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

Abstract

BackgroundIn 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.MethodsMonocytes 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.ResultsWe 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.ConclusionsMonocytes 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.

Inhaled Sargramostim Induces Resolution of Pulmonary Alveolar Proteinosis in Lysinuric Protein Intolerance

“…Our experiences based on two patient cases together with the case previously reported by Barilli et al (2010) suggest that inhaled rhuGM-CSF may be useful in LPIassociated pulmonary alveolar patients. In patient 1, an excellent response to therapy was observed with no compliance problems or side effects.…”

“…Although the exact pathogenesis of PAP in LPI has been unclear, disturbances in the function and phagocytic activity of monocyte-derived macrophages have been demonstrated (Barilli et al 2010(Barilli et al , 2012Kurko et al 2015). Thus, accumulation of proteinous material into the lungs may be caused by insufficient clearance of proteins by poorly functioning alveolar macrophages.…”

“…We hypothesized that increasing the activity and the number of alveolar macrophages in the alveolar fluid by recombinant human GM-CSF (rhuGM-CSF) inhalation could promote the resolution of PAP also in LPI. Barilli et al (2010) have previously reported one Italian patient diagnosed with LPI-associated PAP at the age of 15 years, whose respiratory condition and CT showed marked improvement after rGM-CSF treatment. However, the authors were naturally unable to draw conclusions on the efficacy of rGM-CSF in LPI patients based on a single patient case.…”

Respiratory manifestations in patients with inherited metabolic diseases

“…This would justify the increased availability of arginine and, consequently, an increased synthesis of nitric oxide that, in the presence of inflammatory cytokines and endotoxins, may result in progressive lung disease [83,84]. This hypothesis was confirmed in a study which reported that the transport system of y(+)LAT-1 in the BAL monocytes and alveolar macrophages from an adult with lysinuric protein intolerance and PAP is impaired [85]. Patients with lysinuric protein intolerance do not present high levels of circulating granulocyte-macrophage colony-stimulating factor (GM-CSF) autoantibodies [85,86], thus suggesting that the GM-CSF signalling pathway is unaltered in lysinuric protein intolerance.…”

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“…It has been suggested that this may have a role in the crosstalk between T lymphocytes and macrophage leading to a defect in lymphocyte cytotoxic activity that prevents the efficient removal of antigens and results in abnormal immune activation of CTLs and macrophages explaining HLH in LPI. 18,19 There have been rare case reports of HLH secondary to other inborn errors of metabolism. HLH was described in Wolman disease, a severe systemic disease manifesting in the first days of life with vomiting, diarrhea, failure to thrive, hepatosplenomegaly, jaundice, anemia, and thrombocytopenia.…”