A fetal wound healing program after intrauterine bile duct injury may contribute to biliary atresia

IgG4-Related Cholangitis

IgG4-related cholangitis (IRC) is a rare fibroinflammatory disease of the biliary tree and liver and presents the major hepatobiliary manifestation of IgG4-related systemic disease (IgG4-RD). IRC also includes the IgG4-related inflammatory pseudotumor of the liver and IgG4-related cholecystitis. IRC mimics other cholangiopathies such as primary sclerosing cholangitis or cholangiocarcinoma. IRC may be found in 30 to 60% of cases with type 1 autoimmune pancreatitis, the most frequent manifestation of IgG4-RD. The pathogenesis of IRC (and IgG4-RD) is incompletely understood. Genetic predisposition, environmental factors, oligoclonal glucocorticosteroid-sensitive expansion of IgG4+ B cells/plasmablasts in blood and affected tissue and blocking autoantibody formation against protective IgG4-specific autoantigens such as annexin A11 and laminin 511-E8 with impaired protection of biliary epithelia against toxic bile acids have been described in IRC. Specific T cell subtypes are involved in the inflammatory process. The diagnosis of IRC is made according to HISORt criteria comprising histopathology, imaging, serology, other organ manifestations, and response to therapy. Treatment of IRC aiming to prevent organ failure and improve symptoms includes remission induction with highly effective glucocorticosteroids and long-term maintenance of remission with immunomodulators such as glucocorticosteroid sparing additives or B cell depleting approaches.

Evolving Concepts in Etiology of Biliary Atresia: Insights and Perspectives from India

Introduction: Biliary atresia (BA) is a potentially fatal newborn cholestatic disease. It is a rapidly advancing fibro-obliterative cholangiopathy that leads to liver failure and death if not treated early. The well-known multihit hypothesis proposes that viral or chemical disruption to the biliary epithelium triggers an immune-mediated inflammatory response, resulting in fibrosis and blockage of the intra and extrahepatic biliary systems. Methods: In recent years, several papers have noticed an upsurge in many aspects of BA, particularly its etiopathogenesis, which has opened a vista of various probable mechanisms currently being examined. This review brings them together with an emphasis on reflecting current scientific views for those interested in this illness. Conclusions: Among the different etiological factors proposed for BA, viruses and immune-mediated injury are the strongest contenders as contributors to the disease onset and pathogenesis.

Transcriptional analysis of murine biliary atresia identifies macrophage heterogeneity and subset-specific macrophage functions

Introduction

Macrophages play an important role in disease progression of pediatric cholestatic liver disease, particularly biliary atresia (BA); however, the restorative versus pathogenic role for precise macrophage subsets remains poorly defined. We aimed to distinguish the transcriptional profiles and roles of defined macrophage subset(s) in murine BA.

Methods

We used multiparameter flow cytometry and RNA-sequencing analysis to profile recruited CD11bhiCD64+ hepatic macrophages by cell surface expression of MHCII and Ly6c in the Rhesus rotavirus (RRV)-induced murine model of BA versus saline controls. Modulation of macrophage numbers via intra-peritoneal injections of clodronate-loaded liposomes was performed to determine the association between macrophage numbers and histologic injury (Ishak score).

Results

Ly6c+ macrophages demonstrated the greatest increase in numbers and percent of total macrophages in murine BA versus saline controls whereas MHCII+ macrophages decreased. Transcriptional changes in murine BA MHCII+ macrophages included reduced expression of the Kupffer cell gene signature, lower expression of genes involved in homeostatic processes, and increased expression of genes involved in inflammatory processes. Ly6c+ macrophages in murine BA showed increased expression for Hif1a and other genes involved in the cellular response to hypoxia. Among all subsets, the number of Ly6c+ macrophages exhibited the strongest correlation with severity of histologic liver injury by Ishak score.

Conclusions

Our data identify specific pathways upregulated in Ly6c vs MHCII+ macrophage subsets in murine BA. Transcriptional similarities between murine BA and human cholestatic macrophages may enable translation of future mechanistic studies to new macrophage subset-specific therapies.

