Critical roles of the nuclear receptor PPARβ (peroxisome-proliferator- activated receptor β) in skin wound healing

The PPARs (peroxisome-proliferator-activated receptors) α β/δ and γ belong to the nuclear hormone receptor superfamily. While all three receptors are undetectable in adult mouse interfollicular epidermis, PPARβ expression and activity is strongly re-activated by inflammatory stimuli during epidermal injury. The pro-inflammatory cytokine TNFα (tumour necrosis factor α) stimulates transcription of the PPARβ gene via an activator protein-1 site in its promoter and it also triggers the production of PPARβ ligands in keratinocytes. This increase of PPARβ activity in these cells up-regulates the expression of integrin-linked kinase and 3-phosphoinositide-dependent kinase-1, which phosphorylates protein kinase B-α (Akt1). The resulting increase in Akt1 activity suppresses apoptosis and ensures the presence of a sufficient number of viable keratinocytes at the wound margin for re-epithelialization. Together, these observations reveal that PPARβ takes on multiple roles and contributes favourably to the process of wound closure.