What is PFIC?
 

Progressive Familial Intrahepatic Cholestasis (PFIC) is a group of inherited disorders caused by various autosomal recessive mutations. It results from the inability of hepatocytes to properly form and secrete bile due to specific gene mutations, which can ultimately progress to liver failure. PFIC has three classic types: PFIC-1, PFIC-2, and PFIC-3. The incidence of PFIC-1 and PFIC-2 is approximately 1/100,000 to 1/50,000.
 

Pathogenesis
 

The liver synthesizes bile acids, cholic acid (CA) and chenodeoxycholic acid (CDCA), from cholesterol via the classical (neutral, initiated by CYP7A1) and alternative (acidic, initiated by CYP27A1) pathways. These are conjugated with taurine/glycine to form bile salts. Hepatocytes uptake precursors via basolateral membrane transporters (Phase 0: NTCP, OATPs). Phase I/II involves metabolism and conjugation by enzymes like CYP7A1 and CYP8B1. Phase III involves secretion of bile salts into bile canaliculi via canalicular membrane transporters (e.g., BSEP, MDR3), forming bile acid-phospholipid mixed micelles. Concurrently, cholangiocytes secrete HCO₃⁻ and water via CFTR and bicarbonate-chloride exchangers, diluting bile and reducing viscosity. Bile is finally stored in the gallbladder and released postprandially.
 

Mutations in genes encoding the key proteins in these stages are the root cause of various PFIC types.

 

Image source: Molecular overview of progressive familial intrahepatic cholestasis

 

PFIC-1 Type:​ Caused by mutations in the ATP8B1gene leading to loss of function of its encoded protein, FIC1. FIC1 is an aminophospholipid flippase located on the canalicular membrane, responsible for translocating phosphatidylserine (PS) and phosphatidylethanolamine (PE) from the outer to the inner leaflet, maintaining membrane asymmetry. Mutations impair phospholipid flipping, disrupting membrane asymmetry. This not only weakens the membrane's resistance to hydrophobic bile salts but also impairs the farnesoid X receptor (FXR) signaling pathway, leading to downregulation of downstream bile acid efflux pumps. Together, this exacerbates intracellular bile salt accumulation and bile secretion impairment, ultimately causing hepatocyte injury, cholestasis, and fibrosis. It can be accompanied by extrahepatic symptoms (e.g., diarrhea, hearing loss).
 

PFIC-2 Type:​ Caused by mutations in the ABCB11gene. The ABCB11gene is located on chromosome 2q24 and encodes the bile salt export pump (BSEP), a bile salt transporter on the hepatocyte canalicular membrane. Gene mutations can lead to BSEP expression deficiency, intracellular retention, or transport dysfunction, causing intracellular bile salt accumulation and severe cytotoxicity. Concurrently, activation of the nuclear receptor FXR signaling pathway is impaired, further exacerbating bile excretion disorders. Its clinical features include severe intrahepatic cholestasis, low GGT, significantly elevated bilirubin, and an increased risk of early hepatocellular carcinoma.
 

 PFIC-3 Type:​ Caused by mutations in the ABCB4gene, which encodes the multidrug resistance protein 3 (MDR3). MDR3 is primarily expressed on the hepatocyte canalicular membrane, and its functional product, a phosphatidylcholine (PC) floppase, regulates the outward movement of phospholipids from the bilayer. Normally, PC forms mixed micelles with bile salts, neutralizing the toxicity of hydrophobic bile acids. Gene mutations lead to severely reduced or absent PC secretion, resulting in a lack of protective phospholipids in bile. This allows free hydrophobic bile acids to directly damage bile canaliculi and cholangiocytes, leading to cholestasis, cholangitis, and bile duct proliferation.

 

Image source: Progressive familial intrahepatic cholestasis
 

Mouse Models
 

ATP8B1 KO Mice:​ Complete knockout of the ATP8B1gene, primarily used to model the hepatic and extrahepatic manifestations of human PFIC-1 (Byler disease). Suitable for studying the pathogenesis of phospholipid transport disorders, cholestasis, hearing loss, and enterocyte polarity abnormalities.
 

ATP8B1 G308V Mice:​ Carry the G308V missense mutation in the ATP8B1gene (modeling the human homozygous mutation), leading to mislocalization or loss of function of the FIC1 protein in hepatocytes. This model simulates symptoms of PFIC-1, such as low gamma-glutamyl transferase (GGT) cholestasis.
 

ABCB11 KO Mice:​ Complete knockout of the ABCB11gene, modeling human PFIC-2 (BSEP deficiency disease). Used to study bile acid excretion disorders, hepatotoxicity due to intracellular bile acid accumulation, low GGT cholestasis, and the mechanisms of hepatocellular carcinoma (HCC) development.
 

ABCB11 E297G Mice:​ Carry the E297G point mutation in the ABCB11gene, causing BSEP protein processing or functional defects. This model simulates partial cholestatic phenotypes of PFIC-2 and can be used to evaluate the therapeutic effects of targeted drugs (e.g., IBAT inhibitors) on BSEP dysfunction.
 

MDR2 KO Mice:​ Complete knockout of the MDR2gene, modeling human PFIC-3. This is a classic model for studying bile phospholipid deficiency, bile duct injury, portal inflammation, and hepatic fibrosis, commonly used to evaluate the efficacy of anti-fibrotic and choleretic drugs.
 

Supporting Gene Therapy
 

Gene therapy offers hope for rare diseases, but its development and validation rely heavily on animal model support. MingCeler Biotech, leveraging its self-developed TurboMice™ technology, has developed multiple rare disease mouse models. The TurboMice™ technology overcomes the technical challenges of long mouse model generation cycles and low success rates for complex models, enabling editing at almost any target gene locus. Complete homozygous gene-edited mouse models can be prepared directly from embryonic stem cells in as little as two months.
 

MingCeler Biotech​ can customize various PFIC mouse models according to client needs, such as ATP8B1 KO mice, ATP8B1 G308V mice, ABCB11 KO mice, ABCB11 E297G mice, and MDR2 KO mice. Inquiries are welcome.
 

References:

1.Liu XL, Ma SP, Liu L, Wang XX. [One case of progressive familial intrahepatic cholestasis type 2]. Zhonghua Gan Zang Bing Za Zhi. 2016 Sep 20; 24(9):701-703. Chinese. doi: 10.3760/cma.j.issn.1007-3418.2016.09.014. PMID: 27788730; PMCID: PMC12769895.

2.Davit-Spraul A, Gonzales E, Baussan C, Jacquemin E. Progressive familial intrahepatic cholestasis. Orphanet J Rare Dis. 2009 Jan 8;4:1. doi: 10.1186/1750-1172-4-1. PMID: 19133130; PMCID: PMC2647530.

3.Amirneni S, Haep N, Gad MA, Soto-Gutierrez A, Squires JE, Florentino RM. Molecular overview of progressive familial intrahepatic cholestasis. World J Gastroenterol. 2020 Dec 21;26(47):7470-7484. doi: 10.3748/wjg.v26.i47.7470. PMID: 33384548; PMCID: PMC7754551.