Lysosomal exocytosis of HSP70 stimulates monocytic BMP6 expression in Sjögren’s syndrome
Ying-Qian Mo, … , Blake M. Warner, John A. Chiorini
Ying-Qian Mo, … , Blake M. Warner, John A. Chiorini
Published February 3, 2022
Citation Information: J Clin Invest. 2022;132(6):e152780. https://doi.org/10.1172/JCI152780.
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Research Article Autoimmunity

Lysosomal exocytosis of HSP70 stimulates monocytic BMP6 expression in Sjögren’s syndrome

Abstract

BMP6 is a central cytokine in the induction of Sjögren’s syndrome–associated (SS-associated) secretory hypofunction. However, the upstream initiation leading to the production of this cytokine in SS is unknown. In this study, RNA ISH on salivary gland sections taken from patients with SS indicated monocytic lineage cells as a cellular source of BMP6. RNA-Seq data on human salivary glands suggested that TLR4 signaling was an upstream regulator of BMP6, which was confirmed by in vitro cell assays and single-cell transcriptomics of human PBMCs. Further investigation showed that HSP70 was an endogenous natural TLR4 ligand that stimulated BMP6 expression in SS. Release of HSP70 from epithelial cells could be triggered by overexpression of lysosome-associated membrane protein 3 (LAMP3), a protein also associated with SS in several transcriptome studies. In vitro studies supported the idea that HSP70 was released as a result of lysosomal exocytosis initiated by LAMP3 expression, and reverse transcription PCR on RNA from minor salivary glands of patients with SS confirmed a positive correlation between BMP6 and LAMP3 expression. BMP6 expression could be experimentally induced in mice by overexpression of LAMP3, which developed an SS-like phenotype. The newly identified LAMP3/HSP70/BMP6 axis provided an etiological model for SS gland dysfunction and autoimmunity.

Authors

Ying-Qian Mo, Hiroyuki Nakamura, Tsutomu Tanaka, Toshio Odani, Paola Perez, Youngmi Ji, Benjamin N. French, Thomas J.F. Pranzatelli, Drew G. Michael, Hongen Yin, Susan S. Chow, Maryam Khalaj, Sandra A. Afione, Changyu Zheng, Fabiola Reis Oliveira, Ana Carolina F. Motta, Alfredo Ribeiro-Silva, Eduardo M. Rocha, Cuong Q. Nguyen, Masayuki Noguchi, Tatsuya Atsumi, Blake M. Warner, John A. Chiorini

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Figure 5

LAMP3 expression in salivary gland epithelial cells is involved in BMP6 expression by the release of HSP70.

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LAMP3 expression in salivary gland epithelial cells is involved in BMP6 ...
(A) Scatter plot showing enriched gene ontology in patients with SS with high BMP6 expression compared with those with normal BMP6 expression. (B) Correlation between LAMP3 and BMP6 transcript expression in minor salivary glands of patients with SS (n = 43). (C) Schematic showing the methods used in the in vitro assays. (D) Representative Western blot with the indicated antibodies using lysates of salivary acinar or ductal cells 72 hours after transfection with empty and/or LAMP3 expression plasmids. (E) HSP70 concentration in culture supernatant collected 96 hours after transfection. (F) THP1 cells were treated with the culture supernatant of acinar or ductal cells with or without CUCPT22 (20 μM) or TAK242 (40 μM). BMP6 transcript levels in THP1 cells were evaluated 20 hours after stimulation using the ΔΔCt method relative to ACTB. Values shown are the mean ± SEM of 3 independent experiments. **P < 0.01, by Student’s t test with multiple testing correction using Tukey’s method (E and F).