【Abstract】
Rationale Protein acetylation is tightly linked to transcriptional control and energy metabolism. However, the role of protein acetylation in islet function remains enigmatic. This study aims to determine how protein acetylation controls β-cell function and explore the underlying mechanism.
Methods The gene-expression profiles were analyzed for rat islets in response to two histone deacetylase (HDAC) inhibitors. Insulin secretion, tryptophan hydroxylase 1 (Tph1) expression, and serotonin synthesis of rat islets were detected after HDAC inhibitor treatment both in vivo and ex vivo. β-cell-specific Tph1-overexpressing transgenic rats and β-cell-specific Tph1 knockout mice were constructed to evaluate the role of Tph1 in β-cell function. The deacetylation of PKA in β-cells by HDAC1 was investigated by adenoviral infection, immunoprecipitation, and western blot.
Results Inhibition of HDACs greatly potentiated pancreatic β-cell function and reprogrammed transcriptional landscape of islets. Among the commonly up-regulated genes by two pan-HDAC inhibitors, Tph1 displayed the most prominent change. Specifically, inhibition of HDAC1 and HDAC3 by MS-275 strongly promoted Tph1 expression and endogenous serotonin synthesis in rat islets, concomitantly with enhanced insulin secretory capacity in vivo and ex vivo. β-cell-specific Tph1-overexpressing transgenic rats exhibited improved glucose tolerance and amplified glucose-stimulated insulin secretion. On the contrary, β-cell-specific Tph1 knockout mice displayed glucose intolerance and impaired insulin secretion with aging. Moreover, depletion of Tph1 in β-cells abrogated MS-275-induced insulin hypersecretion. Overexpression of HDAC1, not HDAC3, inhibited Tph1 transcriptional activity and decreased MS-275-stimulated Tph1 expression. Mechanistically, HDAC1 deacetylated PKA catalytic subunit and decreased its activity, resulting in Tph1 transcriptional repression. The acetylation mimetic K62Q mutant of PKA increased its catalytic activity. HDAC1 inhibition exerted a synergistic effect with cAMP/PKA signal on Tph1 expression.
Conclusions The present findings highlight a novel role of HDAC1-PKA-Tph1 signaling in governing β-cell functional compensation by derepressing serotonin synthesis.
【中文摘要】
背景與目的：蛋白乙醯化與轉錄調控及能量代謝密切相關，但是蛋白乙醯化在胰島功能中的作用仍不清楚。本研究旨在闡明蛋白乙醯化如何調控β細胞功能並探討其內在機制。
方法：分析兩種組蛋白去乙醯化酶（HDAC）抑制劑處理的大鼠胰島基因表達譜。在離體和在體水平檢測HDAC抑制劑處理後大鼠胰島的胰島素分泌，色氨酸羥化酶1（Tph1）的表達和血清素合成的變化。構建β細胞特異性Tph1過表達大鼠或β細胞特異性Tph1敲除小鼠以評估Tph1在β細胞功能中的作用。通過腺病毒轉染、免疫共沉澱和Western印跡技術在β細胞中檢測HDAC1對PKA的去乙醯化作用。
結果：HDACs的抑制顯著增強了β細胞功能，並且重編程胰島的轉錄表達譜。在兩種廣譜HDAC抑制劑共同上調的基因中，Tph1的表達變化最為顯著。並且，HDAC1和HDAC3的抑制劑MS-275也顯著促進了大鼠胰島的Tph1表達和內源性血清素合成，同時增強在體和離體的胰島分泌能力。β細胞特異性Tph1過表達大鼠的糖耐量改善，葡萄糖刺激的胰島素分泌增加。與此相反，隨著年齡增大，β細胞特異性Tph1敲除小鼠出現糖耐量下降和胰島素分泌受損。而且，在β細胞敲除Tph1廢除了MS-275誘導的胰島素高分泌作用。過表達HDAC1抑制Tph1的轉錄活性並且降低了MS-275刺激的Tph1表達，而HDAC3無此作用。進一步的機制研究顯示，HDAC1使PKA催化亞基去乙醯化，降低其活性，進而導致Tph1的轉錄抑制，而PKA的K62Q乙醯化模擬突變增加其催化活性。HDAC1抑制和cAMP/PKA信號在Tph1表達調節上存在協同作用。
結論：本研究首次發現HDAC1-PKA-Tph1信號可通過去抑制血清素合成，在β細胞功能代償中發揮重要的調控作用。