Differential routing and disposition of the long-chain saturated fatty acid palmitate in rodent vs human beta-cells

Background: Rodent and human β-cells are differentially susceptible to the lipotoxic effects of long-chain saturated fatty acids (LC-SFA) but the reasons are unclear. The intracellular disposition of the LC-SFA palmitate was compared in human vs rodent β-cells to gain insight into factors regulating β-cell lipotoxicity. Methods: Subcellular distribution of palmitate was studied in rodent (INS-1E and INS-1 823/13) and human (EndoC-BH1) β-cells using confocal fluorescence with a fluorescent palmitate analogue (BODIPY FL C16) and electron microscopy. Protein expression was assessed by Western blotting; cell viability by vital dye staining. Results: Palmitate exposure for 24 h reduced viability of INS-1 cells, whereas EndoC-BH1 cells remained viable even after 72 h at 1 mM palmitate. In INS-1 cells, BODIPY FL C16 localized early to the Golgi apparatus and correlated with distention of intracellular membranes by EM; however, the PERK-dependent ER stress pathway was not activated. In EndoC-BH1 cells, BODIPY FL C16 did not accumulate in the Golgi but co-localized with the lipid droplet protein PLIN2, indicating preferential routing into lipid droplets. Co-treatment of INS-1 cells with palmitate plus oleate attenuated toxicity and redirected BODIPY FL C16 to lipid droplets rather than the Golgi. Conclusion: In rodent β-cells, palmitate accumulates in the Golgi at early time points, while in EndoC-BH1 cells it is routed to lipid droplets. Routing palmitate into lipid droplets is associated with preserved viability and may explain differential sensitivity of rodent vs human β-cells to lipotoxicity.

Patricia Thomas, Catherine Arden, Jenna Corcoran, Christian Hacker, Hannah J. Welters, Noel G. Morgan