Pigmentation Diathesis of Hypertrophic Scar: An Examination of Known Signaling Pathways to Elucidate the Molecular Pathophysiology of Injury-Related Dyschromia

Abstract

Hypertrophic scar (HTS) occurs frequently after burn injury. Treatments for some aspects of scar morbidity exist, however, dyspigmentation treatments are lacking due to limited knowledge about why scars display dyschromic phenotypes. Full thickness wounds were created on duroc pigs that healed to form dyschromic HTS. HTS biopsies and primary cell cultures were then used to study pigmentation signaling. Biopsies of areas of both pigment types were taken for analysis. At the end of the experiment, melanocyte-keratinocyte co-cultures were established from areas of differential pigmentation. Heterogeneously dyspigmented scars formed with regions of hyperpigmentation and hypopigmentation. Melanocytes were present in both pigment types measured by S100β qRT-PCR and immunostaining, and visualized by dendritic cell presence in primary cultures. P53 expression was not different between the two pigment types. Hyperpigmented scars had up regulated levels of POMC, ACTH, α-MSH, SCF, and c-KIT and MC1R receptors compared to hypopigmented regions. Many genes involved in dyspigmentation were differentially regulated by microarray analysis including MITF, TYR, TYRP1, and DCT. MiTF expression was not different upon further exploration, but TYR, TYRP1, and DCT were up regulated in intact biopsies measured by qRT-PCR and confirmed by immunostaining. This is the first work to confirm the presence of melanocytes in hypopigmented scar using qRT-PCR and primary cell culture. An understanding of the initial steps in dyspigmentation signaling, as well as the downstream effects of these signals, will inform treatment options for patients with scars and provide insight to where pharmacotherapy may be directed.

Laser Therapy of Traumatic and Surgical Scars and an Algorithm for Their Treatment

“…The mechanism of melanin‐associated hyperpigmentation in scars is still under investigation. In normal skin, UV light induces pigmentation by activating p53, which upregulates pro‐opiomelanocortin (POMC) . P53 levels in the keratinocytes of hyperpigmented scars are not significantly different than those in hypopigmented scars, suggesting that scar hyperpigmentation occurs via a different pathway .…”

“…In normal skin, UV light induces pigmentation by activating p53, which upregulates pro‐opiomelanocortin (POMC) . P53 levels in the keratinocytes of hyperpigmented scars are not significantly different than those in hypopigmented scars, suggesting that scar hyperpigmentation occurs via a different pathway . However, hyperpigmented scars contain elevated levels of POMC and both of its cleaved products, and various downstream products are capable of inducing pigmentation.…”

“…Hypopigmented scars occur secondary to traumatic wounds or burns, surgery, or deep resurfacing procedures by an unknown mechanism. Within dyschromic scars, hypopigmented areas contain the same number of melanocytes as surrounding hyperpigmented or normally pigmented scar tissue, suggesting that hypopigmentation results from a mechanism other than melanocyte deficiency . Both AFR and NAFR improve the color and texture of hypopigmented scars .…”

Galectin‐1 production is elevated in hypertrophic scar

“…Within this list of DEGs were mostly genes involved in ECM synthesis and remodeling such as collagens and metalloproteinases, including several galectins—fold changes of differentially expressed galectin and collagen genes are listed in Table 2. The full lists of DEGs identified have been previously published elsewhere 21,24,25 . Transcription of LGALS1, 4, and 12 were significantly differentially regulated between porcine NS and HTS (FDR <0.01); LGALS1 mRNA was consistently overexpressed in scar tissues (Table 2).…”

“…Porcine biopsies were taken from NS before injury, as well as from HTS during mid‐to‐late‐stage scar formation (days 91‐136) for microarray analysis. mRNA was isolated from biopsies, quantified and quality was assessed, and a dual‐dye porcine gene expression microarray was carried out as previously described 21 . Hybridized slides were scanned using Agilent DNA microarray scanner (Agilent Technologies, Santa Clara, California).…”