The role of Nocturnin in adipogenesis, obesity and metabolic disorders

近期有越來越多研究指出Nocturnin (Noc, Ccrn4l)可以調控脂肪代謝及脂肪細胞分化。本篇論文我們探討在早期脂肪細胞分化過程中，Noc所參與調控的角色。首先我們發現Noc是唯一在脂肪細胞分化過程中，會呈現雙週期表現情形的已知去腺嘧啶酶 (deadenylase)；而另四個Pan2, Parn, Ccr4, and Caf1去腺嘧啶酶則相對下降或沒變化。而利用Noc-silenced 3T3-L1前驅脂肪細胞及Noc基因剔除小鼠胚胎纖維母細胞primary mouse embryonic fibroblasts (MEFs)，顯示出早期瞬間表現的Noc會調控複製擴增（mitotic clonal expansion）過程及影響cyclin D1的表現。進一步我們利用Noc¬-depleted 3T3-L1 脂肪細胞微陣列分析（microarray），證實大部份差異表現的基因是跟細胞生長及增生有關。在脂肪細胞早期分化期間，Noc會與mRNA 去穩定因子 tristetraprolin (TTP) 作結合。經由篩選TTP的標的基因，我們發現在Noc- / -小鼠的脂肪組織中， Polo-like kinase3 （Plk3）mRNA的表現量明顯上升。而Noc的表現也可進一步抑制Plk3在3T3- L1前脂肪細胞的表現。 另外，在人類的脂肪組織中，NOC mRNA 與空腹胰島素(fasting insulin)及血中胰島素抗性指標（HOMA- IR）呈現負相關性，而與adiponectin mRNA及血中濃度呈正相關性; 同時，NOC mRNA 也與TTP mRNA呈正相關性．另外，PLK3 mRNA表現量與體重指數 (BMI) 不相關，但其位於皮下脂肪（SAT）的表現量顯著高於腹部脂肪 （VAT）。此外，無論是VAT或SAT 的PLK3 mRNA表現量都與adiponectin mRNA及adiponectin血清濃度呈強烈正相關，另外在校正過年齡、性別及BMI後，SAT PLK3 mRNA仍與空腹胰島素(fasting insulin)及血中胰島素抗性指標呈現負相關性．透過本篇論文的研究，我們對於Noc調控脂肪細胞分化的機制有更明確的闡述，也強化了Noc在胰島素於脂肪組織調控代謝功能的重要性。同時，我們的研究結果顯示PLK3與胰島素的敏感性有強烈的相關性。The deadenylase nocturnin (Noc, Ccrn4l) has been recently found to regulate lipid metabolism and to control preadipocyte differentiation. Here we showed that among the five deadenylases tested; only Noc exhibited a biphasic expression during adipocyte differentiation, while the expression levels of other deadenylases, including Pan2, Parn, Ccr4, and Caf1 were relatively unchanged or reduced during adipogenesis. The immediate early-expressed Noc during 3T3-L1 adipogenesis was involved in regulating mitotic clonal expansion and cyclin D1 expression, as demonstrated in Noc-silenced 3T3-L1 cells and Noc-/- primary mouse embryonic fibroblasts (MEFs). Transcriptional profiling of Noc¬-depleted 3T3-L1 adipocytes revealed that most of the differentially expressed genes were related to cell growth and proliferation. An mRNA destabilizer, tristetraprolin (TTP), was further identified as an interacting partner of Noc during early adipogenesis. Screening of TTP mRNA targets in adipose tissue of Noc-/- mice revealed that the Polo-like kinase 3 (Plk3) mRNA expression was significantly upregulated. Ectopic expression of Noc further decreases Plk3 expression in 3T3-L1 preadipocytes. In human adipose tissue, NOC mRNA level negatively associated with both fasting serum insulin and HOMA-IR, and positively associated with both adiponectin mRNA levels and circulating adiponectin levels. Moreover, NOC mRNA levels were also positively correlated with TTP mRNA levels in human adipose tissues. We further found that PLK3 mRNA levels were not associated with BMI, but were significant higher in subcutaneous adipose tissues (SAT) comparing to visceral adipose tissues (VAT). Furthermore, PLK3 mRNA levels in both VAT and SAT were strongly positively correlated with adiponectin gene expression as well as serum concentrations. The SAT PLK3 mRNA expressions were negatively correlated with fasting insulin levels and HOMA-IR even after adjustment of age, sex and BMI. Taken together, these results suggest the role of Noc in the modulation of early adipogenesis as well as systemic insulin sensitivity. Our findings also suggest that PLK3 is associated with systemic insulin sensitivity