背景：

真皮脂肪组织是一种位于皮肤真皮下层的特殊脂肪组织，它与传统的皮下脂肪层有所不同，在维持皮肤稳态、创伤修复和抗衰老过程中起着重要作用。已有研究发现，衰老导致真皮脂肪组织功能障碍，包括脂质代谢异常、细胞衰老。但真皮脂肪功能障碍是否加速皮肤老化并促进纤维化发生尚不明确。同时，导致真皮脂肪功能障碍的上游分子机制尚研究不明。

目的：

本研究旨在系统探讨衰老过程中真皮脂肪组织的功能变化，重点研究PPAR-γ在脂肪细胞成脂、线粒体质量控制、自噬及线粒体自噬中的调控作用，并评估脂肪及其衍生物移植对真皮脂肪功能障碍的干预效果，以探索改善皮肤衰老的潜在策略。

方法：

本研究综合采用体内和体外实验，采用了自然衰老小鼠模型、真皮脂肪功能障碍小鼠模型（PPAR-γ抑制剂GW9662）、双氧水诱导的脂肪前体细胞衰老模型、PPAR-γ过表达和敲低的细胞模型，通过组织学分析（HE染色、Masson染色、免疫组织化学染色）、分子生物学检测（Western blot、qPCR）和细胞功能实验（细胞迁移、成脂分化）等方法，评估真皮脂肪组织的结构变化、成脂功能、纤维化程度及衰老相关蛋白的表达水平。此外，利用Seahorse检测线粒体氧耗率（OCR）、Mitotracker染色和Western blot分析线粒体相关蛋白表达，以评估线粒体功能及其自噬水平。同时，在自然衰老小鼠模型中，进行自体脂肪及其衍生物移植（皮下脂肪、皮内纳米脂肪、皮内脂肪干细胞、皮下脂肪联合皮内脂肪干细胞），评估不同移植方式对真皮脂肪组织功能的改善效果。

结果：

1. 衰老导致真皮脂肪层厚度显著减少，脂肪生成能力降低，并抑制脂肪前体细胞对成纤维细胞的旁分泌作用。

2. PPAR-γ在衰老过程中表达下调，其降低可损害脂肪前体细胞的成脂能力，促进细胞外基质重塑，并加速皮肤纤维化和衰老。

3. 衰老小鼠真皮脂肪组织中自噬和线粒体自噬水平下降，而在体外衰老细胞模型中，自噬和线粒体自噬被激活，提示衰老过程中线粒体质量控制失衡。

4. PPAR-γ表达降低导致脂肪前体细胞线粒体网络破碎化、呼吸功能下降，并引起自噬和PINK-1/PARKIN介导的线粒体自噬障碍，进一步加剧细胞衰老状态。

5. 在自然衰老小鼠中，脂肪及其衍生物移植可通过恢复PPAR-γ的表达，提高脂肪细胞的成脂能力，减少细胞外基质纤维化，同时恢复自噬和线粒体自噬水平。其中，皮下脂肪联合皮内脂肪干细胞移植对改善真皮脂肪层厚度、恢复成脂能力、降低细胞外基质沉积以及促进自噬功能恢复方面效果最好，提示其可能是优化真皮脂肪功能的有效干预方式。

结论：

本研究系统探讨了衰老过程中真皮脂肪组织的功能变化，揭示了PPAR-γ在脂肪前体细胞成脂能力、自噬及线粒体质量控制中的关键作用。PPAR-γ表达降低导致脂肪生成能力下降、细胞外基质过度沉积、线粒体功能障碍及线粒体自噬失衡，从而加剧真皮脂肪功能障碍和皮肤老化、纤维化。此外，本研究证实脂肪及其衍生物移植可通过恢复PPAR-γ的表达，从而恢复脂肪组织功能，改善真皮脂肪纤维化，并提高自噬和线粒体自噬水平，为抗皮肤衰老提供了一种潜在的治疗策略。

Background:
Dermal adipose tissue is a special adipose tissue located in the subcutaneous layer of skin, which is different from the traditional subcutaneous adipose layer and plays an important role in maintaining skin homeostasis, wound repair and anti-aging process. It has been found that aging leads to dysfunction of dermal adipose tissue, including abnormal lipid metabolism and cell aging. However, it remains unclear whether dermal adipose dysfunction accelerates skin aging and promotes fibrosis. In addition, the upstream molecular mechanisms responsible for dermal adipose dysfunction have yet to be fully elucidated.