Biliary atresia susceptibility gene EFEMP1 regulates extrahepatic bile duct elastic fiber formation and mechanics

Background & Aims

EGF-containing fibulin extracellular matrix protein 1 (EFEMP1, also called fibulin-3) is an extracellular matrix protein linked in a genome-wide association study to biliary atresia, a fibrotic disease of the neonatal extrahepatic bile duct. Fibulin-3 is deposited in most tissues and Efemp1 null mice have decreased elastic fibers in visceral fascia; however, fibulin-3 does not have a role in the development of large elastic fibers and its overall function in the extrahepatic bile ducts remains unclear.

Methods

We used staining and histology to define the amount and organization of key extracellular matrix components in the extrahepatic bile ducts. We also repurposed pressure myography, a technique heretofore applied to the vasculature, to determine the contribution of elastin and fibulin-3 to extrahepatic bile duct mechanics. We examined extrahepatic bile duct structure and mechanics in three models: neonatal vs. adult rat ducts (n = 6 each), elastase-treated adult rat ducts (n = 6-7 each), and Efemp1 +/- vs. wild-type mouse ducts (n = 6 each).

Results

We demonstrated that fibulin-3 is expressed in the submucosa of both neonatal and adult mouse, rat and human extrahepatic bile ducts and that, in adult Efemp1 +/- mouse ducts, elastin organization into fibers is decreased by approximately half. Pressure myography showed that Efemp1 +/- ducts have altered mechanics compared to control ducts, with Efemp1 +/- ducts displaying significant stretch compared to controls (p = 0.0376); these changes in stretch are similar to those observed in elastase-treated vs. normal ducts (p <0.0001) and in neonatal ducts vs. adult ducts (p <0.0001).

Conclusion

Fibulin-3 has an important role in the formation of elastic fibers and the mechanical properties of the extrahepatic bile duct. This provides functional relevance for the biliary atresia susceptibility gene EFEMP1.

Impact and implications

The gene EFEMP1 was found via a genome-wide association study to be a susceptibility gene for the neonatal disease biliary atresia. EFEMP1 encodes the protein fibulin-3, which regulates elastic fiber organization in the extrahepatic bile duct (EHBD), the major site of disease in biliary atresia. We showed that neonatal EHBDs as well as mice heterozygous for Efemp1 have decreased numbers of elastic fibers, and that this alters EHBD mechanics. This work is important for understanding the mechanism of biliary atresia, in particular susceptibility to obstruction.

Structural Disruption of Cilia and Increased Cytoplasmic Tubulin in Biliary Atresia-An Exploratory Study Focusing on Early Postoperative Prognosis Following Portoenterostomy

Introduction: Biliary atresia (BA) is a progressive hepatobiliary disease in infants, leading to liver failure and the need for transplantation. While its etiopathogenesis remains unclear, recent studies suggest primary cilia (PC) disruption plays a role. This study investigates correlations between PC and cytoplasmic tubulin (TUBA4A) alterations with hypoxia in patients with the isolated form of BA, focusing on native liver survival. Methods: Using qualitative and quantitative digital image analysis of immunofluorescence-stained liver samples, we assessed PC and TUBA4A features correlating these findings with HIF-1α nuclear positivity, clinical-laboratory data, and early native liver survival. Liver samples from fourteen BA patients and six controls with another liver disease were analyzed by digital image analysis, with data evaluated using Spearman's correlation and independent t-tests. Results: HIF-1α positivity in cholangiocytes was observed in 42.8% of BA patients. While the PC ratio per biliary structure (cilia ratio status, CRs) was similar between BA patients and controls, PC length was decreased in BA patients. Cytoplasmic TUBA4A levels were elevated in BA patients. CRs positively correlated with lower cytoplasmic TUBA4A expression and was higher in patients without HIF-1α nuclear positivity. Reduced cilia length correlated with higher bilirubin levels at portoenterostomy. Predictors of early poor prognosis (death or need for transplantation until 1 year of life) included HIF-1α positivity, elevated direct bilirubin levels, decreased cilia length, PC bending, and increased TUBA4A expression. Conclusions: Reduced PC length, PC bending, and increased intensity of cytoplasmic TUBA4A expression occur in the isolated BA clinical type and negatively impact the early prognosis after post-portoenterostomy. These findings suggest the existence of a disruption in the tubulin transport between cytoplasm and PC. The detrimental effect of HIF-1alpha pathway activation over early native liver survival was confirmed, although independently from PC or cytoplasmic tubulin features.

