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Role of fibroblast-derived growth factors in regulating hyperpigmentation of solar lentigo

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Role of fibroblast-derived growth factors in regulating hyperpigmentation of solar lentigo

Kovacs D et al. · Br J Dermatol 2010;163(5):1020–1027 · doi:10.1111/j.1365-2133.2010.09946.x · PMID 20662835

TL;DR

Demonstrates that dermal fibroblasts in solar lentigo (SL) lesions — persistently activated by cumulative UV exposure — are a source of at least three melanogenic growth factors (HGF, KGF, SCF) that are elevated in the upper dermis of SL lesions and upregulated in in vitro photoaged fibroblasts. Identifies a two-step dermal-to-epidermal relay: KGF (a fibroblast-secreted factor) acts on keratinocytes to induce SCF expression, which then activates KIT on melanocytes. This is a complementary but anatomically distinct mechanism from the epidermal-keratinocyte-driven SCF described by Hattori 2004 — together the two papers reveal that SCF can reach melanocytes from both compartments, with the dermal contribution mediated indirectly via the fibroblast→keratinocyte→melanocyte axis.

Background

Solar lentigines are flat, sharply demarcated hyperpigmented macules on chronically sun-exposed skin, present in >90% of Caucasians over 60. The canonical model at the time of this paper attributed focal melanocyte activation primarily to epidermal factors — particularly membrane-bound SCF from UV-activated keratinocytes (Hattori 2004 1) and ET-1/ET_B signalling. Kovacs 2010 asks whether the dermal compartment — specifically photoaged fibroblasts — also contributes paracrine melanogenic signals.

Methods (best-effort from abstract and PubMed metadata)

Three experimental approaches described in the abstract:

  1. Immunohistochemistry (IHC) on human SL tissue sections — assessed protein expression of HGF, KGF, and SCF in the upper dermis of SL lesions vs. perilesional normal skin. Sample size and patient demographics are not recoverable from the abstract. no-fulltext-access
  2. In vitro photoaged fibroblast model — primary human dermal fibroblasts subjected to repeated UV irradiation to generate a photoaged phenotype; mRNA expression of HGF, KGF, and SCF assessed (method — RT-PCR implied; not confirmed from abstract). Quantitative fold-changes not recoverable. no-fulltext-access
  3. KGF → keratinocyte functional assay — KGF-treated keratinocytes assessed for SCF expression, establishing the indirect relay arm of the pathway. no-fulltext-access

All cell/tissue sources are human-derived, making this a human in vitro / ex vivo study despite the absence of an enrolled clinical cohort.

Key findings

1. HGF, KGF, and SCF are elevated in the upper dermis of SL lesions

IHC demonstrated positive staining for all three growth factors in the upper dermis of solar lentigo tissue. Perilesional normal skin comparator showed reduced signal. This localises fibroblast-derived melanogenic activity to the lesional dermis immediately underlying the hyperpigmented epidermis. Specific fold-changes, n per group, and significance statistics are closed-access. no-fulltext-access

Caveats from abstract-level extraction:

  • The abstract does not specify whether all three factors were quantified with equal rigor (IHC is semi-quantitative by default)
  • Whether HGF, KGF, and SCF are all equally elevated, or whether one dominates, is not extractable from public sources

2. Photoaged fibroblasts upregulate the same three cytokines in vitro

Repeated UV-irradiated (“photoaged”) primary human dermal fibroblasts showed significantly elevated mRNA expression of HGF, KGF, and SCF compared to non-irradiated controls. This establishes that the elevated dermal cytokine pool in SL is a fibroblast-intrinsic response to UV, not solely a bystander effect of the broader lesional microenvironment. no-fulltext-access — magnitude and time-course not recoverable

3. KGF mediates an indirect dermal→epidermal→melanocyte relay via SCF induction

KGF — secreted by dermal fibroblasts — when applied to epidermal keratinocytes, induces SCF expression in those keratinocytes. This identifies a two-step relay:

