Peroxisome proliferator-activated receptors (PPARs) in skin health, repair and disease

Peroxisome proliferator-activated receptors, PPARα, PPARβ/δ and PPARγ, are fatty acid activated transcription factors that belong to the nuclear hormone receptor family. While they are best known as transcriptional regulators of lipid and glucose metabolism, evidence has also accumulated for their importance in skin homeostasis. The three PPAR isotypes are expressed in rodent and human skin. Various cell culture and in vivo approaches suggest that PPARα contributes to fetal skin development, to epidermal barrier maturation and to sebocyte activity. PPARβ/δ regulates sebocyte differentiation, promotes hair follicle growth and has pro-differentiating effects in keratinocytes in normal and inflammatory conditions. In contrast, the role of PPARγ appears to be rather minor in keratinocytes, whereas its activity is required for sebaceous gland differentiation. Importantly, PPARα and β/δ are instrumental in skin repair after an injury, each of them playing specific roles. Due to their collective diverse functions in skin biology, PPARs represent a major research target for the understanding and treatment of many skin diseases, such as benign epidermal tumors, papillomas, acne vulgaris and psoriasis.