Microcystin-RR is a biliary toxin selective for neonatal extrahepatic cholangiocytes

Background & Aims

Biliary atresia is a fibrosing cholangiopathy affecting neonates that is thought to result from a prenatal environmental insult to the bile duct. Biliatresone, a plant toxin with an α-methylene ketone group, was previously implicated in biliary atresia in Australian livestock, but is found in a limited location and is unlikely to be a significant human toxin. We hypothesized that other unsaturated carbonyl compounds, some with the potential for significant human exposure, might also be biliary toxins.

Methods

We focused on the family of microcystins, cyclic peptide toxins from blue-green algae that are found worldwide, particularly during harmful algal blooms. We used primary extrahepatic cholangiocyte spheroids and extrahepatic bile duct explants from both neonatal [a total of 86 postnatal day (P) 2 mouse pups and 18 P2 rat pups (n = 8-10 per condition for both species)] and adult rodents [a total of 31 P15-18 mice (n = 10 or 11 per condition)] to study the biliary toxicity of microcystins and potential mechanisms involved.

Results

Results showed that 400 nM microcystin (MC)-RR, but not six other microcystins or the related algal toxin nodularin, caused >80% lumen closure in cell spheroids made from extrahepatic cholangiocytes isolated from 2-3-day-old mice (p <0.0001). By contrast, 400 nM MC-RR resulted in less than an average 5% lumen closure in spheroids derived from neonatal intrahepatic cholangiocytes or cells from adult mice (p = 0.4366). In addition, MC-RR caused occlusion of extrahepatic bile duct explants from 2-day-old mice (p <0.0001), but not 18-day-old mice. MC-RR also caused a 2.3-times increase in reactive oxygen species in neonatal cholangiocytes (p <0.0001), and treatment with N-acetyl cysteine partially prevented microcystin-RR-induced lumen closure (p = 0.0004), suggesting a role for redox homeostasis in its mechanism of action.

Conclusions

We identified MC-RR as a selective neonatal extrahepatic cholangiocyte toxin and suggest that it acts by increasing redox stress.

Impact and implications

The plant toxin biliatresone causes a biliary atresia-like disease in livestock and vertebrate animal model systems. We tested the widespread blue-green algal toxin, microcystin-RR, another highly electrophilic unsaturated carbonyl compound that is released during harmful algal blooms, and found that it was also a biliary toxin with specificity for neonatal extrahepatic cholangiocytes. This work should drive further animal studies and, ultimately, studies to determine whether human exposure to microcystin-RR causes biliary atresia.

Silencing of maternally expressed RNAs in Dlk1-Dio3 domain causes fatal vascular injury in the fetal liver

The mammalian imprinted Dlk1-Dio3 domain contains multiple lncRNAs, mRNAs, the largest miRNA cluster in the genome and four differentially methylated regions (DMRs), and deletion of maternally expressed RNA within this locus results in embryonic lethality, but the mechanism by which this occurs is not clear. Here, we optimized the model of maternally expressed RNAs transcription termination in the domain and found that the cause of embryonic death was apoptosis in the embryo, particularly in the liver. We generated a mouse model of maternally expressed RNAs silencing in the Dlk1-Dio3 domain by inserting a 3 × polyA termination sequence into the Gtl2 locus. By analyzing RNA-seq data of mouse embryos combined with histological analysis, we found that silencing of maternally expressed RNAs in the domain activated apoptosis, causing vascular rupture of the fetal liver, resulting in hemorrhage and injury. Mechanistically, termination of Gtl2 transcription results in the silencing of maternally expressed RNAs and activation of paternally expressed genes in the interval, and it is the gene itself rather than the IG-DMR and Gtl2-DMR that causes the aforementioned phenotypes. In conclusion, these findings illuminate a novel mechanism by which the silencing of maternally expressed RNAs within Dlk1-Dio3 domain leads to hepatic hemorrhage and embryonic death through the activation of apoptosis.

