Why Blocking a Key Inflammation Protein Failed to Stop Liver Disease
In communities around the world, a silent epidemic is growing—nonalcoholic fatty liver disease (NAFLD). What begins as simple fat accumulation in liver cells can progress to its severe inflammatory form, nonalcoholic steatohepatitis (NASH), characterized by liver cell injury, inflammation, and fibrosis. With no FDA-approved medications available until very recently, NASH represents a significant and growing public health crisis linked to obesity and metabolic syndrome 5 7 .
NASH is estimated to affect 3-5% of the global population, with prevalence increasing alongside obesity rates.
Until 2024, there were no FDA-approved medications specifically for NASH, creating a significant treatment gap.
"The progression from simple fatty liver to NASH represents a critical juncture in liver disease where inflammation becomes the driving force of tissue damage."
The purinergic P2Y6 receptor is widely expressed throughout the body and plays a critical role in physiological processes. When activated by extracellular UDP, it triggers calcium mobilization within cells through the Gαq/11 protein pathway 3 . Under normal circumstances, this signaling helps regulate important cellular functions.
However, in disease states, P2Y6R takes on a more sinister role. Research has demonstrated that this receptor acts as a pro-inflammatory mediator in various conditions. Studies of human tissue revealed a crucial clue: P2Y6R mRNA expression levels were significantly increased during the progression from simple fatty liver (NAFL) to the more severe NASH 1 . Even more telling, these elevated P2Y6R levels showed a positive correlation with key markers of inflammation (CCL2) and fibrosis (Col1a1) 1 2 .
G protein-coupled receptor activated by extracellular UDP
Promotes inflammation in various disease states
Expression increases with disease progression
Associated with inflammation and fibrosis markers
To investigate whether blocking P2Y6R could effectively treat NASH, researchers designed a comprehensive study using a mouse model of the disease. The experimental approach was logical and methodical, moving from observation to intervention 1 .
The team first examined human genomics data from NAFL and NASH patients to confirm that P2Y6R expression was indeed elevated in NASH livers and correlated with disease severity markers 1 .
Researchers used wild-type (WT) and P2Y6R knockout (KO) mice—genetically modified mice lacking the P2Y6 receptor gene. These mice were fed a choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD) for six weeks to induce NASH-like symptoms 1 .
Throughout the study, the team tracked body weight, food and water intake, and excretion patterns to assess overall health and metabolic effects 1 .
After six weeks, researchers measured liver weight, examined liver histology for steatosis and inflammation, analyzed serum markers of liver damage (AST and ALT), and quantified expression of inflammatory and fibrotic genes in liver tissue 1 .
Wild-type and P2Y6R knockout mice were used to compare disease progression with and without the receptor.
Specialized diet inducing NASH-like features in experimental models for rapid disease development.
The findings defied conventional expectations and highlighted the complexity of biological systems.
| Parameter | Wild-Type Mice (CDAHFD) | P2Y6R KO Mice (CDAHFD) | Interpretation |
|---|---|---|---|
| Serum AST | Moderate increase | Significantly higher | Greater liver cell damage in KO mice |
| Serum ALT | Moderate increase | Significantly higher | Greater liver cell injury in KO mice |
| Liver CCL2 mRNA | Elevated | Markedly higher | Enhanced inflammatory response in KO mice |
| Liver Weight | Increased | Reduced compared to WT | Paradoxical improvement despite worse injury markers |
Contrary to the original hypothesis, P2Y6R knockout failed to improve NASH symptoms and actually exacerbated certain aspects of the disease. While P2Y6R deficiency did result in reduced liver weights, this potentially positive effect was overshadowed by increased serum AST levels and heightened expression of CCL2, a key chemokine involved in inflammatory cell recruitment 1 .
Knockout worsened disease despite pro-inflammatory profile of P2Y6R
| Feature | Wild-Type Mice (CDAHFD) | P2Y6R KO Mice (CDAHFD) |
|---|---|---|
| Steatosis | Severe | Equally severe |
| Inflammatory Cell Infiltration | Present | Similarly present |
| Fibrosis Markers (TGFβ1, Col1a1) | Elevated | No significant difference from WT |
| IL-6 mRNA | Increased | Similar to WT levels |
The histological analysis revealed that both WT and P2Y6R KO mice developed comparable degrees of steatosis and inflammatory cell infiltration after CDAHFD feeding. Furthermore, fibrosis markers TGFβ1 and Col1a1 showed similar elevations in both groups, indicating that P2Y6R deficiency did not alleviate the fibrotic process 1 .
| Research Tool | Function/Application | Example in P2Y6R Study |
|---|---|---|
| P2Y6R Knockout Mice | Genetically modified animals lacking specific gene | Test functional importance of P2Y6R in NASH pathogenesis |
| CDAHFD Diet | Specialized diet inducing NASH-like features | Rapid induction of steatohepatitis for experimental studies |
| MRS2578 | Specific pharmacological inhibitor of P2Y6R | Chemical inhibition of receptor function (used in related studies) |
| qPCR Assays | Quantify gene expression levels | Measure mRNA levels of P2Y6R, CCL2, Col1a1, and other targets |
| Histological Staining | Visualize tissue structure and pathology | Assess steatosis, inflammation, and cellular damage in liver sections |
| AST/ALT Serum Tests | Clinical biomarkers of liver damage | Evaluate extent of hepatocellular injury in experimental models |
These unexpected findings demonstrate that biological systems rarely operate through simple, linear pathways. While P2Y6R appears to function as a pro-inflammatory mediator in other disease contexts, its role in NASH pathogenesis may be more nuanced 3 .
Interestingly, P2Y6R appears to play a more straightforward detrimental role in alcoholic steatohepatitis, where its inhibition alleviates liver inflammation by suppressing p38 MAPK signaling in Kupffer cells . This distinction between alcoholic and non-alcoholic liver disease further emphasizes the complexity of purinergic signaling in different disease contexts.
The failure of P2Y6R knockout to improve NASH symptoms provides a powerful reminder that scientific discovery often takes unexpected paths. While these negative results might seem disappointing, they offer crucial insights that can redirect therapeutic efforts toward more promising targets.
As of early 2025, the FDA has approved resmetirom, a thyroid hormone receptor-β agonist, as the first dedicated treatment for NASH, marking a significant milestone in the field 7 . This breakthrough offers new hope for patients while underscoring the importance of continued research into the complex mechanisms underlying fatty liver diseases.
"The story of P2Y6R and NASH exemplifies how each scientific investigation—whether confirming or contradicting initial hypotheses—advances our understanding of disease processes and moves us closer to effective treatments for complex conditions affecting millions worldwide."