Neuropeptides substance P and CGRP activate specific MAPK signaling pathways (ERK1/2 and JNK) in skin cells to drive inflammatory cytokine and nerve growth factor production, revealing therapeutic targets for inflammatory skin diseases and pain syndromes.
ERK1/2 and JNK inhibitors reversed neuropeptide-driven inflammationBlocking these two specific signaling pathways stopped substance P and CGRP from driving inflammatory cytokine and nerve growth factor production in keratinocytes
What the researchers found
Both substance P (SP) and CGRP concentration-dependently stimulated keratinocyte proliferation and production of IL-1β, IL-6, TNF-α, and nerve growth factor (NGF). SP activated all three MAPK families (ERK1/2, JNK, p38) plus NFκB, while CGRP activated only ERK1/2 and p38.
The study revealed several novel findings: CGRP stimulates keratinocyte expression of both CGRP itself and its receptor complex (creating an autocrine amplification loop); SP and CGRP both stimulate IL-6 and TNF-α secretion (previously unknown); SP activates all three MAPK families plus NFκB in keratinocytes; and the inflammatory mediator production driven by both neuropeptides depends specifically on ERK1/2 and JNK activation, as inhibitors of these pathways reversed the effects.
Why it matters
Many chronic skin conditions — including eczema, psoriasis, rosacea, and neurogenic inflammation — involve excessive nerve-skin signaling that drives inflammation and pain. By identifying ERK1/2 and JNK as the specific pathways through which neuropeptides drive keratinocyte inflammation, this study points to concrete drug targets. The discovery of the autocrine amplification loop (neuropeptides causing cells to make more neuropeptides and receptors) also explains how localized nerve irritation can escalate into widespread skin inflammation.
How the study worked
The study used a keratinocyte cell line to perform receptor expression analysis, neuropeptide stimulation assays, proliferation measurements, cytokine/NGF expression and secretion quantification, and MAPK/NFκB signaling pathway activation studies. ERK1/2 and JNK inhibitors were used to confirm the signaling dependencies. Both substance P and CGRP were tested at varying concentrations to establish dose-response relationships.
What this study cannot tell us
The study used a keratinocyte cell line rather than primary keratinocytes or intact skin, which may not fully replicate the complexity of in vivo neuropeptide-keratinocyte interactions. Rat-derived cells were used, and species differences in neuropeptide signaling may exist. The study did not test whether ERK1/2 or JNK inhibition would reduce inflammation in animal models of skin disease. The role of other cell types present in skin (immune cells, fibroblasts, endothelial cells) was not addressed.
How to read the evidence
This is a preclinical in vitro study using a keratinocyte cell line with well-controlled experiments including dose-response analyses and specific pathway inhibitors. The findings are mechanistically robust but limited to cell culture conditions without in vivo validation.
When this study was published
Published in 2013, this study is over a decade old. Since then, anti-CGRP therapies have become clinically successful for migraine, validating the importance of neuropeptide signaling. The MAPK pathway findings remain relevant for developing skin-specific anti-inflammatory approaches.
The bigger picture
The nerve-skin axis is increasingly recognized as a driver of inflammatory disease. CGRP has already become a major therapeutic target — anti-CGRP antibodies (erenumab, fremanezumab, galcanezumab) are FDA-approved for migraine prevention. This study extends the understanding of neuropeptide signaling to skin cells specifically, and the MAPK pathway dependence it identifies could inform the development of topical therapies that interrupt neurogenic inflammation at the skin level rather than systemically blocking neuropeptides.
Questions still open
- Would topical ERK1/2 or JNK inhibitors effectively reduce neurogenic skin inflammation in vivo without systemic side effects?
- Does the neuropeptide amplification loop (keratinocytes producing SP and CGRP in response to neuropeptide stimulation) occur in human skin, and does it drive flares in conditions like psoriasis?
- Could combined SP and CGRP receptor antagonists be more effective than targeting either neuropeptide alone for inflammatory skin conditions?
Common questions
What are substance P and CGRP, and why are they important for skin health?
Could this research lead to new treatments for skin conditions?
Read the original research
Keratinocytes express cytokines and nerve growth factor in response to neuropeptide activation of the ERK1/2 and JNK MAPK transcription pathways.
Regulatory peptides, 186, 92-103
Citation
Shi, Xiaoyou; Wang, Liping; Clark, J David; Kingery, Wade S. (2013). Keratinocytes express cytokines and nerve growth factor in response to neuropeptide activation of the ERK1/2 and JNK MAPK transcription pathways.. Regulatory peptides, 186, 92-103. https://doi.org/10.1016/j.regpep.2013.08.001