M1- and M2-macrophage polarization in thioacetamide (TAA)-induced rat liver lesions; a possible analysis for
Kavindra Kumara Wijesundera1, Takeshi Izawa1, Hiroshi Murakami1
1Laboratory of Veterinary Pathology, Division of Veterinary Sciences, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Izumisano city, Osaka. Japan.
Abstract:
"Classically activated macrophages (M1)" and "alternatively activated macrophages (M2)", which appear in injured tissues, control either inflammation or remodeling. The mechanism remains unclear. To clarify the M1-/M2-macrophage polarization in acute liver injury, M1- and M2-related factors were analysed in F344 rats by a single injection of TAA (300 mg/kg BW), and liver samples were collected on post injection (PI) hour 10 and days 1 to 10. Macrophage immunophenotypes were analyzed by single and double immunolabeling. M1-/M2-related factors were analyzed by real-time RT-PCR. On PI hour 10 (when centrilobular lesions were not still developed), expressions of IFN-γ, TNF-α, IL-1β, and IL-6 for M1, and IL-4 for M2 were already increased, followed by increased expressions of IL-10 and TGF-β1 for M2 on PI days 1-3 with development of centrilobular lesions and subsequent reparative fibrosis. On PI hour 10, CD204⁺ and MHC class II⁺ macrophages already increased in the intact periportal/Glisson's sheath regions, accompanied by an increased number of granzyme B⁺ NK cells. Reactive cells at PI hour 10 might produce M1-related factors. In addition to these macrophages, CD68⁺ and CD163⁺ macrophages, and CD3⁺ T cells appeared in the injured centrilobular region on PI days 1-3; there were macrophages reacting simultaneously to CD68/MHC class II, CD163/MHC class II, CD68/CD204, CD163/CD204, and MHC class II/CD204 in varying degrees. Although CD68⁺ and CD163⁺ macrophages are regarded as M1- and M2-types, respectively, the double labeling indicated that macrophage immunophenotypes are interchangeable in injured regions and subsequent fibrosis. An M1-/M2-macrophage paradigm would be useful to analyze hepatotoxicity and to understand the pathogenesis.
Insights
In acute liver injury, classically activated macrophages (M1) and alternatively activated macrophages (M2) show dynamic polarization. Macrophage phenotypes are interchangeable during injury and repair, impacting pathogenesis.
Area of Science:
- Immunology
- Hepatology
- Toxicology
Background:
- Classically activated macrophages (M1) and alternatively activated macrophages (M2) play distinct roles in tissue inflammation and repair.
- The precise mechanisms governing M1/M2 macrophage polarization in acute liver injury remain incompletely understood.
- Understanding macrophage dynamics is crucial for elucidating hepatotoxicity and liver injury pathogenesis.
Purpose of the Study:
- To investigate the temporal dynamics of M1 and M2 macrophage polarization in a rat model of acute liver injury induced by thioacetamide (TAA).
- To analyze the expression of key M1 and M2 related factors and macrophage immunophenotypes during liver injury and repair.
- To clarify the role of macrophage polarization in the pathogenesis of acute liver injury and subsequent fibrosis.
Main Methods:
- Acute liver injury was induced in F344 rats via a single injection of thioacetamide (TAA).
- Liver samples were collected at various time points post-injection (10 hours to 10 days) for analysis.
- Macrophage immunophenotyping was performed using single and double immunolabeling, and M1/M2-related factors were quantified by real-time RT-PCR.
Main Results:
- Early increases in M1 (IFN-γ, TNF-α, IL-1β, IL-6) and M2 (IL-4) related factors were observed by 10 hours post-TAA injection.
- Subsequent increases in M2 factors (IL-10, TGF-β1) correlated with lesion development and reparative fibrosis (days 1-3).
- Macrophage immunophenotypes (e.g., CD68, CD163, CD204, MHC class II) were found to be dynamic and interchangeable in injured liver regions.
Conclusions:
- Macrophage polarization into M1 and M2 phenotypes is a dynamic process during acute liver injury and repair.
- The interchangeability of macrophage immunophenotypes suggests a complex regulatory mechanism in response to liver damage.
- The M1/M2 macrophage paradigm provides a valuable framework for analyzing hepatotoxicity and understanding liver injury pathogenesis.
