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Nalfurafine Hydrochloride, a κ-Opioid Receptor Agonist, Induces Melanophagy via PKA Inhibition in B16F1 Cells
Ha Jung Lee1, Seong Hyun Kim1, Yong Hwan Kim1
1BK21 FOUR KNU Creative BioResearch Group, School of Life Sciences, Kyungpook National University, Daegu 41566, Republic of Korea.
Abstract:
Selective autophagy controls cellular homeostasis by degrading unnecessary or damaged cellular components. Melanosomes are specialized organelles that regulate the biogenesis, storage, and transport of melanin in melanocytes. However, the mechanisms underlying melanosomal autophagy, known as the melanophagy pathway, are poorly understood. To better understand the mechanism of melanophagy, we screened an endocrine-hormone chemical library and identified nalfurafine hydrochlorides, a κ-opioid receptor agonist, as a potent inducer of melanophagy. Treatment with nalfurafine hydrochloride increased autophagy and reduced melanin content in alpha-melanocyte-stimulating hormone (α-MSH)-treated cells. Furthermore, inhibition of autophagy blocked melanosomal degradation and reversed the nalfurafine hydrochloride-induced decrease in melanin content in α-MSH-treated cells. Consistently, treatment with other κ-opioid receptor agonists, such as MCOPPB or mianserin, inhibited excessive melanin production but induced autophagy in B16F1 cells. Furthermore, nalfurafine hydrochloride inhibited protein kinase A (PKA) activation, which was notably restored by forskolin, a PKA activator. Additionally, forskolin treatment further suppressed melanosomal degradation as well as the anti-pigmentation activity of nalfurafine hydrochloride in α-MSH-treated cells. Collectively, our data suggest that stimulation of κ-opioid receptors induces melanophagy by inhibiting PKA activation in α-MSH-treated B16F1 cells.
Insights
Nalfurafine hydrochloride, a κ-opioid receptor agonist, was found to induce melanophagy, a cellular process that degrades melanosomes. This drug reduces melanin content by inhibiting protein kinase A (PKA) activation.
Area of Science:
- Cell Biology
- Autophagy Research
- Melanogenesis Regulation
Background:
- Selective autophagy maintains cellular homeostasis by degrading damaged components.
- Melanosomes are key organelles for melanin production, storage, and transport in melanocytes.
- The precise mechanisms of melanophagy, the autophagy of melanosomes, remain largely unknown.
Purpose of the Study:
- To elucidate the molecular mechanisms governing melanophagy.
- To identify novel inducers of the melanophagy pathway.
- To investigate the role of protein kinase A (PKA) in melanosome degradation.
Main Methods:
- Screening of an endocrine-hormone chemical library to identify melanophagy inducers.
- Treatment of melanocytes with nalfurafine hydrochloride and other κ-opioid receptor agonists.
- Assessment of autophagy levels, melanosome degradation, and melanin content.
- Investigation of the involvement of PKA signaling pathway using activators and inhibitors.
Main Results:
- Nalfurafine hydrochloride was identified as a potent inducer of melanophagy.
- Treatment with nalfurafine hydrochloride increased autophagy and decreased melanin content in α-MSH-treated cells.
- Inhibition of autophagy counteracted the effects of nalfurafine hydrochloride, confirming its role in melanosomal degradation.
- Nalfurafine hydrochloride inhibited PKA activation, and this inhibition was crucial for its melanophagy-inducing and anti-pigmentation effects.
Conclusions:
- Stimulation of κ-opioid receptors, specifically with nalfurafine hydrochloride, effectively induces melanophagy.
- The mechanism involves the inhibition of PKA signaling in α-MSH-treated melanocytes.
- These findings provide new insights into the regulation of melanosome turnover and potential therapeutic targets for pigmentation disorders.
