Related Experiment Videos
A novel rat lipoxin A4 receptor that is conserved in structure and function
Nan Chiang1, Tomoko Takano, Makoto Arita
1Center for Experimental Therapeutics and Reperfusion Injury, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, U.S.A.
This study explores the rat version of a receptor called ALX, which interacts with natural compounds like LXA4 and ATL to regulate immune responses. The researchers cloned the rat ALX receptor and found it to be structurally similar to human and mouse ALX. They also showed that the receptor is active in tissues like the lung and kidney, where LXA4 is known to act. Experiments using a rat model of inflammation demonstrated that activating ALX reduced neutrophil infiltration and protein leakage. The receptor also inhibited a key inflammatory signaling pathway. These findings suggest that ALX is functionally conserved across species and plays a key role in modulating immune responses.
Area of Science:
- Immunology and inflammation research
- G protein-coupled receptor signaling
- Lipid mediator biology
Background:
Lipoxin A4 (LXA4) and its aspirin-triggered analog (ATL) are lipid-derived mediators that regulate immune responses by interacting with the ALX receptor. These molecules are known to influence leukocyte trafficking and promote anti-inflammatory effects. While LXA4 and ATL are produced in rat tissues both in vitro and in vivo, the presence and function of the ALX receptor in rats had not been fully characterized. Prior research has shown that ALX is a G protein-coupled receptor involved in resolving inflammation in human and mouse models. However, no prior work had resolved whether a rat orthologue of ALX exists and how it might function in similar biological processes. This gap motivated the investigation into rat ALX receptor structure and function.
Purpose Of The Study:
The study aimed to determine whether the ALX receptor is expressed in rat tissues and whether it modulates leukocyte trafficking in response to LXA4 and ATL. The researchers sought to identify the rat orthologue of ALX and evaluate its structural and functional conservation compared to human and mouse ALX. They also wanted to assess the receptor's tissue distribution and its ability to bind LXA4 and ATL analogs. The study was driven by the need to understand the role of ALX in rat models of inflammation and immune regulation. By cloning and characterizing the rat ALX receptor, the authors aimed to establish its relevance in physiological and pathophysiological contexts.
Main Methods:
The researchers cloned the rat orthologue of ALX from peripheral blood leukocytes and analyzed its sequence homology with human and mouse ALX. They used RNase protection assays to determine the receptor's tissue distribution in rat organs. Radioligand binding experiments with [(3)H]LXA4 and [(125)I-Tyr]-annexin 1-derived peptide were performed to assess receptor function. Neutrophil infiltration and protein extravasation were measured in a rat model of peritonitis following administration of an ATL analog. A luciferase reporter gene system was used to evaluate the receptor's role in inhibiting nuclear factor kappaB activity. These methods allowed the team to evaluate both structural and functional conservation of the rat ALX receptor.
Main Results:
The rat orthologue of ALX was cloned and showed approximately 74% homology with human ALX and 84% with mouse ALX. The receptor was expressed in lung, kidney, and leukocytes—tissues where LXA4 is active. Radioligand binding confirmed specific interactions with [(3)H]LXA4 and [(125)I-Tyr]-annexin 1-derived peptide, with Kd values of 5 nM and 820 nM, respectively. Intravenous administration of an ATL analog reduced neutrophil infiltration by 43% and protein extravasation by 42% in a rat peritonitis model. Activation of rat ALX inhibited tumor necrosis factor alpha-mediated nuclear factor kappaB activity in a ligand-dependent manner. These findings suggest that rat ALX is structurally and functionally conserved. The receptor's ability to bind LXA4 and ATL analogs was comparable to human ALX. The observed inhibition of inflammatory responses supports the receptor's role in modulating immune activity.
Conclusions:
The study demonstrates that a rat orthologue of ALX exists and is functionally conserved. The receptor's structural similarity to human and mouse ALX supports its role in regulating immune responses. The observed inhibition of neutrophil infiltration and nuclear factor kappaB activity in rat models aligns with ALX's known anti-inflammatory functions in other species. Tissue expression in lung, kidney, and leukocytes matches the sites of LXA4 activity. Radioligand binding data confirm the receptor's specificity for LXA4 and ATL. The luciferase reporter system results support the receptor's role in modulating signaling pathways. These findings suggest that rat ALX is a key player in immune regulation. The study provides the first evidence of ALX conservation across species, from murine to human.
Frequently Asked Questions
The rat ALX receptor modulates immune responses by inhibiting neutrophil infiltration and nuclear factor kappaB activity in rat models of inflammation.
The receptor was cloned from peripheral blood leukocytes and compared to human and mouse ALX sequences, showing 74% and 84% homology, respectively.
Lung tissue is a site where LXA4 and ATL exert physiological and pathophysiological effects, making it a logical location for ALX expression.
A rat model of casein-induced peritonitis was used to evaluate the effects of an ATL analog on neutrophil infiltration and protein extravasation.
The Kd values were 5 nM for [(3)H]LXA4 and 820 nM for [(125)I-Tyr]-annexin 1-derived peptide.
The study suggests that ALX is conserved in structure and function from rats to humans, supporting its role in immune regulation across species.