Muscle-specific E3 ubiquitin ligases have been identified in muscle atrophy-inducing conditions. The purpose of the current study was to explore the functional role of Fbxl22, and a newly identified splice variant (Fbxl22-193), in skeletal muscle homeostasis and neurogenic muscle atrophy. In mouse C₂C₁₂ muscle cells, promoter fragments of the Fbxl22 gene were cloned and fused with the secreted alkaline phosphatase reporter gene to assess the transcriptional regulation of Fbxl22. The tibialis anterior muscles of male C57/BL6 mice (12-16 weeks old) were electroporated with expression plasmids containing the cDNA of two Fbxl22 splice variants and tissues collected after 7, 14 and 28 days. Gastrocnemius muscles of wild type and MuRF1 knockout mice were electroporated with an Fbxl22 RNAi or empty plasmid, denervated three days post-transfection, and tissues collected 7 days post-denervation. The full-length gene and novel splice variant are transcriptionally induced early (after 3 days) during neurogenic muscle atrophy. In vivo overexpression of Fbxl22 isoforms in mouse skeletal muscle lead to evidence of myopathy/atrophy suggesting that both are involved in the process of neurogenic muscle atrophy. Knockdown of Fbxl22 in MuRF1 KO muscles resulted in significant additive muscle sparing at 7 days of denervation. Targeting two E3 ubiquitin ligases appears to have a strong additive effect on protecting muscle mass loss with denervation and these findings have important implications in the development of therapeutic strategies to treat muscle atrophy.

中文翻译：

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新型骨骼肌萎缩促进E3泛素连接酶Fbxl22的鉴定和表征。

已经在诱导肌肉萎缩的条件下鉴定了肌肉特异性E3泛素连接酶。本研究的目的是探讨Fbxl22和新近鉴定的剪接变体（Fbxl22-193）在骨骼肌稳态和神经源性肌肉萎缩中的功能作用。在鼠标C ₂ C _12中克隆肌细胞，克隆Fbxl22基因的启动子片段，并与分泌的碱性磷酸酶报道基因融合，以评估Fbxl22的转录调控。用含有两个Fbxl22剪接变体的cDNA的表达质粒电穿孔雄性C57 / BL6小鼠（12-16周龄）的胫骨前肌，并在7、14和28天后收集组织。用Fbxl22 RNAi或空质粒对野生型和MuRF1基因敲除小鼠的腓肠肌进行电穿孔，转染后三天去除神经支配，去神经后7天收集组织。全长基因和新型剪接变体在神经源性肌肉萎缩过程的早期（3天后）转录诱导。小鼠骨骼肌中Fbxl22亚型的体内过表达导致肌病/萎缩的迹象，表明两者均参与了神经源性肌肉萎缩的过程。剔除MubRF1 KO肌肉中的Fbxl22会在去神经7天时产生明显的累加肌肉保留。靶向两个E3泛素连接酶似乎在保护神经失活和失重方面具有很强的累加作用，这些发现对治疗肌肉萎缩的治疗策略具有重要意义。