UV-activated dermal fibroblast → KGF secretion
  → KGF acts on epidermal keratinocyte
    → keratinocyte upregulates SCF
      → membrane-bound SCF activates KIT on melanocyte
        → melanocyte proliferation + melanogenesis

This is mechanistically distinct from the direct KGF→melanocyte action: KGF does not appear to act directly on melanocytes in this model (KGF receptor / KGFR / FGFR2-IIIb is expressed primarily on epithelial cells, not melanocytes). Instead, the fibroblast-derived KGF amplifies the keratinocyte SCF signal that Hattori 2004 characterised as the primary keratinocyte output. no-fulltext-access — the indirect mechanism inference is drawn from abstract language; the paper may provide additional direct evidence.

4. Author conclusion on fibroblast activation model

The authors conclude that “fibroblasts may be persistently activated by UV exposure to release melanogenic growth factors; this inducible cytokine network acts both directly and indirectly” on skin cells to produce hyperpigmentation. This framing implies a chronic UV-memory state in dermal fibroblasts — consistent with stress-induced premature senescence (SIPS) phenotype — that sustains lesional melanocyte activity even between UV exposures.

Distinction from Hattori 2004 — compartment analysis

This is the critical interpretive context for placing this paper in the solar lentigo literature.

FeatureHattori 2004 1Kovacs 2010
Experimental systemIn vivo: human lentigo senilis tissue (epidermal sheets separated from dermis)In vitro / ex vivo: human SL tissue IHC + photoaged fibroblast cultures
Compartment studiedEpidermis — keratinocytes in the basal layerDermis — fibroblasts in upper dermis
Source of SCF signalEpidermal keratinocytes (membrane-bound, 3.9-fold mRNA increase)Dermal fibroblasts (plus indirect relay: KGF→keratinocyte→SCF)
bFGF / KGF in lesional epidermisbFGF: not elevated (NS by IHC, n=10)KGF: elevated in fibroblasts and upper dermis
GROαNot elevated (1.13-fold, NS)Not tested (not in abstract)
HGFNot mentionedElevated in dermis and in photoaged fibroblasts
Key mechanistic claimSCF is the dominant keratinocyte-melanocyte paracrine signal; epidermal originUV-activated fibroblasts produce HGF, KGF, SCF; KGF amplifies keratinocyte SCF production
Human in vivo statusYes — excised human lesion tissuePartial — IHC is on human tissue, but mechanistic assays are in vitro

These two papers are complementary, not competing. Both identify SCF/KIT as a final common pathway, but the source and route differ:

  • Hattori: membrane-bound SCF from UV-stressed keratinocytes directly activating adjacent melanocytes in the epidermis
  • Kovacs: fibroblast-secreted KGF acting on keratinocytes to induce SCF, representing a secondary amplifying relay from the dermis

The relative contribution of epidermal vs. dermal signals to solar lentigo pathogenesis in vivo is unresolved. No study has directly compared the quantitative contribution of each compartment under matched conditions. contradictory-evidence — not a contradiction per se, but the field lacks the in vivo quantification needed to rank these pathways.

Note on bFGF terminology: The skin-aging footnote [^kovacs2010] previously stated “bFGF and SCF from solar lentigo fibroblasts.” This was a minor inaccuracy introduced during abstract-level extraction. The PubMed abstract (PMID 20662835) explicitly names the three growth factors as HGF, KGF, and SCF — bFGF (FGF-2 / basic FGF) is not mentioned and is a distinct FGF family member from KGF (FGF-7). The skin-aging.md footnote has been corrected to read “HGF, KGF (FGF-7), and SCF” as of 2026-05-19 verification pass.

