All types of facioscapulohumeral muscular dystrophy (FSHD) are caused by the aberrant activation of the somatically silent DUX4 gene, the expression of which initiates a cascade of cellular events ultimately leading to FSHD pathophysiology. Typically, progressive skeletal muscle weakness becomes noticeable in the second or third decade of life, yet there are many individuals who are genetically FSHD but develop symptoms much later in life or remain relatively asymptomatic throughout their lives. Conversely, FSHD may clinically present prior to 5–10 years of age, ultimately manifesting as a severe early-onset form of the disease. These phenotypic differences are thought to be due to the timing and levels of DUX4 misexpression. FSHD is a dominant gain-of-function disease that is amenable to modeling by DUX4 overexpression. We have recently created a line of conditional DUX4 transgenic mice, FLExDUX4, that develop a myopathy upon induction of human DUX4-fl expression in skeletal muscle. Here, we use the FLExDUX4 mouse crossed with the skeletal muscle-specific and tamoxifen-inducible line ACTA1-MerCreMer to generate a highly versatile bi-transgenic mouse model with chronic, low-level DUX4-fl expression and cumulative mild FSHD-like pathology that can be reproducibly induced to develop more severe pathology via tamoxifen induction of DUX4-fl in skeletal muscles. We identified conditions to generate FSHD-like models exhibiting reproducibly mild, moderate, or severe DUX4-dependent pathophysiology and characterized progression of pathology. We assayed DUX4-fl mRNA and protein levels, fitness, strength, global gene expression, and histopathology, all of which are consistent with an FSHD-like myopathic phenotype. Importantly, we identified sex-specific and muscle-specific differences that should be considered when using these models for preclinical studies. The ACTA1-MCM;FLExDUX4 bi-transgenic mouse model has mild FSHD-like pathology and detectable muscle weakness. The onset and progression of more severe DUX4-dependent pathologies can be controlled via tamoxifen injection to increase the levels of mosaic DUX4-fl expression, providing consistent and readily screenable phenotypes for assessing therapies targeting DUX4-fl mRNA and/or protein and are useful to investigate certain conserved downstream FSHD-like pathophysiology. Overall, this model supports that DUX4 expression levels in skeletal muscle directly correlate with FSHD-like pathology by numerous metrics.

中文翻译：

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表达可调节水平的 DUX4 的转基因小鼠会出现特征性面肩肱型肌营养不良症样病理生理学，其严重程度不等。


所有类型的面肩肱型肌营养不良症 (FSHD) 都是由体细胞沉默 DUX4 基因的异常激活引起的，该基因的表达引发一系列细胞事件，最终导致 FSHD 病理生理学。通常情况下，进行性骨骼肌无力在生命的第二个或第三个十年中变得明显，但有许多人患有遗传性 FSHD，但在生命后期才出现症状或在一生中保持相对无症状。相反，FSHD 可能在 5-10 岁之前出现临床症状，最终表现为该疾病的严重早发形式。这些表型差异被认为是由于 DUX4 错误表达的时间和水平造成的。 FSHD 是一种主要的功能获得性疾病，可以通过 DUX4 过表达进行建模。我们最近创建了一系列条件性 DUX4 转基因小鼠 FLExDUX4，它们在骨骼肌中诱导人 DUX4-fl 表达后出现肌病。在这里，我们使用 FLExDUX4 小鼠与骨骼肌特异性和他莫昔芬诱导品系 ACTA1-MerCreMer 杂交来生成高度通用的双转基因小鼠模型，该模型具有慢性、低水平的 DUX4-fl 表达和累积的轻度 FSHD 样病理学，通过他莫昔芬诱导骨骼肌中的 DUX4-fl，可重复诱导产生更严重的病理学。我们确定了生成 FSHD 样模型的条件，这些模型表现出可重复的轻度、中度或重度 DUX4 依赖性病理生理学，并表征了病理学进展。我们检测了 DUX4-fl mRNA 和蛋白质水平、健康度、力量、整体基因表达和组织病理学，所有这些都与 FSHD 样肌病表型一致。 重要的是，我们确定了使用这些模型进行临床前研究时应考虑的性别特异性和肌肉特异性差异。 ACTA1-MCM;FLExDUX4 双转基因小鼠模型具有轻度 FSHD 样病理学和可检测到的肌肉无力。更严重的 DUX4 依赖性病理的发作和进展可以通过注射他莫昔芬来控制，以增加嵌合 DUX4-fl 表达水平，为评估针对 DUX4-fl mRNA 和/或蛋白质的治疗提供一致且易于筛选的表型，并有助于研究某些保守的下游 FSHD 样病理生理学。总体而言，该模型通过多种指标支持骨骼肌中 DUX4 表达水平与 FSHD 样病理直接相关。