Functional analysis of human tissue kallikrein in transgenic mouse models

Clinical studies show that an inverse correlation exists between blood pressure and urinary kallikrein levels. It has been postulated that the tissue kallikrein-kinin system contributes to the maintenance of normal blood pressure. To test this hypothesis, we have established transgenic mice that overexpress human tissue kallikrein under the promoter control of the mouse metallothionein gene and a liver-targeted albumin gene. These animals secrete human tissue kallikrein in plasma at levels 10- to 40-fold higher than that found in normal human serum, and they are chronically hypotensive. This hypotensive effect can be reversed by the injection of aprotinin, a potent tissue kallikrein inhibitor, or Hoe 140, a specific bradykinin receptor antagonist. Transgenic mice overexpressing human tissue kallikrein show a sustained reduction in blood pressure throughout their life spans, indicating the lack of sufficient compensatory mechanisms to reverse the hypotensive effect of kallikrein. Somatic gene delivery of rat kallikrein-binding protein by muscle injection increases the blood pressure of the hypotensive transgenic mice to levels comparable with those in normotensive control mice. These results indicate that a direct link exists between kallikrein gene expression and alterations in blood pressure. In addition, we have developed normotensive transgenic mice that harbor the human tissue kallikrein gene containing 801 bp of its native promoter. The tissue distribution pattern of human kallikrein in these transgenic mice is similar to that in human tissues, with the highest level in the pancreas and much lower levels in the kidney and salivary gland. These transgenic mice provide new animal models for investigating the tissue-specific regulation of tissue kallikrein and its role in altering blood pressure.