ADA2 deficiency (DADA2) as an unrecognised cause of early onset polyarteritis nodosa and stroke: a multicentre national study.

OBJECTIVES: To analyse the prevalence of CECR1 mutations in patients diagnosed with early onset livedo reticularis and/or haemorrhagic/ischaemic strokes in the context of inflammation or polyarteritis nodosa (PAN). Forty-eight patients from 43 families were included in the study. METHODS: Direct sequencing of CECR1 was performed by Sanger analysis. Adenosine deaminase 2 (ADA2) enzymatic activity was analysed in monocyte isolated from patients and healthy controls incubated with adenosine and with or without an ADA1 inhibitor. RESULTS: Biallelic homozygous or compound heterozygous CECR1 mutations were detected in 15/48 patients. A heterozygous disease-associated mutation (p.G47V) was observed in two affected brothers. The mean age of onset of the genetically positive patients was 24 months (6 months to 7 years). Ten patients displayed one or more cerebral strokes during their disease course. Low immunoglobulin levels were detected in six patients. Thalidomide and anti-TNF (tumour necrosis factor) blockers were the most effective drugs. Patients without CECR1 mutations had a later age at disease onset, a lower prevalence of neurological and skin manifestations; one of these patients displayed all the clinical features of adenosine deaminase 2deficiency (DADA2) and a defective enzymatic activity suggesting the presence of a missed mutation or a synthesis defect. CONCLUSIONS: DADA2 accounts for paediatric patients diagnosed with PAN-like disease and strokes and might explain an unrecognised condition in patients followed by adult rheumatologist. Timely diagnosis and treatment with anti-TNF agents are crucial for the prevention of severe complications of the disease. Functional assay to measure ADA2 activity should complement genetic testing in patients with non-confirming genotypes.

Disease activity accounts for long-term efficacy of IL-1 blockers in pyogenic sterile arthritis pyoderma gangrenosum and severe acne syndrome.

OBJECTIVE: To provide a rationale for anti-IL-1 treatment in pyogenic sterile arthritis, pyoderma gangrenosum and acne (PAPA) by defining whether IL-1ß secretion is enhanced; requires NLRP3; and correlates with proline-serine-threonine phosphatase-interacting protein 1 mutations, disease activity and/or the clinical picture in PAPA. METHODS: Monocytes were isolated from 13 patients and 35 healthy donors and studied at baseline and following activation. Secretion pattern of IL-1ß, IL-1α, IL-1Ra, IL-6, IL-18 and TNF-α was assessed in supernatants by ELISA. The NLRP3 requirement for IL-1ß secretion was investigated by silencing technique in PAPA and healthy donor monocytes. Long-term follow-up (mean 26 months, range 4-38) was performed in five patients enrolled in an anti-IL-1 regimen. RESULTS: IL-1ß secretion in PAPA is increased, requires NLRP3 and correlates with disease activity. Patients with a history of osteoarticular flares release more IL-1ß, IL-6 and TNF-α compared with those with predominant cutaneous recurrences. Monocytes from patients in anti-IL-1 treatment dramatically reduced IL-1ß secretion after ex vivo activation, and long-term follow-up demonstrated decreased frequency of flares and normalization of acute phase reactants in all the patients. A straightforward correlation between genotype and IL-1ß signalling was not observed suggesting that factors other than mutation itself may play a role in regulating IL-1ß secretion and response to treatment in PAPA. CONCLUSION: PAPA patients with active lesions display increased NLRP3-mediated IL-1ß secretion, and long-term efficacy of IL-1 blockade was demonstrated. Even if other mechanisms related to the complex proline-serine-threonine phosphatase-interacting protein 1 protein networking might play additional roles, this study further supports the potential of IL-1 blockade as an effective therapeutic strategy in PAPA syndrome.

Single amino acid charge switch defines clinically distinct proline-serine-threonine phosphatase-interacting protein 1 (PSTPIP1)-associated inflammatory diseases.

