A new mechanism has been identified by Walter Wahli and colleagues at the University of Lausanne, Switzerland, which underlies the differential expression of proteins in male and female mice.

The difference is in relation to the expression of liver proteins that control a large amount of whole-body processes such as energy generation and steroid hormone production.

From Sciencedaily.com:

The protein PPAR-alpha is able to enter the nucleus, where it acts to control the expression of a large number of genes. In the study, PPAR-alpha was found to repress the expression of many liver genes responsible for making proteins involved in immunity and steroid production and turnover only in female mice. One of the genes most strongly repressed in female mice by PPAR-alpha was Cyp7b1, which generates a protein involved in drug breakdown and the generation of cholesterol, steroids, and other fats. Detailed analysis revealed the mechanism by which PPAR-alpha repressed Cyp7b1 expression, it was modified by a process known as sumoylation.

Importantly, this only occurred in female mice. As PPAR-alpha–mediated repression protected female mice from estrogen-induced intrahepatic cholestasis, the most common liver disease during pregnancy, the authors suggest that PPAR-alpha agonists might provide a new approach to prevent this disease.

The research appeared in the Sept. 1, 2009 issue of the Journal of Clinical Investigation.