Transcriptomic analysis of keloid fibroblasts demonstrates reduced expression of vitamin D binding partner Retinoid-X receptor α: Implications for clinical treatment

Keloids are benign fibroproliferative tumours resulting from skin damage such as trauma, burns or surgery. Keloids are more prevalent in populations with darkly pigmented skin. Links between skin pigmentation and vitamin D production have been established and some studies indicate involvement of vitamin D signalling in keloid pathology. This study assessed the impact of paricalcitol (a selective vitamin D signalling activator) on fibroblasts derived from keloid and normal skin, to further investigate the role and potential clinical relevance of vitamin D signalling in keloid pathology. Analysis of keloid and normal skin tissue using immunohistochemistry demonstrated a significant reduction of nuclear vitamin D receptor (VDR) in keloid tissue. After treatment with paricalcitol, nuclear VDR was increased in both keloid and normal fibroblasts. RNA sequencing of normal fibroblasts treated with paricalcitol demonstrated significant changes in gene expression, with many upregulated genes identified to have anti-fibrotic effects. However, paricalcitol failed to alter gene expression in Keloid fibroblasts. To investigate this further, we performed RNA sequencing of normal and keloid fibroblasts and found that retinoid-X receptor α (RXRα), a key binding partner of VDR required for downstream transcriptional activation, is significantly downregulated in keloid fibroblasts. Our results indicate that paricalcitol can effectively activate VDR translocation to the nucleus but is unable to effect change at the transcriptional level in keloid fibroblasts, most likely due to the reduced expression of RXRα. This suggests Vitamin D signalling may be aberrant in keloids, and that supplementation with Vitamin D alone would likely be ineffective in restoring signalling. Keywords: Keloid, Vitamin D receptor, Paricalcitol, Retinoid-X receptor α