The natural aging process affects many biological mechanisms in the body; the large majority of changes begin with modifications in gene control and result in visible signs of aging on the skin [1]. Generally, characteristics of cells differ depending on age. Pluripotent stem cells have the ability to differentiate into different tissues to replace senescent cells. These newly differentiated and functional cells exhibit remarkable vitality and proliferation capacity, which naturally declines with age [2]. As they age, stem cell number and self-renewal capabilities do not necessarily decline; rather, they progressively lose their DNA repair capacities, while their ability to produce new progenitors and differentiated effector cells is affected [3]. As a result, there is a reduction in tissue regenerative potential and an accumulation of non-functional cells throughout life [4].

Stem cells present an important role in different skin layers; their function in the epidermis is well documented in the literature. Indeed, the epidermis is the first part of the body to be exposed to external aggressors, submitting epidermal cells to stress and damage. Accordingly, the multi-layered stratified squamous epithelium requires constant renewal due to its high turnover [5]. The role of stem cells in the dermis, though less described, is equally important: stem cells are present in the dermal tissue and play a role in maintaining homeostasis and regenerating injured skin [6]. Indeed, they have the capacity to differentiate in new functional fibroblasts capable of synthesizing molecules from the extracellular matrix and the elastic network, with a higher proliferation rate than cells becoming senescent.

When skin cells lose their pluripotency and functionality, cell regeneration and repair functions slow down, and their role in driving skin remodeling other activities diminishes. This process leads to the progressive appearance of visible signs of aging such as wrinkles, under-eye bags, and aging spots [7]. Based on this knowledge, we hypothesized that reactivating cell memory to bring cells closer to a pluripotent state could be an effective and innovative strategy for rejuvenating cells.

Recent discoveries in ethnobotany and the traditional use of plants have highlighted the fact that certain botanical compounds have the ability to significantly stimulate genes involved in rejuvenation mechanisms. One such compound is found in the Miombo forest of Tanzania, home to the common Terminalia sericea (aka silver tree), which plays a role in maintaining biodiversity. The plant produces sericoside, a pentacyclic terpenoid that accumulates in the bark of its roots, and which is obtained by extraction and purification [INCI: Sericoside]. Sericoside is already known and widely used for its various medicinal properties such as antibacterial, antioxidant or even anti-inflammatory properties [8, 9, 10, 11].

In this study, we evaluated the capacities of sericoside to reprogram cells to a younger stage to determine whether it could be an effective candidate for reactivating skin cell memory for a rejuvenation process. We analyzed its effects on stem cells maintenance, DNA repair, cell pluripotency, cell proliferation properties, and broader anti-aging properties on a global scale.

We first demonstrated that sericoside is capable of rejuvenating cells by stimulating cell memory, leading to the reprogrammation of cell pluripotency. Indeed, our active ingredient stimulated the expression of genes such as SOX2, NANOG or C-MYC whose expression is decreased while aging, positioning these targets as an efficient cocktail for a natural iPS cell reprogramming [18]. Interestingly, SOX2 has been shown by Narayan et al. [19] to work with POU5F1 as activators during the reprogramming of human fibroblasts to iPS cells. NANOG gene is an embryonic stem cell marker involved in the maintenance of undifferentiated state of pluripotent stem cells [20]. In the context of cellular reprogramming, C-MYC enhances the conversion of somatic cells into induced pluripotent stem cells [21]. Sericoside also stimulates the expression of XPC, XPA, OGG1 and GADD45A, genes involved in DNA repair, which is a function of stem cells that can be negatively impacted during aging [22]. These transcriptomic results highlighted sericoside as a good candidate to reactivate cell memory to restore them to pluripotency state.

