Role of pro-oxidative connective tissue in skin aging – Molecular mechanisms and therapeutic strategies

为了了解成纤维细胞在器官衰老和组织衰退中的作用，我们将分析早期生成的结缔组织特异性小鼠模型，该模型描述了增强的衰老，并将其与本质衰老的对照小鼠进行比较。先前建立的结缔组织特异性缺失锰超氧化物歧化酶（SOD2）的小鼠衰老模型显示，p16INK4A（一种促进不可逆成纤维细胞衰老的细胞周期抑制剂）上调，胰岛素样生长因子1 (IGF-1)（一种重要的生长和组织维持因子）显著下降。IGF-1的抑制释放是衰老成纤维细胞衰老相关分泌表型（SASP）的一个关键标志。这种老化程序的安装强制严重的结缔组织老化和整体皮肤老化。我们实验室的间接证据表明，氧化还原依赖的转录因子同时诱导p16INK4A，同时抑制IGF-1。在这里，我们将遵循两个相互关联的主要目标：1 .确定氧化还原敏感转录因子JunB/AP1在皮肤衰老中的作用，揭示其在组织衰退中的作用模式；评估衰老成纤维细胞清除能力降低的先天免疫系统细胞是否对老年小鼠皮肤中衰老成纤维细胞的进一步积累负责。这两个研究重点是密切相关的，都有助于更好地理解衰老细胞在富含结缔组织的器官中的积累。使用结缔组织特异性双Sod2/JunB缺陷小鼠，我们将解剖氧化还原依赖性JunB是否负责皮肤老化，以及这是否依赖于抑制IGF-1的选择性翻译。通过基因操纵缺乏自然杀伤细胞（NK细胞）或巨噬细胞的小鼠模型，我们将探索衰老细胞是否在皮肤等富含结缔组织的器官中积累。此外，我们将采用诸如过继性转移年轻NK细胞/巨噬细胞（骨髓）和天然IgM等策略来更有效地去除衰老细胞，并将研究SASP重编程是否可能减轻甚至恢复延迟的衰老和皮肤稳态，包括干细胞更新和增强再生能力。该项目将有助于确定成纤维细胞衰老在皮肤衰老和其他结缔组织丰富的器官（如骨骼和肌肉）中的核心作用。预期的结果将为器官和组织老化/组织衰退的适当干预措施的发展带来前所未有的希望。

To understand the role of fibroblasts in organ aging and tissue decline, we will analyze our earlier generated connective tissue specific murine model depicting enhanced aging and compare it to intrinsically aged control mice. The previously established murine aging model with a connective tissue specific deletion of the manganese superoxide dismutase (SOD2) revealed concomitant up-regulation of p16INK4A, a cell cycle inhibitor promoting irreversible fibroblasts senescence, and a profound decline of Insulin-like Growth Factor 1 (IGF-1), an important growth and tissue maintenance factor. Suppressed release of IGF-1 constitutes a key hallmark of the senescence-associated secretory phenotype (SASP) of senescent fibroblasts. The installment of such an aging program enforces severe connective tissue aging and overall skin aging. Indirect evidence of our laboratory suggests that a redox-dependent transcription factor concomitantly induces p16INK4A, while suppressing IGF-1. We here will follow two main interconnected objectives: 1. to establish the role of the redox sensitive transcription factor JunB/AP1 in skin aging and to unravel its mode of action in tissue decline, and 2. to assess whether cells of the innate immune system with reduced removal capacity of senescent fibroblasts are responsible for further accumulation of senescent fibroblasts in the skin of aged mice. These two research foci are intimately interrelated, and both contribute to a better understanding of enhanced accumulation of senescent cells in connective tissue rich organs. Using connective tissue specific double Sod2/JunB deficient mice, we will dissect whether redox-dependent JunB is responsible for skin aging and whether this depends on selective translation with suppression of IGF-1. By means of genetically manipulated murine models which lack natural killer cells (NK cells) or macrophages, we will explore whether senescent cells accumulate in connective tissue rich organ like skin. In addition, we will employ strategies, like adoptive transfer of young NK cells/macrophages (bone marrow) and natural IgM to more efficiently remove senescent cells and will study the likely possibility that reprogramming of the SASP will attenuate or even restore delayed aging and skin homoeostasis including stem cell renewal and enhanced regenerative capacity. This project will help to define the central role of fibroblast senescence on skin aging, and on other connective tissue rich organs, such as bone and muscle. The expected results will hold unprecedented promise for the development of appropriate interventions for organ and organismal aging/tissue decline.