Genomic insertion of ancestral uricase into human liver cells to determine metabolic consequences of pseudogenization.

The biological role of urate (uric acid) during primate evolution has been unclear ever since it was discovered over 100 years ago that humans have unusually high levels of the small molecule compared to most other mammals. Humans (including all apes) are uncharacteristically susceptible to the build-up of urate because we no longer have a functional uricase enzyme capable of oxidizing this highly insoluble molecule. We have now utilized CRISPR technology to insert functional ancestral uricase into the genome of human liver cells to address recent metabolic hypotheses that our ancestral primates inactivated uricase as a mechanism to increase triglyceride production in response to fructose and/or starvation. Uricase expression is confirmed in both hepatocyte monolayer and spheroid tissue cultures, and its expression reduces intracellular urate levels. The presence of uricase is also shown to prevent an increase in triglyceride production upon cellular uptake of fructose in both culture conditions. Our results make progress that further describes a potential advantageous biological role of urate during primate evolution.