Poly-L-lactic acid (PLLA) fillers correct cutaneous volume loss by stimulating fibroblasts to synthesize collagen and by augmenting the volume. PLLA triggers the macrophage-induced activation of fibroblasts that secrete transforming growth factor-β (TGF-β). However, whether M2 macrophage polarization is involved in PLLA-induced collagen synthesis via fibroblast activation in aged skin is not known. Therefore, we evaluated the effect of PLLA on dermal collagen synthesis via M2 polarization in an H₂O₂-induced cellular senescence model and aged animal skin. H₂O₂-treated macrophages had increased expression levels of the M1 marker CD80 and decreased expression levels of the M2 marker CD163, which were reversed by PLLA. The expression levels of interleukin (IL)-4 and IL-13, which mediate M2 polarization, were decreased in H₂O₂-treated macrophages and increased upon the PLLA treatment. CD163, IL-4, and IL-13 expression levels were decreased in aged skin, but increased after the PLLA treatment. The expression levels of TGF-β, pSMAD2/SMAD2, connective tissue growth factor (CTGF), alpha-smooth muscle actin (α-SMA), collagen type 1A1 (COL1A1), and COL3A1 were also decreased in aged skin, but increased after the PLLA treatment. Moreover, PLLA upregulated phosphatidylinositol 3-kinase p85α (PI3-kinase p85α)/protein kinase B (AKT) signaling, leading to fibroblast proliferation. PLLA decreased the expression of matrix metalloproteinase (MMP) 2 and MMP3, which destroy collagen and elastin fibers in aged skin. The amount of collagen and elastin fibers in aged skin increased following the PLLA treatment. In conclusion, PLLA causes M2 polarization by increasing IL-4 and IL-13 levels and upregulating TGF-β expression and collagen synthesis in aged skin.

Poly L-lactic acid (PLLA) fillers stimulate collagen synthesis by activating various immune cells and fibroblasts. Piezo1, an ion channel, responds to mechanical stimuli, including changes in extracellular matrix stiffness, by mediating Ca²⁺ influx. Given that elevated intracellular Ca²⁺ levels trigger signaling pathways associated with fibroblast proliferation, Piezo1 is a pivotal regulator of collagen synthesis and tissue fibrosis. The aim of the present study was to investigate the impact of PLLA on dermal collagen synthesis by activating Piezo1 in both an H₂O₂-induced cellular senescence model in vitro and aged animal skin in vivo. PLLA elevated intracellular Ca²⁺ levels in senescent fibroblasts, which was attenuated by the Piezo1 inhibitor GsMTx4. Furthermore, PLLA treatment increased the expression of phosphorylated ERK1/2 to total ERK1/2 (pERK1/2/ERK1/2) and phosphorylated AKT to total AKT (pAKT/AKT), indicating enhanced pathway activation. This was accompanied by upregulation of cell cycle-regulating proteins (CDK4 and cyclin D1), promoting the proliferation of senescent fibroblasts. Additionally, PLLA promoted the expression of phosphorylated mTOR/S6K1/4EBP1, TGF-β, and Collagen I/III in senescent fibroblasts, with GsMTx4 treatment mitigating these effects. In aged skin, PLLA treatment similarly upregulated the expression of pERK1/2/ERK1/2, pAKT/AKT, CDK4, cyclin D1, mTOR/S6K1/4EBP1, TGF-β, and Collagen I/III. In summary, our findings suggest Piezo1′s involvement in PLLA-induced collagen synthesis, mediated by heightened activation of cell proliferation signaling pathways such as pERK1/2/ERK1/2, pAKT/AKT, and phosphorylated mTOR/S6K1/4EBP1, underscoring the therapeutic potential of PLLA in tissue regeneration.

