Max-Harry Ibiagbani M, Ajmal Nida, Khan Palwasha, Davis Landen E, Hashmi Waleed J, Kantake Noriko, Corbin Kathryn L, Rosol Thomas J, Nunemaker Craig S
Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, OH 45701, USA.
Diabetes Institute, Heritage College of Osteopathic Medicine, Ohio University, Athens, OH 45701, USA.
Endocrinology. 2025 Jun 10;166(8). doi: 10.1210/endocr/bqaf086.
Administration of parathyroid hormone-related protein (PTHrP) has been shown to increase insulin content and secretion in mice. PTHrP also increases β-cell mass and proliferation. However, the mechanisms for these effects are unknown, and investigations have yet to examine PTHrP in the transcriptome. In this study, we transiently transfected a mouse β-cell line (MIN6) with either full-length PTHrP or DSred vector. Insulin content and glucose-stimulated insulin secretion were measured, and RNA from the cells after incubating in 20 mM glucose was collected. The results showed that PTHrP overexpression increased insulin content and the ratio of insulin secretion between low and high glucose (stimulation index). RNA sequencing showed that PTHrP overexpression downregulated many genes associated with responses to endoplasmic reticulum (ER) stress such as Hspa40, Dnajc3, and Xbp1. Among enriched Kyoto Encyclopedia of Genes and Genomes pathways, the ER stress gene pathway was the most strongly downregulated by far, and the most upregulated pathway was for biosynthesis of amino acids required for protein synthesis. These pathways suggest increased rates of protein biosynthesis. Quantitative polymerase chain reaction supported RNA-sequencing results for several ER stress genes (Xbp1, Bax, Bip). MIN6 cells transfected with PTHrP also had lower proinsulin-to-insulin ratio, indicating that PTHrP enhanced insulin processing in the ER. Our working hypothesis is that PTHrP augments insulin production and ER efficiency, which is consistent with observations of increased insulin content, decreased proinsulin-to-insulin ratio and reduced ER stress markers in MIN6 cells. In conclusion, our findings suggest a previously unknown role for PTHrP in β-cell endoplasmic reticulum, which may have therapeutic implications for enhancing insulin production.
甲状旁腺激素相关蛋白（PTHrP）的给药已被证明可增加小鼠的胰岛素含量和分泌。PTHrP还可增加β细胞质量和增殖。然而，这些作用的机制尚不清楚，且尚未有研究在转录组水平上检测PTHrP。在本研究中，我们用全长PTHrP或DSred载体瞬时转染小鼠β细胞系（MIN6）。测量胰岛素含量和葡萄糖刺激的胰岛素分泌，并收集在20 mM葡萄糖中孵育后的细胞RNA。结果显示，PTHrP过表达增加了胰岛素含量以及低葡萄糖和高葡萄糖之间的胰岛素分泌比率（刺激指数）。RNA测序表明，PTHrP过表达下调了许多与内质网（ER）应激反应相关的基因，如Hspa40、Dnajc3和Xbp1。在富集的京都基因与基因组百科全书通路中，ER应激基因通路是迄今为止下调最强烈的，而上调最明显的通路是蛋白质合成所需氨基酸的生物合成。这些通路表明蛋白质生物合成速率增加。定量聚合酶链反应支持了几个ER应激基因（Xbp1、Bax、Bip）的RNA测序结果。用PTHrP转染的MIN6细胞的胰岛素原与胰岛素比率也较低，表明PTHrP增强了ER中的胰岛素加工。我们的工作假设是，PTHrP增强胰岛素产生和ER效率，这与MIN6细胞中胰岛素含量增加、胰岛素原与胰岛素比率降低以及ER应激标志物减少的观察结果一致。总之，我们的研究结果表明PTHrP在β细胞内质网中具有以前未知的作用，这可能对增强胰岛素产生具有治疗意义。
