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Pentraxin 3 (PTX3) exhibits resistance to sepsis by inhibiting extracellular histones from impairing blood vessels: Key role of aggregate formation between extracellular histones and PTX3

Protective effect of the long pentraxin PTX3 against histone-mediated endothelial cell cytotoxicity in sepsis
Kenji Daigo, Makoto Nakakido, Riuko Ohashi, Rie Fukuda, Koichi Matsubara, Takashi Minami, Naotaka Yamaguchi, Kenji Inoue, Shuying Jiang, Makoto Naito, Kouhei Tsumoto, Takao Hamakubo.
Sci. Signal., 16 September 2014; Vol. 7, Issue 343, p. ra88
(Reprint (PDF) can be downloaded freely from the Journal site by clicking "Full Text" on Publications page.)

Pentraxin 3 (PTX3) is a secretory protein that plays an important role in innate immune responses as a soluble pattern-recognition receptor. It is also one of the acute-phase proteins, like C-reactive protein (CRP) and serum amyloid P component (SAP). CRP, SAP, and PTX3 are members of the pentraxin family, which is characterized by a pentraxin domain at the carboxy terminal, and PTX3 is categorized as a long pentraxin because it has a relatively long amino-terminal domain. PTX3 recognizes certain types of fungi, Pseudomonas aeruginosa, and viruses and eliminates them through the complement system and opsonization.

In sepsis, the level of PTX3 in the blood increases by about 100-fold. PTX3 is known to have several defensive mechanisms in sepsis; however, the details have remained unclear. We previously reported our attempt to identify proteins that bind PTX3 to elucidate a novel role of PTX3 in sepsis, which revealed extracellular histones. It has also been revealed recently that extracellular histones are major mediators of death in sepsis because they appear in the blood of patients with sepsis and impair vascular endothelial cells. In this study, we analyzed this in detail and reported the mechanism of binding of histones to PTX3 and its influence on the cytotoxicity of histones.

Figure 1. Electron micrograph of histone–PTX3 aggregates

A common method for analyzing protein binding revealed that histones and PTX3 showed binding that was extremely strong for a normal protein interaction. We further analyzed this in detail in collaboration with the group led by Professor Kouhei Tsumoto, Graduate School of Engineering, The University of Tokyo, and revealed that the binding was an aggregation reaction, in which the protein structures were not maintained (Figure 1).

We also found, using cultured human vascular endothelial cells, that PTX3 inhibited the cytotoxicity of histones to endothelial cells. Interestingly, it was shown that the amino-terminal domain of PTX3 was sufficient for both the aggregability with histones and the inhibitory effect on the cytotoxicity of histones to endothelial cells. Accordingly, we confirmed experimentally using mice that administration of the amino-terminal domain of PTX3 was effective for controlling sepsis. It has been shown that the administration of histones to mice caused pulmonary hemorrhage and resultant death; however, the administration of PTX3 suppressed the cytotoxicity to endothelial cells and pulmonary hemorrhage and improved the survival rate of mice (Figure 2). In sepsis model mice, the administration of PTX3 also inhibited inflammatory responses and improved the survival rate.

Figure 2. Protective effect of PTX3 administration on pulmonary hemorrhage of a histone-administered mouse Lung sections of a histone-administered mouse were observed by hematoxylin–eosin staining. Pulmonary hemorrhage was clearly suppressed by preadministration of PTX3 (right).

These results reveal novel innate immune system involvement of PTX3 and are expected to promote the development of therapeutics for diseases caused by sepsis and extracellular histones (Figure 3).

Figure 3. Long pentraxin 3 (PTX3) protects endothelial cell from extracellular histone cytotoxicity.
In severe sepsis, extracellular histones are originated from large amount of Neutrophil extracellular traps (NETs) or various damged cells.

This study was conducted in collaboration with
the group led by Professor Kouhei Tsumoto of the Department of Bioengineering, Graduate School of Engineering, The University of Tokyo, Tokyo;
the group led by Professor Makoto Naito of the Division of Cellular and Molecular Pathology, Niigata University Graduate School Medical and Dental Sciences;
and by Assistant Professor Riuko Ohashi of Department of Pathology, Niigata University Medical and Dental Hospital, Niigata;
and the group led by Associate Professor Kenji Inoue of Department of Cardiology, Juntendo University Nerima Hospital, Tokyo.