BACKGROUND: Hyperzincemia and hypercalprotectinemia (Hz/Hc) is a distinct autoinflammatory entity involving extremely high serum concentrations of the proinflammatory alarmin myeloid-related protein (MRP) 8/14 (S100A8/S100A9 and calprotectin). OBJECTIVE: We sought to characterize the genetic cause and clinical spectrum of Hz/Hc. METHODS: Proline-serine-threonine phosphatase-interacting protein 1 (PSTPIP1) gene sequencing was performed in 14 patients with Hz/Hc, and their clinical phenotype was compared with that of 11 patients with pyogenic arthritis, pyoderma gangrenosum, and acne (PAPA) syndrome. PSTPIP1-pyrin interactions were analyzed by means of immunoprecipitation and Western blotting. A structural model of the PSTPIP1 dimer was generated. Cytokine profiles were analyzed by using the multiplex immunoassay, and MRP8/14 serum concentrations were analyzed by using an ELISA. RESULTS: Thirteen patients were heterozygous for a missense mutation in the PSTPIP1 gene, resulting in a p.E250K mutation, and 1 carried a mutation resulting in p.E257K. Both mutations substantially alter the electrostatic potential of the PSTPIP1 dimer model in a region critical for protein-protein interaction. Patients with Hz/Hc have extremely high MRP8/14 concentrations (2045 ± 1300 µg/mL) compared with those with PAPA syndrome (116 ± 74 µg/mL) and have a distinct clinical phenotype. A specific cytokine profile is associated with Hz/Hc. Hz/Hc mutations altered protein binding of PSTPIP1, increasing interaction with pyrin through phosphorylation of PSTPIP1. CONCLUSION: Mutations resulting in charge reversal in the y-domain of PSTPIP1 (E→K) and increased interaction with pyrin cause a distinct autoinflammatory disorder defined by clinical and biochemical features not found in patients with PAPA syndrome, indicating a unique genotype-phenotype correlation for mutations in the PSTPIP1 gene. This is the first inborn autoinflammatory syndrome in which inflammation is driven by uncontrolled release of members of the alarmin family.

Increased NLRP3-dependent interleukin 1ß secretion in patients with familial Mediterranean fever: correlation with MEFV genotype.

OBJECTIVES: To define in patients affected by familial Mediterranean fever (FMF) whether or not interleukin (IL)-1ß secretion (1) is enhanced, (2) correlates with the type of MEFV mutation and (3) is mediated by NLRP3. METHODS: Freshly isolated monocytes from 21 patients with FMF (12 homozygous and 9 heterozygous), 14 MEFV healthy carriers and 30 healthy donors (HDs), unstimulated or after lipopolysaccharide (LPS)-induced activation, were analysed for redox state (production of reactive oxygen species (ROS) and antioxidant responses) and IL-1ß and IL-1 receptor antagonist (IL-1Ra) secretion. NLRP3 down-modulation was induced by in vitro silencing of the NLRP3 gene. RESULTS: LPS-stimulated monocytes from patients with FMF displayed enhanced IL-1ß secretion, which correlated with number and penetrance of MEFV mutations. Silencing of NLRP3 consistently inhibited IL-1ß secretion. As in other autoinflammatory diseases, FMF monocytes produced more ROS than genetically negative cells from HDs. Unlike in cryopyrin-associated periodic fever syndromes (CAPS), however, they were characterised by a conserved and sustained antioxidant response. Consistent with this finding, activated MEFV-mutated monocytes did not exhibit the functional indicators of oxidative stress observed in CAPS, including accelerated IL-1ß secretion and deficient production of IL-1Ra. CONCLUSIONS: MEFV-mutated monocytes display enhanced IL-1ß secretion, which correlates with number of high-penetrance mutations and level of endogenous ROS. Unlike NLRP3-mutated cells, monocytes carrying MEFV mutations withstand oxidative stress and preserve IL-1Ra production, thereby limiting inflammation. Finally, in contrast with that found in the animal model, the increased secretion of IL-1ß by LPS-stimulated FMF monocytes is NLRP3-dependent.

Serial cardiac magnetic resonance imaging for guidance of therapy management in patients treated with anakinra due to recurrent pericarditis.