Objectives:

This study aims to systematically investigate the functional changes in dermal adipose tissue during aging, focusing on the regulatory role of PPAR-γ in adipocyte adipogenic capacity, mitochondrial quality control, autophagy, and mitophagy. Furthermore, we evaluated the therapeutic effects of adipose tissue and its derivatives on dermal adipose dysfunction to explore potential strategies for mitigating skin aging.

Methods:
This study integrated both in vivo and in vitro experiments. We utilized a naturally aged mouse model, a dermal adipose dysfunction mouse model (induced by the PPAR-γ inhibitor GW9662), an H2O2-induced adipocyte precursor cell senescence model, and PPAR-γ overexpression and knockdown cell models. Histological analysis (HE staining, Masson staining, and immunohistochemistry), molecular biology techniques (Western blot, qPCR), and cellular functional assays (cell migration and adipogenic differentiation) were performed to evaluate structural changes in dermal adipose tissue, adipogenic capacity, fibrosis progression, and the expression of senescence-associated proteins. Additionally, mitochondrial function and autophagy levels were assessed using Seahorse-based oxygen consumption rate (OCR) measurements, Mitotracker staining, and Western blot analysis of mitochondrial-related proteins. In the naturally aged mouse model, we performed autologous adipose and derivative transplantation, including subcutaneous fat (SD), intradermal nanofat (D-nanofat), intradermal adipose-derived stem cells (D-ADSC), and a combination of subcutaneous fat and intradermal adipose-derived stem cells (SD+D), to evaluate the efficacy of different transplantation methods in improving dermal adipose tissue function.

Results:

Aging significantly reduced dermal adipose layer thickness, impaired adipogenesis, and suppressed the paracrine effects of adipocyte precursor cells on fibroblasts.

2. PPAR-γ expression was downregulated during aging, which disrupted adipogenesis, promoted ECM remodeling, and accelerated skin fibrosis and aging.

3. Autophagy and mitophagy levels decreased in the dermal adipose tissue of aged mice, while they were activated in in vitro senescent adipocyte models, suggesting mitochondrial quality control imbalance during aging.

4. PPAR-γ downregulation led to mitochondrial fragmentation, reduced respiratory function, and impaired autophagy and PINK1/PARKIN-mediated mitophagy, further exacerbating cellular senescence.

5. In naturally aged mouse models, transplantation of adipose tissue and its derivatives improved adipogenesis, reduced ECM fibrosis, and restored autophagy and mitophagy by activating the PPAR-γ signaling pathway. Among the transplantation strategies, the combination of subcutaneous fat and intradermal adipose-derived stem cells (SD+D) showed the most significant improvement in dermal adipose layer thickness, adipogenic capacity, ECM reduction, and autophagy restoration, suggesting it as a promising intervention for optimizing dermal adipose function.

Conclusion:
This study systematically investigated the functional changes in dermal adipose tissue during aging and elucidated the critical role of PPAR-γ in regulating adipogenic capacity, autophagy, and mitochondrial quality control in adipocytes. The downregulation of PPAR-γ expression during aging resulted in impaired adipogenesis, excessive ECM deposition, mitochondrial dysfunction, and mitophagy imbalance, exacerbating dermal adipose dysfunction and skin aging. Moreover, we demonstrated that adipose tissue and its derivative transplantation could restore dermal adipose function, alleviate fibrosis, and enhance autophagy and mitophagy by activating the PPAR-γ signaling pathway. These findings provide a potential therapeutic strategy for combating skin aging, and future studies should further explore the molecular mechanisms underlying PPAR-γ regulation in dermal adipose homeostasis and its clinical applications in anti-aging therapies.