Objectives Low-density granulocytes (LDGs) are a distinct subset of proinflammatory and vasculopathic neutrophils expanded in systemic lupus erythematosus (SLE). Neutrophil trafficking and immune function are intimately linked to cellular biophysical properties. This study used proteomic, biomechanical and functional analyses to further define neutrophil heterogeneity in the context of SLE.
Methods Proteomic/phosphoproteomic analyses were performed in healthy control (HC) normal density neutrophils (NDNs), SLE NDNs and autologous SLE LDGs. The biophysical properties of these neutrophil subsets were analysed by real-time deformability cytometry and lattice light-sheet microscopy. A two-dimensional endothelial flow system and a three-dimensional microfluidic microvasculature mimetic (MMM) were used to decouple the contributions of cell surface mediators and biophysical properties to neutrophil trafficking, respectively.
Results Proteomic and phosphoproteomic differences were detected between HC and SLE neutrophils and between SLE NDNs and LDGs. Increased abundance of type 1 interferon-regulated proteins and differential phosphorylation of proteins associated with cytoskeletal organisation were identified in SLE LDGs relative to SLE NDNs. The cell surface of SLE LDGs was rougher than in SLE and HC NDNs, suggesting membrane perturbances. While SLE LDGs did not display increased binding to endothelial cells in the two-dimensional assay, they were increasingly retained/trapped in the narrow channels of the lung MMM.
Conclusions Modulation of the neutrophil proteome and distinct changes in biophysical properties are observed alongside differences in neutrophil trafficking. SLE LDGs may be increasingly retained in microvasculature networks, which has important pathogenic implications in the context of lupus organ damage and small vessel vasculopathy.
- lupus erythematosus
- cardiovascular diseases
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Handling editor Josef S Smolen
ERC and CS contributed equally.
Funding This research was supported by the Intramural Research programs at NIAMS (ZIA-AR041199), NHLBI and NIBIB. ACM is supported by a Clinical Research Career Development Fellowship from the Wellcome Trust (WT 2055214/Z/16/Z). CS is funded by Medical Research Council, Wellcome Trust, British Heart Foundation, Glaxo Smith Kline, Astra Zeneca and NIHR Cambridge Biomedical Research Centre. ERC receives funding from MRC, Wellcome Trust, GlaxoSmithKline, the NHLI Foundation and the NIHR Imperial Biomedical Research Centre. AJTW was supported by a Gates Cambridge Scholarship. KRB was also supported by a National Institutes of Health OxCam Scholarship.
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval All studies were approved by site-specific IRBs: the Cambridge Local Research Ethics Committee (REC reference 06/Q0108/281) and NIAMS/NIDDK IRB (NIH 94-AR-0066). All subjects signed informed consent.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement The mass spectrometry proteomics data have been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the dataset identifier PXD021096 and 10.6019/PXD021096. Transcriptomics data are in GEO database GSE139358