Aims: To determine the utility of serial cardiac magnetic resonance (CMR) imaging for guidance of therapy management in patients treated with anakinra due to recurrent pericarditis (RP), compared with C-reactive protein (CRP) assay alone. Methods and results: In 2018-21, we enrolled 18 (14.5 ± 1.8 years old, 72% males) consecutive RP patients treated with anakinra (100 mg/day in patients ≥ 18 years old; 2 mg/kg/day < 18 years old) due to RP corticosteroid-dependent or not responsive to colchicine or non-steroidal anti-inflammatory drugs. After hospitalization, they were 1:1 randomized to CMR [no pericardial oedema and/or late gadolinium enchantment (LGE)] or CRP (<0.6 mg/dL). Tests were repeated every 3 months until negative to halve the anakinra dosage and cessation. The idiopathic aetiology was the most prevalent (n = 8, 44%), followed by post-pericardiotomy (n = 6, 33%). After a median treatment period of 8.7 ± 3.6 months, CRP-guided RP patients experienced more recurrences than CMR-guided ones (6 vs. 1, P = 0.016), with the worst prognosis in terms of recurrences (log-rank, P = 0.025) and significantly increased time of treatment (12.7 ± 2 vs. 16.1 ± 3.4 months, P = 0.019). In a multivariable exploratory Cox regression model, the number of previous recurrences and the idiopathic aetiology were independent predictors of RP during the anakinra treatment. New recurrences were subsequently directed to CMR imaging, and therapy was modified according to the LGE/oedema trend. After 1-year follow-up, no further recurrence was detected. Conclusion: Among patients with RP and treated with anakinra, serial CMR imaging of the pericardium can be utilized as an imaging biomarker, more informative for therapy duration than the solely CRP assessment. ClinicalTrialsgov Identifier: NCT06071156.

Autophagy contributes to inflammation in patients with TNFR-associated periodic syndrome (TRAPS).

OBJECTIVES: Tumour necrosis factor (TNF) receptor-associated periodic syndrome (TRAPS) is caused by TNFRSF1A mutations, known to induce intracellular retention of the TNFα receptor 1 (TNFR1) protein, defective TNFα-induced apoptosis, and production of reactive oxygen species. As downregulation of autophagy, the main cellular pathway involved in insoluble aggregate elimination, has been observed to increase the inflammatory response, we investigated whether it plays a role in TRAPS pathogenesis. METHODS: The possible link between TNFRSF1A mutations and inflammation in TRAPS was studied in HEK-293T cells, transfected with expression constructs for wild-type and mutant TNFR1 proteins, and in monocytes derived from patients with TRAPS, by investigating autophagy function, NF-κB activation and interleukin (IL)-1ß secretion. RESULTS: We found that autophagy is responsible for clearance of wild-type TNFR1, but when TNFR1 is mutated, the autophagy process is defective, probably accounting for mutant TNFR1 accumulation as well as TRAPS-associated induction of NF-κB activity and excessive IL-1ß secretion, leading to chronic inflammation. Autophagy inhibition due to TNFR1 mutant proteins can be reversed, as demonstrated by the effects of the antibiotic geldanamycin, which was found to rescue the membrane localisation of mutant TNFR1 proteins, reduce their accumulation and counteract the increased inflammation by decreasing IL-1ß secretion. CONCLUSIONS: Autophagy appears to be an important mechanism in the pathogenesis of TRAPS, an observation that provides a rationale for the most effective therapy in this autoinflammatory disorder. Our findings also suggest that autophagy could be proposed as a novel therapeutic target for TRAPS and possibly other similar diseases.

Associations of depression, anxiety and antidepressants with histological severity of nonalcoholic fatty liver disease.

