Study of the tRNA-derived fragment expression profile in rat pancreatic islets of diabetes-susceptible low-protein (LP) exposed rats

In this study, we discovered cytosolic and mitochondrial fragments resulting from tRNA and mt-tRNA cleavage, which may act as new regulators of cellular and metabolic functions. The so-called LP rat model consists of 22-day-old rats whose mothers have been subjected to a low protein diet during gestation and lactation. These offspring have impaired pancreatic development with reduced ß-cell mass, glucose-stimulated insulin secretion defect and are more prone to develop diabetes in adulthood. We identified hundreds of these fragments as being changed in the pancreatic islets of LP rats and compared them to chow diet (CD) exposed rats. In our analysis, we identified 6164 tRFs in the islets of LP rats, among which 256 exhibited significant changes (≥ 2 fold; adjusted p value ≤ 0.05) compared to controls. Of these, 113 tRFs showed increased levels, while 143 tRFs showed decreased levels in the LP rats. We focused our investigations on mitochondrial tRFs (mt-tRFs) that show significant alterations in both, adult pre-diabetic mice (db/db) and LP rats. We selected the mt-tRF-LeuTAA fragment for further investigation, as its level is reduced in the islets of db/db mice and LP rats, while being abundant in ß-cells. mt-tRF-LeuTAA fragment is derived from the cleavage of tRNA-LeuTAA encoded by the mitochondrial genome. We demonstrated that mt-tRF-LeuTAA acts as a key regulator of mitochondrial OXPHOS functions, mitochondrial membrane potential, the insulin secretory capacity of ß-cells, and the insulin sensitivity of myotube muscle cells.本研究中，我们发现了由转运RNA（tRNA）和线粒体转运RNA（mt-tRNA）剪切产生的胞质与线粒体片段，这类片段或可作为细胞功能与代谢功能的新型调控因子。本研究涉及的低蛋白（LP）大鼠模型，指母鼠在妊娠及哺乳期间饲喂低蛋白饮食后所产下的22日龄子代大鼠。此类子代大鼠存在胰腺发育受损的表型：β细胞（β-cell）质量减少、葡萄糖刺激的胰岛素分泌功能缺陷，且成年后更易罹患糖尿病。我们在LP大鼠的胰岛中鉴定出数百个表达异常的此类片段，并将其与普通饲料（CD）组大鼠进行对照分析。 在本次研究中，我们在LP大鼠的胰岛内共鉴定出6164个tRNA衍生片段（tRFs），其中256个与对照组相比存在显著表达差异（差异倍数≥2，校正后P值≤0.05）。在这些差异表达的tRFs中，113个在LP大鼠胰岛中表达上调，143个则表达下调。我们将研究重点聚焦于在成年前驱糖尿病db/db小鼠与LP大鼠中均存在显著表达异常的线粒体tRNA衍生片段（mt-tRFs）。我们选择mt-tRF-LeuTAA片段开展后续功能验证：该片段在db/db小鼠与LP大鼠的胰岛中表达水平降低，而在β细胞中含量丰富。mt-tRF-LeuTAA片段源自线粒体基因组编码的tRNA-LeuTAA的剪切产物。本研究证实，mt-tRF-LeuTAA是线粒体氧化磷酸化（OXPHOS）功能、线粒体膜电位、β细胞胰岛素分泌能力以及肌管细胞胰岛素敏感性的关键调控因子。