Targeting Sphingolipid Metabolism in Natural Killer Cell Large Granular Lymphocyte Leukemia

Open Access
- Author:
- Watters, Rebecca Jean
- Graduate Program:
- Molecular Medicine
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 29, 2011
- Committee Members:
- Thomas Loughran, Dissertation Advisor/Co-Advisor
Thomas Loughran, Committee Chair/Co-Chair
Xin Liu, Committee Chair/Co-Chair
Charles H Lang, Committee Member
Lisa M Shantz, Committee Member - Keywords:
- NK LGL Leukemia
nanoliposomes
ceramide
sphingolipid - Abstract:
- Large granular lymphocyte (LGL) leukemia is a rare disorder characterized by clonal expansion of cytotoxic lymphocytes. LGL cells play an integral role in the immune system and are divided into two major lineages of CD3- NK cells and CD3+ T cells that circulate throughout the blood in search of infected cells, in which they make contact through a receptor ligand to induce cell death. LGL cells are also programmed to undergo apoptosis after contact with an infected target cell; however they continue to survive in individuals with LGL leukemia. This unchecked proliferation and cytotoxicity of LGL in patients results in autoimmunity or malignancy. Although rheumatoid arthritis is the most common autoimmune condition seen in individuals with LGL leukemia, it is also associated with a wide spectrum of other autoimmune diseases. Patients may also suffer from other hematological conditions including hemolytic anemia, pure red cell aplasia, and neutropenia which lead to fatigue and recurrent bacterial infections. Currently, the only established treatment involves a low dose of an immunosuppressive regimen in combination with Methotrexate, approximately 40-50% of patients are either resistant or do not respond. As a result, no effective treatment exists, thus producing the need for novel therapeutics to be identified. The sphingolipid metabolism network has been identified as deregulated in LGL leukemia. Lipidomic studies revealed deregulated sphingolipid metabolism as evidenced by decreased levels of overall ceramide species and increased levels of glycoslyated ceramides in leukemic NK cells, concomitant with increased glucosylceramide synthase (GCS) expression. GCS, a key enzyme of this pathway, neutralizes pro-apoptotic ceramide by transfer of a UDP-glucose. Thus, we treated both rat and human leukemic NK cells in combination with: 1) exogenous C6-ceramide incorporated into nanoliposomes in order to target mitochondria and increase physiological pro-apoptotic levels of long chain ceramide, and 2) 1-phenyl-2-palmitoylamino-3-morpholino-1-propanol (PPMP), an inhibitor of GCS. Co-administration of C6-ceramide nanoliposomes and PPMP elicited an increase in endogenous long-chain ceramide species, which led to cellular apoptosis in a synergistic manner via the mitochondrial intrinsic cell death pathway in leukemic NK cells. These results suggest that targeting ceramide metabolism may be an effective and novel strategy for treatment of NK-LGL leukemia.