BACKGROUND: Depression and anxiety are common in patients with nonalcoholic fatty liver disease (NAFLD). However, their associations with histological severity of NAFLD are unknown. AIM: This study examined the association(s) of depression, anxiety and antidepressant pharmacotherapy with severity of histological features in patients with NAFLD. METHODS: We analysed 567 patients with biopsy-proven NAFLD enrolled in the Duke NAFLD Clinical Database. Depressive and anxiety symptoms were assessed using the Hospital Anxiety & Depression Scale (HADS). The associations of depression and anxiety with severity of histological features of NAFLD were analysed using multiple logistic (or ordinal logistic) regression models with and without adjusting for confounding factors. RESULT: Subclinical and clinical depression was noted in 53% and 14% of patients respectively. Subclinical and clinical anxiety was noted in 45% and 25% of patients respectively. After adjusting for confounders, depression was significantly associated with more severe hepatocyte ballooning in a dose-dependent manner (likelihood ratio test, P = 0.0201); adjusted cumulative odds ratio (COR) of subclinical and clinical depression for having a higher grade of hepatocyte ballooning were 2.1 [95% CI, 1.0, 4.4] and 3.6 [95% CI, 1.4, 8.8]. CONCLUSIONS: In patients with NAFLD, depression was associated with more severe hepatocyte ballooning. Further investigation exploring pathobiological mechanisms underlying the observed associations and potential effects of antidepressant pharmacotherapy on NAFLD liver histology is warranted.

Inherited autoinflammatory diseases: a critical digest of the recent literature.

In this paper we provide a critical digest of the recent literature on inherited autoinflammatory diseases. We reviewed all the articles published during the last 24 months on monogenic autoinflammatory diseases and selected the most relevant studies regarding the pathogenesis, clinical aspects and management of these conditions. In particular, we focused the attention on the more frequent conditions, familial Mediterranean fever (FMF), cryopyrin-associated periodic syndrome (CAPS) and TNF-receptor associated periodic syndrome (TRAPS).

Deficient production of IL-1 receptor antagonist and IL-6 coupled to oxidative stress in cryopyrin-associated periodic syndrome monocytes.

OBJECTIVE: To determine whether dysregulated production of cytokines downstream of interleukin (IL)-1 participates in the pathophysiology of cryopyrin-associated periodic syndromes (CAPS). METHODS: Primary monocytes from patients with CAPS, unstimulated or after stimulation with lipopolysaccharide (LPS) and other Toll-like receptor (TLR) agonists, were examined for signs of stress and production of IL-1ß, IL-1 receptor antagonist (IL-1Ra) and IL-6 in comparison with monocytes from patients with autoimmune diseases and from healthy donors. RESULTS: Unstimulated CAPS monocytes showed mild signs of stress including elevated levels of reactive oxygen species and fragmented mitochondria. Stress signs were worsened by TLR stimulation and eventually led to protein synthesis inhibition with strong impairment of production of cytokines downstream of IL-1, such as IL-1Ra and IL-6. These defects were not detected in monocytes from autoimmune patients and healthy donors. CONCLUSIONS: The stress state of LPS-stimulated CAPS monocytes and the consequent inhibition of translation are likely to be responsible for the impaired production of IL-1Ra and IL-6. The deficient secretion of these cytokines coupled with increased IL-1ß release explains the severity of the IL-1-related clinical manifestations and the predominant implication of innate immunity in CAPS.

Hedgehog activity, epithelial-mesenchymal transitions, and biliary dysmorphogenesis in biliary atresia.

UNLABELLED: Biliary atresia (BA) is notable for marked ductular reaction and rapid development of fibrosis. Activation of the Hedgehog (Hh) pathway promotes the expansion of populations of immature epithelial cells that coexpress mesenchymal markers and may be profibrogenic. We examined the hypothesis that in BA excessive Hh activation impedes ductular morphogenesis and enhances fibrogenesis by promoting accumulation of immature ductular cells with a mesenchymal phenotype. Livers and remnant extrahepatic ducts from BA patients were evaluated by quantitative reverse-transcription polymerase chain reaction (QRT-PCR) and immunostaining for Hh ligands, target genes, and markers of mesenchymal cells or ductular progenitors. Findings were compared to children with genetic cholestatic disease, age-matched deceased donor controls, and adult controls. Ductular cells isolated from adult rats with and without bile duct ligation were incubated with Hh ligand-enriched medium ± Hh-neutralizing antibody to determine direct effects of Hh ligands on epithelial to mesenchymal transition (EMT) marker expression. Livers from pediatric controls showed greater innate Hh activation than adult controls. In children with BA, both intra- and extrahepatic ductular cells demonstrated striking up-regulation of Hh ligand production and increased expression of Hh target genes. Excessive accumulation of Hh-producing cells and Hh-responsive cells also occurred in other infantile cholestatic diseases. Further analysis of the BA samples demonstrated that immature ductular cells with a mesenchymal phenotype were Hh-responsive. Treating immature ductular cells with Hh ligand-enriched medium induced mesenchymal genes; neutralizing Hh ligands inhibited this. CONCLUSION: BA is characterized by excessive Hh pathway activity, which stimulates biliary EMT and may contribute to biliary dysmorphogenesis. Other cholestatic diseases show similar activation, suggesting that this is a common response to cholestatic injury in infancy.