This rejuvenation process induced by sericoside leads to a reactivation of cell functions. Indeed, the active ingredient also stimulated the expression of genes involved in various pathways: reactivation of antioxidant defense with G6PD, GPX1, GSTT1, HMOX1, MSRA and SOD2; extracellular matrix composition with CD44, CYR61, FBN1, HAS2, TIMP1, SDC1 and VCAN; cell proliferation with IGFBP3, IGF1R, IGF1, FGF7 and MKI67; and even dermo-epidermal junction integrity with COL7A1 and COL4A1. These genes are involved in biological pathways that contribute to skin rejuvenation and youthfulness. The role of genes involved in antioxidant defense is to stimulate the skin defenses against oxidative stress induced by various factors from the exposome. Unfortunately, during the chronologic aging process, there is an increase of reactive oxygen species production associated with a decrease of antioxidant defense [23]. Fibroblasts’ proliferative capacity, a key factor in skin maintenance and renewal, is impaired during skin aging, leading to an impairment of these capacities. In the case of IGF1 and IGF1R, two genes involved in cell proliferation, recent publications have evidenced the crucial role of IGF1 that activates IGF1 receptor to induce an appropriate protective response against UV-induced DNA damages [24, 25]. Lewis et al. [24] described the loss of IGF1 expression in ageing skin to be linked to a high occurrence of skin cancers. More, cells’ proliferation impairment provokes a reduction of the extracellular matrix component synthesis such as collagen, elastin, hyaluronic acid and chondroitin [26]. The extracellular matrix components are known to be involved in the composition of a tissue framework and cell niche that provides a micro- and macro-architecture that helps drive cell behavior and function [27]. Li et al. [27] also showed that the alteration of the dermal extracellular matrix composition and organization is a major driver of human skin aging. The dermis is impacted by skin aging, but not only because the overlying dermoepidermal junction is submitted to skin aging. Langton et al. [28] described a reduction of collagen IV and collagen VII expression among other proteins during skin aging, resulting in a flattened dermoepidermal junction. These data, taken together with our findings, confirm that reactivating these pathways that are downregulated by the aging process proves the efficacy of sericoside in promoting cellular rejuvenation. Indeed, the upregulation of these genes in aged skin will rebalance their expression closer to a balanced state, leading to a reactivation of cell metabolism, without being abnormally overexpressed.

Cell rejuvenation was assumed thank to a proliferation study evidencing that aged fibroblasts treated with sericoside showed a strong decrease of their doubling time, underscoring the effectiveness of our active ingredient on cell rejuvenation (data not shown). This rejuvenation of fibroblasts’ metabolism was also confirmed with an increase of protein synthesis by 54%, and especially the collagen as observed by the 10% increase of proline content, reinforcing the set of data showing a rejuvenation of cells with sericoside.

Our clinical studies demonstrate that cell rejuvenation led to a wide anti-aging efficacy with an improvement of skin elasticity and firmness after 30 days of application. This anti-aging effect can be linked to the stimulated expression of genes involved in the protection and production of the extracellular matrix. We further demonstrated a reduction of wrinkles and an improvement of skin texture by reducing skin roughness on the periorbital area and eye bag volume. These clinical benefits go hand in hand with the transcriptomic study which showed an improvement of extracellular matrix composition, cell proliferation and dermo-epidermal junction. Finally, sericoside reduced dark circles, confirming the antioxidant properties of the active ingredient [29].

This study demonstrated that stimulating the natural tools available in our DNA to reprogram cells is an innovative method of skin rejuvenation. Sericoside has shown strong efficacy in numerous applications.

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

RR, AS, MM and GM designed the research study. MM and MB performed the research. JT provided help for the isolation of human skin cells. MM and AS analyzed the data. MM wrote the manuscript. All authors contributed to editorial changes in the manuscript. All authors read and approved the final manuscript. All authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work.

This clinical study follows the European law and has been carried out in compliance with the most recent recommendations of the World Medical Association Declaration of Helsinki- ethical principles for medical research involving human subjects (Helsinki Declaration 64th WMA General Assembly, Fortaleza, Brazil, October 2013) and according to the Colipa Guidelines for the evaluation of the efficacy of cosmetic products. Only after having signed the informed consent the participation in the study was permitted. The original of the informed consent forms were archived at the Abich Clinical study Center under the codification number 8693/15-04. All subjects signed a consent allowing to treat personal data according to the Italian law (privacy. D.Lgs 196/2003).

Many thanks to all the people participating to this study, from the design of the product until the clinical evaluation.

This research received no external funding.

The authors declare no conflict of interest.