背景:肌肉萎缩,纤维化和脂肪浸润(FI)常见于肩袖撕裂(RCT),这些是直接决定这种损伤患者临床结局的关键因素。因此,改善RCT术后肌肉质量对改善肌腱修复的临床效果至关重要。近年来,已经发现成人具有功能性米色/棕色脂肪组织(BAT),其可以分泌促肌生长。PRDM16,一种含PR结构域的蛋白质,被发现具有确定棕色脂肪细胞命运并刺激其发育的能力。因此,这项研究的目的是使用PRDM16表达水平升高的转基因小鼠模型,发现PRDM16在改善大量肌腱撕裂后的肌肉功能中的作用。
方法:转基因aP2驱动的PRDM16过表达小鼠和C57BL/6J小鼠进行如前所述的单侧冈上肌(SS)肌腱横断和肩胛上神经横断(TTDN)(每组N=8)。在TTDN损伤后6周进行DigiGait以评估前肢功能。双侧SS肌,肩胛骨间棕色脂肪,附睾白色脂肪,采集腹股沟米色脂肪进行分析。WesternBlot检测脂肪组织中PRDM16的表达。进行Masson毛状体染色以评估肌肉纤维化,并使用油红O染色来确定脂肪浸润。通过免疫染色通过MHC表达确定肌纤维类型。所有数据以平均值±SD的形式呈现。进行T检验和双向ANOVA分析以确定组间的统计学显著差异。当P<0.05时考虑显著性。
结果:蛋白质印迹数据显示,与野生型(WT)小鼠相比,PRDM16过表达小鼠的白色和棕色脂肪中PRDM16蛋白的表达增加。尽管PRDM16过表达对增加肌肉重量没有影响,它通过更长的刹车显著改善了前肢功能,立场和跨步时间,RCT后小鼠步幅和爪面积较大。此外,与WT小鼠相比,PRDM16过表达小鼠的纤维化量没有差异,然而,它们的脂肪浸润面积显著减少。TTDN后,这些小鼠在冈上肌中也表现出丰富的MHC-IIx纤维百分比。
结论:过表达PRDM16可显著改善肩袖撕裂后的肌肉功能和减少脂肪浸润。促进BAT活性有利于改善RCT术后肩袖肌肉质量和肩关节功能。
BACKGROUND: Muscle atrophy, fibrosis and fatty infiltration (FI) are commonly seen in rotator cuff tears (RCT), which are critical factors that directly determine the clinical outcomes for patients with this injury. Therefore, improving muscle quality after RCT is crucial in improving the clinical outcome of tendon repair. In recent years, it has been discovered that adults have functional beige/brown adipose tissue (BAT) which can secrete batokines to promote muscle growth. PRDM16, a PR-domain containing protein, was discovered with the ability to determine the brown fat cell fate and stimulate its development. Thus, the goal of this study is to discover the role of PRDM16 in improving muscle function after massive tendon tears using a transgenic mouse model with an elevated level of PRDM16 expression.
METHODS: Transgenic aP2 driven PRDM16 overexpression mice and C57BL/6J mice underwent unilateral supraspinatus (SS) tendon transection and suprascapular nerve transection (TTDN) as described previously (N=8 in each group). DigiGait was performed to evaluate forelimb function at 6 weeks post the TTDN injury. Bilateral SS muscles, interscapular brown fat, epididymal white fat, and inguinal beige fat were harvested for analysis. The expression of PRDM16 in adipose tissue was detected by Western Blot. Masson\'s trichome staining was conducted to evaluate the muscle fibrosis and Oil Red O staining was used to determine the fat infiltration. Muscle fiber type was determined by MHC expression via immunostaining. All data was presented in the form of mean±SD. T-test and two-way ANOVA analysis was performed to determine a statistically significant difference between groups. Significance was considered when P<0.05.
RESULTS: Western blot data showed an increased expression of PRDM16 protein in both white and brown fat in PRDM16-overexpression mice compared to wild-type (WT) mice. Even though PRDM16 overexpression had no effect on increasing muscle weight, it significantly improved the forelimbs function with longer brake, stance and stride time, larger stride length and paw area in mice after RCT. Additionally, PRDM16 overexpression mice showed no difference in amount of fibrosis when compared to WT mice, however, they had significantly reduced area of fatty infiltration. These mice also exhibited abundant MHC-IIx fiber percentage in supraspinatus muscle after TTDN.
CONCLUSIONS: Overexpression of PRDM16 significantly improved muscle function and reduced fatty infiltration after rotator cuff tears. Promoting BAT activity is beneficial in improving rotator cuff muscle quality and shoulder function after RCT.