Osteopontin is induced by hedgehog pathway activation and promotes fibrosis progression in nonalcoholic steatohepatitis.

UNLABELLED: Nonalcoholic steatohepatitis (NASH) is a leading cause of cirrhosis. Recently, we showed that NASH-related cirrhosis is associated with Hedgehog (Hh) pathway activation. The gene encoding osteopontin (OPN), a profibrogenic extracellular matrix protein and cytokine, is a direct transcriptional target of the Hh pathway. Thus, we hypothesize that Hh signaling induces OPN to promote liver fibrosis in NASH. Hepatic OPN expression and liver fibrosis were analyzed in wild-type (WT) mice, Patched-deficient (Ptc(+/-) ) (overly active Hh signaling) mice, and OPN-deficient mice before and after feeding methionine and choline-deficient (MCD) diets to induce NASH-related fibrosis. Hepatic OPN was also quantified in human NASH and nondiseased livers. Hh signaling was manipulated in cultured liver cells to assess direct effects on OPN expression, and hepatic stellate cells (HSCs) were cultured in medium with different OPN activities to determine effects on HSC phenotype. When fed MCD diets, Ptc(+/-) mice expressed more OPN and developed worse liver fibrosis (P < 0.05) than WT mice, whereas OPN-deficient mice exhibited reduced fibrosis (P < 0.05). In NASH patients, OPN was significantly up-regulated and correlated with Hh pathway activity and fibrosis stage. During NASH, ductular cells strongly expressed OPN. In cultured HSCs, SAG (an Hh agonist) up-regulated, whereas cyclopamine (an Hh antagonist) repressed OPN expression (P < 0.005). Cholangiocyte-derived OPN and recombinant OPN promoted fibrogenic responses in HSCs (P < 0.05); neutralizing OPN with RNA aptamers attenuated this (P < 0.05). CONCLUSION: OPN is Hh-regulated and directly promotes profibrogenic responses. OPN induction correlates with Hh pathway activity and fibrosis stage. Therefore, OPN inhibition may be beneficial in NASH.

Proteomic Signatures of Monocytes in Hereditary Recurrent Fevers.

Hereditary periodic recurrent fevers (HRF) are monogenic autoinflammatory associated to mutations of some genes, such as diseases caused by mutations of including MEFV, TNFRSF1A and MVK genes. Despite the identification of the causative genes, the intracellular implications related to each gene variant are still largely unknown. A large -scale proteomic analysis on monocytes of these patients is aimed to identify with an unbiased approach the mean proteins and molecular interaction networks involved in the pathogenesis of these conditions. Monocytes from HRF 15 patients (5 with MFV, 5 TNFRSF1A and 5with MVK gene mutation) and 15 healthy donors (HDs) were analyzed by liquid chromatography and tandem mass spectrometry before and after lipopolysaccharide (LPS) stimulation. Significant proteins were analyzed through a Cytoscape analysis using the ClueGo app to identify molecular interaction networks. Protein networks for each HRF were performed through a STRING database analysis integrated with a DISEAE database query. About 5000 proteins for each HRF were identified. LPS treatment maximizes differences between up-regulated proteins in monocytes of HRF patients and HDs, independently from the disease's activity and ongoing treatments. Proteins significantly modulated in monocytes of the different HRF allowed creating a disease-specific proteomic signatures and interactive protein network. Proteomic analysis is able to dissect the different intracellular pathways involved in the inflammatory response of circulating monocytes in HRF patients. The present data may help to identify a "monocyte proteomic signature" for each condition and unravel new possible unexplored intracellular pathways possibly involved in their pathogenesis. These data will be also useful to identify possible differences and similarities between the different HRFs and some multifactorial recurrent fevers.

