**7. Antiaging mechanisms of ADSC within TFG-β and GDF11**

#### **7.1 Cellular implication**

*Regenerative Medicine*

**of ADSC in skin**

re-epithelialization.

level [103].

**6. TGF-β and GDF11 impacts on immunoregulatory effects** 

secretion of IL-6, IL-8, and MCP-1 to modulate skin inflammation [72]. TFG-β, secreted by ADSCs and other epithelial cells, is involved in the inflammatory, proliferative, and remodeling phases of wound healing. This factor activates M2 macrophages and secretion of ECM proteins involved in skin structure repair, in angiogenesis, in DF proliferation and cell migration, and

The integrin αβ6 secreted by epithelial cells was reported to activate TGF-β modulation and thus the innate immune surveillance in skin [89]. Recently, the collagen triple helix repeat containing one protein was reported to contribute to healing process via increasing M2 macrophages recruitment and TGF-β expression

In the same way, IL-6, the major proinflammatory component of ADSC's secretome, was reported to initiate the inflammatory phase in injured tissues. Autoactivated ADSCs amplify their secretion and stimulate the secretion of TNF-α, TLR2, TLR4, IL-10, b-FGF, VEGF, TGF-β, and GDF11. These secretions would take place to short and shift the ADSCs profile to an anti-inflammatory profile and enhance angiogenesis, cell migration, and proliferation (**Figure 2**). Like TGF-β,

*Immunomodulatory effects of ADSCs. Through their secretome, these cells change the macrophages' polarization and acquire an anti-inflammatory profile to enhance skin cell proliferation and migration and* 

Evidence of involvement of ADSCs in immunomodulation of tissues and their presence within the epidermal layer have suggested that these cells might play a crucial role in skin immunological functions in physiologic and injured skin. Accumulation of senescent cells is related to the production of proinflammatory factors such as IL-6, IL-8, and TNF-α; we can postulate that the associated chronic inflammation is a promoting age-associated disease due to tissue aging. This skin inflamm-aging was also supported by highly secreted proinflammatory cytokine IL-1 β [32, 33]. Microvascular endothelial cells also interact with ADSCs to increase

**50**

**Figure 2.**

*accelerate angiogenesis.*

The mechanisms inducing tissue degeneration and cell aging remain multifactorial and still unclear. Senescent ADSCs were likely found to be impacted in their ability to sustain tissue hemostasis and hence resulted in loss of tissue and organ integrity. Even these cells display a rich secretory profile; their ability to secrete ECM proteins, cytokines, and chemokines was largely impaired *in vitro* during culture expansion [107].

A recent clinical study has demonstrated that secretome of adipose tissue lipoaspirate extracellular fraction stimulates epidermal and dermal cell proliferation in a dose-dependent manner. This secretome has also the ability to delay apoptosis, enhance fibroblasts proliferation and migration, and reverse specifically the aging process and the associated skin symptoms [25, 28]. Exposure of fibroblasts to UVA was followed by preventing the upregulation of MMP1, MMP2, and α-SMA expression as well as lower elastin and collagen production associated to the senescence-like phenotype [25]. Indeed, ADSCs have proven their superiority in improving and increasing dermal thickness and reducing wrinkles more likely by inducing paracrine DF and angiogenesis [17, 18, 108]. Administrated intradermally to an aged skin, skin texture and wrinkles as well as dermal thickness were found improved 8 weeks after treatment [74]. The extracellular vesicles released in ADSCs' secretome or conditioned media enable the targeted cells to increase the production and deposition of ECM proteins including collagen and elastin [11, 16, 90, 109, 110]. Among these autocrine/paracrine factors, TGF-β and GDF11 appeared to be strongly associated (**Figure 1**).

Indeed, ADSCs-conditioned media *in vitro* and *in vivo* have proven their efficiency in stimulating rejuvenation of human skin by improving skin elasticity and reducing wrinkles in a GDF11-dependent manner [111–113]. Their extract acted in a similar manner by activating DF and keratinocytes to proliferate and migrate into damaged sites [114]. An anti-wrinkle effect and dermal density increase were shown after *in vivo* treatment [23]. Moreover, the young cells secreting more GDF11 supported higher proliferation rate of keratinocyte stem cells than those from aged

donors [115]. In the same manner, using platelets-rich plasma (PRP) for anti-wrinkle and anti-aging skin aspects appeared legitime related to its higher quantities of GDF11 [116]. Interestingly, GDF11 expression and activity were reduced in adult DF compared to the neonatal ones [95].

Fibroblasts were also recognized to play a crucial role in skin regeneration through GDF11 secretion in both neonatal and adult cells [95]. MSCs derived from placenta and umbilical cord blood promote fibroblasts plasticity [117] probably through GDF11 release, thus stimulating the rejuvenation of human skin [118]. These authors have effectively demonstrated that GDF11 activated fibroblasts to increase ECM proteins' production and especially collagen I and III and fibronectin [23]. Also, MSCs have proven their proliferative superiority in young donors rather than the elderly [18].

In an animal model, transplanted autologous ADSCs improved skin-graft survival through secreting factors presenting anti-apoptotic activity [119]. In addition to ADSC, DF also appeared attractive in terms of protein secretion [109]. ADSC-conditioned media were anti-apoptotic and ensured skin tissue regeneration [119]; their protective and antiaging properties have been demonstrated on DF by preventing their oxidative stress and increasing their superoxide dismutase and glutathione peroxidase activities [120]. These cells act through their different and directed secretome to improve and induce tissue repair, consolidating their place as better candidate for regenerative medicine and opening recently the way for a new cell-free therapy [109, 121].

Moreover, by increasing collagenase matrix metalloproteinase-9 (MMP-9) secretion, rGDF11 participated in matrix remodeling maybe through interaction of MMP-9 with TGF-β1 to facilitate skin wound closure [97, 122]. These cell interactions reveal the role of the TFG-β and GDF11 mechanisms used by ADSCs to interfere with the aging process [24, 95, 101].
