Melanocyte transformation requires complete loss of all pocket protein function via a mechanism that mitigates the need for MAPK pathway activation

Astragaloside IV ameliorates radiation-induced senescence via antioxidative mechanism

OBJECTIVES

Ageing is a universal and gradual process of organ deterioration. Radiation induces oxidative stress in cells, which leads to genetic damage and affects cell growth, differentiation and senescence. Astragaloside (AS)-IV has antioxidative, anti-apoptotic and anti-inflammatory properties.

METHODS

To study the protective mechanism of AS-IV on radiation-induced brain cell senescence, we constructed a radiation-induced brain cell ageing model, using biochemical indicators, senescence-associated galactosidase (SA-β-gal) senescence staining, flow cytometry and Western blotting to analyse the AS-IV resistance mechanism to radiation-induced brain cell senescence.

KEY FINDINGS

Radiation reduced superoxide dismutase (SOD) activity and expressions of cyclin-dependent kinase (CDK2), CDK4, cyclin E and transcription factor E2F1 proteins, and increased expressions of p21, p16, cyclin D and retinoblastoma (RB) proteins, malondialdehyde (MDA) activity, SA-β-gal-positive cells and cells stagnating in G1 phase. After treatment with AS-IV, the level of oxidative stress in cells significantly decreased and expression of proteins related to the cell cycle and ageing significantly changed. In addition, SA-β-gal-positive cells and cells arrested in G1 phase were significantly reduced.

CONCLUSIONS

These data suggest that AS-IV can antagonize radiation-induced brain cells senescence; and its mechanism may be related to p53-p21 and p16-RB signalling pathways of ageing regulation.

Exposure of human melanocytes to UVB twice and subsequent incubation leads to cellular senescence and senescence-associated pigmentation through the prolonged p53 expression

BACKGROUND

Ultraviolet radiation (UVR) is a well-known factor in skin aging and pigmentation, and daily exposure to subcytotoxic doses of UVR might accelerate senescence and senescence-associated phenomena in human melanocytes.

OBJECTIVE

To establish an in vitro melanocyte model to mimic the conditions of repeated exposure to subcytotoxic doses of UVB irradiation and to investigate key factor(s) for melanocyte senescence and senescence-associated phenomena.

METHODS

Human epidermal melanocytes were exposed twice with 20 mJ/cm² UVB over a 24-h interval and subsequently cultivated for 2 weeks. Senescent phenotypes were addressed morphologically, and by measuring the senescence-associated β-galactosidase (SA-β-Gal) activity, cell proliferation capacity with cell cycle analysis, and melanin content.

RESULTS

The established protocol successfully induced melanocyte senescence, and senescent melanocytes accompanied hyperpigmentation. Prolonged expression of p53 was responsible for melanocyte senescence and hyperpigmentation, and treatment with the p53-inhibitor pifithrin-α at 2-weeks post-UVB irradiation, but not at 48 h, significantly reduced melanin content along with decreases in tyrosinase levels.

CONCLUSION

Melanocyte senescence model will be useful for studying the long-term effects of UVB irradiation and pigmentation relevant to physiological photoaging, and screening compounds effective for senescence-associated p53-mediated pigmentation.