Agouti Mediated Alterations of Thiol Concentrations (Cysteine and Glutathione) in Regenerating Hair Follicles, Serum, and Extrafollicular Tissues of Agouti Mutant Mice (Ay/a, AwJ/AwJ, and a/a)

Normal expression of the agouti protein (AP) is responsible for the yellow banded agouti hair in the healthy agouti mouse (AwJ/AwJ). Ectopic overexpression of AP is responsible for the abnormally intense yellow of the lethal yellow (Ay/a) mouse coat as well as the pleiotropic effects of the lethal yellow syndrome (Miller et al., 1993). As dopaquinone (an intermediate at a key melanogenic branch point) has a high affinity for cysteine and glutathione (GSH) (Prota, 1988), thiol concentrations may dictate whether hair follicle melanocytes of wild-type agouti mice synthesize eu-or phaeomelanin. GSH is also known to play many important roles in cellular health and maintenance (Meister, 1983). Cysteine and GSH were measured in hair follicles and serum in AwJ/AwJ, Ay/a and a/a mice over a hair regeneration period using HPLC analysis with fluorescent detection. Analysis of three extra-follicular tissues (liver, spleen, and adipose) on day 9 of the regeneration period provided a snapshot of interorgan thiol relationships. Our data support the hypothesis that expression of the agouti product mediates differential thiol metabolism. Ay/a hair follicles showed higher total thiol levels and an increased amount of cysteine relative to GSH. AwJ/AwJ mice showed intermediate levels, while a/a mice had the lowest total thiol concentrations and a decreased relative ratio of cysteine to GSH. In the hair follicle, cysteine (likely derived from enzymatic degradation of GSH) appears to be the primary melanogenic thiol. This free cysteine could conjugate with dopaquinone in the melanocyte to form cys-dopas and ultimately phaeomelanin. Follicle demands for cysteine and GSH appear to be met through transport in the blood and an increased synthesis of GSH in the liver. Ay-induced overexpression of AP may create a long-term and chronic shift in thiol species. Present data from spleen extracts suggest that aberrant AP expression in the Ay/a mouse may affect thiol concentrations in tissues other than the hair follicle. In light of the ubiquitous role GSH plays in cell metabolism, an Ay-induced imbalance of thiol metabolism (altering GSH concentrations in multiple tissues) may contribute to the range of pleiotropic defects characterized as the lethal yellow syndrome