Constitutive Expression of Pentraxin 3 (PTX3) Protein by Human Amniotic Membrane Cells Leads to Formation of the Heavy Chain (HC)-Hyaluronan (HA)-PTX3 Complex

Heavy chain (HC)-hyaluronan (HA), a complex formed by the covalent linkage between HC1 from the inter-α-trypsin inhibitor (IαI) and HA, purified from the human amniotic membrane (AM), is responsible for the anti-inflammatory, antiscarring, and antiangiogenic actions of the AM. This HC-HA complex is produced by constitutive expression of TNF-stimulated gene 6 and endogenous production of IαI by AM cells. Pentraxin 3 (PTX3), a prototypic long pentraxin that plays a non-redundant role in innate immunity against selected pathogens, also helps stabilize HC-HA to ensure female fertility. Here we noted strong positive PTX3 staining in the AM epithelium and compact stroma. PTX3 was constitutively expressed and secreted by cultured AM epithelial and stromal cells and, further, greatly up-regulated by TNF and IL-1β. Using an agarose overlay to trap the HA-containing matrix, the HC-HA-PTX3 complex was formed, as analyzed by Western blot analysis, by AM cells but not human skin fibroblasts, despite being cultured in the presence of serum and TNF. However, exogenous PTX3 helps human skin fibroblasts form the HC-HA-PTX3 complex with an agarose overlay. Furthermore, PTX3 can be coimmunoprecipitated with the HC-HA complex from agarose-overlaid AM cell extracts by an anti-human IαI antibody. Such a HC-HA-PTX3 complex can be reconstituted in vitro and exhibit similar effects as those reported for AM HC-HA-PTX3 on polarization of M2 macrophages. The tight binding between PTX3 and AM HC-HA withstands four runs of CsCl ultracentrifugation in the presence of 4 m GnHCl. These results indicate that PTX3 is constitutively expressed and secreted by AM cells as an integral component of the AM HC-HA-PTX3 complex and contributes to the biological function of AM HC-HA-PTX3.