Leptin promotes the myofibroblastic phenotype in hepatic stellate cells by activating the hedgehog pathway.

Trans-differentiation of quiescent hepatic stellate cells (Q-HSCs), which exhibit epithelial and adipocytic features, into myofibroblastic-HSC (MF-HSCs) is a key event in liver fibrosis. Culture models demonstrated that Hedgehog (Hh) pathway activation is required for transition of epithelioid/adipocytic Q-HSCs into MF-HSCs. Hh signaling inhibits adiposity and promotes epithelial-to-mesenchymal transitions (EMTs). Leptin (anti-adipogenic, pro-EMT factor) promotes HSC trans-differentiation and liver fibrosis, suggesting that the pathways may interact to modulate cell fate. This study aimed to determine whether leptin activates Hh signaling and whether this is required for the fibrogenic effects of leptin. Cultures of primary HSCs from lean and fa/fa rats with an inherited ObRb defect were examined. Inhibitors of PI3K/Akt, JAK/STAT, and Hh signaling were used to delineate how ObRb activation influenced Hh signaling and HSC trans-differentiation. Fibrogenesis was compared in wild type and db/db mice (impaired ObRb function) to assess the profibrotic role of leptin. The results demonstrate that leptin-ObR interactions activate Hh signaling with the latter necessary to promote trans-differentiation. Leptin-related increases in Hh signaling required ObR induction of PI3K/Akt, which was sufficient for leptin to repress the epithelioid/adipocytic program. Leptin-mediated induction of JAK/STAT was required for mesenchymal gene expression. Leptin-ObRb interactions were not necessary for HSC trans-differentiation to occur in vitro or in vivo but are important because liver fibrogenesis was attenuated in db/db mice. These findings reveal that leptin activates Hh signaling to alter gene expression programs that control cell fate and have important implications for liver fibrosis and other leptin-regulated processes involving EMTs, including development, obesity, and cancer metastasis.

Hedgehog signaling in the liver.

Reactivation of Hedgehog (Hh), a morphogenic signaling pathway that controls progenitor cell fate and tissue construction during embryogenesis occurs during many types of liver injury in adult. The net effects of activating the Hedgehog pathway include expansion of liver progenitor populations to promote liver regeneration, but also hepatic accumulation of inflammatory cells, liver fibrogenesis, and vascular remodeling. All of these latter responses are known to be involved in the pathogenesis of cirrhosis. In addition, Hh signaling may play a role in primary liver cancers, such as cholangiocarcinoma and hepatocellular carcinoma. Study of Hedgehog signaling in liver cells is in its infancy. Additional research in this area is justified given growing experimental and clinical data supporting a role for the pathway in regulating outcomes of liver injury.

Hedgehog signaling regulates epithelial-mesenchymal transition during biliary fibrosis in rodents and humans.

Epithelial-mesenchymal transitions (EMTs) play an important role in tissue construction during embryogenesis, and evidence suggests that this process may also help to remodel some adult tissues after injury. Activation of the hedgehog (Hh) signaling pathway regulates EMT during development. This pathway is also induced by chronic biliary injury, a condition in which EMT has been suggested to have a role. We evaluated the hypothesis that Hh signaling promotes EMT in adult bile ductular cells (cholangiocytes). In liver sections from patients with chronic biliary injury and in primary cholangiocytes isolated from rats that had undergone bile duct ligation (BDL), an experimental model of biliary fibrosis, EMT was localized to cholangiocytes with Hh pathway activity. Relief of ductal obstruction in BDL rats reduced Hh pathway activity, EMT, and biliary fibrosis. In mouse cholangiocytes, coculture with myofibroblastic hepatic stellate cells, a source of soluble Hh ligands, promoted EMT and cell migration. Addition of Hh-neutralizing antibodies to cocultures blocked these effects. Finally, we found that EMT responses to BDL were enhanced in patched-deficient mice, which display excessive activation of the Hh pathway. Together, these data suggest that activation of Hh signaling promotes EMT and contributes to the evolution of biliary fibrosis during chronic cholestasis.

