Abstract
Background:
Ultraviolet B (UVB) exposure causes collagen loss and photoaging by increasing pro-inflammatory and senescence-associated genes, such as tumour necrosis factor-alpha (TNF-α) and p21, in the skin. Hypoxia-treated mesenchymal stem cell exosomes (hypMSC-Exos) and hyaluronic acid (HA) are proposed as potential therapeutic agents for skin regeneration and repair related to UVB-induced collagen depletion.

Aim:
This study aimed to assess the impact of hypMSC-Exos and HA on the gene expression of TNF‑α and p21 in the skin of Wistar rats exposed to UVB.

Methods:
Thirty male Wistar rats were randomly assigned to five groups: the healthy control, UVB + NaCl (200 μl of 0.9% NaCl), UVB + HA (200 μl of HA), UVB + hypMSC-Exos (200 μl of an exosome preparation equivalent to 2.5 × 105 cells), and UVB + hypMSC-Exos+HA (200 μl of HA combined with 200 μl of exosomes). UVB irradiation (302 nm, 150 mJ/cm²) was applied to a 2 × 3 cm dorsal area for 8 minutes, five times weekly over 2 weeks to induce collagen depletion. Treatments were administered once after UVB exposure. TNF-α and p21 gene expression in the skin tissue was measured using qRT-PCR.

Results:
TNF‑α gene expression was 0.073 ± 0.003, 0.19 ± 0.018, 0.17 ± 0.02, 0.135 ± 0.022, and 0.067 ± 0.004 for the control, UVB+NaCl, UVB+HA, UVB+ hypMSC-Exos, and UV+ hypMSC-Exos +HA, respectively. The p21 gene expression was 0.085 ± 0.012, 0.38 ± 0.033, 0.32 ± 0.024, 0.30 ± 0.01, and 0.19 ± 0.015 for control, UVB+NaCl, UVB+HA, UVB+ hypMSC-Exos, and UV+ hypMSC-Exos +HA, respectively. UVB exposure increased TNF‑α and p21 gene expression compared with healthy skin. Using hypMSC-Exos or HA alone reduced TNF‑α and p21 levels compared with the UVB-exposed control group, whereas the combination of both treatments produced the greatest decreases in both genes, with significant differences between groups (p < 0.05).

Conclusion:
The combination of hypoxic MSC-derived exosomes with hyaluronic acid offers a promising therapeutic strategy for reducing TNF-α and p21 gene expression in UVB-induced collagen loss in Wistar rat skin. This approach utilizes the anti-inflammatory, antioxidant, and regenerative properties of hypMSC-Exos, which are enhanced by the stability and sustained-release features of HA hydrogels. Further research and clinical trials are necessary to fully understand the mechanisms and optimize the therapeutic potential of this treatment.

Key words: Hyaluronic acid; Mesenchymal stem cell; p21; TNF‑α; UVB radiation.