In Vivo Biosynthesis of Endogenous and of Human C1 Inhibitor in Transgenic Mice: Tissue Distribution and Colocalization of Their Expression

Abstract

We have produced transgenic mice expressing human C1 inhibitor mRNA and protein under the control of the human promoter and regulatory elements. The transgene was generated using a minigene construct in which most of the human C1 inhibitor gene (C1NH) was replaced by C1 inhibitor cDNA. The construct retained the promoter region extending 1.18 kb upstream of the transcription start site, introns 1 and 2 as well as a stretch of 2.5 kb downstream of the polyadenylation site, and therefore carried all known elements involved in transcriptional regulation of the C1NH gene. Mice with high serum levels of human C1 inhibitor, resulting from multiple tandem integrations of the C1 inhibitor transgene, were selected. Immunohistochemistry in combination with in situ hybridization was applied to localize the sites of C1 inhibitor biosynthesis and to demonstrate its local production in brain, spleen, liver, heart, kidney, and lung. The distribution of human C1 inhibitor-expressing cells was qualitatively indistinguishable from that of its mouse counterpart, but expression levels of the transgene were significantly higher. In the spleen, production of C1 inhibitor was colocalized with that of a specific marker for white pulp follicular dendritic cells. This study demonstrates a stringently regulated expression of both the endogenous and the transgenic human C1 inhibitor gene and reveals local biosynthesis of C1 inhibitor at multiple sites in which the components of the macromolecular C1 complex are also produced.

Complement Regulatory Protein C1 Inhibitor Binds to Selectins and Interferes with Endothelial-Leukocyte Adhesion

“…Interestingly, in sharp contrast to the situation in the human, sialyl Lewis x epitopes do not occur on APPs in the mouse, probably because of the absence of ␣1,3-fucosyltransferase in mouse liver, thereby making the mouse incapable of producing the sialyl Lewis x epitope on APPs (37). Liver is the major source of human C1INH, although a large variety of other cells can also produce limited amounts (38,39). It has been demonstrated that ␣1,3-fucosyltransferase-VI is expressed in human liver (40) as well as in hepatocyte-derived HepG2 cells (41).…”

Local and Remote Ischemia-Reperfusion Injury Is Mitigated in Mice Overexpressing Human C1 Inhibitor

“…Transgenic human C1 inhibitor overexpressing mice were generated as described and were kindly prepared by G. Vinci, Institut Pasteur, Paris, France [11]. Only animals with high plasma expression of human C1 inhibitor (i.e.…”

“…C1 inhibitor is the only known physiological inhibitor of the classical complement cascade activation [9]. It belongs to the superfamily of serinprotease inhibitors and is a heavily glycosylated serum protein of 105 kD [10,11]. It inhibits the antibody-depen-dent formation of C1 by steric interaction with the C1-subunits C1r and C1s.…”

“…Due to the proven protective in vivo effect of human C1 inhibitor in ischemia-reperfusion experimentation [21] but also because of the short half-life of administered C1 inhibitor [16], it seemed attractive to test the capacity of human C1 inhibitor overexpressing transgenic mice [11] to resist complement-mediated endothelial cell disruption in ischemia-reperfusion injury. Using the wellestablished method of intravenous 125 I-labelled bovine albumin injection, the integrity of tissue-specific endothelium is assessed by the use of the permeability index, and a destroyed vascular endothelium is characterized by elevated permeability index values due to extravasation of tagged albumin [2,23,24].…”

Complement levels and activity in the normal and LPS-injured lung

“…Complement-mediated tissue damage is normally modulated by a group of at least 11 regulatory proteins that control complement activation by inhibiting formation of active complement complexes or by cleaving specific active complement protein fragments (29). C1 inhibitor, which inhibits classical pathway activation through interaction with the C1 complex, has been detected in human BAL and is expressed in mouse lung (43,46). However, little else is know about which complement regulatory proteins are present in the lung and how they may function to protect this delicate tissue.…”