Background/Purpose:  We and others have previously reported that pulmonary fibrosis in patients with scleroderma is accompanied by pulmonary accumulation of predominantly CD8+ T lymphocytes. Earlier reports also suggested that NEU1, a sialidase that removes terminal sialic acid from glycoproteins, is associated with and may contribute to both fibrotic changes and immune disturbances in the lungs, but the mechanistic details of such contributions remain unclear.

Methods:  Immunohistochemical analyses were used to analyze NEU1 expression in the lung of patients with scleroderma and healthy controls. Cell culture studies were performed in normal adult primary pulmonary fibroblasts (PF). Overexpression of human NEU1 in mouse lungs in vivo and in cultured human lung fibroblasts was performed utilizing a replication-deficient recombinant adenovirus. In PF cell cultures, the effect of NEU1 overexpression on the levels of type I collagen protein were assessed utilizing western blotting. In the in vivo experiments, total and differential bronchoalveolar lavage (BAL) cells counts, flow cytometry of BAL cells, immunohistochemistry of lung tissues, trichrome staining for collagen, and total lung collagen measurements were utilized to characterize NEU1 overexpression-induced changes.

Results:  NEU1 was expressed in airway epithelial cells, endothelial cells, and parenchymal cells in all tested lung tissue samples, but the expression was more pronounced in the lungs of scleroderma patients with pulmonary fibrosis. Western blot analyses revealed a strong increase in NEU1 expression in cultured PF from patients with scleroderma compared to healthy controls. NEU1 overexpression in normal fibroblast cultures led to a significant elevation in collagen levels, without increasing TGF-β mRNA or total or active TGF-β protein. Simultaneously, overexpression of NEU1 caused autocatalytic proteolysis of MMP14, a collagen-degrading enzyme, whose desialylation state is known to accelerate self-proteolysis. Intratracheal instillation of a NEU1-encoding but not a control adenovirus in mice in vivo caused accumulation of lymphocytes in BAL and lung tissue, elevation in total pulmonary TGF-β, and increases in pulmonary collagen. The accumulating lymphocytes were predominantly T cells, with CD8+ cells exceeding CD4+ cells by nearly 2 fold.

Conclusion:  NEU1 expression is elevated in the lungs of scleroderma patients with pulmonary fibrosis, contributing to collagen protein accumulation by activating autocatalytic proteolysis of the collagen-degrading enzyme MMP14. In vivo, NEU1 gene delivery causes pulmonary fibrosis and lymphocytosis with predominant accumulation of CD8+ T cells, which are also seen in patients with scleroderma lung disease. Together, these data suggest an important pathophysiological role for NEU1 in pulmonary abnormalities observed in patients with scleroderma.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/expression-of-neuraminidase-1-neu1-is-upregulated-in-the-lungs-of-scleroderma-patients-with-pulmonary-fibrosis-and-gene-delivery-of-neu1-to-mouse-lungs-elicits-accumulation-of-cd8-lymphocytes-and/