Inoue Takao, Hagiyama Man, Yoneshige Azusa, Kato Takashi, Enoki Eisuke, Maenishi Osamu, Chikugo Takaaki, Kimura Masatomo, Satou Takao, Ito Akihiko
Department of Pathology, Faculty of Medicine, Kinki University, Osaka, Japan.
PLoS One. 2014 Jun 25;9(6):e100988. doi: 10.1371/journal.pone.0100988. eCollection 2014.
Pulmonary emphysema and type 2 diabetes mellitus (T2DM), both caused by lifestyle factors, frequently concur. Respectively, the diseases affect lung alveolar and pancreatic islet cells, which express cell adhesion molecule 1 (CADM1), an immunoglobulin superfamily member. Protease-mediated ectodomain shedding of full-length CADM1 produces C-terminal fragments (CTFs) with proapoptotic activity. In emphysematous lungs, the CADM1 shedding rate and thus the level of CTFs in alveolar cells increase. In this study, CADM1 expression in islet cells was examined by western blotting. Protein was extracted from formalin-fixed, paraffin-embedded sections of pancreata isolated from patients with T2DM (n = 12) or from patients without pancreatic disease (n = 8) at autopsy. After adjusting for the number of islet cells present in the adjacent section, we found that full-length CADM1 decreased in T2DM islets, while ectodomain shedding increased. Hemoglobin A1c levels, measured when patients were alive, correlated inversely with full-length CADM1 levels (P = 0.041) and positively with ectodomain shedding rates (P = 0.001). In immunofluorescence images of T2DM islet cells, CADM1 was detected in the cytoplasm, but not on the cell membrane. Consistently, when MIN6-m9 mouse beta cells were treated with phorbol ester and trypsin to induce shedding, CADM1 immunostaining was diffuse in the cytoplasm. When a form of CTFs was exogenously expressed in MIN6-m9 cells, it localized diffusely in the cytoplasm and increased the number of apoptotic cells. These results suggest that increased CADM1 ectodomain shedding contributes to blood glucose dysregulation in T2DM by decreasing full-length CADM1 and producing CTFs that accumulate in the cytoplasm and promote apoptosis of beta cells. Thus, this study has identified a molecular alteration shared by pulmonary emphysema and T2DM.
肺气肿和2型糖尿病（T2DM）均由生活方式因素引起，常同时出现。这两种疾病分别影响肺泡和胰岛细胞，这些细胞表达细胞黏附分子1（CADM1），它是免疫球蛋白超家族成员。蛋白酶介导的全长CADM1胞外域脱落产生具有促凋亡活性的C端片段（CTF）。在肺气肿肺组织中，CADM1的脱落率以及肺泡细胞中CTF的水平均升高。在本研究中，通过蛋白质印迹法检测了胰岛细胞中CADM1的表达。从尸检时分离的T2DM患者（n = 12）或无胰腺疾病患者（n = 8）的胰腺福尔马林固定石蜡包埋切片中提取蛋白质。在调整相邻切片中胰岛细胞数量后，我们发现T2DM胰岛中全长CADM1减少，而胞外域脱落增加。患者生前测得的糖化血红蛋白A1c水平与全长CADM1水平呈负相关（P = 0.041），与胞外域脱落率呈正相关（P = 0.001）。在T2DM胰岛细胞的免疫荧光图像中，CADM1在细胞质中被检测到，但不在细胞膜上。同样，当用佛波酯和胰蛋白酶处理MIN6 - m9小鼠β细胞以诱导脱落时，CADM1免疫染色在细胞质中呈弥漫性。当一种形式的CTF在MIN6 - m9细胞中过表达时，它在细胞质中呈弥漫性定位并增加了凋亡细胞的数量。这些结果表明，CADM1胞外域脱落增加通过减少全长CADM1并产生在细胞质中积累并促进β细胞凋亡的CTF，导致T2DM患者血糖失调。因此，本研究确定了肺气肿和T2DM共有的分子改变。
