Cutaneous JAK Expression in Vitiligo and Acne Vulgaris.

The JAK/STAT signaling pathway transmits information from extracellular chemical signals to the nucleus resulting in DNA transcription. Binding of ligands, such as interferon and interleukins, to their specific transmembrane receptors activate associated JAKs. Phosphorylation of STAT follows, and the phosphorylated STAT translocates to the cell nucleus and activates transcription or suppression of target genes .

The JAK family of non-receptor intracellular tyrosine kinases is comprised of four members, JAK1, JAK2, JAK3 and tyrosine kinase (TyK)2. The JAKs are selectively activated by different receptors and have, therefore, distinct in vivo roles. JAK1 is mainly activated by type II cytokine receptors. JAK2 is crucial in transducing signals for cytokine receptors involved in hematopoiesis (erythropoietin, thrombopoietin and haematopoietic cell development cytokines). JAK3 is mainly expressed in B and T lymphocytes, and TYK2 associates commonly with other JAKs.

Cutaneous JAK overexpression has already been demonstrated in a number of inflammatory skin diseases (ISDs) including psoriasis, lichen planus (LP), atopic dermatitis (AD), pyoderma gangrenosum (PG) and alopecia areata (AA); indicating its crucial role in inflammatory keratinocytes.

Furthermore, the recent discovery of the JAK/STAT signaling pathway opened a new window of opportunity for the treatment of ISDs and promoted the development of drugs that block JAK activation.

JAK inhibitors in oral and topical formulations have shown beneficial results in psoriasis and alopecia areata. Patients suffering from vitiligo might also benefit from JAK inhibition. Recently, significant repigmentation was reported in a patient with vitiligo after treatment with tofacitinib, an oral JAK 1/3 inhibitor . However, the knowledge of the cutaneous JAK involvement in vitiligo is scarce. Similarly, little is known about cutaneous JAK expression in acne vulgaris.