Significance in the solar lentigo field

This paper advances the solar lentigo model by:

  1. Adding fibroblasts as active participants. Prior models were predominantly keratinocyte-centric. Kovacs establishes that the dermis is not merely a passive structural compartment but an active UV-sensing signalling source.
  2. Identifying HGF as a candidate melanogenic factor. HGF (hepatocyte growth factor / scatter factor) activates the MET receptor, which is expressed on melanocytes; MET→RAS→MAPK→MITF is a known melanogenesis pathway. This widens the therapeutic target space for lentigo treatment beyond SCF/KIT.
  3. Describing a UV-memory state in fibroblasts. The in vitro photoaging model implies that repeated sublethal UV doses cumulatively activate the fibroblast cytokine program — consistent with clinical observations that lentigines accumulate proportionally to lifetime UV dose rather than to individual episodes.
  4. Proposing a fibroblast→keratinocyte communication relay. The indirect KGF→keratinocyte→SCF pathway is an example of altered intercellular communication — the altered-intercellular-communication hallmark of aging — operating in UV-damaged tissue.

Limitations

  • Closed-access; full quantitative content unverifiable. All sample sizes, fold-changes, and p-values are closed-access. This page should not be cited for quantitative claims. no-fulltext-access
  • In vitro photoaging model validity. Repeated UV irradiation of cultured fibroblasts may not fully recapitulate the chronic in vivo fibroblast activation state (which includes extracellular matrix context, immune cell crosstalk, and accumulated somatic mutations). Whether the photoaged fibroblast phenotype persists under normal in vivo matrix conditions is not addressed.
  • IHC semi-quantitative. The tissue data depends on IHC, which has known antibody-specificity and antigen-retrieval limitations. Without ELISA or mass spectrometry confirmation of soluble concentrations, the IHC results describe protein localisation rather than secreted levels.
  • n not reported in abstract. Study group sizes, patient age range, sex, Fitzpatrick phototype, and sun exposure history are not extractable from public sources. This makes critical appraisal of statistical power impossible from this study page. no-fulltext-access
  • No functional melanocyte proliferation endpoint in abstract. The abstract describes the cytokine network; whether the authors directly measured melanocyte number, KIT activation, or DOPA reaction in the same samples is not apparent from public metadata.
  • No in vivo intervention arm. The paper is descriptive/mechanistic — it identifies the cytokine network but does not test whether blocking HGF, KGF, or fibroblast-derived SCF prevents lentigo formation or causes regression.
  • 115 citations as of 2026 (per a local paper DOI lookup; citation_percentile: 100th; FWCI 2.48) — well-cited for a descriptive mechanistic paper, indicating the findings are considered credible by the field despite the in vitro limitation.

Relationship to other wiki pages

  • skin-aging — solar lentigo section, footnote [^kovacs2010]; corrected from “bFGF and SCF” to “HGF, KGF (FGF-7), and SCF” on 2026-05-19 verification pass (PubMed abstract confirms HGF/KGF/SCF; bFGF not present in this paper)
  • hattori-2004-scf-solar-lentigo — complementary compartment (epidermal SCF); Hattori is the in vivo counterpart to this in vitro dermal study
  • altered-intercellular-communication — fibroblast→keratinocyte KGF relay is a canonical example of UV-driven paracrine signalling changes in aged tissue
  • cellular-senescence — photoaged fibroblast state in this paper is consistent with SIPS; not directly characterised as senescent in the abstract but implicit in the “persistent activation” framing
  • kit (stub — planned) — KIT receptor is the terminal effector of both the Hattori 2004 epidermal-SCF and the Kovacs dermal-KGF→SCF pathways
  • met (stub — planned) — MET is the receptor for HGF; HGF→MET→melanocyte signalling in lentigo not yet documented on a dedicated page

Footnotes

Footnotes

  1. hattori-2004-scf-solar-lentigo · doi:10.1111/j.0022-202x.2004.22503.x · Hattori H et al. · in-vivo · J Invest Dermatol 2004;122(5):1256-1265 · n=7 (SCF mRNA), n=6 (SCF protein), n=10 (GROα + bFGF IHC) · p<0.01 (SCF mRNA), p<0.05 (SCF protein) · model: 29 Japanese patients with lentigo senilis; epidermal sheets separated from dermis · Membrane-bound SCF 3.9-fold elevated in lesional vs. perilesional keratinocytes; bFGF NOT elevated in epidermis (NS by IHC, n=10); ET-1/ET_B cascade acts synergistically with SCF/KIT ↩ ↩2

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