Integrin-YAP-CTGF Pathway Links Liver Blood Congestion to Fibrosis and Tumor Formation

When blood stagnates in the liver over months and years - a condition called chronic liver congestion, or congestive hepatopathy - the consequences can be severe. Fibrosis, in which scar tissue replaces healthy liver cells, can progress to cirrhosis. Portal hypertension, in which pressure builds within the liver's blood vessel network, follows. Liver cancer can develop. The clinical associations between congestion and these outcomes have been recognized for a long time.

What has remained unclear is the molecular chain of events that connects the physical problem - abnormally elevated pressure inside the liver's tiny blood vessels - to the cellular changes that produce fibrosis and tumor formation. Without knowing the mechanism, identifying specific molecular targets for prevention or treatment is not possible. Researchers at The University of Osaka set out to trace this pathway, and their findings, published in Gastroenterology, point to a specific signaling cascade in a cell type that sits at the interface between blood flow and liver tissue.

The Cell Type at the Center

Liver sinusoidal endothelial cells, known as LSECs, form the inner lining of the liver's sinusoids - the tiny, fenestrated blood vessels through which blood filters as it passes through the organ. Their location makes them directly and immediately responsive to changes in blood flow and pressure. When congestion slows blood movement and elevates pressure within the sinusoids, the LSECs are the first cells to experience that altered mechanical environment.

Lead author Seiya Kato and the team used single-cell transcriptomics and spatial transcriptomics - tools that reveal gene activity in individual cells while preserving their physical location in tissue - to study LSEC responses in both a mouse model of liver congestion and in human patient samples from conditions including Fontan-associated liver disease, a form of congestion that occurs in patients who have undergone the Fontan cardiac surgical procedure.

The Pathway: From Pressure to Protein Activation

The analyses revealed elevated activity of two key molecules in LSECs under congestion: Yes-associated protein (YAP) and connective tissue growth factor (CTGF). YAP is a mechanosensitive transcriptional regulator - a protein that detects physical forces and translates them into changes in gene expression. CTGF is a downstream target of YAP that promotes extracellular matrix production, driving fibrosis.

Experiments with LSECs grown under elevated hydrostatic pressure - mimicking the physical conditions of congestion - demonstrated that the pressure activates YAP through a cell surface receptor called integrin alphaV. YAP then upregulates CTGF. The researchers validated the pathway's functional importance by inhibiting integrin alphaV or removing CTGF from LSECs: both interventions improved outcomes in the mouse congestion model.

Crucially, the same pattern - YAP activation leading to elevated CTGF in LSECs - was observed in human patient tissue samples, not just in mice. Senior author Hayato Hikita noted that this newly identified integrin alphaV-YAP-CTGF pathway could offer a new treatment direction.

Who Might Benefit From This Knowledge

The immediate clinical population of interest includes patients with Fontan-associated liver disease. The Fontan procedure is used to manage certain complex congenital heart defects, but it creates chronic elevated venous pressure that, over time, congests the liver. These patients are at substantially increased risk of liver fibrosis, portal hypertension, and hepatocellular carcinoma as they age, and there are currently few disease-modifying treatment options.

The potential relevance extends further. Portal hypertension - elevated pressure in the portal vein system - occurs in liver cirrhosis from many different causes, including viral hepatitis, alcohol, and non-alcoholic fatty liver disease. If the sinusoidal pressure increases associated with cirrhosis activate the same integrin-YAP-CTGF axis, the pathway identified here might be relevant to a much larger population of liver disease patients.

Distance From Mouse Model to Clinical Application

The evidence from mouse models and human tissue is mechanistically coherent and internally consistent, but the path from identifying a pathway to deploying a therapy targeting it involves substantial additional work. Inhibiting integrin alphaV or CTGF in the context of an already complex liver disease would require demonstrating safety and efficacy in larger animal models, and eventually in clinical trials with appropriate endpoints. Off-target effects and the behavior of pathway inhibitors in patients with compromised liver function are considerations that preclinical data cannot fully address.

The study establishes the pathway's existence and its relevance to both mouse congestion models and human patient tissue. That is a meaningful advance from the prior state of the field, where the molecular connection between pressure and fibrosis in congestive hepatopathy was essentially unknown.