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Characterization of membrane-associated prothrombin activator in normal and injured murine tissues
Y Shikamoto1, S Shibusawa, I Okuyama
1Department of Biochemistry, Meiji College of Pharmacy, Tokyo, Japan.
Abstract:
Thrombin is a multifunctional enzyme involved in coagulation, cell modulation and inflammation. We recently reported a novel membrane-associated prothrombin activator, abbreviated as MAPA, found in cultured fibroblasts and glial cell lines. In this study, we examined the physiological role of this enzyme. MAPA-like activity was detected in the liver, kidney, lung and heart but not in the spleen or brain in normal mice. To examine whether MAPA participates in biological reactions, hepatic and renal injury were induced by administration of CCl4 and HgCl2, respectively. MAPA-like activity was specifically increased in the injured tissues: the activity was elevated by about 100-fold in 48 h in the liver and increased by about 5-fold in 12 h in the kidney. Their enzymatic properties were the same as those of MAPA in 8C feline kidney fibroblast cells. Phospholipids are required for activation of prothrombin by MAPA obtained from both 8C cells and tissues. These results suggest that MAPA activates prothrombin on the cell surface in injured tissue and participates in inflammation and regeneration associated with tissue injury.
Insights
A novel enzyme, membrane-associated prothrombin activator (MAPA), was found to significantly increase in injured liver and kidney tissues. This suggests MAPA plays a role in inflammation and regeneration following tissue damage.
Area of Science:
- Biochemistry
- Cell Biology
- Physiology
Background:
- Thrombin is a key enzyme in coagulation, inflammation, and cell modulation.
- A novel membrane-associated prothrombin activator (MAPA) was previously identified in cell lines.
- The physiological role and tissue distribution of MAPA were previously unknown.
Purpose of the Study:
- To investigate the physiological role of membrane-associated prothrombin activator (MAPA).
- To determine the distribution of MAPA-like activity in various mouse tissues.
- To assess changes in MAPA activity during induced tissue injury.
Main Methods:
- MAPA-like activity was measured in homogenates from normal mouse tissues (liver, kidney, lung, heart, spleen, brain).
- Hepatic and renal injury were induced using CCl4 and HgCl2, respectively.
- MAPA-like activity was quantified in injured tissues over time and compared to normal tissues.
- Enzymatic properties of tissue-derived MAPA were characterized and compared to cell-derived MAPA.
Main Results:
- MAPA-like activity was detected in the liver, kidney, lung, and heart of normal mice.
- MAPA-like activity significantly increased in the liver (approx. 100-fold) and kidney (approx. 5-fold) following induced injury.
- The enzymatic properties of MAPA from both cell lines and injured tissues were consistent.
- Phospholipids were essential for prothrombin activation by MAPA.
Conclusions:
- MAPA is present in several key organs and its activity is upregulated in response to tissue injury.
- MAPA likely activates prothrombin on the cell surface within injured tissues.
- These findings suggest MAPA plays a role in the inflammatory and regenerative processes associated with tissue damage.