Small-interfering RNA targeted at antiapoptotic mRNA increases keratinocyte sensitivity to apoptosis

Gene silencing RNA interference technology concentrates on downregulation of gene expression using specific double-stranded RNA molecules (small-interfering RNA, siRNA), which induce the degradation of complementary mRNA. SiRNA therapeutics is currently being tested in several clinical trials. Skin disorders are an attractive target for siRNA-based technology because effective agents can be delivered by topical application. In several inflammatory skin disorders, the barrier function of the skin is markedly impaired and this may increase the delivery efficiency. Psoriasis is a very common skin disorder. The characteristics of this disorder are abnormal keratinocyte proliferation and inflammation. Keratinocytes from psoriatic epidermis express much higher levels of the antiapoptotic protein, Bcl-xL, compared with normal keratinocytes. Insulin-like growth factor 1 receptor (IGF-1R) plays a major role in cell growth, differentiation and apoptosis in many cell types, including keratinocytes and IGF-1R activation plays an important role in the pathogenesis of psoriasis. Keratinocytes from patients with psoriasis are more susceptible to IGF-1-stimulated proliferation compared with normal keratinocytes. IGF-1R is expressed by proliferating basal and suprabasal keratinocytes and is more abundant in psoriatic lesions.

To prove the validity of IGF-1R and Bcl-xL as useful targets for siRNA-based therapeutics and to deliver siRNA selectively and efficiently to primary human keratinocytes; this is a primary essential step in the development of siRNA.

Primary normal human keratinocytes were transfected with various siRNA molecules, and transfection efficiency was monitored by fluorescent labelling. Cell growth and apoptosis induction were evaluated in the transfected cells.

We were able to deliver efficiently siRNA targeting Bcl-xL or IGF-1R to primary human keratinocyte cultures. We also showed that siRNAs targeting Bcl-xL and IGF-1R induce growth inhibition, apoptosis and increased sensitivity to ultraviolet B in keratinocytes.

The present findings demonstrate that Bcl-xL and IGF-1R are valid, important targets for siRNA-based technology directed at the suppression of keratinocyte hyperproliferation.