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 7

Epithelial LAMP3 expression stimulates monocytic BMP6 expression via TLR4 in murine salivary glands.

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Epithelial LAMP3 expression stimulates monocytic BMP6 expression via TLR...
(A) Submandibular glands of C57BL/6 mice were instilled with an AAV2 vectors encoding LAMP3 (AAV2-LAMP3) or GFP (AAV2-GFP), and the tissues and saliva flow rate were evaluated 6 months later. Mice were given i.p. injections of TAK242 or vehicle for the last 10 days. (B) Representative images of dual ISH for Bmp6 (white) and IF for CD68 (magenta) and nucleus (DAPI, blue) (upper panel), and images of IF for BMP6 (green) and nuclei (DAPI, blue) (lower panel) in submandibular gland sections. Scale bars: 20 μm. Enlargement original magnification, 100×. Quantification of (C) Bmp6+ dots per mm2 (n = 5 each) and (D) BMP6 expression area (n = 3 each). (E) Representative IF images for BMP6 (green, upper panel), AQP5 (red, lower panel), and nuclei (DAPI, blue) in submandibular gland sections. Scale bars: 20 μm. Quantification of (F) BMP6 and (G) AQP5 expression area. Values shown are the mean ± SD. **P < 0.01, by Student’s t test (C, D, F, and G). (H) Pilocarpine-stimulated salivary flow per body weight over 20 minutes in TAK242-treated mice (n = 4) and vehicle-treated mice (n = 3). Values shown indicate the median and the range. †P < 0.05, by Wilcoxon test.