Protease Activity in Sickle Cell Disease Liver

Sickle cell disease (SCD) is a group of inherited blood disorders caused by autosomal genetic mutations in hemoglobin subunit β. Homozygosity for the β-globin sickle mutation (SS) causes polymerization of hemoglobin molecules into rigid fibers within red blood cells (RBCs), and a deformation into “sickle” shapes, an event that leads to obstruction of blood flow. Chronic inflammation is a common symptom in SCD, but the mechanism underlying chronic inflammation in sickle cell disease liver is not well understood, despite studies showing that inflammation in the SCD liver leads to fibrosis, cholestasis, and cirrhotic livers. Studies have shown that deoxygenated microenvironment of the sickle liver affects the distribution of oxygen and nutrients and contribute to dysfunction of regulation, aberrant signaling and disease. The goal of this project is to investigate the mechanisms of protease activity in SCD liver and contribution of SCD deoxygenation on liver metabolism function and zonal architecture in the liver. We hypothesize that the deoxygenated state of sickle cell disease increases the proteolytic activity of cathepsins, leading to impaired hepatic zonal function and liver injury. To test this hypothesis, we use the humanized Townes mice model. At three months old, blood and liver tissues were harvested and analyzed for protein levels and activity. Initial results showed that SS mice liver had increased cathepsin protease activity compared to controls. We observed that cathepsin L protein levels in SS mice liver was upregulated compared to controls with immunoblotting, however, the difference in cathepsin protein levels was not significant in cathepsin K. In conclusion, we showed that liver dysfunction in sickle cell disease leads to increased cathepsin activity. Addressing the dynamic between protease activity and liver dysfunction in sickle cell disease may lead to better therapies.