This is a mechanism module, not a specific disease. Disorder entries reference individual nodes via conforms_to (e.g. "cholestatic_liver_injury#Hepatocellular and Biliary Bile Acid Retention"). The key conformance target is the central_effector node "Bile Acid-Mediated Hepatocyte and Cholangiocyte Injury" - the disorder-agnostic, rate-limiting step every conformer funnels through.
Disorder-specific substitutions at the trigger node: a canalicular transporter or tight-junction defect in progressive familial intrahepatic cholestasis (ATP8B1/FIC1, ABCB11/BSEP, ABCB4/MDR3, TJP2, NR1H4/FXR); autoimmune destruction of small intrahepatic bile ducts in primary biliary cholangitis; fibro-obliterative inflammation of larger ducts in primary sclerosing cholangitis and IgG4-related sclerosing cholangitis; congenital paucity of interlobular bile ducts in Alagille syndrome; perinatal obliteration of the extrahepatic biliary tree in biliary atresia; oestrogen/progesterone-metabolite inhibition of canalicular export in intrahepatic cholestasis of pregnancy; and drug or metabolite inhibition of BSEP in drug-induced cholestasis.
Scope boundaries. This module is deliberately NOT an Xogenesis module: its terminal output is failure of a normal secretory process and the fibrotic remodelling that follows, not the formation of a discrete pathological structure. It is distinct from - and complementary to - `cholelithiasis_biliary_supersaturation`, which models the physical-chemical formation of gallstones from supersaturated bile rather than the consequences of retained bile acids; a disorder in which an impacted stone obstructs the biliary tree may conform to both. The generic mesenchymal arm of the fibrosis it produces is modelled by `fibrotic_response`, and the drug-toxicity arm of cholestatic drug reactions by `drug_induced_liver_injury`; this module contributes the bile-acid-retention and cholangiocyte-hub steps that neither of those carries. Hyperbilirubinaemia arising from a pure conjugation or bilirubin-transport defect with intact bile acid secretion (Gilbert, Crigler-Najjar, Dubin-Johnson, Rotor) is NOT cholestasis in this sense and does not conform: those disorders lack bile acid retention and do not produce this injury chain.
Does any therapy act on the ductular reaction and cholestatic fibrogenesis node itself, rather than only on upstream bile acid retention?
KNOWLEDGE GAP
ductular_reaction_undruggable
Attached to:
Ductular Reaction and Cholangiocyte-Driven Fibrogenesis
Both curated treatments in this module (UDCA, obeticholic acid) act on the retention amplifier, and the one randomized trial with fibrosis endpoints showed no significant effect on noninvasive fibrosis measures at 12 months. The ductular reaction node is explicitly described in the literature as having no drugs targeting it. This is the therapeutic gap that makes the cholangiopathies a "black box" in clinical hepatology, and conforming entries should not imply that upstream bile-acid-directed therapy addresses it.
Proposed experiments:
Randomized trial with histological fibrosis endpoints in cholestatic disease
Hepatocellular and Biliary Bile Acid Retention
amplifier
Bile acids that cannot be exported accumulate to supraphysiological concentrations inside hepatocytes, in the biliary tree, and in the systemic circulation. Retention drives two opposing responses: a deteriorative response, in which the accumulated hydrophobic bile acids act as detergents and signalling molecules that injure cells, and an adaptive response, in which alternative basolateral export pumps, bile acid hydroxylation, and FXR-mediated repression of bile acid synthesis act to lower the intracellular load. The balance between these two responses sets whether cholestasis stays compensated or progresses, and it is the node on which the bile-acid-directed drugs act.
Downstream
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Bile Acid-Mediated Hepatocyte and Cholangiocyte Injury
Retained hydrophobic bile acids reach concentrations that are directly cytotoxic to hepatocytes and to the cholangiocytes lining the bile ducts.
Show evidence (2 references)
"it can be triggered by a variety of factors that induce 2 types of biological responses, namely a deteriorative response, caused by bile acid accumulation, and an adaptive response, aimed at removing the accumulated bile acids."
States the two-response structure of this node - injury driven by bile acid accumulation, opposed by an adaptive removal response - and that diverse upstream triggers converge on it. Evidence source is OTHER because this is a review of mechanisms and in vitro models.
"Hereditary cholestasis is a heterogeneous group of rare autosomal recessive liver disorders, which are characterised by intrahepatic cholestasis, pruritus, and jaundice and caused by defects in genes related to the secretion and transport of bile salts and lipids."
Links the retention state to its systemic clinical readouts (pruritus, jaundice) and confirms that heterogeneous genetic lesions converge on it. Evidence source is OTHER because this is a review.
