Mice homozygous for the SM22α-mTFPI transgene are viable and fertile, with the mouse SM22α promoter fragment directing expression of a mouse tissue factor pathway inhibitor cDNA sequence encoding the TFPIα isoform (TFPIα is the predominant TFPI protein isoform in humans).
As such, SM22α-mTFPI transgenic mice have vascular smooth muscle cell-directed overexpression of TFPI in a tissue-specific and local manner. Specifically, homozygous SM22α-mTFPI transgenic mice from founder line 1661 have transgene mRNA levels approximately 4-fold higher than endogenous TFPI mRNA in aortic homogenates. Similarly, TFPI activity of carotid artery homogenates from homozygous transgenic mice showed 2- to 3-fold increase compared to wildtype mice. SM22α-mTFPI mice have increased circulating levels of TFPI antigen, but no increase in TFPI activity in plasma, compared to wildtype mice. Transgenic TFPI expression is also observed in smooth muscle-rich tissues such as lung, heart and kidney. Local TFPI overexpression does not affect hemostasis, but significantly attenuates ferric chloride-induced arterial thrombosis.
When SM22α-TFPI transgenic mice are made deficient of endogenous TFPI expression (by breeding with Tfpi-knockout mice), the resulting double mutant homozygous mice demonstrate that transgenic SM22α-directed TFPI overexpression is not sufficient to rescue TFPI-null embryonic lethality.
Additionally, SM22α-TFPI mice fed a high-fat diet demonstrate lower cholesterol levels than wildtype mice. Similarly, when SM22α-TFPI transgenic mice are made deficient of endogenous apolipoprotein E (by breeding with apoE-knockout mice) for high-fat diet studies, SM22α-directed TFPI overexpression attenuates aortic plaque burden and results in lower plasma cholesterol levels compared to apoE-/- mice.
