Decrease of galectin-3 in keratinocytes: A potential diagnostic marker and a critical contributor to the pathogenesis of psoriasis

Psoriasis-specific proteins dysregulated in keratinocytes and involved in the pathophysiological process of psoriasis remains elusive. We report here that epidermal Galectin-3 expression is significantly downregulated in lesional skin, but not in non-lesional skin in psoriasis patients, nor in a group of diseases known as psoriasiform dermatitis clinically and histologically similar to psoriasis. The deficiency of epidermal Galectin-3 is sufficient to promote development of psoriatic lesions, as evidenced by more severe skin inflammation in Galectin-3 knockout (gal3^-/-) mice, compared to wild-type mice, after imiquimod treatment, and in skin from gal3^-/- mice grafted onto wildtype mice. The development of psoriatic-like lesions is attributable to 1) the spontaneously tuning up of psoriasis signatures in keratinocytes through JNK pathway; and 2) neutrophil accumulation caused by the enhanced leukocyte-recruiting capacity associated with overexpression of S100A7-9 and CXCL-1, 8 in keratinocytes with impaired Galectin-3 expression. Psoriasis-like skin inflammation is significantly improved in gal-3^-/- mice both by inhibition of neutrophils accumulation with a selective CXCR2 Antagonist of SB225002, and by intracutaneous injection of recombinant Galectin-3. Overall, these findings offer promising galectin-3-related diagnostic and therapeutic resolutions of psoriasis.