Reduced late endosome/lysosome function promotes SLE through chronic PI3K activity and SHP-1/SHIP-1 defects
SunAh Kang, Andrew J. Monteith, Liubov Arbeeva, Karissa Grier, Shruti Saxena Beem, Anthony C. Trujillo, Xinyun Bi, Kai Sun, Rebecca E. Sadun, Mithu Maheswaranathan, Megan E.B. Clowse, Saira Z. Sheikh, Jennifer L. Rogers, Barbara J. Vilen
SunAh Kang, Andrew J. Monteith, Liubov Arbeeva, Karissa Grier, Shruti Saxena Beem, Anthony C. Trujillo, Xinyun Bi, Kai Sun, Rebecca E. Sadun, Mithu Maheswaranathan, Megan E.B. Clowse, Saira Z. Sheikh, Jennifer L. Rogers, Barbara J. Vilen
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Research Article Immunology

Reduced late endosome/lysosome function promotes SLE through chronic PI3K activity and SHP-1/SHIP-1 defects

Abstract

Degradation of cellular waste from phagocytosis, endocytosis, and autophagy occurs through hydrolases that become activated during acidification of late endosomes and lysosomes (LELs). In our cross-sectional study, we showed diminished LEL acidification and the accumulation of surface-bound nucleosome on monocytes, dendritic cells, B cells, neutrophils, and T cells from patients with systemic lupus erythematosus (SLE). Diminished acidification and exocytosis of undegraded IgG-immune complexes were evident in active, but not inactive, disease. This was supported by our murine study in which LEL acidification was diminished, promoting exocytosis and the accumulation of cell surface IgG-immune complexes. Mechanistically, LEL dysfunction was induced by chronic PI3K activation in lupus-prone MRL/lpr mice. We also showed that on a non-autoimmune C57BL/6 background, deficiency in SHP-1 and inhibition of SHIP-1 activity were sufficient to recapitulate LEL dysfunction found in MRL/lpr mice. Non-acidic LELs were evident in the majority of patients and associated with SLEDAI arthritis, rash, and nephritis. The high frequency of LEL dysfunction in SLE suggests that it could serve as a biomarker identifying a specific disease endotype.

Authors

SunAh Kang, Andrew J. Monteith, Liubov Arbeeva, Karissa Grier, Shruti Saxena Beem, Anthony C. Trujillo, Xinyun Bi, Kai Sun, Rebecca E. Sadun, Mithu Maheswaranathan, Megan E.B. Clowse, Saira Z. Sheikh, Jennifer L. Rogers, Barbara J. Vilen

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Figure 5

LEL defects are induced by chronic PI3K activation and SHIP-1 defects and evident in FcγRI–/–/MRL/lpr mice.

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LEL defects are induced by chronic PI3K activation and SHIP-1 defects an...
(A–J) BMMφs were stimulated with IgG-ICs (25 μL IgG-ICs per 0.25 × 106 cells). At designated times, LEL pH (A and C), ROS (B), exocytosis (D), PIP3 (E), PI(3,4)P2 (F), and p–SHIP-1Y1022 (G) were measured by flow cytometry. vATPase activity in unstimulated samples [t0(CMA)] was inhibited with concanamycin A (CMA; 2 ng/mL) (A and C). ROS levels (B) were measured using CellROX including t0 samples untreated with IgG-ICs. BMMφs were preloaded (t0) with Alexa Fluor 488–labeled IgG-ICs, and exocytosis was measured at designated times (C). Surface-bound fluorescence was assessed by subtraction of internalized fluorescence (surface quenched) from total (unquenched) and normalized to individual t0. The effect of PI3K was measured using PI3K-p110 inhibitors (p110α, β, and δ) (100 nM, 2 hours before IgG-IC treatment) (C and D). The colocalization of IgG-ICs (red) and p–SHIP-1Y1022 (green) with cholera toxin–positive lipid rafts (CTx, blue) (H) in BMMφs was analyzed by confocal microscopy (I and J). Images were processed using ImageJ (NIH). Representative images are shown. White in merged images depicts colocalized IgG-ICs, p–SHIP-1Y1022, and CTx. Statistical analysis used 2-way ANOVA with multiple comparisons (A–G) and Mann-Whitney test (H). Adjusted P values with significance are shown. N = 2–8, 2–5 experiments (A–H); N = 3, 3 experiments, total of 50 cells per mouse line (H–J). Bars, median; boxes, 25th–75th percentiles; whiskers, minimum and maximum values.