High-fidelity and iterative affinity extraction of hyaluronan

The glycosaminoglycan hyaluronan (HA) serves a variety of crucial physiological functions in vertebrates. Synthesized at the plasma membrane and secreted into the extracellular environment, HA polymers span a wide range of molecular weights (MW) that define their activity through a notable size-function relationship. Analytical technologies for determining HA MW distributions typically require selective extraction from complex biofluids or tissues. A common method for achieving this is immunoprecipitation-like pull-down using specific HA-binding proteins bound to magnetic beads. Here, we present a systematic investigation of experimental variables involved in this process, leading to an affinity extraction protocol that enables iterative bead reuse and reagent lifetime maximization, thereby enhancing the efficiency of the HA extraction process. Our methods provide a framework for general optimization of immunoprecipitation in other contexts with heterogenous analyte sizes.

Biliary atresia

Biliary atresia (BA) is a progressive inflammatory fibrosclerosing disease of the biliary system and a major cause of neonatal cholestasis. It affects 1:5,000-20,000 live births, with the highest incidence in Asia. The pathogenesis is still unknown, but emerging research suggests a role for ciliary dysfunction, redox stress and hypoxia. The study of the underlying mechanisms can be conceptualized along the likely prenatal timing of an initial insult and the distinction between the injury and prenatal and postnatal responses to injury. Although still speculative, these emerging concepts, new diagnostic tools and early diagnosis might enable neoadjuvant therapy (possibly aimed at oxidative stress) before a Kasai portoenterostomy (KPE). This is particularly important, as timely KPE restores bile flow in only 50-75% of patients of whom many subsequently develop cholangitis, portal hypertension and progressive fibrosis; 60-75% of patients require liver transplantation by the age of 18 years. Early diagnosis, multidisciplinary management, centralization of surgery and optimized interventions for complications after KPE lead to better survival. Postoperative corticosteroid use has shown benefits, whereas the role of other adjuvant therapies remains to be evaluated. Continued research to better understand disease mechanisms is necessary to develop innovative treatments, including adjuvant therapies targeting the immune response, regenerative medicine approaches and new clinical tests to improve patient outcomes.

In Utero Extrahepatic Bile Duct Damage and Repair: Implications for Biliary Atresia

Biliary atresia (BA) is a cholangiopathy affecting the extrahepatic bile duct (EHBD) of newborns. The etiology and pathophysiology of BA are not fully understood; however, multiple causes of damage and obstruction of the neonatal EHBD have been identified. Initial damage to the EHBD likely occurs before birth. We discuss how different developmental stages in utero and birth itself could influence the susceptibility of the fetal EHBD to damage and a damaging wound-healing response. We propose that a damage-repair response of the fetal and neonatal EHBD involving redox stress and a program of fetal wound healing could-regardless of the cause of the initial damage-lead to either obstruction and BA or repair of the duct and recovery. This overarching concept should guide future research targeted toward identification of factors that contribute to recovery as opposed to progression of injury and fibrosis. Viewing BA through the lens of an in utero damage-repair response could open up new avenues for research and suggests exciting new therapeutic targets.

Targeted Analysis of the Size Distribution of Heavy Chain-Modified Hyaluronan with Solid-State Nanopores

The glycosaminoglycan hyaluronan (HA) plays important roles in diverse physiological functions where the distribution of its molecular weight (MW) can influence its behavior and is known to change in response to disease conditions. During inflammation, HA undergoes a covalent modification in which heavy chain subunits of the inter-alpha-inhibitor family of proteins are transferred to its structure, forming heavy chain-HA (HC•HA) complexes. While limited assessments of HC•HA have been performed previously, determining the size distribution of its HA component remains a challenge. Here, we describe a selective method for extracting HC•HA from mixtures that yields material amenable to MW analysis with a solid-state nanopore sensor. After demonstrating the approach in vitro, we validate extraction of HC•HA from osteoarthritic human synovial fluid as a model complex biological matrix. Finally, we apply our technique to pathophysiology by measuring the size distributions of HC•HA and total HA in an equine model of synovitis.