4-nonylphenol triggers apoptosis and affects 17-β-estradiol receptors in calvarial osteoblasts

Area of Science:

• Environmental Toxicology
• Cell Biology
• Endocrinology

Background:

• 4-nonylphenol (4-NP) is an environmental endocrine-disrupting chemical.
• Osteoblasts are crucial for bone formation and maintenance.
• Estrogen plays a vital role in regulating osteoblast function.

Purpose of the Study:

• To investigate the impact of 4-NP on mouse primary calvarial osteoblasts (COBs).
• To elucidate the molecular mechanisms underlying 4-NP-induced osteoblast apoptosis.
• To compare the effects of 4-NP with 17-β-estradiol (17-β E2) on osteoblasts.

Main Methods:

• Primary mouse calvarial osteoblasts (COBs) were treated with varying concentrations of 4-NP.
• Cell viability and phosphatidylserine (PS) exposure were assessed using Annexin V.
• Mitochondrial membrane potential (ΔΨm), caspase activity (caspase 9, 3, 8), Bax/Bcl2 ratio, and truncated Bid (t-Bid) were analyzed.
• The interaction between 4-NP and 17-β E2 effects on osteoblasts and estrogen receptor expression was examined.

Main Results:

• 4-NP significantly decreased COB viability and increased PS exposure in a dose-dependent manner.
• 4-NP induced apoptosis via the mitochondrial pathway, evidenced by increased Bax/Bcl2 ratio, decreased ΔΨm, and elevated cleaved caspase 9 and 3.
• 4-NP also activated the extrinsic pathway, increasing cleaved caspase 8 and t-Bid, indicating crosstalk between apoptotic pathways.
• 4-NP's apoptotic effects counteracted 17-β E2-induced survival and interfered with 17-β E2-regulated estrogen receptor expression.

Conclusions:

• 4-NP induces osteoblast apoptosis through a combined intrinsic and extrinsic mitochondrial-dependent pathway.
• The detrimental effects of 4-NP on osteoblasts are more potent than the protective effects of 17-β E2.
• 4-NP disrupts normal osteoblast function and estrogen signaling, posing a risk to bone health.