Abstract
Background/Objectives: This study aims to investigate the effects of 4-methylumbelliferone (4-MU) on islet morphology, cell phenotype and function, and to explore possible mechanisms of β cell regeneration. Methods: The Type 1 diabetes (T1D) model was induced by continuous dose injection of streptozotocin (STZ), and mice were treated with 4-MU for 3 weeks. Plasma insulin level, islet cell phenotype and immune infiltration were determined by IPGTT, ELISA, HE and immunofluorescence. The Ins2(Cre/+)/Rosa26-eGFP transgenic mice model was used to detect β identity change. Primary rodent islets were incubated with 4-MU or vehicle in the presence or absence of STZ, AO/PI staining, and a scanning electron microscope (SEM), PCR and ELISA were used to evaluated islet viability, islet morphology, the specific markers of islet β cells and insulin secretion. Results: Treatment with 4-MU significantly decreased blood glucose and increased plasma insulin levels in STZ-induced diabetes. The plasma insulin level in the STZ group was 7.211 ± 2.602 ng/mL, which was significantly lower than the control group level (26.94 ± 4.300 ng/mL, p < 0.001). In contrast, the plasma insulin level in the STZ + 4-MU group was 22.29 ± 7.791 ng/mL, which was significantly higher than the STZ group (p < 0.05). The 4-MU treatment increased islet and β cells numbers and decreased α cell numbers in STZ-induced diabetes. Conclusions: Islet inflammation as indicated by insulin and CD3 was caused by infiltrates, and the β cell proliferation as indicated by insulin and Ki67 was boosted by 4-MU. β cell dedifferentiation was inhibited by 4-MU as assessed by insulin and glucagon double-positive cells and confirmed by Ins2(Cre/+)/Rosa26-eGFP mice. In cultured primary rodent islets, 4-MU restored islet viability, protected islet morphology, inhibited β-cell dedifferentiation, and promoted insulin secretion. The benefits of 4-MU in T1D have been proved to be associated with β cells self-replication, dedifferentiation inhibition and immune progression suppression, which help to maintain β cell mass.