The caspase inhibitor Ac‐DEVD‐CMK decreases the availability Ro antigen triggered by apoptosis

Abstract

Mechanisms that trigger autoantibody production still partially known; such phenomenon seems to be linked to autoantigen availability. It has been recognized that the epidermal apoptotic cells constitute a major source of autoantigens; especially those linked to the photosensitive subacute cutaneous lupus erythematosus (SCLE) that produce anti-Ro antibodies. Our major goal was to demonstrate whether UV light induces apoptosis and increase the availability of Ro autoantigen. Also the blocking effect of a caspase inhibitor was assessed. For this purpose newborn Balb/c mice (n= 6/group), were UVB irradiated (5–30 mJ/cm2) equivalent to a moderate to severe sunburn. Irradiated and non-irradiated animals were injected with monoclonal anti-Ro antibodies or with a polyclonal anti-Ro from a SCLE patient, or with normal IgG. In other group the apoptosis was induced with an anti-Fas monoclonal antibody. Some animals were treated with the caspase inhibitor Ac-DEVD-CMK. The skin was examined by direct immunofluorescence, by TUNEL. The epidermis was obtained by splitting the skin with dispase, epidermal DNA and RNA were isolated by TRIsol followed by RT-PCR for caspase 3, Fas, FasL, Bax, and DFF40. Major findings of present studies were: 1. UVB irradiation induces apoptosis of keratinocytes. 2. UVB and anti-Fas induced apoptosis and redistribution of the Ro antigen on cell surface. 3. Apoptotic keratinocytes are better triggered by the monoclonal or polyclonal anti-Ro antibodies. 4. The blocking effect of Ac-DEVD-CMK on caspases decreases the Ro autoantigen availability and the anti-Ro antibody deposition. Finally the caspase pathway would be blocked to prevent the cutaneous lupus flare ups of SCLE.