TAR DNA-binding protein 43 kDa (TDP-43), encoded by TARDBP, is an RNA-binding protein, the nuclear depletion of which is the histopathological hallmark of amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disorder affecting both upper and lower motor neurons. Besides motor symptoms, patients with ALS often develop nonneuronal signs including glucose intolerance, but the underlying pathomechanism is still controversial, i.e., whether it is impaired insulin secretion and/or insulin resistance. Here, we showed that ALS subjects reduced early-phase insulin secretion and that the nuclear localization of TDP-43 was lost in the islets of autopsied ALS pancreas. Loss of TDP-43 inhibited exocytosis by downregulating CaV1.2 calcium channels, thereby reducing early-phase insulin secretion in a cultured β cell line (MIN6) and β cell–specific Tardbp–knockout mice. Overexpression of CaV1.2 restored early-phase insulin secretion in Tardbp–knocked-down MIN6 cells. Our findings suggest that TDP-43 regulates cellular exocytosis mediated by L-type voltage–dependent calcium channels and, thus, plays an important role in the early phase of insulin secretion by pancreatic islets. Thus, nuclear loss of TDP-43 is implicated in not only the selective loss of motor neurons, but also in glucose intolerance due to impaired insulin secretion at an early stage of ALS.
Kunihiko Araki, Amane Araki, Daiyu Honda, Takako Izumoto, Atsushi Hashizume, Yasuhiro Hijikata, Shinichiro Yamada, Yohei Iguchi, Akitoshi Hara, Kazuhiro Ikumi, Kaori Kawai, Shinsuke Ishigaki, Yoko Nakamichi, Shin Tsunekawa, Yusuke Seino, Akiko Yamamoto, Yasunori Takayama, Shihomi Hidaka, Makoto Tominaga, Mica Ohara-Imaizumi, Atsushi Suzuki, Hiroshi Ishiguro, Atsushi Enomoto, Mari Yoshida, Hiroshi Arima, Shin-ichi Muramatsu, Gen Sobue, Masahisa Katsuno
Endogenous TDP-43 depletion suppresses the first phase of insulin secretion in MIN6 cells.