Ductular Reaction and Cholangiocyte-Driven Fibrogenesis
effector
Cholangiocyte proliferation at the portal-parenchymal interface produces the ductular reaction, the histological hallmark of chronic cholestasis. The reactive ductular cells secrete cytokines including TNF-alpha and TGF-beta that recruit and activate macrophages (Kupffer cells) and hepatic stellate cells, and they engage in direct crosstalk with portal fibroblasts. The result is portal-based collagen deposition - cholestatic fibrogenesis - which is anatomically distinct from the pericentral fibrosis of steatohepatitis and alcohol-related liver disease. The extent of ductular reaction tracks with the rate of disease progression.
Downstream
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Biliary Fibrosis Progressing to Biliary Cirrhosis
Sustained portal fibrogenesis accumulates as bridging biliary fibrosis and ultimately remodels the liver into biliary cirrhosis.
Show evidence (3 references)
"Herein, we review the pivotal role of cholangiocytes in cholestatic fibrogenesis, focusing on the crosstalk between cholangiocytes and portal fibroblasts and HSCs."
Names the cholangiocyte-portal fibroblast-hepatic stellate cell crosstalk that constitutes this node. Evidence source is OTHER because this is a review.
"Txnip deficiency increases TNF-α and TGF-β secretion by cholangiocytes to stimulate Kupffer cells and hepatic stellate cells, consequently leading to inflammation and collagen deposition."
Provides the mechanistic link from cholangiocyte cytokine secretion to Kupffer cell and stellate cell activation and thence to collagen deposition. Evidence source is MODEL_ORGANISM because the causal chain was established in cholangiocyte-specific knockout mice.
"Ductular reaction is associated with liver disease progression, but there are no drugs targeting ductular reaction."
Establishes that the extent of ductular reaction tracks with progression of chronic liver disease, and records that this node has no approved therapy. Evidence source is OTHER, not HUMAN_CLINICAL: this is the paper's framing sentence citing prior literature rather than a measurement in its own cohort, and the study itself is a mouse-genetics paper (its other snippets here are correctly tagged MODEL_ORGANISM).
Biliary Fibrosis Progressing to Biliary Cirrhosis
consequence
Persistent cholestatic fibrogenesis produces progressive portal and periportal fibrosis, bridging fibrosis, and finally biliary cirrhosis with its sequelae - portal hypertension, hepatic decompensation, and the need for liver transplantation. This is the shared clinical endpoint of the cholangiopathies and of untreated hepatocellular cholestasis, and it is the outcome that conforming entries are ultimately describing.
Show evidence (3 references)
"Cholangiopathies comprise a spectrum of chronic intrahepatic and extrahepatic biliary tract disorders culminating in progressive cholestatic liver injury, fibrosis, and often cirrhosis and its sequela."
States the terminal step of the module - progressive cholestatic injury and fibrosis culminating in cirrhosis - and that it is shared across the whole cholangiopathy spectrum. Evidence source is OTHER because this is a review.
"Sclerosing cholangitis (SC) is defined as a condition with progressive stenosis and destruction of the bile ducts due to diffuse inflammation and fibrosis"
Confirms that progressive inflammation and fibrosis destroying bile ducts is the defining disease process for a major conforming disorder class, the sclerosing cholangitides. Evidence source is OTHER because this is a clinical review.
"with onset in early infancy and progression to end-stage liver disease"
Records that the severe end of the inherited cholestasis spectrum reaches the same end-stage liver disease endpoint this node describes. Evidence source is OTHER because this is a review.
Ursodeoxycholic Acid
Platform:
Small molecule
Ursodeoxycholic acid (UDCA) is a hydrophilic bile acid and the first-line therapy for most cholestatic liver diseases. It acts on the bile acid retention node rather than on the downstream fibrosis: it enriches the bile acid pool with a non-cytotoxic species, stimulates bile flow, and - as shown in an experimental model of inflammatory cholestasis - restores expression and plasma-membrane localisation of the canalicular bile salt export pump BSEP, protecting hepatocytes against the bile acids accumulated by the secretory failure. This is the anticholestatic drug-target design pattern for conforming disorders: act upstream on the retention amplifier, not on the structural endpoint.
Evidence: 2
Farnesoid X Receptor Agonist (Obeticholic Acid)
Platform:
Small molecule
Obeticholic acid is a semisynthetic bile acid and agonist of the nuclear bile acid receptor FXR (NR1H4). FXR activation represses de novo bile acid synthesis and induces bile acid export, reinforcing the adaptive arm of the retention node. In patients with primary biliary cholangitis and an inadequate response to ursodiol it lowered alkaline phosphatase and bilirubin significantly more than placebo. Two caveats conforming entries must preserve: the trial showed no significant difference in noninvasive fibrosis measures at 12 months, so it is not evidence of an effect on the downstream fibrosis nodes; and it aggravates pruritus, the symptom most directly attributable to bile acid retention.
Evidence: 2