Re‐evaluation of mouse tissue factor pathway inhibitor and comparison of mouse and human tissue factor pathway inhibitor physiology

摘要

Summary Essentials Mouse models are often used to define roles of tissue factor pathway inhibitor (TFPI) in man. TFPI isoform‐specific KOs reveal unexpected differences between mouse and human TFPI physiology. Mouse plasma contains 20 times more TFPI than man, derived from TFPIγ, a form not found in man. TFPIγ null mice, expressing only TFPI isoforms α and β, may better reflect the human situation. Summary Background Mouse models can provide insight into the pathophysiology of human thrombosis and hemostasis. Tissue factor pathway inhibitor ( TFPI ) regulates coagulation through protein S ( PS )‐enhanced factor (F) Xa inhibition and FX a‐dependent inhibition of FVII a/tissue factor ( TF ) activity. TFPI is expressed as isoforms α and β in man, and α, β and γ in the mouse. Objective Assess the reliability of extending TFPI ‐related studies in mice to humans. Method Compare mouse and human TFPI physiology using a variety of methods. Results Mouse TFPI and human TFPI are similar in regard to: (i) the mechanisms for FVII a/ TF and FX a inhibition; (ii) TFPI α is a soluble form and TFPI β is glycosyl phosphatidyl inositol ( GPI ) membrane anchored; (iii) the predominant circulating form of TFPI in plasma is lipoprotein‐associated; (iv) low levels of TFPI α circulate in plasma and increase following heparin treatment; and (v) TFPI α is the isoform in platelets. They differ in that: (i) mouse TFPI circulates at a ~20‐fold higher concentration; (ii) mouse lines with isolated isoform deletions show this circulating mouse TFPI is derived from TFPI γ; (iii) sequences homologous to the mouse TFPI γ exon are present in many species, including man, but in primates are unfavorable for splicing; and (iv) tandem mass spectrometry ( MS / MS ) detects sequences for TFPI isoforms α and β in human plasma and α and γ in mouse plasma. Conclusion To dissect the pathophysiological roles of human TFPI α and TFPI β, studies in TFPI γ null mice, expressing only α and β, only α or only β should better reflect the human situation.