β-Cell keratin 8 maintains islet mechanical integrity, mitochondrial ultrastructure, and β-cell glucose transporter 2 plasma membrane targeting

Baghestani, Sarah; Haldin, Caroline; Kosijer, Petar; Alam, Catharina M.; Toivola, Diana M.

Abstract

Islet β-cell dysfunction is an underlying factor for type I diabetes (T1D) development. Insulin sensing and secretion are tightly regulated in β-cells at multiple subcellular levels. The epithelial intermediate filament (IF) protein keratin (K) 8 is the main β-cell keratin, constituting the filament network with K18. To identify the cell-autonomous functions of K8 in β-cells, mice with targeted deletion of β-cell K8 (K8flox/flox; Ins-Cre) were analyzed for islet morphology, ultrastructure, and integrity, as well as blood glucose regulation and streptozotocin (STZ)-induced diabetes development. Glucose transporter 2 (GLUT2) localization was studied in β-cells in vivo and in MIN6 cells with intact or disrupted K8/K18 filaments. Loss of β-cell K8 leads to a major reduction in K18. Islets without β-cell K8 are more fragile, and these β-cells display disjointed plasma membrane organization with less membranous E-cadherin and smaller mitochondria with diffuse cristae. Lack of β-cell K8 also leads to a reduced glucose-stimulated insulin secretion (GSIS) response in vivo, despite undisturbed systemic blood glucose regulation. K8flox/flox, Ins-Cre mice have a decreased sensitivity to STZ compared with K8 wild-type mice, which is in line with decreased membranous GLUT2 expression observed in vivo, as GLUT2 is required for STZ uptake in β-cells. In vitro, MIN6 cell plasma membrane GLUT2 is rescued in cells overexpressing K8/K18 filaments but mistargeted in cells with disrupted K8/K18 filaments. β-Cell K8 is required for islet and β-cell structural integrity, normal mitochondrial morphology, and GLUT2 plasma membrane targeting, and has implications on STZ sensitivity as well as systemic insulin responses.NEW & NOTEWORTHY Keratin 8 is the main cytoskeletal protein in the cytoplasmic intermediate filament network in β-cells. Here for the first time, we assessed the β-cell autonomous mechanical and nonmechanical roles of keratin 8 in β-cell function. We demonstrated the importance of keratin 8 in islet and β-cell structural integrity, maintaining mitochondrial morphology and GLUT2 plasma membrane targeting.

Citation

Baghestani, S., Haldin, C., Kosijer, P., Alam, C. M., & Toivola, D. M. (2024). β-Cell keratin 8 maintains islet mechanical integrity, mitochondrial ultrastructure, and β-cell glucose transporter 2 plasma membrane targeting. American Journal of Physiology - Cell Physiology, 327(2), C462-C476. https://doi.org/10.1152/ajpcell.00123.2024

• Journal Article Type: Article
• Acceptance Date: Jun 12, 2024
• Online Publication Date: Jun 24, 2024
• Publication Date: 2024-08
• Deposit Date: Oct 18, 2024
• Publicly Available Date: Oct 18, 2024
• Journal: American Journal of Physiology-Cell Physiology
• Print ISSN: 0363-6143
• Electronic ISSN: 1522-1563
• Publisher: American Physiological Society
• Peer Reviewed: Peer Reviewed
• Volume: 327
• Issue: 2
• Pages: C462-C476
• DOI: https://doi.org/10.1152/ajpcell.00123.2024
• Keywords: GLUT2; intermediate filament; islet integrity; keratin; β-cell ultrastructure
• PMID: 38912736
• External URL: https://pubmed.ncbi.nlm.nih.gov/38912736/