Objective: To investigate the role and underlying mechanisms of methyltransferase (Mettl) 3 in the process of angiotensin Ⅱ (Ang Ⅱ)-induced pericyte-to-myofibroblast transdifferentiation and renal fibrosis. Methods: C57BL/6J mice were used, in cell experiments, mouse renal pericytes were isolated and cultured using magnetic bead sorting. These pericytes were then induced to transdifferentiate into myofibroblasts with 1×106 mmol/L Ang Ⅱ, which was the Ang Ⅱ group, while pericytes cultured in normal conditions served as the control group. Successful transdifferentiation was verified by immunofluorescence staining, Western blotting, and real-time reverse transcription PCR (RT-qPCR) for α-smooth muscle actin (α-SMA). The levels of m6A modifications and related enzymes (Mettl3, Mettl14), Wilms tumor 1-associated protein (WTAP), fat mass and obesity protein (FTO), ALKBH5, YTHDF1, YTHDF2, YTHDC1, YTHDC2, YTHDC3 were assessed by Dot blot, RT-qPCR and Western blot. Mettl3 expression was inhibited in cells using lentivirus-mediated Mettl3-shRNA transfection, creating sh-Mettl3 and Ang Ⅱ+sh-Mettl3 groups, while lentivirus empty vector transfection served as the negative control (Ang Ⅱ+sh-NC group). The impact of Ang Ⅱ on pericyte transdifferentiation was observed, and the expression of downstream phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway proteins, including PI3K, AKT, phosphorylated AKT at serine 473 (p-AKT (S473)), and phosphorylated AKT at threonine 308 (p-AKT (T308)), were examined. PI3K gene transcription was inhibited by co-culturing cells with actinomycin D, and the half-life of PI3K mRNA was calculated by measuring residual PI3K mRNA expression over different co-culture time. The reversibility of Mettl3 inhibition on Ang Ⅱ-induced pericyte-to-myofibroblast transdifferentiation was assessed by adding the AKT activator SC79 to the Ang Ⅱ+sh-Mettl3 group. In animal experiments, mice were divided into these groups: sham group (administered 0.9% sterile saline), Ang Ⅱ group (infused with Ang Ⅱ solution), sh-Mettl3 group (injected with Mettl3 shRNA lentivirus solution), Ang Ⅱ+sh-Mettl3 group (infused with Ang Ⅱ solution and injected with Mettl3 shRNA lentivirus solution), and Ang Ⅱ+sh-Mettl3+SC79 group (administered Ang Ⅱ solution and Mettl3 shRNA lentivirus, with an additional injection of SC79). Each group consisted of six subject mice. Blood pressure was measured using the tail-cuff method before and after surgery, and serum creatinine, urea, and urinary albumin levels were determined 4 weeks post-surgery. Kidney tissues were collected at 28 days and stained using hematoxylin-eosin (HE) and Masson's trichrome to assess the extent of renal fibrosis. Results: Primary renal pericytes were successfully obtained by magnetic bead sorting, and intervened with 1×106 mmol/L Ang Ⅱ for 48 hours to induce pericyte-to-myofibroblast transdifferentiation. Dot blot results indicated higher m6A modification levels in the Ang Ⅱ group compared to the control group (P<0.05). RT-qPCR and Western blot results showed upregulation of Mettl3 mRNA and protein levels in the Ang Ⅱ group compared to the control group (both P<0.05). In the Ang Ⅱ+sh-Mettl3 group, Mettl3 protein expression was lower than that in the Ang Ⅱ group, with reduced expression levels of α-SMA, vimentin, desmin, fibroblast agonist protein (FAPa) and type Ⅰ collagen (all P<0.05). Compared to the control group, PI3K mRNA expression level was elevated in the Ang Ⅱ group, along with increased p-AKT (S473) and p-AKT (T308) expressions. In the Ang Ⅱ+sh-Mettl3 group, PI3K mRNA expression and p-AKT (S473) and p-AKT (T308) levels were decreased (all P<0.05). The half-life of PI3K mRNA was shorter in the Ang Ⅱ+sh-Mettl3 group than that in the Ang Ⅱ+sh-NC group (2.34 h vs. 3.42 h). The ameliorative effect of Mettl3 inhibition on Ang Ⅱ-induced pericyte-to-myofibroblast transdifferentiation was reversible by SC79. Animal experiments showed higher blood pressure, serum creatinine, urea, and 24-hour urinary protein levels, and a larger fibrosis area in the Ang Ⅱ group compared to the sham group (all P<0.05). The fibrosis area was smaller in the Ang Ⅱ+sh-Mettl3 group than that in the Ang Ⅱ group (P<0.05), but increased again upon addition of SC79. Conclusion: Mettl3-mediated RNA m6A epigenetic regulation is involved in Ang Ⅱ-induced pericyte-to-myofibroblast transdifferentiation and renal fibrosis, potentially by affecting PI3K stability and regulating the PI3K/AKT signaling pathway.
