Post-mitotic, non-proliferative dermal fibroblasts have crucial functions in maintenance and restoration of tissue homeostasis. They are involved in essential processes such as wound healing, pigmentation and hair growth, but also tumor development and aging-associated diseases. These processes are energetically highly demanding and error prone when mitochondrial damage occurs. However, mitochondrial function in fibroblasts and the influence of mitochondrial dysfunction on fibroblast-specific demands are still unclear. To address these questions, we created a mouse model in which accelerated cell-specific mitochondrial DNA (mtDNA) damage accumulates. We crossed mice carrying a dominant-negative mutant of the mitochondrial replicative helicase Twinkle (RosaSTOP system) with mice that express fibroblast-specific Cre Recombinase (Collagen1A2 Cre) which can be activated by Tamoxifen (Twinkle). Thus, we are able to induce mtDNA deletions and duplications in specific cells, a process which resembles the physiological aging process in humans, where this damage accumulates in all tissues. Upon proliferation , Tamoxifen induced Twinkle fibroblasts deplete most of their mitochondrial DNA which, although not disturbing the stoichiometry of the respiratory chain complexes, leads to reduced ROS production and mitochondrial membrane potential as well as an anti-inflammatory and anti-fibrotic profile of the cells. In Sodium Azide treated wildtype fibroblasts, without a functioning respiratory chain, we observe the opposite, a rather pro-inflammatory and pro-fibrotic signature. Upon accumulation of mitochondrial DNA mutations the Twinkle mice are protected from fibrosis development induced by intradermal Bleomycin injections. This is due to dampened differentiation of the dermal fibroblasts into α−smooth-muscle-actin positive myofibroblasts in Twinkle mice. We thus provide evidence for striking differences of the impact that mtDNA mutations have in contrast to blunted mitochondrial function in dermal fibroblasts and skin homeostasis. These data contribute to improved understanding of mitochondrial function and dysfunction in skin and provide mechanistic insight into potential targets to treat skin fibrosis in the future.

中文翻译：

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线粒体 DNA 突变通过抑制分化为肌成纤维细胞来减轻博莱霉素诱导的真皮纤维化


有丝分裂后、非增殖性真皮成纤维细胞在维持和恢复组织稳态方面具有重要功能。它们参与伤口愈合、色素沉着和毛发生长等重要过程，还参与肿瘤发展和衰老相关疾病。这些过程对能量的要求很高，并且当线粒体损伤发生时容易出错。然而，成纤维细胞中的线粒体功能以及线粒体功能障碍对成纤维细胞特异性需求的影响仍不清楚。为了解决这些问题，我们创建了一个小鼠模型，其中细胞特异性线粒体 DNA (mtDNA) 损伤加速累积。我们将携带线粒体复制解旋酶 Twinkle（RosaSTOP 系统）显性失活突变体的小鼠与表达成纤维细胞特异性 Cre 重组酶（Collagen1A2 Cre）的小鼠进行杂交，后者可被他莫昔芬（Twinkle）激活。因此，我们能够在特定细胞中诱导 mtDNA 缺失和复制，这一过程类似于人类的生理衰老过程，这种损伤会在所有组织中累积。增殖后，Tamoxifen 诱导 Twinkle 成纤维细胞耗尽大部分线粒体 DNA，虽然不会干扰呼吸链复合物的化学计量，但会导致 ROS 产生和线粒体膜电位减少以及细胞的抗炎和抗纤维化特征。在叠氮化钠处理的野生型成纤维细胞中，没有功能性呼吸链，我们观察到相反的情况，即相当促炎症和促纤维化的特征。在线粒体 DNA 突变积累后，Twinkle 小鼠可免受皮内注射博莱霉素诱导的纤维化发展。 这是由于 Twinkle 小鼠中真皮成纤维细胞向 α-平滑肌肌动蛋白阳性肌成纤维细胞的分化受到抑制。因此，我们提供了证据，证明线粒体 DNA 突变与真皮成纤维细胞和皮肤稳态中线粒体功能减弱的影响存在显着差异。这些数据有助于提高对皮肤线粒体功能和功能障碍的了解，并为未来治疗皮肤纤维化的潜在目标提供机制见解。