th2 response in asthma patients is associated with increased expression of PlGF and its downstream genes in respiratory epithelial cells. In an SCD mouse model, we observed increased AHR and higher leukotriene levels that were abrogated by anti-PlGF Ab or the 5-lipoxygenase inhibitor zileuton. Overall, our findings indicate that PlGF exacerbates AHR and uniquely links the leukotriene and Th2 pathways in asthma. These data also suggest that zileuton and anti-PlGF Ab could be promising therapies to reduce pulmonary morbidity in SCD.

Compartmentalized accumulation of cAMP near complexes of multidrug resistance protein 4 (MRP4) and cystic fibrosis transmembrane conductance regulator (CFTR) contributes to drug-induced diarrhea

Diarrhea is one of the most common adverse side effects observed in ∼7% of individuals consuming Food and Drug Administration (FDA)-approved drugs. The mechanism of how these drugs alter fluid secretion in the gut and induce diarrhea is not clearly understood. Several drugs are either substrates or inhibitors of multidrug resistance protein 4 (MRP4), such as the anti-colon cancer drug irinotecan and an anti-retroviral used to treat HIV infection, 3'-azido-3'-deoxythymidine (AZT). These drugs activate cystic fibrosis transmembrane conductance regulator (CFTR)-mediated fluid secretion by inhibiting MRP4-mediated cAMP efflux. Binding of drugs to MRP4 augments the formation of MRP4-CFTR-containing macromolecular complexes that is mediated via scaffolding protein PDZK1. Importantly, HIV patients on AZT treatment demonstrate augmented MRP4-CFTR complex formation in the colon, which defines a novel paradigm of drug-induced diarrhea.

Myeloid dendritic cells maintain Th17 lymphocyte responses during the obstructive phase of experimental biliary atresia (IRC10P.471)

Biliary atresia (BA) is a fibro-inflammatory obstruction of the extrahepatic biliary tree in newborns. It leads to rapid biliary fibrosis and is the most common indication for pediatric liver transplantation. In a model of rhesus rotavirus (RRV)-induced murine BA, plasmacytoid dendritic cells (DC) initiate NK-cell mediated hepatobiliary injury at 3 days post infection (dpi). We hypothesize that myeloid (m)DC coordinate T-cell driven injury during the later obstructive phase of BA. Following RRV injection into CD11c-DTR GFP pups on day 1 of life, frequency of hepatic DC increased 6fold at 12dpi compared with non-infected controls. Expansion of mDCs was accompanied by accumulation of activated CD4 cells in the liver. Plasma IL17A/F levels were increased at 8 and 12dpi (p<0.01) and hepatic IL17A mRNA increased 9fold between 8 and 12dpi. In vitro coculture of DC from 12dpi pups with naïve CD4 cells induced IL17A/6 production. DC-depletion following RRV infection with diphtheria toxin reduced the number of hepatic CD4 cells by 3fold which was associated with 2fold decrease in hepatic IL17A mRNA expression and plasma Th17-associated cytokine levels (IL-17F/6) at 12dpi. Importantly, diminished Th17 responses correlated with reduced plasma total bilirubin levels (6.1 vs 11.3mg/dL in control; p<0.01), a biomarker for biliary obstruction. We conclude that mDC maintain hepatic Th17 responses and regulate cholestatic liver injury during the obstructive phase of experimental BA.

Lampe1: an ENU-germline mutation causing spontaneous hepatosteatosis identified through targeted exon-enrichment and next-generation sequencing

Using a small scale ENU mutagenesis approach we identified a recessive germline mutant, designated Lampe1 that exhibited growth retardation and spontaneous hepatosteatosis. Low resolution mapping based on 20 intercrossed Lampe1 mice revealed linkage to a ∼14 Mb interval on the distal site of chromosome 11 containing a total of 285 genes. Exons and 50 bp flanking sequences within the critical region were enriched with sequence capture microarrays and subsequently analyzed by next-generation sequencing. Using this approach 98.1 percent of the targeted DNA was covered with a depth of 10 or more reads per nucleotide and 3 homozygote mutations were identified. Two mutations represented intronic nucleotide changes whereas one mutation affected a splice donor site in intron 11–12 of Palmitoyl Acetyl-coenzyme A oxygenase-1 (Acox1), causing skipping of exon 12. Phenotyping of Acox1^Lampe1 mutants revealed a progression from hepatosteatosis to steatohepatitis, and ultimately hepatocellular carcinoma. The current approach provides a highly efficient and affordable method to identify causative mutations induced by ENU mutagenesis and animal models relevant to human pathology.