An artificially designed elastin-like recombinant ...

Background: As a substrate for cell growth, elastin can promote the regeneration and remodeling of the epidermis, which plays an important role in delaying skin aging. However, elastin proteins are more than 700 amino acids long and cannot be absorbed through the skin, which prevents the direct utilization of elastin in the prevention and treatment of aging skin. Methods: We designed an elastin-like recombinant polypeptide (ELR) which could be absorbed through the skin based on the property of hexapeptide VGVAPG. Thirty healthy Chinese Han female participants which met the criteria were enrolled in this study and all of them completed the tests including elasticity, tightness, and wrinkle detection. The participants used this polypeptide for 4 weeks and were tested in three visits: one day before trial started (D0), and 14 and 28 days after the trial (D14 and D28, respectively). Paired t-tests or Wilcoxon signed-rank tests for non-parametric measures were used to determine the difference between D0 and D14, or D0 and D28. Results: The skin elasticity level in the thirty participants was significantly increased after using ELR for 28 days (P=0.024), and the average value of skin firmness (Uf) declined from 3.313 (D0) to 3.292 (D14) and 3.265 (D28), although there was no statistically significant difference between treatment and pre-treatment. Furthermore, the wrinkle count (D14: P<0.001; D28: P<0.001), wrinkles volume (D14: P<0.001; D28: P=0.008), and wrinkles area (D14: P<0.001; D28: P<0.001) of Crow&#;s feet were significantly improved by using ELR for 14 days or 28 days. Conclusion: Continuous use of ELR could significantly improve skin elasticity and reduce wrinkles.

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Introduction

As the largest organ of the human body exposed to the external environment, the skin protects us while being exposed to the effects of external and internal aging factors, causing skin aging [1]. The typical characteristics of aging skin include wrinkles, loss of elasticity, relaxation, and roughness, along with the loss of moisture, the reduction of superficial fat, and pigmentation [2].

Since skin aging is caused by a combination of intrinsic and extrinsic factors, and as a result it can be divided into both intrinsic aging and extrinsic aging [3]. Intrinsic aging is regulated by genetic factors, and the most significant histological change is the decreased proliferation of skin basal layer cells which increases age-like effects, also known as the process of cell senescence [4]. Cell senescence leads to a decreased ability of skin fibroblasts to synthesize collagen and elastin, thereby leading to a decreased production of the extracellular matrix, with an increased melanin production in melanocytes, resulting in epidermal atrophy, dermal thinning, wrinkle and elastic loss, and ultimately skin aging [5].

The progressive reduction and loss in the density of collagen and elastin in the skin are a sign of both intrinsic and extrinsic skin aging. Elastin is an extracellular matrix protein and endows vertebrate tissues with unique physiological elasticity [6]. It provides elasticity to tissues such as arteries, lungs, skin, and elastic cartilage, and also plays a key role in maintaining healthy cells [7]. As the main component of elastic fibers, elastin is composed of cross-linked convective elastin, which is then cross-linked and combined with microfibers to form elastic fibers, so that the skin has ductility and reversible recoil, enabling it to withstand repeated mechanical deformation pressure and avoid irreversible damage [8]. Although it accounts for only 2% of dermal components, elastin is important in inhibiting the formation of wrinkles and maintaining skin homeostasis, which is indispensable to the young, healthy state, and normal function of skin [9].

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Extrinsic aging is caused by environmental factors, including solar radiation, air pollution, and cosmetics, which will in turn accelerate intrinsic aging [10]. Studies have shown that reactive oxygen species (ROS) play an important role in skin aging [11]. ROS can activate numerous signaling pathways, resulting in the activation of the transcription of various matrixes metalloproteases (MMP), thereby leading to abnormal matrix degradation and the accumulation of non-functional matrix components [12]. Furthermore, MMP can degrade various protein components in the extracellular matrix, including collagen and elastin, thus accelerating the process of skin aging [13]. &#;Photoaging&#;, an exposure to ultraviolet radiation, is the main factor of extrinsic aging, accounting for approximately 80% of facial aging [14]. Ultraviolet radiation can also generate ROS in the skin, causing destructive oxidative stress and mediating inflammatory reactions. It reduces the activity and the renewal of keratinocytes, thus resulting in dry and desquamated skin [15]. Moreover, during photoaging, the number of fibroblasts in the dermis decreases gradually, while the synthesis of collagen and elastin slows down and decomposition accelerates. Hence, the symptoms of &#;photoaging&#; are more severe than intrinsic aging. Many biochemical and histological studies on photoaging skin show that the abnormal accumulation of elastic fibers and the pathological changes such as disorganized and damaged collagen fibers in the dermis lead to the formation of skin wrinkles [16].

Although elastin is considered an inert protein, it is strongly resistant to protease degradation with a low turnover rate in healthy tissues and a half-life of more than 70 years, it is vulnerable to many factors, such as disease, solar radiation, free radicals and inflammation [18]. Elastin will be gradually degraded, crosslinked, and broken down under the exposure of harmful factors in the environment. In addition, the production of elastin declines as the body matures. Together, these factors contribute to the loss of structural integrity and elasticity of the skin. Moreover, the reduction of subcutaneous fat causes skin relaxation, which shows the symptom of skin aging [19].

Elastin not only provides mechanical elasticity for the skin but also acts as a substrate for cell growth to promote the regeneration and remodeling of the epidermis, which plays an important role in delaying skin aging [20]. However, elastin protein is usually more than 700 amino acids long and cannot be absorbed through the skin. Hence, currently, several synthetic forms of elastin have been designed, including: VGVAPG, GPGVGAGVP, GLGBGAGVP, PGAIPG, and LREGDPS, among which elastin-derived peptides, the VGVAPG hexapeptide, is known for its chemotactic activity and metalloproteinases upregulation properties. VGVAPG hexapeptide not only has chemotactic activity against monocytes, fibroblasts, and tumor cells [21,22], but it also activates metalloproteinases [23,24]. Therefore, VGVAPG oligopeptide has been widely used as a cosmetic and skin care additive [25]. In this study, by bioinformatics analysis and codon optimization, we designed an elastin sequence based on this hexapeptide to investigate the ameliorative effect of this sequence on the human skin.

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