The effect of aspartame on accelerating caspase-dependent apoptosis of pancreatic islet via ZIPK/STAT3/caspase 3 signaling pathway.

Aspartame (ASP) as an important sugar substitute is widely used in pharmaceutical and food processing. Here, we compared the effects of ASP and sucrose on mice pancreatic islet cells in vivo and observed that ASP with the condition of high concentration and long-term exposure (HASP) could cause insulin secretion (500 mg/kg for 1 month). Next, we conducted iTRAQ mass spectrometry to profile the global phosphoproteome and found that phosphorylation of zipper-interacting protein kinase (ZIPK) in murine pancreatic islet tissues were induced at Thr197, Thr242, Thr282, and Ser328 by high-sucrose (HS) treatment, but only induced at Thr197 and Ser328 by HASP treatment. Simultaneously, phosphorylation of STAT3 could be induced at Tyr705 and Ser727 by HS but not by HASP. Furthermore, presence of activated STAT3 accompanied with autophagy was observed in HS treatment. In turn, the inactivation of STAT3 as well as enhanced expression of caspase 3 was observed in HASP treatment. We generated Thr242APro and Thr282Pro on ZIPK using CRISPR-Cas9 in β-TC3 cells and found the weakened interaction with STAT3 as well as the reduced phosphorylation of STAT3 even under HS stimulation. Finally, we observed that ankyrin repeat domain containing 11 (ANKRD11) could interact with ZIPK and play an inhibitory role in the phosphorylation of Thr242APro and Thr282Pro of ZIPK. However, HASP can induce the retention of ANKRD11 in the cytoplasm by phenylpyruvic acid (the metabolite of ASP). Taken together, this study determined that ASP with high concentration and long-term exposure could lead to caspase-dependent apoptosis of pancreatic islet cells through ANKRD11/ZIPK/STAT3 inhibition. Our results give evidence of adverse effects of aspartame on islet cells in some extreme conditions, which might help people to reconsider the biosafety of non-nutritive sweeteners.