In Lysinuric Protein Intolerance system y+L activity is defective in monocytes and in GM-CSF-differentiated macrophages

Orphanet J Rare Dis. 2010 Nov 26;5:32. doi: 10.1186/1750-1172-5-32.

Abstract

Background: In the recessive aminoaciduria Lysinuric Protein Intolerance (LPI), mutations of SLC7A7/y+LAT1 impair system y+L transport activity for cationic amino acids. A severe complication of LPI is a form of Pulmonary Alveolar Proteinosis (PAP), in which alveolar spaces are filled with lipoproteinaceous material because of the impaired surfactant clearance by resident macrophages. The pathogenesis of LPI-associated PAP remains still obscure. The present study investigates for the first time the expression and function of y+LAT1 in monocytes and macrophages isolated from a patient affected by LPI-associated PAP. A comparison with mesenchymal cells from the same subject has been also performed.

Methods: Monocytes from peripheral blood were isolated from a 21-year-old patient with LPI. Alveolar macrophages and fibroblastic-like mesenchymal cells were obtained from a whole lung lavage (WLL) performed on the same patient. System y+L activity was determined measuring the 1-min uptake of [3H]-arginine under discriminating conditions. Gene expression was evaluated through qRT-PCR.

Results: We have found that: 1) system y+L activity is markedly lowered in monocytes and alveolar macrophages from the LPI patient, because of the prevailing expression of SLC7A7/y+LAT1 in these cells; 2) on the contrary, fibroblasts isolated from the same patient do not display the transport defect due to compensation by the SLC7A6/y+LAT2 isoform; 3) in both normal and LPI monocytes, GM-CSF induces the expression of SLC7A7, suggesting that the gene is a target of the cytokine; 4) GM-CSF-induced differentiation of LPI monocytes is comparable to that of normal cells, demonstrating that GM-CSF signalling is unaltered; 5) general and respiratory conditions of the patient, along with PAP-associated parameters, markedly improved after GM-CSF therapy through aerosolization.

Conclusions: Monocytes and macrophages, but not fibroblasts, derived from a LPI patient clearly display the defect in system y+L-mediated arginine transport. The different transport phenotypes are referable to the relative levels of expression of SLC7A7 and SLC7A6. Moreover, the expression of SLC7A7 is regulated by GM-CSF in monocytes, pointing to a role of y+LAT1 in the pathogenesis of LPI associated PAP.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Amino Acid Metabolism, Inborn Errors / complications*
  • Amino Acid Transport System y+L
  • Cell Differentiation
  • Cells, Cultured
  • Fusion Regulatory Protein 1, Light Chains / genetics
  • Fusion Regulatory Protein 1, Light Chains / metabolism*
  • Granulocyte-Macrophage Colony-Stimulating Factor / immunology*
  • Granulocyte-Macrophage Colony-Stimulating Factor / metabolism
  • Granulocyte-Macrophage Colony-Stimulating Factor / therapeutic use
  • Humans
  • Lysine / metabolism
  • Macrophages, Alveolar / cytology
  • Macrophages, Alveolar / immunology
  • Macrophages, Alveolar / metabolism*
  • Male
  • Monocytes / immunology
  • Monocytes / metabolism*
  • Pulmonary Alveolar Proteinosis / immunology
  • Pulmonary Alveolar Proteinosis / physiopathology*
  • Pulmonary Alveolar Proteinosis / therapy
  • Young Adult

Substances

  • Amino Acid Transport System y+L
  • Fusion Regulatory Protein 1, Light Chains
  • SLC7A7 protein, human
  • Granulocyte-Macrophage Colony-Stimulating Factor
  • Lysine