OBJECTIVE Progressive beta-cell dysfunction is a hallmark of type 2 diabetes (T2D). Increasing evidence indicates that over-stimulating proinsulin synthesis causes proinsulin misfolding and impairs insulin maturation and storage in db/db mice. However, defective insulin maturation in patients with T2D remains unknown. METHODS We examined intra-islet and intra-cellular distributions of proinsulin and insulin and proinsulin to insulin ratio in the islets of patients with T2D. The expression of transcription factor NKX6.1 and dedifferentiation marker ALDH1A3, as well as glucagon, were detected by immunofluorescence. RESULTS We identified a novel subgroup of beta cells expressing only proinsulin but not insulin. Importantly, significantly increased proinsulin positive and insulin negative (PI+/INS-) cells were evident in T2D, and this increase was strongly correlated with levels of hemoglobin A1C (HbA1c) in T2D and prediabetes. The percentages of beta cells expressing prohormone convertase 1/3 and carboxypeptidase E were not reduced. Indeed, while proinsulin displayed a higher degree of co-localization with the golgi markers GM130/TGN46 in control beta cells, it appeared to be more diffused within the cytoplasm and less co-localized with GM130/TGN46 in PI+/INS- cells. Furthermore, the key functional transcription factor NKX6.1 markedly decreased in the islets of T2D, especially in the cells with PI+/INS-. The decreased NKX6.1+/PI+/INS+ was strongly correlated with levels of HbA1c in T2D. Almost all PI+/INS- cells showed absence of NKX6.1. Moreover, the percentages of PI+/INS- cells expressing ALDH1A3 were elevated along with an increased acquisition of glucagon immunostaining. CONCLUSION Our data demonstrate defective insulin maturation in patients with T2D.

中文翻译：

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2型糖尿病患者的胰岛素成熟缺陷。

目的 进行性 β 细胞功能障碍是 2 型糖尿病 (T2D) 的标志。越来越多的证据表明，过度刺激胰岛素原合成会导致 db/db 小鼠的胰岛素原错误折叠并损害胰岛素成熟和储存。然而，T2D 患者的胰岛素成熟缺陷仍然未知。方法 我们检查了 T2D 患者胰岛中胰岛素原和胰岛素的胰岛内和细胞内分布以及胰岛素原与胰岛素的比率。免疫荧光检测转录因子NKX6.1和去分化标志物ALDH1A3以及胰高血糖素的表达。结果 我们发现了一个新的β细胞亚群，它只表达胰岛素原而不表达胰岛素。重要的是，T2D 中明显增加的胰岛素原阳性和胰岛素阴性 (PI+/INS-) 细胞，这种增加与 T2D 和前驱糖尿病患者的血红蛋白 A1C (HbA1c) 水平密切相关。表达激素原转化酶 1/3 和羧肽酶 E 的 β 细胞的百分比没有降低。事实上，虽然胰岛素原在对照 β 细胞中与高尔基体标记 GM130/TGN46 显示出更高程度的共定位，但在 PI+/INS-细胞中，它似乎更分散在细胞质内，与 GM130/TGN46 的共定位更少。此外，关键功能转录因子NKX6.1在T2D胰岛中显着降低，尤其是在PI+/INS-细胞中。降低的 NKX6.1+/PI+/INS+ 与 T2D 中的 HbA1c 水平密切相关。几乎所有的 PI+/INS- 细胞都显示不存在 NKX6.1。而且，表达 ALDH1A3 的 PI+/INS- 细胞的百分比随着胰高血糖素免疫染色的增加而升高。结论 我们的数据表明 T2D 患者的胰岛素成熟有缺陷。