Hepatic Lymphatics and the Immune Response in Acute Liver Failure

About This Grant

PROJECT SUMMARY Though the liver produces most of the lymph in the body, the role of hepatic lymphatics in liver disease is relatively less studied. While it is recognized that alterations in hepatic lymphatics cause ascites formation in chronic liver disease like cirrhosis, its contribution to acute liver failure (ALF), like that caused by drugs such as acetaminophen (APAP) are not well characterized. An APAP overdose is the most common cause of ALF in the United States, partly due to the short therapeutic window of the only FDA approved antidote, N-acetylcysteine (NAC). Excess APAP induces centrilobular necrosis, and a failure of inherent liver regeneration in a significant percentage of patients, especially after a severe overdose, causes ALF. Thus, insight into mechanisms of liver recovery which are compromised in patients with ALF, would allow their targeting to complement NAC treatment. One such beneficial phenomenon is the innate immune response induced by hepatocyte necrosis. Though interaction between the infiltrating immune cells and surviving hepatocytes facilitates their regeneration, repopulation of areas of necrosis also requires an orderly exit of the infiltrating immune cells to allow coordinated reestablishment of liver infrastructure and lymphatics to regain functional homeostasis. The lymphatic system is a central mode of immune cell emigration from tissues, and specific pro-resolving lipid mediators (SPMs) facilitate resolution of inflammation. However, their role in immune cell exit after acute APAP-induced ALF is unknown. Our preliminary data shows transient changes in hepatic lymphatics after APAP overdose with elevations in SPMs, which are known to facilitate lymphangiogenesis and immune cell clearance. Blocking lymphangiogenesis after an APAP overdose also extended hepatic residency of immune cells. Treatment with Wharton's Jelly mesenchymal stem cells (WJMSC) which are cleared for human use, also enhanced liver recovery in the mouse model with elevation in circulating VEGF-D, which activates lymphangiogenesis. This data led to the hypothesis that hepatic lymphatics play a critical role in immune cell clearance during liver recovery from an APAP overdose, a process facilitated by SPMs which could be targeted by WJMSC treatment to enhance liver recovery. This hypothesis will be tested by 1) evaluating mechanisms of immune cell clearance through hepatic lymphatics after acute APAP overdose, and 2) examining the role of SPMs and immune cell clearance as mechanisms facilitating recovery after delayed treatment with WJMSC. Collectively, we will define the molecular mechanisms responsible for efficient immune cell exit through hepatic lymphatics after reconstruction of areas of hepatic necrosis and study the consequence when this exit is compromised such as ALF. We will also evaluate a therapeutic intervention to enhance recovery, which can be rapidly translated to the clinic.