Abstract: FR-PO737
Role of Cargo Receptor Surf4 in Podocyte Proteostasis
Session Information
- Glomerular Diseases: Mechanisms and Podocyte Biology
October 25, 2024 | Location: Exhibit Hall, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Glomerular Diseases
- 1401 Glomerular Diseases: Mechanisms, including Podocyte Biology
Authors
- Cybulsky, Andrey V., McGill University, Montreal, Quebec, Canada
- Papillon, Joan, McGill University, Montreal, Quebec, Canada
- Konde Bilogui, Christian-Landry, McGill University, Montreal, Quebec, Canada
Background
Protein misfolding in the endoplasmic reticulum (ER) of podocytes/glomerular epithelial cells (GECs) induces ER stress, and contributes to the pathogenesis of glomerular diseases. The unfolded protein response (UPR) and autophagy may be activated to sustain proteostasis. In GECs during ER stress, the COPII vesicle component Sec23B localizes in autophagosomes along with collagen IV-α5 (COL4A5). Thus, the secretory pathway is redirected to ERphagy (ER-specific autophagy), with COL4A5 being a potential ERphagy substrate. In GECs, ERphagy was facilitated by the activation of the UPR transducer IRE1α. Discovery proteomics in GECs exposed to ER stress showed that IRE1α facilitated expression of Surf4, an ER-COPII vesicle cargo receptor. The present study examines whether Surf4 may redirect misfolded proteins for autophagosomal degradation.
Methods
We studied IRE1α-replete (control) GECs in culture and GECs with genetic knockout (KO) of IRE1α. Immunofluorescence microscopy was used to quantify autophagosome number/area by setting a suitable particle size/threshold.
Results
Basal Surf4 expression was greater in control compared to IRE1α KO GECs. During ER stress induced with tunicamycin (TM), there was activation of the UPR, although Surf4 did not increase above basal levels. TM increased LC3-II and Surf4 particle areas, as well as colocalization of LC3 and Surf4; increases were smaller in KO GECs compared to control. Thus, during ER stress, a subset of Surf4 localizes in autophagosomes. TM increased COL4A5 particle area and colocalization of Surf4 with COL4A5 in control and KO GECs, implying that during ER stress, some of the COL4A5 localizes in autophagosomes. The GEC toxin adriamycin (ADR) induced autophagy (LC3-II), but not the UPR. Unlike TM, ADR did not promote localization of Surf4 or COL4A5 in autophagosomes. However, both TM and ADR could enhance colocalization of LC3-II and Hsp60 (a mitochondrial protein), consistent with mitophagy. Analysis of a human glomerular gene expression dataset showed increased Surf4 and UPR gene expression in membranous nephropathy and focal segmental glomerulosclerosis compared to healthy controls.
Conclusion
During ER stress, Surf4 is redirected from the secretory pathway to autophagosomes. Surf4 may help deliver misfolded ER cargo such as COL4A5 for degradation. This represents a novel role for Surf4 in sustaining proteostasis.
Funding
- Private Foundation Support