AAT, an acute phase reactant serine protease inhibitor, exerts protective effects on islets under stress. We reported that AAT inhibits β cell death through the suppression of cytokine-induced c-Jun N-terminal kinases (JNK) activation, in addition to its anti-inflammatory effects extracellularly in an islet transplantation model. To further understand the direct effects of AAT on β cells, we studied AAT endocytosis in human islets and a murine insulinoma cell line, βTC3 cells. We found that AAT was internalized by β cells in a time- and dose-dependent manner. AAT internalization was mediated by clathrin as treatment with chlorpromazine (CPZ), a drug that disrupts clathrin-mediated endocytosis, profoundly decreased AAT internalization. Besides, AAT inhibited cytokine-induced JNK activation, caspase 9 cleavage and DNA fragmentation, which were also overturned by the addition of CPZ. Meanwhile, although evidence suggests that clathrin interacts with autophagy related 16 like 1 (Atg16L1) which results in autophagy in several types of cells, we observed only mild induction of Atg16L1 and autophagy after AAT treatment in β cells.

In summary, as shown in the image, we found that AAT is internalized by β cells via clathrin-mediated endocytosis. Moreover, our finding that AAT endocytosis is required for its protective effects on β cells provides new insight into the usage of AAT-based therapy in diabetes and related diseases.

J. Wang: None. D. Kim: None. C. Strange: Research Support; Self; Grifols, CSL Behring, Shire. Consultant; Self; Shire. Stock/Shareholder; Self; Abeona. Consultant; Self; CSL Behring. Research Support; Self; Adverum. Consultant; Self; Adverum. Research Support; Self; MatRx. H. Wang: None.

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