Steroids, which are often used to treat the inflammation associated with various skin diseases, have several negative side effects. As Ecklonia cava extract has anti-inflammatory effects in various diseases, we evaluated the efficacy of Ecklonia cava-derived extracellular vesicles (EVEs) in decreasing 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inflammation. We determined the effect of the EVEs on the TLR4/NF-κB/NLRP3 inflammasome in human keratinocytes and mouse ear skin. TPA-treated human keratinocytes showed an increased expression of TLR4 and its ligands HMGB1 and S100A8. TPA also increased the expression of (1) NF-κB; (2) the NLRP3 inflammasome components NLRP3, ASC, and caspase 1; and (3) the pyroptosis-related factors GSDMD-NT, IL-18, and IL-1β. However, the expression of these molecules decreased in the TPA-treated human keratinocytes after EVE treatment. Similar to the in vitro results, TPA increased the expression of these molecules in mouse ear skin, and EVE treatment decreased their expression. The TPA treatment of skin increased edema, redness, neutrophil infiltration, and epidermal thickness, and EVE reduced these symptoms of inflammation. In conclusion, the EVEs decreased TPA-induced skin inflammation, which was associated with a decrease in the TLR4/NF-κB/NLRP3 inflammasome.

Oxidative stress-induced cellular senescence and mitochondrial dysfunction result in skin aging by increasing ECM levels-degrading proteins such as MMPs, and decreasing collagen synthesis. MMPs also destroy the basement membrane, which is involved in skin elasticity. The extracellular matrix vitalizer RA^TM (RA) contains various antioxidants and sodium hyaluronate, which lead to skin rejuvenation. We evaluated whether RA decreases oxidative stress and mitochondrial dysfunction, eventually increasing skin elasticity in aged animals. Oxidative stress was assessed by assaying NADPH oxidase activity, which is involved in ROS generation, and the expression of SOD, which removes ROS. NADPH oxidase activity was increased in aged skin and decreased by RA injection. SOD expression was decreased in aged skin and increased by RA injection. Damage to mitochondrial DNA and mitochondrial fusion markers was increased in aged skin and decreased by RA. The levels of mitochondrial biogenesis markers and fission markers were decreased in aged skin and increased by RA. The levels of NF-κB/AP-1 and MMP1/2/3/9 were increased in aged skin and decreased by RA. The levels of TGF-β, CTGF, and collagen I/III were decreased in aged skin and increased by RA. The expression of laminin and nidogen and basement membrane density were decreased in aged skin and increased by RA. RA increased collagen fiber accumulation and elasticity in aged skin. In conclusion, RA improves skin rejuvenation by decreasing oxidative stress and mitochondrial dysfunction in aged skin.

Decreased medial cheek fat volume during aging leads to loss of a youthful facial shape. Increasing facial volume by methods such as adipose-derived stem cell (ASC) injection can produce facial rejuvenation. High-intensity focused ultrasound (HIFU) can increase adipogenesis in subcutaneous fat by modulating cilia on ASCs, which is accompanied by increased HSP70 and decreased NF-κB expression. Thus, we evaluated the effect of HIFU on increasing facial adipogenesis in swine (n = 2) via modulation of ASC cilia. Expression of CD166, an ASC marker, differed by subcutaneous adipose tissue location. CD166 expression in the zygomatic arch (ZA) was significantly higher than that in the subcutaneous adipose tissue in the mandible or lateral temporal areas. HIFU was applied only on the right side of the face, which was compared with the left side, where HIFU was not applied, as a control. HIFU produced a significant increase in HSP70 expression, decreased expression of NF-κB and a cilia disassembly factor (AURKA), and increased expression of a cilia increasing factor (ARL13B) and PPARG and CEBPA, which are the main regulators of adipogenesis. All of these changes were most prominent at the ZA. Facial adipose tissue thickness was also increased by HIFU. Adipose tissue volume, evaluated by magnetic resonance imaging, was increased by HIFU, most prominently in the ZA. In conclusion, HIFU increased ASC marker expression, accompanied by increased HSP70 and decreased NF-κB expression. Additionally, changes in cilia disassembly and length and expression of adipogenesis were observed. These results suggest that HIFU could be used to increase facial volume by modulating adipogenesis.

Hyun Jin Cho, MD, Seung Min Oh, MD, MMBA, HyunJun Park, MD, Je Hyuk Lee, MD, Dae-Geun Song, MD, Geebum Kim, MD, PhD, MBA, Seon Oh Kim, MD, Gwahn Woo Cheon, MD, Sang Bong Lee, MD, Hoon-Young Kim, MD, Wan Jae Kim, MD. The AESTHETICS 2025;5:19-26. https://doi.org/10.46738/Aesthetics.25.0003