Critical role of the mTOR pathway in development and function of myeloid-derived suppressor cells in lal-/- mice

Am J Pathol. 2014 Feb;184(2):397-408. doi: 10.1016/j.ajpath.2013.10.015. Epub 2013 Nov 26.

Abstract

Lysosomal acid lipase (LAL) is essential for the hydrolysis of cholesteryl esters and triglycerides to generate cholesterol and free fatty acids in cellular lysosomes. Ablation of the lal gene (lal(-/-)) systemically increased expansion of cluster of differentiation molecule 11b (CD11b), lymphocyte antigen 6G (Ly6G) myeloid-derived suppressor cells (MDSCs) that caused myeloproliferative neoplasms in mice. Study of lal(-/-) bone marrow Ly6G(+) MDSCs via transcriptional profiling showed increases in mammalian target of rapamycin (mTOR) signaling pathway transcripts. Injection of mTOR pharmacologic inhibitors into lal(-/-) mice significantly reduced bone marrow myelopoiesis and systemic CD11b(+)Ly6G(+) cell expansion. Rapamycin treatment of lal(-/-) mice stimulated a shift from immature CD11b(+)Ly6G(+) cells to CD11b(+) single-positive cells in marrow and tissues and partially reversed the increased cell proliferation, decreased apoptosis, increased ATP synthesis, and increased cell cycling of bone marrow CD11b(+)Ly6G(+) cells obtained from lal(-/-) mice. Pharmacologic and siRNA suppression of mTOR, regulatory-associated protein of mTOR, rapamycin-insensitive companion of mTOR, and Akt1 function corrected CD11b(+)Ly6G(+) cell in lal(-/-) mice development from Lin(-) progenitor cells and reversed the immune suppression on T-cell proliferation and function in association with decreased reactive oxygen species production, and recovery from impairment of mitochondrial membrane potential compared with control mutant cells. These results indicate a crucial role of LAL-regulated mTOR signaling in the production and function of CD11b(+)Ly6G(+) cells. The mTOR pathway may serve as a novel target to modulate the emergence of MDSCs in those pathophysiologic states in which these cells play an immunosuppressive role.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adaptor Proteins, Signal Transducing / metabolism
  • Animals
  • Antigens, Ly / metabolism
  • Apoptosis / drug effects
  • Bone Marrow Cells / cytology
  • Bone Marrow Cells / drug effects
  • Bone Marrow Cells / metabolism
  • CD11b Antigen / metabolism
  • Carrier Proteins / metabolism
  • Cell Proliferation / drug effects
  • Gene Knockdown Techniques
  • Immunosuppression Therapy
  • Membrane Potential, Mitochondrial / drug effects
  • Mice
  • Myeloid Cells / cytology*
  • Phosphorylation / drug effects
  • Proto-Oncogene Proteins c-akt / metabolism
  • Rapamycin-Insensitive Companion of mTOR Protein
  • Reactive Oxygen Species / metabolism
  • Regulatory-Associated Protein of mTOR
  • STAT Transcription Factors / metabolism
  • Signal Transduction* / drug effects
  • Sirolimus / pharmacology
  • Sterol Esterase / deficiency*
  • Sterol Esterase / metabolism
  • TOR Serine-Threonine Kinases / metabolism*

Substances

  • Adaptor Proteins, Signal Transducing
  • Antigens, Ly
  • CD11b Antigen
  • Carrier Proteins
  • Ly6G antigen, mouse
  • Rapamycin-Insensitive Companion of mTOR Protein
  • Reactive Oxygen Species
  • Regulatory-Associated Protein of mTOR
  • Rptor protein, mouse
  • STAT Transcription Factors
  • rictor protein, mouse
  • Proto-Oncogene Proteins c-akt
  • TOR Serine-Threonine Kinases
  • Sterol Esterase
  • lysosomal acid lipase, mouse
  • Sirolimus