A Standardized Protocol for Inducing Stress-Induced Premature Senescence in Primary Human Melanocytes Using Tert-butyl Hydroperoxide

Summary

A standardized protocol for inducing premature senescence in HNM using tBHP, standardized protocols for analyzing key senescence markers, including growth arrest, SA-β-galactosidase activity, and SASP factors.

Abstract

Environmental stressors, including UV radiation, air pollution, or cigarette smoke, drive extrinsic skin aging. Exposure to these extrinsic aging factors promotes the accumulation of senescent cells, which contributes to the formation of wrinkles and pigmentation disorders. Melanocytes, which provide primary UV protection, exhibit reduced activity with age. Senescent melanocytes accumulate in aged skin and contribute to its aging appearance; However, there are few models to study melanocyte senescence, and this work aims to develop a reproducible model for further research. In this study, we present a senescence model of human neonatal melanocytes (HNM) using tert-butyl hydroperoxide (tBHP), a well-characterized oxidative stress inducer. tBHP disrupts redox homeostasis by depleting cellular antioxidant defenses and promoting radical overproduction, resulting in DNA and protein damage. We characterize the senescence phenotype of tBHP-treated melanocytes through the analysis of established senescence markers, including restricted growth potential, morphological changes, and SA-β-Galactosidase activity. This model provides a valuable tool for investigating stress-induced premature senescence in melanocytes, offering insight into their role in extrinsic skin aging and pigmentation disorders.

Introduction

Skin aging is composed of two distinct factors: intrinsic and extrinsic aging^1,2. Intrinsic aging is caused by natural chronological processes and genetic factors, while extrinsic aging results from cumulative exposure to environmental stressors, primarily ultraviolet radiation, but also air pollution, cigarette smoke, and chemical agents, which accelerate the aging process beyond normal chronological rates^3,4. Environmental exposures generate oxidative stress that overwhelms cellular antioxidant defenses, resulting in DNA damage, protein oxidation, an....

Protocol

This protocol was optimized for research on primary human neonatal melanocytes (HNM) to study the mechanisms of stress-induced premature senescence induced by tBHP (Figure 1). The melanocytes were derived from neonatal Caucasian foreskin (light pigmentation phototype) and obtained from a commercial source. According to the supplier’s documentation, human tissues are collected from donors who are fully informed and have provided consent, in compliance with established ethical and legal frameworks, including the Declaration of Helsinki and applicable data protection regulations. The cells were provided in a de-identified form. No addi....

Results

tBHP treatment induces growth arrest in human neonatal melanocytes.
tBHP treatment inhibits melanocyte proliferation compared to untreated controls (n = 3) (Figure 2A). By day 9, treated cells reach only 1.4 cPDL, whereas controls reach 3.1 cPDL. This divergence increases over time, with treated melanocytes approaching a plateau of 1.9 cPDL by day 15, while controls continue to expand to nearly 5.1 cPDL. The sustained reduction in proliferative capacity is consistent wit.......

Discussion

This protocol establishes a standardized approach for inducing stress-induced premature senescence (SIPS) in human neonatal melanocytes using tBHP, offering a robust model for studying senescence specifically in this cell type. Consistent changes in proliferation, morphology, SA-β-gal activity, DNA damage markers, and SASP components support the induced phenotype. By focusing on melanocytes, cells that remain understudied in senescence research despite their key roles in skin physiology and pigmentation disorders

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
0.22 µm membrane filter	Merck	SLGVR33RS
1 M citric acid	Merck	K91567844	prepare in aq. dest.
1 M MgCl2	Merck	A649033	prepare in aq. dest.
1 M Na2HPO4	Merck	K56036736	prepare in aq. dest.
10 M NaOH	Lab Honeywell	30620	prepare in aq. dest.
37% formaldehyde	Sigma	252549
4% paraformaldehyde	CarlRoth	0335.3
5 M Sodium Chloride	Sigma	S3014	prepare in aq. dest.
50% glutaraldehyde	Sigma	G6403
5-Brom-4-Chlor-3-indolyl-β-D-Galactopyranosid (X-Gal)	Sigma	B9146
Alexa Fluor-conjugated secondary antibody 2 mg/mL	Invitrogen	A11008
BSA (bovine serum albumin)	Sigma	A7030
Chemiluminescent substrate	Sigma	WBKLS0500
Costar CellLifter	Corning	3008
Coverslips for cell culture/microscopy	Epredia	CB00200RA120MNZ0
DermaLife Basal Medium	CellSystems	LM-0004
DermaLife M Melanocyte Kit	CellSystems	LS-1041
Dulbecco's Phosphate Buffered Saline	Sigma	D8537
Human neonatal melanocytes	CellSystems	FC-0023
LaminB1 antibody (rabbit)	Abcam	AB16048	Dilution 1:1000 in 5% BSA
Mounting medium containing DAPI	Abcam	AB104139
Penicillin-Streptomycin solution	Sigma	P4333
Polyacrylamide gradient gels	Bio-Rad	456-8095
Poly-D-Lysine, 0.1 mg/mL	Gibco	A38904-01
Potassium ferricyanide	Sigma	P8131
Potassium ferrocyanide	Sigma	P-9387
pRB antibody (rabbit)	CellSignalling	93085	Dilution 1:1000 in 5% BSA
Protease inhibitor cocktail	self prepared	N/A	500 mM NaF; 2 µg/ml Aprotinin; 1 mM PMSF; 1 mM activated Na-Orthovanadate
RIPA buffer	self prepared	N/A	containing: 50 mM Tris-HCl; 1% NP-40; 0.5% Na-deoxycholate; 0.1% SDS; 150 mM NaCl; 2 mM EDTA
RLT buffer	Qiagen	1015762	Included in RNeasy Mini Kit
RNeasy Mini Kit	Qiagen	74106
Skim milk powder (for 5% milk in TBS-T)	Sigma	70166
Sodium citrate (for 0.1% solution)	Sigma	S4641
Soybean trypsin inhibitor, 0.5 mg/mL	Thermofisher	17075-029
tert-Butyl hydroperoxide (tBHP)	Sigma	458139
Triton X-100 (for 0.3% solution)	Sigma	T9284
Trypsin-EDTA solution	Sigma	T3924
β-mercaptoethanol	CarlRoth	4227.3
γH2AX antibody (rabbit)	CellSignalling	2577S	Dilution 1:200