Abstract: SA-PO191

Diagnostic Biomarkers of Endoplasmic Reticulum Stress in Glomerular Disease

Session Information

  • Glomerular: Cell Biology
    November 04, 2017 | Location: Hall H, Morial Convention Center
    Abstract Time: 10:00 AM - 10:00 AM

Category: Glomerular

  • 1003 Glomerular: Cell Biology

Authors

  • Abouelazm, Nihad T, McGill University, Montreal, Quebec, Canada
  • Papillon, Joan, McGill University, Montreal, Quebec, Canada
  • Guillemette, Julie, McGill University, Montreal, Quebec, Canada
  • Cybulsky, Andrey V., McGill University, Montreal, Quebec, Canada
Background

Endoplasmic reticulum (ER) stress has been implicated in the pathogenesis of various glomerular and tubular diseases. ER chaperones lacking the KDEL motif, e.g. ERdj3 and mesencephalic astrocyte-derived neurotrophic factor (MANF), can be secreted extracellularly. We propose that induction of ER stress in glomerular diseases may lead to accumulation of secreted ER chaperones in the urine. Such chaperones may potentially serve as biomarkers for diagnosis and therapy.

Methods

ER stress was induced in cultured glomerular epithelial cells (GECs) and in vivo with tunicamycin (TM). In addition, complement-induced ER stress in podocytes was studied in passive Heymann nephritis (PHN), a rat model of human membranous nephropathy. Intracellular expression and secretion of ER chaperones was monitored by immunoblotting. The protective effect of the chemical chaperone, 4-phenyl butyric acid (4-PBA), on complement-mediated podocyte injury was examined by adding 4-PBA to the drinking water of rats with PHN.

Results

In cultured GECs, TM upregulated ER chaperones, ERdj3 and MANF, intracellularly and in culture medium, whereas GRP94 (KDEL chaperone) increased only intracellularly. ERdj3 and MANF extracellular secretion was blocked by the secretory trafficking inhibitor, brefeldin A. ERdj3 and MANF immunoreactivity was stimulated in urines and glomerular lysates of TM-injected rats after 24 h and was independent of proteinuria. Compared to control, ERdj3 and MANF were increased significantly in the urine of PHN rats on days 7-14 after injection of nephritogenic antibody, and coincided with the onset of proteinuria on day 7. Moreover, in PHN, there were concomitant increases in glomerular ER chaperones, GRP94, ERP57, and MANF, compared to control. Rats with PHN were treated with 4-PBA starting at the time of disease induction, or on day 7, until day 14. In both protocols, 4-PBA reduced proteinuria (on days 7-14), as well as urinary ER chaperone secretion, compared to PHN rats treated with saline.

Conclusion

ERdj3 and MANF secreted into the urine reflect glomerular ER stress. 4-PBA protected against complement-mediated podocyte injury and the therapeutic response could be monitored by ERdj3 and MANF secretion. Urinary ER chaperones may potentially serve as diagnostic biomarkers for identifying patients with glomerular ER dysfunction.

Funding

  • Government Support - Non-U.S.