Enhanced insulin secretion of physically crosslinked pancreatic β-cells by using a poly(ethylene glycol) derivative with oleyl groups

A polymeric crosslinker was developed to promote the formation of cellular spheroids. Our approach was based on the crosslinking of cell membrane using a polymeric crosslinker that worked via hydrophobic interaction. The crosslinker, a poly(ethylene glycol) derivative with oleyl groups as a hydrophobic group at both ends, was synthesized and characterized by gel permeation chromatography and Fourier-transform infrared spectroscopy. Cell culture experiments were then performed to confirm spheroid formation. The rat pancreatic islet β-cell line RIN, which possesses the ability to secrete insulin, was cultured with the crosslinker in a round-bottomed 96-well plate. The formation of a spheroid was achieved when the crosslinker was added to the cell suspension, especially in the absence of serum. The size of the spheroid decreased with time and with increasing crosslinker concentration, and depended on the number of cells plated in each well. The number of cells cultured with crosslinker was almost constant during 7 days and hardly proliferated in crosslinker concentrations of 0–2.5 mg ml−1, while the number of cells showed a decrease in the 25 mg ml−1 crosslinker concentration. It was shown that the insulin protein secretion in the spheroid cultured with crosslinker for 1 week was enhanced. The cell adhesion protein E-cadherin mRNA expression of the resulting spheroid was also enhanced. These results indicate that the promoted cell function was due to the cell–cell and cell–matrix interactions in the spheroid, suggesting that this polymeric crosslinker was useful for the formation of cell spheroids.