目的： 探讨甲基转移酶3（Mettl3）在血管紧张素Ⅱ（Ang Ⅱ）诱导周细胞向肌成纤维细胞转分化及肾脏纤维化过程中的作用及相关机制。 方法： 使用C57BL/6J小鼠，（1）细胞实验中，采用磁珠分选法培养纯化小鼠肾脏周细胞，并予以1×106 mmol/L的Ang Ⅱ诱导周细胞-肌成纤维细胞转分化，为Ang Ⅱ组；正常培养的周细胞为对照组。采用免疫荧光染色、蛋白质印迹（Western blot）及实时反转录PCR（RT-qPCR）检测α平滑肌肌动蛋白（α-SMA）以验证转分化成功。采用斑点印迹、RT-qPCR、Western blot检测N6-甲基腺苷（m6A）修饰水平及相关酶［Mettl3、Mettl14、Wilms肿瘤蛋白1相关蛋白（WTAP）、肥胖相关蛋白（FTO）、ALKB同源蛋白5（ALKBH5）、YTH结构域家族蛋白（YTHDF）1、YTHDF2、YTHDC1、YTHDC2、YTHDC3］的表达水平。采用慢病毒转染Mettl3 shRNA的方法抑制细胞中的Mettl3表达，为sh-Mettl3组、Ang Ⅱ+sh-Mettl3组；以转染慢病毒空载体作为阴性对照，为Ang Ⅱ+sh-NC组，观察Ang Ⅱ对周细胞转分化的影响，并检测下游磷脂酰肌醇3激酶（PI3K）/蛋白激酶B（AKT）信号通路蛋白的表达，包括PI3K、AKT（丝氨酸磷酸化位点473）［p-AKT（S473）］、AKT（苏氨酸磷酸化位点308）［p-AKT（T308）］等。加入放线菌素D与各组周细胞共培养以抑制PI3K基因的转录，通过检测不同共培养时间残余PI3K mRNA表达量以计算PI3K mRNA半衰期。在Ang Ⅱ+sh-Mettl3组周细胞中加入AKT激动剂SC79，观察是否可逆转Mettl3抑制对Ang Ⅱ诱导周细胞-肌成纤维细胞转分化的作用。（2）动物实验中，分为假手术组（仅给予0.9%无菌生理盐水）、Ang Ⅱ组（泵入Ang Ⅱ溶液）、sh-Mettl3组（注射Mettl3 shRNA慢病毒溶液）、Ang Ⅱ+sh-Mettl3组（泵入Ang Ⅱ溶液+注射Mettl3 shRNA慢病毒溶液）、Ang Ⅱ+sh-Mettl3+SC79组（Ang Ⅱ+sh-Mettl3组处理基础上注射SC79），每组6只。手术前后采用尾夹法测定血压，术后4周测定血清肌酐、尿素含量及尿液白蛋白含量。28 d后取肾脏组织，采用苏木精-伊红（HE）及Masson三色法对组织切片进行染色，检测肾脏纤维化程度。 结果： （1）磁珠分选法可获得原代肾脏周细胞，以1×106 mmol/L的Ang Ⅱ处理周细胞48 h可成功诱导其向肌成纤维细胞转分化。斑点印迹结果显示，Ang Ⅱ组总RNA的m6A修饰水平高于对照组（P<0.05），RT-qPCR及Western blot结果显示，与对照组相比，Ang Ⅱ组中Mettl3 mRNA及蛋白表达水平上调（P均<0.05）。Ang Ⅱ+sh-Mettl3组细胞中的Mettl3蛋白表达水平低于Ang Ⅱ组，α-SMA、波形蛋白、肌间线蛋白、成纤维细胞激活蛋白a（FAPa）以及Ⅰ型胶原蛋白的表达水平亦低于Ang Ⅱ组（P均<0.05）。与对照组相比，Ang Ⅱ组的PI3K mRNA表达水平上调，且p-AKT（S473）和p-AKT（T308）蛋白高表达；Ang Ⅱ+sh-Mettl3组的PI3K mRNA表达水平低于Ang Ⅱ组，p-AKT（S473）和p-AKT（T308）蛋白表达下调（P均<0.05）。Ang Ⅱ+sh-Mettl3组的半衰期短于Ang Ⅱ+sh-NC组（2.34 h比3.42 h）。而Mettl3抑制对Ang Ⅱ诱导周细胞-肌成纤维细胞转分化的改善作用可被SC79逆转。（2）动物实验结果显示，与假手术组比较，Ang Ⅱ组小鼠的血压更高，血清肌酐、尿素及24 h尿蛋白测量值更高，纤维化面积更大（P均<0.05）；而Ang Ⅱ+sh-Mettle3组的纤维化面积小于Ang Ⅱ组（P<0.05），但在加入SC79后肾脏纤维化又加重。 结论： Mettl3介导的RNA m6A表观遗传调控参与Ang Ⅱ诱导的肾脏周细胞-肌成纤维细胞转分化及肾脏纤维化，Mettl3可能通过影响PI3K的稳定性，进而影响PI3K/AKT信号通路发挥调控作用。.