Paracrine modulation of cholangiocyte serotonin synthesis orchestrates biliary remodeling in adults.

Paracrine signaling between cholangiocytes and stromal cells regulates biliary remodeling. Cholangiocytes have neuroepithelial characteristics and serotonin receptor agonists inhibit their growth, but whether they are capable of serotonin biosynthesis is unknown. We hypothesized that cholangiocytes synthesize serotonin and that cross talk between liver myofibroblasts (MF) and cholangiocytes regulates this process to influence biliary remodeling. Transwell cultures of cholangiocytes ± MF, and tryptophan hydroxylase-2 knockin (TPH2KI) mice with an inactivating mutation of the neuronal tryptophan hydroxylase (TPH) isoform, TPH2, were evaluated. Results in the cell culture models confirm that cholangiocytes have serotonin receptors and demonstrate for the first time that these cells express TPH2 and produce serotonin, which autoinhibits their growth but stimulates MF production of TGF-ß(1). Increased TGF-ß(1), in turn, counteracts autocrine inhibition of cholangiocyte growth by repressing cholangiocyte TPH2 expression. Studies of TPH2KI mice confirm that TPH2-mediated production of serotonin plays an important role in remodeling damaged bile ducts because mice with decreased TPH2 function have reduced biliary serotonin levels and exhibit excessive cholangiocyte proliferation, accumulation of aberrant ductules and liver progenitors, and increased liver fibrosis after bile duct ligation. This new evidence that cholangiocytes express the so-called neuronal isoform of TPH, synthesize serotonin de novo, and deploy serotonin as an autocrine/paracrine signal to regulate regeneration of the biliary tree complements earlier work that revealed that passive release of serotonin from platelets stimulates hepatocyte proliferation. Given the prevalent use of serotonin-modulating drugs, these findings have potentially important implications for recovery from various types of liver damage.

Hedgehog signaling is critical for normal liver regeneration after partial hepatectomy in mice.

UNLABELLED: Distinct mechanisms are believed to regulate growth of the liver during fetal development and after injury in adults, because the former relies on progenitors and the latter generally involves replication of mature hepatocytes. However, chronic liver injury in adults increases production of Hedgehog (Hh) ligands, developmental morphogens that control progenitor cell fate and orchestrate various aspects of tissue construction during embryogenesis. This raises the possibility that similar Hh-dependent mechanisms also might regulate adult liver regeneration. The current analysis of murine liver regeneration after 70% partial hepatectomy (PH), an established model of adult liver regeneration, demonstrated that PH induced production of Hh ligands and activated Hh signaling in liver cells. Treatment with a specific Hh signaling inhibitor interfered with several key components of normal liver regeneration, significantly inhibiting progenitor responses, matrix remodeling, proliferation of hepatocytes and ductular cells, and restoration of liver mass. These global inhibitory effects on liver regeneration dramatically reduced survival after PH. CONCLUSION: Mechanisms that mediate liver organogenesis, such as Hh pathway activation, are retained and promote reconstruction of adult livers after injury.

Activation of Rac1 promotes hedgehog-mediated acquisition of the myofibroblastic phenotype in rat and human hepatic stellate cells.

UNLABELLED: Hepatic accumulation of myofibroblastic hepatic stellate cells (MF-HSCs) is pivotal in the pathogenesis of cirrhosis. Two events are necessary for MF-HSCs to accumulate in damaged livers: transition of resident, quiescent hepatic stellate cells (Q-HSCs) to MF-HSCs and expansion of MF-HSC numbers through increased proliferation and/or reduced apoptosis. In this study, we identified two novel mediators of MF-HSC accumulation: Ras-related C3 botulinum toxin substrate 1 (Rac1) and Hedgehog (Hh). It is unclear whether Rac1 and Hh interact to regulate the accumulation of MF-HSCs. We evaluated the hypothesis that Rac1 promotes activation of the Hh pathway, thereby stimulating signals that promote transition of Q-HSCs into MF-HSCs and enhance the viability of MF-HSCs. Using both in vitro and in vivo model systems, Rac1 activity was manipulated through adenoviral vector-mediated delivery of constitutively active or dominant-negative rac1. Rac1-transgenic mice with targeted myofibroblast expression of a mutated human rac1 transgene that produces constitutively active Rac1 were also examined. Results in all models demonstrated that activating Rac1 in HSC enhanced Hh signaling, promoted acquisition/maintenance of the MF-HSC phenotype, increased MF-HSC viability, and exacerbated fibrogenesis. Conversely, inhibiting Rac1 with dominant-negative rac1 reversed these effects in all systems examined. Pharmacologic manipulation of Hh signaling demonstrated that profibrogenic actions of Rac1 were mediated by its ability to activate Hh pathway-dependent mechanisms that stimulated myofibroblastic transition of HSCs and enhanced MF-HSC viability. CONCLUSION: These findings demonstrate that interactions between Rac1 and the Hh pathway control the size of MF-HSC populations and have important implications for the pathogenesis of cirrhosis.

