Biophysical Society Conference | Estes Park 2023

Membrane Budding and Fusion

Poster Abstracts

35-POS Board 12 DYNAMIN: A MASTER REGULATOR OF MEMBRANE TRAFFICKING IN PANCREATIC BETA CELLS

Fan Fan 1 ; Jennifer Wendlick; Michael Abiola 1 ; Xuelin Lou 1 ; 1 Medical College of Wisconsin, The Department of Cell Biology, Neurobiology and Anatomy, Milwaukee, WI, USA

Insulin secretion is essential for glucose homeostasis. Decades of research have expanded our knowledge on the secretory pathway in β cells, but a significant gap remains about their endocytosis pathway until recently. Our work on dynamin has started to gain new insights into this gap, highlighting the significance of endocytosis in insulin secretion failure (Fan et al. J Clin Invest. 2015, PNAS 2021). We show that dynamin-2 and -3 are abundant, but dynamin-1 is undetectable in β cells from mice and humans. Unlike neurons, β -cells are more tolerant to triple dynamin knockout (TKO). TKO cells maintain a similar cell diameter and contain numerous granules, implying the operation of dynamin-independent endocytosis. Dynamin regulates the capacity and timing of glucose-stimulated insulin secretion (GSIS). DNM2KO selectively reduces the 2 nd GSIS phase, and TKO impairs both GSIS phases, indicating a partially overlapping function between DNM2 and DNM3. The impaired insulin secretion is partially mediated by F-actin remodeling and Munc13 reduction. Interestingly, beyond endocytosis, dynamin also regulates membrane fission intracellularly in β cells. TKO induces autophagy disruption as evidenced by the accumulation of enlarged autophagic structures. These structures are positive for both autophagic marker LC3 (microtubule-associated protein 1A/1B light chain 3) and Lamp1, suggesting they are autolysosomes (ALS). TIRFM imaging reveals that dynamin 2-EGFP interacts with ALS and sometimes stays on ALS with a transient increase right before the ALS tubular fission. In this experiment, we expressed dynamin-2-EGFP in TKO rather than WT β -cells to avoid unlabeled endogenous dynamin, allowing more faithful monitoring of dynamin behaviors. Thus, dynamin may regulate β -cell autophagy by facilitating ALS membrane fission and budding. Together, dynamin is a master regulator of membrane trafficking in endocytosis and autophagic recycling in β cells, and both pathways share the same intrinsic feature of dynamin as a membrane fission GTPase.

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