Accumulation of natural killer T cells in progressive nonalcoholic fatty liver disease.

UNLABELLED: Liver inflammation is greater in nonalcoholic steatohepatitis (NASH) than steatosis, suggesting that immune responses contribute to nonalcoholic fatty liver disease (NAFLD) progression. Livers normally contain many natural killer T (NKT) cells that produce factors that modulate inflammatory and fibrogenic responses. Such cells are relatively depleted in steatosis, but their status in more advanced NAFLD is uncertain. We hypothesized that NKT cells accumulate and promote fibrosis progression in NASH. We aimed to determine if livers become enriched with NKT cells during NASH-related fibrosis; identify responsible mechanisms; and assess if NKT cells stimulate fibrogenesis. NKT cells were analyzed in wildtype mice and Patched-deficient (Ptc(+/-)) mice with an overly active Hedgehog (Hh) pathway, before and after feeding methionine choline-deficient (MCD) diets to induce NASH-related fibrosis. Effects of NKT cell-derived factors on hepatic stellate cells (HSC) were examined and fibrogenesis was evaluated in CD1d-deficient mice that lack NKT cells. NKT cells were quantified in human cirrhotic and nondiseased livers. During NASH-related fibrogenesis in wildtype mice, Hh pathway activation occurred, leading to induction of factors that promoted NKT cell recruitment, retention, and viability, plus liver enrichment with NKT cells. Ptc(+/-) mice accumulated more NKT cells and developed worse liver fibrosis; CD1d-deficient mice that lack NKT cells were protected from fibrosis. NKT cell-conditioned medium stimulated HSC to become myofibroblastic. Liver explants were 2-fold enriched with NKT cells in patients with non-NASH cirrhosis, and 4-fold enriched in patients with NASH cirrhosis. CONCLUSION: Hh pathway activation leads to hepatic enrichment with NKT cells that contribute to fibrosis progression in NASH.

Hedgehog signaling in cholangiocytes.

PURPOSE OF REVIEW: Cells lining the biliary tree are targets of injury, but also orchestrate liver repair. The latter involves autocrine/paracrine signaling that enhances the viability and growth of residual ductular cells and promotes accumulation of inflammatory and myofibroblastic cells. The mechanisms mediating this so-called 'ductular reaction' need to be better understood to improve injury outcomes. Studies are revealing that ductular cells produce and respond to hedgehog (Hh) ligands, developmental morphogens that control progenitor cell fate and tissue construction during embryogenesis. Because this has potential implications for liver repair, this review will summarize current knowledge about Hh signaling and cholangiocytes. RECENT FINDINGS: Diverse types of liver injury stimulate cholangiocytes to generate Hh ligands, and cholangiocyte-derived Hh ligands interact with receptors on cholangiocytes and neighboring cells to modulate virtually every aspect of the ductular reaction to injury. Excessive Hh signaling promotes dysfunctional repair and results in chronic hepatic inflammation, fibrogenesis, and carcinogenesis. SUMMARY: The Hh pathway is part of the complex signaling network that orchestrates liver repair. How other pathways and posttranscriptional mechanisms modulate Hh signaling in ductular cells remains unclear. Further research in this area may identify novel therapeutic targets for the treatment of cholangiopathies and cholangiocarcinoma.